1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36 package java.util.concurrent;
37 import java.util.*;
38
39 /**
40 * A scalable concurrent {@link ConcurrentNavigableMap} implementation.
41 * The map is sorted according to the {@linkplain Comparable natural
42 * ordering} of its keys, or by a {@link Comparator} provided at map
43 * creation time, depending on which constructor is used.
44 *
45 * <p>This class implements a concurrent variant of <a
46 * href="http://en.wikipedia.org/wiki/Skip_list" target="_top">SkipLists</a>
47 * providing expected average <i>log(n)</i> time cost for the
48 * <tt>containsKey</tt>, <tt>get</tt>, <tt>put</tt> and
49 * <tt>remove</tt> operations and their variants. Insertion, removal,
50 * update, and access operations safely execute concurrently by
51 * multiple threads. Iterators are <i>weakly consistent</i>, returning
52 * elements reflecting the state of the map at some point at or since
53 * the creation of the iterator. They do <em>not</em> throw {@link
54 * ConcurrentModificationException}, and may proceed concurrently with
55 * other operations. Ascending key ordered views and their iterators
56 * are faster than descending ones.
57 *
58 * <p>All <tt>Map.Entry</tt> pairs returned by methods in this class
59 * and its views represent snapshots of mappings at the time they were
60 * produced. They do <em>not</em> support the <tt>Entry.setValue</tt>
61 * method. (Note however that it is possible to change mappings in the
62 * associated map using <tt>put</tt>, <tt>putIfAbsent</tt>, or
63 * <tt>replace</tt>, depending on exactly which effect you need.)
64 *
65 * <p>Beware that, unlike in most collections, the <tt>size</tt>
66 * method is <em>not</em> a constant-time operation. Because of the
67 * asynchronous nature of these maps, determining the current number
68 * of elements requires a traversal of the elements, and so may report
69 * inaccurate results if this collection is modified during traversal.
70 * Additionally, the bulk operations <tt>putAll</tt>, <tt>equals</tt>,
71 * <tt>toArray</tt>, <tt>containsValue</tt>, and <tt>clear</tt> are
72 * <em>not</em> guaranteed to be performed atomically. For example, an
73 * iterator operating concurrently with a <tt>putAll</tt> operation
74 * might view only some of the added elements.
75 *
76 * <p>This class and its views and iterators implement all of the
77 * <em>optional</em> methods of the {@link Map} and {@link Iterator}
78 * interfaces. Like most other concurrent collections, this class does
79 * <em>not</em> permit the use of <tt>null</tt> keys or values because some
80 * null return values cannot be reliably distinguished from the absence of
81 * elements.
82 *
83 * <p>This class is a member of the
84 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
85 * Java Collections Framework</a>.
86 *
87 * @author Doug Lea
88 * @param <K> the type of keys maintained by this map
89 * @param <V> the type of mapped values
90 * @since 1.6
91 */
92 @SuppressWarnings("unchecked")
93 public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V>
94 implements ConcurrentNavigableMap<K,V>,
95 Cloneable,
96 java.io.Serializable {
97 /*
98 * This class implements a tree-like two-dimensionally linked skip
99 * list in which the index levels are represented in separate
100 * nodes from the base nodes holding data. There are two reasons
101 * for taking this approach instead of the usual array-based
102 * structure: 1) Array based implementations seem to encounter
103 * more complexity and overhead 2) We can use cheaper algorithms
104 * for the heavily-traversed index lists than can be used for the
105 * base lists. Here's a picture of some of the basics for a
106 * possible list with 2 levels of index:
107 *
108 * Head nodes Index nodes
109 * +-+ right +-+ +-+
110 * |2|---------------->| |--------------------->| |->null
111 * +-+ +-+ +-+
112 * | down | |
113 * v v v
114 * +-+ +-+ +-+ +-+ +-+ +-+
115 * |1|----------->| |->| |------>| |----------->| |------>| |->null
116 * +-+ +-+ +-+ +-+ +-+ +-+
117 * v | | | | |
118 * Nodes next v v v v v
119 * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
120 * | |->|A|->|B|->|C|->|D|->|E|->|F|->|G|->|H|->|I|->|J|->|K|->null
121 * +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
122 *
123 * The base lists use a variant of the HM linked ordered set
124 * algorithm. See Tim Harris, "A pragmatic implementation of
125 * non-blocking linked lists"
126 * http://www.cl.cam.ac.uk/~tlh20/publications.html and Maged
127 * Michael "High Performance Dynamic Lock-Free Hash Tables and
128 * List-Based Sets"
129 * http://www.research.ibm.com/people/m/michael/pubs.htm. The
130 * basic idea in these lists is to mark the "next" pointers of
131 * deleted nodes when deleting to avoid conflicts with concurrent
132 * insertions, and when traversing to keep track of triples
133 * (predecessor, node, successor) in order to detect when and how
134 * to unlink these deleted nodes.
135 *
136 * Rather than using mark-bits to mark list deletions (which can
137 * be slow and space-intensive using AtomicMarkedReference), nodes
138 * use direct CAS'able next pointers. On deletion, instead of
139 * marking a pointer, they splice in another node that can be
140 * thought of as standing for a marked pointer (indicating this by
141 * using otherwise impossible field values). Using plain nodes
142 * acts roughly like "boxed" implementations of marked pointers,
143 * but uses new nodes only when nodes are deleted, not for every
144 * link. This requires less space and supports faster
145 * traversal. Even if marked references were better supported by
146 * JVMs, traversal using this technique might still be faster
147 * because any search need only read ahead one more node than
148 * otherwise required (to check for trailing marker) rather than
149 * unmasking mark bits or whatever on each read.
150 *
151 * This approach maintains the essential property needed in the HM
152 * algorithm of changing the next-pointer of a deleted node so
153 * that any other CAS of it will fail, but implements the idea by
154 * changing the pointer to point to a different node, not by
155 * marking it. While it would be possible to further squeeze
156 * space by defining marker nodes not to have key/value fields, it
157 * isn't worth the extra type-testing overhead. The deletion
158 * markers are rarely encountered during traversal and are
159 * normally quickly garbage collected. (Note that this technique
160 * would not work well in systems without garbage collection.)
161 *
162 * In addition to using deletion markers, the lists also use
163 * nullness of value fields to indicate deletion, in a style
164 * similar to typical lazy-deletion schemes. If a node's value is
165 * null, then it is considered logically deleted and ignored even
166 * though it is still reachable. This maintains proper control of
167 * concurrent replace vs delete operations -- an attempted replace
168 * must fail if a delete beat it by nulling field, and a delete
169 * must return the last non-null value held in the field. (Note:
170 * Null, rather than some special marker, is used for value fields
171 * here because it just so happens to mesh with the Map API
172 * requirement that method get returns null if there is no
173 * mapping, which allows nodes to remain concurrently readable
174 * even when deleted. Using any other marker value here would be
175 * messy at best.)
176 *
177 * Here's the sequence of events for a deletion of node n with
178 * predecessor b and successor f, initially:
179 *
180 * +------+ +------+ +------+
181 * ... | b |------>| n |----->| f | ...
182 * +------+ +------+ +------+
183 *
184 * 1. CAS n's value field from non-null to null.
185 * From this point on, no public operations encountering
186 * the node consider this mapping to exist. However, other
187 * ongoing insertions and deletions might still modify
188 * n's next pointer.
189 *
190 * 2. CAS n's next pointer to point to a new marker node.
191 * From this point on, no other nodes can be appended to n.
192 * which avoids deletion errors in CAS-based linked lists.
193 *
194 * +------+ +------+ +------+ +------+
195 * ... | b |------>| n |----->|marker|------>| f | ...
196 * +------+ +------+ +------+ +------+
197 *
198 * 3. CAS b's next pointer over both n and its marker.
199 * From this point on, no new traversals will encounter n,
200 * and it can eventually be GCed.
201 * +------+ +------+
202 * ... | b |----------------------------------->| f | ...
203 * +------+ +------+
204 *
205 * A failure at step 1 leads to simple retry due to a lost race
206 * with another operation. Steps 2-3 can fail because some other
207 * thread noticed during a traversal a node with null value and
208 * helped out by marking and/or unlinking. This helping-out
209 * ensures that no thread can become stuck waiting for progress of
210 * the deleting thread. The use of marker nodes slightly
211 * complicates helping-out code because traversals must track
212 * consistent reads of up to four nodes (b, n, marker, f), not
213 * just (b, n, f), although the next field of a marker is
214 * immutable, and once a next field is CAS'ed to point to a
215 * marker, it never again changes, so this requires less care.
216 *
217 * Skip lists add indexing to this scheme, so that the base-level
218 * traversals start close to the locations being found, inserted
219 * or deleted -- usually base level traversals only traverse a few
220 * nodes. This doesn't change the basic algorithm except for the
221 * need to make sure base traversals start at predecessors (here,
222 * b) that are not (structurally) deleted, otherwise retrying
223 * after processing the deletion.
224 *
225 * Index levels are maintained as lists with volatile next fields,
226 * using CAS to link and unlink. Races are allowed in index-list
227 * operations that can (rarely) fail to link in a new index node
228 * or delete one. (We can't do this of course for data nodes.)
229 * However, even when this happens, the index lists remain sorted,
230 * so correctly serve as indices. This can impact performance,
231 * but since skip lists are probabilistic anyway, the net result
232 * is that under contention, the effective "p" value may be lower
233 * than its nominal value. And race windows are kept small enough
234 * that in practice these failures are rare, even under a lot of
235 * contention.
236 *
237 * The fact that retries (for both base and index lists) are
238 * relatively cheap due to indexing allows some minor
239 * simplifications of retry logic. Traversal restarts are
240 * performed after most "helping-out" CASes. This isn't always
241 * strictly necessary, but the implicit backoffs tend to help
242 * reduce other downstream failed CAS's enough to outweigh restart
243 * cost. This worsens the worst case, but seems to improve even
244 * highly contended cases.
245 *
246 * Unlike most skip-list implementations, index insertion and
247 * deletion here require a separate traversal pass occuring after
248 * the base-level action, to add or remove index nodes. This adds
249 * to single-threaded overhead, but improves contended
250 * multithreaded performance by narrowing interference windows,
251 * and allows deletion to ensure that all index nodes will be made
252 * unreachable upon return from a public remove operation, thus
253 * avoiding unwanted garbage retention. This is more important
254 * here than in some other data structures because we cannot null
255 * out node fields referencing user keys since they might still be
256 * read by other ongoing traversals.
257 *
258 * Indexing uses skip list parameters that maintain good search
259 * performance while using sparser-than-usual indices: The
260 * hardwired parameters k=1, p=0.5 (see method randomLevel) mean
261 * that about one-quarter of the nodes have indices. Of those that
262 * do, half have one level, a quarter have two, and so on (see
263 * Pugh's Skip List Cookbook, sec 3.4). The expected total space
264 * requirement for a map is slightly less than for the current
265 * implementation of java.util.TreeMap.
266 *
267 * Changing the level of the index (i.e, the height of the
268 * tree-like structure) also uses CAS. The head index has initial
269 * level/height of one. Creation of an index with height greater
270 * than the current level adds a level to the head index by
271 * CAS'ing on a new top-most head. To maintain good performance
272 * after a lot of removals, deletion methods heuristically try to
273 * reduce the height if the topmost levels appear to be empty.
274 * This may encounter races in which it possible (but rare) to
275 * reduce and "lose" a level just as it is about to contain an
276 * index (that will then never be encountered). This does no
277 * structural harm, and in practice appears to be a better option
278 * than allowing unrestrained growth of levels.
279 *
280 * The code for all this is more verbose than you'd like. Most
281 * operations entail locating an element (or position to insert an
282 * element). The code to do this can't be nicely factored out
283 * because subsequent uses require a snapshot of predecessor
284 * and/or successor and/or value fields which can't be returned
285 * all at once, at least not without creating yet another object
286 * to hold them -- creating such little objects is an especially
287 * bad idea for basic internal search operations because it adds
288 * to GC overhead. (This is one of the few times I've wished Java
289 * had macros.) Instead, some traversal code is interleaved within
290 * insertion and removal operations. The control logic to handle
291 * all the retry conditions is sometimes twisty. Most search is
292 * broken into 2 parts. findPredecessor() searches index nodes
293 * only, returning a base-level predecessor of the key. findNode()
294 * finishes out the base-level search. Even with this factoring,
295 * there is a fair amount of near-duplication of code to handle
296 * variants.
297 *
298 * For explanation of algorithms sharing at least a couple of
299 * features with this one, see Mikhail Fomitchev's thesis
300 * (http://www.cs.yorku.ca/~mikhail/), Keir Fraser's thesis
301 * (http://www.cl.cam.ac.uk/users/kaf24/), and Hakan Sundell's
302 * thesis (http://www.cs.chalmers.se/~phs/).
303 *
304 * Given the use of tree-like index nodes, you might wonder why
305 * this doesn't use some kind of search tree instead, which would
306 * support somewhat faster search operations. The reason is that
307 * there are no known efficient lock-free insertion and deletion
308 * algorithms for search trees. The immutability of the "down"
309 * links of index nodes (as opposed to mutable "left" fields in
310 * true trees) makes this tractable using only CAS operations.
311 *
312 * Notation guide for local variables
313 * Node: b, n, f for predecessor, node, successor
314 * Index: q, r, d for index node, right, down.
315 * t for another index node
316 * Head: h
317 * Levels: j
318 * Keys: k, key
319 * Values: v, value
320 * Comparisons: c
321 */
322
323 private static final long serialVersionUID = -8627078645895051609L;
324
325 /**
326 * Generates the initial random seed for the cheaper per-instance
327 * random number generators used in randomLevel.
328 */
329 private static final Random seedGenerator = new Random();
330
331 /**
332 * Special value used to identify base-level header
333 */
334 private static final Object BASE_HEADER = new Object();
335
336 /**
337 * The topmost head index of the skiplist.
338 */
339 private transient volatile HeadIndex<K,V> head;
340
341 /**
342 * The comparator used to maintain order in this map, or null
343 * if using natural ordering.
344 * @serial
345 */
346 private final Comparator<? super K> comparator;
347
348 /**
349 * Seed for simple random number generator. Not volatile since it
350 * doesn't matter too much if different threads don't see updates.
351 */
352 private transient int randomSeed;
353
354 /** Lazily initialized key set */
355 private transient KeySet<K> keySet;
356 /** Lazily initialized entry set */
357 private transient EntrySet<K,V> entrySet;
358 /** Lazily initialized values collection */
359 private transient Values<V> values;
360 /** Lazily initialized descending key set */
361 private transient ConcurrentNavigableMap<K,V> descendingMap;
362
363 /**
364 * Initializes or resets state. Needed by constructors, clone,
365 * clear, readObject. and ConcurrentSkipListSet.clone.
366 * (Note that comparator must be separately initialized.)
367 */
368 final void initialize() {
369 keySet = null;
370 entrySet = null;
371 values = null;
372 descendingMap = null;
373 randomSeed = seedGenerator.nextInt() | 0x0100; // ensure nonzero
374 head = new HeadIndex<K,V>(new Node<K,V>(null, BASE_HEADER, null),
375 null, null, 1);
376 }
377
378 /**
379 * compareAndSet head node
380 */
381 private boolean casHead(HeadIndex<K,V> cmp, HeadIndex<K,V> val) {
382 return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
383 }
384
385 /* ---------------- Nodes -------------- */
386
387 /**
388 * Nodes hold keys and values, and are singly linked in sorted
389 * order, possibly with some intervening marker nodes. The list is
390 * headed by a dummy node accessible as head.node. The value field
391 * is declared only as Object because it takes special non-V
392 * values for marker and header nodes.
393 */
394 static final class Node<K,V> {
395 final K key;
396 volatile Object value;
397 volatile Node<K,V> next;
398
399 /**
400 * Creates a new regular node.
401 */
402 Node(K key, Object value, Node<K,V> next) {
403 this.key = key;
404 this.value = value;
405 this.next = next;
406 }
407
408 /**
409 * Creates a new marker node. A marker is distinguished by
410 * having its value field point to itself. Marker nodes also
411 * have null keys, a fact that is exploited in a few places,
412 * but this doesn't distinguish markers from the base-level
413 * header node (head.node), which also has a null key.
414 */
415 Node(Node<K,V> next) {
416 this.key = null;
417 this.value = this;
418 this.next = next;
419 }
420
421 /**
422 * compareAndSet value field
423 */
424 boolean casValue(Object cmp, Object val) {
425 return UNSAFE.compareAndSwapObject(this, valueOffset, cmp, val);
426 }
427
428 /**
429 * compareAndSet next field
430 */
431 boolean casNext(Node<K,V> cmp, Node<K,V> val) {
432 return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
433 }
434
435 /**
436 * Returns true if this node is a marker. This method isn't
437 * actually called in any current code checking for markers
438 * because callers will have already read value field and need
439 * to use that read (not another done here) and so directly
440 * test if value points to node.
441 * @param n a possibly null reference to a node
442 * @return true if this node is a marker node
443 */
444 boolean isMarker() {
445 return value == this;
446 }
447
448 /**
449 * Returns true if this node is the header of base-level list.
450 * @return true if this node is header node
451 */
452 boolean isBaseHeader() {
453 return value == BASE_HEADER;
454 }
455
456 /**
457 * Tries to append a deletion marker to this node.
458 * @param f the assumed current successor of this node
459 * @return true if successful
460 */
461 boolean appendMarker(Node<K,V> f) {
462 return casNext(f, new Node<K,V>(f));
463 }
464
465 /**
466 * Helps out a deletion by appending marker or unlinking from
467 * predecessor. This is called during traversals when value
468 * field seen to be null.
469 * @param b predecessor
470 * @param f successor
471 */
472 void helpDelete(Node<K,V> b, Node<K,V> f) {
473 /*
474 * Rechecking links and then doing only one of the
475 * help-out stages per call tends to minimize CAS
476 * interference among helping threads.
477 */
478 if (f == next && this == b.next) {
479 if (f == null || f.value != f) // not already marked
480 appendMarker(f);
481 else
482 b.casNext(this, f.next);
483 }
484 }
485
486 /**
487 * Returns value if this node contains a valid key-value pair,
488 * else null.
489 * @return this node's value if it isn't a marker or header or
490 * is deleted, else null.
491 */
492 V getValidValue() {
493 Object v = value;
494 if (v == this || v == BASE_HEADER)
495 return null;
496 return (V)v;
497 }
498
499 /**
500 * Creates and returns a new SimpleImmutableEntry holding current
501 * mapping if this node holds a valid value, else null.
502 * @return new entry or null
503 */
504 AbstractMap.SimpleImmutableEntry<K,V> createSnapshot() {
505 V v = getValidValue();
506 if (v == null)
507 return null;
508 return new AbstractMap.SimpleImmutableEntry<K,V>(key, v);
509 }
510
511 // UNSAFE mechanics
512
513 private static final sun.misc.Unsafe UNSAFE;
514 private static final long valueOffset;
515 private static final long nextOffset;
516
517 static {
518 try {
519 UNSAFE = sun.misc.Unsafe.getUnsafe();
520 Class<?> k = Node.class;
521 valueOffset = UNSAFE.objectFieldOffset
522 (k.getDeclaredField("value"));
523 nextOffset = UNSAFE.objectFieldOffset
524 (k.getDeclaredField("next"));
525 } catch (Exception e) {
526 throw new Error(e);
527 }
528 }
529 }
530
531 /* ---------------- Indexing -------------- */
532
533 /**
534 * Index nodes represent the levels of the skip list. Note that
535 * even though both Nodes and Indexes have forward-pointing
536 * fields, they have different types and are handled in different
537 * ways, that can't nicely be captured by placing field in a
538 * shared abstract class.
539 */
540 static class Index<K,V> {
541 final Node<K,V> node;
542 final Index<K,V> down;
543 volatile Index<K,V> right;
544
545 /**
546 * Creates index node with given values.
547 */
548 Index(Node<K,V> node, Index<K,V> down, Index<K,V> right) {
549 this.node = node;
550 this.down = down;
551 this.right = right;
552 }
553
554 /**
555 * compareAndSet right field
556 */
557 final boolean casRight(Index<K,V> cmp, Index<K,V> val) {
558 return UNSAFE.compareAndSwapObject(this, rightOffset, cmp, val);
559 }
560
561 /**
562 * Returns true if the node this indexes has been deleted.
563 * @return true if indexed node is known to be deleted
564 */
565 final boolean indexesDeletedNode() {
566 return node.value == null;
567 }
568
569 /**
570 * Tries to CAS newSucc as successor. To minimize races with
571 * unlink that may lose this index node, if the node being
572 * indexed is known to be deleted, it doesn't try to link in.
573 * @param succ the expected current successor
574 * @param newSucc the new successor
575 * @return true if successful
576 */
577 final boolean link(Index<K,V> succ, Index<K,V> newSucc) {
578 Node<K,V> n = node;
579 newSucc.right = succ;
580 return n.value != null && casRight(succ, newSucc);
581 }
582
583 /**
584 * Tries to CAS right field to skip over apparent successor
585 * succ. Fails (forcing a retraversal by caller) if this node
586 * is known to be deleted.
587 * @param succ the expected current successor
588 * @return true if successful
589 */
590 final boolean unlink(Index<K,V> succ) {
591 return !indexesDeletedNode() && casRight(succ, succ.right);
592 }
593
594 // Unsafe mechanics
595 private static final sun.misc.Unsafe UNSAFE;
596 private static final long rightOffset;
597 static {
598 try {
599 UNSAFE = sun.misc.Unsafe.getUnsafe();
600 Class<?> k = Index.class;
601 rightOffset = UNSAFE.objectFieldOffset
602 (k.getDeclaredField("right"));
603 } catch (Exception e) {
604 throw new Error(e);
605 }
606 }
607 }
608
609 /* ---------------- Head nodes -------------- */
610
611 /**
612 * Nodes heading each level keep track of their level.
613 */
614 static final class HeadIndex<K,V> extends Index<K,V> {
615 final int level;
616 HeadIndex(Node<K,V> node, Index<K,V> down, Index<K,V> right, int level) {
617 super(node, down, right);
618 this.level = level;
619 }
620 }
621
622 /* ---------------- Comparison utilities -------------- */
623
624 /**
625 * Represents a key with a comparator as a Comparable.
626 *
627 * Because most sorted collections seem to use natural ordering on
628 * Comparables (Strings, Integers, etc), most internal methods are
629 * geared to use them. This is generally faster than checking
630 * per-comparison whether to use comparator or comparable because
631 * it doesn't require a (Comparable) cast for each comparison.
632 * (Optimizers can only sometimes remove such redundant checks
633 * themselves.) When Comparators are used,
634 * ComparableUsingComparators are created so that they act in the
635 * same way as natural orderings. This penalizes use of
636 * Comparators vs Comparables, which seems like the right
637 * tradeoff.
638 */
639 static final class ComparableUsingComparator<K> implements Comparable<K> {
640 final K actualKey;
641 final Comparator<? super K> cmp;
642 ComparableUsingComparator(K key, Comparator<? super K> cmp) {
643 this.actualKey = key;
644 this.cmp = cmp;
645 }
646 public int compareTo(K k2) {
647 return cmp.compare(actualKey, k2);
648 }
649 }
650
651 /**
652 * If using comparator, return a ComparableUsingComparator, else
653 * cast key as Comparable, which may cause ClassCastException,
654 * which is propagated back to caller.
655 */
656 private Comparable<? super K> comparable(Object key)
657 throws ClassCastException {
658 if (key == null)
659 throw new NullPointerException();
660 if (comparator != null)
661 return new ComparableUsingComparator<K>((K)key, comparator);
662 else
663 return (Comparable<? super K>)key;
664 }
665
666 /**
667 * Compares using comparator or natural ordering. Used when the
668 * ComparableUsingComparator approach doesn't apply.
669 */
670 int compare(K k1, K k2) throws ClassCastException {
671 Comparator<? super K> cmp = comparator;
672 if (cmp != null)
673 return cmp.compare(k1, k2);
674 else
675 return ((Comparable<? super K>)k1).compareTo(k2);
676 }
677
678 /**
679 * Returns true if given key greater than or equal to least and
680 * strictly less than fence, bypassing either test if least or
681 * fence are null. Needed mainly in submap operations.
682 */
683 boolean inHalfOpenRange(K key, K least, K fence) {
684 if (key == null)
685 throw new NullPointerException();
686 return ((least == null || compare(key, least) >= 0) &&
687 (fence == null || compare(key, fence) < 0));
688 }
689
690 /**
691 * Returns true if given key greater than or equal to least and less
692 * or equal to fence. Needed mainly in submap operations.
693 */
694 boolean inOpenRange(K key, K least, K fence) {
695 if (key == null)
696 throw new NullPointerException();
697 return ((least == null || compare(key, least) >= 0) &&
698 (fence == null || compare(key, fence) <= 0));
699 }
700
701 /* ---------------- Traversal -------------- */
702
703 /**
704 * Returns a base-level node with key strictly less than given key,
705 * or the base-level header if there is no such node. Also
706 * unlinks indexes to deleted nodes found along the way. Callers
707 * rely on this side-effect of clearing indices to deleted nodes.
708 * @param key the key
709 * @return a predecessor of key
710 */
711 private Node<K,V> findPredecessor(Comparable<? super K> key) {
712 if (key == null)
713 throw new NullPointerException(); // don't postpone errors
714 for (;;) {
715 Index<K,V> q = head;
716 Index<K,V> r = q.right;
717 for (;;) {
718 if (r != null) {
719 Node<K,V> n = r.node;
720 K k = n.key;
721 if (n.value == null) {
722 if (!q.unlink(r))
723 break; // restart
724 r = q.right; // reread r
725 continue;
726 }
727 if (key.compareTo(k) > 0) {
728 q = r;
729 r = r.right;
730 continue;
731 }
732 }
733 Index<K,V> d = q.down;
734 if (d != null) {
735 q = d;
736 r = d.right;
737 } else
738 return q.node;
739 }
740 }
741 }
742
743 /**
744 * Returns node holding key or null if no such, clearing out any
745 * deleted nodes seen along the way. Repeatedly traverses at
746 * base-level looking for key starting at predecessor returned
747 * from findPredecessor, processing base-level deletions as
748 * encountered. Some callers rely on this side-effect of clearing
749 * deleted nodes.
750 *
751 * Restarts occur, at traversal step centered on node n, if:
752 *
753 * (1) After reading n's next field, n is no longer assumed
754 * predecessor b's current successor, which means that
755 * we don't have a consistent 3-node snapshot and so cannot
756 * unlink any subsequent deleted nodes encountered.
757 *
758 * (2) n's value field is null, indicating n is deleted, in
759 * which case we help out an ongoing structural deletion
760 * before retrying. Even though there are cases where such
761 * unlinking doesn't require restart, they aren't sorted out
762 * here because doing so would not usually outweigh cost of
763 * restarting.
764 *
765 * (3) n is a marker or n's predecessor's value field is null,
766 * indicating (among other possibilities) that
767 * findPredecessor returned a deleted node. We can't unlink
768 * the node because we don't know its predecessor, so rely
769 * on another call to findPredecessor to notice and return
770 * some earlier predecessor, which it will do. This check is
771 * only strictly needed at beginning of loop, (and the
772 * b.value check isn't strictly needed at all) but is done
773 * each iteration to help avoid contention with other
774 * threads by callers that will fail to be able to change
775 * links, and so will retry anyway.
776 *
777 * The traversal loops in doPut, doRemove, and findNear all
778 * include the same three kinds of checks. And specialized
779 * versions appear in findFirst, and findLast and their
780 * variants. They can't easily share code because each uses the
781 * reads of fields held in locals occurring in the orders they
782 * were performed.
783 *
784 * @param key the key
785 * @return node holding key, or null if no such
786 */
787 private Node<K,V> findNode(Comparable<? super K> key) {
788 for (;;) {
789 Node<K,V> b = findPredecessor(key);
790 Node<K,V> n = b.next;
791 for (;;) {
792 if (n == null)
793 return null;
794 Node<K,V> f = n.next;
795 if (n != b.next) // inconsistent read
796 break;
797 Object v = n.value;
798 if (v == null) { // n is deleted
799 n.helpDelete(b, f);
800 break;
801 }
802 if (v == n || b.value == null) // b is deleted
803 break;
804 int c = key.compareTo(n.key);
805 if (c == 0)
806 return n;
807 if (c < 0)
808 return null;
809 b = n;
810 n = f;
811 }
812 }
813 }
814
815 /**
816 * Gets value for key using findNode.
817 * @param okey the key
818 * @return the value, or null if absent
819 */
820 private V doGet(Object okey) {
821 Comparable<? super K> key = comparable(okey);
822 /*
823 * Loop needed here and elsewhere in case value field goes
824 * null just as it is about to be returned, in which case we
825 * lost a race with a deletion, so must retry.
826 */
827 for (;;) {
828 Node<K,V> n = findNode(key);
829 if (n == null)
830 return null;
831 Object v = n.value;
832 if (v != null)
833 return (V)v;
834 }
835 }
836
837 /* ---------------- Insertion -------------- */
838
839 /**
840 * Main insertion method. Adds element if not present, or
841 * replaces value if present and onlyIfAbsent is false.
842 * @param kkey the key
843 * @param value the value that must be associated with key
844 * @param onlyIfAbsent if should not insert if already present
845 * @return the old value, or null if newly inserted
846 */
847 private V doPut(K kkey, V value, boolean onlyIfAbsent) {
848 Comparable<? super K> key = comparable(kkey);
849 for (;;) {
850 Node<K,V> b = findPredecessor(key);
851 Node<K,V> n = b.next;
852 for (;;) {
853 if (n != null) {
854 Node<K,V> f = n.next;
855 if (n != b.next) // inconsistent read
856 break;
857 Object v = n.value;
858 if (v == null) { // n is deleted
859 n.helpDelete(b, f);
860 break;
861 }
862 if (v == n || b.value == null) // b is deleted
863 break;
864 int c = key.compareTo(n.key);
865 if (c > 0) {
866 b = n;
867 n = f;
868 continue;
869 }
870 if (c == 0) {
871 if (onlyIfAbsent || n.casValue(v, value))
872 return (V)v;
873 else
874 break; // restart if lost race to replace value
875 }
876 // else c < 0; fall through
877 }
878
879 Node<K,V> z = new Node<K,V>(kkey, value, n);
880 if (!b.casNext(n, z))
881 break; // restart if lost race to append to b
882 int level = randomLevel();
883 if (level > 0)
884 insertIndex(z, level);
885 return null;
886 }
887 }
888 }
889
890 /**
891 * Returns a random level for inserting a new node.
892 * Hardwired to k=1, p=0.5, max 31 (see above and
893 * Pugh's "Skip List Cookbook", sec 3.4).
894 *
895 * This uses the simplest of the generators described in George
896 * Marsaglia's "Xorshift RNGs" paper. This is not a high-quality
897 * generator but is acceptable here.
898 */
899 private int randomLevel() {
900 int x = randomSeed;
901 x ^= x << 13;
902 x ^= x >>> 17;
903 randomSeed = x ^= x << 5;
904 if ((x & 0x80000001) != 0) // test highest and lowest bits
905 return 0;
906 int level = 1;
907 while (((x >>>= 1) & 1) != 0) ++level;
908 return level;
909 }
910
911 /**
912 * Creates and adds index nodes for the given node.
913 * @param z the node
914 * @param level the level of the index
915 */
916 private void insertIndex(Node<K,V> z, int level) {
917 HeadIndex<K,V> h = head;
918 int max = h.level;
919
920 if (level <= max) {
921 Index<K,V> idx = null;
922 for (int i = 1; i <= level; ++i)
923 idx = new Index<K,V>(z, idx, null);
924 addIndex(idx, h, level);
925
926 } else { // Add a new level
927 /*
928 * To reduce interference by other threads checking for
929 * empty levels in tryReduceLevel, new levels are added
930 * with initialized right pointers. Which in turn requires
931 * keeping levels in an array to access them while
932 * creating new head index nodes from the opposite
933 * direction.
934 */
935 level = max + 1;
936 Index<K,V>[] idxs = (Index<K,V>[])new Index<?,?>[level+1];
937 Index<K,V> idx = null;
938 for (int i = 1; i <= level; ++i)
939 idxs[i] = idx = new Index<K,V>(z, idx, null);
940
941 HeadIndex<K,V> oldh;
942 int k;
943 for (;;) {
944 oldh = head;
945 int oldLevel = oldh.level;
946 if (level <= oldLevel) { // lost race to add level
947 k = level;
948 break;
949 }
950 HeadIndex<K,V> newh = oldh;
951 Node<K,V> oldbase = oldh.node;
952 for (int j = oldLevel+1; j <= level; ++j)
953 newh = new HeadIndex<K,V>(oldbase, newh, idxs[j], j);
954 if (casHead(oldh, newh)) {
955 k = oldLevel;
956 break;
957 }
958 }
959 addIndex(idxs[k], oldh, k);
960 }
961 }
962
963 /**
964 * Adds given index nodes from given level down to 1.
965 * @param idx the topmost index node being inserted
966 * @param h the value of head to use to insert. This must be
967 * snapshotted by callers to provide correct insertion level
968 * @param indexLevel the level of the index
969 */
970 private void addIndex(Index<K,V> idx, HeadIndex<K,V> h, int indexLevel) {
971 // Track next level to insert in case of retries
972 int insertionLevel = indexLevel;
973 Comparable<? super K> key = comparable(idx.node.key);
974 if (key == null) throw new NullPointerException();
975
976 // Similar to findPredecessor, but adding index nodes along
977 // path to key.
978 for (;;) {
979 int j = h.level;
980 Index<K,V> q = h;
981 Index<K,V> r = q.right;
982 Index<K,V> t = idx;
983 for (;;) {
984 if (r != null) {
985 Node<K,V> n = r.node;
986 // compare before deletion check avoids needing recheck
987 int c = key.compareTo(n.key);
988 if (n.value == null) {
989 if (!q.unlink(r))
990 break;
991 r = q.right;
992 continue;
993 }
994 if (c > 0) {
995 q = r;
996 r = r.right;
997 continue;
998 }
999 }
1000
1001 if (j == insertionLevel) {
1002 // Don't insert index if node already deleted
1003 if (t.indexesDeletedNode()) {
1004 findNode(key); // cleans up
1005 return;
1006 }
1007 if (!q.link(r, t))
1008 break; // restart
1009 if (--insertionLevel == 0) {
1010 // need final deletion check before return
1011 if (t.indexesDeletedNode())
1012 findNode(key);
1013 return;
1014 }
1015 }
1016
1017 if (--j >= insertionLevel && j < indexLevel)
1018 t = t.down;
1019 q = q.down;
1020 r = q.right;
1021 }
1022 }
1023 }
1024
1025 /* ---------------- Deletion -------------- */
1026
1027 /**
1028 * Main deletion method. Locates node, nulls value, appends a
1029 * deletion marker, unlinks predecessor, removes associated index
1030 * nodes, and possibly reduces head index level.
1031 *
1032 * Index nodes are cleared out simply by calling findPredecessor.
1033 * which unlinks indexes to deleted nodes found along path to key,
1034 * which will include the indexes to this node. This is done
1035 * unconditionally. We can't check beforehand whether there are
1036 * index nodes because it might be the case that some or all
1037 * indexes hadn't been inserted yet for this node during initial
1038 * search for it, and we'd like to ensure lack of garbage
1039 * retention, so must call to be sure.
1040 *
1041 * @param okey the key
1042 * @param value if non-null, the value that must be
1043 * associated with key
1044 * @return the node, or null if not found
1045 */
1046 final V doRemove(Object okey, Object value) {
1047 Comparable<? super K> key = comparable(okey);
1048 for (;;) {
1049 Node<K,V> b = findPredecessor(key);
1050 Node<K,V> n = b.next;
1051 for (;;) {
1052 if (n == null)
1053 return null;
1054 Node<K,V> f = n.next;
1055 if (n != b.next) // inconsistent read
1056 break;
1057 Object v = n.value;
1058 if (v == null) { // n is deleted
1059 n.helpDelete(b, f);
1060 break;
1061 }
1062 if (v == n || b.value == null) // b is deleted
1063 break;
1064 int c = key.compareTo(n.key);
1065 if (c < 0)
1066 return null;
1067 if (c > 0) {
1068 b = n;
1069 n = f;
1070 continue;
1071 }
1072 if (value != null && !value.equals(v))
1073 return null;
1074 if (!n.casValue(v, null))
1075 break;
1076 if (!n.appendMarker(f) || !b.casNext(n, f))
1077 findNode(key); // Retry via findNode
1078 else {
1079 findPredecessor(key); // Clean index
1080 if (head.right == null)
1081 tryReduceLevel();
1082 }
1083 return (V)v;
1084 }
1085 }
1086 }
1087
1088 /**
1089 * Possibly reduce head level if it has no nodes. This method can
1090 * (rarely) make mistakes, in which case levels can disappear even
1091 * though they are about to contain index nodes. This impacts
1092 * performance, not correctness. To minimize mistakes as well as
1093 * to reduce hysteresis, the level is reduced by one only if the
1094 * topmost three levels look empty. Also, if the removed level
1095 * looks non-empty after CAS, we try to change it back quick
1096 * before anyone notices our mistake! (This trick works pretty
1097 * well because this method will practically never make mistakes
1098 * unless current thread stalls immediately before first CAS, in
1099 * which case it is very unlikely to stall again immediately
1100 * afterwards, so will recover.)
1101 *
1102 * We put up with all this rather than just let levels grow
1103 * because otherwise, even a small map that has undergone a large
1104 * number of insertions and removals will have a lot of levels,
1105 * slowing down access more than would an occasional unwanted
1106 * reduction.
1107 */
1108 private void tryReduceLevel() {
1109 HeadIndex<K,V> h = head;
1110 HeadIndex<K,V> d;
1111 HeadIndex<K,V> e;
1112 if (h.level > 3 &&
1113 (d = (HeadIndex<K,V>)h.down) != null &&
1114 (e = (HeadIndex<K,V>)d.down) != null &&
1115 e.right == null &&
1116 d.right == null &&
1117 h.right == null &&
1118 casHead(h, d) && // try to set
1119 h.right != null) // recheck
1120 casHead(d, h); // try to backout
1121 }
1122
1123 /* ---------------- Finding and removing first element -------------- */
1124
1125 /**
1126 * Specialized variant of findNode to get first valid node.
1127 * @return first node or null if empty
1128 */
1129 Node<K,V> findFirst() {
1130 for (;;) {
1131 Node<K,V> b = head.node;
1132 Node<K,V> n = b.next;
1133 if (n == null)
1134 return null;
1135 if (n.value != null)
1136 return n;
1137 n.helpDelete(b, n.next);
1138 }
1139 }
1140
1141 /**
1142 * Removes first entry; returns its snapshot.
1143 * @return null if empty, else snapshot of first entry
1144 */
1145 Map.Entry<K,V> doRemoveFirstEntry() {
1146 for (;;) {
1147 Node<K,V> b = head.node;
1148 Node<K,V> n = b.next;
1149 if (n == null)
1150 return null;
1151 Node<K,V> f = n.next;
1152 if (n != b.next)
1153 continue;
1154 Object v = n.value;
1155 if (v == null) {
1156 n.helpDelete(b, f);
1157 continue;
1158 }
1159 if (!n.casValue(v, null))
1160 continue;
1161 if (!n.appendMarker(f) || !b.casNext(n, f))
1162 findFirst(); // retry
1163 clearIndexToFirst();
1164 return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, (V)v);
1165 }
1166 }
1167
1168 /**
1169 * Clears out index nodes associated with deleted first entry.
1170 */
1171 private void clearIndexToFirst() {
1172 for (;;) {
1173 Index<K,V> q = head;
1174 for (;;) {
1175 Index<K,V> r = q.right;
1176 if (r != null && r.indexesDeletedNode() && !q.unlink(r))
1177 break;
1178 if ((q = q.down) == null) {
1179 if (head.right == null)
1180 tryReduceLevel();
1181 return;
1182 }
1183 }
1184 }
1185 }
1186
1187
1188 /* ---------------- Finding and removing last element -------------- */
1189
1190 /**
1191 * Specialized version of find to get last valid node.
1192 * @return last node or null if empty
1193 */
1194 Node<K,V> findLast() {
1195 /*
1196 * findPredecessor can't be used to traverse index level
1197 * because this doesn't use comparisons. So traversals of
1198 * both levels are folded together.
1199 */
1200 Index<K,V> q = head;
1201 for (;;) {
1202 Index<K,V> d, r;
1203 if ((r = q.right) != null) {
1204 if (r.indexesDeletedNode()) {
1205 q.unlink(r);
1206 q = head; // restart
1207 }
1208 else
1209 q = r;
1210 } else if ((d = q.down) != null) {
1211 q = d;
1212 } else {
1213 Node<K,V> b = q.node;
1214 Node<K,V> n = b.next;
1215 for (;;) {
1216 if (n == null)
1217 return b.isBaseHeader() ? null : b;
1218 Node<K,V> f = n.next; // inconsistent read
1219 if (n != b.next)
1220 break;
1221 Object v = n.value;
1222 if (v == null) { // n is deleted
1223 n.helpDelete(b, f);
1224 break;
1225 }
1226 if (v == n || b.value == null) // b is deleted
1227 break;
1228 b = n;
1229 n = f;
1230 }
1231 q = head; // restart
1232 }
1233 }
1234 }
1235
1236 /**
1237 * Specialized variant of findPredecessor to get predecessor of last
1238 * valid node. Needed when removing the last entry. It is possible
1239 * that all successors of returned node will have been deleted upon
1240 * return, in which case this method can be retried.
1241 * @return likely predecessor of last node
1242 */
1243 private Node<K,V> findPredecessorOfLast() {
1244 for (;;) {
1245 Index<K,V> q = head;
1246 for (;;) {
1247 Index<K,V> d, r;
1248 if ((r = q.right) != null) {
1249 if (r.indexesDeletedNode()) {
1250 q.unlink(r);
1251 break; // must restart
1252 }
1253 // proceed as far across as possible without overshooting
1254 if (r.node.next != null) {
1255 q = r;
1256 continue;
1257 }
1258 }
1259 if ((d = q.down) != null)
1260 q = d;
1261 else
1262 return q.node;
1263 }
1264 }
1265 }
1266
1267 /**
1268 * Removes last entry; returns its snapshot.
1269 * Specialized variant of doRemove.
1270 * @return null if empty, else snapshot of last entry
1271 */
1272 Map.Entry<K,V> doRemoveLastEntry() {
1273 for (;;) {
1274 Node<K,V> b = findPredecessorOfLast();
1275 Node<K,V> n = b.next;
1276 if (n == null) {
1277 if (b.isBaseHeader()) // empty
1278 return null;
1279 else
1280 continue; // all b's successors are deleted; retry
1281 }
1282 for (;;) {
1283 Node<K,V> f = n.next;
1284 if (n != b.next) // inconsistent read
1285 break;
1286 Object v = n.value;
1287 if (v == null) { // n is deleted
1288 n.helpDelete(b, f);
1289 break;
1290 }
1291 if (v == n || b.value == null) // b is deleted
1292 break;
1293 if (f != null) {
1294 b = n;
1295 n = f;
1296 continue;
1297 }
1298 if (!n.casValue(v, null))
1299 break;
1300 K key = n.key;
1301 Comparable<? super K> ck = comparable(key);
1302 if (!n.appendMarker(f) || !b.casNext(n, f))
1303 findNode(ck); // Retry via findNode
1304 else {
1305 findPredecessor(ck); // Clean index
1306 if (head.right == null)
1307 tryReduceLevel();
1308 }
1309 return new AbstractMap.SimpleImmutableEntry<K,V>(key, (V)v);
1310 }
1311 }
1312 }
1313
1314 /* ---------------- Relational operations -------------- */
1315
1316 // Control values OR'ed as arguments to findNear
1317
1318 private static final int EQ = 1;
1319 private static final int LT = 2;
1320 private static final int GT = 0; // Actually checked as !LT
1321
1322 /**
1323 * Utility for ceiling, floor, lower, higher methods.
1324 * @param kkey the key
1325 * @param rel the relation -- OR'ed combination of EQ, LT, GT
1326 * @return nearest node fitting relation, or null if no such
1327 */
1328 Node<K,V> findNear(K kkey, int rel) {
1329 Comparable<? super K> key = comparable(kkey);
1330 for (;;) {
1331 Node<K,V> b = findPredecessor(key);
1332 Node<K,V> n = b.next;
1333 for (;;) {
1334 if (n == null)
1335 return ((rel & LT) == 0 || b.isBaseHeader()) ? null : b;
1336 Node<K,V> f = n.next;
1337 if (n != b.next) // inconsistent read
1338 break;
1339 Object v = n.value;
1340 if (v == null) { // n is deleted
1341 n.helpDelete(b, f);
1342 break;
1343 }
1344 if (v == n || b.value == null) // b is deleted
1345 break;
1346 int c = key.compareTo(n.key);
1347 if ((c == 0 && (rel & EQ) != 0) ||
1348 (c < 0 && (rel & LT) == 0))
1349 return n;
1350 if ( c <= 0 && (rel & LT) != 0)
1351 return b.isBaseHeader() ? null : b;
1352 b = n;
1353 n = f;
1354 }
1355 }
1356 }
1357
1358 /**
1359 * Returns SimpleImmutableEntry for results of findNear.
1360 * @param key the key
1361 * @param rel the relation -- OR'ed combination of EQ, LT, GT
1362 * @return Entry fitting relation, or null if no such
1363 */
1364 AbstractMap.SimpleImmutableEntry<K,V> getNear(K key, int rel) {
1365 for (;;) {
1366 Node<K,V> n = findNear(key, rel);
1367 if (n == null)
1368 return null;
1369 AbstractMap.SimpleImmutableEntry<K,V> e = n.createSnapshot();
1370 if (e != null)
1371 return e;
1372 }
1373 }
1374
1375
1376 /* ---------------- Constructors -------------- */
1377
1378 /**
1379 * Constructs a new, empty map, sorted according to the
1380 * {@linkplain Comparable natural ordering} of the keys.
1381 */
1382 public ConcurrentSkipListMap() {
1383 this.comparator = null;
1384 initialize();
1385 }
1386
1387 /**
1388 * Constructs a new, empty map, sorted according to the specified
1389 * comparator.
1390 *
1391 * @param comparator the comparator that will be used to order this map.
1392 * If <tt>null</tt>, the {@linkplain Comparable natural
1393 * ordering} of the keys will be used.
1394 */
1395 public ConcurrentSkipListMap(Comparator<? super K> comparator) {
1396 this.comparator = comparator;
1397 initialize();
1398 }
1399
1400 /**
1401 * Constructs a new map containing the same mappings as the given map,
1402 * sorted according to the {@linkplain Comparable natural ordering} of
1403 * the keys.
1404 *
1405 * @param m the map whose mappings are to be placed in this map
1406 * @throws ClassCastException if the keys in <tt>m</tt> are not
1407 * {@link Comparable}, or are not mutually comparable
1408 * @throws NullPointerException if the specified map or any of its keys
1409 * or values are null
1410 */
1411 public ConcurrentSkipListMap(Map<? extends K, ? extends V> m) {
1412 this.comparator = null;
1413 initialize();
1414 putAll(m);
1415 }
1416
1417 /**
1418 * Constructs a new map containing the same mappings and using the
1419 * same ordering as the specified sorted map.
1420 *
1421 * @param m the sorted map whose mappings are to be placed in this
1422 * map, and whose comparator is to be used to sort this map
1423 * @throws NullPointerException if the specified sorted map or any of
1424 * its keys or values are null
1425 */
1426 public ConcurrentSkipListMap(SortedMap<K, ? extends V> m) {
1427 this.comparator = m.comparator();
1428 initialize();
1429 buildFromSorted(m);
1430 }
1431
1432 /**
1433 * Returns a shallow copy of this <tt>ConcurrentSkipListMap</tt>
1434 * instance. (The keys and values themselves are not cloned.)
1435 *
1436 * @return a shallow copy of this map
1437 */
1438 public ConcurrentSkipListMap<K,V> clone() {
1439 try {
1440 @SuppressWarnings("unchecked")
1441 ConcurrentSkipListMap<K,V> clone =
1442 (ConcurrentSkipListMap<K,V>) super.clone();
1443 clone.initialize();
1444 clone.buildFromSorted(this);
1445 return clone;
1446 } catch (CloneNotSupportedException e) {
1447 throw new InternalError();
1448 }
1449 }
1450
1451 /**
1452 * Streamlined bulk insertion to initialize from elements of
1453 * given sorted map. Call only from constructor or clone
1454 * method.
1455 */
1456 private void buildFromSorted(SortedMap<K, ? extends V> map) {
1457 if (map == null)
1458 throw new NullPointerException();
1459
1460 HeadIndex<K,V> h = head;
1461 Node<K,V> basepred = h.node;
1462
1463 // Track the current rightmost node at each level. Uses an
1464 // ArrayList to avoid committing to initial or maximum level.
1465 ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
1466
1467 // initialize
1468 for (int i = 0; i <= h.level; ++i)
1469 preds.add(null);
1470 Index<K,V> q = h;
1471 for (int i = h.level; i > 0; --i) {
1472 preds.set(i, q);
1473 q = q.down;
1474 }
1475
1476 Iterator<? extends Map.Entry<? extends K, ? extends V>> it =
1477 map.entrySet().iterator();
1478 while (it.hasNext()) {
1479 Map.Entry<? extends K, ? extends V> e = it.next();
1480 int j = randomLevel();
1481 if (j > h.level) j = h.level + 1;
1482 K k = e.getKey();
1483 V v = e.getValue();
1484 if (k == null || v == null)
1485 throw new NullPointerException();
1486 Node<K,V> z = new Node<K,V>(k, v, null);
1487 basepred.next = z;
1488 basepred = z;
1489 if (j > 0) {
1490 Index<K,V> idx = null;
1491 for (int i = 1; i <= j; ++i) {
1492 idx = new Index<K,V>(z, idx, null);
1493 if (i > h.level)
1494 h = new HeadIndex<K,V>(h.node, h, idx, i);
1495
1496 if (i < preds.size()) {
1497 preds.get(i).right = idx;
1498 preds.set(i, idx);
1499 } else
1500 preds.add(idx);
1501 }
1502 }
1503 }
1504 head = h;
1505 }
1506
1507 /* ---------------- Serialization -------------- */
1508
1509 /**
1510 * Saves the state of this map to a stream (that is, serializes it).
1511 *
1512 * @serialData The key (Object) and value (Object) for each
1513 * key-value mapping represented by the map, followed by
1514 * <tt>null</tt>. The key-value mappings are emitted in key-order
1515 * (as determined by the Comparator, or by the keys' natural
1516 * ordering if no Comparator).
1517 */
1518 private void writeObject(java.io.ObjectOutputStream s)
1519 throws java.io.IOException {
1520 // Write out the Comparator and any hidden stuff
1521 s.defaultWriteObject();
1522
1523 // Write out keys and values (alternating)
1524 for (Node<K,V> n = findFirst(); n != null; n = n.next) {
1525 V v = n.getValidValue();
1526 if (v != null) {
1527 s.writeObject(n.key);
1528 s.writeObject(v);
1529 }
1530 }
1531 s.writeObject(null);
1532 }
1533
1534 /**
1535 * Reconstitutes the map from a stream (that is, deserializes it).
1536 *
1537 * @param s the stream
1538 */
1539 private void readObject(final java.io.ObjectInputStream s)
1540 throws java.io.IOException, ClassNotFoundException {
1541 // Read in the Comparator and any hidden stuff
1542 s.defaultReadObject();
1543 // Reset transients
1544 initialize();
1545
1546 /*
1547 * This is nearly identical to buildFromSorted, but is
1548 * distinct because readObject calls can't be nicely adapted
1549 * as the kind of iterator needed by buildFromSorted. (They
1550 * can be, but doing so requires type cheats and/or creation
1551 * of adaptor classes.) It is simpler to just adapt the code.
1552 */
1553
1554 HeadIndex<K,V> h = head;
1555 Node<K,V> basepred = h.node;
1556 ArrayList<Index<K,V>> preds = new ArrayList<Index<K,V>>();
1557 for (int i = 0; i <= h.level; ++i)
1558 preds.add(null);
1559 Index<K,V> q = h;
1560 for (int i = h.level; i > 0; --i) {
1561 preds.set(i, q);
1562 q = q.down;
1563 }
1564
1565 for (;;) {
1566 Object k = s.readObject();
1567 if (k == null)
1568 break;
1569 Object v = s.readObject();
1570 if (v == null)
1571 throw new NullPointerException();
1572 K key = (K) k;
1573 V val = (V) v;
1574 int j = randomLevel();
1575 if (j > h.level) j = h.level + 1;
1576 Node<K,V> z = new Node<K,V>(key, val, null);
1577 basepred.next = z;
1578 basepred = z;
1579 if (j > 0) {
1580 Index<K,V> idx = null;
1581 for (int i = 1; i <= j; ++i) {
1582 idx = new Index<K,V>(z, idx, null);
1583 if (i > h.level)
1584 h = new HeadIndex<K,V>(h.node, h, idx, i);
1585
1586 if (i < preds.size()) {
1587 preds.get(i).right = idx;
1588 preds.set(i, idx);
1589 } else
1590 preds.add(idx);
1591 }
1592 }
1593 }
1594 head = h;
1595 }
1596
1597 /* ------ Map API methods ------ */
1598
1599 /**
1600 * Returns <tt>true</tt> if this map contains a mapping for the specified
1601 * key.
1602 *
1603 * @param key key whose presence in this map is to be tested
1604 * @return <tt>true</tt> if this map contains a mapping for the specified key
1605 * @throws ClassCastException if the specified key cannot be compared
1606 * with the keys currently in the map
1607 * @throws NullPointerException if the specified key is null
1608 */
1609 public boolean containsKey(Object key) {
1610 return doGet(key) != null;
1611 }
1612
1613 /**
1614 * Returns the value to which the specified key is mapped,
1615 * or {@code null} if this map contains no mapping for the key.
1616 *
1617 * <p>More formally, if this map contains a mapping from a key
1618 * {@code k} to a value {@code v} such that {@code key} compares
1619 * equal to {@code k} according to the map's ordering, then this
1620 * method returns {@code v}; otherwise it returns {@code null}.
1621 * (There can be at most one such mapping.)
1622 *
1623 * @throws ClassCastException if the specified key cannot be compared
1624 * with the keys currently in the map
1625 * @throws NullPointerException if the specified key is null
1626 */
1627 public V get(Object key) {
1628 return doGet(key);
1629 }
1630
1631 /**
1632 * Associates the specified value with the specified key in this map.
1633 * If the map previously contained a mapping for the key, the old
1634 * value is replaced.
1635 *
1636 * @param key key with which the specified value is to be associated
1637 * @param value value to be associated with the specified key
1638 * @return the previous value associated with the specified key, or
1639 * <tt>null</tt> if there was no mapping for the key
1640 * @throws ClassCastException if the specified key cannot be compared
1641 * with the keys currently in the map
1642 * @throws NullPointerException if the specified key or value is null
1643 */
1644 public V put(K key, V value) {
1645 if (value == null)
1646 throw new NullPointerException();
1647 return doPut(key, value, false);
1648 }
1649
1650 /**
1651 * Removes the mapping for the specified key from this map if present.
1652 *
1653 * @param key key for which mapping should be removed
1654 * @return the previous value associated with the specified key, or
1655 * <tt>null</tt> if there was no mapping for the key
1656 * @throws ClassCastException if the specified key cannot be compared
1657 * with the keys currently in the map
1658 * @throws NullPointerException if the specified key is null
1659 */
1660 public V remove(Object key) {
1661 return doRemove(key, null);
1662 }
1663
1664 /**
1665 * Returns <tt>true</tt> if this map maps one or more keys to the
1666 * specified value. This operation requires time linear in the
1667 * map size. Additionally, it is possible for the map to change
1668 * during execution of this method, in which case the returned
1669 * result may be inaccurate.
1670 *
1671 * @param value value whose presence in this map is to be tested
1672 * @return <tt>true</tt> if a mapping to <tt>value</tt> exists;
1673 * <tt>false</tt> otherwise
1674 * @throws NullPointerException if the specified value is null
1675 */
1676 public boolean containsValue(Object value) {
1677 if (value == null)
1678 throw new NullPointerException();
1679 for (Node<K,V> n = findFirst(); n != null; n = n.next) {
1680 V v = n.getValidValue();
1681 if (v != null && value.equals(v))
1682 return true;
1683 }
1684 return false;
1685 }
1686
1687 /**
1688 * Returns the number of key-value mappings in this map. If this map
1689 * contains more than <tt>Integer.MAX_VALUE</tt> elements, it
1690 * returns <tt>Integer.MAX_VALUE</tt>.
1691 *
1692 * <p>Beware that, unlike in most collections, this method is
1693 * <em>NOT</em> a constant-time operation. Because of the
1694 * asynchronous nature of these maps, determining the current
1695 * number of elements requires traversing them all to count them.
1696 * Additionally, it is possible for the size to change during
1697 * execution of this method, in which case the returned result
1698 * will be inaccurate. Thus, this method is typically not very
1699 * useful in concurrent applications.
1700 *
1701 * @return the number of elements in this map
1702 */
1703 public int size() {
1704 long count = 0;
1705 for (Node<K,V> n = findFirst(); n != null; n = n.next) {
1706 if (n.getValidValue() != null)
1707 ++count;
1708 }
1709 return (count >= Integer.MAX_VALUE) ? Integer.MAX_VALUE : (int) count;
1710 }
1711
1712 /**
1713 * Returns <tt>true</tt> if this map contains no key-value mappings.
1714 * @return <tt>true</tt> if this map contains no key-value mappings
1715 */
1716 public boolean isEmpty() {
1717 return findFirst() == null;
1718 }
1719
1720 /**
1721 * Removes all of the mappings from this map.
1722 */
1723 public void clear() {
1724 initialize();
1725 }
1726
1727 /* ---------------- View methods -------------- */
1728
1729 /*
1730 * Note: Lazy initialization works for views because view classes
1731 * are stateless/immutable so it doesn't matter wrt correctness if
1732 * more than one is created (which will only rarely happen). Even
1733 * so, the following idiom conservatively ensures that the method
1734 * returns the one it created if it does so, not one created by
1735 * another racing thread.
1736 */
1737
1738 /**
1739 * Returns a {@link NavigableSet} view of the keys contained in this map.
1740 * The set's iterator returns the keys in ascending order.
1741 * The set is backed by the map, so changes to the map are
1742 * reflected in the set, and vice-versa. The set supports element
1743 * removal, which removes the corresponding mapping from the map,
1744 * via the {@code Iterator.remove}, {@code Set.remove},
1745 * {@code removeAll}, {@code retainAll}, and {@code clear}
1746 * operations. It does not support the {@code add} or {@code addAll}
1747 * operations.
1748 *
1749 * <p>The view's {@code iterator} is a "weakly consistent" iterator
1750 * that will never throw {@link ConcurrentModificationException},
1751 * and guarantees to traverse elements as they existed upon
1752 * construction of the iterator, and may (but is not guaranteed to)
1753 * reflect any modifications subsequent to construction.
1754 *
1755 * <p>This method is equivalent to method {@code navigableKeySet}.
1756 *
1757 * @return a navigable set view of the keys in this map
1758 */
1759 public NavigableSet<K> keySet() {
1760 KeySet<K> ks = keySet;
1761 return (ks != null) ? ks : (keySet = new KeySet<K>(this));
1762 }
1763
1764 public NavigableSet<K> navigableKeySet() {
1765 KeySet<K> ks = keySet;
1766 return (ks != null) ? ks : (keySet = new KeySet<K>(this));
1767 }
1768
1769 /**
1770 * Returns a {@link Collection} view of the values contained in this map.
1771 * The collection's iterator returns the values in ascending order
1772 * of the corresponding keys.
1773 * The collection is backed by the map, so changes to the map are
1774 * reflected in the collection, and vice-versa. The collection
1775 * supports element removal, which removes the corresponding
1776 * mapping from the map, via the <tt>Iterator.remove</tt>,
1777 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
1778 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
1779 * support the <tt>add</tt> or <tt>addAll</tt> operations.
1780 *
1781 * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1782 * that will never throw {@link ConcurrentModificationException},
1783 * and guarantees to traverse elements as they existed upon
1784 * construction of the iterator, and may (but is not guaranteed to)
1785 * reflect any modifications subsequent to construction.
1786 */
1787 public Collection<V> values() {
1788 Values<V> vs = values;
1789 return (vs != null) ? vs : (values = new Values<V>(this));
1790 }
1791
1792 /**
1793 * Returns a {@link Set} view of the mappings contained in this map.
1794 * The set's iterator returns the entries in ascending key order.
1795 * The set is backed by the map, so changes to the map are
1796 * reflected in the set, and vice-versa. The set supports element
1797 * removal, which removes the corresponding mapping from the map,
1798 * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
1799 * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
1800 * operations. It does not support the <tt>add</tt> or
1801 * <tt>addAll</tt> operations.
1802 *
1803 * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1804 * that will never throw {@link ConcurrentModificationException},
1805 * and guarantees to traverse elements as they existed upon
1806 * construction of the iterator, and may (but is not guaranteed to)
1807 * reflect any modifications subsequent to construction.
1808 *
1809 * <p>The <tt>Map.Entry</tt> elements returned by
1810 * <tt>iterator.next()</tt> do <em>not</em> support the
1811 * <tt>setValue</tt> operation.
1812 *
1813 * @return a set view of the mappings contained in this map,
1814 * sorted in ascending key order
1815 */
1816 public Set<Map.Entry<K,V>> entrySet() {
1817 EntrySet<K,V> es = entrySet;
1818 return (es != null) ? es : (entrySet = new EntrySet<K,V>(this));
1819 }
1820
1821 public ConcurrentNavigableMap<K,V> descendingMap() {
1822 ConcurrentNavigableMap<K,V> dm = descendingMap;
1823 return (dm != null) ? dm : (descendingMap = new SubMap<K,V>
1824 (this, null, false, null, false, true));
1825 }
1826
1827 public NavigableSet<K> descendingKeySet() {
1828 return descendingMap().navigableKeySet();
1829 }
1830
1831 /* ---------------- AbstractMap Overrides -------------- */
1832
1833 /**
1834 * Compares the specified object with this map for equality.
1835 * Returns <tt>true</tt> if the given object is also a map and the
1836 * two maps represent the same mappings. More formally, two maps
1837 * <tt>m1</tt> and <tt>m2</tt> represent the same mappings if
1838 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This
1839 * operation may return misleading results if either map is
1840 * concurrently modified during execution of this method.
1841 *
1842 * @param o object to be compared for equality with this map
1843 * @return <tt>true</tt> if the specified object is equal to this map
1844 */
1845 public boolean equals(Object o) {
1846 if (o == this)
1847 return true;
1848 if (!(o instanceof Map))
1849 return false;
1850 Map<?,?> m = (Map<?,?>) o;
1851 try {
1852 for (Map.Entry<K,V> e : this.entrySet())
1853 if (! e.getValue().equals(m.get(e.getKey())))
1854 return false;
1855 for (Map.Entry<?,?> e : m.entrySet()) {
1856 Object k = e.getKey();
1857 Object v = e.getValue();
1858 if (k == null || v == null || !v.equals(get(k)))
1859 return false;
1860 }
1861 return true;
1862 } catch (ClassCastException unused) {
1863 return false;
1864 } catch (NullPointerException unused) {
1865 return false;
1866 }
1867 }
1868
1869 /* ------ ConcurrentMap API methods ------ */
1870
1871 /**
1872 * {@inheritDoc}
1873 *
1874 * @return the previous value associated with the specified key,
1875 * or <tt>null</tt> if there was no mapping for the key
1876 * @throws ClassCastException if the specified key cannot be compared
1877 * with the keys currently in the map
1878 * @throws NullPointerException if the specified key or value is null
1879 */
1880 public V putIfAbsent(K key, V value) {
1881 if (value == null)
1882 throw new NullPointerException();
1883 return doPut(key, value, true);
1884 }
1885
1886 /**
1887 * {@inheritDoc}
1888 *
1889 * @throws ClassCastException if the specified key cannot be compared
1890 * with the keys currently in the map
1891 * @throws NullPointerException if the specified key is null
1892 */
1893 public boolean remove(Object key, Object value) {
1894 if (key == null)
1895 throw new NullPointerException();
1896 if (value == null)
1897 return false;
1898 return doRemove(key, value) != null;
1899 }
1900
1901 /**
1902 * {@inheritDoc}
1903 *
1904 * @throws ClassCastException if the specified key cannot be compared
1905 * with the keys currently in the map
1906 * @throws NullPointerException if any of the arguments are null
1907 */
1908 public boolean replace(K key, V oldValue, V newValue) {
1909 if (oldValue == null || newValue == null)
1910 throw new NullPointerException();
1911 Comparable<? super K> k = comparable(key);
1912 for (;;) {
1913 Node<K,V> n = findNode(k);
1914 if (n == null)
1915 return false;
1916 Object v = n.value;
1917 if (v != null) {
1918 if (!oldValue.equals(v))
1919 return false;
1920 if (n.casValue(v, newValue))
1921 return true;
1922 }
1923 }
1924 }
1925
1926 /**
1927 * {@inheritDoc}
1928 *
1929 * @return the previous value associated with the specified key,
1930 * or <tt>null</tt> if there was no mapping for the key
1931 * @throws ClassCastException if the specified key cannot be compared
1932 * with the keys currently in the map
1933 * @throws NullPointerException if the specified key or value is null
1934 */
1935 public V replace(K key, V value) {
1936 if (value == null)
1937 throw new NullPointerException();
1938 Comparable<? super K> k = comparable(key);
1939 for (;;) {
1940 Node<K,V> n = findNode(k);
1941 if (n == null)
1942 return null;
1943 Object v = n.value;
1944 if (v != null && n.casValue(v, value))
1945 return (V)v;
1946 }
1947 }
1948
1949 /* ------ SortedMap API methods ------ */
1950
1951 public Comparator<? super K> comparator() {
1952 return comparator;
1953 }
1954
1955 /**
1956 * @throws NoSuchElementException {@inheritDoc}
1957 */
1958 public K firstKey() {
1959 Node<K,V> n = findFirst();
1960 if (n == null)
1961 throw new NoSuchElementException();
1962 return n.key;
1963 }
1964
1965 /**
1966 * @throws NoSuchElementException {@inheritDoc}
1967 */
1968 public K lastKey() {
1969 Node<K,V> n = findLast();
1970 if (n == null)
1971 throw new NoSuchElementException();
1972 return n.key;
1973 }
1974
1975 /**
1976 * @throws ClassCastException {@inheritDoc}
1977 * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
1978 * @throws IllegalArgumentException {@inheritDoc}
1979 */
1980 public ConcurrentNavigableMap<K,V> subMap(K fromKey,
1981 boolean fromInclusive,
1982 K toKey,
1983 boolean toInclusive) {
1984 if (fromKey == null || toKey == null)
1985 throw new NullPointerException();
1986 return new SubMap<K,V>
1987 (this, fromKey, fromInclusive, toKey, toInclusive, false);
1988 }
1989
1990 /**
1991 * @throws ClassCastException {@inheritDoc}
1992 * @throws NullPointerException if {@code toKey} is null
1993 * @throws IllegalArgumentException {@inheritDoc}
1994 */
1995 public ConcurrentNavigableMap<K,V> headMap(K toKey,
1996 boolean inclusive) {
1997 if (toKey == null)
1998 throw new NullPointerException();
1999 return new SubMap<K,V>
2000 (this, null, false, toKey, inclusive, false);
2001 }
2002
2003 /**
2004 * @throws ClassCastException {@inheritDoc}
2005 * @throws NullPointerException if {@code fromKey} is null
2006 * @throws IllegalArgumentException {@inheritDoc}
2007 */
2008 public ConcurrentNavigableMap<K,V> tailMap(K fromKey,
2009 boolean inclusive) {
2010 if (fromKey == null)
2011 throw new NullPointerException();
2012 return new SubMap<K,V>
2013 (this, fromKey, inclusive, null, false, false);
2014 }
2015
2016 /**
2017 * @throws ClassCastException {@inheritDoc}
2018 * @throws NullPointerException if {@code fromKey} or {@code toKey} is null
2019 * @throws IllegalArgumentException {@inheritDoc}
2020 */
2021 public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey) {
2022 return subMap(fromKey, true, toKey, false);
2023 }
2024
2025 /**
2026 * @throws ClassCastException {@inheritDoc}
2027 * @throws NullPointerException if {@code toKey} is null
2028 * @throws IllegalArgumentException {@inheritDoc}
2029 */
2030 public ConcurrentNavigableMap<K,V> headMap(K toKey) {
2031 return headMap(toKey, false);
2032 }
2033
2034 /**
2035 * @throws ClassCastException {@inheritDoc}
2036 * @throws NullPointerException if {@code fromKey} is null
2037 * @throws IllegalArgumentException {@inheritDoc}
2038 */
2039 public ConcurrentNavigableMap<K,V> tailMap(K fromKey) {
2040 return tailMap(fromKey, true);
2041 }
2042
2043 /* ---------------- Relational operations -------------- */
2044
2045 /**
2046 * Returns a key-value mapping associated with the greatest key
2047 * strictly less than the given key, or <tt>null</tt> if there is
2048 * no such key. The returned entry does <em>not</em> support the
2049 * <tt>Entry.setValue</tt> method.
2050 *
2051 * @throws ClassCastException {@inheritDoc}
2052 * @throws NullPointerException if the specified key is null
2053 */
2054 public Map.Entry<K,V> lowerEntry(K key) {
2055 return getNear(key, LT);
2056 }
2057
2058 /**
2059 * @throws ClassCastException {@inheritDoc}
2060 * @throws NullPointerException if the specified key is null
2061 */
2062 public K lowerKey(K key) {
2063 Node<K,V> n = findNear(key, LT);
2064 return (n == null) ? null : n.key;
2065 }
2066
2067 /**
2068 * Returns a key-value mapping associated with the greatest key
2069 * less than or equal to the given key, or <tt>null</tt> if there
2070 * is no such key. The returned entry does <em>not</em> support
2071 * the <tt>Entry.setValue</tt> method.
2072 *
2073 * @param key the key
2074 * @throws ClassCastException {@inheritDoc}
2075 * @throws NullPointerException if the specified key is null
2076 */
2077 public Map.Entry<K,V> floorEntry(K key) {
2078 return getNear(key, LT|EQ);
2079 }
2080
2081 /**
2082 * @param key the key
2083 * @throws ClassCastException {@inheritDoc}
2084 * @throws NullPointerException if the specified key is null
2085 */
2086 public K floorKey(K key) {
2087 Node<K,V> n = findNear(key, LT|EQ);
2088 return (n == null) ? null : n.key;
2089 }
2090
2091 /**
2092 * Returns a key-value mapping associated with the least key
2093 * greater than or equal to the given key, or <tt>null</tt> if
2094 * there is no such entry. The returned entry does <em>not</em>
2095 * support the <tt>Entry.setValue</tt> method.
2096 *
2097 * @throws ClassCastException {@inheritDoc}
2098 * @throws NullPointerException if the specified key is null
2099 */
2100 public Map.Entry<K,V> ceilingEntry(K key) {
2101 return getNear(key, GT|EQ);
2102 }
2103
2104 /**
2105 * @throws ClassCastException {@inheritDoc}
2106 * @throws NullPointerException if the specified key is null
2107 */
2108 public K ceilingKey(K key) {
2109 Node<K,V> n = findNear(key, GT|EQ);
2110 return (n == null) ? null : n.key;
2111 }
2112
2113 /**
2114 * Returns a key-value mapping associated with the least key
2115 * strictly greater than the given key, or <tt>null</tt> if there
2116 * is no such key. The returned entry does <em>not</em> support
2117 * the <tt>Entry.setValue</tt> method.
2118 *
2119 * @param key the key
2120 * @throws ClassCastException {@inheritDoc}
2121 * @throws NullPointerException if the specified key is null
2122 */
2123 public Map.Entry<K,V> higherEntry(K key) {
2124 return getNear(key, GT);
2125 }
2126
2127 /**
2128 * @param key the key
2129 * @throws ClassCastException {@inheritDoc}
2130 * @throws NullPointerException if the specified key is null
2131 */
2132 public K higherKey(K key) {
2133 Node<K,V> n = findNear(key, GT);
2134 return (n == null) ? null : n.key;
2135 }
2136
2137 /**
2138 * Returns a key-value mapping associated with the least
2139 * key in this map, or <tt>null</tt> if the map is empty.
2140 * The returned entry does <em>not</em> support
2141 * the <tt>Entry.setValue</tt> method.
2142 */
2143 public Map.Entry<K,V> firstEntry() {
2144 for (;;) {
2145 Node<K,V> n = findFirst();
2146 if (n == null)
2147 return null;
2148 AbstractMap.SimpleImmutableEntry<K,V> e = n.createSnapshot();
2149 if (e != null)
2150 return e;
2151 }
2152 }
2153
2154 /**
2155 * Returns a key-value mapping associated with the greatest
2156 * key in this map, or <tt>null</tt> if the map is empty.
2157 * The returned entry does <em>not</em> support
2158 * the <tt>Entry.setValue</tt> method.
2159 */
2160 public Map.Entry<K,V> lastEntry() {
2161 for (;;) {
2162 Node<K,V> n = findLast();
2163 if (n == null)
2164 return null;
2165 AbstractMap.SimpleImmutableEntry<K,V> e = n.createSnapshot();
2166 if (e != null)
2167 return e;
2168 }
2169 }
2170
2171 /**
2172 * Removes and returns a key-value mapping associated with
2173 * the least key in this map, or <tt>null</tt> if the map is empty.
2174 * The returned entry does <em>not</em> support
2175 * the <tt>Entry.setValue</tt> method.
2176 */
2177 public Map.Entry<K,V> pollFirstEntry() {
2178 return doRemoveFirstEntry();
2179 }
2180
2181 /**
2182 * Removes and returns a key-value mapping associated with
2183 * the greatest key in this map, or <tt>null</tt> if the map is empty.
2184 * The returned entry does <em>not</em> support
2185 * the <tt>Entry.setValue</tt> method.
2186 */
2187 public Map.Entry<K,V> pollLastEntry() {
2188 return doRemoveLastEntry();
2189 }
2190
2191
2192 /* ---------------- Iterators -------------- */
2193
2194 /**
2195 * Base of iterator classes:
2196 */
2197 abstract class Iter<T> implements Iterator<T> {
2198 /** the last node returned by next() */
2199 Node<K,V> lastReturned;
2200 /** the next node to return from next(); */
2201 Node<K,V> next;
2202 /** Cache of next value field to maintain weak consistency */
2203 V nextValue;
2204
2205 /** Initializes ascending iterator for entire range. */
2206 Iter() {
2207 for (;;) {
2208 next = findFirst();
2209 if (next == null)
2210 break;
2211 Object x = next.value;
2212 if (x != null && x != next) {
2213 nextValue = (V) x;
2214 break;
2215 }
2216 }
2217 }
2218
2219 public final boolean hasNext() {
2220 return next != null;
2221 }
2222
2223 /** Advances next to higher entry. */
2224 final void advance() {
2225 if (next == null)
2226 throw new NoSuchElementException();
2227 lastReturned = next;
2228 for (;;) {
2229 next = next.next;
2230 if (next == null)
2231 break;
2232 Object x = next.value;
2233 if (x != null && x != next) {
2234 nextValue = (V) x;
2235 break;
2236 }
2237 }
2238 }
2239
2240 public void remove() {
2241 Node<K,V> l = lastReturned;
2242 if (l == null)
2243 throw new IllegalStateException();
2244 // It would not be worth all of the overhead to directly
2245 // unlink from here. Using remove is fast enough.
2246 ConcurrentSkipListMap.this.remove(l.key);
2247 lastReturned = null;
2248 }
2249
2250 }
2251
2252 final class ValueIterator extends Iter<V> {
2253 public V next() {
2254 V v = nextValue;
2255 advance();
2256 return v;
2257 }
2258 }
2259
2260 final class KeyIterator extends Iter<K> {
2261 public K next() {
2262 Node<K,V> n = next;
2263 advance();
2264 return n.key;
2265 }
2266 }
2267
2268 final class EntryIterator extends Iter<Map.Entry<K,V>> {
2269 public Map.Entry<K,V> next() {
2270 Node<K,V> n = next;
2271 V v = nextValue;
2272 advance();
2273 return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, v);
2274 }
2275 }
2276
2277 // Factory methods for iterators needed by ConcurrentSkipListSet etc
2278
2279 Iterator<K> keyIterator() {
2280 return new KeyIterator();
2281 }
2282
2283 Iterator<V> valueIterator() {
2284 return new ValueIterator();
2285 }
2286
2287 Iterator<Map.Entry<K,V>> entryIterator() {
2288 return new EntryIterator();
2289 }
2290
2291 /* ---------------- View Classes -------------- */
2292
2293 /*
2294 * View classes are static, delegating to a ConcurrentNavigableMap
2295 * to allow use by SubMaps, which outweighs the ugliness of
2296 * needing type-tests for Iterator methods.
2297 */
2298
2299 static final <E> List<E> toList(Collection<E> c) {
2300 // Using size() here would be a pessimization.
2301 List<E> list = new ArrayList<E>();
2302 for (E e : c)
2303 list.add(e);
2304 return list;
2305 }
2306
2307 static final class KeySet<E>
2308 extends AbstractSet<E> implements NavigableSet<E> {
2309 private final ConcurrentNavigableMap<E,?> m;
2310 KeySet(ConcurrentNavigableMap<E,?> map) { m = map; }
2311 public int size() { return m.size(); }
2312 public boolean isEmpty() { return m.isEmpty(); }
2313 public boolean contains(Object o) { return m.containsKey(o); }
2314 public boolean remove(Object o) { return m.remove(o) != null; }
2315 public void clear() { m.clear(); }
2316 public E lower(E e) { return m.lowerKey(e); }
2317 public E floor(E e) { return m.floorKey(e); }
2318 public E ceiling(E e) { return m.ceilingKey(e); }
2319 public E higher(E e) { return m.higherKey(e); }
2320 public Comparator<? super E> comparator() { return m.comparator(); }
2321 public E first() { return m.firstKey(); }
2322 public E last() { return m.lastKey(); }
2323 public E pollFirst() {
2324 Map.Entry<E,?> e = m.pollFirstEntry();
2325 return (e == null) ? null : e.getKey();
2326 }
2327 public E pollLast() {
2328 Map.Entry<E,?> e = m.pollLastEntry();
2329 return (e == null) ? null : e.getKey();
2330 }
2331 public Iterator<E> iterator() {
2332 if (m instanceof ConcurrentSkipListMap)
2333 return ((ConcurrentSkipListMap<E,Object>)m).keyIterator();
2334 else
2335 return ((ConcurrentSkipListMap.SubMap<E,Object>)m).keyIterator();
2336 }
2337 public boolean equals(Object o) {
2338 if (o == this)
2339 return true;
2340 if (!(o instanceof Set))
2341 return false;
2342 Collection<?> c = (Collection<?>) o;
2343 try {
2344 return containsAll(c) && c.containsAll(this);
2345 } catch (ClassCastException unused) {
2346 return false;
2347 } catch (NullPointerException unused) {
2348 return false;
2349 }
2350 }
2351 public Object[] toArray() { return toList(this).toArray(); }
2352 public <T> T[] toArray(T[] a) { return toList(this).toArray(a); }
2353 public Iterator<E> descendingIterator() {
2354 return descendingSet().iterator();
2355 }
2356 public NavigableSet<E> subSet(E fromElement,
2357 boolean fromInclusive,
2358 E toElement,
2359 boolean toInclusive) {
2360 return new KeySet<E>(m.subMap(fromElement, fromInclusive,
2361 toElement, toInclusive));
2362 }
2363 public NavigableSet<E> headSet(E toElement, boolean inclusive) {
2364 return new KeySet<E>(m.headMap(toElement, inclusive));
2365 }
2366 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
2367 return new KeySet<E>(m.tailMap(fromElement, inclusive));
2368 }
2369 public NavigableSet<E> subSet(E fromElement, E toElement) {
2370 return subSet(fromElement, true, toElement, false);
2371 }
2372 public NavigableSet<E> headSet(E toElement) {
2373 return headSet(toElement, false);
2374 }
2375 public NavigableSet<E> tailSet(E fromElement) {
2376 return tailSet(fromElement, true);
2377 }
2378 public NavigableSet<E> descendingSet() {
2379 return new KeySet<E>(m.descendingMap());
2380 }
2381 }
2382
2383 static final class Values<E> extends AbstractCollection<E> {
2384 private final ConcurrentNavigableMap<?, E> m;
2385 Values(ConcurrentNavigableMap<?, E> map) {
2386 m = map;
2387 }
2388 public Iterator<E> iterator() {
2389 if (m instanceof ConcurrentSkipListMap)
2390 return ((ConcurrentSkipListMap<?,E>)m).valueIterator();
2391 else
2392 return ((SubMap<?,E>)m).valueIterator();
2393 }
2394 public boolean isEmpty() {
2395 return m.isEmpty();
2396 }
2397 public int size() {
2398 return m.size();
2399 }
2400 public boolean contains(Object o) {
2401 return m.containsValue(o);
2402 }
2403 public void clear() {
2404 m.clear();
2405 }
2406 public Object[] toArray() { return toList(this).toArray(); }
2407 public <T> T[] toArray(T[] a) { return toList(this).toArray(a); }
2408 }
2409
2410 static final class EntrySet<K1,V1> extends AbstractSet<Map.Entry<K1,V1>> {
2411 private final ConcurrentNavigableMap<K1, V1> m;
2412 EntrySet(ConcurrentNavigableMap<K1, V1> map) {
2413 m = map;
2414 }
2415
2416 public Iterator<Map.Entry<K1,V1>> iterator() {
2417 if (m instanceof ConcurrentSkipListMap)
2418 return ((ConcurrentSkipListMap<K1,V1>)m).entryIterator();
2419 else
2420 return ((SubMap<K1,V1>)m).entryIterator();
2421 }
2422
2423 public boolean contains(Object o) {
2424 if (!(o instanceof Map.Entry))
2425 return false;
2426 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
2427 V1 v = m.get(e.getKey());
2428 return v != null && v.equals(e.getValue());
2429 }
2430 public boolean remove(Object o) {
2431 if (!(o instanceof Map.Entry))
2432 return false;
2433 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
2434 return m.remove(e.getKey(),
2435 e.getValue());
2436 }
2437 public boolean isEmpty() {
2438 return m.isEmpty();
2439 }
2440 public int size() {
2441 return m.size();
2442 }
2443 public void clear() {
2444 m.clear();
2445 }
2446 public boolean equals(Object o) {
2447 if (o == this)
2448 return true;
2449 if (!(o instanceof Set))
2450 return false;
2451 Collection<?> c = (Collection<?>) o;
2452 try {
2453 return containsAll(c) && c.containsAll(this);
2454 } catch (ClassCastException unused) {
2455 return false;
2456 } catch (NullPointerException unused) {
2457 return false;
2458 }
2459 }
2460 public Object[] toArray() { return toList(this).toArray(); }
2461 public <T> T[] toArray(T[] a) { return toList(this).toArray(a); }
2462 }
2463
2464 /**
2465 * Submaps returned by {@link ConcurrentSkipListMap} submap operations
2466 * represent a subrange of mappings of their underlying
2467 * maps. Instances of this class support all methods of their
2468 * underlying maps, differing in that mappings outside their range are
2469 * ignored, and attempts to add mappings outside their ranges result
2470 * in {@link IllegalArgumentException}. Instances of this class are
2471 * constructed only using the <tt>subMap</tt>, <tt>headMap</tt>, and
2472 * <tt>tailMap</tt> methods of their underlying maps.
2473 *
2474 * @serial include
2475 */
2476 static final class SubMap<K,V> extends AbstractMap<K,V>
2477 implements ConcurrentNavigableMap<K,V>, Cloneable,
2478 java.io.Serializable {
2479 private static final long serialVersionUID = -7647078645895051609L;
2480
2481 /** Underlying map */
2482 private final ConcurrentSkipListMap<K,V> m;
2483 /** lower bound key, or null if from start */
2484 private final K lo;
2485 /** upper bound key, or null if to end */
2486 private final K hi;
2487 /** inclusion flag for lo */
2488 private final boolean loInclusive;
2489 /** inclusion flag for hi */
2490 private final boolean hiInclusive;
2491 /** direction */
2492 private final boolean isDescending;
2493
2494 // Lazily initialized view holders
2495 private transient KeySet<K> keySetView;
2496 private transient Set<Map.Entry<K,V>> entrySetView;
2497 private transient Collection<V> valuesView;
2498
2499 /**
2500 * Creates a new submap, initializing all fields
2501 */
2502 SubMap(ConcurrentSkipListMap<K,V> map,
2503 K fromKey, boolean fromInclusive,
2504 K toKey, boolean toInclusive,
2505 boolean isDescending) {
2506 if (fromKey != null && toKey != null &&
2507 map.compare(fromKey, toKey) > 0)
2508 throw new IllegalArgumentException("inconsistent range");
2509 this.m = map;
2510 this.lo = fromKey;
2511 this.hi = toKey;
2512 this.loInclusive = fromInclusive;
2513 this.hiInclusive = toInclusive;
2514 this.isDescending = isDescending;
2515 }
2516
2517 /* ---------------- Utilities -------------- */
2518
2519 private boolean tooLow(K key) {
2520 if (lo != null) {
2521 int c = m.compare(key, lo);
2522 if (c < 0 || (c == 0 && !loInclusive))
2523 return true;
2524 }
2525 return false;
2526 }
2527
2528 private boolean tooHigh(K key) {
2529 if (hi != null) {
2530 int c = m.compare(key, hi);
2531 if (c > 0 || (c == 0 && !hiInclusive))
2532 return true;
2533 }
2534 return false;
2535 }
2536
2537 private boolean inBounds(K key) {
2538 return !tooLow(key) && !tooHigh(key);
2539 }
2540
2541 private void checkKeyBounds(K key) throws IllegalArgumentException {
2542 if (key == null)
2543 throw new NullPointerException();
2544 if (!inBounds(key))
2545 throw new IllegalArgumentException("key out of range");
2546 }
2547
2548 /**
2549 * Returns true if node key is less than upper bound of range
2550 */
2551 private boolean isBeforeEnd(ConcurrentSkipListMap.Node<K,V> n) {
2552 if (n == null)
2553 return false;
2554 if (hi == null)
2555 return true;
2556 K k = n.key;
2557 if (k == null) // pass by markers and headers
2558 return true;
2559 int c = m.compare(k, hi);
2560 if (c > 0 || (c == 0 && !hiInclusive))
2561 return false;
2562 return true;
2563 }
2564
2565 /**
2566 * Returns lowest node. This node might not be in range, so
2567 * most usages need to check bounds
2568 */
2569 private ConcurrentSkipListMap.Node<K,V> loNode() {
2570 if (lo == null)
2571 return m.findFirst();
2572 else if (loInclusive)
2573 return m.findNear(lo, GT|EQ);
2574 else
2575 return m.findNear(lo, GT);
2576 }
2577
2578 /**
2579 * Returns highest node. This node might not be in range, so
2580 * most usages need to check bounds
2581 */
2582 private ConcurrentSkipListMap.Node<K,V> hiNode() {
2583 if (hi == null)
2584 return m.findLast();
2585 else if (hiInclusive)
2586 return m.findNear(hi, LT|EQ);
2587 else
2588 return m.findNear(hi, LT);
2589 }
2590
2591 /**
2592 * Returns lowest absolute key (ignoring directonality)
2593 */
2594 private K lowestKey() {
2595 ConcurrentSkipListMap.Node<K,V> n = loNode();
2596 if (isBeforeEnd(n))
2597 return n.key;
2598 else
2599 throw new NoSuchElementException();
2600 }
2601
2602 /**
2603 * Returns highest absolute key (ignoring directonality)
2604 */
2605 private K highestKey() {
2606 ConcurrentSkipListMap.Node<K,V> n = hiNode();
2607 if (n != null) {
2608 K last = n.key;
2609 if (inBounds(last))
2610 return last;
2611 }
2612 throw new NoSuchElementException();
2613 }
2614
2615 private Map.Entry<K,V> lowestEntry() {
2616 for (;;) {
2617 ConcurrentSkipListMap.Node<K,V> n = loNode();
2618 if (!isBeforeEnd(n))
2619 return null;
2620 Map.Entry<K,V> e = n.createSnapshot();
2621 if (e != null)
2622 return e;
2623 }
2624 }
2625
2626 private Map.Entry<K,V> highestEntry() {
2627 for (;;) {
2628 ConcurrentSkipListMap.Node<K,V> n = hiNode();
2629 if (n == null || !inBounds(n.key))
2630 return null;
2631 Map.Entry<K,V> e = n.createSnapshot();
2632 if (e != null)
2633 return e;
2634 }
2635 }
2636
2637 private Map.Entry<K,V> removeLowest() {
2638 for (;;) {
2639 Node<K,V> n = loNode();
2640 if (n == null)
2641 return null;
2642 K k = n.key;
2643 if (!inBounds(k))
2644 return null;
2645 V v = m.doRemove(k, null);
2646 if (v != null)
2647 return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
2648 }
2649 }
2650
2651 private Map.Entry<K,V> removeHighest() {
2652 for (;;) {
2653 Node<K,V> n = hiNode();
2654 if (n == null)
2655 return null;
2656 K k = n.key;
2657 if (!inBounds(k))
2658 return null;
2659 V v = m.doRemove(k, null);
2660 if (v != null)
2661 return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
2662 }
2663 }
2664
2665 /**
2666 * Submap version of ConcurrentSkipListMap.getNearEntry
2667 */
2668 private Map.Entry<K,V> getNearEntry(K key, int rel) {
2669 if (isDescending) { // adjust relation for direction
2670 if ((rel & LT) == 0)
2671 rel |= LT;
2672 else
2673 rel &= ~LT;
2674 }
2675 if (tooLow(key))
2676 return ((rel & LT) != 0) ? null : lowestEntry();
2677 if (tooHigh(key))
2678 return ((rel & LT) != 0) ? highestEntry() : null;
2679 for (;;) {
2680 Node<K,V> n = m.findNear(key, rel);
2681 if (n == null || !inBounds(n.key))
2682 return null;
2683 K k = n.key;
2684 V v = n.getValidValue();
2685 if (v != null)
2686 return new AbstractMap.SimpleImmutableEntry<K,V>(k, v);
2687 }
2688 }
2689
2690 // Almost the same as getNearEntry, except for keys
2691 private K getNearKey(K key, int rel) {
2692 if (isDescending) { // adjust relation for direction
2693 if ((rel & LT) == 0)
2694 rel |= LT;
2695 else
2696 rel &= ~LT;
2697 }
2698 if (tooLow(key)) {
2699 if ((rel & LT) == 0) {
2700 ConcurrentSkipListMap.Node<K,V> n = loNode();
2701 if (isBeforeEnd(n))
2702 return n.key;
2703 }
2704 return null;
2705 }
2706 if (tooHigh(key)) {
2707 if ((rel & LT) != 0) {
2708 ConcurrentSkipListMap.Node<K,V> n = hiNode();
2709 if (n != null) {
2710 K last = n.key;
2711 if (inBounds(last))
2712 return last;
2713 }
2714 }
2715 return null;
2716 }
2717 for (;;) {
2718 Node<K,V> n = m.findNear(key, rel);
2719 if (n == null || !inBounds(n.key))
2720 return null;
2721 K k = n.key;
2722 V v = n.getValidValue();
2723 if (v != null)
2724 return k;
2725 }
2726 }
2727
2728 /* ---------------- Map API methods -------------- */
2729
2730 public boolean containsKey(Object key) {
2731 if (key == null) throw new NullPointerException();
2732 K k = (K)key;
2733 return inBounds(k) && m.containsKey(k);
2734 }
2735
2736 public V get(Object key) {
2737 if (key == null) throw new NullPointerException();
2738 K k = (K)key;
2739 return (!inBounds(k)) ? null : m.get(k);
2740 }
2741
2742 public V put(K key, V value) {
2743 checkKeyBounds(key);
2744 return m.put(key, value);
2745 }
2746
2747 public V remove(Object key) {
2748 K k = (K)key;
2749 return (!inBounds(k)) ? null : m.remove(k);
2750 }
2751
2752 public int size() {
2753 long count = 0;
2754 for (ConcurrentSkipListMap.Node<K,V> n = loNode();
2755 isBeforeEnd(n);
2756 n = n.next) {
2757 if (n.getValidValue() != null)
2758 ++count;
2759 }
2760 return count >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int)count;
2761 }
2762
2763 public boolean isEmpty() {
2764 return !isBeforeEnd(loNode());
2765 }
2766
2767 public boolean containsValue(Object value) {
2768 if (value == null)
2769 throw new NullPointerException();
2770 for (ConcurrentSkipListMap.Node<K,V> n = loNode();
2771 isBeforeEnd(n);
2772 n = n.next) {
2773 V v = n.getValidValue();
2774 if (v != null && value.equals(v))
2775 return true;
2776 }
2777 return false;
2778 }
2779
2780 public void clear() {
2781 for (ConcurrentSkipListMap.Node<K,V> n = loNode();
2782 isBeforeEnd(n);
2783 n = n.next) {
2784 if (n.getValidValue() != null)
2785 m.remove(n.key);
2786 }
2787 }
2788
2789 /* ---------------- ConcurrentMap API methods -------------- */
2790
2791 public V putIfAbsent(K key, V value) {
2792 checkKeyBounds(key);
2793 return m.putIfAbsent(key, value);
2794 }
2795
2796 public boolean remove(Object key, Object value) {
2797 K k = (K)key;
2798 return inBounds(k) && m.remove(k, value);
2799 }
2800
2801 public boolean replace(K key, V oldValue, V newValue) {
2802 checkKeyBounds(key);
2803 return m.replace(key, oldValue, newValue);
2804 }
2805
2806 public V replace(K key, V value) {
2807 checkKeyBounds(key);
2808 return m.replace(key, value);
2809 }
2810
2811 /* ---------------- SortedMap API methods -------------- */
2812
2813 public Comparator<? super K> comparator() {
2814 Comparator<? super K> cmp = m.comparator();
2815 if (isDescending)
2816 return Collections.reverseOrder(cmp);
2817 else
2818 return cmp;
2819 }
2820
2821 /**
2822 * Utility to create submaps, where given bounds override
2823 * unbounded(null) ones and/or are checked against bounded ones.
2824 */
2825 private SubMap<K,V> newSubMap(K fromKey,
2826 boolean fromInclusive,
2827 K toKey,
2828 boolean toInclusive) {
2829 if (isDescending) { // flip senses
2830 K tk = fromKey;
2831 fromKey = toKey;
2832 toKey = tk;
2833 boolean ti = fromInclusive;
2834 fromInclusive = toInclusive;
2835 toInclusive = ti;
2836 }
2837 if (lo != null) {
2838 if (fromKey == null) {
2839 fromKey = lo;
2840 fromInclusive = loInclusive;
2841 }
2842 else {
2843 int c = m.compare(fromKey, lo);
2844 if (c < 0 || (c == 0 && !loInclusive && fromInclusive))
2845 throw new IllegalArgumentException("key out of range");
2846 }
2847 }
2848 if (hi != null) {
2849 if (toKey == null) {
2850 toKey = hi;
2851 toInclusive = hiInclusive;
2852 }
2853 else {
2854 int c = m.compare(toKey, hi);
2855 if (c > 0 || (c == 0 && !hiInclusive && toInclusive))
2856 throw new IllegalArgumentException("key out of range");
2857 }
2858 }
2859 return new SubMap<K,V>(m, fromKey, fromInclusive,
2860 toKey, toInclusive, isDescending);
2861 }
2862
2863 public SubMap<K,V> subMap(K fromKey,
2864 boolean fromInclusive,
2865 K toKey,
2866 boolean toInclusive) {
2867 if (fromKey == null || toKey == null)
2868 throw new NullPointerException();
2869 return newSubMap(fromKey, fromInclusive, toKey, toInclusive);
2870 }
2871
2872 public SubMap<K,V> headMap(K toKey,
2873 boolean inclusive) {
2874 if (toKey == null)
2875 throw new NullPointerException();
2876 return newSubMap(null, false, toKey, inclusive);
2877 }
2878
2879 public SubMap<K,V> tailMap(K fromKey,
2880 boolean inclusive) {
2881 if (fromKey == null)
2882 throw new NullPointerException();
2883 return newSubMap(fromKey, inclusive, null, false);
2884 }
2885
2886 public SubMap<K,V> subMap(K fromKey, K toKey) {
2887 return subMap(fromKey, true, toKey, false);
2888 }
2889
2890 public SubMap<K,V> headMap(K toKey) {
2891 return headMap(toKey, false);
2892 }
2893
2894 public SubMap<K,V> tailMap(K fromKey) {
2895 return tailMap(fromKey, true);
2896 }
2897
2898 public SubMap<K,V> descendingMap() {
2899 return new SubMap<K,V>(m, lo, loInclusive,
2900 hi, hiInclusive, !isDescending);
2901 }
2902
2903 /* ---------------- Relational methods -------------- */
2904
2905 public Map.Entry<K,V> ceilingEntry(K key) {
2906 return getNearEntry(key, GT|EQ);
2907 }
2908
2909 public K ceilingKey(K key) {
2910 return getNearKey(key, GT|EQ);
2911 }
2912
2913 public Map.Entry<K,V> lowerEntry(K key) {
2914 return getNearEntry(key, LT);
2915 }
2916
2917 public K lowerKey(K key) {
2918 return getNearKey(key, LT);
2919 }
2920
2921 public Map.Entry<K,V> floorEntry(K key) {
2922 return getNearEntry(key, LT|EQ);
2923 }
2924
2925 public K floorKey(K key) {
2926 return getNearKey(key, LT|EQ);
2927 }
2928
2929 public Map.Entry<K,V> higherEntry(K key) {
2930 return getNearEntry(key, GT);
2931 }
2932
2933 public K higherKey(K key) {
2934 return getNearKey(key, GT);
2935 }
2936
2937 public K firstKey() {
2938 return isDescending ? highestKey() : lowestKey();
2939 }
2940
2941 public K lastKey() {
2942 return isDescending ? lowestKey() : highestKey();
2943 }
2944
2945 public Map.Entry<K,V> firstEntry() {
2946 return isDescending ? highestEntry() : lowestEntry();
2947 }
2948
2949 public Map.Entry<K,V> lastEntry() {
2950 return isDescending ? lowestEntry() : highestEntry();
2951 }
2952
2953 public Map.Entry<K,V> pollFirstEntry() {
2954 return isDescending ? removeHighest() : removeLowest();
2955 }
2956
2957 public Map.Entry<K,V> pollLastEntry() {
2958 return isDescending ? removeLowest() : removeHighest();
2959 }
2960
2961 /* ---------------- Submap Views -------------- */
2962
2963 public NavigableSet<K> keySet() {
2964 KeySet<K> ks = keySetView;
2965 return (ks != null) ? ks : (keySetView = new KeySet<K>(this));
2966 }
2967
2968 public NavigableSet<K> navigableKeySet() {
2969 KeySet<K> ks = keySetView;
2970 return (ks != null) ? ks : (keySetView = new KeySet<K>(this));
2971 }
2972
2973 public Collection<V> values() {
2974 Collection<V> vs = valuesView;
2975 return (vs != null) ? vs : (valuesView = new Values<V>(this));
2976 }
2977
2978 public Set<Map.Entry<K,V>> entrySet() {
2979 Set<Map.Entry<K,V>> es = entrySetView;
2980 return (es != null) ? es : (entrySetView = new EntrySet<K,V>(this));
2981 }
2982
2983 public NavigableSet<K> descendingKeySet() {
2984 return descendingMap().navigableKeySet();
2985 }
2986
2987 Iterator<K> keyIterator() {
2988 return new SubMapKeyIterator();
2989 }
2990
2991 Iterator<V> valueIterator() {
2992 return new SubMapValueIterator();
2993 }
2994
2995 Iterator<Map.Entry<K,V>> entryIterator() {
2996 return new SubMapEntryIterator();
2997 }
2998
2999 /**
3000 * Variant of main Iter class to traverse through submaps.
3001 */
3002 abstract class SubMapIter<T> implements Iterator<T> {
3003 /** the last node returned by next() */
3004 Node<K,V> lastReturned;
3005 /** the next node to return from next(); */
3006 Node<K,V> next;
3007 /** Cache of next value field to maintain weak consistency */
3008 V nextValue;
3009
3010 SubMapIter() {
3011 for (;;) {
3012 next = isDescending ? hiNode() : loNode();
3013 if (next == null)
3014 break;
3015 Object x = next.value;
3016 if (x != null && x != next) {
3017 if (! inBounds(next.key))
3018 next = null;
3019 else
3020 nextValue = (V) x;
3021 break;
3022 }
3023 }
3024 }
3025
3026 public final boolean hasNext() {
3027 return next != null;
3028 }
3029
3030 final void advance() {
3031 if (next == null)
3032 throw new NoSuchElementException();
3033 lastReturned = next;
3034 if (isDescending)
3035 descend();
3036 else
3037 ascend();
3038 }
3039
3040 private void ascend() {
3041 for (;;) {
3042 next = next.next;
3043 if (next == null)
3044 break;
3045 Object x = next.value;
3046 if (x != null && x != next) {
3047 if (tooHigh(next.key))
3048 next = null;
3049 else
3050 nextValue = (V) x;
3051 break;
3052 }
3053 }
3054 }
3055
3056 private void descend() {
3057 for (;;) {
3058 next = m.findNear(lastReturned.key, LT);
3059 if (next == null)
3060 break;
3061 Object x = next.value;
3062 if (x != null && x != next) {
3063 if (tooLow(next.key))
3064 next = null;
3065 else
3066 nextValue = (V) x;
3067 break;
3068 }
3069 }
3070 }
3071
3072 public void remove() {
3073 Node<K,V> l = lastReturned;
3074 if (l == null)
3075 throw new IllegalStateException();
3076 m.remove(l.key);
3077 lastReturned = null;
3078 }
3079
3080 }
3081
3082 final class SubMapValueIterator extends SubMapIter<V> {
3083 public V next() {
3084 V v = nextValue;
3085 advance();
3086 return v;
3087 }
3088 }
3089
3090 final class SubMapKeyIterator extends SubMapIter<K> {
3091 public K next() {
3092 Node<K,V> n = next;
3093 advance();
3094 return n.key;
3095 }
3096 }
3097
3098 final class SubMapEntryIterator extends SubMapIter<Map.Entry<K,V>> {
3099 public Map.Entry<K,V> next() {
3100 Node<K,V> n = next;
3101 V v = nextValue;
3102 advance();
3103 return new AbstractMap.SimpleImmutableEntry<K,V>(n.key, v);
3104 }
3105 }
3106 }
3107
3108 // Unsafe mechanics
3109 private static final sun.misc.Unsafe UNSAFE;
3110 private static final long headOffset;
3111 static {
3112 try {
3113 UNSAFE = sun.misc.Unsafe.getUnsafe();
3114 Class<?> k = ConcurrentSkipListMap.class;
3115 headOffset = UNSAFE.objectFieldOffset
3116 (k.getDeclaredField("head"));
3117 } catch (Exception e) {
3118 throw new Error(e);
3119 }
3120 }
3121 }