util/concurrent/CopyOnWriteArraySet.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.*;

/**
 * A {@link java.util.Set} that uses {@link
 * java.util.concurrent.CopyOnWriteArrayList} for all of its
 * operations.  Thus, it shares the same basic properties:
 * <ul>
 *  <li>It is best suited for applications in which set sizes generally
 *       stay small, read-only operations
 *       vastly outnumber mutative operations, and you need
 *       to prevent interference among threads during traversal.
 *  <li>Mutative operations(add, set, remove, etc) are expensive
 *      since they usually entail copying the entire underlying array.
 *  <li>Iterators do not support the mutative remove operation
 *  <li>Traversal via iterators is very fast and cannot ever encounter
 *      interference from other threads. Iterators rely on
 *      unchanging snapshots of the array at the time the iterators were
 *     constructed.
 * </ul>
 * <p>
 * <b>Sample Usage.</b> Probably the main application
 * of copy-on-write sets are classes that maintain
 * sets of Handler objects
 * that must be multicasted to upon an update command. This
 * is a classic case where you do not want to be holding a
 * lock while sending a message, and where traversals normally
 * vastly overwhelm additions.
 * <pre>
 * class Handler { void handle(); ... }
 *
 * class X {
 *    private final CopyOnWriteArraySet&lt;Handler&gt; handlers = new CopyOnWriteArraySet&lt;Handler&gt;();
 *    public void addHandler(Handler h) { handlers.add(h); }
 *
 *    private long internalState;
 *    private synchronized void changeState() { internalState = ...; }
 *
 *    public void update() {
 *       changeState();
 *       Iterator it = handlers.iterator();
 *       while (it.hasNext())
 *          it.next().handle();
 *    }
 * }
 * </pre>
 * @see CopyOnWriteArrayList
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
        implements Cloneable, java.io.Serializable {
    private static final long serialVersionUID = 5457747651344034263L;

    private final CopyOnWriteArrayList<E> al;

    /**
     * Constructs an empty set.
     */
    public CopyOnWriteArraySet() {
        al = new CopyOnWriteArrayList<E>();
    }

    /**
     * Constructs a set containing all of the elements of the specified
     * Collection.
     * @param c the collection
     */
    public CopyOnWriteArraySet(Collection<? extends E> c) {
        al = new CopyOnWriteArrayList<E>();
        al.addAllAbsent(c);
    }


    public int      size()                    { return al.size(); }
    public boolean  isEmpty()                 { return al.isEmpty(); }
    public boolean  contains(Object o)        { return al.contains(o); }
    public Object[] toArray()                 { return al.toArray(); }
    public <T> T[]  toArray(T[] a)            { return al.toArray(a); }
    public void     clear()                   {        al.clear(); }
    public Iterator<E>  iterator()            { return al.iterator(); }
    public boolean  remove(Object o)          { return al.remove(o); }
    public boolean  add(E o)                  { return al.addIfAbsent(o); }
    public boolean  containsAll(Collection<?> c)      { return al.containsAll(c); }
    public boolean  addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; }
    public boolean  removeAll(Collection<?> c)        { return al.removeAll(c); }
    public boolean  retainAll(Collection<?> c)        { return al.retainAll(c); }

}
Revision:	1.14
Committed:	Tue Jan 27 11:36:31 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.13:	+5 -0 lines
Log Message:	Add Collection framework membership doc
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain. Use, modify, and
4	* redistribute this code in any way without acknowledgement.
5	*/
6
7	package java.util.concurrent;
8	import java.util.*;
9
10	/**
11	* A {@link java.util.Set} that uses {@link
12	* java.util.concurrent.CopyOnWriteArrayList} for all of its
13	* operations. Thus, it shares the same basic properties:
14	* <ul>
15	* <li>It is best suited for applications in which set sizes generally
16	* stay small, read-only operations
17	* vastly outnumber mutative operations, and you need
18	* to prevent interference among threads during traversal.
19	* <li>Mutative operations(add, set, remove, etc) are expensive
20	* since they usually entail copying the entire underlying array.
21	* <li>Iterators do not support the mutative remove operation
22	* <li>Traversal via iterators is very fast and cannot ever encounter
23	* interference from other threads. Iterators rely on
24	* unchanging snapshots of the array at the time the iterators were
25	* constructed.
26	* </ul>
27	* <p>
28	* <b>Sample Usage.</b> Probably the main application
29	* of copy-on-write sets are classes that maintain
30	* sets of Handler objects
31	* that must be multicasted to upon an update command. This
32	* is a classic case where you do not want to be holding a
33	* lock while sending a message, and where traversals normally
34	* vastly overwhelm additions.
35	* <pre>
36	* class Handler { void handle(); ... }
37	*
38	* class X {
39	* private final CopyOnWriteArraySet<Handler> handlers = new CopyOnWriteArraySet<Handler>();
40	* public void addHandler(Handler h) { handlers.add(h); }
41	*
42	* private long internalState;
43	* private synchronized void changeState() { internalState = ...; }
44	*
45	* public void update() {
46	* changeState();
47	* Iterator it = handlers.iterator();
48	* while (it.hasNext())
49	* it.next().handle();
50	* }
51	* }
52	* </pre>
53	* @see CopyOnWriteArrayList
54	*
55	* <p>This class is a member of the
56	* <a href="{@docRoot}/../guide/collections/index.html">
57	* Java Collections Framework</a>.
58	*
59	* @since 1.5
60	* @author Doug Lea
61	* @param <E> the type of elements held in this collection
62	*/
63	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
64	implements Cloneable, java.io.Serializable {
65	private static final long serialVersionUID = 5457747651344034263L;
66
67	private final CopyOnWriteArrayList<E> al;
68
69	/**
70	* Constructs an empty set.
71	*/
72	public CopyOnWriteArraySet() {
73	al = new CopyOnWriteArrayList<E>();
74	}
75
76	/**
77	* Constructs a set containing all of the elements of the specified
78	* Collection.
79	* @param c the collection
80	*/
81	public CopyOnWriteArraySet(Collection<? extends E> c) {
82	al = new CopyOnWriteArrayList<E>();
83	al.addAllAbsent(c);
84	}
85
86
87	public int size() { return al.size(); }
88	public boolean isEmpty() { return al.isEmpty(); }
89	public boolean contains(Object o) { return al.contains(o); }
90	public Object[] toArray() { return al.toArray(); }
91	public <T> T[] toArray(T[] a) { return al.toArray(a); }
92	public void clear() { al.clear(); }
93	public Iterator<E> iterator() { return al.iterator(); }
94	public boolean remove(Object o) { return al.remove(o); }
95	public boolean add(E o) { return al.addIfAbsent(o); }
96	public boolean containsAll(Collection<?> c) { return al.containsAll(c); }
97	public boolean addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; }
98	public boolean removeAll(Collection<?> c) { return al.removeAll(c); }
99	public boolean retainAll(Collection<?> c) { return al.retainAll(c); }
100
101	}