J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2004 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 20 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 21 | * have any questions. |
| 22 | */ |
| 23 | |
| 24 | /* |
| 25 | * |
| 26 | * @summary Thiseclass is used to synchronize execution off two threads. |
| 27 | * @author Swamy Venkataramanappa |
| 28 | */ |
| 29 | |
| 30 | import java.util.concurrent.Semaphore; |
| 31 | |
| 32 | public class ThreadExecutionSynchronizer { |
| 33 | |
| 34 | private boolean waiting; |
| 35 | private Semaphore semaphore; |
| 36 | |
| 37 | public ThreadExecutionSynchronizer() { |
| 38 | semaphore = new Semaphore(1); |
| 39 | waiting = false; |
| 40 | } |
| 41 | |
| 42 | // Synchronizes two threads execution points. |
| 43 | // Basically any thread could get scheduled to run and |
| 44 | // it is not possible to know which thread reaches expected |
| 45 | // execution point. So whichever thread reaches a execution |
| 46 | // point first wait for the second thread. When the second thread |
| 47 | // reaches the expected execution point will wake up |
| 48 | // the thread which is waiting here. |
| 49 | void stopOrGo() { |
| 50 | semaphore.acquireUninterruptibly(); // Thread can get blocked. |
| 51 | if (!waiting) { |
| 52 | waiting = true; |
| 53 | // Wait for second thread to enter this method. |
| 54 | while(!semaphore.hasQueuedThreads()) { |
| 55 | try { |
| 56 | Thread.sleep(20); |
| 57 | } catch (InterruptedException xx) {} |
| 58 | } |
| 59 | semaphore.release(); |
| 60 | } else { |
| 61 | waiting = false; |
| 62 | semaphore.release(); |
| 63 | } |
| 64 | } |
| 65 | |
| 66 | // Wrapper function just for code readability. |
| 67 | void waitForSignal() { |
| 68 | stopOrGo(); |
| 69 | goSleep(50); |
| 70 | } |
| 71 | |
| 72 | void signal() { |
| 73 | stopOrGo(); |
| 74 | goSleep(50); |
| 75 | } |
| 76 | |
| 77 | private static void goSleep(long ms) { |
| 78 | try { |
| 79 | Thread.sleep(ms); |
| 80 | } catch (InterruptedException e) { |
| 81 | e.printStackTrace(); |
| 82 | System.out.println("Unexpected exception."); |
| 83 | } |
| 84 | } |
| 85 | } |