1 /*
2 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 import java.lang.ref.WeakReference;
29 import java.lang.ref.ReferenceQueue;
30 import java.util.concurrent.ThreadLocalRandom;
31 import java.util.function.BiConsumer;
32 import java.util.function.BiFunction;
33 import java.util.function.Consumer;
34
35
36 /**
37 * Hash table based implementation of the <tt>Map</tt> interface, with
38 * <em>weak keys</em>.
39 * An entry in a <tt>WeakHashMap</tt> will automatically be removed when
40 * its key is no longer in ordinary use. More precisely, the presence of a
41 * mapping for a given key will not prevent the key from being discarded by the
42 * garbage collector, that is, made finalizable, finalized, and then reclaimed.
43 * When a key has been discarded its entry is effectively removed from the map,
44 * so this class behaves somewhat differently from other <tt>Map</tt>
45 * implementations.
46 *
47 * <p> Both null values and the null key are supported. This class has
48 * performance characteristics similar to those of the <tt>HashMap</tt>
49 * class, and has the same efficiency parameters of <em>initial capacity</em>
50 * and <em>load factor</em>.
51 *
52 * <p> Like most collection classes, this class is not synchronized.
53 * A synchronized <tt>WeakHashMap</tt> may be constructed using the
54 * {@link Collections#synchronizedMap Collections.synchronizedMap}
55 * method.
56 *
57 * <p> This class is intended primarily for use with key objects whose
58 * <tt>equals</tt> methods test for object identity using the
59 * <tt>==</tt> operator. Once such a key is discarded it can never be
60 * recreated, so it is impossible to do a lookup of that key in a
61 * <tt>WeakHashMap</tt> at some later time and be surprised that its entry
62 * has been removed. This class will work perfectly well with key objects
63 * whose <tt>equals</tt> methods are not based upon object identity, such
64 * as <tt>String</tt> instances. With such recreatable key objects,
65 * however, the automatic removal of <tt>WeakHashMap</tt> entries whose
66 * keys have been discarded may prove to be confusing.
67 *
68 * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon
69 * the actions of the garbage collector, so several familiar (though not
70 * required) <tt>Map</tt> invariants do not hold for this class. Because
71 * the garbage collector may discard keys at any time, a
72 * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently
73 * removing entries. In particular, even if you synchronize on a
74 * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it
75 * is possible for the <tt>size</tt> method to return smaller values over
76 * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and
77 * then <tt>true</tt>, for the <tt>containsKey</tt> method to return
78 * <tt>true</tt> and later <tt>false</tt> for a given key, for the
79 * <tt>get</tt> method to return a value for a given key but later return
80 * <tt>null</tt>, for the <tt>put</tt> method to return
81 * <tt>null</tt> and the <tt>remove</tt> method to return
82 * <tt>false</tt> for a key that previously appeared to be in the map, and
83 * for successive examinations of the key set, the value collection, and
84 * the entry set to yield successively smaller numbers of elements.
85 *
86 * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as
87 * the referent of a weak reference. Therefore a key will automatically be
88 * removed only after the weak references to it, both inside and outside of the
89 * map, have been cleared by the garbage collector.
90 *
91 * <p> <strong>Implementation note:</strong> The value objects in a
92 * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care
93 * should be taken to ensure that value objects do not strongly refer to their
94 * own keys, either directly or indirectly, since that will prevent the keys
95 * from being discarded. Note that a value object may refer indirectly to its
96 * key via the <tt>WeakHashMap</tt> itself; that is, a value object may
97 * strongly refer to some other key object whose associated value object, in
98 * turn, strongly refers to the key of the first value object. If the values
99 * in the map do not rely on the map holding strong references to them, one way
100 * to deal with this is to wrap values themselves within
101 * <tt>WeakReferences</tt> before
102 * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>,
103 * and then unwrapping upon each <tt>get</tt>.
104 *
105 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
106 * returned by all of this class's "collection view methods" are
107 * <i>fail-fast</i>: if the map is structurally modified at any time after the
108 * iterator is created, in any way except through the iterator's own
109 * <tt>remove</tt> method, the iterator will throw a {@link
110 * ConcurrentModificationException}. Thus, in the face of concurrent
111 * modification, the iterator fails quickly and cleanly, rather than risking
112 * arbitrary, non-deterministic behavior at an undetermined time in the future.
113 *
114 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
115 * as it is, generally speaking, impossible to make any hard guarantees in the
116 * presence of unsynchronized concurrent modification. Fail-fast iterators
117 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
118 * Therefore, it would be wrong to write a program that depended on this
119 * exception for its correctness: <i>the fail-fast behavior of iterators
120 * should be used only to detect bugs.</i>
121 *
122 * <p>This class is a member of the
123 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
124 * Java Collections Framework</a>.
125 *
126 * @param <K> the type of keys maintained by this map
127 * @param <V> the type of mapped values
128 *
129 * @author Doug Lea
130 * @author Josh Bloch
131 * @author Mark Reinhold
132 * @since 1.2
133 * @see java.util.HashMap
134 * @see java.lang.ref.WeakReference
135 */
136 public class WeakHashMap<K,V>
137 extends AbstractMap<K,V>
138 implements Map<K,V> {
139
140 /**
141 * The default initial capacity -- MUST be a power of two.
142 */
143 private static final int DEFAULT_INITIAL_CAPACITY = 16;
144
145 /**
146 * The maximum capacity, used if a higher value is implicitly specified
147 * by either of the constructors with arguments.
148 * MUST be a power of two <= 1<<30.
149 */
150 private static final int MAXIMUM_CAPACITY = 1 << 30;
151
152 /**
153 * The load factor used when none specified in constructor.
154 */
155 private static final float DEFAULT_LOAD_FACTOR = 0.75f;
156
157 /**
158 * The table, resized as necessary. Length MUST Always be a power of two.
159 */
160 Entry<K,V>[] table;
161
162 /**
163 * The number of key-value mappings contained in this weak hash map.
164 */
165 private int size;
166
167 /**
168 * The next size value at which to resize (capacity * load factor).
169 */
170 private int threshold;
171
172 /**
173 * The load factor for the hash table.
174 */
175 private final float loadFactor;
176
177 /**
178 * Reference queue for cleared WeakEntries
179 */
180 private final ReferenceQueue<Object> queue = new ReferenceQueue<>();
181
182 /**
183 * The number of times this WeakHashMap has been structurally modified.
184 * Structural modifications are those that change the number of
185 * mappings in the map or otherwise modify its internal structure
186 * (e.g., rehash). This field is used to make iterators on
187 * Collection-views of the map fail-fast.
188 *
189 * @see ConcurrentModificationException
190 */
191 int modCount;
192
193 @SuppressWarnings("unchecked")
194 private Entry<K,V>[] newTable(int n) {
195 return (Entry<K,V>[]) new Entry<?,?>[n];
196 }
197
198 /**
199 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
200 * capacity and the given load factor.
201 *
202 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
203 * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
204 * @throws IllegalArgumentException if the initial capacity is negative,
205 * or if the load factor is nonpositive.
206 */
207 public WeakHashMap(int initialCapacity, float loadFactor) {
208 if (initialCapacity < 0)
209 throw new IllegalArgumentException("Illegal Initial Capacity: "+
210 initialCapacity);
211 if (initialCapacity > MAXIMUM_CAPACITY)
212 initialCapacity = MAXIMUM_CAPACITY;
213
214 if (loadFactor <= 0 || Float.isNaN(loadFactor))
215 throw new IllegalArgumentException("Illegal Load factor: "+
216 loadFactor);
217 int capacity = 1;
218 while (capacity < initialCapacity)
219 capacity <<= 1;
220 table = newTable(capacity);
221 this.loadFactor = loadFactor;
222 threshold = (int)(capacity * loadFactor);
223 }
224
225 /**
226 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
227 * capacity and the default load factor (0.75).
228 *
229 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
230 * @throws IllegalArgumentException if the initial capacity is negative
231 */
232 public WeakHashMap(int initialCapacity) {
233 this(initialCapacity, DEFAULT_LOAD_FACTOR);
234 }
235
236 /**
237 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
238 * capacity (16) and load factor (0.75).
239 */
240 public WeakHashMap() {
241 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
242 }
243
244 /**
245 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
246 * specified map. The <tt>WeakHashMap</tt> is created with the default
247 * load factor (0.75) and an initial capacity sufficient to hold the
248 * mappings in the specified map.
249 *
250 * @param m the map whose mappings are to be placed in this map
251 * @throws NullPointerException if the specified map is null
252 * @since 1.3
253 */
254 public WeakHashMap(Map<? extends K, ? extends V> m) {
255 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
256 DEFAULT_INITIAL_CAPACITY),
257 DEFAULT_LOAD_FACTOR);
258 putAll(m);
259 }
260
261 // internal utilities
262
263 /**
264 * Value representing null keys inside tables.
265 */
266 private static final Object NULL_KEY = new Object();
267
268 /**
269 * Use NULL_KEY for key if it is null.
270 */
271 private static Object maskNull(Object key) {
272 return (key == null) ? NULL_KEY : key;
273 }
274
275 /**
276 * Returns internal representation of null key back to caller as null.
277 */
278 static Object unmaskNull(Object key) {
279 return (key == NULL_KEY) ? null : key;
280 }
281
282 /**
283 * Checks for equality of non-null reference x and possibly-null y. By
284 * default uses Object.equals.
285 */
286 private static boolean eq(Object x, Object y) {
287 return x == y || x.equals(y);
288 }
289
290 /**
291 * Retrieve object hash code and applies a supplemental hash function to the
292 * result hash, which defends against poor quality hash functions. This is
293 * critical because HashMap uses power-of-two length hash tables, that
294 * otherwise encounter collisions for hashCodes that do not differ
295 * in lower bits.
296 */
297 final int hash(Object k) {
298 int h = k.hashCode();
299
300 // This function ensures that hashCodes that differ only by
301 // constant multiples at each bit position have a bounded
302 // number of collisions (approximately 8 at default load factor).
303 h ^= (h >>> 20) ^ (h >>> 12);
304 return h ^ (h >>> 7) ^ (h >>> 4);
305 }
306
307 /**
308 * Returns index for hash code h.
309 */
310 private static int indexFor(int h, int length) {
311 return h & (length-1);
312 }
313
314 /**
315 * Expunges stale entries from the table.
316 */
317 private void expungeStaleEntries() {
318 for (Object x; (x = queue.poll()) != null; ) {
319 synchronized (queue) {
320 @SuppressWarnings("unchecked")
321 Entry<K,V> e = (Entry<K,V>) x;
322 int i = indexFor(e.hash, table.length);
323
324 Entry<K,V> prev = table[i];
325 Entry<K,V> p = prev;
326 while (p != null) {
327 Entry<K,V> next = p.next;
328 if (p == e) {
329 if (prev == e)
330 table[i] = next;
331 else
332 prev.next = next;
333 // Must not null out e.next;
334 // stale entries may be in use by a HashIterator
335 e.value = null; // Help GC
336 size--;
337 break;
338 }
339 prev = p;
340 p = next;
341 }
342 }
343 }
344 }
345
346 /**
347 * Returns the table after first expunging stale entries.
348 */
349 private Entry<K,V>[] getTable() {
350 expungeStaleEntries();
351 return table;
352 }
353
354 /**
355 * Returns the number of key-value mappings in this map.
356 * This result is a snapshot, and may not reflect unprocessed
357 * entries that will be removed before next attempted access
358 * because they are no longer referenced.
359 */
360 public int size() {
361 if (size == 0)
362 return 0;
363 expungeStaleEntries();
364 return size;
365 }
366
367 /**
368 * Returns <tt>true</tt> if this map contains no key-value mappings.
369 * This result is a snapshot, and may not reflect unprocessed
370 * entries that will be removed before next attempted access
371 * because they are no longer referenced.
372 */
373 public boolean isEmpty() {
374 return size() == 0;
375 }
376
377 /**
378 * Returns the value to which the specified key is mapped,
379 * or {@code null} if this map contains no mapping for the key.
380 *
381 * <p>More formally, if this map contains a mapping from a key
382 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
383 * key.equals(k))}, then this method returns {@code v}; otherwise
384 * it returns {@code null}. (There can be at most one such mapping.)
385 *
386 * <p>A return value of {@code null} does not <i>necessarily</i>
387 * indicate that the map contains no mapping for the key; it's also
388 * possible that the map explicitly maps the key to {@code null}.
389 * The {@link #containsKey containsKey} operation may be used to
390 * distinguish these two cases.
391 *
392 * @see #put(Object, Object)
393 */
394 public V get(Object key) {
395 Object k = maskNull(key);
396 int h = hash(k);
397 Entry<K,V>[] tab = getTable();
398 int index = indexFor(h, tab.length);
399 Entry<K,V> e = tab[index];
400 while (e != null) {
401 if (e.hash == h && eq(k, e.get()))
402 return e.value;
403 e = e.next;
404 }
405 return null;
406 }
407
408 /**
409 * Returns <tt>true</tt> if this map contains a mapping for the
410 * specified key.
411 *
412 * @param key The key whose presence in this map is to be tested
413 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
414 * <tt>false</tt> otherwise
415 */
416 public boolean containsKey(Object key) {
417 return getEntry(key) != null;
418 }
419
420 /**
421 * Returns the entry associated with the specified key in this map.
422 * Returns null if the map contains no mapping for this key.
423 */
424 Entry<K,V> getEntry(Object key) {
425 Object k = maskNull(key);
426 int h = hash(k);
427 Entry<K,V>[] tab = getTable();
428 int index = indexFor(h, tab.length);
429 Entry<K,V> e = tab[index];
430 while (e != null && !(e.hash == h && eq(k, e.get())))
431 e = e.next;
432 return e;
433 }
434
435 /**
436 * Associates the specified value with the specified key in this map.
437 * If the map previously contained a mapping for this key, the old
438 * value is replaced.
439 *
440 * @param key key with which the specified value is to be associated.
441 * @param value value to be associated with the specified key.
442 * @return the previous value associated with <tt>key</tt>, or
443 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
444 * (A <tt>null</tt> return can also indicate that the map
445 * previously associated <tt>null</tt> with <tt>key</tt>.)
446 */
447 public V put(K key, V value) {
448 Object k = maskNull(key);
449 int h = hash(k);
450 Entry<K,V>[] tab = getTable();
451 int i = indexFor(h, tab.length);
452
453 for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
454 if (h == e.hash && eq(k, e.get())) {
455 V oldValue = e.value;
456 if (value != oldValue)
457 e.value = value;
458 return oldValue;
459 }
460 }
461
462 modCount++;
463 Entry<K,V> e = tab[i];
464 tab[i] = new Entry<>(k, value, queue, h, e);
465 if (++size >= threshold)
466 resize(tab.length * 2);
467 return null;
468 }
469
470 /**
471 * Rehashes the contents of this map into a new array with a
472 * larger capacity. This method is called automatically when the
473 * number of keys in this map reaches its threshold.
474 *
475 * If current capacity is MAXIMUM_CAPACITY, this method does not
476 * resize the map, but sets threshold to Integer.MAX_VALUE.
477 * This has the effect of preventing future calls.
478 *
479 * @param newCapacity the new capacity, MUST be a power of two;
480 * must be greater than current capacity unless current
481 * capacity is MAXIMUM_CAPACITY (in which case value
482 * is irrelevant).
483 */
484 void resize(int newCapacity) {
485 Entry<K,V>[] oldTable = getTable();
486 int oldCapacity = oldTable.length;
487 if (oldCapacity == MAXIMUM_CAPACITY) {
488 threshold = Integer.MAX_VALUE;
489 return;
490 }
491
492 Entry<K,V>[] newTable = newTable(newCapacity);
493 transfer(oldTable, newTable);
494 table = newTable;
495
496 /*
497 * If ignoring null elements and processing ref queue caused massive
498 * shrinkage, then restore old table. This should be rare, but avoids
499 * unbounded expansion of garbage-filled tables.
500 */
501 if (size >= threshold / 2) {
502 threshold = (int)(newCapacity * loadFactor);
503 } else {
504 expungeStaleEntries();
505 transfer(newTable, oldTable);
506 table = oldTable;
507 }
508 }
509
510 /** Transfers all entries from src to dest tables */
511 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
512 for (int j = 0; j < src.length; ++j) {
513 Entry<K,V> e = src[j];
514 src[j] = null;
515 while (e != null) {
516 Entry<K,V> next = e.next;
517 Object key = e.get();
518 if (key == null) {
519 e.next = null; // Help GC
520 e.value = null; // " "
521 size--;
522 } else {
523 int i = indexFor(e.hash, dest.length);
524 e.next = dest[i];
525 dest[i] = e;
526 }
527 e = next;
528 }
529 }
530 }
531
532 /**
533 * Copies all of the mappings from the specified map to this map.
534 * These mappings will replace any mappings that this map had for any
535 * of the keys currently in the specified map.
536 *
537 * @param m mappings to be stored in this map.
538 * @throws NullPointerException if the specified map is null.
539 */
540 public void putAll(Map<? extends K, ? extends V> m) {
541 int numKeysToBeAdded = m.size();
542 if (numKeysToBeAdded == 0)
543 return;
544
545 /*
546 * Expand the map if the map if the number of mappings to be added
547 * is greater than or equal to threshold. This is conservative; the
548 * obvious condition is (m.size() + size) >= threshold, but this
549 * condition could result in a map with twice the appropriate capacity,
550 * if the keys to be added overlap with the keys already in this map.
551 * By using the conservative calculation, we subject ourself
552 * to at most one extra resize.
553 */
554 if (numKeysToBeAdded > threshold) {
555 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
556 if (targetCapacity > MAXIMUM_CAPACITY)
557 targetCapacity = MAXIMUM_CAPACITY;
558 int newCapacity = table.length;
559 while (newCapacity < targetCapacity)
560 newCapacity <<= 1;
561 if (newCapacity > table.length)
562 resize(newCapacity);
563 }
564
565 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
566 put(e.getKey(), e.getValue());
567 }
568
569 /**
570 * Removes the mapping for a key from this weak hash map if it is present.
571 * More formally, if this map contains a mapping from key <tt>k</tt> to
572 * value <tt>v</tt> such that <code>(key==null ? k==null :
573 * key.equals(k))</code>, that mapping is removed. (The map can contain
574 * at most one such mapping.)
575 *
576 * <p>Returns the value to which this map previously associated the key,
577 * or <tt>null</tt> if the map contained no mapping for the key. A
578 * return value of <tt>null</tt> does not <i>necessarily</i> indicate
579 * that the map contained no mapping for the key; it's also possible
580 * that the map explicitly mapped the key to <tt>null</tt>.
581 *
582 * <p>The map will not contain a mapping for the specified key once the
583 * call returns.
584 *
585 * @param key key whose mapping is to be removed from the map
586 * @return the previous value associated with <tt>key</tt>, or
587 * <tt>null</tt> if there was no mapping for <tt>key</tt>
588 */
589 public V remove(Object key) {
590 Object k = maskNull(key);
591 int h = hash(k);
592 Entry<K,V>[] tab = getTable();
593 int i = indexFor(h, tab.length);
594 Entry<K,V> prev = tab[i];
595 Entry<K,V> e = prev;
596
597 while (e != null) {
598 Entry<K,V> next = e.next;
599 if (h == e.hash && eq(k, e.get())) {
600 modCount++;
601 size--;
602 if (prev == e)
603 tab[i] = next;
604 else
605 prev.next = next;
606 return e.value;
607 }
608 prev = e;
609 e = next;
610 }
611
612 return null;
613 }
614
615 /** Special version of remove needed by Entry set */
616 boolean removeMapping(Object o) {
617 if (!(o instanceof Map.Entry))
618 return false;
619 Entry<K,V>[] tab = getTable();
620 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
621 Object k = maskNull(entry.getKey());
622 int h = hash(k);
623 int i = indexFor(h, tab.length);
624 Entry<K,V> prev = tab[i];
625 Entry<K,V> e = prev;
626
627 while (e != null) {
628 Entry<K,V> next = e.next;
629 if (h == e.hash && e.equals(entry)) {
630 modCount++;
631 size--;
632 if (prev == e)
633 tab[i] = next;
634 else
635 prev.next = next;
636 return true;
637 }
638 prev = e;
639 e = next;
640 }
641
642 return false;
643 }
644
645 /**
646 * Removes all of the mappings from this map.
647 * The map will be empty after this call returns.
648 */
649 public void clear() {
650 // clear out ref queue. We don't need to expunge entries
651 // since table is getting cleared.
652 while (queue.poll() != null)
653 ;
654
655 modCount++;
656 Arrays.fill(table, null);
657 size = 0;
658
659 // Allocation of array may have caused GC, which may have caused
660 // additional entries to go stale. Removing these entries from the
661 // reference queue will make them eligible for reclamation.
662 while (queue.poll() != null)
663 ;
664 }
665
666 /**
667 * Returns <tt>true</tt> if this map maps one or more keys to the
668 * specified value.
669 *
670 * @param value value whose presence in this map is to be tested
671 * @return <tt>true</tt> if this map maps one or more keys to the
672 * specified value
673 */
674 public boolean containsValue(Object value) {
675 if (value==null)
676 return containsNullValue();
677
678 Entry<K,V>[] tab = getTable();
679 for (int i = tab.length; i-- > 0;)
680 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
681 if (value.equals(e.value))
682 return true;
683 return false;
684 }
685
686 /**
687 * Special-case code for containsValue with null argument
688 */
689 private boolean containsNullValue() {
690 Entry<K,V>[] tab = getTable();
691 for (int i = tab.length; i-- > 0;)
692 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
693 if (e.value==null)
694 return true;
695 return false;
696 }
697
698 /**
699 * The entries in this hash table extend WeakReference, using its main ref
700 * field as the key.
701 */
702 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {
703 V value;
704 final int hash;
705 Entry<K,V> next;
706
707 /**
708 * Creates new entry.
709 */
710 Entry(Object key, V value,
711 ReferenceQueue<Object> queue,
712 int hash, Entry<K,V> next) {
713 super(key, queue);
714 this.value = value;
715 this.hash = hash;
716 this.next = next;
717 }
718
719 @SuppressWarnings("unchecked")
720 public K getKey() {
721 return (K) WeakHashMap.unmaskNull(get());
722 }
723
724 public V getValue() {
725 return value;
726 }
727
728 public V setValue(V newValue) {
729 V oldValue = value;
730 value = newValue;
731 return oldValue;
732 }
733
734 public boolean equals(Object o) {
735 if (!(o instanceof Map.Entry))
736 return false;
737 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
738 K k1 = getKey();
739 Object k2 = e.getKey();
740 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
741 V v1 = getValue();
742 Object v2 = e.getValue();
743 if (v1 == v2 || (v1 != null && v1.equals(v2)))
744 return true;
745 }
746 return false;
747 }
748
749 public int hashCode() {
750 K k = getKey();
751 V v = getValue();
752 return Objects.hashCode(k) ^ Objects.hashCode(v);
753 }
754
755 public String toString() {
756 return getKey() + "=" + getValue();
757 }
758 }
759
760 private abstract class HashIterator<T> implements Iterator<T> {
761 private int index;
762 private Entry<K,V> entry;
763 private Entry<K,V> lastReturned;
764 private int expectedModCount = modCount;
765
766 /**
767 * Strong reference needed to avoid disappearance of key
768 * between hasNext and next
769 */
770 private Object nextKey;
771
772 /**
773 * Strong reference needed to avoid disappearance of key
774 * between nextEntry() and any use of the entry
775 */
776 private Object currentKey;
777
778 HashIterator() {
779 index = isEmpty() ? 0 : table.length;
780 }
781
782 public boolean hasNext() {
783 Entry<K,V>[] t = table;
784
785 while (nextKey == null) {
786 Entry<K,V> e = entry;
787 int i = index;
788 while (e == null && i > 0)
789 e = t[--i];
790 entry = e;
791 index = i;
792 if (e == null) {
793 currentKey = null;
794 return false;
795 }
796 nextKey = e.get(); // hold on to key in strong ref
797 if (nextKey == null)
798 entry = entry.next;
799 }
800 return true;
801 }
802
803 /** The common parts of next() across different types of iterators */
804 protected Entry<K,V> nextEntry() {
805 if (modCount != expectedModCount)
806 throw new ConcurrentModificationException();
807 if (nextKey == null && !hasNext())
808 throw new NoSuchElementException();
809
810 lastReturned = entry;
811 entry = entry.next;
812 currentKey = nextKey;
813 nextKey = null;
814 return lastReturned;
815 }
816
817 public void remove() {
818 if (lastReturned == null)
819 throw new IllegalStateException();
820 if (modCount != expectedModCount)
821 throw new ConcurrentModificationException();
822
823 WeakHashMap.this.remove(currentKey);
824 expectedModCount = modCount;
825 lastReturned = null;
826 currentKey = null;
827 }
828
829 }
830
831 private class ValueIterator extends HashIterator<V> {
832 public V next() {
833 return nextEntry().value;
834 }
835 }
836
837 private class KeyIterator extends HashIterator<K> {
838 public K next() {
839 return nextEntry().getKey();
840 }
841 }
842
843 private class EntryIterator extends HashIterator<Map.Entry<K,V>> {
844 public Map.Entry<K,V> next() {
845 return nextEntry();
846 }
847 }
848
849 // Views
850
851 private transient Set<Map.Entry<K,V>> entrySet;
852
853 /**
854 * Returns a {@link Set} view of the keys contained in this map.
855 * The set is backed by the map, so changes to the map are
856 * reflected in the set, and vice-versa. If the map is modified
857 * while an iteration over the set is in progress (except through
858 * the iterator's own <tt>remove</tt> operation), the results of
859 * the iteration are undefined. The set supports element removal,
860 * which removes the corresponding mapping from the map, via the
861 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
862 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
863 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
864 * operations.
865 */
866 public Set<K> keySet() {
867 Set<K> ks = keySet;
868 return (ks != null ? ks : (keySet = new KeySet()));
869 }
870
871 private class KeySet extends AbstractSet<K> {
872 public Iterator<K> iterator() {
873 return new KeyIterator();
874 }
875
876 public int size() {
877 return WeakHashMap.this.size();
878 }
879
880 public boolean contains(Object o) {
881 return containsKey(o);
882 }
883
884 public boolean remove(Object o) {
885 if (containsKey(o)) {
886 WeakHashMap.this.remove(o);
887 return true;
888 }
889 else
890 return false;
891 }
892
893 public void clear() {
894 WeakHashMap.this.clear();
895 }
896
897 public Spliterator<K> spliterator() {
898 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
899 }
900 }
901
902 /**
903 * Returns a {@link Collection} view of the values contained in this map.
904 * The collection is backed by the map, so changes to the map are
905 * reflected in the collection, and vice-versa. If the map is
906 * modified while an iteration over the collection is in progress
907 * (except through the iterator's own <tt>remove</tt> operation),
908 * the results of the iteration are undefined. The collection
909 * supports element removal, which removes the corresponding
910 * mapping from the map, via the <tt>Iterator.remove</tt>,
911 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
912 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
913 * support the <tt>add</tt> or <tt>addAll</tt> operations.
914 */
915 public Collection<V> values() {
916 Collection<V> vs = values;
917 return (vs != null) ? vs : (values = new Values());
918 }
919
920 private class Values extends AbstractCollection<V> {
921 public Iterator<V> iterator() {
922 return new ValueIterator();
923 }
924
925 public int size() {
926 return WeakHashMap.this.size();
927 }
928
929 public boolean contains(Object o) {
930 return containsValue(o);
931 }
932
933 public void clear() {
934 WeakHashMap.this.clear();
935 }
936
937 public Spliterator<V> spliterator() {
938 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
939 }
940 }
941
942 /**
943 * Returns a {@link Set} view of the mappings contained in this map.
944 * The set is backed by the map, so changes to the map are
945 * reflected in the set, and vice-versa. If the map is modified
946 * while an iteration over the set is in progress (except through
947 * the iterator's own <tt>remove</tt> operation, or through the
948 * <tt>setValue</tt> operation on a map entry returned by the
949 * iterator) the results of the iteration are undefined. The set
950 * supports element removal, which removes the corresponding
951 * mapping from the map, via the <tt>Iterator.remove</tt>,
952 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
953 * <tt>clear</tt> operations. It does not support the
954 * <tt>add</tt> or <tt>addAll</tt> operations.
955 */
956 public Set<Map.Entry<K,V>> entrySet() {
957 Set<Map.Entry<K,V>> es = entrySet;
958 return es != null ? es : (entrySet = new EntrySet());
959 }
960
961 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
962 public Iterator<Map.Entry<K,V>> iterator() {
963 return new EntryIterator();
964 }
965
966 public boolean contains(Object o) {
967 if (!(o instanceof Map.Entry))
968 return false;
969 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
970 Entry<K,V> candidate = getEntry(e.getKey());
971 return candidate != null && candidate.equals(e);
972 }
973
974 public boolean remove(Object o) {
975 return removeMapping(o);
976 }
977
978 public int size() {
979 return WeakHashMap.this.size();
980 }
981
982 public void clear() {
983 WeakHashMap.this.clear();
984 }
985
986 private List<Map.Entry<K,V>> deepCopy() {
987 List<Map.Entry<K,V>> list = new ArrayList<>(size());
988 for (Map.Entry<K,V> e : this)
989 list.add(new AbstractMap.SimpleEntry<>(e));
990 return list;
991 }
992
993 public Object[] toArray() {
994 return deepCopy().toArray();
995 }
996
997 public <T> T[] toArray(T[] a) {
998 return deepCopy().toArray(a);
999 }
1000
1001 public Spliterator<Map.Entry<K,V>> spliterator() {
1002 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);
1003 }
1004 }
1005
1006 @SuppressWarnings("unchecked")
1007 @Override
1008 public void forEach(BiConsumer<? super K, ? super V> action) {
1009 Objects.requireNonNull(action);
1010 int expectedModCount = modCount;
1011
1012 Entry<K, V>[] tab = getTable();
1013 for (Entry<K, V> entry : tab) {
1014 while (entry != null) {
1015 Object key = entry.get();
1016 if (key != null) {
1017 action.accept((K)WeakHashMap.unmaskNull(key), entry.value);
1018 }
1019 entry = entry.next;
1020
1021 if (expectedModCount != modCount) {
1022 throw new ConcurrentModificationException();
1023 }
1024 }
1025 }
1026 }
1027
1028 @SuppressWarnings("unchecked")
1029 @Override
1030 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
1031 Objects.requireNonNull(function);
1032 int expectedModCount = modCount;
1033
1034 Entry<K, V>[] tab = getTable();;
1035 for (Entry<K, V> entry : tab) {
1036 while (entry != null) {
1037 Object key = entry.get();
1038 if (key != null) {
1039 entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value);
1040 }
1041 entry = entry.next;
1042
1043 if (expectedModCount != modCount) {
1044 throw new ConcurrentModificationException();
1045 }
1046 }
1047 }
1048 }
1049
1050 /**
1051 * Similar form as other hash Spliterators, but skips dead
1052 * elements.
1053 */
1054 static class WeakHashMapSpliterator<K,V> {
1055 final WeakHashMap<K,V> map;
1056 WeakHashMap.Entry<K,V> current; // current node
1057 int index; // current index, modified on advance/split
1058 int fence; // -1 until first use; then one past last index
1059 int est; // size estimate
1060 int expectedModCount; // for comodification checks
1061
1062 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin,
1063 int fence, int est,
1064 int expectedModCount) {
1065 this.map = m;
1066 this.index = origin;
1067 this.fence = fence;
1068 this.est = est;
1069 this.expectedModCount = expectedModCount;
1070 }
1071
1072 final int getFence() { // initialize fence and size on first use
1073 int hi;
1074 if ((hi = fence) < 0) {
1075 WeakHashMap<K,V> m = map;
1076 est = m.size();
1077 expectedModCount = m.modCount;
1078 hi = fence = m.table.length;
1079 }
1080 return hi;
1081 }
1082
1083 public final long estimateSize() {
1084 getFence(); // force init
1085 return (long) est;
1086 }
1087 }
1088
1089 static final class KeySpliterator<K,V>
1090 extends WeakHashMapSpliterator<K,V>
1091 implements Spliterator<K> {
1092 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,
1093 int expectedModCount) {
1094 super(m, origin, fence, est, expectedModCount);
1095 }
1096
1097 public KeySpliterator<K,V> trySplit() {
1098 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1099 return (lo >= mid) ? null :
1100 new KeySpliterator<>(map, lo, index = mid, est >>>= 1,
1101 expectedModCount);
1102 }
1103
1104 public void forEachRemaining(Consumer<? super K> action) {
1105 int i, hi, mc;
1106 if (action == null)
1107 throw new NullPointerException();
1108 WeakHashMap<K,V> m = map;
1109 WeakHashMap.Entry<K,V>[] tab = m.table;
1110 if ((hi = fence) < 0) {
1111 mc = expectedModCount = m.modCount;
1112 hi = fence = tab.length;
1113 }
1114 else
1115 mc = expectedModCount;
1116 if (tab.length >= hi && (i = index) >= 0 &&
1117 (i < (index = hi) || current != null)) {
1118 WeakHashMap.Entry<K,V> p = current;
1119 current = null; // exhaust
1120 do {
1121 if (p == null)
1122 p = tab[i++];
1123 else {
1124 Object x = p.get();
1125 p = p.next;
1126 if (x != null) {
1127 @SuppressWarnings("unchecked") K k =
1128 (K) WeakHashMap.unmaskNull(x);
1129 action.accept(k);
1130 }
1131 }
1132 } while (p != null || i < hi);
1133 }
1134 if (m.modCount != mc)
1135 throw new ConcurrentModificationException();
1136 }
1137
1138 public boolean tryAdvance(Consumer<? super K> action) {
1139 int hi;
1140 if (action == null)
1141 throw new NullPointerException();
1142 WeakHashMap.Entry<K,V>[] tab = map.table;
1143 if (tab.length >= (hi = getFence()) && index >= 0) {
1144 while (current != null || index < hi) {
1145 if (current == null)
1146 current = tab[index++];
1147 else {
1148 Object x = current.get();
1149 current = current.next;
1150 if (x != null) {
1151 @SuppressWarnings("unchecked") K k =
1152 (K) WeakHashMap.unmaskNull(x);
1153 action.accept(k);
1154 if (map.modCount != expectedModCount)
1155 throw new ConcurrentModificationException();
1156 return true;
1157 }
1158 }
1159 }
1160 }
1161 return false;
1162 }
1163
1164 public int characteristics() {
1165 return Spliterator.DISTINCT;
1166 }
1167 }
1168
1169 static final class ValueSpliterator<K,V>
1170 extends WeakHashMapSpliterator<K,V>
1171 implements Spliterator<V> {
1172 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,
1173 int expectedModCount) {
1174 super(m, origin, fence, est, expectedModCount);
1175 }
1176
1177 public ValueSpliterator<K,V> trySplit() {
1178 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1179 return (lo >= mid) ? null :
1180 new ValueSpliterator<>(map, lo, index = mid, est >>>= 1,
1181 expectedModCount);
1182 }
1183
1184 public void forEachRemaining(Consumer<? super V> action) {
1185 int i, hi, mc;
1186 if (action == null)
1187 throw new NullPointerException();
1188 WeakHashMap<K,V> m = map;
1189 WeakHashMap.Entry<K,V>[] tab = m.table;
1190 if ((hi = fence) < 0) {
1191 mc = expectedModCount = m.modCount;
1192 hi = fence = tab.length;
1193 }
1194 else
1195 mc = expectedModCount;
1196 if (tab.length >= hi && (i = index) >= 0 &&
1197 (i < (index = hi) || current != null)) {
1198 WeakHashMap.Entry<K,V> p = current;
1199 current = null; // exhaust
1200 do {
1201 if (p == null)
1202 p = tab[i++];
1203 else {
1204 Object x = p.get();
1205 V v = p.value;
1206 p = p.next;
1207 if (x != null)
1208 action.accept(v);
1209 }
1210 } while (p != null || i < hi);
1211 }
1212 if (m.modCount != mc)
1213 throw new ConcurrentModificationException();
1214 }
1215
1216 public boolean tryAdvance(Consumer<? super V> action) {
1217 int hi;
1218 if (action == null)
1219 throw new NullPointerException();
1220 WeakHashMap.Entry<K,V>[] tab = map.table;
1221 if (tab.length >= (hi = getFence()) && index >= 0) {
1222 while (current != null || index < hi) {
1223 if (current == null)
1224 current = tab[index++];
1225 else {
1226 Object x = current.get();
1227 V v = current.value;
1228 current = current.next;
1229 if (x != null) {
1230 action.accept(v);
1231 if (map.modCount != expectedModCount)
1232 throw new ConcurrentModificationException();
1233 return true;
1234 }
1235 }
1236 }
1237 }
1238 return false;
1239 }
1240
1241 public int characteristics() {
1242 return 0;
1243 }
1244 }
1245
1246 static final class EntrySpliterator<K,V>
1247 extends WeakHashMapSpliterator<K,V>
1248 implements Spliterator<Map.Entry<K,V>> {
1249 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,
1250 int expectedModCount) {
1251 super(m, origin, fence, est, expectedModCount);
1252 }
1253
1254 public EntrySpliterator<K,V> trySplit() {
1255 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1256 return (lo >= mid) ? null :
1257 new EntrySpliterator<>(map, lo, index = mid, est >>>= 1,
1258 expectedModCount);
1259 }
1260
1261
1262 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) {
1263 int i, hi, mc;
1264 if (action == null)
1265 throw new NullPointerException();
1266 WeakHashMap<K,V> m = map;
1267 WeakHashMap.Entry<K,V>[] tab = m.table;
1268 if ((hi = fence) < 0) {
1269 mc = expectedModCount = m.modCount;
1270 hi = fence = tab.length;
1271 }
1272 else
1273 mc = expectedModCount;
1274 if (tab.length >= hi && (i = index) >= 0 &&
1275 (i < (index = hi) || current != null)) {
1276 WeakHashMap.Entry<K,V> p = current;
1277 current = null; // exhaust
1278 do {
1279 if (p == null)
1280 p = tab[i++];
1281 else {
1282 Object x = p.get();
1283 V v = p.value;
1284 p = p.next;
1285 if (x != null) {
1286 @SuppressWarnings("unchecked") K k =
1287 (K) WeakHashMap.unmaskNull(x);
1288 action.accept
1289 (new AbstractMap.SimpleImmutableEntry<>(k, v));
1290 }
1291 }
1292 } while (p != null || i < hi);
1293 }
1294 if (m.modCount != mc)
1295 throw new ConcurrentModificationException();
1296 }
1297
1298 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
1299 int hi;
1300 if (action == null)
1301 throw new NullPointerException();
1302 WeakHashMap.Entry<K,V>[] tab = map.table;
1303 if (tab.length >= (hi = getFence()) && index >= 0) {
1304 while (current != null || index < hi) {
1305 if (current == null)
1306 current = tab[index++];
1307 else {
1308 Object x = current.get();
1309 V v = current.value;
1310 current = current.next;
1311 if (x != null) {
1312 @SuppressWarnings("unchecked") K k =
1313 (K) WeakHashMap.unmaskNull(x);
1314 action.accept
1315 (new AbstractMap.SimpleImmutableEntry<>(k, v));
1316 if (map.modCount != expectedModCount)
1317 throw new ConcurrentModificationException();
1318 return true;
1319 }
1320 }
1321 }
1322 }
1323 return false;
1324 }
1325
1326 public int characteristics() {
1327 return Spliterator.DISTINCT;
1328 }
1329 }
1330
1331 }