/*
* Copyright 2010 the original author or 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 org.gradle.messaging.dispatch;
import org.gradle.messaging.concurrent.AsyncStoppable;
import org.gradle.util.UncheckedException;
import java.util.LinkedList;
import java.util.concurrent.Executor;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* <p>A {@link org.gradle.messaging.dispatch.Dispatch} implementation which delivers messages asynchronously. Calls to
* {@link #dispatch} queue the message. Worker threads delivers the messages in the order they have been received to one
* of a pool of delegate {@link org.gradle.messaging.dispatch.Dispatch} instances.</p>
*
* <p>One or more {@link org.gradle.messaging.dispatch.Receive} instances can use used as a source of messages.</p>
*/
public class AsyncDispatch<T> implements StoppableDispatch<T>, AsyncStoppable {
private enum State {
Init, Stopped
}
private static final int MAX_QUEUE_SIZE = 200;
private final Lock lock = new ReentrantLock();
private final Condition condition = lock.newCondition();
private final LinkedList<T> queue = new LinkedList<T>();
private final Executor executor;
private final int maxQueueSize;
private int dispatchers;
private State state;
public AsyncDispatch(Executor executor) {
this(executor, null, MAX_QUEUE_SIZE);
}
public AsyncDispatch(Executor executor, final Dispatch<? super T> dispatch) {
this(executor, dispatch, MAX_QUEUE_SIZE);
}
public AsyncDispatch(Executor executor, final Dispatch<? super T> dispatch, int maxQueueSize) {
this.executor = executor;
this.maxQueueSize = maxQueueSize;
state = State.Init;
if (dispatch != null) {
dispatchTo(dispatch);
}
}
public void dispatchTo(final Dispatch<? super T> dispatch) {
onDispatchThreadStart();
executor.execute(new Runnable() {
public void run() {
try {
dispatchMessages(dispatch);
} finally {
onDispatchThreadExit();
}
}
});
}
private void onDispatchThreadStart() {
lock.lock();
try {
if (state != State.Init) {
throw new IllegalStateException("This dispatch has been stopped.");
}
dispatchers++;
} finally {
lock.unlock();
}
}
private void onDispatchThreadExit() {
lock.lock();
try {
dispatchers--;
condition.signalAll();
} finally {
lock.unlock();
}
}
private void setState(State state) {
this.state = state;
condition.signalAll();
}
private void dispatchMessages(Dispatch<? super T> dispatch) {
while (true) {
T message = null;
lock.lock();
try {
while (state != State.Stopped && queue.isEmpty()) {
try {
condition.await();
} catch (InterruptedException e) {
throw new UncheckedException(e);
}
}
if (!queue.isEmpty()) {
message = queue.remove();
condition.signalAll();
}
} finally {
lock.unlock();
}
if (message == null) {
// Have been stopped and nothing to deliver
return;
}
dispatch.dispatch(message);
}
}
public void dispatch(final T message) {
lock.lock();
try {
while (state != State.Stopped && queue.size() >= maxQueueSize) {
try {
condition.await();
} catch (InterruptedException e) {
throw new UncheckedException(e);
}
}
if (state == State.Stopped) {
throw new IllegalStateException("This message dispatch has been stopped.");
}
queue.add(message);
condition.signalAll();
} finally {
lock.unlock();
}
}
/**
* Commences a shutdown of this dispatch.
*/
public void requestStop() {
lock.lock();
try {
doRequestStop();
} finally {
lock.unlock();
}
}
private void doRequestStop() {
setState(State.Stopped);
}
public void stop() {
lock.lock();
try {
setState(State.Stopped);
while (dispatchers > 0) {
condition.await();
}
if (!queue.isEmpty()) {
throw new IllegalStateException(
"Cannot wait for messages to be dispatched, as there are no dispatch threads running.");
}
} catch (InterruptedException e) {
throw new UncheckedException(e);
} finally {
lock.unlock();
}
}
}