Mercurial > dive4elements > gnv-client
comparison gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 875:5e9efdda6894
merged gnv-artifacts/1.0
| author | Thomas Arendsen Hein <thomas@intevation.de> |
|---|---|
| date | Fri, 28 Sep 2012 12:13:56 +0200 |
| parents | 22c18083225e |
| children | f953c9a559d8 |
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| 722:bb3ffe7d719e | 875:5e9efdda6894 |
|---|---|
| 1 package de.intevation.gnv.utils; | |
| 2 | |
| 3 import java.util.HashMap; | |
| 4 | |
| 5 /** | |
| 6 * This class can be used to synchronize threads with a given key. To use this | |
| 7 * synchronization, you first need to do call {@link #acquire(java.lang.Object)} | |
| 8 * to retrieve a {@link UniqueKey}. After this, you can call the code being | |
| 9 * synchronized. After this execution, you need to call | |
| 10 * {@link #release(UniqueKey)} with your token you retrieved from {@link | |
| 11 * #acquire(java.lang.Object)}. A thread needs to wait for another thread if their keys | |
| 12 * are equal. Threads with different keys don't need to wait for each other. | |
| 13 * | |
| 14 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a> | |
| 15 * @author <a href="mailto:ingo.weinzierl@intevation.de">Ingo Weinzierl</a> | |
| 16 */ | |
| 17 public final class ExclusiveExec | |
| 18 { | |
| 19 /** | |
| 20 * The only instance of this singleton. | |
| 21 */ | |
| 22 public static final ExclusiveExec INSTANCE = new ExclusiveExec(); | |
| 23 | |
| 24 private HashMap tokens; | |
| 25 | |
| 26 /** | |
| 27 * This class represents a unique key with a reference counter. | |
| 28 */ | |
| 29 public static class UniqueKey { | |
| 30 Object key; | |
| 31 int [] refs; | |
| 32 | |
| 33 /** | |
| 34 * Constructs a new UniqueKey. | |
| 35 * | |
| 36 * @param key The key of this unique key. | |
| 37 */ | |
| 38 public UniqueKey(Object key) { | |
| 39 this.key = key; | |
| 40 refs = new int[1]; | |
| 41 } | |
| 42 } | |
| 43 | |
| 44 /** | |
| 45 * Private constructor. Use {@link #INSTANCE} instead. | |
| 46 */ | |
| 47 private ExclusiveExec() { | |
| 48 tokens = new HashMap(); | |
| 49 } | |
| 50 | |
| 51 /** | |
| 52 * This method serves a {@link UniqueKey} and starts a synchronized code | |
| 53 * block. | |
| 54 * | |
| 55 * @param key The key used to identify same threads. | |
| 56 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)} | |
| 57 * at the end of your code being synchronized. | |
| 58 */ | |
| 59 public UniqueKey acquire(Object key) { | |
| 60 | |
| 61 try { | |
| 62 UniqueKey internalKey = null; | |
| 63 synchronized (tokens) { | |
| 64 internalKey = (UniqueKey)tokens.get(key); | |
| 65 | |
| 66 if (internalKey == null) { | |
| 67 tokens.put(key, internalKey = new UniqueKey(key)); | |
| 68 } | |
| 69 } | |
| 70 | |
| 71 synchronized (internalKey) { | |
| 72 ++internalKey.refs[0]; | |
| 73 while (internalKey.refs[0] > 1) { | |
| 74 internalKey.wait(10000L); | |
| 75 } | |
| 76 } | |
| 77 | |
| 78 return internalKey; | |
| 79 } | |
| 80 catch (InterruptedException ie) { | |
| 81 return null; | |
| 82 } | |
| 83 } | |
| 84 | |
| 85 /** | |
| 86 * This method releases a lock. Call this method at the end of your code | |
| 87 * being synchronized. | |
| 88 * | |
| 89 * @param internalKey Token retrieved by {@link #acquire(Object)}. | |
| 90 */ | |
| 91 public void release(UniqueKey internalKey) { | |
| 92 if (internalKey != null) { | |
| 93 synchronized (internalKey) { | |
| 94 if (--internalKey.refs[0] < 1) { | |
| 95 synchronized (tokens) { | |
| 96 tokens.remove(internalKey.key); | |
| 97 } | |
| 98 } | |
| 99 internalKey.notifyAll(); | |
| 100 } | |
| 101 } | |
| 102 } | |
| 103 } | |
| 104 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 : |