001/*
002 * Copyright 2009-2014 UnboundID Corp.
003 * All Rights Reserved.
004 */
005/*
006 * Copyright (C) 2009-2014 UnboundID Corp.
007 *
008 * This program is free software; you can redistribute it and/or modify
009 * it under the terms of the GNU General Public License (GPLv2 only)
010 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
011 * as published by the Free Software Foundation.
012 *
013 * This program is distributed in the hope that it will be useful,
014 * but WITHOUT ANY WARRANTY; without even the implied warranty of
015 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
016 * GNU General Public License for more details.
017 *
018 * You should have received a copy of the GNU General Public License
019 * along with this program; if not, see <http://www.gnu.org/licenses>.
020 */
021package com.unboundid.util;
022
023
024
025import java.io.Serializable;
026import java.util.concurrent.atomic.AtomicBoolean;
027import java.util.concurrent.atomic.AtomicLong;
028
029
030
031/**
032 * This class provides a utility that can be used to sleep for a specified
033 * period of time in a manner that allows it to be woken up if necessary.  A
034 * single instance of this class may only be used to allow one thread to sleep
035 * at any given time, so if multiple threads need to sleep at the same time then
036 * a separate {@code WakeableSleeper} instance should be used for each.
037 */
038@ThreadSafety(level=ThreadSafetyLevel.MOSTLY_NOT_THREADSAFE)
039public final class WakeableSleeper
040       implements Serializable
041{
042  /**
043   * The serial version UID for this serializable class.
044   */
045  private static final long serialVersionUID = 755656862953269760L;
046
047
048
049  // A flag used to prevent multiple concurrent attempts to sleep.
050  private final AtomicBoolean sleeping;
051
052  // A flag used to indicate that this WakeableSleeper has been shut down.
053  private final AtomicBoolean shutDown;
054
055  // The number of attempts to wake up this sleeper.
056  private final AtomicLong wakeupCount;
057
058
059
060  /**
061   * Creates a new instance of this wakeable sleeper.
062   */
063  public WakeableSleeper()
064  {
065    sleeping    = new AtomicBoolean(false);
066    shutDown    = new AtomicBoolean(false);
067    wakeupCount = new AtomicLong(0L);
068  }
069
070
071
072  /**
073   * Return {@code true} if this {@code WakeableSleeper} instance has been
074   * shutdown via the {@code shutDown()} method and {@code false} otherwise.
075   *
076   * @return  {@code true} if this {@code WakeableSleeper} instance has been
077   *          shutdown via the {@code shutDown()} method and {@code false}
078   *          otherwise.
079   */
080  public boolean isShutDown()
081  {
082    return shutDown.get();
083  }
084
085
086
087  /**
088   * Attempts to sleep for the specified length of time in milliseconds, subject
089   * to the accuracy available within the JVM and underlying system.  It may
090   * wake up prematurely if the wakeup method is called, or if the thread is
091   * interrupted.  If {@code shutDown()} is called, then any active caller of
092   * this method will return immediately, and subsequent calls will return
093   * without sleeping.
094   * <BR><BR>
095   * This method must not be called on the same {@code WakeableSleeper} instance
096   * by multiple threads at the same time.
097   *
098   * @param  time  The length of time in milliseconds to sleep.
099   *
100   * @return  {@code true} if the sleep completed, or {@code false} if it was
101   *          woken or interrupted prematurely.
102   */
103  @ThreadSafety(level=ThreadSafetyLevel.NOT_THREADSAFE)
104  public boolean sleep(final long time)
105  {
106    synchronized (wakeupCount)
107    {
108      if (isShutDown())
109      {
110        return false;
111      }
112
113      Validator.ensureTrue(sleeping.compareAndSet(false, true),
114           "WakeableSleeper.sleep() must not be invoked concurrently by " +
115                "multiple threads against the same instance.");
116
117      try
118      {
119        final long beforeCount = wakeupCount.get();
120        wakeupCount.wait(time);
121        final long afterCount = wakeupCount.get();
122        return (beforeCount == afterCount);
123      }
124      catch (final InterruptedException ie)
125      {
126        Debug.debugException(ie);
127        return false;
128      }
129      finally
130      {
131        sleeping.set(false);
132      }
133    }
134  }
135
136
137
138  /**
139   * Permanently shuts down this {@code WakeableSleeper} instance.  If a thread
140   * is currently blocked in the {@code sleep} method, it will return
141   * immediately, and all subsequent calls to that method will return without
142   * sleeping.  It is safe to call this method multiple times.
143   */
144  @ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
145  public void shutDown()
146  {
147    shutDown.set(true);
148    wakeup();
149  }
150
151
152
153  /**
154   * Indicates that the sleeper should wake up if it is currently sleeping.
155   * This method will not make any attempt to ensure that the thread had woken
156   * up before returning.  If multiple threads attempt to wake up the sleeper at
157   * the same time, then it will have the same effect as a single wakeup
158   * request.
159   */
160  @ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
161  public void wakeup()
162  {
163    synchronized (wakeupCount)
164    {
165      wakeupCount.incrementAndGet();
166      wakeupCount.notifyAll();
167    }
168  }
169}