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| 1 | /* | ||
| 2 | * Copyright (c) 1994, 2005, 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. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package sun.misc; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * The Lock class provides a simple, useful interface to a lock. | ||
| 30 | * Unlike monitors which synchronize access to an object, locks | ||
| 31 | * synchronize access to an arbitrary set of resources (objects, | ||
| 32 | * methods, variables, etc.). <p> | ||
| 33 | * | ||
| 34 | * The programmer using locks must be responsible for clearly defining | ||
| 35 | * the semantics of their use and should handle deadlock avoidance in | ||
| 36 | * the face of exceptions. <p> | ||
| 37 | * | ||
| 38 | * For example, if you want to protect a set of method invocations with | ||
| 39 | * a lock, and one of the methods may throw an exception, you must be | ||
| 40 | * prepared to release the lock similarly to the following example: | ||
| 41 | * <pre> | ||
| 42 | * class SomeClass { | ||
| 43 | * Lock myLock = new Lock(); | ||
| 44 | |||
| 45 | * void someMethod() { | ||
| 46 | * myLock.lock(); | ||
| 47 | * try { | ||
| 48 | * StartOperation(); | ||
| 49 | * ContinueOperation(); | ||
| 50 | * EndOperation(); | ||
| 51 | * } finally { | ||
| 52 | * myLock.unlock(); | ||
| 53 | * } | ||
| 54 | * } | ||
| 55 | * } | ||
| 56 | * </pre> | ||
| 57 | * | ||
| 58 | * @author Peter King | ||
| 59 | */ | ||
| 60 | public | ||
| 61 | class Lock { | ||
| 62 | private boolean locked = false; | ||
| 63 | |||
| 64 | /** | ||
| 65 | * Create a lock, which is initially not locked. | ||
| 66 | */ | ||
| 67 | public Lock () { | ||
| 68 | } | ||
| 69 | |||
| 70 | /** | ||
| 71 | * Acquire the lock. If someone else has the lock, wait until it | ||
| 72 | * has been freed, and then try to acquire it again. This method | ||
| 73 | * will not return until the lock has been acquired. | ||
| 74 | * | ||
| 75 | * @exception java.lang.InterruptedException if any thread has | ||
| 76 | * interrupted this thread. | ||
| 77 | */ | ||
| 78 | public final synchronized void lock() throws InterruptedException { | ||
| 79 | while (locked) { | ||
| 80 | wait(); | ||
| 81 | } | ||
| 82 | locked = true; | ||
| 83 | } | ||
| 84 | |||
| 85 | /** | ||
| 86 | * Release the lock. If someone else is waiting for the lock, the | ||
| 87 | * will be notitified so they can try to acquire the lock again. | ||
| 88 | */ | ||
| 89 | public final synchronized void unlock() { | ||
| 90 | locked = false; | ||
| 91 | notifyAll(); | ||
| 92 | } | ||
| 93 | } | ||