/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.eventbus;
import com.google.common.annotations.Beta;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executor;
/**
* An {@link EventBus} that takes the Executor of your choice and uses it to
* dispatch events, allowing dispatch to occur asynchronously.
*
* @author Cliff Biffle
* @since 10.0
*/
@Beta
public class AsyncEventBus extends EventBus {
private final Executor executor;
/** the queue of events is shared across all threads */
private final ConcurrentLinkedQueue<EventWithHandler> eventsToDispatch =
new ConcurrentLinkedQueue<EventWithHandler>();
/**
* Creates a new AsyncEventBus that will use {@code executor} to dispatch
* events. Assigns {@code identifier} as the bus's name for logging purposes.
*
* @param identifier short name for the bus, for logging purposes.
* @param executor Executor to use to dispatch events. It is the caller's
* responsibility to shut down the executor after the last event has
* been posted to this event bus.
*/
public AsyncEventBus(String identifier, Executor executor) {
super(identifier);
this.executor = executor;
}
/**
* Creates a new AsyncEventBus that will use {@code executor} to dispatch
* events.
*
* @param executor Executor to use to dispatch events. It is the caller's
* responsibility to shut down the executor after the last event has
* been posted to this event bus.
*/
public AsyncEventBus(Executor executor) {
this.executor = executor;
}
@Override
protected void enqueueEvent(Object event, EventHandler handler) {
eventsToDispatch.offer(new EventWithHandler(event, handler));
}
/**
* Dispatch {@code events} in the order they were posted, regardless of
* the posting thread.
*/
@Override
protected void dispatchQueuedEvents() {
while (true) {
EventWithHandler eventWithHandler = eventsToDispatch.poll();
if (eventWithHandler == null) {
break;
}
dispatch(eventWithHandler.event, eventWithHandler.handler);
}
}
/**
* Calls the {@link #executor} to dispatch {@code event} to {@code handler}.
*/
@Override
protected void dispatch(final Object event, final EventHandler handler) {
executor.execute(new Runnable() {
@Override
@SuppressWarnings("synthetic-access")
public void run() {
AsyncEventBus.super.dispatch(event, handler);
}
});
}
}
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