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    • io.netty.util.concurrent.GlobalEventExecutor Maven / Gradle / Ivy

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    This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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    /*
 * 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:
 *
 *   https://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.ObjectUtil;
import io.netty.util.internal.SystemPropertyUtil;
import io.netty.util.internal.ThreadExecutorMap;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import org.jetbrains.annotations.Async.Schedule;

import java.security.AccessController;
import java.security.PrivilegedAction;
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 {@code io.netty.globalEventExecutor.quietPeriodSeconds} second
 * (default is 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 implements OrderedEventExecutor {
    private static final InternalLogger logger = InternalLoggerFactory.getInstance(GlobalEventExecutor.class);

    private static final long SCHEDULE_QUIET_PERIOD_INTERVAL;

    static {
        int quietPeriod = SystemPropertyUtil.getInt("io.netty.globalEventExecutor.quietPeriodSeconds", 1);
        if (quietPeriod <= 0) {
            quietPeriod = 1;
        }
        logger.debug("-Dio.netty.globalEventExecutor.quietPeriodSeconds: {}", quietPeriod);

        SCHEDULE_QUIET_PERIOD_INTERVAL = TimeUnit.SECONDS.toNanos(quietPeriod);
    }

    public static final GlobalEventExecutor INSTANCE = new GlobalEventExecutor();

    final BlockingQueue taskQueue = new LinkedBlockingQueue();
    final ScheduledFutureTask quietPeriodTask = new ScheduledFutureTask(
            this, Executors.callable(new Runnable() {
        @Override
        public void run() {
            // NOOP
        }
    }, null),
            // note: the getCurrentTimeNanos() call here only works because this is a final class, otherwise the method
            // could be overridden leading to unsafe initialization here!
            deadlineNanos(getCurrentTimeNanos(), SCHEDULE_QUIET_PERIOD_INTERVAL),
            -SCHEDULE_QUIET_PERIOD_INTERVAL
    );

    // because the GlobalEventExecutor is a singleton, tasks submitted to it can come from arbitrary threads and this
    // can trigger the creation of a thread from arbitrary thread groups; for this reason, the thread factory must not
    // be sticky about its thread group
    // visible for testing
    final ThreadFactory threadFactory;
    private final TaskRunner taskRunner = new TaskRunner();
    private final AtomicBoolean started = new AtomicBoolean();
    volatile Thread thread;

    private final Future terminationFuture = new FailedFuture(this, new UnsupportedOperationException());

    private GlobalEventExecutor() {
        scheduledTaskQueue().add(quietPeriodTask);
        threadFactory = ThreadExecutorMap.apply(new DefaultThreadFactory(
                DefaultThreadFactory.toPoolName(getClass()), false, Thread.NORM_PRIORITY, null), this);
    }

    /**
     * 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 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 = null;
                if (delayNanos > 0) {
                    try {
                        task = taskQueue.poll(delayNanos, TimeUnit.NANOSECONDS);
                    } catch (InterruptedException e) {
                        // Waken up.
                        return null;
                    }
                }
                if (task == null) {
                    // We need to fetch the scheduled tasks now as otherwise there may be a chance that
                    // scheduled tasks are never executed if there is always one task in the taskQueue.
                    // This is for example true for the read task of OIO Transport
                    // See https://github.com/netty/netty/issues/1614
                    fetchFromScheduledTaskQueue();
                    task = taskQueue.poll();
                }

                if (task != null) {
                    return task;
                }
            }
        }
    }

    private void fetchFromScheduledTaskQueue() {
        long nanoTime = getCurrentTimeNanos();
        Runnable scheduledTask = pollScheduledTask(nanoTime);
        while (scheduledTask != null) {
            taskQueue.add(scheduledTask);
            scheduledTask = pollScheduledTask(nanoTime);
        }
    }

    /**
     * Return the number of tasks that are pending for processing.
     */
    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) {
        taskQueue.add(ObjectUtil.checkNotNull(task, "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 after 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 {
        ObjectUtil.checkNotNull(unit, "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) {
        execute0(task);
    }

    private void execute0(@Schedule Runnable task) {
        addTask(ObjectUtil.checkNotNull(task, "task"));
        if (!inEventLoop()) {
            startThread();
        }
    }

    private void startThread() {
        if (started.compareAndSet(false, true)) {
            final Thread t = threadFactory.newThread(taskRunner);
            // Set to null to ensure we not create classloader leaks by holds a strong reference to the inherited
            // classloader.
            // See:
            // - https://github.com/netty/netty/issues/7290
            // - https://bugs.openjdk.java.net/browse/JDK-7008595
            AccessController.doPrivileged(new PrivilegedAction() {
                @Override
                public Void run() {
                    t.setContextClassLoader(null);
                    return null;
                }
            });

            // Set the thread before starting it as otherwise inEventLoop() may return false and so produce
            // an assert error.
            // See https://github.com/netty/netty/issues/4357
            thread = t;
            t.start();
        }
    }

    final class TaskRunner implements Runnable {
        @Override
        public void run() {
            for (;;) {
                Runnable task = takeTask();
                if (task != null) {
                    try {
                        runTask(task);
                    } catch (Throwable t) {
                        logger.warn("Unexpected exception from the global event executor: ", t);
                    }

                    if (task != quietPeriodTask) {
                        continue;
                    }
                }

                Queue> scheduledTaskQueue = GlobalEventExecutor.this.scheduledTaskQueue;
                // Terminate if there is no task in the queue (except the noop 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.
                    // Do not check scheduledTaskQueue because it is not thread-safe and can only be mutated from a
                    // TaskRunner actively running tasks.
                    if (taskQueue.isEmpty()) {
                        // 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.
                }
            }
        }
    }
}
    
    
    
    

    




    
    
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