jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent;
jaroslav@1890: import java.util.*;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * A scalable concurrent {@link NavigableSet} implementation based on
jaroslav@1890:  * a {@link ConcurrentSkipListMap}.  The elements of the set are kept
jaroslav@1890:  * sorted according to their {@linkplain Comparable natural ordering},
jaroslav@1890:  * or by a {@link Comparator} provided at set creation time, depending
jaroslav@1890:  * on which constructor is used.
jaroslav@1890:  *
jaroslav@1890:  * <p>This implementation provides expected average <i>log(n)</i> time
jaroslav@1890:  * cost for the <tt>contains</tt>, <tt>add</tt>, and <tt>remove</tt>
jaroslav@1890:  * operations and their variants.  Insertion, removal, and access
jaroslav@1890:  * operations safely execute concurrently by multiple threads.
jaroslav@1890:  * Iterators are <i>weakly consistent</i>, returning elements
jaroslav@1890:  * reflecting the state of the set at some point at or since the
jaroslav@1890:  * creation of the iterator.  They do <em>not</em> throw {@link
jaroslav@1890:  * ConcurrentModificationException}, and may proceed concurrently with
jaroslav@1890:  * other operations.  Ascending ordered views and their iterators are
jaroslav@1890:  * faster than descending ones.
jaroslav@1890:  *
jaroslav@1890:  * <p>Beware that, unlike in most collections, the <tt>size</tt>
jaroslav@1890:  * method is <em>not</em> a constant-time operation. Because of the
jaroslav@1890:  * asynchronous nature of these sets, determining the current number
jaroslav@1890:  * of elements requires a traversal of the elements, and so may report
jaroslav@1890:  * inaccurate results if this collection is modified during traversal.
jaroslav@1890:  * Additionally, the bulk operations <tt>addAll</tt>,
jaroslav@1890:  * <tt>removeAll</tt>, <tt>retainAll</tt>, <tt>containsAll</tt>,
jaroslav@1890:  * <tt>equals</tt>, and <tt>toArray</tt> are <em>not</em> guaranteed
jaroslav@1890:  * to be performed atomically. For example, an iterator operating
jaroslav@1890:  * concurrently with an <tt>addAll</tt> operation might view only some
jaroslav@1890:  * of the added elements.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class and its iterators implement all of the
jaroslav@1890:  * <em>optional</em> methods of the {@link Set} and {@link Iterator}
jaroslav@1890:  * interfaces. Like most other concurrent collection implementations,
jaroslav@1890:  * this class does not permit the use of <tt>null</tt> elements,
jaroslav@1890:  * because <tt>null</tt> arguments and return values cannot be reliably
jaroslav@1890:  * distinguished from the absence of elements.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class is a member of the
jaroslav@1890:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@1890:  * Java Collections Framework</a>.
jaroslav@1890:  *
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  * @param <E> the type of elements maintained by this set
jaroslav@1890:  * @since 1.6
jaroslav@1890:  */
jaroslav@1890: public class ConcurrentSkipListSet<E>
jaroslav@1890:     extends AbstractSet<E>
jaroslav@1890:     implements NavigableSet<E>, Cloneable, java.io.Serializable {
jaroslav@1890: 
jaroslav@1890:     private static final long serialVersionUID = -2479143111061671589L;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The underlying map. Uses Boolean.TRUE as value for each
jaroslav@1890:      * element.  This field is declared final for the sake of thread
jaroslav@1890:      * safety, which entails some ugliness in clone()
jaroslav@1890:      */
jaroslav@1895:     private ConcurrentNavigableMap<E,Object> m;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Constructs a new, empty set that orders its elements according to
jaroslav@1890:      * their {@linkplain Comparable natural ordering}.
jaroslav@1890:      */
jaroslav@1890:     public ConcurrentSkipListSet() {
jaroslav@1890:         m = new ConcurrentSkipListMap<E,Object>();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Constructs a new, empty set that orders its elements according to
jaroslav@1890:      * the specified comparator.
jaroslav@1890:      *
jaroslav@1890:      * @param comparator the comparator that will be used to order this set.
jaroslav@1890:      *        If <tt>null</tt>, the {@linkplain Comparable natural
jaroslav@1890:      *        ordering} of the elements will be used.
jaroslav@1890:      */
jaroslav@1890:     public ConcurrentSkipListSet(Comparator<? super E> comparator) {
jaroslav@1890:         m = new ConcurrentSkipListMap<E,Object>(comparator);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Constructs a new set containing the elements in the specified
jaroslav@1890:      * collection, that orders its elements according to their
jaroslav@1890:      * {@linkplain Comparable natural ordering}.
jaroslav@1890:      *
jaroslav@1890:      * @param c The elements that will comprise the new set
jaroslav@1890:      * @throws ClassCastException if the elements in <tt>c</tt> are
jaroslav@1890:      *         not {@link Comparable}, or are not mutually comparable
jaroslav@1890:      * @throws NullPointerException if the specified collection or any
jaroslav@1890:      *         of its elements are null
jaroslav@1890:      */
jaroslav@1890:     public ConcurrentSkipListSet(Collection<? extends E> c) {
jaroslav@1890:         m = new ConcurrentSkipListMap<E,Object>();
jaroslav@1890:         addAll(c);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Constructs a new set containing the same elements and using the
jaroslav@1890:      * same ordering as the specified sorted set.
jaroslav@1890:      *
jaroslav@1890:      * @param s sorted set whose elements will comprise the new set
jaroslav@1890:      * @throws NullPointerException if the specified sorted set or any
jaroslav@1890:      *         of its elements are null
jaroslav@1890:      */
jaroslav@1890:     public ConcurrentSkipListSet(SortedSet<E> s) {
jaroslav@1890:         m = new ConcurrentSkipListMap<E,Object>(s.comparator());
jaroslav@1890:         addAll(s);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * For use by submaps
jaroslav@1890:      */
jaroslav@1890:     ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) {
jaroslav@1890:         this.m = m;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a shallow copy of this <tt>ConcurrentSkipListSet</tt>
jaroslav@1890:      * instance. (The elements themselves are not cloned.)
jaroslav@1890:      *
jaroslav@1890:      * @return a shallow copy of this set
jaroslav@1890:      */
jaroslav@1890:     public ConcurrentSkipListSet<E> clone() {
jaroslav@1890:         ConcurrentSkipListSet<E> clone = null;
jaroslav@1890:         try {
jaroslav@1890:             clone = (ConcurrentSkipListSet<E>) super.clone();
jaroslav@1890:             clone.setMap(new ConcurrentSkipListMap(m));
jaroslav@1890:         } catch (CloneNotSupportedException e) {
jaroslav@1890:             throw new InternalError();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         return clone;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /* ---------------- Set operations -------------- */
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the number of elements in this set.  If this set
jaroslav@1890:      * contains more than <tt>Integer.MAX_VALUE</tt> elements, it
jaroslav@1890:      * returns <tt>Integer.MAX_VALUE</tt>.
jaroslav@1890:      *
jaroslav@1890:      * <p>Beware that, unlike in most collections, this method is
jaroslav@1890:      * <em>NOT</em> a constant-time operation. Because of the
jaroslav@1890:      * asynchronous nature of these sets, determining the current
jaroslav@1890:      * number of elements requires traversing them all to count them.
jaroslav@1890:      * Additionally, it is possible for the size to change during
jaroslav@1890:      * execution of this method, in which case the returned result
jaroslav@1890:      * will be inaccurate. Thus, this method is typically not very
jaroslav@1890:      * useful in concurrent applications.
jaroslav@1890:      *
jaroslav@1890:      * @return the number of elements in this set
jaroslav@1890:      */
jaroslav@1890:     public int size() {
jaroslav@1890:         return m.size();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns <tt>true</tt> if this set contains no elements.
jaroslav@1890:      * @return <tt>true</tt> if this set contains no elements
jaroslav@1890:      */
jaroslav@1890:     public boolean isEmpty() {
jaroslav@1890:         return m.isEmpty();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns <tt>true</tt> if this set contains the specified element.
jaroslav@1890:      * More formally, returns <tt>true</tt> if and only if this set
jaroslav@1890:      * contains an element <tt>e</tt> such that <tt>o.equals(e)</tt>.
jaroslav@1890:      *
jaroslav@1890:      * @param o object to be checked for containment in this set
jaroslav@1890:      * @return <tt>true</tt> if this set contains the specified element
jaroslav@1890:      * @throws ClassCastException if the specified element cannot be
jaroslav@1890:      *         compared with the elements currently in this set
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean contains(Object o) {
jaroslav@1890:         return m.containsKey(o);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Adds the specified element to this set if it is not already present.
jaroslav@1890:      * More formally, adds the specified element <tt>e</tt> to this set if
jaroslav@1890:      * the set contains no element <tt>e2</tt> such that <tt>e.equals(e2)</tt>.
jaroslav@1890:      * If this set already contains the element, the call leaves the set
jaroslav@1890:      * unchanged and returns <tt>false</tt>.
jaroslav@1890:      *
jaroslav@1890:      * @param e element to be added to this set
jaroslav@1890:      * @return <tt>true</tt> if this set did not already contain the
jaroslav@1890:      *         specified element
jaroslav@1890:      * @throws ClassCastException if <tt>e</tt> cannot be compared
jaroslav@1890:      *         with the elements currently in this set
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean add(E e) {
jaroslav@1890:         return m.putIfAbsent(e, Boolean.TRUE) == null;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes the specified element from this set if it is present.
jaroslav@1890:      * More formally, removes an element <tt>e</tt> such that
jaroslav@1890:      * <tt>o.equals(e)</tt>, if this set contains such an element.
jaroslav@1890:      * Returns <tt>true</tt> if this set contained the element (or
jaroslav@1890:      * equivalently, if this set changed as a result of the call).
jaroslav@1890:      * (This set will not contain the element once the call returns.)
jaroslav@1890:      *
jaroslav@1890:      * @param o object to be removed from this set, if present
jaroslav@1890:      * @return <tt>true</tt> if this set contained the specified element
jaroslav@1890:      * @throws ClassCastException if <tt>o</tt> cannot be compared
jaroslav@1890:      *         with the elements currently in this set
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean remove(Object o) {
jaroslav@1890:         return m.remove(o, Boolean.TRUE);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes all of the elements from this set.
jaroslav@1890:      */
jaroslav@1890:     public void clear() {
jaroslav@1890:         m.clear();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an iterator over the elements in this set in ascending order.
jaroslav@1890:      *
jaroslav@1890:      * @return an iterator over the elements in this set in ascending order
jaroslav@1890:      */
jaroslav@1890:     public Iterator<E> iterator() {
jaroslav@1890:         return m.navigableKeySet().iterator();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an iterator over the elements in this set in descending order.
jaroslav@1890:      *
jaroslav@1890:      * @return an iterator over the elements in this set in descending order
jaroslav@1890:      */
jaroslav@1890:     public Iterator<E> descendingIterator() {
jaroslav@1890:         return m.descendingKeySet().iterator();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /* ---------------- AbstractSet Overrides -------------- */
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Compares the specified object with this set for equality.  Returns
jaroslav@1890:      * <tt>true</tt> if the specified object is also a set, the two sets
jaroslav@1890:      * have the same size, and every member of the specified set is
jaroslav@1890:      * contained in this set (or equivalently, every member of this set is
jaroslav@1890:      * contained in the specified set).  This definition ensures that the
jaroslav@1890:      * equals method works properly across different implementations of the
jaroslav@1890:      * set interface.
jaroslav@1890:      *
jaroslav@1890:      * @param o the object to be compared for equality with this set
jaroslav@1890:      * @return <tt>true</tt> if the specified object is equal to this set
jaroslav@1890:      */
jaroslav@1890:     public boolean equals(Object o) {
jaroslav@1890:         // Override AbstractSet version to avoid calling size()
jaroslav@1890:         if (o == this)
jaroslav@1890:             return true;
jaroslav@1890:         if (!(o instanceof Set))
jaroslav@1890:             return false;
jaroslav@1890:         Collection<?> c = (Collection<?>) o;
jaroslav@1890:         try {
jaroslav@1890:             return containsAll(c) && c.containsAll(this);
jaroslav@1890:         } catch (ClassCastException unused)   {
jaroslav@1890:             return false;
jaroslav@1890:         } catch (NullPointerException unused) {
jaroslav@1890:             return false;
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes from this set all of its elements that are contained in
jaroslav@1890:      * the specified collection.  If the specified collection is also
jaroslav@1890:      * a set, this operation effectively modifies this set so that its
jaroslav@1890:      * value is the <i>asymmetric set difference</i> of the two sets.
jaroslav@1890:      *
jaroslav@1890:      * @param  c collection containing elements to be removed from this set
jaroslav@1890:      * @return <tt>true</tt> if this set changed as a result of the call
jaroslav@1890:      * @throws ClassCastException if the types of one or more elements in this
jaroslav@1890:      *         set are incompatible with the specified collection
jaroslav@1890:      * @throws NullPointerException if the specified collection or any
jaroslav@1890:      *         of its elements are null
jaroslav@1890:      */
jaroslav@1890:     public boolean removeAll(Collection<?> c) {
jaroslav@1890:         // Override AbstractSet version to avoid unnecessary call to size()
jaroslav@1890:         boolean modified = false;
jaroslav@1890:         for (Iterator<?> i = c.iterator(); i.hasNext(); )
jaroslav@1890:             if (remove(i.next()))
jaroslav@1890:                 modified = true;
jaroslav@1890:         return modified;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /* ---------------- Relational operations -------------- */
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public E lower(E e) {
jaroslav@1890:         return m.lowerKey(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public E floor(E e) {
jaroslav@1890:         return m.floorKey(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public E ceiling(E e) {
jaroslav@1890:         return m.ceilingKey(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public E higher(E e) {
jaroslav@1890:         return m.higherKey(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollFirst() {
jaroslav@1890:         Map.Entry<E,Object> e = m.pollFirstEntry();
jaroslav@1890:         return (e == null) ? null : e.getKey();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollLast() {
jaroslav@1890:         Map.Entry<E,Object> e = m.pollLastEntry();
jaroslav@1890:         return (e == null) ? null : e.getKey();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /* ---------------- SortedSet operations -------------- */
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     public Comparator<? super E> comparator() {
jaroslav@1890:         return m.comparator();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E first() {
jaroslav@1890:         return m.firstKey();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E last() {
jaroslav@1890:         return m.lastKey();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code fromElement} or
jaroslav@1890:      *         {@code toElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> subSet(E fromElement,
jaroslav@1890:                                   boolean fromInclusive,
jaroslav@1890:                                   E toElement,
jaroslav@1890:                                   boolean toInclusive) {
jaroslav@1890:         return new ConcurrentSkipListSet<E>
jaroslav@1890:             (m.subMap(fromElement, fromInclusive,
jaroslav@1890:                       toElement,   toInclusive));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code toElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> headSet(E toElement, boolean inclusive) {
jaroslav@1890:         return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code fromElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
jaroslav@1890:         return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code fromElement} or
jaroslav@1890:      *         {@code toElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> subSet(E fromElement, E toElement) {
jaroslav@1890:         return subSet(fromElement, true, toElement, false);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code toElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> headSet(E toElement) {
jaroslav@1890:         return headSet(toElement, false);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws ClassCastException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException if {@code fromElement} is null
jaroslav@1890:      * @throws IllegalArgumentException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> tailSet(E fromElement) {
jaroslav@1890:         return tailSet(fromElement, true);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a reverse order view of the elements contained in this set.
jaroslav@1890:      * The descending set is backed by this set, so changes to the set are
jaroslav@1890:      * reflected in the descending set, and vice-versa.
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned set has an ordering equivalent to
jaroslav@1890:      * <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
jaroslav@1890:      * The expression {@code s.descendingSet().descendingSet()} returns a
jaroslav@1890:      * view of {@code s} essentially equivalent to {@code s}.
jaroslav@1890:      *
jaroslav@1890:      * @return a reverse order view of this set
jaroslav@1890:      */
jaroslav@1890:     public NavigableSet<E> descendingSet() {
jaroslav@1890:         return new ConcurrentSkipListSet(m.descendingMap());
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Support for resetting map in clone
jaroslav@1890:     private void setMap(ConcurrentNavigableMap<E,Object> map) {
jaroslav@1895:         this.m = map;
jaroslav@1890:     }
jaroslav@1890: }