copyonwritearrayset.java

来自「SRI international 发布的OAA框架软件」· Java 代码 · 共 102 行

/*
 * 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 edu.emory.mathcs.backport.java.util.concurrent;

import java.util.*;

/**
 * A {@link java.util.Set} that uses {@link
 * edu.emory.mathcs.backport.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
 */
public class CopyOnWriteArraySet extends AbstractSet
        implements java.io.Serializable {
    private static final long serialVersionUID = 5457747651344034263L;

    private final CopyOnWriteArrayList al;

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

    /**
     * Creates a set containing all of the elements of the specified
     * Collection.
     * @param c the collection
     */
    public CopyOnWriteArraySet(Collection c) {
        al = new CopyOnWriteArrayList();
        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 Object[] toArray(Object[] a)       { return al.toArray(a); }
    public void     clear()                   {        al.clear(); }
    /**
     * Returns an iterator over the elements contained in this collection
     * in the order in which these elements were added.
     */
    public Iterator iterator()                { return al.iterator(); }
    public boolean  remove(Object o)          { return al.remove(o); }
    public boolean  add(Object o)             { return al.addIfAbsent(o); }
    public boolean  containsAll(Collection c)      { return al.containsAll(c); }
    public boolean  addAll(Collection c)           { return al.addAllAbsent(c) > 0; }
    public boolean  removeAll(Collection c)        { return al.removeAll(c); }
    public boolean  retainAll(Collection c)        { return al.retainAll(c); }
}