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/*
* 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/licenses/publicdomain
*
* JSR 166 interest web site:
* http://gee.cs.oswego.edu/dl/concurrency-interest/
*
* File download location:
* http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jdk7/java/util/concurrent/ConcurrentSkipListSet.java?revision=1.1
*/
/*
* Customized version for GemFireXD distributed data platform.
*
* Portions Copyright (c) 2010-2015 Pivotal Software, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you
* may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License. See accompanying
* LICENSE file.
*/
package com.gemstone.gemfire.internal.concurrent;
import java.util.*;
import java.util.concurrent.ConcurrentNavigableMap;
/**
* 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.
*
* This implementation provides expected average log(n) time
* cost for the contains, add, and remove
* operations and their variants. Insertion, removal, and access
* operations safely execute concurrently by multiple threads.
* Iterators are weakly consistent, returning elements
* reflecting the state of the set at some point at or since the
* creation of the iterator. They do not throw
* ConcurrentModificationException, and may proceed concurrently with
* other operations. Ascending ordered views and their iterators are
* faster than descending ones.
*
*
Beware that, unlike in most collections, the size
* method is not 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 addAll,
* removeAll, retainAll, containsAll,
* equals, and toArray are not guaranteed
* to be performed atomically. For example, an iterator operating
* concurrently with an addAll operation might view only some
* of the added elements.
*
*
This class and its iterators implement all of the
* optional methods of the {@link Set} and {@link Iterator}
* interfaces. Like most other concurrent collection implementations,
* this class does not permit the use of null elements,
* because null arguments and return values cannot be reliably
* distinguished from the absence of elements.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @author Doug Lea
* @param the type of elements maintained by this set
* @since 1.6
*/
public final class ConcurrentSkipListSet
extends AbstractSet
implements NavigableSet, 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 m;
/**
* Constructs a new, empty set that orders its elements according to
* their {@linkplain Comparable natural ordering}.
*/
public ConcurrentSkipListSet() {
m = new ConcurrentSkipListMap();
}
/**
* 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 null, the {@linkplain Comparable natural
* ordering} of the elements will be used.
*/
public ConcurrentSkipListSet(Comparator comparator) {
m = new ConcurrentSkipListMap(comparator, false, false);
}
/**
* 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 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 c) {
m = new ConcurrentSkipListMap();
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 s) {
m = new ConcurrentSkipListMap(s.comparator(), false, false);
addAll(s);
}
/**
* For use by submaps
*/
@SuppressWarnings("unchecked")
ConcurrentSkipListSet(ConcurrentNavigableMap m) {
this.m = (ConcurrentNavigableMap)m;
}
/**
* Returns a shallow copy of this ConcurrentSkipListSet
* instance. (The elements themselves are not cloned.)
*
* @return a shallow copy of this set
*/
public Object clone() {
if (this.getClass() != ConcurrentSkipListSet.class) {
// can't change m, since it is final
throw new UnsupportedOperationException("Can't clone subclasses");
}
return new ConcurrentSkipListSet(
new ConcurrentSkipListMap(this.m));
}
/* ---------------- Set operations -------------- */
/**
* Returns the number of elements in this set. If this set
* contains more than Integer.MAX_VALUE elements, it
* returns Integer.MAX_VALUE.
*
* Beware that, unlike in most collections, this method is
* NOT 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 true if this set contains no elements.
* @return true if this set contains no elements
*/
public boolean isEmpty() {
return m.isEmpty();
}
/**
* Returns true if this set contains the specified element.
* More formally, returns true if and only if this set
* contains an element e such that o.equals(e).
*
* @param o object to be checked for containment in this set
* @return 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 e to this set if
* the set contains no element e2 such that e.equals(e2).
* If this set already contains the element, the call leaves the set
* unchanged and returns false.
*
* @param e element to be added to this set
* @return true if this set did not already contain the
* specified element
* @throws ClassCastException if 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 e such that
* o.equals(e), if this set contains such an element.
* Returns 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 true if this set contained the specified element
* @throws ClassCastException if 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 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 descendingIterator() {
return m.descendingKeySet().iterator();
}
/* ---------------- AbstractSet Overrides -------------- */
/**
* Compares the specified object with this set for equality. Returns
* 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 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 asymmetric set difference of the two sets.
*
* @param c collection containing elements to be removed from this set
* @return 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 (Iterator i = c.iterator(); i.hasNext(); )
if (remove(i.next()))
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 = m.pollFirstEntry();
return e == null? null : e.getKey();
}
public E pollLast() {
Map.Entry e = m.pollLastEntry();
return e == null? null : e.getKey();
}
/* ---------------- SortedSet operations -------------- */
public Comparator comparator() {
return m.comparator();
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E first() {
return m.firstKey();
}
/**
* @throws 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 subSet(E fromElement,
boolean fromInclusive,
E toElement,
boolean toInclusive) {
return new ConcurrentSkipListSet
((ConcurrentNavigableMap)
m.subMap(fromElement, fromInclusive,
toElement, toInclusive));
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code toElement} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public NavigableSet headSet(E toElement, boolean inclusive) {
return new ConcurrentSkipListSet(
(ConcurrentNavigableMap)m.headMap(toElement,
inclusive));
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromElement} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public NavigableSet tailSet(E fromElement, boolean inclusive) {
return new ConcurrentSkipListSet(
(ConcurrentNavigableMap)m.tailMap(fromElement,
inclusive));
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromElement} or
* {@code toElement} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public SortedSet 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 SortedSet headSet(E toElement) {
return headSet(toElement, false);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromElement} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public SortedSet 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.
*
* The returned set has an ordering equivalent to
* {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(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 descendingSet() {
return new ConcurrentSkipListSet(
(ConcurrentNavigableMap)m.descendingMap());
}
}