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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.*; |
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|
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/** |
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* A {@link java.util.Set} that uses {@link |
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* java.util.concurrent.CopyOnWriteArrayList} for all of its |
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* operations. Thus, it shares the same basic properties: |
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* <ul> |
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* <li>It is best suited for applications in which set sizes generally |
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* stay small, read-only operations |
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* vastly outnumber mutative operations, and you need |
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* to prevent interference among threads during traversal. |
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* <li>Mutative operations(add, set, remove, etc) are expensive |
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* since they usually entail copying the entire underlying array. |
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* <li>Loops involving repeated element-by-element mutative operations |
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* are so expensive that they should generally be avoided. |
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* <li>Iterators do not support the mutative remove operation |
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* <li>Traversal via iterators is very fast and cannot ever encounter |
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* interference from other threads. Iterators rely on |
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* unchanging snapshots of the array at the time the iterators were |
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* constructed. |
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* </ul> |
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* <p> |
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* <b>Sample Usage.</b> Probably the main application |
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* of copy-on-write sets are classes that maintain |
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* sets of Handler objects |
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* that must be multicasted to upon an update command. This |
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* is a classic case where you do not want to be holding a |
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* lock while sending a message, and where traversals normally |
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* vastly overwhelm additions. |
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* <pre> |
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* class Handler { void handle(); ... } |
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* |
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* class X { |
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* private final CopyOnWriteArraySet handlers = new CopyOnWriteArraySet(); |
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* public void addHandler(Handler h) { handlers.add(h); } |
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* |
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* private long internalState; |
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* private synchronized void changeState() { internalState = ...; } |
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* |
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* public void update() { |
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* changeState(); |
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* Iterator it = handlers.iterator(); |
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* while (it.hasNext()) |
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* ((Handler)(it.next()).handle(); |
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* } |
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* } |
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* </pre> |
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* @see CopyOnWriteArrayList |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class CopyOnWriteArraySet<E> extends AbstractSet<E> |
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implements Cloneable, java.io.Serializable { |
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private static final long serialVersionUID = 5457747651344034263L; |
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|
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private final CopyOnWriteArrayList<E> al; |
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|
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/** |
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* Constructs an empty set. |
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*/ |
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public CopyOnWriteArraySet() { |
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al = new CopyOnWriteArrayList<E>(); |
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} |
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|
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/** |
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* Constructs a set containing all of the elements of the specified |
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* Collection. |
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* @param c the collection |
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*/ |
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public <T extends E> CopyOnWriteArraySet(Collection<T> c) { |
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al = new CopyOnWriteArrayList<E>(); |
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al.addAllAbsent(c); |
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} |
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|
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|
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public int size() { return al.size(); } |
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public boolean isEmpty() { return al.isEmpty(); } |
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public boolean contains(Object o) { return al.contains(o); } |
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public Object[] toArray() { return al.toArray(); } |
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public <T> T[] toArray(T[] a) { return al.toArray(a); } |
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public void clear() { al.clear(); } |
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public Iterator<E> iterator() { return al.iterator(); } |
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public boolean remove(Object o) { return al.remove(o); } |
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public boolean add(E o) { return al.addIfAbsent(o); } |
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public boolean containsAll(Collection<?> c) { return al.containsAll(c); } |
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public boolean addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; } |
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public boolean removeAll(Collection<?> c) { return al.removeAll(c); } |
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public boolean retainAll(Collection<?> c) { return al.retainAll(c); } |
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|
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} |
