/*
* Copyright (c) 2004, 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.
*/
/*
*
* @summary Thiseclass is used to synchronize execution off two threads.
* @author Swamy Venkataramanappa
*/
import java.util.concurrent.Semaphore;
public class ThreadExecutionSynchronizer {
private boolean waiting;
private Semaphore semaphore;
public ThreadExecutionSynchronizer() {
semaphore = new Semaphore(1);
waiting = false;
}
// Synchronizes two threads execution points.
// Basically any thread could get scheduled to run and
// it is not possible to know which thread reaches expected
// execution point. So whichever thread reaches a execution
// point first wait for the second thread. When the second thread
// reaches the expected execution point will wake up
// the thread which is waiting here.
void stopOrGo() {
semaphore.acquireUninterruptibly(); // Thread can get blocked.
if (!waiting) {
waiting = true;
// Wait for second thread to enter this method.
while(!semaphore.hasQueuedThreads()) {
try {
Thread.sleep(20);
} catch (InterruptedException xx) {}
}
semaphore.release();
} else {
waiting = false;
semaphore.release();
}
}
// Wrapper function just for code readability.
void waitForSignal() {
stopOrGo();
goSleep(50);
}
void signal() {
stopOrGo();
goSleep(50);
}
private static void goSleep(long ms) {
try {
Thread.sleep(ms);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("Unexpected exception.");
}
}
}