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Utility classes for Jetty
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//
//  ========================================================================
//  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.util.thread;

import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

import org.eclipse.jetty.util.component.AbstractLifeCycle;

/**
 * Implementation of {@link Scheduler} based on JDK's {@link ScheduledThreadPoolExecutor}.
 * 
 * While use of {@link ScheduledThreadPoolExecutor} creates futures that will not be used,
 * it has the advantage of allowing to set a property to remove cancelled tasks from its
 * queue even if the task did not fire, which provides a huge benefit in the performance
 * of garbage collection in young generation.
 */
public class ScheduledExecutorScheduler extends AbstractLifeCycle implements Scheduler
{
    private final String name;
    private final boolean daemon;
    private volatile ScheduledThreadPoolExecutor scheduler;

    public ScheduledExecutorScheduler()
    {
        this(null, false);
    }

    public ScheduledExecutorScheduler(String name, boolean daemon)
    {
        this.name = name == null ? "Scheduler-" + hashCode() : name;
        this.daemon = daemon;
    }

    @Override
    protected void doStart() throws Exception
    {
        scheduler = new ScheduledThreadPoolExecutor(1, new ThreadFactory()
        {
            @Override
            public Thread newThread(Runnable r)
            {
                Thread thread = new Thread(r, name);
                thread.setDaemon(daemon);
                return thread;
            }
        });
        scheduler.setRemoveOnCancelPolicy(true);
        super.doStart();
    }

    @Override
    protected void doStop() throws Exception
    {
        scheduler.shutdownNow();
        super.doStop();
        scheduler = null;
    }

    @Override
    public Task schedule(Runnable task, long delay, TimeUnit unit)
    {
        ScheduledFuture result = scheduler.schedule(task, delay, unit);
        return new ScheduledFutureTask(result);
    }

    private class ScheduledFutureTask implements Task
    {
        private final ScheduledFuture scheduledFuture;

        public ScheduledFutureTask(ScheduledFuture scheduledFuture)
        {
            this.scheduledFuture = scheduledFuture;
        }

        @Override
        public boolean cancel()
        {
            return scheduledFuture.cancel(false);
        }
    }
}