/*
* Copyright 2012 The Netty Project
*
* The Netty Project licenses this file to you 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 io.netty.util.concurrent;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* Single-thread singleton {@link EventExecutor}. It starts the thread automatically and stops it when there is no
* task pending in the task queue for 1 second. Please note it is not scalable to schedule large number of tasks to
* this executor; use a dedicated executor.
*/
public final class GlobalEventExecutor extends AbstractScheduledEventExecutor {
private static final InternalLogger logger = InternalLoggerFactory.getInstance(GlobalEventExecutor.class);
private static final long SCHEDULE_PURGE_INTERVAL = TimeUnit.SECONDS.toNanos(1);
public static final GlobalEventExecutor INSTANCE = new GlobalEventExecutor();
final BlockingQueue<Runnable> taskQueue = new LinkedBlockingQueue<Runnable>();
final ScheduledFutureTask<Void> purgeTask = new ScheduledFutureTask<Void>(
this, Executors.<Void>callable(new PurgeTask(), null),
ScheduledFutureTask.deadlineNanos(SCHEDULE_PURGE_INTERVAL), -SCHEDULE_PURGE_INTERVAL);
private final ThreadFactory threadFactory = new DefaultThreadFactory(getClass());
private final TaskRunner taskRunner = new TaskRunner();
private final AtomicBoolean started = new AtomicBoolean();
volatile Thread thread;
private final Future<?> terminationFuture = new FailedFuture<Object>(this, new UnsupportedOperationException());
private GlobalEventExecutor() {
scheduledTaskQueue().add(purgeTask);
}
@Override
public EventExecutorGroup parent() {
return null;
}
/**
* Take the next {@link Runnable} from the task queue and so will block if no task is currently present.
*
* @return {@code null} if the executor thread has been interrupted or waken up.
*/
Runnable takeTask() {
BlockingQueue<Runnable> taskQueue = this.taskQueue;
for (;;) {
ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
if (scheduledTask == null) {
Runnable task = null;
try {
task = taskQueue.take();
} catch (InterruptedException e) {
// Ignore
}
return task;
} else {
long delayNanos = scheduledTask.delayNanos();
Runnable task;
if (delayNanos > 0) {
try {
task = taskQueue.poll(delayNanos, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
return null;
}
} else {
task = taskQueue.poll();
}
if (task == null) {
fetchFromScheduledTaskQueue();
task = taskQueue.poll();
}
if (task != null) {
return task;
}
}
}
}
private void fetchFromScheduledTaskQueue() {
if (hasScheduledTasks()) {
long nanoTime = AbstractScheduledEventExecutor.nanoTime();
for (;;) {
Runnable scheduledTask = pollScheduledTask(nanoTime);
if (scheduledTask == null) {
break;
}
taskQueue.add(scheduledTask);
}
}
}
/**
* Return the number of tasks that are pending for processing.
*
* <strong>Be aware that this operation may be expensive as it depends on the internal implementation of the
* SingleThreadEventExecutor. So use it was care!</strong>
*/
public int pendingTasks() {
return taskQueue.size();
}
/**
* Add a task to the task queue, or throws a {@link RejectedExecutionException} if this instance was shutdown
* before.
*/
private void addTask(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
taskQueue.add(task);
}
@Override
public boolean inEventLoop(Thread thread) {
return thread == this.thread;
}
@Override
public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
return terminationFuture();
}
@Override
public Future<?> terminationFuture() {
return terminationFuture;
}
@Override
@Deprecated
public void shutdown() {
throw new UnsupportedOperationException();
}
@Override
public boolean isShuttingDown() {
return false;
}
@Override
public boolean isShutdown() {
return false;
}
@Override
public boolean isTerminated() {
return false;
}
@Override
public boolean awaitTermination(long timeout, TimeUnit unit) {
return false;
}
/**
* Waits until the worker thread of this executor has no tasks left in its task queue and terminates itself.
* Because a new worker thread will be started again when a new task is submitted, this operation is only useful
* when you want to ensure that the worker thread is terminated <strong>after</strong> your application is shut
* down and there's no chance of submitting a new task afterwards.
*
* @return {@code true} if and only if the worker thread has been terminated
*/
public boolean awaitInactivity(long timeout, TimeUnit unit) throws InterruptedException {
if (unit == null) {
throw new NullPointerException("unit");
}
final Thread thread = this.thread;
if (thread == null) {
throw new IllegalStateException("thread was not started");
}
thread.join(unit.toMillis(timeout));
return !thread.isAlive();
}
@Override
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
addTask(task);
if (!inEventLoop()) {
startThread();
}
}
private void startThread() {
if (started.compareAndSet(false, true)) {
Thread t = threadFactory.newThread(taskRunner);
t.start();
thread = t;
}
}
final class TaskRunner implements Runnable {
@Override
public void run() {
for (;;) {
Runnable task = takeTask();
if (task != null) {
try {
task.run();
} catch (Throwable t) {
logger.warn("Unexpected exception from the global event executor: ", t);
}
if (task != purgeTask) {
continue;
}
}
Queue<ScheduledFutureTask<?>> scheduledTaskQueue = GlobalEventExecutor.this.scheduledTaskQueue;
// Terminate if there is no task in the queue (except the purge task).
if (taskQueue.isEmpty() && (scheduledTaskQueue == null || scheduledTaskQueue.size() == 1)) {
// Mark the current thread as stopped.
// The following CAS must always success and must be uncontended,
// because only one thread should be running at the same time.
boolean stopped = started.compareAndSet(true, false);
assert stopped;
// Check if there are pending entries added by execute() or schedule*() while we do CAS above.
if (taskQueue.isEmpty() && (scheduledTaskQueue == null || scheduledTaskQueue.size() == 1)) {
// A) No new task was added and thus there's nothing to handle
// -> safe to terminate because there's nothing left to do
// B) A new thread started and handled all the new tasks.
// -> safe to terminate the new thread will take care the rest
break;
}
// There are pending tasks added again.
if (!started.compareAndSet(false, true)) {
// startThread() started a new thread and set 'started' to true.
// -> terminate this thread so that the new thread reads from taskQueue exclusively.
break;
}
// New tasks were added, but this worker was faster to set 'started' to true.
// i.e. a new worker thread was not started by startThread().
// -> keep this thread alive to handle the newly added entries.
}
}
}
}
private final class PurgeTask implements Runnable {
@Override
public void run() {
purgeCancelledScheduledTasks();
}
}
}