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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/licenses/publicdomain |
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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 SortedSet} and (priority) {@link |
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* Queue} implementation based on a {@link ConcurrentSkipListMap}. |
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* This class maintains a set in ascending order, sorted according to |
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* the <i>natural order</i> for the element's class (see {@link |
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* Comparable}), or by the comparator provided at creation time, |
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* depending on which constructor is used.<p> |
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* |
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* This implementation provides expected average <i>log(n)</i> time |
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* cost for the <tt>contains</tt>, <tt>add</tt>, and <tt>remove</tt> |
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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 procede concurrently with |
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* other operations. |
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* |
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* <p>This class provides extended <tt>SortedSet</tt> methods |
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* searching for closest matches. Methods <tt>lower</tt>, |
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* <tt>floor</tt>, <tt>ceiling</tt>, and <tt>higher</tt> return |
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* elements respectively less, less than or equal, greater than or |
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* equal, and greater than a given value, returning null if there is |
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* no such element. These methods are designed for locating, not |
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* traversing entries. To traverse, use iterators and/or |
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* <tt>subset</tt>. |
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* |
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* <p>The class additionally supports {@link Queue} methods such as |
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* <tt>poll</tt> that atomically returns and removes the first |
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* element, if one exists. Thus, this class can serve as a priority |
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* queue in which there are no duplicate elements. |
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* |
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* <p>The {@link ConcurrentSkipListSubSet} objects returned by methods |
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* <tt>subset</tt>, <tt>headSet</tt>, and <tt>tailSet</tt> support the |
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* same extended set of operations as this class, but operate on their |
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* designated subrange of elements. |
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* |
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* <p>Beware that, unlike in most collections, the <tt>size</tt> |
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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. |
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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 <tt>null</tt> elements. |
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* because 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 SortedSet<E>, Queue<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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* <tt>null</tt> 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 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 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 <tt>Integer.MAX_VALUE</tt> elements, it |
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* returns <tt>Integer.MAX_VALUE</tt>. |
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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 <tt>true</tt> if this set contains no elements. |
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* @return <tt>true</tt> 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 <tt>true</tt> 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 <tt>true</tt> 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 <tt>null</tt>. |
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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 <tt>true</tt> 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 <tt>null</tt>. |
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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 <tt>true</tt> 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 <tt>null</tt>. |
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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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/* ---------------- Queue operations -------------- */ |
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|
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/** |
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* Adds the specified element, or fails if this element is already |
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* present. |
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* @param o the element to insert. |
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* @return <tt>true</tt> if it was possible to add the element, |
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* else <tt>false</tt> |
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*/ |
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public boolean offer(E o) { |
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return add(o); |
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} |
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|
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/** |
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* Retrieves and removes the first (lowest) element. |
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* |
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* @return the least element, or <tt>null</tt> if empty. |
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*/ |
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public E poll() { |
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return m.removeFirstKey(); |
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} |
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|
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/** |
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* Retrieves and removes the first (lowest) element. This method |
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* differs from the <tt>poll</tt> method in that it throws an |
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* exception if empty. |
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* |
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* @return the first (lowest) element. |
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* @throws NoSuchElementException if empty. |
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*/ |
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public E remove() { |
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E x = m.removeFirstKey(); |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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/** |
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* Retrieves, but does not remove, the first (lowest) element, |
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* returning <tt>null</tt> if empty. |
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* |
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* @return the first (lowest) element, or <tt>null</tt> if empty. |
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*/ |
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public E peek() { |
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return m.lowestKey(); |
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} |
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|
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/** |
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* Retrieves, but does not remove, the first (lowest) element. |
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* This method differs from the <tt>peek</tt> method only in that |
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* it throws an exception if empty. |
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* |
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* @return the first (lowest) element. |
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* @throws NoSuchElementException if empty. |
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*/ |
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public E element() { |
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return m.firstKey(); |
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} |
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|
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/* ---------------- Relational operations -------------- */ |
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|
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/** |
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* Returns an element greater than or equal to the given element, or |
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* null if there is no such element. |
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* |
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* @param o the value to match |
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* @return an element greater than or equal to given element, or null |
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* if there is no such element. |
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* @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 <tt>null</tt> |
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*/ |
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public E ceiling(E o) { |
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return m.ceilingKey(o); |
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} |
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|
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/** |
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* Returns an element strictly less than the given element, or null if |
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* there is no such element. |
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* |
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* @param o the value to match |
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* @return the greatest element less than the given element, or |
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* null if there is no such element. |
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* @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 <tt>null</tt>. |
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*/ |
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public E lower(E o) { |
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return m.lowerKey(o); |
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} |
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|
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/** |
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* Returns an element less than or equal to the given element, or null |
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* if there is no such element. |
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* |
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* @param o the value to match |
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* @return the greatest element less than or equal to given |
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* element, or null if there is no such element. |
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* @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 <tt>null</tt>. |
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*/ |
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public E floor(E o) { |
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return m.floorKey(o); |
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} |
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|
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/** |
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* Returns an element strictly greater than the given element, or null |
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* if there is no such element. |
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* |
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* @param o the value to match |
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* @return the least element greater than the given element, or |
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* null if there is no such element. |
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* @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 <tt>null</tt>. |
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*/ |
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public E higher(E o) { |
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return m.higherKey(o); |
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} |
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|
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/* ---------------- SortedSet operations -------------- */ |
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|
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|
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/** |
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* Returns the comparator used to order this set, or <tt>null</tt> |
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* if this set uses its elements natural ordering. |
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* |
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* @return the comparator used to order this set, or <tt>null</tt> |
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* if this set uses its elements natural ordering. |
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*/ |
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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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/** |
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* Returns the first (lowest) element currently in this set. |
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* |
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* @return the first (lowest) element currently in this set. |
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* @throws NoSuchElementException sorted set is empty. |
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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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/** |
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* Returns the last (highest) element currently in this set. |
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* |
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* @return the last (highest) element currently in this set. |
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* @throws NoSuchElementException sorted set is empty. |
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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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/** |
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* Returns a view of the portion of this set whose elements range from |
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* <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>, exclusive. (If |
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* <tt>fromElement</tt> and <tt>toElement</tt> are equal, the returned |
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* sorted set is empty.) The returned sorted set is backed by this set, |
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* so changes in the returned sorted set are reflected in this set, and |
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* vice-versa. |
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* @param fromElement low endpoint (inclusive) of the subSet. |
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* @param toElement high endpoint (exclusive) of the subSet. |
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* @return a view of the portion of this set whose elements range from |
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* <tt>fromElement</tt>, inclusive, to <tt>toElement</tt>, |
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* exclusive. |
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* @throws ClassCastException if <tt>fromElement</tt> and |
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* <tt>toElement</tt> cannot be compared to one another using |
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* this set's comparator (or, if the set has no comparator, |
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* using natural ordering). |
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* @throws IllegalArgumentException if <tt>fromElement</tt> is |
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* greater than <tt>toElement</tt>. |
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* @throws NullPointerException if <tt>fromElement</tt> or |
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* <tt>toElement</tt> is <tt>null</tt>. |
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*/ |
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public ConcurrentSkipListSubSet<E> subSet(E fromElement, E toElement) { |
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return new ConcurrentSkipListSubSet<E>(m, fromElement, toElement); |
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} |
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|
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/** |
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* Returns a view of the portion of this set whose elements are strictly |
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* less than <tt>toElement</tt>. The returned sorted set is backed by |
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* this set, so changes in the returned sorted set are reflected in this |
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* set, and vice-versa. |
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* @param toElement high endpoint (exclusive) of the headSet. |
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* @return a view of the portion of this set whose elements are strictly |
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* less than toElement. |
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* @throws ClassCastException if <tt>toElement</tt> is not compatible |
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* with this set's comparator (or, if the set has no comparator, |
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* if <tt>toElement</tt> does not implement <tt>Comparable</tt>). |
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* @throws NullPointerException if <tt>toElement</tt> is <tt>null</tt>. |
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*/ |
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public ConcurrentSkipListSubSet<E> headSet(E toElement) { |
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return new ConcurrentSkipListSubSet<E>(m, null, toElement); |
| 430 |
} |
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|
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|
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/** |
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* Returns a view of the portion of this set whose elements are |
| 435 |
* greater than or equal to <tt>fromElement</tt>. The returned |
| 436 |
* sorted set is backed by this set, so changes in the returned |
| 437 |
* sorted set are reflected in this set, and vice-versa. |
| 438 |
* @param fromElement low endpoint (inclusive) of the tailSet. |
| 439 |
* @return a view of the portion of this set whose elements are |
| 440 |
* greater than or equal to <tt>fromElement</tt>. |
| 441 |
* @throws ClassCastException if <tt>fromElement</tt> is not |
| 442 |
* compatible with this set's comparator (or, if the set has no |
| 443 |
* comparator, if <tt>fromElement</tt> does not implement |
| 444 |
* <tt>Comparable</tt>). |
| 445 |
* @throws NullPointerException if <tt>fromElement</tt> is <tt>null</tt>. |
| 446 |
*/ |
| 447 |
public ConcurrentSkipListSubSet<E> tailSet(E fromElement) { |
| 448 |
return new ConcurrentSkipListSubSet<E>(m, fromElement, null); |
| 449 |
} |
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} |
