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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 | |||
| 39 | /** | ||
| 40 | * A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList} | ||
| 41 | * for all of its operations. Thus, it shares the same basic properties: | ||
| 42 | * <ul> | ||
| 43 | * <li>It is best suited for applications in which set sizes generally | ||
| 44 | * stay small, read-only operations | ||
| 45 | * vastly outnumber mutative operations, and you need | ||
| 46 | * to prevent interference among threads during traversal. | ||
| 47 | * <li>It is thread-safe. | ||
| 48 | * <li>Mutative operations (<tt>add</tt>, <tt>set</tt>, <tt>remove</tt>, etc.) | ||
| 49 | * are expensive since they usually entail copying the entire underlying | ||
| 50 | * array. | ||
| 51 | * <li>Iterators do not support the mutative <tt>remove</tt> operation. | ||
| 52 | * <li>Traversal via iterators is fast and cannot encounter | ||
| 53 | * interference from other threads. Iterators rely on | ||
| 54 | * unchanging snapshots of the array at the time the iterators were | ||
| 55 | * constructed. | ||
| 56 | * </ul> | ||
| 57 | * | ||
| 58 | * <p> <b>Sample Usage.</b> The following code sketch uses a | ||
| 59 | * copy-on-write set to maintain a set of Handler objects that | ||
| 60 | * perform some action upon state updates. | ||
| 61 | * | ||
| 62 | * <pre> {@code | ||
| 63 | * class Handler { void handle(); ... } | ||
| 64 | * | ||
| 65 | * class X { | ||
| 66 | * private final CopyOnWriteArraySet<Handler> handlers | ||
| 67 | * = new CopyOnWriteArraySet<Handler>(); | ||
| 68 | * public void addHandler(Handler h) { handlers.add(h); } | ||
| 69 | * | ||
| 70 | * private long internalState; | ||
| 71 | * private synchronized void changeState() { internalState = ...; } | ||
| 72 | * | ||
| 73 | * public void update() { | ||
| 74 | * changeState(); | ||
| 75 | * for (Handler handler : handlers) | ||
| 76 | * handler.handle(); | ||
| 77 | * } | ||
| 78 | * }}</pre> | ||
| 79 | * | ||
| 80 | * <p>This class is a member of the | ||
| 81 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 82 | * Java Collections Framework</a>. | ||
| 83 | * | ||
| 84 | * @see CopyOnWriteArrayList | ||
| 85 | * @since 1.5 | ||
| 86 | * @author Doug Lea | ||
| 87 | * @param <E> the type of elements held in this collection | ||
| 88 | */ | ||
| 89 | public class CopyOnWriteArraySet<E> extends AbstractSet<E> | ||
| 90 | implements java.io.Serializable { | ||
| 91 | private static final long serialVersionUID = 5457747651344034263L; | ||
| 92 | |||
| 93 | private final CopyOnWriteArrayList<E> al; | ||
| 94 | |||
| 95 | /** | ||
| 96 | * Creates an empty set. | ||
| 97 | */ | ||
| 98 | public CopyOnWriteArraySet() { | ||
| 99 | al = new CopyOnWriteArrayList<E>(); | ||
| 100 | } | ||
| 101 | |||
| 102 | /** | ||
| 103 | * Creates a set containing all of the elements of the specified | ||
| 104 | * collection. | ||
| 105 | * | ||
| 106 | * @param c the collection of elements to initially contain | ||
| 107 | * @throws NullPointerException if the specified collection is null | ||
| 108 | */ | ||
| 109 | public CopyOnWriteArraySet(Collection<? extends E> c) { | ||
| 110 | al = new CopyOnWriteArrayList<E>(); | ||
| 111 | al.addAllAbsent(c); | ||
| 112 | } | ||
| 113 | |||
| 114 | /** | ||
| 115 | * Returns the number of elements in this set. | ||
| 116 | * | ||
| 117 | * @return the number of elements in this set | ||
| 118 | */ | ||
| 119 | public int size() { | ||
| 120 | return al.size(); | ||
| 121 | } | ||
| 122 | |||
| 123 | /** | ||
| 124 | * Returns <tt>true</tt> if this set contains no elements. | ||
| 125 | * | ||
| 126 | * @return <tt>true</tt> if this set contains no elements | ||
| 127 | */ | ||
| 128 | public boolean isEmpty() { | ||
| 129 | return al.isEmpty(); | ||
| 130 | } | ||
| 131 | |||
| 132 | /** | ||
| 133 | * Returns <tt>true</tt> if this set contains the specified element. | ||
| 134 | * More formally, returns <tt>true</tt> if and only if this set | ||
| 135 | * contains an element <tt>e</tt> such that | ||
| 136 | * <tt>(o==null ? e==null : o.equals(e))</tt>. | ||
| 137 | * | ||
| 138 | * @param o element whose presence in this set is to be tested | ||
| 139 | * @return <tt>true</tt> if this set contains the specified element | ||
| 140 | */ | ||
| 141 | public boolean contains(Object o) { | ||
| 142 | return al.contains(o); | ||
| 143 | } | ||
| 144 | |||
| 145 | /** | ||
| 146 | * Returns an array containing all of the elements in this set. | ||
| 147 | * If this set makes any guarantees as to what order its elements | ||
| 148 | * are returned by its iterator, this method must return the | ||
| 149 | * elements in the same order. | ||
| 150 | * | ||
| 151 | * <p>The returned array will be "safe" in that no references to it | ||
| 152 | * are maintained by this set. (In other words, this method must | ||
| 153 | * allocate a new array even if this set is backed by an array). | ||
| 154 | * The caller is thus free to modify the returned array. | ||
| 155 | * | ||
| 156 | * <p>This method acts as bridge between array-based and collection-based | ||
| 157 | * APIs. | ||
| 158 | * | ||
| 159 | * @return an array containing all the elements in this set | ||
| 160 | */ | ||
| 161 | public Object[] toArray() { | ||
| 162 | return al.toArray(); | ||
| 163 | } | ||
| 164 | |||
| 165 | /** | ||
| 166 | * Returns an array containing all of the elements in this set; the | ||
| 167 | * runtime type of the returned array is that of the specified array. | ||
| 168 | * If the set fits in the specified array, it is returned therein. | ||
| 169 | * Otherwise, a new array is allocated with the runtime type of the | ||
| 170 | * specified array and the size of this set. | ||
| 171 | * | ||
| 172 | * <p>If this set fits in the specified array with room to spare | ||
| 173 | * (i.e., the array has more elements than this set), the element in | ||
| 174 | * the array immediately following the end of the set is set to | ||
| 175 | * <tt>null</tt>. (This is useful in determining the length of this | ||
| 176 | * set <i>only</i> if the caller knows that this set does not contain | ||
| 177 | * any null elements.) | ||
| 178 | * | ||
| 179 | * <p>If this set makes any guarantees as to what order its elements | ||
| 180 | * are returned by its iterator, this method must return the elements | ||
| 181 | * in the same order. | ||
| 182 | * | ||
| 183 | * <p>Like the {@link #toArray()} method, this method acts as bridge between | ||
| 184 | * array-based and collection-based APIs. Further, this method allows | ||
| 185 | * precise control over the runtime type of the output array, and may, | ||
| 186 | * under certain circumstances, be used to save allocation costs. | ||
| 187 | * | ||
| 188 | * <p>Suppose <tt>x</tt> is a set known to contain only strings. | ||
| 189 | * The following code can be used to dump the set into a newly allocated | ||
| 190 | * array of <tt>String</tt>: | ||
| 191 | * | ||
| 192 | * <pre> | ||
| 193 | * String[] y = x.toArray(new String[0]);</pre> | ||
| 194 | * | ||
| 195 | * Note that <tt>toArray(new Object[0])</tt> is identical in function to | ||
| 196 | * <tt>toArray()</tt>. | ||
| 197 | * | ||
| 198 | * @param a the array into which the elements of this set are to be | ||
| 199 | * stored, if it is big enough; otherwise, a new array of the same | ||
| 200 | * runtime type is allocated for this purpose. | ||
| 201 | * @return an array containing all the elements in this set | ||
| 202 | * @throws ArrayStoreException if the runtime type of the specified array | ||
| 203 | * is not a supertype of the runtime type of every element in this | ||
| 204 | * set | ||
| 205 | * @throws NullPointerException if the specified array is null | ||
| 206 | */ | ||
| 207 | public <T> T[] toArray(T[] a) { | ||
| 208 | return al.toArray(a); | ||
| 209 | } | ||
| 210 | |||
| 211 | /** | ||
| 212 | * Removes all of the elements from this set. | ||
| 213 | * The set will be empty after this call returns. | ||
| 214 | */ | ||
| 215 | public void clear() { | ||
| 216 | al.clear(); | ||
| 217 | } | ||
| 218 | |||
| 219 | /** | ||
| 220 | * Removes the specified element from this set if it is present. | ||
| 221 | * More formally, removes an element <tt>e</tt> such that | ||
| 222 | * <tt>(o==null ? e==null : o.equals(e))</tt>, | ||
| 223 | * if this set contains such an element. Returns <tt>true</tt> if | ||
| 224 | * this set contained the element (or equivalently, if this set | ||
| 225 | * changed as a result of the call). (This set will not contain the | ||
| 226 | * element once the call returns.) | ||
| 227 | * | ||
| 228 | * @param o object to be removed from this set, if present | ||
| 229 | * @return <tt>true</tt> if this set contained the specified element | ||
| 230 | */ | ||
| 231 | public boolean remove(Object o) { | ||
| 232 | return al.remove(o); | ||
| 233 | } | ||
| 234 | |||
| 235 | /** | ||
| 236 | * Adds the specified element to this set if it is not already present. | ||
| 237 | * More formally, adds the specified element <tt>e</tt> to this set if | ||
| 238 | * the set contains no element <tt>e2</tt> such that | ||
| 239 | * <tt>(e==null ? e2==null : e.equals(e2))</tt>. | ||
| 240 | * If this set already contains the element, the call leaves the set | ||
| 241 | * unchanged and returns <tt>false</tt>. | ||
| 242 | * | ||
| 243 | * @param e element to be added to this set | ||
| 244 | * @return <tt>true</tt> if this set did not already contain the specified | ||
| 245 | * element | ||
| 246 | */ | ||
| 247 | public boolean add(E e) { | ||
| 248 | return al.addIfAbsent(e); | ||
| 249 | } | ||
| 250 | |||
| 251 | /** | ||
| 252 | * Returns <tt>true</tt> if this set contains all of the elements of the | ||
| 253 | * specified collection. If the specified collection is also a set, this | ||
| 254 | * method returns <tt>true</tt> if it is a <i>subset</i> of this set. | ||
| 255 | * | ||
| 256 | * @param c collection to be checked for containment in this set | ||
| 257 | * @return <tt>true</tt> if this set contains all of the elements of the | ||
| 258 | * specified collection | ||
| 259 | * @throws NullPointerException if the specified collection is null | ||
| 260 | * @see #contains(Object) | ||
| 261 | */ | ||
| 262 | public boolean containsAll(Collection<?> c) { | ||
| 263 | return al.containsAll(c); | ||
| 264 | } | ||
| 265 | |||
| 266 | /** | ||
| 267 | * Adds all of the elements in the specified collection to this set if | ||
| 268 | * they're not already present. If the specified collection is also a | ||
| 269 | * set, the <tt>addAll</tt> operation effectively modifies this set so | ||
| 270 | * that its value is the <i>union</i> of the two sets. The behavior of | ||
| 271 | * this operation is undefined if the specified collection is modified | ||
| 272 | * while the operation is in progress. | ||
| 273 | * | ||
| 274 | * @param c collection containing elements to be added to this set | ||
| 275 | * @return <tt>true</tt> if this set changed as a result of the call | ||
| 276 | * @throws NullPointerException if the specified collection is null | ||
| 277 | * @see #add(Object) | ||
| 278 | */ | ||
| 279 | public boolean addAll(Collection<? extends E> c) { | ||
| 280 | return al.addAllAbsent(c) > 0; | ||
| 281 | } | ||
| 282 | |||
| 283 | /** | ||
| 284 | * Removes from this set all of its elements that are contained in the | ||
| 285 | * specified collection. If the specified collection is also a set, | ||
| 286 | * this operation effectively modifies this set so that its value is the | ||
| 287 | * <i>asymmetric set difference</i> of the two sets. | ||
| 288 | * | ||
| 289 | * @param c collection containing elements to be removed from this set | ||
| 290 | * @return <tt>true</tt> if this set changed as a result of the call | ||
| 291 | * @throws ClassCastException if the class of an element of this set | ||
| 292 | * is incompatible with the specified collection (optional) | ||
| 293 | * @throws NullPointerException if this set contains a null element and the | ||
| 294 | * specified collection does not permit null elements (optional), | ||
| 295 | * or if the specified collection is null | ||
| 296 | * @see #remove(Object) | ||
| 297 | */ | ||
| 298 | public boolean removeAll(Collection<?> c) { | ||
| 299 | return al.removeAll(c); | ||
| 300 | } | ||
| 301 | |||
| 302 | /** | ||
| 303 | * Retains only the elements in this set that are contained in the | ||
| 304 | * specified collection. In other words, removes from this set all of | ||
| 305 | * its elements that are not contained in the specified collection. If | ||
| 306 | * the specified collection is also a set, this operation effectively | ||
| 307 | * modifies this set so that its value is the <i>intersection</i> of the | ||
| 308 | * two sets. | ||
| 309 | * | ||
| 310 | * @param c collection containing elements to be retained in this set | ||
| 311 | * @return <tt>true</tt> if this set changed as a result of the call | ||
| 312 | * @throws ClassCastException if the class of an element of this set | ||
| 313 | * is incompatible with the specified collection (optional) | ||
| 314 | * @throws NullPointerException if this set contains a null element and the | ||
| 315 | * specified collection does not permit null elements (optional), | ||
| 316 | * or if the specified collection is null | ||
| 317 | * @see #remove(Object) | ||
| 318 | */ | ||
| 319 | public boolean retainAll(Collection<?> c) { | ||
| 320 | return al.retainAll(c); | ||
| 321 | } | ||
| 322 | |||
| 323 | /** | ||
| 324 | * Returns an iterator over the elements contained in this set | ||
| 325 | * in the order in which these elements were added. | ||
| 326 | * | ||
| 327 | * <p>The returned iterator provides a snapshot of the state of the set | ||
| 328 | * when the iterator was constructed. No synchronization is needed while | ||
| 329 | * traversing the iterator. The iterator does <em>NOT</em> support the | ||
| 330 | * <tt>remove</tt> method. | ||
| 331 | * | ||
| 332 | * @return an iterator over the elements in this set | ||
| 333 | */ | ||
| 334 | public Iterator<E> iterator() { | ||
| 335 | return al.iterator(); | ||
| 336 | } | ||
| 337 | |||
| 338 | /** | ||
| 339 | * Compares the specified object with this set for equality. | ||
| 340 | * Returns {@code true} if the specified object is the same object | ||
| 341 | * as this object, or if it is also a {@link Set} and the elements | ||
| 342 | * returned by an {@linkplain List#iterator() iterator} over the | ||
| 343 | * specified set are the same as the elements returned by an | ||
| 344 | * iterator over this set. More formally, the two iterators are | ||
| 345 | * considered to return the same elements if they return the same | ||
| 346 | * number of elements and for every element {@code e1} returned by | ||
| 347 | * the iterator over the specified set, there is an element | ||
| 348 | * {@code e2} returned by the iterator over this set such that | ||
| 349 | * {@code (e1==null ? e2==null : e1.equals(e2))}. | ||
| 350 | * | ||
| 351 | * @param o object to be compared for equality with this set | ||
| 352 | * @return {@code true} if the specified object is equal to this set | ||
| 353 | */ | ||
| 354 | public boolean equals(Object o) { | ||
| 355 | if (o == this) | ||
| 356 | return true; | ||
| 357 | if (!(o instanceof Set)) | ||
| 358 | return false; | ||
| 359 | Set<?> set = (Set<?>)(o); | ||
| 360 | Iterator<?> it = set.iterator(); | ||
| 361 | |||
| 362 | // Uses O(n^2) algorithm that is only appropriate | ||
| 363 | // for small sets, which CopyOnWriteArraySets should be. | ||
| 364 | |||
| 365 | // Use a single snapshot of underlying array | ||
| 366 | Object[] elements = al.getArray(); | ||
| 367 | int len = elements.length; | ||
| 368 | // Mark matched elements to avoid re-checking | ||
| 369 | boolean[] matched = new boolean[len]; | ||
| 370 | int k = 0; | ||
| 371 | outer: while (it.hasNext()) { | ||
| 372 | if (++k > len) | ||
| 373 | return false; | ||
| 374 | Object x = it.next(); | ||
| 375 | for (int i = 0; i < len; ++i) { | ||
| 376 | if (!matched[i] && eq(x, elements[i])) { | ||
| 377 | matched[i] = true; | ||
| 378 | continue outer; | ||
| 379 | } | ||
| 380 | } | ||
| 381 | return false; | ||
| 382 | } | ||
| 383 | return k == len; | ||
| 384 | } | ||
| 385 | |||
| 386 | /** | ||
| 387 | * Test for equality, coping with nulls. | ||
| 388 | */ | ||
| 389 | private static boolean eq(Object o1, Object o2) { | ||
| 390 | return (o1 == null ? o2 == null : o1.equals(o2)); | ||
| 391 | } | ||
| 392 | } | ||