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/*
* Copyright 2006 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* 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.amazon.carbonado.util;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;
/**
* Simple generic queue for running tasks from a single thread. Be sure to call
* shutdown or interrupt when done using the thread, or else it will never exit.
*
* @author Brian S O'Neill
*/
public class TaskQueueThread extends Thread implements Executor {
private static final int
STATE_NOT_STARTED = 0,
STATE_RUNNING = 1,
STATE_SHOULD_STOP = 2,
STATE_STOPPED = 3;
private static final Runnable STOP_TASK = new Runnable() {public void run() {}};
private final BlockingQueue<Runnable> mQueue;
private final long mTimeoutMillis;
private int mState = STATE_NOT_STARTED;
/**
* @param name name to give this thread
* @param queueSize fixed size of queue
*/
public TaskQueueThread(String name, int queueSize) {
this(name, queueSize, 0);
}
/**
* @param name name to give this thread
* @param queueSize fixed size of queue
* @param timeoutMillis default maximum time to wait for queue to have an available slot
*/
public TaskQueueThread(String name, int queueSize, long timeoutMillis) {
super(name);
mQueue = new ArrayBlockingQueue<Runnable>(queueSize, true);
mTimeoutMillis = timeoutMillis;
}
/**
* Enqueue a task to run.
*
* @param task task to enqueue
* @throws RejectedExecutionException if wait interrupted, timeout expires,
* or shutdown has been called
*/
public void execute(Runnable task) throws RejectedExecutionException {
execute(task, mTimeoutMillis);
}
/**
* Enqueue a task to run.
*
* @param task task to enqueue
* @param timeoutMillis maximum time to wait for queue to have an available slot
* @throws RejectedExecutionException if wait interrupted, timeout expires,
* or shutdown has been called
*/
public void execute(Runnable task, long timeoutMillis) throws RejectedExecutionException {
if (task == null) {
throw new NullPointerException("Cannot accept null task");
}
synchronized (this) {
if (mState != STATE_RUNNING && mState != STATE_NOT_STARTED) {
throw new RejectedExecutionException("Task queue is shutdown");
}
}
try {
if (!mQueue.offer(task, timeoutMillis, TimeUnit.MILLISECONDS)) {
throw new RejectedExecutionException("Unable to enqueue task after waiting " +
timeoutMillis + " milliseconds");
}
} catch (InterruptedException e) {
throw new RejectedExecutionException(e);
}
}
/**
* Indicate that this task queue thread should finish running its enqueued
* tasks and then exit. Enqueueing new tasks will result in a
* RejectedExecutionException being thrown. Join on this thread to wait for
* it to exit.
*/
public synchronized void shutdown() {
if (mState == STATE_STOPPED) {
return;
}
if (mState == STATE_NOT_STARTED) {
mState = STATE_STOPPED;
return;
}
mState = STATE_SHOULD_STOP;
// Inject stop task into the queue so it knows to stop, in case we're blocked.
mQueue.offer(STOP_TASK);
}
@Override
public void run() {
synchronized (this) {
if (mState == STATE_SHOULD_STOP || mState == STATE_STOPPED) {
return;
}
if (mState == STATE_RUNNING) {
throw new IllegalStateException("Already running");
}
mState = STATE_RUNNING;
}
try {
while (true) {
boolean isStopping;
synchronized (this) {
isStopping = mState != STATE_RUNNING;
}
Runnable task;
if (isStopping) {
// Poll the queue so this thread doesn't block when it
// should be stopping.
task = mQueue.poll();
} else {
try {
task = mQueue.take();
} catch (InterruptedException e) {
break;
}
}
if (task == null || task == STOP_TASK) {
// Marker to indicate we should stop.
break;
}
try {
task.run();
} catch (ThreadDeath e) {
throw e;
} catch (Throwable e) {
try {
Thread t = Thread.currentThread();
t.getUncaughtExceptionHandler().uncaughtException(t, e);
} catch (Throwable e2) {
// If there is an exception reporting the exception, throw the original.
org.cojen.util.ThrowUnchecked.fire(e);
}
}
}
} finally {
synchronized (this) {
mState = STATE_STOPPED;
}
}
}
}
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