TimerScheduler.java

//
//  ========================================================================
//  Copyright (c) 1995-2017 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.Timer;
import java.util.TimerTask;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;

import org.eclipse.jetty.util.component.AbstractLifeCycle;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;


/* ------------------------------------------------------------ */
/** A scheduler based on the the JVM Timer class
 */
public class TimerScheduler extends AbstractLifeCycle implements Scheduler, Runnable
{
    private static final Logger LOG = Log.getLogger(TimerScheduler.class);

    /*
     * This class uses the Timer class rather than an ScheduledExecutionService because
     * it uses the same algorithm internally and the signature is cheaper to use as there are no
     * Futures involved (which we do not need).
     * However, Timer is still locking and a concurrent queue would be better.
     */

    private final String _name;
    private final boolean _daemon;
    private Timer _timer;

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

    public TimerScheduler(String name, boolean daemon)
    {
        _name = name;
        _daemon = daemon;
    }

    @Override
    protected void doStart() throws Exception
    {
        _timer = _name == null ? new Timer() : new Timer(_name, _daemon);
        run();
        super.doStart();
    }

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

    @Override
    public Task schedule(final Runnable task, final long delay, final TimeUnit units)
    {
        Timer timer = _timer;
        if (timer == null)
            throw new RejectedExecutionException("STOPPED: " + this);
        SimpleTask t = new SimpleTask(task);
        timer.schedule(t, units.toMillis(delay));
        return t;
    }

    @Override
    public void run()
    {
        Timer timer = _timer;
        if (timer != null)
        {
            timer.purge();
            schedule(this, 1, TimeUnit.SECONDS);
        }
    }

    private static class SimpleTask extends TimerTask implements Task
    {
        private final Runnable _task;

        private SimpleTask(Runnable runnable)
        {
            _task = runnable;
        }

        @Override
        public void run()
        {
            try
            {
                _task.run();
            }
            catch (Throwable x)
            {
                LOG.warn("Exception while executing task " + _task, x);
            }
        }

        @Override
        public String toString()
        {
            return String.format("%s.%s@%x",
                    TimerScheduler.class.getSimpleName(),
                    SimpleTask.class.getSimpleName(),
                    hashCode());
        }
    }
}