| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| import java.util.*; |
| |
| /** |
| * A {@link java.util.Set} that uses an internal {@link 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 (<tt>add</tt>, <tt>set</tt>, <tt>remove</tt>, etc.) |
| * are expensive since they usually entail copying the entire underlying |
| * array. |
| * <li>Iterators do not support the mutative <tt>remove</tt> 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> {@code |
| * class Handler { void handle(); ... } |
| * |
| * class X { |
| * private final CopyOnWriteArraySet<Handler> handlers |
| * = new CopyOnWriteArraySet<Handler>(); |
| * 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}/../technotes/guides/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 of elements to initially contain |
| * @throws NullPointerException if the specified collection is null |
| */ |
| public CopyOnWriteArraySet(Collection<? extends E> c) { |
| al = new CopyOnWriteArrayList<E>(); |
| al.addAllAbsent(c); |
| } |
| |
| /** |
| * Returns the number of elements in this set. |
| * |
| * @return the number of elements in this set |
| */ |
| public int size() { |
| return al.size(); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this set contains no elements. |
| * |
| * @return <tt>true</tt> if this set contains no elements |
| */ |
| public boolean isEmpty() { |
| return al.isEmpty(); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this set contains the specified element. |
| * More formally, returns <tt>true</tt> if and only if this set |
| * contains an element <tt>e</tt> such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| * |
| * @param o element whose presence in this set is to be tested |
| * @return <tt>true</tt> if this set contains the specified element |
| */ |
| public boolean contains(Object o) { |
| return al.contains(o); |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this set. |
| * If this set makes any guarantees as to what order its elements |
| * are returned by its iterator, this method must return the |
| * elements in the same order. |
| * |
| * <p>The returned array will be "safe" in that no references to it |
| * are maintained by this set. (In other words, this method must |
| * allocate a new array even if this set is backed by an array). |
| * The caller is thus free to modify the returned array. |
| * |
| * <p>This method acts as bridge between array-based and collection-based |
| * APIs. |
| * |
| * @return an array containing all the elements in this set |
| */ |
| public Object[] toArray() { |
| return al.toArray(); |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this set; the |
| * runtime type of the returned array is that of the specified array. |
| * If the set fits in the specified array, it is returned therein. |
| * Otherwise, a new array is allocated with the runtime type of the |
| * specified array and the size of this set. |
| * |
| * <p>If this set fits in the specified array with room to spare |
| * (i.e., the array has more elements than this set), the element in |
| * the array immediately following the end of the set is set to |
| * <tt>null</tt>. (This is useful in determining the length of this |
| * set <i>only</i> if the caller knows that this set does not contain |
| * any null elements.) |
| * |
| * <p>If this set makes any guarantees as to what order its elements |
| * are returned by its iterator, this method must return the elements |
| * in the same order. |
| * |
| * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| * array-based and collection-based APIs. Further, this method allows |
| * precise control over the runtime type of the output array, and may, |
| * under certain circumstances, be used to save allocation costs. |
| * |
| * <p>Suppose <tt>x</tt> is a set known to contain only strings. |
| * The following code can be used to dump the set into a newly allocated |
| * array of <tt>String</tt>: |
| * |
| * <pre> |
| * String[] y = x.toArray(new String[0]);</pre> |
| * |
| * Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| * <tt>toArray()</tt>. |
| * |
| * @param a the array into which the elements of this set are to be |
| * stored, if it is big enough; otherwise, a new array of the same |
| * runtime type is allocated for this purpose. |
| * @return an array containing all the elements in this set |
| * @throws ArrayStoreException if the runtime type of the specified array |
| * is not a supertype of the runtime type of every element in this |
| * set |
| * @throws NullPointerException if the specified array is null |
| */ |
| public <T> T[] toArray(T[] a) { |
| return al.toArray(a); |
| } |
| |
| /** |
| * Removes all of the elements from this set. |
| * The set will be empty after this call returns. |
| */ |
| public void clear() { |
| al.clear(); |
| } |
| |
| /** |
| * Removes the specified element from this set if it is present. |
| * More formally, removes an element <tt>e</tt> such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt>, |
| * if this set contains such an element. Returns <tt>true</tt> if |
| * this set contained the element (or equivalently, if this set |
| * changed as a result of the call). (This set will not contain the |
| * element once the call returns.) |
| * |
| * @param o object to be removed from this set, if present |
| * @return <tt>true</tt> if this set contained the specified element |
| */ |
| public boolean remove(Object o) { |
| return al.remove(o); |
| } |
| |
| /** |
| * Adds the specified element to this set if it is not already present. |
| * More formally, adds the specified element <tt>e</tt> to this set if |
| * the set contains no element <tt>e2</tt> such that |
| * <tt>(e==null ? e2==null : e.equals(e2))</tt>. |
| * If this set already contains the element, the call leaves the set |
| * unchanged and returns <tt>false</tt>. |
| * |
| * @param e element to be added to this set |
| * @return <tt>true</tt> if this set did not already contain the specified |
| * element |
| */ |
| public boolean add(E e) { |
| return al.addIfAbsent(e); |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this set contains all of the elements of the |
| * specified collection. If the specified collection is also a set, this |
| * method returns <tt>true</tt> if it is a <i>subset</i> of this set. |
| * |
| * @param c collection to be checked for containment in this set |
| * @return <tt>true</tt> if this set contains all of the elements of the |
| * specified collection |
| * @throws NullPointerException if the specified collection is null |
| * @see #contains(Object) |
| */ |
| public boolean containsAll(Collection<?> c) { |
| return al.containsAll(c); |
| } |
| |
| /** |
| * Adds all of the elements in the specified collection to this set if |
| * they're not already present. If the specified collection is also a |
| * set, the <tt>addAll</tt> operation effectively modifies this set so |
| * that its value is the <i>union</i> of the two sets. The behavior of |
| * this operation is undefined if the specified collection is modified |
| * while the operation is in progress. |
| * |
| * @param c collection containing elements to be added to this set |
| * @return <tt>true</tt> if this set changed as a result of the call |
| * @throws NullPointerException if the specified collection is null |
| * @see #add(Object) |
| */ |
| public boolean addAll(Collection<? extends E> c) { |
| return al.addAllAbsent(c) > 0; |
| } |
| |
| /** |
| * Removes from this set all of its elements that are contained in the |
| * specified collection. If the specified collection is also a set, |
| * this operation effectively modifies this set so that its value is the |
| * <i>asymmetric set difference</i> of the two sets. |
| * |
| * @param c collection containing elements to be removed from this set |
| * @return <tt>true</tt> if this set changed as a result of the call |
| * @throws ClassCastException if the class of an element of this set |
| * is incompatible with the specified collection (optional) |
| * @throws NullPointerException if this set contains a null element and the |
| * specified collection does not permit null elements (optional), |
| * or if the specified collection is null |
| * @see #remove(Object) |
| */ |
| public boolean removeAll(Collection<?> c) { |
| return al.removeAll(c); |
| } |
| |
| /** |
| * Retains only the elements in this set that are contained in the |
| * specified collection. In other words, removes from this set all of |
| * its elements that are not contained in the specified collection. If |
| * the specified collection is also a set, this operation effectively |
| * modifies this set so that its value is the <i>intersection</i> of the |
| * two sets. |
| * |
| * @param c collection containing elements to be retained in this set |
| * @return <tt>true</tt> if this set changed as a result of the call |
| * @throws ClassCastException if the class of an element of this set |
| * is incompatible with the specified collection (optional) |
| * @throws NullPointerException if this set contains a null element and the |
| * specified collection does not permit null elements (optional), |
| * or if the specified collection is null |
| * @see #remove(Object) |
| */ |
| public boolean retainAll(Collection<?> c) { |
| return al.retainAll(c); |
| } |
| |
| /** |
| * Returns an iterator over the elements contained in this set |
| * in the order in which these elements were added. |
| * |
| * <p>The returned iterator provides a snapshot of the state of the set |
| * when the iterator was constructed. No synchronization is needed while |
| * traversing the iterator. The iterator does <em>NOT</em> support the |
| * <tt>remove</tt> method. |
| * |
| * @return an iterator over the elements in this set |
| */ |
| public Iterator<E> iterator() { |
| return al.iterator(); |
| } |
| |
| /** |
| * Compares the specified object with this set for equality. |
| * Returns {@code true} if the specified object is the same object |
| * as this object, or if it is also a {@link Set} and the elements |
| * returned by an {@linkplain List#iterator() iterator} over the |
| * specified set are the same as the elements returned by an |
| * iterator over this set. More formally, the two iterators are |
| * considered to return the same elements if they return the same |
| * number of elements and for every element {@code e1} returned by |
| * the iterator over the specified set, there is an element |
| * {@code e2} returned by the iterator over this set such that |
| * {@code (e1==null ? e2==null : e1.equals(e2))}. |
| * |
| * @param o object to be compared for equality with this set |
| * @return {@code true} if the specified object is equal to this set |
| */ |
| public boolean equals(Object o) { |
| if (o == this) |
| return true; |
| if (!(o instanceof Set)) |
| return false; |
| Set<?> set = (Set<?>)(o); |
| Iterator<?> it = set.iterator(); |
| |
| // Uses O(n^2) algorithm that is only appropriate |
| // for small sets, which CopyOnWriteArraySets should be. |
| |
| // Use a single snapshot of underlying array |
| Object[] elements = al.getArray(); |
| int len = elements.length; |
| // Mark matched elements to avoid re-checking |
| boolean[] matched = new boolean[len]; |
| int k = 0; |
| outer: while (it.hasNext()) { |
| if (++k > len) |
| return false; |
| Object x = it.next(); |
| for (int i = 0; i < len; ++i) { |
| if (!matched[i] && eq(x, elements[i])) { |
| matched[i] = true; |
| continue outer; |
| } |
| } |
| return false; |
| } |
| return k == len; |
| } |
| |
| /** |
| * Test for equality, coping with nulls. |
| */ |
| private static boolean eq(Object o1, Object o2) { |
| return (o1 == null ? o2 == null : o1.equals(o2)); |
| } |
| } |
