Mercurial > dive4elements > gnv-client

annotate gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 1129:ccfa07b88476

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merged geo-backend
author Thomas Arendsen Hein <thomas@intevation.de>
date Fri, 28 Sep 2012 12:14:01 +0200
parents f953c9a559d8
children
rev   line source
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1 /*
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2 * Copyright (c) 2010 by Intevation GmbH
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3 *
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4 * This program is free software under the LGPL (>=v2.1)
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5 * Read the file LGPL.txt coming with the software for details
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6 * or visit http://www.gnu.org/licenses/ if it does not exist.
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7 */
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8
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9 package de.intevation.gnv.utils;
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10
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11 import java.util.HashMap;
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12
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13 /**
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14 * This class can be used to synchronize threads with a given key. To use this
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15 * synchronization, you first need to do call {@link #acquire(java.lang.Object)}
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16 * to retrieve a {@link UniqueKey}. After this, you can call the code being
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17 * synchronized. After this execution, you need to call
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18 * {@link #release(UniqueKey)} with your token you retrieved from {@link
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19 * #acquire(java.lang.Object)}. A thread needs to wait for another thread if their keys
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20 * are equal. Threads with different keys don't need to wait for each other.
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21 *
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22 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
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23 * @author <a href="mailto:ingo.weinzierl@intevation.de">Ingo Weinzierl</a>
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24 */
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25 public final class ExclusiveExec
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26 {
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27 /**
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28 * The only instance of this singleton.
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29 */
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30 public static final ExclusiveExec INSTANCE = new ExclusiveExec();
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31
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32 private HashMap tokens;
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33
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34 /**
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35 * This class represents a unique key with a reference counter.
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36 */
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37 public static class UniqueKey {
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38 Object key;
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39 int [] refs;
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40
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41 /**
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42 * Constructs a new UniqueKey.
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43 *
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44 * @param key The key of this unique key.
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45 */
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46 public UniqueKey(Object key) {
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47 this.key = key;
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48 refs = new int[1];
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49 }
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50 }
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51
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52 /**
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53 * Private constructor. Use {@link #INSTANCE} instead.
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54 */
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55 private ExclusiveExec() {
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56 tokens = new HashMap();
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57 }
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58
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59 /**
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60 * This method serves a {@link UniqueKey} and starts a synchronized code
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61 * block.
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62 *
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63 * @param key The key used to identify same threads.
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64 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)}
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65 * at the end of your code being synchronized.
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66 */
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67 public UniqueKey acquire(Object key) {
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68
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69 try {
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70 UniqueKey internalKey = null;
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71 synchronized (tokens) {
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72 internalKey = (UniqueKey)tokens.get(key);
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73
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74 if (internalKey == null) {
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75 tokens.put(key, internalKey = new UniqueKey(key));
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76 }
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77 }
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78
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79 synchronized (internalKey) {
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80 ++internalKey.refs[0];
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81 while (internalKey.refs[0] > 1) {
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82 internalKey.wait(10000L);
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83 }
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84 }
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85
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86 return internalKey;
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87 }
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88 catch (InterruptedException ie) {
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89 return null;
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90 }
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91 }
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92
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93 /**
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94 * This method releases a lock. Call this method at the end of your code
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95 * being synchronized.
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96 *
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97 * @param internalKey Token retrieved by {@link #acquire(Object)}.
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98 */
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99 public void release(UniqueKey internalKey) {
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100 if (internalKey != null) {
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101 synchronized (internalKey) {
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102 if (--internalKey.refs[0] < 1) {
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103 synchronized (tokens) {
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104 tokens.remove(internalKey.key);
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105 }
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106 }
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107 internalKey.notifyAll();
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108 }
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109 }
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110 }
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111 }
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112 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :
http://dive4elements.wald.intevation.org