erlang (erts v15.2.5)
View SourceThe Erlang BIFs and predefined types.
By convention, most Built-In Functions
(BIFs) and all predefined types are included
in this module. Some of the BIFs and all of the predefined types are viewed more
or less as part of the Erlang programming language and are auto-imported.
Thus, it is not necessary to specify the module name. For example, the calls
atom_to_list(erlang) and erlang:atom_to_list(erlang)
are identical.
Auto-imported BIFs are annotated with auto-imported and predefined types are
annotated with predefined.
Some auto-imported BIFs are also allowed in guard expression.
Such BIFs are annoted with both auto-imported and guard-bif.
BIFs can fail for various reasons. All BIFs fail with reason badarg if they
are called with arguments of an incorrect type. The other reasons are described
in the description of each individual BIF.
Summary
Predefined datatypes
The arity of a function or type.
An Erlang bitstring.
A byte of data represented by an integer.
An Erlang fun.
A binary or list containing bytes and/or iodata.
A list containing bytes and/or iodata.
An Erlang list containing terms of the type
ContentType.
A three-tuple representing a Module:Function/Arity function signature.
An Erlang module represented by an atom.
A negative integer.
The type used to show that a function will never return a value, that is it will always throw an exception.
A non-negative integer, that is any positive integer or 0.
This type is used to show that a function will never return a value; that is it will always throw an exception.
A binary/0 that contains some data.
A bitstring/0 that contains some data.
A maybe_improper_list/2 that contains some items.
A list/0 that contains some items.
A list(ContentType) that contains some items.
A maybe_improper_list/0 that contains some items.
A maybe_improper_list(ContentType, TerminationType) that contains some items.
A string/0 that contains some characters.
An Erlang process identifier.
An Erlang port identifier.
An integer greater than zero.
An Erlang reference.
A character string represented by a list of ASCII characters or unicode codepoints.
A timeout value that can be passed to a receive expression.
Types
The current cpu topology.
The time_unit/0 type also consist of the following deprecated symbolic
time units
An opaque handle identifying a distribution channel.
A binary data object, structured according to the Erlang external term format.
A term of type iovec/0, structured according to the Erlang external term
format.
A list with the system wide garbage collection defaults.
A list of binaries. This datatype is useful to use together with
enif_inspect_iovec.
Process max heap size configuration. For more info see
process_flag(max_heap_size, MaxHeapSize)
An opaque handle identifying a NIF resource object .
Process priority level. For more info see
process_flag(priority, Level)
A extended stacktrace/0 that can be passed to raise/3.
The requested scheduler bind type.
The destination for a send operation.
Options for spawn_opt().
An Erlang stacktrace as described by Errors and Error Handling section in the Erlang Reference Manual.
The time unit used by erlang time APIs.
Checksum
Computes and returns the adler32 checksum for Data.
Continues computing the adler32 checksum by combining the previous checksum,
OldAdler, with the checksum of Data.
Combines two previously computed adler32 checksums.
Computes and returns the crc32 (IEEE 802.3 style) checksum for Data.
Continues computing the crc32 checksum by combining the previous checksum,
OldCrc, with the checksum of Data.
Combines two previously computed crc32 checksums.
Computes an MD5 message digest from Data, where the length of the digest is
128 bits (16 bytes). Data is a binary or a list of small integers and
binaries.
Finishes the update of an MD5 Context and returns the computed MD5 message
digest.
Creates an MD5 context, to be used in the following calls to
md5_update/2.
Update an MD5 Context with Data and returns a NewContext.
Code
Returns true if Module has
old code, otherwise false.
Checks if the node local process identified by Pid executes old code for
Module.
Makes the current code for Module become old code and deletes all references
for this module from the export table. Returns undefined if the module does
not exist, otherwise true.
Returns true if the module Module is
current and contains an exported
function Function/Arity, or if there is a BIF (a built-in function implemented
in C) with the specified name, otherwise returns false.
This BIF is useful for builders of cross-reference tools.
Loads Module described by the object code contained within Binary.
Loads and links a dynamic library containing native implemented functions (NIFs) for a module.
Returns a list of all loaded Erlang modules (current and old code), including preloaded modules.
Returns true if the module Module is loaded as
current code; otherwise,
false. It does not attempt to load the module.
Returns a list of Erlang modules that are preloaded in the run-time system.
Removes old code for Module. Before this BIF is used, check_process_code/2
is to be called to check that no processes execute old code in the module.
Distributed Erlang
Forces the disconnection of a node.
Get distribution channel data from the local node that is to be passed to the remote node.
Request notification when more data is available to fetch using
erlang:dist_ctrl_get_data(DHandle) for the
distribution channel identified by DHandle.
Returns the value of the get_size option on the distribution channel
identified by DHandle. For more information see the documentation of the
get_size option for the erlang:dist_ctrl_set_opt/3
function.
Register an alternate input handler process for the distribution channel
identified by DHandle.
Deliver distribution channel data from a remote node to the local node.
Sets the value of the get_size option on the distribution channel identified
by DHandle.
Returns the magic cookie of the local node if the node is alive, otherwise the
atom nocookie. This value is set by set_cookie/1.
Returns the magic cookie for node Node if the local node is alive, otherwise
the atom nocookie. This value is set by set_cookie/2.
Returns true if the local node is alive (that is, if the node can be part of a
distributed system), otherwise false. A node is alive if it is started with
Monitor the status of the node Node. If Flag is true, monitoring is turned
on. If Flag is false, monitoring is turned off.
Behaves as monitor_node/2 except that it allows an extra option to be
specified, namely allow_passive_connect.
Returns the name of the local node. If the node is not alive, nonode@nohost is
returned instead.
Returns a list of all nodes connected to this node through normal connections (that is, hidden nodes are not listed). Same as nodes(visible).
Returns a list of nodes according to the argument specified. The returned result, when the argument is a list, is the list of nodes satisfying the disjunction(s) of the list elements.
Returns a list of NodeInfo tuples.
Sets the magic cookie of the local node to the atom Cookie, which is also the
cookie for all nodes that have no explicit cookie set with set_cookie/2
Cookie.
Sets the magic cookie for Node to the atom Cookie. If Node is the local
node, the function sets the cookie of all other nodes (that have no explicit
cookie set with this function) to Cookie.
Erlang Terms
Returns an integer or float that is the arithmetical absolute value of Float
or Int.
Returns a new tuple that has one element more than Tuple1, and contains the
elements in Tuple1 followed by Term as the last element.
Equivalent to atom_to_binary(Atom, utf8).
Returns a binary corresponding to the text representation of Atom.
Returns a list of unicode code points corresponding to the text representation
of Atom.
Extracts the part of the binary described by PosLen.
Equivalent to binary_to_atom(Binary, utf8).
Returns the atom whose text representation is Binary. If Encoding is utf8
or unicode, the binary must contain valid UTF-8 sequences.
As binary_to_atom/2, but the atom must exist.
Returns the float whose text representation is Binary.
Returns an integer whose text representation is Binary.
Returns an integer whose text representation in base Base is Binary.
Returns a list of integers corresponding to the bytes of Binary.
As binary_to_list/1, but returns a list of integers
corresponding to the bytes from position Start to position Stop in Binary.
The positions in the binary are numbered starting from 1.
Returns an Erlang term that is the result of decoding binary object Binary,
which must be encoded according to the
Erlang external term format.
Equivalent to binary_to_term(Binary), but can be configured to
fit special purposes.
Returns an integer that is the size in bits of Bitstring.
Returns a list of integers corresponding to the bytes of Bitstring.
Returns an integer that is the number of bytes needed to contain Bitstring.
That is, if the number of bits in Bitstring is not divisible by 8, the
resulting number of bytes is rounded up.
Returns the smallest integer not less than Number.
Decodes the binary Bin according to the packet protocol specified by Type.
Similar to the packet handling done by sockets with option {packet,Type}.
Returns a new tuple with element at Index removed from tuple Tuple1.
Prints a text representation of Term on the standard output.
Returns the Nth element (numbering from 1) of Tuple.
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format.
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format.
Returns a float by converting Number to a float.
Equivalent to float_to_binary(Float, [{scientific, 20}]).
Returns a binary corresponding to the text representation of Float using fixed
decimal point formatting.
Equivalent to float_to_list(Float, [{scientific, 20}]).
Returns a string corresponding to the text representation of Float using fixed
decimal point formatting.
Returns the largest integer not greater than Number.
Returns a list with information about the fun Fun. Each list element is a
tuple. The order of the tuples is undefined, and more tuples can be added in a
future release.
Returns information about Fun as specified by Item, in the form
{Item,Info}.
Returns String that represents the code that created Fun.
Returns the head of List, that is, the first element.
Returns a new tuple with element Term inserted at position Index in tuple
Tuple1. All elements from position Index and upwards are pushed one step
higher in the new tuple Tuple2.
Returns a binary corresponding to the text representation of Integer.
Returns a binary corresponding to the text representation of Integer in base
Base.
Returns a string corresponding to the text representation of Integer.
Returns a string corresponding to the text representation of Integer in base
Base.
Returns an integer, that is the size in bytes, of the binary that would be the
result of iolist_to_binary(Item).
Returns a binary that is made from the integers and binaries in
IoListOrBinary.
Returns an iovec that is made from the integers and binaries in
IoListOrBinary. This function is useful when you want to flatten an iolist but
you do not need a single binary. This can be useful for passing the data to nif
functions such as enif_inspect_iovec or do
more efficient message passing. The advantage of using this function over
iolist_to_binary/1 is that it does not have to copy
off-heap binaries.
Returns true if Term is an atom, otherwise false.
Returns true if Term is a binary, otherwise false.
Returns true if Term is a bitstring (including a binary), otherwise false.
Returns true if Term is the atom true or the atom false (that is, a
boolean). Otherwise returns false.
Returns true if Term is a floating point number, otherwise false.
Returns true if Term is a fun, otherwise false.
Returns true if Term is a fun that can be applied with Arity number of
arguments, otherwise false.
Returns true if Term is an integer, otherwise false.
Returns true if Term is a list with zero or more elements, otherwise
false.
Returns true if Term is a map, otherwise false.
Returns true if map Map contains Key and returns false if it does not
contain the Key.
Returns true if Term is an integer or a floating point number. Otherwise
returns false.
Returns true if Term is a process identifier, otherwise false.
Returns true if Term is a port identifier, otherwise false.
Returns true if Term is a tuple and its first element is RecordTag.
Otherwise returns false.
RecordTag must be an atom.
Returns true if Term is a reference, otherwise false.
Returns true if Term is a tuple, otherwise false.
Returns the length of List.
Returns the atom whose text representation is String.
Returns a binary that is made from the integers and binaries in IoList.
Returns a bitstring that is made from the integers and bitstrings in
BitstringList. (The last tail in BitstringList is allowed to be a
bitstring.)
Returns the atom whose text representation is String, but only if there
already exists such atom. An atom exists if it has been created by the run-time
system by either loading code or creating a term in which the atom is part.
Returns the float whose text representation is String.
Returns an integer whose text representation is String.
Returns an integer whose text representation in base Base is String.
Returns a process identifier whose text representation is a String.
Returns a port identifier whose text representation is a String.
Returns a reference whose text representation is a String.
Returns a tuple corresponding to List, for example
Returns a unique reference. The reference is unique among connected nodes.
Creates a new tuple of the specified Arity, where all elements are
InitialValue.
Creates a tuple of size Arity, where each element has value DefaultValue,
and then fills in values from InitList.
Returns value Value associated with Key if Map contains Key.
Returns an integer, which is the number of key-value pairs in Map.
Tests a match specification used in calls to ets:select/2 and
trace:function/4.
Returns the largest of Term1 and Term2. If the terms compare equal with the
== operator, Term1 is returned.
Returns the smallest of Term1 and Term2. If the terms compare equal with the
== operator, Term1 is returned.
Returns the node where Arg originates. Arg can be a process identifier, a
reference, or a port. If Arg originates from the local node and the local node
is not alive, nonode@nohost is returned.
Equivalent to phash2/2.
Portable hash function that gives the same hash for the same Erlang term regardless of machine architecture and ERTS version.
Returns a string corresponding to the text representation of Pid.
Returns a string corresponding to the text representation of the port identifier
Port.
Returns a string corresponding to the text representation of Ref.
Returns an integer by rounding Number.
Returns a tuple that is a copy of argument Tuple1 with the element specified
by integer argument Index (the first element is the element with index 1)
replaced by argument Value.
Returns the number of elements in a tuple or the number of bytes in a binary or bitstring.
Returns a tuple containing the binaries that are the result of splitting Bin
into two parts at position Pos.
Returns a binary data object that is the result of encoding Term according to
the Erlang external term format.
Returns a binary data object that is the result of encoding Term according to
the Erlang external term format.
Returns the encoding of Term according to the Erlang external term format as
ext_iovec/0.
Returns the encoding of Term according to the Erlang external term format as
ext_iovec/0.
Returns the tail of List, that is, the list minus the first element
Truncates the decimals of Number.
Returns an integer that is the number of elements in Tuple.
Returns a list corresponding to Tuple. Tuple can contain any Erlang terms.
Example
Generates and returns an
integer unique on current runtime system instance.
Equivalent to calling erlang:unique_integer([]).
Generates and returns an integer unique on current runtime system instance. The integer is unique in the sense that this BIF, using the same set of modifiers, does not return the same integer more than once on the current runtime system instance. Each integer value can of course be constructed by other means.
Processes and Ports
Create an alias which can be used when sending messages to the process that
created the alias. When the alias has been deactivated, messages sent using the
alias will be dropped. An alias can be deactivated using unalias/1.
Calls a fun, passing the elements in Args as arguments.
Returns the result of applying Function in Module to Args. The applied
function must be exported from Module. The arity of the function is the length
of Args.
This implementation-dependent function increments the reduction counter for the calling process.
If MonitorRef is a reference that the calling process obtained by calling
monitor/2, this monitoring is turned off. If the monitoring is already turned
off, nothing happens.
The returned value is true unless info is part of OptionList.
Returns the process dictionary and deletes it.
Returns the value Val associated with Key and deletes it from the process
dictionary. Returns undefined if no value is associated with Key.
Raises an exception of class error with the reason Reason.
Raises an exception of class error with the reason Reason. Args is
expected to be the list of arguments for the current function or the atom
none.
Raises an exception of class error with the reason Reason. Args is
expected to be the list of arguments for the current function or the atom
none.
Raises an exception of class exit with exit reason Reason.
Sends an exit signal with exit reason Reason to the process or port identified
by Pid.
Forces an immediate garbage collection of the executing process.
Equivalent to garbage_collect(Pid, []).
Garbage collects the node local process identified by Pid.
Returns the process dictionary as a list of {Key, Val} tuples. The items in
the returned list can be in any order.
Returns the value Val associated with Key in the process dictionary, or
undefined if Key does not exist.
Returns a list of all keys present in the process dictionary. The items in the returned list can be in any order.
Returns a list of keys that are associated with the value Val in the process
dictionary. The items in the returned list can be in any order.
Returns the process identifier of the group leader for the process evaluating the function.
Sets the group leader of Pid to GroupLeader. Typically, this is used when a
process started from a certain shell is to have another group leader than
init.
Puts the calling process into a wait state where its memory allocation has been reduced as much as possible. This is useful if the process does not expect to receive any messages soon.
Pid must refer to a process at the local node.
Sets up and activates a link between the calling process and another process or
a port identified by PidOrPort.
Sends a monitor request of type Type to the entity identified by Item.
Works exactly like error/1, but Dialyzer thinks that this BIF will return an
arbitrary term. When used in a stub function for a NIF to generate an exception
when the NIF library is not loaded, Dialyzer does not generate false warnings.
Works exactly like error/2, but Dialyzer thinks that this BIF will return an
arbitrary term. When used in a stub function for a NIF to generate an exception
when the NIF library is not loaded, Dialyzer does not generate false warnings.
Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process.
Performs a synchronous call to a port. The meaning of Operation and Data
depends on the port, that is, on the port driver. Not all port drivers support
this feature.
Closes an open port. Roughly the same as Port ! {self(), close} except for the
error behavior (see below), being synchronous, and that the port does not
reply with {Port, closed}.
Sends data to a port. Same as Port ! {PortOwner, {command, Data}} except for
the error behavior and being synchronous (see below).
Sends data to a port. port_command(Port, Data, []) equals
port_command(Port, Data).
Sets the port owner (the connected port) to Pid. Roughly the same as
Port ! {Owner, {connect, Pid}} except for the following
Performs a synchronous control operation on a port. The meaning of Operation
and Data depends on the port, that is, on the port driver. Not all port
drivers support this control feature.
Returns a list containing tuples with information about Port, or undefined
if the port is not open.
Returns information about Port.
Returns a list of port identifiers corresponding to all the ports existing on the local node.
Writes information about the local process Pid on standard error.
Sets the process flag indicated to the specified value. Returns the previous value of the flag.
Sets certain flags for the process Pid, in the same manner as
process_flag/2. Returns the old value of the flag. The valid values for Flag
are only a subset of those allowed in process_flag/2,
namely save_calls.
Returns a list containing InfoTuples with miscellaneous information about the
process identified by Pid, or undefined if the process is not alive.
Returns information about the process identified by Pid, as specified by
Item or ItemList. Returns undefined if the process is not alive.
Returns a list of process identifiers corresponding to all the processes currently existing on the local node.
Adds a new Key to the process dictionary, associated with the value Val, and
returns undefined. If Key exists, the old value is deleted and replaced by
Val, and the function returns the old value.
Raises an exception of the specified class, reason, and call stack backtrace (stacktrace).
Registers the name RegName with a process identifier (pid) or a port
identifier in the
name registry.
RegName, which must be an atom, can be used instead of the pid or port
identifier in send operator (RegName ! Message) and most other BIFs that take
a pid or port identifies as an argument.
Returns a list of names that have been registered using register/2.
Decreases the suspend count on the process identified by Suspendee.
Returns the process identifier of the calling process.
Sends a message and returns Msg. This is the same as using the
send operator: Dest ! Msg.
Either sends a message and returns ok, or does not send the message but
returns something else (see below). Otherwise the same as
erlang:send/2.
Send a message without suspending the caller.
Equivalent to erlang:send(Dest, Msg, [nosuspend | Options]), but
with a Boolean return value.
Returns the process identifier of a new process started by the application of
Fun to the empty list []. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Fun to the empty list [] on Node. If Node does not exist, a useless pid
is returned. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Module:Function to Args.
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Fun to the empty list []. A link is created between the calling process and
the new process, atomically. Otherwise works like spawn/3.
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. A link is created between the calling
process and the new process, atomically. If Node does not exist, a useless pid
is returned and an exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Module:Function to Args. A link is created between the calling process and
the new process, atomically. Otherwise works like spawn/3.
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. A link is created between the calling
process and the new process, atomically. If Node does not exist, a useless pid
is returned and an exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
Returns the process identifier of a new process, started by the application of
Fun to the empty list [], and a reference for a monitor created to the new
process. Otherwise works like spawn/3.
Returns the process identifier of a new process, started by the application of
Fun to the empty list [] on the node Node, and a reference for a monitor
created to the new process. Otherwise works like spawn/3.
A new process is started by the application of Module:Function to Args. The
process is monitored at the same time. Returns the process identifier and a
reference for the monitor. Otherwise works like spawn/3.
A new process is started by the application of Module:Function to Args on
the node Node. The process is monitored at the same time. Returns the process
identifier and a reference for the monitor. Otherwise works like spawn/3.
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list []. Otherwise works like spawn_opt/4.
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn_opt/4.
Works as spawn/3, except that an extra option list is specified when creating
the process.
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn_opt/4.
Equivalent to the call spawn_request(node(),Fun,[]). That
is, a spawn request on the local node with no options.
Equivalent to spawn_request(node(),Fun,Options) or
spawn_request(Node,Fun,[]) depending on the arguments.
Equivalent to
spawn_request(Node,erlang,apply,[Fun,[]],Options) or
spawn_request(node(),Module,Function,Args,[]) depending
on the arguments.
Equivalent to
spawn_request(Node,Module,Function,Args,[]) or
spawn_request(node(),Module,Function,Args,Options)
depending on the arguments.
Asynchronously send a spawn request. Returns a request identifier ReqId.
Abandon a previously issued spawn request. ReqId corresponds to a request
identifier previously returned by spawn_request() in a
call from current process. That is, only the process that has made the request
can abandon the request.
Suspends the process identified by Suspendee. Equivalent to calling
erlang:suspend_process(Suspendee, []).
Increases the suspend count on the process identified by Suspendee and puts it
in the suspended state if it is not already in that state. A suspended process
is not scheduled for execution until the process has been resumed.
Raises an exception of class throw. Intended to be used to do non-local
returns from functions.
Deactivate the alias Alias previously created by the calling process.
Removes a link between the calling process and another process or a port
identified by Id.
Removes the registered name RegName associated with a
process identifier or a port identifier from the
name registry.
Returns the process identifier or port identifier with the
registered name RegName from the
name registry. Returns
undefined if the name is not registered.
Tries to give other processes with the same or higher priority (if any) a chance
to execute before returning. There is no guarantee that any other process runs
between the invocation and return of erlang:yield/0.
System
Equivalent to calling halt(0, []).
Equivalent to calling halt(HaltType, []).
Halt the runtime system.
Returns a list with information about memory dynamically allocated by the Erlang emulator.
Returns the memory size in bytes allocated for memory of type Type. The
argument can also be specified as a list of memory_type/0 atoms, in which case
a corresponding list of {memory_type(), Size :: integer >= 0} tuples is
returned.
Returns statistics about the current system.
Sets a system flag to the given value.
Returns information about the current system.
Returns the current system monitoring settings set by
erlang:system_monitor/2 as {MonitorPid, Options}, or
undefined if no settings exist.
When called with argument undefined, all system performance monitoring
settings are cleared.
Sets the system performance monitoring options. MonitorPid is a local process
identifier (pid) receiving system monitor messages.
Returns the current system profiling settings set by
erlang:system_profile/2 as {ProfilerPid, Options}, or
undefined if there are no settings. The order of the options can be different
from the one that was set.
Sets system profiler options. ProfilerPid is a local process identifier (pid)
or port receiving profiling messages. The receiver is excluded from all
profiling. The second argument is a list of profiling options
Time and timers
Equivalent to erlang:cancel_timer(TimerRef, []).
Cancels a timer that has been created by erlang:start_timer
or erlang:send_after. TimerRef identifies the timer, and
was returned by the BIF that created the timer.
Converts the Time value of time unit FromUnit to the corresponding
ConvertedTime value of time unit ToUnit. The result is rounded using the
floor/1 function.
Returns the current date as {Year, Month, Day}.
Returns the current local date and time,
{{Year, Month, Day}, {Hour, Minute, Second}}.
Converts local date and time to Universal Time Coordinated (UTC), if supported
by the underlying OS. Otherwise no conversion is done and Localtime is
returned.
Converts local date and time to Universal Time Coordinated (UTC) as
erlang:localtime_to_universaltime/1, but the caller decides if Daylight Saving
Time is active.
Returns the current
Erlang monotonic time in native
time unit. This is a monotonically increasing time
since some unspecified point in time.
Returns the current
Erlang monotonic time converted into
the Unit passed as argument.
Equivalent to erlang:read_timer(TimerRef, []).
Reads the state of a timer that has been created by either
erlang:start_timer or
erlang:send_after. TimerRef identifies the timer, and was
returned by the BIF that created the timer.
Equivalent to erlang:send_after(Time, Dest, Msg, []).
Starts a timer. When the timer expires, the message Msg is sent to the process
identified by Dest. Apart from the format of the time-out message, this
function works exactly as erlang:start_timer/4.
Equivalent to erlang:start_timer(Time, Dest, Msg, []).
Starts a timer. When the timer expires, the message {timeout, TimerRef, Msg}
is sent to the process identified by Dest.
Returns current Erlang system time in
native time unit.
Returns current Erlang system time
converted into the Unit passed as argument.
Returns the current time as {Hour, Minute, Second}.
Returns the current time offset between
Erlang monotonic time and
Erlang system time in native
time unit. Current time offset added to an Erlang
monotonic time gives corresponding Erlang system time.
Returns the current time offset between
Erlang monotonic time and
Erlang system time converted into the
Unit passed as argument.
Returns current Erlang system time on
the format {MegaSecs, Secs, MicroSecs}.
Returns the current date and time according to Universal Time Coordinated (UTC)
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the
underlying OS. Otherwise erlang:universaltime() is equivalent to
erlang:localtime(). The return value is based on the
OS System Time.
Converts Universal Time Coordinated (UTC) date and time to local date and time
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the
underlying OS. Otherwise no conversion is done, and Universaltime is returned.
Tracing
Turn on or off trace flags on processes or ports for the static legacy trace session.
Calling this function makes sure all trace messages have been delivered.
Returns trace information about a port, process, function, or event for the static legacy trace session.
Equivalent to erlang:trace_pattern(Event, MatchSpec, []),
retained for backward compatibility.
Set trace pattern for call, send and receive tracing on the static legacy trace session.
Deprecated functions
Warning
This function is deprecated. Do not use it.
Warning
This function is deprecated as erlang:phash2/2 should be used
for new code. Note that erlang:phash(X,N) is not necessary equal to
erlang:phash2(X,N)
Predefined datatypes
-type nil() :: [].
The empty list/0.
-type any() :: any().
All possible Erlang terms. Synonym for term/0.
-type arity() :: arity().
The arity of a function or type.
-type atom() :: atom().
An Erlang atom.
-type binary() :: <<_:_*8>>.
An Erlang binary, that is, a bitstring with a size divisible by 8.
-type bitstring() :: <<_:_*1>>.
An Erlang bitstring.
-type boolean() :: true | false.
A boolean value.
-type byte() :: 0..255.
A byte of data represented by an integer.
-type char() :: 0..1114111.
An ASCII character or a unicode codepoint presented by an integer.
-type dynamic() :: dynamic().
The dynamic type, which represents a statically unknown type
-type float() :: float().
An Erlang float.
-type function() :: fun().
An Erlang fun.
An unique identifier for some entity, for example a process, port or monitor.
-type integer() :: integer().
An Erlang integer.
A binary or list containing bytes and/or iodata.
This datatype is used to represent data that is meant to be output using
any I/O module. For example: file:write/2 or gen_tcp:send/2.
To convert an iodata/0 term to binary/0 you can use
iolist_to_binary/2. To transcode a string/0 or
unicode:chardata/0 to iodata/0 you can use unicode:characters_to_binary/1.
-type iolist() :: maybe_improper_list(byte() | binary() | iolist(), binary() | []).
A list containing bytes and/or iodata.
This datatype is used to represent data that is meant to be output using any
I/O module. For example: file:write/2 or gen_tcp:send/2.
In most use cases you want to use iodata/0 instead of this type.
-type list() :: [any()].
An Erlang list containing terms of any type.
-type list(ContentType) :: [ContentType].
An Erlang list containing terms of the type
ContentType.
An Erlang map containing any number of key and value associations.
-type maybe_improper_list() :: maybe_improper_list(any(), any()).
An Erlang list that is not guaranteed to end
with a [], and where the list elements can be of any type.
-type maybe_improper_list(ContentType, TerminationType) :: maybe_improper_list(ContentType, TerminationType).
An Erlang list, that is not guaranteed to end
with a [], and where the list elements are of the type
ContentType.
A three-tuple representing a Module:Function/Arity function signature.
-type module() :: atom().
An Erlang module represented by an atom.
-type neg_integer() :: neg_integer().
A negative integer.
-type no_return() :: none().
The type used to show that a function will never return a value, that is it will always throw an exception.
-type node() :: atom().
An Erlang node represented by an atom.
-type non_neg_integer() :: non_neg_integer().
A non-negative integer, that is any positive integer or 0.
-type none() :: none().
This type is used to show that a function will never return a value; that is it will always throw an exception.
In a spec, use no_return/0 for the sake of clarity.
-type nonempty_binary() :: <<_:8, _:_*8>>.
A binary/0 that contains some data.
-type nonempty_bitstring() :: <<_:1, _:_*1>>.
A bitstring/0 that contains some data.
-type nonempty_improper_list(ContentType, TerminationType) :: nonempty_improper_list(ContentType, TerminationType).
A maybe_improper_list/2 that contains some items.
-type nonempty_list() :: [any(), ...].
A list/0 that contains some items.
-type nonempty_list(ContentType) :: [ContentType, ...].
A list(ContentType) that contains some items.
-type nonempty_maybe_improper_list() :: nonempty_maybe_improper_list(any(), any()).
A maybe_improper_list/0 that contains some items.
-type nonempty_maybe_improper_list(ContentType, TerminationType) :: nonempty_maybe_improper_list(ContentType, TerminationType).
A maybe_improper_list(ContentType, TerminationType) that contains some items.
-type nonempty_string() :: [char(), ...].
A string/0 that contains some characters.
An Erlang number.
-type pid() :: pid().
An Erlang process identifier.
-type port() :: port().
An Erlang port identifier.
-type pos_integer() :: pos_integer().
An integer greater than zero.
-type reference() :: reference().
An Erlang reference.
-type string() :: [char()].
A character string represented by a list of ASCII characters or unicode codepoints.
-type term() :: any().
All possible Erlang terms. Synonym for any/0.
-type timeout() :: infinity | non_neg_integer().
A timeout value that can be passed to a receive expression.
-type tuple() :: tuple().
An Erlang tuple.
Types
-type bitstring_list() :: maybe_improper_list(byte() | bitstring() | bitstring_list(), bitstring() | []).
-type cpu_topology() :: [LevelEntry :: level_entry()] | undefined.
The current cpu topology.
node refers to Non-Uniform Memory Access (NUMA) nodes. thread refers
to hardware threads (for example, Intel hyper-threads).
A level in term CpuTopology can be omitted if only one entry exists and
InfoList is empty.
thread can only be a sublevel to core. core can be a sublevel to
processor or node. processor can be on the top level or a sublevel to
node. node can be on the top level or a sublevel to processor. That
is, NUMA nodes can be processor internal or processor external. A CPU
topology can consist of a mix of processor internal and external NUMA nodes,
as long as each logical CPU belongs to one NUMA node. Cache hierarchy is
not part of the CpuTopology type, but will be in a future release. Other
things can also make it into the CPU topology in a future release. So, expect
the CpuTopology type to change.
-type deprecated_time_unit() :: seconds | milli_seconds | micro_seconds | nano_seconds.
The time_unit/0 type also consist of the following deprecated symbolic
time units:
seconds- Same assecond.milli_seconds- Same asmillisecond.micro_seconds- Same asmicrosecond.nano_seconds- Same asnanosecond.
-opaque dist_handle()
An opaque handle identifying a distribution channel.
-type ext_binary() :: binary().
A binary data object, structured according to the Erlang external term format.
-type ext_iovec() :: iovec().
A term of type iovec/0, structured according to the Erlang external term
format.
-type fun_info_item() :: arity | env | index | name | module | new_index | new_uniq | pid | type | uniq.
-type garbage_collection_defaults() :: [{max_heap_size, non_neg_integer()} | {min_bin_vheap_size, non_neg_integer()} | {min_heap_size, non_neg_integer()} | {fullsweep_after, non_neg_integer()}].
A list with the system wide garbage collection defaults.
-type halt_options() :: [{flush, boolean()} | {flush_timeout, Timeout :: 0..2147483647 | infinity}].
-type info_list() :: [].
-type iovec() :: [binary()].
A list of binaries. This datatype is useful to use together with
enif_inspect_iovec.
-type level_tag() :: core | node | processor | thread.
-type match_variable() :: atom().
-type max_heap_size() :: Size :: non_neg_integer() | #{size => non_neg_integer(), kill => boolean(), error_logger => boolean(), include_shared_binaries => boolean()}.
Process max heap size configuration. For more info see
process_flag(max_heap_size, MaxHeapSize)
-type memory_type() ::
total | processes | processes_used | system | atom | atom_used | binary | code | ets.
-type message_queue_data() :: off_heap | on_heap.
See
process_flag(message_queue_data, MQD).
Process message queue data configuration. For more information, see
process_flag(message_queue_data, MQD)
-type monitor_option() :: {alias, explicit_unalias | demonitor | reply_demonitor} | {tag, term()}.
See monitor/3.
-type monitor_port_identifier() :: port() | registered_name().
-type monitor_process_identifier() :: pid() | registered_process_identifier().
-opaque nif_resource()
An opaque handle identifying a NIF resource object .
-opaque prepared_code()
-type priority_level() :: low | normal | high | max.
Process priority level. For more info see
process_flag(priority, Level)
-type process_info_item() :: async_dist | backtrace | binary | catchlevel | current_function | current_location | current_stacktrace | dictionary | {dictionary, Key :: term()} | error_handler | garbage_collection | garbage_collection_info | group_leader | heap_size | initial_call | links | label | last_calls | memory | message_queue_len | messages | min_heap_size | min_bin_vheap_size | monitored_by | monitors | message_queue_data | parent | priority | reductions | registered_name | sequential_trace_token | stack_size | status | suspending | total_heap_size | trace | trap_exit.
-type process_info_result_item() :: {async_dist, Enabled :: boolean()} | {backtrace, Bin :: binary()} | {binary, BinInfo :: [{non_neg_integer(), non_neg_integer(), non_neg_integer()}]} | {catchlevel, CatchLevel :: non_neg_integer()} | {current_function, {Module :: module(), Function :: atom(), Arity :: arity()} | undefined} | {current_location, {Module :: module(), Function :: atom(), Arity :: arity(), Location :: [{file, Filename :: string()} | {line, Line :: pos_integer()}]}} | {current_stacktrace, Stack :: [stack_item()]} | {dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} | {{dictionary, Key :: term()}, Value :: term()} | {error_handler, Module :: module()} | {garbage_collection, GCInfo :: [{atom(), non_neg_integer()}]} | {garbage_collection_info, GCInfo :: [{atom(), non_neg_integer()}]} | {group_leader, GroupLeader :: pid()} | {heap_size, Size :: non_neg_integer()} | {initial_call, mfa()} | {links, PidsAndPorts :: [pid() | port()]} | {label, term()} | {last_calls, false | (Calls :: [mfa()])} | {memory, Size :: non_neg_integer()} | {message_queue_len, MessageQueueLen :: non_neg_integer()} | {messages, MessageQueue :: [term()]} | {min_heap_size, MinHeapSize :: non_neg_integer()} | {min_bin_vheap_size, MinBinVHeapSize :: non_neg_integer()} | {max_heap_size, MaxHeapSize :: max_heap_size()} | {monitored_by, MonitoredBy :: [pid() | port() | nif_resource()]} | {monitors, Monitors :: [{process | port, Pid :: pid() | port() | {RegName :: atom(), Node :: node()}}]} | {message_queue_data, MQD :: message_queue_data()} | {parent, pid() | undefined} | {priority, Level :: priority_level()} | {reductions, Number :: non_neg_integer()} | {registered_name, [] | (Atom :: atom())} | {sequential_trace_token, [] | (SequentialTraceToken :: term())} | {stack_size, Size :: non_neg_integer()} | {status, Status :: exiting | garbage_collecting | waiting | running | runnable | suspended} | {suspending, SuspendeeList :: [{Suspendee :: pid(), ActiveSuspendCount :: non_neg_integer(), OutstandingSuspendCount :: non_neg_integer()}]} | {total_heap_size, Size :: non_neg_integer()} | {trace, InternalTraceFlags :: non_neg_integer()} | {trap_exit, Boolean :: boolean()}.
-type raise_stacktrace() :: [{module(), atom(), arity() | [term()]} | {function(), arity() | [term()]}] | stacktrace().
A extended stacktrace/0 that can be passed to raise/3.
-type registered_name() :: atom().
-type registered_process_identifier() :: registered_name() | {registered_name(), node()}.
-type scheduler_bind_type() ::
no_node_processor_spread | no_node_thread_spread | no_spread | processor_spread | spread |
thread_spread | thread_no_node_processor_spread | unbound.
The requested scheduler bind type.
-type send_destination() :: pid() | reference() | port() | (RegName :: atom()) | {RegName :: atom(), Node :: node()}.
The destination for a send operation.
This can be a remote or local process identifier, a (local) port, a reference
denoting a process alias, a locally registered name, or a tuple {RegName, Node}
for a registered name at another node.
-type spawn_opt_option() :: link | monitor | {monitor, MonitorOpts :: [monitor_option()]} | {priority, Level :: priority_level()} | {fullsweep_after, Number :: non_neg_integer()} | {min_heap_size, Size :: non_neg_integer()} | {min_bin_vheap_size, VSize :: non_neg_integer()} | {max_heap_size, Size :: max_heap_size()} | {message_queue_data, MQD :: message_queue_data()} | {async_dist, Enabled :: boolean()}.
Options for spawn_opt().
-type stacktrace() :: [{module(), atom(), arity() | [term()], [stacktrace_extrainfo()]} | {function(), arity() | [term()], [stacktrace_extrainfo()]}].
An Erlang stacktrace as described by Errors and Error Handling section in the Erlang Reference Manual.
-type stacktrace_extrainfo() :: {line, pos_integer()} | {file, unicode:chardata()} | {error_info, #{module => module(), function => atom(), cause => term()}} | {atom(), term()}.
-type sub_level() :: [LevelEntry :: level_entry()] | (LogicalCpuId :: {logical, non_neg_integer()}).
-type system_monitor_option() :: busy_port | busy_dist_port | {long_gc, non_neg_integer()} | {long_message_queue, {Disable :: non_neg_integer(), Enable :: pos_integer()}} | {long_schedule, non_neg_integer()} | {large_heap, non_neg_integer()}.
-type system_profile_option() ::
exclusive | runnable_ports | runnable_procs | scheduler | timestamp | monotonic_timestamp |
strict_monotonic_timestamp.
-type time_unit() :: pos_integer() | second | millisecond | microsecond | nanosecond | native | perf_counter | deprecated_time_unit().
The time unit used by erlang time APIs.
Supported time unit representations:
PartsPerSecond :: integer() >= 1- Time unit expressed in parts per second. That is, the time unit equals1/PartsPerSecondsecond.second- Symbolic representation of the time unit represented by the integer1.millisecond- Symbolic representation of the time unit represented by the integer1000.microsecond- Symbolic representation of the time unit represented by the integer1000_000.nanosecond- Symbolic representation of the time unit represented by the integer1000_000_000.native- Symbolic representation of the native time unit used by the Erlang runtime system.The
nativetime unit is determined at runtime system start, and remains the same until the runtime system terminates. If a runtime system is stopped and then started again (even on the same machine), thenativetime unit of the new runtime system instance can differ from thenativetime unit of the old runtime system instance.One can get an approximation of the
nativetime unit by callingerlang:convert_time_unit(1, second, native). The result equals the number of wholenativetime units per second. If the number ofnativetime units per second does not add up to a whole number, the result is rounded downwards.Note
The value of the
nativetime unit gives you more or less no information about the quality of time values. It sets a limit for the resolution and for the precision of time values, but it gives no information about the accuracy of time values. The resolution of thenativetime unit and the resolution of time values can differ significantly.perf_counter- Symbolic representation of the performance counter time unit used by the Erlang runtime system.The
perf_countertime unit behaves much in the same way as thenativetime unit. That is, it can differ between runtime restarts. To get values of this type, callos:perf_counter/0.deprecated_time_unit/0- Deprecated symbolic representations kept for backwards-compatibility.
The time_unit/0 type can be extended. To convert time values between time
units, use erlang:convert_time_unit/3.
-type timestamp() :: {MegaSecs :: non_neg_integer(), Secs :: non_neg_integer(), MicroSecs :: non_neg_integer()}.
See erlang:timestamp/0.
-type trace_flag() :: all | send | 'receive' | procs | ports | call | arity | return_to | silent | running | exiting | running_procs | running_ports | garbage_collection | timestamp | cpu_timestamp | monotonic_timestamp | strict_monotonic_timestamp | set_on_spawn | set_on_first_spawn | set_on_link | set_on_first_link | {tracer, pid() | port()} | {tracer, module(), term()}.
-type trace_info_flag() ::
send | 'receive' | set_on_spawn | call | return_to | procs | set_on_first_spawn |
set_on_link | running | garbage_collection | timestamp | monotonic_timestamp |
strict_monotonic_timestamp | arity.
-type trace_info_item_result() :: {traced, global | local | false | undefined} | {match_spec, trace_match_spec() | false | undefined} | {meta, pid() | port() | false | undefined | []} | {meta, module(), term()} | {meta_match_spec, trace_match_spec() | false | undefined} | {call_count, non_neg_integer() | boolean() | undefined} | {call_time | call_memory, [{pid(), non_neg_integer(), non_neg_integer(), non_neg_integer()}] | boolean() | undefined}.
-type trace_info_return() :: undefined | {flags, [trace_info_flag()]} | {tracer, pid() | port() | []} | {tracer, module(), term()} | trace_info_item_result() | {all, [trace_info_item_result()] | false | undefined}.
-type trace_match_spec() :: [{[term()] | '_' | match_variable(), [term()], [term()]}].
Checksum
-spec adler32(Data) -> non_neg_integer() when Data :: iodata().
Computes and returns the adler32 checksum for Data.
-spec adler32(OldAdler, Data) -> non_neg_integer() when OldAdler :: non_neg_integer(), Data :: iodata().
Continues computing the adler32 checksum by combining the previous checksum,
OldAdler, with the checksum of Data.
The following code:
X = erlang:adler32(Data1),
Y = erlang:adler32(X,Data2).assigns the same value to Y as this:
Y = erlang:adler32([Data1,Data2]).
-spec adler32_combine(FirstAdler, SecondAdler, SecondSize) -> non_neg_integer() when FirstAdler :: non_neg_integer(), SecondAdler :: non_neg_integer(), SecondSize :: non_neg_integer().
Combines two previously computed adler32 checksums.
This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:adler32(Data1),
Z = erlang:adler32(Y,Data2).assigns the same value to Z as this:
X = erlang:adler32(Data1),
Y = erlang:adler32(Data2),
Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
-spec crc32(Data) -> non_neg_integer() when Data :: iodata().
Computes and returns the crc32 (IEEE 802.3 style) checksum for Data.
-spec crc32(OldCrc, Data) -> non_neg_integer() when OldCrc :: non_neg_integer(), Data :: iodata().
Continues computing the crc32 checksum by combining the previous checksum,
OldCrc, with the checksum of Data.
The following code:
X = erlang:crc32(Data1),
Y = erlang:crc32(X,Data2).assigns the same value to Y as this:
Y = erlang:crc32([Data1,Data2]).
-spec crc32_combine(FirstCrc, SecondCrc, SecondSize) -> non_neg_integer() when FirstCrc :: non_neg_integer(), SecondCrc :: non_neg_integer(), SecondSize :: non_neg_integer().
Combines two previously computed crc32 checksums.
This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:crc32(Data1),
Z = erlang:crc32(Y,Data2).assigns the same value to Z as this:
X = erlang:crc32(Data1),
Y = erlang:crc32(Data2),
Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
Computes an MD5 message digest from Data, where the length of the digest is
128 bits (16 bytes). Data is a binary or a list of small integers and
binaries.
For more information about MD5, see RFC 1321 - The MD5 Message-Digest Algorithm.
Warning
The MD5 Message-Digest Algorithm is not considered safe for code-signing or software-integrity purposes.
Finishes the update of an MD5 Context and returns the computed MD5 message
digest.
-spec md5_init() -> Context when Context :: binary().
Creates an MD5 context, to be used in the following calls to
md5_update/2.
-spec md5_update(Context, Data) -> NewContext when Context :: binary(), Data :: iodata(), NewContext :: binary().
Update an MD5 Context with Data and returns a NewContext.
Code
Returns true if Module has
old code, otherwise false.
See also code.
-spec check_process_code(Pid, Module) -> CheckResult when Pid :: pid(), Module :: module(), CheckResult :: boolean().
Equivalent to check_process_code(Pid, Module, []).
-spec check_process_code(Pid, Module, OptionList) -> CheckResult | async when Pid :: pid(), Module :: module(), RequestId :: term(), Option :: {async, RequestId} | {allow_gc, boolean()}, OptionList :: [Option], CheckResult :: boolean() | aborted.
Checks if the node local process identified by Pid executes old code for
Module.
Options:
{allow_gc, boolean()}- Determines if garbage collection is allowed when performing the operation. If{allow_gc, false}is passed, and a garbage collection is needed to determine the result of the operation, the operation is aborted (see information onCheckResultbelow). The default is to allow garbage collection, that is,{allow_gc, true}.{async, RequestId}- The functioncheck_process_code/3returns the valueasyncimmediately after the request has been sent. When the request has been processed, the process that called this function is passed a message on the form{check_process_code, RequestId, CheckResult}.
If Pid equals self/0, and no async option has been passed, the operation
is performed at once. Otherwise a request for the operation is sent to the
process identified by Pid, and is handled when appropriate. If no async
option has been passed, the caller blocks until CheckResult is available and
can be returned.
CheckResult informs about the result of the request as follows:
true- The process identified byPidexecutes old code forModule. That is, the current call of the process executes old code for this module, or the process has references to old code for this module, or the process contains funs that references old code for this module.false- The process identified byPiddoes not execute old code forModule.aborted- The operation was aborted, as the process needed to be garbage collected to determine the operation result, and the operation was requested by passing option{allow_gc, false}.
Change
Up until ERTS version 8.*, the check process code operation checks for all
types of references to the old code. That is, direct references (e.g. return
addresses on the process stack), indirect references (funs in process
context), and references to literals in the code.
As of ERTS version 9.0, the check process code operation only checks for
direct references to the code. Indirect references via funs will be ignored.
If such funs exist and are used after a purge of the old code, an exception
will be raised upon usage (same as the case when the fun is received by the
process after the purge). Literals will be taken care of (copied) at a later
stage. This behavior can as of ERTS version 8.1 be enabled when
building OTP,
and will automatically be enabled if dirty scheduler support is enabled.
See also code.
Failures:
badarg- IfPidis not a node local process identifier.badarg- IfModuleis not an atom.badarg- IfOptionListis an invalid list of options.
-spec delete_module(Module) -> true | undefined when Module :: module().
Makes the current code for Module become old code and deletes all references
for this module from the export table. Returns undefined if the module does
not exist, otherwise true.
Warning
This BIF is intended for the code server (see code) and is not to be used
elsewhere.
Failure: badarg if there already is an old version of Module.
-spec function_exported(Module, Function, Arity) -> boolean() when Module :: module(), Function :: atom(), Arity :: arity().
Returns true if the module Module is
current and contains an exported
function Function/Arity, or if there is a BIF (a built-in function implemented
in C) with the specified name, otherwise returns false.
-spec is_builtin(Module, Function, Arity) -> boolean() when Module :: module(), Function :: atom(), Arity :: arity().
This BIF is useful for builders of cross-reference tools.
Returns true if Module:Function/Arity is a BIF implemented in C, otherwise
false.
-spec load_module(Module, Binary) -> {module, Module} | {error, Reason} when Module :: module(), Binary :: binary(), Reason :: badfile | not_purged | on_load | {features_not_allowed, [atom()]}.
Loads Module described by the object code contained within Binary.
If the code for module Module already exists, all export
references are replaced so they point to the newly loaded code. The previously
loaded code is kept in the system as old code, as there can still be processes
executing that code.
Returns either {module, Module}, or {error, Reason} if loading fails.
Reason is one of the following:
badfile- The object code inBinaryhas an incorrect format or the object code contains code for another module thanModule.not_purged-Binarycontains a module that cannot be loaded because old code for this module already exists.on_load- The code inBinarycontains anon_loaddeclaration that must be executed beforeBinarycan become the current code. Any previous current code forModulewill remain until theon_loadcall has finished.not_allowed - The code in
Binaryhas been compiled with features that are currently not enabled in the runtime system.
Warning
This BIF is intended for the code server (see code) and is not to be used
elsewhere.
-spec load_nif(Path, LoadInfo) -> ok | Error when Path :: string(), LoadInfo :: term(), Error :: {error, {Reason, Text :: string()}}, Reason :: load_failed | bad_lib | load | reload | upgrade | old_code.
Loads and links a dynamic library containing native implemented functions (NIFs) for a module.
Path is a file path to the shareable object/dynamic library file
minus the OS-dependent file extension (.so for Unix and .dll for Windows).
Notice that on most OSs the library has to have a different name on disc when an
upgrade of the nif is done. If the name is the same, but the contents differ,
the old library may be loaded instead. For information on how to implement a NIF
library, see erl_nif(3).
LoadInfo can be any term. It is passed on to the library as part of the
initialization. A good practice is to include a module version number to support
future code upgrade scenarios.
The call to load_nif/2 must be made directly from the Erlang
code of the module that the NIF library belongs to. It returns either ok, or
{error,{Reason,Text}} if loading fails. Reason is one of the following atoms
while Text is a human readable string that can give more information about the
failure:
load_failed- The OS failed to load the NIF library.bad_lib- The library did not fulfill the requirements as a NIF library of the calling module.load | upgrade- The corresponding library callback was unsuccessful.reload- A NIF library is already loaded for this module instance. The previously deprecatedreloadfeature was removed in OTP 20.old_code- The call toload_nif/2was made from the old code of a module that has been upgraded; this is not allowed.
If the -nifs() attribute is used
(which is recommended), all NIFs in the dynamic library must be declared as such
for load_nif/2 to succeed. On the other hand, all functions
declared with the -nifs() attribute do not have to be implemented by the
dynamic library. This allows a target independent Erlang file to contain
fallback implementations for functions that may lack NIF support depending on
target OS/hardware platform.
-spec loaded() -> [Module] when Module :: module().
Returns a list of all loaded Erlang modules (current and old code), including preloaded modules.
See also code.
Returns true if the module Module is loaded as
current code; otherwise,
false. It does not attempt to load the module.
-spec pre_loaded() -> [module()].
Returns a list of Erlang modules that are preloaded in the run-time system.
Pre-loaded modules are Erlang modules that are needed to bootstrap the system to
load the first Erlang modules from either disk or by using erl_boot_server.
-spec purge_module(Module) -> true when Module :: atom().
Removes old code for Module. Before this BIF is used, check_process_code/2
is to be called to check that no processes execute old code in the module.
Warning
This BIF is intended for the code server (see code) and is not to be used
elsewhere.
Change
As from ERTS 8.0 (Erlang/OTP 19), any lingering processes that still execute the old code is killed by this function. In earlier versions, such incorrect use could cause much more fatal failures, like emulator crash.
Failure: badarg if there is no old code for Module.
Distributed Erlang
Forces the disconnection of a node.
Doing this makes it appears to the node Node as if the local node has crashed.
This BIF is mainly used in the Erlang network authentication protocols.
Returns true if disconnection succeeds, otherwise false. If the local node
is not alive, ignored is returned.
Note
This function may return before nodedown messages have
been delivered.
-spec dist_ctrl_get_data(DHandle) -> {Size, Data} | Data | none when Size :: non_neg_integer(), DHandle :: dist_handle(), Data :: iovec().
Get distribution channel data from the local node that is to be passed to the remote node.
The distribution channel is identified by DHandle. If no data is
available, the atom none is returned. One can request to be informed by a
message when more data is available by calling
erlang:dist_ctrl_get_data_notification(DHandle).
The returned value when there are data available depends on the value of the
get_size option configured on the distribution channel identified by
DHandle. For more information see the documentation of the get_size option
for the erlang:dist_ctrl_set_opt/3 function.
Note
Only the process registered as distribution controller for the distribution
channel identified by DHandle is allowed to call this function.
This function is used when implementing an alternative distribution carrier
using processes as distribution controllers. DHandle is retrieved via the
callback f_handshake_complete.
More information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec dist_ctrl_get_data_notification(DHandle) -> ok when DHandle :: dist_handle().
Request notification when more data is available to fetch using
erlang:dist_ctrl_get_data(DHandle) for the
distribution channel identified by DHandle.
When more data is present, the caller will be sent the message dist_data.
Once a dist_data messages has been sent, no more dist_data messages will
be sent until the dist_ctrl_get_data_notification/1
function has been called again.
Note
Only the process registered as distribution controller for the distribution
channel identified by DHandle is allowed to call this function.
This function is used when implementing an alternative distribution carrier
using processes as distribution controllers. DHandle is retrieved via the
callback f_handshake_complete.
More information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec dist_ctrl_get_opt(DHandle, get_size) -> Value when DHandle :: dist_handle(), Value :: boolean().
Returns the value of the get_size option on the distribution channel
identified by DHandle. For more information see the documentation of the
get_size option for the erlang:dist_ctrl_set_opt/3
function.
Note
Only the process registered as distribution controller for the distribution
channel identified by DHandle is allowed to call this function.
This function is used when implementing an alternative distribution carrier
using processes as distribution controllers. DHandle is retrieved via the
callback f_handshake_complete.
More information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec dist_ctrl_input_handler(DHandle, InputHandler) -> ok when DHandle :: dist_handle(), InputHandler :: pid().
Register an alternate input handler process for the distribution channel
identified by DHandle.
Once this function has been called, InputHandler is the only process allowed to call
erlang:dist_ctrl_put_data(DHandle, Data) with the
DHandle identifying this distribution channel.
Note
When the distribution controller for the distribution channel identified by
DHandle is a process, it is the only process allowed to call this function.
This function is also allowed to be called when the distribution controller
for the distribution channel identified by DHandle is a port. The data
received by the port should in this case be delivered to the process
identified by InputHandler which in turn should call
erlang:dist_ctrl_put_data/2.
This function is used when implementing an alternative distribution carrier.
DHandle is retrieved via the callback
f_handshake_complete. More
information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec dist_ctrl_put_data(DHandle, Data) -> ok when DHandle :: dist_handle(), Data :: iodata().
Deliver distribution channel data from a remote node to the local node.
Note
Only the process registered as distribution controller for the distribution
channel identified by DHandle is allowed to call this function unless an
alternate input handler process has been registered using
erlang:dist_ctrl_input_handler(DHandle, InputHandler).
If an alternate input handler has been registered, only the registered input
handler process is allowed to call this function.
This function is used when implementing an alternative distribution carrier.
DHandle is retrieved via the callback
f_handshake_complete. More
information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec dist_ctrl_set_opt(DHandle, get_size, Value) -> OldValue when DHandle :: dist_handle(), Value :: boolean(), OldValue :: boolean().
Sets the value of the get_size option on the distribution channel identified
by DHandle.
This option controls the return value of calls to
erlang:dist_ctrl_get_data(DHandle) where DHandle
equals DHandle used when setting this option. When the get_size option is:
false- and there are distribution data available, a call toerlang:dist_ctrl_get_data(DHandle)will just returnDatato pass over the channel. This is the default value of theget_sizeoption.true- and there are distribution data available, a call toerlang:dist_ctrl_get_data(DHandle)will returnDatato pass over the channel as well as theSizeofDatain bytes. This is returned as a tuple on the form{Size, Data}.
All options are set to default when a channel is closed.
Note
Only the process registered as distribution controller for the distribution
channel identified by DHandle is allowed to call this function.
This function is used when implementing an alternative distribution carrier
using processes as distribution controllers. DHandle is retrieved via the
callback f_handshake_complete.
More information can be found in the documentation of
ERTS User's Guide ➜ How to implement an Alternative Carrier for the Erlang Distribution ➜ Distribution Module.
-spec get_cookie() -> Cookie | nocookie when Cookie :: atom().
Returns the magic cookie of the local node if the node is alive, otherwise the
atom nocookie. This value is set by set_cookie/1.
Returns the magic cookie for node Node if the local node is alive, otherwise
the atom nocookie. This value is set by set_cookie/2.
-spec is_alive() -> boolean().
Returns true if the local node is alive (that is, if the node can be part of a
distributed system), otherwise false. A node is alive if it is started with:
A node can also be alive if it has got a name from a call to
net_kernel:start/2 and has not been stopped by a call to net_kernel:stop/0.
Monitor the status of the node Node. If Flag is true, monitoring is turned
on. If Flag is false, monitoring is turned off.
Making several calls to monitor_node(Node, true) for the
same Node is not an error; it results in as many independent monitoring
instances.
If Node fails or does not exist, the message {nodedown, Node} is delivered
to the process. If a process has made two calls to
monitor_node(Node, true) and Node terminates, two
nodedown messages are delivered to the process. If there is no connection to
Node, an attempt is made to create one. If this fails, a nodedown message is
delivered.
The delivery of the nodedown signal is not ordered with respect to other link
or monitor signals from the node that goes down. If you need a guarantee that
all signals from the remote node has been delivered before the nodedown signal
is sent, you should use net_kernel:monitor_nodes/1.
Nodes connected through hidden connections can be monitored as any other nodes.
Failure: notalive if the local node is not alive.
-spec monitor_node(Node, Flag, Options) -> true when Node :: node(), Flag :: boolean(), Options :: [Option], Option :: allow_passive_connect.
Behaves as monitor_node/2 except that it allows an extra option to be
specified, namely allow_passive_connect.
This option allows the BIF to wait the normal network connection time-out
for the monitored node to connect itself, even if it cannot be actively
connected from this node (that is, it is blocked). The state where this can
be useful can only be achieved by using the Kernel option dist_auto_connect once.
If that option is not used, option allow_passive_connect has no effect.
Note
Option allow_passive_connect is used internally and is seldom needed in
applications where the network topology and the Kernel options in effect are
known in advance.
Failure: badarg if the local node is not alive or the option list is
malformed.
-spec node() -> Node when Node :: node().
Returns the name of the local node. If the node is not alive, nonode@nohost is
returned instead.
-spec nodes() -> Nodes when Nodes :: [node()].
Returns a list of all nodes connected to this node through normal connections (that is, hidden nodes are not listed). Same as nodes(visible).
-spec nodes(Arg) -> Nodes when Arg :: NodeType | [NodeType], NodeType :: visible | hidden | connected | this | known, Nodes :: [node()].
Returns a list of nodes according to the argument specified. The returned result, when the argument is a list, is the list of nodes satisfying the disjunction(s) of the list elements.
NodeTypes:
visible- Nodes connected to this node through normal connections.hidden- Nodes connected to this node through hidden connections.connected- All nodes connected to this node.this- This node.known- Nodes that are known to this node. That is, connected nodes and nodes referred to by process identifiers, port identifiers, and references located on this node. The set of known nodes is garbage collected. Notice that this garbage collection can be delayed. For more information, seeerlang:system_info(delayed_node_table_gc).
Some equalities: [node()] = nodes(this),
nodes(connected) = nodes([visible, hidden]), and nodes() = nodes(visible).
-spec nodes(Arg, InfoOpts) -> [NodeInfo] when NodeType :: visible | hidden | connected | this | known, Arg :: NodeType | [NodeType], InfoOpts :: #{connection_id => boolean(), node_type => boolean()}, NodeTypeInfo :: visible | hidden | this | known, ConnectionId :: undefined | integer(), Info :: #{connection_id => ConnectionId, node_type => NodeTypeInfo}, NodeInfo :: {node(), Info}.
Returns a list of NodeInfo tuples.
The first element is the node name. Nodes to be included in the list are determined
by the first argument Arg in the same way as for nodes(Arg).
The second element of NodeInfo tuples is a map containing further information
about the node identified by the first element.
The information present in this map is determined by the
InfoOpts map passed as the second argument. Currently the following
associations are allowed in the InfoOpts map:
connection_id => boolean()- If the value of the association equalstrue, theInfomap in the returned result will contain the keyconnection_idassociated with the valueConnectionId. IfConnectionIdequalsundefined, the node is not connected to the node which the caller is executing on, or is the node which the caller is executing on. IfConnectionIdis an integer, the node is currently connected to the node which the caller is executing on.The integer connection identifier value together with a node name identifies a specific connection instance to the node with that node name. The connection identifier value is node local. That is, on the other node the connection identifier will not be the same value. If a connection is taken down and then taken up again, the connection identifier value will change for the connection to that node. The amount of values for connection identifiers are limited, so it is possible to see the same value for different instances, but quite unlikely. It is undefined how the value change between two consecutive connection instances.
node_type => boolean()- If the value of the association equalstrue, theInfomap in the returned result will contain the keynode_typeassociated with the valueNodeTypeInfo. Currently the following node types exist:visible- The node is connected to the node of the calling process through an ordinary visible connection. That is, the node name would appear in the result returned bynodes/0.hidden- The node is connected to the node of the calling process through a hidden connection. That is, the node name would not appear in the result returned bynodes/0.this- This is the node of the calling process.known- The node is not connected but known to the node of the calling process.
Example:
(a@localhost)1> nodes([this, connected], #{connection_id=>true, node_type=>true}).
[{c@localhost,#{connection_id => 13892108,node_type => hidden}},
{b@localhost,#{connection_id => 3067553,node_type => visible}},
{a@localhost,#{connection_id => undefined,node_type => this}}]
(a@localhost)2>
-spec set_cookie(Cookie) -> true when Cookie :: atom().
Sets the magic cookie of the local node to the atom Cookie, which is also the
cookie for all nodes that have no explicit cookie set with set_cookie/2
Cookie.
See section Distributed Erlang in the Erlang Reference Manual in System Documentation for more information.
You can get this value using get_cookie/0.
Failure: function_clause if the local node is not alive.
Sets the magic cookie for Node to the atom Cookie. If Node is the local
node, the function sets the cookie of all other nodes (that have no explicit
cookie set with this function) to Cookie.
See section Distributed Erlang in the Erlang Reference Manual in System Documentation for more information.
You can get this value using get_cookie/1.
Failure: function_clause if the local node is not alive.
Erlang Terms
-spec abs(Float) -> float() when Float :: float(); (Int) -> non_neg_integer() when Int :: integer().
Returns an integer or float that is the arithmetical absolute value of Float
or Int.
For example:
> abs(-3.33).
3.33
> abs(-3).
3
-spec append_element(Tuple1, Term) -> Tuple2 when Tuple1 :: tuple(), Tuple2 :: tuple(), Term :: term().
Returns a new tuple that has one element more than Tuple1, and contains the
elements in Tuple1 followed by Term as the last element.
Semantically equivalent to
list_to_tuple(tuple_to_list(Tuple1) ++ [Term]), but much
faster.
For example:
> erlang:append_element({one, two}, three).
{one,two,three}
Equivalent to atom_to_binary(Atom, utf8).
-spec atom_to_binary(Atom, Encoding) -> binary() when Atom :: atom(), Encoding :: latin1 | unicode | utf8.
Returns a binary corresponding to the text representation of Atom.
If Encoding is latin1, one byte exists for each character in the text
representation. If Encoding is utf8 or unicode, the characters are encoded
using UTF-8 where characters may require multiple bytes.
Change
As from Erlang/OTP 20, atoms can contain any Unicode character and
atom_to_binary(Atom, latin1) may fail if the text
representation for Atom contains a Unicode character > 255.
Example:
> atom_to_binary('Erlang', latin1).
<<"Erlang">>
Returns a list of unicode code points corresponding to the text representation
of Atom.
For example:
> atom_to_list('Erlang').
"Erlang"> atom_to_list('你好').
[20320,22909]See unicode for how to convert the resulting list to different formats.
-spec binary_part(Subject, PosLen) -> binary() when Subject :: binary(), PosLen :: {Start :: non_neg_integer(), Length :: integer()}.
Extracts the part of the binary described by PosLen.
Negative length can be used to extract bytes at the end of a binary.
For example:
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
2> binary_part(Bin,{byte_size(Bin), -5}).
<<6,7,8,9,10>>Failure: badarg if PosLen in any way references outside the binary.
Start is zero-based, that is:
1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>For details about the PosLen semantics, see binary.
-spec binary_part(Subject, Start, Length) -> binary() when Subject :: binary(), Start :: non_neg_integer(), Length :: integer().
Equivalent to binary_part(Subject, {Start, Length}).
Equivalent to binary_to_atom(Binary, utf8).
-spec binary_to_atom(Binary, Encoding) -> atom() when Binary :: binary(), Encoding :: latin1 | unicode | utf8.
Returns the atom whose text representation is Binary. If Encoding is utf8
or unicode, the binary must contain valid UTF-8 sequences.
Change
As from Erlang/OTP 20, binary_to_atom(Binary, utf8) is
capable of decoding any Unicode character. Earlier versions would fail if the
binary contained Unicode characters > 255.
Note
The number of characters that are permitted in an atom name is limited. The default limits can be found in the Efficiency Guide (section System Limits).
Note
There is configurable limit on how many atoms that can exist and atoms are not
garbage collected. Therefore, it is recommended to consider whether
binary_to_existing_atom/2 is a better option
than binary_to_atom/2. The default limits can be found
in Efficiency Guide (section System Limits).
Examples:
> binary_to_atom(<<"Erlang">>, latin1).
'Erlang'> binary_to_atom(<<1024/utf8>>, utf8).
'Ѐ'
Equivalent to binary_to_existing_atom(Binary, utf8).
-spec binary_to_existing_atom(Binary, Encoding) -> atom() when Binary :: binary(), Encoding :: latin1 | unicode | utf8.
As binary_to_atom/2, but the atom must exist.
The Erlang system has a configurable limit for the
total number of atoms that can exist, and atoms are not garbage collected.
Therefore, it is not safe to create many atoms from binaries that come from an
untrusted source (for example, a file fetched from the Internet), for example,
using binary_to_atom/2. This function is thus the appropriate option when the
input binary comes from an untrusted source.
An atom exists in an Erlang system when included in a loaded Erlang module or
when created programmatically (for example, by
binary_to_atom/2). See the next note for an example of
when an atom exists in the source code for an Erlang module but not in the
compiled version of the same module.
Failure: badarg if the atom does not exist.
Note
Note that the compiler may optimize away atoms. For example, the compiler will
rewrite atom_to_list(some_atom) to "some_atom". If
that expression is the only mention of the atom some_atom in the containing
module, the atom will not be created when the module is loaded, and a
subsequent call to
binary_to_existing_atom(<<"some_atom">>, utf8)
will fail.
Note
The number of characters that are permitted in an atom name is limited. The default limits can be found in the Efficiency Guide (section System Limits).
Returns the float whose text representation is Binary.
For example:
> binary_to_float(<<"2.2017764e+0">>).
2.2017764The float string format is the same as the format for Erlang float literals except for that underscores are not permitted.
Failure: badarg if Binary contains a bad representation of a float.
Returns an integer whose text representation is Binary.
For example:
> binary_to_integer(<<"123">>).
123binary_to_integer/1 accepts the same string formats
as list_to_integer/1.
Failure: badarg if Binary contains a bad representation of an integer.
Returns an integer whose text representation in base Base is Binary.
For example:
> binary_to_integer(<<"3FF">>, 16).
1023binary_to_integer/2 accepts the same string formats
as list_to_integer/2.
Failure: badarg if Binary contains a bad representation of an integer.
Returns a list of integers corresponding to the bytes of Binary.
-spec binary_to_list(Binary, Start, Stop) -> [byte()] when Binary :: binary(), Start :: pos_integer(), Stop :: pos_integer().
As binary_to_list/1, but returns a list of integers
corresponding to the bytes from position Start to position Stop in Binary.
The positions in the binary are numbered starting from 1.
Note
The one-based indexing for binaries used by this function is deprecated. New
code is to use binary:bin_to_list/3 in STDLIB instead. All functions in
module binary consistently use zero-based indexing.
-spec binary_to_term(Binary) -> term() when Binary :: ext_binary().
Returns an Erlang term that is the result of decoding binary object Binary,
which must be encoded according to the
Erlang external term format.
> Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>>
> hello = binary_to_term(Bin).
helloWarning
When decoding binaries from untrusted sources, the untrusted source may submit
data in a way to create resources, such as atoms and remote references, that
cannot be garbage collected and lead to Denial of Service attack. In such
cases, consider using binary_to_term/2 with the safe
option.
See also term_to_binary/1 and binary_to_term/2.
-spec binary_to_term(Binary, Opts) -> term() | {term(), Used} when Binary :: ext_binary(), Opt :: safe | used, Opts :: [Opt], Used :: pos_integer().
Equivalent to binary_to_term(Binary), but can be configured to
fit special purposes.
The allowed options are:
safe- Use this option when receiving binaries from an untrusted source.When enabled, it prevents decoding data that can be used to attack the Erlang runtime. In the event of receiving unsafe data, decoding fails with a
badargerror.This prevents creation of new atoms directly, creation of new atoms indirectly (as they are embedded in certain structures, such as process identifiers, refs, and funs), and creation of new external function references. None of those resources are garbage collected, so unchecked creation of them can exhaust available memory.
> binary_to_term(<<131,100,0,5,"hello">>, [safe]). ** exception error: bad argument > hello. hello > binary_to_term(<<131,100,0,5,"hello">>, [safe]). helloWarning
The
safeoption ensures the data is safely processed by the Erlang runtime but it does not guarantee the data is safe to your application. You must always validate data from untrusted sources. If the binary is stored or transits through untrusted sources, you should also consider cryptographically signing it.used- Changes the return value to{Term, Used}whereUsedis the number of bytes actually read fromBinary.> Input = <<131,100,0,5,"hello","world">>. <<131,100,0,5,104,101,108,108,111,119,111,114,108,100>> > {Term, Used} = binary_to_term(Input, [used]). {hello, 9} > split_binary(Input, Used). {<<131,100,0,5,104,101,108,108,111>>, <<"world">>}
Failure: badarg if safe is specified and unsafe data is decoded.
See also term_to_binary/1, binary_to_term/1, and list_to_existing_atom/1.
-spec bit_size(Bitstring) -> non_neg_integer() when Bitstring :: bitstring().
Returns an integer that is the size in bits of Bitstring.
For example:
> bit_size(<<433:16,3:3>>).
19
> bit_size(<<1,2,3>>).
24
Returns a list of integers corresponding to the bytes of Bitstring.
If the number of bits in the binary is not divisible by 8, the last element of the list is a bitstring containing the remaining 1-7 bits.
For example:
> bitstring_to_list(<<433:16>>).
[1,177]> bitstring_to_list(<<433:16,3:3>>).
[1,177,<<3:3>>]
-spec byte_size(Bitstring) -> non_neg_integer() when Bitstring :: bitstring().
Returns an integer that is the number of bytes needed to contain Bitstring.
That is, if the number of bits in Bitstring is not divisible by 8, the
resulting number of bytes is rounded up.
For example:
> byte_size(<<433:16,3:3>>).
3
> byte_size(<<1,2,3>>).
3
Returns the smallest integer not less than Number.
For example:
> ceil(5.5).
6
-spec decode_packet(Type, Bin, Options) -> {ok, Packet, Rest} | {more, Length} | {error, Reason} when Type :: raw | 0 | 1 | 2 | 4 | asn1 | cdr | sunrm | fcgi | tpkt | line | http | http_bin | httph | httph_bin, Bin :: binary(), Options :: [Opt], Opt :: {packet_size, non_neg_integer()} | {line_length, non_neg_integer()}, Packet :: binary() | HttpPacket, Rest :: binary(), Length :: non_neg_integer() | undefined, Reason :: term(), HttpPacket :: HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError, HttpRequest :: {http_request, HttpMethod, HttpUri, HttpVersion}, HttpResponse :: {http_response, HttpVersion, integer(), HttpString}, HttpHeader :: {http_header, integer(), HttpField, UnmodifiedField :: HttpString, Value :: HttpString}, HttpError :: {http_error, HttpString}, HttpMethod :: 'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' | 'TRACE' | HttpString, HttpUri :: '*' | {absoluteURI, http | https, Host :: HttpString, Port :: inet:port_number() | undefined, Path :: HttpString} | {scheme, Scheme :: HttpString, HttpString} | {abs_path, HttpString} | HttpString, HttpVersion :: {Major :: non_neg_integer(), Minor :: non_neg_integer()}, HttpField :: 'Cache-Control' | 'Connection' | 'Date' | 'Pragma' | 'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' | 'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language' | 'Authorization' | 'From' | 'Host' | 'If-Modified-Since' | 'If-Match' | 'If-None-Match' | 'If-Range' | 'If-Unmodified-Since' | 'Max-Forwards' | 'Proxy-Authorization' | 'Range' | 'Referer' | 'User-Agent' | 'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' | 'Retry-After' | 'Server' | 'Vary' | 'Warning' | 'Www-Authenticate' | 'Allow' | 'Content-Base' | 'Content-Encoding' | 'Content-Language' | 'Content-Length' | 'Content-Location' | 'Content-Md5' | 'Content-Range' | 'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' | 'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' | 'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' | 'Proxy-Connection' | HttpString, HttpString :: string() | binary().
Decodes the binary Bin according to the packet protocol specified by Type.
Similar to the packet handling done by sockets with option {packet,Type}.
If an entire packet is contained in Bin, it is returned together with the
remainder of the binary as {ok,Packet,Rest}.
If Bin does not contain the entire packet, {more,Length} is returned.
Length is either the expected total size of the packet, or undefined if
the expected packet size is unknown. decode_packet can then be called again
with more data added.
If the packet does not conform to the protocol format, {error,Reason} is
returned.
Types:
raw | 0- No packet handling is done. The entire binary is returned unless it is empty.1 | 2 | 4- Packets consist of a header specifying the number of bytes in the packet, followed by that number of bytes. The length of the header can be one, two, or four bytes; the order of the bytes is big-endian. The header is stripped off when the packet is returned.line- A packet is a line-terminated by a delimiter byte, default is the latin-1 newline character. The delimiter byte is included in the returned packet unless the line was truncated according to optionline_length.asn1 | cdr | sunrm | fcgi | tpkt- The header is not stripped off.The meanings of the packet types are as follows:
asn1- ASN.1 BERsunrm- Sun's RPC encodingcdr- CORBA (GIOP 1.1)fcgi- Fast CGItpkt- TPKT format [RFC1006]
http | httph | http_bin | httph_bin- The Hypertext Transfer Protocol. The packets are returned with the format according toHttpPacketdescribed earlier. A packet is either a request, a response, a header, or an end of header mark. Invalid lines are returned asHttpError.Recognized request methods and header fields are returned as atoms. Others are returned as strings. Strings of unrecognized header fields are formatted with only capital letters first and after hyphen characters, for example,
"Sec-Websocket-Key". Header field names are also returned inUnmodifiedFieldas strings, without any conversion or formatting.The protocol type
httpis only to be used for the first line when anHttpRequestor anHttpResponseis expected. The following calls are to usehttphto getHttpHeaders untilhttp_eohis returned, which marks the end of the headers and the beginning of any following message body.The variants
http_binandhttph_binreturn strings (HttpString) as binaries instead of lists.Since OTP 26.0,
Hostmay be an IPv6 address enclosed in[], as defined in RFC2732 .
Options:
{packet_size, integer() >= 0}- Sets the maximum allowed size of the packet body. If the packet header indicates that the length of the packet is longer than the maximum allowed length, the packet is considered invalid. Defaults to 0, which means no size limit.{line_length, integer() >= 0}- For packet typeline, lines longer than the indicated length are truncated.Option
line_lengthalso applies tohttp*packet types as an alias for optionpacket_sizeifpacket_sizeitself is not set. This use is only intended for backward compatibility.{line_delimiter, 0 =< byte() =< 255}- For packet typeline, sets the delimiting byte. Default is the latin-1 character$\n.
Examples:
> erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>}
> erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
-spec delete_element(Index, Tuple1) -> Tuple2 when Index :: pos_integer(), Tuple1 :: tuple(), Tuple2 :: tuple().
Returns a new tuple with element at Index removed from tuple Tuple1.
For example:
> erlang:delete_element(2, {one, two, three}).
{one,three}
-spec display(Term) -> true when Term :: term().
Prints a text representation of Term on the standard output.
Warning
This BIF is intended for debugging only. The printed representation may contain internal details that do not match the high-level representation of the term in Erlang.
-spec element(N, Tuple) -> term() when N :: pos_integer(), Tuple :: tuple().
Returns the Nth element (numbering from 1) of Tuple.
For example:
> element(2, {a, b, c}).
b
-spec external_size(Term) -> non_neg_integer() when Term :: term().
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format.
The following condition applies always:
> Size1 = byte_size(term_to_binary(Term)),
> Size2 = erlang:external_size(Term),
> true = Size1 =< Size2.
trueThis is equivalent to a call to:
erlang:external_size(Term, [])
-spec external_size(Term, Options) -> non_neg_integer() when Term :: term(), Options :: [compressed | {compressed, Level :: 0..9} | deterministic | {minor_version, Version :: 0..2} | local].
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format.
The following condition applies always:
> Size1 = byte_size(term_to_binary(Term, Options)),
> Size2 = erlang:external_size(Term, Options),
> true = Size1 =< Size2.
trueOption {minor_version, Version} specifies how floats are encoded. For a
detailed description, see term_to_binary/2.
Returns a float by converting Number to a float.
For example:
> float(55).
55.0Note
If used on the top level in a guard, it tests whether the argument is a
floating point number; for clarity, use is_float/1 instead.
When float/1 is used in an expression in a guard, such as
'float(A) == 4.0', it converts a number as described earlier.
Equivalent to float_to_binary(Float, [{scientific, 20}]).
-spec float_to_binary(Float, Options) -> binary() when Float :: float(), Options :: [Option], Option :: {decimals, Decimals :: 0..253} | {scientific, Decimals :: 0..249} | compact | short.
Returns a binary corresponding to the text representation of Float using fixed
decimal point formatting.
Options behaves in the same way as float_to_list/2.
For example:
> float_to_binary(7.12, [{decimals, 4}]).
<<"7.1200">>
> float_to_binary(7.12, [{decimals, 4}, compact]).
<<"7.12">>
> float_to_binary(7.12, [{scientific, 3}]).
<<"7.120e+00">>
> float_to_binary(7.12, [short]).
<<"7.12">>
> float_to_binary(0.1+0.2, [short]).
<<"0.30000000000000004">>
> float_to_binary(0.1+0.2)
<<"3.00000000000000044409e-01">>
Equivalent to float_to_list(Float, [{scientific, 20}]).
-spec float_to_list(Float, Options) -> string() when Float :: float(), Options :: [Option], Option :: {decimals, Decimals :: 0..253} | {scientific, Decimals :: 0..249} | compact | short.
Returns a string corresponding to the text representation of Float using fixed
decimal point formatting.
Available options:
- If option
decimalsis specified, the returned value contains at mostDecimalsnumber of digits past the decimal point. If the number does not fit in the internal static buffer of 256 bytes, the function throwsbadarg. - If option
compactis specified, the trailing zeros at the end of the list are truncated. This option is only meaningful together with optiondecimals. - If option
scientificis specified, the float is formatted using scientific notation withDecimalsdigits of precision. - If option
shortis specified, the float is formatted with the smallest number of digits that still guarantees thatF =:= list_to_float(float_to_list(F, [short])). When the float is inside the range (-2⁵³, 2⁵³), the notation that yields the smallest number of characters is used (scientific notation or normal decimal notation). Floats outside the range (-2⁵³, 2⁵³) are always formatted using scientific notation to avoid confusing results when doing arithmetic operations. - If
Optionsis[], the function behaves asfloat_to_list/1.
Examples:
> float_to_list(7.12, [{decimals, 4}]).
"7.1200"
> float_to_list(7.12, [{decimals, 4}, compact]).
"7.12"
> float_to_list(7.12, [{scientific, 3}]).
"7.120e+00"
> float_to_list(7.12, [short]).
"7.12"
> float_to_list(0.1+0.2, [short]).
"0.30000000000000004"
> float_to_list(0.1+0.2)
"3.00000000000000044409e-01"In the last example, float_to_list(0.1+0.2) evaluates to
"3.00000000000000044409e-01". The reason for this is explained in
Representation of Floating Point Numbers.
Returns the largest integer not greater than Number.
For example:
> floor(-10.5).
-11
-spec fun_info(Fun) -> [{Item, Info}] when Fun :: function(), Item :: arity | env | index | name | module | new_index | new_uniq | pid | type | uniq, Info :: term().
Returns a list with information about the fun Fun. Each list element is a
tuple. The order of the tuples is undefined, and more tuples can be added in a
future release.
Warning
This BIF is mainly intended for debugging, but it can sometimes be useful in library functions that need to verify, for example, the arity of a fun.
Two types of funs have slightly different semantics:
- A fun created by
fun M:F/Ais called an external fun. Calling it will always call the functionFwith arityAin the latest code for moduleM. Notice that moduleMdoes not even need to be loaded when the funfun M:F/Ais created. - All other funs are called local. When a local fun is called, the same version of the code that created the fun is called (even if a newer version of the module has been loaded).
The following elements are always present in the list for both local and external funs:
{type, Type}-Typeislocalorexternal.{module, Module}-Module(an atom) is the module name.If
Funis a local fun,Moduleis the module in which the fun is defined.If
Funis an external fun,Moduleis the module that the fun refers to.{name, Name}-Name(an atom) is a function name.If
Funis a local fun,Nameis the name of the local function that implements the fun. (This name was generated by the compiler, and is only of informational use. As it is a local function, it cannot be called directly.) If no code is currently loaded for the fun,[]is returned instead of an atom.If
Funis an external fun,Nameis the name of the exported function that the fun refers to.{arity, Arity}-Arityis the number of arguments that the fun is to be called with.{env, Env}-Env(a list) is the environment or free variables for the fun. For external funs, the returned list is always empty.
The following elements are only present in the list if Fun is local:
{pid, Pid}-Pidis the process identifier ofinitprocess on the local node.Change
Starting in Erlang/OTP 27,
Pidalways points to the localinitprocess, regardless of which process or node the fun was originally created on.{index, Index}-Index(an integer) is an index into the module fun table.{new_index, Index}-Index(an integer) is an index into the module fun table.{new_uniq, Uniq}-Uniq(a binary) is a unique value for this fun. It is calculated from the compiled code for the entire module.{uniq, Uniq}-Uniq(an integer) is a unique value for this fun. As from Erlang/OTP R15, this integer is calculated from the compiled code for the entire module. Before Erlang/OTP R15, this integer was based on only the body of the fun.
-spec fun_info(Fun, Item) -> {Item, Info} when Fun :: function(), Item :: fun_info_item(), Info :: term().
Returns information about Fun as specified by Item, in the form
{Item,Info}.
For any fun, Item can be any of the atoms module, name, arity, env, or
type.
For a local fun, Item can also be any of the atoms index, new_index,
new_uniq, uniq, and pid. For an external fun, the value of any of these
items is always the atom undefined.
See erlang:fun_info/1.
Returns String that represents the code that created Fun.
String has the following form, if Fun was created by a
fun expression of the form
fun ModuleName:FuncName/Arity:
"fun ModuleName:FuncName/Arity"
The form of String when Fun is created from other types of
fun expressions differs depending
on if the fun expression was executed while executing compiled code or if the
fun expression was executed while executing uncompiled code (uncompiled
escripts, the Erlang shell, and other code executed by the erl_eval module):
compiled code -
"#Fun<M.I.U>", where M, I and U correspond to the values namedmodule,indexanduniqin the result oferlang:fun_info(Fun).uncompiled code - All funs created from fun expressions in uncompiled code with the same arity are mapped to the same list by
fun_to_list/1.
Note
Generally, one can not use fun_to_list/1 to check if two
funs are equal as fun_to_list/1 does not take the fun's
environment into account. See erlang:fun_info/1 for how to
get the environment of a fun.
Change
The output of fun_to_list/1 can differ between Erlang
implementations and may change in future versions.
Examples:
-module(test).
-export([add/1, add2/0, fun_tuple/0]).
add(A) -> fun(B) -> A + B end.
add2() -> fun add/1.
fun_tuple() -> {fun() -> 1 end, fun() -> 1 end}.> {fun test:add/1, test:add2()}.
{fun test:add/1,#Fun<test.1.107738983>}Explanation: fun test:add/1 is upgradable but test:add2() is not upgradable.
> {test:add(1), test:add(42)}.
{#Fun<test.0.107738983>,#Fun<test.0.107738983>}Explanation: test:add(1) and test:add(42) has the same string representation
as the environment is not taken into account.
>test:fun_tuple().
{#Fun<test.2.107738983>,#Fun<test.3.107738983>}Explanation: The string representations differ because the funs come from different fun expressions.
> {fun() -> 1 end, fun() -> 1 end}. >
{#Fun<erl_eval.45.97283095>,#Fun<erl_eval.45.97283095>}Explanation: All funs created from fun expressions of this form in uncompiled
code with the same arity are mapped to the same list by
fun_to_list/1.
-spec hd(List) -> Head when List :: nonempty_maybe_improper_list(), Head :: term().
Returns the head of List, that is, the first element.
It works with improper lists.
Examples:
> hd([1,2,3,4,5]).
1> hd([first, second, third, so_on | improper_end]).
firstFailure: badarg if List is an empty list [].
-spec insert_element(Index, Tuple1, Term) -> Tuple2 when Index :: pos_integer(), Tuple1 :: tuple(), Tuple2 :: tuple(), Term :: term().
Returns a new tuple with element Term inserted at position Index in tuple
Tuple1. All elements from position Index and upwards are pushed one step
higher in the new tuple Tuple2.
For example:
> erlang:insert_element(2, {one, two, three}, new).
{one,new,two,three}
Returns a binary corresponding to the text representation of Integer.
For example:
> integer_to_binary(77).
<<"77">>
Returns a binary corresponding to the text representation of Integer in base
Base.
For example:
> integer_to_binary(1023, 16).
<<"3FF">>
Returns a string corresponding to the text representation of Integer.
For example:
> integer_to_list(77).
"77"
Returns a string corresponding to the text representation of Integer in base
Base.
For example:
> integer_to_list(1023, 16).
"3FF"
-spec iolist_size(Item) -> non_neg_integer() when Item :: iolist() | binary().
Returns an integer, that is the size in bytes, of the binary that would be the
result of iolist_to_binary(Item).
For example:
> iolist_size([1,2|<<3,4>>]).
4
Returns a binary that is made from the integers and binaries in
IoListOrBinary.
For example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
Returns an iovec that is made from the integers and binaries in
IoListOrBinary. This function is useful when you want to flatten an iolist but
you do not need a single binary. This can be useful for passing the data to nif
functions such as enif_inspect_iovec or do
more efficient message passing. The advantage of using this function over
iolist_to_binary/1 is that it does not have to copy
off-heap binaries.
For example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
%% If you pass small binaries and integers it works as iolist_to_binary
> erlang:iolist_to_iovec([Bin1,1,[2,3,Bin2],4|Bin3]).
[<<1,2,3,1,2,3,4,5,4,6>>]
%% If you pass larger binaries, they are split and returned in a form
%% optimized for calling the C function writev.
> erlang:iolist_to_iovec([<<1>>,<<2:8096>>,<<3:8096>>]).
[<<1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,...>>,
<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
...>>,
<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,...>>]
Returns true if Term is an atom, otherwise false.
Returns true if Term is a binary, otherwise false.
A binary always contains a complete number of bytes.
Returns true if Term is a bitstring (including a binary), otherwise false.
Returns true if Term is the atom true or the atom false (that is, a
boolean). Otherwise returns false.
Returns true if Term is a floating point number, otherwise false.
Returns true if Term is a fun, otherwise false.
Returns true if Term is a fun that can be applied with Arity number of
arguments, otherwise false.
Returns true if Term is an integer, otherwise false.
Returns true if Term is a list with zero or more elements, otherwise
false.
Returns true if Term is a map, otherwise false.
Returns true if map Map contains Key and returns false if it does not
contain the Key.
The call fails with a {badmap,Map} exception if Map is not a map.
Example:
> Map = #{"42" => value}.
#{"42" => value}
> is_map_key("42",Map).
true
> is_map_key(value,Map).
false
Returns true if Term is an integer or a floating point number. Otherwise
returns false.
Returns true if Term is a process identifier, otherwise false.
Returns true if Term is a port identifier, otherwise false.
Returns true if Term is a tuple and its first element is RecordTag.
Otherwise returns false.
Note
Normally the compiler treats calls to is_record/2
especially. It emits code to verify that Term is a tuple, that its first
element is RecordTag, and that the size is correct. However, if RecordTag
is not a literal atom, the BIF is_record/2 is called
instead and the size of the tuple is not verified.
Allowed in guard tests, if RecordTag is a literal atom.
-spec is_record(Term, RecordTag, Size) -> boolean() when Term :: term(), RecordTag :: atom(), Size :: non_neg_integer().
RecordTag must be an atom.
Returns true if Term is a tuple, its first element is RecordTag, and its
size is Size. Otherwise returns false.
Allowed in guard tests if RecordTag is a literal atom and Size is a literal
integer.
Note
This BIF is documented for completeness. Usually
is_record/2 is to be used.
Returns true if Term is a reference, otherwise false.
Returns true if Term is a tuple, otherwise false.
-spec length(List) -> non_neg_integer() when List :: [term()].
Returns the length of List.
For example:
> length([1,2,3,4,5,6,7,8,9]).
9
Returns the atom whose text representation is String.
As from Erlang/OTP 20, String may contain any Unicode character. Earlier
versions allowed only ISO-latin-1 characters as the implementation did not allow
Unicode characters above 255.
Note
The number of characters that are permitted in an atom name is limited. The default limits can be found in the efficiency guide (section System Limits).
Note
There is a configurable limit
on how many atoms that can exist and atoms are not
garbage collected. Therefore, it is recommended to consider if
list_to_existing_atom/1 is a better option than
list_to_atom/1. The default limits can be found in the
Efficiency Guide (section System Limits).
Example:
> list_to_atom("Erlang").
'Erlang'
Returns a binary that is made from the integers and binaries in IoList.
For example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
-spec list_to_bitstring(BitstringList) -> bitstring() when BitstringList :: bitstring_list().
Returns a bitstring that is made from the integers and bitstrings in
BitstringList. (The last tail in BitstringList is allowed to be a
bitstring.)
For example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6,7:4>>.
<<6,7:4>>
> list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6,7:4>>
Returns the atom whose text representation is String, but only if there
already exists such atom. An atom exists if it has been created by the run-time
system by either loading code or creating a term in which the atom is part.
Failure: badarg if there does not already exist an atom whose text
representation is String.
Note
Note that the compiler may optimize away atoms. For example, the compiler will
rewrite atom_to_list(some_atom) to "some_atom". If
that expression is the only mention of the atom some_atom in the containing
module, the atom will not be created when the module is loaded, and a
subsequent call to
list_to_existing_atom("some_atom") will fail.
Returns the float whose text representation is String.
For example:
> list_to_float("2.2017764e+0").
2.2017764The float string format is the same as the format for Erlang float literals except for that underscores are not permitted.
Failure: badarg if String contains a bad representation of a float.
Returns an integer whose text representation is String.
For example:
> list_to_integer("123").
123> list_to_integer("-123").
-123> list_to_integer("+123234982304982309482093833234234").
123234982304982309482093833234234String must contain at least one digit character and can have an optional
prefix consisting of a single "+" or "-" character (that is, String must
match the regular expression "^[+-]?[0-9]+$").
Failure: badarg if String contains a bad representation of an integer.
Returns an integer whose text representation in base Base is String.
For example:
> list_to_integer("3FF", 16).
1023> list_to_integer("+3FF", 16).
1023> list_to_integer("3ff", 16).
1023> list_to_integer("3fF", 16).
1023> list_to_integer("-3FF", 16).
-1023For example, when Base is 16, String must match the regular expression
"^[+-]?([0-9]|[A-F]|[a-f])+$".
Failure: badarg if String contains a bad representation of an integer.
Returns a process identifier whose text representation is a String.
For example:
> list_to_pid("<0.4.1>").
<0.4.1>Failure: badarg if String contains a bad representation of a process
identifier.
Warning
This BIF is intended for debugging and is not to be used in application programs.
Returns a port identifier whose text representation is a String.
For example:
> list_to_port("#Port<0.4>").
#Port<0.4>Failure: badarg if String contains a bad representation of a port
identifier.
Warning
This BIF is intended for debugging and is not to be used in application programs.
Returns a reference whose text representation is a String.
For example:
> list_to_ref("#Ref<0.4192537678.4073193475.71181>").
#Ref<0.4192537678.4073193475.71181>Failure: badarg if String contains a bad representation of a reference.
Warning
This BIF is intended for debugging and is not to be used in application programs.
Returns a tuple corresponding to List, for example
> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}List can contain any Erlang terms.
-spec make_ref() -> reference().
Returns a unique reference. The reference is unique among connected nodes.
Warning
Before OTP 23 when a node is restarted multiple times with the same node name, references created on a newer node can be mistaken for a reference created on an older node with the same node name.
Creates a new tuple of the specified Arity, where all elements are
InitialValue.
For example:
> erlang:make_tuple(4, []).
{[],[],[],[]}
-spec make_tuple(Arity, DefaultValue, InitList) -> tuple() when Arity :: arity(), DefaultValue :: term(), InitList :: [{Position :: pos_integer(), term()}].
Creates a tuple of size Arity, where each element has value DefaultValue,
and then fills in values from InitList.
Each list element in InitList must be a two-tuple, where the first element is
a position in the newly created tuple and the second element is any term. If a
position occurs more than once in the list, the term corresponding to the last
occurrence is used.
For example:
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
{[],aa,[],[],zz}
Returns value Value associated with Key if Map contains Key.
The call fails with a {badmap,Map} exception if Map is not a map, or with a
{badkey,Key} exception if no value is associated with Key.
Example:
> Key = 1337,
Map = #{42 => value_two,1337 => "value one","a" => 1},
map_get(Key,Map).
"value one"
-spec map_size(Map) -> non_neg_integer() when Map :: map().
Returns an integer, which is the number of key-value pairs in Map.
For example:
> map_size(#{a=>1, b=>2, c=>3}).
3
-spec match_spec_test(MatchAgainst, MatchSpec, Type) -> TestResult when MatchAgainst :: [term()] | tuple(), MatchSpec :: term(), Type :: table | trace, TestResult :: {ok, term(), [return_trace], [{error | warning, string()}]} | {error, [{error | warning, string()}]}.
Tests a match specification used in calls to ets:select/2 and
trace:function/4.
The function tests both a match specification for "syntactic" correctness and
runs the match specification against the object.
If the match specification contains errors, the tuple
{error, Errors} is returned, where Errors is a list of natural language
descriptions of what was wrong with the match specification.
If Type is table, the object to match against is to be a tuple. The function
then returns {ok,Result,[],Warnings}, where Result is what would have been
the result in a real ets:select/2 call, or false if the match specification
does not match the object tuple.
If Type is trace, the object to match against is to be a list. The function
returns {ok, Result, Flags, Warnings}, where Result is one of the following:
trueif a trace message is to be emittedfalseif a trace message is not to be emitted- The message term to be appended to the trace message
Flags is a list containing all the trace flags to be enabled, currently this
is only return_trace.
This is a useful debugging and test tool, especially when writing complicated match specifications.
See also ets:test_ms/2.
Returns the largest of Term1 and Term2. If the terms compare equal with the
== operator, Term1 is returned.
The Expressions section contains
descriptions of the == operator and how terms are ordered.
Examples:
> max(1, 2).
2> max(1.0, 1).
1.0> max(1, 1.0).
1> max("abc", "b").
"b"Change
Allowed in guards tests from Erlang/OTP 26.
Returns the smallest of Term1 and Term2. If the terms compare equal with the
== operator, Term1 is returned.
The Expressions section contains
descriptions of the == operator and how terms are ordered.
Examples:
> min(1, 2).
1> min(1.0, 1).
1.0> min(1, 1.0).
1> min("abc", "b").
"abc"Change
Allowed in guards tests from Erlang/OTP 26.
Returns the node where Arg originates. Arg can be a process identifier, a
reference, or a port. If Arg originates from the local node and the local node
is not alive, nonode@nohost is returned.
-spec phash2(Term) -> Hash when Term :: term(), Hash :: non_neg_integer().
Equivalent to phash2/2.
-spec phash2(Term, Range) -> Hash when Term :: term(), Range :: pos_integer(), Hash :: non_neg_integer().
Portable hash function that gives the same hash for the same Erlang term regardless of machine architecture and ERTS version.
The function returns a hash value for Term within the range
0..Range-1. The maximum value for Range is 2^32. When without argument
Range, a value in the range 0..2^27-1 is returned.
This BIF is always to be used for hashing terms. It distributes small integers
better than phash/2, and it is faster for bignums and binaries.
Notice that the range 0..Range-1 is different from the range of
phash/2, which is 1..Range.
Returns a string corresponding to the text representation of Pid.
For example:
> erlang:pid_to_list(self()).
"<0.85.0>"Note
The creation for the node is not included in the list
representation of Pid. This means that processes in different incarnations
of a node with a specific name can get the same list representation.
Returns a string corresponding to the text representation of the port identifier
Port.
Returns a string corresponding to the text representation of Ref.
Warning
This BIF is intended for debugging and is not to be used in application programs.
Returns an integer by rounding Number.
For example:
round(42.1).
42round(5.5).
6round(-5.5).
-6round(36028797018963969.0).
36028797018963968In the last example, round(36028797018963969.0) evaluates to
36028797018963968. The reason for this is that the number
36028797018963969.0 cannot be represented exactly as a float value. Instead,
the float literal is represented as 36028797018963968.0, which is the closest
number that can be represented exactly as a float value. See
Representation of Floating Point Numbers
for additional information.
-spec setelement(Index, Tuple1, Value) -> Tuple2 when Index :: pos_integer(), Tuple1 :: tuple(), Tuple2 :: tuple(), Value :: term().
Returns a tuple that is a copy of argument Tuple1 with the element specified
by integer argument Index (the first element is the element with index 1)
replaced by argument Value.
For example:
> setelement(2, {10, green, bottles}, red).
{10,red,bottles}
-spec size(Item) -> non_neg_integer() when Item :: tuple() | binary().
Returns the number of elements in a tuple or the number of bytes in a binary or bitstring.
For example:
> size({morni, mulle, bwange}).
3
> size(<<11, 22, 33>>).
3For bitstrings, the number of whole bytes is returned. That is, if the number of bits in the bitstring is not divisible by 8, the resulting number of bytes is rounded down.
See also tuple_size/1, byte_size/1, and bit_size/1.
-spec split_binary(Bin, Pos) -> {binary(), binary()} when Bin :: binary(), Pos :: non_neg_integer().
Returns a tuple containing the binaries that are the result of splitting Bin
into two parts at position Pos.
This is not a destructive operation. After the operation, there are three binaries altogether.
For example:
> B = list_to_binary("0123456789").
<<"0123456789">>
> byte_size(B).
10
> {B1, B2} = split_binary(B,3).
{<<"012">>,<<"3456789">>}
> byte_size(B1).
3
> byte_size(B2).
7
-spec term_to_binary(Term) -> ext_binary() when Term :: term().
Returns a binary data object that is the result of encoding Term according to
the Erlang external term format.
This can be used for various purposes, for example, writing a term to a file in an efficient way, or sending an Erlang term to some type of communications channel not supported by distributed Erlang.
> Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>>
> hello = binary_to_term(Bin).
helloSee also binary_to_term/1.
Note
There is no guarantee that this function will return the same encoded representation for the same term.
-spec term_to_binary(Term, Options) -> ext_binary() when Term :: term(), Options :: [compressed | {compressed, Level :: 0..9} | deterministic | {minor_version, Version :: 0..2} | local].
Returns a binary data object that is the result of encoding Term according to
the Erlang external term format.
Currently supported options:
compressed- Compress the external term format. The compressed format is automatically recognized bybinary_to_term/1as from Erlang/OTP R7B.{compressed, Level}- Compress the external term format to a given level. The compression level is specified byLevelwhich is an integer in the range 0..9, where:0- No compression is done (it is the same as giving nocompressedoption).1- Takes least time but may not compress as well as the higher levels.6- Default level when optioncompressedis provided.9- Takes most time and tries to produce a smaller result. Notice "tries" in the preceding sentence; depending on the input term, level 9 compression either does or does not produce a smaller result than level 1 compression.
{minor_version, Version}(Since R11B-4)
The option can be used to control some encoding details. Valid values forVersionare:0- Floats are encoded using a textual representation.Atoms that can be represented by a latin1 string are encoded using latin1 while only atoms that cannot be represented by latin1 are encoded using utf8.
1- Floats are encoded in a more space-efficient and exact way (namely in the 64-bit IEEE format, rather than converted to a textual representation). As from Erlang/OTP R11B-4,binary_to_term/1can decode this representation.Atoms that can be represented by a latin1 string are encoded using latin1 while only atoms that cannot be represented by latin1 are encoded using utf8.
2- This is as of Erlang/OTP 26.0 the default. Atoms are unconditionally encoded using utf8. Erlang/OTP systems as of R16B can decode this representation.
deterministic(Since OTP 24.1)
This option can be used to ensure that, within the same major release of Erlang/OTP, the same encoded representation is returned for the same term. There is still no guarantee that the encoded representation remains the same between major releases of Erlang/OTP.This option cannot be combined with the
localoption.local(Since OTP 26.0)
This option will cause encoding ofTermto an alternative local version of the external term format which when decoded by the same runtime system instance will produce a term identical to the encoded term even when the node name and/or creation of the current runtime system instance have changed between encoding and decoding. When encoding without thelocaloption, local identifiers such as pids, ports and references will not be the same if node name and/or creation of the current runtime system instance changed between encoding and decoding. This since such identifiers refer to a specific node by node name and creation.Node name and creation of a runtime system instance change when the distribution is started or stopped. The distribution is started when the runtime system is started using the
-nameor-snamecommand line arguments. Note that the actual start of the distribution happens after other code in the startup phase has begun executing. The distribution can also be started by callingnet_kernel:start/2and stopped by callingnet_kernel:stop/1if it has not been started via the command line.The decoding of a term encoded with the
localoption, using for examplebinary_to_term(), will try to verify that the term actually was encoded by the same runtime system instance, and will in the vast majority of cases fail if the encoding was performed by another runtime system instance. You should however not trust that this verification will work in all cases. You should make sure to only decode terms encoded with thelocaloption on the same Erlang runtime system instance as the one that encoded the terms.Since it is only the runtime system that encoded a term using the
localoption that can decode it, the local encoding is typically pieced together with something else to produce a reply to where thelocalencoding originates from. If a term encoded using thelocaloption is stripped of its leading version number, it can be added as part of a larger term (for example as an element in a tuple) when encoding on the external term format using, for example, ei. In theeicase, you would strip it of the version number usingei_decode_version()and then add the remaining local encoding to what you are encoding using for exampleei_x_append_buf().A good example of when you want to use the
localoption, is when you want to make a request from a process to a port driver and utilize the selective receive optimization when receiving the reply. In this scenario you want to create a reference, serialize the reference on the external term format using thelocaloption, pass this to the driver in the request, and then wait for the reply message in a selective receive matching on the reference. The driver should send the reply using eithererl_drv_output_term()orerl_drv_send_term()using the term typeERL_DRV_EXT2TERMfor the, in the request, previously received reference on the external term format. Note that you should not strip the leading version number from the local encoding when using the term typeERL_DRV_EXT2TERMof this functionality. If you in this example do not encode the reference using thelocaloption, and the distribution is started or stopped while the request is ongoing, the process that made the request will hang indefinitely since the reference in the reply message will never match.This option cannot be combined with the
deterministicoption.For more information see the
LOCAL_EXTtag in the documentation of the external term format.
See also binary_to_term/1.
Returns the encoding of Term according to the Erlang external term format as
ext_iovec/0.
This function produce the same encoding as term_to_binary/1, but with another
return type. The call
iolist_to_binary(term_to_iovec(Term)) will produce
exactly the same result as the call
term_to_binary(Term).
term_to_iovec() is a pure optimization of the functionality term_to_binary()
provide. term_to_iovec() can for example refer directly to off heap binaries
instead of copying the binary data into the result.
See also term_to_binary/1.
-spec term_to_iovec(Term, Options) -> ext_iovec() when Term :: term(), Options :: [compressed | {compressed, Level :: 0..9} | deterministic | {minor_version, Version :: 0..2} | local].
Returns the encoding of Term according to the Erlang external term format as
ext_iovec/0.
This function produce the same encoding as term_to_binary/2, but with another
return type. The call
iolist_to_binary(term_to_iovec(Term, Opts)) will
produce exactly the same result as
term_to_binary(Term, Opts).
Currently recognised options are all options recognised by term_to_binary/2.
term_to_iovec() is a pure optimization of the functionality term_to_binary()
provide. term_to_iovec() can for example refer directly to off heap binaries
instead of copying the binary data into the result.
See also term_to_binary/2.
-spec tl(List) -> Tail when List :: nonempty_maybe_improper_list(), Tail :: term().
Returns the tail of List, that is, the list minus the first element
It works with improper lists.
Examples:
> tl([geesties, guilies, beasties]).
[guilies, beasties]> tl([geesties]).
[]> tl([geesties, guilies, beasties | improper_end]).
[guilies, beasties | improper_end]> tl([geesties | improper_end]).
improper_endFailure: badarg if List is an empty list [].
Truncates the decimals of Number.
For example:
> trunc(5.7).
5> trunc(-5.7).
-5> trunc(5).
5> trunc(36028797018963969.0).
36028797018963968In the last example, trunc(36028797018963969.0) evaluates to
36028797018963968. The reason for this is that the number
36028797018963969.0 cannot be represented exactly as a float value. Instead,
the float literal is represented as 36028797018963968.0, which is the closest
number that can be represented exactly as a float value. See
Representation of Floating Point Numbers
for additional information.
-spec tuple_size(Tuple) -> non_neg_integer() when Tuple :: tuple().
Returns an integer that is the number of elements in Tuple.
For example:
> tuple_size({morni, mulle, bwange}).
3
Returns a list corresponding to Tuple. Tuple can contain any Erlang terms.
Example:
> tuple_to_list({share, {'Ericsson_B', 163}}).
[share,{'Ericsson_B',163}]
-spec unique_integer() -> integer().
Generates and returns an
integer unique on current runtime system instance.
Equivalent to calling erlang:unique_integer([]).
-spec unique_integer(ModifierList) -> integer() when ModifierList :: [Modifier], Modifier :: positive | monotonic.
Generates and returns an integer unique on current runtime system instance. The integer is unique in the sense that this BIF, using the same set of modifiers, does not return the same integer more than once on the current runtime system instance. Each integer value can of course be constructed by other means.
By default, when [] is passed as ModifierList, both negative and positive
integers can be returned. This to use the range of integers that do not need
heap memory allocation as much as possible. By default the returned integers are
also only guaranteed to be unique, that is, any returned integer can be smaller
or larger than previously returned integers.
Modifiers:
positive - Returns only positive integers.
Notice that by passing the
positivemodifier you will get heap allocated integers (bignums) quicker.monotonic - Returns strictly monotonically increasing integers corresponding to creation time. That is, the integer returned is always larger than previously returned integers on the current runtime system instance.
These values can be used to determine order between events on the runtime system instance. That is, if both
X = erlang:unique_integer([monotonic])andY = erlang:unique_integer([monotonic])are executed by different processes (or the same process) on the same runtime system instance andX < Y, we know thatXwas created beforeY.Warning
Strictly monotonically increasing values are inherently quite expensive to generate and scales poorly. This is because the values need to be synchronized between CPU cores. That is, do not pass the
monotonicmodifier unless you really need strictly monotonically increasing values.
All valid Modifiers can be combined. Repeated (valid) Modifiers in the
ModifierList are ignored.
Note
The set of integers returned by erlang:unique_integer/1 using different sets
of Modifiers will overlap. For example, by calling
unique_integer([monotonic]), and
unique_integer([positive, monotonic]) repeatedly, you
will eventually see some integers that are returned by both calls.
Failures:
badarg- ifModifierListis not a proper list.badarg- ifModifieris not a valid modifier.
Processes and Ports
-spec alias() -> Alias when Alias :: reference().
Equivalent to alias([]).
-spec alias(Opts) -> Alias when Alias :: reference(), Opts :: [explicit_unalias | reply].
Create an alias which can be used when sending messages to the process that
created the alias. When the alias has been deactivated, messages sent using the
alias will be dropped. An alias can be deactivated using unalias/1.
Currently available options for alias/1:
explicit_unalias- The alias can only be deactivated via a call tounalias/1. This is also the default behaviour if no options are passed or ifalias/0is called.reply- The alias will be automatically deactivated when a reply message sent via the alias is received. The alias can also still be deactivated via a call tounalias/1.
Example:
server() ->
receive
{request, AliasReqId, Request} ->
Result = perform_request(Request),
AliasReqId ! {reply, AliasReqId, Result}
end,
server().
client(ServerPid, Request) ->
AliasReqId = alias([reply]),
ServerPid ! {request, AliasReqId, Request},
%% Alias will be automatically deactivated if we receive a reply
%% since we used the 'reply' option...
receive
{reply, AliasReqId, Result} -> Result
after 5000 ->
unalias(AliasReqId),
%% Flush message queue in case the reply arrived
%% just before the alias was deactivated...
receive {reply, AliasReqId, Result} -> Result
after 0 -> exit(timeout)
end
end.Note that both the server and the client in this example must be executing on at least OTP 24 systems in order for this to work.
For more information on process aliases see the Process Aliases section of the Erlang Reference Manual.
Calls a fun, passing the elements in Args as arguments.
If the number of elements in the arguments are known at compile time, the call
is better written as Fun(Arg1, Arg2, ... ArgN).
Warning
Earlier, Fun could also be specified as {Module, Function}, equivalent to
apply(Module, Function, Args). This use is deprecated and will
stop working in a future release.
-spec apply(Module, Function, Args) -> term() when Module :: module(), Function :: atom(), Args :: [term()].
Returns the result of applying Function in Module to Args. The applied
function must be exported from Module. The arity of the function is the length
of Args.
For example:
> apply(lists, reverse, [[a, b, c]]).
[c,b,a]
> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"If the number of arguments are known at compile time, the call is better written
as Module:Function(Arg1, Arg2, ..., ArgN).
Failure: error_handler:undefined_function/3 is called if the applied function
is not exported. The error handler can be redefined (see process_flag/2). If
error_handler is undefined, or if the user has redefined the default
error_handler so the replacement module is undefined, an error with reason
undef is generated.
-spec bump_reductions(Reductions) -> true when Reductions :: pos_integer().
This implementation-dependent function increments the reduction counter for the calling process.
In the Beam emulator, the reduction counter is normally incremented by one for each function and BIF call. A context switch is forced when the counter reaches the maximum number of reductions for a process (4000 reductions in Erlang/OTP 19.2 and later).
Warning
This BIF can be removed in a future version of the Beam machine without prior warning. It is unlikely to be implemented in other Erlang implementations.
-spec demonitor(MonitorRef) -> true when MonitorRef :: reference().
If MonitorRef is a reference that the calling process obtained by calling
monitor/2, this monitoring is turned off. If the monitoring is already turned
off, nothing happens.
Once demonitor(MonitorRef) has returned, it is guaranteed
that no {'DOWN', MonitorRef, _, _, _} message, because of the monitor, will be
placed in the caller message queue in the future. However, a
{'DOWN', MonitorRef, _, _, _} message can have been placed in the caller
message queue before the call. It is therefore usually advisable to remove such
a 'DOWN' message from the message queue after monitoring has been stopped.
demonitor(MonitorRef, [flush]) can be used instead of
demonitor(MonitorRef) if this cleanup is wanted.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
Change
Before Erlang/OTP R11B (ERTS 5.5) demonitor/1 behaved
completely asynchronously, that is, the monitor was active until the
"demonitor signal" reached the monitored entity. This had one undesirable
effect. You could never know when you were guaranteed not to receive a
DOWN message because of the monitor.
The current behavior can be viewed as two combined operations: asynchronously send a "demonitor signal" to the monitored entity and ignore any future results of the monitor.
Failure: It is an error if MonitorRef refers to a monitoring started by
another process. Not all such cases are cheap to check. If checking is cheap,
the call fails with badarg, for example if MonitorRef is a remote reference.
-spec demonitor(MonitorRef, OptionList) -> boolean() when MonitorRef :: reference(), OptionList :: [Option], Option :: flush | info.
The returned value is true unless info is part of OptionList.
demonitor(MonitorRef, []) is equivalent to
demonitor(MonitorRef).
Options:
flush- Removes (one){_, MonitorRef, _, _, _}message, if there is one, from the caller message queue after monitoring has been stopped.Calling
demonitor(MonitorRef, [flush])is equivalent to the following, but more efficient:demonitor(MonitorRef), receive {_, MonitorRef, _, _, _} -> true after 0 -> true endinfo- The returned value is one of the following:true- The monitor was found and removed. In this case, no'DOWN'message corresponding to this monitor has been delivered and will not be delivered.false- The monitor was not found and could not be removed. This probably because someone already has placed a'DOWN'message corresponding to this monitor in the caller message queue.
If option
infois combined with optionflush,falseis returned if a flush was needed, otherwisetrue.
Change
More options can be added in a future release.
Failures:
badarg- IfOptionListis not a list.badarg- IfOptionis an invalid option.badarg- The same failure as fordemonitor/1.
Returns the process dictionary and deletes it.
For example:
> put(key1, {1, 2, 3}),
put(key2, [a, b, c]),
erase().
[{key1,{1,2,3}},{key2,[a,b,c]}]
Returns the value Val associated with Key and deletes it from the process
dictionary. Returns undefined if no value is associated with Key.
The average time complexity for the current implementation of this function is
O(1) and the worst case time complexity is O(N), where N is the number of
items in the process dictionary.
For example:
> put(key1, {merry, lambs, are, playing}),
X = erase(key1),
{X, erase(key1)}.
{{merry,lambs,are,playing},undefined}
Raises an exception of class error with the reason Reason.
As evaluating this function causes an exception to be thrown, it has no return value.
The intent of the exception class error is to signal that an unexpected error
has happened (for example, a function is called with a parameter that has an
incorrect type). See the guide about
errors and error handling for additional information.
Example:
> catch error(foobar).
{'EXIT',{foobar,[{shell,apply_fun,3,
[{file,"shell.erl"},{line,906}]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,677}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,430}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
Raises an exception of class error with the reason Reason. Args is
expected to be the list of arguments for the current function or the atom
none.
If Args is a list, it is used to provide the arguments for the current
function in the stack back-trace. If it is none, the arity of the calling
function is used in the stacktrace. As evaluating this function causes an
exception to be raised, it has no return value.
The intent of the exception class error is to signal that an unexpected error
has happened (for example, a function is called with a parameter that has an
incorrect type). See the guide about
errors and error handling for additional information.
Example:
test.erl:
-module(test).
-export([example_fun/2]).
example_fun(A1, A2) ->
erlang:error(my_error, [A1, A2]).Erlang shell:
6> c(test).
{ok,test}
7> test:example_fun(arg1,"this is the second argument").
** exception error: my_error
in function test:example_fun/2
called as test:example_fun(arg1,"this is the second argument")
-spec error(Reason, Args, Options) -> no_return() when Reason :: term(), Args :: [term()] | none, Options :: [Option], Option :: {error_info, ErrorInfoMap}, ErrorInfoMap :: #{cause => term(), module => module(), function => atom()}.
Raises an exception of class error with the reason Reason. Args is
expected to be the list of arguments for the current function or the atom
none.
If Args is a list, it is used to provide the arguments for the current
function in the stack back-trace. If it is none, the arity of the calling
function is used in the stacktrace. As evaluating this function causes an
exception to be raised, it has no return value.
If the error_info option is given, the ErrorInfoMap will be inserted into
the stacktrace. The information given in the ErrorInfoMap is to be used by
error formatters such as erl_error to
provide more context around an error.
The default module of the ErrorInfoMap is the module that the call to
error/3 is made. The default function is format_error. See
format_error/2 for more details on how this
Module:Function/2 is to be used
The intent of the exception class error is to signal that an unexpected error
has happened (for example, a function is called with a parameter that has an
incorrect type). See the guide about
errors and error handling for additional information.
Raises an exception of class exit with exit reason Reason.
As evaluating this function causes an exception to be raised, it has no return value.
The intent of the exception class exit is that the current process should be
stopped (for example when a message telling a process to stop is received).
This function differ from error/1,2,3 by causing an exception of
a different class and by having a reason that does not include the list of
functions from the call stack.
See the guide about errors and error handling for additional information.
Example:
> exit(foobar).
** exception exit: foobar
> catch exit(foobar).
{'EXIT',foobar}Note
If a process calls exit(kill) and does not catch the exception,
it will terminate with exit reason kill and also emit exit signals with exit
reason kill (not killed) to all linked processes. Such exit signals with
exit reason kill can be trapped by the linked processes. Note that this
means that signals with exit reason kill behave differently depending on how
they are sent because the signal will be untrappable if a process sends such a
signal to another process with erlang:exit/2.
Sends an exit signal with exit reason Reason to the process or port identified
by Pid.
The following behavior applies if Reason is any term, except normal or
kill, and P is the process or port identified by Pid:
- If
Pis not trapping exits,Pexits with exit reasonReason. - If
Pis trapping exits, the exit signal is transformed into a message{'EXIT', From, Reason}, whereFromis the process identifier of the process that sent the exit signal, and delivered to the message queue ofP.
The following behavior applies if Reason is the term normal and Pid is the
identifier of a process P which is not the same as the process that invoked
erlang:exit(Pid, normal) (the behavior when a process sends a signal with the
normal reason to itself is described in the warning):
- If
Pis trapping exits, the exit signal is transformed into a message{'EXIT', From, normal}, whereFromis the process identifier of the process that sent the exit signal, and delivered toP's message queue. - The signal has no effect if
Pis not trapping exits.
If Reason is the atom kill, that is, if exit(Pid, kill) is
called, an untrappable exit signal is sent to the process that is identified by
Pid, which unconditionally exits with exit reason killed. The exit reason is
changed from kill to killed to hint to linked processes that the killed
process got killed by a call to exit(Pid, kill).
Note
The functions erlang:exit/1 and erlang:exit/2 are
named similarly but provide very different functionalities. The
erlang:exit/1 function should be used when the intent is to stop the current
process while erlang:exit/2 should be used when the intent is to send an
exit signal to another process. Note also that erlang:exit/1 raises an
exception that can be caught while erlang:exit/2 does not cause any
exception to be raised.
Warning
The only scenario that has not been covered by the description above is when a
process P sends an exit signal with reason normal to itself, that is
erlang:exit(self(), normal). The behavior in this scenario is as follows:
- If
Pis trapping exits, the exit signal is transformed into a message{'EXIT', From, normal}, whereFromisP's process identifier, and delivered toP's message queue. Pexits with reasonnormalifPis not trapping exits.
Note that the behavior described above is different from when a process sends
an exit signal with reason normal to another process. This is arguably
strange but this behavior is kept for backward compatibility reasons.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
-spec garbage_collect() -> true.
Forces an immediate garbage collection of the executing process.
The function is not to be used unless it has been noticed (or there are good reasons to suspect) that the spontaneous garbage collection will occur too late or not at all.
Warning
Improper use can seriously degrade system performance.
Equivalent to garbage_collect(Pid, []).
-spec garbage_collect(Pid, OptionList) -> GCResult | async when Pid :: pid(), RequestId :: term(), Option :: {async, RequestId} | {type, major | minor}, OptionList :: [Option], GCResult :: boolean().
Garbage collects the node local process identified by Pid.
Option:
{async, RequestId}- The functiongarbage_collect/2returns the valueasyncimmediately after the request has been sent. When the request has been processed, the process that called this function is passed a message on the form{garbage_collect, RequestId, GCResult}.{type, 'major' | 'minor'}- Triggers garbage collection of requested type. Default value is'major', which would trigger a fullsweep GC. The option'minor'is considered a hint and may lead to either minor or major GC run.
If Pid equals self/0, and no async option has been passed, the garbage
collection is performed at once, that is, the same as calling
garbage_collect/0. Otherwise a request for garbage collection is sent to the
process identified by Pid, and will be handled when appropriate. If no async
option has been passed, the caller blocks until GCResult is available and can
be returned.
GCResult informs about the result of the garbage collection request as
follows:
true- The process identified byPidhas been garbage collected.false- No garbage collection was performed, as the process identified byPidterminated before the request could be satisfied.
Notice that the same caveats apply as for garbage_collect/0.
Failures:
badarg- IfPidis not a node local process identifier.badarg- IfOptionListis an invalid list of options.
Returns the process dictionary as a list of {Key, Val} tuples. The items in
the returned list can be in any order.
For example:
> put(key1, merry),
put(key2, lambs),
put(key3, {are, playing}),
get().
[{key1,merry},{key2,lambs},{key3,{are,playing}}]
Returns the value Val associated with Key in the process dictionary, or
undefined if Key does not exist.
The expected time complexity for the current implementation of this function is
O(1) and the worst case time complexity is O(N), where N is the number of
items in the process dictionary.
For example:
> put(key1, merry),
put(key2, lambs),
put({any, [valid, term]}, {are, playing}),
get({any, [valid, term]}).
{are,playing}
-spec get_keys() -> [Key] when Key :: term().
Returns a list of all keys present in the process dictionary. The items in the returned list can be in any order.
For example:
> put(dog, {animal,1}),
put(cow, {animal,2}),
put(lamb, {animal,3}),
get_keys().
[dog,cow,lamb]
Returns a list of keys that are associated with the value Val in the process
dictionary. The items in the returned list can be in any order.
For example:
> put(mary, {1, 2}),
put(had, {1, 2}),
put(a, {1, 2}),
put(little, {1, 2}),
put(dog, {1, 3}),
put(lamb, {1, 2}),
get_keys({1, 2}).
[mary,had,a,little,lamb]
-spec group_leader() -> pid().
Returns the process identifier of the group leader for the process evaluating the function.
Every process is a member of some process group and all groups have a group leader. All I/O from the group is channeled to the group leader. When a new process is spawned, it gets the same group leader as the spawning process.
Initially, at system startup, init is both its own group leader and the group
leader of all processes. During the boot of a system the group leader for
processes will be changed depending on the need of the system. Some examples
where this is done are:
- When an application is started, the top supervisor of that application will
have its group leader set to the application master. See
application:start/2for more details. - When running tests, both
common_testandeunitset the group leader in order to capture any I/O from the testcase. - The interactive shell sets the group leader to intercept I/O.
Sets the group leader of Pid to GroupLeader. Typically, this is used when a
process started from a certain shell is to have another group leader than
init.
The group leader should be rarely changed in applications with a supervision tree, because OTP assumes the group leader of their processes is their application master.
Setting the group leader follows the signal ordering guarantees described in the Processes Chapter in the Erlang Reference Manual.
See also group_leader/0 and
OTP design principles related to starting
and stopping applications.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
-spec hibernate(Module, Function, Args) -> no_return() when Module :: module(), Function :: atom(), Args :: [term()].
Puts the calling process into a wait state where its memory allocation has been reduced as much as possible. This is useful if the process does not expect to receive any messages soon.
The process is awaken when a message is sent to it, and control resumes in
Module:Function with the arguments specified by Args with the call stack
emptied, meaning that the process terminates when that function returns. Thus
erlang:hibernate/3 never returns to its caller. The resume function
Module:Function/Arity must be exported (Arity =:=
length(Args)).
If the process has any message in its message queue, the process is awakened immediately in the same way as described earlier.
In more technical terms, erlang:hibernate/3 discards the call stack for the
process, and then garbage collects the process. After this, all live data is in
one continuous heap. The heap is then shrunken to the exact same size as the
live data that it holds (even if that size is less than the minimum heap size
for the process).
If the size of the live data in the process is less than the minimum heap size, the first garbage collection occurring after the process is awakened ensures that the heap size is changed to a size not smaller than the minimum heap size.
Notice that emptying the call stack means that any surrounding catch is
removed and must be re-inserted after hibernation. One effect of this is that
processes started using proc_lib (also indirectly, such as gen_server
processes), are to use proc_lib:hibernate/3 instead, to ensure that the
exception handler continues to work when the process wakes up.
Pid must refer to a process at the local node.
Returns true if the process exists and is alive, that is, is not exiting and
has not exited. Otherwise returns false.
If process P1 calls is_process_alive(P2Pid) it is
guaranteed that all signals, sent from P1 to P2 (P2 is the process with
identifier P2Pid) before the call, will be delivered to P2 before the
aliveness of P2 is checked. This guarantee means that one can use
is_process_alive/1 to let a process P1 wait until a
process P2, which has got an exit signal with reason kill from P1, is
killed.
For example:
exit(P2Pid, kill),
% P2 might not be killed
is_process_alive(P2Pid),
% P2 is not alive (the call above always return false)See the documentation about signals and erlang:exit/2 for more information about signals and exit signals.
Sets up and activates a link between the calling process and another process or
a port identified by PidOrPort.
We will from here on call the identified process or port linkee. If the linkee is a port, it must reside on the same node as the caller.
If one of the participants of a link terminates, it will
send an exit signal to
the other participant. The exit signal will contain the
exit reason of the
terminated participant. Other cases when exit signals are triggered due to a
link are when no linkee exist (noproc exit reason) and when the connection
between linked processes on different nodes is lost or cannot be established
(noconnection exit reason).
An existing link can be removed by calling unlink/1. For more information on
links and exit signals due to links, see the Processes chapter in the Erlang
Reference Manual:
For historical reasons, link/1 has a strange semi-synchronous
behavior when it is "cheap" to check if the linkee exists or not, and the caller
does not trap exits. If the above is true
and the linkee does not exist, link/1 will raise a noproc error
exception. The expected behavior would instead have been that
link/1 returned true, and the caller later was sent an exit
signal with noproc exit reason, but this is unfortunately not the case. The
noproc exception is not to be confused with
an exit signal with exit
reason noproc. Currently it is "cheap" to check if the linkee exists when it
is supposed to reside on the same node as the calling process.
The link setup and activation is performed asynchronously. If the link already exists, or if the caller attempts to create a link to itself, nothing is done. A detailed description of the link protocol can be found in the Distribution Protocol chapter of the ERTS User's Guide.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
Failure:
badargifPidOrPortdoes not identify a process or a node local port.noproclinkee does not exist and it is "cheap" to check if it exists as described above.
-spec monitor(process, monitor_process_identifier()) -> MonitorRef when MonitorRef :: reference(); (port, monitor_port_identifier()) -> MonitorRef when MonitorRef :: reference(); (time_offset, clock_service) -> MonitorRef when MonitorRef :: reference().
Sends a monitor request of type Type to the entity identified by Item.
If the monitored entity does not exist or it changes monitored state, the caller
of monitor/2 is notified by a message on the following format:
{Tag, MonitorRef, Type, Object, Info}Note
The monitor request is an asynchronous signal. That is, it takes time before the signal reaches its destination.
Type can be one of the following atoms: process, port or time_offset.
A process or port monitor is triggered only once, after that it is removed
from both monitoring process and the monitored entity. Monitors are fired when
the monitored process or port terminates, does not exist at the moment of
creation, or if the connection to it is lost. If the connection to it is lost,
we do not know if it still exists. The monitoring is also turned off when
demonitor/1 is called.
A process or port monitor by name resolves the RegisteredName to pid/0
or port/0 only once at the moment of monitor instantiation, later changes to
the name registration will not affect the existing monitor.
When a process or port monitor is triggered, a 'DOWN' message is sent that
has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}In the monitor message MonitorRef and Type are the same as described
earlier, and:
Object- The monitored entity, which triggered the event. When monitoring a process or a local port,Objectwill be equal to thepid/0orport/0that was being monitored. When monitoring process or port by name,Objectwill have format{RegisteredName, Node}whereRegisteredNameis the name which has been used withmonitor/2call andNodeis local or remote node name (for ports monitored by name,Nodeis always local node name).Info- Either the exit reason of the process,noproc(process or port did not exist at the time of monitor creation), ornoconnection(no connection to the node where the monitored process resides).Monitoring a
process- Creates monitor between the current process and another process identified byItem, which can be apid/0(local or remote), an atomRegisteredNameor a tuple{RegisteredName, Node}for a registered process, located elsewhere.Change
Before ERTS 10.0 (OTP 21.0), monitoring a process could fail with
badargif the monitored process resided on a primitive node (such as erl_interface or jinterface), where remote process monitoring is not implemented.Now, such a call to
monitorwill instead succeed and a monitor is created. But the monitor will only supervise the connection. That is, a{'DOWN', _, process, _, noconnection}is the only message that may be received, as the primitive node have no way of reporting the status of the monitored process.Monitoring a
port- Creates monitor between the current process and a port identified byItem, which can be aport/0(only local), an atomRegisteredNameor a tuple{RegisteredName, Node}for a registered port, located on this node. Note, that attempt to monitor a remote port will result inbadarg.Available since OTP 19.0.
Monitoring a
time_offset- Monitors changes intime_offset/0between Erlang monotonic time and Erlang system time. One validItemexists in combination with thetime_offset Type, namely the atomclock_service. Notice that the atomclock_serviceis not the registered name of a process. In this case it serves as an identifier of the runtime system internal clock service at current runtime system instance.The monitor is triggered when the time offset is changed. This either if the time offset value is changed, or if the offset is changed from preliminary to final during finalization of the time offset when the single time warp mode is used. When a change from preliminary to final time offset is made, the monitor is triggered once regardless of whether the time offset value was changed or not.
If the runtime system is in multi time warp mode, the time offset is changed when the runtime system detects that the OS system time has changed. The runtime system does, however, not detect this immediately when it occurs. A task checking the time offset is scheduled to execute at least once a minute, so under normal operation this is to be detected within a minute, but during heavy load it can take longer time.
The monitor is not automatically removed after it has been triggered. That is, repeated changes of the time offset trigger the monitor repeatedly.
When the monitor is triggered a
'CHANGE'message is sent to the monitoring process. A'CHANGE'message has the following pattern:{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}where
MonitorRef,Type, andItemare the same as described above, andNewTimeOffsetis the new time offset.When the
'CHANGE'message has been received you are guaranteed not to retrieve the old time offset when callingerlang:time_offset/0. Notice that you can observe the change of the time offset when callingerlang:time_offset/0before you get the'CHANGE'message.Available since OTP 18.0.
Making several calls to monitor/2 for the same Item and/or
Type is not an error; it results in as many independent monitoring instances.
The monitor functionality is expected to be extended. That is, other Types and
Items are expected to be supported in a future release.
Note
If or when monitor/2 is extended, other possible values for
Tag, Object, and Info in the monitor message will be introduced.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
-spec monitor(process, monitor_process_identifier(), [monitor_option()]) -> MonitorRef when MonitorRef :: reference(); (port, monitor_port_identifier(), [monitor_option()]) -> MonitorRef when MonitorRef :: reference(); (time_offset, clock_service, [monitor_option()]) -> MonitorRef when MonitorRef :: reference().
Provides an option list for modification of monitoring functionality provided by
monitor/2. The Type and Item arguments have the same meaning as when
passed to monitor/2.
Currently available options:
{alias, UnaliasOpt}- The returned monitor reference will also become an alias for the calling process. That is, the returned reference can be used for sending messages to the calling process. See alsoalias/0. TheUnaliasOptdetermines how the alias should be deactivated.explicit_unalias- Only an explicit call tounalias/1will deactivate the alias.demonitor- The alias will be automatically deactivated when the monitor is removed. This either via an explicit call todemonitor/1or when it is automatically removed at the same time as a'DOWN'message is delivered due to the monitor. The alias can also still be deactivated via a call tounalias/1.reply_demonitor- The alias will be automatically deactivated when the monitor is removed (seedemonitoroption above) or a reply message sent via the alias is received. When a reply message is received via the alias the monitor will also be automatically removed. This is useful in client/server scenarios when a client monitors the server and will get the reply via the alias. Once the response is received both the alias and the monitor will be automatically removed regardless of whether the response is a reply or a'DOWN'message. The alias can also still be deactivated via a call tounalias/1. Note that if the alias is removed using theunalias/1BIF, the monitor will still be left active.
Example:
server() -> receive {request, AliasReqId, Request} -> Result = perform_request(Request), AliasReqId ! {reply, AliasReqId, Result} end, server(). client(ServerPid, Request) -> AliasMonReqId = monitor(process, ServerPid, [{alias, reply_demonitor}]), ServerPid ! {request, AliasMonReqId, Request}, %% Alias as well as monitor will be automatically deactivated if we %% receive a reply or a 'DOWN' message since we used 'reply_demonitor' %% as unalias option... receive {reply, AliasMonReqId, Result} -> Result; {'DOWN', AliasMonReqId, process, ServerPid, ExitReason} -> error(ExitReason) end.Note that both the server and the client in this example must be executing on at least OTP 24 systems in order for this to work.
For more information on process aliases see the Process Aliases section of the Erlang Reference Manual.
{tag, UserDefinedTag}- Replace the defaultTagwithUserDefinedTagin the monitor message delivered when the monitor is triggered. For example, when monitoring a process, the'DOWN'tag in the down message will be replaced byUserDefinedTag.An example of how the
{tag, UserDefinedTag}option can be used in order to enable the new selective receive optimization, introduced in OTP 24, when making multiple requests to different servers:server() -> receive {request, From, ReqId, Request} -> Result = perform_request(Request), From ! {reply, self(), ReqId, Result} end, server(). client(ServerPids, Request) when is_list(ServerPids) -> ReqId = make_ref(), lists:foreach(fun (ServerPid) -> _ = monitor(process, ServerPid, [{tag, {'DOWN', ReqId}}]), ServerPid ! {request, self(), ReqId, Request} end, ServerPids), receive_replies(ReqId, length(ServerPids), []). receive_replies(_ReqId, 0, Acc) -> Acc; receive_replies(ReqId, N, Acc) -> %% The compiler will detect that we match on the 'ReqId' %% reference in all clauses, and will enable the selective %% receive optimization which makes the receive able to %% skip past all messages present in the message queue at %% the time when the 'ReqId' reference was created... Res = receive {reply, ServerPid, ReqId, Result} -> %% Here we typically would have deactivated the %% monitor by a call to demonitor(Mon, [flush]) but %% we ignore this in this example for simplicity... {ok, ServerPid, Result}; {{'DOWN', ReqId}, _Mon, process, ServerPid, ExitReason} -> {error, ServerPid, ExitReason} end, receive_replies(ReqId, N-1, [Res | Acc]).In order for this example to work as intended, the client must be executing on at least an OTP 24 system, but the servers may execute on older systems.
Works exactly like error/1, but Dialyzer thinks that this BIF will return an
arbitrary term. When used in a stub function for a NIF to generate an exception
when the NIF library is not loaded, Dialyzer does not generate false warnings.
Works exactly like error/2, but Dialyzer thinks that this BIF will return an
arbitrary term. When used in a stub function for a NIF to generate an exception
when the NIF library is not loaded, Dialyzer does not generate false warnings.
-spec open_port(PortName, PortSettings) -> port() when PortName :: {spawn, Command :: string() | binary()} | {spawn_driver, Command :: string() | binary()} | {spawn_executable, FileName :: file:name_all()} | {fd, In :: non_neg_integer(), Out :: non_neg_integer()}, PortSettings :: [Opt], Opt :: {packet, N :: 1 | 2 | 4} | stream | {line, L :: non_neg_integer()} | {cd, Dir :: string() | binary()} | {env, Env :: [{Name :: os:env_var_name(), Val :: os:env_var_value() | [] | false}]} | {args, [string() | binary()]} | {arg0, string() | binary()} | exit_status | use_stdio | nouse_stdio | stderr_to_stdout | in | out | binary | eof | {parallelism, Boolean :: boolean()} | hide | {busy_limits_port, {non_neg_integer(), non_neg_integer()} | disabled} | {busy_limits_msgq, {non_neg_integer(), non_neg_integer()} | disabled}.
Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process.
The name of the executable as well as the arguments specified in cd, env,
args, and arg0 are subject to Unicode filename translation if the system is
running in Unicode filename mode. To avoid translation or to force, for example
UTF-8, supply the executable and/or arguments as a binary in the correct
encoding. For details, see the module file, the function
file:native_name_encoding/0 in Kernel, and the
Using Unicode in Erlang User's Guide.
Note
The characters in the name (if specified as a list) can only be > 255 if the Erlang virtual machine is started in Unicode filename translation mode. Otherwise the name of the executable is limited to the ISO Latin-1 character set.
PortNames:
{spawn, Command}- Starts an external program.Commandis the name of the external program to be run.Commandruns outside the Erlang work space unless an Erlang driver with the nameCommandis found. If found, that driver is started. A driver runs in the Erlang work space, which means that it is linked with the Erlang runtime system.For external programs,
PATHis searched (or an equivalent method is used to find programs, depending on the OS). This is done by invoking the shell on certain platforms. The first space-separated token of the command is considered as the name of the executable (or driver). This (among other things) makes this option unsuitable for running programs with spaces in filenames or directory names. If spaces in executable filenames are desired, use{spawn_executable, Command}instead.Warning
On Unix systems, arguments are passed to a new operating system process as an array of strings but on Windows it is up to the child process to parse them and some Windows programs may apply their own rules, which are inconsistent with the standard C runtime
argvparsing.This is particularly troublesome when invoking
.bat,.cmd, or.comfiles as these run implicitly throughcmd.exe, whose argument parsing is vulnerable to malicious input and can be used to run arbitrary shell commands.Therefore, if you are running on Windows and you execute batch files or
.comapplications, you must not pass untrusted input as arguments to the program. This affects bothspawnandspawn_executable.{spawn_executable, FileName}- Works like{spawn, FileName}, but only runs external executables.FileNamein its whole is used as the name of the executable, including any spaces. If arguments are to be passed, thePortSettingsargsandarg0can be used.The shell is usually not invoked to start the program, it is executed directly.
PATH(or equivalent) is not searched. To find a program inPATHto execute, useos:find_executable/1.Only if a shell script or
.batfile is executed, the appropriate command interpreter is invoked implicitly, but there is still no command-argument expansion or implicitPATHsearch.If
FileNamecannot be run, an error exception is raised, with the POSIX error code as the reason. The error reason can differ between OSs. Typically the errorenoentis raised when an attempt is made to run a program that is not found andeaccesis raised when the specified file is not executable.{spawn_driver, Command}- Works like{spawn, Command}, but demands the first (space-separated) token of the command to be the name of a loaded driver. If no driver with that name is loaded, abadargerror is raised.{fd, In, Out}- Allows an Erlang process to access any currently opened file descriptors used by Erlang. The file descriptorIncan be used for standard input, and the file descriptorOutfor standard output. It is only used for various servers in the Erlang OS (shellanduser). Hence, its use is limited.
PortSettings is a list of settings for the port. The valid settings are as
follows:
{packet, N}- Messages are preceded by their length, sent inNbytes, with the most significant byte first. The valid values forNare 1, 2, and 4.stream- Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.{line, L}- Messages are delivered on a per line basis. Each line (delimited by the OS-dependent newline sequence) is delivered in a single message. The message data format is{Flag, Line}, whereFlagiseolornoeol, andLineis the data delivered (without the newline sequence).Lspecifies the maximum line length in bytes. Lines longer than this are delivered in more than one message, withFlagset tonoeolfor all but the last message. If end of file is encountered anywhere else than immediately following a newline sequence, the last line is also delivered withFlagset tonoeol. Otherwise lines are delivered withFlagset toeol.The
{packet, N}and{line, L}settings are mutually exclusive.{cd, Dir}- Only valid for{spawn, Command}and{spawn_executable, FileName}. The external program starts usingDiras its working directory.Dirmust be a string.{env, Env}- Only valid for{spawn, Command}, and{spawn_executable, FileName}. The environment of the started process is extended using the environment specifications inEnv.Envis to be a list of tuples{Name, Val}, whereNameis aos:env_var_name/0representing the name of an environment variable, andValis aos:env_var_name/0representing the value it is to have in the spawned port process. BothNameandValmust be strings.If
Valis set to the atomfalseor the empty string (that is""or[]), open_port will consider those variables unset just as ifos:unsetenv/1had been called.For information about encoding requirements, see documentation of the types for
NameandVal.{args, [ string() | binary() ]}- Only valid for{spawn_executable, FileName}and specifies arguments to the executable. Each argument is specified as a separate string and (on Unix) eventually ends up as one element each in the argument vector. On other platforms, a similar behavior is mimicked.The arguments are not expanded by the shell before they are supplied to the executable. Most notably this means that file wildcard expansion does not occur. To expand wildcards for the arguments, use
filelib:wildcard/1. Notice that even if the program is a Unix shell script, meaning that the shell ultimately is invoked, wildcard expansion does not occur, and the script is provided with the untouched arguments. On Windows, wildcard expansion is always up to the program itself, therefore this is not an issue.The executable name (also known as
argv[0]) is not to be specified in this list. The proper executable name is automatically used asargv[0], where applicable.If you explicitly want to set the program name in the argument vector, option
arg0can be used.{arg0, string() | binary()}- Only valid for{spawn_executable, FileName}and explicitly specifies the program name argument when running an executable. This can in some circumstances, on some OSs, be desirable. How the program responds to this is highly system-dependent and no specific effect is guaranteed.exit_status- Only valid for{spawn, Command}, whereCommandrefers to an external program, and for{spawn_executable, FileName}.When the external process connected to the port exits, a message of the form
{Port,{exit_status,Status}}is sent to the connected process, whereStatusis the exit status of the external process. If the program aborts on Unix, the same convention is used as the shells do (that is, 128+signal).If option
eofis specified also, the messageseofandexit_statusappear in an unspecified order.use_stdio- Only valid for{spawn, Command}and{spawn_executable, FileName}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (Unix) process for communication with Erlang.nouse_stdio- The opposite ofuse_stdio. It uses file descriptors 3 and 4 for communication with Erlang.stderr_to_stdout- Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file.stderr_to_stdoutandnouse_stdioare mutually exclusive.overlapped_io- Affects ports to external programs on Windows only. The standard input and standard output handles of the port program are, if this option is supplied, opened with flagFILE_FLAG_OVERLAPPED, so that the port program can (and must) do overlapped I/O on its standard handles. This is not normally the case for simple port programs, but an option of value for the experienced Windows programmer. On all other platforms, this option is silently discarded.in- The port can only be used for input.out- The port can only be used for output.binary- All I/O from the port is binary data objects as opposed to lists of bytes.eof- The port is not closed at the end of the file and does not produce an exit signal. Instead, it remains open and a{Port, eof}message is sent to the process holding the port.hide- When running on Windows, suppresses creation of a new console window when spawning the port program. (This option has no effect on other platforms.){parallelism, Boolean}- Sets scheduler hint for port parallelism. If set totrue, the virtual machine schedules port tasks; when doing so, it improves parallelism in the system. If set tofalse, the virtual machine tries to perform port tasks immediately, improving latency at the expense of parallelism. The default can be set at system startup by passing command-line argument+sppto erl.{busy_limits_port, {Low, High} | disabled}- Sets limits that will be used for controlling the busy state of the port.When the ports internal output queue size becomes larger than or equal to
Highbytes, it enters the busy state. When it becomes less thanLowbytes it leaves the busy state. When the port is in the busy state, processes sending commands to it will be suspended until the port leaves the busy state. Commands are in this context eitherPort ! {Owner, {command, Data}}orport_command/[2,3].The
Lowlimit is automatically adjusted to the same asHighif it is set larger thenHigh. Valid range of values forLowandHighis[1, (1 bsl (8*erlang:system_info(wordsize)))-2]. If the atomdisabledis passed, the port will never enter the busy state.The defaults are
Low = 4096andHigh = 8192.Note that this option is only valid when spawning an executable (port program) by opening the spawn driver and when opening the
fddriver. This option will cause a failure with abadargexception when opening other drivers.{busy_limits_msgq, {Low, High} | disabled}- Sets limits that will be used for controlling the busy state of the port message queue.When the ports message queue size becomes larger than or equal to
Highbytes it enters the busy state. When it becomes less thanLowbytes it leaves the busy state. When the port message queue is in the busy state, processes sending commands to it will be suspended until the port message queue leaves the busy state. Commands are in this context eitherPort ! {Owner, {command, Data}}orport_command/[2,3].The
Lowlimit is automatically adjusted to the same asHighif it is set larger thenHigh. Valid range of values forLowandHighis[1, (1 bsl (8*erlang:system_info(wordsize)))-2]. If the atomdisabledis passed, the port message queue will never enter the busy state.Note that if the driver statically has disabled the use of this feature, a failure with a
badargexception will be raised unless this option also is set todisableor not passed at all.The defaults are
Low = 4096andHigh = 8192unless the driver itself does modifications of these values.Note that the driver might fail if it also adjust these limits by itself and you have disabled this feature.
The spawn driver (used when spawning an executable) and the
fddriver do not disable this feature and do not adjust these limits by themselves.For more information see the documentation
erl_drv_busy_msgq_limits().
Default is stream for all port types and use_stdio for spawned ports.
Failure: if the port cannot be opened, the exit reason is badarg,
system_limit, or the POSIX error code that most closely describes the error,
or einval if no POSIX code is appropriate:
badarg- Bad input arguments toopen_port.system_limit- All available ports in the Erlang emulator are in use.enomem- Not enough memory to create the port.eagain- No more available OS processes.enametoolong- Too long external command.emfile- No more available file descriptors (for the OS process that the Erlang emulator runs in).enfile- Full file table (for the entire OS).eacces-Commandspecified in{spawn_executable, Command}does not point out an executable file.enoent-FileNamespecified in{spawn_executable, FileName}does not point out an existing file.
During use of a port opened using {spawn, Name}, {spawn_driver, Name}, or
{spawn_executable, Name}, errors arising when sending messages to it are
reported to the owning process using signals of the form
{'EXIT', Port, PosixCode}. For the possible values of PosixCode, see
file.
The maximum number of ports that can be open at the same time can be configured
by passing command-line flag +Q to erl.
-spec port_call(Port, Operation, Data) -> term() when Port :: port() | atom(), Operation :: integer(), Data :: term().
Performs a synchronous call to a port. The meaning of Operation and Data
depends on the port, that is, on the port driver. Not all port drivers support
this feature.
Port is a port identifier, referring to a driver.
Operation is an integer, which is passed on to the driver.
Data is any Erlang term. This data is converted to binary term format and sent
to the port.
Returns a term from the driver. The meaning of the returned data also depends on the port driver.
Failures:
badarg- IfPortis not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified byPort, the exit signal from the port is guaranteed to be delivered before thisbadargexception occurs.badarg- IfOperationdoes not fit in a 32-bit integer.badarg- If the port driver does not support synchronous control operations.badarg- If the port driver so decides for any reason (probably something wrong withOperationorData).Warning
Do not call
port_callwith an unknownPortidentifier and expectbadargexception. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the supplied arguments.
Closes an open port. Roughly the same as Port ! {self(), close} except for the
error behavior (see below), being synchronous, and that the port does not
reply with {Port, closed}.
Any process can close a port with port_close/1, not only the
port owner (the connected process). If the calling process is linked to the port
identified by Port, the exit signal from the port is guaranteed to be delivered before
port_close/1 returns.
For comparison: Port ! {self(), close} only fails with badarg if Port does
not refer to a port or a process. If Port is a closed port, nothing happens.
If Port is an open port and the calling process is the port owner, the port
replies with {Port, closed} when all buffers have been flushed and the port
really closes. If the calling process is not the port owner, the port owner
fails with badsig.
Notice that any process can close a port using Port ! {PortOwner, close} as if
it itself was the port owner, but the reply always goes to the port owner.
As from Erlang/OTP R16, Port ! {PortOwner, close} is truly asynchronous.
Notice that this operation has always been documented as an asynchronous
operation, while the underlying implementation has been synchronous.
port_close/1 is however still fully synchronous because of
its error behavior.
Failure: badarg if Port is not an identifier of an open port, or the
registered name of an open port. If the calling process was previously linked to
the closed port, identified by Port, the exit signal from the port is
guaranteed to be delivered before this badarg exception occurs.
Sends data to a port. Same as Port ! {PortOwner, {command, Data}} except for
the error behavior and being synchronous (see below).
Any process can send data to a port with port_command/2,
not only the port owner (the connected process).
For comparison: Port ! {PortOwner, {command, Data}} only fails with badarg
if Port does not refer to a port or a process. If Port is a closed port, the
data message disappears without a sound. If Port is open and the calling
process is not the port owner, the port owner fails with badsig. The port
owner fails with badsig also if Data is an invalid I/O list.
Notice that any process can send to a port using
Port ! {PortOwner, {command, Data}} as if it itself was the port owner.
If the port is busy, the calling process is suspended until the port is not busy any more.
As from Erlang/OTP R16, Port ! {PortOwner, {command, Data}} is truly
asynchronous. Notice that this operation has always been documented as an
asynchronous operation, while the underlying implementation has been
synchronous. port_command/2 is however still fully
synchronous because of its error behavior.
Failures:
badarg- IfPortis not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified byPort, the exit signal from the port is guaranteed to be delivered before thisbadargexception occurs.badarg- IfDatais an invalid I/O list.
Warning
Do not send data to an unknown port. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the data.
-spec port_command(Port, Data, OptionList) -> boolean() when Port :: port() | atom(), Data :: iodata(), Option :: force | nosuspend, OptionList :: [Option].
Sends data to a port. port_command(Port, Data, []) equals
port_command(Port, Data).
If the port command is aborted, false is returned, otherwise true.
If the port is busy, the calling process is suspended until the port is not busy anymore.
Options:
force- The calling process is not suspended if the port is busy, instead the port command is forced through. The call fails with anotsupexception if the driver of the port does not support this. For more information, see driver flagERL_DRV_FLAG_SOFT_BUSY.nosuspend- The calling process is not suspended if the port is busy, instead the port command is aborted andfalseis returned.
Change
More options can be added in a future release.
Failures:
badarg- IfPortis not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified byPort, the exit signal from the port is guaranteed to be delivered before thisbadargexception occurs.badarg- IfDatais an invalid I/O list.badarg- IfOptionListis an invalid option list.notsup- If optionforcehas been passed, but the driver of the port does not allow forcing through a busy port.
Warning
Do not send data to an unknown port. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the data.
Sets the port owner (the connected port) to Pid. Roughly the same as
Port ! {Owner, {connect, Pid}} except for the following:
- The error behavior differs, see below.
- The port does not reply with
{Port,connected}. port_connect/1is synchronous, see below.- The new port owner gets linked to the port.
The old port owner stays linked to the port and must call
unlink(Port) if this is not desired. Any process can set the
port owner to be any process with port_connect/2.
For comparison: Port ! {self(), {connect, Pid}} only fails with badarg if
Port does not refer to a port or a process. If Port is a closed port,
nothing happens. If Port is an open port and the calling process is the port
owner, the port replies with {Port, connected} to the old port owner. Notice
that the old port owner is still linked to the port, while the new is not. If
Port is an open port and the calling process is not the port owner, the port
owner fails with badsig. The port owner fails with badsig also if Pid is
not an existing local process identifier.
Notice that any process can set the port owner using
Port ! {PortOwner, {connect, Pid}} as if it itself was the port owner, but the
reply always goes to the port owner.
As from Erlang/OTP R16, Port ! {PortOwner, {connect, Pid}} is truly
asynchronous. Notice that this operation has always been documented as an
asynchronous operation, while the underlying implementation has been
synchronous. port_connect/2 is however still fully
synchronous because of its error behavior.
Failures:
badarg- IfPortis not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified byPort, the exit signal from the port is guaranteed to be delivered before thisbadargexception occurs.badarg- If the process identified byPidis not an existing local process.
-spec port_control(Port, Operation, Data) -> iodata() | binary() when Port :: port() | atom(), Operation :: integer(), Data :: iodata().
Performs a synchronous control operation on a port. The meaning of Operation
and Data depends on the port, that is, on the port driver. Not all port
drivers support this control feature.
Returns a list of integers in the range 0..255, or a binary, depending on the port driver. The meaning of the returned data also depends on the port driver.
Failures:
badarg- IfPortis not an open port or the registered name of an open port.badarg- IfOperationcannot fit in a 32-bit integer.badarg- If the port driver does not support synchronous control operations.badarg- If the port driver so decides for any reason (probably something wrong withOperationorData).Warning
Do not call
port_control/3with an unknownPortidentifier and expectbadargexception. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the supplied arguments.
-spec port_info(Port) -> Result when Port :: port() | atom(), ResultItem :: {registered_name, RegisteredName :: atom()} | {id, Index :: non_neg_integer()} | {connected, Pid :: pid()} | {links, Pids :: [pid()]} | {name, String :: string()} | {input, Bytes :: non_neg_integer()} | {output, Bytes :: non_neg_integer()} | {os_pid, OsPid :: non_neg_integer() | undefined}, Result :: [ResultItem] | undefined.
Returns a list containing tuples with information about Port, or undefined
if the port is not open.
The order of the tuples is undefined, and all the tuples are not mandatory.
If the port is closed and the calling process was
previously linked to the port, the exit signal from the port is guaranteed to be
delivered before port_info/1 returns undefined.
The result contains information about the following Items:
registered_name(if the port has a registered name)idconnectedlinksnameinputoutput
For more information about the different Items, see port_info/2.
Failure: badarg if Port is not a local port identifier, or an atom.
-spec port_info(Port, Item :: connected) -> {connected, Pid} | undefined when Port :: port() | atom(), Pid :: pid(); (Port, Item :: id) -> {id, Index} | undefined when Port :: port() | atom(), Index :: non_neg_integer(); (Port, Item :: input) -> {input, Bytes} | undefined when Port :: port() | atom(), Bytes :: non_neg_integer(); (Port, Item :: links) -> {links, Pids} | undefined when Port :: port() | atom(), Pids :: [pid()]; (Port, Item :: locking) -> {locking, Locking} | undefined when Port :: port() | atom(), Locking :: false | port_level | driver_level; (Port, Item :: memory) -> {memory, Bytes} | undefined when Port :: port() | atom(), Bytes :: non_neg_integer(); (Port, Item :: monitors) -> {monitors, Monitors} | undefined when Port :: port() | atom(), Monitors :: [{process, pid()}]; (Port, Item :: monitored_by) -> {monitored_by, MonitoredBy} | undefined when Port :: port() | atom(), MonitoredBy :: [pid()]; (Port, Item :: name) -> {name, Name} | undefined when Port :: port() | atom(), Name :: string(); (Port, Item :: os_pid) -> {os_pid, OsPid} | undefined when Port :: port() | atom(), OsPid :: non_neg_integer() | undefined; (Port, Item :: output) -> {output, Bytes} | undefined when Port :: port() | atom(), Bytes :: non_neg_integer(); (Port, Item :: parallelism) -> {parallelism, Boolean} | undefined when Port :: port() | atom(), Boolean :: boolean(); (Port, Item :: queue_size) -> {queue_size, Bytes} | undefined when Port :: port() | atom(), Bytes :: non_neg_integer(); (Port, Item :: registered_name) -> {registered_name, RegisteredName} | [] | undefined when Port :: port() | atom(), RegisteredName :: atom().
Returns information about Port.
If the port identified by Port is not open, undefined is returned. If the port is closed and the calling process was previously linked to the port, the exit signal from the port is guaranteed to be delivered before port_info/2 returns undefined.
Item is one of the following and can be used to get various information about the Port.
connected- returns{connected, Pid}wherePidis the process identifier of the process connected to the port.id- returns{id, Index}whereIndexis the internal index of the port. This index can be used to separate ports.input- returns{input, Bytes}whereBytesis the total number of bytes read from the port.links- returns{links, Pids}wherePidsis a list of the process identifiers of the processes that the port is linked to.locking- returns{locking, Locking}whereLockingis one of the following:port_level(port-specific locking)driver_level(driver-specific locking) Notice that these results are highly implementation-specific and can change in a future release.
Since: OTP R16B
memory- returns{memory, Bytes}whereBytesis the total number of bytes allocated for this port by the runtime system. The port itself can have allocated memory that is not included inBytes.Since: OTP R16B
monitors- returns{monitors, Monitors}whereMonitorsrepresent processes monitored by this port.Since: OTP R16B
monitored_by- returns{monitored_by, MonitoredBy}whereMonitoredByis a list of pids that are monitoring given port at the moment.Since: OTP 19.0
name- returns{name, Name}whereNameis the command name set byopen_port/2.os_pid- returns{os_pid, OsPid}whereOsPidis the process identifier (or equivalent) of an OS process created withopen_port({spawn | spawn_executable, Command}, Options). If the port is not the result of spawning an OS process, the value isundefined.Since: OTP R16B
output- returns{output, Bytes}whereBytesis the total number of bytes written to the port from Erlang processes usingport_command/2,port_command/3, orPort ! {Owner, {command, Data}.parallelism- returns{parallelism, Boolean}whereBooleancorresponds to the port parallelism hint used by this port. For more information, see optionparallelismofopen_port/2.Since: OTP R16B
queue_size- returns{queue_size, Bytes}whereBytesis the total number of bytes queued by the port using the ERTS driver queue implementation.Since: OTP R16B
registered_name- returns{registered_name, RegisteredName}whereRegisteredNameis the registered name of the port. If the port has no registered name,[]is returned.
Failure: badarg if Port is not a local port identifier, or an atom.
-spec ports() -> [port()].
Returns a list of port identifiers corresponding to all the ports existing on the local node.
Notice that an exiting port exists, but is not open.
-spec process_display(Pid, Type) -> true when Pid :: pid(), Type :: backtrace.
Writes information about the local process Pid on standard error.
The only allowed value for the atom Type is backtrace, which shows the contents of
the call stack, including information about the call chain, with the current
function printed first. The format of the output is not further defined.
-spec process_flag(async_dist, Boolean) -> OldBoolean when Boolean :: boolean(), OldBoolean :: boolean(); (trap_exit, Boolean) -> OldBoolean when Boolean :: boolean(), OldBoolean :: boolean(); (error_handler, Module) -> OldModule when Module :: atom(), OldModule :: atom(); (fullsweep_after, FullsweepAfter) -> OldFullsweepAfter when FullsweepAfter :: non_neg_integer(), OldFullsweepAfter :: non_neg_integer(); (min_heap_size, MinHeapSize) -> OldMinHeapSize when MinHeapSize :: non_neg_integer(), OldMinHeapSize :: non_neg_integer(); (min_bin_vheap_size, MinBinVHeapSize) -> OldMinBinVHeapSize when MinBinVHeapSize :: non_neg_integer(), OldMinBinVHeapSize :: non_neg_integer(); (max_heap_size, MaxHeapSize) -> OldMaxHeapSize when MaxHeapSize :: max_heap_size(), OldMaxHeapSize :: max_heap_size(); (message_queue_data, MQD) -> OldMQD when MQD :: message_queue_data(), OldMQD :: message_queue_data(); (priority, Level) -> OldLevel when Level :: priority_level(), OldLevel :: priority_level(); (save_calls, N) -> OldN when N :: 0..10000, OldN :: 0..10000; (sensitive, Boolean) -> OldBoolean when Boolean :: boolean(), OldBoolean :: boolean(); ({monitor_nodes, term()}, term()) -> term(); (monitor_nodes, term()) -> term().
Sets the process flag indicated to the specified value. Returns the previous value of the flag.
Flag is one of the following:
process_flag(async_dist, boolean())Enable or disable fully asynchronous distributed signaling for the calling process. When disabled, which is the default, the process sending a distributed signal will block in the send operation if the buffer for the distribution channel reach the distribution buffer busy limit. The process will remain blocked until the buffer shrinks enough. This might in some cases take a substantial amount of time. When
async_distis enabled, send operations of distributed signals will always buffer the signal on the outgoing distribution channel and then immediately return. That is, these send operations will never block the sending process.Note
Since no flow control is enforced by the runtime system when
async_distprocess flag is enabled, you need to make sure that flow control for such data is implemented, or that the amount of such data is known to always be limited. Unlimited signaling withasync_distenabled in the absence of flow control will typically cause the sending runtime system to crash on an out of memory condition.Blocking due to disabled
async_distcan be monitored byerlang:system_monitor()using thebusy_dist_portoption. Only data buffered by processes which (at the time of sending a signal) have disabledasync_distwill be counted when determining whether or not an operation should block the caller.The
async_distflag can also be set on a new process when spawning it using thespawn_opt()BIF with the option{async_dist, Enable}. The defaultasync_distflag to use on newly spawned processes can be set by passing the command line argument+pad <boolean>when starting the runtime system. If the+pad <boolean>command line argument is not passed, the default value of theasync_distflag will befalse.You can inspect the state of the
async_distprocess flag of a process by callingprocess_info(Pid, async_dist).process_flag(trap_exit, boolean())When
trap_exitis set totrue, exit signals arriving to a process are converted to{'EXIT', From, Reason}messages, which can be received as ordinary messages. Iftrap_exitis set tofalse, the process exits if it receives an exit signal other thannormaland the exit signal is propagated to its linked processes. Application processes are normally not to trap exits.See also
exit/2.process_flag(error_handler, module())Used by a process to redefine the
error_handlerfor undefined function calls and undefined registered processes. Use this flag with substantial caution, as code auto-loading depends on the correct operation of the error handling module.process_flag(fullsweep_after, non_neg_integer())Changes the maximum number of generational collections before forcing a fullsweep for the calling process.
process_flag(min_heap_size, non_neg_integer())Changes the minimum heap size for the calling process.
process_flag(min_bin_vheap_size, non_neg_integer())Changes the minimum binary virtual heap size for the calling process.
process_flag(max_heap_size, max_heap_size())This flag sets the maximum heap size for the calling process. If
MaxHeapSizeis an integer, the system default values forkillanderror_loggerare used.For details on how the heap grows, see Sizing the heap in the ERTS internal documentation.
size- The maximum size in words of the process. If set to zero, the heap size limit is disabled.badargis be thrown if the value is smaller thanmin_heap_size. The size check is only done when a garbage collection is triggered.sizeis the entire heap of the process when garbage collection is triggered. This includes all generational heaps, the process stack, any messages that are considered to be part of the heap, and any extra memory that the garbage collector needs during collection.sizeis the same as can be retrieved usingerlang:process_info(Pid, total_heap_size), or by addingheap_block_size,old_heap_block_sizeandmbuf_sizefromerlang:process_info(Pid, garbage_collection_info).kill- When set totrue, the runtime system sends an untrappable exit signal with reasonkillto the process if the maximum heap size is reached. The garbage collection that triggered thekillis not completed, instead the process exits as soon as possible. When set tofalse, no exit signal is sent to the process, instead it continues executing.If
killis not defined in the map, the system default will be used. The default system default istrue. It can be changed by either option +hmaxk in erl, orerlang:system_flag(max_heap_size, MaxHeapSize).error_logger- When set totrue, the runtime system logs an error event vialogger, containing details about the process when the maximum heap size is reached. One log event is sent each time the limit is reached.If
error_loggeris not defined in the map, the system default is used. The default system default istrue. It can be changed by either the option +hmaxel int erl, orerlang:system_flag(max_heap_size, MaxHeapSize).include_shared_binaries- When set totrue, off-heap binaries are included in the total sum compared against thesizelimit. Off-heap binaries are typically larger binaries that may be shared between processes. The size of a shared binary is included by all processes that are referring it. Also, the entire size of a large binary may be included even if only a smaller part of it is referred by the process.If
include_shared_binariesis not defined in the map, the system default is used. The default system default isfalse. It can be changed by either the option +hmaxib in erl, orerlang:system_flag(max_heap_size, MaxHeapSize).
The heap size of a process is quite hard to predict, especially the amount of memory that is used during the garbage collection. When contemplating using this option, it is recommended to first run it in production with
killset tofalseand inspect the log events to see what the normal peak sizes of the processes in the system is and then tune the value accordingly.process_flag(message_queue_data, message_queue_data())Determines how messages in the message queue are stored, as follows:
off_heap- All messages in the message queue will be stored outside the process heap. This implies that no messages in the message queue will be part of a garbage collection of the process.on_heap- All messages in the message queue will eventually be placed on the process heap. They can, however, be temporarily stored off the heap. This is how messages have always been stored up until ERTS 8.0.
The default value of the
message_queue_dataprocess flag is determined by the command-line argument+hmqdin erl.If the process may potentially accumulate a large number of messages in its queue it is recommended to set the flag value to
off_heap. This is due to the fact that the garbage collection of a process that has a large number of messages stored on the heap can become extremely expensive and the process can consume large amounts of memory. The performance of the actual message passing is, however, generally better when the flag value ison_heap.Changing the flag value causes any existing messages to be moved. The move operation is initiated, but not necessarily completed, by the time the function returns.
process_flag(priority, priority_level())Sets the process priority.
Levelis an atom. Four priority levels exist:low,normal,high, andmax. Default isnormal.Note
Priority level
maxis reserved for internal use in the Erlang runtime system, and is not to be used by others.Internally in each priority level, processes are scheduled in a round robin fashion.
Execution of processes on priority
normalandloware interleaved. Processes on priorityloware selected for execution less frequently than processes on prioritynormal.When runnable processes on priority
highexist, no processes on prioritylowornormalare selected for execution. Notice however that this does not mean that no processes on prioritylowornormalcan run when processes are running on priorityhigh. When using multiple schedulers, more processes can be running in parallel than processes on priorityhigh. That is, alowand ahighpriority process can execute at the same time.When runnable processes on priority
maxexist, no processes on prioritylow,normal, orhighare selected for execution. As with priorityhigh, processes on lower priorities can execute in parallel with processes on prioritymax.Scheduling is pre-emptive. Regardless of priority, a process is pre-empted when it has consumed more than a certain number of reductions since the last time it was selected for execution.
Note
Do not depend on the scheduling to remain exactly as it is today. Scheduling is likely to be changed in a future release to use available processor cores better.
There is no automatic mechanism for avoiding priority inversion, such as priority inheritance or priority ceilings. When using priorities, take this into account and handle such scenarios by yourself.
Making calls from a
highpriority process into code that you has no control over can cause thehighpriority process to wait for a process with lower priority. That is, effectively decreasing the priority of thehighpriority process during the call. Even if this is not the case with one version of the code that you have no control over, it can be the case in a future version of it. This can, for example, occur if ahighpriority process triggers code loading, as the code server runs on prioritynormal.Other priorities than
normalare normally not needed. When other priorities are used, use them with care, especially priorityhigh. A process on priorityhighis only to perform work for short periods. Busy looping for long periods in ahighpriority process causes most likely problems, as important OTP servers run on prioritynormal.process_flag(save_calls, 0..10000)Nmust be an integer in the interval 0..10000. IfN> 0, call saving is made active for the process. This means that information about theNmost recent global function calls, BIF calls, sends, and receives made by the process are saved in a list, which can be retrieved withprocess_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved, as follows:- A tuple
{Module, Function, Arity}for function calls - The atoms
send,'receive', andtimeoutfor sends and receives ('receive'when a message is received andtimeoutwhen a receive times out)
If
N= 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.- A tuple
process_flag(sensitive, boolean())Sets or clears flag
sensitivefor the current process. When a process has been marked as sensitive by callingprocess_flag(sensitive, true), features in the runtime system that can be used for examining the data or inner working of the process are silently disabled.Features that are disabled include (but are not limited to) the following:
- Tracing. Trace flags can still be set for the process, but no trace messages
of any kind are generated. (If flag
sensitiveis turned off, trace messages are again generated if any trace flags are set.) - Sequential tracing. The sequential trace token is propagated as usual, but no sequential trace messages are generated.
process_info/1,2cannot be used to read out the message queue or the process dictionary (both are returned as empty lists).Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary are omitted.
If
{save_calls,N}has been set for the process, no function calls are saved to the call saving list. (The call saving list is not cleared. Also, send, receive, and time-out events are still added to the list.)- Tracing. Trace flags can still be set for the process, but no trace messages
of any kind are generated. (If flag
-spec process_flag(Pid, Flag, Value) -> OldValue when Pid :: pid(), Flag :: save_calls, Value :: non_neg_integer(), OldValue :: non_neg_integer().
Sets certain flags for the process Pid, in the same manner as
process_flag/2. Returns the old value of the flag. The valid values for Flag
are only a subset of those allowed in process_flag/2,
namely save_calls.
Failure: badarg if Pid is not a local process.
-spec process_info(Pid) -> Info when Pid :: pid(), Info :: [InfoTuple] | undefined, InfoTuple :: process_info_result_item().
Returns a list containing InfoTuples with miscellaneous information about the
process identified by Pid, or undefined if the process is not alive.
The order of the InfoTuples is undefined and all InfoTuples are not
mandatory. The InfoTuples part of the result can be changed without prior
notice.
The InfoTuples with the following items are part of the result:
current_functioninitial_callstatusmessage_queue_lenlinksdictionarytrap_exiterror_handlerprioritygroup_leadertotal_heap_sizeheap_sizestack_sizereductionsgarbage_collection
If the process identified by Pid has a registered name, also an InfoTuple
with item registered_name is included.
For information about specific InfoTuples, see process_info/2.
Warning
This BIF is intended for debugging only. For all other purposes, use
process_info/2.
Failure: badarg if Pid is not a local process.
-spec process_info(Pid, Item) -> InfoTuple | [] | undefined when Pid :: pid(), Item :: process_info_item(), InfoTuple :: process_info_result_item(); (Pid, ItemList) -> InfoTupleList | [] | undefined when Pid :: pid(), ItemList :: [Item], Item :: process_info_item(), InfoTupleList :: [InfoTuple], InfoTuple :: process_info_result_item().
Returns information about the process identified by Pid, as specified by
Item or ItemList. Returns undefined if the process is not alive.
If the process is alive and a single Item is specified, the returned value is
the corresponding InfoTuple, unless Item =:= registered_name and the process
has no registered name. In this case, [] is returned. This strange behavior is
because of historical reasons, and is kept for backward compatibility.
If ItemList is specified, the result is InfoTupleList. The InfoTuples in
InfoTupleList are included with the corresponding Items in the same order as
the Items were included in ItemList. Valid Items can be included multiple
times in ItemList.
Getting process information follows the signal ordering guarantees described in the Processes Chapter in the Erlang Reference Manual.
Note
If registered_name is part of ItemList and the process has no name
registered, a {registered_name, []}, InfoTuple will be included in the
resulting InfoTupleList. This behavior is different when a single
Item =:= registered_name is specified, and when
process_info/1 is used.
Valid InfoTuples with corresponding Items:
{async_dist, Enabled}- Since: OTP 25.3Current value of the
async_distprocess flag.{backtrace, Bin}- BinaryBincontains the same information as the output fromerlang:process_display(Pid, backtrace). Usebinary_to_list/1to obtain the string of characters from the binary.{binary, BinInfo}-BinInfois a list containing miscellaneous information about binaries on the heap of this process. ThisInfoTuplecan be changed or removed without prior notice. In the current implementationBinInfois a list of tuples. The tuples contain;BinaryId,BinarySize,BinaryRefcCount.Depending on the value of the
message_queue_dataprocess flag the message queue may be stored on the heap.{catchlevel, CatchLevel}-CatchLevelis the number of currently active catches in this process. ThisInfoTuplecan be changed or removed without prior notice.{current_function, {Module, Function, Arity} | undefined}-Module,Function,Arityis the current function call of the process. The valueundefinedcan be returned if the process is currently executing native compiled code.{current_location, {Module, Function, Arity, Location}}-Module,Function,Arityis the current function call of the process.Locationis a list of two-tuples describing the location in the source code.{current_stacktrace, Stack}- Returns the current call stack back-trace (stacktrace) of the process. The stack has the same format as in thecatchpart of atry. See The call-stack back trace (stacktrace). The depth of the stacktrace is truncated according to thebacktrace_depthsystem flag setting.{dictionary, Dictionary}-Dictionaryis the process dictionary.{{dictionary, Key}, Value}-Valueassociated withKeyin the process dictionary.{error_handler, Module}-Moduleis theerror_handlermodule used by the process (for undefined function calls, for example).{garbage_collection, GCInfo}-GCInfois a list containing miscellaneous information about garbage collection for this process. The content ofGCInfocan be changed without prior notice.{garbage_collection_info, GCInfo}-GCInfois a list containing miscellaneous detailed information about garbage collection for this process. The content ofGCInfocan be changed without prior notice. For details about the meaning of each item, seegc_minor_startintrace:process/4.{group_leader, GroupLeader}-GroupLeaderis the group leader for the I/O of the process.{heap_size, Size}-Sizeis the size in words of the youngest heap generation of the process. This generation includes the process stack. This information is highly implementation-dependent, and can change if the implementation changes.{initial_call, {Module, Function, Arity}}-Module,Function,Arityis the initial function call with which the process was spawned.{links, PidsAndPorts}-PidsAndPortsis a list of process identifiers and port identifiers, with processes or ports to which the process has a link.{label, Label}-Labelis the label for the process. Seeproc_lib:get_label/1.Since: OTP 27.2
{last_calls, false|Calls}- The value isfalseif call saving is not active for the process (seeprocess_flag/3). If call saving is active, a list is returned, in which the last element is the most recent called.{memory, Size}-Sizeis the size in bytes of the process. This includes call stack, heap, and internal structures.{message_queue_len, MessageQueueLen}-MessageQueueLenis the number of messages currently in the message queue of the process. This is the length of the listMessageQueuereturned as the information itemmessages(see below).{messages, MessageQueue}-MessageQueueis a list of the messages to the process, which have not yet been processed.{min_heap_size, MinHeapSize}-MinHeapSizeis the minimum heap size for the process.{min_bin_vheap_size, MinBinVHeapSize}-MinBinVHeapSizeis the minimum binary virtual heap size for the process.{monitored_by, MonitoredBy}- A list of identifiers for all the processes, ports and NIF resources, that are monitoring the process.{monitors, Monitors}- A list of monitors (started bymonitor/2) that are active for the process. For a local process monitor or a remote process monitor by a process identifier, the list consists of:{process, Pid}- Process is monitored by pid.{process, {RegName, Node}}- Local or remote process is monitored by name.{port, PortId}- Local port is monitored by port id.{port, {RegName, Node}}- Local port is monitored by name. Please note, that remote port monitors are not supported, soNodewill always be the local node name.
{message_queue_data, MQD}-MQDis the current value of themessage_queue_dataprocess flag, which can be eitheroff_heaporon_heap. For more information, see the documentation ofprocess_flag(message_queue_data, MQD).{parent, Pid}-Pidis the identifier of the parent process, the one that spawned current process. When the process does not have a parentundefinedis returned. Only the initial process (init) on a node lacks a parent, though.{priority, Level}-Levelis the current priority level for the process. For more information on priorities, seeprocess_flag(priority, Level).{reductions, Number}-Numberis the number of reductions executed by the process.{registered_name, Atom}-Atomis the registered process name. If the process has no registered name, this tuple is not present in the list.{sequential_trace_token, [] | SequentialTraceToken}-SequentialTraceTokenis the sequential trace token for the process. ThisInfoTuplecan be changed or removed without prior notice.{stack_size, Size}-Sizeis the stack size, in words, of the process.{status, Status}-Statusis the status of the process and is one of the following:exitinggarbage_collectingwaiting(for a message)runningrunnable(ready to run, but another process is running)suspended(suspended on a "busy" port or by the BIFerlang:suspend_process/1,2)
{suspending, SuspendeeList}-SuspendeeListis a list of{Suspendee, ActiveSuspendCount, OutstandingSuspendCount}tuples.Suspendeeis the process identifier of a process that has been, or is to be, suspended by the process identified byPidthrough the BIFerlang:suspend_process/2orerlang:suspend_process/1.ActiveSuspendCountis the number of timesSuspendeehas been suspended byPid.OutstandingSuspendCountis the number of not yet completed suspend requests sent byPid, that is:- If
ActiveSuspendCount =/= 0,Suspendeeis currently in the suspended state. - If
OutstandingSuspendCount =/= 0, optionasynchronousoferlang:suspend_process/2has been used and the suspendee has not yet been suspended byPid.
Notice that
ActiveSuspendCountandOutstandingSuspendCountare not the total suspend count onSuspendee, only the parts contributed byPid.- If
{total_heap_size, Size}-Sizeis the total size, in words, of all heap fragments of the process. This includes the process stack and any unreceived messages that are considered to be part of the heap.{trace, InternalTraceFlags}-InternalTraceFlagsis an integer representing the internal trace flag for this process. ThisInfoTuplecan be changed or removed without prior notice.{trap_exit, Boolean}-Booleanistrueif the process is trapping exits, otherwisefalse.
Notice that not all implementations support all these Items.
Failures:
badarg- IfPidis not a local process.badarg- IfItemis an invalid item.
-spec processes() -> [pid()].
Returns a list of process identifiers corresponding to all the processes currently existing on the local node.
Notice that an exiting process exists, but is not alive. That is,
is_process_alive/1 returns false for an exiting
process, but its process identifier is part of the result returned from
processes/0.
Example:
> processes().
[<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]
Adds a new Key to the process dictionary, associated with the value Val, and
returns undefined. If Key exists, the old value is deleted and replaced by
Val, and the function returns the old value.
The average time complexity for the current implementation of this function is
O(1) and the worst case time complexity is O(N), where N is the number of
items in the process dictionary.
For example:
> X = put(name, walrus), Y = put(name, carpenter),
Z = get(name),
{X, Y, Z}.
{undefined,walrus,carpenter}Note
The values stored when put is evaluated within the scope of a catch are
not retracted if a throw is evaluated, or if an error occurs.
-spec raise(Class, Reason, Stacktrace) -> badarg when Class :: error | exit | throw, Reason :: term(), Stacktrace :: raise_stacktrace().
Raises an exception of the specified class, reason, and call stack backtrace (stacktrace).
Class is error, exit, or throw. So, if it were not for the stacktrace,
erlang:raise(Class, Reason, Stacktrace) is equivalent to
erlang:Class(Reason) (given that Class is a valid class).
Reason can be any term.
Stacktrace is a list as provided in a try-catch clause.
try
...
catch Class:Reason:Stacktrace ->
...
endThat is, a list of four-tuples {Module, Function, Arity | Args, ExtraInfo},
where Module and Function are atoms, and the third element is an integer
arity or an argument list. The stacktrace can also contain
{Fun, Args, ExtraInfo} tuples, where Fun is a local fun and Args is an
argument list.
Element ExtraInfo at the end is optional. Omitting it is equivalent to
specifying an empty list.
The stacktrace is used as the exception stacktrace for the calling process; it is truncated to the current maximum stacktrace depth.
As evaluating this function causes the process to terminate, it has no return
value unless the arguments are invalid, in which case the function returns the
error reason badarg. If you want to be sure not to return, you can call
error(erlang:raise(Class, Reason, Stacktrace)) and hope to
distinguish exceptions later.
See the reference manual about errors and error handling for more information about exception classes and how to catch exceptions.
Registers the name RegName with a process identifier (pid) or a port
identifier in the
name registry.
RegName, which must be an atom, can be used instead of the pid or port
identifier in send operator (RegName ! Message) and most other BIFs that take
a pid or port identifies as an argument.
For example:
> register(db, Pid).
trueThe registered name is considered a Directly Visible Erlang Resource and is automatically unregistered when the process terminates.
Failures:
badarg- IfPidOrPortis not an existing local process or port.badarg- IfRegNameis already in use.badarg- If the process or port is already registered (already has a name).badarg- IfRegNameis the atomundefined.
-spec registered() -> [RegName] when RegName :: atom().
Returns a list of names that have been registered using register/2.
For example:
> registered().
[code_server, file_server, init, user, my_db]
-spec resume_process(Suspendee) -> true when Suspendee :: pid().
Decreases the suspend count on the process identified by Suspendee.
Suspendee is previously to have been suspended through
erlang:suspend_process/2 or
erlang:suspend_process/1 by the process calling
erlang:resume_process(Suspendee). When the suspend count on Suspendee
reaches zero, Suspendee is resumed, that is, its state is changed from
suspended into the state it had before it was suspended.
Warning
This BIF is intended for debugging only.
Failures:
badarg- IfSuspendeeis not a process identifier.badarg- If the process callingerlang:resume_process/1had not previously increased the suspend count on the process identified bySuspendee.badarg- If the process identified bySuspendeeis not alive.
-spec self() -> pid().
Returns the process identifier of the calling process.
For example:
> self().
<0.26.0>
-spec send(Dest, Msg) -> Msg when Dest :: send_destination(), Msg :: term().
Sends a message and returns Msg. This is the same as using the
send operator: Dest ! Msg.
Dest can be a remote or local process identifier, an alias, a (local) port, a
locally registered name, or a tuple {RegName, Node} for a registered name at
another node.
The function fails with a badarg run-time error if Dest is an atom name, but
this name is not registered. This is the only case when send fails for an
unreachable destination Dest (of correct type).
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
-spec send(Dest, Msg, Options) -> Res when Dest :: send_destination(), Msg :: term(), Options :: [nosuspend | noconnect], Res :: ok | nosuspend | noconnect.
Either sends a message and returns ok, or does not send the message but
returns something else (see below). Otherwise the same as
erlang:send/2.
For more detailed explanation and warnings, see erlang:send_nosuspend/2,3.
Options:
nosuspend- If the sender would have to be suspended to do the send,nosuspendis returned instead.noconnect- If the destination node would have to be auto-connected to do the send,noconnectis returned instead.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
Warning
As with erlang:send_nosuspend/2,3: use with extreme care.
-spec send_nosuspend(Dest, Msg) -> boolean() when Dest :: send_destination(), Msg :: term().
Send a message without suspending the caller.
Equivalent to erlang:send(Dest, Msg, [nosuspend]), but returns
true if the message was sent and false if the message was not sent because
the sender would have had to be suspended.
This function is intended for send operations to an unreliable remote node
without ever blocking the sending (Erlang) process. If the connection to the
remote node (usually not a real Erlang node, but a node written in C or Java) is
overloaded, this function does not send the message and returns false.
The same occurs if Dest refers to a local port that is busy. For all other
destinations (allowed for the ordinary send operator '!'), this function sends
the message and returns true.
This function is only to be used in rare circumstances where a process
communicates with Erlang nodes that can disappear without any trace, causing the
TCP buffers and the drivers queue to be over-full before the node is shut down
(because of tick time-outs) by net_kernel. The normal reaction to take when
this occurs is some kind of premature shutdown of the other node.
Notice that ignoring the return value from this function would result in an
unreliable message passing, which is contradictory to the Erlang programming
model. The message is not sent if this function returns false.
In many systems, transient states of overloaded queues are normal. Although this
function returns false does not mean that the other node is guaranteed to be
non-responsive, it could be a temporary overload. Also, a return value of true
does only mean that the message can be sent on the (TCP) channel without
blocking; the message is not guaranteed to arrive at the remote node. For a
disconnected non-responsive node, the return value is true (mimics the
behavior of operator !). The expected behavior and the actions to take when
the function returns false are application- and hardware-specific.
Warning
Use with extreme care.
-spec send_nosuspend(Dest, Msg, Options) -> boolean() when Dest :: send_destination(), Msg :: term(), Options :: [noconnect].
Equivalent to erlang:send(Dest, Msg, [nosuspend | Options]), but
with a Boolean return value.
This function behaves like erlang:send_nosuspend/2, but
takes a third parameter, a list of options. The only option is noconnect,
which makes the function return false if the remote node is not currently
reachable by the local node. The normal behavior is to try to connect to the
node, which can stall the process during a short period. The use of option
noconnect makes it possible to be sure not to get the slightest delay when
sending to a remote process. This is especially useful when communicating with
nodes that expect to always be the connecting part (that is, nodes written in C
or Java).
Whenever the function returns false (either when a suspend would occur or when
noconnect was specified and the node was not already connected), the message
is guaranteed not to have been sent.
Warning
Use with extreme care.
Returns the process identifier of a new process started by the application of
Fun to the empty list []. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Fun to the empty list [] on Node. If Node does not exist, a useless pid
is returned. Otherwise works like spawn/3.
-spec spawn(Module, Function, Args) -> pid() when Module :: module(), Function :: atom(), Args :: [term()].
Returns the process identifier of a new process started by the application of
Module:Function to Args.
error_handler:undefined_function(Module, Function, Args) is
evaluated by the new process if Module:Function/Arity does not exist
(where Arity is the length of Args). The error handler can be redefined
(see process_flag/2). If
error_handler is undefined, or the user has redefined the default
error_handler and its replacement is undefined, a failure with reason undef
occurs.
Example:
> spawn(speed, regulator, [high_speed, thin_cut]).
<0.13.1>
-spec spawn(Node, Module, Function, Args) -> pid() when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()].
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn/3.
Returns the process identifier of a new process started by the application of
Fun to the empty list []. A link is created between the calling process and
the new process, atomically. Otherwise works like spawn/3.
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. A link is created between the calling
process and the new process, atomically. If Node does not exist, a useless pid
is returned and an exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
-spec spawn_link(Module, Function, Args) -> pid() when Module :: module(), Function :: atom(), Args :: [term()].
Returns the process identifier of a new process started by the application of
Module:Function to Args. A link is created between the calling process and
the new process, atomically. Otherwise works like spawn/3.
-spec spawn_link(Node, Module, Function, Args) -> pid() when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()].
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. A link is created between the calling
process and the new process, atomically. If Node does not exist, a useless pid
is returned and an exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
Returns the process identifier of a new process, started by the application of
Fun to the empty list [], and a reference for a monitor created to the new
process. Otherwise works like spawn/3.
Returns the process identifier of a new process, started by the application of
Fun to the empty list [] on the node Node, and a reference for a monitor
created to the new process. Otherwise works like spawn/3.
If the node identified by Node does not support distributed spawn_monitor(),
the call will fail with a notsup exception.
-spec spawn_monitor(Module, Function, Args) -> {pid(), reference()} when Module :: module(), Function :: atom(), Args :: [term()].
A new process is started by the application of Module:Function to Args. The
process is monitored at the same time. Returns the process identifier and a
reference for the monitor. Otherwise works like spawn/3.
-spec spawn_monitor(Node, Module, Function, Args) -> {pid(), reference()} when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()].
A new process is started by the application of Module:Function to Args on
the node Node. The process is monitored at the same time. Returns the process
identifier and a reference for the monitor. Otherwise works like spawn/3.
If the node identified by Node does not support distributed spawn_monitor(),
the call will fail with a notsup exception.
-spec spawn_opt(Fun, Options) -> pid() | {pid(), reference()} when Fun :: function(), Options :: [spawn_opt_option()].
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list []. Otherwise works like spawn_opt/4.
If option monitor is specified, the newly created process is monitored, and
both the pid and reference for the monitor are returned.
-spec spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()} when Node :: node(), Fun :: function(), Options :: [monitor | {monitor, [monitor_option()]} | link | OtherOption], OtherOption :: term().
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn_opt/4.
Valid options depends on what options are supported by the node identified by
Node. A description of valid Options for the local node of current OTP
version can be found in the documentation of spawn_opt/4.
-spec spawn_opt(Module, Function, Args, Options) -> Pid | {Pid, MonitorRef} when Module :: module(), Function :: atom(), Args :: [term()], Options :: [spawn_opt_option()], Pid :: pid(), MonitorRef :: reference().
Works as spawn/3, except that an extra option list is specified when creating
the process.
If option monitor is specified, the newly created process is monitored, and
both the pid and reference for the monitor are returned.
Options:
link- Sets a link to the parent process (likespawn_link/3does).monitor- Monitors the new process (likemonitor(process, Pid)does). A{Pid, MonitorRef}tuple will be returned instead of just aPid.{monitor, MonitorOpts}- Monitors the new process with options (likemonitor(process, Pid, MonitorOpts)does). A{Pid, MonitorRef}tuple will be returned instead of just aPid.{priority, Level}- Sets the priority of the new process. Equivalent to executingprocess_flag(priority, Level)in the start function of the new process, except that the priority is set before the process is selected for execution for the first time. For more information on priorities, seeprocess_flag(priority, Level).{fullsweep_after, Number}- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.The Erlang runtime system uses a generational garbage collection scheme, using an "old heap" for data that has survived at least one garbage collection. When there is no more room on the old heap, a fullsweep garbage collection is done.
Option
fullsweep_aftermakes it possible to specify the maximum number of generational collections before forcing a fullsweep, even if there is room on the old heap. Setting the number to zero disables the general collection algorithm, that is, all live data is copied at every garbage collection.A few cases when it can be useful to change
fullsweep_after:- If binaries that are no longer used are to be thrown away as soon as
possible. (Set
Numberto zero.) - A process that mostly have short-lived data is fullsweeped seldom or never,
that is, the old heap contains mostly garbage. To ensure a fullsweep
occasionally, set
Numberto a suitable value, such as 10 or 20. - In embedded systems with a limited amount of RAM and no virtual memory, you
might want to preserve memory by setting
Numberto zero. (The value can be set globally, seeerlang:system_flag/2.)
- If binaries that are no longer used are to be thrown away as soon as
possible. (Set
{min_heap_size, Size}- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.Gives a minimum heap size, in words. Setting this value higher than the system default can speed up some processes because less garbage collection is done. However, setting a too high value can waste memory and slow down the system because of worse data locality. Therefore, use this option only for fine-tuning an application and to measure the execution time with various
Sizevalues.{min_bin_vheap_size, VSize}- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.Gives a minimum binary virtual heap size, in words. Setting this value higher than the system default can speed up some processes because less garbage collection is done. However, setting a too high value can waste memory. Therefore, use this option only for fine-tuning an application and to measure the execution time with various
VSizevalues.{max_heap_size, Size}- Sets themax_heap_sizeprocess flag. The defaultmax_heap_sizeis determined by command-line argument+hmaxin erl. For more information, see the documentation ofprocess_flag(max_heap_size, Size).{message_queue_data, MQD}- Sets the value of themessage_queue_dataprocess flag.MQDcan be eitheroff_heaporon_heap. The default value of themessage_queue_dataprocess flag is determined by the command-line argument+hmqdin erl. For more information, see the documentation ofprocess_flag(message_queue_data, MQD).{async_dist, Enabled}- Since: OTP 25.3Set the
async_distprocess flag of the spawned process. This option will override the default value set by the command line argument+pad <boolean>.
-spec spawn_opt(Node, Module, Function, Args, Options) -> pid() | {pid(), reference()} when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()], Options :: [monitor | {monitor, [monitor_option()]} | link | OtherOption], OtherOption :: term().
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn_opt/4.
Valid options depends on what options are supported by the node identified by
Node. A description of valid Options for the local node of current OTP
version can be found in the documentation of spawn_opt/4.
Equivalent to the call spawn_request(node(),Fun,[]). That
is, a spawn request on the local node with no options.
-spec spawn_request(Fun, Options) -> ReqId when Fun :: function(), Option :: {reply_tag, ReplyTag} | {reply, Reply} | spawn_opt_option(), ReplyTag :: term(), Reply :: yes | no | error_only | success_only, Options :: [Option], ReqId :: reference(); (Node, Fun) -> ReqId when Node :: node(), Fun :: function(), ReqId :: reference().
Equivalent to spawn_request(node(),Fun,Options) or
spawn_request(Node,Fun,[]) depending on the arguments.
That is either:
- a spawn request on the local node.
- a spawn request with no options.
-spec spawn_request(Node, Fun, Options) -> ReqId when Node :: node(), Fun :: function(), Options :: [Option], Option :: monitor | {monitor, [monitor_option()]} | link | {reply_tag, ReplyTag} | {reply, Reply} | OtherOption, ReplyTag :: term(), Reply :: yes | no | error_only | success_only, OtherOption :: term(), ReqId :: reference(); (Module, Function, Args) -> ReqId when Module :: module(), Function :: atom(), Args :: [term()], ReqId :: reference().
Equivalent to
spawn_request(Node,erlang,apply,[Fun,[]],Options) or
spawn_request(node(),Module,Function,Args,[]) depending
on the arguments.
That is either:
- a spawn request using the fun
Funof arity zero as entry point - a spawn request on the local node with no options.
This function will fail with a badarg exception if:
Nodeis not an atom.Funis not a fun of arity zero.Optionsis not a proper list of terms.
-spec spawn_request(Node, Module, Function, Args) -> ReqId when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()], ReqId :: reference(); (Module, Function, Args, Options) -> ReqId when Module :: module(), Function :: atom(), Args :: [term()], Option :: {reply_tag, ReplyTag} | {reply, Reply} | spawn_opt_option(), ReplyTag :: term(), Reply :: yes | no | error_only | success_only, Options :: [Option], ReqId :: reference().
Equivalent to
spawn_request(Node,Module,Function,Args,[]) or
spawn_request(node(),Module,Function,Args,Options)
depending on the arguments.
That is either:
- a spawn request with no options.
- a spawn request on the local node.
-spec spawn_request(Node, Module, Function, Args, Options) -> ReqId when Node :: node(), Module :: module(), Function :: atom(), Args :: [term()], Options :: [Option], Option :: monitor | {monitor, [monitor_option()]} | link | {reply_tag, ReplyTag} | {reply, Reply} | OtherOption, ReplyTag :: term(), Reply :: yes | no | error_only | success_only, OtherOption :: term(), ReqId :: reference().
Asynchronously send a spawn request. Returns a request identifier ReqId.
If the spawn operation succeeds, a new process is created on the node identified
by Node. When a spawn operation succeeds, the caller will by default be sent a
message on the form {ReplyTag, ReqId, ok, Pid} where Pid is the process
identifier of the newly created process. Such a message is referred to as a
success message below in the text. ReplyTag is by default the atom
spawn_reply unless modified by the {reply_tag, ReplyTag} option. The new
process is started by the application of Module:Function to Args.
The spawn operation fails either if creation of a new process failed or if the
spawn operation was interrupted by a connection failure. When a spawn operation
fails, the caller will by default be sent a message on the form
{ReplyTag, ReqId, error, Reason} where Reason is the error reason. Such a
message is referred to as an error message below in the text. Currently the
following spawn error Reasons are defined, but other reasons can appear at any
time without prior notice:
badopt- An invalidOptionwas passed as argument. Note that different runtime systems may support different options.notsup- The node identified byNodedoes not support spawn operations issued byspawn_request().noconnection- Failure to set up a connection to the node identified byNodeor the connection to that node was lost during the spawn operation. In the case the connection was lost, a process may or may not have been created.system_limit- Could not create a new process due to that some system limit was reached. Typically the process table was full.
Valid Options:
monitor- In the absence of spawn operation failures, atomically sets up a monitor to the newly created process. That is, as if the calling process had calledmonitor(process, Pid)wherePidis the process identifier of the newly created process. TheReqIdreturned byspawn_request()is also used as monitor reference as if it was returned frommonitor(process, Pid).The monitor will not be activated for the calling process until the spawn operation has succeeded. The monitor can not be demonitored before the operation has succeeded. A
'DOWN'message for the corresponding monitor is guaranteed not to be delivered before a success message that corresponds to the spawn operation. If the spawn operation fails, no'DOWN'message will be delivered.If the connection between the nodes involved in the spawn operation is lost during the spawn operation, the spawn operation will fail with an error reason of
noconnection. A new process may or may not have been created.{monitor, MonitorOpts}- In the absence of spawn operation failures, atomically sets up a monitor to the newly created process. That is, as if the calling process had calledmonitor(process, Pid, MonitorOpts)wherePidis the process identifier of the newly created process. See themonitoroption above for more information.Note that the monitor will not be activated for the calling process until the spawn operation has succeeded. For example, in the case that an alias is created using the monitor option, the alias will not be active until the monitor is activated.
link- In absence of spawn operation failures, atomically sets up a link between the calling process and the newly created process. That is, as if the calling process had calledlink(Pid)wherePidis the process identifier of the newly created process.The link will not be activated for the calling process until the spawn operation has succeeded. The link can not be removed before the operation has succeeded. An exit signal due to the link is guaranteed not to be delivered before a success message that corresponds to the spawn operation. If the spawn operation fails, no exit signal due to the link will be delivered to the caller of
spawn_request().If the connection between the nodes involved in the spawn operation is lost during the spawn operation, the spawn operation will fail with an error reason of
noconnection. A new process may or may not have been created. If it has been created, it will be delivered an exit signal with an exit reason ofnoconnection.{reply, Reply}- ValidReplyvalues:yes- A spawn reply message will be sent to the caller regardless of whether the operation succeeds or not. If the call tospawn_request()returns without raising an exception and thereplyoption is set toyes, the caller is guaranteed to be delivered either a success message or an error message. Thereplyoption is by default set toyes.no- No spawn reply message will be sent to the caller when the spawn operation completes. This regardless of whether the operation succeeds or not.error_only- No spawn reply message will be sent to the caller if the spawn operation succeeds, but an error message will be sent to the caller if the operation fails.success_only- No spawn reply message will be sent to the caller if the spawn operation fails, but a success message will be sent to the caller if the operation succeeds.
{reply_tag, ReplyTag}- Sets the reply tag toReplyTagin the reply message. That is, in the success or error message that is sent to the caller due to the spawn operation. The default reply tag is the atomspawn_reply.OtherOption- Other valid options depends on what options are supported by the node identified byNode. A description of other validOptions for the local node of current OTP version can be found in the documentation ofspawn_opt/4.
If a spawn reply message is delivered, it is guaranteed to be delivered before any other signals from the newly spawned process are delivered to the process issuing the spawn request.
This function will fail with a badarg exception if:
Nodeis not an atom.Moduleis not an atom.Functionis not an atom.Argsis not a proper list of terms.Optionsis not a proper list of terms.
Note that not all individual Options are checked when the spawn request is
sent. Some Options can only be checked on reception of the request. Therefore
an invalid option does not cause a badarg exception, but will cause the
spawn operation to fail with an error reason of badopt.
A spawn request can be abandoned by calling spawn_request_abandon/1.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
Abandon a previously issued spawn request. ReqId corresponds to a request
identifier previously returned by spawn_request() in a
call from current process. That is, only the process that has made the request
can abandon the request.
A spawn request can only be successfully abandoned until the spawn request has
completed. When a spawn request has been successfully abandoned, the caller will
not be effected by future direct effects of the spawn request itself. For
example, it will not receive a spawn reply message. The request is however not
withdrawn, so a new process may or may not be created due to the request. If a
new process is created after the spawn request was abandoned, no monitors nor
links will be set up to the caller of
spawn_request_abandon/1 due to the spawn request.
If the spawn request included the link option, the process created due to this
request will be sent an exit signal from its parent with the exit reason
abandoned when it is detected that the spawn operation has succeeded.
Note
A process created due to a spawn request that has been abandoned may communicate with its parent as any other process. It is only the direct effects on the parent of the actual spawn request, that will be canceled by abandoning a spawn request.
Return values:
true- The spawn request was successfully abandoned.false- No spawn request was abandoned. TheReqIdrequest identifier did not correspond to an outstanding spawn request issued by the calling process. The reason for this is either:ReqIdcorresponds to a spawn request previoulsy made by the calling process. The spawn operation has completed and a spawn reply has already been delivered to the calling process unless the spawn reply was disabled in the request.ReqIddoes not correspond to a spawn request that has been made by the calling process.
This function fail with a badarg exception if ReqId is not a reference.
-spec suspend_process(Suspendee) -> true when Suspendee :: pid().
Suspends the process identified by Suspendee. Equivalent to calling
erlang:suspend_process(Suspendee, []).
Warning
This BIF is intended for debugging only.
-spec suspend_process(Suspendee, OptList) -> boolean() when Suspendee :: pid(), OptList :: [Opt], Opt :: unless_suspending | asynchronous | {asynchronous, term()}.
Increases the suspend count on the process identified by Suspendee and puts it
in the suspended state if it is not already in that state. A suspended process
is not scheduled for execution until the process has been resumed.
A process can be suspended by multiple processes and can be suspended multiple
times by a single process. A suspended process does not leave the suspended
state until its suspend count reaches zero. The suspend count of Suspendee is
decreased when erlang:resume_process(Suspendee) is
called by the same process that called erlang:suspend_process(Suspendee). All
increased suspend counts on other processes acquired by a process are
automatically decreased when the process terminates.
Options (Opts):
asynchronous- A suspend request is sent to the process identified bySuspendee.Suspendeeeventually suspends unless it is resumed before it could suspend. The caller oferlang:suspend_process/2returns immediately, regardless of whetherSuspendeehas suspended yet or not. The point in time whenSuspendeesuspends cannot be deduced from other events in the system. It is only guaranteed thatSuspendeeeventually suspends (unless it is resumed). If noasynchronousoptions has been passed, the caller oferlang:suspend_process/2is blocked untilSuspendeehas suspended.{asynchronous, ReplyTag}- A suspend request is sent to the process identified bySuspendee. When the suspend request has been processed, a reply message is sent to the caller of this function. The reply is on the form{ReplyTag, State}whereStateis either:exited-Suspendeehas exited.suspended-Suspendeeis now suspended.not_suspended-Suspendeeis not suspended. This can only happen when the process that issued this request, have calledresume_process(Suspendee)before getting the reply.
Apart from the reply message, the
{asynchronous, ReplyTag}option behaves exactly the same as theasynchronousoption without reply tag.unless_suspending- The process identified bySuspendeeis suspended unless the calling process already is suspendingSuspendee. Ifunless_suspendingis combined with optionasynchronous, a suspend request is sent unless the calling process already is suspendingSuspendeeor if a suspend request already has been sent and is in transit. If the calling process already is suspendingSuspendee, or if combined with optionasynchronousand a send request already is in transit,falseis returned and the suspend count onSuspendeeremains unchanged.
If the suspend count on the process identified by Suspendee is increased,
true is returned, otherwise false.
Warning
This BIF is intended for debugging only.
Warning
You can easily create deadlocks if processes suspends each other (directly or in circles). In ERTS versions prior to ERTS version 10.0, the runtime system prevented such deadlocks, but this prevention has now been removed due to performance reasons.
Failures:
badarg- IfSuspendeeis not a process identifier.badarg- If the process identified bySuspendeeis the same process as the process callingerlang:suspend_process/2.badarg- If the process identified bySuspendeeis not alive.badarg- If the process identified bySuspendeeresides on another node.badarg- IfOptListis not a proper list of validOpts.system_limit- If the process identified bySuspendeehas been suspended more times by the calling process than can be represented by the currently used internal data structures. The system limit is greater than 2,000,000,000 suspends and will never be lower.
Raises an exception of class throw. Intended to be used to do non-local
returns from functions.
If evaluated within a catch expression, the
catch expression returns value Any.
For example:
> catch throw({hello, there}).
{hello,there}If evaluated within a try-block of a
try expression, the value Any can be caught
within the catch block.
For example:
try
throw({my_exception, "Something happened"})
catch
throw:{my_exception, Desc} ->
io:format(standard_error, "Error: ~s~n", [Desc])
endFailure: nocatch if not caught by an exception handler.
See the guide about errors and error handling for additional information.
Deactivate the alias Alias previously created by the calling process.
An alias can, for example, be created via alias/0 or monitor/3.
unalias/1 will always deactivate the alias regardless of
options used when creating the alias.
Returns true if Alias was a currently active alias for current processes;
otherwise, false.
For more information on process aliases see the Process Aliases section of the Erlang Reference Manual.
Removes a link between the calling process and another process or a port
identified by Id.
We will from here on call the identified process or port unlinkee.
A link can be set up using the link/1 BIF. For more information on links and
exit signals due to links, see the Processes chapter in the Erlang Reference
Manual:
Once unlink(Id) has returned, it is guaranteed that the link
between the caller and the unlinkee has no effect on the caller in the future
(unless the link is setup again). Note that if the caller is
trapping exits, an
{'EXIT', Id, ExitReason} message due to the link may have been placed in the
message queue of the caller before the unlink(Id) call
completed. Also note that the {'EXIT', Id, ExitReason} message may be the
result of the link, but may also be the result of the unlikee sending the caller
an exit signal by calling the exit/2 BIF. Therefore, it may or may not be
appropriate to clean up the message queue after a call to
unlink(Id) as follows, when trapping exits:
unlink(Id),
receive
{'EXIT', Id, _} ->
true
after 0 ->
true
endThe link removal is performed asynchronously. If such a link does not exist, nothing is done. A detailed description of the link protocol can be found in the Distribution Protocol chapter of the ERTS User's Guide.
Note
For some important information about distributed signals, see the Blocking Signaling Over Distribution section in the Processes chapter of the Erlang Reference Manual.
Failure: badarg if Id does not identify a process or a node local port.
-spec unregister(RegName) -> true when RegName :: atom().
Removes the registered name RegName associated with a
process identifier or a port identifier from the
name registry.
For example:
> unregister(db).
trueKeep in mind that you can still receive signals associated with the registered name after it has been unregistered as the sender may have looked up the name before sending to it.
Users are advised not to unregister system processes.
Failure: badarg if RegName is not a registered name.
Returns the process identifier or port identifier with the
registered name RegName from the
name registry. Returns
undefined if the name is not registered.
For example:
> whereis(db).
<0.43.0>
-spec yield() -> true.
Tries to give other processes with the same or higher priority (if any) a chance
to execute before returning. There is no guarantee that any other process runs
between the invocation and return of erlang:yield/0.
See the documentation for
receive-after expressions for how to make
the current process sleep for a specific number of milliseconds.
Warning
There is seldom or never any need to use this BIF. Using this BIF without a thorough grasp of how the scheduler works can cause performance degradation. The current implementation of this function puts the current process last in the current scheduler's queue for processes of the same priority as the current process.
System
-spec halt() -> no_return().
Equivalent to calling halt(0, []).
For example:
> halt().
os_prompt%
-spec halt(Status :: non_neg_integer()) -> no_return(); (Abort :: abort) -> no_return(); (CrashDumpSlogan :: string()) -> no_return().
Equivalent to calling halt(HaltType, []).
For example:
> halt(17).
os_prompt% echo $?
17
os_prompt%
-spec halt(Status :: non_neg_integer(), Options :: halt_options()) -> no_return(); (Abort :: abort, Options :: halt_options()) -> no_return(); (CrashDumpSlogan :: string(), Options :: halt_options()) -> no_return().
Halt the runtime system.
halt(Status :: non_neg_integer(), Options :: halt_options())Halt the runtime system with status code
Status.Note
On many platforms, the OS supports only status codes 0-255. A too large status code is truncated by clearing the high bits.
Currently the following options are valid:
{flush, EnableFlushing}- IfEnableFlushingequalstrue, which also is the default behavior, the runtime system will perform the following operations before terminating:- Flush all outstanding output.
- Send all Erlang ports exit signals and wait for them to exit.
- Wait for all async threads to complete all outstanding async jobs.
- Call all installed NIF on halt callbacks.
- Wait for all ongoing NIF calls with the delay halt setting enabled to return.
- Call all installed
atexit/on_exitcallbacks.
If
EnableFlushingequalsfalse, the runtime system will terminate immediately without performing any of the above listed operations.Change
Runtime systems prior to OTP 26.0 called all installed
atexit/on_exitcallbacks also whenflushwas disabled, but as of OTP 26.0 this is no longer the case.{flush_timeout, Timeout :: 0..2147483647 | infinity}- Sets a limit on the time allowed for flushing prior to termination of the runtime system.Timeoutis in milliseconds. The default value is determined by the theerl+zhft <Timeout>command line flag.If flushing has been ongoing for
Timeoutmilliseconds, flushing operations will be interrupted and the runtime system will immediately be terminated with the exit code255. If flushing is not enabled, the timeout will have no effect on the system.See also the
erl+zhft <Timeout>command line flag. Note that the shortest timeout set by the command line flag and theflush_timeoutoption will be the actual timeout value in effect.Since: OTP 27.0
halt(Abort :: abort, Options :: halt_options())Halt the Erlang runtime system by aborting and produce a core dump if core dumping has been enabled in the environment that the runtime system is executing in.
Note
The
{flush, boolean()}option will be ignored, and flushing will be disabled.halt(CrashDumpSlogan :: string(), Options :: halt_options())Halt the Erlang runtime system and generate an Erlang crash dump. The string
CrashDumpSloganwill be used as slogan in the Erlang crash dump created. The slogan will be trunkated ifCrashDumpSloganis longer than 1023 characters.Note
The
{flush, boolean()}option will be ignored, and flushing will be disabled.Change
Behavior changes compared to earlier versions:
- Before OTP 24.2, the slogan was truncated if
CrashDumpSloganwas longer than 200 characters. Now it will be truncated if longer than 1023 characters. - Before OTP 20.1, only code points in the range 0-255 were accepted in the slogan. Now any Unicode string is valid.
- Before OTP 24.2, the slogan was truncated if
-spec memory() -> [{Type, Size}] when Type :: memory_type(), Size :: non_neg_integer().
Returns a list with information about memory dynamically allocated by the Erlang emulator.
Each list element is a tuple {Type, Size}. The first element Type
is an atom describing memory type. The second element Size is the memory size
in bytes.
Memory types:
total- The total amount of memory currently allocated. This is the same as the sum of the memory size forprocessesandsystem.processes- The total amount of memory currently allocated for the Erlang processes.processes_used- The total amount of memory currently used by the Erlang processes. This is part of the memory presented asprocessesmemory.system- The total amount of memory currently allocated for the emulator that is not directly related to any Erlang process. Memory presented asprocessesis not included in this memory.instrumentcan be used to get a more detailed breakdown of what memory is part of this type.atom- The total amount of memory currently allocated for atoms. This memory is part of the memory presented assystemmemory.atom_used- The total amount of memory currently used for atoms. This memory is part of the memory presented asatommemory.binary- The total amount of memory currently allocated for binaries. This memory is part of the memory presented assystemmemory.code- The total amount of memory currently allocated for Erlang code. This memory is part of the memory presented assystemmemory.ets- The total amount of memory currently allocated for ETS tables. This memory is part of the memory presented assystemmemory.maximum- The maximum total amount of memory allocated since the emulator was started. This tuple is only present when the emulator is run with instrumentation.For information on how to run the emulator with instrumentation, see
instrumentand/orerl(1).
Note
The system value is not complete. Some allocated memory that is to be part
of this value is not.
When the emulator is run with instrumentation, the system value is more
accurate, but memory directly allocated for malloc (and friends) is still
not part of the system value. Direct calls to malloc are only done from
OS-specific runtime libraries and perhaps from user-implemented Erlang drivers
that do not use the memory allocation functions in the driver interface.
As the total value is the sum of processes and system, the error in
system propagates to the total value.
The different amounts of memory that are summed are not gathered atomically, which introduces an error in the result.
The different values have the following relation to each other. Values beginning with an uppercase letter is not part of the result.
total = processes + system
processes = processes_used + ProcessesNotUsed
system = atom + binary + code + ets + OtherSystem
atom = atom_used + AtomNotUsed
RealTotal = processes + RealSystem
RealSystem = system + MissedSystemMore tuples in the returned list can be added in a future release.
Note
The total value is supposed to be the total amount of memory dynamically
allocated by the emulator. Shared libraries, the code of the emulator itself,
and the emulator stacks are not supposed to be included. That is, the total
value is not supposed to be equal to the total size of all pages mapped to
the emulator.
Also, because of fragmentation and prereservation of memory areas, the size of the memory segments containing the dynamically allocated memory blocks can be much larger than the total size of the dynamically allocated memory blocks.
Change
As from ERTS 5.6.4, erlang:memory/0 requires that all
erts_alloc(3) allocators are enabled (default behavior).
Failure: notsup if an erts_alloc(3) allocator has been
disabled.
-spec memory(Type :: memory_type()) -> non_neg_integer(); (TypeList :: [memory_type()]) -> [{memory_type(), non_neg_integer()}].
Returns the memory size in bytes allocated for memory of type Type. The
argument can also be specified as a list of memory_type/0 atoms, in which case
a corresponding list of {memory_type(), Size :: integer >= 0} tuples is
returned.
Change
As from ERTS 5.6.4, erlang:memory/1 requires that all
erts_alloc(3) allocators are enabled (default behavior).
Failures:
badarg- IfTypeis not one of the memory types listed in the description oferlang:memory/0.badarg- Ifmaximumis passed asTypeand the emulator is not run in instrumented mode.notsup- If anerts_alloc(3)allocator has been disabled.
See also erlang:memory/0.
-spec statistics(active_tasks) -> [ActiveTasks] when ActiveTasks :: non_neg_integer(); (active_tasks_all) -> [ActiveTasks] when ActiveTasks :: non_neg_integer(); (context_switches) -> {ContextSwitches, 0} when ContextSwitches :: non_neg_integer(); (exact_reductions) -> {Total_Exact_Reductions, Exact_Reductions_Since_Last_Call} when Total_Exact_Reductions :: non_neg_integer(), Exact_Reductions_Since_Last_Call :: non_neg_integer(); (garbage_collection) -> {Number_of_GCs, Words_Reclaimed, 0} when Number_of_GCs :: non_neg_integer(), Words_Reclaimed :: non_neg_integer(); (io) -> {{input, Input}, {output, Output}} when Input :: non_neg_integer(), Output :: non_neg_integer(); (microstate_accounting) -> [MSAcc_Thread] | undefined when MSAcc_Thread :: #{type := MSAcc_Thread_Type, id := MSAcc_Thread_Id, counters := MSAcc_Counters}, MSAcc_Thread_Type :: async | aux | dirty_io_scheduler | dirty_cpu_scheduler | poll | scheduler, MSAcc_Thread_Id :: non_neg_integer(), MSAcc_Counters :: #{MSAcc_Thread_State => non_neg_integer()}, MSAcc_Thread_State :: alloc | aux | bif | busy_wait | check_io | emulator | ets | gc | gc_fullsweep | nif | other | port | send | sleep | timers; (reductions) -> {Total_Reductions, Reductions_Since_Last_Call} when Total_Reductions :: non_neg_integer(), Reductions_Since_Last_Call :: non_neg_integer(); (run_queue) -> non_neg_integer(); (run_queue_lengths) -> [RunQueueLength] when RunQueueLength :: non_neg_integer(); (run_queue_lengths_all) -> [RunQueueLength] when RunQueueLength :: non_neg_integer(); (runtime) -> {Total_Run_Time, Time_Since_Last_Call} when Total_Run_Time :: non_neg_integer(), Time_Since_Last_Call :: non_neg_integer(); (scheduler_wall_time) -> [{SchedulerId, ActiveTime, TotalTime}] | undefined when SchedulerId :: pos_integer(), ActiveTime :: non_neg_integer(), TotalTime :: non_neg_integer(); (scheduler_wall_time_all) -> [{SchedulerId, ActiveTime, TotalTime}] | undefined when SchedulerId :: pos_integer(), ActiveTime :: non_neg_integer(), TotalTime :: non_neg_integer(); (total_active_tasks) -> ActiveTasks when ActiveTasks :: non_neg_integer(); (total_active_tasks_all) -> ActiveTasks when ActiveTasks :: non_neg_integer(); (total_run_queue_lengths) -> TotalRunQueueLengths when TotalRunQueueLengths :: non_neg_integer(); (total_run_queue_lengths_all) -> TotalRunQueueLengths when TotalRunQueueLengths :: non_neg_integer(); (wall_clock) -> {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call} when Total_Wallclock_Time :: non_neg_integer(), Wallclock_Time_Since_Last_Call :: non_neg_integer().
Returns statistics about the current system.
The possible flags are:
statistics(active_tasks) -> [non_neg_integer()]Returns the same as
statistics(active_tasks_all)with the exception that no information about the dirty IO run queue and its associated schedulers is part of the result. That is, only tasks that are expected to be CPU bound are part of the result.Available since OTP 18.3
statistics(active_tasks_all) -> [non_neg_integer()]Returns a list where each element represents the amount of active processes and ports on each run queue and its associated schedulers. That is, the number of processes and ports that are ready to run, or are currently running. Values for normal run queues and their associated schedulers are located first in the resulting list. The first element corresponds to scheduler number 1 and so on. If support for dirty schedulers exist, an element with the value for the dirty CPU run queue and its associated dirty CPU schedulers follow and then as last element the value for the dirty IO run queue and its associated dirty IO schedulers follow. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered.
Note
Each normal scheduler has one run queue that it manages. If dirty schedulers are supported, all dirty CPU schedulers share one run queue, and all dirty IO schedulers share one run queue. That is, we have multiple normal run queues, one dirty CPU run queue and one dirty IO run queue. Work can not migrate between the different types of run queues. Only work in normal run queues can migrate to other normal run queues. This has to be taken into account when evaluating the result.
See also
statistics(total_active_tasks),statistics(run_queue_lengths),statistics(run_queue_lengths_all),statistics(total_run_queue_lengths), andstatistics(total_run_queue_lengths_all).Available since OTP 20.0
statistics(context_switches) -> {non_neg_integer(), 0}Returns the total number of context switches since the system started.
statistics(exact_reductions) -> {Total :: non_neg_integer(), SinceLastCall :: non_neg_integer()}Returns the number of exact reductions.
Note
statistics(exact_reductions)is a more expensive operation than statistics(reductions).statistics(garbage_collection) -> { NumerOfGCs :: non_neg_integer(), WordsReclaimed :: non_neg_integer(), 0}Returns information about garbage collection, for example:
> statistics(garbage_collection). {85,23961,0}This information can be invalid for some implementations.
statistics(io) -> {{input, non_neg_integer()}, {output, non_neg_integer()}}Returns
Input, which is the total number of bytes received through ports, andOutput, which is the total number of bytes output to ports.statistics(microstate_accounting) -> [MSAcc_Thread]Microstate accounting can be used to measure how much time the Erlang runtime system spends doing various tasks. It is designed to be as lightweight as possible, but some overhead exists when this is enabled. Microstate accounting is meant to be a profiling tool to help finding performance bottlenecks. To
start/stop/resetmicrostate accounting, use system flagmicrostate_accounting.statistics(microstate_accounting)returns a list of maps representing some of the OS threads within ERTS. Each map containstypeandidfields that can be used to identify what thread it is, and also a counters field that contains data about how much time has been spent in the various states.Example:
> erlang:statistics(microstate_accounting). [#{counters => #{aux => 1899182914, check_io => 2605863602, emulator => 45731880463, gc => 1512206910, other => 5421338456, port => 221631, sleep => 5150294100}, id => 1, type => scheduler}|...]The time unit is the same as returned by
os:perf_counter/0. So, to convert it to milliseconds, you can do something like this:lists:map( fun(#{ counters := Cnt } = M) -> MsCnt = maps:map(fun(_K, PerfCount) -> erlang:convert_time_unit(PerfCount, perf_counter, 1000) end, Cnt), M#{ counters := MsCnt } end, erlang:statistics(microstate_accounting)).Notice that these values are not guaranteed to be the exact time spent in each state. This is because of various optimisation done to keep the overhead as small as possible.
MSAcc_Thread_Types:scheduler- The main execution threads that do most of the work. See erl +S for more details.dirty_cpu_scheduler- The threads for long running cpu intensive work. See erl +SDcpu for more details.dirty_io_scheduler- The threads for long running I/O work. See erl +SDio for more details.async- Async threads are used by various linked-in drivers (mainly the file drivers) do offload non-CPU intensive work. See erl +A for more details.aux- Takes care of any work that is not specifically assigned to a scheduler.poll- Does the IO polling for the emulator. See erl +IOt for more details.
The following
MSAcc_Thread_States are available. All states are exclusive, meaning that a thread cannot be in two states at once. So, if you add the numbers of all counters in a thread, you get the total runtime for that thread.aux- Time spent handling auxiliary jobs.check_io- Time spent checking for new I/O events.emulator- Time spent executing Erlang processes.gc- Time spent doing garbage collection. When extra states are enabled this is the time spent doing non-fullsweep garbage collections.other- Time spent doing unaccounted things.port- Time spent executing ports.sleep- Time spent sleeping.
More fine-grained
MSAcc_Thread_States can be added through configure (such as./configure --with-microstate-accounting=extra). Enabling these states causes performance degradation when microstate accounting is turned off and increases the overhead when it is turned on.alloc- Time spent managing memory. Without extra states this time is spread out over all other states.bif- Time spent in BIFs. Without extra states this time is part of theemulatorstate.busy_wait- Time spent busy waiting. This is also the state where a scheduler no longer reports that it is active when usingstatistics(scheduler_wall_time). So, if you add all other states but this and sleep, and then divide that by all time in the thread, you should get something very similar to thescheduler_wall_timefraction. Without extra states this time is part of theotherstate.ets- Time spent executing ETS BIFs. Without extra states this time is part of theemulatorstate.gc_full- Time spent doing fullsweep garbage collection. Without extra states this time is part of thegcstate.nif- Time spent in NIFs. Without extra states this time is part of theemulatorstate.send- Time spent sending messages (processes only). Without extra states this time is part of theemulatorstate.timers- Time spent managing timers. Without extra states this time is part of theotherstate.
The utility module
msacccan be used to more easily analyse these statistics.Returns
undefinedif system flagmicrostate_accountingis turned off.The list of thread information is unsorted and can appear in different order between calls.
Note
The threads and states are subject to change without any prior notice.
Available since OTP 19.0
statistics(reductions) -> {Reductions :: non_neg_integer(), SinceLastCall :: non_neg_integer()}Returns information about reductions, for example:
> statistics(reductions). {2046,11}Change
As from ERTS 5.5 (Erlang/OTP R11B), this value does not include reductions performed in current time slices of currently scheduled processes. If an exact value is wanted, use
statistics(exact_reductions).statistics(run_queue) -> non_neg_integer()Returns the total length of all normal and dirty CPU run queues. That is, queued work that is expected to be CPU bound. The information is gathered atomically. That is, the result is a consistent snapshot of the state, but this operation is much more expensive compared to
statistics(total_run_queue_lengths), especially when a large amount of schedulers is used.statistics(run_queue_lengths) -> [non_neg_integer()]Returns the same as
statistics(run_queue_lengths_all)with the exception that no information about the dirty IO run queue is part of the result. That is, only run queues with work that is expected to be CPU bound is part of the result.Available since OTP 18.3
statistics(run_queue_lengths_all) -> [non_neg_integer()]Returns a list where each element represents the amount of processes and ports ready to run for each run queue. Values for normal run queues are located first in the resulting list. The first element corresponds to the normal run queue of scheduler number 1 and so on. If support for dirty schedulers exist, values for the dirty CPU run queue and the dirty IO run queue follow (in that order) at the end. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered.
Note
Each normal scheduler has one run queue that it manages. If dirty schedulers are supported, all dirty CPU schedulers share one run queue, and all dirty IO schedulers share one run queue. That is, we have multiple normal run queues, one dirty CPU run queue and one dirty IO run queue. Work can not migrate between the different types of run queues. Only work in normal run queues can migrate to other normal run queues. This has to be taken into account when evaluating the result.
See also
statistics(run_queue_lengths),statistics(total_run_queue_lengths_all),statistics(total_run_queue_lengths),statistics(active_tasks),statistics(active_tasks_all), andstatistics(total_active_tasks),statistics(total_active_tasks_all).Available since OTP 20.0
statistics(runtime) -> {Total :: non_neg_integer(), SinceLastCall :: non_neg_integer()}Returns information about runtime, in milliseconds.
This is the sum of the runtime for all threads in the Erlang runtime system and can therefore be greater than the wall clock time.
Warning
This value might wrap due to limitations in the underlying functionality provided by the operating system that is used.
Example:
> statistics(runtime). {1690,1620}statistics(scheduler_wall_time) -> [{Id :: pos_integer, ActiveTime :: non_neg_integer(), TotalTime :: non_neg_integer()}] | undefinedReturns information describing how much time normal and dirty CPU schedulers in the system have been busy. This value is normally a better indicator of how much load an Erlang node is under instead of looking at the CPU utilization provided by tools such as
toporsysstat. This is becausescheduler_wall_timealso includes time where the scheduler is waiting for some other reasource (such as an internal mutex) to be available but does not use the CPU. In order to better understand what a scheduler is busy doing you can use microstate accounting.The definition of a busy scheduler is when it is not idle and not busy waiting for new work, that is:
- Executing process code
- Executing linked-in driver or NIF code
- Executing BIFs, or any other runtime handling
- Garbage collecting
- Handling any other memory management
Notice that a scheduler can also be busy even if the OS has scheduled out the scheduler thread.
Note
It is recommended to use the module
schedulerinstead of this function directly as it provides an easier way to get the information that you usually want.If enabled this function returns a list of tuples with
{SchedulerId, ActiveTime, TotalTime}, whereSchedulerIdis an integer ID of the scheduler,ActiveTimeis the duration the scheduler has been busy, andTotalTimeis the total time duration sincescheduler_wall_timeactivation for the specific scheduler. The time unit returned is undefined and can be subject to change between releases, OSs, and system restarts.scheduler_wall_timeis only to be used to calculate relative values for scheduler utilization. TheActiveTimecan never exceedTotalTime. The list of scheduler information is unsorted and can appear in different order between calls.The disabled this function returns
undefined.The activation time can differ significantly between schedulers. Currently dirty schedulers are activated at system start while normal schedulers are activated some time after the
scheduler_wall_timefunctionality is enabled.Only information about schedulers that are expected to handle CPU bound work is included in the return values from this function. If you also want information about dirty I/O schedulers, use
statistics(scheduler_wall_time_all)instead.Normal schedulers will have scheduler identifiers in the range
1 =< SchedulerId =<erlang:system_info(schedulers). Dirty CPU schedulers will have scheduler identifiers in the rangeerlang:system_info(schedulers) < SchedulerId =< erlang:system_info(schedulers) +erlang:system_info(dirty_cpu_schedulers).Note
The different types of schedulers handle specific types of jobs. Every job is assigned to a specific scheduler type. Jobs can migrate between different schedulers of the same type, but never between schedulers of different types. This fact has to be taken under consideration when evaluating the result returned.
You can use
scheduler_wall_timeto calculate scheduler utilization. First you take a sample of the values returned byerlang:statistics(scheduler_wall_time).> erlang:system_flag(scheduler_wall_time, true). false > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. okSome time later the user takes another snapshot and calculates scheduler utilization per scheduler, for example:
> Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. ok > lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)). [{1,0.9743474730177548}, {2,0.9744843782751444}, {3,0.9995902361669045}, {4,0.9738012596572161}, {5,0.9717956667018103}, {6,0.9739235846420741}, {7,0.973237033077876}, {8,0.9741297293248656}]Using the same snapshots to calculate a total scheduler utilization:
> {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), TotalSchedulerUtilization = A/T. 0.9769136803764825Total scheduler utilization will equal
1.0when all schedulers have been active all the time between the two measurements.Another (probably more) useful value is to calculate total scheduler utilization weighted against maximum amount of available CPU time:
> WeightedSchedulerUtilization = (TotalSchedulerUtilization * (erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers))) / erlang:system_info(logical_processors_available). 0.9769136803764825This weighted scheduler utilization will reach
1.0when schedulers are active the same amount of time as maximum available CPU time. If more schedulers exist than available logical processors, this value may be greater than1.0.As of ERTS version 9.0, the Erlang runtime system will as default have more schedulers than logical processors. This due to the dirty schedulers.
Note
scheduler_wall_timeis by default disabled. To enable it, useerlang:system_flag(scheduler_wall_time, true).Available since OTP R15B01
statistics(scheduler_wall_time_all) -> [{Id :: pos_integer, ActiveTime :: non_neg_integer(), TotalTime :: non_neg_integer()}] | undefinedEquivalent to
statistics(scheduler_wall_time), except that it also include information about all dirty I/O schedulers.Dirty IO schedulers will have scheduler identifiers in the range
erlang:system_info(schedulers)+erlang:system_info(dirty_cpu_schedulers)< SchedulerId =< erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers) +erlang:system_info(dirty_io_schedulers).Note
Note that work executing on dirty I/O schedulers are expected to mainly wait for I/O. That is, when you get high scheduler utilization on dirty I/O schedulers, CPU utilization is not expected to be high due to this work.
Available since OTP 20.0
statistics(total_active_tasks) -> non_neg_integer()Equivalent to calling
lists:sum(statistics(active_tasks)), but more efficient.Available since OTP 18.3
statistics(total_active_tasks_all) -> non_neg_integer()Equivalent to calling
lists:sum(statistics(active_tasks_all)), but more efficient.Available since OTP 20.0
statistics(total_run_queue_lengths) -> non_neg_integer()Equivalent to calling
lists:sum(statistics(run_queue_lengths)), but more efficient.Available since OTP 18.3
statistics(total_run_queue_lengths_all) -> non_neg_integer()Equivalent to calling
lists:sum(statistics(run_queue_lengths_all)), but more efficient.Available since OTP 20.0
statistics(wall_clock) -> {Total :: non_neg_integer(), SinceLastCall :: non_neg_integer()}Returns information about wall clock.
wall_clockcan be used in the same manner asruntime, except that real time is measured as opposed to runtime or CPU time.
-spec system_flag(backtrace_depth, Depth) -> OldDepth when Depth :: non_neg_integer(), OldDepth :: non_neg_integer(); (cpu_topology, CpuTopology) -> OldCpuTopology when CpuTopology :: cpu_topology(), OldCpuTopology :: cpu_topology(); (dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline) -> OldDirtyCPUSchedulersOnline when DirtyCPUSchedulersOnline :: pos_integer(), OldDirtyCPUSchedulersOnline :: pos_integer(); (erts_alloc, {Alloc, F, V}) -> ok | notsup when Alloc :: atom(), F :: atom(), V :: integer(); (fullsweep_after, Number) -> OldNumber when Number :: non_neg_integer(), OldNumber :: non_neg_integer(); (microstate_accounting, Action) -> OldState when Action :: true | false | reset, OldState :: true | false; (min_heap_size, MinHeapSize) -> OldMinHeapSize when MinHeapSize :: non_neg_integer(), OldMinHeapSize :: non_neg_integer(); (min_bin_vheap_size, MinBinVHeapSize) -> OldMinBinVHeapSize when MinBinVHeapSize :: non_neg_integer(), OldMinBinVHeapSize :: non_neg_integer(); (max_heap_size, MaxHeapSize) -> OldMaxHeapSize when MaxHeapSize :: max_heap_size(), OldMaxHeapSize :: max_heap_size(); (multi_scheduling, BlockState) -> OldBlockState when BlockState :: block | unblock | block_normal | unblock_normal, OldBlockState :: blocked | disabled | enabled; (outstanding_system_requests_limit, NewLimit) -> OldLimit when NewLimit :: 1..134217727, OldLimit :: 1..134217727; (scheduler_bind_type, How) -> OldBindType when How :: scheduler_bind_type() | default_bind, OldBindType :: scheduler_bind_type(); (scheduler_wall_time, Boolean) -> OldBoolean when Boolean :: boolean(), OldBoolean :: boolean(); (schedulers_online, SchedulersOnline) -> OldSchedulersOnline when SchedulersOnline :: pos_integer(), OldSchedulersOnline :: pos_integer(); (system_logger, Logger) -> PrevLogger when Logger :: logger | undefined | pid(), PrevLogger :: logger | undefined | pid(); (trace_control_word, TCW) -> OldTCW when TCW :: non_neg_integer(), OldTCW :: non_neg_integer(); (time_offset, finalize) -> OldState when OldState :: preliminary | final | volatile; (internal_cpu_topology, term()) -> term(); (sequential_tracer, Tracer) -> PrevTracer | false when Tracer :: pid() | port() | {module(), term()} | false, PrevTracer :: pid() | port() | {module(), term()} | false; (reset_seq_trace, true) -> true.
Sets a system flag to the given value.
The possible flags to set are:
system_flag(backtrace_depths, non_neg_integer()) -> non_neg_integer()Sets the maximum depth of call stack back-traces in the exit reason element of
'EXIT'tuples. The flag also limits the stacktrace depth returned byprocess_info/2itemcurrent_stacktrace.Returns the old value of the flag.
system_flag(cpu_topology, cpu_topology()) -> cpu_topology()Warning
This argument is deprecated. Instead of using this argument, use command-line argument
+sctin erl.When this argument is removed, a final CPU topology to use is determined at emulator boot time.
Sets the user-defined
CpuTopology. The user-defined CPU topology overrides any automatically detected CPU topology. By passingundefinedasCpuTopology, the system reverts to the CPU topology automatically detected. The returned value equals the value returned fromerlang:system_info(cpu_topology)before the change was made.Returns the old value of the flag.
The CPU topology is used when binding schedulers to logical processors. If schedulers are already bound when the CPU topology is changed, the schedulers are sent a request to rebind according to the new CPU topology.
The user-defined CPU topology can also be set by passing command-line argument
+sctto erl.For information on type
CpuTopologyand more, seeerlang:system_info(cpu_topology)as well as command-line flags+sctand+sbtin erl.system_flag(dirty_cpu_schedulers_online, pos_integer()) -> pos_integer()Sets the number of dirty CPU schedulers online. Range is
1 <= DirtyCPUSchedulersOnline <= N, whereNis the smallest of the return values oferlang:system_info(dirty_cpu_schedulers)anderlang:system_info(schedulers_online).Returns the old value of the flag.
The number of dirty CPU schedulers online can change if the number of schedulers online changes. For example, if 12 schedulers and 6 dirty CPU schedulers are online, and
system_flag/2is used to set the number of schedulers online to 6, then the number of dirty CPU schedulers online is automatically decreased by half as well, down to 3. Similarly, the number of dirty CPU schedulers online increases proportionally to increases in the number of schedulers online.For more information, see
erlang:system_info(dirty_cpu_schedulers)anderlang:system_info(dirty_cpu_schedulers_online).Available since OTP 17.0
system_flag(erts_alloc, {Alloc :: atom(), F :: atom(), V :: integer()}) -> ok | notsupSets system flags for
erts_alloc(3).Allocis the allocator to affect, for examplebinary_alloc.Fis the flag to change andVis the new value.Only a subset of all
erts_allocflags can be changed at run time. This subset is currently only the flagsbct.Returns
okif the flag was set ornotsupif not supported byerts_alloc.Available since OTP 20.2.3
system_flag(fullsweep_after, non_neg_integer()) -> non_neg_integer()Sets system flag
fullsweep_after.Numberis a non-negative integer indicating how many times generational garbage collections can be done without forcing a fullsweep collection. The value applies to new processes, while processes already running are not affected.Returns the old value of the flag.
In low-memory systems (especially without virtual memory), setting the value to
0can help to conserve memory.This value can also be set through (OS) environment variable
ERL_FULLSWEEP_AFTER.system_flag(microstate_accounting, true | false | reset) -> boolean()Turns on/off microstate accounting measurements. When passing reset, all counters are reset to 0.
For more information see
statistics(microstate_accounting).Available since OTP 19.0
system_flag(min_heap_size, non_neg_integer()) -> non_neg_integer()Sets the default minimum heap size for processes. The size is specified in words. The new
min_heap_sizeeffects only processes spawned after the change ofmin_heap_sizehas been made.min_heap_sizecan be set for individual processes by usingspawn_opt/4orprocess_flag/2.Returns the old value of the flag.
system_flag(min_bin_vheap_size, non_neg_integer()) -> non_neg_integer()Sets the default minimum binary virtual heap size for processes. The size is specified in words. The new
min_bin_vhheap_sizeeffects only processes spawned after the change ofmin_bin_vheap_sizehas been made.min_bin_vheap_sizecan be set for individual processes by usingspawn_opt/2,3,4orprocess_flag/2.Returns the old value of the flag.
Available since OTP R13B04
system_flag(max_heap_size, max_heap_size()) -> max_heap_size()Sets the default maximum heap size settings for processes. The size is specified in words. The new
max_heap_sizeeffects only processes spawned after the change has been made.max_heap_sizecan be set for individual processes usingspawn_opt/2,3,4orprocess_flag/2.Returns the old value of the flag.
For details on how the heap grows, see Sizing the heap in the ERTS internal documentation.
Available since OTP 19.0
system_flag(multi_scheduling, BlockState) -> OldBlockState when BlockState :: block | unblock | block_normal | unblock_normal, OldBlockState :: blocked | disabled | enabledIf multi-scheduling is enabled, more than one scheduler thread is used by the emulator. Multi-scheduling can be blocked in two different ways. Either all schedulers but one is blocked, or all normal schedulers but one is blocked. When only normal schedulers are blocked, dirty schedulers are free to continue to schedule processes.
If
BlockState =:= block, multi-scheduling is blocked. That is, one and only one scheduler thread will execute. IfBlockState =:= unblockand no one else blocks multi-scheduling, and this process has blocked only once, multi-scheduling is unblocked.If
BlockState =:= block_normal, normal multi-scheduling is blocked. That is, only one normal scheduler thread will execute, but multiple dirty schedulers can execute. IfBlockState =:= unblock_normaland no one else blocks normal multi-scheduling, and this process has blocked only once, normal multi-scheduling is unblocked.One process can block multi-scheduling and normal multi-scheduling multiple times. If a process has blocked multiple times, it must unblock exactly as many times as it has blocked before it has released its multi-scheduling block. If a process that has blocked multi-scheduling or normal multi-scheduling exits, it automatically releases its blocking of multi-scheduling and normal multi-scheduling.
The return values are
disabled,blocked,blocked_normal, orenabled. The returned value describes the state just after the call toerlang:system_flag(multi_scheduling, BlockState)has been made. For information about the return values, seeerlang:system_info(multi_scheduling).Note
Blocking of multi-scheduling and normal multi-scheduling is normally not needed. If you feel that you need to use these features, consider it a few more times again. Blocking multi-scheduling is only to be used as a last resort, as it is most likely a very inefficient way to solve the problem.
See also
erlang:system_info(multi_scheduling),erlang:system_info(normal_multi_scheduling_blockers),erlang:system_info(multi_scheduling_blockers), anderlang:system_info(schedulers).system_flag(outstanding_system_requests_limit, 1..134217727) -> 1..134217727Sets a limit on the amount of outstanding requests made by a system process orchestrating system wide changes. Currently there are two such processes:
The Code Purger - The code purger orchestrates checking of references to old code before old code is removed from the system.
The Literal Area Collector - The literal area collector orchestrates copying of references from old literal areas before removal of such areas from the system.
Each of these processes are allowed to have as many outstanding requests as this limit is set to. By default this limit is set to twice the amount of schedulers on the system. This will ensure that schedulers will have enough work scheduled to perform these operations as quickly as possible at the same time as other work will be interleaved with this work. Currently used limit can be checked by calling
erlang:system_info(outstanding_system_requests_limit).This limit can also be set by passing the command line argument
+zosrl <Limit>toerl.Available since OTP 24.2
system_flag(scheduler_bind_type, scheduler_bind_type() | default_bind) -> scheduler_bind_type()Warning
This argument is deprecated. Instead of using this argument, use command-line argument
+sbtin erl. When this argument is removed, a final scheduler bind type to use is determined at emulator boot time.Controls if and how schedulers are bound to logical processors.
When
erlang:system_flag(scheduler_bind_type, How)is called, an asynchronous signal is sent to all schedulers online, causing them to try to bind or unbind as requested.Note
If a scheduler fails to bind, this is often silently ignored, as it is not always possible to verify valid logical processor identifiers. If an error is reported, an error event is logged. To verify that the schedulers have bound as requested, call
erlang:system_info(scheduler_bindings).Schedulers can be bound on newer Linux, Solaris, FreeBSD, and Windows systems, but more systems will be supported in future releases.
In order for the runtime system to be able to bind schedulers, the CPU topology must be known. If the runtime system fails to detect the CPU topology automatically, it can be defined. For more information on how to define the CPU topology, see command-line flag
+sctin erl.The runtime system does by default not bind schedulers to logical processors.
Note
If the Erlang runtime system is the only OS process binding threads to logical processors, this improves the performance of the runtime system. However, if other OS processes (for example, another Erlang runtime system) also bind threads to logical processors, there can be a performance penalty instead. Sometimes this performance penalty can be severe. If so, it is recommended to not bind the schedulers.
Schedulers can be bound in different ways. Argument
Howdetermines how schedulers are bound and can be any of the following:thread_spread- Same as command-line argument+sbt tsin erl.processor_spread- Same as command-line argument+sbt psin erl.no_node_thread_spread- Same as command-line argument+sbt nntsin erl.no_node_processor_spread- Same as command-line argument+sbt nnpsin erl.thread_no_node_processor_spread- Same as command-line argument+sbt tnnpsin erl.default_bind- Same as command-line argument+sbt dbin erl.
The returned value equals
Howbefore flagscheduler_bind_typewas changed.Failures:
notsup- If binding of schedulers is not supported.badarg- IfHowis not one of the documented alternatives.badarg- If CPU topology information is unavailable.
The scheduler bind type can also be set by passing command-line argument
+sbtto erl.For more information, see
erlang:system_info(scheduler_bind_type),erlang:system_info(scheduler_bindings), as well as command-line flags+sbtand+sctin erl.system_flag(scheduler_wall_time, boolean()) -> boolean()Try enable or disable scheduler wall time measurements by passing
Booleanas eithertrueorfalse.For more information about how to use scheduler wall time measurements, see
statistics(scheduler_wall_time).Scheduler wall time measurements has a node global state. It is either enabled for all processes on the node or disabled for all processes. Each process has a logical counter initialized as zero. A call with
Booleanastruewill increase that counter one step for the calling process. A call withfalsewill decrease it one step unless it already is zero. The node global state forscheduler_wall_timewill be enabled as long as there is at least one process alive with a counter value larger than zero. When a process terminates, its counter will also disappear. To ensurescheduler_wall_timeis kept enabled, the process that enabled it must therefore be kept alive.Returns the old value of the node global state,
trueif scheduler wall time measurements were enabled,falseif it were disabled.Scheduler wall time measurements do consume some cpu overhead and should not be left turned on unless used.
Available since OTP R15B01
system_flag(schedulers_online, pos_integer()) -> pos_integer()Sets the number of schedulers online. Range is
1 <= SchedulersOnline <= erlang:system_info(schedulers).Returns the old value of the flag.
If the emulator was built with support for dirty schedulers, changing the number of schedulers online can also change the number of dirty CPU schedulers online. For example, if 12 schedulers and 6 dirty CPU schedulers are online, and
system_flag/2is used to set the number of schedulers online to 6, then the number of dirty CPU schedulers online is automatically decreased by half as well, down to 3. Similarly, the number of dirty CPU schedulers online increases proportionally to increases in the number of schedulers online.For more information, see
erlang:system_info(schedulers)anderlang:system_info(schedulers_online).system_flag(system_logger, logger | undefined | pid()) -> logger | undefined | pid()Sets the process that will receive the logging messages generated by ERTS. If set to
undefined, all logging messages generated by ERTS will be dropped. The messages will be in the format:{log,Level,Format,ArgList,Metadata} where Level = atom(), Format = string(), ArgList = list(term()), Metadata = #{ pid => pid(), group_leader => pid(), time := logger:timestamp(), error_logger := #{ emulator := true, tag := atom() }If the
system_loggerprocess dies, this flag will be reset tologger.The default is the process named
logger.Returns the old value of the flag.
Note
This function is designed to be used by the KERNEL
logger. Be careful if you change it to something else as log messages may be lost. If you want to intercept emulator log messages, do it by adding a specialized handler to the KERNEL logger.Available since OTP 21.2
system_flag(trace_control_word, non_neg_integer()) -> non_neg_integer()Sets the value of the node trace control word to
TCW, which is to be an unsigned integer. For more information, see functionset_tcwin section "Match Specifications in Erlang" in the User's Guide.Returns the old value of the flag.
system_flag(time_offset, finalize) -> preliminary | final | volatileFinalizes the time offset when single time warp mode is used. If another time warp mode is used, the time offset state is left unchanged.
Returns the old state identifier, that is:
- If
preliminaryis returned, finalization was performed and the time offset is now final. - If
finalis returned, the time offset was already in the final state. This either because anothererlang:system_flag(time_offset, finalize)call or because no time warp mode is used. - If
volatileis returned, the time offset cannot be finalized because multi-time warp mode is used.
Available since OTP 18.0
- If
-spec system_info(allocated_areas) -> [tuple()]; (allocator) -> {Allocator, Version, Features, Settings} when Allocator :: undefined | glibc, Version :: [non_neg_integer()], Features :: [atom()], Settings :: [{Subsystem :: atom(), [{Parameter :: atom(), Value :: term()}]}]; ({allocator, Alloc}) -> [_] when Alloc :: atom(); (alloc_util_allocators) -> [Alloc] when Alloc :: atom(); ({allocator_sizes, Alloc}) -> [_] when Alloc :: atom(); (atom_count) -> pos_integer(); (atom_limit) -> pos_integer(); (build_type) -> opt | debug | gcov | valgrind | gprof | lcnt | frmptr; (c_compiler_used) -> {atom(), term()}; (check_io) -> [_]; (compat_rel) -> integer(); (cpu_topology) -> CpuTopology when CpuTopology :: cpu_topology(); ({cpu_topology, defined | detected | used}) -> CpuTopology when CpuTopology :: cpu_topology(); (cpu_quota) -> pos_integer() | unknown; (creation) -> integer(); (debug_compiled) -> boolean(); (delayed_node_table_gc) -> infinity | non_neg_integer(); (dirty_cpu_schedulers) -> non_neg_integer(); (dirty_cpu_schedulers_online) -> non_neg_integer(); (dirty_io_schedulers) -> non_neg_integer(); (dist) -> binary(); (dist_buf_busy_limit) -> non_neg_integer(); (dist_ctrl) -> [{Node :: node(), ControllingEntity :: port() | pid()}]; (driver_version) -> string(); (dynamic_trace) -> none | dtrace | systemtap; (dynamic_trace_probes) -> boolean(); (eager_check_io) -> boolean(); (emu_flavor) -> emu | jit; (emu_type) -> opt | debug | gcov | valgrind | gprof | lcnt | frmptr; (end_time) -> non_neg_integer(); (ets_count) -> pos_integer(); (ets_limit) -> pos_integer(); (fullsweep_after) -> {fullsweep_after, non_neg_integer()}; (garbage_collection) -> garbage_collection_defaults(); (heap_sizes) -> [non_neg_integer()]; (heap_type) -> private; (info) -> binary(); (kernel_poll) -> boolean(); (loaded) -> binary(); (logical_processors | logical_processors_available | logical_processors_online) -> unknown | pos_integer(); (machine) -> string(); (max_heap_size) -> {max_heap_size, MaxHeapSize :: max_heap_size()}; (message_queue_data) -> message_queue_data(); (min_heap_size) -> {min_heap_size, MinHeapSize :: pos_integer()}; (min_bin_vheap_size) -> {min_bin_vheap_size, MinBinVHeapSize :: pos_integer()}; (modified_timing_level) -> integer() | undefined; (multi_scheduling) -> disabled | blocked | blocked_normal | enabled; (multi_scheduling_blockers) -> [Pid :: pid()]; (nif_version) -> string(); (normal_multi_scheduling_blockers) -> [Pid :: pid()]; (otp_release) -> string(); (os_monotonic_time_source) -> [{atom(), term()}]; (os_system_time_source) -> [{atom(), term()}]; (outstanding_system_requests_limit) -> 1..134217727; (port_parallelism) -> boolean(); (port_count) -> non_neg_integer(); (port_limit) -> pos_integer(); (process_count) -> pos_integer(); (process_limit) -> pos_integer(); (procs) -> binary(); (scheduler_bind_type) -> scheduler_bind_type(); (scheduler_bindings) -> tuple(); (scheduler_id) -> SchedulerId :: pos_integer(); (schedulers | schedulers_online) -> pos_integer(); (smp_support) -> boolean(); (start_time) -> integer(); (system_architecture) -> string(); (system_logger) -> logger | undefined | pid(); (system_version) -> string(); (threads) -> boolean(); (thread_pool_size) -> non_neg_integer(); (time_correction) -> true | false; (time_offset) -> preliminary | final | volatile; (time_warp_mode) -> no_time_warp | single_time_warp | multi_time_warp; (tolerant_timeofday) -> enabled | disabled; (trace_control_word) -> non_neg_integer(); (update_cpu_info) -> changed | unchanged; (version) -> string(); (wordsize | {wordsize, internal} | {wordsize, external}) -> 4 | 8; (async_dist) -> boolean(); (halt_flush_timeout) -> non_neg_integer() | infinity.
Returns information about the current system.
The documentation of this function is broken into the following sections in order to make it easier to navigate.
Memory Allocation-allocated_areas,allocator,alloc_util_allocators,allocator_sizesCPU Topology-cpu_topology,logical_processors,update_cpu_infoProcess Information-fullsweep_after,garbage_collection,heap_sizes,heap_type,max_heap_size,message_queue_data,min_heap_size,min_bin_vheap_size,procsSystem Limits-atom_count,atom_limit,ets_count,ets_limit,port_count,port_limit,process_count,process_limitSystem Time-end_time,os_monotonic_time_source,os_system_time_source,start_time,time_correction,time_offset,time_warp_mode,tolerant_timeofdayScheduler Information-dirty_cpu_schedulers,dirty_cpu_schedulers_online,dirty_io_schedulers,multi_scheduling,multi_scheduling_blockers,normal_multi_scheduling_blockers,scheduler_bind_type,scheduler_bindings,scheduler_id,schedulers,smp_support,threads,thread_pool_sizeDistribution Information-creation,delayed_node_table_gc,dist,dist_buf_busy_limit,dist_ctrlSystem Information-c_compiler_used,check_io,compat_rel,debug_compiled,driver_version,dynamic_trace,dynamic_trace_probes,emu_flavor,emu_type,info,kernel_poll,loaded,machine,modified_timing_level,nif_version,otp_release,outstanding_system_requests_limit,port_parallelism,system_architecture,system_logger,system_version,trace_control_word,version,wordsize
Memory Allocation
Returns various information about the memory allocators of the current system (emulator) as specified by Item:
allocated_areas- Returns[tuple()]with information about miscellaneous allocated memory areas.Each tuple contains an atom describing the type of memory as first element and the amount of allocated memory in bytes as second element. When information about allocated and used memory is present, also a third element is present, containing the amount of used memory in bytes.
erlang:system_info(allocated_areas)is intended for debugging, and the content is highly implementation-dependent. The content of the results therefore changes when needed without prior notice.Notice that the sum of these values is not the total amount of memory allocated by the emulator. Some values are part of other values, and some memory areas are not part of the result. For information about the total amount of memory allocated by the emulator, see
erlang:memory/0,1.
allocator- Returns{Allocator :: undefined | glibc, Version :: [non_neg_integer()], Features :: [atom()], Settings :: [{Subsystem :: atom(), [{Parameter :: atom(), Value :: term()}] }] }where
Allocatorcorresponds to themalloc()implementation used. IfAllocatorequalsundefined, themalloc()implementation used cannot be identified.glibccan be identified.Versionis a list of integers (but not a string) representing the version of themalloc()implementation used.Featuresis a list of atoms representing the allocation features used.Settingsis a list of subsystems, their configurable parameters, and used values. Settings can differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.
See also "System Flags Effecting erts_alloc" in
erts_alloc(3).{allocator, Alloc}- Returns information about the specified allocator. As from ERTS 5.6.1, the return value is a list of{instance, InstanceNo, InstanceInfo}tuples, whereInstanceInfocontains information about a specific instance of the allocator. IfAllocis not a recognized allocator,undefinedis returned. IfAllocis disabled,falseis returned.Notice that the information returned is highly implementation-dependent and can be changed or removed at any time without prior notice. It was initially intended as a tool when developing new allocators, but as it can be of interest for others it has been briefly documented.
The recognized allocators are listed in
erts_alloc(3). Information about super carriers can be obtained from ERTS 8.0 with{allocator, erts_mmap}or from ERTS 5.10.4; the returned list when calling with{allocator, mseg_alloc}also includes an{erts_mmap, _}tuple as one element in the list.After reading the
erts_alloc(3)documentation, the returned information more or less speaks for itself, but it can be worth explaining some things. Call counts are presented by two values, the first value is giga calls, and the second value is calls.mbcsandsbcsdenote multi-block carriers, and single-block carriers, respectively. Sizes are presented in bytes. When a size is not presented, it is the amount of something. Sizes and amounts are often presented by three values:- The first is the current value.
- The second is the maximum value since the last call to
erlang:system_info({allocator, Alloc}). - The third is the maximum value since the emulator was started.
If only one value is present, it is the current value.
fix_allocmemory block types are presented by two values. The first value is the memory pool size and the second value is the used memory size.alloc_util_allocators- Returns a list of the names of all allocators using the ERTS internalalloc_utilframework as atoms. For more information, see section The alloc_util framework inerts_alloc(3).{allocator_sizes, Alloc}- Returns various size information for the specified allocator. The information returned is a subset of the information returned byerlang:system_info({allocator, Alloc}).
CPU Topology
Returns various information about the CPU topology of the current system (emulator) as specified by Item:
cpu_topology- Returns thet:cpu_topology()currently used by the emulator. The CPU topology is used when binding schedulers to logical processors. The CPU topology used is the user-defined CPU topology, if such exists, otherwise the automatically detected CPU topology, if such exists. If no CPU topology exists,undefinedis returned.{cpu_topology, defined}- Returns the user-definedt:cpu_topology(). For more information, see command-line flag+sctinerl(1)and argumentcpu_topology.{cpu_topology, detected}- Returns the automatically detectedt:cpu_topology(). The emulator detects the CPU topology on some newer Linux, Solaris, FreeBSD, and Windows systems. On Windows system with more than 32 logical processors, the CPU topology is not detected.For more information, see argument
cpu_topology.{cpu_topology, used}- ReturnsCpuTopologyused by the emulator. For more information, see argumentcpu_topology.logical_processors- Returns the detected number of logical processors configured in the system. The return value is either an integer, or the atomunknownif the emulator cannot detect the configured logical processors.logical_processors_available- Returns the detected number of logical processors available to the Erlang runtime system. The return value is either an integer, or the atomunknownif the emulator cannot detect the available logical processors. The number of available logical processors is less than or equal to the number of logical processors online.logical_processors_online- Returns the detected number of logical processors online on the system. The return value is either an integer, or the atomunknownif the emulator cannot detect logical processors online. The number of logical processors online is less than or equal to the number of logical processors configured.cpu_quota- Returns the detected CPU quota the emulator is limited by. The return value is an integer saying how many processors' worth of runtime we get (between 1 and the number of logical processors), or the atomunknownif the emulator cannot detect a quota.update_cpu_info- The runtime system rereads the CPU information available and updates its internally stored information about the detected CPU topology and the number of logical processors configured, online, available, and cpu quota.If the CPU information has changed since the last time it was read, the atom
changedis returned, otherwise the atomunchanged. If the CPU information has changed, you probably want to adjust the number of schedulers online. You typically want to have as many schedulers online as logical processors available.Since: OTP R14B
Process Information
Returns information about the default process heap settings:
fullsweep_after- Returns{fullsweep_after, integer() >= 0}, which is thefullsweep_aftergarbage collection setting used by default. For more information, seegarbage_collectiondescribed below.garbage_collection- Returnsgarbage_collection_defaults/0describing the default garbage collection settings. A process spawned on the local node by aspawnorspawn_linkuses these garbage collection settings. The default settings can be changed by usingerlang:system_flag/2.spawn_opt/2,3,4can spawn a process that does not use the default settings.heap_sizes- Returns a list of integers representing valid heap sizes in words. All Erlang heaps are sized from sizes in this list.heap_type- Returns the heap type used by the current emulator. One heap type exists:private- Each process has a heap reserved for its use and no references between heaps of different processes are allowed. Messages passed between processes are copied between heaps.
max_heap_size- Returns{max_heap_size, MaxHeapSize}, whereMaxHeapSizeis the current system-wide maximum heap size settings for spawned processes. This setting can be set using the command-line flags+hmax,+hmaxk,+hmaxeland+hmaxiblinerl(1). It can also be changed at runtime usingerlang:system_flag(max_heap_size, MaxHeapSize). For more details about themax_heap_sizeprocess flag, seeprocess_flag(max_heap_size, MaxHeapSize).Since: OTP 19.0
message_queue_data- Returns the default value of themessage_queue_dataprocess flag, which can be eitheroff_heaporon_heap. The default value is set by the command-line argument+hmqdinerl(1). For more information, see the documentation ofprocess_flag(message_queue_data, MQD).Since: OTP 19.0
min_heap_size- Returns{min_heap_size, MinHeapSize}, whereMinHeapSizeis the current system-wide minimum heap size for spawned processes.Since: OTP R13B04
min_bin_vheap_size- Returns{min_bin_vheap_size, MinBinVHeapSize}, whereMinBinVHeapSizeis the current system-wide minimum binary virtual heap size for spawned processes.Since: OTP R13B04
procs- Returns a binary containing a string of process and port information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.
System Limits
Returns information about the current system (emulator) limits as specified by Item:
atom_count- Returns the number of atoms currently existing at the local node. The value is given as an integer.Since: OTP 20.0
atom_limit- Returns the maximum number of atoms allowed. This limit can be increased at startup by passing command-line flag+ttoerl(1).Since: OTP 20.0
ets_count- Returns the number of ETS tables currently existing at the local node.Since: OTP 21.1
ets_limit- Returns the limit for number of ETS tables. This limit is partially obsolete and number of tables are only limited by available memory.Since: OTP R16B03
port_count- Returns the number of ports currently existing at the local node. The value is given as an integer. This is the same value as returned bylength(erlang:ports()), but more efficient.Since: OTP R16B
port_limit- Returns the maximum number of simultaneously existing ports at the local node as an integer. This limit can be configured at startup by using command-line flag+Qinerl(1).Since OTP R16B
process_count- Returns the number of processes currently existing at the local node. The value is given as an integer. This is the same value as returned bylength(processes()), but more efficient.process_limit- Returns the maximum number of simultaneously existing processes at the local node. The value is given as an integer. This limit can be configured at startup by using command-line flag+Pinerl(1).
System Time
Returns information about the current system (emulator) time as specified by Item:
end_time- The last Erlang monotonic time innativetime unit that can be represented internally in the current Erlang runtime system instance. The time between the start time and the end time is at least a quarter of a millennium.Since: OTP 18.0
os_monotonic_time_source- Returns a list containing information about the source of OS monotonic time that is used by the runtime system.If
[]is returned, no OS monotonic time is available. The list contains two-tuples withKeys as first element, andValues as second element. The order of these tuples is undefined. The following tuples can be part of the list, but more tuples can be introduced in the future:{function, Function}-Functionis the name of the function used. This tuple always exists if OS monotonic time is available to the runtime system.{clock_id, ClockId}- This tuple only exists ifFunctioncan be used with different clocks.ClockIdcorresponds to the clock identifier used when callingFunction.{resolution, OsMonotonicTimeResolution}- Highest possible resolution of current OS monotonic time source as parts per second. If no resolution information can be retrieved from the OS,OsMonotonicTimeResolutionis set to the resolution of the time unit ofFunctions return value. That is, the actual resolution can be lower thanOsMonotonicTimeResolution. Notice that the resolution does not say anything about the accuracy or whether the precision aligns with the resolution. You do, however, know that the precision is not better thanOsMonotonicTimeResolution.{used_resolution, UsedOsMonotonicTimeResolution}- The OS monotonic time resolution used by the runtime system. This is very often the same asOsMonotonicTimeResolution. However, on some systems the resolution has to be reduced in order to reliably produce monotonic timestamps. An example of this is whenQueryPerformanceCounter()is used as OS monotonic time source on Windows. If such a reduction of the resolution has been done,UsedOsMonotonicTimeResolutionwill be smaller thanOsMonotonicTimeResolution.{extended, Extended}-Extendedequalsyesif the range of time values has been extended; otherwiseExtendedequalsno. The range must be extended ifFunctionreturns values that wrap fast. This typically is the case when the return value is a 32-bit value.{parallel, Parallel}-ParallelequalsyesifFunctionis called in parallel from multiple threads. If it is not called in parallel, because calls must be serialized,Parallelequalsno.{time, OsMonotonicTime}-OsMonotonicTimeequals current OS monotonic time innativetime unit.
Since: OTP 18.0
os_system_time_source- Returns a list containing information about the source of OS system time that is used by the runtime system.The list contains two-tuples with
Keys as first element, andValues as second element. The order of these tuples is undefined. The following tuples can be part of the list, but more tuples can be introduced in the future:{function, Function}-Functionis the name of the function used.{clock_id, ClockId}- Exists only ifFunctioncan be used with different clocks.ClockIdcorresponds to the clock identifier used when callingFunction.{resolution, OsSystemTimeResolution}- Highest possible resolution of current OS system time source as parts per second. If no resolution information can be retrieved from the OS,OsSystemTimeResolutionis set to the resolution of the time unit ofFunctions return value. That is, the actual resolution can be lower thanOsSystemTimeResolution. Notice that the resolution does not say anything about the accuracy or whether the precision do align with the resolution. You do, however, know that the precision is not better thanOsSystemTimeResolution.{parallel, Parallel}-ParallelequalsyesifFunctionis called in parallel from multiple threads. If it is not called in parallel, because calls needs to be serialized,Parallelequalsno.{time, OsSystemTime}-OsSystemTimeequals current OS system time innativetime unit.
Since: OTP 18.0
start_time- The Erlang monotonic time innativetime unit at the time when current Erlang runtime system instance started.See also
erlang:system_info(end_time).Since: OTP 18.0
time_correction- Returns at:boolean()value indicating whether time correction is enabled or not.Since: OTP 18.0
time_offset- Returns the state of the time offset:preliminary- The time offset is preliminary, and will be changed and finalized later. The preliminary time offset is used during the preliminary phase of the single time warp mode.final- The time offset is final. This either because no time warp mode is used, or because the time offset have been finalized when single time warp mode is used.volatile- The time offset is volatile. That is, it can change at any time. This is because multi-time warp mode is used.
Since: OTP 18.0
time_warp_mode- Returns a value identifying the time warp mode that is used:no_time_warp- The no time warp mode is used.single_time_warp- The single time warp mode is used.multi_time_warp- The multi-time warp mode is used.
Since: OTP 18.0
tolerant_timeofday- Returns whether a pre ERTS 7.0 backwards compatible compensation for sudden changes of system time isenabledordisabled. Such compensation isenabledwhen the time offset isfinal, and time correction is enabled.Since: OTP 17.1
Scheduler Information
Returns information about schedulers, scheduling and threads in the current system as specified by Item:
dirty_cpu_schedulers- Returns the number of dirty CPU scheduler threads used by the emulator. Dirty CPU schedulers execute CPU-bound native functions, such as NIFs, linked-in driver code, and BIFs that cannot be managed cleanly by the normal emulator schedulers.The number of dirty CPU scheduler threads is determined at emulator boot time and cannot be changed after that. However, the number of dirty CPU scheduler threads online can be changed at any time. The number of dirty CPU schedulers can be set at startup by passing command-line flag
+SDcpuor+SDPcpuinerl(1).See also
erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline),erlang:system_info(dirty_cpu_schedulers_online),erlang:system_info(dirty_io_schedulers),erlang:system_info(schedulers),erlang:system_info(schedulers_online), anderlang:system_flag(schedulers_online, SchedulersOnline).Since: OTP 17.0
dirty_cpu_schedulers_online- Returns the number of dirty CPU schedulers online. The return value satisfies1 <= DirtyCPUSchedulersOnline <= N, whereNis the smallest of the return values oferlang:system_info(dirty_cpu_schedulers)anderlang:system_info(schedulers_online).The number of dirty CPU schedulers online can be set at startup by passing command-line flag
+SDcpuinerl(1).For more information, see
erlang:system_info(dirty_cpu_schedulers),erlang:system_info(dirty_io_schedulers),erlang:system_info(schedulers_online), anderlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).Since: OTP 17.0
dirty_io_schedulers- Returns the number of dirty I/O schedulers as an integer. Dirty I/O schedulers execute I/O-bound native functions, such as NIFs and linked-in driver code, which cannot be managed cleanly by the normal emulator schedulers.This value can be set at startup by passing command-line argument
+SDioinerl(1).For more information, see
erlang:system_info(dirty_cpu_schedulers),erlang:system_info(dirty_cpu_schedulers_online), anderlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).Since: OTP 17.0
multi_scheduling- Returns one of the following:disabled- The emulator has been started with only one scheduler thread.blocked- The emulator has more than one scheduler thread, but all scheduler threads except one are blocked. That is, only one scheduler thread schedules Erlang processes and executes Erlang code.blocked_normal- The emulator has more than one scheduler thread, but all normal scheduler threads except one are blocked. Notice that dirty schedulers are not blocked, and can schedule Erlang processes and execute native code.enabled- The emulator has more than one scheduler thread, and no scheduler threads are blocked. That is, all available scheduler threads schedule Erlang processes and execute Erlang code.
See also
erlang:system_flag(multi_scheduling, BlockState),erlang:system_info(multi_scheduling_blockers),erlang:system_info(normal_multi_scheduling_blockers), anderlang:system_info(schedulers).multi_scheduling_blockers- Returns a list ofPids when multi-scheduling is blocked, otherwise the empty list is returned. ThePids in the list represent all the processes currently blocking multi-scheduling. APidoccurs only once in the list, even if the corresponding process has blocked multiple times.See also
erlang:system_flag(multi_scheduling, BlockState),erlang:system_info(multi_scheduling),erlang:system_info(normal_multi_scheduling_blockers), anderlang:system_info(schedulers).normal_multi_scheduling_blockers- Returns a list ofPids when normal multi-scheduling is blocked (that is, all normal schedulers but one is blocked), otherwise the empty list is returned. ThePids in the list represent all the processes currently blocking normal multi-scheduling. APidoccurs only once in the list, even if the corresponding process has blocked multiple times.See also
erlang:system_flag(multi_scheduling, BlockState),erlang:system_info(multi_scheduling),erlang:system_info(multi_scheduling_blockers), anderlang:system_info(schedulers).Since: OTP 19.0
scheduler_bind_type- Returnst:scheduler_bind_type(), information about how the user has requested schedulers to be bound or not bound.Notice that although a user has requested schedulers to be bound, they can silently have failed to bind. To inspect the scheduler bindings, call
erlang:system_info(scheduler_bindings).For more information, see command-line argument
+sbtinerl(1)anderlang:system_info(scheduler_bindings).scheduler_bindings- Returns information about the currently used scheduler bindings.A tuple of a size equal to
erlang:system_info(schedulers)is returned. The tuple elements are integers or the atomunbound. Logical processor identifiers are represented as integers. TheNth element of the tuple equals the current binding for the scheduler with the scheduler identifier equal toN. For example, if the schedulers are bound,element(erlang:system_info(scheduler_id), erlang:system_info(scheduler_bindings))returns the identifier of the logical processor that the calling process is executing on.Notice that only schedulers online can be bound to logical processors.
For more information, see command-line argument
+sbtinerl(1)anderlang:system_info(schedulers_online).scheduler_id- Returns the scheduler ID (SchedulerId) of the scheduler thread that the calling process is executing on.SchedulerIdis a positive integer, where1 <= SchedulerId <= erlang:system_info(schedulers).See also
erlang:system_info(schedulers).schedulers- Returns the number of scheduler threads used by the emulator. Scheduler threads online schedules Erlang processes and Erlang ports, and execute Erlang code and Erlang linked-in driver code.The number of scheduler threads is determined at emulator boot time and cannot be changed later. However, the number of schedulers online can be changed at any time.
See also
erlang:system_flag(schedulers_online, SchedulersOnline),erlang:system_info(schedulers_online),erlang:system_info(scheduler_id),erlang:system_flag(multi_scheduling, BlockState),erlang:system_info(multi_scheduling),erlang:system_info(normal_multi_scheduling_blockers)anderlang:system_info(multi_scheduling_blockers).schedulers_online- Returns the number of schedulers online. The scheduler identifiers of schedulers online satisfy the relationship1 <= SchedulerId <= erlang:system_info(schedulers_online).For more information, see
erlang:system_info(schedulers)anderlang:system_flag(schedulers_online, SchedulersOnline).smp_support- Returnstrue.threads- Returnstrue.thread_pool_size- Returns the number of async threads in the async thread pool used for asynchronous driver calls (erl_driver:driver_async()). The value is given as an integer.
Distribution Information
Returns information about Erlang Distribution in the current system as specified by Item:
async_dist- Returns the value of the command line argument +pad <boolean> which the runtime system use. This value determines the defaultasync_distvalue for newly spawned processes.Since: OTP 25.3
creation- Returns the "creation" value of the local node as an integer. The creation is changed when a node is restarted. The creation of a node is stored in process identifiers, port identifiers, and references. This makes it possible to distinguish between identifiers from different incarnations of a node. Creation values are currently 32-bit positive integers, but this may change in future releases. If the node is not alive,0is returned.delayed_node_table_gc- Returns the amount of time in seconds garbage collection of an entry in a node table is delayed. This limit can be set on startup by passing command-line flag+zdntgctoerl(1). For more information, see the documentation of the command-line flag.Since: OTP 18.0
dist- Returns a binary containing a string of distribution information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.dist_buf_busy_limit- Returns the value of the distribution buffer busy limit in bytes. This limit can be set at startup by passing command-line flag+zdbbltoerl(1).Since: OTP R14B01
dist_ctrl- Returns a list of tuples{Node :: node(), ControllingEntity :: port() | pid()}, one entry for each connected remote node.Nodeis the node name andControllingEntityis the port or process identifier responsible for the communication to that node. More specifically,ControllingEntityfor nodes connected through TCP/IP (the normal case) is the socket used in communication with the specific node.
System Information
Returns various information about the current system (emulator) as specified by Item:
c_compiler_used- Returns a two-tuple describing the C compiler used when compiling the runtime system. The first element is an atom describing the name of the compiler, orundefinedif unknown. The second element is a term describing the version of the compiler, orundefinedif unknown.check_io- Returns a list containing miscellaneous information about the emulators internal I/O checking. Notice that the content of the returned list can vary between platforms and over time. It is only guaranteed that a list is returned.compat_rel- Returns the compatibility mode of the local node as an integer. The integer returned represents the Erlang/OTP release that the current emulator has been set to be backward compatible with. The compatibility mode can be configured at startup by using command-line flag+Rinerl(1).debug_compiled- Returnstrueif the emulator has been debug-compiled, otherwisefalse.driver_version- Returns a string containing the Erlang driver version used by the runtime system. It has the form "<major ver>.<minor ver>".dynamic_trace- Returns an atom describing the dynamic trace framework compiled into the virtual machine. It can bedtrace,systemtap, ornone. For a commercial or standard build, it is alwaysnone. The other return values indicate a custom configuration (for example,./configure --with-dynamic-trace=dtrace). For more information about dynamic tracing, seedyntrace(3)manual page and theREADME.dtrace/README.systemtapfiles in the Erlang source code top directory.Since: OTP R15B01
dynamic_trace_probes- Returns at:boolean()indicating if dynamic trace probes (dtraceorsystemtap) are built into the emulator. This can only betrueif the virtual machine was built for dynamic tracing (that is,system_info(dynamic_trace)returnsdtraceorsystemtap).Since: OTP R15B01
emu_flavor- Returns an atom describing the flavor of the runtime system. This will be eitheremuorjit. Possible return values can be added or removed at any time without prior notice.Since: OTP 24.0
emu_type- Returns an atom describing the build type of the runtime system. This is normally the atomoptfor optimized. Other possible return values aredebug,gcov,valgrind,gprof, andlcnt. Possible return values can be added or removed at any time without prior notice.Since: OTP 24.0
halt_flush_timeout- Returns the default halt flush timeout set by theerl+zhft <Timeout>command line flag.Since: OTP 27.0
info- Returns a binary containing a string of miscellaneous system information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.kernel_poll- Returnstrueif the emulator uses some kind of kernel-poll implementation, otherwisefalse.loaded- Returns a binary containing a string of loaded module information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.machine- Returns a string containing the Erlang machine name.modified_timing_level- Returns the modified timing-level (ant:integer()) if modified timing is enabled, otherwiseundefined. For more information about modified timing, see command-line flag+Tinerl(1)nif_version- Returns a string containing the version of the Erlang NIF interface used by the runtime system. It is on the form "<major ver>.<minor ver>".Since: OTP 17.4
otp_release- Returns a string containing the OTP release number of the OTP release that the currently executing ERTS application is part of.As from Erlang/OTP 17, the OTP release number corresponds to the major OTP version number. No
erlang:system_info()argument gives the exact OTP version. This is because the exact OTP version in the general case is difficult to determine. For more information, see the description of versions in System principles in System Documentation.outstanding_system_requests_limit- Returns the limit on the amount of outstanding requests made by a system process orchestrating system wide changes. Seeerlang:system_flag(outstanding_system_requests_limit, Limit)for more information.Since: OTP 24.2
port_parallelism- Returns the default port parallelism scheduling hint used. For more information, see command-line argument+sppinerl(1).Since: OTP R16B
system_architecture- Returns a string containing the processor and OS architecture the emulator is built for.system_logger- Returns the currentsystem_loggeras set byerlang:system_flag(system_logger, *).Since: OTP 21.3
system_version- Returns a string containing version number and some important properties, such as the number of schedulers.trace_control_word- Returns the value of the node trace control word. For more information, see functionget_tcwin section Match Specifications in Erlang in the User's Guide.version- Returns a string containing the version number of the emulator.wordsize- Same as{wordsize, internal}.{wordsize, internal}- Returns the size of Erlang term words in bytes as an integer, that is, 4 is returned on a 32-bit architecture, and 8 is returned on a 64-bit architecture.{wordsize, external}- Returns the true word size of the emulator, that is, the size of a pointer. The value is given in bytes as an integer. On a pure 32-bit architecture, 4 is returned. On a 64-bit architecture, 8 is returned.
-spec system_monitor() -> MonSettings when MonSettings :: undefined | {MonitorPid, Options}, MonitorPid :: pid(), Options :: [system_monitor_option()].
Returns the current system monitoring settings set by
erlang:system_monitor/2 as {MonitorPid, Options}, or
undefined if no settings exist.
The order of the options can be different from the one that was set.
-spec system_monitor(Arg) -> MonSettings when Arg :: undefined | {MonitorPid, Options}, MonSettings :: undefined | {MonitorPid, Options}, MonitorPid :: pid(), Options :: [system_monitor_option()].
When called with argument undefined, all system performance monitoring
settings are cleared.
Calling the function with {MonitorPid, Options} as argument is the same as
calling erlang:system_monitor(MonitorPid, Options).
Returns the previous system monitor settings just like
erlang:system_monitor/0.
-spec system_monitor(MonitorPid, Options) -> MonSettings when MonitorPid :: pid(), Options :: [system_monitor_option()], MonSettings :: undefined | {OldMonitorPid, OldOptions}, OldMonitorPid :: pid(), OldOptions :: [system_monitor_option()].
Sets the system performance monitoring options. MonitorPid is a local process
identifier (pid) receiving system monitor messages.
The second argument is a list of monitoring options:
{long_gc, Time}- If a garbage collection in the system takes at leastTimewall clock milliseconds, a message{monitor, GcPid, long_gc, Info}is sent toMonitorPid.GcPidis the pid that was garbage collected.Infois a list of two-element tuples describing the result of the garbage collection.One of the tuples is
{timeout, GcTime}, whereGcTimeis the time for the garbage collection in milliseconds. The other tuples are tagged withheap_size,heap_block_size,stack_size,mbuf_size,old_heap_size, andold_heap_block_size. These tuples are explained in the description of trace messagegc_minor_start(seetrace:process/4). New tuples can be added, and the order of the tuples in theInfolist can be changed at any time without prior notice.{long_message_queue, {Disable, Enable}}- If the message queue length of a process in the system reachEnablelength, along_message_queuemonitor message is sent to the process identified byMonitorPid. The monitor message will be on the form{monitor, Pid, long_message_queue, Long}, wherePidis the process identifier of the process that got a long message queue andLongwill equaltrueindicating that it is in a long message queue state. No morelong_message_queuemonitor messages will be sent due to the process identified byPiduntil its message queue length falls down to a length ofDisablelength. When this happens, along_message_queuemonitor message withLongequal tofalsewill be sent to the process identified byMonitorPidindicating that the process is no longer in a long message queue state. As of this, if the message queue length should again reachEnablelength, a newlong_message_queuemonitor message withLongset totruewill again be sent. That is, along_message_queuemonitor message is sent when a process enters or leaves a long message queue state where these state changes are defined by theEnableandDisableparameters.Enablelength must be an integer larger than zero andDisablelength must be an integer larger than or equal to zero.Disablelength must also be smaller thanEnablelength. If the above is not satisfied the operation will fail with abadargerror exception. You are recommended to use a much smaller value forDisablelength thanEnablelength in order not to be flooded withlong_message_queuemonitor messages.{long_schedule, Time}- If a process or port in the system runs uninterrupted for at leastTimewall clock milliseconds, a message{monitor, PidOrPort, long_schedule, Info}is sent toMonitorPid.PidOrPortis the process or port that was running.Infois a list of two-element tuples describing the event.If a
pid/0, the tuples{timeout, Millis},{in, Location}, and{out, Location}are present, whereLocationis either an MFA ({Module, Function, Arity}) describing the function where the process was scheduled in/out, or the atomundefined.If a
port/0, the tuples{timeout, Millis}and{port_op,Op}are present.Opis one ofproc_sig,timeout,input,output,event, ordist_cmd, depending on which driver callback was executing.proc_sigis an internal operation and is never to appear, while the others represent the corresponding driver callbackstimeout,ready_input,ready_output,event, andoutputv(when the port is used by distribution). ValueMillisin tupletimeoutinforms about the uninterrupted execution time of the process or port, which always is equal to or higher than theTimevalue supplied when starting the trace. New tuples can be added to theInfolist in a future release. The order of the tuples in the list can be changed at any time without prior notice.This can be used to detect problems with NIFs or drivers that take too long to execute. 1 ms is considered a good maximum time for a driver callback or a NIF. However, a time-sharing system is usually to consider everything < 100 ms as "possible" and fairly "normal". However, longer schedule times can indicate swapping or a misbehaving NIF/driver. Misbehaving NIFs and drivers can cause bad resource utilization and bad overall system performance.
{large_heap, Size}- If a garbage collection in the system results in the allocated size of a heap being at leastSizewords, a message{monitor, GcPid, large_heap, Info}is sent toMonitorPid.GcPidandInfoare the same as forlong_gcearlier, except that the tuple tagged withtimeoutis not present.The monitor message is sent if the sum of the sizes of all memory blocks allocated for all heap generations after a garbage collection is equal to or higher than
Size.When a process is killed by
max_heap_size, it is killed before the garbage collection is complete and thus no large heap message is sent.busy_port- If a process in the system gets suspended because it sends to a busy port, a message{monitor, SusPid, busy_port, Port}is sent toMonitorPid.SusPidis the pid that got suspended when sending toPort.busy_dist_port
If a process in the system gets suspended because it sends to a process on a remote node whose inter-node communication was handled by a busy port, a message{monitor, SusPid, busy_dist_port, Port}is sent toMonitorPid.SusPidis the pid that got suspended when sending through the inter-node communication portPort.
Returns the previous system monitor settings just like
erlang:system_monitor/0.
The arguments to system_monitor/2 specifies how all
system monitoring on the node should be done, not how it should be changed. This
means only one process at a time (MonitorPid) can be the receiver of system
monitor messages. Also, the way to clear a specific monitor option is to not
include it in the list Options. All system monitoring will, however, be
cleared if the process identified by MonitorPid terminates.
There are no special option values (like zero) to clear an option. Some of the
options have a unspecified minimum value. Lower values will be adjusted to the
minimum value. For example, it is currently not possible to monitor all garbage
collections with {long_gc, 0}.
Note
If a monitoring process gets so large that it itself starts to cause system monitor messages when garbage collecting, the messages enlarge the process message queue and probably make the problem worse.
Keep the monitoring process neat and do not set the system monitor limits too tight.
Failures:
badarg- IfMonitorPiddoes not exist.badarg- IfMonitorPidis not a local process.
-spec system_profile() -> ProfilerSettings when ProfilerSettings :: undefined | {ProfilerPid, Options}, ProfilerPid :: pid() | port(), Options :: [system_profile_option()].
Returns the current system profiling settings set by
erlang:system_profile/2 as {ProfilerPid, Options}, or
undefined if there are no settings. The order of the options can be different
from the one that was set.
-spec system_profile(ProfilerPid, Options) -> ProfilerSettings when ProfilerPid :: pid() | port() | undefined, Options :: [system_profile_option()], ProfilerSettings :: undefined | {pid() | port(), [system_profile_option()]}.
Sets system profiler options. ProfilerPid is a local process identifier (pid)
or port receiving profiling messages. The receiver is excluded from all
profiling. The second argument is a list of profiling options:
exclusive- If a synchronous call to a port from a process is done, the calling process is considered not runnable during the call runtime to the port. The calling process is notified asinactive, and lateractivewhen the port callback returns.monotonic_timestamp- Time stamps in profile messages use Erlang monotonic time. The time stamp (Ts) has the same format and value as produced byerlang:monotonic_time(nanosecond).runnable_procs- If a process is put into or removed from the run queue, a message,{profile, Pid, State, Mfa, Ts}, is sent toProfilerPid. Running processes that are reinserted into the run queue after having been pre-empted do not trigger this message.runnable_ports- If a port is put into or removed from the run queue, a message,{profile, Port, State, 0, Ts}, is sent toProfilerPid.scheduler- If a scheduler is put to sleep or awoken, a message,{profile, scheduler, Id, State, NoScheds, Ts}, is sent toProfilerPid.strict_monotonic_timestamp- Time stamps in profile messages consist of Erlang monotonic time and a monotonically increasing integer. The time stamp (Ts) has the same format and value as produced by{erlang:monotonic_time(nanosecond), erlang:unique_integer([monotonic])}.timestamp- Time stamps in profile messages include a time stamp (Ts) that has the same form as returned byerlang:now(). This is also the default if no time stamp flag is specified. Ifcpu_timestamphas been enabled throughtrace:process/4, this also effects the time stamp produced in profiling messages when flagtimestampis enabled.
Note
erlang:system_profile behavior can change in a future release.
Time and timers
-spec cancel_timer(TimerRef) -> Result when TimerRef :: reference(), Time :: non_neg_integer(), Result :: Time | false.
Equivalent to erlang:cancel_timer(TimerRef, []).
-spec cancel_timer(TimerRef, Options) -> Result | ok when TimerRef :: reference(), Async :: boolean(), Info :: boolean(), Option :: {async, Async} | {info, Info}, Options :: [Option], Time :: non_neg_integer(), Result :: Time | false.
Cancels a timer that has been created by erlang:start_timer
or erlang:send_after. TimerRef identifies the timer, and
was returned by the BIF that created the timer.
Options:
{async, Async}- Asynchronous request for cancellation.Asyncdefaults tofalse, which causes the cancellation to be performed synchronously. WhenAsyncis set totrue, the cancel operation is performed asynchronously. That is,cancel_timer()sends an asynchronous request for cancellation to the timer service that manages the timer, and then returnsok.{info, Info}- Requests information about theResultof the cancellation.Infodefaults totrue, which means theResultis given. WhenInfois set tofalse, no information about the result of the cancellation is given.- When
Asyncisfalse: ifInfoistrue, theResultis returned byerlang:cancel_timer(). otherwiseokis returned. - When
Asyncistrue: ifInfoistrue, a message on the form{cancel_timer, TimerRef, Result}is sent to the caller oferlang:cancel_timer()when the cancellation operation has been performed, otherwise no message is sent.
- When
More Options may be added in the future.
If Result is an integer, it represents the time in milliseconds left until the
canceled timer would have expired.
If Result is false, a timer corresponding to TimerRef could not be found.
This can be either because the timer had expired, already had been canceled, or
because TimerRef never corresponded to a timer. Even if the timer had expired,
it does not tell you if the time-out message has arrived at its destination yet.
Note
The timer service that manages the timer can be co-located with another
scheduler than the scheduler that the calling process is executing on. If so,
communication with the timer service takes much longer time than if it is
located locally. If the calling process is in critical path, and can do other
things while waiting for the result of this operation, or is not interested in
the result of the operation, you want to use option {async, true}. If using
option {async, false}, the calling process blocks until the operation has
been performed.
See also erlang:send_after/4,
erlang:start_timer/4, and
erlang:read_timer/2.
-spec convert_time_unit(Time, FromUnit, ToUnit) -> ConvertedTime when Time :: integer(), ConvertedTime :: integer(), FromUnit :: time_unit(), ToUnit :: time_unit().
Converts the Time value of time unit FromUnit to the corresponding
ConvertedTime value of time unit ToUnit. The result is rounded using the
floor/1 function.
Warning
You can lose accuracy and precision when converting between time units. To
minimize such loss, collect all data at native time unit and do the
conversion on the end result.
-spec date() -> Date when Date :: calendar:date().
Returns the current date as {Year, Month, Day}.
The time zone and Daylight Saving Time correction depend on the underlying OS. The return value is based on the OS System Time.
For example:
> date().
{1995,2,19}
-spec localtime() -> DateTime when DateTime :: calendar:datetime().
Returns the current local date and time,
{{Year, Month, Day}, {Hour, Minute, Second}}.
For example:
> erlang:localtime().
{{1996,11,6},{14,45,17}}The time zone and Daylight Saving Time correction depend on the underlying OS. The return value is based on the OS System Time.
-spec localtime_to_universaltime(Localtime) -> Universaltime when Localtime :: calendar:datetime(), Universaltime :: calendar:datetime().
Converts local date and time to Universal Time Coordinated (UTC), if supported
by the underlying OS. Otherwise no conversion is done and Localtime is
returned.
For example:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}Failure: badarg if Localtime denotes an invalid date and time.
-spec localtime_to_universaltime(Localtime, IsDst) -> Universaltime when Localtime :: calendar:datetime(), Universaltime :: calendar:datetime(), IsDst :: true | false | undefined.
Converts local date and time to Universal Time Coordinated (UTC) as
erlang:localtime_to_universaltime/1, but the caller decides if Daylight Saving
Time is active.
If IsDst == true, Localtime is during Daylight Saving Time, if
IsDst == false it is not. If IsDst == undefined, the underlying OS can
guess, which is the same as calling
erlang:localtime_to_universaltime(Localtime).
Examples:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
{{1996,11,6},{12,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
{{1996,11,6},{13,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
{{1996,11,6},{13,45,17}}Failure: badarg if Localtime denotes an invalid date and time.
-spec monotonic_time() -> integer().
Returns the current
Erlang monotonic time in native
time unit. This is a monotonically increasing time
since some unspecified point in time.
Note
This is a
monotonically increasing time,
but not a
strictly monotonically increasing
time. That is, consecutive calls to erlang:monotonic_time/0 can produce the
same result.
Different runtime system instances will use different unspecified points in
time as base for their Erlang monotonic clocks. That is, it is pointless
comparing monotonic times from different runtime system instances. Different
runtime system instances can also place this unspecified point in time
different relative runtime system start. It can be placed in the future (time
at start is a negative value), the past (time at start is a positive value),
or the runtime system start (time at start is zero). The monotonic time at
runtime system start can be retrieved by calling
erlang:system_info(start_time).
Returns the current
Erlang monotonic time converted into
the Unit passed as argument.
Same as calling
erlang:convert_time_unit( erlang:monotonic_time(), native, Unit),
however optimized for commonly used Units.
-spec read_timer(TimerRef) -> Result when TimerRef :: reference(), Time :: non_neg_integer(), Result :: Time | false.
Equivalent to erlang:read_timer(TimerRef, []).
-spec read_timer(TimerRef, Options) -> Result | ok when TimerRef :: reference(), Async :: boolean(), Option :: {async, Async}, Options :: [Option], Time :: non_neg_integer(), Result :: Time | false.
Reads the state of a timer that has been created by either
erlang:start_timer or
erlang:send_after. TimerRef identifies the timer, and was
returned by the BIF that created the timer.
Options:
{async, Async}- Asynchronous request for state information.Asyncdefaults tofalse, which causes the operation to be performed synchronously. In this case, theResultis returned byerlang:read_timer. WhenAsyncistrue,erlang:read_timersends an asynchronous request for the state information to the timer service that manages the timer, and then returnsok. A message on the format{read_timer, TimerRef, Result}is sent to the caller oferlang:read_timerwhen the operation has been processed.
More Options can be added in the future.
If Result is an integer, it represents the time in milliseconds left until the
timer expires.
If Result is false, a timer corresponding to TimerRef could not be found.
This because the timer had expired, or been canceled, or because TimerRef
never has corresponded to a timer. Even if the timer has expired, it does not
tell you whether or not the time-out message has arrived at its destination yet.
Note
The timer service that manages the timer can be co-located with another
scheduler than the scheduler that the calling process is executing on. If so,
communication with the timer service takes much longer time than if it is
located locally. If the calling process is in a critical path, and can do
other things while waiting for the result of this operation, you want to use
option {async, true}. If using option {async, false}, the calling process
is blocked until the operation has been performed.
See also erlang:send_after/4,
erlang:start_timer/4, and
erlang:cancel_timer/2.
-spec send_after(Time, Dest, Msg) -> TimerRef when Time :: non_neg_integer(), Dest :: pid() | atom(), Msg :: term(), TimerRef :: reference().
Equivalent to erlang:send_after(Time, Dest, Msg, []).
-spec send_after(Time, Dest, Msg, Options) -> TimerRef when Time :: integer(), Dest :: pid() | atom(), Msg :: term(), Options :: [Option], Abs :: boolean(), Option :: {abs, Abs}, TimerRef :: reference().
Starts a timer. When the timer expires, the message Msg is sent to the process
identified by Dest. Apart from the format of the time-out message, this
function works exactly as erlang:start_timer/4.
-spec start_timer(Time, Dest, Msg) -> TimerRef when Time :: non_neg_integer(), Dest :: pid() | atom(), Msg :: term(), TimerRef :: reference().
Equivalent to erlang:start_timer(Time, Dest, Msg, []).
-spec start_timer(Time, Dest, Msg, Options) -> TimerRef when Time :: integer(), Dest :: pid() | atom(), Msg :: term(), Options :: [Option], Abs :: boolean(), Option :: {abs, Abs}, TimerRef :: reference().
Starts a timer. When the timer expires, the message {timeout, TimerRef, Msg}
is sent to the process identified by Dest.
Options:
{abs, false}- This is the default. It means theTimevalue is interpreted as a time in milliseconds relative current Erlang monotonic time.{abs, true}- AbsoluteTimevalue. TheTimevalue is interpreted as an absolute Erlang monotonic time in milliseconds.
More Options can be added in the future.
The absolute point in time, the timer is set to expire on, must be in the
interval
[erlang:convert_time_unit(erlang:system_info(start_time), native, millisecond),erlang:convert_time_unit(erlang:system_info(end_time), native, millisecond) ].
If a relative time is specified, the Time value is not allowed to be negative.
If Dest is a pid/0, it must be a pid/0 of a process created on the
current runtime system instance. This process has either terminated or not. If
Dest is an atom/0, it is interpreted as the name of a locally registered
process. The process referred to by the name is looked up at the time of timer
expiration. No error is returned if the name does not refer to a process.
If Dest is a pid/0, the timer is automatically canceled if the process
referred to by the pid/0 is not alive, or if the process exits. This feature
was introduced in ERTS 5.4.11. Notice that timers are not automatically canceled
when Dest is an atom/0.
See also erlang:send_after/4,
erlang:cancel_timer/2, and
erlang:read_timer/2.
For more information on timers in Erlang in general, see the Timers section of the Time and Time Correction in Erlang ERTS User's guide.
Failure: badarg if the arguments do not satisfy the requirements specified
here.
-spec system_time() -> integer().
Returns current Erlang system time in
native time unit.
Calling erlang:system_time() is equivalent to
erlang:monotonic_time()+erlang:time_offset().
Note
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
Returns current Erlang system time
converted into the Unit passed as argument.
Calling erlang:system_time(Unit) is equivalent to
erlang:convert_time_unit(erlang:system_time(), native, Unit).
Note
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
-spec time() -> Time when Time :: calendar:time().
Returns the current time as {Hour, Minute, Second}.
The time zone and Daylight Saving Time correction depend on the underlying OS. The return value is based on the OS System Time.
For example:
> time().
{9,42,44}
-spec time_offset() -> integer().
Returns the current time offset between
Erlang monotonic time and
Erlang system time in native
time unit. Current time offset added to an Erlang
monotonic time gives corresponding Erlang system time.
The time offset may or may not change during operation depending on the time warp mode used.
Note
A change in time offset can be observed at slightly different points in time by different processes.
If the runtime system is in multi-time warp mode, the time offset is changed when the runtime system detects that the OS system time has changed. The runtime system will, however, not detect this immediately when it occurs. A task checking the time offset is scheduled to execute at least once a minute; so, under normal operation this is to be detected within a minute, but during heavy load it can take longer time.
Returns the current time offset between
Erlang monotonic time and
Erlang system time converted into the
Unit passed as argument.
Same as calling
erlang:convert_time_unit( erlang:time_offset(), native, Unit)
however optimized for commonly used Units.
-spec timestamp() -> Timestamp when Timestamp :: timestamp().
Returns current Erlang system time on
the format {MegaSecs, Secs, MicroSecs}.
This format is the same as os:timestamp/0 and the deprecated erlang:now/0 use.
The reason for the existence of erlang:timestamp() is purely to simplify use for existing
code that assumes this time stamp format. Current Erlang system time can more
efficiently be retrieved in the time unit of your choice using
erlang:system_time/1.
The erlang:timestamp() BIF is equivalent to:
timestamp() ->
ErlangSystemTime = erlang:system_time(microsecond),
MegaSecs = ErlangSystemTime div 1000_000_000_000,
Secs = ErlangSystemTime div 1000_000 - MegaSecs*1000_000,
MicroSecs = ErlangSystemTime rem 1000_000,
{MegaSecs, Secs, MicroSecs}.It, however, uses a native implementation that does not build garbage on the heap and with slightly better performance.
Note
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
-spec universaltime() -> DateTime when DateTime :: calendar:datetime().
Returns the current date and time according to Universal Time Coordinated (UTC)
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the
underlying OS. Otherwise erlang:universaltime() is equivalent to
erlang:localtime(). The return value is based on the
OS System Time.
For example:
> erlang:universaltime().
{{1996,11,6},{14,18,43}}
-spec universaltime_to_localtime(Universaltime) -> Localtime when Localtime :: calendar:datetime(), Universaltime :: calendar:datetime().
Converts Universal Time Coordinated (UTC) date and time to local date and time
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the
underlying OS. Otherwise no conversion is done, and Universaltime is returned.
For example:
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
{{1996,11,7},{15,18,43}}Failure: badarg if Universaltime denotes an invalid date and time.
Tracing
-spec trace(PidPortSpec, How, FlagList) -> integer() when PidPortSpec :: pid() | port() | all | processes | ports | existing | existing_processes | existing_ports | new | new_processes | new_ports, How :: boolean(), FlagList :: [trace_flag()].
Turn on or off trace flags on processes or ports for the static legacy trace session.
Change
This function is superseded by trace:process/4 and trace:port/4 that
operate on dynamic trace sessions.
Argument FlagList can contain two additional options:
{tracer, Tracer}- Specifies where to send the trace messages.Tracermust be the process identifier of a local process or the port identifier of a local port.{tracer, TracerModule, TracerState}- Specifies that a tracer module is to be called instead of sending a trace message. The tracer module can then ignore or change the trace message. For more details on how to write a tracer module, seeerl_tracer.
If no tracer is specified, the calling process receives all the trace
messages. The legacy trace session has no specified tracer.
For further documentation see trace:process/4 and trace:port/4.
Calling this function makes sure all trace messages have been delivered.
The delivery of trace messages (generated by erlang:trace/3,
seq_trace, or erlang:system_profile/2) is dislocated
on the time-line compared to other events in the system. If you know that
Tracee has passed some specific point in its execution, and you want to know
when at least all trace messages corresponding to events up to this point have
reached the tracer, use erlang:trace_delivered(Tracee).
When it is guaranteed that all trace messages are delivered to the tracer up to
the point that Tracee reached at the time of the call to
erlang:trace_delivered(Tracee), then a {trace_delivered, Tracee, Ref}
message is sent to the caller of erlang:trace_delivered(Tracee) .
Notice that message trace_delivered does not imply that trace messages have
been delivered. Instead it implies that all trace messages that are to be
delivered have been delivered. It is not an error if Tracee is not, and has
not been traced by someone, but if this is the case, no trace messages have
been delivered when the trace_delivered message arrives.
Notice that Tracee must refer to a process currently or previously existing on
the same node as the caller of erlang:trace_delivered(Tracee) resides on. The
special Tracee atom all denotes all processes that currently are traced in
the node.
When used together with a Tracer Module, any message sent in
the trace callback is guaranteed to have reached its recipient before the
trace_delivered message is sent.
Example: Process A is Tracee, port B is tracer, and process C is the
port owner of B. C wants to close B when A exits. To ensure that the
trace is not truncated, C can call erlang:trace_delivered(A) when A exits,
and wait for message {trace_delivered, A, Ref} before closing B.
Failure: badarg if Tracee does not refer to a process (dead or alive) on the
same node as the caller of erlang:trace_delivered(Tracee) resides on.
-spec trace_info(PidPortFuncEvent, Item) -> Res when PidPortFuncEvent :: pid() | port() | new | new_processes | new_ports | {Module, Function, Arity} | on_load | send | 'receive', Module :: module(), Function :: atom(), Arity :: arity(), Item :: flags | tracer | traced | match_spec | meta | meta_match_spec | call_count | call_time | call_memory | all, Res :: trace_info_return().
Returns trace information about a port, process, function, or event for the static legacy trace session.
Change
This function is superseded by trace:info/3 that operates on dynamic trace
sessions.
-spec trace_pattern(MFA, MatchSpec) -> non_neg_integer() when MFA :: trace_pattern_mfa() | send | 'receive', MatchSpec :: (MatchSpecList :: trace_match_spec()) | boolean() | restart | pause.
Equivalent to erlang:trace_pattern(Event, MatchSpec, []),
retained for backward compatibility.
-spec trace_pattern(send, MatchSpec, []) -> non_neg_integer() when MatchSpec :: (MatchSpecList :: trace_match_spec()) | boolean(); ('receive', MatchSpec, []) -> non_neg_integer() when MatchSpec :: (MatchSpecList :: trace_match_spec()) | boolean(); (MFA, MatchSpec, FlagList) -> non_neg_integer() when MFA :: trace_pattern_mfa(), MatchSpec :: (MatchSpecList :: trace_match_spec()) | boolean() | restart | pause, FlagList :: [trace_pattern_flag()].
Set trace pattern for call, send and receive tracing on the static legacy trace session.
Change
This function is superseded by trace:function/4, trace:send/3 and
trace:recv/3 that operate on dynamic trace sessions.
Argument FlagList can contain two additional options for call tracing:
{meta, Pid} | {meta, TracerModule, TracerState}- Turns on or off meta-tracing for all types of function calls. Trace messages are sent to the tracer whenever any of the specified functions are called. If no tracer is specified,self/0is used as a default tracer process.
For further documentation see trace:function/4 , trace:send/3 and
trace:recv/3.
Deprecated functions
-spec now() -> Timestamp when Timestamp :: timestamp().
Warning
This function is deprecated. Do not use it.
For more information, see section
Time and Time Correction in the User's Guide.
Specifically, section Dos and Dont's
describes what to use instead of erlang:now/0.
Returns the tuple {MegaSecs, Secs, MicroSecs}, which is the elapsed time since
00:00 GMT, January 1, 1970 (zero hour), if provided by the underlying OS.
Otherwise some other point in time is chosen. It is also guaranteed that the
following calls to this BIF return continuously increasing values. Hence, the
return value from erlang:now/0 can be used to generate unique time stamps. If
it is called in a tight loop on a fast machine, the time of the node can become
skewed.
Can only be used to check the local time of day if the time-zone information of the underlying OS is properly configured.
-spec phash(Term, Range) -> Hash when Term :: term(), Range :: pos_integer(), Hash :: pos_integer().
Warning
This function is deprecated as erlang:phash2/2 should be used
for new code. Note that erlang:phash(X,N) is not necessary equal to
erlang:phash2(X,N)
Portable hash function that gives the same hash for the same Erlang term
regardless of machine architecture and ERTS version (the BIF was introduced in
ERTS 4.9.1.1). The function returns a hash value for Term within the range
1..Range. The maximum value for Range is 2^32.