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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.*; | ||
| 38 | import sun.misc.Unsafe; | ||
| 39 | |||
| 40 | /** | ||
| 41 | * A scalable concurrent {@link NavigableSet} implementation based on | ||
| 42 | * a {@link ConcurrentSkipListMap}. The elements of the set are kept | ||
| 43 | * sorted according to their {@linkplain Comparable natural ordering}, | ||
| 44 | * or by a {@link Comparator} provided at set creation time, depending | ||
| 45 | * on which constructor is used. | ||
| 46 | * | ||
| 47 | * <p>This implementation provides expected average <i>log(n)</i> time | ||
| 48 | * cost for the <tt>contains</tt>, <tt>add</tt>, and <tt>remove</tt> | ||
| 49 | * operations and their variants. Insertion, removal, and access | ||
| 50 | * operations safely execute concurrently by multiple threads. | ||
| 51 | * Iterators are <i>weakly consistent</i>, returning elements | ||
| 52 | * reflecting the state of the set at some point at or since the | ||
| 53 | * creation of the iterator. They do <em>not</em> throw {@link | ||
| 54 | * ConcurrentModificationException}, and may proceed concurrently with | ||
| 55 | * other operations. Ascending ordered views and their iterators are | ||
| 56 | * faster than descending ones. | ||
| 57 | * | ||
| 58 | * <p>Beware that, unlike in most collections, the <tt>size</tt> | ||
| 59 | * method is <em>not</em> a constant-time operation. Because of the | ||
| 60 | * asynchronous nature of these sets, determining the current number | ||
| 61 | * of elements requires a traversal of the elements, and so may report | ||
| 62 | * inaccurate results if this collection is modified during traversal. | ||
| 63 | * Additionally, the bulk operations <tt>addAll</tt>, | ||
| 64 | * <tt>removeAll</tt>, <tt>retainAll</tt>, <tt>containsAll</tt>, | ||
| 65 | * <tt>equals</tt>, and <tt>toArray</tt> are <em>not</em> guaranteed | ||
| 66 | * to be performed atomically. For example, an iterator operating | ||
| 67 | * concurrently with an <tt>addAll</tt> operation might view only some | ||
| 68 | * of the added elements. | ||
| 69 | * | ||
| 70 | * <p>This class and its iterators implement all of the | ||
| 71 | * <em>optional</em> methods of the {@link Set} and {@link Iterator} | ||
| 72 | * interfaces. Like most other concurrent collection implementations, | ||
| 73 | * this class does not permit the use of <tt>null</tt> elements, | ||
| 74 | * because <tt>null</tt> arguments and return values cannot be reliably | ||
| 75 | * distinguished from the absence of elements. | ||
| 76 | * | ||
| 77 | * <p>This class is a member of the | ||
| 78 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 79 | * Java Collections Framework</a>. | ||
| 80 | * | ||
| 81 | * @author Doug Lea | ||
| 82 | * @param <E> the type of elements maintained by this set | ||
| 83 | * @since 1.6 | ||
| 84 | */ | ||
| 85 | public class ConcurrentSkipListSet<E> | ||
| 86 | extends AbstractSet<E> | ||
| 87 | implements NavigableSet<E>, Cloneable, java.io.Serializable { | ||
| 88 | |||
| 89 | private static final long serialVersionUID = -2479143111061671589L; | ||
| 90 | |||
| 91 | /** | ||
| 92 | * The underlying map. Uses Boolean.TRUE as value for each | ||
| 93 | * element. This field is declared final for the sake of thread | ||
| 94 | * safety, which entails some ugliness in clone() | ||
| 95 | */ | ||
| 96 | private final ConcurrentNavigableMap<E,Object> m; | ||
| 97 | |||
| 98 | /** | ||
| 99 | * Constructs a new, empty set that orders its elements according to | ||
| 100 | * their {@linkplain Comparable natural ordering}. | ||
| 101 | */ | ||
| 102 | public ConcurrentSkipListSet() { | ||
| 103 | m = new ConcurrentSkipListMap<E,Object>(); | ||
| 104 | } | ||
| 105 | |||
| 106 | /** | ||
| 107 | * Constructs a new, empty set that orders its elements according to | ||
| 108 | * the specified comparator. | ||
| 109 | * | ||
| 110 | * @param comparator the comparator that will be used to order this set. | ||
| 111 | * If <tt>null</tt>, the {@linkplain Comparable natural | ||
| 112 | * ordering} of the elements will be used. | ||
| 113 | */ | ||
| 114 | public ConcurrentSkipListSet(Comparator<? super E> comparator) { | ||
| 115 | m = new ConcurrentSkipListMap<E,Object>(comparator); | ||
| 116 | } | ||
| 117 | |||
| 118 | /** | ||
| 119 | * Constructs a new set containing the elements in the specified | ||
| 120 | * collection, that orders its elements according to their | ||
| 121 | * {@linkplain Comparable natural ordering}. | ||
| 122 | * | ||
| 123 | * @param c The elements that will comprise the new set | ||
| 124 | * @throws ClassCastException if the elements in <tt>c</tt> are | ||
| 125 | * not {@link Comparable}, or are not mutually comparable | ||
| 126 | * @throws NullPointerException if the specified collection or any | ||
| 127 | * of its elements are null | ||
| 128 | */ | ||
| 129 | public ConcurrentSkipListSet(Collection<? extends E> c) { | ||
| 130 | m = new ConcurrentSkipListMap<E,Object>(); | ||
| 131 | addAll(c); | ||
| 132 | } | ||
| 133 | |||
| 134 | /** | ||
| 135 | * Constructs a new set containing the same elements and using the | ||
| 136 | * same ordering as the specified sorted set. | ||
| 137 | * | ||
| 138 | * @param s sorted set whose elements will comprise the new set | ||
| 139 | * @throws NullPointerException if the specified sorted set or any | ||
| 140 | * of its elements are null | ||
| 141 | */ | ||
| 142 | public ConcurrentSkipListSet(SortedSet<E> s) { | ||
| 143 | m = new ConcurrentSkipListMap<E,Object>(s.comparator()); | ||
| 144 | addAll(s); | ||
| 145 | } | ||
| 146 | |||
| 147 | /** | ||
| 148 | * For use by submaps | ||
| 149 | */ | ||
| 150 | ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) { | ||
| 151 | this.m = m; | ||
| 152 | } | ||
| 153 | |||
| 154 | /** | ||
| 155 | * Returns a shallow copy of this <tt>ConcurrentSkipListSet</tt> | ||
| 156 | * instance. (The elements themselves are not cloned.) | ||
| 157 | * | ||
| 158 | * @return a shallow copy of this set | ||
| 159 | */ | ||
| 160 | public ConcurrentSkipListSet<E> clone() { | ||
| 161 | ConcurrentSkipListSet<E> clone = null; | ||
| 162 | try { | ||
| 163 | clone = (ConcurrentSkipListSet<E>) super.clone(); | ||
| 164 | clone.setMap(new ConcurrentSkipListMap(m)); | ||
| 165 | } catch (CloneNotSupportedException e) { | ||
| 166 | throw new InternalError(); | ||
| 167 | } | ||
| 168 | |||
| 169 | return clone; | ||
| 170 | } | ||
| 171 | |||
| 172 | /* ---------------- Set operations -------------- */ | ||
| 173 | |||
| 174 | /** | ||
| 175 | * Returns the number of elements in this set. If this set | ||
| 176 | * contains more than <tt>Integer.MAX_VALUE</tt> elements, it | ||
| 177 | * returns <tt>Integer.MAX_VALUE</tt>. | ||
| 178 | * | ||
| 179 | * <p>Beware that, unlike in most collections, this method is | ||
| 180 | * <em>NOT</em> a constant-time operation. Because of the | ||
| 181 | * asynchronous nature of these sets, determining the current | ||
| 182 | * number of elements requires traversing them all to count them. | ||
| 183 | * Additionally, it is possible for the size to change during | ||
| 184 | * execution of this method, in which case the returned result | ||
| 185 | * will be inaccurate. Thus, this method is typically not very | ||
| 186 | * useful in concurrent applications. | ||
| 187 | * | ||
| 188 | * @return the number of elements in this set | ||
| 189 | */ | ||
| 190 | public int size() { | ||
| 191 | return m.size(); | ||
| 192 | } | ||
| 193 | |||
| 194 | /** | ||
| 195 | * Returns <tt>true</tt> if this set contains no elements. | ||
| 196 | * @return <tt>true</tt> if this set contains no elements | ||
| 197 | */ | ||
| 198 | public boolean isEmpty() { | ||
| 199 | return m.isEmpty(); | ||
| 200 | } | ||
| 201 | |||
| 202 | /** | ||
| 203 | * Returns <tt>true</tt> if this set contains the specified element. | ||
| 204 | * More formally, returns <tt>true</tt> if and only if this set | ||
| 205 | * contains an element <tt>e</tt> such that <tt>o.equals(e)</tt>. | ||
| 206 | * | ||
| 207 | * @param o object to be checked for containment in this set | ||
| 208 | * @return <tt>true</tt> if this set contains the specified element | ||
| 209 | * @throws ClassCastException if the specified element cannot be | ||
| 210 | * compared with the elements currently in this set | ||
| 211 | * @throws NullPointerException if the specified element is null | ||
| 212 | */ | ||
| 213 | public boolean contains(Object o) { | ||
| 214 | return m.containsKey(o); | ||
| 215 | } | ||
| 216 | |||
| 217 | /** | ||
| 218 | * Adds the specified element to this set if it is not already present. | ||
| 219 | * More formally, adds the specified element <tt>e</tt> to this set if | ||
| 220 | * the set contains no element <tt>e2</tt> such that <tt>e.equals(e2)</tt>. | ||
| 221 | * If this set already contains the element, the call leaves the set | ||
| 222 | * unchanged and returns <tt>false</tt>. | ||
| 223 | * | ||
| 224 | * @param e element to be added to this set | ||
| 225 | * @return <tt>true</tt> if this set did not already contain the | ||
| 226 | * specified element | ||
| 227 | * @throws ClassCastException if <tt>e</tt> cannot be compared | ||
| 228 | * with the elements currently in this set | ||
| 229 | * @throws NullPointerException if the specified element is null | ||
| 230 | */ | ||
| 231 | public boolean add(E e) { | ||
| 232 | return m.putIfAbsent(e, Boolean.TRUE) == null; | ||
| 233 | } | ||
| 234 | |||
| 235 | /** | ||
| 236 | * Removes the specified element from this set if it is present. | ||
| 237 | * More formally, removes an element <tt>e</tt> such that | ||
| 238 | * <tt>o.equals(e)</tt>, if this set contains such an element. | ||
| 239 | * Returns <tt>true</tt> if this set contained the element (or | ||
| 240 | * equivalently, if this set changed as a result of the call). | ||
| 241 | * (This set will not contain the element once the call returns.) | ||
| 242 | * | ||
| 243 | * @param o object to be removed from this set, if present | ||
| 244 | * @return <tt>true</tt> if this set contained the specified element | ||
| 245 | * @throws ClassCastException if <tt>o</tt> cannot be compared | ||
| 246 | * with the elements currently in this set | ||
| 247 | * @throws NullPointerException if the specified element is null | ||
| 248 | */ | ||
| 249 | public boolean remove(Object o) { | ||
| 250 | return m.remove(o, Boolean.TRUE); | ||
| 251 | } | ||
| 252 | |||
| 253 | /** | ||
| 254 | * Removes all of the elements from this set. | ||
| 255 | */ | ||
| 256 | public void clear() { | ||
| 257 | m.clear(); | ||
| 258 | } | ||
| 259 | |||
| 260 | /** | ||
| 261 | * Returns an iterator over the elements in this set in ascending order. | ||
| 262 | * | ||
| 263 | * @return an iterator over the elements in this set in ascending order | ||
| 264 | */ | ||
| 265 | public Iterator<E> iterator() { | ||
| 266 | return m.navigableKeySet().iterator(); | ||
| 267 | } | ||
| 268 | |||
| 269 | /** | ||
| 270 | * Returns an iterator over the elements in this set in descending order. | ||
| 271 | * | ||
| 272 | * @return an iterator over the elements in this set in descending order | ||
| 273 | */ | ||
| 274 | public Iterator<E> descendingIterator() { | ||
| 275 | return m.descendingKeySet().iterator(); | ||
| 276 | } | ||
| 277 | |||
| 278 | |||
| 279 | /* ---------------- AbstractSet Overrides -------------- */ | ||
| 280 | |||
| 281 | /** | ||
| 282 | * Compares the specified object with this set for equality. Returns | ||
| 283 | * <tt>true</tt> if the specified object is also a set, the two sets | ||
| 284 | * have the same size, and every member of the specified set is | ||
| 285 | * contained in this set (or equivalently, every member of this set is | ||
| 286 | * contained in the specified set). This definition ensures that the | ||
| 287 | * equals method works properly across different implementations of the | ||
| 288 | * set interface. | ||
| 289 | * | ||
| 290 | * @param o the object to be compared for equality with this set | ||
| 291 | * @return <tt>true</tt> if the specified object is equal to this set | ||
| 292 | */ | ||
| 293 | public boolean equals(Object o) { | ||
| 294 | // Override AbstractSet version to avoid calling size() | ||
| 295 | if (o == this) | ||
| 296 | return true; | ||
| 297 | if (!(o instanceof Set)) | ||
| 298 | return false; | ||
| 299 | Collection<?> c = (Collection<?>) o; | ||
| 300 | try { | ||
| 301 | return containsAll(c) && c.containsAll(this); | ||
| 302 | } catch (ClassCastException unused) { | ||
| 303 | return false; | ||
| 304 | } catch (NullPointerException unused) { | ||
| 305 | return false; | ||
| 306 | } | ||
| 307 | } | ||
| 308 | |||
| 309 | /** | ||
| 310 | * Removes from this set all of its elements that are contained in | ||
| 311 | * the specified collection. If the specified collection is also | ||
| 312 | * a set, this operation effectively modifies this set so that its | ||
| 313 | * value is the <i>asymmetric set difference</i> of the two sets. | ||
| 314 | * | ||
| 315 | * @param c collection containing elements to be removed from this set | ||
| 316 | * @return <tt>true</tt> if this set changed as a result of the call | ||
| 317 | * @throws ClassCastException if the types of one or more elements in this | ||
| 318 | * set are incompatible with the specified collection | ||
| 319 | * @throws NullPointerException if the specified collection or any | ||
| 320 | * of its elements are null | ||
| 321 | */ | ||
| 322 | public boolean removeAll(Collection<?> c) { | ||
| 323 | // Override AbstractSet version to avoid unnecessary call to size() | ||
| 324 | boolean modified = false; | ||
| 325 | for (Iterator<?> i = c.iterator(); i.hasNext(); ) | ||
| 326 | if (remove(i.next())) | ||
| 327 | modified = true; | ||
| 328 | return modified; | ||
| 329 | } | ||
| 330 | |||
| 331 | /* ---------------- Relational operations -------------- */ | ||
| 332 | |||
| 333 | /** | ||
| 334 | * @throws ClassCastException {@inheritDoc} | ||
| 335 | * @throws NullPointerException if the specified element is null | ||
| 336 | */ | ||
| 337 | public E lower(E e) { | ||
| 338 | return m.lowerKey(e); | ||
| 339 | } | ||
| 340 | |||
| 341 | /** | ||
| 342 | * @throws ClassCastException {@inheritDoc} | ||
| 343 | * @throws NullPointerException if the specified element is null | ||
| 344 | */ | ||
| 345 | public E floor(E e) { | ||
| 346 | return m.floorKey(e); | ||
| 347 | } | ||
| 348 | |||
| 349 | /** | ||
| 350 | * @throws ClassCastException {@inheritDoc} | ||
| 351 | * @throws NullPointerException if the specified element is null | ||
| 352 | */ | ||
| 353 | public E ceiling(E e) { | ||
| 354 | return m.ceilingKey(e); | ||
| 355 | } | ||
| 356 | |||
| 357 | /** | ||
| 358 | * @throws ClassCastException {@inheritDoc} | ||
| 359 | * @throws NullPointerException if the specified element is null | ||
| 360 | */ | ||
| 361 | public E higher(E e) { | ||
| 362 | return m.higherKey(e); | ||
| 363 | } | ||
| 364 | |||
| 365 | public E pollFirst() { | ||
| 366 | Map.Entry<E,Object> e = m.pollFirstEntry(); | ||
| 367 | return (e == null) ? null : e.getKey(); | ||
| 368 | } | ||
| 369 | |||
| 370 | public E pollLast() { | ||
| 371 | Map.Entry<E,Object> e = m.pollLastEntry(); | ||
| 372 | return (e == null) ? null : e.getKey(); | ||
| 373 | } | ||
| 374 | |||
| 375 | |||
| 376 | /* ---------------- SortedSet operations -------------- */ | ||
| 377 | |||
| 378 | |||
| 379 | public Comparator<? super E> comparator() { | ||
| 380 | return m.comparator(); | ||
| 381 | } | ||
| 382 | |||
| 383 | /** | ||
| 384 | * @throws NoSuchElementException {@inheritDoc} | ||
| 385 | */ | ||
| 386 | public E first() { | ||
| 387 | return m.firstKey(); | ||
| 388 | } | ||
| 389 | |||
| 390 | /** | ||
| 391 | * @throws NoSuchElementException {@inheritDoc} | ||
| 392 | */ | ||
| 393 | public E last() { | ||
| 394 | return m.lastKey(); | ||
| 395 | } | ||
| 396 | |||
| 397 | /** | ||
| 398 | * @throws ClassCastException {@inheritDoc} | ||
| 399 | * @throws NullPointerException if {@code fromElement} or | ||
| 400 | * {@code toElement} is null | ||
| 401 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 402 | */ | ||
| 403 | public NavigableSet<E> subSet(E fromElement, | ||
| 404 | boolean fromInclusive, | ||
| 405 | E toElement, | ||
| 406 | boolean toInclusive) { | ||
| 407 | return new ConcurrentSkipListSet<E> | ||
| 408 | (m.subMap(fromElement, fromInclusive, | ||
| 409 | toElement, toInclusive)); | ||
| 410 | } | ||
| 411 | |||
| 412 | /** | ||
| 413 | * @throws ClassCastException {@inheritDoc} | ||
| 414 | * @throws NullPointerException if {@code toElement} is null | ||
| 415 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 416 | */ | ||
| 417 | public NavigableSet<E> headSet(E toElement, boolean inclusive) { | ||
| 418 | return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive)); | ||
| 419 | } | ||
| 420 | |||
| 421 | /** | ||
| 422 | * @throws ClassCastException {@inheritDoc} | ||
| 423 | * @throws NullPointerException if {@code fromElement} is null | ||
| 424 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 425 | */ | ||
| 426 | public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { | ||
| 427 | return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive)); | ||
| 428 | } | ||
| 429 | |||
| 430 | /** | ||
| 431 | * @throws ClassCastException {@inheritDoc} | ||
| 432 | * @throws NullPointerException if {@code fromElement} or | ||
| 433 | * {@code toElement} is null | ||
| 434 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 435 | */ | ||
| 436 | public NavigableSet<E> subSet(E fromElement, E toElement) { | ||
| 437 | return subSet(fromElement, true, toElement, false); | ||
| 438 | } | ||
| 439 | |||
| 440 | /** | ||
| 441 | * @throws ClassCastException {@inheritDoc} | ||
| 442 | * @throws NullPointerException if {@code toElement} is null | ||
| 443 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 444 | */ | ||
| 445 | public NavigableSet<E> headSet(E toElement) { | ||
| 446 | return headSet(toElement, false); | ||
| 447 | } | ||
| 448 | |||
| 449 | /** | ||
| 450 | * @throws ClassCastException {@inheritDoc} | ||
| 451 | * @throws NullPointerException if {@code fromElement} is null | ||
| 452 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 453 | */ | ||
| 454 | public NavigableSet<E> tailSet(E fromElement) { | ||
| 455 | return tailSet(fromElement, true); | ||
| 456 | } | ||
| 457 | |||
| 458 | /** | ||
| 459 | * Returns a reverse order view of the elements contained in this set. | ||
| 460 | * The descending set is backed by this set, so changes to the set are | ||
| 461 | * reflected in the descending set, and vice-versa. | ||
| 462 | * | ||
| 463 | * <p>The returned set has an ordering equivalent to | ||
| 464 | * <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>. | ||
| 465 | * The expression {@code s.descendingSet().descendingSet()} returns a | ||
| 466 | * view of {@code s} essentially equivalent to {@code s}. | ||
| 467 | * | ||
| 468 | * @return a reverse order view of this set | ||
| 469 | */ | ||
| 470 | public NavigableSet<E> descendingSet() { | ||
| 471 | return new ConcurrentSkipListSet(m.descendingMap()); | ||
| 472 | } | ||
| 473 | |||
| 474 | // Support for resetting map in clone | ||
| 475 | private void setMap(ConcurrentNavigableMap<E,Object> map) { | ||
| 476 | UNSAFE.putObjectVolatile(this, mapOffset, map); | ||
| 477 | } | ||
| 478 | |||
| 479 | private static final sun.misc.Unsafe UNSAFE; | ||
| 480 | private static final long mapOffset; | ||
| 481 | static { | ||
| 482 | try { | ||
| 483 | UNSAFE = sun.misc.Unsafe.getUnsafe(); | ||
| 484 | Class k = ConcurrentSkipListSet.class; | ||
| 485 | mapOffset = UNSAFE.objectFieldOffset | ||
| 486 | (k.getDeclaredField("m")); | ||
| 487 | } catch (Exception e) { | ||
| 488 | throw new Error(e); | ||
| 489 | } | ||
| 490 | } | ||
| 491 | } | ||