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>It is thread-safe.
 *  <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 fast and cannot 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> The following code sketch uses a
 * copy-on-write set to maintain a set of Handler objects that
 * perform some action upon state updates.
 *
 * <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();
 *       for (Handler handler : handlers)
 *          handler.handle();
 *    }
 * }
 * </pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @see CopyOnWriteArrayList
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
        implements java.io.Serializable {
    private static final long serialVersionUID = 5457747651344034263L;

    private final CopyOnWriteArrayList<E> al;

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

    /**
     * Creates 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 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); }

    /**
     * Returns an iterator over the elements contained in this collection
     * in the order in which these elements were added.
     */
    public Iterator<E>  iterator()            { return al.iterator(); }

}
Revision:	1.21
Committed:	Tue Apr 26 01:17:18 2005 UTC (19 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.20:	+2 -2 lines
Log Message:	doc fixes
#	User	Rev	Content
1	dl	1.2	/*
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	tim	1.1	package java.util.concurrent;
8			import java.util.*;
9
10			/**
11	dl	1.3	* 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	tim	1.1	* <ul>
15	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
16	tim	1.1	* stay small, read-only operations
17			* vastly outnumber mutative operations, and you need
18			* to prevent interference among threads during traversal.
19	dl	1.16	* <li>It is thread-safe.
20	dl	1.18	* <li>Mutative operations (add, set, remove, etc) are expensive
21	tim	1.1	* since they usually entail copying the entire underlying array.
22	dl	1.18	* <li>Iterators do not support the mutative remove operation.
23			* <li>Traversal via iterators is fast and cannot encounter
24	tim	1.1	* interference from other threads. Iterators rely on
25			* unchanging snapshots of the array at the time the iterators were
26			* constructed.
27			* </ul>
28	dl	1.18	*
29			* <p> <b>Sample Usage.</b> The following code sketch uses a
30	jsr166	1.21	* copy-on-write set to maintain a set of Handler objects that
31			* perform some action upon state updates.
32	dl	1.18	*
33	tim	1.1	* <pre>
34	tim	1.6	* class Handler { void handle(); ... }
35	tim	1.1	*
36			* class X {
37	dl	1.13	* private final CopyOnWriteArraySet<Handler> handlers = new CopyOnWriteArraySet<Handler>();
38	tim	1.1	* public void addHandler(Handler h) { handlers.add(h); }
39			*
40			* private long internalState;
41			* private synchronized void changeState() { internalState = ...; }
42			*
43			* public void update() {
44			* changeState();
45	dl	1.18	* for (Handler handler : handlers)
46	dl	1.19	* handler.handle();
47	tim	1.1	* }
48			* }
49	tim	1.6	* </pre>
50	dl	1.14	*
51			* <p>This class is a member of the
52			* <a href="{@docRoot}/../guide/collections/index.html">
53			* Java Collections Framework</a>.
54			*
55	dl	1.16	* @see CopyOnWriteArrayList
56	dl	1.4	* @since 1.5
57			* @author Doug Lea
58	dl	1.11	* @param <E> the type of elements held in this collection
59	dl	1.4	*/
60	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
61	dl	1.18	implements java.io.Serializable {
62	dl	1.8	private static final long serialVersionUID = 5457747651344034263L;
63	tim	1.1
64			private final CopyOnWriteArrayList<E> al;
65
66			/**
67	dl	1.15	* Creates an empty set.
68	tim	1.1	*/
69			public CopyOnWriteArraySet() {
70			al = new CopyOnWriteArrayList<E>();
71			}
72
73			/**
74	dl	1.15	* Creates a set containing all of the elements of the specified
75	tim	1.1	* Collection.
76	dl	1.4	* @param c the collection
77	tim	1.1	*/
78	tim	1.12	public CopyOnWriteArraySet(Collection<? extends E> c) {
79	tim	1.1	al = new CopyOnWriteArrayList<E>();
80			al.addAllAbsent(c);
81			}
82
83
84			public int size() { return al.size(); }
85			public boolean isEmpty() { return al.isEmpty(); }
86			public boolean contains(Object o) { return al.contains(o); }
87			public Object[] toArray() { return al.toArray(); }
88			public <T> T[] toArray(T[] a) { return al.toArray(a); }
89			public void clear() { al.clear(); }
90			public boolean remove(Object o) { return al.remove(o); }
91			public boolean add(E o) { return al.addIfAbsent(o); }
92	tim	1.5	public boolean containsAll(Collection<?> c) { return al.containsAll(c); }
93			public boolean addAll(Collection<? extends E> c) { return al.addAllAbsent(c) > 0; }
94			public boolean removeAll(Collection<?> c) { return al.removeAll(c); }
95			public boolean retainAll(Collection<?> c) { return al.retainAll(c); }
96	tim	1.1
97	dl	1.20	/**
98			* Returns an iterator over the elements contained in this collection
99			* in the order in which these elements were added.
100			*/
101			public Iterator<E> iterator() { return al.iterator(); }
102
103	tim	1.1	}