util/concurrent/ConcurrentSkipListSet.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.NavigableMap;
import java.util.NavigableSet;
import java.util.Set;
import java.util.SortedSet;
import java.util.Spliterator;

/**
 * A scalable concurrent {@link NavigableSet} implementation based on
 * a {@link ConcurrentSkipListMap}.  The elements of the set are kept
 * sorted according to their {@linkplain Comparable natural ordering},
 * or by a {@link Comparator} provided at set creation time, depending
 * on which constructor is used.
 *
 * <p>This implementation provides expected average <i>log(n)</i> time
 * cost for the {@code contains}, {@code add}, and {@code remove}
 * operations and their variants.  Insertion, removal, and access
 * operations safely execute concurrently by multiple threads.
 *
 * <p>Iterators and spliterators are
 * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
 *
 * <p>Ascending ordered views and their iterators are faster than
 * descending ones.
 *
 * <p>Beware that, unlike in most collections, the {@code size}
 * method is <em>not</em> a constant-time operation. Because of the
 * asynchronous nature of these sets, determining the current number
 * of elements requires a traversal of the elements, and so may report
 * inaccurate results if this collection is modified during traversal.
 * Additionally, the bulk operations {@code addAll},
 * {@code removeAll}, {@code retainAll}, {@code containsAll},
 * {@code equals}, and {@code toArray} are <em>not</em> guaranteed
 * to be performed atomically. For example, an iterator operating
 * concurrently with an {@code addAll} operation might view only some
 * of the added elements.
 *
 * <p>This class and its iterators implement all of the
 * <em>optional</em> methods of the {@link Set} and {@link Iterator}
 * interfaces. Like most other concurrent collection implementations,
 * this class does not permit the use of {@code null} elements,
 * because {@code null} arguments and return values cannot be reliably
 * distinguished from the absence of elements.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author Doug Lea
 * @param <E> the type of elements maintained by this set
 * @since 1.6
 */
public class ConcurrentSkipListSet<E>
    extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable {

    private static final long serialVersionUID = -2479143111061671589L;

    /**
     * The underlying map. Uses Boolean.TRUE as value for each
     * element.  This field is declared final for the sake of thread
     * safety, which entails some ugliness in clone().
     */
    private final ConcurrentNavigableMap<E,Object> m;

    /**
     * Constructs a new, empty set that orders its elements according to
     * their {@linkplain Comparable natural ordering}.
     */
    public ConcurrentSkipListSet() {
        m = new ConcurrentSkipListMap<E,Object>();
    }

    /**
     * Constructs a new, empty set that orders its elements according to
     * the specified comparator.
     *
     * @param comparator the comparator that will be used to order this set.
     *        If {@code null}, the {@linkplain Comparable natural
     *        ordering} of the elements will be used.
     */
    public ConcurrentSkipListSet(Comparator<? super E> comparator) {
        m = new ConcurrentSkipListMap<E,Object>(comparator);
    }

    /**
     * Constructs a new set containing the elements in the specified
     * collection, that orders its elements according to their
     * {@linkplain Comparable natural ordering}.
     *
     * @param c The elements that will comprise the new set
     * @throws ClassCastException if the elements in {@code c} are
     *         not {@link Comparable}, or are not mutually comparable
     * @throws NullPointerException if the specified collection or any
     *         of its elements are null
     */
    public ConcurrentSkipListSet(Collection<? extends E> c) {
        m = new ConcurrentSkipListMap<E,Object>();
        addAll(c);
    }

    /**
     * Constructs a new set containing the same elements and using the
     * same ordering as the specified sorted set.
     *
     * @param s sorted set whose elements will comprise the new set
     * @throws NullPointerException if the specified sorted set or any
     *         of its elements are null
     */
    public ConcurrentSkipListSet(SortedSet<E> s) {
        m = new ConcurrentSkipListMap<E,Object>(s.comparator());
        addAll(s);
    }

    /**
     * For use by submaps
     */
    ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) {
        this.m = m;
    }

    /**
     * Returns a shallow copy of this {@code ConcurrentSkipListSet}
     * instance. (The elements themselves are not cloned.)
     *
     * @return a shallow copy of this set
     */
    public ConcurrentSkipListSet<E> clone() {
        try {
            @SuppressWarnings("unchecked")
            ConcurrentSkipListSet<E> clone =
                (ConcurrentSkipListSet<E>) super.clone();
            clone.setMap(new ConcurrentSkipListMap<E,Object>(m));
            return clone;
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
    }

    /* ---------------- Set operations -------------- */

    /**
     * Returns the number of elements in this set.  If this set
     * contains more than {@code Integer.MAX_VALUE} elements, it
     * returns {@code Integer.MAX_VALUE}.
     *
     * <p>Beware that, unlike in most collections, this method is
     * <em>NOT</em> a constant-time operation. Because of the
     * asynchronous nature of these sets, determining the current
     * number of elements requires traversing them all to count them.
     * Additionally, it is possible for the size to change during
     * execution of this method, in which case the returned result
     * will be inaccurate. Thus, this method is typically not very
     * useful in concurrent applications.
     *
     * @return the number of elements in this set
     */
    public int size() {
        return m.size();
    }

    /**
     * Returns {@code true} if this set contains no elements.
     * @return {@code true} if this set contains no elements
     */
    public boolean isEmpty() {
        return m.isEmpty();
    }

    /**
     * Returns {@code true} if this set contains the specified element.
     * More formally, returns {@code true} if and only if this set
     * contains an element {@code e} such that {@code o.equals(e)}.
     *
     * @param o object to be checked for containment in this set
     * @return {@code true} if this set contains the specified element
     * @throws ClassCastException if the specified element cannot be
     *         compared with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element {@code e} to this set if
     * the set contains no element {@code e2} such that {@code e.equals(e2)}.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns {@code false}.
     *
     * @param e element to be added to this set
     * @return {@code true} if this set did not already contain the
     *         specified element
     * @throws ClassCastException if {@code e} cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     */
    public boolean add(E e) {
        return m.putIfAbsent(e, Boolean.TRUE) == null;
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element {@code e} such that
     * {@code o.equals(e)}, if this set contains such an element.
     * Returns {@code true} if this set contained the element (or
     * equivalently, if this set changed as a result of the call).
     * (This set will not contain the element once the call returns.)
     *
     * @param o object to be removed from this set, if present
     * @return {@code true} if this set contained the specified element
     * @throws ClassCastException if {@code o} cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     */
    public boolean remove(Object o) {
        return m.remove(o, Boolean.TRUE);
    }

    /**
     * Removes all of the elements from this set.
     */
    public void clear() {
        m.clear();
    }

    /**
     * Returns an iterator over the elements in this set in ascending order.
     *
     * @return an iterator over the elements in this set in ascending order
     */
    public Iterator<E> iterator() {
        return m.navigableKeySet().iterator();
    }

    /**
     * Returns an iterator over the elements in this set in descending order.
     *
     * @return an iterator over the elements in this set in descending order
     */
    public Iterator<E> descendingIterator() {
        return m.descendingKeySet().iterator();
    }


    /* ---------------- AbstractSet Overrides -------------- */

    /**
     * Compares the specified object with this set for equality.  Returns
     * {@code true} if the specified object is also a set, the two sets
     * have the same size, and every member of the specified set is
     * contained in this set (or equivalently, every member of this set is
     * contained in the specified set).  This definition ensures that the
     * equals method works properly across different implementations of the
     * set interface.
     *
     * @param o the object to be compared for equality with this set
     * @return {@code true} if the specified object is equal to this set
     */
    public boolean equals(Object o) {
        // Override AbstractSet version to avoid calling size()
        if (o == this)
            return true;
        if (!(o instanceof Set))
            return false;
        Collection<?> c = (Collection<?>) o;
        try {
            return containsAll(c) && c.containsAll(this);
        } catch (ClassCastException unused) {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }
    }

    /**
     * Removes from this set all of its elements that are contained in
     * the specified collection.  If the specified collection is also
     * a set, this operation effectively modifies this set so that its
     * value is the <i>asymmetric set difference</i> of the two sets.
     *
     * @param  c collection containing elements to be removed from this set
     * @return {@code true} if this set changed as a result of the call
     * @throws ClassCastException if the types of one or more elements in this
     *         set are incompatible with the specified collection
     * @throws NullPointerException if the specified collection or any
     *         of its elements are null
     */
    public boolean removeAll(Collection<?> c) {
        // Override AbstractSet version to avoid unnecessary call to size()
        boolean modified = false;
        for (Object e : c)
            if (remove(e))
                modified = true;
        return modified;
    }

    /* ---------------- Relational operations -------------- */

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     */
    public E lower(E e) {
        return m.lowerKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     */
    public E floor(E e) {
        return m.floorKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     */
    public E ceiling(E e) {
        return m.ceilingKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     */
    public E higher(E e) {
        return m.higherKey(e);
    }

    public E pollFirst() {
        Map.Entry<E,Object> e = m.pollFirstEntry();
        return (e == null) ? null : e.getKey();
    }

    public E pollLast() {
        Map.Entry<E,Object> e = m.pollLastEntry();
        return (e == null) ? null : e.getKey();
    }


    /* ---------------- SortedSet operations -------------- */


    public Comparator<? super E> comparator() {
        return m.comparator();
    }

    /**
     * @throws java.util.NoSuchElementException {@inheritDoc}
     */
    public E first() {
        return m.firstKey();
    }

    /**
     * @throws java.util.NoSuchElementException {@inheritDoc}
     */
    public E last() {
        return m.lastKey();
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} or
     *         {@code toElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> subSet(E fromElement,
                                  boolean fromInclusive,
                                  E toElement,
                                  boolean toInclusive) {
        return new ConcurrentSkipListSet<E>
            (m.subMap(fromElement, fromInclusive,
                      toElement,   toInclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> headSet(E toElement, boolean inclusive) {
        return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
        return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} or
     *         {@code toElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> subSet(E fromElement, E toElement) {
        return subSet(fromElement, true, toElement, false);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> headSet(E toElement) {
        return headSet(toElement, false);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} is null
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> tailSet(E fromElement) {
        return tailSet(fromElement, true);
    }

    /**
     * Returns a reverse order view of the elements contained in this set.
     * The descending set is backed by this set, so changes to the set are
     * reflected in the descending set, and vice-versa.
     *
     * <p>The returned set has an ordering equivalent to
     * {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
     * The expression {@code s.descendingSet().descendingSet()} returns a
     * view of {@code s} essentially equivalent to {@code s}.
     *
     * @return a reverse order view of this set
     */
    public NavigableSet<E> descendingSet() {
        return new ConcurrentSkipListSet<E>(m.descendingMap());
    }

    /**
     * Returns a {@link Spliterator} over the elements in this set.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
     * {@link Spliterator#NONNULL}, {@link Spliterator#DISTINCT},
     * {@link Spliterator#SORTED} and {@link Spliterator#ORDERED}, with an
     * encounter order that is ascending order.  Overriding implementations
     * should document the reporting of additional characteristic values.
     *
     * <p>The spliterator's comparator (see
     * {@link java.util.Spliterator#getComparator()}) is {@code null} if
     * the set's comparator (see {@link #comparator()}) is {@code null}.
     * Otherwise, the spliterator's comparator is the same as or imposes the
     * same total ordering as the set's comparator.
     *
     * @return a {@code Spliterator} over the elements in this set
     * @since 1.8
     */
    @SuppressWarnings("unchecked")
    public Spliterator<E> spliterator() {
        if (m instanceof ConcurrentSkipListMap)
            return ((ConcurrentSkipListMap<E,?>)m).keySpliterator();
        else
            return (Spliterator<E>)((ConcurrentSkipListMap.SubMap<E,?>)m).keyIterator();
    }

    // Support for resetting map in clone
    private void setMap(ConcurrentNavigableMap<E,Object> map) {
        UNSAFE.putObjectVolatile(this, mapOffset, map);
    }

    private static final sun.misc.Unsafe UNSAFE;
    private static final long mapOffset;
    static {
        try {
            UNSAFE = sun.misc.Unsafe.getUnsafe();
            Class<?> k = ConcurrentSkipListSet.class;
            mapOffset = UNSAFE.objectFieldOffset
                (k.getDeclaredField("m"));
        } catch (Exception e) {
            throw new Error(e);
        }
    }
}
Revision:	1.44
Committed:	Wed Dec 31 09:37:20 2014 UTC (9 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.43:	+0 -1 lines
Log Message:	remove unused/redundant imports
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4	jsr166	1.22	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			package java.util.concurrent;
8	jsr166	1.43
9	dl	1.32	import java.util.AbstractSet;
10			import java.util.Collection;
11			import java.util.Collections;
12			import java.util.Comparator;
13			import java.util.Iterator;
14			import java.util.Map;
15			import java.util.NavigableMap;
16			import java.util.NavigableSet;
17			import java.util.Set;
18			import java.util.SortedSet;
19	dl	1.31	import java.util.Spliterator;
20	dl	1.1
21			/**
22			* A scalable concurrent {@link NavigableSet} implementation based on
23	jsr166	1.11	* a {@link ConcurrentSkipListMap}. The elements of the set are kept
24			* sorted according to their {@linkplain Comparable natural ordering},
25			* or by a {@link Comparator} provided at set creation time, depending
26			* on which constructor is used.
27	dl	1.1	*
28	jsr166	1.11	* <p>This implementation provides expected average <i>log(n)</i> time
29	jsr166	1.30	* cost for the {@code contains}, {@code add}, and {@code remove}
30	dl	1.1	* operations and their variants. Insertion, removal, and access
31	jsr166	1.11	* operations safely execute concurrently by multiple threads.
32	jsr166	1.42	*
33			* <p>Iterators and spliterators are
34			* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
35			*
36			* <p>Ascending ordered views and their iterators are faster than
37			* descending ones.
38	dl	1.1	*
39	jsr166	1.30	* <p>Beware that, unlike in most collections, the {@code size}
40	dl	1.1	* method is <em>not</em> a constant-time operation. Because of the
41			* asynchronous nature of these sets, determining the current number
42	dl	1.23	* of elements requires a traversal of the elements, and so may report
43			* inaccurate results if this collection is modified during traversal.
44	jsr166	1.30	* Additionally, the bulk operations {@code addAll},
45			* {@code removeAll}, {@code retainAll}, {@code containsAll},
46			* {@code equals}, and {@code toArray} are <em>not</em> guaranteed
47	dl	1.23	* to be performed atomically. For example, an iterator operating
48	jsr166	1.30	* concurrently with an {@code addAll} operation might view only some
49	dl	1.23	* of the added elements.
50	dl	1.1	*
51			* <p>This class and its iterators implement all of the
52			* <em>optional</em> methods of the {@link Set} and {@link Iterator}
53			* interfaces. Like most other concurrent collection implementations,
54	jsr166	1.30	* this class does not permit the use of {@code null} elements,
55			* because {@code null} arguments and return values cannot be reliably
56	dl	1.1	* distinguished from the absence of elements.
57			*
58	jsr166	1.10	* <p>This class is a member of the
59	jsr166	1.18	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
60	jsr166	1.10	* Java Collections Framework</a>.
61			*
62	dl	1.1	* @author Doug Lea
63			* @param <E> the type of elements maintained by this set
64	jsr166	1.9	* @since 1.6
65	dl	1.1	*/
66			public class ConcurrentSkipListSet<E>
67			extends AbstractSet<E>
68			implements NavigableSet<E>, Cloneable, java.io.Serializable {
69
70			private static final long serialVersionUID = -2479143111061671589L;
71
72			/**
73			* The underlying map. Uses Boolean.TRUE as value for each
74	dl	1.15	* element. This field is declared final for the sake of thread
75	jsr166	1.34	* safety, which entails some ugliness in clone().
76	dl	1.1	*/
77	dl	1.15	private final ConcurrentNavigableMap<E,Object> m;
78	dl	1.1
79			/**
80	jsr166	1.11	* Constructs a new, empty set that orders its elements according to
81			* their {@linkplain Comparable natural ordering}.
82	dl	1.1	*/
83			public ConcurrentSkipListSet() {
84			m = new ConcurrentSkipListMap<E,Object>();
85			}
86
87			/**
88	jsr166	1.11	* Constructs a new, empty set that orders its elements according to
89			* the specified comparator.
90	dl	1.1	*
91	jsr166	1.11	* @param comparator the comparator that will be used to order this set.
92	jsr166	1.30	* If {@code null}, the {@linkplain Comparable natural
93	jsr166	1.11	* ordering} of the elements will be used.
94	dl	1.1	*/
95	jsr166	1.11	public ConcurrentSkipListSet(Comparator<? super E> comparator) {
96			m = new ConcurrentSkipListMap<E,Object>(comparator);
97	dl	1.1	}
98
99			/**
100			* Constructs a new set containing the elements in the specified
101	jsr166	1.11	* collection, that orders its elements according to their
102			* {@linkplain Comparable natural ordering}.
103	dl	1.1	*
104	jsr166	1.11	* @param c The elements that will comprise the new set
105	jsr166	1.30	* @throws ClassCastException if the elements in {@code c} are
106	jsr166	1.11	* not {@link Comparable}, or are not mutually comparable
107			* @throws NullPointerException if the specified collection or any
108			* of its elements are null
109	dl	1.1	*/
110			public ConcurrentSkipListSet(Collection<? extends E> c) {
111			m = new ConcurrentSkipListMap<E,Object>();
112			addAll(c);
113			}
114
115			/**
116	jsr166	1.11	* Constructs a new set containing the same elements and using the
117			* same ordering as the specified sorted set.
118	dl	1.1	*
119	jsr166	1.11	* @param s sorted set whose elements will comprise the new set
120			* @throws NullPointerException if the specified sorted set or any
121			* of its elements are null
122	dl	1.1	*/
123			public ConcurrentSkipListSet(SortedSet<E> s) {
124			m = new ConcurrentSkipListMap<E,Object>(s.comparator());
125			addAll(s);
126			}
127
128			/**
129	dl	1.15	* For use by submaps
130			*/
131			ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) {
132			this.m = m;
133			}
134
135			/**
136	jsr166	1.30	* Returns a shallow copy of this {@code ConcurrentSkipListSet}
137	jsr166	1.11	* instance. (The elements themselves are not cloned.)
138	dl	1.1	*
139	jsr166	1.11	* @return a shallow copy of this set
140	dl	1.1	*/
141	jsr166	1.7	public ConcurrentSkipListSet<E> clone() {
142	jsr166	1.19	try {
143	jsr166	1.28	@SuppressWarnings("unchecked")
144			ConcurrentSkipListSet<E> clone =
145			(ConcurrentSkipListSet<E>) super.clone();
146	jsr166	1.24	clone.setMap(new ConcurrentSkipListMap<E,Object>(m));
147	jsr166	1.28	return clone;
148	jsr166	1.19	} catch (CloneNotSupportedException e) {
149			throw new InternalError();
150			}
151	dl	1.1	}
152
153			/* ---------------- Set operations -------------- */
154
155			/**
156			* Returns the number of elements in this set. If this set
157	jsr166	1.30	* contains more than {@code Integer.MAX_VALUE} elements, it
158			* returns {@code Integer.MAX_VALUE}.
159	dl	1.1	*
160			* <p>Beware that, unlike in most collections, this method is
161			* <em>NOT</em> a constant-time operation. Because of the
162			* asynchronous nature of these sets, determining the current
163			* number of elements requires traversing them all to count them.
164			* Additionally, it is possible for the size to change during
165			* execution of this method, in which case the returned result
166			* will be inaccurate. Thus, this method is typically not very
167			* useful in concurrent applications.
168			*
169	jsr166	1.12	* @return the number of elements in this set
170	dl	1.1	*/
171			public int size() {
172	jsr166	1.19	return m.size();
173	dl	1.1	}
174
175			/**
176	jsr166	1.30	* Returns {@code true} if this set contains no elements.
177			* @return {@code true} if this set contains no elements
178	dl	1.1	*/
179			public boolean isEmpty() {
180	jsr166	1.19	return m.isEmpty();
181	dl	1.1	}
182
183			/**
184	jsr166	1.30	* Returns {@code true} if this set contains the specified element.
185			* More formally, returns {@code true} if and only if this set
186			* contains an element {@code e} such that {@code o.equals(e)}.
187	dl	1.1	*
188	jsr166	1.14	* @param o object to be checked for containment in this set
189	jsr166	1.30	* @return {@code true} if this set contains the specified element
190	jsr166	1.11	* @throws ClassCastException if the specified element cannot be
191	jsr166	1.14	* compared with the elements currently in this set
192	jsr166	1.11	* @throws NullPointerException if the specified element is null
193	dl	1.1	*/
194			public boolean contains(Object o) {
195	jsr166	1.19	return m.containsKey(o);
196	dl	1.1	}
197
198			/**
199			* Adds the specified element to this set if it is not already present.
200	jsr166	1.30	* More formally, adds the specified element {@code e} to this set if
201			* the set contains no element {@code e2} such that {@code e.equals(e2)}.
202	jsr166	1.14	* If this set already contains the element, the call leaves the set
203	jsr166	1.30	* unchanged and returns {@code false}.
204	dl	1.1	*
205	jsr166	1.11	* @param e element to be added to this set
206	jsr166	1.30	* @return {@code true} if this set did not already contain the
207	jsr166	1.11	* specified element
208	jsr166	1.30	* @throws ClassCastException if {@code e} cannot be compared
209	jsr166	1.14	* with the elements currently in this set
210	jsr166	1.11	* @throws NullPointerException if the specified element is null
211	dl	1.1	*/
212	jsr166	1.5	public boolean add(E e) {
213	jsr166	1.19	return m.putIfAbsent(e, Boolean.TRUE) == null;
214	dl	1.1	}
215
216			/**
217			* Removes the specified element from this set if it is present.
218	jsr166	1.30	* More formally, removes an element {@code e} such that
219			* {@code o.equals(e)}, if this set contains such an element.
220			* Returns {@code true} if this set contained the element (or
221	jsr166	1.14	* equivalently, if this set changed as a result of the call).
222			* (This set will not contain the element once the call returns.)
223	dl	1.1	*
224	jsr166	1.11	* @param o object to be removed from this set, if present
225	jsr166	1.30	* @return {@code true} if this set contained the specified element
226			* @throws ClassCastException if {@code o} cannot be compared
227	jsr166	1.14	* with the elements currently in this set
228	jsr166	1.11	* @throws NullPointerException if the specified element is null
229	dl	1.1	*/
230			public boolean remove(Object o) {
231	jsr166	1.19	return m.remove(o, Boolean.TRUE);
232	dl	1.1	}
233
234			/**
235			* Removes all of the elements from this set.
236			*/
237			public void clear() {
238	jsr166	1.19	m.clear();
239	dl	1.1	}
240
241			/**
242	jsr166	1.11	* Returns an iterator over the elements in this set in ascending order.
243	dl	1.1	*
244	jsr166	1.11	* @return an iterator over the elements in this set in ascending order
245	dl	1.1	*/
246			public Iterator<E> iterator() {
247	dl	1.15	return m.navigableKeySet().iterator();
248	dl	1.1	}
249
250			/**
251	jsr166	1.11	* Returns an iterator over the elements in this set in descending order.
252	dl	1.1	*
253	jsr166	1.11	* @return an iterator over the elements in this set in descending order
254	dl	1.1	*/
255			public Iterator<E> descendingIterator() {
256	jsr166	1.19	return m.descendingKeySet().iterator();
257	dl	1.1	}
258
259	dl	1.15
260	dl	1.1	/* ---------------- AbstractSet Overrides -------------- */
261
262			/**
263			* Compares the specified object with this set for equality. Returns
264	jsr166	1.30	* {@code true} if the specified object is also a set, the two sets
265	dl	1.1	* have the same size, and every member of the specified set is
266			* contained in this set (or equivalently, every member of this set is
267			* contained in the specified set). This definition ensures that the
268			* equals method works properly across different implementations of the
269			* set interface.
270			*
271	jsr166	1.11	* @param o the object to be compared for equality with this set
272	jsr166	1.30	* @return {@code true} if the specified object is equal to this set
273	dl	1.1	*/
274			public boolean equals(Object o) {
275			// Override AbstractSet version to avoid calling size()
276	jsr166	1.19	if (o == this)
277			return true;
278			if (!(o instanceof Set))
279			return false;
280			Collection<?> c = (Collection<?>) o;
281	dl	1.1	try {
282			return containsAll(c) && c.containsAll(this);
283	jsr166	1.29	} catch (ClassCastException unused) {
284	dl	1.1	return false;
285	jsr166	1.6	} catch (NullPointerException unused) {
286	dl	1.1	return false;
287			}
288			}
289	jsr166	1.8
290	dl	1.1	/**
291			* Removes from this set all of its elements that are contained in
292			* the specified collection. If the specified collection is also
293			* a set, this operation effectively modifies this set so that its
294			* value is the <i>asymmetric set difference</i> of the two sets.
295			*
296	jsr166	1.11	* @param c collection containing elements to be removed from this set
297	jsr166	1.30	* @return {@code true} if this set changed as a result of the call
298	dl	1.1	* @throws ClassCastException if the types of one or more elements in this
299	jsr166	1.11	* set are incompatible with the specified collection
300			* @throws NullPointerException if the specified collection or any
301			* of its elements are null
302	dl	1.1	*/
303			public boolean removeAll(Collection<?> c) {
304			// Override AbstractSet version to avoid unnecessary call to size()
305			boolean modified = false;
306	jsr166	1.27	for (Object e : c)
307			if (remove(e))
308	dl	1.1	modified = true;
309			return modified;
310			}
311	jsr166	1.8
312	dl	1.1	/* ---------------- Relational operations -------------- */
313
314			/**
315	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
316			* @throws NullPointerException if the specified element is null
317	dl	1.1	*/
318	jsr166	1.11	public E lower(E e) {
319			return m.lowerKey(e);
320	dl	1.1	}
321
322			/**
323	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
324			* @throws NullPointerException if the specified element is null
325	dl	1.1	*/
326	jsr166	1.11	public E floor(E e) {
327			return m.floorKey(e);
328	dl	1.1	}
329
330			/**
331	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
332			* @throws NullPointerException if the specified element is null
333	dl	1.1	*/
334	jsr166	1.11	public E ceiling(E e) {
335			return m.ceilingKey(e);
336	dl	1.1	}
337
338			/**
339	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
340			* @throws NullPointerException if the specified element is null
341	dl	1.1	*/
342	jsr166	1.5	public E higher(E e) {
343			return m.higherKey(e);
344	dl	1.1	}
345
346			public E pollFirst() {
347	dl	1.15	Map.Entry<E,Object> e = m.pollFirstEntry();
348	jsr166	1.20	return (e == null) ? null : e.getKey();
349	dl	1.1	}
350
351			public E pollLast() {
352	dl	1.15	Map.Entry<E,Object> e = m.pollLastEntry();
353	jsr166	1.20	return (e == null) ? null : e.getKey();
354	dl	1.1	}
355
356
357			/* ---------------- SortedSet operations -------------- */
358
359
360			public Comparator<? super E> comparator() {
361			return m.comparator();
362			}
363
364			/**
365	jsr166	1.37	* @throws java.util.NoSuchElementException {@inheritDoc}
366	dl	1.1	*/
367			public E first() {
368			return m.firstKey();
369			}
370
371			/**
372	jsr166	1.37	* @throws java.util.NoSuchElementException {@inheritDoc}
373	dl	1.1	*/
374			public E last() {
375			return m.lastKey();
376			}
377
378			/**
379	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
380	jsr166	1.17	* @throws NullPointerException if {@code fromElement} or
381			* {@code toElement} is null
382	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
383	dl	1.1	*/
384	dl	1.16	public NavigableSet<E> subSet(E fromElement,
385			boolean fromInclusive,
386			E toElement,
387			boolean toInclusive) {
388	jsr166	1.19	return new ConcurrentSkipListSet<E>
389	dl	1.16	(m.subMap(fromElement, fromInclusive,
390			toElement, toInclusive));
391	dl	1.1	}
392
393			/**
394	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
395	jsr166	1.17	* @throws NullPointerException if {@code toElement} is null
396	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
397	dl	1.1	*/
398	dl	1.16	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
399	jsr166	1.19	return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
400	dl	1.1	}
401
402			/**
403	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
404	jsr166	1.17	* @throws NullPointerException if {@code fromElement} is null
405	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
406	dl	1.1	*/
407	dl	1.16	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
408	jsr166	1.19	return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive));
409	dl	1.3	}
410
411			/**
412	jsr166	1.17	* @throws ClassCastException {@inheritDoc}
413			* @throws NullPointerException if {@code fromElement} or
414			* {@code toElement} is null
415	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
416	dl	1.3	*/
417	jsr166	1.18	public NavigableSet<E> subSet(E fromElement, E toElement) {
418	jsr166	1.19	return subSet(fromElement, true, toElement, false);
419	dl	1.3	}
420
421			/**
422	jsr166	1.17	* @throws ClassCastException {@inheritDoc}
423			* @throws NullPointerException if {@code toElement} is null
424	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
425	dl	1.3	*/
426	jsr166	1.18	public NavigableSet<E> headSet(E toElement) {
427	jsr166	1.19	return headSet(toElement, false);
428	dl	1.3	}
429
430			/**
431	jsr166	1.17	* @throws ClassCastException {@inheritDoc}
432			* @throws NullPointerException if {@code fromElement} is null
433	jsr166	1.11	* @throws IllegalArgumentException {@inheritDoc}
434	dl	1.3	*/
435	jsr166	1.18	public NavigableSet<E> tailSet(E fromElement) {
436	jsr166	1.19	return tailSet(fromElement, true);
437	dl	1.1	}
438
439			/**
440	jsr166	1.18	* Returns a reverse order view of the elements contained in this set.
441			* The descending set is backed by this set, so changes to the set are
442			* reflected in the descending set, and vice-versa.
443			*
444			* <p>The returned set has an ordering equivalent to
445	jsr166	1.35	* {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
446	jsr166	1.18	* The expression {@code s.descendingSet().descendingSet()} returns a
447			* view of {@code s} essentially equivalent to {@code s}.
448			*
449			* @return a reverse order view of this set
450	dl	1.15	*/
451			public NavigableSet<E> descendingSet() {
452	jsr166	1.24	return new ConcurrentSkipListSet<E>(m.descendingMap());
453	dl	1.15	}
454	dl	1.1
455	jsr166	1.40	/**
456			* Returns a {@link Spliterator} over the elements in this set.
457			*
458			* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
459			* {@link Spliterator#NONNULL}, {@link Spliterator#DISTINCT},
460	jsr166	1.41	* {@link Spliterator#SORTED} and {@link Spliterator#ORDERED}, with an
461	jsr166	1.40	* encounter order that is ascending order. Overriding implementations
462			* should document the reporting of additional characteristic values.
463			*
464			* <p>The spliterator's comparator (see
465			* {@link java.util.Spliterator#getComparator()}) is {@code null} if
466			* the set's comparator (see {@link #comparator()}) is {@code null}.
467			* Otherwise, the spliterator's comparator is the same as or imposes the
468			* same total ordering as the set's comparator.
469			*
470			* @return a {@code Spliterator} over the elements in this set
471			* @since 1.8
472			*/
473	dl	1.32	@SuppressWarnings("unchecked")
474	dl	1.36	public Spliterator<E> spliterator() {
475	dl	1.31	if (m instanceof ConcurrentSkipListMap)
476	dl	1.32	return ((ConcurrentSkipListMap<E,?>)m).keySpliterator();
477	dl	1.31	else
478	dl	1.32	return (Spliterator<E>)((ConcurrentSkipListMap.SubMap<E,?>)m).keyIterator();
479	dl	1.31	}
480
481	dl	1.15	// Support for resetting map in clone
482	dl	1.21	private void setMap(ConcurrentNavigableMap<E,Object> map) {
483			UNSAFE.putObjectVolatile(this, mapOffset, map);
484			}
485
486			private static final sun.misc.Unsafe UNSAFE;
487	dl	1.15	private static final long mapOffset;
488			static {
489			try {
490	dl	1.21	UNSAFE = sun.misc.Unsafe.getUnsafe();
491	jsr166	1.24	Class<?> k = ConcurrentSkipListSet.class;
492	dl	1.21	mapOffset = UNSAFE.objectFieldOffset
493			(k.getDeclaredField("m"));
494			} catch (Exception e) {
495			throw new Error(e);
496			}
497	dl	1.15	}
498	jsr166	1.8	}