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") newTable(int n)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 */ WeakHashMap(int initialCapacity, float loadFactor)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 */ WeakHashMap(int initialCapacity)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 */ WeakHashMap()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 */ WeakHashMap(Map<? extends K, ? extends V> m)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 */ maskNull(Object key)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 */ unmaskNull(Object key)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 */ eq(Object x, Object y)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 */ hash(Object k)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 */ indexFor(int h, int length)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 */ expungeStaleEntries()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 */ getTable()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 */ size()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 */ isEmpty()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 */ get(Object key)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 */ containsKey(Object key)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 */ getEntry(Object key)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 */ put(K key, V value)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 */ resize(int newCapacity)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 */ transfer(Entry<K,V>[] src, Entry<K,V>[] dest)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 */ putAll(Map<? extends K, ? extends V> m)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 */ remove(Object key)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 */ removeMapping(Object o)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 */ clear()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 */ containsValue(Object value)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 */ containsNullValue()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 */ Entry(Object key, V value, ReferenceQueue<Object> queue, int hash, Entry<K,V> next)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") getKey()720 public K getKey() { 721 return (K) WeakHashMap.unmaskNull(get()); 722 } 723 getValue()724 public V getValue() { 725 return value; 726 } 727 setValue(V newValue)728 public V setValue(V newValue) { 729 V oldValue = value; 730 value = newValue; 731 return oldValue; 732 } 733 equals(Object o)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 hashCode()749 public int hashCode() { 750 K k = getKey(); 751 V v = getValue(); 752 return Objects.hashCode(k) ^ Objects.hashCode(v); 753 } 754 toString()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 HashIterator()778 HashIterator() { 779 index = isEmpty() ? 0 : table.length; 780 } 781 hasNext()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 */ nextEntry()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 remove()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> { next()832 public V next() { 833 return nextEntry().value; 834 } 835 } 836 837 private class KeyIterator extends HashIterator<K> { next()838 public K next() { 839 return nextEntry().getKey(); 840 } 841 } 842 843 private class EntryIterator extends HashIterator<Map.Entry<K,V>> { next()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 */ keySet()866 public Set<K> keySet() { 867 Set<K> ks = keySet; 868 if (ks == null) { 869 ks = new KeySet(); 870 keySet = ks; 871 } 872 return ks; 873 } 874 875 private class KeySet extends AbstractSet<K> { iterator()876 public Iterator<K> iterator() { 877 return new KeyIterator(); 878 } 879 size()880 public int size() { 881 return WeakHashMap.this.size(); 882 } 883 contains(Object o)884 public boolean contains(Object o) { 885 return containsKey(o); 886 } 887 remove(Object o)888 public boolean remove(Object o) { 889 if (containsKey(o)) { 890 WeakHashMap.this.remove(o); 891 return true; 892 } 893 else 894 return false; 895 } 896 clear()897 public void clear() { 898 WeakHashMap.this.clear(); 899 } 900 spliterator()901 public Spliterator<K> spliterator() { 902 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 903 } 904 } 905 906 /** 907 * Returns a {@link Collection} view of the values contained in this map. 908 * The collection is backed by the map, so changes to the map are 909 * reflected in the collection, and vice-versa. If the map is 910 * modified while an iteration over the collection is in progress 911 * (except through the iterator's own <tt>remove</tt> operation), 912 * the results of the iteration are undefined. The collection 913 * supports element removal, which removes the corresponding 914 * mapping from the map, via the <tt>Iterator.remove</tt>, 915 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 916 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 917 * support the <tt>add</tt> or <tt>addAll</tt> operations. 918 */ values()919 public Collection<V> values() { 920 Collection<V> vs = values; 921 if (vs == null) { 922 vs = new Values(); 923 values = vs; 924 } 925 return vs; 926 } 927 928 private class Values extends AbstractCollection<V> { iterator()929 public Iterator<V> iterator() { 930 return new ValueIterator(); 931 } 932 size()933 public int size() { 934 return WeakHashMap.this.size(); 935 } 936 contains(Object o)937 public boolean contains(Object o) { 938 return containsValue(o); 939 } 940 clear()941 public void clear() { 942 WeakHashMap.this.clear(); 943 } 944 spliterator()945 public Spliterator<V> spliterator() { 946 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 947 } 948 } 949 950 /** 951 * Returns a {@link Set} view of the mappings contained in this map. 952 * The set is backed by the map, so changes to the map are 953 * reflected in the set, and vice-versa. If the map is modified 954 * while an iteration over the set is in progress (except through 955 * the iterator's own <tt>remove</tt> operation, or through the 956 * <tt>setValue</tt> operation on a map entry returned by the 957 * iterator) the results of the iteration are undefined. The set 958 * supports element removal, which removes the corresponding 959 * mapping from the map, via the <tt>Iterator.remove</tt>, 960 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 961 * <tt>clear</tt> operations. It does not support the 962 * <tt>add</tt> or <tt>addAll</tt> operations. 963 */ entrySet()964 public Set<Map.Entry<K,V>> entrySet() { 965 Set<Map.Entry<K,V>> es = entrySet; 966 return es != null ? es : (entrySet = new EntrySet()); 967 } 968 969 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { iterator()970 public Iterator<Map.Entry<K,V>> iterator() { 971 return new EntryIterator(); 972 } 973 contains(Object o)974 public boolean contains(Object o) { 975 if (!(o instanceof Map.Entry)) 976 return false; 977 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 978 Entry<K,V> candidate = getEntry(e.getKey()); 979 return candidate != null && candidate.equals(e); 980 } 981 remove(Object o)982 public boolean remove(Object o) { 983 return removeMapping(o); 984 } 985 size()986 public int size() { 987 return WeakHashMap.this.size(); 988 } 989 clear()990 public void clear() { 991 WeakHashMap.this.clear(); 992 } 993 deepCopy()994 private List<Map.Entry<K,V>> deepCopy() { 995 List<Map.Entry<K,V>> list = new ArrayList<>(size()); 996 for (Map.Entry<K,V> e : this) 997 list.add(new AbstractMap.SimpleEntry<>(e)); 998 return list; 999 } 1000 toArray()1001 public Object[] toArray() { 1002 return deepCopy().toArray(); 1003 } 1004 toArray(T[] a)1005 public <T> T[] toArray(T[] a) { 1006 return deepCopy().toArray(a); 1007 } 1008 spliterator()1009 public Spliterator<Map.Entry<K,V>> spliterator() { 1010 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 1011 } 1012 } 1013 1014 @SuppressWarnings("unchecked") 1015 @Override forEach(BiConsumer<? super K, ? super V> action)1016 public void forEach(BiConsumer<? super K, ? super V> action) { 1017 Objects.requireNonNull(action); 1018 int expectedModCount = modCount; 1019 1020 Entry<K, V>[] tab = getTable(); 1021 for (Entry<K, V> entry : tab) { 1022 while (entry != null) { 1023 Object key = entry.get(); 1024 if (key != null) { 1025 action.accept((K)WeakHashMap.unmaskNull(key), entry.value); 1026 } 1027 entry = entry.next; 1028 1029 if (expectedModCount != modCount) { 1030 throw new ConcurrentModificationException(); 1031 } 1032 } 1033 } 1034 } 1035 1036 @SuppressWarnings("unchecked") 1037 @Override replaceAll(BiFunction<? super K, ? super V, ? extends V> function)1038 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1039 Objects.requireNonNull(function); 1040 int expectedModCount = modCount; 1041 1042 Entry<K, V>[] tab = getTable();; 1043 for (Entry<K, V> entry : tab) { 1044 while (entry != null) { 1045 Object key = entry.get(); 1046 if (key != null) { 1047 entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value); 1048 } 1049 entry = entry.next; 1050 1051 if (expectedModCount != modCount) { 1052 throw new ConcurrentModificationException(); 1053 } 1054 } 1055 } 1056 } 1057 1058 /** 1059 * Similar form as other hash Spliterators, but skips dead 1060 * elements. 1061 */ 1062 static class WeakHashMapSpliterator<K,V> { 1063 final WeakHashMap<K,V> map; 1064 WeakHashMap.Entry<K,V> current; // current node 1065 int index; // current index, modified on advance/split 1066 int fence; // -1 until first use; then one past last index 1067 int est; // size estimate 1068 int expectedModCount; // for comodification checks 1069 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1070 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, 1071 int fence, int est, 1072 int expectedModCount) { 1073 this.map = m; 1074 this.index = origin; 1075 this.fence = fence; 1076 this.est = est; 1077 this.expectedModCount = expectedModCount; 1078 } 1079 getFence()1080 final int getFence() { // initialize fence and size on first use 1081 int hi; 1082 if ((hi = fence) < 0) { 1083 WeakHashMap<K,V> m = map; 1084 est = m.size(); 1085 expectedModCount = m.modCount; 1086 hi = fence = m.table.length; 1087 } 1088 return hi; 1089 } 1090 estimateSize()1091 public final long estimateSize() { 1092 getFence(); // force init 1093 return (long) est; 1094 } 1095 } 1096 1097 static final class KeySpliterator<K,V> 1098 extends WeakHashMapSpliterator<K,V> 1099 implements Spliterator<K> { KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1100 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1101 int expectedModCount) { 1102 super(m, origin, fence, est, expectedModCount); 1103 } 1104 trySplit()1105 public KeySpliterator<K,V> trySplit() { 1106 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1107 return (lo >= mid) ? null : 1108 new KeySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1109 expectedModCount); 1110 } 1111 forEachRemaining(Consumer<? super K> action)1112 public void forEachRemaining(Consumer<? super K> action) { 1113 int i, hi, mc; 1114 if (action == null) 1115 throw new NullPointerException(); 1116 WeakHashMap<K,V> m = map; 1117 WeakHashMap.Entry<K,V>[] tab = m.table; 1118 if ((hi = fence) < 0) { 1119 mc = expectedModCount = m.modCount; 1120 hi = fence = tab.length; 1121 } 1122 else 1123 mc = expectedModCount; 1124 if (tab.length >= hi && (i = index) >= 0 && 1125 (i < (index = hi) || current != null)) { 1126 WeakHashMap.Entry<K,V> p = current; 1127 current = null; // exhaust 1128 do { 1129 if (p == null) 1130 p = tab[i++]; 1131 else { 1132 Object x = p.get(); 1133 p = p.next; 1134 if (x != null) { 1135 @SuppressWarnings("unchecked") K k = 1136 (K) WeakHashMap.unmaskNull(x); 1137 action.accept(k); 1138 } 1139 } 1140 } while (p != null || i < hi); 1141 } 1142 if (m.modCount != mc) 1143 throw new ConcurrentModificationException(); 1144 } 1145 tryAdvance(Consumer<? super K> action)1146 public boolean tryAdvance(Consumer<? super K> action) { 1147 int hi; 1148 if (action == null) 1149 throw new NullPointerException(); 1150 WeakHashMap.Entry<K,V>[] tab = map.table; 1151 if (tab.length >= (hi = getFence()) && index >= 0) { 1152 while (current != null || index < hi) { 1153 if (current == null) 1154 current = tab[index++]; 1155 else { 1156 Object x = current.get(); 1157 current = current.next; 1158 if (x != null) { 1159 @SuppressWarnings("unchecked") K k = 1160 (K) WeakHashMap.unmaskNull(x); 1161 action.accept(k); 1162 if (map.modCount != expectedModCount) 1163 throw new ConcurrentModificationException(); 1164 return true; 1165 } 1166 } 1167 } 1168 } 1169 return false; 1170 } 1171 characteristics()1172 public int characteristics() { 1173 return Spliterator.DISTINCT; 1174 } 1175 } 1176 1177 static final class ValueSpliterator<K,V> 1178 extends WeakHashMapSpliterator<K,V> 1179 implements Spliterator<V> { ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1180 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1181 int expectedModCount) { 1182 super(m, origin, fence, est, expectedModCount); 1183 } 1184 trySplit()1185 public ValueSpliterator<K,V> trySplit() { 1186 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1187 return (lo >= mid) ? null : 1188 new ValueSpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1189 expectedModCount); 1190 } 1191 forEachRemaining(Consumer<? super V> action)1192 public void forEachRemaining(Consumer<? super V> action) { 1193 int i, hi, mc; 1194 if (action == null) 1195 throw new NullPointerException(); 1196 WeakHashMap<K,V> m = map; 1197 WeakHashMap.Entry<K,V>[] tab = m.table; 1198 if ((hi = fence) < 0) { 1199 mc = expectedModCount = m.modCount; 1200 hi = fence = tab.length; 1201 } 1202 else 1203 mc = expectedModCount; 1204 if (tab.length >= hi && (i = index) >= 0 && 1205 (i < (index = hi) || current != null)) { 1206 WeakHashMap.Entry<K,V> p = current; 1207 current = null; // exhaust 1208 do { 1209 if (p == null) 1210 p = tab[i++]; 1211 else { 1212 Object x = p.get(); 1213 V v = p.value; 1214 p = p.next; 1215 if (x != null) 1216 action.accept(v); 1217 } 1218 } while (p != null || i < hi); 1219 } 1220 if (m.modCount != mc) 1221 throw new ConcurrentModificationException(); 1222 } 1223 tryAdvance(Consumer<? super V> action)1224 public boolean tryAdvance(Consumer<? super V> action) { 1225 int hi; 1226 if (action == null) 1227 throw new NullPointerException(); 1228 WeakHashMap.Entry<K,V>[] tab = map.table; 1229 if (tab.length >= (hi = getFence()) && index >= 0) { 1230 while (current != null || index < hi) { 1231 if (current == null) 1232 current = tab[index++]; 1233 else { 1234 Object x = current.get(); 1235 V v = current.value; 1236 current = current.next; 1237 if (x != null) { 1238 action.accept(v); 1239 if (map.modCount != expectedModCount) 1240 throw new ConcurrentModificationException(); 1241 return true; 1242 } 1243 } 1244 } 1245 } 1246 return false; 1247 } 1248 characteristics()1249 public int characteristics() { 1250 return 0; 1251 } 1252 } 1253 1254 static final class EntrySpliterator<K,V> 1255 extends WeakHashMapSpliterator<K,V> 1256 implements Spliterator<Map.Entry<K,V>> { EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1257 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1258 int expectedModCount) { 1259 super(m, origin, fence, est, expectedModCount); 1260 } 1261 trySplit()1262 public EntrySpliterator<K,V> trySplit() { 1263 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1264 return (lo >= mid) ? null : 1265 new EntrySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1266 expectedModCount); 1267 } 1268 1269 forEachRemaining(Consumer<? super Map.Entry<K, V>> action)1270 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1271 int i, hi, mc; 1272 if (action == null) 1273 throw new NullPointerException(); 1274 WeakHashMap<K,V> m = map; 1275 WeakHashMap.Entry<K,V>[] tab = m.table; 1276 if ((hi = fence) < 0) { 1277 mc = expectedModCount = m.modCount; 1278 hi = fence = tab.length; 1279 } 1280 else 1281 mc = expectedModCount; 1282 if (tab.length >= hi && (i = index) >= 0 && 1283 (i < (index = hi) || current != null)) { 1284 WeakHashMap.Entry<K,V> p = current; 1285 current = null; // exhaust 1286 do { 1287 if (p == null) 1288 p = tab[i++]; 1289 else { 1290 Object x = p.get(); 1291 V v = p.value; 1292 p = p.next; 1293 if (x != null) { 1294 @SuppressWarnings("unchecked") K k = 1295 (K) WeakHashMap.unmaskNull(x); 1296 action.accept 1297 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1298 } 1299 } 1300 } while (p != null || i < hi); 1301 } 1302 if (m.modCount != mc) 1303 throw new ConcurrentModificationException(); 1304 } 1305 tryAdvance(Consumer<? super Map.Entry<K,V>> action)1306 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { 1307 int hi; 1308 if (action == null) 1309 throw new NullPointerException(); 1310 WeakHashMap.Entry<K,V>[] tab = map.table; 1311 if (tab.length >= (hi = getFence()) && index >= 0) { 1312 while (current != null || index < hi) { 1313 if (current == null) 1314 current = tab[index++]; 1315 else { 1316 Object x = current.get(); 1317 V v = current.value; 1318 current = current.next; 1319 if (x != null) { 1320 @SuppressWarnings("unchecked") K k = 1321 (K) WeakHashMap.unmaskNull(x); 1322 action.accept 1323 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1324 if (map.modCount != expectedModCount) 1325 throw new ConcurrentModificationException(); 1326 return true; 1327 } 1328 } 1329 } 1330 } 1331 return false; 1332 } 1333 characteristics()1334 public int characteristics() { 1335 return Spliterator.DISTINCT; 1336 } 1337 } 1338 1339 } 1340