readwritelock.java

Jive是基于JSP/JAVA技术构架的一个大型BBS论坛系统,这是Jive论坛2.6版本的源程序

/**
 * $RCSfile: ReadWriteLock.java,v $
 * $Revision: 1.1 $
 * $Date: 2002/07/07 16:29:08 $
 *
 * Copyright (C) 2002 CoolServlets, Inc. All rights reserved.
 *
 * This software is the proprietary information of CoolServlets, Inc.
 * Use is subject to license terms.
 */

package com.jivesoftware.util;

/**
 * Simple read write lock class that allows multiple readers but only 1 writer. Waiting writers are
 * treated preferentially to waiting readers.
 */
public class ReadWriteLock {

    private int readers = 0;
    private boolean writingInProgress = false;
    private boolean waitingWriter = false;

    public ReadWriteLock() { }


    public synchronized void acquireReadLock() {
        while (writingInProgress || waitingWriter == true) {
            try {
                wait();
            }
            catch (InterruptedException ie) { /* ignore */ }
        }
        readers++;
    }

    public synchronized void releaseReadLock() {
        readers--;

        if (readers == 0) {
            notify();
        }
    }

    public synchronized void acquireWriteLock() {
        while (readers > 0 || writingInProgress) {
            try {
                waitingWriter = true;
                wait();
            }
            catch (InterruptedException ie) { /* ignore */ }
        }
        writingInProgress = true;
        waitingWriter = false;
    }

    public synchronized void releaseWriteLock() {
        writingInProgress = false;
        notifyAll();
    }
}