Barrier.java revision 324c4644fee44b9898524c09511bd33c3f12e2df 
1/*
2 * [The "BSD license"]
3 *  Copyright (c) 2010 Terence Parr
4 *  All rights reserved.
5 *
6 *  Redistribution and use in source and binary forms, with or without
7 *  modification, are permitted provided that the following conditions
8 *  are met:
9 *  1. Redistributions of source code must retain the above copyright
10 *      notice, this list of conditions and the following disclaimer.
11 *  2. Redistributions in binary form must reproduce the above copyright
12 *      notice, this list of conditions and the following disclaimer in the
13 *      documentation and/or other materials provided with the distribution.
14 *  3. The name of the author may not be used to endorse or promote products
15 *      derived from this software without specific prior written permission.
16 *
17 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28package org.antlr.misc;
29
30/**A very simple barrier wait.  Once a thread has requested a
31 * wait on the barrier with waitForRelease, it cannot fool the
32 * barrier into releasing by "hitting" the barrier multiple times--
33 * the thread is blocked on the wait().
34 */
35public class Barrier {
36    protected int threshold;
37    protected int count = 0;
38
39    public Barrier(int t) {
40        threshold = t;
41    }
42
43    public synchronized void waitForRelease()
44        throws InterruptedException
45    {
46        count++;
47        // The final thread to reach barrier resets barrier and
48        // releases all threads
49        if ( count==threshold ) {
50            // notify blocked threads that threshold has been reached
51            action(); // perform the requested operation
52            notifyAll();
53        }
54        else while ( count<threshold ) {
55            wait();
56        }
57    }
58
59    /** What to do when everyone reaches barrier */
60    public void action() {
61    }
62}
63