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annotate src/EDU/oswego/cs/dl/util/concurrent/CopyOnWriteArraySet.java @ 27:511648fa4d64 Version 2.1

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Version to 2.1
author Dan Creswell <dan.creswell@gmail.com>
date Mon, 04 Jan 2010 13:00:40 +0000
parents 3dc0c5604566
children
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1 /*
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2 File: CopyOnWriteArraySet.java
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3
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4 Originally written by Doug Lea and released into the public domain.
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5 This may be used for any purposes whatsoever without acknowledgment.
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6 Thanks for the assistance and support of Sun Microsystems Labs,
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7 and everyone contributing, testing, and using this code.
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8
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9 History:
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10 Date Who What
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11 22Jun1998 dl Create public version
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12 */
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13
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14 package EDU.oswego.cs.dl.util.concurrent;
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15 import java.util.*;
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16
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17 /**
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18 * This class implements a java.util.Set that uses a
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19 * CopyOnWriteArrayList for all of its operations.
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20 * Thus, it shares the same basic properties:
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21 * <ul>
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22 * <li> It is best suited for applications in which set sizes generally
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23 * stay small, read-only operations
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24 * vastly outnumber mutative operations, and you need
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25 * to prevent interference among threads during traversal.
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26 * <li> Mutative operations(add, set, remove, etc) are fairly expensive
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27 * since they usually entail copying the entire underlying array.
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28 * <li> Loops involving repeated element-by-element mutative operations
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29 * are so expensive that they should generally be avoided.
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30 * <li> Iterators do not support the mutative remove operation
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31 * <li> Traversal via iterators is very fast and cannot ever encounter
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32 * interference from other threads. Iterators rely on
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33 * unchanging snapshots of the array at the time the iterators were
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34 * constructed
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35 * </ul>
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36 * <p>
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37 * <b>Sample Usage.</b> Probably the main application
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38 * of copy-on-write sets are classes that maintain
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39 * sets of Handler objects
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40 * that must be multicasted to upon an update command. This
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41 * is a classic case where you do not want to be holding a synch
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42 * lock while sending a message, and where traversals normally
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43 * vastly overwhelm additions.
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44 * <pre>
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45 * class Handler { void handle(); ... }
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46 *
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47 * class X {
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48 * private final CopyOnWriteArraySet handlers = new CopyOnWriteArraySet();
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49 * public void addHandler(Handler h) { handlers.add(h); }
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50 *
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51 * private long internalState;
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52 * private synchronized void changeState() { internalState = ...; }
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53 *
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54 * public void update() {
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55 * changeState();
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56 * Iterator it = handlers.iterator();
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57 * while (it.hasNext())
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58 * ((Handler)(it.next()).handle();
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59 * }
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60 * }
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61 * </pre>
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62 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
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63 * @see CopyOnWriteArrayList
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64 **/
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65
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66
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67 public class CopyOnWriteArraySet extends AbstractSet implements Cloneable, java.io.Serializable {
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68
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69 protected final CopyOnWriteArrayList al;
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70
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71 /**
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72 * Constructs an empty set
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73 */
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74 public CopyOnWriteArraySet() {
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75 al = new CopyOnWriteArrayList();
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76 }
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77
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78 /**
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79 * Constructs a set containing all of the elements of the specified
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80 * Collection.
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81 */
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82 public CopyOnWriteArraySet(Collection c) {
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83 al = new CopyOnWriteArrayList();
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84 al.addAllAbsent(c);
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85 }
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86
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87
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88 public int size() { return al.size(); }
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89 public boolean isEmpty() { return al.isEmpty(); }
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90 public boolean contains(Object o) { return al.contains(o); }
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91 public Object[] toArray() { return al.toArray(); }
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92 public Object[] toArray(Object[] a) { return al.toArray(a); }
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93 public void clear() { al.clear(); }
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94 public Iterator iterator() { return al.iterator(); }
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95 public boolean remove(Object o) { return al.remove(o); }
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96 public boolean containsAll(Collection c) { return al.containsAll(c); }
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97 public boolean addAll(Collection c) { return al.addAllAbsent(c) > 0; }
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98 public boolean removeAll(Collection c) { return al.removeAll(c); }
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99 public boolean retainAll(Collection c) { return al.retainAll(c); }
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100 public boolean add(Object o) { return al.addIfAbsent(o); }
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101
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102 }