--- jsr166/src/jsr166x/ConcurrentSkipListSet.java 2004/08/11 10:58:15 1.1 +++ jsr166/src/jsr166x/ConcurrentSkipListSet.java 2013/01/16 00:53:17 1.18 @@ -1,61 +1,47 @@ /* * 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 + * http://creativecommons.org/publicdomain/zero/1.0/ */ -package jsr166x; +package jsr166x; import java.util.*; import java.util.concurrent.*; /** - * A scalable concurrent {@link SortedSet} and (priority) {@link - * Queue} 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.

+ * 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 + *

This implementation provides expected average log(n) 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. 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 procede concurrently with + * ConcurrentModificationException}, and may proceed concurrently with * other operations. * - *

This class provides extended SortedSet methods - * searching for closest matches. Methods lower, - * floor, ceiling, and higher return - * elements respectively less, less than or equal, greater than or - * equal, and greater than a given value, returning null if there is - * no such element. These methods are designed for locating, not - * traversing entries. To traverse, use iterators and/or - * subset. - * - *

The class additionally supports {@link Queue} methods such as - * poll that atomically returns and removes the first - * element, if one exists. Thus, this class can serve as a priority - * queue in which there are no duplicate elements. - * - *

The {@link ConcurrentSkipListSubSet} objects returned by methods - * subset, headSet, and tailSet support the - * same extended set of operations as this class, but operate on their - * designated subrange of elements. - * - *

Beware that, unlike in most collections, the size - * method is NOT a constant-time operation. Because of the + *

Beware that, unlike in most collections, the {@code 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. + * of elements requires a traversal of the elements. Additionally, the + * bulk operations {@code addAll}, {@code removeAll}, + * {@code retainAll}, and {@code containsAll} are not + * guaranteed to be performed atomically. For example, an iterator + * operating concurrently with an {@code 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 + * 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. * * @author Doug Lea @@ -63,7 +49,7 @@ import java.util.concurrent.*; */ public class ConcurrentSkipListSet extends AbstractSet - implements SortedSet, Queue, Cloneable, java.io.Serializable { + implements NavigableSet, Cloneable, java.io.Serializable { private static final long serialVersionUID = -2479143111061671589L; @@ -74,11 +60,11 @@ public class ConcurrentSkipListSet * fields of underlying map, but enables this field to be declared * final, which is necessary for thread safety. */ - private final ConcurrentSkipListMap m; + private final ConcurrentSkipListMap m; /** * Constructs a new, empty set, sorted according to the elements' natural - * order. + * order. */ public ConcurrentSkipListSet() { m = new ConcurrentSkipListMap(); @@ -86,10 +72,10 @@ public class ConcurrentSkipListSet /** * Constructs a new, empty set, sorted according to the specified - * comparator. + * comparator. * * @param c the comparator that will be used to sort this set. A - * null value indicates that the elements' natural + * {@code null} value indicates that the elements' natural * ordering should be used. */ public ConcurrentSkipListSet(Comparator c) { @@ -100,11 +86,12 @@ public class ConcurrentSkipListSet * 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. + * @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. + * collection are not comparable, or are not mutually comparable + * @throws NullPointerException if the specified collection is + * {@code null} */ public ConcurrentSkipListSet(Collection c) { m = new ConcurrentSkipListMap(); @@ -115,8 +102,9 @@ public class ConcurrentSkipListSet * 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. + * @param s sorted set whose elements will comprise the new set + * @throws NullPointerException if the specified sorted set is + * {@code null} */ public ConcurrentSkipListSet(SortedSet s) { m = new ConcurrentSkipListMap(s.comparator()); @@ -127,15 +115,15 @@ public class ConcurrentSkipListSet * Returns a shallow copy of this set. (The elements themselves * are not cloned.) * - * @return a shallow copy of this set. + * @return a shallow copy of this set */ public Object clone() { ConcurrentSkipListSet clone = null; - try { - clone = (ConcurrentSkipListSet) super.clone(); - } catch (CloneNotSupportedException e) { - throw new InternalError(); - } + try { + clone = (ConcurrentSkipListSet) super.clone(); + } catch (CloneNotSupportedException e) { + throw new InternalError(); + } clone.m.initialize(); clone.addAll(this); @@ -146,8 +134,8 @@ public class ConcurrentSkipListSet /** * Returns the number of elements in this set. If this set - * contains more than Integer.MAX_VALUE elements, it - * returns Integer.MAX_VALUE. + * contains more than {@code Integer.MAX_VALUE} elements, it + * returns {@code Integer.MAX_VALUE}. * *

Beware that, unlike in most collections, this method is * NOT a constant-time operation. Because of the @@ -158,210 +146,234 @@ public class ConcurrentSkipListSet * will be inaccurate. Thus, this method is typically not very * useful in concurrent applications. * - * @return the number of elements in this set. + * @return the number of elements in this set */ public int size() { - return m.size(); + return m.size(); } /** - * Returns true if this set contains no elements. - * @return true if this set contains no elements. + * Returns {@code true} if this set contains no elements. + * @return {@code true} if this set contains no elements */ public boolean isEmpty() { - return m.isEmpty(); + return m.isEmpty(); } /** - * Returns true if this set contains the specified element. + * Returns {@code 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. + * @param o the object to be checked for containment in this set + * @return {@code 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. + * with the elements currently in the set + * @throws NullPointerException if o is {@code null} */ public boolean contains(Object o) { - return m.containsKey(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. + * @param o element to be added to this set + * @return {@code 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. + * with the elements currently in the set + * @throws NullPointerException if o is {@code null} */ public boolean add(E o) { - return m.putIfAbsent(o, Boolean.TRUE) == null; + 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. + * @param o object to be removed from this set, if present + * @return {@code 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. + * with the elements currently in the set + * @throws NullPointerException if o is {@code null} */ public boolean remove(Object o) { - return m.removep(o); + return m.removep(o); } /** * Removes all of the elements from this set. */ public void clear() { - m.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. + * @return an iterator over the elements in this set */ public Iterator iterator() { - return m.keyIterator(); - } - - /* ---------------- Queue operations -------------- */ - - /** - * Adds the specified element, or fails if this element is already - * present. - * @param o the element to insert. - * @return true if it was possible to add the element, - * else false - */ - public boolean offer(E o) { - return add(o); + return m.keyIterator(); } /** - * Retrieves and removes the first (lowest) element. + * Returns an iterator over the elements in this set. The elements + * are returned in descending order. * - * @return the least element, or null if empty. + * @return an iterator over the elements in this set */ - public E poll() { - return m.removeFirstKey(); + public Iterator descendingIterator() { + return m.descendingKeyIterator(); } - /** - * Retrieves and removes the first (lowest) element. This method - * differs from the poll method in that it throws an - * exception if empty. - * - * @return the first (lowest) element. - * @throws NoSuchElementException if empty. - */ - public E remove() { - E x = m.removeFirstKey(); - if (x == null) - throw new NoSuchElementException(); - return x; + /* ---------------- 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 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; + } } /** - * Retrieves, but does not remove, the first (lowest) element, - * returning null if empty. - * - * @return the first (lowest) element, or null if empty. - */ - public E peek() { - return m.lowestKey(); + * 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 {@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 {@code 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; } - /** - * Retrieves, but does not remove, the first (lowest) element. - * This method differs from the peek method only in that - * it throws an exception if empty. - * - * @return the first (lowest) element. - * @throws NoSuchElementException if empty. - */ - public E element() { - return m.firstKey(); - } - /* ---------------- Relational operations -------------- */ /** * Returns an element greater than or equal to the given element, or - * null if there is no such element. - * + * {@code 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. + * @return an element greater than or equal to given element, or + * {@code 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 + * currently in the set + * @throws NullPointerException if o is {@code 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. - * + * Returns an element strictly less than the given element, or + * {@code 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. + * {@code 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. + * currently in the set + * @throws NullPointerException if o is {@code 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. - * + * Returns an element less than or equal to the given element, or + * {@code 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. + * element, or {@code 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. + * currently in the set + * @throws NullPointerException if o is {@code 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. - * + * Returns an element strictly greater than the given element, or + * {@code 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. + * {@code 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. + * currently in the set + * @throws NullPointerException if o is {@code null} */ public E higher(E o) { return m.higherKey(o); } + /** + * Retrieves and removes the first (lowest) element. + * + * @return the least element, or {@code null} if empty + */ + public E pollFirst() { + return m.pollFirstKey(); + } + + /** + * Retrieves and removes the last (highest) element. + * + * @return the last element, or {@code null} if empty + */ + public E pollLast() { + return m.pollLastKey(); + } + + /* ---------------- SortedSet operations -------------- */ /** - * Returns the comparator used to order this set, or null + * Returns the comparator used to order this set, or {@code 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. + * @return the comparator used to order this set, or {@code null} + * if this set uses its elements natural ordering */ public Comparator comparator() { return m.comparator(); @@ -370,8 +382,8 @@ public class ConcurrentSkipListSet /** * Returns the first (lowest) element currently in this set. * - * @return the first (lowest) element currently in this set. - * @throws NoSuchElementException sorted set is empty. + * @return the first (lowest) element currently in this set + * @throws NoSuchElementException sorted set is empty */ public E first() { return m.firstKey(); @@ -380,71 +392,160 @@ public class ConcurrentSkipListSet /** * Returns the last (highest) element currently in this set. * - * @return the last (highest) element currently in this set. - * @throws NoSuchElementException sorted set is empty. + * @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 + * {@code fromElement}, inclusive, to {@code toElement}, exclusive. (If + * {@code fromElement} and {@code 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. + * 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 + * {@code fromElement}, inclusive, to {@code toElement}, + * exclusive + * @throws ClassCastException if {@code fromElement} and + * {@code 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. + * using natural ordering) + * @throws IllegalArgumentException if {@code fromElement} is + * greater than {@code toElement} + * @throws NullPointerException if {@code fromElement} or + * {@code toElement} is {@code null} */ - public ConcurrentSkipListSubSet subSet(E fromElement, E toElement) { - return new ConcurrentSkipListSubSet(m, fromElement, toElement); + 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 + * less than {@code 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. + * 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 + * less than toElement + * @throws ClassCastException if {@code 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. + * if {@code toElement} does not implement {@code Comparable}) + * @throws NullPointerException if {@code toElement} is {@code null} */ - public ConcurrentSkipListSubSet headSet(E toElement) { - return new ConcurrentSkipListSubSet(m, null, toElement); + 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 + * greater than or equal to {@code 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. + * @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 + * greater than or equal to {@code fromElement} + * @throws ClassCastException if {@code 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 ConcurrentSkipListSubSet tailSet(E fromElement) { - return new ConcurrentSkipListSubSet(m, fromElement, null); + * comparator, if {@code fromElement} does not implement + * {@code Comparable}) + * @throws NullPointerException if {@code fromElement} is {@code 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 {@code subSet}, {@code headSet}, and + * {@code 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 {@code null} if from start + * @param toElement exclusive upper bound or {@code 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(); + } + } -} +}