001 /* ====================================================================
002 * The Apache Software License, Version 1.1
003 *
004 * Copyright (c) 2003 The Apache Software Foundation. All rights
005 * reserved.
006 *
007 * Redistribution and use in source and binary forms, with or without
008 * modification, are permitted provided that the following conditions
009 * are met:
010 *
011 * 1. Redistributions of source code must retain the above copyright
012 * notice, this list of conditions and the following disclaimer.
013 *
014 * 2. Redistributions in binary form must reproduce the above copyright
015 * notice, this list of conditions and the following disclaimer in
016 * the documentation and/or other materials provided with the
017 * distribution.
018 *
019 * 3. The end-user documentation included with the redistribution,
020 * if any, must include the following acknowledgment:
021 * "This product includes software developed by the
022 * Apache Software Foundation (http://www.apache.org/)."
023 * Alternately, this acknowledgment may appear in the software itself,
024 * if and wherever such third-party acknowledgments normally appear.
025 *
026 * 4. The names "The Jakarta Project", "Commons", and "Apache Software
027 * Foundation" must not be used to endorse or promote products derived
028 * from this software without prior written permission. For written
029 * permission, please contact apache@apache.org.
030 *
031 * 5. Products derived from this software may not be called "Apache",
032 * nor may "Apache" appear in their name, without prior written
033 * permission of the Apache Software Foundation.
034 *
035 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
036 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
037 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
038 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
039 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
040 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
041 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
042 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
043 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
044 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
045 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
046 * SUCH DAMAGE.
047 * ====================================================================
048 *
049 * This software consists of voluntary contributions made by many
050 * individuals on behalf of the Apache Software Foundation. For more
051 * information on the Apache Software Foundation, please see
052 * <http://www.apache.org/>.
053 *
054 */
055 package org.jpu.patterns.common;
056
057 public class ReentrantLock implements IReentrantLock {
058
059 /**
060 * Default constructor.
061 */
062 public ReentrantLock() {
063 }
064
065 /**
066 * Acquires the lock.
067 */
068 public void lock() {
069 Thread caller = Thread.currentThread();
070 synchronized(this) {
071 if (caller == _owner) {
072 _count++;
073 } else {
074 try {
075 while (_owner != null) {
076 this.wait();
077 }
078 _owner = caller;
079 _count = 1;
080 } catch (InterruptedException exception) {
081 return;
082 }
083 }
084 }
085 }
086
087 /**
088 * Acquires the lock only if it not held by another thread.
089 *
090 * @return <code>true</code> if the lock was free and was acquired by the
091 * current thread, or the lock was already held by the current
092 * thread; <code>false</code> otherwise.
093 */
094 public boolean tryLock() {
095 synchronized(this) {
096 if (_owner == null) {
097 lock();
098 return true;
099 } else {
100 return false;
101 }
102 }
103 }
104
105 /**
106 * Attempts to release this lock. The lock is actually released if at
107 * least as many {@link #unlock} as {@link #lock} have been performed
108 * on this {@link ReentrantLock} by the current thread.
109 *
110 * throws IllegalMonitorStateExeception if the current thread does not hold
111 * this lock.
112 */
113 public void unlock() {
114 synchronized (this) {
115 if (Thread.currentThread() == _owner) {
116 if (--_count == 0) {
117 _owner = null;
118 this.notify();
119 }
120 } else {
121 throw new IllegalMonitorStateException(
122 "Current thread does not hold this lock");
123 }
124 }
125 }
126
127 public String toString() {
128 return "ReentrantLock(_owner=" + _owner + ", _count=" + _count + ")";
129 }
130
131 /**
132 * Returns the thread owner of this {@link ReentrantLock}.
133 *
134 * @return the owner of this lock.
135 */
136 public Thread getOwner() {
137 return _owner;
138 }
139
140 /**
141 * Holds the owner of this lock.
142 */
143 private Thread _owner;
144
145 /**
146 * Holds the number of time this lock has been acquired by its owner.
147 */
148 private long _count;
149 }
150