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 | |
| 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> |
| 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 | * } |
| 79 | * </pre> |
| 80 | * |
| 81 | * <p>This class is a member of the |
| 82 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 83 | * Java Collections Framework</a>. |
| 84 | * |
| 85 | * @see CopyOnWriteArrayList |
| 86 | * @since 1.5 |
| 87 | * @author Doug Lea |
| 88 | * @param <E> the type of elements held in this collection |
| 89 | */ |
| 90 | public class CopyOnWriteArraySet<E> extends AbstractSet<E> |
| 91 | implements java.io.Serializable { |
| 92 | private static final long serialVersionUID = 5457747651344034263L; |
| 93 | |
| 94 | private final CopyOnWriteArrayList<E> al; |
| 95 | |
| 96 | /** |
| 97 | * Creates an empty set. |
| 98 | */ |
| 99 | public CopyOnWriteArraySet() { |
| 100 | al = new CopyOnWriteArrayList<E>(); |
| 101 | } |
| 102 | |
| 103 | /** |
| 104 | * Creates a set containing all of the elements of the specified |
| 105 | * collection. |
| 106 | * |
| 107 | * @param c the collection of elements to initially contain |
| 108 | * @throws NullPointerException if the specified collection is null |
| 109 | */ |
| 110 | public CopyOnWriteArraySet(Collection<? extends E> c) { |
| 111 | al = new CopyOnWriteArrayList<E>(); |
| 112 | al.addAllAbsent(c); |
| 113 | } |
| 114 | |
| 115 | /** |
| 116 | * Returns the number of elements in this set. |
| 117 | * |
| 118 | * @return the number of elements in this set |
| 119 | */ |
| 120 | public int size() { |
| 121 | return al.size(); |
| 122 | } |
| 123 | |
| 124 | /** |
| 125 | * Returns <tt>true</tt> if this set contains no elements. |
| 126 | * |
| 127 | * @return <tt>true</tt> if this set contains no elements |
| 128 | */ |
| 129 | public boolean isEmpty() { |
| 130 | return al.isEmpty(); |
| 131 | } |
| 132 | |
| 133 | /** |
| 134 | * Returns <tt>true</tt> if this set contains the specified element. |
| 135 | * More formally, returns <tt>true</tt> if and only if this set |
| 136 | * contains an element <tt>e</tt> such that |
| 137 | * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| 138 | * |
| 139 | * @param o element whose presence in this set is to be tested |
| 140 | * @return <tt>true</tt> if this set contains the specified element |
| 141 | */ |
| 142 | public boolean contains(Object o) { |
| 143 | return al.contains(o); |
| 144 | } |
| 145 | |
| 146 | /** |
| 147 | * Returns an array containing all of the elements in this set. |
| 148 | * If this set makes any guarantees as to what order its elements |
| 149 | * are returned by its iterator, this method must return the |
| 150 | * elements in the same order. |
| 151 | * |
| 152 | * <p>The returned array will be "safe" in that no references to it |
| 153 | * are maintained by this set. (In other words, this method must |
| 154 | * allocate a new array even if this set is backed by an array). |
| 155 | * The caller is thus free to modify the returned array. |
| 156 | * |
| 157 | * <p>This method acts as bridge between array-based and collection-based |
| 158 | * APIs. |
| 159 | * |
| 160 | * @return an array containing all the elements in this set |
| 161 | */ |
| 162 | public Object[] toArray() { |
| 163 | return al.toArray(); |
| 164 | } |
| 165 | |
| 166 | /** |
| 167 | * Returns an array containing all of the elements in this set; the |
| 168 | * runtime type of the returned array is that of the specified array. |
| 169 | * If the set fits in the specified array, it is returned therein. |
| 170 | * Otherwise, a new array is allocated with the runtime type of the |
| 171 | * specified array and the size of this set. |
| 172 | * |
| 173 | * <p>If this set fits in the specified array with room to spare |
| 174 | * (i.e., the array has more elements than this set), the element in |
| 175 | * the array immediately following the end of the set is set to |
| 176 | * <tt>null</tt>. (This is useful in determining the length of this |
| 177 | * set <i>only</i> if the caller knows that this set does not contain |
| 178 | * any null elements.) |
| 179 | * |
| 180 | * <p>If this set makes any guarantees as to what order its elements |
| 181 | * are returned by its iterator, this method must return the elements |
| 182 | * in the same order. |
| 183 | * |
| 184 | * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| 185 | * array-based and collection-based APIs. Further, this method allows |
| 186 | * precise control over the runtime type of the output array, and may, |
| 187 | * under certain circumstances, be used to save allocation costs. |
| 188 | * |
| 189 | * <p>Suppose <tt>x</tt> is a set known to contain only strings. |
| 190 | * The following code can be used to dump the set into a newly allocated |
| 191 | * array of <tt>String</tt>: |
| 192 | * |
| 193 | * <pre> |
| 194 | * String[] y = x.toArray(new String[0]);</pre> |
| 195 | * |
| 196 | * Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| 197 | * <tt>toArray()</tt>. |
| 198 | * |
| 199 | * @param a the array into which the elements of this set are to be |
| 200 | * stored, if it is big enough; otherwise, a new array of the same |
| 201 | * runtime type is allocated for this purpose. |
| 202 | * @return an array containing all the elements in this set |
| 203 | * @throws ArrayStoreException if the runtime type of the specified array |
| 204 | * is not a supertype of the runtime type of every element in this |
| 205 | * set |
| 206 | * @throws NullPointerException if the specified array is null |
| 207 | */ |
| 208 | public <T> T[] toArray(T[] a) { |
| 209 | return al.toArray(a); |
| 210 | } |
| 211 | |
| 212 | /** |
| 213 | * Removes all of the elements from this set. |
| 214 | * The set will be empty after this call returns. |
| 215 | */ |
| 216 | public void clear() { |
| 217 | al.clear(); |
| 218 | } |
| 219 | |
| 220 | /** |
| 221 | * Removes the specified element from this set if it is present. |
| 222 | * More formally, removes an element <tt>e</tt> such that |
| 223 | * <tt>(o==null ? e==null : o.equals(e))</tt>, |
| 224 | * if this set contains such an element. Returns <tt>true</tt> if |
| 225 | * this set contained the element (or equivalently, if this set |
| 226 | * changed as a result of the call). (This set will not contain the |
| 227 | * element once the call returns.) |
| 228 | * |
| 229 | * @param o object to be removed from this set, if present |
| 230 | * @return <tt>true</tt> if this set contained the specified element |
| 231 | */ |
| 232 | public boolean remove(Object o) { |
| 233 | return al.remove(o); |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Adds the specified element to this set if it is not already present. |
| 238 | * More formally, adds the specified element <tt>e</tt> to this set if |
| 239 | * the set contains no element <tt>e2</tt> such that |
| 240 | * <tt>(e==null ? e2==null : e.equals(e2))</tt>. |
| 241 | * If this set already contains the element, the call leaves the set |
| 242 | * unchanged and returns <tt>false</tt>. |
| 243 | * |
| 244 | * @param e element to be added to this set |
| 245 | * @return <tt>true</tt> if this set did not already contain the specified |
| 246 | * element |
| 247 | */ |
| 248 | public boolean add(E e) { |
| 249 | return al.addIfAbsent(e); |
| 250 | } |
| 251 | |
| 252 | /** |
| 253 | * Returns <tt>true</tt> if this set contains all of the elements of the |
| 254 | * specified collection. If the specified collection is also a set, this |
| 255 | * method returns <tt>true</tt> if it is a <i>subset</i> of this set. |
| 256 | * |
| 257 | * @param c collection to be checked for containment in this set |
| 258 | * @return <tt>true</tt> if this set contains all of the elements of the |
| 259 | * specified collection |
| 260 | * @throws NullPointerException if the specified collection is null |
| 261 | * @see #contains(Object) |
| 262 | */ |
| 263 | public boolean containsAll(Collection<?> c) { |
| 264 | return al.containsAll(c); |
| 265 | } |
| 266 | |
| 267 | /** |
| 268 | * Adds all of the elements in the specified collection to this set if |
| 269 | * they're not already present. If the specified collection is also a |
| 270 | * set, the <tt>addAll</tt> operation effectively modifies this set so |
| 271 | * that its value is the <i>union</i> of the two sets. The behavior of |
| 272 | * this operation is undefined if the specified collection is modified |
| 273 | * while the operation is in progress. |
| 274 | * |
| 275 | * @param c collection containing elements to be added to this set |
| 276 | * @return <tt>true</tt> if this set changed as a result of the call |
| 277 | * @throws NullPointerException if the specified collection is null |
| 278 | * @see #add(Object) |
| 279 | */ |
| 280 | public boolean addAll(Collection<? extends E> c) { |
| 281 | return al.addAllAbsent(c) > 0; |
| 282 | } |
| 283 | |
| 284 | /** |
| 285 | * Removes from this set all of its elements that are contained in the |
| 286 | * specified collection. If the specified collection is also a set, |
| 287 | * this operation effectively modifies this set so that its value is the |
| 288 | * <i>asymmetric set difference</i> of the two sets. |
| 289 | * |
| 290 | * @param c collection containing elements to be removed from this set |
| 291 | * @return <tt>true</tt> if this set changed as a result of the call |
| 292 | * @throws ClassCastException if the class of an element of this set |
| 293 | * is incompatible with the specified collection (optional) |
| 294 | * @throws NullPointerException if this set contains a null element and the |
| 295 | * specified collection does not permit null elements (optional), |
| 296 | * or if the specified collection is null |
| 297 | * @see #remove(Object) |
| 298 | */ |
| 299 | public boolean removeAll(Collection<?> c) { |
| 300 | return al.removeAll(c); |
| 301 | } |
| 302 | |
| 303 | /** |
| 304 | * Retains only the elements in this set that are contained in the |
| 305 | * specified collection. In other words, removes from this set all of |
| 306 | * its elements that are not contained in the specified collection. If |
| 307 | * the specified collection is also a set, this operation effectively |
| 308 | * modifies this set so that its value is the <i>intersection</i> of the |
| 309 | * two sets. |
| 310 | * |
| 311 | * @param c collection containing elements to be retained in this set |
| 312 | * @return <tt>true</tt> if this set changed as a result of the call |
| 313 | * @throws ClassCastException if the class of an element of this set |
| 314 | * is incompatible with the specified collection (optional) |
| 315 | * @throws NullPointerException if this set contains a null element and the |
| 316 | * specified collection does not permit null elements (optional), |
| 317 | * or if the specified collection is null |
| 318 | * @see #remove(Object) |
| 319 | */ |
| 320 | public boolean retainAll(Collection<?> c) { |
| 321 | return al.retainAll(c); |
| 322 | } |
| 323 | |
| 324 | /** |
| 325 | * Returns an iterator over the elements contained in this set |
| 326 | * in the order in which these elements were added. |
| 327 | * |
| 328 | * <p>The returned iterator provides a snapshot of the state of the set |
| 329 | * when the iterator was constructed. No synchronization is needed while |
| 330 | * traversing the iterator. The iterator does <em>NOT</em> support the |
| 331 | * <tt>remove</tt> method. |
| 332 | * |
| 333 | * @return an iterator over the elements in this set |
| 334 | */ |
| 335 | public Iterator<E> iterator() { |
| 336 | return al.iterator(); |
| 337 | } |
| 338 | |
| 339 | /** |
| 340 | * Compares the specified object with this set for equality. |
| 341 | * Returns {@code true} if the specified object is the same object |
| 342 | * as this object, or if it is also a {@link Set} and the elements |
| 343 | * returned by an {@linkplain List#iterator() iterator} over the |
| 344 | * specified set are the same as the elements returned by an |
| 345 | * iterator over this set. More formally, the two iterators are |
| 346 | * considered to return the same elements if they return the same |
| 347 | * number of elements and for every element {@code e1} returned by |
| 348 | * the iterator over the specified set, there is an element |
| 349 | * {@code e2} returned by the iterator over this set such that |
| 350 | * {@code (e1==null ? e2==null : e1.equals(e2))}. |
| 351 | * |
| 352 | * @param o object to be compared for equality with this set |
| 353 | * @return {@code true} if the specified object is equal to this set |
| 354 | */ |
| 355 | public boolean equals(Object o) { |
| 356 | if (o == this) |
| 357 | return true; |
| 358 | if (!(o instanceof Set)) |
| 359 | return false; |
| 360 | Set<?> set = (Set<?>)(o); |
| 361 | Iterator<?> it = set.iterator(); |
| 362 | |
| 363 | // Uses O(n^2) algorithm that is only appropriate |
| 364 | // for small sets, which CopyOnWriteArraySets should be. |
| 365 | |
| 366 | // Use a single snapshot of underlying array |
| 367 | Object[] elements = al.getArray(); |
| 368 | int len = elements.length; |
| 369 | // Mark matched elements to avoid re-checking |
| 370 | boolean[] matched = new boolean[len]; |
| 371 | int k = 0; |
| 372 | outer: while (it.hasNext()) { |
| 373 | if (++k > len) |
| 374 | return false; |
| 375 | Object x = it.next(); |
| 376 | for (int i = 0; i < len; ++i) { |
| 377 | if (!matched[i] && eq(x, elements[i])) { |
| 378 | matched[i] = true; |
| 379 | continue outer; |
| 380 | } |
| 381 | } |
| 382 | return false; |
| 383 | } |
| 384 | return k == len; |
| 385 | } |
| 386 | |
| 387 | /** |
| 388 | * Test for equality, coping with nulls. |
| 389 | */ |
| 390 | private static boolean eq(Object o1, Object o2) { |
| 391 | return (o1 == null ? o2 == null : o1.equals(o2)); |
| 392 | } |
| 393 | } |