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| 1 | /* | ||
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 3 | * | ||
| 4 | * This code is free software; you can redistribute it and/or modify it | ||
| 5 | * under the terms of the GNU General Public License version 2 only, as | ||
| 6 | * published by the Free Software Foundation. Oracle designates this | ||
| 7 | * particular file as subject to the "Classpath" exception as provided | ||
| 8 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 9 | * | ||
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 13 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 14 | * accompanied this code). | ||
| 15 | * | ||
| 16 | * You should have received a copy of the GNU General Public License version | ||
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 19 | * | ||
| 20 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 21 | * or visit www.oracle.com if you need additional information or have any | ||
| 22 | * questions. | ||
| 23 | */ | ||
| 24 | |||
| 25 | /* | ||
| 26 | * This file is available under and governed by the GNU General Public | ||
| 27 | * License version 2 only, as published by the Free Software Foundation. | ||
| 28 | * However, the following notice accompanied the original version of this | ||
| 29 | * file: | ||
| 30 | * | ||
| 31 | * Written by Doug Lea with assistance from members of JCP JSR-166 | ||
| 32 | * Expert Group and released to the public domain, as explained at | ||
| 33 | * http://creativecommons.org/publicdomain/zero/1.0/ | ||
| 34 | */ | ||
| 35 | |||
| 36 | package java.util.concurrent; | ||
| 37 | import java.util.concurrent.locks.*; | ||
| 38 | import java.util.*; | ||
| 39 | import java.io.Serializable; | ||
| 40 | import java.io.IOException; | ||
| 41 | import java.io.ObjectInputStream; | ||
| 42 | import java.io.ObjectOutputStream; | ||
| 43 | |||
| 44 | /** | ||
| 45 | * A hash table supporting full concurrency of retrievals and | ||
| 46 | * adjustable expected concurrency for updates. This class obeys the | ||
| 47 | * same functional specification as {@link java.util.Hashtable}, and | ||
| 48 | * includes versions of methods corresponding to each method of | ||
| 49 | * <tt>Hashtable</tt>. However, even though all operations are | ||
| 50 | * thread-safe, retrieval operations do <em>not</em> entail locking, | ||
| 51 | * and there is <em>not</em> any support for locking the entire table | ||
| 52 | * in a way that prevents all access. This class is fully | ||
| 53 | * interoperable with <tt>Hashtable</tt> in programs that rely on its | ||
| 54 | * thread safety but not on its synchronization details. | ||
| 55 | * | ||
| 56 | * <p> Retrieval operations (including <tt>get</tt>) generally do not | ||
| 57 | * block, so may overlap with update operations (including | ||
| 58 | * <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results | ||
| 59 | * of the most recently <em>completed</em> update operations holding | ||
| 60 | * upon their onset. For aggregate operations such as <tt>putAll</tt> | ||
| 61 | * and <tt>clear</tt>, concurrent retrievals may reflect insertion or | ||
| 62 | * removal of only some entries. Similarly, Iterators and | ||
| 63 | * Enumerations return elements reflecting the state of the hash table | ||
| 64 | * at some point at or since the creation of the iterator/enumeration. | ||
| 65 | * They do <em>not</em> throw {@link ConcurrentModificationException}. | ||
| 66 | * However, iterators are designed to be used by only one thread at a time. | ||
| 67 | * | ||
| 68 | * <p> The allowed concurrency among update operations is guided by | ||
| 69 | * the optional <tt>concurrencyLevel</tt> constructor argument | ||
| 70 | * (default <tt>16</tt>), which is used as a hint for internal sizing. The | ||
| 71 | * table is internally partitioned to try to permit the indicated | ||
| 72 | * number of concurrent updates without contention. Because placement | ||
| 73 | * in hash tables is essentially random, the actual concurrency will | ||
| 74 | * vary. Ideally, you should choose a value to accommodate as many | ||
| 75 | * threads as will ever concurrently modify the table. Using a | ||
| 76 | * significantly higher value than you need can waste space and time, | ||
| 77 | * and a significantly lower value can lead to thread contention. But | ||
| 78 | * overestimates and underestimates within an order of magnitude do | ||
| 79 | * not usually have much noticeable impact. A value of one is | ||
| 80 | * appropriate when it is known that only one thread will modify and | ||
| 81 | * all others will only read. Also, resizing this or any other kind of | ||
| 82 | * hash table is a relatively slow operation, so, when possible, it is | ||
| 83 | * a good idea to provide estimates of expected table sizes in | ||
| 84 | * constructors. | ||
| 85 | * | ||
| 86 | * <p>This class and its views and iterators implement all of the | ||
| 87 | * <em>optional</em> methods of the {@link Map} and {@link Iterator} | ||
| 88 | * interfaces. | ||
| 89 | * | ||
| 90 | * <p> Like {@link Hashtable} but unlike {@link HashMap}, this class | ||
| 91 | * does <em>not</em> allow <tt>null</tt> to be used as a key or value. | ||
| 92 | * | ||
| 93 | * <p>This class is a member of the | ||
| 94 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 95 | * Java Collections Framework</a>. | ||
| 96 | * | ||
| 97 | * @since 1.5 | ||
| 98 | * @author Doug Lea | ||
| 99 | * @param <K> the type of keys maintained by this map | ||
| 100 | * @param <V> the type of mapped values | ||
| 101 | */ | ||
| 102 | public class ConcurrentHashMap<K, V> extends AbstractMap<K, V> | ||
| 103 | implements ConcurrentMap<K, V>, Serializable { | ||
| 104 | private static final long serialVersionUID = 7249069246763182397L; | ||
| 105 | |||
| 106 | /* | ||
| 107 | * The basic strategy is to subdivide the table among Segments, | ||
| 108 | * each of which itself is a concurrently readable hash table. To | ||
| 109 | * reduce footprint, all but one segments are constructed only | ||
| 110 | * when first needed (see ensureSegment). To maintain visibility | ||
| 111 | * in the presence of lazy construction, accesses to segments as | ||
| 112 | * well as elements of segment's table must use volatile access, | ||
| 113 | * which is done via Unsafe within methods segmentAt etc | ||
| 114 | * below. These provide the functionality of AtomicReferenceArrays | ||
| 115 | * but reduce the levels of indirection. Additionally, | ||
| 116 | * volatile-writes of table elements and entry "next" fields | ||
| 117 | * within locked operations use the cheaper "lazySet" forms of | ||
| 118 | * writes (via putOrderedObject) because these writes are always | ||
| 119 | * followed by lock releases that maintain sequential consistency | ||
| 120 | * of table updates. | ||
| 121 | * | ||
| 122 | * Historical note: The previous version of this class relied | ||
| 123 | * heavily on "final" fields, which avoided some volatile reads at | ||
| 124 | * the expense of a large initial footprint. Some remnants of | ||
| 125 | * that design (including forced construction of segment 0) exist | ||
| 126 | * to ensure serialization compatibility. | ||
| 127 | */ | ||
| 128 | |||
| 129 | /* ---------------- Constants -------------- */ | ||
| 130 | |||
| 131 | /** | ||
| 132 | * The default initial capacity for this table, | ||
| 133 | * used when not otherwise specified in a constructor. | ||
| 134 | */ | ||
| 135 | static final int DEFAULT_INITIAL_CAPACITY = 16; | ||
| 136 | |||
| 137 | /** | ||
| 138 | * The default load factor for this table, used when not | ||
| 139 | * otherwise specified in a constructor. | ||
| 140 | */ | ||
| 141 | static final float DEFAULT_LOAD_FACTOR = 0.75f; | ||
| 142 | |||
| 143 | /** | ||
| 144 | * The default concurrency level for this table, used when not | ||
| 145 | * otherwise specified in a constructor. | ||
| 146 | */ | ||
| 147 | static final int DEFAULT_CONCURRENCY_LEVEL = 16; | ||
| 148 | |||
| 149 | /** | ||
| 150 | * The maximum capacity, used if a higher value is implicitly | ||
| 151 | * specified by either of the constructors with arguments. MUST | ||
| 152 | * be a power of two <= 1<<30 to ensure that entries are indexable | ||
| 153 | * using ints. | ||
| 154 | */ | ||
| 155 | static final int MAXIMUM_CAPACITY = 1 << 30; | ||
| 156 | |||
| 157 | /** | ||
| 158 | * The minimum capacity for per-segment tables. Must be a power | ||
| 159 | * of two, at least two to avoid immediate resizing on next use | ||
| 160 | * after lazy construction. | ||
| 161 | */ | ||
| 162 | static final int MIN_SEGMENT_TABLE_CAPACITY = 2; | ||
| 163 | |||
| 164 | /** | ||
| 165 | * The maximum number of segments to allow; used to bound | ||
| 166 | * constructor arguments. Must be power of two less than 1 << 24. | ||
| 167 | */ | ||
| 168 | static final int MAX_SEGMENTS = 1 << 16; // slightly conservative | ||
| 169 | |||
| 170 | /** | ||
| 171 | * Number of unsynchronized retries in size and containsValue | ||
| 172 | * methods before resorting to locking. This is used to avoid | ||
| 173 | * unbounded retries if tables undergo continuous modification | ||
| 174 | * which would make it impossible to obtain an accurate result. | ||
| 175 | */ | ||
| 176 | static final int RETRIES_BEFORE_LOCK = 2; | ||
| 177 | |||
| 178 | /* ---------------- Fields -------------- */ | ||
| 179 | |||
| 180 | /** | ||
| 181 | * Mask value for indexing into segments. The upper bits of a | ||
| 182 | * key's hash code are used to choose the segment. | ||
| 183 | */ | ||
| 184 | final int segmentMask; | ||
| 185 | |||
| 186 | /** | ||
| 187 | * Shift value for indexing within segments. | ||
| 188 | */ | ||
| 189 | final int segmentShift; | ||
| 190 | |||
| 191 | /** | ||
| 192 | * The segments, each of which is a specialized hash table. | ||
| 193 | */ | ||
| 194 | final Segment<K,V>[] segments; | ||
| 195 | |||
| 196 | transient Set<K> keySet; | ||
| 197 | transient Set<Map.Entry<K,V>> entrySet; | ||
| 198 | transient Collection<V> values; | ||
| 199 | |||
| 200 | /** | ||
| 201 | * ConcurrentHashMap list entry. Note that this is never exported | ||
| 202 | * out as a user-visible Map.Entry. | ||
| 203 | */ | ||
| 204 | static final class HashEntry<K,V> { | ||
| 205 | final int hash; | ||
| 206 | final K key; | ||
| 207 | volatile V value; | ||
| 208 | volatile HashEntry<K,V> next; | ||
| 209 | |||
| 210 | HashEntry(int hash, K key, V value, HashEntry<K,V> next) { | ||
| 211 | this.hash = hash; | ||
| 212 | this.key = key; | ||
| 213 | this.value = value; | ||
| 214 | this.next = next; | ||
| 215 | } | ||
| 216 | |||
| 217 | /** | ||
| 218 | * Sets next field with volatile write semantics. (See above | ||
| 219 | * about use of putOrderedObject.) | ||
| 220 | */ | ||
| 221 | final void setNext(HashEntry<K,V> n) { | ||
| 222 | UNSAFE.putOrderedObject(this, nextOffset, n); | ||
| 223 | } | ||
| 224 | |||
| 225 | // Unsafe mechanics | ||
| 226 | static final sun.misc.Unsafe UNSAFE; | ||
| 227 | static final long nextOffset; | ||
| 228 | static { | ||
| 229 | try { | ||
| 230 | UNSAFE = sun.misc.Unsafe.getUnsafe(); | ||
| 231 | Class k = HashEntry.class; | ||
| 232 | nextOffset = UNSAFE.objectFieldOffset | ||
| 233 | (k.getDeclaredField("next")); | ||
| 234 | } catch (Exception e) { | ||
| 235 | throw new Error(e); | ||
| 236 | } | ||
| 237 | } | ||
| 238 | } | ||
| 239 | |||
| 240 | /** | ||
| 241 | * Gets the ith element of given table (if nonnull) with volatile | ||
| 242 | * read semantics. Note: This is manually integrated into a few | ||
| 243 | * performance-sensitive methods to reduce call overhead. | ||
| 244 | */ | ||
| 245 | @SuppressWarnings("unchecked") | ||
| 246 | static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) { | ||
| 247 | return (tab == null) ? null : | ||
| 248 | (HashEntry<K,V>) UNSAFE.getObjectVolatile | ||
| 249 | (tab, ((long)i << TSHIFT) + TBASE); | ||
| 250 | } | ||
| 251 | |||
| 252 | /** | ||
| 253 | * Sets the ith element of given table, with volatile write | ||
| 254 | * semantics. (See above about use of putOrderedObject.) | ||
| 255 | */ | ||
| 256 | static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i, | ||
| 257 | HashEntry<K,V> e) { | ||
| 258 | UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e); | ||
| 259 | } | ||
| 260 | |||
| 261 | /** | ||
| 262 | * Applies a supplemental hash function to a given hashCode, which | ||
| 263 | * defends against poor quality hash functions. This is critical | ||
| 264 | * because ConcurrentHashMap uses power-of-two length hash tables, | ||
| 265 | * that otherwise encounter collisions for hashCodes that do not | ||
| 266 | * differ in lower or upper bits. | ||
| 267 | */ | ||
| 268 | private static int hash(int h) { | ||
| 269 | // Spread bits to regularize both segment and index locations, | ||
| 270 | // using variant of single-word Wang/Jenkins hash. | ||
| 271 | h += (h << 15) ^ 0xffffcd7d; | ||
| 272 | h ^= (h >>> 10); | ||
| 273 | h += (h << 3); | ||
| 274 | h ^= (h >>> 6); | ||
| 275 | h += (h << 2) + (h << 14); | ||
| 276 | return h ^ (h >>> 16); | ||
| 277 | } | ||
| 278 | |||
| 279 | /** | ||
| 280 | * Segments are specialized versions of hash tables. This | ||
| 281 | * subclasses from ReentrantLock opportunistically, just to | ||
| 282 | * simplify some locking and avoid separate construction. | ||
| 283 | */ | ||
| 284 | static final class Segment<K,V> extends ReentrantLock implements Serializable { | ||
| 285 | /* | ||
| 286 | * Segments maintain a table of entry lists that are always | ||
| 287 | * kept in a consistent state, so can be read (via volatile | ||
| 288 | * reads of segments and tables) without locking. This | ||
| 289 | * requires replicating nodes when necessary during table | ||
| 290 | * resizing, so the old lists can be traversed by readers | ||
| 291 | * still using old version of table. | ||
| 292 | * | ||
| 293 | * This class defines only mutative methods requiring locking. | ||
| 294 | * Except as noted, the methods of this class perform the | ||
| 295 | * per-segment versions of ConcurrentHashMap methods. (Other | ||
| 296 | * methods are integrated directly into ConcurrentHashMap | ||
| 297 | * methods.) These mutative methods use a form of controlled | ||
| 298 | * spinning on contention via methods scanAndLock and | ||
| 299 | * scanAndLockForPut. These intersperse tryLocks with | ||
| 300 | * traversals to locate nodes. The main benefit is to absorb | ||
| 301 | * cache misses (which are very common for hash tables) while | ||
| 302 | * obtaining locks so that traversal is faster once | ||
| 303 | * acquired. We do not actually use the found nodes since they | ||
| 304 | * must be re-acquired under lock anyway to ensure sequential | ||
| 305 | * consistency of updates (and in any case may be undetectably | ||
| 306 | * stale), but they will normally be much faster to re-locate. | ||
| 307 | * Also, scanAndLockForPut speculatively creates a fresh node | ||
| 308 | * to use in put if no node is found. | ||
| 309 | */ | ||
| 310 | |||
| 311 | private static final long serialVersionUID = 2249069246763182397L; | ||
| 312 | |||
| 313 | /** | ||
| 314 | * The maximum number of times to tryLock in a prescan before | ||
| 315 | * possibly blocking on acquire in preparation for a locked | ||
| 316 | * segment operation. On multiprocessors, using a bounded | ||
| 317 | * number of retries maintains cache acquired while locating | ||
| 318 | * nodes. | ||
| 319 | */ | ||
| 320 | static final int MAX_SCAN_RETRIES = | ||
| 321 | Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1; | ||
| 322 | |||
| 323 | /** | ||
| 324 | * The per-segment table. Elements are accessed via | ||
| 325 | * entryAt/setEntryAt providing volatile semantics. | ||
| 326 | */ | ||
| 327 | transient volatile HashEntry<K,V>[] table; | ||
| 328 | |||
| 329 | /** | ||
| 330 | * The number of elements. Accessed only either within locks | ||
| 331 | * or among other volatile reads that maintain visibility. | ||
| 332 | */ | ||
| 333 | transient int count; | ||
| 334 | |||
| 335 | /** | ||
| 336 | * The total number of mutative operations in this segment. | ||
| 337 | * Even though this may overflows 32 bits, it provides | ||
| 338 | * sufficient accuracy for stability checks in CHM isEmpty() | ||
| 339 | * and size() methods. Accessed only either within locks or | ||
| 340 | * among other volatile reads that maintain visibility. | ||
| 341 | */ | ||
| 342 | transient int modCount; | ||
| 343 | |||
| 344 | /** | ||
| 345 | * The table is rehashed when its size exceeds this threshold. | ||
| 346 | * (The value of this field is always <tt>(int)(capacity * | ||
| 347 | * loadFactor)</tt>.) | ||
| 348 | */ | ||
| 349 | transient int threshold; | ||
| 350 | |||
| 351 | /** | ||
| 352 | * The load factor for the hash table. Even though this value | ||
| 353 | * is same for all segments, it is replicated to avoid needing | ||
| 354 | * links to outer object. | ||
| 355 | * @serial | ||
| 356 | */ | ||
| 357 | final float loadFactor; | ||
| 358 | |||
| 359 | Segment(float lf, int threshold, HashEntry<K,V>[] tab) { | ||
| 360 | this.loadFactor = lf; | ||
| 361 | this.threshold = threshold; | ||
| 362 | this.table = tab; | ||
| 363 | } | ||
| 364 | |||
| 365 | final V put(K key, int hash, V value, boolean onlyIfAbsent) { | ||
| 366 | HashEntry<K,V> node = tryLock() ? null : | ||
| 367 | scanAndLockForPut(key, hash, value); | ||
| 368 | V oldValue; | ||
| 369 | try { | ||
| 370 | HashEntry<K,V>[] tab = table; | ||
| 371 | int index = (tab.length - 1) & hash; | ||
| 372 | HashEntry<K,V> first = entryAt(tab, index); | ||
| 373 | for (HashEntry<K,V> e = first;;) { | ||
| 374 | if (e != null) { | ||
| 375 | K k; | ||
| 376 | if ((k = e.key) == key || | ||
| 377 | (e.hash == hash && key.equals(k))) { | ||
| 378 | oldValue = e.value; | ||
| 379 | if (!onlyIfAbsent) { | ||
| 380 | e.value = value; | ||
| 381 | ++modCount; | ||
| 382 | } | ||
| 383 | break; | ||
| 384 | } | ||
| 385 | e = e.next; | ||
| 386 | } | ||
| 387 | else { | ||
| 388 | if (node != null) | ||
| 389 | node.setNext(first); | ||
| 390 | else | ||
| 391 | node = new HashEntry<K,V>(hash, key, value, first); | ||
| 392 | int c = count + 1; | ||
| 393 | if (c > threshold && tab.length < MAXIMUM_CAPACITY) | ||
| 394 | rehash(node); | ||
| 395 | else | ||
| 396 | setEntryAt(tab, index, node); | ||
| 397 | ++modCount; | ||
| 398 | count = c; | ||
| 399 | oldValue = null; | ||
| 400 | break; | ||
| 401 | } | ||
| 402 | } | ||
| 403 | } finally { | ||
| 404 | unlock(); | ||
| 405 | } | ||
| 406 | return oldValue; | ||
| 407 | } | ||
| 408 | |||
| 409 | /** | ||
| 410 | * Doubles size of table and repacks entries, also adding the | ||
| 411 | * given node to new table | ||
| 412 | */ | ||
| 413 | @SuppressWarnings("unchecked") | ||
| 414 | private void rehash(HashEntry<K,V> node) { | ||
| 415 | /* | ||
| 416 | * Reclassify nodes in each list to new table. Because we | ||
| 417 | * are using power-of-two expansion, the elements from | ||
| 418 | * each bin must either stay at same index, or move with a | ||
| 419 | * power of two offset. We eliminate unnecessary node | ||
| 420 | * creation by catching cases where old nodes can be | ||
| 421 | * reused because their next fields won't change. | ||
| 422 | * Statistically, at the default threshold, only about | ||
| 423 | * one-sixth of them need cloning when a table | ||
| 424 | * doubles. The nodes they replace will be garbage | ||
| 425 | * collectable as soon as they are no longer referenced by | ||
| 426 | * any reader thread that may be in the midst of | ||
| 427 | * concurrently traversing table. Entry accesses use plain | ||
| 428 | * array indexing because they are followed by volatile | ||
| 429 | * table write. | ||
| 430 | */ | ||
| 431 | HashEntry<K,V>[] oldTable = table; | ||
| 432 | int oldCapacity = oldTable.length; | ||
| 433 | int newCapacity = oldCapacity << 1; | ||
| 434 | threshold = (int)(newCapacity * loadFactor); | ||
| 435 | HashEntry<K,V>[] newTable = | ||
| 436 | (HashEntry<K,V>[]) new HashEntry[newCapacity]; | ||
| 437 | int sizeMask = newCapacity - 1; | ||
| 438 | for (int i = 0; i < oldCapacity ; i++) { | ||
| 439 | HashEntry<K,V> e = oldTable[i]; | ||
| 440 | if (e != null) { | ||
| 441 | HashEntry<K,V> next = e.next; | ||
| 442 | int idx = e.hash & sizeMask; | ||
| 443 | if (next == null) // Single node on list | ||
| 444 | newTable[idx] = e; | ||
| 445 | else { // Reuse consecutive sequence at same slot | ||
| 446 | HashEntry<K,V> lastRun = e; | ||
| 447 | int lastIdx = idx; | ||
| 448 | for (HashEntry<K,V> last = next; | ||
| 449 | last != null; | ||
| 450 | last = last.next) { | ||
| 451 | int k = last.hash & sizeMask; | ||
| 452 | if (k != lastIdx) { | ||
| 453 | lastIdx = k; | ||
| 454 | lastRun = last; | ||
| 455 | } | ||
| 456 | } | ||
| 457 | newTable[lastIdx] = lastRun; | ||
| 458 | // Clone remaining nodes | ||
| 459 | for (HashEntry<K,V> p = e; p != lastRun; p = p.next) { | ||
| 460 | V v = p.value; | ||
| 461 | int h = p.hash; | ||
| 462 | int k = h & sizeMask; | ||
| 463 | HashEntry<K,V> n = newTable[k]; | ||
| 464 | newTable[k] = new HashEntry<K,V>(h, p.key, v, n); | ||
| 465 | } | ||
| 466 | } | ||
| 467 | } | ||
| 468 | } | ||
| 469 | int nodeIndex = node.hash & sizeMask; // add the new node | ||
| 470 | node.setNext(newTable[nodeIndex]); | ||
| 471 | newTable[nodeIndex] = node; | ||
| 472 | table = newTable; | ||
| 473 | } | ||
| 474 | |||
| 475 | /** | ||
| 476 | * Scans for a node containing given key while trying to | ||
| 477 | * acquire lock, creating and returning one if not found. Upon | ||
| 478 | * return, guarantees that lock is held. UNlike in most | ||
| 479 | * methods, calls to method equals are not screened: Since | ||
| 480 | * traversal speed doesn't matter, we might as well help warm | ||
| 481 | * up the associated code and accesses as well. | ||
| 482 | * | ||
| 483 | * @return a new node if key not found, else null | ||
| 484 | */ | ||
| 485 | private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) { | ||
| 486 | HashEntry<K,V> first = entryForHash(this, hash); | ||
| 487 | HashEntry<K,V> e = first; | ||
| 488 | HashEntry<K,V> node = null; | ||
| 489 | int retries = -1; // negative while locating node | ||
| 490 | while (!tryLock()) { | ||
| 491 | HashEntry<K,V> f; // to recheck first below | ||
| 492 | if (retries < 0) { | ||
| 493 | if (e == null) { | ||
| 494 | if (node == null) // speculatively create node | ||
| 495 | node = new HashEntry<K,V>(hash, key, value, null); | ||
| 496 | retries = 0; | ||
| 497 | } | ||
| 498 | else if (key.equals(e.key)) | ||
| 499 | retries = 0; | ||
| 500 | else | ||
| 501 | e = e.next; | ||
| 502 | } | ||
| 503 | else if (++retries > MAX_SCAN_RETRIES) { | ||
| 504 | lock(); | ||
| 505 | break; | ||
| 506 | } | ||
| 507 | else if ((retries & 1) == 0 && | ||
| 508 | (f = entryForHash(this, hash)) != first) { | ||
| 509 | e = first = f; // re-traverse if entry changed | ||
| 510 | retries = -1; | ||
| 511 | } | ||
| 512 | } | ||
| 513 | return node; | ||
| 514 | } | ||
| 515 | |||
| 516 | /** | ||
| 517 | * Scans for a node containing the given key while trying to | ||
| 518 | * acquire lock for a remove or replace operation. Upon | ||
| 519 | * return, guarantees that lock is held. Note that we must | ||
| 520 | * lock even if the key is not found, to ensure sequential | ||
| 521 | * consistency of updates. | ||
| 522 | */ | ||
| 523 | private void scanAndLock(Object key, int hash) { | ||
| 524 | // similar to but simpler than scanAndLockForPut | ||
| 525 | HashEntry<K,V> first = entryForHash(this, hash); | ||
| 526 | HashEntry<K,V> e = first; | ||
| 527 | int retries = -1; | ||
| 528 | while (!tryLock()) { | ||
| 529 | HashEntry<K,V> f; | ||
| 530 | if (retries < 0) { | ||
| 531 | if (e == null || key.equals(e.key)) | ||
| 532 | retries = 0; | ||
| 533 | else | ||
| 534 | e = e.next; | ||
| 535 | } | ||
| 536 | else if (++retries > MAX_SCAN_RETRIES) { | ||
| 537 | lock(); | ||
| 538 | break; | ||
| 539 | } | ||
| 540 | else if ((retries & 1) == 0 && | ||
| 541 | (f = entryForHash(this, hash)) != first) { | ||
| 542 | e = first = f; | ||
| 543 | retries = -1; | ||
| 544 | } | ||
| 545 | } | ||
| 546 | } | ||
| 547 | |||
| 548 | /** | ||
| 549 | * Remove; match on key only if value null, else match both. | ||
| 550 | */ | ||
| 551 | final V remove(Object key, int hash, Object value) { | ||
| 552 | if (!tryLock()) | ||
| 553 | scanAndLock(key, hash); | ||
| 554 | V oldValue = null; | ||
| 555 | try { | ||
| 556 | HashEntry<K,V>[] tab = table; | ||
| 557 | int index = (tab.length - 1) & hash; | ||
| 558 | HashEntry<K,V> e = entryAt(tab, index); | ||
| 559 | HashEntry<K,V> pred = null; | ||
| 560 | while (e != null) { | ||
| 561 | K k; | ||
| 562 | HashEntry<K,V> next = e.next; | ||
| 563 | if ((k = e.key) == key || | ||
| 564 | (e.hash == hash && key.equals(k))) { | ||
| 565 | V v = e.value; | ||
| 566 | if (value == null || value == v || value.equals(v)) { | ||
| 567 | if (pred == null) | ||
| 568 | setEntryAt(tab, index, next); | ||
| 569 | else | ||
| 570 | pred.setNext(next); | ||
| 571 | ++modCount; | ||
| 572 | --count; | ||
| 573 | oldValue = v; | ||
| 574 | } | ||
| 575 | break; | ||
| 576 | } | ||
| 577 | pred = e; | ||
| 578 | e = next; | ||
| 579 | } | ||
| 580 | } finally { | ||
| 581 | unlock(); | ||
| 582 | } | ||
| 583 | return oldValue; | ||
| 584 | } | ||
| 585 | |||
| 586 | final boolean replace(K key, int hash, V oldValue, V newValue) { | ||
| 587 | if (!tryLock()) | ||
| 588 | scanAndLock(key, hash); | ||
| 589 | boolean replaced = false; | ||
| 590 | try { | ||
| 591 | HashEntry<K,V> e; | ||
| 592 | for (e = entryForHash(this, hash); e != null; e = e.next) { | ||
| 593 | K k; | ||
| 594 | if ((k = e.key) == key || | ||
| 595 | (e.hash == hash && key.equals(k))) { | ||
| 596 | if (oldValue.equals(e.value)) { | ||
| 597 | e.value = newValue; | ||
| 598 | ++modCount; | ||
| 599 | replaced = true; | ||
| 600 | } | ||
| 601 | break; | ||
| 602 | } | ||
| 603 | } | ||
| 604 | } finally { | ||
| 605 | unlock(); | ||
| 606 | } | ||
| 607 | return replaced; | ||
| 608 | } | ||
| 609 | |||
| 610 | final V replace(K key, int hash, V value) { | ||
| 611 | if (!tryLock()) | ||
| 612 | scanAndLock(key, hash); | ||
| 613 | V oldValue = null; | ||
| 614 | try { | ||
| 615 | HashEntry<K,V> e; | ||
| 616 | for (e = entryForHash(this, hash); e != null; e = e.next) { | ||
| 617 | K k; | ||
| 618 | if ((k = e.key) == key || | ||
| 619 | (e.hash == hash && key.equals(k))) { | ||
| 620 | oldValue = e.value; | ||
| 621 | e.value = value; | ||
| 622 | ++modCount; | ||
| 623 | break; | ||
| 624 | } | ||
| 625 | } | ||
| 626 | } finally { | ||
| 627 | unlock(); | ||
| 628 | } | ||
| 629 | return oldValue; | ||
| 630 | } | ||
| 631 | |||
| 632 | final void clear() { | ||
| 633 | lock(); | ||
| 634 | try { | ||
| 635 | HashEntry<K,V>[] tab = table; | ||
| 636 | for (int i = 0; i < tab.length ; i++) | ||
| 637 | setEntryAt(tab, i, null); | ||
| 638 | ++modCount; | ||
| 639 | count = 0; | ||
| 640 | } finally { | ||
| 641 | unlock(); | ||
| 642 | } | ||
| 643 | } | ||
| 644 | } | ||
| 645 | |||
| 646 | // Accessing segments | ||
| 647 | |||
| 648 | /** | ||
| 649 | * Gets the jth element of given segment array (if nonnull) with | ||
| 650 | * volatile element access semantics via Unsafe. (The null check | ||
| 651 | * can trigger harmlessly only during deserialization.) Note: | ||
| 652 | * because each element of segments array is set only once (using | ||
| 653 | * fully ordered writes), some performance-sensitive methods rely | ||
| 654 | * on this method only as a recheck upon null reads. | ||
| 655 | */ | ||
| 656 | @SuppressWarnings("unchecked") | ||
| 657 | static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) { | ||
| 658 | long u = (j << SSHIFT) + SBASE; | ||
| 659 | return ss == null ? null : | ||
| 660 | (Segment<K,V>) UNSAFE.getObjectVolatile(ss, u); | ||
| 661 | } | ||
| 662 | |||
| 663 | /** | ||
| 664 | * Returns the segment for the given index, creating it and | ||
| 665 | * recording in segment table (via CAS) if not already present. | ||
| 666 | * | ||
| 667 | * @param k the index | ||
| 668 | * @return the segment | ||
| 669 | */ | ||
| 670 | @SuppressWarnings("unchecked") | ||
| 671 | private Segment<K,V> ensureSegment(int k) { | ||
| 672 | final Segment<K,V>[] ss = this.segments; | ||
| 673 | long u = (k << SSHIFT) + SBASE; // raw offset | ||
| 674 | Segment<K,V> seg; | ||
| 675 | if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) { | ||
| 676 | Segment<K,V> proto = ss[0]; // use segment 0 as prototype | ||
| 677 | int cap = proto.table.length; | ||
| 678 | float lf = proto.loadFactor; | ||
| 679 | int threshold = (int)(cap * lf); | ||
| 680 | HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry[cap]; | ||
| 681 | if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) | ||
| 682 | == null) { // recheck | ||
| 683 | Segment<K,V> s = new Segment<K,V>(lf, threshold, tab); | ||
| 684 | while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) | ||
| 685 | == null) { | ||
| 686 | if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s)) | ||
| 687 | break; | ||
| 688 | } | ||
| 689 | } | ||
| 690 | } | ||
| 691 | return seg; | ||
| 692 | } | ||
| 693 | |||
| 694 | // Hash-based segment and entry accesses | ||
| 695 | |||
| 696 | /** | ||
| 697 | * Get the segment for the given hash | ||
| 698 | */ | ||
| 699 | @SuppressWarnings("unchecked") | ||
| 700 | private Segment<K,V> segmentForHash(int h) { | ||
| 701 | long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; | ||
| 702 | return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u); | ||
| 703 | } | ||
| 704 | |||
| 705 | /** | ||
| 706 | * Gets the table entry for the given segment and hash | ||
| 707 | */ | ||
| 708 | @SuppressWarnings("unchecked") | ||
| 709 | static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) { | ||
| 710 | HashEntry<K,V>[] tab; | ||
| 711 | return (seg == null || (tab = seg.table) == null) ? null : | ||
| 712 | (HashEntry<K,V>) UNSAFE.getObjectVolatile | ||
| 713 | (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); | ||
| 714 | } | ||
| 715 | |||
| 716 | /* ---------------- Public operations -------------- */ | ||
| 717 | |||
| 718 | /** | ||
| 719 | * Creates a new, empty map with the specified initial | ||
| 720 | * capacity, load factor and concurrency level. | ||
| 721 | * | ||
| 722 | * @param initialCapacity the initial capacity. The implementation | ||
| 723 | * performs internal sizing to accommodate this many elements. | ||
| 724 | * @param loadFactor the load factor threshold, used to control resizing. | ||
| 725 | * Resizing may be performed when the average number of elements per | ||
| 726 | * bin exceeds this threshold. | ||
| 727 | * @param concurrencyLevel the estimated number of concurrently | ||
| 728 | * updating threads. The implementation performs internal sizing | ||
| 729 | * to try to accommodate this many threads. | ||
| 730 | * @throws IllegalArgumentException if the initial capacity is | ||
| 731 | * negative or the load factor or concurrencyLevel are | ||
| 732 | * nonpositive. | ||
| 733 | */ | ||
| 734 | @SuppressWarnings("unchecked") | ||
| 735 | public ConcurrentHashMap(int initialCapacity, | ||
| 736 | float loadFactor, int concurrencyLevel) { | ||
| 737 | if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) | ||
| 738 | throw new IllegalArgumentException(); | ||
| 739 | if (concurrencyLevel > MAX_SEGMENTS) | ||
| 740 | concurrencyLevel = MAX_SEGMENTS; | ||
| 741 | // Find power-of-two sizes best matching arguments | ||
| 742 | int sshift = 0; | ||
| 743 | int ssize = 1; | ||
| 744 | while (ssize < concurrencyLevel) { | ||
| 745 | ++sshift; | ||
| 746 | ssize <<= 1; | ||
| 747 | } | ||
| 748 | this.segmentShift = 32 - sshift; | ||
| 749 | this.segmentMask = ssize - 1; | ||
| 750 | if (initialCapacity > MAXIMUM_CAPACITY) | ||
| 751 | initialCapacity = MAXIMUM_CAPACITY; | ||
| 752 | int c = initialCapacity / ssize; | ||
| 753 | if (c * ssize < initialCapacity) | ||
| 754 | ++c; | ||
| 755 | int cap = MIN_SEGMENT_TABLE_CAPACITY; | ||
| 756 | while (cap < c) | ||
| 757 | cap <<= 1; | ||
| 758 | // create segments and segments[0] | ||
| 759 | Segment<K,V> s0 = | ||
| 760 | new Segment<K,V>(loadFactor, (int)(cap * loadFactor), | ||
| 761 | (HashEntry<K,V>[])new HashEntry[cap]); | ||
| 762 | Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize]; | ||
| 763 | UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0] | ||
| 764 | this.segments = ss; | ||
| 765 | } | ||
| 766 | |||
| 767 | /** | ||
| 768 | * Creates a new, empty map with the specified initial capacity | ||
| 769 | * and load factor and with the default concurrencyLevel (16). | ||
| 770 | * | ||
| 771 | * @param initialCapacity The implementation performs internal | ||
| 772 | * sizing to accommodate this many elements. | ||
| 773 | * @param loadFactor the load factor threshold, used to control resizing. | ||
| 774 | * Resizing may be performed when the average number of elements per | ||
| 775 | * bin exceeds this threshold. | ||
| 776 | * @throws IllegalArgumentException if the initial capacity of | ||
| 777 | * elements is negative or the load factor is nonpositive | ||
| 778 | * | ||
| 779 | * @since 1.6 | ||
| 780 | */ | ||
| 781 | public ConcurrentHashMap(int initialCapacity, float loadFactor) { | ||
| 782 | this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL); | ||
| 783 | } | ||
| 784 | |||
| 785 | /** | ||
| 786 | * Creates a new, empty map with the specified initial capacity, | ||
| 787 | * and with default load factor (0.75) and concurrencyLevel (16). | ||
| 788 | * | ||
| 789 | * @param initialCapacity the initial capacity. The implementation | ||
| 790 | * performs internal sizing to accommodate this many elements. | ||
| 791 | * @throws IllegalArgumentException if the initial capacity of | ||
| 792 | * elements is negative. | ||
| 793 | */ | ||
| 794 | public ConcurrentHashMap(int initialCapacity) { | ||
| 795 | this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); | ||
| 796 | } | ||
| 797 | |||
| 798 | /** | ||
| 799 | * Creates a new, empty map with a default initial capacity (16), | ||
| 800 | * load factor (0.75) and concurrencyLevel (16). | ||
| 801 | */ | ||
| 802 | public ConcurrentHashMap() { | ||
| 803 | this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); | ||
| 804 | } | ||
| 805 | |||
| 806 | /** | ||
| 807 | * Creates a new map with the same mappings as the given map. | ||
| 808 | * The map is created with a capacity of 1.5 times the number | ||
| 809 | * of mappings in the given map or 16 (whichever is greater), | ||
| 810 | * and a default load factor (0.75) and concurrencyLevel (16). | ||
| 811 | * | ||
| 812 | * @param m the map | ||
| 813 | */ | ||
| 814 | public ConcurrentHashMap(Map<? extends K, ? extends V> m) { | ||
| 815 | this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, | ||
| 816 | DEFAULT_INITIAL_CAPACITY), | ||
| 817 | DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL); | ||
| 818 | putAll(m); | ||
| 819 | } | ||
| 820 | |||
| 821 | /** | ||
| 822 | * Returns <tt>true</tt> if this map contains no key-value mappings. | ||
| 823 | * | ||
| 824 | * @return <tt>true</tt> if this map contains no key-value mappings | ||
| 825 | */ | ||
| 826 | public boolean isEmpty() { | ||
| 827 | /* | ||
| 828 | * Sum per-segment modCounts to avoid mis-reporting when | ||
| 829 | * elements are concurrently added and removed in one segment | ||
| 830 | * while checking another, in which case the table was never | ||
| 831 | * actually empty at any point. (The sum ensures accuracy up | ||
| 832 | * through at least 1<<31 per-segment modifications before | ||
| 833 | * recheck.) Methods size() and containsValue() use similar | ||
| 834 | * constructions for stability checks. | ||
| 835 | */ | ||
| 836 | long sum = 0L; | ||
| 837 | final Segment<K,V>[] segments = this.segments; | ||
| 838 | for (int j = 0; j < segments.length; ++j) { | ||
| 839 | Segment<K,V> seg = segmentAt(segments, j); | ||
| 840 | if (seg != null) { | ||
| 841 | if (seg.count != 0) | ||
| 842 | return false; | ||
| 843 | sum += seg.modCount; | ||
| 844 | } | ||
| 845 | } | ||
| 846 | if (sum != 0L) { // recheck unless no modifications | ||
| 847 | for (int j = 0; j < segments.length; ++j) { | ||
| 848 | Segment<K,V> seg = segmentAt(segments, j); | ||
| 849 | if (seg != null) { | ||
| 850 | if (seg.count != 0) | ||
| 851 | return false; | ||
| 852 | sum -= seg.modCount; | ||
| 853 | } | ||
| 854 | } | ||
| 855 | if (sum != 0L) | ||
| 856 | return false; | ||
| 857 | } | ||
| 858 | return true; | ||
| 859 | } | ||
| 860 | |||
| 861 | /** | ||
| 862 | * Returns the number of key-value mappings in this map. If the | ||
| 863 | * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns | ||
| 864 | * <tt>Integer.MAX_VALUE</tt>. | ||
| 865 | * | ||
| 866 | * @return the number of key-value mappings in this map | ||
| 867 | */ | ||
| 868 | public int size() { | ||
| 869 | // Try a few times to get accurate count. On failure due to | ||
| 870 | // continuous async changes in table, resort to locking. | ||
| 871 | final Segment<K,V>[] segments = this.segments; | ||
| 872 | int size; | ||
| 873 | boolean overflow; // true if size overflows 32 bits | ||
| 874 | long sum; // sum of modCounts | ||
| 875 | long last = 0L; // previous sum | ||
| 876 | int retries = -1; // first iteration isn't retry | ||
| 877 | try { | ||
| 878 | for (;;) { | ||
| 879 | if (retries++ == RETRIES_BEFORE_LOCK) { | ||
| 880 | for (int j = 0; j < segments.length; ++j) | ||
| 881 | ensureSegment(j).lock(); // force creation | ||
| 882 | } | ||
| 883 | sum = 0L; | ||
| 884 | size = 0; | ||
| 885 | overflow = false; | ||
| 886 | for (int j = 0; j < segments.length; ++j) { | ||
| 887 | Segment<K,V> seg = segmentAt(segments, j); | ||
| 888 | if (seg != null) { | ||
| 889 | sum += seg.modCount; | ||
| 890 | int c = seg.count; | ||
| 891 | if (c < 0 || (size += c) < 0) | ||
| 892 | overflow = true; | ||
| 893 | } | ||
| 894 | } | ||
| 895 | if (sum == last) | ||
| 896 | break; | ||
| 897 | last = sum; | ||
| 898 | } | ||
| 899 | } finally { | ||
| 900 | if (retries > RETRIES_BEFORE_LOCK) { | ||
| 901 | for (int j = 0; j < segments.length; ++j) | ||
| 902 | segmentAt(segments, j).unlock(); | ||
| 903 | } | ||
| 904 | } | ||
| 905 | return overflow ? Integer.MAX_VALUE : size; | ||
| 906 | } | ||
| 907 | |||
| 908 | /** | ||
| 909 | * Returns the value to which the specified key is mapped, | ||
| 910 | * or {@code null} if this map contains no mapping for the key. | ||
| 911 | * | ||
| 912 | * <p>More formally, if this map contains a mapping from a key | ||
| 913 | * {@code k} to a value {@code v} such that {@code key.equals(k)}, | ||
| 914 | * then this method returns {@code v}; otherwise it returns | ||
| 915 | * {@code null}. (There can be at most one such mapping.) | ||
| 916 | * | ||
| 917 | * @throws NullPointerException if the specified key is null | ||
| 918 | */ | ||
| 919 | public V get(Object key) { | ||
| 920 | Segment<K,V> s; // manually integrate access methods to reduce overhead | ||
| 921 | HashEntry<K,V>[] tab; | ||
| 922 | int h = hash(key.hashCode()); | ||
| 923 | long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; | ||
| 924 | if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && | ||
| 925 | (tab = s.table) != null) { | ||
| 926 | for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile | ||
| 927 | (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); | ||
| 928 | e != null; e = e.next) { | ||
| 929 | K k; | ||
| 930 | if ((k = e.key) == key || (e.hash == h && key.equals(k))) | ||
| 931 | return e.value; | ||
| 932 | } | ||
| 933 | } | ||
| 934 | return null; | ||
| 935 | } | ||
| 936 | |||
| 937 | /** | ||
| 938 | * Tests if the specified object is a key in this table. | ||
| 939 | * | ||
| 940 | * @param key possible key | ||
| 941 | * @return <tt>true</tt> if and only if the specified object | ||
| 942 | * is a key in this table, as determined by the | ||
| 943 | * <tt>equals</tt> method; <tt>false</tt> otherwise. | ||
| 944 | * @throws NullPointerException if the specified key is null | ||
| 945 | */ | ||
| 946 | @SuppressWarnings("unchecked") | ||
| 947 | public boolean containsKey(Object key) { | ||
| 948 | Segment<K,V> s; // same as get() except no need for volatile value read | ||
| 949 | HashEntry<K,V>[] tab; | ||
| 950 | int h = hash(key.hashCode()); | ||
| 951 | long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE; | ||
| 952 | if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null && | ||
| 953 | (tab = s.table) != null) { | ||
| 954 | for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile | ||
| 955 | (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE); | ||
| 956 | e != null; e = e.next) { | ||
| 957 | K k; | ||
| 958 | if ((k = e.key) == key || (e.hash == h && key.equals(k))) | ||
| 959 | return true; | ||
| 960 | } | ||
| 961 | } | ||
| 962 | return false; | ||
| 963 | } | ||
| 964 | |||
| 965 | /** | ||
| 966 | * Returns <tt>true</tt> if this map maps one or more keys to the | ||
| 967 | * specified value. Note: This method requires a full internal | ||
| 968 | * traversal of the hash table, and so is much slower than | ||
| 969 | * method <tt>containsKey</tt>. | ||
| 970 | * | ||
| 971 | * @param value value whose presence in this map is to be tested | ||
| 972 | * @return <tt>true</tt> if this map maps one or more keys to the | ||
| 973 | * specified value | ||
| 974 | * @throws NullPointerException if the specified value is null | ||
| 975 | */ | ||
| 976 | public boolean containsValue(Object value) { | ||
| 977 | // Same idea as size() | ||
| 978 | if (value == null) | ||
| 979 | throw new NullPointerException(); | ||
| 980 | final Segment<K,V>[] segments = this.segments; | ||
| 981 | boolean found = false; | ||
| 982 | long last = 0; | ||
| 983 | int retries = -1; | ||
| 984 | try { | ||
| 985 | outer: for (;;) { | ||
| 986 | if (retries++ == RETRIES_BEFORE_LOCK) { | ||
| 987 | for (int j = 0; j < segments.length; ++j) | ||
| 988 | ensureSegment(j).lock(); // force creation | ||
| 989 | } | ||
| 990 | long hashSum = 0L; | ||
| 991 | int sum = 0; | ||
| 992 | for (int j = 0; j < segments.length; ++j) { | ||
| 993 | HashEntry<K,V>[] tab; | ||
| 994 | Segment<K,V> seg = segmentAt(segments, j); | ||
| 995 | if (seg != null && (tab = seg.table) != null) { | ||
| 996 | for (int i = 0 ; i < tab.length; i++) { | ||
| 997 | HashEntry<K,V> e; | ||
| 998 | for (e = entryAt(tab, i); e != null; e = e.next) { | ||
| 999 | V v = e.value; | ||
| 1000 | if (v != null && value.equals(v)) { | ||
| 1001 | found = true; | ||
| 1002 | break outer; | ||
| 1003 | } | ||
| 1004 | } | ||
| 1005 | } | ||
| 1006 | sum += seg.modCount; | ||
| 1007 | } | ||
| 1008 | } | ||
| 1009 | if (retries > 0 && sum == last) | ||
| 1010 | break; | ||
| 1011 | last = sum; | ||
| 1012 | } | ||
| 1013 | } finally { | ||
| 1014 | if (retries > RETRIES_BEFORE_LOCK) { | ||
| 1015 | for (int j = 0; j < segments.length; ++j) | ||
| 1016 | segmentAt(segments, j).unlock(); | ||
| 1017 | } | ||
| 1018 | } | ||
| 1019 | return found; | ||
| 1020 | } | ||
| 1021 | |||
| 1022 | /** | ||
| 1023 | * Legacy method testing if some key maps into the specified value | ||
| 1024 | * in this table. This method is identical in functionality to | ||
| 1025 | * {@link #containsValue}, and exists solely to ensure | ||
| 1026 | * full compatibility with class {@link java.util.Hashtable}, | ||
| 1027 | * which supported this method prior to introduction of the | ||
| 1028 | * Java Collections framework. | ||
| 1029 | |||
| 1030 | * @param value a value to search for | ||
| 1031 | * @return <tt>true</tt> if and only if some key maps to the | ||
| 1032 | * <tt>value</tt> argument in this table as | ||
| 1033 | * determined by the <tt>equals</tt> method; | ||
| 1034 | * <tt>false</tt> otherwise | ||
| 1035 | * @throws NullPointerException if the specified value is null | ||
| 1036 | */ | ||
| 1037 | public boolean contains(Object value) { | ||
| 1038 | return containsValue(value); | ||
| 1039 | } | ||
| 1040 | |||
| 1041 | /** | ||
| 1042 | * Maps the specified key to the specified value in this table. | ||
| 1043 | * Neither the key nor the value can be null. | ||
| 1044 | * | ||
| 1045 | * <p> The value can be retrieved by calling the <tt>get</tt> method | ||
| 1046 | * with a key that is equal to the original key. | ||
| 1047 | * | ||
| 1048 | * @param key key with which the specified value is to be associated | ||
| 1049 | * @param value value to be associated with the specified key | ||
| 1050 | * @return the previous value associated with <tt>key</tt>, or | ||
| 1051 | * <tt>null</tt> if there was no mapping for <tt>key</tt> | ||
| 1052 | * @throws NullPointerException if the specified key or value is null | ||
| 1053 | */ | ||
| 1054 | @SuppressWarnings("unchecked") | ||
| 1055 | public V put(K key, V value) { | ||
| 1056 | Segment<K,V> s; | ||
| 1057 | if (value == null) | ||
| 1058 | throw new NullPointerException(); | ||
| 1059 | int hash = hash(key.hashCode()); | ||
| 1060 | int j = (hash >>> segmentShift) & segmentMask; | ||
| 1061 | if ((s = (Segment<K,V>)UNSAFE.getObject // nonvolatile; recheck | ||
| 1062 | (segments, (j << SSHIFT) + SBASE)) == null) // in ensureSegment | ||
| 1063 | s = ensureSegment(j); | ||
| 1064 | return s.put(key, hash, value, false); | ||
| 1065 | } | ||
| 1066 | |||
| 1067 | /** | ||
| 1068 | * {@inheritDoc} | ||
| 1069 | * | ||
| 1070 | * @return the previous value associated with the specified key, | ||
| 1071 | * or <tt>null</tt> if there was no mapping for the key | ||
| 1072 | * @throws NullPointerException if the specified key or value is null | ||
| 1073 | */ | ||
| 1074 | @SuppressWarnings("unchecked") | ||
| 1075 | public V putIfAbsent(K key, V value) { | ||
| 1076 | Segment<K,V> s; | ||
| 1077 | if (value == null) | ||
| 1078 | throw new NullPointerException(); | ||
| 1079 | int hash = hash(key.hashCode()); | ||
| 1080 | int j = (hash >>> segmentShift) & segmentMask; | ||
| 1081 | if ((s = (Segment<K,V>)UNSAFE.getObject | ||
| 1082 | (segments, (j << SSHIFT) + SBASE)) == null) | ||
| 1083 | s = ensureSegment(j); | ||
| 1084 | return s.put(key, hash, value, true); | ||
| 1085 | } | ||
| 1086 | |||
| 1087 | /** | ||
| 1088 | * Copies all of the mappings from the specified map to this one. | ||
| 1089 | * These mappings replace any mappings that this map had for any of the | ||
| 1090 | * keys currently in the specified map. | ||
| 1091 | * | ||
| 1092 | * @param m mappings to be stored in this map | ||
| 1093 | */ | ||
| 1094 | public void putAll(Map<? extends K, ? extends V> m) { | ||
| 1095 | for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) | ||
| 1096 | put(e.getKey(), e.getValue()); | ||
| 1097 | } | ||
| 1098 | |||
| 1099 | /** | ||
| 1100 | * Removes the key (and its corresponding value) from this map. | ||
| 1101 | * This method does nothing if the key is not in the map. | ||
| 1102 | * | ||
| 1103 | * @param key the key that needs to be removed | ||
| 1104 | * @return the previous value associated with <tt>key</tt>, or | ||
| 1105 | * <tt>null</tt> if there was no mapping for <tt>key</tt> | ||
| 1106 | * @throws NullPointerException if the specified key is null | ||
| 1107 | */ | ||
| 1108 | public V remove(Object key) { | ||
| 1109 | int hash = hash(key.hashCode()); | ||
| 1110 | Segment<K,V> s = segmentForHash(hash); | ||
| 1111 | return s == null ? null : s.remove(key, hash, null); | ||
| 1112 | } | ||
| 1113 | |||
| 1114 | /** | ||
| 1115 | * {@inheritDoc} | ||
| 1116 | * | ||
| 1117 | * @throws NullPointerException if the specified key is null | ||
| 1118 | */ | ||
| 1119 | public boolean remove(Object key, Object value) { | ||
| 1120 | int hash = hash(key.hashCode()); | ||
| 1121 | Segment<K,V> s; | ||
| 1122 | return value != null && (s = segmentForHash(hash)) != null && | ||
| 1123 | s.remove(key, hash, value) != null; | ||
| 1124 | } | ||
| 1125 | |||
| 1126 | /** | ||
| 1127 | * {@inheritDoc} | ||
| 1128 | * | ||
| 1129 | * @throws NullPointerException if any of the arguments are null | ||
| 1130 | */ | ||
| 1131 | public boolean replace(K key, V oldValue, V newValue) { | ||
| 1132 | int hash = hash(key.hashCode()); | ||
| 1133 | if (oldValue == null || newValue == null) | ||
| 1134 | throw new NullPointerException(); | ||
| 1135 | Segment<K,V> s = segmentForHash(hash); | ||
| 1136 | return s != null && s.replace(key, hash, oldValue, newValue); | ||
| 1137 | } | ||
| 1138 | |||
| 1139 | /** | ||
| 1140 | * {@inheritDoc} | ||
| 1141 | * | ||
| 1142 | * @return the previous value associated with the specified key, | ||
| 1143 | * or <tt>null</tt> if there was no mapping for the key | ||
| 1144 | * @throws NullPointerException if the specified key or value is null | ||
| 1145 | */ | ||
| 1146 | public V replace(K key, V value) { | ||
| 1147 | int hash = hash(key.hashCode()); | ||
| 1148 | if (value == null) | ||
| 1149 | throw new NullPointerException(); | ||
| 1150 | Segment<K,V> s = segmentForHash(hash); | ||
| 1151 | return s == null ? null : s.replace(key, hash, value); | ||
| 1152 | } | ||
| 1153 | |||
| 1154 | /** | ||
| 1155 | * Removes all of the mappings from this map. | ||
| 1156 | */ | ||
| 1157 | public void clear() { | ||
| 1158 | final Segment<K,V>[] segments = this.segments; | ||
| 1159 | for (int j = 0; j < segments.length; ++j) { | ||
| 1160 | Segment<K,V> s = segmentAt(segments, j); | ||
| 1161 | if (s != null) | ||
| 1162 | s.clear(); | ||
| 1163 | } | ||
| 1164 | } | ||
| 1165 | |||
| 1166 | /** | ||
| 1167 | * Returns a {@link Set} view of the keys contained in this map. | ||
| 1168 | * The set is backed by the map, so changes to the map are | ||
| 1169 | * reflected in the set, and vice-versa. The set supports element | ||
| 1170 | * removal, which removes the corresponding mapping from this map, | ||
| 1171 | * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, | ||
| 1172 | * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> | ||
| 1173 | * operations. It does not support the <tt>add</tt> or | ||
| 1174 | * <tt>addAll</tt> operations. | ||
| 1175 | * | ||
| 1176 | * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator | ||
| 1177 | * that will never throw {@link ConcurrentModificationException}, | ||
| 1178 | * and guarantees to traverse elements as they existed upon | ||
| 1179 | * construction of the iterator, and may (but is not guaranteed to) | ||
| 1180 | * reflect any modifications subsequent to construction. | ||
| 1181 | */ | ||
| 1182 | public Set<K> keySet() { | ||
| 1183 | Set<K> ks = keySet; | ||
| 1184 | return (ks != null) ? ks : (keySet = new KeySet()); | ||
| 1185 | } | ||
| 1186 | |||
| 1187 | /** | ||
| 1188 | * Returns a {@link Collection} view of the values contained in this map. | ||
| 1189 | * The collection is backed by the map, so changes to the map are | ||
| 1190 | * reflected in the collection, and vice-versa. The collection | ||
| 1191 | * supports element removal, which removes the corresponding | ||
| 1192 | * mapping from this map, via the <tt>Iterator.remove</tt>, | ||
| 1193 | * <tt>Collection.remove</tt>, <tt>removeAll</tt>, | ||
| 1194 | * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not | ||
| 1195 | * support the <tt>add</tt> or <tt>addAll</tt> operations. | ||
| 1196 | * | ||
| 1197 | * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator | ||
| 1198 | * that will never throw {@link ConcurrentModificationException}, | ||
| 1199 | * and guarantees to traverse elements as they existed upon | ||
| 1200 | * construction of the iterator, and may (but is not guaranteed to) | ||
| 1201 | * reflect any modifications subsequent to construction. | ||
| 1202 | */ | ||
| 1203 | public Collection<V> values() { | ||
| 1204 | Collection<V> vs = values; | ||
| 1205 | return (vs != null) ? vs : (values = new Values()); | ||
| 1206 | } | ||
| 1207 | |||
| 1208 | /** | ||
| 1209 | * Returns a {@link Set} view of the mappings contained in this map. | ||
| 1210 | * The set is backed by the map, so changes to the map are | ||
| 1211 | * reflected in the set, and vice-versa. The set supports element | ||
| 1212 | * removal, which removes the corresponding mapping from the map, | ||
| 1213 | * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, | ||
| 1214 | * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> | ||
| 1215 | * operations. It does not support the <tt>add</tt> or | ||
| 1216 | * <tt>addAll</tt> operations. | ||
| 1217 | * | ||
| 1218 | * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator | ||
| 1219 | * that will never throw {@link ConcurrentModificationException}, | ||
| 1220 | * and guarantees to traverse elements as they existed upon | ||
| 1221 | * construction of the iterator, and may (but is not guaranteed to) | ||
| 1222 | * reflect any modifications subsequent to construction. | ||
| 1223 | */ | ||
| 1224 | public Set<Map.Entry<K,V>> entrySet() { | ||
| 1225 | Set<Map.Entry<K,V>> es = entrySet; | ||
| 1226 | return (es != null) ? es : (entrySet = new EntrySet()); | ||
| 1227 | } | ||
| 1228 | |||
| 1229 | /** | ||
| 1230 | * Returns an enumeration of the keys in this table. | ||
| 1231 | * | ||
| 1232 | * @return an enumeration of the keys in this table | ||
| 1233 | * @see #keySet() | ||
| 1234 | */ | ||
| 1235 | public Enumeration<K> keys() { | ||
| 1236 | return new KeyIterator(); | ||
| 1237 | } | ||
| 1238 | |||
| 1239 | /** | ||
| 1240 | * Returns an enumeration of the values in this table. | ||
| 1241 | * | ||
| 1242 | * @return an enumeration of the values in this table | ||
| 1243 | * @see #values() | ||
| 1244 | */ | ||
| 1245 | public Enumeration<V> elements() { | ||
| 1246 | return new ValueIterator(); | ||
| 1247 | } | ||
| 1248 | |||
| 1249 | /* ---------------- Iterator Support -------------- */ | ||
| 1250 | |||
| 1251 | abstract class HashIterator { | ||
| 1252 | int nextSegmentIndex; | ||
| 1253 | int nextTableIndex; | ||
| 1254 | HashEntry<K,V>[] currentTable; | ||
| 1255 | HashEntry<K, V> nextEntry; | ||
| 1256 | HashEntry<K, V> lastReturned; | ||
| 1257 | |||
| 1258 | HashIterator() { | ||
| 1259 | nextSegmentIndex = segments.length - 1; | ||
| 1260 | nextTableIndex = -1; | ||
| 1261 | advance(); | ||
| 1262 | } | ||
| 1263 | |||
| 1264 | /** | ||
| 1265 | * Set nextEntry to first node of next non-empty table | ||
| 1266 | * (in backwards order, to simplify checks). | ||
| 1267 | */ | ||
| 1268 | final void advance() { | ||
| 1269 | for (;;) { | ||
| 1270 | if (nextTableIndex >= 0) { | ||
| 1271 | if ((nextEntry = entryAt(currentTable, | ||
| 1272 | nextTableIndex--)) != null) | ||
| 1273 | break; | ||
| 1274 | } | ||
| 1275 | else if (nextSegmentIndex >= 0) { | ||
| 1276 | Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--); | ||
| 1277 | if (seg != null && (currentTable = seg.table) != null) | ||
| 1278 | nextTableIndex = currentTable.length - 1; | ||
| 1279 | } | ||
| 1280 | else | ||
| 1281 | break; | ||
| 1282 | } | ||
| 1283 | } | ||
| 1284 | |||
| 1285 | final HashEntry<K,V> nextEntry() { | ||
| 1286 | HashEntry<K,V> e = nextEntry; | ||
| 1287 | if (e == null) | ||
| 1288 | throw new NoSuchElementException(); | ||
| 1289 | lastReturned = e; // cannot assign until after null check | ||
| 1290 | if ((nextEntry = e.next) == null) | ||
| 1291 | advance(); | ||
| 1292 | return e; | ||
| 1293 | } | ||
| 1294 | |||
| 1295 | public final boolean hasNext() { return nextEntry != null; } | ||
| 1296 | public final boolean hasMoreElements() { return nextEntry != null; } | ||
| 1297 | |||
| 1298 | public final void remove() { | ||
| 1299 | if (lastReturned == null) | ||
| 1300 | throw new IllegalStateException(); | ||
| 1301 | ConcurrentHashMap.this.remove(lastReturned.key); | ||
| 1302 | lastReturned = null; | ||
| 1303 | } | ||
| 1304 | } | ||
| 1305 | |||
| 1306 | final class KeyIterator | ||
| 1307 | extends HashIterator | ||
| 1308 | implements Iterator<K>, Enumeration<K> | ||
| 1309 | { | ||
| 1310 | public final K next() { return super.nextEntry().key; } | ||
| 1311 | public final K nextElement() { return super.nextEntry().key; } | ||
| 1312 | } | ||
| 1313 | |||
| 1314 | final class ValueIterator | ||
| 1315 | extends HashIterator | ||
| 1316 | implements Iterator<V>, Enumeration<V> | ||
| 1317 | { | ||
| 1318 | public final V next() { return super.nextEntry().value; } | ||
| 1319 | public final V nextElement() { return super.nextEntry().value; } | ||
| 1320 | } | ||
| 1321 | |||
| 1322 | /** | ||
| 1323 | * Custom Entry class used by EntryIterator.next(), that relays | ||
| 1324 | * setValue changes to the underlying map. | ||
| 1325 | */ | ||
| 1326 | final class WriteThroughEntry | ||
| 1327 | extends AbstractMap.SimpleEntry<K,V> | ||
| 1328 | { | ||
| 1329 | WriteThroughEntry(K k, V v) { | ||
| 1330 | super(k,v); | ||
| 1331 | } | ||
| 1332 | |||
| 1333 | /** | ||
| 1334 | * Set our entry's value and write through to the map. The | ||
| 1335 | * value to return is somewhat arbitrary here. Since a | ||
| 1336 | * WriteThroughEntry does not necessarily track asynchronous | ||
| 1337 | * changes, the most recent "previous" value could be | ||
| 1338 | * different from what we return (or could even have been | ||
| 1339 | * removed in which case the put will re-establish). We do not | ||
| 1340 | * and cannot guarantee more. | ||
| 1341 | */ | ||
| 1342 | public V setValue(V value) { | ||
| 1343 | if (value == null) throw new NullPointerException(); | ||
| 1344 | V v = super.setValue(value); | ||
| 1345 | ConcurrentHashMap.this.put(getKey(), value); | ||
| 1346 | return v; | ||
| 1347 | } | ||
| 1348 | } | ||
| 1349 | |||
| 1350 | final class EntryIterator | ||
| 1351 | extends HashIterator | ||
| 1352 | implements Iterator<Entry<K,V>> | ||
| 1353 | { | ||
| 1354 | public Map.Entry<K,V> next() { | ||
| 1355 | HashEntry<K,V> e = super.nextEntry(); | ||
| 1356 | return new WriteThroughEntry(e.key, e.value); | ||
| 1357 | } | ||
| 1358 | } | ||
| 1359 | |||
| 1360 | final class KeySet extends AbstractSet<K> { | ||
| 1361 | public Iterator<K> iterator() { | ||
| 1362 | return new KeyIterator(); | ||
| 1363 | } | ||
| 1364 | public int size() { | ||
| 1365 | return ConcurrentHashMap.this.size(); | ||
| 1366 | } | ||
| 1367 | public boolean isEmpty() { | ||
| 1368 | return ConcurrentHashMap.this.isEmpty(); | ||
| 1369 | } | ||
| 1370 | public boolean contains(Object o) { | ||
| 1371 | return ConcurrentHashMap.this.containsKey(o); | ||
| 1372 | } | ||
| 1373 | public boolean remove(Object o) { | ||
| 1374 | return ConcurrentHashMap.this.remove(o) != null; | ||
| 1375 | } | ||
| 1376 | public void clear() { | ||
| 1377 | ConcurrentHashMap.this.clear(); | ||
| 1378 | } | ||
| 1379 | } | ||
| 1380 | |||
| 1381 | final class Values extends AbstractCollection<V> { | ||
| 1382 | public Iterator<V> iterator() { | ||
| 1383 | return new ValueIterator(); | ||
| 1384 | } | ||
| 1385 | public int size() { | ||
| 1386 | return ConcurrentHashMap.this.size(); | ||
| 1387 | } | ||
| 1388 | public boolean isEmpty() { | ||
| 1389 | return ConcurrentHashMap.this.isEmpty(); | ||
| 1390 | } | ||
| 1391 | public boolean contains(Object o) { | ||
| 1392 | return ConcurrentHashMap.this.containsValue(o); | ||
| 1393 | } | ||
| 1394 | public void clear() { | ||
| 1395 | ConcurrentHashMap.this.clear(); | ||
| 1396 | } | ||
| 1397 | } | ||
| 1398 | |||
| 1399 | final class EntrySet extends AbstractSet<Map.Entry<K,V>> { | ||
| 1400 | public Iterator<Map.Entry<K,V>> iterator() { | ||
| 1401 | return new EntryIterator(); | ||
| 1402 | } | ||
| 1403 | public boolean contains(Object o) { | ||
| 1404 | if (!(o instanceof Map.Entry)) | ||
| 1405 | return false; | ||
| 1406 | Map.Entry<?,?> e = (Map.Entry<?,?>)o; | ||
| 1407 | V v = ConcurrentHashMap.this.get(e.getKey()); | ||
| 1408 | return v != null && v.equals(e.getValue()); | ||
| 1409 | } | ||
| 1410 | public boolean remove(Object o) { | ||
| 1411 | if (!(o instanceof Map.Entry)) | ||
| 1412 | return false; | ||
| 1413 | Map.Entry<?,?> e = (Map.Entry<?,?>)o; | ||
| 1414 | return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()); | ||
| 1415 | } | ||
| 1416 | public int size() { | ||
| 1417 | return ConcurrentHashMap.this.size(); | ||
| 1418 | } | ||
| 1419 | public boolean isEmpty() { | ||
| 1420 | return ConcurrentHashMap.this.isEmpty(); | ||
| 1421 | } | ||
| 1422 | public void clear() { | ||
| 1423 | ConcurrentHashMap.this.clear(); | ||
| 1424 | } | ||
| 1425 | } | ||
| 1426 | |||
| 1427 | /* ---------------- Serialization Support -------------- */ | ||
| 1428 | |||
| 1429 | /** | ||
| 1430 | * Save the state of the <tt>ConcurrentHashMap</tt> instance to a | ||
| 1431 | * stream (i.e., serialize it). | ||
| 1432 | * @param s the stream | ||
| 1433 | * @serialData | ||
| 1434 | * the key (Object) and value (Object) | ||
| 1435 | * for each key-value mapping, followed by a null pair. | ||
| 1436 | * The key-value mappings are emitted in no particular order. | ||
| 1437 | */ | ||
| 1438 | private void writeObject(java.io.ObjectOutputStream s) throws IOException { | ||
| 1439 | // force all segments for serialization compatibility | ||
| 1440 | for (int k = 0; k < segments.length; ++k) | ||
| 1441 | ensureSegment(k); | ||
| 1442 | s.defaultWriteObject(); | ||
| 1443 | |||
| 1444 | final Segment<K,V>[] segments = this.segments; | ||
| 1445 | for (int k = 0; k < segments.length; ++k) { | ||
| 1446 | Segment<K,V> seg = segmentAt(segments, k); | ||
| 1447 | seg.lock(); | ||
| 1448 | try { | ||
| 1449 | HashEntry<K,V>[] tab = seg.table; | ||
| 1450 | for (int i = 0; i < tab.length; ++i) { | ||
| 1451 | HashEntry<K,V> e; | ||
| 1452 | for (e = entryAt(tab, i); e != null; e = e.next) { | ||
| 1453 | s.writeObject(e.key); | ||
| 1454 | s.writeObject(e.value); | ||
| 1455 | } | ||
| 1456 | } | ||
| 1457 | } finally { | ||
| 1458 | seg.unlock(); | ||
| 1459 | } | ||
| 1460 | } | ||
| 1461 | s.writeObject(null); | ||
| 1462 | s.writeObject(null); | ||
| 1463 | } | ||
| 1464 | |||
| 1465 | /** | ||
| 1466 | * Reconstitute the <tt>ConcurrentHashMap</tt> instance from a | ||
| 1467 | * stream (i.e., deserialize it). | ||
| 1468 | * @param s the stream | ||
| 1469 | */ | ||
| 1470 | @SuppressWarnings("unchecked") | ||
| 1471 | private void readObject(java.io.ObjectInputStream s) | ||
| 1472 | throws IOException, ClassNotFoundException { | ||
| 1473 | s.defaultReadObject(); | ||
| 1474 | |||
| 1475 | // Re-initialize segments to be minimally sized, and let grow. | ||
| 1476 | int cap = MIN_SEGMENT_TABLE_CAPACITY; | ||
| 1477 | final Segment<K,V>[] segments = this.segments; | ||
| 1478 | for (int k = 0; k < segments.length; ++k) { | ||
| 1479 | Segment<K,V> seg = segments[k]; | ||
| 1480 | if (seg != null) { | ||
| 1481 | seg.threshold = (int)(cap * seg.loadFactor); | ||
| 1482 | seg.table = (HashEntry<K,V>[]) new HashEntry[cap]; | ||
| 1483 | } | ||
| 1484 | } | ||
| 1485 | |||
| 1486 | // Read the keys and values, and put the mappings in the table | ||
| 1487 | for (;;) { | ||
| 1488 | K key = (K) s.readObject(); | ||
| 1489 | V value = (V) s.readObject(); | ||
| 1490 | if (key == null) | ||
| 1491 | break; | ||
| 1492 | put(key, value); | ||
| 1493 | } | ||
| 1494 | } | ||
| 1495 | |||
| 1496 | // Unsafe mechanics | ||
| 1497 | private static final sun.misc.Unsafe UNSAFE; | ||
| 1498 | private static final long SBASE; | ||
| 1499 | private static final int SSHIFT; | ||
| 1500 | private static final long TBASE; | ||
| 1501 | private static final int TSHIFT; | ||
| 1502 | |||
| 1503 | static { | ||
| 1504 | int ss, ts; | ||
| 1505 | try { | ||
| 1506 | UNSAFE = sun.misc.Unsafe.getUnsafe(); | ||
| 1507 | Class tc = HashEntry[].class; | ||
| 1508 | Class sc = Segment[].class; | ||
| 1509 | TBASE = UNSAFE.arrayBaseOffset(tc); | ||
| 1510 | SBASE = UNSAFE.arrayBaseOffset(sc); | ||
| 1511 | ts = UNSAFE.arrayIndexScale(tc); | ||
| 1512 | ss = UNSAFE.arrayIndexScale(sc); | ||
| 1513 | } catch (Exception e) { | ||
| 1514 | throw new Error(e); | ||
| 1515 | } | ||
| 1516 | if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0) | ||
| 1517 | throw new Error("data type scale not a power of two"); | ||
| 1518 | SSHIFT = 31 - Integer.numberOfLeadingZeros(ss); | ||
| 1519 | TSHIFT = 31 - Integer.numberOfLeadingZeros(ts); | ||
| 1520 | } | ||
| 1521 | |||
| 1522 | } | ||