diff -r 000000000000 -r 212417b74b72 rt/emul/compact/src/main/java/java/util/concurrent/ConcurrentSkipListMap.java
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/rt/emul/compact/src/main/java/java/util/concurrent/ConcurrentSkipListMap.java Sat Mar 19 10:46:31 2016 +0100
@@ -0,0 +1,3119 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+import java.util.*;
+import java.util.concurrent.atomic.*;
+
+/**
+ * A scalable concurrent {@link ConcurrentNavigableMap} implementation.
+ * The map is sorted according to the {@linkplain Comparable natural
+ * ordering} of its keys, or by a {@link Comparator} provided at map
+ * creation time, depending on which constructor is used.
+ *
+ * This class implements a concurrent variant of SkipLists
+ * providing expected average log(n) time cost for the
+ * containsKey, get, put and
+ * remove operations and their variants. Insertion, removal,
+ * update, and access operations safely execute concurrently by
+ * multiple threads. Iterators are weakly consistent, returning
+ * elements reflecting the state of the map at some point at or since
+ * the creation of the iterator. They do not throw {@link
+ * ConcurrentModificationException}, and may proceed concurrently with
+ * other operations. Ascending key ordered views and their iterators
+ * are faster than descending ones.
+ *
+ *
All Map.Entry pairs returned by methods in this class
+ * and its views represent snapshots of mappings at the time they were
+ * produced. They do not support the Entry.setValue
+ * method. (Note however that it is possible to change mappings in the
+ * associated map using put, putIfAbsent, or
+ * replace, depending on exactly which effect you need.)
+ *
+ *
Beware that, unlike in most collections, the size
+ * method is not a constant-time operation. Because of the
+ * asynchronous nature of these maps, determining the current number
+ * of elements requires a traversal of the elements, and so may report
+ * inaccurate results if this collection is modified during traversal.
+ * Additionally, the bulk operations putAll, equals,
+ * toArray, containsValue, and clear are
+ * not guaranteed to be performed atomically. For example, an
+ * iterator operating concurrently with a putAll operation
+ * might view only some of the added elements.
+ *
+ *
This class and its views and iterators implement all of the
+ * optional methods of the {@link Map} and {@link Iterator}
+ * interfaces. Like most other concurrent collections, this class does
+ * not permit the use of null keys or values because some
+ * null return values cannot be reliably distinguished from the absence of
+ * elements.
+ *
+ *
This class is a member of the
+ *
+ * Java Collections Framework.
+ *
+ * @author Doug Lea
+ * @param the type of keys maintained by this map
+ * @param the type of mapped values
+ * @since 1.6
+ */
+public class ConcurrentSkipListMap extends AbstractMap
+ implements ConcurrentNavigableMap,
+ 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;
+
+ /**
+ * Generates the initial random seed for the cheaper per-instance
+ * random number generators used in randomLevel.
+ */
+ private static final Random seedGenerator = new Random();
+
+ /**
+ * 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 head;
+
+ /**
+ * The comparator used to maintain order in this map, or null
+ * if using natural ordering.
+ * @serial
+ */
+ private final Comparator 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 ConcurrentNavigableMap descendingMap;
+
+ /**
+ * Initializes or resets 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;
+ descendingMap = null;
+ randomSeed = seedGenerator.nextInt() | 0x0100; // ensure nonzero
+ head = new HeadIndex(new Node(null, BASE_HEADER, null),
+ null, null, 1);
+ }
+
+ /**
+ * compareAndSet head node
+ */
+ private boolean casHead(HeadIndex cmp, HeadIndex val) {
+ return UNSAFE.compareAndSwapObject(this, headOffset, 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 {
+ final K key;
+ volatile Object value;
+ volatile Node next;
+
+ /**
+ * Creates a new regular node.
+ */
+ Node(K key, Object value, Node 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 next) {
+ this.key = null;
+ this.value = this;
+ this.next = next;
+ }
+
+ /**
+ * compareAndSet value field
+ */
+ boolean casValue(Object cmp, Object val) {
+ return UNSAFE.compareAndSwapObject(this, valueOffset, cmp, val);
+ }
+
+ /**
+ * compareAndSet next field
+ */
+ boolean casNext(Node cmp, Node val) {
+ return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
+ }
+
+ /**
+ * Returns true if this node is a marker. This method isn't
+ * actually called in 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;
+ }
+
+ /**
+ * Returns 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 f) {
+ return casNext(f, new Node(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 b, Node 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);
+ }
+ }
+
+ /**
+ * Returns 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;
+ }
+
+ /**
+ * Creates and returns a new SimpleImmutableEntry holding current
+ * mapping if this node holds a valid value, else null.
+ * @return new entry or null
+ */
+ AbstractMap.SimpleImmutableEntry createSnapshot() {
+ V v = getValidValue();
+ if (v == null)
+ return null;
+ return new AbstractMap.SimpleImmutableEntry(key, v);
+ }
+
+ // UNSAFE mechanics
+
+ private static final sun.misc.Unsafe UNSAFE;
+ private static final long valueOffset;
+ private static final long nextOffset;
+
+ static {
+ try {
+ UNSAFE = sun.misc.Unsafe.getUnsafe();
+ Class k = Node.class;
+ valueOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("value"));
+ nextOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("next"));
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ }
+ }
+
+ /* ---------------- Indexing -------------- */
+
+ /**
+ * Index nodes represent the levels of the skip list. 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 {
+ final Node node;
+ final Index down;
+ volatile Index right;
+
+ /**
+ * Creates index node with given values.
+ */
+ Index(Node node, Index down, Index right) {
+ this.node = node;
+ this.down = down;
+ this.right = right;
+ }
+
+ /**
+ * compareAndSet right field
+ */
+ final boolean casRight(Index cmp, Index val) {
+ return UNSAFE.compareAndSwapObject(this, rightOffset, 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 succ, Index newSucc) {
+ Node 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 succ) {
+ return !indexesDeletedNode() && casRight(succ, succ.right);
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe UNSAFE;
+ private static final long rightOffset;
+ static {
+ try {
+ UNSAFE = sun.misc.Unsafe.getUnsafe();
+ Class k = Index.class;
+ rightOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("right"));
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ }
+ }
+
+ /* ---------------- Head nodes -------------- */
+
+ /**
+ * Nodes heading each level keep track of their level.
+ */
+ static final class HeadIndex extends Index {
+ final int level;
+ HeadIndex(Node node, Index down, Index right, int level) {
+ super(node, down, right);
+ this.level = level;
+ }
+ }
+
+ /* ---------------- Comparison utilities -------------- */
+
+ /**
+ * Represents a key with a comparator as a Comparable.
+ *
+ * Because most sorted collections seem to use natural ordering 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 implements Comparable {
+ final K actualKey;
+ final Comparator cmp;
+ ComparableUsingComparator(K key, Comparator 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 Comparable, which may cause ClassCastException,
+ * which is propagated back to caller.
+ */
+ private Comparable comparable(Object key)
+ throws ClassCastException {
+ if (key == null)
+ throw new NullPointerException();
+ if (comparator != null)
+ return new ComparableUsingComparator((K)key, comparator);
+ else
+ return (Comparable)key;
+ }
+
+ /**
+ * Compares using comparator or natural ordering. Used when the
+ * ComparableUsingComparator approach doesn't apply.
+ */
+ int compare(K k1, K k2) throws ClassCastException {
+ Comparator cmp = comparator;
+ if (cmp != null)
+ return cmp.compare(k1, k2);
+ else
+ return ((Comparable)k1).compareTo(k2);
+ }
+
+ /**
+ * Returns true if given key greater than or equal to least and
+ * strictly less than fence, bypassing either test if least or
+ * fence are 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));
+ }
+
+ /**
+ * Returns 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 -------------- */
+
+ /**
+ * Returns 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 findPredecessor(Comparable key) {
+ if (key == null)
+ throw new NullPointerException(); // don't postpone errors
+ for (;;) {
+ Index q = head;
+ Index r = q.right;
+ for (;;) {
+ if (r != null) {
+ Node n = r.node;
+ K k = n.key;
+ if (n.value == null) {
+ if (!q.unlink(r))
+ break; // restart
+ r = q.right; // reread r
+ continue;
+ }
+ if (key.compareTo(k) > 0) {
+ q = r;
+ r = r.right;
+ continue;
+ }
+ }
+ Index d = q.down;
+ if (d != null) {
+ q = d;
+ r = d.right;
+ } else
+ return q.node;
+ }
+ }
+ }
+
+ /**
+ * Returns 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 findFirst, and findLast and their
+ * variants. 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 findNode(Comparable key) {
+ for (;;) {
+ Node b = findPredecessor(key);
+ Node n = b.next;
+ for (;;) {
+ if (n == null)
+ return null;
+ Node 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 n;
+ if (c < 0)
+ return null;
+ b = n;
+ n = f;
+ }
+ }
+ }
+
+ /**
+ * Gets value for key using findNode.
+ * @param okey the key
+ * @return the value, or null if absent
+ */
+ private V doGet(Object okey) {
+ Comparable key = comparable(okey);
+ /*
+ * 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 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 key = comparable(kkey);
+ for (;;) {
+ Node b = findPredecessor(key);
+ Node n = b.next;
+ for (;;) {
+ if (n != null) {
+ Node 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 z = new Node(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;
+ }
+ }
+ }
+
+ /**
+ * Returns a random level for inserting a new node.
+ * Hardwired to k=1, p=0.5, max 31 (see above and
+ * Pugh's "Skip List Cookbook", sec 3.4).
+ *
+ * This uses the simplest of the generators described in George
+ * Marsaglia's "Xorshift RNGs" paper. This is not a high-quality
+ * generator but is acceptable here.
+ */
+ private int randomLevel() {
+ int x = randomSeed;
+ x ^= x << 13;
+ x ^= x >>> 17;
+ randomSeed = x ^= x << 5;
+ if ((x & 0x80000001) != 0) // test highest and lowest bits
+ return 0;
+ int level = 1;
+ while (((x >>>= 1) & 1) != 0) ++level;
+ return level;
+ }
+
+ /**
+ * Creates and adds index nodes for the given node.
+ * @param z the node
+ * @param level the level of the index
+ */
+ private void insertIndex(Node z, int level) {
+ HeadIndex h = head;
+ int max = h.level;
+
+ if (level <= max) {
+ Index idx = null;
+ for (int i = 1; i <= level; ++i)
+ idx = new Index(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[] idxs = (Index[])new Index[level+1];
+ Index idx = null;
+ for (int i = 1; i <= level; ++i)
+ idxs[i] = idx = new Index(z, idx, null);
+
+ HeadIndex oldh;
+ int k;
+ for (;;) {
+ oldh = head;
+ int oldLevel = oldh.level;
+ if (level <= oldLevel) { // lost race to add level
+ k = level;
+ break;
+ }
+ HeadIndex newh = oldh;
+ Node oldbase = oldh.node;
+ for (int j = oldLevel+1; j <= level; ++j)
+ newh = new HeadIndex(oldbase, newh, idxs[j], j);
+ if (casHead(oldh, newh)) {
+ k = oldLevel;
+ break;
+ }
+ }
+ addIndex(idxs[k], oldh, k);
+ }
+ }
+
+ /**
+ * Adds 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 idx, HeadIndex h, int indexLevel) {
+ // Track next level to insert in case of retries
+ int insertionLevel = indexLevel;
+ Comparable key = comparable(idx.node.key);
+ if (key == null) throw new NullPointerException();
+
+ // Similar to findPredecessor, but adding index nodes along
+ // path to key.
+ for (;;) {
+ int j = h.level;
+ Index q = h;
+ Index r = q.right;
+ Index t = idx;
+ for (;;) {
+ if (r != null) {
+ Node n = r.node;
+ // compare before deletion check avoids needing recheck
+ int c = key.compareTo(n.key);
+ if (n.value == null) {
+ if (!q.unlink(r))
+ break;
+ r = q.right;
+ continue;
+ }
+ if (c > 0) {
+ q = r;
+ r = r.right;
+ 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;
+ r = q.right;
+ }
+ }
+ }
+
+ /* ---------------- 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
+ */
+ final V doRemove(Object okey, Object value) {
+ Comparable key = comparable(okey);
+ for (;;) {
+ Node b = findPredecessor(key);
+ Node n = b.next;
+ for (;;) {
+ if (n == null)
+ return null;
+ Node 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 h = head;
+ HeadIndex d;
+ HeadIndex e;
+ if (h.level > 3 &&
+ (d = (HeadIndex)h.down) != null &&
+ (e = (HeadIndex)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
+ }
+
+ /* ---------------- Finding and removing first element -------------- */
+
+ /**
+ * Specialized variant of findNode to get first valid node.
+ * @return first node or null if empty
+ */
+ Node findFirst() {
+ for (;;) {
+ Node b = head.node;
+ Node n = b.next;
+ if (n == null)
+ return null;
+ if (n.value != null)
+ return n;
+ n.helpDelete(b, n.next);
+ }
+ }
+
+ /**
+ * Removes first entry; returns its snapshot.
+ * @return null if empty, else snapshot of first entry
+ */
+ Map.Entry doRemoveFirstEntry() {
+ for (;;) {
+ Node b = head.node;
+ Node n = b.next;
+ if (n == null)
+ return null;
+ Node 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();
+ return new AbstractMap.SimpleImmutableEntry(n.key, (V)v);
+ }
+ }
+
+ /**
+ * Clears out index nodes associated with deleted first entry.
+ */
+ private void clearIndexToFirst() {
+ for (;;) {
+ Index q = head;
+ for (;;) {
+ Index r = q.right;
+ if (r != null && r.indexesDeletedNode() && !q.unlink(r))
+ break;
+ if ((q = q.down) == null) {
+ if (head.right == null)
+ tryReduceLevel();
+ return;
+ }
+ }
+ }
+ }
+
+
+ /* ---------------- Finding and removing last element -------------- */
+
+ /**
+ * Specialized version of find to get last valid node.
+ * @return last node or null if empty
+ */
+ Node 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 q = head;
+ for (;;) {
+ Index 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 b = q.node;
+ Node n = b.next;
+ for (;;) {
+ if (n == null)
+ return b.isBaseHeader() ? null : b;
+ Node 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 variant of findPredecessor to get predecessor of last
+ * valid node. Needed when removing the last entry. 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 findPredecessorOfLast() {
+ for (;;) {
+ Index q = head;
+ for (;;) {
+ Index 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;
+ }
+ }
+ }
+
+ /**
+ * Removes last entry; returns its snapshot.
+ * Specialized variant of doRemove.
+ * @return null if empty, else snapshot of last entry
+ */
+ Map.Entry doRemoveLastEntry() {
+ for (;;) {
+ Node b = findPredecessorOfLast();
+ Node n = b.next;
+ if (n == null) {
+ if (b.isBaseHeader()) // empty
+ return null;
+ else
+ continue; // all b's successors are deleted; retry
+ }
+ for (;;) {
+ Node 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 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 new AbstractMap.SimpleImmutableEntry(key, (V)v);
+ }
+ }
+ }
+
+ /* ---------------- 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 findNear(K kkey, int rel) {
+ Comparable key = comparable(kkey);
+ for (;;) {
+ Node b = findPredecessor(key);
+ Node n = b.next;
+ for (;;) {
+ if (n == null)
+ return ((rel & LT) == 0 || b.isBaseHeader()) ? null : b;
+ Node 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;
+ }
+ }
+ }
+
+ /**
+ * Returns SimpleImmutableEntry for results of findNear.
+ * @param key the key
+ * @param rel the relation -- OR'ed combination of EQ, LT, GT
+ * @return Entry fitting relation, or null if no such
+ */
+ AbstractMap.SimpleImmutableEntry getNear(K key, int rel) {
+ for (;;) {
+ Node n = findNear(key, rel);
+ if (n == null)
+ return null;
+ AbstractMap.SimpleImmutableEntry e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+
+ /* ---------------- Constructors -------------- */
+
+ /**
+ * Constructs a new, empty map, sorted according to the
+ * {@linkplain Comparable natural ordering} of the keys.
+ */
+ public ConcurrentSkipListMap() {
+ this.comparator = null;
+ initialize();
+ }
+
+ /**
+ * Constructs a new, empty map, sorted according to the specified
+ * comparator.
+ *
+ * @param comparator the comparator that will be used to order this map.
+ * If null, the {@linkplain Comparable natural
+ * ordering} of the keys will be used.
+ */
+ public ConcurrentSkipListMap(Comparator comparator) {
+ this.comparator = comparator;
+ initialize();
+ }
+
+ /**
+ * Constructs a new map containing the same mappings as the given map,
+ * sorted according to the {@linkplain Comparable natural ordering} of
+ * the keys.
+ *
+ * @param m the map whose mappings are to be placed in this map
+ * @throws ClassCastException if the keys in m are not
+ * {@link Comparable}, or are not mutually comparable
+ * @throws NullPointerException if the specified map or any of its keys
+ * or values are null
+ */
+ public ConcurrentSkipListMap(Map m) {
+ this.comparator = null;
+ initialize();
+ putAll(m);
+ }
+
+ /**
+ * Constructs a new map containing the same mappings and using the
+ * same ordering as the specified sorted map.
+ *
+ * @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 or any of
+ * its keys or values are null
+ */
+ public ConcurrentSkipListMap(SortedMap m) {
+ this.comparator = m.comparator();
+ initialize();
+ buildFromSorted(m);
+ }
+
+ /**
+ * Returns a shallow copy of this ConcurrentSkipListMap
+ * instance. (The keys and values themselves are not cloned.)
+ *
+ * @return a shallow copy of this map
+ */
+ public ConcurrentSkipListMap clone() {
+ ConcurrentSkipListMap clone = null;
+ try {
+ clone = (ConcurrentSkipListMap) 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 map) {
+ if (map == null)
+ throw new NullPointerException();
+
+ HeadIndex h = head;
+ Node basepred = h.node;
+
+ // Track the current rightmost node at each level. Uses an
+ // ArrayList to avoid committing to initial or maximum level.
+ ArrayList> preds = new ArrayList>();
+
+ // initialize
+ for (int i = 0; i <= h.level; ++i)
+ preds.add(null);
+ Index q = h;
+ for (int i = h.level; i > 0; --i) {
+ preds.set(i, q);
+ q = q.down;
+ }
+
+ Iterator> it =
+ map.entrySet().iterator();
+ while (it.hasNext()) {
+ Map.Entry 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 z = new Node(k, v, null);
+ basepred.next = z;
+ basepred = z;
+ if (j > 0) {
+ Index idx = null;
+ for (int i = 1; i <= j; ++i) {
+ idx = new Index(z, idx, null);
+ if (i > h.level)
+ h = new HeadIndex(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 this map to a stream.
+ *
+ * @serialData The key (Object) and value (Object) for each
+ * key-value mapping represented by the map, followed by
+ * null. 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 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 map 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 h = head;
+ Node basepred = h.node;
+ ArrayList> preds = new ArrayList>();
+ for (int i = 0; i <= h.level; ++i)
+ preds.add(null);
+ Index 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 z = new Node(key, val, null);
+ basepred.next = z;
+ basepred = z;
+ if (j > 0) {
+ Index idx = null;
+ for (int i = 1; i <= j; ++i) {
+ idx = new Index(z, idx, null);
+ if (i > h.level)
+ h = new HeadIndex(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 true if this map contains a mapping for the specified
+ * key.
+ *
+ * @param key key whose presence in this map is to be tested
+ * @return true if this map contains a mapping for the specified key
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key is null
+ */
+ public boolean containsKey(Object key) {
+ return doGet(key) != null;
+ }
+
+ /**
+ * Returns the value to which the specified key is mapped,
+ * or {@code null} if this map contains no mapping for the key.
+ *
+ * More formally, if this map contains a mapping from a key
+ * {@code k} to a value {@code v} such that {@code key} compares
+ * equal to {@code k} according to the map's ordering, then this
+ * method returns {@code v}; otherwise it returns {@code null}.
+ * (There can be at most one such mapping.)
+ *
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key is null
+ */
+ 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 the 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 the previous value associated with the specified key, or
+ * null if there was no mapping for the key
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key or value is null
+ */
+ public V put(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ return doPut(key, value, false);
+ }
+
+ /**
+ * Removes the mapping for the specified key from this map if present.
+ *
+ * @param key key for which mapping should be removed
+ * @return the previous value associated with the specified key, or
+ * null if there was no mapping for the key
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key is null
+ */
+ public V remove(Object key) {
+ return doRemove(key, null);
+ }
+
+ /**
+ * Returns true if this map maps one or more keys to the
+ * specified value. This operation requires time linear in the
+ * map size. Additionally, it is possible for the map to change
+ * during execution of this method, in which case the returned
+ * result may be inaccurate.
+ *
+ * @param value value whose presence in this map is to be tested
+ * @return true if a mapping to value exists;
+ * false otherwise
+ * @throws NullPointerException if the specified value is null
+ */
+ public boolean containsValue(Object value) {
+ if (value == null)
+ throw new NullPointerException();
+ for (Node 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 key-value mappings in this map. If this map
+ * contains more than Integer.MAX_VALUE elements, it
+ * returns Integer.MAX_VALUE.
+ *
+ * Beware that, unlike in most collections, this method is
+ * NOT a constant-time operation. Because of the
+ * asynchronous nature of these 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 n = findFirst(); n != null; n = n.next) {
+ if (n.getValidValue() != null)
+ ++count;
+ }
+ return (count >= Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int) count;
+ }
+
+ /**
+ * Returns true if this map contains no key-value mappings.
+ * @return true if this map contains no key-value mappings
+ */
+ public boolean isEmpty() {
+ return findFirst() == null;
+ }
+
+ /**
+ * Removes all of the mappings from this map.
+ */
+ public void clear() {
+ initialize();
+ }
+
+ /* ---------------- View methods -------------- */
+
+ /*
+ * Note: Lazy initialization works for 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.
+ */
+
+ /**
+ * Returns a {@link NavigableSet} view of the keys contained in this map.
+ * The set's iterator returns the keys in ascending 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 the map,
+ * via the {@code Iterator.remove}, {@code Set.remove},
+ * {@code removeAll}, {@code retainAll}, and {@code clear}
+ * operations. It does not support the {@code add} or {@code addAll}
+ * operations.
+ *
+ * The view's {@code iterator} is a "weakly consistent" iterator
+ * that will never throw {@link ConcurrentModificationException},
+ * and guarantees to traverse elements as they existed upon
+ * construction of the iterator, and may (but is not guaranteed to)
+ * reflect any modifications subsequent to construction.
+ *
+ *
This method is equivalent to method {@code navigableKeySet}.
+ *
+ * @return a navigable set view of the keys in this map
+ */
+ public NavigableSet keySet() {
+ KeySet ks = keySet;
+ return (ks != null) ? ks : (keySet = new KeySet(this));
+ }
+
+ public NavigableSet navigableKeySet() {
+ KeySet ks = keySet;
+ return (ks != null) ? ks : (keySet = new KeySet(this));
+ }
+
+ /**
+ * Returns a {@link Collection} view of the values contained in this map.
+ * The collection's iterator returns the values in ascending order
+ * of the corresponding keys.
+ * 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 Iterator.remove,
+ * Collection.remove, removeAll,
+ * retainAll and clear operations. It does not
+ * support the add or addAll operations.
+ *
+ * The view's iterator is a "weakly consistent" iterator
+ * that will never throw {@link ConcurrentModificationException},
+ * and guarantees to traverse elements as they existed upon
+ * construction of the iterator, and may (but is not guaranteed to)
+ * reflect any modifications subsequent to construction.
+ */
+ public Collection values() {
+ Values vs = values;
+ return (vs != null) ? vs : (values = new Values(this));
+ }
+
+ /**
+ * Returns a {@link Set} view of the mappings contained in this map.
+ * The set's iterator returns the entries in ascending key 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 the map,
+ * via the Iterator.remove, Set.remove,
+ * removeAll, retainAll and clear
+ * operations. It does not support the add or
+ * addAll operations.
+ *
+ * The view's iterator is a "weakly consistent" iterator
+ * that will never throw {@link ConcurrentModificationException},
+ * and guarantees to traverse elements as they existed upon
+ * construction of the iterator, and may (but is not guaranteed to)
+ * reflect any modifications subsequent to construction.
+ *
+ *
The Map.Entry elements returned by
+ * iterator.next() do not support the
+ * setValue operation.
+ *
+ * @return a set view of the mappings contained in this map,
+ * sorted in ascending key order
+ */
+ public Set> entrySet() {
+ EntrySet es = entrySet;
+ return (es != null) ? es : (entrySet = new EntrySet(this));
+ }
+
+ public ConcurrentNavigableMap descendingMap() {
+ ConcurrentNavigableMap dm = descendingMap;
+ return (dm != null) ? dm : (descendingMap = new SubMap
+ (this, null, false, null, false, true));
+ }
+
+ public NavigableSet descendingKeySet() {
+ return descendingMap().navigableKeySet();
+ }
+
+ /* ---------------- AbstractMap Overrides -------------- */
+
+ /**
+ * Compares the specified object with this map for equality.
+ * Returns true if the given object is also a map and the
+ * two maps represent the same mappings. More formally, two maps
+ * m1 and m2 represent the same mappings if
+ * m1.entrySet().equals(m2.entrySet()). 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 true 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 m = (Map) o;
+ try {
+ for (Map.Entry e : this.entrySet())
+ if (! e.getValue().equals(m.get(e.getKey())))
+ return false;
+ for (Map.Entry e : m.entrySet()) {
+ Object k = e.getKey();
+ Object v = e.getValue();
+ if (k == null || v == null || !v.equals(get(k)))
+ return false;
+ }
+ return true;
+ } catch (ClassCastException unused) {
+ return false;
+ } catch (NullPointerException unused) {
+ return false;
+ }
+ }
+
+ /* ------ ConcurrentMap API methods ------ */
+
+ /**
+ * {@inheritDoc}
+ *
+ * @return the previous value associated with the specified key,
+ * or null if there was no mapping for the key
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key or value is null
+ */
+ public V putIfAbsent(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ return doPut(key, value, true);
+ }
+
+ /**
+ * {@inheritDoc}
+ *
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key is null
+ */
+ public boolean remove(Object key, Object value) {
+ if (key == null)
+ throw new NullPointerException();
+ if (value == null)
+ return false;
+ return doRemove(key, value) != null;
+ }
+
+ /**
+ * {@inheritDoc}
+ *
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if any of the arguments are null
+ */
+ public boolean replace(K key, V oldValue, V newValue) {
+ if (oldValue == null || newValue == null)
+ throw new NullPointerException();
+ Comparable k = comparable(key);
+ for (;;) {
+ Node 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;
+ }
+ }
+ }
+
+ /**
+ * {@inheritDoc}
+ *
+ * @return the previous value associated with the specified key,
+ * or null if there was no mapping for the key
+ * @throws ClassCastException if the specified key cannot be compared
+ * with the keys currently in the map
+ * @throws NullPointerException if the specified key or value is null
+ */
+ public V replace(K key, V value) {
+ if (value == null)
+ throw new NullPointerException();
+ Comparable k = comparable(key);
+ for (;;) {
+ Node 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 ------ */
+
+ public Comparator comparator() {
+ return comparator;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public K firstKey() {
+ Node n = findFirst();
+ if (n == null)
+ throw new NoSuchElementException();
+ return n.key;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public K lastKey() {
+ Node n = findLast();
+ if (n == null)
+ throw new NoSuchElementException();
+ return n.key;
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap subMap(K fromKey,
+ boolean fromInclusive,
+ K toKey,
+ boolean toInclusive) {
+ if (fromKey == null || toKey == null)
+ throw new NullPointerException();
+ return new SubMap
+ (this, fromKey, fromInclusive, toKey, toInclusive, false);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code toKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap headMap(K toKey,
+ boolean inclusive) {
+ if (toKey == null)
+ throw new NullPointerException();
+ return new SubMap
+ (this, null, false, toKey, inclusive, false);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code fromKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap tailMap(K fromKey,
+ boolean inclusive) {
+ if (fromKey == null)
+ throw new NullPointerException();
+ return new SubMap
+ (this, fromKey, inclusive, null, false, false);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap subMap(K fromKey, K toKey) {
+ return subMap(fromKey, true, toKey, false);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code toKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap headMap(K toKey) {
+ return headMap(toKey, false);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if {@code fromKey} is null
+ * @throws IllegalArgumentException {@inheritDoc}
+ */
+ public ConcurrentNavigableMap tailMap(K fromKey) {
+ return tailMap(fromKey, true);
+ }
+
+ /* ---------------- Relational operations -------------- */
+
+ /**
+ * Returns a key-value mapping associated with the greatest key
+ * strictly less than the given key, or null if there is
+ * no such key. The returned entry does not support the
+ * Entry.setValue method.
+ *
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public Map.Entry lowerEntry(K key) {
+ return getNear(key, LT);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public K lowerKey(K key) {
+ Node 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 null if there
+ * is no such key. The returned entry does not support
+ * the Entry.setValue method.
+ *
+ * @param key the key
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public Map.Entry floorEntry(K key) {
+ return getNear(key, LT|EQ);
+ }
+
+ /**
+ * @param key the key
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public K floorKey(K key) {
+ Node n = findNear(key, LT|EQ);
+ return (n == null) ? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the least key
+ * greater than or equal to the given key, or null if
+ * there is no such entry. The returned entry does not
+ * support the Entry.setValue method.
+ *
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public Map.Entry ceilingEntry(K key) {
+ return getNear(key, GT|EQ);
+ }
+
+ /**
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public K ceilingKey(K key) {
+ Node n = findNear(key, GT|EQ);
+ return (n == null) ? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the least key
+ * strictly greater than the given key, or null if there
+ * is no such key. The returned entry does not support
+ * the Entry.setValue method.
+ *
+ * @param key the key
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public Map.Entry higherEntry(K key) {
+ return getNear(key, GT);
+ }
+
+ /**
+ * @param key the key
+ * @throws ClassCastException {@inheritDoc}
+ * @throws NullPointerException if the specified key is null
+ */
+ public K higherKey(K key) {
+ Node n = findNear(key, GT);
+ return (n == null) ? null : n.key;
+ }
+
+ /**
+ * Returns a key-value mapping associated with the least
+ * key in this map, or null if the map is empty.
+ * The returned entry does not support
+ * the Entry.setValue method.
+ */
+ public Map.Entry firstEntry() {
+ for (;;) {
+ Node n = findFirst();
+ if (n == null)
+ return null;
+ AbstractMap.SimpleImmutableEntry e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ /**
+ * Returns a key-value mapping associated with the greatest
+ * key in this map, or null if the map is empty.
+ * The returned entry does not support
+ * the Entry.setValue method.
+ */
+ public Map.Entry lastEntry() {
+ for (;;) {
+ Node n = findLast();
+ if (n == null)
+ return null;
+ AbstractMap.SimpleImmutableEntry e = n.createSnapshot();
+ if (e != null)
+ return e;
+ }
+ }
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the least key in this map, or null if the map is empty.
+ * The returned entry does not support
+ * the Entry.setValue method.
+ */
+ public Map.Entry pollFirstEntry() {
+ return doRemoveFirstEntry();
+ }
+
+ /**
+ * Removes and returns a key-value mapping associated with
+ * the greatest key in this map, or null if the map is empty.
+ * The returned entry does not support
+ * the Entry.setValue method.
+ */
+ public Map.Entry pollLastEntry() {
+ return doRemoveLastEntry();
+ }
+
+
+ /* ---------------- Iterators -------------- */
+
+ /**
+ * Base of iterator classes:
+ */
+ abstract class Iter implements Iterator {
+ /** the last node returned by next() */
+ Node lastReturned;
+ /** the next node to return from next(); */
+ Node next;
+ /** Cache of next value field to maintain weak consistency */
+ V nextValue;
+
+ /** Initializes ascending iterator for entire range. */
+ Iter() {
+ for (;;) {
+ next = findFirst();
+ if (next == null)
+ break;
+ Object x = next.value;
+ if (x != null && x != next) {
+ nextValue = (V) x;
+ break;
+ }
+ }
+ }
+
+ public final boolean hasNext() {
+ return next != null;
+ }
+
+ /** Advances next to higher entry. */
+ final void advance() {
+ if (next == null)
+ throw new NoSuchElementException();
+ lastReturned = next;
+ for (;;) {
+ next = next.next;
+ if (next == null)
+ break;
+ Object x = next.value;
+ if (x != null && x != next) {
+ nextValue = (V) x;
+ break;
+ }
+ }
+ }
+
+ public void remove() {
+ Node l = lastReturned;
+ 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);
+ lastReturned = null;
+ }
+
+ }
+
+ final class ValueIterator extends Iter {
+ public V next() {
+ V v = nextValue;
+ advance();
+ return v;
+ }
+ }
+
+ final class KeyIterator extends Iter {
+ public K next() {
+ Node n = next;
+ advance();
+ return n.key;
+ }
+ }
+
+ final class EntryIterator extends Iter> {
+ public Map.Entry next() {
+ Node n = next;
+ V v = nextValue;
+ advance();
+ return new AbstractMap.SimpleImmutableEntry(n.key, v);
+ }
+ }
+
+ // Factory methods for iterators needed by ConcurrentSkipListSet etc
+
+ Iterator keyIterator() {
+ return new KeyIterator();
+ }
+
+ Iterator valueIterator() {
+ return new ValueIterator();
+ }
+
+ Iterator> entryIterator() {
+ return new EntryIterator();
+ }
+
+ /* ---------------- View Classes -------------- */
+
+ /*
+ * View classes are static, delegating to a ConcurrentNavigableMap
+ * to allow use by SubMaps, which outweighs the ugliness of
+ * needing type-tests for Iterator methods.
+ */
+
+ static final List toList(Collection c) {
+ // Using size() here would be a pessimization.
+ List list = new ArrayList();
+ for (E e : c)
+ list.add(e);
+ return list;
+ }
+
+ static final class KeySet
+ extends AbstractSet implements NavigableSet {
+ private final ConcurrentNavigableMap m;
+ KeySet(ConcurrentNavigableMap map) { m = map; }
+ public int size() { return m.size(); }
+ public boolean isEmpty() { return m.isEmpty(); }
+ public boolean contains(Object o) { return m.containsKey(o); }
+ public boolean remove(Object o) { return m.remove(o) != null; }
+ public void clear() { m.clear(); }
+ public E lower(E e) { return m.lowerKey(e); }
+ public E floor(E e) { return m.floorKey(e); }
+ public E ceiling(E e) { return m.ceilingKey(e); }
+ public E higher(E e) { return m.higherKey(e); }
+ public Comparator comparator() { return m.comparator(); }
+ public E first() { return m.firstKey(); }
+ public E last() { return m.lastKey(); }
+ public E pollFirst() {
+ Map.Entry e = m.pollFirstEntry();
+ return (e == null) ? null : e.getKey();
+ }
+ public E pollLast() {
+ Map.Entry e = m.pollLastEntry();
+ return (e == null) ? null : e.getKey();
+ }
+ public Iterator iterator() {
+ if (m instanceof ConcurrentSkipListMap)
+ return ((ConcurrentSkipListMap)m).keyIterator();
+ else
+ return ((ConcurrentSkipListMap.SubMap)m).keyIterator();
+ }
+ public boolean equals(Object o) {
+ if (o == this)
+ return true;
+ if (!(o instanceof Set))
+ return false;
+ Collection c = (Collection) o;
+ try {
+ return containsAll(c) && c.containsAll(this);
+ } catch (ClassCastException unused) {
+ return false;
+ } catch (NullPointerException unused) {
+ return false;
+ }
+ }
+ public Object[] toArray() { return toList(this).toArray(); }
+ public T[] toArray(T[] a) { return toList(this).toArray(a); }
+ public Iterator descendingIterator() {
+ return descendingSet().iterator();
+ }
+ public NavigableSet subSet(E fromElement,
+ boolean fromInclusive,
+ E toElement,
+ boolean toInclusive) {
+ return new KeySet(m.subMap(fromElement, fromInclusive,
+ toElement, toInclusive));
+ }
+ public NavigableSet headSet(E toElement, boolean inclusive) {
+ return new KeySet(m.headMap(toElement, inclusive));
+ }
+ public NavigableSet tailSet(E fromElement, boolean inclusive) {
+ return new KeySet(m.tailMap(fromElement, inclusive));
+ }
+ public NavigableSet subSet(E fromElement, E toElement) {
+ return subSet(fromElement, true, toElement, false);
+ }
+ public NavigableSet headSet(E toElement) {
+ return headSet(toElement, false);
+ }
+ public NavigableSet tailSet(E fromElement) {
+ return tailSet(fromElement, true);
+ }
+ public NavigableSet descendingSet() {
+ return new KeySet(m.descendingMap());
+ }
+ }
+
+ static final class Values extends AbstractCollection {
+ private final ConcurrentNavigableMap m;
+ Values(ConcurrentNavigableMap map) {
+ m = map;
+ }
+ public Iterator iterator() {
+ if (m instanceof ConcurrentSkipListMap)
+ return ((ConcurrentSkipListMap)m).valueIterator();
+ else
+ return ((SubMap)m).valueIterator();
+ }
+ public boolean isEmpty() {
+ return m.isEmpty();
+ }
+ public int size() {
+ return m.size();
+ }
+ public boolean contains(Object o) {
+ return m.containsValue(o);
+ }
+ public void clear() {
+ m.clear();
+ }
+ public Object[] toArray() { return toList(this).toArray(); }
+ public T[] toArray(T[] a) { return toList(this).toArray(a); }
+ }
+
+ static final class EntrySet extends AbstractSet> {
+ private final ConcurrentNavigableMap m;
+ EntrySet(ConcurrentNavigableMap map) {
+ m = map;
+ }
+
+ public Iterator> iterator() {
+ if (m instanceof ConcurrentSkipListMap)
+ return ((ConcurrentSkipListMap)m).entryIterator();
+ else
+ return ((SubMap)m).entryIterator();
+ }
+
+ public boolean contains(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry e = (Map.Entry)o;
+ V1 v = m.get(e.getKey());
+ return v != null && v.equals(e.getValue());
+ }
+ public boolean remove(Object o) {
+ if (!(o instanceof Map.Entry))
+ return false;
+ Map.Entry e = (Map.Entry)o;
+ return m.remove(e.getKey(),
+ e.getValue());
+ }
+ public boolean isEmpty() {
+ return m.isEmpty();
+ }
+ public int size() {
+ return m.size();
+ }
+ public void clear() {
+ m.clear();
+ }
+ public boolean equals(Object o) {
+ if (o == this)
+ return true;
+ if (!(o instanceof Set))
+ return false;
+ Collection c = (Collection) o;
+ try {
+ return containsAll(c) && c.containsAll(this);
+ } catch (ClassCastException unused) {
+ return false;
+ } catch (NullPointerException unused) {
+ return false;
+ }
+ }
+ public Object[] toArray() { return toList(this).toArray(); }
+ public T[] toArray(T[] a) { return toList(this).toArray(a); }
+ }
+
+ /**
+ * 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 subMap, headMap, and
+ * tailMap methods of their underlying maps.
+ *
+ * @serial include
+ */
+ static final class SubMap extends AbstractMap
+ implements ConcurrentNavigableMap