antlr-3.4/tool/src/main/java/org/antlr/misc/Barrier.java

/*
 * [The "BSD license"]
 *  Copyright (c) 2010 Terence Parr
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *  1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *      derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.antlr.misc;

/**A very simple barrier wait.  Once a thread has requested a
 * wait on the barrier with waitForRelease, it cannot fool the
 * barrier into releasing by "hitting" the barrier multiple times--
 * the thread is blocked on the wait().
 */
public class Barrier {
    protected int threshold;
    protected int count = 0;

    public Barrier(int t) {
        threshold = t;
    }

    public synchronized void waitForRelease()
        throws InterruptedException
    {
        count++;
        // The final thread to reach barrier resets barrier and
        // releases all threads
        if ( count==threshold ) {
            // notify blocked threads that threshold has been reached
            action(); // perform the requested operation
            notifyAll();
        }
        else while ( count<threshold ) {
            wait();
        }
    }

    /** What to do when everyone reaches barrier */
    public void action() {
    }
}