package skiplists.lockfree;
/*
* 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. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
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.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NavigableSet;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.Set;
import java.util.SortedMap;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListSet;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import contention.abstractions.CompositionalMap;
import contention.abstractions.CompositionalMap.Vars;
/**
* 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://www.cs.umd.edu/~pugh/">SkipLists</a> providing expected average
* <i>log(n)</i> time cost for the <tt>containsKey</tt>, <tt>get</tt>,
* <tt>put</tt> and <tt>remove</tt> operations and their variants. Insertion,
* removal, update, and access operations safely execute concurrently by
* multiple threads. Iterators are <i>weakly consistent</i>, returning elements
* reflecting the state of the map at some point at or since the creation of the
* iterator. They do <em>not</em> throw {@link ConcurrentModificationException},
* and may proceed concurrently with other operations. Ascending key ordered
* views and their iterators are faster than descending ones.
*
* <p>
* All <tt>Map.Entry</tt> pairs returned by methods in this class and its views
* represent snapshots of mappings at the time they were produced. They do
* <em>not</em> support the <tt>Entry.setValue</tt> method. (Note however that
* it is possible to change mappings in the associated map using <tt>put</tt>,
* <tt>putIfAbsent</tt>, or <tt>replace</tt>, depending on exactly which effect
* you need.)
*
* <p>
* Beware that, unlike in most collections, the <tt>size</tt> method is
* <em>not</em> a constant-time operation. Because of the asynchronous nature of
* these maps, determining the current number of elements requires a traversal
* of the elements. Additionally, the bulk operations <tt>putAll</tt>,
* <tt>equals</tt>, and <tt>clear</tt> are <em>not</em> guaranteed to be
* performed atomically. For example, an iterator operating concurrently with a
* <tt>putAll</tt> operation might view only some of the added elements.
*
* <p>
* This class and its views and iterators implement all of the <em>optional</em>
* methods of the {@link Map} and {@link Iterator} interfaces. Like most other
* concurrent collections, this class does <em>not</em> permit the use of
* <tt>null</tt> 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 NonBlockingJavaSkipListMap<K, V> extends AbstractMap<K, V>
implements ConcurrentNavigableMap<K, V>, CompositionalMap<K, V>,
Cloneable, java.io.Serializable {
/*
* This class implements a tree-like two-dimensionally linked skip list in
* which the index levels are represented in separate nodes from the base
* nodes holding data. There are two reasons for taking this approach
* instead of the usual array-based structure: 1) Array based
* implementations seem to encounter more complexity and overhead 2) We can
* use cheaper algorithms for the heavily-traversed index lists than can be
* used for the base lists. Here's a picture of some of the basics for a
* possible list with 2 levels of index:
*
* Head nodes Index nodes +-+ right +-+ +-+ |2|---------------->|
* |--------------------->| |->null +-+ +-+ +-+ | down | | v v v +-+ +-+ +-+
* +-+ +-+ +-+ |1|----------->| |->| |------>| |----------->| |------>|
* |->null +-+ +-+ +-+ +-+ +-+ +-+ v | | | | | Nodes next v v v v v +-+ +-+
* +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ |
* |->|A|->|B|->|C|->|D|->|E|->|F|->|G|->|H|->|I|->|J|->|K|->null +-+ +-+
* +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
*
* The base lists use a variant of the HM linked ordered set algorithm. See
* Tim Harris, "A pragmatic implementation of non-blocking linked lists"
* http://www.cl.cam.ac.uk/~tlh20/publications.html and Maged Michael "High
* Performance Dynamic Lock-Free Hash Tables and List-Based Sets"
* http://www.research.ibm.com/people/m/michael/pubs.htm. The basic idea in
* these lists is to mark the "next" pointers of deleted nodes when deleting
* to avoid conflicts with concurrent insertions, and when traversing to
* keep track of triples (predecessor, node, successor) in order to detect
* when and how to unlink these deleted nodes.
*
* Rather than using mark-bits to mark list deletions (which can be slow and
* space-intensive using AtomicMarkedReference), nodes use direct CAS'able
* next pointers. On deletion, instead of marking a pointer, they splice in
* another node that can be thought of as standing for a marked pointer
* (indicating this by using otherwise impossible field values). Using plain
* nodes acts roughly like "boxed" implementations of marked pointers, but
* uses new nodes only when nodes are deleted, not for every link. This
* requires less space and supports faster traversal. Even if marked
* references were better supported by JVMs, traversal using this technique
* might still be faster because any search need only read ahead one more
* node than otherwise required (to check for trailing marker) rather than
* unmasking mark bits or whatever on each read.
*
* This approach maintains the essential property needed in the HM algorithm
* of changing the next-pointer of a deleted node so that any other CAS of
* it will fail, but implements the idea by changing the pointer to point to
* a different node, not by marking it. While it would be possible to
* further squeeze space by defining marker nodes not to have key/value
* fields, it isn't worth the extra type-testing overhead. The deletion
* markers are rarely encountered during traversal and are normally quickly
* garbage collected. (Note that this technique would not work well in
* systems without garbage collection.)
*
* In addition to using deletion markers, the lists also use nullness of
* value fields to indicate deletion, in a style similar to typical
* lazy-deletion schemes. If a node's value is null, then it is considered
* logically deleted and ignored even though it is still reachable. This
* maintains proper control of concurrent replace vs delete operations -- an
* attempted replace must fail if a delete beat it by nulling field, and a
* delete must return the last non-null value held in the field. (Note:
* Null, rather than some special marker, is used for value fields here
* because it just so happens to mesh with the Map API requirement that
* method get returns null if there is no mapping, which allows nodes to
* remain concurrently readable even when deleted. Using any other marker
* value here would be messy at best.)
*
* Here's the sequence of events for a deletion of node n with predecessor b
* and successor f, initially:
*
* +------+ +------+ +------+ ... | b |------>| n |----->| f | ... +------+
* +------+ +------+
*
* 1. CAS n's value field from non-null to null. From this point on, no
* public operations encountering the node consider this mapping to exist.
* However, other ongoing insertions and deletions might still modify n's
* next pointer.
*
* 2. CAS n's next pointer to point to a new marker node. From this point
* on, no other nodes can be appended to n. which avoids deletion errors in
* CAS-based linked lists.
*
* +------+ +------+ +------+ +------+ ... | b |------>| n
* |----->|marker|------>| f | ... +------+ +------+ +------+ +------+
*
* 3. CAS b's next pointer over both n and its marker. From this point on,
* no new traversals will encounter n, and it can eventually be GCed.
* +------+ +------+ ... | b |----------------------------------->| f | ...
* +------+ +------+
*
* A failure at step 1 leads to simple retry due to a lost race with another
* operation. Steps 2-3 can fail because some other thread noticed during a
* traversal a node with null value and helped out by marking and/or
* unlinking. This helping-out ensures that no thread can become stuck
* waiting for progress of the deleting thread. The use of marker nodes
* slightly complicates helping-out code because traversals must track
* consistent reads of up to four nodes (b, n, marker, f), not just (b, n,
* f), although the next field of a marker is immutable, and once a next
* field is CAS'ed to point to a marker, it never again changes, so this
* requires less care.
*
* Skip lists add indexing to this scheme, so that the base-level traversals
* start close to the locations being found, inserted or deleted -- usually
* base level traversals only traverse a few nodes. This doesn't change the
* basic algorithm except for the need to make sure base traversals start at
* predecessors (here, b) that are not (structurally) deleted, otherwise
* retrying after processing the deletion.
*
* Index levels are maintained as lists with volatile next fields, using CAS
* to link and unlink. Races are allowed in index-list operations that can
* (rarely) fail to link in a new index node or delete one. (We can't do
* this of course for data nodes.) However, even when this happens, the
* index lists remain sorted, so correctly serve as indices. This can impact
* performance, but since skip lists are probabilistic anyway, the net
* result is that under contention, the effective "p" value may be lower
* than its nominal value. And race windows are kept small enough that in
* practice these failures are rare, even under a lot of contention.
*
* The fact that retries (for both base and index lists) are relatively
* cheap due to indexing allows some minor simplifications of retry logic.
* Traversal restarts are performed after most "helping-out" CASes. This
* isn't always strictly necessary, but the implicit backoffs tend to help
* reduce other downstream failed CAS's enough to outweigh restart cost.
* This worsens the worst case, but seems to improve even highly contended
* cases.
*
* Unlike most skip-list implementations, index insertion and deletion here
* require a separate traversal pass occuring after the base-level action,
* to add or remove index nodes. This adds to single-threaded overhead, but
* improves contended multithreaded performance by narrowing interference
* windows, and allows deletion to ensure that all index nodes will be made
* unreachable upon return from a public remove operation, thus avoiding
* unwanted garbage retention. This is more important here than in some
* other data structures because we cannot null out node fields referencing
* user keys since they might still be read by other ongoing traversals.
*
* Indexing uses skip list parameters that maintain good search performance
* while using sparser-than-usual indices: The hardwired parameters k=1,
* p=0.5 (see method randomLevel) mean that about one-quarter of the nodes
* have indices. Of those that do, half have one level, a quarter have two,
* and so on (see Pugh's Skip List Cookbook, sec 3.4). The expected total
* space requirement for a map is slightly less than for the current
* implementation of java.util.TreeMap.
*
* Changing the level of the index (i.e, the height of the tree-like
* structure) also uses CAS. The head index has initial level/height of one.
* Creation of an index with height greater than the current level adds a
* level to the head index by CAS'ing on a new top-most head. To maintain
* good performance after a lot of removals, deletion methods heuristically
* try to reduce the height if the topmost levels appear to be empty. This
* may encounter races in which it possible (but rare) to reduce and "lose"
* a level just as it is about to contain an index (that will then never be
* encountered). This does no structural harm, and in practice appears to be
* a better option than allowing unrestrained growth of levels.
*
* The code for all this is more verbose than you'd like. Most operations
* entail locating an element (or position to insert an element). The code
* to do this can't be nicely factored out because subsequent uses require a
* snapshot of predecessor and/or successor and/or value fields which can't
* be returned all at once, at least not without creating yet another object
* to hold them -- creating such little objects is an especially bad idea
* for basic internal search operations because it adds to GC overhead.
* (This is one of the few times I've wished Java had macros.) Instead, some
* traversal code is interleaved within insertion and removal operations.
* The control logic to handle all the retry conditions is sometimes twisty.
* Most search is broken into 2 parts. findPredecessor() searches index
* nodes only, returning a base-level predecessor of the key. findNode()
* finishes out the base-level search. Even with this factoring, there is a
* fair amount of near-duplication of code to handle variants.
*
* For explanation of algorithms sharing at least a couple of features with
* this one, see Mikhail Fomitchev's thesis
* (http://www.cs.yorku.ca/~mikhail/), Keir Fraser's thesis
* (http://www.cl.cam.ac.uk/users/kaf24/), and Hakan Sundell's thesis
* (http://www.cs.chalmers.se/~phs/).
*
* Given the use of tree-like index nodes, you might wonder why this doesn't
* use some kind of search tree instead, which would support somewhat faster
* search operations. The reason is that there are no known efficient
* lock-free insertion and deletion algorithms for search trees. The
* immutability of the "down" links of index nodes (as opposed to mutable
* "left" fields in true trees) makes this tractable using only CAS
* operations.
*
* Notation guide for local variables Node: b, n, f for predecessor, node,
* successor Index: q, r, d for index node, right, down. t for another index
* node Head: h Levels: j Keys: k, key Values: v, value Comparisons: c
*/
private static final long serialVersionUID = -8627078645895051609L;
/**
* Special value used to identify base-level header
*/
private static final Object BASE_HEADER = new Object();
/**
* The topmost head index of the skiplist.
*/
private transient volatile HeadIndex<K, V> head;
/**
* The comparator used to maintain order in this map, or null if using
* natural ordering.
*
* @serial
*/
private final Comparator<? super K> comparator;
/** Lazily initialized key set */
private transient KeySet keySet;
/** Lazily initialized entry set */
private transient EntrySet entrySet;
/** Lazily initialized values collection */
private transient Values values;
/** Lazily initialized descending key set */
private transient ConcurrentNavigableMap<K, V> descendingMap;
/**
* Initializes or resets state. Needed by constructors, clone, clear,
* readObject. and ConcurrentSkipListSet.clone. (Note that comparator must
* be separately initialized.)
*/
final void initialize() {
keySet = null;
entrySet = null;
values = null;
descendingMap = null;
head = new HeadIndex<K, V>(new Node<K, V>(null, BASE_HEADER, null),
null, null, 1);
}
/** Updater for casHead */
private static final AtomicReferenceFieldUpdater<NonBlockingJavaSkipListMap, HeadIndex> headUpdater = AtomicReferenceFieldUpdater
.newUpdater(NonBlockingJavaSkipListMap.class, HeadIndex.class,
"head");
/**
* compareAndSet head node
*/
private boolean casHead(HeadIndex<K, V> cmp, HeadIndex<K, V> val) {
return headUpdater.compareAndSet(this, cmp, val);
}
/* ---------------- Nodes -------------- */
/**
* Nodes hold keys and values, and are singly linked in sorted order,
* possibly with some intervening marker nodes. The list is headed by a
* dummy node accessible as head.node. The value field is declared only as
* Object because it takes special non-V values for marker and header nodes.
*/
static final class Node<K, V> {
final K key;
volatile Object value;
volatile Node<K, V> next;
/**
* Creates a new regular node.
*/
Node(K key, Object value, Node<K, V> next) {
this.key = key;
this.value = value;
this.next = next;
}
/**
* Creates a new marker node. A marker is distinguished by having its
* value field point to itself. Marker nodes also have null keys, a fact
* that is exploited in a few places, but this doesn't distinguish
* markers from the base-level header node (head.node), which also has a
* null key.
*/
Node(Node<K, V> next) {
this.key = null;
this.value = this;
this.next = next;
}
/** Updater for casNext */
static final AtomicReferenceFieldUpdater<Node, Node> nextUpdater = AtomicReferenceFieldUpdater
.newUpdater(Node.class, Node.class, "next");
/** Updater for casValue */
static final AtomicReferenceFieldUpdater<Node, Object> valueUpdater = AtomicReferenceFieldUpdater
.newUpdater(Node.class, Object.class, "value");
/**
* compareAndSet value field
*/
boolean casValue(Object cmp, Object val) {
return valueUpdater.compareAndSet(this, cmp, val);
}
/**
* compareAndSet next field
*/
boolean casNext(Node<K, V> cmp, Node<K, V> val) {
return nextUpdater.compareAndSet(this, cmp, val);
}
/**
* Returns true if this node is a marker. This method isn't actually
* called in any current code checking for markers because callers will
* have already read value field and need to use that read (not another
* done here) and so directly test if value points to node.
*
* @param n
* a possibly null reference to a node
* @return true if this node is a marker node
*/
boolean isMarker() {
return value == this;
}
/**
* Returns true if this node is the header of base-level list.
*
* @return true if this node is header node
*/
boolean isBaseHeader() {
return value == BASE_HEADER;
}
/**
* Tries to append a deletion marker to this node.
*
* @param f
* the assumed current successor of this node
* @return true if successful
*/
boolean appendMarker(Node<K, V> f) {
return casNext(f, new Node<K, V>(f));
}
/**
* Helps out a deletion by appending marker or unlinking from
* predecessor. This is called during traversals when value field seen
* to be null.
*
* @param b
* predecessor
* @param f
* successor
*/
void helpDelete(Node<K, V> b, Node<K, V> f) {
/*
* Rechecking links and then doing only one of the help-out stages
* per call tends to minimize CAS interference among helping
* threads.
*/
if (f == next && this == b.next) {
if (f == null || f.value != f) // not already marked
appendMarker(f);
else
b.casNext(this, f.next);
}
}
/**
* Returns value if this node contains a valid key-value pair, else
* null.
*
* @return this node's value if it isn't a marker or header or is
* deleted, else null.
*/
V getValidValue() {
Object v = value;
if (v == this || v == BASE_HEADER)
return null;
return (V) v;
}
/**
* Creates and returns a new SimpleImmutableEntry holding current
* mapping if this node holds a valid value, else null.
*
* @return new entry or null
*/
AbstractMap.SimpleImmutableEntry<K, V> createSnapshot() {
V v = getValidValue();
if (v == null)
return null;
return new AbstractMap.SimpleImmutableEntry<K, V>(key, v);
}
}
/* ---------------- 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;
}
/** Updater for casRight */
static final AtomicReferenceFieldUpdater<Index, Index> rightUpdater = AtomicReferenceFieldUpdater
.newUpdater(Index.class, Index.class, "right");
/**
* compareAndSet right field
*/
final boolean casRight(Index<K, V> cmp, Index<K, V> val) {
return rightUpdater.compareAndSet(this, cmp, val);
}
/**
* Returns true if the node this indexes has been deleted.
*
* @return true if indexed node is known to be deleted
*/
final boolean indexesDeletedNode() {
return node.value == null;
}
/**
* Tries to CAS newSucc as successor. To minimize races with unlink that
* may lose this index node, if the node being indexed is known to be
* deleted, it doesn't try to link in.
*
* @param succ
* the expected current successor
* @param newSucc
* the new successor
* @return true if successful
*/
final boolean link(Index<K, V> succ, Index<K, V> newSucc) {
Node<K, V> n = node;
newSucc.right = succ;
return n.value != null && casRight(succ, newSucc);
}
/**
* Tries to CAS right field to skip over apparent successor succ. Fails
* (forcing a retraversal by caller) if this node is known to be
* deleted.
*
* @param succ
* the expected current successor
* @return true if successful
*/
final boolean unlink(Index<K, V> succ) {
// if(STRUCT_MODS)
// counts.get().structMods++;
return !indexesDeletedNode() && casRight(succ, succ.right);
}
}
/* ---------------- Head nodes -------------- */
/**
* Nodes heading each level keep track of their level.
*/
static final class HeadIndex<K, V> extends Index<K, V> {
final int level;
HeadIndex(Node<K, V> node, Index<K, V> down, Index<K, V> right,
int level) {
super(node, down, right);
this.level = level;
}
}
/* ---------------- Comparison utilities -------------- */
/**
* Represents a key with a comparator as a Comparable.
*
* Because most sorted collections seem to use natural ordering on
* Comparables (Strings, Integers, etc), most internal methods are geared to
* use them. This is generally faster than checking per-comparison whether
* to use comparator or comparable because it doesn't require a (Comparable)
* cast for each comparison. (Optimizers can only sometimes remove such
* redundant checks themselves.) When Comparators are used,
* ComparableUsingComparators are created so that they act in the same way
* as natural orderings. This penalizes use of Comparators vs Comparables,
* which seems like the right tradeoff.
*/
static final class ComparableUsingComparator<K> implements Comparable<K> {
final K actualKey;
final Comparator<? super K> cmp;
ComparableUsingComparator(K key, Comparator<? super K> cmp) {
this.actualKey = key;
this.cmp = cmp;
}
public int compareTo(K k2) {
return cmp.compare(actualKey, k2);
}
}
/**
* If using comparator, return a ComparableUsingComparator, else cast key as
* Comparable, which may cause ClassCastException, which is propagated back
* to caller.
*/
private Comparable<? super K> comparable(Object key)
throws ClassCastException {
if (key == null)
throw new NullPointerException();
if (comparator != null)
return new ComparableUsingComparator<K>((K) key, comparator);
else
return (Comparable<? super K>) key;
}
/**
* Compares using comparator or natural ordering. Used when the
* ComparableUsingComparator approach doesn't apply.
*/
int compare(K k1, K k2) throws ClassCastException {
Comparator<? super K> cmp = comparator;
if (cmp != null)
return cmp.compare(k1, k2);
else
return ((Comparable<? super K>) 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<K, V> findPredecessor(Comparable<? super K> key) {
if (key == null)
throw new NullPointerException(); // don't postpone errors
for (;;) {
Index<K, V> q = head;
Index<K, V> r = q.right;
for (;;) {
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 (key.compareTo(k) > 0) {
q = r;
r = r.right;
continue;
}
}
Index<K, V> d = q.down;
if (d != null) {
q = d;
r = d.right;
} else
return q.node;
}
}
}
/**
* Returns node holding key or null if no such, clearing out any deleted
* nodes seen along the way. Repeatedly traverses at base-level looking for
* key starting at predecessor returned from findPredecessor, processing
* base-level deletions as encountered. Some callers rely on this
* side-effect of clearing deleted nodes.
*
* Restarts occur, at traversal step centered on node n, if:
*
* (1) After reading n's next field, n is no longer assumed predecessor b's
* current successor, which means that we don't have a consistent 3-node
* snapshot and so cannot unlink any subsequent deleted nodes encountered.
*
* (2) n's value field is null, indicating n is deleted, in which case we
* help out an ongoing structural deletion before retrying. Even though
* there are cases where such unlinking doesn't require restart, they aren't
* sorted out here because doing so would not usually outweigh cost of
* restarting.
*
* (3) n is a marker or n's predecessor's value field is null, indicating
* (among other possibilities) that findPredecessor returned a deleted node.
* We can't unlink the node because we don't know its predecessor, so rely
* on another call to findPredecessor to notice and return some earlier
* predecessor, which it will do. This check is only strictly needed at
* beginning of loop, (and the b.value check isn't strictly needed at all)
* but is done each iteration to help avoid contention with other threads by
* callers that will fail to be able to change links, and so will retry
* anyway.
*
* The traversal loops in doPut, doRemove, and findNear all include the same
* three kinds of checks. And specialized versions appear in findFirst, and
* findLast and their variants. They can't easily share code because each
* uses the reads of fields held in locals occurring in the orders they were
* performed.
*
* @param key
* the key
* @return node holding key, or null if no such
*/
private Node<K, V> findNode(Comparable<? super K> key) {
for (;;) {
Node<K, V> b = findPredecessor(key);
Node<K, V> n = b.next;
for (;;) {
if (n == null)
return null;
Node<K, V> f = n.next;
if (n != b.next) // inconsistent read
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (v == n || b.value == null) // b is deleted
break;
int c = key.compareTo(n.key);
if (c == 0)
return n;
if (c < 0)
return null;
b = n;
n = f;
}
}
}
void finishCount2(int nodesTraversed) {
Vars vars = counts.get();
vars.nodesTraversed += nodesTraversed;
}
void finishCount1(int nodesTraversed) {
Vars vars = counts.get();
vars.getCount++;
vars.nodesTraversed += nodesTraversed;
}
// Extra version so we count the get traversals
private Node<K, V> findGetNode(Comparable<? super K> key) {
int nodesTraversed = 0;
for (;;) {
Node<K, V> b = findPredecessor(key);
Node<K, V> n = b.next;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
for (;;) {
if (n == null) {
if (TRAVERSAL_COUNT) {
finishCount2(nodesTraversed);
}
return null;
}
Node<K, V> f = n.next;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
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) {
if (TRAVERSAL_COUNT) {
finishCount2(nodesTraversed);
}
return n;
}
if (c < 0) {
if (TRAVERSAL_COUNT) {
finishCount2(nodesTraversed);
}
return null;
}
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<? super K> key = comparable(okey);
Node<K, V> bound = null;
Index<K, V> q = head;
Index<K, V> r = q.right;
Node<K, V> n;
K k;
int c;
int nodesTraversed = 0;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
for (;;) {
Index<K, V> d;
// Traverse rights
if (r != null && (n = r.node) != bound && (k = n.key) != null) {
if ((c = key.compareTo(k)) > 0) {
q = r;
r = r.right;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
continue;
} else if (c == 0) {
Object v = n.value;
if (TRAVERSAL_COUNT) {
finishCount1(nodesTraversed);
}
return (v != null) ? (V) v : getUsingFindNode(key);
} else
bound = n;
}
// Traverse down
if ((d = q.down) != null) {
q = d;
r = d.right;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
} else
break;
}
// Traverse nexts
for (n = q.node.next; n != null; n = n.next) {
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
if ((k = n.key) != null) {
if ((c = key.compareTo(k)) == 0) {
Object v = n.value;
if (TRAVERSAL_COUNT) {
finishCount1(nodesTraversed);
}
return (v != null) ? (V) v : getUsingFindNode(key);
} else if (c < 0)
break;
}
}
if (TRAVERSAL_COUNT) {
finishCount1(nodesTraversed);
}
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<? super K> key) {
/*
* Loop needed here and elsewhere in case value field goes null just as
* it is about to be returned, in which case we lost a race with a
* deletion, so must retry.
*/
for (;;) {
Node<K, V> n = findGetNode(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<? super K> key = comparable(kkey);
for (;;) {
Node<K, V> b = findPredecessor(key);
Node<K, V> n = b.next;
for (;;) {
if (n != null) {
Node<K, V> f = n.next;
if (n != b.next) // inconsistent read
break;
;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (v == n || b.value == null) // b is deleted
break;
int c = key.compareTo(n.key);
if (c > 0) {
b = n;
n = f;
continue;
}
if (c == 0) {
if (onlyIfAbsent || n.casValue(v, value))
return (V) v;
else
break; // restart if lost race to replace value
}
// else c < 0; fall through
}
Node<K, V> z = new Node<K, V>(kkey, value, n);
if (!b.casNext(n, z))
break; // restart if lost race to append to b
int level = randomLevel();
if (level > 0) {
// if(STRUCT_MODS)
// counts.get().structMods += level - 1;
insertIndex(z, level);
}
return null;
}
}
}
/**
* Returns a random level for inserting a new node. Hardwired to k=1, p=0.5,
* max 31 (see above and Pugh's "Skip List Cookbook", sec 3.4).
*
* This uses the simplest of the generators described in George Marsaglia's
* "Xorshift RNGs" paper. This is not a high-quality generator but is
* acceptable here.
*/
private int randomLevel() {
return skiplists.RandomLevelGenerator.randomLevel();
}
/**
* Creates and adds index nodes for the given node.
*
* @param z
* the node
* @param level
* the level of the index
*/
private void insertIndex(Node<K, V> z, int level) {
HeadIndex<K, V> h = head;
int max = h.level;
if (level <= max) {
Index<K, V> idx = null;
for (int i = 1; i <= level; ++i)
idx = new Index<K, V>(z, idx, null);
addIndex(idx, h, level);
} else { // Add a new level
/*
* To reduce interference by other threads checking for empty levels
* in tryReduceLevel, new levels are added with initialized right
* pointers. Which in turn requires keeping levels in an array to
* access them while creating new head index nodes from the opposite
* direction.
*/
level = max + 1;
Index<K, V>[] idxs = (Index<K, V>[]) new Index[level + 1];
Index<K, V> idx = null;
for (int i = 1; i <= level; ++i)
idxs[i] = idx = new Index<K, V>(z, idx, null);
HeadIndex<K, V> oldh;
int k;
for (;;) {
oldh = head;
int oldLevel = oldh.level;
if (level <= oldLevel) { // lost race to add level
k = level;
break;
}
HeadIndex<K, V> newh = oldh;
Node<K, V> oldbase = oldh.node;
for (int j = oldLevel + 1; j <= level; ++j)
newh = new HeadIndex<K, V>(oldbase, newh, idxs[j], j);
if (casHead(oldh, newh)) {
k = oldLevel;
break;
}
}
addIndex(idxs[k], oldh, k);
}
}
/**
* 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<K, V> idx, HeadIndex<K, V> h, int indexLevel) {
// Track next level to insert in case of retries
int insertionLevel = indexLevel;
Comparable<? super K> key = comparable(idx.node.key);
if (key == null)
throw new NullPointerException();
// Similar to findPredecessor, but adding index nodes along
// path to key.
for (;;) {
int j = h.level;
Index<K, V> q = h;
Index<K, V> r = q.right;
Index<K, V> t = idx;
for (;;) {
if (r != null) {
Node<K, V> n = r.node;
// compare before deletion check avoids needing recheck
int c = key.compareTo(n.key);
if (n.value == null) {
if (!q.unlink(r))
break;
r = q.right;
continue;
}
if (c > 0) {
q = r;
r = r.right;
continue;
}
}
if (j == insertionLevel) {
// Don't insert index if node already deleted
if (t.indexesDeletedNode()) {
findNode(key); // cleans up
return;
}
if (!q.link(r, t))
break; // restart
if (--insertionLevel == 0) {
// need final deletion check before return
if (t.indexesDeletedNode())
findNode(key);
return;
}
}
if (--j >= insertionLevel && j < indexLevel)
t = t.down;
q = q.down;
r = q.right;
}
}
}
/* ---------------- Deletion -------------- */
/**
* Main deletion method. Locates node, nulls value, appends a deletion
* marker, unlinks predecessor, removes associated index nodes, and possibly
* reduces head index level.
*
* Index nodes are cleared out simply by calling findPredecessor. which
* unlinks indexes to deleted nodes found along path to key, which will
* include the indexes to this node. This is done unconditionally. We can't
* check beforehand whether there are index nodes because it might be the
* case that some or all indexes hadn't been inserted yet for this node
* during initial search for it, and we'd like to ensure lack of garbage
* retention, so must call to be sure.
*
* @param okey
* the key
* @param value
* if non-null, the value that must be associated with key
* @return the node, or null if not found
*/
final V doRemove(Object okey, Object value) {
Comparable<? super K> key = comparable(okey);
for (;;) {
Node<K, V> b = findPredecessor(key);
Node<K, V> n = b.next;
for (;;) {
if (n == null)
return null;
Node<K, V> f = n.next;
if (n != b.next) // inconsistent read
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (v == n || b.value == null) // b is deleted
break;
int c = key.compareTo(n.key);
if (c < 0)
return null;
if (c > 0) {
b = n;
n = f;
continue;
}
if (value != null && !value.equals(v))
return null;
if (!n.casValue(v, null))
break;
if (STRUCT_MODS) {
Vars vars = counts.get();
vars.structMods++;
}
if (!n.appendMarker(f) || !b.casNext(n, f))
findNode(key); // Retry via findNode
else {
findPredecessor(key); // Clean index
if (head.right == null)
tryReduceLevel();
}
return (V) v;
}
}
}
/**
* Possibly reduce head level if it has no nodes. This method can (rarely)
* make mistakes, in which case levels can disappear even though they are
* about to contain index nodes. This impacts performance, not correctness.
* To minimize mistakes as well as to reduce hysteresis, the level is
* reduced by one only if the topmost three levels look empty. Also, if the
* removed level looks non-empty after CAS, we try to change it back quick
* before anyone notices our mistake! (This trick works pretty well because
* this method will practically never make mistakes unless current thread
* stalls immediately before first CAS, in which case it is very unlikely to
* stall again immediately afterwards, so will recover.)
*
* We put up with all this rather than just let levels grow because
* otherwise, even a small map that has undergone a large number of
* insertions and removals will have a lot of levels, slowing down access
* more than would an occasional unwanted reduction.
*/
private void tryReduceLevel() {
HeadIndex<K, V> h = head;
HeadIndex<K, V> d;
HeadIndex<K, V> e;
if (h.level > 3 && (d = (HeadIndex<K, V>) h.down) != null
&& (e = (HeadIndex<K, V>) d.down) != null && e.right == null
&& d.right == null && h.right == null && casHead(h, d) && // try
// to
// set
h.right != null) // recheck
casHead(d, h); // try to backout
}
/* ---------------- Finding and removing first element -------------- */
/**
* Specialized variant of findNode to get first valid node.
*
* @return first node or null if empty
*/
Node<K, V> findFirst() {
for (;;) {
Node<K, V> b = head.node;
Node<K, V> n = b.next;
if (n == null)
return null;
if (n.value != null)
return n;
n.helpDelete(b, n.next);
}
}
/**
* Removes first entry; returns its snapshot.
*
* @return null if empty, else snapshot of first entry
*/
Map.Entry<K, V> doRemoveFirstEntry() {
for (;;) {
Node<K, V> b = head.node;
Node<K, V> n = b.next;
if (n == null)
return null;
Node<K, V> f = n.next;
if (n != b.next)
continue;
Object v = n.value;
if (v == null) {
n.helpDelete(b, f);
continue;
}
if (!n.casValue(v, null))
continue;
if (!n.appendMarker(f) || !b.casNext(n, f))
findFirst(); // retry
clearIndexToFirst();
return new AbstractMap.SimpleImmutableEntry<K, V>(n.key, (V) v);
}
}
/**
* Clears out index nodes associated with deleted first entry.
*/
private void clearIndexToFirst() {
for (;;) {
Index<K, V> q = head;
for (;;) {
Index<K, V> r = q.right;
if (r != null && r.indexesDeletedNode() && !q.unlink(r))
break;
if ((q = q.down) == null) {
if (head.right == null)
tryReduceLevel();
return;
}
}
}
}
/* ---------------- Finding and removing last element -------------- */
/**
* Specialized version of find to get last valid node.
*
* @return last node or null if empty
*/
Node<K, V> findLast() {
/*
* findPredecessor can't be used to traverse index level because this
* doesn't use comparisons. So traversals of both levels are folded
* together.
*/
Index<K, V> q = head;
for (;;) {
Index<K, V> d, r;
if ((r = q.right) != null) {
if (r.indexesDeletedNode()) {
q.unlink(r);
q = head; // restart
} else
q = r;
} else if ((d = q.down) != null) {
q = d;
} else {
Node<K, V> b = q.node;
Node<K, V> n = b.next;
for (;;) {
if (n == null)
return (b.isBaseHeader()) ? null : b;
Node<K, V> f = n.next; // inconsistent read
if (n != b.next)
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (v == n || b.value == null) // b is deleted
break;
b = n;
n = f;
}
q = head; // restart
}
}
}
/**
* Specialized 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 (;;) {
Index<K, V> q = head;
for (;;) {
Index<K, V> d, r;
if ((r = q.right) != null) {
if (r.indexesDeletedNode()) {
q.unlink(r);
break; // must restart
}
// proceed as far across as possible without overshooting
if (r.node.next != null) {
q = r;
continue;
}
}
if ((d = q.down) != null)
q = d;
else
return q.node;
}
}
}
/**
* Removes last entry; returns its snapshot. Specialized variant of
* doRemove.
*
* @return null if empty, else snapshot of last entry
*/
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 (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<? super K> ck = comparable(key);
if (!n.appendMarker(f) || !b.casNext(n, f))
findNode(ck); // Retry via findNode
else {
findPredecessor(ck); // Clean index
if (head.right == null)
tryReduceLevel();
}
return new AbstractMap.SimpleImmutableEntry<K, V>(key, (V) v);
}
}
}
/* ---------------- Relational operations -------------- */
// Control values OR'ed as arguments to findNear
private static final int EQ = 1;
private static final int LT = 2;
private static final int GT = 0; // Actually checked as !LT
/**
* Utility for ceiling, floor, lower, higher methods.
*
* @param kkey
* the key
* @param rel
* the relation -- OR'ed combination of EQ, LT, GT
* @return nearest node fitting relation, or null if no such
*/
Node<K, V> findNear(K kkey, int rel) {
Comparable<? super K> key = comparable(kkey);
for (;;) {
Node<K, V> b = findPredecessor(key);
Node<K, V> n = b.next;
for (;;) {
if (n == null)
return ((rel & LT) == 0 || b.isBaseHeader()) ? null : b;
Node<K, V> f = n.next;
if (n != b.next) // inconsistent read
break;
Object v = n.value;
if (v == null) { // n is deleted
n.helpDelete(b, f);
break;
}
if (v == n || b.value == null) // b is deleted
break;
int c = key.compareTo(n.key);
if ((c == 0 && (rel & EQ) != 0) || (c < 0 && (rel & LT) == 0))
return n;
if (c <= 0 && (rel & LT) != 0)
return (b.isBaseHeader()) ? null : b;
b = n;
n = f;
}
}
}
/**
* Returns SimpleImmutableEntry for results of findNear.
*
* @param key
* the key
* @param rel
* the relation -- OR'ed combination of EQ, LT, GT
* @return Entry fitting relation, or null if no such
*/
AbstractMap.SimpleImmutableEntry<K, V> getNear(K key, int rel) {
for (;;) {
Node<K, V> n = findNear(key, rel);
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 NonBlockingJavaSkipListMap() {
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
* <tt>null</tt>, the {@linkplain Comparable natural ordering} of
* the keys will be used.
*/
public NonBlockingJavaSkipListMap(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 <tt>m</tt> 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 NonBlockingJavaSkipListMap(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 NonBlockingJavaSkipListMap(SortedMap<K, ? extends V> m) {
this.comparator = m.comparator();
initialize();
buildFromSorted(m);
}
/**
* Returns a shallow copy of this <tt>ConcurrentSkipListMap</tt> instance.
* (The keys and values themselves are not cloned.)
*
* @return a shallow copy of this map
*/
public NonBlockingJavaSkipListMap<K, V> clone() {
NonBlockingJavaSkipListMap<K, V> clone = null;
try {
clone = (NonBlockingJavaSkipListMap<K, V>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
clone.initialize();
clone.buildFromSorted(this);
return clone;
}
/**
* Streamlined bulk insertion to initialize from elements of given sorted
* map. Call only from constructor or clone method.
*/
private void buildFromSorted(SortedMap<K, ? extends V> map) {
if (map == null)
throw new NullPointerException();
HeadIndex<K, V> h = head;
Node<K, V> basepred = h.node;
// Track the current rightmost node at each level. Uses an
// ArrayList to avoid committing to initial or maximum level.
ArrayList<Index<K, V>> preds = new ArrayList<Index<K, V>>();
// initialize
for (int i = 0; i <= h.level; ++i)
preds.add(null);
Index<K, V> q = h;
for (int i = h.level; i > 0; --i) {
preds.set(i, q);
q = q.down;
}
Iterator<? extends Map.Entry<? extends K, ? extends V>> it = map
.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<? extends K, ? extends V> e = it.next();
int j = randomLevel();
if (j > h.level)
j = h.level + 1;
K k = e.getKey();
V v = e.getValue();
if (k == null || v == null)
throw new NullPointerException();
Node<K, V> z = new Node<K, V>(k, v, null);
basepred.next = z;
basepred = z;
if (j > 0) {
Index<K, V> idx = null;
for (int i = 1; i <= j; ++i) {
idx = new Index<K, V>(z, idx, null);
if (i > h.level)
h = new HeadIndex<K, V>(h.node, h, idx, i);
if (i < preds.size()) {
preds.get(i).right = idx;
preds.set(i, idx);
} else
preds.add(idx);
}
}
}
head = h;
}
/* ---------------- Serialization -------------- */
/**
* Save the state of this map to a stream.
*
* @serialData The key (Object) and value (Object) for each key-value
* mapping represented by the map, followed by <tt>null</tt>.
* The key-value mappings are emitted in key-order (as
* determined by the Comparator, or by the keys' natural
* ordering if no Comparator).
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// Write out the Comparator and any hidden stuff
s.defaultWriteObject();
// Write out keys and values (alternating)
for (Node<K, V> n = findFirst(); n != null; n = n.next) {
V v = n.getValidValue();
if (v != null) {
s.writeObject(n.key);
s.writeObject(v);
}
}
s.writeObject(null);
}
/**
* Reconstitute the map from a stream.
*/
private void readObject(final java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in the Comparator and any hidden stuff
s.defaultReadObject();
// Reset transients
initialize();
/*
* This is nearly identical to buildFromSorted, but is distinct because
* readObject calls can't be nicely adapted as the kind of iterator
* needed by buildFromSorted. (They can be, but doing so requires type
* cheats and/or creation of adaptor classes.) It is simpler to just
* adapt the code.
*/
HeadIndex<K, V> h = head;
Node<K, V> basepred = h.node;
ArrayList<Index<K, V>> preds = new ArrayList<Index<K, V>>();
for (int i = 0; i <= h.level; ++i)
preds.add(null);
Index<K, V> q = h;
for (int i = h.level; i > 0; --i) {
preds.set(i, q);
q = q.down;
}
for (;;) {
Object k = s.readObject();
if (k == null)
break;
Object v = s.readObject();
if (v == null)
throw new NullPointerException();
K key = (K) k;
V val = (V) v;
int j = randomLevel();
if (j > h.level)
j = h.level + 1;
Node<K, V> z = new Node<K, V>(key, val, null);
basepred.next = z;
basepred = z;
if (j > 0) {
Index<K, V> idx = null;
for (int i = 1; i <= j; ++i) {
idx = new Index<K, V>(z, idx, null);
if (i > h.level)
h = new HeadIndex<K, V>(h.node, h, idx, i);
if (i < preds.size()) {
preds.get(i).right = idx;
preds.set(i, idx);
} else
preds.add(idx);
}
}
}
head = h;
}
/* ------ Map API methods ------ */
/**
* Returns <tt>true</tt> if this map contains a mapping for the specified
* key.
*
* @param key
* key whose presence in this map is to be tested
* @return <tt>true</tt> if this map contains a mapping for the specified
* key
* @throws ClassCastException
* if the 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);
}
/**
* 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
* <tt>null</tt> 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
* <tt>null</tt> 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 <tt>true</tt> if this map maps one or more keys to the specified
* value. This operation requires time linear in the map size.
*
* @param value
* value whose presence in this map is to be tested
* @return <tt>true</tt> if a mapping to <tt>value</tt> exists;
* <tt>false</tt> otherwise
* @throws NullPointerException
* if the 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 <tt>Integer.MAX_VALUE</tt> elements, it returns
* <tt>Integer.MAX_VALUE</tt>.
*
* <p>
* Beware that, unlike in most collections, this method is <em>NOT</em> a
* constant-time operation. Because of the asynchronous nature of these
* maps, determining the current number of elements requires traversing them
* all to count them. Additionally, it is possible for the size to change
* during execution of this method, in which case the returned result will
* be inaccurate. Thus, this method is typically not very useful in
* concurrent applications.
*
* @return the number of elements in this map
*/
public int size() {
long count = 0;
for (Node<K, V> n = findFirst(); n != null; n = n.next) {
if (n.getValidValue() != null)
++count;
}
return (count >= Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int) count;
}
/**
* Returns <tt>true</tt> if this map contains no key-value mappings.
*
* @return <tt>true</tt> if this map contains no key-value mappings
*/
public boolean isEmpty() {
return findFirst() == null;
}
/**
* Removes all of the mappings from this map.
*/
public void clear() {
initialize();
}
/* ---------------- View methods -------------- */
/*
* Note: Lazy initialization works for views because view classes are
* stateless/immutable so it doesn't matter wrt correctness if more than one
* is created (which will only rarely happen). Even so, the following idiom
* conservatively ensures that the method returns the one it created if it
* does so, not one created by another racing thread.
*/
/**
* Returns a {@link NavigableSet} view of the keys contained in this map.
* The set's iterator returns the keys in ascending order. The set is backed
* by the map, so changes to the map are reflected in the set, and
* vice-versa. The set supports element removal, which removes the
* corresponding mapping from the map, via the {@code Iterator.remove},
* {@code Set.remove}, {@code removeAll}, {@code retainAll}, and
* {@code clear} operations. It does not support the {@code add} or
* {@code addAll} operations.
*
* <p>
* The view's {@code iterator} is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*
* <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 ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet(this));
}
public NavigableSet<K> navigableKeySet() {
KeySet ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet(this));
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection's iterator returns the values in ascending order of the
* corresponding keys. The collection is backed by the map, so changes to
* the map are reflected in the collection, and vice-versa. The collection
* supports element removal, which removes the corresponding mapping from
* the map, via the <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations. It
* does not support the <tt>add</tt> or <tt>addAll</tt> operations.
*
* <p>
* The view's <tt>iterator</tt> is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*/
public Collection<V> values() {
Values vs = values;
return (vs != null) ? vs : (values = new Values(this));
}
/**
* Returns a {@link Set} view of the mappings contained in this map. The
* set's iterator returns the entries in ascending key order. The set is
* backed by the map, so changes to the map are reflected in the set, and
* vice-versa. The set supports element removal, which removes the
* corresponding mapping from the map, via the <tt>Iterator.remove</tt>,
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or
* <tt>addAll</tt> operations.
*
* <p>
* The view's <tt>iterator</tt> is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*
* <p>
* The <tt>Map.Entry</tt> elements returned by <tt>iterator.next()</tt> do
* <em>not</em> support the <tt>setValue</tt> 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 es = entrySet;
return (es != null) ? es : (entrySet = new EntrySet(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
* <tt>true</tt> if the given object is also a map and the two maps
* represent the same mappings. More formally, two maps <tt>m1</tt> and
* <tt>m2</tt> represent the same mappings if
* <tt>m1.entrySet().equals(m2.entrySet())</tt>. This operation may return
* misleading results if either map is concurrently modified during
* execution of this method.
*
* @param o
* object to be compared for equality with this map
* @return <tt>true</tt> if the specified object is equal to this map
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map<?, ?> 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
* <tt>null</tt> if there was no mapping for the key
* @throws ClassCastException
* if the specified key cannot be compared with the keys
* currently in the map
* @throws NullPointerException
* if the specified key or value is null
*/
public V putIfAbsent(K key, V value) {
if (value == null)
throw new NullPointerException();
return doPut(key, value, true);
}
/**
* {@inheritDoc}
*
* @throws ClassCastException
* if the specified key cannot be compared with the keys
* currently in the map
* @throws NullPointerException
* if the specified key is null
*/
public boolean remove(Object key, Object value) {
if (key == null)
throw new NullPointerException();
if (value == null)
return false;
return doRemove(key, value) != null;
}
/**
* {@inheritDoc}
*
* @throws ClassCastException
* if the specified key cannot be compared with the keys
* currently in the map
* @throws NullPointerException
* if any of the arguments are null
*/
public boolean replace(K key, V oldValue, V newValue) {
if (oldValue == null || newValue == null)
throw new NullPointerException();
Comparable<? super K> k = comparable(key);
for (;;) {
Node<K, V> n = findNode(k);
if (n == null)
return false;
Object v = n.value;
if (v != null) {
if (!oldValue.equals(v))
return false;
if (n.casValue(v, newValue))
return true;
}
}
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or
* <tt>null</tt> if there was no mapping for the key
* @throws ClassCastException
* if the specified key cannot be compared with the keys
* currently in the map
* @throws NullPointerException
* if the specified key or value is null
*/
public V replace(K key, V value) {
if (value == null)
throw new NullPointerException();
Comparable<? super K> k = comparable(key);
for (;;) {
Node<K, V> n = findNode(k);
if (n == null)
return null;
Object v = n.value;
if (v != null && n.casValue(v, value))
return (V) v;
}
}
/* ------ SortedMap API methods ------ */
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 <tt>null</tt> if there is no such key. The
* returned entry does <em>not</em> support the <tt>Entry.setValue</tt>
* 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);
return (n == null) ? null : n.key;
}
/**
* Returns a key-value mapping associated with the greatest key less than or
* equal to the given key, or <tt>null</tt> if there is no such key. The
* returned entry does <em>not</em> support the <tt>Entry.setValue</tt>
* 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);
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 <tt>null</tt> if there is no such entry. The
* returned entry does <em>not</em> support the <tt>Entry.setValue</tt>
* 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);
return (n == null) ? null : n.key;
}
/**
* Returns a key-value mapping associated with the least key strictly
* greater than the given key, or <tt>null</tt> if there is no such key. The
* returned entry does <em>not</em> support the <tt>Entry.setValue</tt>
* 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);
return (n == null) ? null : n.key;
}
/**
* Returns a key-value mapping associated with the least key in this map, or
* <tt>null</tt> if the map is empty. The returned entry does <em>not</em>
* support the <tt>Entry.setValue</tt> method.
*/
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 <tt>null</tt> if the map is empty. The returned entry does
* <em>not</em> support the <tt>Entry.setValue</tt> 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 <tt>null</tt> if the map is empty. The returned entry does
* <em>not</em> support the <tt>Entry.setValue</tt> 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 <tt>null</tt> if the map is empty. The returned entry
* does <em>not</em> support the <tt>Entry.setValue</tt> 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() {
for (;;) {
next = findFirst();
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
nextValue = (V) x;
break;
}
}
}
public final boolean hasNext() {
return next != null;
}
/** Advances next to higher entry. */
final void advance() {
if (next == null)
throw new NoSuchElementException();
lastReturned = next;
for (;;) {
next = next.next;
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
nextValue = (V) x;
break;
}
}
}
public void remove() {
Node<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.
NonBlockingJavaSkipListMap.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.
List<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> {
private final ConcurrentNavigableMap<E, Object> m;
KeySet(ConcurrentNavigableMap<E, Object> 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, Object> e = m.pollFirstEntry();
return e == null ? null : e.getKey();
}
public E pollLast() {
Map.Entry<E, Object> e = m.pollLastEntry();
return e == null ? null : e.getKey();
}
public Iterator<E> iterator() {
if (m instanceof NonBlockingJavaSkipListMap)
return ((NonBlockingJavaSkipListMap<E, Object>) m)
.keyIterator();
else
return ((NonBlockingJavaSkipListMap.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) {
//TODO this is not implemented
return null;
// return new ConcurrentSkipListSet<E>(m.subMap(fromElement,
// fromInclusive, toElement, toInclusive));
}
public NavigableSet<E> headSet(E toElement, boolean inclusive) {
//TODO this is not implemented
return null;
// return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
}
public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
//TODO this is not implemented
return null;
// return new ConcurrentSkipListSet<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() {
//TODO this is not implemented
return null;
// return new ConcurrentSkipListSet(m.descendingMap());
}
}
static final class Values<E> extends AbstractCollection<E> {
private final ConcurrentNavigableMap<Object, E> m;
Values(ConcurrentNavigableMap<Object, E> map) {
m = map;
}
public Iterator<E> iterator() {
if (m instanceof NonBlockingJavaSkipListMap)
return ((NonBlockingJavaSkipListMap<Object, E>) m)
.valueIterator();
else
return ((SubMap<Object, 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);
}
}
static final class EntrySet<K1, V1> extends AbstractSet<Map.Entry<K1, V1>> {
private final ConcurrentNavigableMap<K1, V1> m;
EntrySet(ConcurrentNavigableMap<K1, V1> map) {
m = map;
}
public Iterator<Map.Entry<K1, V1>> iterator() {
if (m instanceof NonBlockingJavaSkipListMap)
return ((NonBlockingJavaSkipListMap<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<K1, V1> e = (Map.Entry<K1, V1>) 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<K1, V1> e = (Map.Entry<K1, V1>) 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);
}
}
/**
* Submaps returned by {@link NonBlockingJavaSkipListMap} submap operations
* represent a subrange of mappings of their underlying maps. Instances of
* this class support all methods of their underlying maps, differing in
* that mappings outside their range are ignored, and attempts to add
* mappings outside their ranges result in {@link IllegalArgumentException}.
* Instances of this class are constructed only using the <tt>subMap</tt>,
* <tt>headMap</tt>, and <tt>tailMap</tt> methods of their underlying maps.
*
* @serial include
*/
static final class SubMap<K, V> extends AbstractMap<K, V> implements
ConcurrentNavigableMap<K, V>, Cloneable, java.io.Serializable {
private static final long serialVersionUID = -7647078645895051609L;
/** Underlying map */
private final NonBlockingJavaSkipListMap<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(NonBlockingJavaSkipListMap<K, V> map, K fromKey,
boolean fromInclusive, K toKey, boolean toInclusive,
boolean isDescending) {
if (fromKey != null && toKey != null
&& map.compare(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 -------------- */
private boolean tooLow(K key) {
if (lo != null) {
int c = m.compare(key, lo);
if (c < 0 || (c == 0 && !loInclusive))
return true;
}
return false;
}
private boolean tooHigh(K key) {
if (hi != null) {
int c = m.compare(key, hi);
if (c > 0 || (c == 0 && !hiInclusive))
return true;
}
return false;
}
private boolean inBounds(K key) {
return !tooLow(key) && !tooHigh(key);
}
private void checkKeyBounds(K key) throws IllegalArgumentException {
if (key == null)
throw new NullPointerException();
if (!inBounds(key))
throw new IllegalArgumentException("key out of range");
}
/**
* Returns true if node key is less than upper bound of range
*/
private boolean isBeforeEnd(NonBlockingJavaSkipListMap.Node<K, V> n) {
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 = m.compare(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
*/
private NonBlockingJavaSkipListMap.Node<K, V> loNode() {
if (lo == null)
return m.findFirst();
else if (loInclusive)
return m.findNear(lo, m.GT | m.EQ);
else
return m.findNear(lo, m.GT);
}
/**
* Returns highest node. This node might not be in range, so most usages
* need to check bounds
*/
private NonBlockingJavaSkipListMap.Node<K, V> hiNode() {
if (hi == null)
return m.findLast();
else if (hiInclusive)
return m.findNear(hi, m.LT | m.EQ);
else
return m.findNear(hi, m.LT);
}
/**
* Returns lowest absolute key (ignoring directonality)
*/
private K lowestKey() {
NonBlockingJavaSkipListMap.Node<K, V> n = loNode();
if (isBeforeEnd(n))
return n.key;
else
throw new NoSuchElementException();
}
/**
* Returns highest absolute key (ignoring directonality)
*/
private K highestKey() {
NonBlockingJavaSkipListMap.Node<K, V> n = hiNode();
if (n != null) {
K last = n.key;
if (inBounds(last))
return last;
}
throw new NoSuchElementException();
}
private Map.Entry<K, V> lowestEntry() {
for (;;) {
NonBlockingJavaSkipListMap.Node<K, V> n = loNode();
if (!isBeforeEnd(n))
return null;
Map.Entry<K, V> e = n.createSnapshot();
if (e != null)
return e;
}
}
private Map.Entry<K, V> highestEntry() {
for (;;) {
NonBlockingJavaSkipListMap.Node<K, V> n = hiNode();
if (n == null || !inBounds(n.key))
return null;
Map.Entry<K, V> e = n.createSnapshot();
if (e != null)
return e;
}
}
private Map.Entry<K, V> removeLowest() {
for (;;) {
Node<K, V> n = loNode();
if (n == null)
return null;
K k = n.key;
if (!inBounds(k))
return null;
V v = m.doRemove(k, null);
if (v != null)
return new AbstractMap.SimpleImmutableEntry<K, V>(k, v);
}
}
private Map.Entry<K, V> removeHighest() {
for (;;) {
Node<K, V> n = hiNode();
if (n == null)
return null;
K k = n.key;
if (!inBounds(k))
return null;
V v = m.doRemove(k, null);
if (v != null)
return new AbstractMap.SimpleImmutableEntry<K, V>(k, v);
}
}
/**
* Submap version of ConcurrentSkipListMap.getNearEntry
*/
private Map.Entry<K, V> getNearEntry(K key, int rel) {
if (isDescending) { // adjust relation for direction
if ((rel & m.LT) == 0)
rel |= m.LT;
else
rel &= ~m.LT;
}
if (tooLow(key))
return ((rel & m.LT) != 0) ? null : lowestEntry();
if (tooHigh(key))
return ((rel & m.LT) != 0) ? highestEntry() : null;
for (;;) {
Node<K, V> n = m.findNear(key, rel);
if (n == null || !inBounds(n.key))
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
private K getNearKey(K key, int rel) {
if (isDescending) { // adjust relation for direction
if ((rel & m.LT) == 0)
rel |= m.LT;
else
rel &= ~m.LT;
}
if (tooLow(key)) {
if ((rel & m.LT) == 0) {
NonBlockingJavaSkipListMap.Node<K, V> n = loNode();
if (isBeforeEnd(n))
return n.key;
}
return null;
}
if (tooHigh(key)) {
if ((rel & m.LT) != 0) {
NonBlockingJavaSkipListMap.Node<K, V> n = hiNode();
if (n != null) {
K last = n.key;
if (inBounds(last))
return last;
}
}
return null;
}
for (;;) {
Node<K, V> n = m.findNear(key, rel);
if (n == null || !inBounds(n.key))
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();
K k = (K) key;
return inBounds(k) && m.containsKey(k);
}
public V get(Object key) {
if (key == null)
throw new NullPointerException();
K k = (K) key;
return ((!inBounds(k)) ? null : m.get(k));
}
public V put(K key, V value) {
checkKeyBounds(key);
return m.put(key, value);
}
public V remove(Object key) {
K k = (K) key;
return (!inBounds(k)) ? null : m.remove(k);
}
public int size() {
long count = 0;
for (NonBlockingJavaSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
if (n.getValidValue() != null)
++count;
}
return count >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) count;
}
public boolean isEmpty() {
return !isBeforeEnd(loNode());
}
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
for (NonBlockingJavaSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
V v = n.getValidValue();
if (v != null && value.equals(v))
return true;
}
return false;
}
public void clear() {
for (NonBlockingJavaSkipListMap.Node<K, V> n = loNode(); isBeforeEnd(n); n = n.next) {
if (n.getValidValue() != null)
m.remove(n.key);
}
}
/* ---------------- ConcurrentMap API methods -------------- */
public V putIfAbsent(K key, V value) {
checkKeyBounds(key);
return m.putIfAbsent(key, value);
}
public boolean remove(Object key, Object value) {
K k = (K) key;
return inBounds(k) && m.remove(k, value);
}
public boolean replace(K key, V oldValue, V newValue) {
checkKeyBounds(key);
return m.replace(key, oldValue, newValue);
}
public V replace(K key, V value) {
checkKeyBounds(key);
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.
*/
private SubMap<K, V> newSubMap(K fromKey, boolean fromInclusive,
K toKey, boolean toInclusive) {
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 = m.compare(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 = m.compare(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, (m.GT | m.EQ));
}
public K ceilingKey(K key) {
return getNearKey(key, (m.GT | m.EQ));
}
public Map.Entry<K, V> lowerEntry(K key) {
return getNearEntry(key, (m.LT));
}
public K lowerKey(K key) {
return getNearKey(key, (m.LT));
}
public Map.Entry<K, V> floorEntry(K key) {
return getNearEntry(key, (m.LT | m.EQ));
}
public K floorKey(K key) {
return getNearKey(key, (m.LT | m.EQ));
}
public Map.Entry<K, V> higherEntry(K key) {
return getNearEntry(key, (m.GT));
}
public K higherKey(K key) {
return getNearKey(key, (m.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(this));
}
public NavigableSet<K> navigableKeySet() {
KeySet<K> ks = keySetView;
return (ks != null) ? ks : (keySetView = new KeySet(this));
}
public Collection<V> values() {
Collection<V> vs = valuesView;
return (vs != null) ? vs : (valuesView = new Values(this));
}
public Set<Map.Entry<K, V>> entrySet() {
Set<Map.Entry<K, V>> es = entrySetView;
return (es != null) ? es : (entrySetView = new EntrySet(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.
*/
abstract class SubMapIter<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;
SubMapIter() {
for (;;) {
next = isDescending ? hiNode() : loNode();
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (!inBounds(next.key))
next = null;
else
nextValue = (V) x;
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() {
for (;;) {
next = next.next;
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (tooHigh(next.key))
next = null;
else
nextValue = (V) x;
break;
}
}
}
private void descend() {
for (;;) {
next = m.findNear(lastReturned.key, LT);
if (next == null)
break;
Object x = next.value;
if (x != null && x != next) {
if (tooLow(next.key))
next = null;
else
nextValue = (V) x;
break;
}
}
}
public void remove() {
Node<K, V> l = lastReturned;
if (l == null)
throw new IllegalStateException();
m.remove(l.key);
lastReturned = null;
}
}
final class SubMapValueIterator extends SubMapIter<V> {
public V next() {
V v = nextValue;
advance();
return v;
}
}
final class SubMapKeyIterator extends SubMapIter<K> {
public K next() {
Node<K, V> n = next;
advance();
return n.key;
}
}
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);
}
}
}
}