Mercurial > dive4elements > gnv-client
comparison gnv-artifacts/src/main/java/de/intevation/gnv/utils/ExclusiveExec.java @ 775:eedad2ddad14
Removed race-condition while shapefile creation (issue164).
gnv-artifacts/trunk@841 c6561f87-3c4e-4783-a992-168aeb5c3f6f
| author | Ingo Weinzierl <ingo.weinzierl@intevation.de> |
|---|---|
| date | Fri, 26 Mar 2010 15:20:32 +0000 |
| parents | |
| children | 9a828e5a2390 |
comparison
equal
deleted
inserted
replaced
| 774:d0a39efbfd96 | 775:eedad2ddad14 |
|---|---|
| 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(String)} to | |
| 8 * 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(String)}. 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 Sascha L. Teichmann (sascha.teichmann@intevation.de) | |
| 15 * @author Ingo Weinzierl (ingo.weinzierl@intevation.de) | |
| 16 */ | |
| 17 public final class ExclusiveExec | |
| 18 { | |
| 19 public static final ExclusiveExec INSTANCE = new ExclusiveExec(); | |
| 20 | |
| 21 private HashMap tokens; | |
| 22 | |
| 23 public static class UniqueKey { | |
| 24 Object key; | |
| 25 int [] refs; | |
| 26 public UniqueKey(Object key) { | |
| 27 this.key = key; | |
| 28 refs = new int[1]; | |
| 29 } | |
| 30 } | |
| 31 | |
| 32 /** | |
| 33 * Private constructor. Use {@link #INSTANCE} instead. | |
| 34 */ | |
| 35 private ExclusiveExec() { | |
| 36 tokens = new HashMap(); | |
| 37 } | |
| 38 | |
| 39 /** | |
| 40 * This method serves a {@link UniqueKey} and starts a synchronized code | |
| 41 * block. | |
| 42 * | |
| 43 * @param key The key used to identify same threads. | |
| 44 * | |
| 45 * @return UniqueKey. Use this object to call {@link #release(UniqueKey)} | |
| 46 * at the end of your code being synchronized. | |
| 47 */ | |
| 48 public UniqueKey acquire(Object key) { | |
| 49 | |
| 50 try { | |
| 51 UniqueKey internalKey = null; | |
| 52 synchronized (tokens) { | |
| 53 internalKey = (UniqueKey)tokens.get(key); | |
| 54 | |
| 55 if (internalKey == null) { | |
| 56 tokens.put(key, internalKey = new UniqueKey(key)); | |
| 57 } | |
| 58 } | |
| 59 | |
| 60 synchronized (internalKey) { | |
| 61 ++internalKey.refs[0]; | |
| 62 while (internalKey.refs[0] > 1) { | |
| 63 internalKey.wait(10000L); | |
| 64 } | |
| 65 } | |
| 66 | |
| 67 return internalKey; | |
| 68 } | |
| 69 catch (InterruptedException ie) { | |
| 70 return null; | |
| 71 } | |
| 72 } | |
| 73 | |
| 74 /** | |
| 75 * This method releases a lock. Call this method at the end of your code | |
| 76 * being synchronized. | |
| 77 * | |
| 78 * @param internalKey Token retrieved by {@link #acquire(Object)}. | |
| 79 */ | |
| 80 public void release(UniqueKey internalKey) { | |
| 81 if (internalKey != null) { | |
| 82 synchronized (internalKey) { | |
| 83 if (--internalKey.refs[0] < 1) { | |
| 84 synchronized (tokens) { | |
| 85 tokens.remove(internalKey.key); | |
| 86 } | |
| 87 } | |
| 88 internalKey.notifyAll(); | |
| 89 } | |
| 90 } | |
| 91 } | |
| 92 } | |
| 93 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 : |