1 /* |
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2 * Copyright (c) 1994, 2005, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 package sun.misc; |
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27 |
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28 /** |
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29 * The Lock class provides a simple, useful interface to a lock. |
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30 * Unlike monitors which synchronize access to an object, locks |
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31 * synchronize access to an arbitrary set of resources (objects, |
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32 * methods, variables, etc.). <p> |
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33 * |
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34 * The programmer using locks must be responsible for clearly defining |
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35 * the semantics of their use and should handle deadlock avoidance in |
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36 * the face of exceptions. <p> |
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37 * |
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38 * For example, if you want to protect a set of method invocations with |
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39 * a lock, and one of the methods may throw an exception, you must be |
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40 * prepared to release the lock similarly to the following example: |
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41 * <pre> |
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42 * class SomeClass { |
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43 * Lock myLock = new Lock(); |
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44 |
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45 * void someMethod() { |
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46 * myLock.lock(); |
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47 * try { |
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48 * StartOperation(); |
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49 * ContinueOperation(); |
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50 * EndOperation(); |
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51 * } finally { |
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52 * myLock.unlock(); |
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53 * } |
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54 * } |
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55 * } |
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56 * </pre> |
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57 * |
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58 * @author Peter King |
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59 */ |
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60 public |
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61 class Lock { |
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62 private boolean locked = false; |
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63 |
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64 /** |
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65 * Create a lock, which is initially not locked. |
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66 */ |
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67 public Lock () { |
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68 } |
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69 |
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70 /** |
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71 * Acquire the lock. If someone else has the lock, wait until it |
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72 * has been freed, and then try to acquire it again. This method |
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73 * will not return until the lock has been acquired. |
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74 * |
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75 * @exception java.lang.InterruptedException if any thread has |
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76 * interrupted this thread. |
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77 */ |
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78 public final synchronized void lock() throws InterruptedException { |
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79 while (locked) { |
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80 wait(); |
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81 } |
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82 locked = true; |
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83 } |
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84 |
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85 /** |
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86 * Release the lock. If someone else is waiting for the lock, the |
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87 * will be notitified so they can try to acquire the lock again. |
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88 */ |
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89 public final synchronized void unlock() { |
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90 locked = false; |
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91 notifyAll(); |
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92 } |
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93 } |
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