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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 jsr166x; |
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|
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import java.util.*; |
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import java.util.concurrent.*; |
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|
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/** |
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* A scalable concurrent {@link NavigableSet} implementation based on |
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* a {@link ConcurrentSkipListMap}. This class maintains a set in |
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* ascending order, sorted according to the <i>natural order</i> for |
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* the element's class (see {@link Comparable}), or by the comparator |
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* provided at creation time, depending on which constructor is |
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* used. |
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* |
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* <p>This implementation provides expected average <i>log(n)</i> time |
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* cost for the {@code contains}, {@code add}, and {@code remove} |
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* operations and their variants. Insertion, removal, and access |
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* operations safely execute concurrently by multiple |
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* threads. Iterators are <i>weakly consistent</i>, returning elements |
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* reflecting the state of the set at some point at or since the |
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* creation of the iterator. They do <em>not</em> throw {@link |
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* ConcurrentModificationException}, and may proceed concurrently with |
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* other operations. |
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* |
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* <p>Beware that, unlike in most collections, the {@code size} |
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* method is <em>not</em> a constant-time operation. Because of the |
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* asynchronous nature of these sets, determining the current number |
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* of elements requires a traversal of the elements. Additionally, the |
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* bulk operations {@code addAll}, {@code removeAll}, |
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* {@code retainAll}, and {@code containsAll} are <em>not</em> |
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* guaranteed to be performed atomically. For example, an iterator |
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* operating concurrently with an {@code addAll} operation might view |
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* only some of the added elements. |
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* |
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* <p>This class and its iterators implement all of the |
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* <em>optional</em> methods of the {@link Set} and {@link Iterator} |
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* interfaces. Like most other concurrent collection implementations, |
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* this class does not permit the use of {@code null} elements. |
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* because {@code null} arguments and return values cannot be reliably |
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* distinguished from the absence of elements. |
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* |
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* @author Doug Lea |
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* @param <E> the type of elements maintained by this set |
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*/ |
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public class ConcurrentSkipListSet<E> |
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extends AbstractSet<E> |
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implements NavigableSet<E>, Cloneable, java.io.Serializable { |
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|
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private static final long serialVersionUID = -2479143111061671589L; |
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|
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/** |
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* The underlying map. Uses Boolean.TRUE as value for each |
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* element. Note that this class relies on default serialization, |
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* which is a little wasteful in saving all of the useless value |
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* fields of underlying map, but enables this field to be declared |
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* final, which is necessary for thread safety. |
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*/ |
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private final ConcurrentSkipListMap<E,Object> m; |
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|
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/** |
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* Constructs a new, empty set, sorted according to the elements' natural |
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* order. |
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*/ |
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public ConcurrentSkipListSet() { |
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m = new ConcurrentSkipListMap<E,Object>(); |
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} |
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|
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/** |
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* Constructs a new, empty set, sorted according to the specified |
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* comparator. |
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* |
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* @param c the comparator that will be used to sort this set. A |
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* {@code null} value indicates that the elements' <i>natural |
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* ordering</i> should be used. |
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*/ |
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public ConcurrentSkipListSet(Comparator<? super E> c) { |
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m = new ConcurrentSkipListMap<E,Object>(c); |
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} |
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|
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/** |
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* Constructs a new set containing the elements in the specified |
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* collection, sorted according to the elements' <i>natural order</i>. |
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* |
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* @param c The elements that will comprise the new set |
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* |
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* @throws ClassCastException if the elements in the specified |
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* collection are not comparable, or are not mutually comparable |
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* @throws NullPointerException if the specified collection is |
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* {@code null} |
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*/ |
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public ConcurrentSkipListSet(Collection<? extends E> c) { |
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m = new ConcurrentSkipListMap<E,Object>(); |
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addAll(c); |
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} |
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|
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/** |
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* Constructs a new set containing the same elements as the specified |
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* sorted set, sorted according to the same ordering. |
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* |
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* @param s sorted set whose elements will comprise the new set |
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* @throws NullPointerException if the specified sorted set is |
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* {@code null} |
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*/ |
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public ConcurrentSkipListSet(SortedSet<E> s) { |
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m = new ConcurrentSkipListMap<E,Object>(s.comparator()); |
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addAll(s); |
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} |
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|
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/** |
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* Returns a shallow copy of this set. (The elements themselves |
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* are not cloned.) |
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* |
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* @return a shallow copy of this set |
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*/ |
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public Object clone() { |
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ConcurrentSkipListSet<E> clone = null; |
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try { |
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clone = (ConcurrentSkipListSet<E>) super.clone(); |
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} catch (CloneNotSupportedException e) { |
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throw new InternalError(); |
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} |
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|
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clone.m.initialize(); |
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clone.addAll(this); |
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return clone; |
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} |
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|
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/* ---------------- Set operations -------------- */ |
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|
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/** |
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* Returns the number of elements in this set. If this set |
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* contains more than {@code Integer.MAX_VALUE} elements, it |
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* returns {@code Integer.MAX_VALUE}. |
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* |
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* <p>Beware that, unlike in most collections, this method is |
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* <em>NOT</em> a constant-time operation. Because of the |
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* asynchronous nature of these sets, determining the current |
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* number of elements requires traversing them all to count them. |
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* Additionally, it is possible for the size to change during |
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* execution of this method, in which case the returned result |
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* will be inaccurate. Thus, this method is typically not very |
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* useful in concurrent applications. |
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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 m.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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* @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 m.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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* |
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* @param o the object to be checked for containment in this set |
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* @return {@code true} if this set contains the specified element |
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* |
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* @throws ClassCastException if the specified object cannot be compared |
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* with the elements currently in the set |
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* @throws NullPointerException if o is {@code null} |
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*/ |
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public boolean contains(Object o) { |
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return m.containsKey(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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* |
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* @param o element to be added to this set |
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* @return {@code true} if the set did not already contain the specified |
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* element |
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* |
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* @throws ClassCastException if the specified object cannot be compared |
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* with the elements currently in the set |
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* @throws NullPointerException if o is {@code null} |
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*/ |
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public boolean add(E o) { |
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return m.putIfAbsent(o, Boolean.TRUE) == null; |
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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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* |
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* @param o object to be removed from this set, if present |
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* @return {@code true} if the set contained the specified element |
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* |
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* @throws ClassCastException if the specified object cannot be compared |
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* with the elements currently in the set |
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* @throws NullPointerException if o is {@code null} |
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*/ |
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public boolean remove(Object o) { |
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return m.removep(o); |
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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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*/ |
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public void clear() { |
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m.clear(); |
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} |
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|
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/** |
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* Returns an iterator over the elements in this set. The elements |
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* are returned in ascending order. |
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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 m.keyIterator(); |
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} |
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|
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/** |
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* Returns an iterator over the elements in this set. The elements |
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* are returned in descending order. |
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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> descendingIterator() { |
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return m.descendingKeyIterator(); |
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} |
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|
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/* ---------------- AbstractSet Overrides -------------- */ |
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|
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/** |
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* Compares the specified object with this set for equality. Returns |
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* {@code true} if the specified object is also a set, the two sets |
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* have the same size, and every member of the specified set is |
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* contained in this set (or equivalently, every member of this set is |
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* contained in the specified set). This definition ensures that the |
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* equals method works properly across different implementations of the |
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* set interface. |
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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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// Override AbstractSet version to avoid calling size() |
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if (o == this) |
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return true; |
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if (!(o instanceof Set)) |
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return false; |
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Collection c = (Collection) o; |
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try { |
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return containsAll(c) && c.containsAll(this); |
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} catch (ClassCastException unused) { |
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return false; |
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} catch (NullPointerException unused) { |
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return false; |
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} |
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} |
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|
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/** |
| 264 |
* Removes from this set all of its elements that are contained in |
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* the specified collection. If the specified collection is also |
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* a set, this operation effectively modifies this set so that its |
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* value is the <i>asymmetric set difference</i> of the two sets. |
| 268 |
* |
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* @param c collection that defines which elements will be removed from |
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* this set |
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* @return {@code true} if this set changed as a result of the call |
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* |
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* @throws ClassCastException if the types of one or more elements in this |
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* set are incompatible with the specified collection |
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* @throws NullPointerException if the specified collection, or any |
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* of its elements are {@code null} |
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*/ |
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public boolean removeAll(Collection<?> c) { |
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// Override AbstractSet version to avoid unnecessary call to size() |
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boolean modified = false; |
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for (Iterator<?> i = c.iterator(); i.hasNext(); ) |
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if (remove(i.next())) |
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modified = true; |
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return modified; |
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} |
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|
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/* ---------------- Relational operations -------------- */ |
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|
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/** |
| 290 |
* Returns an element greater than or equal to the given element, or |
| 291 |
* {@code null} if there is no such element. |
| 292 |
* |
| 293 |
* @param o the value to match |
| 294 |
* @return an element greater than or equal to given element, or |
| 295 |
* {@code null} if there is no such element |
| 296 |
* @throws ClassCastException if o cannot be compared with the elements |
| 297 |
* currently in the set |
| 298 |
* @throws NullPointerException if o is {@code null} |
| 299 |
*/ |
| 300 |
public E ceiling(E o) { |
| 301 |
return m.ceilingKey(o); |
| 302 |
} |
| 303 |
|
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/** |
| 305 |
* Returns an element strictly less than the given element, or |
| 306 |
* {@code null} if there is no such element. |
| 307 |
* |
| 308 |
* @param o the value to match |
| 309 |
* @return the greatest element less than the given element, or |
| 310 |
* {@code null} if there is no such element |
| 311 |
* @throws ClassCastException if o cannot be compared with the elements |
| 312 |
* currently in the set |
| 313 |
* @throws NullPointerException if o is {@code null} |
| 314 |
*/ |
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public E lower(E o) { |
| 316 |
return m.lowerKey(o); |
| 317 |
} |
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|
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/** |
| 320 |
* Returns an element less than or equal to the given element, or |
| 321 |
* {@code null} if there is no such element. |
| 322 |
* |
| 323 |
* @param o the value to match |
| 324 |
* @return the greatest element less than or equal to given |
| 325 |
* element, or {@code null} if there is no such element |
| 326 |
* @throws ClassCastException if o cannot be compared with the elements |
| 327 |
* currently in the set |
| 328 |
* @throws NullPointerException if o is {@code null} |
| 329 |
*/ |
| 330 |
public E floor(E o) { |
| 331 |
return m.floorKey(o); |
| 332 |
} |
| 333 |
|
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/** |
| 335 |
* Returns an element strictly greater than the given element, or |
| 336 |
* {@code null} if there is no such element. |
| 337 |
* |
| 338 |
* @param o the value to match |
| 339 |
* @return the least element greater than the given element, or |
| 340 |
* {@code null} if there is no such element |
| 341 |
* @throws ClassCastException if o cannot be compared with the elements |
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* currently in the set |
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* @throws NullPointerException if o is {@code null} |
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*/ |
| 345 |
public E higher(E o) { |
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return m.higherKey(o); |
| 347 |
} |
| 348 |
|
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/** |
| 350 |
* Retrieves and removes the first (lowest) element. |
| 351 |
* |
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* @return the least element, or {@code null} if empty |
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*/ |
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public E pollFirst() { |
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return m.pollFirstKey(); |
| 356 |
} |
| 357 |
|
| 358 |
/** |
| 359 |
* Retrieves and removes the last (highest) element. |
| 360 |
* |
| 361 |
* @return the last element, or {@code null} if empty |
| 362 |
*/ |
| 363 |
public E pollLast() { |
| 364 |
return m.pollLastKey(); |
| 365 |
} |
| 366 |
|
| 367 |
|
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/* ---------------- SortedSet operations -------------- */ |
| 369 |
|
| 370 |
|
| 371 |
/** |
| 372 |
* Returns the comparator used to order this set, or {@code null} |
| 373 |
* if this set uses its elements natural ordering. |
| 374 |
* |
| 375 |
* @return the comparator used to order this set, or {@code null} |
| 376 |
* if this set uses its elements natural ordering |
| 377 |
*/ |
| 378 |
public Comparator<? super E> comparator() { |
| 379 |
return m.comparator(); |
| 380 |
} |
| 381 |
|
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/** |
| 383 |
* Returns the first (lowest) element currently in this set. |
| 384 |
* |
| 385 |
* @return the first (lowest) element currently in this set |
| 386 |
* @throws NoSuchElementException sorted set is empty |
| 387 |
*/ |
| 388 |
public E first() { |
| 389 |
return m.firstKey(); |
| 390 |
} |
| 391 |
|
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/** |
| 393 |
* Returns the last (highest) element currently in this set. |
| 394 |
* |
| 395 |
* @return the last (highest) element currently in this set |
| 396 |
* @throws NoSuchElementException sorted set is empty |
| 397 |
*/ |
| 398 |
public E last() { |
| 399 |
return m.lastKey(); |
| 400 |
} |
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|
| 402 |
|
| 403 |
|
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/** |
| 405 |
* Returns a view of the portion of this set whose elements range from |
| 406 |
* {@code fromElement}, inclusive, to {@code toElement}, exclusive. (If |
| 407 |
* {@code fromElement} and {@code toElement} are equal, the returned |
| 408 |
* sorted set is empty.) The returned sorted set is backed by this set, |
| 409 |
* so changes in the returned sorted set are reflected in this set, and |
| 410 |
* vice-versa. |
| 411 |
* @param fromElement low endpoint (inclusive) of the subSet |
| 412 |
* @param toElement high endpoint (exclusive) of the subSet |
| 413 |
* @return a view of the portion of this set whose elements range from |
| 414 |
* {@code fromElement}, inclusive, to {@code toElement}, |
| 415 |
* exclusive |
| 416 |
* @throws ClassCastException if {@code fromElement} and |
| 417 |
* {@code toElement} cannot be compared to one another using |
| 418 |
* this set's comparator (or, if the set has no comparator, |
| 419 |
* using natural ordering) |
| 420 |
* @throws IllegalArgumentException if {@code fromElement} is |
| 421 |
* greater than {@code toElement} |
| 422 |
* @throws NullPointerException if {@code fromElement} or |
| 423 |
* {@code toElement} is {@code null} |
| 424 |
*/ |
| 425 |
public NavigableSet<E> subSet(E fromElement, E toElement) { |
| 426 |
return new ConcurrentSkipListSubSet<E>(m, fromElement, toElement); |
| 427 |
} |
| 428 |
|
| 429 |
/** |
| 430 |
* Returns a view of the portion of this set whose elements are strictly |
| 431 |
* less than {@code toElement}. The returned sorted set is backed by |
| 432 |
* this set, so changes in the returned sorted set are reflected in this |
| 433 |
* set, and vice-versa. |
| 434 |
* @param toElement high endpoint (exclusive) of the headSet |
| 435 |
* @return a view of the portion of this set whose elements are strictly |
| 436 |
* less than toElement |
| 437 |
* @throws ClassCastException if {@code toElement} is not compatible |
| 438 |
* with this set's comparator (or, if the set has no comparator, |
| 439 |
* if {@code toElement} does not implement {@code Comparable}) |
| 440 |
* @throws NullPointerException if {@code toElement} is {@code null} |
| 441 |
*/ |
| 442 |
public NavigableSet<E> headSet(E toElement) { |
| 443 |
return new ConcurrentSkipListSubSet<E>(m, null, toElement); |
| 444 |
} |
| 445 |
|
| 446 |
|
| 447 |
/** |
| 448 |
* Returns a view of the portion of this set whose elements are |
| 449 |
* greater than or equal to {@code fromElement}. The returned |
| 450 |
* sorted set is backed by this set, so changes in the returned |
| 451 |
* sorted set are reflected in this set, and vice-versa. |
| 452 |
* @param fromElement low endpoint (inclusive) of the tailSet |
| 453 |
* @return a view of the portion of this set whose elements are |
| 454 |
* greater than or equal to {@code fromElement} |
| 455 |
* @throws ClassCastException if {@code fromElement} is not |
| 456 |
* compatible with this set's comparator (or, if the set has no |
| 457 |
* comparator, if {@code fromElement} does not implement |
| 458 |
* {@code Comparable}) |
| 459 |
* @throws NullPointerException if {@code fromElement} is {@code null} |
| 460 |
*/ |
| 461 |
public NavigableSet<E> tailSet(E fromElement) { |
| 462 |
return new ConcurrentSkipListSubSet<E>(m, fromElement, null); |
| 463 |
} |
| 464 |
|
| 465 |
/** |
| 466 |
* Subsets returned by {@link ConcurrentSkipListSet} subset operations |
| 467 |
* represent a subrange of elements of their underlying |
| 468 |
* sets. Instances of this class support all methods of their |
| 469 |
* underlying sets, differing in that elements outside their range are |
| 470 |
* ignored, and attempts to add elements outside their ranges result |
| 471 |
* in {@link IllegalArgumentException}. Instances of this class are |
| 472 |
* constructed only using the {@code subSet}, {@code headSet}, and |
| 473 |
* {@code tailSet} methods of their underlying sets. |
| 474 |
*/ |
| 475 |
static class ConcurrentSkipListSubSet<E> |
| 476 |
extends AbstractSet<E> |
| 477 |
implements NavigableSet<E>, java.io.Serializable { |
| 478 |
|
| 479 |
private static final long serialVersionUID = -7647078645896651609L; |
| 480 |
|
| 481 |
/** The underlying submap */ |
| 482 |
private final ConcurrentSkipListMap.ConcurrentSkipListSubMap<E,Object> s; |
| 483 |
|
| 484 |
/** |
| 485 |
* Creates a new submap. |
| 486 |
* @param fromElement inclusive least value, or {@code null} if from start |
| 487 |
* @param toElement exclusive upper bound, or {@code null} if to end |
| 488 |
* @throws IllegalArgumentException if fromElement and toElement |
| 489 |
* non-null and fromElement greater than toElement |
| 490 |
*/ |
| 491 |
ConcurrentSkipListSubSet(ConcurrentSkipListMap<E,Object> map, |
| 492 |
E fromElement, E toElement) { |
| 493 |
s = new ConcurrentSkipListMap.ConcurrentSkipListSubMap<E,Object> |
| 494 |
(map, fromElement, toElement); |
| 495 |
} |
| 496 |
|
| 497 |
// subsubset construction |
| 498 |
|
| 499 |
public NavigableSet<E> subSet(E fromElement, E toElement) { |
| 500 |
if (!s.inOpenRange(fromElement) || !s.inOpenRange(toElement)) |
| 501 |
throw new IllegalArgumentException("element out of range"); |
| 502 |
return new ConcurrentSkipListSubSet<E>(s.getMap(), |
| 503 |
fromElement, toElement); |
| 504 |
} |
| 505 |
|
| 506 |
public NavigableSet<E> headSet(E toElement) { |
| 507 |
E least = s.getLeast(); |
| 508 |
if (!s.inOpenRange(toElement)) |
| 509 |
throw new IllegalArgumentException("element out of range"); |
| 510 |
return new ConcurrentSkipListSubSet<E>(s.getMap(), |
| 511 |
least, toElement); |
| 512 |
} |
| 513 |
|
| 514 |
public NavigableSet<E> tailSet(E fromElement) { |
| 515 |
E fence = s.getFence(); |
| 516 |
if (!s.inOpenRange(fromElement)) |
| 517 |
throw new IllegalArgumentException("element out of range"); |
| 518 |
return new ConcurrentSkipListSubSet<E>(s.getMap(), |
| 519 |
fromElement, fence); |
| 520 |
} |
| 521 |
|
| 522 |
// relays to submap methods |
| 523 |
|
| 524 |
public int size() { return s.size(); } |
| 525 |
public boolean isEmpty() { return s.isEmpty(); } |
| 526 |
public boolean contains(Object o) { return s.containsKey(o); } |
| 527 |
public void clear() { s.clear(); } |
| 528 |
public E first() { return s.firstKey(); } |
| 529 |
public E last() { return s.lastKey(); } |
| 530 |
public E ceiling(E o) { return s.ceilingKey(o); } |
| 531 |
public E lower(E o) { return s.lowerKey(o); } |
| 532 |
public E floor(E o) { return s.floorKey(o); } |
| 533 |
public E higher(E o) { return s.higherKey(o); } |
| 534 |
public boolean remove(Object o) { return s.remove(o)==Boolean.TRUE; } |
| 535 |
public boolean add(E o) { return s.put(o, Boolean.TRUE)==null; } |
| 536 |
public Comparator<? super E> comparator() { return s.comparator(); } |
| 537 |
public Iterator<E> iterator() { return s.keySet().iterator(); } |
| 538 |
public Iterator<E> descendingIterator() { |
| 539 |
return s.descendingKeySet().iterator(); |
| 540 |
} |
| 541 |
public E pollFirst() { |
| 542 |
Map.Entry<E,?> e = s.pollFirstEntry(); |
| 543 |
return (e == null) ? null : e.getKey(); |
| 544 |
} |
| 545 |
public E pollLast() { |
| 546 |
Map.Entry<E,?> e = s.pollLastEntry(); |
| 547 |
return (e == null) ? null : e.getKey(); |
| 548 |
} |
| 549 |
|
| 550 |
} |
| 551 |
} |
