jFuzzyLogic/antlr_3_1_source/misc/Barrier.java

/*
 [The "BSD licence"]
 Copyright (c) 2005-2008 Terence Parr
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
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 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,
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 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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*/
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() {
    }
}