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package java.util.concurrent; |
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import java.util.*; |
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/** |
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* CopyOnWriteArraySets implement a java.util.Set that uses |
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* CopyOnWriteArrayList for all of its operations. |
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* 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 synch |
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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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* <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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* @see CopyOnWriteArrayList |
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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 final CopyOnWriteArrayList<E> al; |
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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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* Constructs a set containing all of the elements of the specified |
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* 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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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 <T> boolean containsAll(Collection<T> c) { return al.containsAll(c); } |
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public <T extends E> boolean addAll(Collection<T> c) { return al.addAllAbsent(c) > 0; } |
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public <T> boolean removeAll(Collection<T> c) { return al.removeAll(c); } |
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public <T> boolean retainAll(Collection<T> c) { return al.retainAll(c); } |
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} |
