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 */
021 package com.unboundid.util;
022
023
024
025 import java.io.Serializable;
026 import java.util.concurrent.atomic.AtomicBoolean;
027 import 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 public final class WakeableSleeper
039 implements Serializable
040 {
041 /**
042 * The serial version UID for this serializable class.
043 */
044 private static final long serialVersionUID = 755656862953269760L;
045
046
047
048 // A flag used to prevent multiple concurrent attempts to sleep.
049 private final AtomicBoolean sleeping;
050
051 // A flag used to indicate that this WakeableSleeper has been shut down.
052 private final AtomicBoolean shutDown;
053
054 // The number of attempts to wake up this sleeper.
055 private final AtomicLong wakeupCount;
056
057
058
059 /**
060 * Creates a new instance of this wakeable sleeper.
061 */
062 public WakeableSleeper()
063 {
064 sleeping = new AtomicBoolean(false);
065 shutDown = new AtomicBoolean(false);
066 wakeupCount = new AtomicLong(0L);
067 }
068
069
070
071 /**
072 * Return {@code true} if this {@code WakeableSleeper} instance has been
073 * shutdown via the {@code shutDown()} method and {@code false} otherwise.
074 *
075 * @return {@code true} if this {@code WakeableSleeper} instance has been
076 * shutdown via the {@code shutDown()} method and {@code false}
077 * otherwise.
078 */
079 public boolean isShutDown()
080 {
081 return shutDown.get();
082 }
083
084
085
086 /**
087 * Attempts to sleep for the specified length of time in milliseconds, subject
088 * to the accuracy available within the JVM and underlying system. It may
089 * wake up prematurely if the wakeup method is called, or if the thread is
090 * interrupted. If {@code shutDown()} is called, then any active caller of
091 * this method will return immediately, and subsequent calls will return
092 * without sleeping.
093 * <BR><BR>
094 * This method must not be called on the same {@code WakeableSleeper} instance
095 * by multiple threads at the same time.
096 *
097 * @param time The length of time in milliseconds to sleep.
098 *
099 * @return {@code true} if the sleep completed, or {@code false} if it was
100 * woken or interrupted prematurely.
101 */
102 public boolean sleep(final long time)
103 {
104 synchronized (wakeupCount)
105 {
106 if (isShutDown())
107 {
108 return false;
109 }
110
111 Validator.ensureTrue(sleeping.compareAndSet(false, true),
112 "WakeableSleeper.sleep() must not be invoked concurrently by " +
113 "multiple threads against the same instance.");
114
115 try
116 {
117 final long beforeCount = wakeupCount.get();
118 wakeupCount.wait(time);
119 final long afterCount = wakeupCount.get();
120 return (beforeCount == afterCount);
121 }
122 catch (final InterruptedException ie)
123 {
124 Debug.debugException(ie);
125 return false;
126 }
127 finally
128 {
129 sleeping.set(false);
130 }
131 }
132 }
133
134
135
136 /**
137 * Permanently shuts down this {@code WakeableSleeper} instance. If a thread
138 * is currently blocked in the {@code sleep} method, it will return
139 * immediately, and all subsequent calls to that method will return without
140 * sleeping. It is safe to call this method multiple times.
141 */
142 public void shutDown()
143 {
144 shutDown.set(true);
145 wakeup();
146 }
147
148
149
150 /**
151 * Indicates that the sleeper should wake up if it is currently sleeping.
152 * This method will not make any attempt to ensure that the thread had woken
153 * up before returning. If multiple threads attempt to wake up the sleeper at
154 * the same time, then it will have the same effect as a single wakeup
155 * request.
156 */
157 public void wakeup()
158 {
159 synchronized (wakeupCount)
160 {
161 wakeupCount.incrementAndGet();
162 wakeupCount.notifyAll();
163 }
164 }
165 }