1 /* 2 * Copyright (c) 1998, 2020, 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.function.BiConsumer; 31 import java.util.function.BiFunction; 32 import java.util.function.Consumer; 33 34 35 /** 36 * Hash table based implementation of the {@code Map} interface, with 37 * <em>weak keys</em>. 38 * An entry in a {@code WeakHashMap} will automatically be removed when 39 * its key is no longer in ordinary use. More precisely, the presence of a 40 * mapping for a given key will not prevent the key from being discarded by the 41 * garbage collector, that is, made finalizable, finalized, and then reclaimed. 42 * When a key has been discarded its entry is effectively removed from the map, 43 * so this class behaves somewhat differently from other {@code Map} 44 * implementations. 45 * 46 * <p> Both null values and the null key are supported. This class has 47 * performance characteristics similar to those of the {@code HashMap} 48 * class, and has the same efficiency parameters of <em>initial capacity</em> 49 * and <em>load factor</em>. 50 * 51 * <p> Like most collection classes, this class is not synchronized. 52 * A synchronized {@code WeakHashMap} may be constructed using the 53 * {@link Collections#synchronizedMap Collections.synchronizedMap} 54 * method. 55 * 56 * <p> This class is intended primarily for use with key objects whose 57 * {@code equals} methods test for object identity using the 58 * {@code ==} operator. Once such a key is discarded it can never be 59 * recreated, so it is impossible to do a lookup of that key in a 60 * {@code WeakHashMap} at some later time and be surprised that its entry 61 * has been removed. This class will work perfectly well with key objects 62 * whose {@code equals} methods are not based upon object identity, such 63 * as {@code String} instances. With such recreatable key objects, 64 * however, the automatic removal of {@code WeakHashMap} entries whose 65 * keys have been discarded may prove to be confusing. 66 * 67 * <p> The behavior of the {@code WeakHashMap} class depends in part upon 68 * the actions of the garbage collector, so several familiar (though not 69 * required) {@code Map} invariants do not hold for this class. Because 70 * the garbage collector may discard keys at any time, a 71 * {@code WeakHashMap} may behave as though an unknown thread is silently 72 * removing entries. In particular, even if you synchronize on a 73 * {@code WeakHashMap} instance and invoke none of its mutator methods, it 74 * is possible for the {@code size} method to return smaller values over 75 * time, for the {@code isEmpty} method to return {@code false} and 76 * then {@code true}, for the {@code containsKey} method to return 77 * {@code true} and later {@code false} for a given key, for the 78 * {@code get} method to return a value for a given key but later return 79 * {@code null}, for the {@code put} method to return 80 * {@code null} and the {@code remove} method to return 81 * {@code false} for a key that previously appeared to be in the map, and 82 * for successive examinations of the key set, the value collection, and 83 * the entry set to yield successively smaller numbers of elements. 84 * 85 * <p> Each key object in a {@code WeakHashMap} is stored indirectly as 86 * the referent of a weak reference. Therefore a key will automatically be 87 * removed only after the weak references to it, both inside and outside of the 88 * map, have been cleared by the garbage collector. 89 * 90 * <p> <strong>Implementation note:</strong> The value objects in a 91 * {@code WeakHashMap} are held by ordinary strong references. Thus care 92 * should be taken to ensure that value objects do not strongly refer to their 93 * own keys, either directly or indirectly, since that will prevent the keys 94 * from being discarded. Note that a value object may refer indirectly to its 95 * key via the {@code WeakHashMap} itself; that is, a value object may 96 * strongly refer to some other key object whose associated value object, in 97 * turn, strongly refers to the key of the first value object. If the values 98 * in the map do not rely on the map holding strong references to them, one way 99 * to deal with this is to wrap values themselves within 100 * {@code WeakReferences} before 101 * inserting, as in: {@code m.put(key, new WeakReference(value))}, 102 * and then unwrapping upon each {@code get}. 103 * 104 * <p>The iterators returned by the {@code iterator} method of the collections 105 * returned by all of this class's "collection view methods" are 106 * <i>fail-fast</i>: if the map is structurally modified at any time after the 107 * iterator is created, in any way except through the iterator's own 108 * {@code remove} method, the iterator will throw a {@link 109 * ConcurrentModificationException}. Thus, in the face of concurrent 110 * modification, the iterator fails quickly and cleanly, rather than risking 111 * arbitrary, non-deterministic behavior at an undetermined time in the future. 112 * 113 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 114 * as it is, generally speaking, impossible to make any hard guarantees in the 115 * presence of unsynchronized concurrent modification. Fail-fast iterators 116 * throw {@code ConcurrentModificationException} on a best-effort basis. 117 * Therefore, it would be wrong to write a program that depended on this 118 * exception for its correctness: <i>the fail-fast behavior of iterators 119 * should be used only to detect bugs.</i> 120 * 121 * <p>This class is a member of the 122 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 123 * Java Collections Framework</a>. 124 * 125 * @param <K> the type of keys maintained by this map 126 * @param <V> the type of mapped values 127 * 128 * @author Doug Lea 129 * @author Josh Bloch 130 * @author Mark Reinhold 131 * @since 1.2 132 * @see java.util.HashMap 133 * @see java.lang.ref.WeakReference 134 */ 135 public class WeakHashMap<K,V> 136 extends AbstractMap<K,V> 137 implements Map<K,V> { 138 139 /** 140 * The default initial capacity -- MUST be a power of two. 141 */ 142 private static final int DEFAULT_INITIAL_CAPACITY = 16; 143 144 /** 145 * The maximum capacity, used if a higher value is implicitly specified 146 * by either of the constructors with arguments. 147 * MUST be a power of two <= 1<<30. 148 */ 149 private static final int MAXIMUM_CAPACITY = 1 << 30; 150 151 /** 152 * The load factor used when none specified in constructor. 153 */ 154 private static final float DEFAULT_LOAD_FACTOR = 0.75f; 155 156 /** 157 * The table, resized as necessary. Length MUST Always be a power of two. 158 */ 159 Entry<K,V>[] table; 160 161 /** 162 * The number of key-value mappings contained in this weak hash map. 163 */ 164 private int size; 165 166 /** 167 * The next size value at which to resize (capacity * load factor). 168 */ 169 private int threshold; 170 171 /** 172 * The load factor for the hash table. 173 */ 174 private final float loadFactor; 175 176 /** 177 * Reference queue for cleared WeakEntries 178 */ 179 private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); 180 181 /** 182 * The number of times this WeakHashMap has been structurally modified. 183 * Structural modifications are those that change the number of 184 * mappings in the map or otherwise modify its internal structure 185 * (e.g., rehash). This field is used to make iterators on 186 * Collection-views of the map fail-fast. 187 * 188 * @see ConcurrentModificationException 189 */ 190 int modCount; 191 192 @SuppressWarnings("unchecked") newTable(int n)193 private Entry<K,V>[] newTable(int n) { 194 return (Entry<K,V>[]) new Entry<?,?>[n]; 195 } 196 197 /** 198 * Constructs a new, empty {@code WeakHashMap} with the given initial 199 * capacity and the given load factor. 200 * 201 * @param initialCapacity The initial capacity of the {@code WeakHashMap} 202 * @param loadFactor The load factor of the {@code WeakHashMap} 203 * @throws IllegalArgumentException if the initial capacity is negative, 204 * or if the load factor is nonpositive. 205 */ WeakHashMap(int initialCapacity, float loadFactor)206 public WeakHashMap(int initialCapacity, float loadFactor) { 207 if (initialCapacity < 0) 208 throw new IllegalArgumentException("Illegal Initial Capacity: "+ 209 initialCapacity); 210 if (initialCapacity > MAXIMUM_CAPACITY) 211 initialCapacity = MAXIMUM_CAPACITY; 212 213 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 214 throw new IllegalArgumentException("Illegal Load factor: "+ 215 loadFactor); 216 int capacity = 1; 217 while (capacity < initialCapacity) 218 capacity <<= 1; 219 table = newTable(capacity); 220 this.loadFactor = loadFactor; 221 threshold = (int)(capacity * loadFactor); 222 } 223 224 /** 225 * Constructs a new, empty {@code WeakHashMap} with the given initial 226 * capacity and the default load factor (0.75). 227 * 228 * @param initialCapacity The initial capacity of the {@code WeakHashMap} 229 * @throws IllegalArgumentException if the initial capacity is negative 230 */ WeakHashMap(int initialCapacity)231 public WeakHashMap(int initialCapacity) { 232 this(initialCapacity, DEFAULT_LOAD_FACTOR); 233 } 234 235 /** 236 * Constructs a new, empty {@code WeakHashMap} with the default initial 237 * capacity (16) and load factor (0.75). 238 */ WeakHashMap()239 public WeakHashMap() { 240 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 241 } 242 243 /** 244 * Constructs a new {@code WeakHashMap} with the same mappings as the 245 * specified map. The {@code WeakHashMap} is created with the default 246 * load factor (0.75) and an initial capacity sufficient to hold the 247 * mappings in the specified map. 248 * 249 * @param m the map whose mappings are to be placed in this map 250 * @throws NullPointerException if the specified map is null 251 * @since 1.3 252 */ WeakHashMap(Map<? extends K, ? extends V> m)253 public WeakHashMap(Map<? extends K, ? extends V> m) { 254 this(Math.max((int) ((float)m.size() / DEFAULT_LOAD_FACTOR + 1.0F), 255 DEFAULT_INITIAL_CAPACITY), 256 DEFAULT_LOAD_FACTOR); 257 putAll(m); 258 } 259 260 // internal utilities 261 262 /** 263 * Value representing null keys inside tables. 264 */ 265 private static final Object NULL_KEY = new Object(); 266 267 /** 268 * Use NULL_KEY for key if it is null. 269 */ maskNull(Object key)270 private static Object maskNull(Object key) { 271 return (key == null) ? NULL_KEY : key; 272 } 273 274 /** 275 * Returns internal representation of null key back to caller as null. 276 */ unmaskNull(Object key)277 static Object unmaskNull(Object key) { 278 return (key == NULL_KEY) ? null : key; 279 } 280 281 /** 282 * Checks for equality of non-null reference x and possibly-null y. By 283 * default uses Object.equals. 284 */ matchesKey(Entry<K,V> e, Object key)285 private boolean matchesKey(Entry<K,V> e, Object key) { 286 // check if the given entry refers to the given key without 287 // keeping a strong reference to the entry's referent 288 if (e.refersTo(key)) return true; 289 290 // then check for equality if the referent is not cleared 291 Object k = e.get(); 292 return k != null && key.equals(k); 293 } 294 295 /** 296 * Retrieve object hash code and applies a supplemental hash function to the 297 * result hash, which defends against poor quality hash functions. This is 298 * critical because HashMap uses power-of-two length hash tables, that 299 * otherwise encounter collisions for hashCodes that do not differ 300 * in lower bits. 301 */ hash(Object k)302 final int hash(Object k) { 303 int h = k.hashCode(); 304 305 // This function ensures that hashCodes that differ only by 306 // constant multiples at each bit position have a bounded 307 // number of collisions (approximately 8 at default load factor). 308 h ^= (h >>> 20) ^ (h >>> 12); 309 return h ^ (h >>> 7) ^ (h >>> 4); 310 } 311 312 /** 313 * Returns index for hash code h. 314 */ indexFor(int h, int length)315 private static int indexFor(int h, int length) { 316 return h & (length-1); 317 } 318 319 /** 320 * Expunges stale entries from the table. 321 */ expungeStaleEntries()322 private void expungeStaleEntries() { 323 for (Object x; (x = queue.poll()) != null; ) { 324 synchronized (queue) { 325 @SuppressWarnings("unchecked") 326 Entry<K,V> e = (Entry<K,V>) x; 327 int i = indexFor(e.hash, table.length); 328 329 Entry<K,V> prev = table[i]; 330 Entry<K,V> p = prev; 331 while (p != null) { 332 Entry<K,V> next = p.next; 333 if (p == e) { 334 if (prev == e) 335 table[i] = next; 336 else 337 prev.next = next; 338 // Must not null out e.next; 339 // stale entries may be in use by a HashIterator 340 e.value = null; // Help GC 341 size--; 342 break; 343 } 344 prev = p; 345 p = next; 346 } 347 } 348 } 349 } 350 351 /** 352 * Returns the table after first expunging stale entries. 353 */ getTable()354 private Entry<K,V>[] getTable() { 355 expungeStaleEntries(); 356 return table; 357 } 358 359 /** 360 * Returns the number of key-value mappings in this map. 361 * This result is a snapshot, and may not reflect unprocessed 362 * entries that will be removed before next attempted access 363 * because they are no longer referenced. 364 */ size()365 public int size() { 366 if (size == 0) 367 return 0; 368 expungeStaleEntries(); 369 return size; 370 } 371 372 /** 373 * Returns {@code true} if this map contains no key-value mappings. 374 * This result is a snapshot, and may not reflect unprocessed 375 * entries that will be removed before next attempted access 376 * because they are no longer referenced. 377 */ isEmpty()378 public boolean isEmpty() { 379 return size() == 0; 380 } 381 382 /** 383 * Returns the value to which the specified key is mapped, 384 * or {@code null} if this map contains no mapping for the key. 385 * 386 * <p>More formally, if this map contains a mapping from a key 387 * {@code k} to a value {@code v} such that 388 * {@code Objects.equals(key, k)}, 389 * then this method returns {@code v}; otherwise 390 * it returns {@code null}. (There can be at most one such mapping.) 391 * 392 * <p>A return value of {@code null} does not <i>necessarily</i> 393 * indicate that the map contains no mapping for the key; it's also 394 * possible that the map explicitly maps the key to {@code null}. 395 * The {@link #containsKey containsKey} operation may be used to 396 * distinguish these two cases. 397 * 398 * @see #put(Object, Object) 399 */ get(Object key)400 public V get(Object key) { 401 Object k = maskNull(key); 402 int h = hash(k); 403 Entry<K,V>[] tab = getTable(); 404 int index = indexFor(h, tab.length); 405 Entry<K,V> e = tab[index]; 406 while (e != null) { 407 if (e.hash == h && matchesKey(e, k)) 408 return e.value; 409 e = e.next; 410 } 411 return null; 412 } 413 414 /** 415 * Returns {@code true} if this map contains a mapping for the 416 * specified key. 417 * 418 * @param key The key whose presence in this map is to be tested 419 * @return {@code true} if there is a mapping for {@code key}; 420 * {@code false} otherwise 421 */ containsKey(Object key)422 public boolean containsKey(Object key) { 423 return getEntry(key) != null; 424 } 425 426 /** 427 * Returns the entry associated with the specified key in this map. 428 * Returns null if the map contains no mapping for this key. 429 */ getEntry(Object key)430 Entry<K,V> getEntry(Object key) { 431 Object k = maskNull(key); 432 int h = hash(k); 433 Entry<K,V>[] tab = getTable(); 434 int index = indexFor(h, tab.length); 435 Entry<K,V> e = tab[index]; 436 while (e != null && !(e.hash == h && matchesKey(e, k))) 437 e = e.next; 438 return e; 439 } 440 441 /** 442 * Associates the specified value with the specified key in this map. 443 * If the map previously contained a mapping for this key, the old 444 * value is replaced. 445 * 446 * @param key key with which the specified value is to be associated. 447 * @param value value to be associated with the specified key. 448 * @return the previous value associated with {@code key}, or 449 * {@code null} if there was no mapping for {@code key}. 450 * (A {@code null} return can also indicate that the map 451 * previously associated {@code null} with {@code key}.) 452 */ put(K key, V value)453 public V put(K key, V value) { 454 Object k = maskNull(key); 455 int h = hash(k); 456 Entry<K,V>[] tab = getTable(); 457 int i = indexFor(h, tab.length); 458 459 for (Entry<K,V> e = tab[i]; e != null; e = e.next) { 460 if (h == e.hash && matchesKey(e, k)) { 461 V oldValue = e.value; 462 if (value != oldValue) 463 e.value = value; 464 return oldValue; 465 } 466 } 467 468 modCount++; 469 Entry<K,V> e = tab[i]; 470 tab[i] = new Entry<>(k, value, queue, h, e); 471 if (++size >= threshold) 472 resize(tab.length * 2); 473 return null; 474 } 475 476 /** 477 * Rehashes the contents of this map into a new array with a 478 * larger capacity. This method is called automatically when the 479 * number of keys in this map reaches its threshold. 480 * 481 * If current capacity is MAXIMUM_CAPACITY, this method does not 482 * resize the map, but sets threshold to Integer.MAX_VALUE. 483 * This has the effect of preventing future calls. 484 * 485 * @param newCapacity the new capacity, MUST be a power of two; 486 * must be greater than current capacity unless current 487 * capacity is MAXIMUM_CAPACITY (in which case value 488 * is irrelevant). 489 */ resize(int newCapacity)490 void resize(int newCapacity) { 491 Entry<K,V>[] oldTable = getTable(); 492 int oldCapacity = oldTable.length; 493 if (oldCapacity == MAXIMUM_CAPACITY) { 494 threshold = Integer.MAX_VALUE; 495 return; 496 } 497 498 Entry<K,V>[] newTable = newTable(newCapacity); 499 transfer(oldTable, newTable); 500 table = newTable; 501 502 /* 503 * If ignoring null elements and processing ref queue caused massive 504 * shrinkage, then restore old table. This should be rare, but avoids 505 * unbounded expansion of garbage-filled tables. 506 */ 507 if (size >= threshold / 2) { 508 threshold = (int)(newCapacity * loadFactor); 509 } else { 510 expungeStaleEntries(); 511 transfer(newTable, oldTable); 512 table = oldTable; 513 } 514 } 515 516 /** Transfers all entries from src to dest tables */ transfer(Entry<K,V>[] src, Entry<K,V>[] dest)517 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { 518 for (int j = 0; j < src.length; ++j) { 519 Entry<K,V> e = src[j]; 520 src[j] = null; 521 while (e != null) { 522 Entry<K,V> next = e.next; 523 if (e.refersTo(null)) { 524 e.next = null; // Help GC 525 e.value = null; // " " 526 size--; 527 } else { 528 int i = indexFor(e.hash, dest.length); 529 e.next = dest[i]; 530 dest[i] = e; 531 } 532 e = next; 533 } 534 } 535 } 536 537 /** 538 * Copies all of the mappings from the specified map to this map. 539 * These mappings will replace any mappings that this map had for any 540 * of the keys currently in the specified map. 541 * 542 * @param m mappings to be stored in this map. 543 * @throws NullPointerException if the specified map is null. 544 */ putAll(Map<? extends K, ? extends V> m)545 public void putAll(Map<? extends K, ? extends V> m) { 546 int numKeysToBeAdded = m.size(); 547 if (numKeysToBeAdded == 0) 548 return; 549 550 /* 551 * Expand the map if the map if the number of mappings to be added 552 * is greater than or equal to threshold. This is conservative; the 553 * obvious condition is (m.size() + size) >= threshold, but this 554 * condition could result in a map with twice the appropriate capacity, 555 * if the keys to be added overlap with the keys already in this map. 556 * By using the conservative calculation, we subject ourself 557 * to at most one extra resize. 558 */ 559 if (numKeysToBeAdded > threshold) { 560 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 561 if (targetCapacity > MAXIMUM_CAPACITY) 562 targetCapacity = MAXIMUM_CAPACITY; 563 int newCapacity = table.length; 564 while (newCapacity < targetCapacity) 565 newCapacity <<= 1; 566 if (newCapacity > table.length) 567 resize(newCapacity); 568 } 569 570 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 571 put(e.getKey(), e.getValue()); 572 } 573 574 /** 575 * Removes the mapping for a key from this weak hash map if it is present. 576 * More formally, if this map contains a mapping from key {@code k} to 577 * value {@code v} such that <code>(key==null ? k==null : 578 * key.equals(k))</code>, that mapping is removed. (The map can contain 579 * at most one such mapping.) 580 * 581 * <p>Returns the value to which this map previously associated the key, 582 * or {@code null} if the map contained no mapping for the key. A 583 * return value of {@code null} does not <i>necessarily</i> indicate 584 * that the map contained no mapping for the key; it's also possible 585 * that the map explicitly mapped the key to {@code null}. 586 * 587 * <p>The map will not contain a mapping for the specified key once the 588 * call returns. 589 * 590 * @param key key whose mapping is to be removed from the map 591 * @return the previous value associated with {@code key}, or 592 * {@code null} if there was no mapping for {@code key} 593 */ remove(Object key)594 public V remove(Object key) { 595 Object k = maskNull(key); 596 int h = hash(k); 597 Entry<K,V>[] tab = getTable(); 598 int i = indexFor(h, tab.length); 599 Entry<K,V> prev = tab[i]; 600 Entry<K,V> e = prev; 601 602 while (e != null) { 603 Entry<K,V> next = e.next; 604 if (h == e.hash && matchesKey(e, k)) { 605 modCount++; 606 size--; 607 if (prev == e) 608 tab[i] = next; 609 else 610 prev.next = next; 611 return e.value; 612 } 613 prev = e; 614 e = next; 615 } 616 617 return null; 618 } 619 620 /** Special version of remove needed by Entry set */ removeMapping(Object o)621 boolean removeMapping(Object o) { 622 if (!(o instanceof Map.Entry<?, ?> entry)) 623 return false; 624 Entry<K,V>[] tab = getTable(); 625 Object k = maskNull(entry.getKey()); 626 int h = hash(k); 627 int i = indexFor(h, tab.length); 628 Entry<K,V> prev = tab[i]; 629 Entry<K,V> e = prev; 630 631 while (e != null) { 632 Entry<K,V> next = e.next; 633 if (h == e.hash && e.equals(entry)) { 634 modCount++; 635 size--; 636 if (prev == e) 637 tab[i] = next; 638 else 639 prev.next = next; 640 return true; 641 } 642 prev = e; 643 e = next; 644 } 645 646 return false; 647 } 648 649 /** 650 * Removes all of the mappings from this map. 651 * The map will be empty after this call returns. 652 */ clear()653 public void clear() { 654 // clear out ref queue. We don't need to expunge entries 655 // since table is getting cleared. 656 while (queue.poll() != null) 657 ; 658 659 modCount++; 660 Arrays.fill(table, null); 661 size = 0; 662 663 // Allocation of array may have caused GC, which may have caused 664 // additional entries to go stale. Removing these entries from the 665 // reference queue will make them eligible for reclamation. 666 while (queue.poll() != null) 667 ; 668 } 669 670 /** 671 * Returns {@code true} if this map maps one or more keys to the 672 * specified value. 673 * 674 * @param value value whose presence in this map is to be tested 675 * @return {@code true} if this map maps one or more keys to the 676 * specified value 677 */ containsValue(Object value)678 public boolean containsValue(Object value) { 679 if (value==null) 680 return containsNullValue(); 681 682 Entry<K,V>[] tab = getTable(); 683 for (int i = tab.length; i-- > 0;) 684 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 685 if (value.equals(e.value)) 686 return true; 687 return false; 688 } 689 690 /** 691 * Special-case code for containsValue with null argument 692 */ containsNullValue()693 private boolean containsNullValue() { 694 Entry<K,V>[] tab = getTable(); 695 for (int i = tab.length; i-- > 0;) 696 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 697 if (e.value==null) 698 return true; 699 return false; 700 } 701 702 /** 703 * The entries in this hash table extend WeakReference, using its main ref 704 * field as the key. 705 */ 706 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { 707 V value; 708 final int hash; 709 Entry<K,V> next; 710 711 /** 712 * Creates new entry. 713 */ Entry(Object key, V value, ReferenceQueue<Object> queue, int hash, Entry<K,V> next)714 Entry(Object key, V value, 715 ReferenceQueue<Object> queue, 716 int hash, Entry<K,V> next) { 717 super(key, queue); 718 this.value = value; 719 this.hash = hash; 720 this.next = next; 721 } 722 723 @SuppressWarnings("unchecked") getKey()724 public K getKey() { 725 return (K) WeakHashMap.unmaskNull(get()); 726 } 727 getValue()728 public V getValue() { 729 return value; 730 } 731 setValue(V newValue)732 public V setValue(V newValue) { 733 V oldValue = value; 734 value = newValue; 735 return oldValue; 736 } 737 equals(Object o)738 public boolean equals(Object o) { 739 if (!(o instanceof Map.Entry<?, ?> e)) 740 return false; 741 K k1 = getKey(); 742 Object k2 = e.getKey(); 743 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 744 V v1 = getValue(); 745 Object v2 = e.getValue(); 746 if (v1 == v2 || (v1 != null && v1.equals(v2))) 747 return true; 748 } 749 return false; 750 } 751 hashCode()752 public int hashCode() { 753 K k = getKey(); 754 V v = getValue(); 755 return Objects.hashCode(k) ^ Objects.hashCode(v); 756 } 757 toString()758 public String toString() { 759 return getKey() + "=" + getValue(); 760 } 761 } 762 763 private abstract class HashIterator<T> implements Iterator<T> { 764 private int index; 765 private Entry<K,V> entry; 766 private Entry<K,V> lastReturned; 767 private int expectedModCount = modCount; 768 769 /** 770 * Strong reference needed to avoid disappearance of key 771 * between hasNext and next 772 */ 773 private Object nextKey; 774 775 /** 776 * Strong reference needed to avoid disappearance of key 777 * between nextEntry() and any use of the entry 778 */ 779 private Object currentKey; 780 HashIterator()781 HashIterator() { 782 index = isEmpty() ? 0 : table.length; 783 } 784 hasNext()785 public boolean hasNext() { 786 Entry<K,V>[] t = table; 787 788 while (nextKey == null) { 789 Entry<K,V> e = entry; 790 int i = index; 791 while (e == null && i > 0) 792 e = t[--i]; 793 entry = e; 794 index = i; 795 if (e == null) { 796 currentKey = null; 797 return false; 798 } 799 nextKey = e.get(); // hold on to key in strong ref 800 if (nextKey == null) 801 entry = entry.next; 802 } 803 return true; 804 } 805 806 /** The common parts of next() across different types of iterators */ nextEntry()807 protected Entry<K,V> nextEntry() { 808 if (modCount != expectedModCount) 809 throw new ConcurrentModificationException(); 810 if (nextKey == null && !hasNext()) 811 throw new NoSuchElementException(); 812 813 lastReturned = entry; 814 entry = entry.next; 815 currentKey = nextKey; 816 nextKey = null; 817 return lastReturned; 818 } 819 remove()820 public void remove() { 821 if (lastReturned == null) 822 throw new IllegalStateException(); 823 if (modCount != expectedModCount) 824 throw new ConcurrentModificationException(); 825 826 WeakHashMap.this.remove(currentKey); 827 expectedModCount = modCount; 828 lastReturned = null; 829 currentKey = null; 830 } 831 832 } 833 834 private class ValueIterator extends HashIterator<V> { next()835 public V next() { 836 return nextEntry().value; 837 } 838 } 839 840 private class KeyIterator extends HashIterator<K> { next()841 public K next() { 842 return nextEntry().getKey(); 843 } 844 } 845 846 private class EntryIterator extends HashIterator<Map.Entry<K,V>> { next()847 public Map.Entry<K,V> next() { 848 return nextEntry(); 849 } 850 } 851 852 // Views 853 854 private transient Set<Map.Entry<K,V>> entrySet; 855 856 /** 857 * Returns a {@link Set} view of the keys contained in this map. 858 * The set is backed by the map, so changes to the map are 859 * reflected in the set, and vice-versa. If the map is modified 860 * while an iteration over the set is in progress (except through 861 * the iterator's own {@code remove} operation), the results of 862 * the iteration are undefined. The set supports element removal, 863 * which removes the corresponding mapping from the map, via the 864 * {@code Iterator.remove}, {@code Set.remove}, 865 * {@code removeAll}, {@code retainAll}, and {@code clear} 866 * operations. It does not support the {@code add} or {@code addAll} 867 * operations. 868 */ keySet()869 public Set<K> keySet() { 870 Set<K> ks = keySet; 871 if (ks == null) { 872 ks = new KeySet(); 873 keySet = ks; 874 } 875 return ks; 876 } 877 878 private class KeySet extends AbstractSet<K> { iterator()879 public Iterator<K> iterator() { 880 return new KeyIterator(); 881 } 882 size()883 public int size() { 884 return WeakHashMap.this.size(); 885 } 886 contains(Object o)887 public boolean contains(Object o) { 888 return containsKey(o); 889 } 890 remove(Object o)891 public boolean remove(Object o) { 892 if (containsKey(o)) { 893 WeakHashMap.this.remove(o); 894 return true; 895 } 896 else 897 return false; 898 } 899 clear()900 public void clear() { 901 WeakHashMap.this.clear(); 902 } 903 spliterator()904 public Spliterator<K> spliterator() { 905 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 906 } 907 } 908 909 /** 910 * Returns a {@link Collection} view of the values contained in this map. 911 * The collection is backed by the map, so changes to the map are 912 * reflected in the collection, and vice-versa. If the map is 913 * modified while an iteration over the collection is in progress 914 * (except through the iterator's own {@code remove} operation), 915 * the results of the iteration are undefined. The collection 916 * supports element removal, which removes the corresponding 917 * mapping from the map, via the {@code Iterator.remove}, 918 * {@code Collection.remove}, {@code removeAll}, 919 * {@code retainAll} and {@code clear} operations. It does not 920 * support the {@code add} or {@code addAll} operations. 921 */ values()922 public Collection<V> values() { 923 Collection<V> vs = values; 924 if (vs == null) { 925 vs = new Values(); 926 values = vs; 927 } 928 return vs; 929 } 930 931 private class Values extends AbstractCollection<V> { iterator()932 public Iterator<V> iterator() { 933 return new ValueIterator(); 934 } 935 size()936 public int size() { 937 return WeakHashMap.this.size(); 938 } 939 contains(Object o)940 public boolean contains(Object o) { 941 return containsValue(o); 942 } 943 clear()944 public void clear() { 945 WeakHashMap.this.clear(); 946 } 947 spliterator()948 public Spliterator<V> spliterator() { 949 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 950 } 951 } 952 953 /** 954 * Returns a {@link Set} view of the mappings contained in this map. 955 * The set is backed by the map, so changes to the map are 956 * reflected in the set, and vice-versa. If the map is modified 957 * while an iteration over the set is in progress (except through 958 * the iterator's own {@code remove} operation, or through the 959 * {@code setValue} operation on a map entry returned by the 960 * iterator) the results of the iteration are undefined. The set 961 * supports element removal, which removes the corresponding 962 * mapping from the map, via the {@code Iterator.remove}, 963 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and 964 * {@code clear} operations. It does not support the 965 * {@code add} or {@code addAll} operations. 966 */ entrySet()967 public Set<Map.Entry<K,V>> entrySet() { 968 Set<Map.Entry<K,V>> es = entrySet; 969 return es != null ? es : (entrySet = new EntrySet()); 970 } 971 972 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { iterator()973 public Iterator<Map.Entry<K,V>> iterator() { 974 return new EntryIterator(); 975 } 976 contains(Object o)977 public boolean contains(Object o) { 978 return o instanceof Map.Entry<?, ?> e 979 && getEntry(e.getKey()) != null 980 && getEntry(e.getKey()).equals(e); 981 } 982 remove(Object o)983 public boolean remove(Object o) { 984 return removeMapping(o); 985 } 986 size()987 public int size() { 988 return WeakHashMap.this.size(); 989 } 990 clear()991 public void clear() { 992 WeakHashMap.this.clear(); 993 } 994 deepCopy()995 private List<Map.Entry<K,V>> deepCopy() { 996 List<Map.Entry<K,V>> list = new ArrayList<>(size()); 997 for (Map.Entry<K,V> e : this) 998 list.add(new AbstractMap.SimpleEntry<>(e)); 999 return list; 1000 } 1001 toArray()1002 public Object[] toArray() { 1003 return deepCopy().toArray(); 1004 } 1005 toArray(T[] a)1006 public <T> T[] toArray(T[] a) { 1007 return deepCopy().toArray(a); 1008 } 1009 spliterator()1010 public Spliterator<Map.Entry<K,V>> spliterator() { 1011 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 1012 } 1013 } 1014 1015 @SuppressWarnings("unchecked") 1016 @Override forEach(BiConsumer<? super K, ? super V> action)1017 public void forEach(BiConsumer<? super K, ? super V> action) { 1018 Objects.requireNonNull(action); 1019 int expectedModCount = modCount; 1020 1021 Entry<K, V>[] tab = getTable(); 1022 for (Entry<K, V> entry : tab) { 1023 while (entry != null) { 1024 Object key = entry.get(); 1025 if (key != null) { 1026 action.accept((K)WeakHashMap.unmaskNull(key), entry.value); 1027 } 1028 entry = entry.next; 1029 1030 if (expectedModCount != modCount) { 1031 throw new ConcurrentModificationException(); 1032 } 1033 } 1034 } 1035 } 1036 1037 @SuppressWarnings("unchecked") 1038 @Override replaceAll(BiFunction<? super K, ? super V, ? extends V> function)1039 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1040 Objects.requireNonNull(function); 1041 int expectedModCount = modCount; 1042 1043 Entry<K, V>[] tab = getTable();; 1044 for (Entry<K, V> entry : tab) { 1045 while (entry != null) { 1046 Object key = entry.get(); 1047 if (key != null) { 1048 entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value); 1049 } 1050 entry = entry.next; 1051 1052 if (expectedModCount != modCount) { 1053 throw new ConcurrentModificationException(); 1054 } 1055 } 1056 } 1057 } 1058 1059 /** 1060 * Similar form as other hash Spliterators, but skips dead 1061 * elements. 1062 */ 1063 static class WeakHashMapSpliterator<K,V> { 1064 final WeakHashMap<K,V> map; 1065 WeakHashMap.Entry<K,V> current; // current node 1066 int index; // current index, modified on advance/split 1067 int fence; // -1 until first use; then one past last index 1068 int est; // size estimate 1069 int expectedModCount; // for comodification checks 1070 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1071 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, 1072 int fence, int est, 1073 int expectedModCount) { 1074 this.map = m; 1075 this.index = origin; 1076 this.fence = fence; 1077 this.est = est; 1078 this.expectedModCount = expectedModCount; 1079 } 1080 getFence()1081 final int getFence() { // initialize fence and size on first use 1082 int hi; 1083 if ((hi = fence) < 0) { 1084 WeakHashMap<K,V> m = map; 1085 est = m.size(); 1086 expectedModCount = m.modCount; 1087 hi = fence = m.table.length; 1088 } 1089 return hi; 1090 } 1091 estimateSize()1092 public final long estimateSize() { 1093 getFence(); // force init 1094 return (long) est; 1095 } 1096 } 1097 1098 static final class KeySpliterator<K,V> 1099 extends WeakHashMapSpliterator<K,V> 1100 implements Spliterator<K> { KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1101 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1102 int expectedModCount) { 1103 super(m, origin, fence, est, expectedModCount); 1104 } 1105 trySplit()1106 public KeySpliterator<K,V> trySplit() { 1107 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1108 return (lo >= mid) ? null : 1109 new KeySpliterator<>(map, lo, index = mid, est >>>= 1, 1110 expectedModCount); 1111 } 1112 forEachRemaining(Consumer<? super K> action)1113 public void forEachRemaining(Consumer<? super K> action) { 1114 int i, hi, mc; 1115 if (action == null) 1116 throw new NullPointerException(); 1117 WeakHashMap<K,V> m = map; 1118 WeakHashMap.Entry<K,V>[] tab = m.table; 1119 if ((hi = fence) < 0) { 1120 mc = expectedModCount = m.modCount; 1121 hi = fence = tab.length; 1122 } 1123 else 1124 mc = expectedModCount; 1125 if (tab.length >= hi && (i = index) >= 0 && 1126 (i < (index = hi) || current != null)) { 1127 WeakHashMap.Entry<K,V> p = current; 1128 current = null; // exhaust 1129 do { 1130 if (p == null) 1131 p = tab[i++]; 1132 else { 1133 Object x = p.get(); 1134 p = p.next; 1135 if (x != null) { 1136 @SuppressWarnings("unchecked") K k = 1137 (K) WeakHashMap.unmaskNull(x); 1138 action.accept(k); 1139 } 1140 } 1141 } while (p != null || i < hi); 1142 } 1143 if (m.modCount != mc) 1144 throw new ConcurrentModificationException(); 1145 } 1146 tryAdvance(Consumer<? super K> action)1147 public boolean tryAdvance(Consumer<? super K> action) { 1148 int hi; 1149 if (action == null) 1150 throw new NullPointerException(); 1151 WeakHashMap.Entry<K,V>[] tab = map.table; 1152 if (tab.length >= (hi = getFence()) && index >= 0) { 1153 while (current != null || index < hi) { 1154 if (current == null) 1155 current = tab[index++]; 1156 else { 1157 Object x = current.get(); 1158 current = current.next; 1159 if (x != null) { 1160 @SuppressWarnings("unchecked") K k = 1161 (K) WeakHashMap.unmaskNull(x); 1162 action.accept(k); 1163 if (map.modCount != expectedModCount) 1164 throw new ConcurrentModificationException(); 1165 return true; 1166 } 1167 } 1168 } 1169 } 1170 return false; 1171 } 1172 characteristics()1173 public int characteristics() { 1174 return Spliterator.DISTINCT; 1175 } 1176 } 1177 1178 static final class ValueSpliterator<K,V> 1179 extends WeakHashMapSpliterator<K,V> 1180 implements Spliterator<V> { ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1181 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1182 int expectedModCount) { 1183 super(m, origin, fence, est, expectedModCount); 1184 } 1185 trySplit()1186 public ValueSpliterator<K,V> trySplit() { 1187 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1188 return (lo >= mid) ? null : 1189 new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, 1190 expectedModCount); 1191 } 1192 forEachRemaining(Consumer<? super V> action)1193 public void forEachRemaining(Consumer<? super V> action) { 1194 int i, hi, mc; 1195 if (action == null) 1196 throw new NullPointerException(); 1197 WeakHashMap<K,V> m = map; 1198 WeakHashMap.Entry<K,V>[] tab = m.table; 1199 if ((hi = fence) < 0) { 1200 mc = expectedModCount = m.modCount; 1201 hi = fence = tab.length; 1202 } 1203 else 1204 mc = expectedModCount; 1205 if (tab.length >= hi && (i = index) >= 0 && 1206 (i < (index = hi) || current != null)) { 1207 WeakHashMap.Entry<K,V> p = current; 1208 current = null; // exhaust 1209 do { 1210 if (p == null) 1211 p = tab[i++]; 1212 else { 1213 Object x = p.get(); 1214 V v = p.value; 1215 p = p.next; 1216 if (x != null) 1217 action.accept(v); 1218 } 1219 } while (p != null || i < hi); 1220 } 1221 if (m.modCount != mc) 1222 throw new ConcurrentModificationException(); 1223 } 1224 tryAdvance(Consumer<? super V> action)1225 public boolean tryAdvance(Consumer<? super V> action) { 1226 int hi; 1227 if (action == null) 1228 throw new NullPointerException(); 1229 WeakHashMap.Entry<K,V>[] tab = map.table; 1230 if (tab.length >= (hi = getFence()) && index >= 0) { 1231 while (current != null || index < hi) { 1232 if (current == null) 1233 current = tab[index++]; 1234 else { 1235 Object x = current.get(); 1236 V v = current.value; 1237 current = current.next; 1238 if (x != null) { 1239 action.accept(v); 1240 if (map.modCount != expectedModCount) 1241 throw new ConcurrentModificationException(); 1242 return true; 1243 } 1244 } 1245 } 1246 } 1247 return false; 1248 } 1249 characteristics()1250 public int characteristics() { 1251 return 0; 1252 } 1253 } 1254 1255 static final class EntrySpliterator<K,V> 1256 extends WeakHashMapSpliterator<K,V> 1257 implements Spliterator<Map.Entry<K,V>> { EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1258 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1259 int expectedModCount) { 1260 super(m, origin, fence, est, expectedModCount); 1261 } 1262 trySplit()1263 public EntrySpliterator<K,V> trySplit() { 1264 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1265 return (lo >= mid) ? null : 1266 new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, 1267 expectedModCount); 1268 } 1269 1270 forEachRemaining(Consumer<? super Map.Entry<K, V>> action)1271 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1272 int i, hi, mc; 1273 if (action == null) 1274 throw new NullPointerException(); 1275 WeakHashMap<K,V> m = map; 1276 WeakHashMap.Entry<K,V>[] tab = m.table; 1277 if ((hi = fence) < 0) { 1278 mc = expectedModCount = m.modCount; 1279 hi = fence = tab.length; 1280 } 1281 else 1282 mc = expectedModCount; 1283 if (tab.length >= hi && (i = index) >= 0 && 1284 (i < (index = hi) || current != null)) { 1285 WeakHashMap.Entry<K,V> p = current; 1286 current = null; // exhaust 1287 do { 1288 if (p == null) 1289 p = tab[i++]; 1290 else { 1291 Object x = p.get(); 1292 V v = p.value; 1293 p = p.next; 1294 if (x != null) { 1295 @SuppressWarnings("unchecked") K k = 1296 (K) WeakHashMap.unmaskNull(x); 1297 action.accept 1298 (new AbstractMap.SimpleImmutableEntry<>(k, v)); 1299 } 1300 } 1301 } while (p != null || i < hi); 1302 } 1303 if (m.modCount != mc) 1304 throw new ConcurrentModificationException(); 1305 } 1306 tryAdvance(Consumer<? super Map.Entry<K,V>> action)1307 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { 1308 int hi; 1309 if (action == null) 1310 throw new NullPointerException(); 1311 WeakHashMap.Entry<K,V>[] tab = map.table; 1312 if (tab.length >= (hi = getFence()) && index >= 0) { 1313 while (current != null || index < hi) { 1314 if (current == null) 1315 current = tab[index++]; 1316 else { 1317 Object x = current.get(); 1318 V v = current.value; 1319 current = current.next; 1320 if (x != null) { 1321 @SuppressWarnings("unchecked") K k = 1322 (K) WeakHashMap.unmaskNull(x); 1323 action.accept 1324 (new AbstractMap.SimpleImmutableEntry<>(k, v)); 1325 if (map.modCount != expectedModCount) 1326 throw new ConcurrentModificationException(); 1327 return true; 1328 } 1329 } 1330 } 1331 } 1332 return false; 1333 } 1334 characteristics()1335 public int characteristics() { 1336 return Spliterator.DISTINCT; 1337 } 1338 } 1339 1340 } 1341