J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 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. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any 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/licenses/publicdomain |
| 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. Additionally, the |
| 62 | * bulk operations <tt>addAll</tt>, <tt>removeAll</tt>, |
| 63 | * <tt>retainAll</tt>, and <tt>containsAll</tt> are <em>not</em> |
| 64 | * guaranteed to be performed atomically. For example, an iterator |
| 65 | * operating concurrently with an <tt>addAll</tt> operation might view |
| 66 | * only some of the added elements. |
| 67 | * |
| 68 | * <p>This class and its iterators implement all of the |
| 69 | * <em>optional</em> methods of the {@link Set} and {@link Iterator} |
| 70 | * interfaces. Like most other concurrent collection implementations, |
| 71 | * this class does not permit the use of <tt>null</tt> elements, |
| 72 | * because <tt>null</tt> arguments and return values cannot be reliably |
| 73 | * distinguished from the absence of elements. |
| 74 | * |
| 75 | * <p>This class is a member of the |
| 76 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 77 | * Java Collections Framework</a>. |
| 78 | * |
| 79 | * @author Doug Lea |
| 80 | * @param <E> the type of elements maintained by this set |
| 81 | * @since 1.6 |
| 82 | */ |
| 83 | public class ConcurrentSkipListSet<E> |
| 84 | extends AbstractSet<E> |
| 85 | implements NavigableSet<E>, Cloneable, java.io.Serializable { |
| 86 | |
| 87 | private static final long serialVersionUID = -2479143111061671589L; |
| 88 | |
| 89 | /** |
| 90 | * The underlying map. Uses Boolean.TRUE as value for each |
| 91 | * element. This field is declared final for the sake of thread |
| 92 | * safety, which entails some ugliness in clone() |
| 93 | */ |
| 94 | private final ConcurrentNavigableMap<E,Object> m; |
| 95 | |
| 96 | /** |
| 97 | * Constructs a new, empty set that orders its elements according to |
| 98 | * their {@linkplain Comparable natural ordering}. |
| 99 | */ |
| 100 | public ConcurrentSkipListSet() { |
| 101 | m = new ConcurrentSkipListMap<E,Object>(); |
| 102 | } |
| 103 | |
| 104 | /** |
| 105 | * Constructs a new, empty set that orders its elements according to |
| 106 | * the specified comparator. |
| 107 | * |
| 108 | * @param comparator the comparator that will be used to order this set. |
| 109 | * If <tt>null</tt>, the {@linkplain Comparable natural |
| 110 | * ordering} of the elements will be used. |
| 111 | */ |
| 112 | public ConcurrentSkipListSet(Comparator<? super E> comparator) { |
| 113 | m = new ConcurrentSkipListMap<E,Object>(comparator); |
| 114 | } |
| 115 | |
| 116 | /** |
| 117 | * Constructs a new set containing the elements in the specified |
| 118 | * collection, that orders its elements according to their |
| 119 | * {@linkplain Comparable natural ordering}. |
| 120 | * |
| 121 | * @param c The elements that will comprise the new set |
| 122 | * @throws ClassCastException if the elements in <tt>c</tt> are |
| 123 | * not {@link Comparable}, or are not mutually comparable |
| 124 | * @throws NullPointerException if the specified collection or any |
| 125 | * of its elements are null |
| 126 | */ |
| 127 | public ConcurrentSkipListSet(Collection<? extends E> c) { |
| 128 | m = new ConcurrentSkipListMap<E,Object>(); |
| 129 | addAll(c); |
| 130 | } |
| 131 | |
| 132 | /** |
| 133 | * Constructs a new set containing the same elements and using the |
| 134 | * same ordering as the specified sorted set. |
| 135 | * |
| 136 | * @param s sorted set whose elements will comprise the new set |
| 137 | * @throws NullPointerException if the specified sorted set or any |
| 138 | * of its elements are null |
| 139 | */ |
| 140 | public ConcurrentSkipListSet(SortedSet<E> s) { |
| 141 | m = new ConcurrentSkipListMap<E,Object>(s.comparator()); |
| 142 | addAll(s); |
| 143 | } |
| 144 | |
| 145 | /** |
| 146 | * For use by submaps |
| 147 | */ |
| 148 | ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) { |
| 149 | this.m = m; |
| 150 | } |
| 151 | |
| 152 | /** |
| 153 | * Returns a shallow copy of this <tt>ConcurrentSkipListSet</tt> |
| 154 | * instance. (The elements themselves are not cloned.) |
| 155 | * |
| 156 | * @return a shallow copy of this set |
| 157 | */ |
| 158 | public ConcurrentSkipListSet<E> clone() { |
| 159 | ConcurrentSkipListSet<E> clone = null; |
| 160 | try { |
| 161 | clone = (ConcurrentSkipListSet<E>) super.clone(); |
| 162 | clone.setMap(new ConcurrentSkipListMap(m)); |
| 163 | } catch (CloneNotSupportedException e) { |
| 164 | throw new InternalError(); |
| 165 | } |
| 166 | |
| 167 | return clone; |
| 168 | } |
| 169 | |
| 170 | /* ---------------- Set operations -------------- */ |
| 171 | |
| 172 | /** |
| 173 | * Returns the number of elements in this set. If this set |
| 174 | * contains more than <tt>Integer.MAX_VALUE</tt> elements, it |
| 175 | * returns <tt>Integer.MAX_VALUE</tt>. |
| 176 | * |
| 177 | * <p>Beware that, unlike in most collections, this method is |
| 178 | * <em>NOT</em> a constant-time operation. Because of the |
| 179 | * asynchronous nature of these sets, determining the current |
| 180 | * number of elements requires traversing them all to count them. |
| 181 | * Additionally, it is possible for the size to change during |
| 182 | * execution of this method, in which case the returned result |
| 183 | * will be inaccurate. Thus, this method is typically not very |
| 184 | * useful in concurrent applications. |
| 185 | * |
| 186 | * @return the number of elements in this set |
| 187 | */ |
| 188 | public int size() { |
| 189 | return m.size(); |
| 190 | } |
| 191 | |
| 192 | /** |
| 193 | * Returns <tt>true</tt> if this set contains no elements. |
| 194 | * @return <tt>true</tt> if this set contains no elements |
| 195 | */ |
| 196 | public boolean isEmpty() { |
| 197 | return m.isEmpty(); |
| 198 | } |
| 199 | |
| 200 | /** |
| 201 | * Returns <tt>true</tt> if this set contains the specified element. |
| 202 | * More formally, returns <tt>true</tt> if and only if this set |
| 203 | * contains an element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
| 204 | * |
| 205 | * @param o object to be checked for containment in this set |
| 206 | * @return <tt>true</tt> if this set contains the specified element |
| 207 | * @throws ClassCastException if the specified element cannot be |
| 208 | * compared with the elements currently in this set |
| 209 | * @throws NullPointerException if the specified element is null |
| 210 | */ |
| 211 | public boolean contains(Object o) { |
| 212 | return m.containsKey(o); |
| 213 | } |
| 214 | |
| 215 | /** |
| 216 | * Adds the specified element to this set if it is not already present. |
| 217 | * More formally, adds the specified element <tt>e</tt> to this set if |
| 218 | * the set contains no element <tt>e2</tt> such that <tt>e.equals(e2)</tt>. |
| 219 | * If this set already contains the element, the call leaves the set |
| 220 | * unchanged and returns <tt>false</tt>. |
| 221 | * |
| 222 | * @param e element to be added to this set |
| 223 | * @return <tt>true</tt> if this set did not already contain the |
| 224 | * specified element |
| 225 | * @throws ClassCastException if <tt>e</tt> cannot be compared |
| 226 | * with the elements currently in this set |
| 227 | * @throws NullPointerException if the specified element is null |
| 228 | */ |
| 229 | public boolean add(E e) { |
| 230 | return m.putIfAbsent(e, Boolean.TRUE) == null; |
| 231 | } |
| 232 | |
| 233 | /** |
| 234 | * Removes the specified element from this set if it is present. |
| 235 | * More formally, removes an element <tt>e</tt> such that |
| 236 | * <tt>o.equals(e)</tt>, if this set contains such an element. |
| 237 | * Returns <tt>true</tt> if this set contained the element (or |
| 238 | * equivalently, if this set changed as a result of the call). |
| 239 | * (This set will not contain the element once the call returns.) |
| 240 | * |
| 241 | * @param o object to be removed from this set, if present |
| 242 | * @return <tt>true</tt> if this set contained the specified element |
| 243 | * @throws ClassCastException if <tt>o</tt> cannot be compared |
| 244 | * with the elements currently in this set |
| 245 | * @throws NullPointerException if the specified element is null |
| 246 | */ |
| 247 | public boolean remove(Object o) { |
| 248 | return m.remove(o, Boolean.TRUE); |
| 249 | } |
| 250 | |
| 251 | /** |
| 252 | * Removes all of the elements from this set. |
| 253 | */ |
| 254 | public void clear() { |
| 255 | m.clear(); |
| 256 | } |
| 257 | |
| 258 | /** |
| 259 | * Returns an iterator over the elements in this set in ascending order. |
| 260 | * |
| 261 | * @return an iterator over the elements in this set in ascending order |
| 262 | */ |
| 263 | public Iterator<E> iterator() { |
| 264 | return m.navigableKeySet().iterator(); |
| 265 | } |
| 266 | |
| 267 | /** |
| 268 | * Returns an iterator over the elements in this set in descending order. |
| 269 | * |
| 270 | * @return an iterator over the elements in this set in descending order |
| 271 | */ |
| 272 | public Iterator<E> descendingIterator() { |
| 273 | return m.descendingKeySet().iterator(); |
| 274 | } |
| 275 | |
| 276 | |
| 277 | /* ---------------- AbstractSet Overrides -------------- */ |
| 278 | |
| 279 | /** |
| 280 | * Compares the specified object with this set for equality. Returns |
| 281 | * <tt>true</tt> if the specified object is also a set, the two sets |
| 282 | * have the same size, and every member of the specified set is |
| 283 | * contained in this set (or equivalently, every member of this set is |
| 284 | * contained in the specified set). This definition ensures that the |
| 285 | * equals method works properly across different implementations of the |
| 286 | * set interface. |
| 287 | * |
| 288 | * @param o the object to be compared for equality with this set |
| 289 | * @return <tt>true</tt> if the specified object is equal to this set |
| 290 | */ |
| 291 | public boolean equals(Object o) { |
| 292 | // Override AbstractSet version to avoid calling size() |
| 293 | if (o == this) |
| 294 | return true; |
| 295 | if (!(o instanceof Set)) |
| 296 | return false; |
| 297 | Collection<?> c = (Collection<?>) o; |
| 298 | try { |
| 299 | return containsAll(c) && c.containsAll(this); |
| 300 | } catch (ClassCastException unused) { |
| 301 | return false; |
| 302 | } catch (NullPointerException unused) { |
| 303 | return false; |
| 304 | } |
| 305 | } |
| 306 | |
| 307 | /** |
| 308 | * Removes from this set all of its elements that are contained in |
| 309 | * the specified collection. If the specified collection is also |
| 310 | * a set, this operation effectively modifies this set so that its |
| 311 | * value is the <i>asymmetric set difference</i> of the two sets. |
| 312 | * |
| 313 | * @param c collection containing elements to be removed from this set |
| 314 | * @return <tt>true</tt> if this set changed as a result of the call |
| 315 | * @throws ClassCastException if the types of one or more elements in this |
| 316 | * set are incompatible with the specified collection |
| 317 | * @throws NullPointerException if the specified collection or any |
| 318 | * of its elements are null |
| 319 | */ |
| 320 | public boolean removeAll(Collection<?> c) { |
| 321 | // Override AbstractSet version to avoid unnecessary call to size() |
| 322 | boolean modified = false; |
| 323 | for (Iterator<?> i = c.iterator(); i.hasNext(); ) |
| 324 | if (remove(i.next())) |
| 325 | modified = true; |
| 326 | return modified; |
| 327 | } |
| 328 | |
| 329 | /* ---------------- Relational operations -------------- */ |
| 330 | |
| 331 | /** |
| 332 | * @throws ClassCastException {@inheritDoc} |
| 333 | * @throws NullPointerException if the specified element is null |
| 334 | */ |
| 335 | public E lower(E e) { |
| 336 | return m.lowerKey(e); |
| 337 | } |
| 338 | |
| 339 | /** |
| 340 | * @throws ClassCastException {@inheritDoc} |
| 341 | * @throws NullPointerException if the specified element is null |
| 342 | */ |
| 343 | public E floor(E e) { |
| 344 | return m.floorKey(e); |
| 345 | } |
| 346 | |
| 347 | /** |
| 348 | * @throws ClassCastException {@inheritDoc} |
| 349 | * @throws NullPointerException if the specified element is null |
| 350 | */ |
| 351 | public E ceiling(E e) { |
| 352 | return m.ceilingKey(e); |
| 353 | } |
| 354 | |
| 355 | /** |
| 356 | * @throws ClassCastException {@inheritDoc} |
| 357 | * @throws NullPointerException if the specified element is null |
| 358 | */ |
| 359 | public E higher(E e) { |
| 360 | return m.higherKey(e); |
| 361 | } |
| 362 | |
| 363 | public E pollFirst() { |
| 364 | Map.Entry<E,Object> e = m.pollFirstEntry(); |
| 365 | return e == null? null : e.getKey(); |
| 366 | } |
| 367 | |
| 368 | public E pollLast() { |
| 369 | Map.Entry<E,Object> e = m.pollLastEntry(); |
| 370 | return e == null? null : e.getKey(); |
| 371 | } |
| 372 | |
| 373 | |
| 374 | /* ---------------- SortedSet operations -------------- */ |
| 375 | |
| 376 | |
| 377 | public Comparator<? super E> comparator() { |
| 378 | return m.comparator(); |
| 379 | } |
| 380 | |
| 381 | /** |
| 382 | * @throws NoSuchElementException {@inheritDoc} |
| 383 | */ |
| 384 | public E first() { |
| 385 | return m.firstKey(); |
| 386 | } |
| 387 | |
| 388 | /** |
| 389 | * @throws NoSuchElementException {@inheritDoc} |
| 390 | */ |
| 391 | public E last() { |
| 392 | return m.lastKey(); |
| 393 | } |
| 394 | |
| 395 | /** |
| 396 | * @throws ClassCastException {@inheritDoc} |
| 397 | * @throws NullPointerException if {@code fromElement} or |
| 398 | * {@code toElement} is null |
| 399 | * @throws IllegalArgumentException {@inheritDoc} |
| 400 | */ |
| 401 | public NavigableSet<E> subSet(E fromElement, |
| 402 | boolean fromInclusive, |
| 403 | E toElement, |
| 404 | boolean toInclusive) { |
| 405 | return new ConcurrentSkipListSet<E> |
| 406 | (m.subMap(fromElement, fromInclusive, |
| 407 | toElement, toInclusive)); |
| 408 | } |
| 409 | |
| 410 | /** |
| 411 | * @throws ClassCastException {@inheritDoc} |
| 412 | * @throws NullPointerException if {@code toElement} is null |
| 413 | * @throws IllegalArgumentException {@inheritDoc} |
| 414 | */ |
| 415 | public NavigableSet<E> headSet(E toElement, boolean inclusive) { |
| 416 | return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive)); |
| 417 | } |
| 418 | |
| 419 | /** |
| 420 | * @throws ClassCastException {@inheritDoc} |
| 421 | * @throws NullPointerException if {@code fromElement} is null |
| 422 | * @throws IllegalArgumentException {@inheritDoc} |
| 423 | */ |
| 424 | public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { |
| 425 | return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive)); |
| 426 | } |
| 427 | |
| 428 | /** |
| 429 | * @throws ClassCastException {@inheritDoc} |
| 430 | * @throws NullPointerException if {@code fromElement} or |
| 431 | * {@code toElement} is null |
| 432 | * @throws IllegalArgumentException {@inheritDoc} |
| 433 | */ |
| 434 | public NavigableSet<E> subSet(E fromElement, E toElement) { |
| 435 | return subSet(fromElement, true, toElement, false); |
| 436 | } |
| 437 | |
| 438 | /** |
| 439 | * @throws ClassCastException {@inheritDoc} |
| 440 | * @throws NullPointerException if {@code toElement} is null |
| 441 | * @throws IllegalArgumentException {@inheritDoc} |
| 442 | */ |
| 443 | public NavigableSet<E> headSet(E toElement) { |
| 444 | return headSet(toElement, false); |
| 445 | } |
| 446 | |
| 447 | /** |
| 448 | * @throws ClassCastException {@inheritDoc} |
| 449 | * @throws NullPointerException if {@code fromElement} is null |
| 450 | * @throws IllegalArgumentException {@inheritDoc} |
| 451 | */ |
| 452 | public NavigableSet<E> tailSet(E fromElement) { |
| 453 | return tailSet(fromElement, true); |
| 454 | } |
| 455 | |
| 456 | /** |
| 457 | * Returns a reverse order view of the elements contained in this set. |
| 458 | * The descending set is backed by this set, so changes to the set are |
| 459 | * reflected in the descending set, and vice-versa. |
| 460 | * |
| 461 | * <p>The returned set has an ordering equivalent to |
| 462 | * <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>. |
| 463 | * The expression {@code s.descendingSet().descendingSet()} returns a |
| 464 | * view of {@code s} essentially equivalent to {@code s}. |
| 465 | * |
| 466 | * @return a reverse order view of this set |
| 467 | */ |
| 468 | public NavigableSet<E> descendingSet() { |
| 469 | return new ConcurrentSkipListSet(m.descendingMap()); |
| 470 | } |
| 471 | |
| 472 | // Support for resetting map in clone |
| 473 | private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| 474 | private static final long mapOffset; |
| 475 | static { |
| 476 | try { |
| 477 | mapOffset = unsafe.objectFieldOffset |
| 478 | (ConcurrentSkipListSet.class.getDeclaredField("m")); |
| 479 | } catch (Exception ex) { throw new Error(ex); } |
| 480 | } |
| 481 | private void setMap(ConcurrentNavigableMap<E,Object> map) { |
| 482 | unsafe.putObjectVolatile(this, mapOffset, map); |
| 483 | } |
| 484 | |
| 485 | } |