[jboss-svn-commits] JBoss Common SVN: r3125 - common-core/trunk/src/main/java/org/jboss/util/collection.
jboss-svn-commits at lists.jboss.org
jboss-svn-commits at lists.jboss.org
Sun Apr 19 23:52:22 EDT 2009
Author: jason.greene at jboss.com
Date: 2009-04-19 23:52:22 -0400 (Sun, 19 Apr 2009)
New Revision: 3125
Added:
common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentNavigableMap.java
common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java
common-core/trunk/src/main/java/org/jboss/util/collection/NavigableMap.java
Log:
JBCOMMON-83 Add ConcurrentSkipListMap
Added: common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentNavigableMap.java
===================================================================
--- common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentNavigableMap.java (rev 0)
+++ common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentNavigableMap.java 2009-04-20 03:52:22 UTC (rev 3125)
@@ -0,0 +1,76 @@
+/*
+ * 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
+ */
+
+package org.jboss.util.collection;
+
+import java.util.concurrent.ConcurrentMap;
+
+/**
+ * A {@link ConcurrentMap} supporting {@link NavigableMap} operations.
+ *
+ * @author Doug Lea
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ */
+public interface ConcurrentNavigableMap<K,V> extends ConcurrentMap<K,V>, NavigableMap<K,V> {
+ /**
+ * Returns a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
+ * <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned sorted map
+ * is empty.) The returned sorted map is backed by this map, so changes
+ * in the returned sorted map are reflected in this map, and vice-versa.
+
+ * @param fromKey low endpoint (inclusive) of the subMap.
+ * @param toKey high endpoint (exclusive) of the subMap.
+ *
+ * @return a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.
+ *
+ * @throws ClassCastException if <tt>fromKey</tt> and
+ * <tt>toKey</tt> cannot be compared to one another using this
+ * map's comparator (or, if the map has no comparator, using
+ * natural ordering).
+ * @throws IllegalArgumentException if <tt>fromKey</tt> is greater
+ * than <tt>toKey</tt>.
+ * @throws NullPointerException if <tt>fromKey</tt> or
+ * <tt>toKey</tt> is <tt>null</tt> and this map does not support
+ * <tt>null</tt> keys.
+ */
+ public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey);
+
+ /**
+ * Returns a view of the portion of this map whose keys are strictly less
+ * than <tt>toKey</tt>. The returned sorted map is backed by this map, so
+ * changes in the returned sorted map are reflected in this map, and
+ * vice-versa.
+ * @param toKey high endpoint (exclusive) of the headMap.
+ * @return a view of the portion of this map whose keys are strictly
+ * less than <tt>toKey</tt>.
+ *
+ * @throws ClassCastException if <tt>toKey</tt> is not compatible
+ * with this map's comparator (or, if the map has no comparator,
+ * if <tt>toKey</tt> does not implement <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>toKey</tt> is <tt>null</tt>
+ * and this map does not support <tt>null</tt> keys.
+ */
+ public ConcurrentNavigableMap<K,V> headMap(K toKey);
+
+ /**
+ * Returns a view of the portion of this map whose keys are
+ * greater than or equal to <tt>fromKey</tt>. The returned sorted
+ * map is backed by this map, so changes in the returned sorted
+ * map are reflected in this map, and vice-versa.
+ * @param fromKey low endpoint (inclusive) of the tailMap.
+ * @return a view of the portion of this map whose keys are greater
+ * than or equal to <tt>fromKey</tt>.
+ * @throws ClassCastException if <tt>fromKey</tt> is not compatible
+ * with this map's comparator (or, if the map has no comparator,
+ * if <tt>fromKey</tt> does not implement <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>fromKey</tt> is <tt>null</tt>
+ * and this map does not support <tt>null</tt> keys.
+ */
+ public ConcurrentNavigableMap<K,V> tailMap(K fromKey);
+}
Property changes on: common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentNavigableMap.java
___________________________________________________________________
Name: svn:keywords
+ Id Revision
Name: svn:eol-style
+ LF
Added: common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java
===================================================================
--- common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java (rev 0)
+++ common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java 2009-04-20 03:52:22 UTC (rev 3125)
@@ -0,0 +1,3472 @@
+/*
+ * 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
+ */
+
+package org.jboss.util.collection;
+
+import java.util.AbstractCollection;
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.SortedMap;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+/**
+ * A scalable {@link ConcurrentNavigableMap} implementation. This
+ * class maintains a map in ascending key order, sorted according to
+ * the <i>natural order</i> for the key's class (see {@link
+ * Comparable}), or by the {@link Comparator} provided at creation
+ * time, depending on which constructor is used.
+ *
+ * <p>This class implements a concurrent variant of <a
+ * href="http://www.cs.umd.edu/~pugh/">SkipLists</a> providing
+ * expected average <i>log(n)</i> time cost for the
+ * <tt>containsKey</tt>, <tt>get</tt>, <tt>put</tt> and
+ * <tt>remove</tt> operations and their variants. Insertion, removal,
+ * update, and access operations safely execute concurrently by
+ * multiple threads. Iterators are <i>weakly consistent</i>, returning
+ * elements reflecting the state of the map at some point at or since
+ * the creation of the iterator. They do <em>not</em> throw {@link
+ * ConcurrentModificationException}, and may proceed concurrently with
+ * other operations. Ascending key ordered views and their iterators
+ * are faster than descending ones.
+ *
+ * <p>All <tt>Map.Entry</tt> pairs returned by methods in this class
+ * and its views represent snapshots of mappings at the time they were
+ * produced. They do <em>not</em> support the <tt>Entry.setValue</tt>
+ * method. (Note however that it is possible to change mappings in the
+ * associated map using <tt>put</tt>, <tt>putIfAbsent</tt>, or
+ * <tt>replace</tt>, depending on exactly which effect you need.)
+ *
+ * <p>Beware that, unlike in most collections, the <tt>size</tt>
+ * method is <em>not</em> a constant-time operation. Because of the
+ * asynchronous nature of these maps, determining the current number
+ * of elements requires a traversal of the elements. Additionally,
+ * the bulk operations <tt>putAll</tt>, <tt>equals</tt>, and
+ * <tt>clear</tt> are <em>not</em> guaranteed to be performed
+ * atomically. For example, an iterator operating concurrently with a
+ * <tt>putAll</tt> operation might view only some of the added
+ * elements.
+ *
+ * <p>This class and its views and iterators implement all of the
+ * <em>optional</em> methods of the {@link Map} and {@link Iterator}
+ * interfaces. Like most other concurrent collections, this class does
+ * not permit the use of <tt>null</tt> keys or values because some
+ * null return values cannot be reliably distinguished from the
+ * absence of elements.
+ *
+ * @author Doug Lea
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ */
+public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V>
+ implements ConcurrentNavigableMap<K,V>,
+ Cloneable,
+ java.io.Serializable {
+ /*
+ * This class implements a tree-like two-dimensionally linked skip
+ * list in which the index levels are represented in separate
+ * nodes from the base nodes holding data. There are two reasons
+ * for taking this approach instead of the usual array-based
+ * structure: 1) Array based implementations seem to encounter
+ * more complexity and overhead 2) We can use cheaper algorithms
+ * for the heavily-traversed index lists than can be used for the
+ * base lists. Here's a picture of some of the basics for a
+ * possible list with 2 levels of index:
+ *
+ * Head nodes Index nodes
+ * +-+ right +-+ +-+
+ * |2|---------------->| |--------------------->| |->null
+ * +-+ +-+ +-+
+ * | down | |
+ * v v v
+ * +-+ +-+ +-+ +-+ +-+ +-+
+ * |1|----------->| |->| |------>| |----------->| |------>| |->null
+ * +-+ +-+ +-+ +-+ +-+ +-+
+ * v | | | | |
+ * Nodes next v v v v v
+ * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
+ * | |->|A|->|B|->|C|->|D|->|E|->|F|->|G|->|H|->|I|->|J|->|K|->null
+ * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
+ *
+ * The base lists use a variant of the HM linked ordered set
+ * algorithm. See Tim Harris, "A pragmatic implementation of
+ * non-blocking linked lists"
+ * http://www.cl.cam.ac.uk/~tlh20/publications.html and Maged
+ * Michael "High Performance Dynamic Lock-Free Hash Tables and
+ * List-Based Sets"
+ * http://www.research.ibm.com/people/m/michael/pubs.htm. The
+ * basic idea in these lists is to mark the "next" pointers of
+ * deleted nodes when deleting to avoid conflicts with concurrent
+ * insertions, and when traversing to keep track of triples
+ * (predecessor, node, successor) in order to detect when and how
+ * to unlink these deleted nodes.
+ *
+ * Rather than using mark-bits to mark list deletions (which can
+ * be slow and space-intensive using AtomicMarkedReference), nodes
+ * use direct CAS'able next pointers. On deletion, instead of
+ * marking a pointer, they splice in another node that can be
+ * thought of as standing for a marked pointer (indicating this by
+ * using otherwise impossible field values). Using plain nodes
+ * acts roughly like "boxed" implementations of marked pointers,
+ * but uses new nodes only when nodes are deleted, not for every
+ * link. This requires less space and supports faster
+ * traversal. Even if marked references were better supported by
+ * JVMs, traversal using this technique might still be faster
+ * because any search need only read ahead one more node than
+ * otherwise required (to check for trailing marker) rather than
+ * unmasking mark bits or whatever on each read.
+ *
+ * This approach maintains the essential property needed in the HM
+ * algorithm of changing the next-pointer of a deleted node so
+ * that any other CAS of it will fail, but implements the idea by
+ * changing the pointer to point to a different node, not by
+ * marking it. While it would be possible to further squeeze
+ * space by defining marker nodes not to have key/value fields, it
+ * isn't worth the extra type-testing overhead. The deletion
+ * markers are rarely encountered during traversal and are
+ * normally quickly garbage collected. (Note that this technique
+ * would not work well in systems without garbage collection.)
+ *
+ * In addition to using deletion markers, the lists also use
+ * nullness of value fields to indicate deletion, in a style
+ * similar to typical lazy-deletion schemes. If a node's value is
+ * null, then it is considered logically deleted and ignored even
+ * though it is still reachable. This maintains proper control of
+ * concurrent replace vs delete operations -- an attempted replace
+ * must fail if a delete beat it by nulling field, and a delete
+ * must return the last non-null value held in the field. (Note:
+ * Null, rather than some special marker, is used for value fields
+ * here because it just so happens to mesh with the Map API
+ * requirement that method get returns null if there is no
+ * mapping, which allows nodes to remain concurrently readable
+ * even when deleted. Using any other marker value here would be
+ * messy at best.)
+ *
+ * Here's the sequence of events for a deletion of node n with
+ * predecessor b and successor f, initially:
+ *
+ * +------+ +------+ +------+
+ * ... | b |------>| n |----->| f | ...
+ * +------+ +------+ +------+
+ *
+ * 1. CAS n's value field from non-null to null.
+ * From this point on, no public operations encountering
+ * the node consider this mapping to exist. However, other
+ * ongoing insertions and deletions might still modify
+ * n's next pointer.
+ *
+ * 2. CAS n's next pointer to point to a new marker node.
+ * From this point on, no other nodes can be appended to n.
+ * which avoids deletion errors in CAS-based linked lists.
+ *
+ * +------+ +------+ +------+ +------+
+ * ... | b |------>| n |----->|marker|------>| f | ...
+ * +------+ +------+ +------+ +------+
+ *
+ * 3. CAS b's next pointer over both n and its marker.
+ * From this point on, no new traversals will encounter n,
+ * and it can eventually be GCed.
+ * +------+ +------+
+ * ... | b |----------------------------------->| f | ...
+ * +------+ +------+
+ *
+ * A failure at step 1 leads to simple retry due to a lost race
+ * with another operation. Steps 2-3 can fail because some other
+ * thread noticed during a traversal a node with null value and
+ * helped out by marking and/or unlinking. This helping-out
+ * ensures that no thread can become stuck waiting for progress of
+ * the deleting thread. The use of marker nodes slightly
+ * complicates helping-out code because traversals must track
+ * consistent reads of up to four nodes (b, n, marker, f), not
+ * just (b, n, f), although the next field of a marker is
+ * immutable, and once a next field is CAS'ed to point to a
+ * marker, it never again changes, so this requires less care.
+ *
+ * Skip lists add indexing to this scheme, so that the base-level
+ * traversals start close to the locations being found, inserted
+ * or deleted -- usually base level traversals only traverse a few
+ * nodes. This doesn't change the basic algorithm except for the
+ * need to make sure base traversals start at predecessors (here,
+ * b) that are not (structurally) deleted, otherwise retrying
+ * after processing the deletion.
+ *
+ * Index levels are maintained as lists with volatile next fields,
+ * using CAS to link and unlink. Races are allowed in index-list
+ * operations that can (rarely) fail to link in a new index node
+ * or delete one. (We can't do this of course for data nodes.)
+ * However, even when this happens, the index lists remain sorted,
+ * so correctly serve as indices. This can impact performance,
+ * but since skip lists are probabilistic anyway, the net result
+ * is that under contention, the effective "p" value may be lower
+ * than its nominal value. And race windows are kept small enough
+ * that in practice these failures are rare, even under a lot of
+ * contention.
+ *
+ * The fact that retries (for both base and index lists) are
+ * relatively cheap due to indexing allows some minor
+ * simplifications of retry logic. Traversal restarts are
+ * performed after most "helping-out" CASes. This isn't always
+ * strictly necessary, but the implicit backoffs tend to help
+ * reduce other downstream failed CAS's enough to outweigh restart
+ * cost. This worsens the worst case, but seems to improve even
+ * highly contended cases.
+ *
+ * Unlike most skip-list implementations, index insertion and
+ * deletion here require a separate traversal pass occuring after
+ * the base-level action, to add or remove index nodes. This adds
+ * to single-threaded overhead, but improves contended
+ * multithreaded performance by narrowing interference windows,
+ * and allows deletion to ensure that all index nodes will be made
+ * unreachable upon return from a public remove operation, thus
+ * avoiding unwanted garbage retention. This is more important
+ * here than in some other data structures because we cannot null
+ * out node fields referencing user keys since they might still be
+ * read by other ongoing traversals.
+ *
+ * Indexing uses skip list parameters that maintain good search
+ * performance while using sparser-than-usual indices: The
+ * hardwired parameters k=1, p=0.5 (see method randomLevel) mean
+ * that about one-quarter of the nodes have indices. Of those that
+ * do, half have one level, a quarter have two, and so on (see
+ * Pugh's Skip List Cookbook, sec 3.4). The expected total space
+ * requirement for a map is slightly less than for the current
+ * implementation of java.util.TreeMap.
+ *
+ * Changing the level of the index (i.e, the height of the
+ * tree-like structure) also uses CAS. The head index has initial
+ * level/height of one. Creation of an index with height greater
+ * than the current level adds a level to the head index by
+ * CAS'ing on a new top-most head. To maintain good performance
+ * after a lot of removals, deletion methods heuristically try to
+ * reduce the height if the topmost levels appear to be empty.
+ * This may encounter races in which it possible (but rare) to
+ * reduce and "lose" a level just as it is about to contain an
+ * index (that will then never be encountered). This does no
+ * structural harm, and in practice appears to be a better option
+ * than allowing unrestrained growth of levels.
+ *
+ * The code for all this is more verbose than you'd like. Most
+ * operations entail locating an element (or position to insert an
+ * element). The code to do this can't be nicely factored out
+ * because subsequent uses require a snapshot of predecessor
+ * and/or successor and/or value fields which can't be returned
+ * all at once, at least not without creating yet another object
+ * to hold them -- creating such little objects is an especially
+ * bad idea for basic internal search operations because it adds
+ * to GC overhead. (This is one of the few times I've wished Java
+ * had macros.) Instead, some traversal code is interleaved within
+ * insertion and removal operations. The control logic to handle
+ * all the retry conditions is sometimes twisty. Most search is
+ * broken into 2 parts. findPredecessor() searches index nodes
+ * only, returning a base-level predecessor of the key. findNode()
+ * finishes out the base-level search. Even with this factoring,
+ * there is a fair amount of near-duplication of code to handle
+ * variants.
+ *
+ * For explanation of algorithms sharing at least a couple of
+ * features with this one, see Mikhail Fomitchev's thesis
+ * (http://www.cs.yorku.ca/~mikhail/), Keir Fraser's thesis
+ * (http://www.cl.cam.ac.uk/users/kaf24/), and Hakan Sundell's
+ * thesis (http://www.cs.chalmers.se/~phs/).
+ *
+ * Given the use of tree-like index nodes, you might wonder why
+ * this doesn't use some kind of search tree instead, which would
+ * support somewhat faster search operations. The reason is that
+ * there are no known efficient lock-free insertion and deletion
+ * algorithms for search trees. The immutability of the "down"
+ * links of index nodes (as opposed to mutable "left" fields in
+ * true trees) makes this tractable using only CAS operations.
+ *
+ * Notation guide for local variables
+ * Node: b, n, f for predecessor, node, successor
+ * Index: q, r, d for index node, right, down.
+ * t for another index node
+ * Head: h
+ * Levels: j
+ * Keys: k, key
+ * Values: v, value
+ * Comparisons: c
+ */
+
+ private static final long serialVersionUID = -8627078645895051609L;
+
+ /**
+ * Special value used to identify base-level header
+ */
+ private static final Object BASE_HEADER = new Object();
+
+ /**
+ * The topmost head index of the skiplist.
+ */
+ private transient volatile HeadIndex<K,V> head;
+
+ /**
+ * The Comparator used to maintain order in this Map, or null
+ * if using natural order.
+ * @serial
+ */
+ private final Comparator<? super K> comparator;
+
+ /**
+ * Seed for simple random number generator. Not volatile since it
+ * doesn't matter too much if different threads don't see updates.
+ */
+ private transient int randomSeed;
+
+ /** Lazily initialized key set */
+ private transient KeySet keySet;
+ /** Lazily initialized entry set */
+ private transient EntrySet entrySet;
+ /** Lazily initialized values collection */
+ private transient Values values;
+ /** Lazily initialized descending key set */
+ private transient DescendingKeySet descendingKeySet;
+ /** Lazily initialized descending entry set */
+ private transient DescendingEntrySet descendingEntrySet;
+
+ /**
+ * Initialize or reset state. Needed by constructors, clone,
+ * clear, readObject. and ConcurrentSkipListSet.clone.
+ * (Note that comparator must be separately initialized.)
+ */
+ final void initialize() {
+ keySet = null;
+ entrySet = null;
+ values = null;
+ descendingEntrySet = null;
+ descendingKeySet = null;
+ randomSeed = (int) System.nanoTime();
+ head = new HeadIndex<K,V>(new Node<K,V>(null, BASE_HEADER, null),
+ null, null, 1);
+ }
+
+ /** Updater for casHead */
+ private static final
+ AtomicReferenceFieldUpdater<ConcurrentSkipListMap, HeadIndex>
+ headUpdater = AtomicReferenceFieldUpdater.newUpdater
+ (ConcurrentSkipListMap.class, HeadIndex.class, "head");
+
+ /**
+ * compareAndSet head node
+ */
+ private boolean casHead(HeadIndex<K,V> cmp, HeadIndex<K,V> val) {
+ return headUpdater.compareAndSet(this, cmp, val);
+ }
+
+ /* ---------------- Nodes -------------- */
+
+ /**
+ * Nodes hold keys and values, and are singly linked in sorted
+ * order, possibly with some intervening marker nodes. The list is
+ * headed by a dummy node accessible as head.node. The value field
+ * is declared only as Object because it takes special non-V
+ * values for marker and header nodes.
+ */
+ static final class Node<K,V> {
+ final K key;
+ volatile Object value;
+ volatile Node<K,V> next;
+
+ /**
+ * Creates a new regular node.
+ */
+ Node(K key, Object value, Node<K,V> next) {
+ this.key = key;
+ this.value = value;
+ this.next = next;
+ }
+
+ /**
+ * Creates a new marker node. A marker is distinguished by
+ * having its value field point to itself. Marker nodes also
+ * have null keys, a fact that is exploited in a few places,
+ * but this doesn't distinguish markers from the base-level
+ * header node (head.node), which also has a null key.
+ */
+ Node(Node<K,V> next) {
+ this.key = null;
+ this.value = this;
+ this.next = next;
+ }
+
+ /** Updater for casNext */
+ static final AtomicReferenceFieldUpdater<Node, Node>
+ nextUpdater = AtomicReferenceFieldUpdater.newUpdater
+ (Node.class, Node.class, "next");
+
+ /** Updater for casValue */
+ static final AtomicReferenceFieldUpdater<Node, Object>
+ valueUpdater = AtomicReferenceFieldUpdater.newUpdater
+ (Node.class, Object.class, "value");
+
+ /**
+ * compareAndSet value field
+ */
+ boolean casValue(Object cmp, Object val) {
+ return valueUpdater.compareAndSet(this, cmp, val);
+ }
+
+ /**
+ * compareAndSet next field
+ */
+ boolean casNext(Node<K,V> cmp, Node<K,V> val) {
+ return nextUpdater.compareAndSet(this, cmp, val);
+ }
+
+ /**
+ * Return true if this node is a marker. This method isn't
+ * actually called in an any current code checking for markers
+ * because callers will have already read value field and need
+ * to use that read (not another done here) and so directly
+ * test if value points to node.
+ * @param n a possibly null reference to a node
+ * @return true if this node is a marker node
+ */
+ boolean isMarker() {
+ return value == this;
+ }
+
+ /**
+ * Return true if this node is the header of base-level list.
+ * @return true if this node is header node
+ */
+ boolean isBaseHeader() {
+ return value == BASE_HEADER;
+ }
+
+ /**
+ * Tries to append a deletion marker to this node.
+ * @param f the assumed current successor of this node
+ * @return true if successful
+ */
+ boolean appendMarker(Node<K,V> f) {
+ return casNext(f, new Node<K,V>(f));
+ }
+
+ /**
+ * Helps out a deletion by appending marker or unlinking from
+ * predecessor. This is called during traversals when value
+ * field seen to be null.
+ * @param b predecessor
+ * @param f successor
+ */
+ void helpDelete(Node<K,V> b, Node<K,V> f) {
+ /*
+ * Rechecking links and then doing only one of the
+ * help-out stages per call tends to minimize CAS
+ * interference among helping threads.
+ */
+ if (f == next && this == b.next) {
+ if (f == null || f.value != f) // not already marked
+ appendMarker(f);
+ else
+ b.casNext(this, f.next);
+ }
+ }
+
+ /**
+ * Return value if this node contains a valid key-value pair,
+ * else null.
+ * @return this node's value if it isn't a marker or header or
+ * is deleted, else null.
+ */
+ V getValidValue() {
+ Object v = value;
+ if (v == this || v == BASE_HEADER)
+ return null;
+ return (V)v;
+ }
+
+ /**
+ * Create and return a new SnapshotEntry holding current
+ * mapping if this node holds a valid value, else null
+ * @return new entry or null
+ */
+ SnapshotEntry<K,V> createSnapshot() {
+ V v = getValidValue();
+ if (v == null)
+ return null;
+ return new SnapshotEntry(key, v);
+ }
+ }
+
+ /* ---------------- Indexing -------------- */
+
+ /**
+ * Index nodes represent the levels of the skip list. To improve
+ * search performance, keys of the underlying nodes are cached.
+ * Note that even though both Nodes and Indexes have
+ * forward-pointing fields, they have different types and are
+ * handled in different ways, that can't nicely be captured by
+ * placing field in a shared abstract class.
+ */
+ static class Index<K,V> {
+ final K key;
+ final Node<K,V> node;
+ final Index<K,V> down;
+ volatile Index<K,V> right;
+
+ /**
+ * Creates index node with given values
+ */
+ Index(Node<K,V> node, Index<K,V> down, Index<K,V> right) {
+ this.node = node;
+ this.key = node.key;
+ this.down = down;
+ this.right = right;
+ }
+
+ /** Updater for casRight */
+ static final AtomicReferenceFieldUpdater<Index, Index>
+ rightUpdater = AtomicReferenceFieldUpdater.newUpdater
+ (Index.class, Index.class, "right");
+
+ /**
+ * compareAndSet right field
+ */
+ final boolean casRight(Index<K,V> cmp, Index<K,V> val) {
+ return rightUpdater.compareAndSet(this, cmp, val);
+ }
+
+ /**
+ * Returns true if the node this indexes has been deleted.
+ * @return true if indexed node is known to be deleted
+ */
+ final boolean indexesDeletedNode() {
+ return node.value == null;
+ }
+
+ /**
+ * Tries to CAS newSucc as successor. To minimize races with
+ * unlink that may lose this index node, if the node being
+ * indexed is known to be deleted, it doesn't try to link in.
+ * @param succ the expected current successor
+ * @param newSucc the new successor
+ * @return true if successful
+ */
+ final boolean link(Index<K,V> succ, Index<K,V> newSucc) {
+ Node<K,V> n = node;
+ newSucc.right = succ;
+ return n.value != null && casRight(succ, newSucc);
+ }
+
+ /**
+ * Tries to CAS right field to skip over apparent successor
+ * succ. Fails (forcing a retraversal by caller) if this node
+ * is known to be deleted.
+ * @param succ the expected current successor
+ * @return true if successful
+ */
+ final boolean unlink(Index<K,V> succ) {
+ return !indexesDeletedNode() && casRight(succ, succ.right);
+ }
+ }
+
+ /* ---------------- Head nodes -------------- */
+
+ /**
+ * Nodes heading each level keep track of their level.
+ */
+ static final class HeadIndex<K,V> extends Index<K,V> {
+ final int level;
+ HeadIndex(Node<K,V> node, Index<K,V> down, Index<K,V> right, int level) {
+ super(node, down, right);
+ this.level = level;
+ }
+ }
+
+ /* ---------------- Map.Entry support -------------- */
+
+ /**
+ * An immutable representation of a key-value mapping as it
+ * existed at some point in time. This class does <em>not</em>
+ * support the <tt>Map.Entry.setValue</tt> method.
+ */
+ static class SnapshotEntry<K,V> implements Map.Entry<K,V> {
+ private final K key;
+ private final V value;
+
+ /**
+ * Creates a new entry representing the given key and value.
+ * @param key the key
+ * @param value the value
+ */
+ SnapshotEntry(K key, V value) {
+ this.key = key;
+ this.value = value;
+ }
+
+ /**
+ * Returns the key corresponding to this entry.
+ *
+ * @return the key corresponding to this entry.
+ */
+ public K getKey() {
+ return key;
+ }
+
+ /**
+ * Returns the value corresponding to this entry.
+ *
+ * @return the value corresponding to this entry.
+ */
+ public V getValue() {
+ return value;
+ }
+
+ /**
+ * Always fails, throwing <tt>UnsupportedOperationException</tt>.
+ * @throws UnsupportedOperationException always.
+ */
+ public V setValue(V value) {
+ throw new UnsupportedOperationException();
+ }
+
+ // inherit javadoc
+ public boolean equals(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry e = (Map.Entry)o;
+ // As mandated by Map.Entry spec:
+ return ((key==null ?
+ e.getKey()==null : key.equals(e.getKey())) &&
+ (value==null ?
+ e.getValue()==null : value.equals(e.getValue())));
+ }
+
+
+ // inherit javadoc
+ public int hashCode() {
+ // As mandated by Map.Entry spec:
+ return ((key==null ? 0 : key.hashCode()) ^
+ (value==null ? 0 : value.hashCode()));
+ }
+
+ /**
+ * Returns a String consisting of the key followed by an
+ * equals sign (<tt>"="</tt>) followed by the associated
+ * value.
+ * @return a String representation of this entry.
+ */
+ public String toString() {
+ return getKey() + "=" + getValue();
+ }
+ }
+
+ /* ---------------- Comparison utilities -------------- */
+
+ /**
+ * Represents a key with a comparator as a Comparable.
+ *
+ * Because most sorted collections seem to use natural order on
+ * Comparables (Strings, Integers, etc), most internal methods are
+ * geared to use them. This is generally faster than checking
+ * per-comparison whether to use comparator or comparable because
+ * it doesn't require a (Comparable) cast for each comparison.
+ * (Optimizers can only sometimes remove such redundant checks
+ * themselves.) When Comparators are used,
+ * ComparableUsingComparators are created so that they act in the
+ * same way as natural orderings. This penalizes use of
+ * Comparators vs Comparables, which seems like the right
+ * tradeoff.
+ */
+ static final class ComparableUsingComparator<K> implements Comparable<K> {
+ final K actualKey;
+ final Comparator<? super K> cmp;
+ ComparableUsingComparator(K key, Comparator<? super K> cmp) {
+ this.actualKey = key;
+ this.cmp = cmp;
+ }
+ public int compareTo(K k2) {
+ return cmp.compare(actualKey, k2);
+ }
+ }
+
+ /**
+ * If using comparator, return a ComparableUsingComparator, else
+ * cast key as Comparator, which may cause ClassCastException,
+ * which is propagated back to caller.
+ */
+ private Comparable<K> comparable(Object key) throws ClassCastException {
+ if (key == null)
+ throw new NullPointerException();
+ return (comparator != null)
+ ? new ComparableUsingComparator(key, comparator)
+ : (Comparable<K>)key;
+ }
+
+ /**
+ * Compare using comparator or natural ordering. Used when the
+ * ComparableUsingComparator approach doesn't apply.
+ */
+ int compare(K k1, K k2) throws ClassCastException {
+ Comparator<? super K> cmp = comparator;
+ if (cmp != null)
+ return cmp.compare(k1, k2);
+ else
+ return ((Comparable<K>)k1).compareTo(k2);
+ }
+
+ /**
+ * Return true if given key greater than or equal to least and
+ * strictly less than fence, bypassing either test if least or
+ * fence oare null. Needed mainly in submap operations.
+ */
+ boolean inHalfOpenRange(K key, K least, K fence) {
+ if (key == null)
+ throw new NullPointerException();
+ return ((least == null || compare(key, least) >= 0) &&
+ (fence == null || compare(key, fence) < 0));
+ }
+
+ /**
+ * Return true if given key greater than or equal to least and less
+ * or equal to fence. Needed mainly in submap operations.
+ */
+ boolean inOpenRange(K key, K least, K fence) {
+ if (key == null)
+ throw new NullPointerException();
+ return ((least == null || compare(key, least) >= 0) &&
+ (fence == null || compare(key, fence) <= 0));
+ }
+
+ /* ---------------- Traversal -------------- */
+
+ /**
+ * Return a base-level node with key strictly less than given key,
+ * or the base-level header if there is no such node. Also
+ * unlinks indexes to deleted nodes found along the way. Callers
+ * rely on this side-effect of clearing indices to deleted nodes.
+ * @param key the key
+ * @return a predecessor of key
+ */
+ private Node<K,V> findPredecessor(Comparable<K> key) {
+ for (;;) {
+ Index<K,V> q = head;
+ for (;;) {
+ Index<K,V> d, r;
+ if ((r = q.right) != null) {
+ if (r.indexesDeletedNode()) {
+ if (q.unlink(r))
+ continue; // reread r
+ else
+ break; // restart
+ }
+ if (key.compareTo(r.key) > 0) {
+ q = r;
+ continue;
+ }
+ }
+ if ((d = q.down) != null)
+ q = d;
+ else
+ return q.node;
+ }
+ }
+ }
+
+ /**
+ * Return node holding key or null if no such, clearing out any
+ * deleted nodes seen along the way. Repeatedly traverses at
+ * base-level looking for key starting at predecessor returned
+ * from findPredecessor, processing base-level deletions as
+ * encountered. Some callers rely on this side-effect of clearing
+ * deleted nodes.
+ *
+ * Restarts occur, at traversal step centered on node n, if:
+ *
+ * (1) After reading n's next field, n is no longer assumed
+ * predecessor b's current successor, which means that
+ * we don't have a consistent 3-node snapshot and so cannot
+ * unlink any subsequent deleted nodes encountered.
+ *
+ * (2) n's value field is null, indicating n is deleted, in
+ * which case we help out an ongoing structural deletion
+ * before retrying. Even though there are cases where such
+ * unlinking doesn't require restart, they aren't sorted out
+ * here because doing so would not usually outweigh cost of
+ * restarting.
+ *
+ * (3) n is a marker or n's predecessor's value field is null,
+ * indicating (among other possibilities) that
+ * findPredecessor returned a deleted node. We can't unlink
+ * the node because we don't know its predecessor, so rely
+ * on another call to findPredecessor to notice and return
+ * some earlier predecessor, which it will do. This check is
+ * only strictly needed at beginning of loop, (and the
+ * b.value check isn't strictly needed at all) but is done
+ * each iteration to help avoid contention with other
+ * threads by callers that will fail to be able to change
+ * links, and so will retry anyway.
+ *
+ * The traversal loops in doPut, doRemove, and findNear all
+ * include the same three kinds of checks. And specialized
+ * versions appear in doRemoveFirst, doRemoveLast, findFirst, and
+ * findLast. They can't easily share code because each uses the
+ * reads of fields held in locals occurring in the orders they
+ * were performed.
+ *
+ * @param key the key
+ * @return node holding key, or null if no such.
+ */
+ private Node<K,V> findNode(Comparable<K> key) {
+ for (;;) {
+ Node<K,V> b = findPredecessor(key);
+ Node<K,V> n = b.next;
+ for (;;) {
+ if (n == null)
+ return null;
+ Node<K,V> f = n.next;
+ if (n != b.next) // inconsistent read
+ break;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ int c = key.compareTo(n.key);
+ if (c < 0)
+ return null;
+ if (c == 0)
+ return n;
+ b = n;
+ n = f;
+ }
+ }
+ }
+
+ /**
+ * Specialized variant of findNode to perform Map.get. Does a weak
+ * traversal, not bothering to fix any deleted index nodes,
+ * returning early if it happens to see key in index, and passing
+ * over any deleted base nodes, falling back to getUsingFindNode
+ * only if it would otherwise return value from an ongoing
+ * deletion. Also uses "bound" to eliminate need for some
+ * comparisons (see Pugh Cookbook). Also folds uses of null checks
+ * and node-skipping because markers have null keys.
+ * @param okey the key
+ * @return the value, or null if absent
+ */
+ private V doGet(Object okey) {
+ Comparable<K> key = comparable(okey);
+ K bound = null;
+ Index<K,V> q = head;
+ for (;;) {
+ K rk;
+ Index<K,V> d, r;
+ if ((r = q.right) != null &&
+ (rk = r.key) != null && rk != bound) {
+ int c = key.compareTo(rk);
+ if (c > 0) {
+ q = r;
+ continue;
+ }
+ if (c == 0) {
+ Object v = r.node.value;
+ return (v != null)? (V)v : getUsingFindNode(key);
+ }
+ bound = rk;
+ }
+ if ((d = q.down) != null)
+ q = d;
+ else {
+ for (Node<K,V> n = q.node.next; n != null; n = n.next) {
+ K nk = n.key;
+ if (nk != null) {
+ int c = key.compareTo(nk);
+ if (c == 0) {
+ Object v = n.value;
+ return (v != null)? (V)v : getUsingFindNode(key);
+ }
+ if (c < 0)
+ return null;
+ }
+ }
+ return null;
+ }
+ }
+ }
+
+ /**
+ * Perform map.get via findNode. Used as a backup if doGet
+ * encounters an in-progress deletion.
+ * @param key the key
+ * @return the value, or null if absent
+ */
+ private V getUsingFindNode(Comparable<K> key) {
+ /*
+ * Loop needed here and elsewhere in case value field goes
+ * null just as it is about to be returned, in which case we
+ * lost a race with a deletion, so must retry.
+ */
+ for (;;) {
+ Node<K,V> n = findNode(key);
+ if (n == null)
+ return null;
+ Object v = n.value;
+ if (v != null)
+ return (V)v;
+ }
+ }
+
+ /* ---------------- Insertion -------------- */
+
+ /**
+ * Main insertion method. Adds element if not present, or
+ * replaces value if present and onlyIfAbsent is false.
+ * @param kkey the key
+ * @param value the value that must be associated with key
+ * @param onlyIfAbsent if should not insert if already present
+ * @return the old value, or null if newly inserted
+ */
+ private V doPut(K kkey, V value, boolean onlyIfAbsent) {
+ Comparable<K> key = comparable(kkey);
+ for (;;) {
+ Node<K,V> b = findPredecessor(key);
+ Node<K,V> n = b.next;
+ for (;;) {
+ if (n != null) {
+ Node<K,V> f = n.next;
+ if (n != b.next) // inconsistent read
+ break;;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ int c = key.compareTo(n.key);
+ if (c > 0) {
+ b = n;
+ n = f;
+ continue;
+ }
+ if (c == 0) {
+ if (onlyIfAbsent || n.casValue(v, value))
+ return (V)v;
+ else
+ break; // restart if lost race to replace value
+ }
+ // else c < 0; fall through
+ }
+
+ Node<K,V> z = new Node<K,V>(kkey, value, n);
+ if (!b.casNext(n, z))
+ break; // restart if lost race to append to b
+ int level = randomLevel();
+ if (level > 0)
+ insertIndex(z, level);
+ return null;
+ }
+ }
+ }
+
+ /**
+ * Return a random level for inserting a new node.
+ * Hardwired to k=1, p=0.5, max 31.
+ *
+ * This uses a cheap pseudo-random function that according to
+ * http://home1.gte.net/deleyd/random/random4.html was used in
+ * Turbo Pascal. It seems the fastest usable one here. The low
+ * bits are apparently not very random (the original used only
+ * upper 16 bits) so we traverse from highest bit down (i.e., test
+ * sign), thus hardly ever use lower bits.
+ */
+ private int randomLevel() {
+ int level = 0;
+ int r = randomSeed;
+ randomSeed = r * 134775813 + 1;
+ if (r < 0) {
+ while ((r <<= 1) > 0)
+ ++level;
+ }
+ return level;
+ }
+
+ /**
+ * Create and add index nodes for given node.
+ * @param z the node
+ * @param level the level of the index
+ */
+ private void insertIndex(Node<K,V> z, int level) {
+ HeadIndex<K,V> h = head;
+ int max = h.level;
+
+ if (level <= max) {
+ Index<K,V> idx = null;
+ for (int i = 1; i <= level; ++i)
+ idx = new Index<K,V>(z, idx, null);
+ addIndex(idx, h, level);
+
+ } else { // Add a new level
+ /*
+ * To reduce interference by other threads checking for
+ * empty levels in tryReduceLevel, new levels are added
+ * with initialized right pointers. Which in turn requires
+ * keeping levels in an array to access them while
+ * creating new head index nodes from the opposite
+ * direction.
+ */
+ level = max + 1;
+ Index<K,V>[] idxs = (Index<K,V>[])new Index[level+1];
+ Index<K,V> idx = null;
+ for (int i = 1; i <= level; ++i)
+ idxs[i] = idx = new Index<K,V>(z, idx, null);
+
+ HeadIndex<K,V> oldh;
+ int k;
+ for (;;) {
+ oldh = head;
+ int oldLevel = oldh.level;
+ if (level <= oldLevel) { // lost race to add level
+ k = level;
+ break;
+ }
+ HeadIndex<K,V> newh = oldh;
+ Node<K,V> oldbase = oldh.node;
+ for (int j = oldLevel+1; j <= level; ++j)
+ newh = new HeadIndex<K,V>(oldbase, newh, idxs[j], j);
+ if (casHead(oldh, newh)) {
+ k = oldLevel;
+ break;
+ }
+ }
+ addIndex(idxs[k], oldh, k);
+ }
+ }
+
+ /**
+ * Add given index nodes from given level down to 1.
+ * @param idx the topmost index node being inserted
+ * @param h the value of head to use to insert. This must be
+ * snapshotted by callers to provide correct insertion level
+ * @param indexLevel the level of the index
+ */
+ private void addIndex(Index<K,V> idx, HeadIndex<K,V> h, int indexLevel) {
+ // Track next level to insert in case of retries
+ int insertionLevel = indexLevel;
+ Comparable<K> key = comparable(idx.key);
+
+ // Similar to findPredecessor, but adding index nodes along
+ // path to key.
+ for (;;) {
+ Index<K,V> q = h;
+ Index<K,V> t = idx;
+ int j = h.level;
+ for (;;) {
+ Index<K,V> r = q.right;
+ if (r != null) {
+ // compare before deletion check avoids needing recheck
+ int c = key.compareTo(r.key);
+ if (r.indexesDeletedNode()) {
+ if (q.unlink(r))
+ continue;
+ else
+ break;
+ }
+ if (c > 0) {
+ q = r;
+ continue;
+ }
+ }
+
+ if (j == insertionLevel) {
+ // Don't insert index if node already deleted
+ if (t.indexesDeletedNode()) {
+ findNode(key); // cleans up
+ return;
+ }
+ if (!q.link(r, t))
+ break; // restart
+ if (--insertionLevel == 0) {
+ // need final deletion check before return
+ if (t.indexesDeletedNode())
+ findNode(key);
+ return;
+ }
+ }
+
+ if (j > insertionLevel && j <= indexLevel)
+ t = t.down;
+ q = q.down;
+ --j;
+ }
+ }
+ }
+
+ /* ---------------- Deletion -------------- */
+
+ /**
+ * Main deletion method. Locates node, nulls value, appends a
+ * deletion marker, unlinks predecessor, removes associated index
+ * nodes, and possibly reduces head index level.
+ *
+ * Index nodes are cleared out simply by calling findPredecessor.
+ * which unlinks indexes to deleted nodes found along path to key,
+ * which will include the indexes to this node. This is done
+ * unconditionally. We can't check beforehand whether there are
+ * index nodes because it might be the case that some or all
+ * indexes hadn't been inserted yet for this node during initial
+ * search for it, and we'd like to ensure lack of garbage
+ * retention, so must call to be sure.
+ *
+ * @param okey the key
+ * @param value if non-null, the value that must be
+ * associated with key
+ * @return the node, or null if not found
+ */
+ private V doRemove(Object okey, Object value) {
+ Comparable<K> key = comparable(okey);
+ for (;;) {
+ Node<K,V> b = findPredecessor(key);
+ Node<K,V> n = b.next;
+ for (;;) {
+ if (n == null)
+ return null;
+ Node<K,V> f = n.next;
+ if (n != b.next) // inconsistent read
+ break;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ int c = key.compareTo(n.key);
+ if (c < 0)
+ return null;
+ if (c > 0) {
+ b = n;
+ n = f;
+ continue;
+ }
+ if (value != null && !value.equals(v))
+ return null;
+ if (!n.casValue(v, null))
+ break;
+ if (!n.appendMarker(f) || !b.casNext(n, f))
+ findNode(key); // Retry via findNode
+ else {
+ findPredecessor(key); // Clean index
+ if (head.right == null)
+ tryReduceLevel();
+ }
+ return (V)v;
+ }
+ }
+ }
+
+ /**
+ * Possibly reduce head level if it has no nodes. This method can
+ * (rarely) make mistakes, in which case levels can disappear even
+ * though they are about to contain index nodes. This impacts
+ * performance, not correctness. To minimize mistakes as well as
+ * to reduce hysteresis, the level is reduced by one only if the
+ * topmost three levels look empty. Also, if the removed level
+ * looks non-empty after CAS, we try to change it back quick
+ * before anyone notices our mistake! (This trick works pretty
+ * well because this method will practically never make mistakes
+ * unless current thread stalls immediately before first CAS, in
+ * which case it is very unlikely to stall again immediately
+ * afterwards, so will recover.)
+ *
+ * We put up with all this rather than just let levels grow
+ * because otherwise, even a small map that has undergone a large
+ * number of insertions and removals will have a lot of levels,
+ * slowing down access more than would an occasional unwanted
+ * reduction.
+ */
+ private void tryReduceLevel() {
+ HeadIndex<K,V> h = head;
+ HeadIndex<K,V> d;
+ HeadIndex<K,V> e;
+ if (h.level > 3 &&
+ (d = (HeadIndex<K,V>)h.down) != null &&
+ (e = (HeadIndex<K,V>)d.down) != null &&
+ e.right == null &&
+ d.right == null &&
+ h.right == null &&
+ casHead(h, d) && // try to set
+ h.right != null) // recheck
+ casHead(d, h); // try to backout
+ }
+
+ /**
+ * Version of remove with boolean return. Needed by view classes
+ */
+ boolean removep(Object key) {
+ return doRemove(key, null) != null;
+ }
+
+ /* ---------------- Finding and removing first element -------------- */
+
+ /**
+ * Specialized variant of findNode to get first valid node
+ * @return first node or null if empty
+ */
+ Node<K,V> findFirst() {
+ for (;;) {
+ Node<K,V> b = head.node;
+ Node<K,V> n = b.next;
+ if (n == null)
+ return null;
+ if (n.value != null)
+ return n;
+ n.helpDelete(b, n.next);
+ }
+ }
+
+ /**
+ * Remove first entry; return either its key or a snapshot.
+ * @param keyOnly if true return key, else return SnapshotEntry
+ * (This is a little ugly, but avoids code duplication.)
+ * @return null if empty, first key if keyOnly true, else key,value entry
+ */
+ Object doRemoveFirst(boolean keyOnly) {
+ for (;;) {
+ Node<K,V> b = head.node;
+ Node<K,V> n = b.next;
+ if (n == null)
+ return null;
+ Node<K,V> f = n.next;
+ if (n != b.next)
+ continue;
+ Object v = n.value;
+ if (v == null) {
+ n.helpDelete(b, f);
+ continue;
+ }
+ if (!n.casValue(v, null))
+ continue;
+ if (!n.appendMarker(f) || !b.casNext(n, f))
+ findFirst(); // retry
+ clearIndexToFirst();
+ K key = n.key;
+ return (keyOnly)? key : new SnapshotEntry<K,V>(key, (V)v);
+ }
+ }
+
+ /**
+ * Clear out index nodes associated with deleted first entry.
+ * Needed by doRemoveFirst
+ */
+ private void clearIndexToFirst() {
+ for (;;) {
+ Index<K,V> q = head;
+ for (;;) {
+ Index<K,V> r = q.right;
+ if (r != null && r.indexesDeletedNode() && !q.unlink(r))
+ break;
+ if ((q = q.down) == null) {
+ if (head.right == null)
+ tryReduceLevel();
+ return;
+ }
+ }
+ }
+ }
+
+ /**
+ * Remove first entry; return key or null if empty.
+ */
+ K pollFirstKey() {
+ return (K)doRemoveFirst(true);
+ }
+
+ /* ---------------- Finding and removing last element -------------- */
+
+ /**
+ * Specialized version of find to get last valid node
+ * @return last node or null if empty
+ */
+ Node<K,V> findLast() {
+ /*
+ * findPredecessor can't be used to traverse index level
+ * because this doesn't use comparisons. So traversals of
+ * both levels are folded together.
+ */
+ Index<K,V> q = head;
+ for (;;) {
+ Index<K,V> d, r;
+ if ((r = q.right) != null) {
+ if (r.indexesDeletedNode()) {
+ q.unlink(r);
+ q = head; // restart
+ }
+ else
+ q = r;
+ } else if ((d = q.down) != null) {
+ q = d;
+ } else {
+ Node<K,V> b = q.node;
+ Node<K,V> n = b.next;
+ for (;;) {
+ if (n == null)
+ return (b.isBaseHeader())? null : b;
+ Node<K,V> f = n.next; // inconsistent read
+ if (n != b.next)
+ break;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ b = n;
+ n = f;
+ }
+ q = head; // restart
+ }
+ }
+ }
+
+
+ /**
+ * Specialized version of doRemove for last entry.
+ * @param keyOnly if true return key, else return SnapshotEntry
+ * @return null if empty, last key if keyOnly true, else key,value entry
+ */
+ Object doRemoveLast(boolean keyOnly) {
+ for (;;) {
+ Node<K,V> b = findPredecessorOfLast();
+ Node<K,V> n = b.next;
+ if (n == null) {
+ if (b.isBaseHeader()) // empty
+ return null;
+ else
+ continue; // all b's successors are deleted; retry
+ }
+ for (;;) {
+ Node<K,V> f = n.next;
+ if (n != b.next) // inconsistent read
+ break;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ if (f != null) {
+ b = n;
+ n = f;
+ continue;
+ }
+ if (!n.casValue(v, null))
+ break;
+ K key = n.key;
+ Comparable<K> ck = comparable(key);
+ if (!n.appendMarker(f) || !b.casNext(n, f))
+ findNode(ck); // Retry via findNode
+ else {
+ findPredecessor(ck); // Clean index
+ if (head.right == null)
+ tryReduceLevel();
+ }
+ return (keyOnly)? key : new SnapshotEntry<K,V>(key, (V)v);
+ }
+ }
+ }
+
+ /**
+ * Specialized variant of findPredecessor to get predecessor of
+ * last valid node. Needed by doRemoveLast. It is possible that
+ * all successors of returned node will have been deleted upon
+ * return, in which case this method can be retried.
+ * @return likely predecessor of last node.
+ */
+ private Node<K,V> findPredecessorOfLast() {
+ for (;;) {
+ Index<K,V> q = head;
+ for (;;) {
+ Index<K,V> d, r;
+ if ((r = q.right) != null) {
+ if (r.indexesDeletedNode()) {
+ q.unlink(r);
+ break; // must restart
+ }
+ // proceed as far across as possible without overshooting
+ if (r.node.next != null) {
+ q = r;
+ continue;
+ }
+ }
+ if ((d = q.down) != null)
+ q = d;
+ else
+ return q.node;
+ }
+ }
+ }
+
+ /**
+ * Remove last entry; return key or null if empty.
+ */
+ K pollLastKey() {
+ return (K)doRemoveLast(true);
+ }
+
+ /* ---------------- Relational operations -------------- */
+
+ // Control values OR'ed as arguments to findNear
+
+ private static final int EQ = 1;
+ private static final int LT = 2;
+ private static final int GT = 0; // Actually checked as !LT
+
+ /**
+ * Utility for ceiling, floor, lower, higher methods.
+ * @param kkey the key
+ * @param rel the relation -- OR'ed combination of EQ, LT, GT
+ * @return nearest node fitting relation, or null if no such
+ */
+ Node<K,V> findNear(K kkey, int rel) {
+ Comparable<K> key = comparable(kkey);
+ for (;;) {
+ Node<K,V> b = findPredecessor(key);
+ Node<K,V> n = b.next;
+ for (;;) {
+ if (n == null)
+ return ((rel & LT) == 0 || b.isBaseHeader())? null : b;
+ Node<K,V> f = n.next;
+ if (n != b.next) // inconsistent read
+ break;
+ Object v = n.value;
+ if (v == null) { // n is deleted
+ n.helpDelete(b, f);
+ break;
+ }
+ if (v == n || b.value == null) // b is deleted
+ break;
+ int c = key.compareTo(n.key);
+ if ((c == 0 && (rel & EQ) != 0) ||
+ (c < 0 && (rel & LT) == 0))
+ return n;
+ if ( c <= 0 && (rel & LT) != 0)
+ return (b.isBaseHeader())? null : b;
+ b = n;
+ n = f;
+ }
+ }
+ }
+
+ /**
+ * Return SnapshotEntry for results of findNear.
+ * @param kkey the key
+ * @param rel the relation -- OR'ed combination of EQ, LT, GT
+ * @return Entry fitting relation, or null if no such
+ */
+ SnapshotEntry<K,V> getNear(K kkey, int rel) {
+ for (;;) {
+ Node<K,V> n = findNear(kkey, rel);
+ if (n == null)
+ return null;
+ SnapshotEntry<K,V> e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ /**
+ * Return ceiling, or first node if key is <tt>null</tt>
+ */
+ Node<K,V> findCeiling(K key) {
+ return (key == null)? findFirst() : findNear(key, GT|EQ);
+ }
+
+ /**
+ * Return lower node, or last node if key is <tt>null</tt>
+ */
+ Node<K,V> findLower(K key) {
+ return (key == null)? findLast() : findNear(key, LT);
+ }
+
+ /**
+ * Return SnapshotEntry or key for results of findNear ofter screening
+ * to ensure result is in given range. Needed by submaps.
+ * @param kkey the key
+ * @param rel the relation -- OR'ed combination of EQ, LT, GT
+ * @param least minimum allowed key value
+ * @param fence key greater than maximum allowed key value
+ * @param keyOnly if true return key, else return SnapshotEntry
+ * @return Key or Entry fitting relation, or <tt>null</tt> if no such
+ */
+ Object getNear(K kkey, int rel, K least, K fence, boolean keyOnly) {
+ K key = kkey;
+ // Don't return keys less than least
+ if ((rel & LT) == 0) {
+ if (compare(key, least) < 0) {
+ key = least;
+ rel = rel | EQ;
+ }
+ }
+
+ for (;;) {
+ Node<K,V> n = findNear(key, rel);
+ if (n == null || !inHalfOpenRange(n.key, least, fence))
+ return null;
+ K k = n.key;
+ V v = n.getValidValue();
+ if (v != null)
+ return keyOnly? k : new SnapshotEntry<K,V>(k, v);
+ }
+ }
+
+ /**
+ * Find and remove least element of subrange.
+ * @param least minimum allowed key value
+ * @param fence key greater than maximum allowed key value
+ * @param keyOnly if true return key, else return SnapshotEntry
+ * @return least Key or Entry, or <tt>null</tt> if no such
+ */
+ Object removeFirstEntryOfSubrange(K least, K fence, boolean keyOnly) {
+ for (;;) {
+ Node<K,V> n = findCeiling(least);
+ if (n == null)
+ return null;
+ K k = n.key;
+ if (fence != null && compare(k, fence) >= 0)
+ return null;
+ V v = doRemove(k, null);
+ if (v != null)
+ return (keyOnly)? k : new SnapshotEntry<K,V>(k, v);
+ }
+ }
+
+ /**
+ * Find and remove greatest element of subrange.
+ * @param least minimum allowed key value
+ * @param fence key greater than maximum allowed key value
+ * @param keyOnly if true return key, else return SnapshotEntry
+ * @return least Key or Entry, or <tt>null</tt> if no such
+ */
+ Object removeLastEntryOfSubrange(K least, K fence, boolean keyOnly) {
+ for (;;) {
+ Node<K,V> n = findLower(fence);
+ if (n == null)
+ return null;
+ K k = n.key;
+ if (least != null && compare(k, least) < 0)
+ return null;
+ V v = doRemove(k, null);
+ if (v != null)
+ return (keyOnly)? k : new SnapshotEntry<K,V>(k, v);
+ }
+ }
+
+ /* ---------------- Constructors -------------- */
+
+ /**
+ * Constructs a new empty map, sorted according to the keys' natural
+ * order.
+ */
+ public ConcurrentSkipListMap() {
+ this.comparator = null;
+ initialize();
+ }
+
+ /**
+ * Constructs a new empty map, sorted according to the given comparator.
+ *
+ * @param c the comparator that will be used to sort this map. A
+ * <tt>null</tt> value indicates that the keys' <i>natural
+ * ordering</i> should be used.
+ */
+ public ConcurrentSkipListMap(Comparator<? super K> c) {
+ this.comparator = c;
+ initialize();
+ }
+
+ /**
+ * Constructs a new map containing the same mappings as the given map,
+ * sorted according to the keys' <i>natural order</i>.
+ *
+ * @param m the map whose mappings are to be placed in this map.
+ * @throws ClassCastException if the keys in m are not Comparable, or
+ * are not mutually comparable.
+ * @throws NullPointerException if the specified map is <tt>null</tt>.
+ */
+ public ConcurrentSkipListMap(Map<? extends K, ? extends V> m) {
+ this.comparator = null;
+ initialize();
+ putAll(m);
+ }
+
+ /**
+ * Constructs a new map containing the same mappings as the given
+ * <tt>SortedMap</tt>, sorted according to the same ordering.
+ * @param m the sorted map whose mappings are to be placed in this
+ * map, and whose comparator is to be used to sort this map.
+ * @throws NullPointerException if the specified sorted map is
+ * <tt>null</tt>.
+ */
+ public ConcurrentSkipListMap(SortedMap<K, ? extends V> m) {
+ this.comparator = m.comparator();
+ initialize();
+ buildFromSorted(m);
+ }
+
+ /**
+ * Returns a shallow copy of this <tt>Map</tt> instance. (The keys and
+ * values themselves are not cloned.)
+ *
+ * @return a shallow copy of this Map.
+ */
+ public Object clone() {
+ ConcurrentSkipListMap<K,V> clone = null;
+ try {
+ clone = (ConcurrentSkipListMap<K,V>) super.clone();
+ } catch (CloneNotSupportedException e) {
+ throw new InternalError();
+ }
+
+ clone.initialize();
+ clone.buildFromSorted(this);
+ return clone;
+ }
+
+ /**
+ * Streamlined bulk insertion to initialize from elements of
+ * given sorted map. Call only from constructor or clone
+ * method.
+ */
+ private void buildFromSorted(SortedMap<K, ? extends V> map) {
+ if (map == null)
+ throw new NullPointerException();
+
+ HeadIndex<K,V> h = head;
+ Node<K,V> basepred = h.node;
+
+ // Track the current rightmost node at each level. Uses an
+ // ArrayList to avoid committing to initial or maximum level.
+ ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
+
+ // initialize
+ for (int i = 0; i <= h.level; ++i)
+ preds.add(null);
+ Index<K,V> q = h;
+ for (int i = h.level; i > 0; --i) {
+ preds.set(i, q);
+ q = q.down;
+ }
+
+ Iterator<? extends Map.Entry<? extends K, ? extends V>> it =
+ map.entrySet().iterator();
+ while (it.hasNext()) {
+ Map.Entry<? extends K, ? extends V> e = it.next();
+ int j = randomLevel();
+ if (j > h.level) j = h.level + 1;
+ K k = e.getKey();
+ V v = e.getValue();
+ if (k == null || v == null)
+ throw new NullPointerException();
+ Node<K,V> z = new Node<K,V>(k, v, null);
+ basepred.next = z;
+ basepred = z;
+ if (j > 0) {
+ Index<K,V> idx = null;
+ for (int i = 1; i <= j; ++i) {
+ idx = new Index<K,V>(z, idx, null);
+ if (i > h.level)
+ h = new HeadIndex<K,V>(h.node, h, idx, i);
+
+ if (i < preds.size()) {
+ preds.get(i).right = idx;
+ preds.set(i, idx);
+ } else
+ preds.add(idx);
+ }
+ }
+ }
+ head = h;
+ }
+
+ /* ---------------- Serialization -------------- */
+
+ /**
+ * Save the state of the <tt>Map</tt> instance to a stream.
+ *
+ * @serialData The key (Object) and value (Object) for each
+ * key-value mapping represented by the Map, followed by
+ * <tt>null</tt>. The key-value mappings are emitted in key-order
+ * (as determined by the Comparator, or by the keys' natural
+ * ordering if no Comparator).
+ */
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ // Write out the Comparator and any hidden stuff
+ s.defaultWriteObject();
+
+ // Write out keys and values (alternating)
+ for (Node<K,V> n = findFirst(); n != null; n = n.next) {
+ V v = n.getValidValue();
+ if (v != null) {
+ s.writeObject(n.key);
+ s.writeObject(v);
+ }
+ }
+ s.writeObject(null);
+ }
+
+ /**
+ * Reconstitute the <tt>Map</tt> instance from a stream.
+ */
+ private void readObject(final java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ // Read in the Comparator and any hidden stuff
+ s.defaultReadObject();
+ // Reset transients
+ initialize();
+
+ /*
+ * This is nearly identical to buildFromSorted, but is
+ * distinct because readObject calls can't be nicely adapted
+ * as the kind of iterator needed by buildFromSorted. (They
+ * can be, but doing so requires type cheats and/or creation
+ * of adaptor classes.) It is simpler to just adapt the code.
+ */
+
+ HeadIndex<K,V> h = head;
+ Node<K,V> basepred = h.node;
+ ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
+ for (int i = 0; i <= h.level; ++i)
+ preds.add(null);
+ Index<K,V> q = h;
+ for (int i = h.level; i > 0; --i) {
+ preds.set(i, q);
+ q = q.down;
+ }
+
+ for (;;) {
+ Object k = s.readObject();
+ if (k == null)
+ break;
+ Object v = s.readObject();
+ if (v == null)
+ throw new NullPointerException();
+ K key = (K) k;
+ V val = (V) v;
+ int j = randomLevel();
+ if (j > h.level) j = h.level + 1;
+ Node<K,V> z = new Node<K,V>(key, val, null);
+ basepred.next = z;
+ basepred = z;
+ if (j > 0) {
+ Index<K,V> idx = null;
+ for (int i = 1; i <= j; ++i) {
+ idx = new Index<K,V>(z, idx, null);
+ if (i > h.level)
+ h = new HeadIndex<K,V>(h.node, h, idx, i);
+
+ if (i < preds.size()) {
+ preds.get(i).right = idx;
+ preds.set(i, idx);
+ } else
+ preds.add(idx);
+ }
+ }
+ }
+ head = h;
+ }
+
+ /* ------ Map API methods ------ */
+
+ /**
+ * Returns <tt>true</tt> if this map contains a mapping for the specified
+ * key.
+ * @param key key whose presence in this map is to be tested.
+ * @return <tt>true</tt> if this map contains a mapping for the
+ * specified key.
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key is <tt>null</tt>.
+ */
+ public boolean containsKey(Object key) {
+ return doGet(key) != null;
+ }
+
+ /**
+ * Returns the value to which this map maps the specified key. Returns
+ * <tt>null</tt> if the map contains no mapping for this key.
+ *
+ * @param key key whose associated value is to be returned.
+ * @return the value to which this map maps the specified key, or
+ * <tt>null</tt> if the map contains no mapping for the key.
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key is <tt>null</tt>.
+ */
+ public V get(Object key) {
+ return doGet(key);
+ }
+
+ /**
+ * Associates the specified value with the specified key in this map.
+ * If the map previously contained a mapping for this key, the old
+ * value is replaced.
+ *
+ * @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.
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key or value are <tt>null</tt>.
+ */
+ public V put(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ return doPut(key, value, false);
+ }
+
+ /**
+ * Removes the mapping for this key from this Map if present.
+ *
+ * @param key key for which mapping should be removed
+ * @return previous value associated with specified key, or <tt>null</tt>
+ * if there was no mapping for key.
+ *
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key is <tt>null</tt>.
+ */
+ public V remove(Object key) {
+ return doRemove(key, null);
+ }
+
+ /**
+ * Returns <tt>true</tt> if this map maps one or more keys to the
+ * specified value. This operation requires time linear in the
+ * Map size.
+ *
+ * @param value value whose presence in this Map is to be tested.
+ * @return <tt>true</tt> if a mapping to <tt>value</tt> exists;
+ * <tt>false</tt> otherwise.
+ * @throws NullPointerException if the value is <tt>null</tt>.
+ */
+ public boolean containsValue(Object value) {
+ if (value == null)
+ throw new NullPointerException();
+ for (Node<K,V> n = findFirst(); n != null; n = n.next) {
+ V v = n.getValidValue();
+ if (v != null && value.equals(v))
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Returns the number of elements in this map. If this map
+ * contains more than <tt>Integer.MAX_VALUE</tt> elements, it
+ * returns <tt>Integer.MAX_VALUE</tt>.
+ *
+ * <p>Beware that, unlike in most collections, this method is
+ * <em>NOT</em> a constant-time operation. Because of the
+ * asynchronous nature of these maps, 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 map.
+ */
+ public int size() {
+ long count = 0;
+ for (Node<K,V> n = findFirst(); n != null; n = n.next) {
+ if (n.getValidValue() != null)
+ ++count;
+ }
+ return (count >= Integer.MAX_VALUE)? Integer.MAX_VALUE : (int)count;
+ }
+
+ /**
+ * Returns <tt>true</tt> if this map contains no key-value mappings.
+ * @return <tt>true</tt> if this map contains no key-value mappings.
+ */
+ public boolean isEmpty() {
+ return findFirst() == null;
+ }
+
+ /**
+ * Removes all mappings from this map.
+ */
+ public void clear() {
+ initialize();
+ }
+
+ /**
+ * Returns a set view of the keys contained in this map. The set is
+ * backed by the map, so changes to the map are reflected in the set, and
+ * vice-versa. The set supports element removal, which removes the
+ * corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
+ * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
+ * <tt>clear</tt> operations. It does not support the <tt>add</tt> or
+ * <tt>addAll</tt> operations.
+ * The view's <tt>iterator</tt> is a "weakly consistent" iterator that
+ * will never throw {@link java.util.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 a set view of the keys contained in this map.
+ */
+ public Set<K> keySet() {
+ /*
+ * Note: Lazy intialization works here and for other views
+ * because view classes are stateless/immutable so it doesn't
+ * matter wrt correctness if more than one is created (which
+ * will only rarely happen). Even so, the following idiom
+ * conservatively ensures that the method returns the one it
+ * created if it does so, not one created by another racing
+ * thread.
+ */
+ KeySet ks = keySet;
+ return (ks != null) ? ks : (keySet = new KeySet());
+ }
+
+ /**
+ * Returns a set view of the keys contained in this map in
+ * descending order. The set is backed by the map, so changes to
+ * the map are reflected in the set, and vice-versa. The set
+ * supports element removal, which removes the corresponding
+ * mapping from this map, via the <tt>Iterator.remove</tt>,
+ * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>,
+ * and <tt>clear</tt> operations. It does not support the
+ * <tt>add</tt> or <tt>addAll</tt> operations. The view's
+ * <tt>iterator</tt> is a "weakly consistent" iterator that will
+ * never throw {@link java.util.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 a set view of the keys contained in this map.
+ */
+ public Set<K> descendingKeySet() {
+ /*
+ * Note: Lazy intialization works here and for other views
+ * because view classes are stateless/immutable so it doesn't
+ * matter wrt correctness if more than one is created (which
+ * will only rarely happen). Even so, the following idiom
+ * conservatively ensures that the method returns the one it
+ * created if it does so, not one created by another racing
+ * thread.
+ */
+ DescendingKeySet ks = descendingKeySet;
+ return (ks != null) ? ks : (descendingKeySet = new DescendingKeySet());
+ }
+
+ /**
+ * Returns a collection view of the values contained in this map.
+ * The collection is backed by the map, so changes to the map are
+ * reflected in the collection, and vice-versa. The collection
+ * supports element removal, which removes the corresponding
+ * mapping from this map, via the <tt>Iterator.remove</tt>,
+ * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
+ * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not
+ * support the <tt>add</tt> or <tt>addAll</tt> operations. The
+ * view's <tt>iterator</tt> is a "weakly consistent" iterator that
+ * will never throw {@link
+ * java.util.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 a collection view of the values contained in this map.
+ */
+ public Collection<V> values() {
+ Values vs = values;
+ return (vs != null) ? vs : (values = new Values());
+ }
+
+ /**
+ * Returns a collection view of the mappings contained in this
+ * map. Each element in the returned collection is a
+ * <tt>Map.Entry</tt>. The collection is backed by the map, so
+ * changes to the map are reflected in the collection, and
+ * vice-versa. The collection supports element removal, which
+ * removes the corresponding mapping from the map, via the
+ * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
+ * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
+ * operations. It does not support the <tt>add</tt> or
+ * <tt>addAll</tt> operations. The view's <tt>iterator</tt> is a
+ * "weakly consistent" iterator that will never throw {@link
+ * java.util.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. The
+ * <tt>Map.Entry</tt> elements returned by
+ * <tt>iterator.next()</tt> do <em>not</em> support the
+ * <tt>setValue</tt> operation.
+ *
+ * @return a collection view of the mappings contained in this map.
+ */
+ public Set<Map.Entry<K,V>> entrySet() {
+ EntrySet es = entrySet;
+ return (es != null) ? es : (entrySet = new EntrySet());
+ }
+
+ /**
+ * Returns a collection view of the mappings contained in this
+ * map, in descending order. Each element in the returned
+ * collection is a <tt>Map.Entry</tt>. The collection is backed
+ * by the map, so changes to the map are reflected in the
+ * collection, and vice-versa. The collection supports element
+ * removal, which removes the corresponding mapping from the map,
+ * via the <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
+ * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
+ * operations. It does not support the <tt>add</tt> or
+ * <tt>addAll</tt> operations. The view's <tt>iterator</tt> is a
+ * "weakly consistent" iterator that will never throw {@link
+ * java.util.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. The
+ * <tt>Map.Entry</tt> elements returned by
+ * <tt>iterator.next()</tt> do <em>not</em> support the
+ * <tt>setValue</tt> operation.
+ *
+ * @return a collection view of the mappings contained in this map.
+ */
+ public Set<Map.Entry<K,V>> descendingEntrySet() {
+ DescendingEntrySet es = descendingEntrySet;
+ return (es != null) ? es : (descendingEntrySet = new DescendingEntrySet());
+ }
+
+ /* ---------------- AbstractMap Overrides -------------- */
+
+ /**
+ * Compares the specified object with this map for equality.
+ * Returns <tt>true</tt> if the given object is also a map and the
+ * two maps represent the same mappings. More formally, two maps
+ * <tt>t1</tt> and <tt>t2</tt> represent the same mappings if
+ * <tt>t1.keySet().equals(t2.keySet())</tt> and for every key
+ * <tt>k</tt> in <tt>t1.keySet()</tt>, <tt> (t1.get(k)==null ?
+ * t2.get(k)==null : t1.get(k).equals(t2.get(k))) </tt>. This
+ * operation may return misleading results if either map is
+ * concurrently modified during execution of this method.
+ *
+ * @param o object to be compared for equality with this map.
+ * @return <tt>true</tt> if the specified object is equal to this map.
+ */
+ public boolean equals(Object o) {
+ if (o == this)
+ return true;
+ if (!(o instanceof Map))
+ return false;
+ Map<K,V> t = (Map<K,V>) o;
+ try {
+ return (containsAllMappings(this, t) &&
+ containsAllMappings(t, this));
+ } catch(ClassCastException unused) {
+ return false;
+ } catch(NullPointerException unused) {
+ return false;
+ }
+ }
+
+ /**
+ * Helper for equals -- check for containment, avoiding nulls.
+ */
+ static <K,V> boolean containsAllMappings(Map<K,V> a, Map<K,V> b) {
+ Iterator<Entry<K,V>> it = b.entrySet().iterator();
+ while (it.hasNext()) {
+ Entry<K,V> e = it.next();
+ Object k = e.getKey();
+ Object v = e.getValue();
+ if (k == null || v == null || !v.equals(a.get(k)))
+ return false;
+ }
+ return true;
+ }
+
+ /* ------ ConcurrentMap API methods ------ */
+
+ /**
+ * If the specified key is not already associated
+ * with a value, associate it with the given value.
+ * This is equivalent to
+ * <pre>
+ * 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.
+ *
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key or value are <tt>null</tt>.
+ */
+ public V putIfAbsent(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ return doPut(key, value, true);
+ }
+
+ /**
+ * 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>
+ * 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 ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key or value are <tt>null</tt>.
+ */
+ public boolean remove(Object key, Object value) {
+ if (value == null)
+ throw new NullPointerException();
+ return doRemove(key, value) != null;
+ }
+
+ /**
+ * 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>
+ * 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 ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key, oldValue or newValue are
+ * <tt>null</tt>.
+ */
+ public boolean replace(K key, V oldValue, V newValue) {
+ if (oldValue == null || newValue == null)
+ throw new NullPointerException();
+ Comparable<K> k = comparable(key);
+ for (;;) {
+ Node<K,V> n = findNode(k);
+ if (n == null)
+ return false;
+ Object v = n.value;
+ if (v != null) {
+ if (!oldValue.equals(v))
+ return false;
+ if (n.casValue(v, newValue))
+ return true;
+ }
+ }
+ }
+
+ /**
+ * 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>
+ * 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.
+ * @throws ClassCastException if the key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if the key or value are <tt>null</tt>.
+ */
+ public V replace(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ Comparable<K> k = comparable(key);
+ for (;;) {
+ Node<K,V> n = findNode(k);
+ if (n == null)
+ return null;
+ Object v = n.value;
+ if (v != null && n.casValue(v, value))
+ return (V)v;
+ }
+ }
+
+ /* ------ SortedMap API methods ------ */
+
+ /**
+ * Returns the comparator used to order this map, or <tt>null</tt>
+ * if this map uses its keys' natural order.
+ *
+ * @return the comparator associated with this map, or
+ * <tt>null</tt> if it uses its keys' natural sort method.
+ */
+ public Comparator<? super K> comparator() {
+ return comparator;
+ }
+
+ /**
+ * Returns the first (lowest) key currently in this map.
+ *
+ * @return the first (lowest) key currently in this map.
+ * @throws NoSuchElementException Map is empty.
+ */
+ public K firstKey() {
+ Node<K,V> n = findFirst();
+ if (n == null)
+ throw new NoSuchElementException();
+ return n.key;
+ }
+
+ /**
+ * Returns the last (highest) key currently in this map.
+ *
+ * @return the last (highest) key currently in this map.
+ * @throws NoSuchElementException Map is empty.
+ */
+ public K lastKey() {
+ Node<K,V> n = findLast();
+ if (n == null)
+ throw new NoSuchElementException();
+ return n.key;
+ }
+
+ /**
+ * Returns a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
+ * <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned sorted map
+ * is empty.) The returned sorted map is backed by this map, so changes
+ * in the returned sorted map are reflected in this map, and vice-versa.
+
+ * @param fromKey low endpoint (inclusive) of the subMap.
+ * @param toKey high endpoint (exclusive) of the subMap.
+ *
+ * @return a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.
+ *
+ * @throws ClassCastException if <tt>fromKey</tt> and <tt>toKey</tt>
+ * cannot be compared to one another using this map's comparator
+ * (or, if the map has no comparator, using natural ordering).
+ * @throws IllegalArgumentException if <tt>fromKey</tt> is greater than
+ * <tt>toKey</tt>.
+ * @throws NullPointerException if <tt>fromKey</tt> or <tt>toKey</tt> is
+ * <tt>null</tt>.
+ */
+ public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey) {
+ if (fromKey == null || toKey == null)
+ throw new NullPointerException();
+ return new ConcurrentSkipListSubMap(this, fromKey, toKey);
+ }
+
+ /**
+ * Returns a view of the portion of this map whose keys are
+ * strictly less than <tt>toKey</tt>. The returned sorted map is
+ * backed by this map, so changes in the returned sorted map are
+ * reflected in this map, and vice-versa.
+ * @param toKey high endpoint (exclusive) of the headMap.
+ * @return a view of the portion of this map whose keys are
+ * strictly less than <tt>toKey</tt>.
+ *
+ * @throws ClassCastException if <tt>toKey</tt> is not compatible
+ * with this map's comparator (or, if the map has no comparator,
+ * if <tt>toKey</tt> does not implement <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>toKey</tt> is <tt>null</tt>.
+ */
+ public ConcurrentNavigableMap<K,V> headMap(K toKey) {
+ if (toKey == null)
+ throw new NullPointerException();
+ return new ConcurrentSkipListSubMap(this, null, toKey);
+ }
+
+ /**
+ * Returns a view of the portion of this map whose keys are
+ * greater than or equal to <tt>fromKey</tt>. The returned sorted
+ * map is backed by this map, so changes in the returned sorted
+ * map are reflected in this map, and vice-versa.
+ * @param fromKey low endpoint (inclusive) of the tailMap.
+ * @return a view of the portion of this map whose keys are
+ * greater than or equal to <tt>fromKey</tt>.
+ * @throws ClassCastException if <tt>fromKey</tt> is not
+ * compatible with this map's comparator (or, if the map has no
+ * comparator, if <tt>fromKey</tt> does not implement
+ * <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>fromKey</tt> is <tt>null</tt>.
+ */
+ public ConcurrentNavigableMap<K,V> tailMap(K fromKey) {
+ if (fromKey == null)
+ throw new NullPointerException();
+ return new ConcurrentSkipListSubMap(this, fromKey, null);
+ }
+
+ /* ---------------- Relational operations -------------- */
+
+ /**
+ * Returns a key-value mapping associated with the least key
+ * greater than or equal to the given key, or <tt>null</tt> if
+ * there is no such entry. The returned entry does <em>not</em>
+ * support the <tt>Entry.setValue</tt> method.
+ *
+ * @param key the key.
+ * @return an Entry associated with ceiling of given key, or
+ * <tt>null</tt> if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the
+ * keys currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public Map.Entry<K,V> ceilingEntry(K key) {
+ return getNear(key, GT|EQ);
+ }
+
+ /**
+ * Returns least key greater than or equal to the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the ceiling key, or <tt>null</tt>
+ * if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public K ceilingKey(K key) {
+ Node<K,V> n = findNear(key, GT|EQ);
+ return (n == null)? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the greatest
+ * key strictly less than the given key, or <tt>null</tt> if there is no
+ * such entry. The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @param key the key.
+ * @return an Entry with greatest key less than the given
+ * key, or <tt>null</tt> if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public Map.Entry<K,V> lowerEntry(K key) {
+ return getNear(key, LT);
+ }
+
+ /**
+ * Returns the greatest key strictly less than the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the greatest key less than the given
+ * key, or <tt>null</tt> if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public K lowerKey(K key) {
+ Node<K,V> n = findNear(key, LT);
+ return (n == null)? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the greatest key
+ * less than or equal to the given key, or <tt>null</tt> if there
+ * is no such entry. The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @param key the key.
+ * @return an Entry associated with floor of given key, or <tt>null</tt>
+ * if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public Map.Entry<K,V> floorEntry(K key) {
+ return getNear(key, LT|EQ);
+ }
+
+ /**
+ * Returns the greatest key
+ * less than or equal to the given key, or <tt>null</tt> if there
+ * is no such key.
+ *
+ * @param key the key.
+ * @return the floor of given key, or <tt>null</tt> if there is no
+ * such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public K floorKey(K key) {
+ Node<K,V> n = findNear(key, LT|EQ);
+ return (n == null)? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the least key
+ * strictly greater than the given key, or <tt>null</tt> if there
+ * is no such entry. The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @param key the key.
+ * @return an Entry with least key greater than the given key, or
+ * <tt>null</tt> if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public Map.Entry<K,V> higherEntry(K key) {
+ return getNear(key, GT);
+ }
+
+ /**
+ * Returns the least key strictly greater than the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the least key greater than the given key, or
+ * <tt>null</tt> if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt>.
+ */
+ public K higherKey(K key) {
+ Node<K,V> n = findNear(key, GT);
+ return (n == null)? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the least
+ * key in this map, or <tt>null</tt> if the map is empty.
+ * The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @return an Entry with least key, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> firstEntry() {
+ for (;;) {
+ Node<K,V> n = findFirst();
+ if (n == null)
+ return null;
+ SnapshotEntry<K,V> e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ /**
+ * Returns a key-value mapping associated with the greatest
+ * key in this map, or <tt>null</tt> if the map is empty.
+ * The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @return an Entry with greatest key, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> lastEntry() {
+ for (;;) {
+ Node<K,V> n = findLast();
+ if (n == null)
+ return null;
+ SnapshotEntry<K,V> e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the least key in this map, or <tt>null</tt> if the map is empty.
+ * The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @return the removed first entry of this map, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> pollFirstEntry() {
+ return (SnapshotEntry<K,V>)doRemoveFirst(false);
+ }
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the greatest key in this map, or <tt>null</tt> if the map is empty.
+ * The returned entry does <em>not</em> support
+ * the <tt>Entry.setValue</tt> method.
+ *
+ * @return the removed last entry of this map, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> pollLastEntry() {
+ return (SnapshotEntry<K,V>)doRemoveLast(false);
+ }
+
+
+ /* ---------------- Iterators -------------- */
+
+ /**
+ * Base of ten kinds of iterator classes:
+ * ascending: {map, submap} X {key, value, entry}
+ * descending: {map, submap} X {key, entry}
+ */
+ abstract class Iter {
+ /** the last node returned by next() */
+ Node<K,V> last;
+ /** the next node to return from next(); */
+ Node<K,V> next;
+ /** Cache of next value field to maintain weak consistency */
+ Object nextValue;
+
+ Iter() {}
+
+ public final boolean hasNext() {
+ return next != null;
+ }
+
+ /** initialize ascending iterator for entire range */
+ final void initAscending() {
+ for (;;) {
+ next = findFirst();
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next)
+ break;
+ }
+ }
+
+ /**
+ * initialize ascending iterator starting at given least key,
+ * or first node if least is <tt>null</tt>, but not greater or
+ * equal to fence, or end if fence is <tt>null</tt>.
+ */
+ final void initAscending(K least, K fence) {
+ for (;;) {
+ next = findCeiling(least);
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next) {
+ if (fence != null && compare(fence, next.key) <= 0) {
+ next = null;
+ nextValue = null;
+ }
+ break;
+ }
+ }
+ }
+ /** advance next to higher entry */
+ final void ascend() {
+ if ((last = next) == null)
+ throw new NoSuchElementException();
+ for (;;) {
+ next = next.next;
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next)
+ break;
+ }
+ }
+
+ /**
+ * Version of ascend for submaps to stop at fence
+ */
+ final void ascend(K fence) {
+ if ((last = next) == null)
+ throw new NoSuchElementException();
+ for (;;) {
+ next = next.next;
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next) {
+ if (fence != null && compare(fence, next.key) <= 0) {
+ next = null;
+ nextValue = null;
+ }
+ break;
+ }
+ }
+ }
+
+ /** initialize descending iterator for entire range */
+ final void initDescending() {
+ for (;;) {
+ next = findLast();
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next)
+ break;
+ }
+ }
+
+ /**
+ * initialize descending iterator starting at key less
+ * than or equal to given fence key, or
+ * last node if fence is <tt>null</tt>, but not less than
+ * least, or beginning if lest is <tt>null</tt>.
+ */
+ final void initDescending(K least, K fence) {
+ for (;;) {
+ next = findLower(fence);
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next) {
+ if (least != null && compare(least, next.key) > 0) {
+ next = null;
+ nextValue = null;
+ }
+ break;
+ }
+ }
+ }
+
+ /** advance next to lower entry */
+ final void descend() {
+ if ((last = next) == null)
+ throw new NoSuchElementException();
+ K k = last.key;
+ for (;;) {
+ next = findNear(k, LT);
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next)
+ break;
+ }
+ }
+
+ /**
+ * Version of descend for submaps to stop at least
+ */
+ final void descend(K least) {
+ if ((last = next) == null)
+ throw new NoSuchElementException();
+ K k = last.key;
+ for (;;) {
+ next = findNear(k, LT);
+ if (next == null)
+ break;
+ nextValue = next.value;
+ if (nextValue != null && nextValue != next) {
+ if (least != null && compare(least, next.key) > 0) {
+ next = null;
+ nextValue = null;
+ }
+ break;
+ }
+ }
+ }
+
+ public void remove() {
+ Node<K,V> l = last;
+ if (l == null)
+ throw new IllegalStateException();
+ // It would not be worth all of the overhead to directly
+ // unlink from here. Using remove is fast enough.
+ ConcurrentSkipListMap.this.remove(l.key);
+ }
+
+ }
+
+ final class ValueIterator extends Iter implements Iterator<V> {
+ ValueIterator() {
+ initAscending();
+ }
+ public V next() {
+ Object v = nextValue;
+ ascend();
+ return (V)v;
+ }
+ }
+
+ final class KeyIterator extends Iter implements Iterator<K> {
+ KeyIterator() {
+ initAscending();
+ }
+ public K next() {
+ Node<K,V> n = next;
+ ascend();
+ return n.key;
+ }
+ }
+
+ class SubMapValueIterator extends Iter implements Iterator<V> {
+ final K fence;
+ SubMapValueIterator(K least, K fence) {
+ initAscending(least, fence);
+ this.fence = fence;
+ }
+
+ public V next() {
+ Object v = nextValue;
+ ascend(fence);
+ return (V)v;
+ }
+ }
+
+ final class SubMapKeyIterator extends Iter implements Iterator<K> {
+ final K fence;
+ SubMapKeyIterator(K least, K fence) {
+ initAscending(least, fence);
+ this.fence = fence;
+ }
+
+ public K next() {
+ Node<K,V> n = next;
+ ascend(fence);
+ return n.key;
+ }
+ }
+
+ final class DescendingKeyIterator extends Iter implements Iterator<K> {
+ DescendingKeyIterator() {
+ initDescending();
+ }
+ public K next() {
+ Node<K,V> n = next;
+ descend();
+ return n.key;
+ }
+ }
+
+ final class DescendingSubMapKeyIterator extends Iter implements Iterator<K> {
+ final K least;
+ DescendingSubMapKeyIterator(K least, K fence) {
+ initDescending(least, fence);
+ this.least = least;
+ }
+
+ public K next() {
+ Node<K,V> n = next;
+ descend(least);
+ return n.key;
+ }
+ }
+
+ /**
+ * Entry iterators use the same trick as in ConcurrentHashMap and
+ * elsewhere of using the iterator itself to represent entries,
+ * thus avoiding having to create entry objects in next().
+ */
+ abstract class EntryIter extends Iter implements Map.Entry<K,V> {
+ /** Cache of last value returned */
+ Object lastValue;
+
+ EntryIter() {
+ }
+
+ public K getKey() {
+ Node<K,V> l = last;
+ if (l == null)
+ throw new IllegalStateException();
+ return l.key;
+ }
+
+ public V getValue() {
+ Object v = lastValue;
+ if (last == null || v == null)
+ throw new IllegalStateException();
+ return (V)v;
+ }
+
+ public V setValue(V value) {
+ throw new UnsupportedOperationException();
+ }
+
+ public boolean equals(Object o) {
+ // If not acting as entry, just use default.
+ if (last == null)
+ return super.equals(o);
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry e = (Map.Entry)o;
+ return (getKey().equals(e.getKey()) &&
+ getValue().equals(e.getValue()));
+ }
+
+ public int hashCode() {
+ // If not acting as entry, just use default.
+ if (last == null)
+ return super.hashCode();
+ return getKey().hashCode() ^ getValue().hashCode();
+ }
+
+ public String toString() {
+ // If not acting as entry, just use default.
+ if (last == null)
+ return super.toString();
+ return getKey() + "=" + getValue();
+ }
+ }
+
+ final class EntryIterator extends EntryIter
+ implements Iterator<Map.Entry<K,V>> {
+ EntryIterator() {
+ initAscending();
+ }
+ public Map.Entry<K,V> next() {
+ lastValue = nextValue;
+ ascend();
+ return this;
+ }
+ }
+
+ final class SubMapEntryIterator extends EntryIter
+ implements Iterator<Map.Entry<K,V>> {
+ final K fence;
+ SubMapEntryIterator(K least, K fence) {
+ initAscending(least, fence);
+ this.fence = fence;
+ }
+
+ public Map.Entry<K,V> next() {
+ lastValue = nextValue;
+ ascend(fence);
+ return this;
+ }
+ }
+
+ final class DescendingEntryIterator extends EntryIter
+ implements Iterator<Map.Entry<K,V>> {
+ DescendingEntryIterator() {
+ initDescending();
+ }
+ public Map.Entry<K,V> next() {
+ lastValue = nextValue;
+ descend();
+ return this;
+ }
+ }
+
+ final class DescendingSubMapEntryIterator extends EntryIter
+ implements Iterator<Map.Entry<K,V>> {
+ final K least;
+ DescendingSubMapEntryIterator(K least, K fence) {
+ initDescending(least, fence);
+ this.least = least;
+ }
+
+ public Map.Entry<K,V> next() {
+ lastValue = nextValue;
+ descend(least);
+ return this;
+ }
+ }
+
+ // Factory methods for iterators needed by submaps and/or
+ // ConcurrentSkipListSet
+
+ Iterator<K> keyIterator() {
+ return new KeyIterator();
+ }
+
+ Iterator<K> descendingKeyIterator() {
+ return new DescendingKeyIterator();
+ }
+
+ SubMapEntryIterator subMapEntryIterator(K least, K fence) {
+ return new SubMapEntryIterator(least, fence);
+ }
+
+ DescendingSubMapEntryIterator descendingSubMapEntryIterator(K least, K fence) {
+ return new DescendingSubMapEntryIterator(least, fence);
+ }
+
+ SubMapKeyIterator subMapKeyIterator(K least, K fence) {
+ return new SubMapKeyIterator(least, fence);
+ }
+
+ DescendingSubMapKeyIterator descendingSubMapKeyIterator(K least, K fence) {
+ return new DescendingSubMapKeyIterator(least, fence);
+ }
+
+ SubMapValueIterator subMapValueIterator(K least, K fence) {
+ return new SubMapValueIterator(least, fence);
+ }
+
+ /* ---------------- Views -------------- */
+
+ class KeySet extends AbstractSet<K> {
+ public Iterator<K> iterator() {
+ return new KeyIterator();
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListMap.this.isEmpty();
+ }
+ public int size() {
+ return ConcurrentSkipListMap.this.size();
+ }
+ public boolean contains(Object o) {
+ return ConcurrentSkipListMap.this.containsKey(o);
+ }
+ public boolean remove(Object o) {
+ return ConcurrentSkipListMap.this.removep(o);
+ }
+ public void clear() {
+ ConcurrentSkipListMap.this.clear();
+ }
+ public Object[] toArray() {
+ Collection<K> c = new ArrayList<K>();
+ for (Iterator<K> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<K> c = new ArrayList<K>();
+ for (Iterator<K> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray(a);
+ }
+ }
+
+ class DescendingKeySet extends KeySet {
+ public Iterator<K> iterator() {
+ return new DescendingKeyIterator();
+ }
+ }
+
+ final class Values extends AbstractCollection<V> {
+ public Iterator<V> iterator() {
+ return new ValueIterator();
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListMap.this.isEmpty();
+ }
+ public int size() {
+ return ConcurrentSkipListMap.this.size();
+ }
+ public boolean contains(Object o) {
+ return ConcurrentSkipListMap.this.containsValue(o);
+ }
+ public void clear() {
+ ConcurrentSkipListMap.this.clear();
+ }
+ public Object[] toArray() {
+ Collection<V> c = new ArrayList<V>();
+ for (Iterator<V> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<V> c = new ArrayList<V>();
+ for (Iterator<V> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray(a);
+ }
+ }
+
+ class EntrySet extends AbstractSet<Map.Entry<K,V>> {
+ public Iterator<Map.Entry<K,V>> iterator() {
+ return new EntryIterator();
+ }
+ public boolean contains(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry<K,V> e = (Map.Entry<K,V>)o;
+ V v = ConcurrentSkipListMap.this.get(e.getKey());
+ return v != null && v.equals(e.getValue());
+ }
+ public boolean remove(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry<K,V> e = (Map.Entry<K,V>)o;
+ return ConcurrentSkipListMap.this.remove(e.getKey(),
+ e.getValue());
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListMap.this.isEmpty();
+ }
+ public int size() {
+ return ConcurrentSkipListMap.this.size();
+ }
+ public void clear() {
+ ConcurrentSkipListMap.this.clear();
+ }
+
+ public Object[] toArray() {
+ Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>();
+ for (Map.Entry e : this)
+ c.add(new SnapshotEntry(e.getKey(), e.getValue()));
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>();
+ for (Map.Entry e : this)
+ c.add(new SnapshotEntry(e.getKey(), e.getValue()));
+ return c.toArray(a);
+ }
+ }
+
+ class DescendingEntrySet extends EntrySet {
+ public Iterator<Map.Entry<K,V>> iterator() {
+ return new DescendingEntryIterator();
+ }
+ }
+
+ /**
+ * Submaps returned by {@link ConcurrentSkipListMap} submap operations
+ * represent a subrange of mappings of their underlying
+ * maps. Instances of this class support all methods of their
+ * underlying maps, differing in that mappings outside their range are
+ * ignored, and attempts to add mappings outside their ranges result
+ * in {@link IllegalArgumentException}. Instances of this class are
+ * constructed only using the <tt>subMap</tt>, <tt>headMap</tt>, and
+ * <tt>tailMap</tt> methods of their underlying maps.
+ */
+ static class ConcurrentSkipListSubMap<K,V> extends AbstractMap<K,V>
+ implements ConcurrentNavigableMap<K,V>, java.io.Serializable {
+
+ private static final long serialVersionUID = -7647078645895051609L;
+
+ /** Underlying map */
+ private final ConcurrentSkipListMap<K,V> m;
+ /** lower bound key, or null if from start */
+ private final K least;
+ /** upper fence key, or null if to end */
+ private final K fence;
+ // Lazily initialized view holders
+ private transient Set<K> keySetView;
+ private transient Set<Map.Entry<K,V>> entrySetView;
+ private transient Collection<V> valuesView;
+ private transient Set<K> descendingKeySetView;
+ private transient Set<Map.Entry<K,V>> descendingEntrySetView;
+
+ /**
+ * Creates a new submap.
+ * @param least inclusive least value, or <tt>null</tt> if from start
+ * @param fence exclusive upper bound or <tt>null</tt> if to end
+ * @throws IllegalArgumentException if least and fence nonnull
+ * and least greater than fence
+ */
+ ConcurrentSkipListSubMap(ConcurrentSkipListMap<K,V> map,
+ K least, K fence) {
+ if (least != null &&
+ fence != null &&
+ map.compare(least, fence) > 0)
+ throw new IllegalArgumentException("inconsistent range");
+ this.m = map;
+ this.least = least;
+ this.fence = fence;
+ }
+
+ /* ---------------- Utilities -------------- */
+
+ boolean inHalfOpenRange(K key) {
+ return m.inHalfOpenRange(key, least, fence);
+ }
+
+ boolean inOpenRange(K key) {
+ return m.inOpenRange(key, least, fence);
+ }
+
+ ConcurrentSkipListMap.Node<K,V> firstNode() {
+ return m.findCeiling(least);
+ }
+
+ ConcurrentSkipListMap.Node<K,V> lastNode() {
+ return m.findLower(fence);
+ }
+
+ boolean isBeforeEnd(ConcurrentSkipListMap.Node<K,V> n) {
+ return (n != null &&
+ (fence == null ||
+ n.key == null || // pass by markers and headers
+ m.compare(fence, n.key) > 0));
+ }
+
+ void checkKey(K key) throws IllegalArgumentException {
+ if (!inHalfOpenRange(key))
+ throw new IllegalArgumentException("key out of range");
+ }
+
+ /**
+ * Returns underlying map. Needed by ConcurrentSkipListSet
+ * @return the backing map
+ */
+ ConcurrentSkipListMap<K,V> getMap() {
+ return m;
+ }
+
+ /**
+ * Returns least key. Needed by ConcurrentSkipListSet
+ * @return least key or <tt>null</tt> if from start
+ */
+ K getLeast() {
+ return least;
+ }
+
+ /**
+ * Returns fence key. Needed by ConcurrentSkipListSet
+ * @return fence key or <tt>null</tt> of to end
+ */
+ K getFence() {
+ return fence;
+ }
+
+
+ /* ---------------- Map API methods -------------- */
+
+ public boolean containsKey(Object key) {
+ K k = (K)key;
+ return inHalfOpenRange(k) && m.containsKey(k);
+ }
+
+ public V get(Object key) {
+ K k = (K)key;
+ return ((!inHalfOpenRange(k)) ? null : m.get(k));
+ }
+
+ public V put(K key, V value) {
+ checkKey(key);
+ return m.put(key, value);
+ }
+
+ public V remove(Object key) {
+ K k = (K)key;
+ return (!inHalfOpenRange(k))? null : m.remove(k);
+ }
+
+ public int size() {
+ long count = 0;
+ for (ConcurrentSkipListMap.Node<K,V> n = firstNode();
+ isBeforeEnd(n);
+ n = n.next) {
+ if (n.getValidValue() != null)
+ ++count;
+ }
+ return count >= Integer.MAX_VALUE? Integer.MAX_VALUE : (int)count;
+ }
+
+ public boolean isEmpty() {
+ return !isBeforeEnd(firstNode());
+ }
+
+ public boolean containsValue(Object value) {
+ if (value == null)
+ throw new NullPointerException();
+ for (ConcurrentSkipListMap.Node<K,V> n = firstNode();
+ isBeforeEnd(n);
+ n = n.next) {
+ V v = n.getValidValue();
+ if (v != null && value.equals(v))
+ return true;
+ }
+ return false;
+ }
+
+ public void clear() {
+ for (ConcurrentSkipListMap.Node<K,V> n = firstNode();
+ isBeforeEnd(n);
+ n = n.next) {
+ if (n.getValidValue() != null)
+ m.remove(n.key);
+ }
+ }
+
+ /* ---------------- ConcurrentMap API methods -------------- */
+
+ public V putIfAbsent(K key, V value) {
+ checkKey(key);
+ return m.putIfAbsent(key, value);
+ }
+
+ public boolean remove(Object key, Object value) {
+ K k = (K)key;
+ return inHalfOpenRange(k) && m.remove(k, value);
+ }
+
+ public boolean replace(K key, V oldValue, V newValue) {
+ checkKey(key);
+ return m.replace(key, oldValue, newValue);
+ }
+
+ public V replace(K key, V value) {
+ checkKey(key);
+ return m.replace(key, value);
+ }
+
+ /* ---------------- SortedMap API methods -------------- */
+
+ public Comparator<? super K> comparator() {
+ return m.comparator();
+ }
+
+ public K firstKey() {
+ ConcurrentSkipListMap.Node<K,V> n = firstNode();
+ if (isBeforeEnd(n))
+ return n.key;
+ else
+ throw new NoSuchElementException();
+ }
+
+ public K lastKey() {
+ ConcurrentSkipListMap.Node<K,V> n = lastNode();
+ if (n != null) {
+ K last = n.key;
+ if (inHalfOpenRange(last))
+ return last;
+ }
+ throw new NoSuchElementException();
+ }
+
+ public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey) {
+ if (fromKey == null || toKey == null)
+ throw new NullPointerException();
+ if (!inOpenRange(fromKey) || !inOpenRange(toKey))
+ throw new IllegalArgumentException("key out of range");
+ return new ConcurrentSkipListSubMap(m, fromKey, toKey);
+ }
+
+ public ConcurrentNavigableMap<K,V> headMap(K toKey) {
+ if (toKey == null)
+ throw new NullPointerException();
+ if (!inOpenRange(toKey))
+ throw new IllegalArgumentException("key out of range");
+ return new ConcurrentSkipListSubMap(m, least, toKey);
+ }
+
+ public ConcurrentNavigableMap<K,V> tailMap(K fromKey) {
+ if (fromKey == null)
+ throw new NullPointerException();
+ if (!inOpenRange(fromKey))
+ throw new IllegalArgumentException("key out of range");
+ return new ConcurrentSkipListSubMap(m, fromKey, fence);
+ }
+
+ /* ---------------- Relational methods -------------- */
+
+ public Map.Entry<K,V> ceilingEntry(K key) {
+ return (SnapshotEntry<K,V>)
+ m.getNear(key, m.GT|m.EQ, least, fence, false);
+ }
+
+ public K ceilingKey(K key) {
+ return (K)
+ m.getNear(key, m.GT|m.EQ, least, fence, true);
+ }
+
+ public Map.Entry<K,V> lowerEntry(K key) {
+ return (SnapshotEntry<K,V>)
+ m.getNear(key, m.LT, least, fence, false);
+ }
+
+ public K lowerKey(K key) {
+ return (K)
+ m.getNear(key, m.LT, least, fence, true);
+ }
+
+ public Map.Entry<K,V> floorEntry(K key) {
+ return (SnapshotEntry<K,V>)
+ m.getNear(key, m.LT|m.EQ, least, fence, false);
+ }
+
+ public K floorKey(K key) {
+ return (K)
+ m.getNear(key, m.LT|m.EQ, least, fence, true);
+ }
+
+
+ public Map.Entry<K,V> higherEntry(K key) {
+ return (SnapshotEntry<K,V>)
+ m.getNear(key, m.GT, least, fence, false);
+ }
+
+ public K higherKey(K key) {
+ return (K)
+ m.getNear(key, m.GT, least, fence, true);
+ }
+
+ public Map.Entry<K,V> firstEntry() {
+ for (;;) {
+ ConcurrentSkipListMap.Node<K,V> n = firstNode();
+ if (!isBeforeEnd(n))
+ return null;
+ Map.Entry<K,V> e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ public Map.Entry<K,V> lastEntry() {
+ for (;;) {
+ ConcurrentSkipListMap.Node<K,V> n = lastNode();
+ if (n == null || !inHalfOpenRange(n.key))
+ return null;
+ Map.Entry<K,V> e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ public Map.Entry<K,V> pollFirstEntry() {
+ return (SnapshotEntry<K,V>)
+ m.removeFirstEntryOfSubrange(least, fence, false);
+ }
+
+ public Map.Entry<K,V> pollLastEntry() {
+ return (SnapshotEntry<K,V>)
+ m.removeLastEntryOfSubrange(least, fence, false);
+ }
+
+ /* ---------------- Submap Views -------------- */
+
+ public Set<K> keySet() {
+ Set<K> ks = keySetView;
+ return (ks != null) ? ks : (keySetView = new KeySetView());
+ }
+
+ class KeySetView extends AbstractSet<K> {
+ public Iterator<K> iterator() {
+ return m.subMapKeyIterator(least, fence);
+ }
+ public int size() {
+ return ConcurrentSkipListSubMap.this.size();
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListSubMap.this.isEmpty();
+ }
+ public boolean contains(Object k) {
+ return ConcurrentSkipListSubMap.this.containsKey(k);
+ }
+ public Object[] toArray() {
+ Collection<K> c = new ArrayList<K>();
+ for (Iterator<K> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<K> c = new ArrayList<K>();
+ for (Iterator<K> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray(a);
+ }
+ }
+
+ public Set<K> descendingKeySet() {
+ Set<K> ks = descendingKeySetView;
+ return (ks != null) ? ks : (descendingKeySetView = new DescendingKeySetView());
+ }
+
+ class DescendingKeySetView extends KeySetView {
+ public Iterator<K> iterator() {
+ return m.descendingSubMapKeyIterator(least, fence);
+ }
+ }
+
+ public Collection<V> values() {
+ Collection<V> vs = valuesView;
+ return (vs != null) ? vs : (valuesView = new ValuesView());
+ }
+
+ class ValuesView extends AbstractCollection<V> {
+ public Iterator<V> iterator() {
+ return m.subMapValueIterator(least, fence);
+ }
+ public int size() {
+ return ConcurrentSkipListSubMap.this.size();
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListSubMap.this.isEmpty();
+ }
+ public boolean contains(Object v) {
+ return ConcurrentSkipListSubMap.this.containsValue(v);
+ }
+ public Object[] toArray() {
+ Collection<V> c = new ArrayList<V>();
+ for (Iterator<V> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<V> c = new ArrayList<V>();
+ for (Iterator<V> i = iterator(); i.hasNext(); )
+ c.add(i.next());
+ return c.toArray(a);
+ }
+ }
+
+ public Set<Map.Entry<K,V>> entrySet() {
+ Set<Map.Entry<K,V>> es = entrySetView;
+ return (es != null) ? es : (entrySetView = new EntrySetView());
+ }
+
+ class EntrySetView extends AbstractSet<Map.Entry<K,V>> {
+ public Iterator<Map.Entry<K,V>> iterator() {
+ return m.subMapEntryIterator(least, fence);
+ }
+ public int size() {
+ return ConcurrentSkipListSubMap.this.size();
+ }
+ public boolean isEmpty() {
+ return ConcurrentSkipListSubMap.this.isEmpty();
+ }
+ public boolean contains(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry<K,V> e = (Map.Entry<K,V>) o;
+ K key = e.getKey();
+ if (!inHalfOpenRange(key))
+ return false;
+ V v = m.get(key);
+ return v != null && v.equals(e.getValue());
+ }
+ public boolean remove(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry<K,V> e = (Map.Entry<K,V>) o;
+ K key = e.getKey();
+ if (!inHalfOpenRange(key))
+ return false;
+ return m.remove(key, e.getValue());
+ }
+ public Object[] toArray() {
+ Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>();
+ for (Map.Entry e : this)
+ c.add(new SnapshotEntry(e.getKey(), e.getValue()));
+ return c.toArray();
+ }
+ public <T> T[] toArray(T[] a) {
+ Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>();
+ for (Map.Entry e : this)
+ c.add(new SnapshotEntry(e.getKey(), e.getValue()));
+ return c.toArray(a);
+ }
+ }
+
+ public Set<Map.Entry<K,V>> descendingEntrySet() {
+ Set<Map.Entry<K,V>> es = descendingEntrySetView;
+ return (es != null) ? es : (descendingEntrySetView = new DescendingEntrySetView());
+ }
+
+ class DescendingEntrySetView extends EntrySetView {
+ public Iterator<Map.Entry<K,V>> iterator() {
+ return m.descendingSubMapEntryIterator(least, fence);
+ }
+ }
+ }
+}
Property changes on: common-core/trunk/src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java
___________________________________________________________________
Name: svn:keywords
+ Id Revision
Name: svn:eol-style
+ LF
Added: common-core/trunk/src/main/java/org/jboss/util/collection/NavigableMap.java
===================================================================
--- common-core/trunk/src/main/java/org/jboss/util/collection/NavigableMap.java (rev 0)
+++ common-core/trunk/src/main/java/org/jboss/util/collection/NavigableMap.java 2009-04-20 03:52:22 UTC (rev 3125)
@@ -0,0 +1,298 @@
+/*
+ * 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
+ */
+
+package org.jboss.util.collection;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.SortedMap;
+
+/**
+ * A {@link SortedMap} extended with navigation methods returning the
+ * closest matches for given search targets. Methods
+ * <tt>lowerEntry</tt>, <tt>floorEntry</tt>, <tt>ceilingEntry</tt>,
+ * and <tt>higherEntry</tt> return <tt>Map.Entry</tt> objects
+ * associated with keys respectively less than, less than or equal,
+ * greater than or equal, and greater than a given key, returning
+ * <tt>null</tt> if there is no such key. Similarly, methods
+ * <tt>lowerKey</tt>, <tt>floorKey</tt>, <tt>ceilingKey</tt>, and
+ * <tt>higherKey</tt> return only the associated keys. All of these
+ * methods are designed for locating, not traversing entries.
+ *
+ * <p>A <tt>NavigableMap</tt> may be viewed and traversed in either
+ * ascending or descending key order. The <tt>Map</tt> methods
+ * <tt>keySet</tt> and <tt>entrySet</tt> return ascending views, and
+ * the additional methods <tt>descendingKeySet</tt> and
+ * <tt>descendingEntrySet</tt> return descending views. The
+ * performance of ascending traversals is likely to be faster than
+ * descending traversals. Notice that it is possible to perform
+ * subrannge traversals in either direction using <tt>SubMap</tt>.
+ *
+ * <p>This interface additionally defines methods <tt>firstEntry</tt>,
+ * <tt>pollFirstEntry</tt>, <tt>lastEntry</tt>, and
+ * <tt>pollLastEntry</tt> that return and/or remove the least and
+ * greatest mappings, if any exist, else returning <tt>null</tt>.
+ *
+ * <p> Implementations of entry-returning methods are expected to
+ * return <tt>Map.Entry</tt> pairs representing snapshots of mappings
+ * at the time they were produced, and thus generally do <em>not</em>
+ * support the optional <tt>Entry.setValue</tt> method. Note however
+ * that it is possible to change mappings in the associated map using
+ * method <tt>put</tt>.
+ *
+ * @author Doug Lea
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ */
+public interface NavigableMap<K,V> extends SortedMap<K,V> {
+ /**
+ * Returns a key-value mapping associated with the least key
+ * greater than or equal to the given key, or <tt>null</tt> if there is
+ * no such entry.
+ *
+ * @param key the key.
+ * @return an Entry associated with ceiling of given key, or <tt>null</tt>
+ * if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public Map.Entry<K,V> ceilingEntry(K key);
+
+ /**
+ * Returns least key greater than or equal to the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the ceiling key, or <tt>null</tt>
+ * if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public K ceilingKey(K key);
+
+ /**
+ * Returns a key-value mapping associated with the greatest
+ * key strictly less than the given key, or <tt>null</tt> if there is no
+ * such entry.
+ *
+ * @param key the key.
+ * @return an Entry with greatest key less than the given
+ * key, or <tt>null</tt> if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public Map.Entry<K,V> lowerEntry(K key);
+
+ /**
+ * Returns the greatest key strictly less than the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the greatest key less than the given
+ * key, or <tt>null</tt> if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public K lowerKey(K key);
+
+ /**
+ * Returns a key-value mapping associated with the greatest key
+ * less than or equal to the given key, or <tt>null</tt> if there
+ * is no such entry.
+ *
+ * @param key the key.
+ * @return an Entry associated with floor of given key, or <tt>null</tt>
+ * if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public Map.Entry<K,V> floorEntry(K key);
+
+ /**
+ * Returns the greatest key
+ * less than or equal to the given key, or <tt>null</tt> if there
+ * is no such key.
+ *
+ * @param key the key.
+ * @return the floor of given key, or <tt>null</tt> if there is no
+ * such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public K floorKey(K key);
+
+ /**
+ * Returns a key-value mapping associated with the least key
+ * strictly greater than the given key, or <tt>null</tt> if there
+ * is no such entry.
+ *
+ * @param key the key.
+ * @return an Entry with least key greater than the given key, or
+ * <tt>null</tt> if there is no such Entry.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public Map.Entry<K,V> higherEntry(K key);
+
+ /**
+ * Returns the least key strictly greater than the given key, or
+ * <tt>null</tt> if there is no such key.
+ *
+ * @param key the key.
+ * @return the least key greater than the given key, or
+ * <tt>null</tt> if there is no such key.
+ * @throws ClassCastException if key cannot be compared with the keys
+ * currently in the map.
+ * @throws NullPointerException if key is <tt>null</tt> and this map
+ * does not support <tt>null</tt> keys.
+ */
+ public K higherKey(K key);
+
+ /**
+ * Returns a key-value mapping associated with the least
+ * key in this map, or <tt>null</tt> if the map is empty.
+ *
+ * @return an Entry with least key, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> firstEntry();
+
+ /**
+ * Returns a key-value mapping associated with the greatest
+ * key in this map, or <tt>null</tt> if the map is empty.
+ *
+ * @return an Entry with greatest key, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> lastEntry();
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the least key in this map, or <tt>null</tt> if the map is empty.
+ *
+ * @return the removed first entry of this map, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> pollFirstEntry();
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the greatest key in this map, or <tt>null</tt> if the map is empty.
+ *
+ * @return the removed last entry of this map, or <tt>null</tt>
+ * if the map is empty.
+ */
+ public Map.Entry<K,V> pollLastEntry();
+
+ /**
+ * Returns a set view of the keys contained in this map, in
+ * descending key order. The set is backed by the map, so changes
+ * to the map are reflected in the set, and vice-versa. If the
+ * map is modified while an iteration over the set is in progress
+ * (except through the iterator's own <tt>remove</tt> operation),
+ * the results of the iteration are undefined. The set supports
+ * element removal, which removes the corresponding mapping from
+ * the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
+ * <tt>removeAll</tt> <tt>retainAll</tt>, and <tt>clear</tt>
+ * operations. It does not support the add or <tt>addAll</tt>
+ * operations.
+ *
+ * @return a set view of the keys contained in this map.
+ */
+ Set<K> descendingKeySet();
+
+ /**
+ * Returns a set view of the mappings contained in this map, in
+ * descending key order. Each element in the returned set is a
+ * <tt>Map.Entry</tt>. The set is backed by the map, so changes to
+ * the map are reflected in the set, and vice-versa. If the map
+ * is modified while an iteration over the set is in progress
+ * (except through the iterator's own <tt>remove</tt> operation,
+ * or through the <tt>setValue</tt> operation on a map entry
+ * returned by the iterator) the results of the iteration are
+ * undefined. The set supports element removal, which removes the
+ * corresponding mapping from the map, via the
+ * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
+ * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
+ * operations. It does not support the <tt>add</tt> or
+ * <tt>addAll</tt> operations.
+ *
+ * @return a set view of the mappings contained in this map.
+ */
+ Set<Map.Entry<K, V>> descendingEntrySet();
+
+ /**
+ * Returns a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
+ * <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned sorted map
+ * is empty.) The returned sorted map is backed by this map, so changes
+ * in the returned sorted map are reflected in this map, and vice-versa.
+
+ * @param fromKey low endpoint (inclusive) of the subMap.
+ * @param toKey high endpoint (exclusive) of the subMap.
+ *
+ * @return a view of the portion of this map whose keys range from
+ * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.
+ *
+ * @throws ClassCastException if <tt>fromKey</tt> and
+ * <tt>toKey</tt> cannot be compared to one another using this
+ * map's comparator (or, if the map has no comparator, using
+ * natural ordering).
+ * @throws IllegalArgumentException if <tt>fromKey</tt> is greater
+ * than <tt>toKey</tt>.
+ * @throws NullPointerException if <tt>fromKey</tt> or
+ * <tt>toKey</tt> is <tt>null</tt> and this map does not support
+ * <tt>null</tt> keys.
+ */
+ public NavigableMap<K,V> subMap(K fromKey, K toKey);
+
+ /**
+ * Returns a view of the portion of this map whose keys are strictly less
+ * than <tt>toKey</tt>. The returned sorted map is backed by this map, so
+ * changes in the returned sorted map are reflected in this map, and
+ * vice-versa.
+ * @param toKey high endpoint (exclusive) of the headMap.
+ * @return a view of the portion of this map whose keys are strictly
+ * less than <tt>toKey</tt>.
+ *
+ * @throws ClassCastException if <tt>toKey</tt> is not compatible
+ * with this map's comparator (or, if the map has no comparator,
+ * if <tt>toKey</tt> does not implement <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>toKey</tt> is <tt>null</tt>
+ * and this map does not support <tt>null</tt> keys.
+ */
+ public NavigableMap<K,V> headMap(K toKey);
+
+ /**
+ * Returns a view of the portion of this map whose keys are
+ * greater than or equal to <tt>fromKey</tt>. The returned sorted
+ * map is backed by this map, so changes in the returned sorted
+ * map are reflected in this map, and vice-versa.
+ * @param fromKey low endpoint (inclusive) of the tailMap.
+ * @return a view of the portion of this map whose keys are greater
+ * than or equal to <tt>fromKey</tt>.
+ * @throws ClassCastException if <tt>fromKey</tt> is not compatible
+ * with this map's comparator (or, if the map has no comparator,
+ * if <tt>fromKey</tt> does not implement <tt>Comparable</tt>).
+ * @throws NullPointerException if <tt>fromKey</tt> is <tt>null</tt>
+ * and this map does not support <tt>null</tt> keys.
+ */
+ public NavigableMap<K,V> tailMap(K fromKey);
+}
Property changes on: common-core/trunk/src/main/java/org/jboss/util/collection/NavigableMap.java
___________________________________________________________________
Name: svn:keywords
+ Id Revision
Name: svn:eol-style
+ LF
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