001 /*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.eventbus;
018
019 import com.google.common.annotations.Beta;
020
021 import java.util.concurrent.ConcurrentLinkedQueue;
022 import java.util.concurrent.Executor;
023
024 /**
025 * An {@link EventBus} that takes the Executor of your choice and uses it to
026 * dispatch events, allowing dispatch to occur asynchronously.
027 *
028 * @author Cliff Biffle
029 * @since 10.0
030 */
031 @Beta
032 public class AsyncEventBus extends EventBus {
033 private final Executor executor;
034
035 /** the queue of events is shared across all threads */
036 private final ConcurrentLinkedQueue<EventWithHandler> eventsToDispatch =
037 new ConcurrentLinkedQueue<EventWithHandler>();
038
039 /**
040 * Creates a new AsyncEventBus that will use {@code executor} to dispatch
041 * events. Assigns {@code identifier} as the bus's name for logging purposes.
042 *
043 * @param identifier short name for the bus, for logging purposes.
044 * @param executor Executor to use to dispatch events. It is the caller's
045 * responsibility to shut down the executor after the last event has
046 * been posted to this event bus.
047 */
048 public AsyncEventBus(String identifier, Executor executor) {
049 super(identifier);
050 this.executor = executor;
051 }
052
053 /**
054 * Creates a new AsyncEventBus that will use {@code executor} to dispatch
055 * events.
056 *
057 * @param executor Executor to use to dispatch events. It is the caller's
058 * responsibility to shut down the executor after the last event has
059 * been posted to this event bus.
060 */
061 public AsyncEventBus(Executor executor) {
062 this.executor = executor;
063 }
064
065 @Override
066 void enqueueEvent(Object event, EventHandler handler) {
067 eventsToDispatch.offer(new EventWithHandler(event, handler));
068 }
069
070 /**
071 * Dispatch {@code events} in the order they were posted, regardless of
072 * the posting thread.
073 */
074 @SuppressWarnings("deprecation") // only deprecated for external subclasses
075 @Override
076 protected void dispatchQueuedEvents() {
077 while (true) {
078 EventWithHandler eventWithHandler = eventsToDispatch.poll();
079 if (eventWithHandler == null) {
080 break;
081 }
082
083 dispatch(eventWithHandler.event, eventWithHandler.handler);
084 }
085 }
086
087 /**
088 * Calls the {@link #executor} to dispatch {@code event} to {@code handler}.
089 */
090 @Override
091 void dispatch(final Object event, final EventHandler handler) {
092 executor.execute(new Runnable() {
093 @Override
094 @SuppressWarnings("synthetic-access")
095 public void run() {
096 AsyncEventBus.super.dispatch(event, handler);
097 }
098 });
099 }
100
101 }