Mercurial > dive4elements > gnv-client
comparison gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 1119:7c4f81f74c47
merged gnv-artifacts
| author | Thomas Arendsen Hein <thomas@intevation.de> |
|---|---|
| date | Fri, 28 Sep 2012 12:14:00 +0200 |
| parents | f953c9a559d8 |
| children |
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| 1027:fca4b5eb8d2f | 1119:7c4f81f74c47 |
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| 1 /* | |
| 2 * Copyright (c) 2010 by Intevation GmbH | |
| 3 * | |
| 4 * This program is free software under the LGPL (>=v2.1) | |
| 5 * Read the file LGPL.txt coming with the software for details | |
| 6 * or visit http://www.gnu.org/licenses/ if it does not exist. | |
| 7 */ | |
| 8 | |
| 9 package de.intevation.gnv.utils; | |
| 10 | |
| 11 import java.util.HashMap; | |
| 12 | |
| 13 /** | |
| 14 * This class can be used to synchronize threads with a given key. To use this | |
| 15 * synchronization, you first need to do call {@link #acquire(java.lang.Object)} | |
| 16 * to retrieve a {@link UniqueKey}. After this, you can call the code being | |
| 17 * synchronized. After this execution, you need to call | |
| 18 * {@link #release(UniqueKey)} with your token you retrieved from {@link | |
| 19 * #acquire(java.lang.Object)}. A thread needs to wait for another thread if their keys | |
| 20 * are equal. Threads with different keys don't need to wait for each other. | |
| 21 * | |
| 22 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a> | |
| 23 * @author <a href="mailto:ingo.weinzierl@intevation.de">Ingo Weinzierl</a> | |
| 24 */ | |
| 25 public final class ExclusiveExec | |
| 26 { | |
| 27 /** | |
| 28 * The only instance of this singleton. | |
| 29 */ | |
| 30 public static final ExclusiveExec INSTANCE = new ExclusiveExec(); | |
| 31 | |
| 32 private HashMap tokens; | |
| 33 | |
| 34 /** | |
| 35 * This class represents a unique key with a reference counter. | |
| 36 */ | |
| 37 public static class UniqueKey { | |
| 38 Object key; | |
| 39 int [] refs; | |
| 40 | |
| 41 /** | |
| 42 * Constructs a new UniqueKey. | |
| 43 * | |
| 44 * @param key The key of this unique key. | |
| 45 */ | |
| 46 public UniqueKey(Object key) { | |
| 47 this.key = key; | |
| 48 refs = new int[1]; | |
| 49 } | |
| 50 } | |
| 51 | |
| 52 /** | |
| 53 * Private constructor. Use {@link #INSTANCE} instead. | |
| 54 */ | |
| 55 private ExclusiveExec() { | |
| 56 tokens = new HashMap(); | |
| 57 } | |
| 58 | |
| 59 /** | |
| 60 * This method serves a {@link UniqueKey} and starts a synchronized code | |
| 61 * block. | |
| 62 * | |
| 63 * @param key The key used to identify same threads. | |
| 64 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)} | |
| 65 * at the end of your code being synchronized. | |
| 66 */ | |
| 67 public UniqueKey acquire(Object key) { | |
| 68 | |
| 69 try { | |
| 70 UniqueKey internalKey = null; | |
| 71 synchronized (tokens) { | |
| 72 internalKey = (UniqueKey)tokens.get(key); | |
| 73 | |
| 74 if (internalKey == null) { | |
| 75 tokens.put(key, internalKey = new UniqueKey(key)); | |
| 76 } | |
| 77 } | |
| 78 | |
| 79 synchronized (internalKey) { | |
| 80 ++internalKey.refs[0]; | |
| 81 while (internalKey.refs[0] > 1) { | |
| 82 internalKey.wait(10000L); | |
| 83 } | |
| 84 } | |
| 85 | |
| 86 return internalKey; | |
| 87 } | |
| 88 catch (InterruptedException ie) { | |
| 89 return null; | |
| 90 } | |
| 91 } | |
| 92 | |
| 93 /** | |
| 94 * This method releases a lock. Call this method at the end of your code | |
| 95 * being synchronized. | |
| 96 * | |
| 97 * @param internalKey Token retrieved by {@link #acquire(Object)}. | |
| 98 */ | |
| 99 public void release(UniqueKey internalKey) { | |
| 100 if (internalKey != null) { | |
| 101 synchronized (internalKey) { | |
| 102 if (--internalKey.refs[0] < 1) { | |
| 103 synchronized (tokens) { | |
| 104 tokens.remove(internalKey.key); | |
| 105 } | |
| 106 } | |
| 107 internalKey.notifyAll(); | |
| 108 } | |
| 109 } | |
| 110 } | |
| 111 } | |
| 112 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 : |