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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 | |||
| 38 | import java.util.Collection; | ||
| 39 | import java.util.Queue; | ||
| 40 | |||
| 41 | /** | ||
| 42 | * A {@link java.util.Queue} that additionally supports operations | ||
| 43 | * that wait for the queue to become non-empty when retrieving an | ||
| 44 | * element, and wait for space to become available in the queue when | ||
| 45 | * storing an element. | ||
| 46 | * | ||
| 47 | * <p><tt>BlockingQueue</tt> methods come in four forms, with different ways | ||
| 48 | * of handling operations that cannot be satisfied immediately, but may be | ||
| 49 | * satisfied at some point in the future: | ||
| 50 | * one throws an exception, the second returns a special value (either | ||
| 51 | * <tt>null</tt> or <tt>false</tt>, depending on the operation), the third | ||
| 52 | * blocks the current thread indefinitely until the operation can succeed, | ||
| 53 | * and the fourth blocks for only a given maximum time limit before giving | ||
| 54 | * up. These methods are summarized in the following table: | ||
| 55 | * | ||
| 56 | * <p> | ||
| 57 | * <table BORDER CELLPADDING=3 CELLSPACING=1> | ||
| 58 | * <tr> | ||
| 59 | * <td></td> | ||
| 60 | * <td ALIGN=CENTER><em>Throws exception</em></td> | ||
| 61 | * <td ALIGN=CENTER><em>Special value</em></td> | ||
| 62 | * <td ALIGN=CENTER><em>Blocks</em></td> | ||
| 63 | * <td ALIGN=CENTER><em>Times out</em></td> | ||
| 64 | * </tr> | ||
| 65 | * <tr> | ||
| 66 | * <td><b>Insert</b></td> | ||
| 67 | * <td>{@link #add add(e)}</td> | ||
| 68 | * <td>{@link #offer offer(e)}</td> | ||
| 69 | * <td>{@link #put put(e)}</td> | ||
| 70 | * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td> | ||
| 71 | * </tr> | ||
| 72 | * <tr> | ||
| 73 | * <td><b>Remove</b></td> | ||
| 74 | * <td>{@link #remove remove()}</td> | ||
| 75 | * <td>{@link #poll poll()}</td> | ||
| 76 | * <td>{@link #take take()}</td> | ||
| 77 | * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td> | ||
| 78 | * </tr> | ||
| 79 | * <tr> | ||
| 80 | * <td><b>Examine</b></td> | ||
| 81 | * <td>{@link #element element()}</td> | ||
| 82 | * <td>{@link #peek peek()}</td> | ||
| 83 | * <td><em>not applicable</em></td> | ||
| 84 | * <td><em>not applicable</em></td> | ||
| 85 | * </tr> | ||
| 86 | * </table> | ||
| 87 | * | ||
| 88 | * <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements. | ||
| 89 | * Implementations throw <tt>NullPointerException</tt> on attempts | ||
| 90 | * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A | ||
| 91 | * <tt>null</tt> is used as a sentinel value to indicate failure of | ||
| 92 | * <tt>poll</tt> operations. | ||
| 93 | * | ||
| 94 | * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given | ||
| 95 | * time it may have a <tt>remainingCapacity</tt> beyond which no | ||
| 96 | * additional elements can be <tt>put</tt> without blocking. | ||
| 97 | * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always | ||
| 98 | * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>. | ||
| 99 | * | ||
| 100 | * <p> <tt>BlockingQueue</tt> implementations are designed to be used | ||
| 101 | * primarily for producer-consumer queues, but additionally support | ||
| 102 | * the {@link java.util.Collection} interface. So, for example, it is | ||
| 103 | * possible to remove an arbitrary element from a queue using | ||
| 104 | * <tt>remove(x)</tt>. However, such operations are in general | ||
| 105 | * <em>not</em> performed very efficiently, and are intended for only | ||
| 106 | * occasional use, such as when a queued message is cancelled. | ||
| 107 | * | ||
| 108 | * <p> <tt>BlockingQueue</tt> implementations are thread-safe. All | ||
| 109 | * queuing methods achieve their effects atomically using internal | ||
| 110 | * locks or other forms of concurrency control. However, the | ||
| 111 | * <em>bulk</em> Collection operations <tt>addAll</tt>, | ||
| 112 | * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are | ||
| 113 | * <em>not</em> necessarily performed atomically unless specified | ||
| 114 | * otherwise in an implementation. So it is possible, for example, for | ||
| 115 | * <tt>addAll(c)</tt> to fail (throwing an exception) after adding | ||
| 116 | * only some of the elements in <tt>c</tt>. | ||
| 117 | * | ||
| 118 | * <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support | ||
| 119 | * any kind of "close" or "shutdown" operation to | ||
| 120 | * indicate that no more items will be added. The needs and usage of | ||
| 121 | * such features tend to be implementation-dependent. For example, a | ||
| 122 | * common tactic is for producers to insert special | ||
| 123 | * <em>end-of-stream</em> or <em>poison</em> objects, that are | ||
| 124 | * interpreted accordingly when taken by consumers. | ||
| 125 | * | ||
| 126 | * <p> | ||
| 127 | * Usage example, based on a typical producer-consumer scenario. | ||
| 128 | * Note that a <tt>BlockingQueue</tt> can safely be used with multiple | ||
| 129 | * producers and multiple consumers. | ||
| 130 | * <pre> | ||
| 131 | * class Producer implements Runnable { | ||
| 132 | * private final BlockingQueue queue; | ||
| 133 | * Producer(BlockingQueue q) { queue = q; } | ||
| 134 | * public void run() { | ||
| 135 | * try { | ||
| 136 | * while (true) { queue.put(produce()); } | ||
| 137 | * } catch (InterruptedException ex) { ... handle ...} | ||
| 138 | * } | ||
| 139 | * Object produce() { ... } | ||
| 140 | * } | ||
| 141 | * | ||
| 142 | * class Consumer implements Runnable { | ||
| 143 | * private final BlockingQueue queue; | ||
| 144 | * Consumer(BlockingQueue q) { queue = q; } | ||
| 145 | * public void run() { | ||
| 146 | * try { | ||
| 147 | * while (true) { consume(queue.take()); } | ||
| 148 | * } catch (InterruptedException ex) { ... handle ...} | ||
| 149 | * } | ||
| 150 | * void consume(Object x) { ... } | ||
| 151 | * } | ||
| 152 | * | ||
| 153 | * class Setup { | ||
| 154 | * void main() { | ||
| 155 | * BlockingQueue q = new SomeQueueImplementation(); | ||
| 156 | * Producer p = new Producer(q); | ||
| 157 | * Consumer c1 = new Consumer(q); | ||
| 158 | * Consumer c2 = new Consumer(q); | ||
| 159 | * new Thread(p).start(); | ||
| 160 | * new Thread(c1).start(); | ||
| 161 | * new Thread(c2).start(); | ||
| 162 | * } | ||
| 163 | * } | ||
| 164 | * </pre> | ||
| 165 | * | ||
| 166 | * <p>Memory consistency effects: As with other concurrent | ||
| 167 | * collections, actions in a thread prior to placing an object into a | ||
| 168 | * {@code BlockingQueue} | ||
| 169 | * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> | ||
| 170 | * actions subsequent to the access or removal of that element from | ||
| 171 | * the {@code BlockingQueue} in another thread. | ||
| 172 | * | ||
| 173 | * <p>This interface is a member of the | ||
| 174 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 175 | * Java Collections Framework</a>. | ||
| 176 | * | ||
| 177 | * @since 1.5 | ||
| 178 | * @author Doug Lea | ||
| 179 | * @param <E> the type of elements held in this collection | ||
| 180 | */ | ||
| 181 | public interface BlockingQueue<E> extends Queue<E> { | ||
| 182 | /** | ||
| 183 | * Inserts the specified element into this queue if it is possible to do | ||
| 184 | * so immediately without violating capacity restrictions, returning | ||
| 185 | * <tt>true</tt> upon success and throwing an | ||
| 186 | * <tt>IllegalStateException</tt> if no space is currently available. | ||
| 187 | * When using a capacity-restricted queue, it is generally preferable to | ||
| 188 | * use {@link #offer(Object) offer}. | ||
| 189 | * | ||
| 190 | * @param e the element to add | ||
| 191 | * @return <tt>true</tt> (as specified by {@link Collection#add}) | ||
| 192 | * @throws IllegalStateException if the element cannot be added at this | ||
| 193 | * time due to capacity restrictions | ||
| 194 | * @throws ClassCastException if the class of the specified element | ||
| 195 | * prevents it from being added to this queue | ||
| 196 | * @throws NullPointerException if the specified element is null | ||
| 197 | * @throws IllegalArgumentException if some property of the specified | ||
| 198 | * element prevents it from being added to this queue | ||
| 199 | */ | ||
| 200 | boolean add(E e); | ||
| 201 | |||
| 202 | /** | ||
| 203 | * Inserts the specified element into this queue if it is possible to do | ||
| 204 | * so immediately without violating capacity restrictions, returning | ||
| 205 | * <tt>true</tt> upon success and <tt>false</tt> if no space is currently | ||
| 206 | * available. When using a capacity-restricted queue, this method is | ||
| 207 | * generally preferable to {@link #add}, which can fail to insert an | ||
| 208 | * element only by throwing an exception. | ||
| 209 | * | ||
| 210 | * @param e the element to add | ||
| 211 | * @return <tt>true</tt> if the element was added to this queue, else | ||
| 212 | * <tt>false</tt> | ||
| 213 | * @throws ClassCastException if the class of the specified element | ||
| 214 | * prevents it from being added to this queue | ||
| 215 | * @throws NullPointerException if the specified element is null | ||
| 216 | * @throws IllegalArgumentException if some property of the specified | ||
| 217 | * element prevents it from being added to this queue | ||
| 218 | */ | ||
| 219 | boolean offer(E e); | ||
| 220 | |||
| 221 | /** | ||
| 222 | * Inserts the specified element into this queue, waiting if necessary | ||
| 223 | * for space to become available. | ||
| 224 | * | ||
| 225 | * @param e the element to add | ||
| 226 | * @throws InterruptedException if interrupted while waiting | ||
| 227 | * @throws ClassCastException if the class of the specified element | ||
| 228 | * prevents it from being added to this queue | ||
| 229 | * @throws NullPointerException if the specified element is null | ||
| 230 | * @throws IllegalArgumentException if some property of the specified | ||
| 231 | * element prevents it from being added to this queue | ||
| 232 | */ | ||
| 233 | void put(E e) throws InterruptedException; | ||
| 234 | |||
| 235 | /** | ||
| 236 | * Inserts the specified element into this queue, waiting up to the | ||
| 237 | * specified wait time if necessary for space to become available. | ||
| 238 | * | ||
| 239 | * @param e the element to add | ||
| 240 | * @param timeout how long to wait before giving up, in units of | ||
| 241 | * <tt>unit</tt> | ||
| 242 | * @param unit a <tt>TimeUnit</tt> determining how to interpret the | ||
| 243 | * <tt>timeout</tt> parameter | ||
| 244 | * @return <tt>true</tt> if successful, or <tt>false</tt> if | ||
| 245 | * the specified waiting time elapses before space is available | ||
| 246 | * @throws InterruptedException if interrupted while waiting | ||
| 247 | * @throws ClassCastException if the class of the specified element | ||
| 248 | * prevents it from being added to this queue | ||
| 249 | * @throws NullPointerException if the specified element is null | ||
| 250 | * @throws IllegalArgumentException if some property of the specified | ||
| 251 | * element prevents it from being added to this queue | ||
| 252 | */ | ||
| 253 | boolean offer(E e, long timeout, TimeUnit unit) | ||
| 254 | throws InterruptedException; | ||
| 255 | |||
| 256 | /** | ||
| 257 | * Retrieves and removes the head of this queue, waiting if necessary | ||
| 258 | * until an element becomes available. | ||
| 259 | * | ||
| 260 | * @return the head of this queue | ||
| 261 | * @throws InterruptedException if interrupted while waiting | ||
| 262 | */ | ||
| 263 | E take() throws InterruptedException; | ||
| 264 | |||
| 265 | /** | ||
| 266 | * Retrieves and removes the head of this queue, waiting up to the | ||
| 267 | * specified wait time if necessary for an element to become available. | ||
| 268 | * | ||
| 269 | * @param timeout how long to wait before giving up, in units of | ||
| 270 | * <tt>unit</tt> | ||
| 271 | * @param unit a <tt>TimeUnit</tt> determining how to interpret the | ||
| 272 | * <tt>timeout</tt> parameter | ||
| 273 | * @return the head of this queue, or <tt>null</tt> if the | ||
| 274 | * specified waiting time elapses before an element is available | ||
| 275 | * @throws InterruptedException if interrupted while waiting | ||
| 276 | */ | ||
| 277 | E poll(long timeout, TimeUnit unit) | ||
| 278 | throws InterruptedException; | ||
| 279 | |||
| 280 | /** | ||
| 281 | * Returns the number of additional elements that this queue can ideally | ||
| 282 | * (in the absence of memory or resource constraints) accept without | ||
| 283 | * blocking, or <tt>Integer.MAX_VALUE</tt> if there is no intrinsic | ||
| 284 | * limit. | ||
| 285 | * | ||
| 286 | * <p>Note that you <em>cannot</em> always tell if an attempt to insert | ||
| 287 | * an element will succeed by inspecting <tt>remainingCapacity</tt> | ||
| 288 | * because it may be the case that another thread is about to | ||
| 289 | * insert or remove an element. | ||
| 290 | * | ||
| 291 | * @return the remaining capacity | ||
| 292 | */ | ||
| 293 | int remainingCapacity(); | ||
| 294 | |||
| 295 | /** | ||
| 296 | * Removes a single instance of the specified element from this queue, | ||
| 297 | * if it is present. More formally, removes an element <tt>e</tt> such | ||
| 298 | * that <tt>o.equals(e)</tt>, if this queue contains one or more such | ||
| 299 | * elements. | ||
| 300 | * Returns <tt>true</tt> if this queue contained the specified element | ||
| 301 | * (or equivalently, if this queue changed as a result of the call). | ||
| 302 | * | ||
| 303 | * @param o element to be removed from this queue, if present | ||
| 304 | * @return <tt>true</tt> if this queue changed as a result of the call | ||
| 305 | * @throws ClassCastException if the class of the specified element | ||
| 306 | * is incompatible with this queue | ||
| 307 | * (<a href="../Collection.html#optional-restrictions">optional</a>) | ||
| 308 | * @throws NullPointerException if the specified element is null | ||
| 309 | * (<a href="../Collection.html#optional-restrictions">optional</a>) | ||
| 310 | */ | ||
| 311 | boolean remove(Object o); | ||
| 312 | |||
| 313 | /** | ||
| 314 | * Returns <tt>true</tt> if this queue contains the specified element. | ||
| 315 | * More formally, returns <tt>true</tt> if and only if this queue contains | ||
| 316 | * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. | ||
| 317 | * | ||
| 318 | * @param o object to be checked for containment in this queue | ||
| 319 | * @return <tt>true</tt> if this queue contains the specified element | ||
| 320 | * @throws ClassCastException if the class of the specified element | ||
| 321 | * is incompatible with this queue | ||
| 322 | * (<a href="../Collection.html#optional-restrictions">optional</a>) | ||
| 323 | * @throws NullPointerException if the specified element is null | ||
| 324 | * (<a href="../Collection.html#optional-restrictions">optional</a>) | ||
| 325 | */ | ||
| 326 | public boolean contains(Object o); | ||
| 327 | |||
| 328 | /** | ||
| 329 | * Removes all available elements from this queue and adds them | ||
| 330 | * to the given collection. This operation may be more | ||
| 331 | * efficient than repeatedly polling this queue. A failure | ||
| 332 | * encountered while attempting to add elements to | ||
| 333 | * collection <tt>c</tt> may result in elements being in neither, | ||
| 334 | * either or both collections when the associated exception is | ||
| 335 | * thrown. Attempts to drain a queue to itself result in | ||
| 336 | * <tt>IllegalArgumentException</tt>. Further, the behavior of | ||
| 337 | * this operation is undefined if the specified collection is | ||
| 338 | * modified while the operation is in progress. | ||
| 339 | * | ||
| 340 | * @param c the collection to transfer elements into | ||
| 341 | * @return the number of elements transferred | ||
| 342 | * @throws UnsupportedOperationException if addition of elements | ||
| 343 | * is not supported by the specified collection | ||
| 344 | * @throws ClassCastException if the class of an element of this queue | ||
| 345 | * prevents it from being added to the specified collection | ||
| 346 | * @throws NullPointerException if the specified collection is null | ||
| 347 | * @throws IllegalArgumentException if the specified collection is this | ||
| 348 | * queue, or some property of an element of this queue prevents | ||
| 349 | * it from being added to the specified collection | ||
| 350 | */ | ||
| 351 | int drainTo(Collection<? super E> c); | ||
| 352 | |||
| 353 | /** | ||
| 354 | * Removes at most the given number of available elements from | ||
| 355 | * this queue and adds them to the given collection. A failure | ||
| 356 | * encountered while attempting to add elements to | ||
| 357 | * collection <tt>c</tt> may result in elements being in neither, | ||
| 358 | * either or both collections when the associated exception is | ||
| 359 | * thrown. Attempts to drain a queue to itself result in | ||
| 360 | * <tt>IllegalArgumentException</tt>. Further, the behavior of | ||
| 361 | * this operation is undefined if the specified collection is | ||
| 362 | * modified while the operation is in progress. | ||
| 363 | * | ||
| 364 | * @param c the collection to transfer elements into | ||
| 365 | * @param maxElements the maximum number of elements to transfer | ||
| 366 | * @return the number of elements transferred | ||
| 367 | * @throws UnsupportedOperationException if addition of elements | ||
| 368 | * is not supported by the specified collection | ||
| 369 | * @throws ClassCastException if the class of an element of this queue | ||
| 370 | * prevents it from being added to the specified collection | ||
| 371 | * @throws NullPointerException if the specified collection is null | ||
| 372 | * @throws IllegalArgumentException if the specified collection is this | ||
| 373 | * queue, or some property of an element of this queue prevents | ||
| 374 | * it from being added to the specified collection | ||
| 375 | */ | ||
| 376 | int drainTo(Collection<? super E> c, int maxElements); | ||
| 377 | } | ||