001/*
002 * Copyright 2009-2022 Ping Identity Corporation
003 * All Rights Reserved.
004 */
005/*
006 * Copyright 2009-2022 Ping Identity Corporation
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *    http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020/*
021 * Copyright (C) 2009-2022 Ping Identity Corporation
022 *
023 * This program is free software; you can redistribute it and/or modify
024 * it under the terms of the GNU General Public License (GPLv2 only)
025 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
026 * as published by the Free Software Foundation.
027 *
028 * This program is distributed in the hope that it will be useful,
029 * but WITHOUT ANY WARRANTY; without even the implied warranty of
030 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
031 * GNU General Public License for more details.
032 *
033 * You should have received a copy of the GNU General Public License
034 * along with this program; if not, see <http://www.gnu.org/licenses>.
035 */
036package com.unboundid.util;
037
038
039
040import java.io.Serializable;
041import java.util.concurrent.atomic.AtomicBoolean;
042import java.util.concurrent.atomic.AtomicLong;
043
044
045
046/**
047 * This class provides a utility that can be used to sleep for a specified
048 * period of time in a manner that allows it to be woken up if necessary.  A
049 * single instance of this class may only be used to allow one thread to sleep
050 * at any given time, so if multiple threads need to sleep at the same time then
051 * a separate {@code WakeableSleeper} instance should be used for each.
052 */
053@ThreadSafety(level=ThreadSafetyLevel.MOSTLY_NOT_THREADSAFE)
054public final class WakeableSleeper
055       implements Serializable
056{
057  /**
058   * The serial version UID for this serializable class.
059   */
060  private static final long serialVersionUID = 755656862953269760L;
061
062
063
064  // A flag used to prevent multiple concurrent attempts to sleep.
065  @NotNull private final AtomicBoolean sleeping;
066
067  // A flag used to indicate that this WakeableSleeper has been shut down.
068  @NotNull private final AtomicBoolean shutDown;
069
070  // The number of attempts to wake up this sleeper.
071  @NotNull private final AtomicLong wakeupCount;
072
073
074
075  /**
076   * Creates a new instance of this wakeable sleeper.
077   */
078  public WakeableSleeper()
079  {
080    sleeping    = new AtomicBoolean(false);
081    shutDown    = new AtomicBoolean(false);
082    wakeupCount = new AtomicLong(0L);
083  }
084
085
086
087  /**
088   * Return {@code true} if this {@code WakeableSleeper} instance has been
089   * shutdown via the {@code shutDown()} method and {@code false} otherwise.
090   *
091   * @return  {@code true} if this {@code WakeableSleeper} instance has been
092   *          shutdown via the {@code shutDown()} method and {@code false}
093   *          otherwise.
094   */
095  public boolean isShutDown()
096  {
097    return shutDown.get();
098  }
099
100
101
102  /**
103   * Attempts to sleep for the specified length of time in milliseconds, subject
104   * to the accuracy available within the JVM and underlying system.  It may
105   * wake up prematurely if the wakeup method is called, or if the thread is
106   * interrupted.  If {@code shutDown()} is called, then any active caller of
107   * this method will return immediately, and subsequent calls will return
108   * without sleeping.
109   * <BR><BR>
110   * This method must not be called on the same {@code WakeableSleeper} instance
111   * by multiple threads at the same time.
112   *
113   * @param  time  The length of time in milliseconds to sleep.
114   *
115   * @return  {@code true} if the sleep completed, or {@code false} if it was
116   *          woken or interrupted prematurely.
117   */
118  @ThreadSafety(level=ThreadSafetyLevel.NOT_THREADSAFE)
119  public boolean sleep(final long time)
120  {
121    synchronized (wakeupCount)
122    {
123      if (isShutDown())
124      {
125        return false;
126      }
127
128      Validator.ensureTrue(sleeping.compareAndSet(false, true),
129           "WakeableSleeper.sleep() must not be invoked concurrently by " +
130                "multiple threads against the same instance.");
131
132      try
133      {
134        final long beforeCount = wakeupCount.get();
135        wakeupCount.wait(time);
136        final long afterCount = wakeupCount.get();
137        return (beforeCount == afterCount);
138      }
139      catch (final InterruptedException ie)
140      {
141        Debug.debugException(ie);
142        return false;
143      }
144      finally
145      {
146        sleeping.set(false);
147      }
148    }
149  }
150
151
152
153  /**
154   * Permanently shuts down this {@code WakeableSleeper} instance.  If a thread
155   * is currently blocked in the {@code sleep} method, it will return
156   * immediately, and all subsequent calls to that method will return without
157   * sleeping.  It is safe to call this method multiple times.
158   */
159  @ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
160  public void shutDown()
161  {
162    shutDown.set(true);
163    wakeup();
164  }
165
166
167
168  /**
169   * Indicates that the sleeper should wake up if it is currently sleeping.
170   * This method will not make any attempt to ensure that the thread had woken
171   * up before returning.  If multiple threads attempt to wake up the sleeper at
172   * the same time, then it will have the same effect as a single wakeup
173   * request.
174   */
175  @ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
176  public void wakeup()
177  {
178    synchronized (wakeupCount)
179    {
180      wakeupCount.incrementAndGet();
181      wakeupCount.notifyAll();
182    }
183  }
184}