/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package jsr166x;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
/**
* A scalable {@link ConcurrentNavigableMap} implementation. This
* class maintains a map in ascending key order, sorted according to
* the natural order for the key's class (see {@link
* Comparable}), or by the {@link Comparator} provided at 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
* {@code containsKey}, {@code get}, {@code put} and
* {@code 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 {@code 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 {@code Entry.setValue}
* method. (Note however that it is possible to change mappings in the
* associated map using {@code put}, {@code putIfAbsent}, or
* {@code replace}, depending on exactly which effect you need.)
*
*
Beware that, unlike in most collections, the {@code 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. Additionally,
* the bulk operations {@code putAll}, {@code equals}, and
* {@code clear} are not guaranteed to be performed
* atomically. For example, an iterator operating concurrently with a
* {@code 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 {@code null} keys or values because some
* null return values cannot be reliably distinguished from the
* absence of elements.
*
* @author Doug Lea
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
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;
/**
* 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 order.
* @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 DescendingKeySet descendingKeySet;
/** Lazily initialized descending entry set */
private transient DescendingEntrySet descendingEntrySet;
/**
* 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;
descendingEntrySet = null;
descendingKeySet = null;
randomSeed = (int) System.nanoTime();
head = new HeadIndex(new Node(null, BASE_HEADER, null),
null, null, 1);
}
/** Updater for casHead */
private static final
AtomicReferenceFieldUpdater
headUpdater = AtomicReferenceFieldUpdater.newUpdater
(ConcurrentSkipListMap.class, HeadIndex.class, "head");
/**
* compareAndSet head node
*/
private boolean casHead(HeadIndex cmp, HeadIndex 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 {
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;
}
/** Updater for casNext */
static final AtomicReferenceFieldUpdater
nextUpdater = AtomicReferenceFieldUpdater.newUpdater
(Node.class, Node.class, "next");
/** Updater for casValue */
static final AtomicReferenceFieldUpdater
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 cmp, Node val) {
return nextUpdater.compareAndSet(this, cmp, val);
}
/**
* Returns 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;
}
/**
* 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 SnapshotEntry holding current
* mapping if this node holds a valid value, else null.
* @return new entry or null
*/
SnapshotEntry 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 {
final K key;
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.key = node.key;
this.down = down;
this.right = right;
}
/** Updater for casRight */
static final AtomicReferenceFieldUpdater
rightUpdater = AtomicReferenceFieldUpdater.newUpdater
(Index.class, Index.class, "right");
/**
* compareAndSet right field
*/
final boolean casRight(Index cmp, Index 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 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);
}
}
/* ---------------- 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;
}
}
/* ---------------- Map.Entry support -------------- */
/**
* An immutable representation of a key-value mapping as it
* existed at some point in time. This class does not
* support the {@code Map.Entry.setValue} method.
*/
static class SnapshotEntry implements Map.Entry {
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 {@code UnsupportedOperationException}.
* @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 ({@code "="}) 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 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 Comparator, which may cause ClassCastException,
* which is propagated back to caller.
*/
private Comparable comparable(Object key) throws ClassCastException {
if (key == null)
throw new NullPointerException();
return (comparator != null)
? new ComparableUsingComparator(key, comparator)
: (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) {
for (;;) {
Index q = head;
for (;;) {
Index 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;
}
}
}
/**
* 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 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 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 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 key = comparable(okey);
K bound = null;
Index q = head;
for (;;) {
K rk;
Index 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 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;
}
}
}
/**
* Performs 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 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 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.
*
* 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;
}
/**
* Creates and adds index nodes for 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.key);
// Similar to findPredecessor, but adding index nodes along
// path to key.
for (;;) {
Index q = h;
Index t = idx;
int j = h.level;
for (;;) {
Index 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 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
}
/**
* 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 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; 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 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();
K key = n.key;
return keyOnly ? key : new SnapshotEntry(key, (V)v);
}
}
/**
* Clears out index nodes associated with deleted first entry.
* Needed by doRemoveFirst.
*/
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;
}
}
}
}
/**
* Removes 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 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 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 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 keyOnly ? key : new SnapshotEntry(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 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; 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 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 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 getNear(K kkey, int rel) {
for (;;) {
Node n = findNear(kkey, rel);
if (n == null)
return null;
SnapshotEntry e = n.createSnapshot();
if (e != null)
return e;
}
}
/**
* Returns ceiling, or first node if key is {@code null}.
*/
Node findCeiling(K key) {
return (key == null) ? findFirst() : findNear(key, GT|EQ);
}
/**
* Returns lower node, or last node if key is {@code null}.
*/
Node findLower(K key) {
return (key == null) ? findLast() : findNear(key, LT);
}
/**
* Returns 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 {@code null} 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 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);
}
}
/**
* Finds and removes 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 {@code null} if no such
*/
Object removeFirstEntryOfSubrange(K least, K fence, boolean keyOnly) {
for (;;) {
Node 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);
}
}
/**
* Finds and removes 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 {@code null} if no such
*/
Object removeLastEntryOfSubrange(K least, K fence, boolean keyOnly) {
for (;;) {
Node 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);
}
}
/* ---------------- 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
* {@code null} value indicates that the keys' natural
* ordering should be used.
*/
public ConcurrentSkipListMap(Comparator c) {
this.comparator = c;
initialize();
}
/**
* Constructs a new map containing the same mappings as the given map,
* sorted according to the keys' natural order.
*
* @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 {@code null}
*/
public ConcurrentSkipListMap(Map m) {
this.comparator = null;
initialize();
putAll(m);
}
/**
* Constructs a new map containing the same mappings as the given
* {@code SortedMap}, 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
* {@code null}.
*/
public ConcurrentSkipListMap(SortedMap m) {
this.comparator = m.comparator();
initialize();
buildFromSorted(m);
}
/**
* Returns a shallow copy of this {@code Map} instance. (The keys and
* values themselves are not cloned.)
*
* @return a shallow copy of this Map
*/
public Object 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 -------------- */
/**
* Saves the state of the {@code Map} instance to a stream.
*
* @serialData The key (Object) and value (Object) for each
* key-value mapping represented by the Map, followed by
* {@code 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);
}
/**
* Reconstitutes the {@code Map} 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 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 {@code true} if this map contains a mapping for the specified
* key.
* @param key key whose presence in this map is to be tested
* @return {@code true} 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 {@code null}
*/
public boolean containsKey(Object key) {
return doGet(key) != null;
}
/**
* Returns the value to which this map maps the specified key. Returns
* {@code null} 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
* {@code null} 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 {@code 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 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 {@code null}
* 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 {@code null}
*/
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 {@code null}
* 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 {@code null}
*/
public V remove(Object key) {
return doRemove(key, null);
}
/**
* Returns {@code true} 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 {@code true} if a mapping to {@code value} exists;
* {@code false} otherwise
* @throws NullPointerException if the value is {@code 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 elements in this map. If this map
* contains more than {@code Integer.MAX_VALUE} elements, it
* returns {@code Integer.MAX_VALUE}.
*
* Beware that, unlike in most collections, this method is
* NOT a constant-time operation. Because of the
* 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 {@code true} if this map contains no key-value mappings.
* @return {@code true} 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 {@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 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 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 {@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 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 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 {@code Iterator.remove},
* {@code Collection.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
* 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 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
* {@code Map.Entry}. 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
* {@code Iterator.remove}, {@code Collection.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
* 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
* {@code Map.Entry} elements returned by
* {@code iterator.next()} do not support the
* {@code setValue} operation.
*
* @return a collection view of the mappings contained in this map
*/
public Set> 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 {@code Map.Entry}. 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 {@code Iterator.remove}, {@code Collection.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
* 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
* {@code Map.Entry} elements returned by
* {@code iterator.next()} do not support the
* {@code setValue} operation.
*
* @return a collection view of the mappings contained in this map
*/
public Set> descendingEntrySet() {
DescendingEntrySet es = descendingEntrySet;
return (es != null) ? es : (descendingEntrySet = new DescendingEntrySet());
}
/* ---------------- AbstractMap Overrides -------------- */
/**
* Compares the specified object with this map for equality.
* Returns {@code true} if the given object is also a map and the
* two maps represent the same mappings. More formally, two maps
* {@code t1} and {@code t2} represent the same mappings if
* {@code t1.keySet().equals(t2.keySet())} and for every key
* {@code k} in {@code t1.keySet()}, {@code (t1.get(k)==null ?
* t2.get(k)==null : t1.get(k).equals(t2.get(k))) }. 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 {@code 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 t = (Map) 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 boolean containsAllMappings(Map a, Map b) {
Iterator> it = b.entrySet().iterator();
while (it.hasNext()) {
Entry 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
*
* if (!map.containsKey(key))
* return map.put(key, value);
* else
* return map.get(key);
*
* 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 {@code null}
* 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 {@code null}
*/
public V putIfAbsent(K key, V value) {
if (value == null)
throw new NullPointerException();
return doPut(key, value, true);
}
/**
* Removes entry for key only if currently mapped to given value.
* Acts as
*
* if ((map.containsKey(key) && map.get(key).equals(value)) {
* map.remove(key);
* return true;
* } else return false;
*
* 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 {@code null}
*/
public boolean remove(Object key, Object value) {
if (value == null)
throw new NullPointerException();
return doRemove(key, value) != null;
}
/**
* Replaces entry for key only if currently mapped to given value.
* Acts as
*
* if ((map.containsKey(key) && map.get(key).equals(oldValue)) {
* map.put(key, newValue);
* return true;
* } else return false;
*
* 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
* {@code 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;
}
}
}
/**
* Replaces entry for key only if currently mapped to some value.
* Acts as
*
* if ((map.containsKey(key)) {
* return map.put(key, value);
* } else return null;
*
* 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 {@code null}
* 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 {@code 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 ------ */
/**
* Returns the comparator used to order this map, or {@code null}
* if this map uses its keys' natural order.
*
* @return the comparator associated with this map, or
* {@code null} if it uses its keys' natural sort method.
*/
public Comparator 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 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 n = findLast();
if (n == null)
throw new NoSuchElementException();
return n.key;
}
/**
* Returns a view of the portion of this map whose keys range from
* {@code fromKey}, inclusive, to {@code toKey}, exclusive. (If
* {@code fromKey} and {@code toKey} 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
* {@code fromKey}, inclusive, to {@code toKey}, exclusive
*
* @throws ClassCastException if {@code fromKey} and {@code toKey}
* cannot be compared to one another using this map's comparator
* (or, if the map has no comparator, using natural ordering)
* @throws IllegalArgumentException if {@code fromKey} is greater than
* {@code toKey}
* @throws NullPointerException if {@code fromKey} or {@code toKey} is
* {@code null}
*/
public ConcurrentNavigableMap 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 {@code toKey}. 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 {@code toKey}
*
* @throws ClassCastException if {@code toKey} is not compatible
* with this map's comparator (or, if the map has no comparator,
* if {@code toKey} does not implement {@code Comparable})
* @throws NullPointerException if {@code toKey} is {@code null}
*/
public ConcurrentNavigableMap 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 {@code fromKey}. 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 {@code fromKey}
* @throws ClassCastException if {@code fromKey} is not
* compatible with this map's comparator (or, if the map has no
* comparator, if {@code fromKey} does not implement
* {@code Comparable})
* @throws NullPointerException if {@code fromKey} is {@code null}
*/
public ConcurrentNavigableMap 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 {@code null} if
* there is no such entry. The returned entry does not
* support the {@code Entry.setValue} method.
*
* @param key the key
* @return an Entry associated with ceiling of given key, or
* {@code null} 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 {@code null}
*/
public Map.Entry ceilingEntry(K key) {
return getNear(key, GT|EQ);
}
/**
* Returns least key greater than or equal to the given key, or
* {@code null} if there is no such key.
*
* @param key the key
* @return the ceiling key, or {@code null}
* 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 {@code 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 greatest
* key strictly less than the given key, or {@code null} if there is no
* such entry. The returned entry does not support
* the {@code Entry.setValue} method.
*
* @param key the key
* @return an Entry with greatest key less than the given
* key, or {@code null} 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 {@code null}
*/
public Map.Entry lowerEntry(K key) {
return getNear(key, LT);
}
/**
* Returns the greatest key strictly less than the given key, or
* {@code null} if there is no such key.
*
* @param key the key
* @return the greatest key less than the given
* key, or {@code null} 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 {@code 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 {@code null} if there
* is no such entry. The returned entry does not support
* the {@code Entry.setValue} method.
*
* @param key the key
* @return an Entry associated with floor of given key, or {@code null}
* 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 {@code null}
*/
public Map.Entry floorEntry(K key) {
return getNear(key, LT|EQ);
}
/**
* Returns the greatest key
* less than or equal to the given key, or {@code null} if there
* is no such key.
*
* @param key the key
* @return the floor of given key, or {@code null} 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 {@code 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
* strictly greater than the given key, or {@code null} if there
* is no such entry. The returned entry does not support
* the {@code Entry.setValue} method.
*
* @param key the key
* @return an Entry with least key greater than the given key, or
* {@code null} 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 {@code null}
*/
public Map.Entry higherEntry(K key) {
return getNear(key, GT);
}
/**
* Returns the least key strictly greater than the given key, or
* {@code null} if there is no such key.
*
* @param key the key
* @return the least key greater than the given key, or
* {@code null} 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 {@code 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 {@code null} if the map is empty.
* The returned entry does not support
* the {@code Entry.setValue} method.
*
* @return an Entry with least key, or {@code null}
* if the map is empty
*/
public Map.Entry firstEntry() {
for (;;) {
Node n = findFirst();
if (n == null)
return null;
SnapshotEntry e = n.createSnapshot();
if (e != null)
return e;
}
}
/**
* Returns a key-value mapping associated with the greatest
* key in this map, or {@code null} if the map is empty.
* The returned entry does not support
* the {@code Entry.setValue} method.
*
* @return an Entry with greatest key, or {@code null}
* if the map is empty
*/
public Map.Entry lastEntry() {
for (;;) {
Node n = findLast();
if (n == null)
return null;
SnapshotEntry e = n.createSnapshot();
if (e != null)
return e;
}
}
/**
* Removes and returns a key-value mapping associated with
* the least key in this map, or {@code null} if the map is empty.
* The returned entry does not support
* the {@code Entry.setValue} method.
*
* @return the removed first entry of this map, or {@code null}
* if the map is empty
*/
public Map.Entry pollFirstEntry() {
return (SnapshotEntry)doRemoveFirst(false);
}
/**
* Removes and returns a key-value mapping associated with
* the greatest key in this map, or {@code null} if the map is empty.
* The returned entry does not support
* the {@code Entry.setValue} method.
*
* @return the removed last entry of this map, or {@code null}
* if the map is empty
*/
public Map.Entry pollLastEntry() {
return (SnapshotEntry)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 last;
/** the next node to return from next(); */
Node 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 {@code null}, but not greater or
* equal to fence, or end if fence is {@code null}.
*/
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 {@code null}, but not less than
* least, or beginning if lest is {@code null}.
*/
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 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 {
ValueIterator() {
initAscending();
}
public V next() {
Object v = nextValue;
ascend();
return (V)v;
}
}
final class KeyIterator extends Iter implements Iterator {
KeyIterator() {
initAscending();
}
public K next() {
Node n = next;
ascend();
return n.key;
}
}
class SubMapValueIterator extends Iter implements Iterator {
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 {
final K fence;
SubMapKeyIterator(K least, K fence) {
initAscending(least, fence);
this.fence = fence;
}
public K next() {
Node n = next;
ascend(fence);
return n.key;
}
}
final class DescendingKeyIterator extends Iter implements Iterator {
DescendingKeyIterator() {
initDescending();
}
public K next() {
Node n = next;
descend();
return n.key;
}
}
final class DescendingSubMapKeyIterator extends Iter implements Iterator {
final K least;
DescendingSubMapKeyIterator(K least, K fence) {
initDescending(least, fence);
this.least = least;
}
public K next() {
Node 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 {
/** Cache of last value returned */
Object lastValue;
EntryIter() {
}
public K getKey() {
Node 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> {
EntryIterator() {
initAscending();
}
public Map.Entry next() {
lastValue = nextValue;
ascend();
return this;
}
}
final class SubMapEntryIterator extends EntryIter
implements Iterator> {
final K fence;
SubMapEntryIterator(K least, K fence) {
initAscending(least, fence);
this.fence = fence;
}
public Map.Entry next() {
lastValue = nextValue;
ascend(fence);
return this;
}
}
final class DescendingEntryIterator extends EntryIter
implements Iterator> {
DescendingEntryIterator() {
initDescending();
}
public Map.Entry next() {
lastValue = nextValue;
descend();
return this;
}
}
final class DescendingSubMapEntryIterator extends EntryIter
implements Iterator> {
final K least;
DescendingSubMapEntryIterator(K least, K fence) {
initDescending(least, fence);
this.least = least;
}
public Map.Entry next() {
lastValue = nextValue;
descend(least);
return this;
}
}
// Factory methods for iterators needed by submaps and/or
// ConcurrentSkipListSet
Iterator keyIterator() {
return new KeyIterator();
}
Iterator 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 {
public Iterator 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 c = new ArrayList();
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray();
}
public T[] toArray(T[] a) {
Collection c = new ArrayList();
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray(a);
}
}
class DescendingKeySet extends KeySet {
public Iterator iterator() {
return new DescendingKeyIterator();
}
}
final class Values extends AbstractCollection {
public Iterator 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 c = new ArrayList();
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray();
}
public T[] toArray(T[] a) {
Collection c = new ArrayList();
for (Iterator i = iterator(); i.hasNext(); )
c.add(i.next());
return c.toArray(a);
}
}
class EntrySet extends AbstractSet> {
public Iterator> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry