mutex.java

Java Communicating Agents是一个用于开发网络反应式信息agent的框架

/*
 * $Source: /home/data/cvsroot/src/jacomma/util/Mutex.java,v $
 * $Revision: 1.6 $
 * $Date: 2000/10/28 20:09:08 $
 *
 * This file is part of the jacomma framework
 * Copyright (c) 2000 	Dimitrios Vyzovitis
 *			mailto:[e-mail]
 *			
 *
 *			
 *			
 *			
 *
 *	This library is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU Library General Public License as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 *	This library is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU Library General Public License for more details.
 *
 *	You should have received a copy of the GNU Library General Public License
 *	along with this library; if not, write to the Free Software
 *	Foundation, Inc., 59 Temple Place, Suite 330, 
 *	Boston, MA  02111-1307  USA
 */

package jacomma.util;

/**
 * Recursive mutex lock
 * Use:
 * mutex.lock();  [or if( mutex.try_lock() ]
 * try {
 *    // do critical section
 * } finally {
 *    mutex.unlock();
 * }
 **/
public class Mutex {
	
	private int count_;
	private Thread owner_;

	public Mutex() {}

	public synchronized void lock() throws InterruptedException {
		while( !_try_lock() ) {
			// Attempt to fix the 100% CPU utilization behavior incurred by LinuxThreads
			Thread.currentThread().yield();
			wait();
		}
	}
	
	public synchronized boolean try_lock() {
		return _try_lock();
	}

	private boolean _try_lock() {
		boolean suc = true;
		if ( count_ == 0 ) {
			owner_ = Thread.currentThread();
			count_ ++;
		} else if ( owner_ == Thread.currentThread() )
			count_ ++;
		else
			suc = false;
		
		return suc;
	}

	public synchronized void unlock() {
		if ( owner_ == Thread.currentThread()
			 && --count_ == 0 ) {
			owner_ = null;
			notify();
		}
	}

}