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Posted to commits@harmony.apache.org by hi...@apache.org on 2009/07/16 16:01:17 UTC
svn commit: r794678 [3/19] - in
/harmony/enhanced/classlib/trunk/modules/concurrent/src:
main/java/java/util/concurrent/ main/java/java/util/concurrent/atomic/
main/java/java/util/concurrent/locks/ test/java/
Modified: harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java?rev=794678&r1=794677&r2=794678&view=diff
==============================================================================
--- harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java (original)
+++ harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java Thu Jul 16 14:01:15 2009
@@ -10,7 +10,7 @@
/**
- * An unbounded thread-safe {@linkplain Queue queue} based on linked nodes.
+ * An unbounded thread-safe {@linkplain Queue queue} based on linked nodes.
* This queue orders elements FIFO (first-in-first-out).
* The <em>head</em> of the queue is that element that has been on the
* queue the longest time.
@@ -18,26 +18,34 @@
* queue the shortest time. New elements
* are inserted at the tail of the queue, and the queue retrieval
* operations obtain elements at the head of the queue.
- * A <tt>ConcurrentLinkedQueue</tt> is an appropriate choice when
+ * A {@code ConcurrentLinkedQueue} is an appropriate choice when
* many threads will share access to a common collection.
- * This queue does not permit <tt>null</tt> elements.
+ * This queue does not permit {@code null} elements.
*
- * <p>This implementation employs an efficient "wait-free"
+ * <p>This implementation employs an efficient "wait-free"
* algorithm based on one described in <a
* href="http://www.cs.rochester.edu/u/michael/PODC96.html"> Simple,
* Fast, and Practical Non-Blocking and Blocking Concurrent Queue
* Algorithms</a> by Maged M. Michael and Michael L. Scott.
*
- * <p>Beware that, unlike in most collections, the <tt>size</tt> method
+ * <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 queues, determining the current number
* of elements requires a traversal of the elements.
*
- * <p>This class implements all of the <em>optional</em> methods
- * of the {@link Collection} and {@link Iterator} interfaces.
+ * <p>This class and its iterator implement all of the
+ * <em>optional</em> methods of the {@link Collection} and {@link
+ * Iterator} interfaces.
+ *
+ * <p>Memory consistency effects: As with other concurrent
+ * collections, actions in a thread prior to placing an object into a
+ * {@code ConcurrentLinkedQueue}
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * actions subsequent to the access or removal of that element from
+ * the {@code ConcurrentLinkedQueue} in another thread.
*
* <p>This class is a member of the
- * <a href="{@docRoot}/../guide/collections/index.html">
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @since 1.5
@@ -50,68 +58,126 @@
private static final long serialVersionUID = 196745693267521676L;
/*
- * This is a straight adaptation of Michael & Scott algorithm.
- * For explanation, read the paper. The only (minor) algorithmic
- * difference is that this version supports lazy deletion of
- * internal nodes (method remove(Object)) -- remove CAS'es item
- * fields to null. The normal queue operations unlink but then
- * pass over nodes with null item fields. Similarly, iteration
- * methods ignore those with nulls.
+ * This is a modification of the Michael & Scott algorithm,
+ * adapted for a garbage-collected environment, with support for
+ * interior node deletion (to support remove(Object)). For
+ * explanation, read the paper.
+ *
+ * Note that like most non-blocking algorithms in this package,
+ * this implementation relies on the fact that in garbage
+ * collected systems, there is no possibility of ABA problems due
+ * to recycled nodes, so there is no need to use "counted
+ * pointers" or related techniques seen in versions used in
+ * non-GC'ed settings.
+ *
+ * The fundamental invariants are:
+ * - There is exactly one (last) Node with a null next reference,
+ * which is CASed when enqueueing. This last Node can be
+ * reached in O(1) time from tail, but tail is merely an
+ * optimization - it can always be reached in O(N) time from
+ * head as well.
+ * - The elements contained in the queue are the non-null items in
+ * Nodes that are reachable from head. CASing the item
+ * reference of a Node to null atomically removes it from the
+ * queue. Reachability of all elements from head must remain
+ * true even in the case of concurrent modifications that cause
+ * head to advance. A dequeued Node may remain in use
+ * indefinitely due to creation of an Iterator or simply a
+ * poll() that has lost its time slice.
+ *
+ * The above might appear to imply that all Nodes are GC-reachable
+ * from a predecessor dequeued Node. That would cause two problems:
+ * - allow a rogue Iterator to cause unbounded memory retention
+ * - cause cross-generational linking of old Nodes to new Nodes if
+ * a Node was tenured while live, which generational GCs have a
+ * hard time dealing with, causing repeated major collections.
+ * However, only non-deleted Nodes need to be reachable from
+ * dequeued Nodes, and reachability does not necessarily have to
+ * be of the kind understood by the GC. We use the trick of
+ * linking a Node that has just been dequeued to itself. Such a
+ * self-link implicitly means to advance to head.
+ *
+ * Both head and tail are permitted to lag. In fact, failing to
+ * update them every time one could is a significant optimization
+ * (fewer CASes). This is controlled by local "hops" variables
+ * that only trigger helping-CASes after experiencing multiple
+ * lags.
+ *
+ * Since head and tail are updated concurrently and independently,
+ * it is possible for tail to lag behind head (why not)?
+ *
+ * CASing a Node's item reference to null atomically removes the
+ * element from the queue. Iterators skip over Nodes with null
+ * items. Prior implementations of this class had a race between
+ * poll() and remove(Object) where the same element would appear
+ * to be successfully removed by two concurrent operations. The
+ * method remove(Object) also lazily unlinks deleted Nodes, but
+ * this is merely an optimization.
+ *
+ * When constructing a Node (before enqueuing it) we avoid paying
+ * for a volatile write to item by using lazySet instead of a
+ * normal write. This allows the cost of enqueue to be
+ * "one-and-a-half" CASes.
+ *
+ * Both head and tail may or may not point to a Node with a
+ * non-null item. If the queue is empty, all items must of course
+ * be null. Upon creation, both head and tail refer to a dummy
+ * Node with null item. Both head and tail are only updated using
+ * CAS, so they never regress, although again this is merely an
+ * optimization.
*/
-
private static class Node<E> {
private volatile E item;
private volatile Node<E> next;
-
- private static final
- AtomicReferenceFieldUpdater<Node, Node>
+
+ private static final
+ AtomicReferenceFieldUpdater<Node, Node>
nextUpdater =
AtomicReferenceFieldUpdater.newUpdater
(Node.class, Node.class, "next");
- private static final
- AtomicReferenceFieldUpdater<Node, Object>
+ private static final
+ AtomicReferenceFieldUpdater<Node, Object>
itemUpdater =
AtomicReferenceFieldUpdater.newUpdater
(Node.class, Object.class, "item");
-
- Node(E x) { item = x; }
-
- Node(E x, Node<E> n) { item = x; next = n; }
-
+
+
+ Node(E item) { setItem(item); }
+
E getItem() {
return item;
}
-
+
boolean casItem(E cmp, E val) {
return itemUpdater.compareAndSet(this, cmp, val);
}
-
+
void setItem(E val) {
itemUpdater.set(this, val);
}
-
+
Node<E> getNext() {
return next;
}
-
+
boolean casNext(Node<E> cmp, Node<E> val) {
return nextUpdater.compareAndSet(this, cmp, val);
}
-
+
void setNext(Node<E> val) {
nextUpdater.set(this, val);
- }
-
}
- private static final
- AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
- tailUpdater =
+ }
+
+ private static final
+ AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
+ tailUpdater =
AtomicReferenceFieldUpdater.newUpdater
(ConcurrentLinkedQueue.class, Node.class, "tail");
- private static final
- AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
- headUpdater =
+ private static final
+ AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
+ headUpdater =
AtomicReferenceFieldUpdater.newUpdater
(ConcurrentLinkedQueue.class, Node.class, "head");
@@ -124,118 +190,141 @@
}
+
/**
- * Pointer to header node, initialized to a dummy node. The first
- * actual node is at head.getNext().
+ * Pointer to first node, initialized to a dummy node.
*/
- private transient volatile Node<E> head = new Node<E>(null, null);
+ private transient volatile Node<E> head = new Node<E>(null);
- /** Pointer to last node on list **/
+ /** Pointer to last node on list */
private transient volatile Node<E> tail = head;
/**
- * Creates a <tt>ConcurrentLinkedQueue</tt> that is initially empty.
+ * Creates a {@code ConcurrentLinkedQueue} that is initially empty.
*/
public ConcurrentLinkedQueue() {}
/**
- * Creates a <tt>ConcurrentLinkedQueue</tt>
+ * Creates a {@code ConcurrentLinkedQueue}
* initially containing the elements of the given collection,
* added in traversal order of the collection's iterator.
* @param c the collection of elements to initially contain
- * @throws NullPointerException if <tt>c</tt> or any element within it
- * is <tt>null</tt>
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
*/
public ConcurrentLinkedQueue(Collection<? extends E> c) {
for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
add(it.next());
}
- // Have to override just to update the javadoc
+ // Have to override just to update the javadoc
/**
- * Adds the specified element to the tail of this queue.
- * @param o the element to add.
- * @return <tt>true</tt> (as per the general contract of
- * <tt>Collection.add</tt>).
+ * Inserts the specified element at the tail of this queue.
*
- * @throws NullPointerException if the specified element is <tt>null</tt>
+ * @return {@code true} (as specified by {@link Collection#add})
+ * @throws NullPointerException if the specified element is null
*/
- public boolean add(E o) {
- return offer(o);
+ public boolean add(E e) {
+ return offer(e);
}
/**
- * Inserts the specified element to the tail of this queue.
+ * We don't bother to update head or tail pointers if less than
+ * HOPS links from "true" location. We assume that volatile
+ * writes are significantly more expensive than volatile reads.
+ */
+ private static final int HOPS = 1;
+
+ /**
+ * Try to CAS head to p. If successful, repoint old head to itself
+ * as sentinel for succ(), below.
+ */
+ final void updateHead(Node<E> h, Node<E> p) {
+ if (h != p && casHead(h, p))
+ h.setNext(h);
+ }
+
+ /**
+ * Returns the successor of p, or the head node if p.next has been
+ * linked to self, which will only be true if traversing with a
+ * stale pointer that is now off the list.
+ */
+ final Node<E> succ(Node<E> p) {
+ Node<E> next = p.getNext();
+ return (p == next) ? head : next;
+ }
+
+ /**
+ * Inserts the specified element at the tail of this queue.
*
- * @param o the element to add.
- * @return <tt>true</tt> (as per the general contract of
- * <tt>Queue.offer</tt>).
- * @throws NullPointerException if the specified element is <tt>null</tt>
+ * @return {@code true} (as specified by {@link Queue#offer})
+ * @throws NullPointerException if the specified element is null
*/
- public boolean offer(E o) {
- if (o == null) throw new NullPointerException();
- Node<E> n = new Node<E>(o, null);
- for(;;) {
+ public boolean offer(E e) {
+ if (e == null) throw new NullPointerException();
+ Node<E> n = new Node<E>(e);
+ retry:
+ for (;;) {
Node<E> t = tail;
- Node<E> s = t.getNext();
- if (t == tail) {
- if (s == null) {
- if (t.casNext(s, n)) {
- casTail(t, n);
- return true;
- }
+ Node<E> p = t;
+ for (int hops = 0; ; hops++) {
+ Node<E> next = succ(p);
+ if (next != null) {
+ if (hops > HOPS && t != tail)
+ continue retry;
+ p = next;
+ } else if (p.casNext(null, n)) {
+ if (hops >= HOPS)
+ casTail(t, n); // Failure is OK.
+ return true;
} else {
- casTail(t, s);
+ p = succ(p);
}
}
}
}
public E poll() {
- for (;;) {
- Node<E> h = head;
- Node<E> t = tail;
- Node<E> first = h.getNext();
- if (h == head) {
- if (h == t) {
- if (first == null)
- return null;
- else
- casTail(t, first);
- } else if (casHead(h, first)) {
- E item = first.getItem();
- if (item != null) {
- first.setItem(null);
- return item;
- }
- // else skip over deleted item, continue loop,
+ Node<E> h = head;
+ Node<E> p = h;
+ for (int hops = 0; ; hops++) {
+ E item = p.getItem();
+
+ if (item != null && p.casItem(item, null)) {
+ if (hops >= HOPS) {
+ Node<E> q = p.getNext();
+ updateHead(h, (q != null) ? q : p);
}
+ return item;
+ }
+ Node<E> next = succ(p);
+ if (next == null) {
+ updateHead(h, p);
+ break;
}
+ p = next;
}
+ return null;
}
- public E peek() { // same as poll except don't remove item
+ public E peek() {
+ Node<E> h = head;
+ Node<E> p = h;
+ E item;
for (;;) {
- Node<E> h = head;
- Node<E> t = tail;
- Node<E> first = h.getNext();
- if (h == head) {
- if (h == t) {
- if (first == null)
- return null;
- else
- casTail(t, first);
- } else {
- E item = first.getItem();
- if (item != null)
- return item;
- else // remove deleted node and continue
- casHead(h, first);
- }
+ item = p.getItem();
+ if (item != null)
+ break;
+ Node<E> next = succ(p);
+ if (next == null) {
+ break;
}
+ p = next;
}
+ updateHead(h, p);
+ return item;
}
/**
@@ -245,46 +334,50 @@
* introducing race.)
*/
Node<E> first() {
+ Node<E> h = head;
+ Node<E> p = h;
+ Node<E> result;
for (;;) {
- Node<E> h = head;
- Node<E> t = tail;
- Node<E> first = h.getNext();
- if (h == head) {
- if (h == t) {
- if (first == null)
- return null;
- else
- casTail(t, first);
- } else {
- if (first.getItem() != null)
- return first;
- else // remove deleted node and continue
- casHead(h, first);
- }
+ E item = p.getItem();
+ if (item != null) {
+ result = p;
+ break;
+ }
+ Node<E> next = succ(p);
+ if (next == null) {
+ result = null;
+ break;
}
+ p = next;
}
+ updateHead(h, p);
+ return result;
}
-
+ /**
+ * Returns {@code true} if this queue contains no elements.
+ *
+ * @return {@code true} if this queue contains no elements
+ */
public boolean isEmpty() {
return first() == null;
}
/**
* Returns the number of elements in this queue. If this queue
- * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
- * <tt>Integer.MAX_VALUE</tt>.
+ * contains more than {@code Integer.MAX_VALUE} elements, 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 queues, determining the current
* number of elements requires an O(n) traversal.
*
- * @return the number of elements in this queue.
+ * @return the number of elements in this queue
*/
public int size() {
int count = 0;
- for (Node<E> p = first(); p != null; p = p.getNext()) {
+ for (Node<E> p = first(); p != null; p = succ(p)) {
if (p.getItem() != null) {
// Collections.size() spec says to max out
if (++count == Integer.MAX_VALUE)
@@ -294,9 +387,17 @@
return count;
}
+ /**
+ * Returns {@code true} if this queue contains the specified element.
+ * More formally, returns {@code true} if and only if this queue contains
+ * at least one element {@code e} such that {@code o.equals(e)}.
+ *
+ * @param o object to be checked for containment in this queue
+ * @return {@code true} if this queue contains the specified element
+ */
public boolean contains(Object o) {
if (o == null) return false;
- for (Node<E> p = first(); p != null; p = p.getNext()) {
+ for (Node<E> p = first(); p != null; p = succ(p)) {
E item = p.getItem();
if (item != null &&
o.equals(item))
@@ -305,22 +406,50 @@
return false;
}
+ /**
+ * Removes a single instance of the specified element from this queue,
+ * if it is present. More formally, removes an element {@code e} such
+ * that {@code o.equals(e)}, if this queue contains one or more such
+ * elements.
+ * Returns {@code true} if this queue contained the specified element
+ * (or equivalently, if this queue changed as a result of the call).
+ *
+ * @param o element to be removed from this queue, if present
+ * @return {@code true} if this queue changed as a result of the call
+ */
public boolean remove(Object o) {
if (o == null) return false;
- for (Node<E> p = first(); p != null; p = p.getNext()) {
+ Node<E> pred = null;
+ for (Node<E> p = first(); p != null; p = succ(p)) {
E item = p.getItem();
- if (item != null &&
- o.equals(item) &&
- p.casItem(item, null))
+ if (item != null && o.equals(item) && p.casItem(item, null)) {
+ Node<E> next = succ(p);
+ if (pred != null && next != null)
+ pred.casNext(p, next);
return true;
+ }
+ pred = p;
}
return false;
}
+ /**
+ * Returns an array containing all of the elements in this queue, in
+ * proper sequence.
+ *
+ * <p>The returned array will be "safe" in that no references to it are
+ * maintained by this queue. (In other words, this method must allocate
+ * a new array). The caller is thus free to modify the returned array.
+ *
+ * <p>This method acts as bridge between array-based and collection-based
+ * APIs.
+ *
+ * @return an array containing all of the elements in this queue
+ */
public Object[] toArray() {
// Use ArrayList to deal with resizing.
ArrayList<E> al = new ArrayList<E>();
- for (Node<E> p = first(); p != null; p = p.getNext()) {
+ for (Node<E> p = first(); p != null; p = succ(p)) {
E item = p.getItem();
if (item != null)
al.add(item);
@@ -328,11 +457,48 @@
return al.toArray();
}
+ /**
+ * Returns an array containing all of the elements in this queue, in
+ * proper sequence; the runtime type of the returned array is that of
+ * the specified array. If the queue fits in the specified array, it
+ * is returned therein. Otherwise, a new array is allocated with the
+ * runtime type of the specified array and the size of this queue.
+ *
+ * <p>If this queue fits in the specified array with room to spare
+ * (i.e., the array has more elements than this queue), the element in
+ * the array immediately following the end of the queue is set to
+ * {@code null}.
+ *
+ * <p>Like the {@link #toArray()} method, this method acts as bridge between
+ * array-based and collection-based APIs. Further, this method allows
+ * precise control over the runtime type of the output array, and may,
+ * under certain circumstances, be used to save allocation costs.
+ *
+ * <p>Suppose {@code x} is a queue known to contain only strings.
+ * The following code can be used to dump the queue into a newly
+ * allocated array of {@code String}:
+ *
+ * <pre>
+ * String[] y = x.toArray(new String[0]);</pre>
+ *
+ * Note that {@code toArray(new Object[0])} is identical in function to
+ * {@code toArray()}.
+ *
+ * @param a the array into which the elements of the queue are to
+ * be stored, if it is big enough; otherwise, a new array of the
+ * same runtime type is allocated for this purpose
+ * @return an array containing all of the elements in this queue
+ * @throws ArrayStoreException if the runtime type of the specified array
+ * is not a supertype of the runtime type of every element in
+ * this queue
+ * @throws NullPointerException if the specified array is null
+ */
+ @SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
// try to use sent-in array
int k = 0;
Node<E> p;
- for (p = first(); p != null && k < a.length; p = p.getNext()) {
+ for (p = first(); p != null && k < a.length; p = succ(p)) {
E item = p.getItem();
if (item != null)
a[k++] = (T)item;
@@ -345,23 +511,23 @@
// If won't fit, use ArrayList version
ArrayList<E> al = new ArrayList<E>();
- for (Node<E> q = first(); q != null; q = q.getNext()) {
+ for (Node<E> q = first(); q != null; q = succ(q)) {
E item = q.getItem();
if (item != null)
al.add(item);
}
- return (T[])al.toArray(a);
+ return al.toArray(a);
}
/**
* Returns an iterator over the elements in this queue in proper sequence.
* The returned iterator is a "weakly consistent" iterator that
- * will never throw {@link java.util.ConcurrentModificationException},
+ * will never throw {@link ConcurrentModificationException},
* and guarantees to traverse elements as they existed upon
* construction of the iterator, and may (but is not guaranteed to)
* reflect any modifications subsequent to construction.
*
- * @return an iterator over the elements in this queue in proper sequence.
+ * @return an iterator over the elements in this queue in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
@@ -378,7 +544,7 @@
* that an element exists in hasNext(), we must return it in
* the following next() call even if it was in the process of
* being removed when hasNext() was called.
- **/
+ */
private E nextItem;
/**
@@ -398,7 +564,15 @@
lastRet = nextNode;
E x = nextItem;
- Node<E> p = (nextNode == null)? first() : nextNode.getNext();
+ Node<E> pred, p;
+ if (nextNode == null) {
+ p = first();
+ pred = null;
+ } else {
+ pred = nextNode;
+ p = succ(nextNode);
+ }
+
for (;;) {
if (p == null) {
nextNode = null;
@@ -410,8 +584,13 @@
nextNode = p;
nextItem = item;
return x;
- } else // skip over nulls
- p = p.getNext();
+ } else {
+ // skip over nulls
+ Node<E> next = succ(p);
+ if (pred != null && next != null)
+ pred.casNext(p, next);
+ p = next;
+ }
}
}
@@ -436,7 +615,7 @@
/**
* Save the state to a stream (that is, serialize it).
*
- * @serialData All of the elements (each an <tt>E</tt>) in
+ * @serialData All of the elements (each an {@code E}) in
* the proper order, followed by a null
* @param s the stream
*/
@@ -447,7 +626,7 @@
s.defaultWriteObject();
// Write out all elements in the proper order.
- for (Node<E> p = first(); p != null; p = p.getNext()) {
+ for (Node<E> p = first(); p != null; p = succ(p)) {
Object item = p.getItem();
if (item != null)
s.writeObject(item);
@@ -466,10 +645,11 @@
throws java.io.IOException, ClassNotFoundException {
// Read in capacity, and any hidden stuff
s.defaultReadObject();
- head = new Node<E>(null, null);
+ head = new Node<E>(null);
tail = head;
// Read in all elements and place in queue
for (;;) {
+ @SuppressWarnings("unchecked")
E item = (E)s.readObject();
if (item == null)
break;
Modified: harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentMap.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentMap.java?rev=794678&r1=794677&r2=794678&view=diff
==============================================================================
--- harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentMap.java (original)
+++ harmony/enhanced/classlib/trunk/modules/concurrent/src/main/java/java/util/concurrent/ConcurrentMap.java Thu Jul 16 14:01:15 2009
@@ -11,14 +11,21 @@
* A {@link java.util.Map} providing additional atomic
* <tt>putIfAbsent</tt>, <tt>remove</tt>, and <tt>replace</tt> methods.
*
+ * <p>Memory consistency effects: As with other concurrent
+ * collections, actions in a thread prior to placing an object into a
+ * {@code ConcurrentMap} as a key or value
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * actions subsequent to the access or removal of that object from
+ * the {@code ConcurrentMap} in another thread.
+ *
* <p>This interface is a member of the
- * <a href="{@docRoot}/../guide/collections/index.html">
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
- *
+ *
* @since 1.5
* @author Doug Lea
* @param <K> the type of keys maintained by this map
- * @param <V> the type of mapped values
+ * @param <V> the type of mapped values
*/
public interface ConcurrentMap<K, V> extends Map<K, V> {
/**
@@ -26,93 +33,102 @@
* with a value, associate it with the given value.
* This is equivalent to
* <pre>
- * if (!map.containsKey(key))
- * return map.put(key, value);
+ * if (!map.containsKey(key))
+ * return map.put(key, value);
* else
- * return map.get(key);
- * </pre>
- * Except that the action is performed atomically.
- * @param key key with which the specified value is to be associated.
- * @param value value to be associated with the specified key.
- * @return previous value associated with specified key, or <tt>null</tt>
- * if there was no mapping for key. A <tt>null</tt> return can
- * also indicate that the map previously associated <tt>null</tt>
- * with the specified key, if the implementation supports
- * <tt>null</tt> values.
+ * return map.get(key);</pre>
+ * except that the action is performed atomically.
*
- * @throws UnsupportedOperationException if the <tt>put</tt> operation is
- * not supported by this map.
+ * @param key key with which the specified value is to be associated
+ * @param value value to be associated with the specified key
+ * @return the previous value associated with the specified key, or
+ * <tt>null</tt> if there was no mapping for the key.
+ * (A <tt>null</tt> return can also indicate that the map
+ * previously associated <tt>null</tt> with the key,
+ * if the implementation supports null values.)
+ * @throws UnsupportedOperationException if the <tt>put</tt> operation
+ * is not supported by this map
* @throws ClassCastException if the class of the specified key or value
- * prevents it from being stored in this map.
- * @throws IllegalArgumentException if some aspect of this key or value
- * prevents it from being stored in this map.
- * @throws NullPointerException if this map does not permit <tt>null</tt>
- * keys or values, and the specified key or value is
- * <tt>null</tt>.
+ * prevents it from being stored in this map
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
*
*/
V putIfAbsent(K key, V value);
/**
- * Remove entry for key only if currently mapped to given value.
- * Acts as
- * <pre>
- * if ((map.containsKey(key) && map.get(key).equals(value)) {
- * map.remove(key);
- * return true;
- * } else return false;
- * </pre>
+ * Removes the entry for a key only if currently mapped to a given value.
+ * This is equivalent to
+ * <pre>
+ * if (map.containsKey(key) && map.get(key).equals(value)) {
+ * map.remove(key);
+ * return true;
+ * } else return false;</pre>
* except that the action is performed atomically.
- * @param key key with which the specified value is associated.
- * @param value value associated with the specified key.
- * @return true if the value was removed, false otherwise
- * @throws NullPointerException if this map does not permit <tt>null</tt>
- * keys or values, and the specified key or value is
- * <tt>null</tt>.
+ *
+ * @param key key with which the specified value is associated
+ * @param value value expected to be associated with the specified key
+ * @return <tt>true</tt> if the value was removed
+ * @throws UnsupportedOperationException if the <tt>remove</tt> operation
+ * is not supported by this map
+ * @throws ClassCastException if the key or value is of an inappropriate
+ * type for this map (optional)
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values (optional)
*/
boolean remove(Object key, Object value);
-
/**
- * Replace entry for key only if currently mapped to given value.
- * Acts as
- * <pre>
- * if ((map.containsKey(key) && map.get(key).equals(oldValue)) {
- * map.put(key, newValue);
- * return true;
- * } else return false;
- * </pre>
+ * Replaces the entry for a key only if currently mapped to a given value.
+ * This is equivalent to
+ * <pre>
+ * if (map.containsKey(key) && map.get(key).equals(oldValue)) {
+ * map.put(key, newValue);
+ * return true;
+ * } else return false;</pre>
* except that the action is performed atomically.
- * @param key key with which the specified value is associated.
- * @param oldValue value expected to be associated with the specified key.
- * @param newValue value to be associated with the specified key.
- * @return true if the value was replaced
- * @throws NullPointerException if this map does not permit <tt>null</tt>
- * keys or values, and the specified key or value is
- * <tt>null</tt>.
+ *
+ * @param key key with which the specified value is associated
+ * @param oldValue value expected to be associated with the specified key
+ * @param newValue value to be associated with the specified key
+ * @return <tt>true</tt> if the value was replaced
+ * @throws UnsupportedOperationException if the <tt>put</tt> operation
+ * is not supported by this map
+ * @throws ClassCastException if the class of a specified key or value
+ * prevents it from being stored in this map
+ * @throws NullPointerException if a specified key or value is null,
+ * and this map does not permit null keys or values
+ * @throws IllegalArgumentException if some property of a specified key
+ * or value prevents it from being stored in this map
*/
boolean replace(K key, V oldValue, V newValue);
/**
- * Replace entry for key only if currently mapped to some value.
- * Acts as
- * <pre>
- * if ((map.containsKey(key)) {
- * return map.put(key, value);
- * } else return null;
- * </pre>
+ * Replaces the entry for a key only if currently mapped to some value.
+ * This is equivalent to
+ * <pre>
+ * if (map.containsKey(key)) {
+ * return map.put(key, value);
+ * } else return null;</pre>
* except that the action is performed atomically.
- * @param key key with which the specified value is associated.
- * @param value value to be associated with the specified key.
- * @return previous value associated with specified key, or <tt>null</tt>
- * if there was no mapping for key. A <tt>null</tt> return can
- * also indicate that the map previously associated <tt>null</tt>
- * with the specified key, if the implementation supports
- * <tt>null</tt> values.
- * @throws NullPointerException if this map does not permit <tt>null</tt>
- * keys or values, and the specified key or value is
- * <tt>null</tt>.
+ *
+ * @param key key with which the specified value is associated
+ * @param value value to be associated with the specified key
+ * @return the previous value associated with the specified key, or
+ * <tt>null</tt> if there was no mapping for the key.
+ * (A <tt>null</tt> return can also indicate that the map
+ * previously associated <tt>null</tt> with the key,
+ * if the implementation supports null values.)
+ * @throws UnsupportedOperationException if the <tt>put</tt> operation
+ * is not supported by this map
+ * @throws ClassCastException if the class of the specified key or value
+ * prevents it from being stored in this map
+ * @throws NullPointerException if the specified key or value is null,
+ * and this map does not permit null keys or values
+ * @throws IllegalArgumentException if some property of the specified key
+ * or value prevents it from being stored in this map
*/
V replace(K key, V value);
-
}