jsr166x.ConcurrentSkipListSet Maven / Gradle / Ivy
/*
* 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 jsr166x;
import java.util.*;
import java.util.concurrent.*;
/**
* A scalable concurrent {@link NavigableSet} implementation based on
* a {@link ConcurrentSkipListMap}. This class maintains a set in
* ascending order, sorted according to the natural order for
* the element's class (see {@link Comparable}), or by the comparator
* provided at 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 {@link
* ConcurrentModificationException}, and may proceed concurrently with
* other operations.
*
*
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. Additionally, the
* bulk operations addAll, removeAll,
* <retainAll, and tt>containsAll 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.
*
* @author Doug Lea
* @param the type of elements maintained by this set
*/
public 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. Note that this class relies on default serialization,
* which is a little wasteful in saving all of the useless value
* fields of underlying map, but enables this field to be declared
* final, which is necessary for thread safety.
*/
private final ConcurrentSkipListMap m;
/**
* Constructs a new, empty set, sorted according to the elements' natural
* order.
*/
public ConcurrentSkipListSet() {
m = new ConcurrentSkipListMap();
}
/**
* Constructs a new, empty set, sorted according to the specified
* comparator.
*
* @param c the comparator that will be used to sort this set. A
* null value indicates that the elements' natural
* ordering should be used.
*/
public ConcurrentSkipListSet(Comparator c) {
m = new ConcurrentSkipListMap(c);
}
/**
* Constructs a new set containing the elements in the specified
* collection, sorted according to the elements' natural order.
*
* @param c The elements that will comprise the new set.
*
* @throws ClassCastException if the elements in the specified
* collection are not comparable, or are not mutually comparable.
* @throws NullPointerException if the specified collection is
* null.
*/
public ConcurrentSkipListSet(Collection c) {
m = new ConcurrentSkipListMap();
addAll(c);
}
/**
* Constructs a new set containing the same elements as the specified
* sorted set, sorted according to the same ordering.
*
* @param s sorted set whose elements will comprise the new set.
* @throws NullPointerException if the specified sorted set is
* null.
*/
public ConcurrentSkipListSet(SortedSet s) {
m = new ConcurrentSkipListMap(s.comparator());
addAll(s);
}
/**
* Returns a shallow copy of this set. (The elements themselves
* are not cloned.)
*
* @return a shallow copy of this set.
*/
public Object clone() {
ConcurrentSkipListSet clone = null;
try {
clone = (ConcurrentSkipListSet) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
clone.m.initialize();
clone.addAll(this);
return clone;
}
/* ---------------- 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.
*
* @param o the object to be checked for containment in this set.
* @return true if this set contains the specified element.
*
* @throws ClassCastException if the specified object cannot be compared
* with the elements currently in the set.
* @throws NullPointerException if o is null.
*/
public boolean contains(Object o) {
return m.containsKey(o);
}
/**
* Adds the specified element to this set if it is not already present.
*
* @param o element to be added to this set.
* @return true if the set did not already contain the specified
* element.
*
* @throws ClassCastException if the specified object cannot be compared
* with the elements currently in the set.
* @throws NullPointerException if o is null.
*/
public boolean add(E o) {
return m.putIfAbsent(o, Boolean.TRUE) == null;
}
/**
* Removes the specified element from this set if it is present.
*
* @param o object to be removed from this set, if present.
* @return true if the set contained the specified element.
*
* @throws ClassCastException if the specified object cannot be compared
* with the elements currently in the set.
* @throws NullPointerException if o is null.
*/
public boolean remove(Object o) {
return m.removep(o);
}
/**
* Removes all of the elements from this set.
*/
public void clear() {
m.clear();
}
/**
* Returns an iterator over the elements in this set. The elements
* are returned in ascending order.
*
* @return an iterator over the elements in this set.
*/
public Iterator iterator() {
return m.keyIterator();
}
/**
* Returns an iterator over the elements in this set. The elements
* are returned in descending order.
*
* @return an iterator over the elements in this set.
*/
public Iterator descendingIterator() {
return m.descendingKeyIterator();
}
/* ---------------- 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 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 that defines which elements will 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 -------------- */
/**
* Returns an element greater than or equal to the given element, or
* null if there is no such element.
*
* @param o the value to match
* @return an element greater than or equal to given element, or
* null if there is no such element.
* @throws ClassCastException if o cannot be compared with the elements
* currently in the set.
* @throws NullPointerException if o is null
*/
public E ceiling(E o) {
return m.ceilingKey(o);
}
/**
* Returns an element strictly less than the given element, or
* null if there is no such element.
*
* @param o the value to match
* @return the greatest element less than the given element, or
* null if there is no such element.
* @throws ClassCastException if o cannot be compared with the elements
* currently in the set.
* @throws NullPointerException if o is null.
*/
public E lower(E o) {
return m.lowerKey(o);
}
/**
* Returns an element less than or equal to the given element, or
* null if there is no such element.
*
* @param o the value to match
* @return the greatest element less than or equal to given
* element, or null if there is no such element.
* @throws ClassCastException if o cannot be compared with the elements
* currently in the set.
* @throws NullPointerException if o is null.
*/
public E floor(E o) {
return m.floorKey(o);
}
/**
* Returns an element strictly greater than the given element, or
* null if there is no such element.
*
* @param o the value to match
* @return the least element greater than the given element, or
* null if there is no such element.
* @throws ClassCastException if o cannot be compared with the elements
* currently in the set.
* @throws NullPointerException if o is null.
*/
public E higher(E o) {
return m.higherKey(o);
}
/**
* Retrieves and removes the first (lowest) element.
*
* @return the least element, or null if empty.
*/
public E pollFirst() {
return m.pollFirstKey();
}
/**
* Retrieves and removes the last (highest) element.
*
* @return the last element, or null if empty.
*/
public E pollLast() {
return m.pollLastKey();
}
/* ---------------- SortedSet operations -------------- */
/**
* Returns the comparator used to order this set, or null
* if this set uses its elements natural ordering.
*
* @return the comparator used to order this set, or null
* if this set uses its elements natural ordering.
*/
public Comparator comparator() {
return m.comparator();
}
/**
* Returns the first (lowest) element currently in this set.
*
* @return the first (lowest) element currently in this set.
* @throws NoSuchElementException sorted set is empty.
*/
public E first() {
return m.firstKey();
}
/**
* Returns the last (highest) element currently in this set.
*
* @return the last (highest) element currently in this set.
* @throws NoSuchElementException sorted set is empty.
*/
public E last() {
return m.lastKey();
}
/**
* Returns a view of the portion of this set whose elements range from
* fromElement, inclusive, to toElement, exclusive. (If
* fromElement and toElement are equal, the returned
* sorted set is empty.) The returned sorted set is backed by this set,
* so changes in the returned sorted set are reflected in this set, and
* vice-versa.
* @param fromElement low endpoint (inclusive) of the subSet.
* @param toElement high endpoint (exclusive) of the subSet.
* @return a view of the portion of this set whose elements range from
* fromElement, inclusive, to toElement,
* exclusive.
* @throws ClassCastException if fromElement and
* toElement cannot be compared to one another using
* this set's comparator (or, if the set has no comparator,
* using natural ordering).
* @throws IllegalArgumentException if fromElement is
* greater than toElement.
* @throws NullPointerException if fromElement or
* toElement is null.
*/
public NavigableSet subSet(E fromElement, E toElement) {
return new ConcurrentSkipListSubSet(m, fromElement, toElement);
}
/**
* Returns a view of the portion of this set whose elements are strictly
* less than toElement. The returned sorted set is backed by
* this set, so changes in the returned sorted set are reflected in this
* set, and vice-versa.
* @param toElement high endpoint (exclusive) of the headSet.
* @return a view of the portion of this set whose elements are strictly
* less than toElement.
* @throws ClassCastException if toElement is not compatible
* with this set's comparator (or, if the set has no comparator,
* if toElement does not implement Comparable).
* @throws NullPointerException if toElement is null.
*/
public NavigableSet headSet(E toElement) {
return new ConcurrentSkipListSubSet(m, null, toElement);
}
/**
* Returns a view of the portion of this set whose elements are
* greater than or equal to fromElement. The returned
* sorted set is backed by this set, so changes in the returned
* sorted set are reflected in this set, and vice-versa.
* @param fromElement low endpoint (inclusive) of the tailSet.
* @return a view of the portion of this set whose elements are
* greater than or equal to fromElement.
* @throws ClassCastException if fromElement is not
* compatible with this set's comparator (or, if the set has no
* comparator, if fromElement does not implement
* Comparable).
* @throws NullPointerException if fromElement is null.
*/
public NavigableSet tailSet(E fromElement) {
return new ConcurrentSkipListSubSet(m, fromElement, null);
}
/**
* Subsets returned by {@link ConcurrentSkipListSet} subset operations
* represent a subrange of elements of their underlying
* sets. Instances of this class support all methods of their
* underlying sets, differing in that elements outside their range are
* ignored, and attempts to add elements outside their ranges result
* in {@link IllegalArgumentException}. Instances of this class are
* constructed only using the subSet, headSet, and
* tailSet methods of their underlying sets.
*
*/
static class ConcurrentSkipListSubSet
extends AbstractSet
implements NavigableSet, java.io.Serializable {
private static final long serialVersionUID = -7647078645896651609L;
/** The underlying submap */
private final ConcurrentSkipListMap.ConcurrentSkipListSubMap s;
/**
* Creates a new submap.
* @param fromElement inclusive least value, or null if from start
* @param toElement exclusive upper bound or null if to end
* @throws IllegalArgumentException if fromElement and toElement
* non-null and fromElement greater than toElement
*/
ConcurrentSkipListSubSet(ConcurrentSkipListMap map,
E fromElement, E toElement) {
s = new ConcurrentSkipListMap.ConcurrentSkipListSubMap
(map, fromElement, toElement);
}
// subsubset construction
public NavigableSet subSet(E fromElement, E toElement) {
if (!s.inOpenRange(fromElement) || !s.inOpenRange(toElement))
throw new IllegalArgumentException("element out of range");
return new ConcurrentSkipListSubSet(s.getMap(),
fromElement, toElement);
}
public NavigableSet headSet(E toElement) {
E least = s.getLeast();
if (!s.inOpenRange(toElement))
throw new IllegalArgumentException("element out of range");
return new ConcurrentSkipListSubSet(s.getMap(),
least, toElement);
}
public NavigableSet tailSet(E fromElement) {
E fence = s.getFence();
if (!s.inOpenRange(fromElement))
throw new IllegalArgumentException("element out of range");
return new ConcurrentSkipListSubSet(s.getMap(),
fromElement, fence);
}
// relays to submap methods
public int size() { return s.size(); }
public boolean isEmpty() { return s.isEmpty(); }
public boolean contains(Object o) { return s.containsKey(o); }
public void clear() { s.clear(); }
public E first() { return s.firstKey(); }
public E last() { return s.lastKey(); }
public E ceiling(E o) { return s.ceilingKey(o); }
public E lower(E o) { return s.lowerKey(o); }
public E floor(E o) { return s.floorKey(o); }
public E higher(E o) { return s.higherKey(o); }
public boolean remove(Object o) { return s.remove(o)==Boolean.TRUE; }
public boolean add(E o) { return s.put(o, Boolean.TRUE)==null; }
public Comparator comparator() { return s.comparator(); }
public Iterator iterator() { return s.keySet().iterator(); }
public Iterator descendingIterator() {
return s.descendingKeySet().iterator();
}
public E pollFirst() {
Map.Entry e = s.pollFirstEntry();
return (e == null) ? null : e.getKey();
}
public E pollLast() {
Map.Entry e = s.pollLastEntry();
return (e == null) ? null : e.getKey();
}
}
}