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/*
* Copyright (c) 2007, 2018, 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.
*/
package nsk.share.locks;
/*
* Thread intended to hold given lock until method releaseLock() not called
*
* Example of usage:
*
* Object lockToHold = new Object();
* MonitorLockingThread lockingThread = new MonitorLockingThread(lockToHold);
*
* // after calling this method lock 'lockToHold' is acquired by lockingThread
* lockingThread.acquireLock();
*
* // after calling this method lockingThread releases 'lockToHold' and finishes execution
* lockingThread.releaseLock();
*/
public class MonitorLockingThread extends Thread {
/*
* Class MonitorLockingThread is written for usage in tests provoking monitor contention.
* Typically in these tests exists thread holding lock (MonitorLockingThread) and another
* thread trying to acquire the same lock. But this scenario also requires one more thread
* which will force MonitorLockingThread to release lock when contention occurred, for this purpose
* auxiliary thread class LockFreeThread is written.
*
* Example of usage of MonitorLockingThread and LockFreeThread:
*
* Object lock = new Object();
* MonitorLockingThread monitorLockingThread = new MonitorLockingThread(lock);
*
* MonitorLockingThread.LockFreeThread lockFreeThread =
* new MonitorLockingThread.LockFreeThread(Thread.currentThread(), monitorLockingThread);
*
* monitorLockingThread.acquireLock();
*
* lockFreeThread.start();
*
* // try to acquire lock which is already held by MonitorLockingThread (here monitor contention should occur),
* // when LockFreeThread finds that contention occurred it forces MonitorLockingThread to release lock
* // and current thread is able to continue execution
* synchronized (lock) {
* }
*/
public static class LockFreeThread extends Thread {
private Thread blockedThread;
private MonitorLockingThread lockingThread;
public LockFreeThread(Thread blockedThread, MonitorLockingThread lockingThread) {
this.blockedThread = blockedThread;
this.lockingThread = lockingThread;
}
public void run() {
/*
* Wait when blockedThread's state will switch to 'BLOCKED' (at that moment monitor contention
* should already occur) and then force MonitorLockingThread to release lock
*/
while (blockedThread.getState() != Thread.State.BLOCKED)
yield();
lockingThread.releaseLock();
}
}
private volatile boolean isRunning = true;
private volatile boolean holdsLock;
private Object lockToHold;
public MonitorLockingThread(Object lockToHold) {
this.lockToHold = lockToHold;
}
public void run() {
synchronized (lockToHold) {
holdsLock = true;
while (isRunning)
yield();
}
holdsLock = false;
}
public void releaseLock() {
isRunning = false;
while (holdsLock)
yield();
}
public void acquireLock() {
start();
while (!holdsLock)
yield();
}
}
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