Mercurial > hg > blitz_condensed
annotate src/EDU/oswego/cs/dl/util/concurrent/CopyOnWriteArraySet.java @ 34:6f68e94c1fb8 default tip
Add CondensedStats monitoring utility, equivalent to vmstat
author | Dominic Cleal <dominic-cleal@cdo2.com> |
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date | Thu, 05 Aug 2010 11:07:25 +0100 |
parents | 3dc0c5604566 |
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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 } |