Mercurial > dive4elements > gnv-client

annotate gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 778:9a828e5a2390

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Removed trailing whitespace gnv-artifacts/trunk@851 c6561f87-3c4e-4783-a992-168aeb5c3f6f
author Sascha L. Teichmann <sascha.teichmann@intevation.de>
date Mon, 29 Mar 2010 07:58:51 +0000
parents eedad2ddad14
children c4156275c1e1
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(String)} to
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8 * 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(String)}. 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 Sascha L. Teichmann (sascha.teichmann@intevation.de)
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15 * @author Ingo Weinzierl (ingo.weinzierl@intevation.de)
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16 */
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17 public final class ExclusiveExec
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18 {
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19 public static final ExclusiveExec INSTANCE = new ExclusiveExec();
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20
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21 private HashMap tokens;
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22
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23 public static class UniqueKey {
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24 Object key;
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25 int [] refs;
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26 public UniqueKey(Object key) {
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27 this.key = key;
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28 refs = new int[1];
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29 }
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30 }
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31
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32 /**
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33 * Private constructor. Use {@link #INSTANCE} instead.
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34 */
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35 private ExclusiveExec() {
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36 tokens = new HashMap();
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37 }
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38
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39 /**
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40 * This method serves a {@link UniqueKey} and starts a synchronized code
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41 * block.
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42 *
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43 * @param key The key used to identify same threads.
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44 *
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45 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)}
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46 * at the end of your code being synchronized.
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47 */
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48 public UniqueKey acquire(Object key) {
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49
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50 try {
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51 UniqueKey internalKey = null;
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52 synchronized (tokens) {
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53 internalKey = (UniqueKey)tokens.get(key);
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54
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55 if (internalKey == null) {
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56 tokens.put(key, internalKey = new UniqueKey(key));
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57 }
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58 }
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59
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60 synchronized (internalKey) {
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61 ++internalKey.refs[0];
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62 while (internalKey.refs[0] > 1) {
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63 internalKey.wait(10000L);
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64 }
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65 }
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66
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67 return internalKey;
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68 }
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69 catch (InterruptedException ie) {
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70 return null;
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71 }
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72 }
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73
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74 /**
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75 * This method releases a lock. Call this method at the end of your code
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76 * being synchronized.
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77 *
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78 * @param internalKey Token retrieved by {@link #acquire(Object)}.
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79 */
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80 public void release(UniqueKey internalKey) {
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81 if (internalKey != null) {
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82 synchronized (internalKey) {
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83 if (--internalKey.refs[0] < 1) {
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84 synchronized (tokens) {
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85 tokens.remove(internalKey.key);
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86 }
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87 }
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88 internalKey.notifyAll();
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89 }
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90 }
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91 }
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92 }
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93 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :
http://dive4elements.wald.intevation.org