Barrier.java

/*
 * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * @bug     4530538
 * @summary A Barrier utility class.
 * @author  Mandy Chung
 */

public class Barrier {
    private Object go = new Object();
    private int count;
    private int waiters = 0;

    public Barrier(int count) {
        if (count <= 0) {
            throw new IllegalArgumentException();
        }
        this.count = count;
    }

    public void set(int count) {
        if (waiters != 0) {
            throw new IllegalArgumentException();
        }
        this.count = count;
        this.waiters = 0;
    }

    public void await() {
        synchronized (go) {
            waiters++;
            while (count > 0) {
                try {
                    go.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    throw new InternalError();
                }
            }
            waiters--;
        }
    }
    public void signal() {
        synchronized (go) {
            count--;
            go.notifyAll();
        }
    }

    public int getWaiterCount() {
        synchronized (go) {
            return waiters;
        }
    }
}