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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.util.AbstractSet; |
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import java.util.Collection; |
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import java.util.Iterator; |
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import java.util.Objects; |
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import java.util.Set; |
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import java.util.Spliterator; |
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import java.util.Spliterators; |
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import java.util.function.Consumer; |
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import java.util.function.Predicate; |
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|
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/** |
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* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList} |
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* for all of its operations. Thus, it shares the same basic properties: |
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* <ul> |
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* <li>It is best suited for applications in which set sizes generally |
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* stay small, read-only operations |
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* vastly outnumber mutative operations, and you need |
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* to prevent interference among threads during traversal. |
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* <li>It is thread-safe. |
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* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.) |
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* are expensive since they usually entail copying the entire underlying |
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* array. |
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* <li>Iterators do not support the mutative {@code remove} operation. |
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* <li>Traversal via iterators is fast and cannot encounter |
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* interference from other threads. Iterators rely on |
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* unchanging snapshots of the array at the time the iterators were |
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* constructed. |
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* </ul> |
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* |
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* <p><b>Sample Usage.</b> The following code sketch uses a |
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* copy-on-write set to maintain a set of Handler objects that |
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* perform some action upon state updates. |
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* |
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* <pre> {@code |
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* class Handler { void handle(); ... } |
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* |
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* class X { |
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* private final CopyOnWriteArraySet<Handler> handlers |
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* = new CopyOnWriteArraySet<>(); |
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* public void addHandler(Handler h) { handlers.add(h); } |
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* |
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* private long internalState; |
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* private synchronized void changeState() { internalState = ...; } |
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* |
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* public void update() { |
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* changeState(); |
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* for (Handler handler : handlers) |
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* handler.handle(); |
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* } |
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* }}</pre> |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @see CopyOnWriteArrayList |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this set |
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*/ |
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public class CopyOnWriteArraySet<E> extends AbstractSet<E> |
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implements java.io.Serializable { |
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private static final long serialVersionUID = 5457747651344034263L; |
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|
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private final CopyOnWriteArrayList<E> al; |
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|
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/** |
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* Creates an empty set. |
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*/ |
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public CopyOnWriteArraySet() { |
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al = new CopyOnWriteArrayList<E>(); |
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} |
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|
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/** |
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* Creates a set containing all of the elements of the specified |
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* collection. |
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* |
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* @param c the collection of elements to initially contain |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public CopyOnWriteArraySet(Collection<? extends E> c) { |
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if (c.getClass() == CopyOnWriteArraySet.class) { |
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@SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc = |
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(CopyOnWriteArraySet<E>)c; |
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al = new CopyOnWriteArrayList<E>(cc.al); |
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} |
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else { |
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al = new CopyOnWriteArrayList<E>(); |
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al.addAllAbsent(c); |
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} |
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} |
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|
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/** |
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* Returns the number of elements in this set. |
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* |
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* @return the number of elements in this set |
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*/ |
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public int size() { |
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return al.size(); |
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} |
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|
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/** |
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* Returns {@code true} if this set contains no elements. |
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* |
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* @return {@code true} if this set contains no elements |
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*/ |
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public boolean isEmpty() { |
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return al.isEmpty(); |
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} |
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|
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/** |
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* Returns {@code true} if this set contains the specified element. |
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* More formally, returns {@code true} if and only if this set |
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* contains an element {@code e} such that {@code Objects.equals(o, e)}. |
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* |
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* @param o element whose presence in this set is to be tested |
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* @return {@code true} if this set contains the specified element |
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*/ |
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public boolean contains(Object o) { |
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return al.contains(o); |
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} |
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|
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/** |
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* Returns an array containing all of the elements in this set. |
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* If this set makes any guarantees as to what order its elements |
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* are returned by its iterator, this method must return the |
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* elements in the same order. |
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* |
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* <p>The returned array will be "safe" in that no references to it |
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* are maintained by this set. (In other words, this method must |
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* allocate a new array even if this set is backed by an array). |
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* The caller is thus free to modify the returned array. |
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* |
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* <p>This method acts as bridge between array-based and collection-based |
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* APIs. |
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* |
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* @return an array containing all the elements in this set |
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*/ |
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public Object[] toArray() { |
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return al.toArray(); |
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} |
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|
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/** |
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* Returns an array containing all of the elements in this set; the |
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* runtime type of the returned array is that of the specified array. |
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* If the set fits in the specified array, it is returned therein. |
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* Otherwise, a new array is allocated with the runtime type of the |
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* specified array and the size of this set. |
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* |
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* <p>If this set fits in the specified array with room to spare |
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* (i.e., the array has more elements than this set), the element in |
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* the array immediately following the end of the set is set to |
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* {@code null}. (This is useful in determining the length of this |
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* set <i>only</i> if the caller knows that this set does not contain |
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* any null elements.) |
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* |
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* <p>If this set makes any guarantees as to what order its elements |
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* are returned by its iterator, this method must return the elements |
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* in the same order. |
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* |
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* <p>Like the {@link #toArray()} method, this method acts as bridge between |
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* array-based and collection-based APIs. Further, this method allows |
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* precise control over the runtime type of the output array, and may, |
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* under certain circumstances, be used to save allocation costs. |
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* |
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* <p>Suppose {@code x} is a set known to contain only strings. |
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* The following code can be used to dump the set into a newly allocated |
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* array of {@code String}: |
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* |
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* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
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* |
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* Note that {@code toArray(new Object[0])} is identical in function to |
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* {@code toArray()}. |
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* |
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* @param a the array into which the elements of this set are to be |
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* stored, if it is big enough; otherwise, a new array of the same |
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* runtime type is allocated for this purpose. |
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* @return an array containing all the elements in this set |
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* @throws ArrayStoreException if the runtime type of the specified array |
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* is not a supertype of the runtime type of every element in this |
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* set |
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* @throws NullPointerException if the specified array is null |
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*/ |
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public <T> T[] toArray(T[] a) { |
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return al.toArray(a); |
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} |
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|
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/** |
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* Removes all of the elements from this set. |
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* The set will be empty after this call returns. |
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*/ |
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public void clear() { |
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al.clear(); |
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} |
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|
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/** |
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* Removes the specified element from this set if it is present. |
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* More formally, removes an element {@code e} such that |
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* {@code Objects.equals(o, e)}, if this set contains such an element. |
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* Returns {@code true} if this set contained the element (or |
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* equivalently, if this set changed as a result of the call). |
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* (This set will not contain the element once the call returns.) |
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* |
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* @param o object to be removed from this set, if present |
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* @return {@code true} if this set contained the specified element |
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*/ |
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public boolean remove(Object o) { |
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return al.remove(o); |
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} |
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|
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/** |
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* Adds the specified element to this set if it is not already present. |
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* More formally, adds the specified element {@code e} to this set if |
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* the set contains no element {@code e2} such that |
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* {@code Objects.equals(e, e2)}. |
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* If this set already contains the element, the call leaves the set |
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* unchanged and returns {@code false}. |
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* |
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* @param e element to be added to this set |
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* @return {@code true} if this set did not already contain the specified |
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* element |
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*/ |
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public boolean add(E e) { |
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return al.addIfAbsent(e); |
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} |
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|
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/** |
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* Returns {@code true} if this set contains all of the elements of the |
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* specified collection. If the specified collection is also a set, this |
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* method returns {@code true} if it is a <i>subset</i> of this set. |
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* |
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* @param c collection to be checked for containment in this set |
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* @return {@code true} if this set contains all of the elements of the |
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* specified collection |
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* @throws NullPointerException if the specified collection is null |
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* @see #contains(Object) |
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*/ |
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public boolean containsAll(Collection<?> c) { |
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return (c instanceof Set) |
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? compareSets(al.getArray(), (Set<?>) c) >= 0 |
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: al.containsAll(c); |
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} |
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|
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/** |
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* Tells whether the objects in snapshot (regarded as a set) are a |
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* superset of the given set. |
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* |
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* @return -1 if snapshot is not a superset, 0 if the two sets |
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* contain precisely the same elements, and 1 if snapshot is a |
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* proper superset of the given set |
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*/ |
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private static int compareSets(Object[] snapshot, Set<?> set) { |
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// Uses O(n^2) algorithm, that is only appropriate for small |
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// sets, which CopyOnWriteArraySets should be. |
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// |
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// Optimize up to O(n) if the two sets share a long common prefix, |
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// as might happen if one set was created as a copy of the other set. |
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|
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final int len = snapshot.length; |
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// Mark matched elements to avoid re-checking |
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final boolean[] matched = new boolean[len]; |
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|
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// j is the largest int with matched[i] true for { i | 0 <= i < j } |
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int j = 0; |
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outer: for (Object x : set) { |
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for (int i = j; i < len; i++) { |
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if (!matched[i] && Objects.equals(x, snapshot[i])) { |
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matched[i] = true; |
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if (i == j) |
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do { j++; } while (j < len && matched[j]); |
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continue outer; |
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} |
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} |
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return -1; |
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} |
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return (j == len) ? 0 : 1; |
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} |
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|
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/** |
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* Adds all of the elements in the specified collection to this set if |
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* they're not already present. If the specified collection is also a |
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* set, the {@code addAll} operation effectively modifies this set so |
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* that its value is the <i>union</i> of the two sets. The behavior of |
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* this operation is undefined if the specified collection is modified |
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* while the operation is in progress. |
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* |
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* @param c collection containing elements to be added to this set |
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* @return {@code true} if this set changed as a result of the call |
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* @throws NullPointerException if the specified collection is null |
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* @see #add(Object) |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return al.addAllAbsent(c) > 0; |
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} |
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|
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/** |
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* Removes from this set all of its elements that are contained in the |
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* specified collection. If the specified collection is also a set, |
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* this operation effectively modifies this set so that its value is the |
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* <i>asymmetric set difference</i> of the two sets. |
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* |
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* @param c collection containing elements to be removed from this set |
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* @return {@code true} if this set changed as a result of the call |
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* @throws ClassCastException if the class of an element of this set |
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* is incompatible with the specified collection |
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* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
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* @throws NullPointerException if this set contains a null element and the |
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* specified collection does not permit null elements |
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* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>), |
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* or if the specified collection is null |
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* @see #remove(Object) |
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*/ |
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public boolean removeAll(Collection<?> c) { |
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return al.removeAll(c); |
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} |
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|
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/** |
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* Retains only the elements in this set that are contained in the |
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* specified collection. In other words, removes from this set all of |
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* its elements that are not contained in the specified collection. If |
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* the specified collection is also a set, this operation effectively |
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* modifies this set so that its value is the <i>intersection</i> of the |
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* two sets. |
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* |
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* @param c collection containing elements to be retained in this set |
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* @return {@code true} if this set changed as a result of the call |
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* @throws ClassCastException if the class of an element of this set |
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* is incompatible with the specified collection |
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* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
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* @throws NullPointerException if this set contains a null element and the |
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* specified collection does not permit null elements |
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* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>), |
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* or if the specified collection is null |
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* @see #remove(Object) |
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*/ |
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public boolean retainAll(Collection<?> c) { |
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return al.retainAll(c); |
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} |
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|
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/** |
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* Returns an iterator over the elements contained in this set |
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* in the order in which these elements were added. |
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* |
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* <p>The returned iterator provides a snapshot of the state of the set |
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* when the iterator was constructed. No synchronization is needed while |
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* traversing the iterator. The iterator does <em>NOT</em> support the |
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* {@code remove} method. |
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* |
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* @return an iterator over the elements in this set |
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*/ |
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public Iterator<E> iterator() { |
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return al.iterator(); |
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} |
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|
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/** |
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* Compares the specified object with this set for equality. |
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* Returns {@code true} if the specified object is the same object |
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* as this object, or if it is also a {@link Set} and the elements |
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* returned by an {@linkplain Set#iterator() iterator} over the |
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* specified set are the same as the elements returned by an |
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* iterator over this set. More formally, the two iterators are |
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* considered to return the same elements if they return the same |
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* number of elements and for every element {@code e1} returned by |
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* the iterator over the specified set, there is an element |
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* {@code e2} returned by the iterator over this set such that |
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* {@code Objects.equals(e1, e2)}. |
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* |
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* @param o object to be compared for equality with this set |
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* @return {@code true} if the specified object is equal to this set |
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*/ |
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public boolean equals(Object o) { |
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return (o == this) |
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|| ((o instanceof Set) |
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&& compareSets(al.getArray(), (Set<?>) o) == 0); |
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} |
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|
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public boolean removeIf(Predicate<? super E> filter) { |
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return al.removeIf(filter); |
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} |
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|
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public void forEach(Consumer<? super E> action) { |
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al.forEach(action); |
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} |
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|
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/** |
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* Returns a {@link Spliterator} over the elements in this set in the order |
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* in which these elements were added. |
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* |
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* <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE}, |
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* {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and |
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* {@link Spliterator#SUBSIZED}. |
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* |
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* <p>The spliterator provides a snapshot of the state of the set |
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* when the spliterator was constructed. No synchronization is needed while |
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* operating on the spliterator. |
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* |
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* @return a {@code Spliterator} over the elements in this set |
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* @since 1.8 |
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*/ |
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public Spliterator<E> spliterator() { |
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return Spliterators.spliterator |
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(al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT); |
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} |
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} |
