001/* 002 * Copyright 2009-2017 UnboundID Corp. 003 * All Rights Reserved. 004 */ 005/* 006 * Copyright (C) 2009-2017 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}