JDK8/Java8源码在线阅读
/*
* 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.
*
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/*
* 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.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NavigableMap;
import java.util.NavigableSet;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.BiConsumer;
import java.util.function.Function;
/**
* 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.
*
* <p>This class implements a concurrent variant of <a
* href="http://en.wikipedia.org/wiki/Skip_list" target="_top">SkipLists</a>
* providing expected average <i>log(n)</i> 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.
*
* <p>Iterators and spliterators are
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>Ascending key ordered views and their iterators are faster than
* descending ones.
*
* <p>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 <em>not</em> 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.)
*
* <p>Beware that, unlike in most collections, the {@code size}
* method is <em>not</em> a constant-time operation. Because of the
* asynchronous nature of these 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 {@code putAll}, {@code equals},
* {@code toArray}, {@code containsValue}, and {@code clear} are
* <em>not</em> guaranteed to be performed atomically. For example, an
* iterator operating concurrently with a {@code putAll} operation
* might view only some of the added elements.
*
* <p>This class and its views and iterators implement all of the
* <em>optional</em> methods of the {@link Map} and {@link Iterator}
* interfaces. Like most other concurrent collections, this class does
* <em>not</em> permit the use of {@code null} keys or values because some
* null return values cannot be reliably distinguished from the absence of
* elements.
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @author Doug Lea
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
* @since 1.6
*/
public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V>
implements ConcurrentNavigableMap<K,V>, Cloneable, 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 occurring 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 doPut) 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.
*
* To produce random values without interference across threads,
* we use within-JDK thread local random support (via the
* "secondary seed", to avoid interference with user-level
* ThreadLocalRandom.)
*
* A previous version of this class wrapped non-comparable keys
* with their comparators to emulate Comparables when using
* comparators vs Comparables. However, JVMs now appear to better
* handle infusing comparator-vs-comparable choice into search
* loops. Static method cpr(comparator, x, y) is used for all
* comparisons, which works well as long as the comparator
* argument is set up outside of loops (thus sometimes passed as
* an argument to internal methods) to avoid field re-reads.
*
* For explanation of algorithms sharing at least a couple of
* features with this one, see Mikhail Fomitchev's thesis
* (http://www.cs.yorku.ca/~mikhail/), Keir Fraser's thesis
* (http://www.cl.cam.ac.uk/users/kaf24/), and Hakan Sundell's
* thesis (http://www.cs.chalmers.se/~phs/).
*
* Given the use of tree-like index nodes, you might wonder why
* this doesn't use some kind of search tree instead, which would
* support somewhat faster search operations. The reason is that
* there are no known efficient lock-free insertion and deletion
* algorithms for search trees. The immutability of the "down"
* links of index nodes (as opposed to mutable "left" fields in
* true trees) makes this tractable using only CAS operations.
*
* Notation guide for local variables
* Node: b, n, f for predecessor, node, successor
* Index: q, r, d for index node, right, down.
* t for another index node
* Head: h
* Levels: j
* Keys: k, key
* Values: v, value
* Comparisons: c
*/
private static final long serialVersionUID = -8627078645895051609L;
/**
* Special value used to identify base-level header
*/
private static final Object BASE_HEADER = new Object();
/**
* The topmost head index of the skiplist.
*/
private transient volatile HeadIndex<K,V> head;
/**
* The comparator used to maintain order in this map, or null if
* using natural ordering. (Non-private to simplify access in
* nested classes.)
* @serial
*/
final Comparator<? super K> comparator;
/** Lazily initialized key set */
private transient KeySet<K> keySet;
/** Lazily initialized entry set */
private transient EntrySet<K,V> entrySet;
/** Lazily initialized values collection */
private transient Values<V> values;
/** Lazily initialized descending key set */
private transient ConcurrentNavigableMap<K,V> descendingMap;
/**
* Initializes or resets state. Needed by constructors, clone,
* clear, readObject. and ConcurrentSkipListSet.clone.
* (Note that comparator must be separately initialized.)
*/
private void initialize() {
keySet = null;
entrySet = null;
values = null;
descendingMap = null;
head = new HeadIndex<K,V>(new Node<K,V>(null, BASE_HEADER, null),
null, null, 1);
}
/**
* compareAndSet head node
*/
private boolean casHead(HeadIndex<K,V> cmp, HeadIndex<K,V> 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<K,V> {
final K key;
volatile Object value;
volatile Node<K,V> next;
/**
* Creates a new regular node.
*/
Node(K key, Object value, Node<K,V> next) {
this.key = key;
this.value = value;
this.next = next;
}
/**
* Creates a new marker node. A marker is distinguished by
* having its value field point to itself. Marker nodes also
* have null keys, a fact that is exploited in a few places,
* but this doesn't distinguish markers from the base-level
* header node (head.node), which also has a null key.
*/
Node(Node<K,V> next) {
this.key = null;
this.value = this;
this.next = next;
}
/**
* compareAndSet value field
*/
boolean casValue(Object cmp, Object val) {
return UNSAFE.compareAndSwapObject(this, valueOffset, cmp, val);
}
/**
* compareAndSet next field
*/
boolean casNext(Node<K,V> cmp, Node<K,V> 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.
*
* @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<K,V> f) {
return casNext(f, new Node<K,V>(f));
}
/**
* Helps out a deletion by appending marker or unlinking from
* predecessor. This is called during traversals when value
* field seen to be null.
* @param b predecessor
* @param f successor
*/
void helpDelete(Node<K,V> b, Node<K,V> f) {
/*
* Rechecking links and then doing only one of the
* help-out stages per call tends to minimize CAS
* interference among helping threads.
*/
if (f == next && this == b.next) {
if (f == null || f.value != f) // not already marked
casNext(f, new Node<K,V>(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;
@SuppressWarnings("unchecked") V vv = (V)v;
return vv;
}
/**
* 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<K,V> createSnapshot() {
Object v = value;
if (v == null || v == this || v == BASE_HEADER)
return null;
@SuppressWarnings("unchecked") V vv = (V)v;
return new AbstractMap.SimpleImmutableEntry<K,V>(key, vv);
}
// 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<K,V> {
final Node<K,V> node;
final Index<K,V> down;
volatile Index<K,V> right;
/**
* Creates index node with given values.
*/
Index(Node<K,V> node, Index<K,V> down, Index<K,V> right) {
this.node = node;
this.down = down;
this.right = right;
}
/**
* compareAndSet right field
*/
final boolean casRight(Index<K,V> cmp, Index<K,V> 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<K,V> succ, Index<K,V> newSucc) {
Node<K,V> n = node;
newSucc.right = succ;
return n.value != null && casRight(succ, newSucc);
}
/**
* Tries to CAS right field to skip over apparent successor
* succ. Fails (forcing a retraversal by caller) if this node
* is known to be deleted.
* @param succ the expected current successor
* @return true if successful
*/
final boolean unlink(Index<K,V> succ) {
return node.value != null && 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<K,V> extends Index<K,V> {
final int level;
HeadIndex(Node<K,V> node, Index<K,V> down, Index<K,V> right, int level) {
super(node, down, right);
this.level = level;
}
}
/* ---------------- Comparison utilities -------------- */
/**
* Compares using comparator or natural ordering if null.
* Called only by methods that have performed required type checks.
*/
@SuppressWarnings({"unchecked", "rawtypes"})
static final int cpr(Comparator c, Object x, Object y) {
return (c != null) ? c.compare(x, y) : ((Comparable)x).compareTo(y);
}
/* ---------------- 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<K,V> findPredecessor(Object key, Comparator<? super K> cmp) {
if (key == null)
throw new NullPointerException(); // don't postpone errors
for (;;) {
for (Index<K,V> q = head, r = q.right, d;;) {
if (r != null) {
Node<K,V> n = r.node;
K k = n.key;
if (n.value == null) {
if (!q.unlink(r))
break; // restart
r = q.right; // reread r
continue;
}
if (cpr(cmp, key, k) > 0) {
q = r;
r = r.right;
continue;
}
}
if ((d = q.down) == null)
return q.node;
q = d;
r = d.right;
}
}
}
/**
* 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<K,V> findNode(Object key) {
if (key == null)
throw new NullPointerException(); // don't postpone errors
Comparator<? super K> cmp = comparator;
outer: for (;;) {
for (Node<K,V> b = findPredecessor(key, cmp), n = b.next;;) {
Object v; int c;
if (n == null)
break outer;
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
if ((v = n.value) == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
if ((c = cpr(cmp, key, n.key)) == 0)
return n;
if (c < 0)
break outer;
b = n;
n = f;
}
}
return null;
}
/**
* Gets value for key. Almost the same as findNode, but returns
* the found value (to avoid retries during re-reads)
*
* @param key the key
* @return the value, or null if absent
*/
private V doGet(Object key) {
if (key == null)
throw new NullPointerException();
Comparator<? super K> cmp = comparator;
outer: for (;;) {
for (Node<K,V> b = findPredecessor(key, cmp), n = b.next;;) {
Object v; int c;
if (n == null)
break outer;
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
if ((v = n.value) == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
if ((c = cpr(cmp, key, n.key)) == 0) {
@SuppressWarnings("unchecked") V vv = (V)v;
return vv;
}
if (c < 0)
break outer;
b = n;
n = f;
}
}
return null;
}
/* ---------------- Insertion -------------- */
/**
* Main insertion method. Adds element if not present, or
* replaces value if present and onlyIfAbsent is false.
* @param key 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 key, V value, boolean onlyIfAbsent) {
Node<K,V> z; // added node
if (key == null)
throw new NullPointerException();
Comparator<? super K> cmp = comparator;
outer: for (;;) {
for (Node<K,V> b = findPredecessor(key, cmp), n = b.next;;) {
if (n != null) {
Object v; int c;
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
if ((v = n.value) == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
if ((c = cpr(cmp, key, n.key)) > 0) {
b = n;
n = f;
continue;
}
if (c == 0) {
if (onlyIfAbsent || n.casValue(v, value)) {
@SuppressWarnings("unchecked") V vv = (V)v;
return vv;
}
break; // restart if lost race to replace value
}
// else c < 0; fall through
}
z = new Node<K,V>(key, value, n);
if (!b.casNext(n, z))
break; // restart if lost race to append to b
break outer;
}
}
int rnd = ThreadLocalRandom.nextSecondarySeed();
if ((rnd & 0x80000001) == 0) { // test highest and lowest bits
int level = 1, max;
while (((rnd >>>= 1) & 1) != 0)
++level;
Index<K,V> idx = null;
HeadIndex<K,V> h = head;
if (level <= (max = h.level)) {
for (int i = 1; i <= level; ++i)
idx = new Index<K,V>(z, idx, null);
}
else { // try to grow by one level
level = max + 1; // hold in array and later pick the one to use
@SuppressWarnings("unchecked")Index<K,V>[] idxs =
(Index<K,V>[])new Index<?,?>[level+1];
for (int i = 1; i <= level; ++i)
idxs[i] = idx = new Index<K,V>(z, idx, null);
for (;;) {
h = head;
int oldLevel = h.level;
if (level <= oldLevel) // lost race to add level
break;
HeadIndex<K,V> newh = h;
Node<K,V> oldbase = h.node;
for (int j = oldLevel+1; j <= level; ++j)
newh = new HeadIndex<K,V>(oldbase, newh, idxs[j], j);
if (casHead(h, newh)) {
h = newh;
idx = idxs[level = oldLevel];
break;
}
}
}
// find insertion points and splice in
splice: for (int insertionLevel = level;;) {
int j = h.level;
for (Index<K,V> q = h, r = q.right, t = idx;;) {
if (q == null || t == null)
break splice;
if (r != null) {
Node<K,V> n = r.node;
// compare before deletion check avoids needing recheck
int c = cpr(cmp, key, 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) {
if (!q.link(r, t))
break; // restart
if (t.node.value == null) {
findNode(key);
break splice;
}
if (--insertionLevel == 0)
break splice;
}
if (--j >= insertionLevel && j < level)
t = t.down;
q = q.down;
r = q.right;
}
}
}
return null;
}
/* ---------------- 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 key 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 key, Object value) {
if (key == null)
throw new NullPointerException();
Comparator<? super K> cmp = comparator;
outer: for (;;) {
for (Node<K,V> b = findPredecessor(key, cmp), n = b.next;;) {
Object v; int c;
if (n == null)
break outer;
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
if ((v = n.value) == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
if ((c = cpr(cmp, key, n.key)) < 0)
break outer;
if (c > 0) {
b = n;
n = f;
continue;
}
if (value != null && !value.equals(v))
break outer;
if (!n.casValue(v, null))
break;
if (!n.appendMarker(f) || !b.casNext(n, f))
findNode(key); // retry via findNode
else {
findPredecessor(key, cmp); // clean index
if (head.right == null)
tryReduceLevel();
}
@SuppressWarnings("unchecked") V vv = (V)v;
return vv;
}
}
return null;
}
/**
* Possibly reduce head level if it has no nodes. This method can
* (rarely) make mistakes, in which case levels can disappear even
* though they are about to contain index nodes. This impacts
* performance, not correctness. To minimize mistakes as well as
* to reduce hysteresis, the level is reduced by one only if the
* topmost three levels look empty. Also, if the removed level
* looks non-empty after CAS, we try to change it back quick
* before anyone notices our mistake! (This trick works pretty
* well because this method will practically never make mistakes
* unless current thread stalls immediately before first CAS, in
* which case it is very unlikely to stall again immediately
* afterwards, so will recover.)
*
* We put up with all this rather than just let levels grow
* because otherwise, even a small map that has undergone a large
* number of insertions and removals will have a lot of levels,
* slowing down access more than would an occasional unwanted
* reduction.
*/
private void tryReduceLevel() {
HeadIndex<K,V> h = head;
HeadIndex<K,V> d;
HeadIndex<K,V> e;
if (h.level > 3 &&
(d = (HeadIndex<K,V>)h.down) != null &&
(e = (HeadIndex<K,V>)d.down) != null &&
e.right == null &&
d.right == null &&
h.right == null &&
casHead(h, d) && // try to set
h.right != null) // recheck
casHead(d, h); // try to backout
}
/* ---------------- Finding and removing first element -------------- */
/**
* Specialized variant of findNode to get first valid node.
* @return first node or null if empty
*/
final Node<K,V> findFirst() {
for (Node<K,V> b, n;;) {
if ((n = (b = head.node).next) == 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
*/
private Map.Entry<K,V> doRemoveFirstEntry() {
for (Node<K,V> b, n;;) {
if ((n = (b = head.node).next) == null)
return null;
Node<K,V> f = n.next;
if (n != b.next)
continue;
Object v = n.value;
if (v == null) {
n.helpDelete(b, f);
continue;
}
if (!n.casValue(v, null))
continue;
if (!n.appendMarker(f) || !b.casNext(n, f))
findFirst(); // retry
clearIndexToFirst();
@SuppressWarnings("unchecked") V vv = (V)v;
return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, vv);
}
}
/**
* Clears out index nodes associated with deleted first entry.
*/
private void clearIndexToFirst() {
for (;;) {
for (Index<K,V> q = head;;) {
Index<K,V> r = q.right;
if (r != null && r.indexesDeletedNode() && !q.unlink(r))
break;
if ((q = q.down) == null) {
if (head.right == null)
tryReduceLevel();
return;
}
}
}
}
/**
* Removes last entry; returns its snapshot.
* Specialized variant of doRemove.
* @return null if empty, else snapshot of last entry
*/
private Map.Entry<K,V> doRemoveLastEntry() {
for (;;) {
Node<K,V> b = findPredecessorOfLast();
Node<K,V> n = b.next;
if (n == null) {
if (b.isBaseHeader()) // empty
return null;
else
continue; // all b's successors are deleted; retry
}
for (;;) {
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
if (f != null) {
b = n;
n = f;
continue;
}
if (!n.casValue(v, null))
break;
K key = n.key;
if (!n.appendMarker(f) || !b.casNext(n, f))
findNode(key); // retry via findNode
else { // clean index
findPredecessor(key, comparator);
if (head.right == null)
tryReduceLevel();
}
@SuppressWarnings("unchecked") V vv = (V)v;
return new AbstractMap.SimpleImmutableEntry<K,V>(key, vv);
}
}
}
/* ---------------- Finding and removing last element -------------- */
/**
* Specialized version of find to get last valid node.
* @return last node or null if empty
*/
final Node<K,V> findLast() {
/*
* findPredecessor can't be used to traverse index level
* because this doesn't use comparisons. So traversals of
* both levels are folded together.
*/
Index<K,V> q = head;
for (;;) {
Index<K,V> d, r;
if ((r = q.right) != null) {
if (r.indexesDeletedNode()) {
q.unlink(r);
q = head; // restart
}
else
q = r;
} else if ((d = q.down) != null) {
q = d;
} else {
for (Node<K,V> b = q.node, n = b.next;;) {
if (n == null)
return b.isBaseHeader() ? null : b;
Node<K,V> f = n.next; // inconsistent read
if (n != b.next)
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // 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<K,V> findPredecessorOfLast() {
for (;;) {
for (Index<K,V> q = head;;) {
Index<K,V> d, r;
if ((r = q.right) != null) {
if (r.indexesDeletedNode()) {
q.unlink(r);
break; // must restart
}
// proceed as far across as possible without overshooting
if (r.node.next != null) {
q = r;
continue;
}
}
if ((d = q.down) != null)
q = d;
else
return q.node;
}
}
}
/* ---------------- 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 key the key
* @param rel the relation -- OR'ed combination of EQ, LT, GT
* @return nearest node fitting relation, or null if no such
*/
final Node<K,V> findNear(K key, int rel, Comparator<? super K> cmp) {
if (key == null)
throw new NullPointerException();
for (;;) {
for (Node<K,V> b = findPredecessor(key, cmp), n = b.next;;) {
Object v;
if (n == null)
return ((rel & LT) == 0 || b.isBaseHeader()) ? null : b;
Node<K,V> f = n.next;
if (n != b.next) // inconsistent read
break;
if ((v = n.value) == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (b.value == null || v == n) // b is deleted
break;
int c = cpr(cmp, key, 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
*/
final AbstractMap.SimpleImmutableEntry<K,V> getNear(K key, int rel) {
Comparator<? super K> cmp = comparator;
for (;;) {
Node<K,V> n = findNear(key, rel, cmp);
if (n == null)
return null;
AbstractMap.SimpleImmutableEntry<K,V> 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 {@code null}, the {@linkplain Comparable natural
* ordering} of the keys will be used.
*/
public ConcurrentSkipListMap(Comparator<? super K> 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 {@code 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<? extends K, ? extends V> 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<K, ? extends V> m) {
this.comparator = m.comparator();
initialize();
buildFromSorted(m);
}
/**
* Returns a shallow copy of this {@code ConcurrentSkipListMap}
* instance. (The keys and values themselves are not cloned.)
*
* @return a shallow copy of this map
*/
public ConcurrentSkipListMap<K,V> clone() {
try {
@SuppressWarnings("unchecked")
ConcurrentSkipListMap<K,V> clone =
(ConcurrentSkipListMap<K,V>) super.clone();
clone.initialize();
clone.buildFromSorted(this);
return clone;
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
/**
* Streamlined bulk insertion to initialize from elements of
* given sorted map. Call only from constructor or clone
* method.
*/
private void buildFromSorted(SortedMap<K, ? extends V> map) {
if (map == null)
throw new NullPointerException();
HeadIndex<K,V> h = head;
Node<K,V> basepred = h.node;
// Track the current rightmost node at each level. Uses an
// ArrayList to avoid committing to initial or maximum level.
ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
// initialize
for (int i = 0; i <= h.level; ++i)
preds.add(null);
Index<K,V> q = h;
for (int i = h.level; i > 0; --i) {
preds.set(i, q);
q = q.down;
}
Iterator<? extends Map.Entry<? extends K, ? extends V>> it =
map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<? extends K, ? extends V> e = it.next();
int rnd = ThreadLocalRandom.current().nextInt();
int j = 0;
if ((rnd & 0x80000001) == 0) {
do {
++j;
} while (((rnd >>>= 1) & 1) != 0);
if (j > h.level) j = h.level + 1;
}
K k = e.getKey();
V v = e.getValue();
if (k == null || v == null)
throw new NullPointerException();
Node<K,V> z = new Node<K,V>(k, v, null);
basepred.next = z;
basepred = z;
if (j > 0) {
Index<K,V> idx = null;
for (int i = 1; i <= j; ++i) {
idx = new Index<K,V>(z, idx, null);
if (i > h.level)
h = new HeadIndex<K,V>(h.node, h, idx, i);
if (i < preds.size()) {
preds.get(i).right = idx;
preds.set(i, idx);
} else
preds.add(idx);
}
}
}
head = h;
}
/* ---------------- Serialization -------------- */
/**
* Saves this map to a stream (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @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<K,V> n = findFirst(); n != null; n = n.next) {
V v = n.getValidValue();
if (v != null) {
s.writeObject(n.key);
s.writeObject(v);
}
}
s.writeObject(null);
}
/**
* Reconstitutes this map from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
@SuppressWarnings("unchecked")
private void readObject(final java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in the Comparator and any hidden stuff
s.defaultReadObject();
// Reset transients
initialize();
/*
* This is nearly identical to buildFromSorted, but is
* distinct because readObject calls can't be nicely adapted
* as the kind of iterator needed by buildFromSorted. (They
* can be, but doing so requires type cheats and/or creation
* of adaptor classes.) It is simpler to just adapt the code.
*/
HeadIndex<K,V> h = head;
Node<K,V> basepred = h.node;
ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
for (int i = 0; i <= h.level; ++i)
preds.add(null);
Index<K,V> q = h;
for (int i = h.level; i > 0; --i) {
preds.set(i, q);
q = q.down;
}
for (;;) {
Object k = s.readObject();
if (k == null)
break;
Object v = s.readObject();
if (v == null)
throw new NullPointerException();
K key = (K) k;
V val = (V) v;
int rnd = ThreadLocalRandom.current().nextInt();
int j = 0;
if ((rnd & 0x80000001) == 0) {
do {
++j;
} while (((rnd >>>= 1) & 1) != 0);
if (j > h.level) j = h.level + 1;
}
Node<K,V> z = new Node<K,V>(key, val, null);
basepred.next = z;
basepred = z;
if (j > 0) {
Index<K,V> idx = null;
for (int i = 1; i <= j; ++i) {
idx = new Index<K,V>(z, idx, null);
if (i > h.level)
h = new HeadIndex<K,V>(h.node, h, idx, i);
if (i < preds.size()) {
preds.get(i).right = idx;
preds.set(i, idx);
} else
preds.add(idx);
}
}
}
head = h;
}
/* ------ Map API methods ------ */
/**
* Returns {@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 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.
*
* <p>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);
}
/**
* Returns the value to which the specified key is mapped,
* or the given defaultValue if this map contains no mapping for the key.
*
* @param key the key
* @param defaultValue the value to return if this map contains
* no mapping for the given key
* @return the mapping for the key, if present; else the defaultValue
* @throws NullPointerException if the specified key is null
* @since 1.8
*/
public V getOrDefault(Object key, V defaultValue) {
V v;
return (v = doGet(key)) == null ? defaultValue : v;
}
/**
* 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
* {@code 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
* {@code 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 {@code 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 {@code true} if a mapping to {@code value} exists;
* {@code false} otherwise
* @throws NullPointerException if the specified value is null
*/
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
for (Node<K,V> n = findFirst(); n != null; n = n.next) {
V v = n.getValidValue();
if (v != null && value.equals(v))
return true;
}
return false;
}
/**
* Returns the number of key-value mappings in this map. If this map
* contains more than {@code Integer.MAX_VALUE} elements, it
* returns {@code Integer.MAX_VALUE}.
*
* <p>Beware that, unlike in most collections, this method is
* <em>NOT</em> a constant-time operation. Because of the
* asynchronous nature of these maps, determining the current
* number of elements requires traversing them all to count them.
* Additionally, it is possible for the size to change during
* execution of this method, in which case the returned result
* will be inaccurate. Thus, this method is typically not very
* useful in concurrent applications.
*
* @return the number of elements in this map
*/
public int size() {
long count = 0;
for (Node<K,V> n = findFirst(); n != null; n = n.next) {
if (n.getValidValue() != null)
++count;
}
return (count >= Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int) count;
}
/**
* Returns {@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 of the mappings from this map.
*/
public void clear() {
initialize();
}
/**
* If the specified key is not already associated with a value,
* attempts to compute its value using the given mapping function
* and enters it into this map unless {@code null}. The function
* is <em>NOT</em> guaranteed to be applied once atomically only
* if the value is not present.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with
* the specified key, or null if the computed value is null
* @throws NullPointerException if the specified key is null
* or the mappingFunction is null
* @since 1.8
*/
public V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
if (key == null || mappingFunction == null)
throw new NullPointerException();
V v, p, r;
if ((v = doGet(key)) == null &&
(r = mappingFunction.apply(key)) != null)
v = (p = doPut(key, r, true)) == null ? r : p;
return v;
}
/**
* If the value for the specified key is present, attempts to
* compute a new mapping given the key and its current mapped
* value. The function is <em>NOT</em> guaranteed to be applied
* once atomically.
*
* @param key key with which a value may be associated
* @param remappingFunction the function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null
* or the remappingFunction is null
* @since 1.8
*/
public V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (key == null || remappingFunction == null)
throw new NullPointerException();
Node<K,V> n; Object v;
while ((n = findNode(key)) != null) {
if ((v = n.value) != null) {
@SuppressWarnings("unchecked") V vv = (V) v;
V r = remappingFunction.apply(key, vv);
if (r != null) {
if (n.casValue(vv, r))
return r;
}
else if (doRemove(key, vv) != null)
break;
}
}
return null;
}
/**
* Attempts to compute a mapping for the specified key and its
* current mapped value (or {@code null} if there is no current
* mapping). The function is <em>NOT</em> guaranteed to be applied
* once atomically.
*
* @param key key with which the specified value is to be associated
* @param remappingFunction the function to compute a value
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key is null
* or the remappingFunction is null
* @since 1.8
*/
public V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
if (key == null || remappingFunction == null)
throw new NullPointerException();
for (;;) {
Node<K,V> n; Object v; V r;
if ((n = findNode(key)) == null) {
if ((r = remappingFunction.apply(key, null)) == null)
break;
if (doPut(key, r, true) == null)
return r;
}
else if ((v = n.value) != null) {
@SuppressWarnings("unchecked") V vv = (V) v;
if ((r = remappingFunction.apply(key, vv)) != null) {
if (n.casValue(vv, r))
return r;
}
else if (doRemove(key, vv) != null)
break;
}
}
return null;
}
/**
* If the specified key is not already associated with a value,
* associates it with the given value. Otherwise, replaces the
* value with the results of the given remapping function, or
* removes if {@code null}. The function is <em>NOT</em>
* guaranteed to be applied once atomically.
*
* @param key key with which the specified value is to be associated
* @param value the value to use if absent
* @param remappingFunction the function to recompute a value if present
* @return the new value associated with the specified key, or null if none
* @throws NullPointerException if the specified key or value is null
* or the remappingFunction is null
* @since 1.8
*/
public V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
if (key == null || value == null || remappingFunction == null)
throw new NullPointerException();
for (;;) {
Node<K,V> n; Object v; V r;
if ((n = findNode(key)) == null) {
if (doPut(key, value, true) == null)
return value;
}
else if ((v = n.value) != null) {
@SuppressWarnings("unchecked") V vv = (V) v;
if ((r = remappingFunction.apply(vv, value)) != null) {
if (n.casValue(vv, r))
return r;
}
else if (doRemove(key, vv) != null)
return null;
}
}
}
/* ---------------- 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.
*
* <p>The set's iterator returns the keys in ascending order.
* The set's spliterator additionally reports {@link Spliterator#CONCURRENT},
* {@link Spliterator#NONNULL}, {@link Spliterator#SORTED} and
* {@link Spliterator#ORDERED}, with an encounter order that is ascending
* key order. The spliterator's comparator (see
* {@link java.util.Spliterator#getComparator()}) is {@code null} if
* the map's comparator (see {@link #comparator()}) is {@code null}.
* Otherwise, the spliterator's comparator is the same as or imposes the
* same total ordering as the map's comparator.
*
* <p>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.
*
* <p>The view's iterators and spliterators are
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>This method is equivalent to method {@code navigableKeySet}.
*
* @return a navigable set view of the keys in this map
*/
public NavigableSet<K> keySet() {
KeySet<K> ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet<K>(this));
}
public NavigableSet<K> navigableKeySet() {
KeySet<K> ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet<K>(this));
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* <p>The collection's iterator returns the values in ascending order
* of the corresponding keys. The collections's spliterator additionally
* reports {@link Spliterator#CONCURRENT}, {@link Spliterator#NONNULL} and
* {@link Spliterator#ORDERED}, with an encounter order that is ascending
* order of the corresponding keys.
*
* <p>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.
*
* <p>The view's iterators and spliterators are
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*/
public Collection<V> values() {
Values<V> vs = values;
return (vs != null) ? vs : (values = new Values<V>(this));
}
/**
* Returns a {@link Set} view of the mappings contained in this map.
*
* <p>The set's iterator returns the entries in ascending key order. The
* set's spliterator additionally reports {@link Spliterator#CONCURRENT},
* {@link Spliterator#NONNULL}, {@link Spliterator#SORTED} and
* {@link Spliterator#ORDERED}, with an encounter order that is ascending
* key order.
*
* <p>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.
*
* <p>The view's iterators and spliterators are
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>The {@code Map.Entry} elements traversed by the {@code iterator}
* or {@code spliterator} do <em>not</em> support the {@code setValue}
* operation.
*
* @return a set view of the mappings contained in this map,
* sorted in ascending key order
*/
public Set<Map.Entry<K,V>> entrySet() {
EntrySet<K,V> es = entrySet;
return (es != null) ? es : (entrySet = new EntrySet<K,V>(this));
}
public ConcurrentNavigableMap<K,V> descendingMap() {
ConcurrentNavigableMap<K,V> dm = descendingMap;
return (dm != null) ? dm : (descendingMap = new SubMap<K,V>
(this, null, false, null, false, true));
}
public NavigableSet<K> descendingKeySet() {
return descendingMap().navigableKeySet();
}
/* ---------------- 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 m1} and {@code m2} represent the same mappings if
* {@code 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 {@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<?,?> m = (Map<?,?>) o;
try {
for (Map.Entry<K,V> 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 {@code 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();
return value != null && 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 (key == null || oldValue == null || newValue == null)
throw new NullPointerException();
for (;;) {
Node<K,V> n; Object v;
if ((n = findNode(key)) == null)
return false;
if ((v = n.value) != 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 {@code 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 (key == null || value == null)
throw new NullPointerException();
for (;;) {
Node<K,V> n; Object v;
if ((n = findNode(key)) == null)
return null;
if ((v = n.value) != null && n.casValue(v, value)) {
@SuppressWarnings("unchecked") V vv = (V)v;
return vv;
}
}
}
/* ------ SortedMap API methods ------ */
public Comparator<? super K> comparator() {
return comparator;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public K firstKey() {
Node<K,V> n = findFirst();
if (n == null)
throw new NoSuchElementException();
return n.key;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public K lastKey() {
Node<K,V> 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<K,V> subMap(K fromKey,
boolean fromInclusive,
K toKey,
boolean toInclusive) {
if (fromKey == null || toKey == null)
throw new NullPointerException();
return new SubMap<K,V>
(this, fromKey, fromInclusive, toKey, toInclusive, false);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code toKey} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public ConcurrentNavigableMap<K,V> headMap(K toKey,
boolean inclusive) {
if (toKey == null)
throw new NullPointerException();
return new SubMap<K,V>
(this, null, false, toKey, inclusive, false);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromKey} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public ConcurrentNavigableMap<K,V> tailMap(K fromKey,
boolean inclusive) {
if (fromKey == null)
throw new NullPointerException();
return new SubMap<K,V>
(this, fromKey, inclusive, null, false, false);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromKey} or {@code toKey} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public ConcurrentNavigableMap<K,V> 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<K,V> headMap(K toKey) {
return headMap(toKey, false);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if {@code fromKey} is null
* @throws IllegalArgumentException {@inheritDoc}
*/
public ConcurrentNavigableMap<K,V> 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 {@code null} if there is
* no such key. The returned entry does <em>not</em> support the
* {@code Entry.setValue} method.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if the specified key is null
*/
public Map.Entry<K,V> lowerEntry(K key) {
return getNear(key, LT);
}
/**
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if the specified key is null
*/
public K lowerKey(K key) {
Node<K,V> n = findNear(key, LT, comparator);
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 key. The returned entry does <em>not</em> support
* the {@code Entry.setValue} method.
*
* @param key the key
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if the specified key is null
*/
public Map.Entry<K,V> 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<K,V> n = findNear(key, LT|EQ, comparator);
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 {@code null} if
* there is no such entry. The returned entry does <em>not</em>
* support the {@code Entry.setValue} method.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if the specified key is null
*/
public Map.Entry<K,V> 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<K,V> n = findNear(key, GT|EQ, comparator);
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 key. The returned entry does <em>not</em> support
* the {@code Entry.setValue} method.
*
* @param key the key
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException if the specified key is null
*/
public Map.Entry<K,V> 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<K,V> n = findNear(key, GT, comparator);
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 <em>not</em> support
* the {@code Entry.setValue} method.
*/
public Map.Entry<K,V> firstEntry() {
for (;;) {
Node<K,V> n = findFirst();
if (n == null)
return null;
AbstractMap.SimpleImmutableEntry<K,V> 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 <em>not</em> support
* the {@code Entry.setValue} method.
*/
public Map.Entry<K,V> lastEntry() {
for (;;) {
Node<K,V> n = findLast();
if (n == null)
return null;
AbstractMap.SimpleImmutableEntry<K,V> e = n.createSnapshot();
if (e != null)
return e;
}
}
/**
* Removes and returns a key-value mapping associated with
* the least key in this map, or {@code null} if the map is empty.
* The returned entry does <em>not</em> support
* the {@code Entry.setValue} method.
*/
public Map.Entry<K,V> pollFirstEntry() {
return doRemoveFirstEntry();
}
/**
* 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 <em>not</em> support
* the {@code Entry.setValue} method.
*/
public Map.Entry<K,V> pollLastEntry() {
return doRemoveLastEntry();
}
/* ---------------- Iterators -------------- */
/**
* Base of iterator classes:
*/
abstract class Iter<T> implements Iterator<T> {
/** the last node returned by next() */
Node<K,V> lastReturned;
/** the next node to return from next(); */
Node<K,V> next;
/** Cache of next value field to maintain weak consistency */
V nextValue;
/** Initializes ascending iterator for entire range. */
Iter() {
while ((next = findFirst()) != null) {
Object x = next.value;
if (x != null && x != next) {
@SuppressWarnings("unchecked") V vv = (V)x;
nextValue = vv;
break;
}
}
}
public final boolean hasNext() {
return next != null;
}
/** Advances next to higher entry. */
final void advance() {
if (next == null)
throw new NoSuchElementException();
lastReturned = next;
while ((next = next.next) != null) {
Object x = next.value;
if (x != null && x != next) {
@SuppressWarnings("unchecked") V vv = (V)x;
nextValue = vv;
break;
}
}
}
public void remove() {
Node<K,V> 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<V> {
public V next() {
V v = nextValue;
advance();
return v;
}
}
final class KeyIterator extends Iter<K> {
public K next() {
Node<K,V> n = next;
advance();
return n.key;
}
}
final class EntryIterator extends Iter<Map.Entry<K,V>> {
public Map.Entry<K,V> next() {
Node<K,V> n = next;
V v = nextValue;
advance();
return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, v);
}
}
// Factory methods for iterators needed by ConcurrentSkipListSet etc
Iterator<K> keyIterator() {
return new KeyIterator();
}
Iterator<V> valueIterator() {
return new ValueIterator();
}
Iterator<Map.Entry<K,V>> 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 <E> List<E> toList(Collection<E> c) {
// Using size() here would be a pessimization.
ArrayList<E> list = new ArrayList<E>();
for (E e : c)
list.add(e);
return list;
}
static final class KeySet<E>
extends AbstractSet<E> implements NavigableSet<E> {
final ConcurrentNavigableMap<E,?> m;
KeySet(ConcurrentNavigableMap<E,?> 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<? super E> comparator() { return m.comparator(); }
public E first() { return m.firstKey(); }
public E last() { return m.lastKey(); }
public E pollFirst() {
Map.Entry<E,?> e = m.pollFirstEntry();
return (e == null) ? null : e.getKey();
}
public E pollLast() {
Map.Entry<E,?> e = m.pollLastEntry();
return (e == null) ? null : e.getKey();
}
@SuppressWarnings("unchecked")
public Iterator<E> iterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<E,Object>)m).keyIterator();
else
return ((ConcurrentSkipListMap.SubMap<E,Object>)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> T[] toArray(T[] a) { return toList(this).toArray(a); }
public Iterator<E> descendingIterator() {
return descendingSet().iterator();
}
public NavigableSet<E> subSet(E fromElement,
boolean fromInclusive,
E toElement,
boolean toInclusive) {
return new KeySet<E>(m.subMap(fromElement, fromInclusive,
toElement, toInclusive));
}
public NavigableSet<E> headSet(E toElement, boolean inclusive) {
return new KeySet<E>(m.headMap(toElement, inclusive));
}
public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
return new KeySet<E>(m.tailMap(fromElement, inclusive));
}
public NavigableSet<E> subSet(E fromElement, E toElement) {
return subSet(fromElement, true, toElement, false);
}
public NavigableSet<E> headSet(E toElement) {
return headSet(toElement, false);
}
public NavigableSet<E> tailSet(E fromElement) {
return tailSet(fromElement, true);
}
public NavigableSet<E> descendingSet() {
return new KeySet<E>(m.descendingMap());
}
@SuppressWarnings("unchecked")
public Spliterator<E> spliterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<E,?>)m).keySpliterator();
else
return (Spliterator<E>)((SubMap<E,?>)m).keyIterator();
}
}
static final class Values<E> extends AbstractCollection<E> {
final ConcurrentNavigableMap<?, E> m;
Values(ConcurrentNavigableMap<?, E> map) {
m = map;
}
@SuppressWarnings("unchecked")
public Iterator<E> iterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<?,E>)m).valueIterator();
else
return ((SubMap<?,E>)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> T[] toArray(T[] a) { return toList(this).toArray(a); }
@SuppressWarnings("unchecked")
public Spliterator<E> spliterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<?,E>)m).valueSpliterator();
else
return (Spliterator<E>)((SubMap<?,E>)m).valueIterator();
}
}
static final class EntrySet<K1,V1> extends AbstractSet<Map.Entry<K1,V1>> {
final ConcurrentNavigableMap<K1, V1> m;
EntrySet(ConcurrentNavigableMap<K1, V1> map) {
m = map;
}
@SuppressWarnings("unchecked")
public Iterator<Map.Entry<K1,V1>> iterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<K1,V1>)m).entryIterator();
else
return ((SubMap<K1,V1>)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> T[] toArray(T[] a) { return toList(this).toArray(a); }
@SuppressWarnings("unchecked")
public Spliterator<Map.Entry<K1,V1>> spliterator() {
if (m instanceof ConcurrentSkipListMap)
return ((ConcurrentSkipListMap<K1,V1>)m).entrySpliterator();
else
return (Spliterator<Map.Entry<K1,V1>>)
((SubMap<K1,V1>)m).entryIterator();
}
}
/**
* 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 {@code subMap}, {@code headMap}, and
* {@code tailMap} methods of their underlying maps.
*
* @serial include
*/
static final class SubMap<K,V> extends AbstractMap<K,V>
implements ConcurrentNavigableMap<K,V>, Cloneable, Serializable {
private static final long serialVersionUID = -7647078645895051609L;
/** Underlying map */
private final ConcurrentSkipListMap<K,V> m;
/** lower bound key, or null if from start */
private final K lo;
/** upper bound key, or null if to end */
private final K hi;
/** inclusion flag for lo */
private final boolean loInclusive;
/** inclusion flag for hi */
private final boolean hiInclusive;
/** direction */
private final boolean isDescending;
// Lazily initialized view holders
private transient KeySet<K> keySetView;
private transient Set<Map.Entry<K,V>> entrySetView;
private transient Collection<V> valuesView;
/**
* Creates a new submap, initializing all fields.
*/
SubMap(ConcurrentSkipListMap<K,V> map,
K fromKey, boolean fromInclusive,
K toKey, boolean toInclusive,
boolean isDescending) {
Comparator<? super K> cmp = map.comparator;
if (fromKey != null && toKey != null &&
cpr(cmp, fromKey, toKey) > 0)
throw new IllegalArgumentException("inconsistent range");
this.m = map;
this.lo = fromKey;
this.hi = toKey;
this.loInclusive = fromInclusive;
this.hiInclusive = toInclusive;
this.isDescending = isDescending;
}
/* ---------------- Utilities -------------- */
boolean tooLow(Object key, Comparator<? super K> cmp) {
int c;
return (lo != null && ((c = cpr(cmp, key, lo)) < 0 ||
(c == 0 && !loInclusive)));
}
boolean tooHigh(Object key, Comparator<? super K> cmp) {
int c;
return (hi != null && ((c = cpr(cmp, key, hi)) > 0 ||
(c == 0 && !hiInclusive)));
}
boolean inBounds(Object key, Comparator<? super K> cmp) {
return !tooLow(key, cmp) && !tooHigh(key, cmp);
}
void checkKeyBounds(K key, Comparator<? super K> cmp) {
if (key == null)
throw new NullPointerException();
if (!inBounds(key, cmp))
throw new IllegalArgumentException("key out of range");
}
/**
* Returns true if node key is less than upper bound of range.
*/
boolean isBeforeEnd(ConcurrentSkipListMap.Node<K,V> n,
Comparator<? super K> cmp) {
if (n == null)
return false;
if (hi == null)
return true;
K k = n.key;
if (k == null) // pass by markers and headers
return true;
int c = cpr(cmp, k, hi);
if (c > 0 || (c == 0 && !hiInclusive))
return false;
return true;
}
/**
* Returns lowest node. This node might not be in range, so
* most usages need to check bounds.
*/
ConcurrentSkipListMap.Node<K,V> loNode(Comparator<? super K> cmp) {
if (lo == null)
return m.findFirst();
else if (loInclusive)
return m.findNear(lo, GT|EQ, cmp);
else
return m.findNear(lo, GT, cmp);
}
/**
* Returns highest node. This node might not be in range, so
* most usages need to check bounds.
*/
ConcurrentSkipListMap.Node<K,V> hiNode(Comparator<? super K> cmp) {
if (hi == null)
return m.findLast();
else if (hiInclusive)
return m.findNear(hi, LT|EQ, cmp);
else
return m.findNear(hi, LT, cmp);
}
/**
* Returns lowest absolute key (ignoring directonality).
*/
K lowestKey() {
Comparator<? super K> cmp = m.comparator;
ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
if (isBeforeEnd(n, cmp))
return n.key;
else
throw new NoSuchElementException();
}
/**
* Returns highest absolute key (ignoring directonality).
*/
K highestKey() {
Comparator<? super K> cmp = m.comparator;
ConcurrentSkipListMap.Node<K,V> n = hiNode(cmp);
if (n != null) {
K last = n.key;
if (inBounds(last, cmp))
return last;
}
throw new NoSuchElementException();
}
Map.Entry<K,V> lowestEntry() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
if (!isBeforeEnd(n, cmp))
return null;
Map.Entry<K,V> e = n.createSnapshot();
if (e != null)
return e;
}
}
Map.Entry<K,V> highestEntry() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
ConcurrentSkipListMap.Node<K,V> n = hiNode(cmp);
if (n == null || !inBounds(n.key, cmp))
return null;
Map.Entry<K,V> e = n.createSnapshot();
if (e != null)
return e;
}
}
Map.Entry<K,V> removeLowest() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
Node<K,V> n = loNode(cmp);
if (n == null)
return null;
K k = n.key;
if (!inBounds(k, cmp))
return null;
V v = m.doRemove(k, null);
if (v != null)
return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
}
}
Map.Entry<K,V> removeHighest() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
Node<K,V> n = hiNode(cmp);
if (n == null)
return null;
K k = n.key;
if (!inBounds(k, cmp))
return null;
V v = m.doRemove(k, null);
if (v != null)
return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
}
}
/**
* Submap version of ConcurrentSkipListMap.getNearEntry
*/
Map.Entry<K,V> getNearEntry(K key, int rel) {
Comparator<? super K> cmp = m.comparator;
if (isDescending) { // adjust relation for direction
if ((rel & LT) == 0)
rel |= LT;
else
rel &= ~LT;
}
if (tooLow(key, cmp))
return ((rel & LT) != 0) ? null : lowestEntry();
if (tooHigh(key, cmp))
return ((rel & LT) != 0) ? highestEntry() : null;
for (;;) {
Node<K,V> n = m.findNear(key, rel, cmp);
if (n == null || !inBounds(n.key, cmp))
return null;
K k = n.key;
V v = n.getValidValue();
if (v != null)
return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
}
}
// Almost the same as getNearEntry, except for keys
K getNearKey(K key, int rel) {
Comparator<? super K> cmp = m.comparator;
if (isDescending) { // adjust relation for direction
if ((rel & LT) == 0)
rel |= LT;
else
rel &= ~LT;
}
if (tooLow(key, cmp)) {
if ((rel & LT) == 0) {
ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
if (isBeforeEnd(n, cmp))
return n.key;
}
return null;
}
if (tooHigh(key, cmp)) {
if ((rel & LT) != 0) {
ConcurrentSkipListMap.Node<K,V> n = hiNode(cmp);
if (n != null) {
K last = n.key;
if (inBounds(last, cmp))
return last;
}
}
return null;
}
for (;;) {
Node<K,V> n = m.findNear(key, rel, cmp);
if (n == null || !inBounds(n.key, cmp))
return null;
K k = n.key;
V v = n.getValidValue();
if (v != null)
return k;
}
}
/* ---------------- Map API methods -------------- */
public boolean containsKey(Object key) {
if (key == null) throw new NullPointerException();
return inBounds(key, m.comparator) && m.containsKey(key);
}
public V get(Object key) {
if (key == null) throw new NullPointerException();
return (!inBounds(key, m.comparator)) ? null : m.get(key);
}
public V put(K key, V value) {
checkKeyBounds(key, m.comparator);
return m.put(key, value);
}
public V remove(Object key) {
return (!inBounds(key, m.comparator)) ? null : m.remove(key);
}
public int size() {
Comparator<? super K> cmp = m.comparator;
long count = 0;
for (ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
isBeforeEnd(n, cmp);
n = n.next) {
if (n.getValidValue() != null)
++count;
}
return count >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int)count;
}
public boolean isEmpty() {
Comparator<? super K> cmp = m.comparator;
return !isBeforeEnd(loNode(cmp), cmp);
}
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
Comparator<? super K> cmp = m.comparator;
for (ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
isBeforeEnd(n, cmp);
n = n.next) {
V v = n.getValidValue();
if (v != null && value.equals(v))
return true;
}
return false;
}
public void clear() {
Comparator<? super K> cmp = m.comparator;
for (ConcurrentSkipListMap.Node<K,V> n = loNode(cmp);
isBeforeEnd(n, cmp);
n = n.next) {
if (n.getValidValue() != null)
m.remove(n.key);
}
}
/* ---------------- ConcurrentMap API methods -------------- */
public V putIfAbsent(K key, V value) {
checkKeyBounds(key, m.comparator);
return m.putIfAbsent(key, value);
}
public boolean remove(Object key, Object value) {
return inBounds(key, m.comparator) && m.remove(key, value);
}
public boolean replace(K key, V oldValue, V newValue) {
checkKeyBounds(key, m.comparator);
return m.replace(key, oldValue, newValue);
}
public V replace(K key, V value) {
checkKeyBounds(key, m.comparator);
return m.replace(key, value);
}
/* ---------------- SortedMap API methods -------------- */
public Comparator<? super K> comparator() {
Comparator<? super K> cmp = m.comparator();
if (isDescending)
return Collections.reverseOrder(cmp);
else
return cmp;
}
/**
* Utility to create submaps, where given bounds override
* unbounded(null) ones and/or are checked against bounded ones.
*/
SubMap<K,V> newSubMap(K fromKey, boolean fromInclusive,
K toKey, boolean toInclusive) {
Comparator<? super K> cmp = m.comparator;
if (isDescending) { // flip senses
K tk = fromKey;
fromKey = toKey;
toKey = tk;
boolean ti = fromInclusive;
fromInclusive = toInclusive;
toInclusive = ti;
}
if (lo != null) {
if (fromKey == null) {
fromKey = lo;
fromInclusive = loInclusive;
}
else {
int c = cpr(cmp, fromKey, lo);
if (c < 0 || (c == 0 && !loInclusive && fromInclusive))
throw new IllegalArgumentException("key out of range");
}
}
if (hi != null) {
if (toKey == null) {
toKey = hi;
toInclusive = hiInclusive;
}
else {
int c = cpr(cmp, toKey, hi);
if (c > 0 || (c == 0 && !hiInclusive && toInclusive))
throw new IllegalArgumentException("key out of range");
}
}
return new SubMap<K,V>(m, fromKey, fromInclusive,
toKey, toInclusive, isDescending);
}
public SubMap<K,V> subMap(K fromKey, boolean fromInclusive,
K toKey, boolean toInclusive) {
if (fromKey == null || toKey == null)
throw new NullPointerException();
return newSubMap(fromKey, fromInclusive, toKey, toInclusive);
}
public SubMap<K,V> headMap(K toKey, boolean inclusive) {
if (toKey == null)
throw new NullPointerException();
return newSubMap(null, false, toKey, inclusive);
}
public SubMap<K,V> tailMap(K fromKey, boolean inclusive) {
if (fromKey == null)
throw new NullPointerException();
return newSubMap(fromKey, inclusive, null, false);
}
public SubMap<K,V> subMap(K fromKey, K toKey) {
return subMap(fromKey, true, toKey, false);
}
public SubMap<K,V> headMap(K toKey) {
return headMap(toKey, false);
}
public SubMap<K,V> tailMap(K fromKey) {
return tailMap(fromKey, true);
}
public SubMap<K,V> descendingMap() {
return new SubMap<K,V>(m, lo, loInclusive,
hi, hiInclusive, !isDescending);
}
/* ---------------- Relational methods -------------- */
public Map.Entry<K,V> ceilingEntry(K key) {
return getNearEntry(key, GT|EQ);
}
public K ceilingKey(K key) {
return getNearKey(key, GT|EQ);
}
public Map.Entry<K,V> lowerEntry(K key) {
return getNearEntry(key, LT);
}
public K lowerKey(K key) {
return getNearKey(key, LT);
}
public Map.Entry<K,V> floorEntry(K key) {
return getNearEntry(key, LT|EQ);
}
public K floorKey(K key) {
return getNearKey(key, LT|EQ);
}
public Map.Entry<K,V> higherEntry(K key) {
return getNearEntry(key, GT);
}
public K higherKey(K key) {
return getNearKey(key, GT);
}
public K firstKey() {
return isDescending ? highestKey() : lowestKey();
}
public K lastKey() {
return isDescending ? lowestKey() : highestKey();
}
public Map.Entry<K,V> firstEntry() {
return isDescending ? highestEntry() : lowestEntry();
}
public Map.Entry<K,V> lastEntry() {
return isDescending ? lowestEntry() : highestEntry();
}
public Map.Entry<K,V> pollFirstEntry() {
return isDescending ? removeHighest() : removeLowest();
}
public Map.Entry<K,V> pollLastEntry() {
return isDescending ? removeLowest() : removeHighest();
}
/* ---------------- Submap Views -------------- */
public NavigableSet<K> keySet() {
KeySet<K> ks = keySetView;
return (ks != null) ? ks : (keySetView = new KeySet<K>(this));
}
public NavigableSet<K> navigableKeySet() {
KeySet<K> ks = keySetView;
return (ks != null) ? ks : (keySetView = new KeySet<K>(this));
}
public Collection<V> values() {
Collection<V> vs = valuesView;
return (vs != null) ? vs : (valuesView = new Values<V>(this));
}
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es = entrySetView;
return (es != null) ? es : (entrySetView = new EntrySet<K,V>(this));
}
public NavigableSet<K> descendingKeySet() {
return descendingMap().navigableKeySet();
}
Iterator<K> keyIterator() {
return new SubMapKeyIterator();
}
Iterator<V> valueIterator() {
return new SubMapValueIterator();
}
Iterator<Map.Entry<K,V>> entryIterator() {
return new SubMapEntryIterator();
}
/**
* Variant of main Iter class to traverse through submaps.
* Also serves as back-up Spliterator for views
*/
abstract class SubMapIter<T> implements Iterator<T>, Spliterator<T> {
/** the last node returned by next() */
Node<K,V> lastReturned;
/** the next node to return from next(); */
Node<K,V> next;
/** Cache of next value field to maintain weak consistency */
V nextValue;
SubMapIter() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
next = isDescending ? hiNode(cmp) : loNode(cmp);
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (! inBounds(next.key, cmp))
next = null;
else {
@SuppressWarnings("unchecked") V vv = (V)x;
nextValue = vv;
}
break;
}
}
}
public final boolean hasNext() {
return next != null;
}
final void advance() {
if (next == null)
throw new NoSuchElementException();
lastReturned = next;
if (isDescending)
descend();
else
ascend();
}
private void ascend() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
next = next.next;
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (tooHigh(next.key, cmp))
next = null;
else {
@SuppressWarnings("unchecked") V vv = (V)x;
nextValue = vv;
}
break;
}
}
}
private void descend() {
Comparator<? super K> cmp = m.comparator;
for (;;) {
next = m.findNear(lastReturned.key, LT, cmp);
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (tooLow(next.key, cmp))
next = null;
else {
@SuppressWarnings("unchecked") V vv = (V)x;
nextValue = vv;
}
break;
}
}
}
public void remove() {
Node<K,V> l = lastReturned;
if (l == null)
throw new IllegalStateException();
m.remove(l.key);
lastReturned = null;
}
public Spliterator<T> trySplit() {
return null;
}
public boolean tryAdvance(Consumer<? super T> action) {
if (hasNext()) {
action.accept(next());
return true;
}
return false;
}
public void forEachRemaining(Consumer<? super T> action) {
while (hasNext())
action.accept(next());
}
public long estimateSize() {
return Long.MAX_VALUE;
}
}
final class SubMapValueIterator extends SubMapIter<V> {
public V next() {
V v = nextValue;
advance();
return v;
}
public int characteristics() {
return 0;
}
}
final class SubMapKeyIterator extends SubMapIter<K> {
public K next() {
Node<K,V> n = next;
advance();
return n.key;
}
public int characteristics() {
return Spliterator.DISTINCT | Spliterator.ORDERED |
Spliterator.SORTED;
}
public final Comparator<? super K> getComparator() {
return SubMap.this.comparator();
}
}
final class SubMapEntryIterator extends SubMapIter<Map.Entry<K,V>> {
public Map.Entry<K,V> next() {
Node<K,V> n = next;
V v = nextValue;
advance();
return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, v);
}
public int characteristics() {
return Spliterator.DISTINCT;
}
}
}
// default Map method overrides
public void forEach(BiConsumer<? super K, ? super V> action) {
if (action == null) throw new NullPointerException();
V v;
for (Node<K,V> n = findFirst(); n != null; n = n.next) {
if ((v = n.getValidValue()) != null)
action.accept(n.key, v);
}
}
public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
if (function == null) throw new NullPointerException();
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