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527 lines
18 KiB
527 lines
18 KiB
/*
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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/*
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*
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*
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*
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*
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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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package java.util.concurrent;
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import java.util.AbstractSet;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.Iterator;
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import java.util.Map;
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import java.util.NavigableMap;
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import java.util.NavigableSet;
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import java.util.Set;
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import java.util.SortedSet;
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import java.util.Spliterator;
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/**
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* A scalable concurrent {@link NavigableSet} implementation based on
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* a {@link ConcurrentSkipListMap}. The elements of the set are kept
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* sorted according to their {@linkplain Comparable natural ordering},
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* or by a {@link Comparator} provided at set creation time, depending
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* on which constructor is 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 threads.
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*
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* <p>Iterators and spliterators are
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* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
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*
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* <p>Ascending ordered views and their iterators are faster than
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* descending ones.
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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, and so may report
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* inaccurate results if this collection is modified during traversal.
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* Additionally, the bulk operations {@code addAll},
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* {@code removeAll}, {@code retainAll}, {@code containsAll},
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* {@code equals}, and {@code toArray} are <em>not</em> guaranteed
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* to be performed atomically. For example, an iterator operating
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* concurrently with an {@code addAll} operation might view only some
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* 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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* <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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* @author Doug Lea
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* @param <E> the type of elements maintained by this set
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* @since 1.6
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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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private static final long serialVersionUID = -2479143111061671589L;
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/**
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* The underlying map. Uses Boolean.TRUE as value for each
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* element. This field is declared final for the sake of thread
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* safety, which entails some ugliness in clone().
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*/
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private final ConcurrentNavigableMap<E,Object> m;
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/**
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* Constructs a new, empty set that orders its elements according to
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* their {@linkplain Comparable natural ordering}.
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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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* Constructs a new, empty set that orders its elements according to
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* the specified comparator.
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*
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* @param comparator the comparator that will be used to order this set.
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* If {@code null}, the {@linkplain Comparable natural
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* ordering} of the elements will be used.
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*/
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public ConcurrentSkipListSet(Comparator<? super E> comparator) {
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m = new ConcurrentSkipListMap<E,Object>(comparator);
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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, that orders its elements according to their
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* {@linkplain Comparable natural ordering}.
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*
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* @param c The elements that will comprise the new set
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* @throws ClassCastException if the elements in {@code c} are
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* not {@link Comparable}, or are not mutually comparable
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* @throws NullPointerException if the specified collection or any
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* of its elements are 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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* Constructs a new set containing the same elements and using the
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* same ordering as the specified sorted set.
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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 or any
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* of its elements are 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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* For use by submaps
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*/
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ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) {
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this.m = m;
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}
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/**
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* Returns a shallow copy of this {@code ConcurrentSkipListSet}
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* instance. (The elements themselves 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 ConcurrentSkipListSet<E> clone() {
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try {
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@SuppressWarnings("unchecked")
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ConcurrentSkipListSet<E> clone =
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(ConcurrentSkipListSet<E>) super.clone();
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clone.setMap(new ConcurrentSkipListMap<E,Object>(m));
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return 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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/* ---------------- Set operations -------------- */
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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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* 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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* 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 o.equals(e)}.
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*
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* @param o 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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* @throws ClassCastException if the specified element cannot be
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* compared with the elements currently in this set
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* @throws NullPointerException if the specified element is 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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* 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 {@code e.equals(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
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* specified element
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* @throws ClassCastException if {@code e} cannot be compared
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* with the elements currently in this set
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* @throws NullPointerException if the specified element is null
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*/
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public boolean add(E e) {
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return m.putIfAbsent(e, Boolean.TRUE) == null;
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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 o.equals(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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* @throws ClassCastException if {@code o} cannot be compared
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* with the elements currently in this set
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* @throws NullPointerException if the specified element is null
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*/
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public boolean remove(Object o) {
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return m.remove(o, Boolean.TRUE);
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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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* Returns an iterator over the elements in this set in ascending order.
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*
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* @return an iterator over the elements in this set in ascending order
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*/
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public Iterator<E> iterator() {
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return m.navigableKeySet().iterator();
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}
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/**
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* Returns an iterator over the elements in this set in descending order.
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*
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* @return an iterator over the elements in this set in descending order
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*/
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public Iterator<E> descendingIterator() {
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return m.descendingKeySet().iterator();
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}
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/* ---------------- AbstractSet Overrides -------------- */
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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 the 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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* 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.
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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 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 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 (Object e : c)
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if (remove(e))
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modified = true;
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return modified;
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}
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/* ---------------- Relational operations -------------- */
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if the specified element is null
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*/
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public E lower(E e) {
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return m.lowerKey(e);
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if the specified element is null
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*/
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public E floor(E e) {
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return m.floorKey(e);
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if the specified element is null
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*/
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public E ceiling(E e) {
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return m.ceilingKey(e);
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if the specified element is null
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*/
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public E higher(E e) {
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return m.higherKey(e);
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}
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public E pollFirst() {
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Map.Entry<E,Object> e = m.pollFirstEntry();
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return (e == null) ? null : e.getKey();
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}
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public E pollLast() {
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Map.Entry<E,Object> e = m.pollLastEntry();
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return (e == null) ? null : e.getKey();
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}
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/* ---------------- SortedSet operations -------------- */
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public Comparator<? super E> comparator() {
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return m.comparator();
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}
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/**
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* @throws java.util.NoSuchElementException {@inheritDoc}
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*/
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public E first() {
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return m.firstKey();
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}
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/**
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* @throws java.util.NoSuchElementException {@inheritDoc}
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*/
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public E last() {
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return m.lastKey();
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code fromElement} or
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* {@code toElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> subSet(E fromElement,
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boolean fromInclusive,
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E toElement,
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boolean toInclusive) {
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return new ConcurrentSkipListSet<E>
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(m.subMap(fromElement, fromInclusive,
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toElement, toInclusive));
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code toElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> headSet(E toElement, boolean inclusive) {
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return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code fromElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
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return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive));
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code fromElement} or
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* {@code toElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> subSet(E fromElement, E toElement) {
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return subSet(fromElement, true, toElement, false);
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code toElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> headSet(E toElement) {
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return headSet(toElement, false);
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}
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if {@code fromElement} is null
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* @throws IllegalArgumentException {@inheritDoc}
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*/
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public NavigableSet<E> tailSet(E fromElement) {
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return tailSet(fromElement, true);
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}
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/**
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* Returns a reverse order view of the elements contained in this set.
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* The descending set is backed by this set, so changes to the set are
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* reflected in the descending set, and vice-versa.
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*
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* <p>The returned set has an ordering equivalent to
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* {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
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* The expression {@code s.descendingSet().descendingSet()} returns a
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* view of {@code s} essentially equivalent to {@code s}.
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*
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* @return a reverse order view of this set
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*/
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public NavigableSet<E> descendingSet() {
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return new ConcurrentSkipListSet<E>(m.descendingMap());
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}
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/**
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* Returns a {@link Spliterator} over the elements in this set.
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*
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* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
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* {@link Spliterator#NONNULL}, {@link Spliterator#DISTINCT},
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* {@link Spliterator#SORTED} and {@link Spliterator#ORDERED}, with an
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* encounter order that is ascending order. Overriding implementations
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* should document the reporting of additional characteristic values.
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*
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* <p>The spliterator's comparator (see
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* {@link java.util.Spliterator#getComparator()}) is {@code null} if
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* the set's comparator (see {@link #comparator()}) is {@code null}.
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* Otherwise, the spliterator's comparator is the same as or imposes the
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* same total ordering as the set's comparator.
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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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@SuppressWarnings("unchecked")
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public Spliterator<E> spliterator() {
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if (m instanceof ConcurrentSkipListMap)
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return ((ConcurrentSkipListMap<E,?>)m).keySpliterator();
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else
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return (Spliterator<E>)((ConcurrentSkipListMap.SubMap<E,?>)m).keyIterator();
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}
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// Support for resetting map in clone
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private void setMap(ConcurrentNavigableMap<E,Object> map) {
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UNSAFE.putObjectVolatile(this, mapOffset, map);
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}
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private static final sun.misc.Unsafe UNSAFE;
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private static final long mapOffset;
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static {
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try {
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UNSAFE = sun.misc.Unsafe.getUnsafe();
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Class<?> k = ConcurrentSkipListSet.class;
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mapOffset = UNSAFE.objectFieldOffset
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(k.getDeclaredField("m"));
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} catch (Exception e) {
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throw new Error(e);
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}
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}
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}
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