1 /* 2 * Copyright (c) 2007, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package nsk.share.locks; 24 25 /* 26 * Thread intended to hold given lock until method releaseLock() not called 27 * 28 * Example of usage: 29 * 30 * Object lockToHold = new Object(); 31 * MonitorLockingThread lockingThread = new MonitorLockingThread(lockToHold); 32 * 33 * // after calling this method lock 'lockToHold' is acquired by lockingThread 34 * lockingThread.acquireLock(); 35 * 36 * // after calling this method lockingThread releases 'lockToHold' and finishes execution 37 * lockingThread.releaseLock(); 38 */ 39 public class MonitorLockingThread extends Thread { 40 /* 41 * Class MonitorLockingThread is written for usage in tests provoking monitor contention. 42 * Typically in these tests exists thread holding lock (MonitorLockingThread) and another 43 * thread trying to acquire the same lock. But this scenario also requires one more thread 44 * which will force MonitorLockingThread to release lock when contention occurred, for this purpose 45 * auxiliary thread class LockFreeThread is written. 46 * 47 * Example of usage of MonitorLockingThread and LockFreeThread: 48 * 49 * Object lock = new Object(); 50 * MonitorLockingThread monitorLockingThread = new MonitorLockingThread(lock); 51 * 52 * MonitorLockingThread.LockFreeThread lockFreeThread = 53 * new MonitorLockingThread.LockFreeThread(Thread.currentThread(), monitorLockingThread); 54 * 55 * monitorLockingThread.acquireLock(); 56 * 57 * lockFreeThread.start(); 58 * 59 * // try to acquire lock which is already held by MonitorLockingThread (here monitor contention should occur), 60 * // when LockFreeThread finds that contention occurred it forces MonitorLockingThread to release lock 61 * // and current thread is able to continue execution 62 * synchronized (lock) { 63 * } 64 */ 65 public static class LockFreeThread extends Thread { 66 private Thread blockedThread; 67 68 private MonitorLockingThread lockingThread; 69 70 public LockFreeThread(Thread blockedThread, MonitorLockingThread lockingThread) { 71 this.blockedThread = blockedThread; 72 this.lockingThread = lockingThread; 73 } 74 75 public void run() { 76 /* 77 * Wait when blockedThread's state will switch to 'BLOCKED' (at that moment monitor contention 78 * should already occur) and then force MonitorLockingThread to release lock 79 */ 80 while (blockedThread.getState() != Thread.State.BLOCKED) 81 yield(); 82 83 lockingThread.releaseLock(); 84 } 85 } 86 87 private volatile boolean isRunning = true; 88 89 private volatile boolean holdsLock; 90 91 private Object lockToHold; 92 93 public MonitorLockingThread(Object lockToHold) { 94 this.lockToHold = lockToHold; 95 } 96 97 public void run() { 98 synchronized (lockToHold) { 99 holdsLock = true; 100 while (isRunning) 101 yield(); 102 } 103 holdsLock = false; 104 } 105 106 public void releaseLock() { 107 isRunning = false; 108 while (holdsLock) 109 yield(); 110 } 111 112 public void acquireLock() { 113 start(); 114 while (!holdsLock) 115 yield(); 116 } 117 }