Source Code Cross Referenced for ReentrantLock.java in  » Development » Javolution » javolution » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Development » Javolution » javolution.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Javolution - Java(TM) Solution for Real-Time and Embedded Systems
003:         * Copyright (C) 2005 - Javolution (http://javolution.org/)
004:         * All rights reserved.
005:         * 
006:         * Permission to use, copy, modify, and distribute this software is
007:         * freely granted, provided that this notice is preserved.
008:         */
009:        package javolution.util;
010:
011:        /**
012:         * <p> This class represents a reentrant lock with the same semantics as
013:         *     built-in Java synchronized locks: Once a thread has a lock, it can
014:         *     re-obtain it any number of times without blocking. </p>
015:         *
016:         * @author  <a href="http://gee.cs.oswego.edu/dl/">Doug Lea</a>
017:         * @author  <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
018:         * @version 1.0, October 4, 2004
019:         */
020:        public class ReentrantLock {
021:
022:            /**
023:             * Holds the owner of this lock.
024:             */
025:            private Thread _owner;
026:
027:            /**
028:             * Holds the number of time this lock has been acquired by its owner.
029:             */
030:            private long _count;
031:
032:            /**
033:             * Default constructor.
034:             */
035:            public ReentrantLock() {
036:            }
037:
038:            /**
039:             * Acquires the lock.
040:             */
041:            public void lock() {
042:                Thread caller = Thread.currentThread();
043:                synchronized (this ) {
044:                    if (caller == _owner) {
045:                        _count++;
046:                    } else {
047:                        try {
048:                            while (_owner != null) {
049:                                this .wait();
050:                            }
051:                            _owner = caller;
052:                            _count = 1;
053:                        } catch (InterruptedException exception) {
054:                            return;
055:                        }
056:                    }
057:                }
058:            }
059:
060:            /**
061:             * Acquires the lock only if it not held by another thread.
062:             *
063:             * @return <code>true</code> if the lock was free and was acquired by the
064:             *         current thread, or the lock was already held by the current
065:             *         thread; <code>false</code> otherwise.
066:             */
067:            public boolean tryLock() {
068:                synchronized (this ) {
069:                    if (_owner == null) {
070:                        lock();
071:                        return true;
072:                    } else {
073:                        return false;
074:                    }
075:                }
076:            }
077:
078:            /**
079:             * Attempts to release this lock. The lock is actually released if at
080:             * least as many {@link #unlock} as {@link #lock} have been performed
081:             * on this {@link ReentrantLock} by the current thread.
082:             *
083:             * throws IllegalMonitorStateExeception if the current thread does not hold
084:             *        this lock.
085:             */
086:            public void unlock() {
087:                synchronized (this ) {
088:                    if (Thread.currentThread() == _owner) {
089:                        if (--_count == 0) {
090:                            _owner = null;
091:                            this .notify();
092:                        }
093:                    } else {
094:                        throw new IllegalMonitorStateException(
095:                                "Current thread does not hold this lock");
096:                    }
097:                }
098:            }
099:
100:            /**
101:             * Returns the thread owner of this {@link ReentrantLock}.
102:             *
103:             * @return the owner of this lock.
104:             */
105:            public Thread getOwner() {
106:                synchronized (this) {
107:                    return _owner;
108:                }
109:            }
110:        }
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