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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/concurrent/CopyOnWriteArraySet.java')
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1 files changed, 364 insertions, 0 deletions
diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/CopyOnWriteArraySet.java b/libjava/classpath/external/jsr166/java/util/concurrent/CopyOnWriteArraySet.java new file mode 100644 index 00000000000..39c0e5868de --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/CopyOnWriteArraySet.java @@ -0,0 +1,364 @@ +/* + * 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 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> + * 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)); + } +} |