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annotate gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 1087:92fce3b3d07f

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Centered histograms in pdf exports. gnv-artifacts/trunk@1189 c6561f87-3c4e-4783-a992-168aeb5c3f6f
author Ingo Weinzierl <ingo.weinzierl@intevation.de>
date Thu, 10 Jun 2010 09:23:33 +0000
parents 22c18083225e
children f953c9a559d8
rev   line source
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1 package de.intevation.gnv.utils;
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2
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3 import java.util.HashMap;
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4
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5 /**
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6 * This class can be used to synchronize threads with a given key. To use this
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7 * synchronization, you first need to do call {@link #acquire(java.lang.Object)}
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8 * to retrieve a {@link UniqueKey}. After this, you can call the code being
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9 * synchronized. After this execution, you need to call
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10 * {@link #release(UniqueKey)} with your token you retrieved from {@link
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11 * #acquire(java.lang.Object)}. A thread needs to wait for another thread if their keys
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12 * are equal. Threads with different keys don't need to wait for each other.
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13 *
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14 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
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15 * @author <a href="mailto:ingo.weinzierl@intevation.de">Ingo Weinzierl</a>
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16 */
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17 public final class ExclusiveExec
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18 {
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19 /**
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20 * The only instance of this singleton.
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21 */
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22 public static final ExclusiveExec INSTANCE = new ExclusiveExec();
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23
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24 private HashMap tokens;
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25
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26 /**
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27 * This class represents a unique key with a reference counter.
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28 */
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29 public static class UniqueKey {
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30 Object key;
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31 int [] refs;
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32
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33 /**
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34 * Constructs a new UniqueKey.
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35 *
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36 * @param key The key of this unique key.
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37 */
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38 public UniqueKey(Object key) {
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39 this.key = key;
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40 refs = new int[1];
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41 }
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42 }
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43
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44 /**
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45 * Private constructor. Use {@link #INSTANCE} instead.
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46 */
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47 private ExclusiveExec() {
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48 tokens = new HashMap();
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49 }
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50
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51 /**
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52 * This method serves a {@link UniqueKey} and starts a synchronized code
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53 * block.
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54 *
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55 * @param key The key used to identify same threads.
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56 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)}
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57 * at the end of your code being synchronized.
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58 */
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59 public UniqueKey acquire(Object key) {
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60
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61 try {
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62 UniqueKey internalKey = null;
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63 synchronized (tokens) {
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64 internalKey = (UniqueKey)tokens.get(key);
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65
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66 if (internalKey == null) {
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67 tokens.put(key, internalKey = new UniqueKey(key));
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68 }
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69 }
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70
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71 synchronized (internalKey) {
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72 ++internalKey.refs[0];
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73 while (internalKey.refs[0] > 1) {
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74 internalKey.wait(10000L);
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75 }
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76 }
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77
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78 return internalKey;
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79 }
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80 catch (InterruptedException ie) {
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81 return null;
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82 }
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83 }
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84
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85 /**
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86 * This method releases a lock. Call this method at the end of your code
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87 * being synchronized.
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88 *
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89 * @param internalKey Token retrieved by {@link #acquire(Object)}.
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90 */
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91 public void release(UniqueKey internalKey) {
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92 if (internalKey != null) {
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93 synchronized (internalKey) {
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94 if (--internalKey.refs[0] < 1) {
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95 synchronized (tokens) {
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96 tokens.remove(internalKey.key);
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97 }
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98 }
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99 internalKey.notifyAll();
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100 }
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101 }
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102 }
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103 }
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104 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :
http://dive4elements.wald.intevation.org