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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.concurrent.locks.*; | ||
| 38 | import java.util.*; | ||
| 39 | |||
| 40 | /** | ||
| 41 | * A bounded {@linkplain BlockingQueue blocking queue} backed by an | ||
| 42 | * array. This queue orders elements FIFO (first-in-first-out). The | ||
| 43 | * <em>head</em> of the queue is that element that has been on the | ||
| 44 | * queue the longest time. The <em>tail</em> of the queue is that | ||
| 45 | * element that has been on the queue the shortest time. New elements | ||
| 46 | * are inserted at the tail of the queue, and the queue retrieval | ||
| 47 | * operations obtain elements at the head of the queue. | ||
| 48 | * | ||
| 49 | * <p>This is a classic "bounded buffer", in which a | ||
| 50 | * fixed-sized array holds elements inserted by producers and | ||
| 51 | * extracted by consumers. Once created, the capacity cannot be | ||
| 52 | * changed. Attempts to {@code put} an element into a full queue | ||
| 53 | * will result in the operation blocking; attempts to {@code take} an | ||
| 54 | * element from an empty queue will similarly block. | ||
| 55 | * | ||
| 56 | * <p>This class supports an optional fairness policy for ordering | ||
| 57 | * waiting producer and consumer threads. By default, this ordering | ||
| 58 | * is not guaranteed. However, a queue constructed with fairness set | ||
| 59 | * to {@code true} grants threads access in FIFO order. Fairness | ||
| 60 | * generally decreases throughput but reduces variability and avoids | ||
| 61 | * starvation. | ||
| 62 | * | ||
| 63 | * <p>This class and its iterator implement all of the | ||
| 64 | * <em>optional</em> methods of the {@link Collection} and {@link | ||
| 65 | * Iterator} interfaces. | ||
| 66 | * | ||
| 67 | * <p>This class is a member of the | ||
| 68 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 69 | * Java Collections Framework</a>. | ||
| 70 | * | ||
| 71 | * @since 1.5 | ||
| 72 | * @author Doug Lea | ||
| 73 | * @param <E> the type of elements held in this collection | ||
| 74 | */ | ||
| 75 | public class ArrayBlockingQueue<E> extends AbstractQueue<E> | ||
| 76 | implements BlockingQueue<E>, java.io.Serializable { | ||
| 77 | |||
| 78 | /** | ||
| 79 | * Serialization ID. This class relies on default serialization | ||
| 80 | * even for the items array, which is default-serialized, even if | ||
| 81 | * it is empty. Otherwise it could not be declared final, which is | ||
| 82 | * necessary here. | ||
| 83 | */ | ||
| 84 | private static final long serialVersionUID = -817911632652898426L; | ||
| 85 | |||
| 86 | /** The queued items */ | ||
| 87 | final Object[] items; | ||
| 88 | |||
| 89 | /** items index for next take, poll, peek or remove */ | ||
| 90 | int takeIndex; | ||
| 91 | |||
| 92 | /** items index for next put, offer, or add */ | ||
| 93 | int putIndex; | ||
| 94 | |||
| 95 | /** Number of elements in the queue */ | ||
| 96 | int count; | ||
| 97 | |||
| 98 | /* | ||
| 99 | * Concurrency control uses the classic two-condition algorithm | ||
| 100 | * found in any textbook. | ||
| 101 | */ | ||
| 102 | |||
| 103 | /** Main lock guarding all access */ | ||
| 104 | final ReentrantLock lock; | ||
| 105 | /** Condition for waiting takes */ | ||
| 106 | private final Condition notEmpty; | ||
| 107 | /** Condition for waiting puts */ | ||
| 108 | private final Condition notFull; | ||
| 109 | |||
| 110 | // Internal helper methods | ||
| 111 | |||
| 112 | /** | ||
| 113 | * Circularly increment i. | ||
| 114 | */ | ||
| 115 | final int inc(int i) { | ||
| 116 | return (++i == items.length) ? 0 : i; | ||
| 117 | } | ||
| 118 | |||
| 119 | /** | ||
| 120 | * Circularly decrement i. | ||
| 121 | */ | ||
| 122 | final int dec(int i) { | ||
| 123 | return ((i == 0) ? items.length : i) - 1; | ||
| 124 | } | ||
| 125 | |||
| 126 | @SuppressWarnings("unchecked") | ||
| 127 | static <E> E cast(Object item) { | ||
| 128 | return (E) item; | ||
| 129 | } | ||
| 130 | |||
| 131 | /** | ||
| 132 | * Returns item at index i. | ||
| 133 | */ | ||
| 134 | final E itemAt(int i) { | ||
| 135 | return this.<E>cast(items[i]); | ||
| 136 | } | ||
| 137 | |||
| 138 | /** | ||
| 139 | * Throws NullPointerException if argument is null. | ||
| 140 | * | ||
| 141 | * @param v the element | ||
| 142 | */ | ||
| 143 | private static void checkNotNull(Object v) { | ||
| 144 | if (v == null) | ||
| 145 | throw new NullPointerException(); | ||
| 146 | } | ||
| 147 | |||
| 148 | /** | ||
| 149 | * Inserts element at current put position, advances, and signals. | ||
| 150 | * Call only when holding lock. | ||
| 151 | */ | ||
| 152 | private void insert(E x) { | ||
| 153 | items[putIndex] = x; | ||
| 154 | putIndex = inc(putIndex); | ||
| 155 | ++count; | ||
| 156 | notEmpty.signal(); | ||
| 157 | } | ||
| 158 | |||
| 159 | /** | ||
| 160 | * Extracts element at current take position, advances, and signals. | ||
| 161 | * Call only when holding lock. | ||
| 162 | */ | ||
| 163 | private E extract() { | ||
| 164 | final Object[] items = this.items; | ||
| 165 | E x = this.<E>cast(items[takeIndex]); | ||
| 166 | items[takeIndex] = null; | ||
| 167 | takeIndex = inc(takeIndex); | ||
| 168 | --count; | ||
| 169 | notFull.signal(); | ||
| 170 | return x; | ||
| 171 | } | ||
| 172 | |||
| 173 | /** | ||
| 174 | * Deletes item at position i. | ||
| 175 | * Utility for remove and iterator.remove. | ||
| 176 | * Call only when holding lock. | ||
| 177 | */ | ||
| 178 | void removeAt(int i) { | ||
| 179 | final Object[] items = this.items; | ||
| 180 | // if removing front item, just advance | ||
| 181 | if (i == takeIndex) { | ||
| 182 | items[takeIndex] = null; | ||
| 183 | takeIndex = inc(takeIndex); | ||
| 184 | } else { | ||
| 185 | // slide over all others up through putIndex. | ||
| 186 | for (;;) { | ||
| 187 | int nexti = inc(i); | ||
| 188 | if (nexti != putIndex) { | ||
| 189 | items[i] = items[nexti]; | ||
| 190 | i = nexti; | ||
| 191 | } else { | ||
| 192 | items[i] = null; | ||
| 193 | putIndex = i; | ||
| 194 | break; | ||
| 195 | } | ||
| 196 | } | ||
| 197 | } | ||
| 198 | --count; | ||
| 199 | notFull.signal(); | ||
| 200 | } | ||
| 201 | |||
| 202 | /** | ||
| 203 | * Creates an {@code ArrayBlockingQueue} with the given (fixed) | ||
| 204 | * capacity and default access policy. | ||
| 205 | * | ||
| 206 | * @param capacity the capacity of this queue | ||
| 207 | * @throws IllegalArgumentException if {@code capacity < 1} | ||
| 208 | */ | ||
| 209 | public ArrayBlockingQueue(int capacity) { | ||
| 210 | this(capacity, false); | ||
| 211 | } | ||
| 212 | |||
| 213 | /** | ||
| 214 | * Creates an {@code ArrayBlockingQueue} with the given (fixed) | ||
| 215 | * capacity and the specified access policy. | ||
| 216 | * | ||
| 217 | * @param capacity the capacity of this queue | ||
| 218 | * @param fair if {@code true} then queue accesses for threads blocked | ||
| 219 | * on insertion or removal, are processed in FIFO order; | ||
| 220 | * if {@code false} the access order is unspecified. | ||
| 221 | * @throws IllegalArgumentException if {@code capacity < 1} | ||
| 222 | */ | ||
| 223 | public ArrayBlockingQueue(int capacity, boolean fair) { | ||
| 224 | if (capacity <= 0) | ||
| 225 | throw new IllegalArgumentException(); | ||
| 226 | this.items = new Object[capacity]; | ||
| 227 | lock = new ReentrantLock(fair); | ||
| 228 | notEmpty = lock.newCondition(); | ||
| 229 | notFull = lock.newCondition(); | ||
| 230 | } | ||
| 231 | |||
| 232 | /** | ||
| 233 | * Creates an {@code ArrayBlockingQueue} with the given (fixed) | ||
| 234 | * capacity, the specified access policy and initially containing the | ||
| 235 | * elements of the given collection, | ||
| 236 | * added in traversal order of the collection's iterator. | ||
| 237 | * | ||
| 238 | * @param capacity the capacity of this queue | ||
| 239 | * @param fair if {@code true} then queue accesses for threads blocked | ||
| 240 | * on insertion or removal, are processed in FIFO order; | ||
| 241 | * if {@code false} the access order is unspecified. | ||
| 242 | * @param c the collection of elements to initially contain | ||
| 243 | * @throws IllegalArgumentException if {@code capacity} is less than | ||
| 244 | * {@code c.size()}, or less than 1. | ||
| 245 | * @throws NullPointerException if the specified collection or any | ||
| 246 | * of its elements are null | ||
| 247 | */ | ||
| 248 | public ArrayBlockingQueue(int capacity, boolean fair, | ||
| 249 | Collection<? extends E> c) { | ||
| 250 | this(capacity, fair); | ||
| 251 | |||
| 252 | final ReentrantLock lock = this.lock; | ||
| 253 | lock.lock(); // Lock only for visibility, not mutual exclusion | ||
| 254 | try { | ||
| 255 | int i = 0; | ||
| 256 | try { | ||
| 257 | for (E e : c) { | ||
| 258 | checkNotNull(e); | ||
| 259 | items[i++] = e; | ||
| 260 | } | ||
| 261 | } catch (ArrayIndexOutOfBoundsException ex) { | ||
| 262 | throw new IllegalArgumentException(); | ||
| 263 | } | ||
| 264 | count = i; | ||
| 265 | putIndex = (i == capacity) ? 0 : i; | ||
| 266 | } finally { | ||
| 267 | lock.unlock(); | ||
| 268 | } | ||
| 269 | } | ||
| 270 | |||
| 271 | /** | ||
| 272 | * Inserts the specified element at the tail of this queue if it is | ||
| 273 | * possible to do so immediately without exceeding the queue's capacity, | ||
| 274 | * returning {@code true} upon success and throwing an | ||
| 275 | * {@code IllegalStateException} if this queue is full. | ||
| 276 | * | ||
| 277 | * @param e the element to add | ||
| 278 | * @return {@code true} (as specified by {@link Collection#add}) | ||
| 279 | * @throws IllegalStateException if this queue is full | ||
| 280 | * @throws NullPointerException if the specified element is null | ||
| 281 | */ | ||
| 282 | public boolean add(E e) { | ||
| 283 | return super.add(e); | ||
| 284 | } | ||
| 285 | |||
| 286 | /** | ||
| 287 | * Inserts the specified element at the tail of this queue if it is | ||
| 288 | * possible to do so immediately without exceeding the queue's capacity, | ||
| 289 | * returning {@code true} upon success and {@code false} if this queue | ||
| 290 | * is full. This method is generally preferable to method {@link #add}, | ||
| 291 | * which can fail to insert an element only by throwing an exception. | ||
| 292 | * | ||
| 293 | * @throws NullPointerException if the specified element is null | ||
| 294 | */ | ||
| 295 | public boolean offer(E e) { | ||
| 296 | checkNotNull(e); | ||
| 297 | final ReentrantLock lock = this.lock; | ||
| 298 | lock.lock(); | ||
| 299 | try { | ||
| 300 | if (count == items.length) | ||
| 301 | return false; | ||
| 302 | else { | ||
| 303 | insert(e); | ||
| 304 | return true; | ||
| 305 | } | ||
| 306 | } finally { | ||
| 307 | lock.unlock(); | ||
| 308 | } | ||
| 309 | } | ||
| 310 | |||
| 311 | /** | ||
| 312 | * Inserts the specified element at the tail of this queue, waiting | ||
| 313 | * for space to become available if the queue is full. | ||
| 314 | * | ||
| 315 | * @throws InterruptedException {@inheritDoc} | ||
| 316 | * @throws NullPointerException {@inheritDoc} | ||
| 317 | */ | ||
| 318 | public void put(E e) throws InterruptedException { | ||
| 319 | checkNotNull(e); | ||
| 320 | final ReentrantLock lock = this.lock; | ||
| 321 | lock.lockInterruptibly(); | ||
| 322 | try { | ||
| 323 | while (count == items.length) | ||
| 324 | notFull.await(); | ||
| 325 | insert(e); | ||
| 326 | } finally { | ||
| 327 | lock.unlock(); | ||
| 328 | } | ||
| 329 | } | ||
| 330 | |||
| 331 | /** | ||
| 332 | * Inserts the specified element at the tail of this queue, waiting | ||
| 333 | * up to the specified wait time for space to become available if | ||
| 334 | * the queue is full. | ||
| 335 | * | ||
| 336 | * @throws InterruptedException {@inheritDoc} | ||
| 337 | * @throws NullPointerException {@inheritDoc} | ||
| 338 | */ | ||
| 339 | public boolean offer(E e, long timeout, TimeUnit unit) | ||
| 340 | throws InterruptedException { | ||
| 341 | |||
| 342 | checkNotNull(e); | ||
| 343 | long nanos = unit.toNanos(timeout); | ||
| 344 | final ReentrantLock lock = this.lock; | ||
| 345 | lock.lockInterruptibly(); | ||
| 346 | try { | ||
| 347 | while (count == items.length) { | ||
| 348 | if (nanos <= 0) | ||
| 349 | return false; | ||
| 350 | nanos = notFull.awaitNanos(nanos); | ||
| 351 | } | ||
| 352 | insert(e); | ||
| 353 | return true; | ||
| 354 | } finally { | ||
| 355 | lock.unlock(); | ||
| 356 | } | ||
| 357 | } | ||
| 358 | |||
| 359 | public E poll() { | ||
| 360 | final ReentrantLock lock = this.lock; | ||
| 361 | lock.lock(); | ||
| 362 | try { | ||
| 363 | return (count == 0) ? null : extract(); | ||
| 364 | } finally { | ||
| 365 | lock.unlock(); | ||
| 366 | } | ||
| 367 | } | ||
| 368 | |||
| 369 | public E take() throws InterruptedException { | ||
| 370 | final ReentrantLock lock = this.lock; | ||
| 371 | lock.lockInterruptibly(); | ||
| 372 | try { | ||
| 373 | while (count == 0) | ||
| 374 | notEmpty.await(); | ||
| 375 | return extract(); | ||
| 376 | } finally { | ||
| 377 | lock.unlock(); | ||
| 378 | } | ||
| 379 | } | ||
| 380 | |||
| 381 | public E poll(long timeout, TimeUnit unit) throws InterruptedException { | ||
| 382 | long nanos = unit.toNanos(timeout); | ||
| 383 | final ReentrantLock lock = this.lock; | ||
| 384 | lock.lockInterruptibly(); | ||
| 385 | try { | ||
| 386 | while (count == 0) { | ||
| 387 | if (nanos <= 0) | ||
| 388 | return null; | ||
| 389 | nanos = notEmpty.awaitNanos(nanos); | ||
| 390 | } | ||
| 391 | return extract(); | ||
| 392 | } finally { | ||
| 393 | lock.unlock(); | ||
| 394 | } | ||
| 395 | } | ||
| 396 | |||
| 397 | public E peek() { | ||
| 398 | final ReentrantLock lock = this.lock; | ||
| 399 | lock.lock(); | ||
| 400 | try { | ||
| 401 | return (count == 0) ? null : itemAt(takeIndex); | ||
| 402 | } finally { | ||
| 403 | lock.unlock(); | ||
| 404 | } | ||
| 405 | } | ||
| 406 | |||
| 407 | // this doc comment is overridden to remove the reference to collections | ||
| 408 | // greater in size than Integer.MAX_VALUE | ||
| 409 | /** | ||
| 410 | * Returns the number of elements in this queue. | ||
| 411 | * | ||
| 412 | * @return the number of elements in this queue | ||
| 413 | */ | ||
| 414 | public int size() { | ||
| 415 | final ReentrantLock lock = this.lock; | ||
| 416 | lock.lock(); | ||
| 417 | try { | ||
| 418 | return count; | ||
| 419 | } finally { | ||
| 420 | lock.unlock(); | ||
| 421 | } | ||
| 422 | } | ||
| 423 | |||
| 424 | // this doc comment is a modified copy of the inherited doc comment, | ||
| 425 | // without the reference to unlimited queues. | ||
| 426 | /** | ||
| 427 | * Returns the number of additional elements that this queue can ideally | ||
| 428 | * (in the absence of memory or resource constraints) accept without | ||
| 429 | * blocking. This is always equal to the initial capacity of this queue | ||
| 430 | * less the current {@code size} of this queue. | ||
| 431 | * | ||
| 432 | * <p>Note that you <em>cannot</em> always tell if an attempt to insert | ||
| 433 | * an element will succeed by inspecting {@code remainingCapacity} | ||
| 434 | * because it may be the case that another thread is about to | ||
| 435 | * insert or remove an element. | ||
| 436 | */ | ||
| 437 | public int remainingCapacity() { | ||
| 438 | final ReentrantLock lock = this.lock; | ||
| 439 | lock.lock(); | ||
| 440 | try { | ||
| 441 | return items.length - count; | ||
| 442 | } finally { | ||
| 443 | lock.unlock(); | ||
| 444 | } | ||
| 445 | } | ||
| 446 | |||
| 447 | /** | ||
| 448 | * Removes a single instance of the specified element from this queue, | ||
| 449 | * if it is present. More formally, removes an element {@code e} such | ||
| 450 | * that {@code o.equals(e)}, if this queue contains one or more such | ||
| 451 | * elements. | ||
| 452 | * Returns {@code true} if this queue contained the specified element | ||
| 453 | * (or equivalently, if this queue changed as a result of the call). | ||
| 454 | * | ||
| 455 | * <p>Removal of interior elements in circular array based queues | ||
| 456 | * is an intrinsically slow and disruptive operation, so should | ||
| 457 | * be undertaken only in exceptional circumstances, ideally | ||
| 458 | * only when the queue is known not to be accessible by other | ||
| 459 | * threads. | ||
| 460 | * | ||
| 461 | * @param o element to be removed from this queue, if present | ||
| 462 | * @return {@code true} if this queue changed as a result of the call | ||
| 463 | */ | ||
| 464 | public boolean remove(Object o) { | ||
| 465 | if (o == null) return false; | ||
| 466 | final Object[] items = this.items; | ||
| 467 | final ReentrantLock lock = this.lock; | ||
| 468 | lock.lock(); | ||
| 469 | try { | ||
| 470 | for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) { | ||
| 471 | if (o.equals(items[i])) { | ||
| 472 | removeAt(i); | ||
| 473 | return true; | ||
| 474 | } | ||
| 475 | } | ||
| 476 | return false; | ||
| 477 | } finally { | ||
| 478 | lock.unlock(); | ||
| 479 | } | ||
| 480 | } | ||
| 481 | |||
| 482 | /** | ||
| 483 | * Returns {@code true} if this queue contains the specified element. | ||
| 484 | * More formally, returns {@code true} if and only if this queue contains | ||
| 485 | * at least one element {@code e} such that {@code o.equals(e)}. | ||
| 486 | * | ||
| 487 | * @param o object to be checked for containment in this queue | ||
| 488 | * @return {@code true} if this queue contains the specified element | ||
| 489 | */ | ||
| 490 | public boolean contains(Object o) { | ||
| 491 | if (o == null) return false; | ||
| 492 | final Object[] items = this.items; | ||
| 493 | final ReentrantLock lock = this.lock; | ||
| 494 | lock.lock(); | ||
| 495 | try { | ||
| 496 | for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) | ||
| 497 | if (o.equals(items[i])) | ||
| 498 | return true; | ||
| 499 | return false; | ||
| 500 | } finally { | ||
| 501 | lock.unlock(); | ||
| 502 | } | ||
| 503 | } | ||
| 504 | |||
| 505 | /** | ||
| 506 | * Returns an array containing all of the elements in this queue, in | ||
| 507 | * proper sequence. | ||
| 508 | * | ||
| 509 | * <p>The returned array will be "safe" in that no references to it are | ||
| 510 | * maintained by this queue. (In other words, this method must allocate | ||
| 511 | * a new array). The caller is thus free to modify the returned array. | ||
| 512 | * | ||
| 513 | * <p>This method acts as bridge between array-based and collection-based | ||
| 514 | * APIs. | ||
| 515 | * | ||
| 516 | * @return an array containing all of the elements in this queue | ||
| 517 | */ | ||
| 518 | public Object[] toArray() { | ||
| 519 | final Object[] items = this.items; | ||
| 520 | final ReentrantLock lock = this.lock; | ||
| 521 | lock.lock(); | ||
| 522 | try { | ||
| 523 | final int count = this.count; | ||
| 524 | Object[] a = new Object[count]; | ||
| 525 | for (int i = takeIndex, k = 0; k < count; i = inc(i), k++) | ||
| 526 | a[k] = items[i]; | ||
| 527 | return a; | ||
| 528 | } finally { | ||
| 529 | lock.unlock(); | ||
| 530 | } | ||
| 531 | } | ||
| 532 | |||
| 533 | /** | ||
| 534 | * Returns an array containing all of the elements in this queue, in | ||
| 535 | * proper sequence; the runtime type of the returned array is that of | ||
| 536 | * the specified array. If the queue fits in the specified array, it | ||
| 537 | * is returned therein. Otherwise, a new array is allocated with the | ||
| 538 | * runtime type of the specified array and the size of this queue. | ||
| 539 | * | ||
| 540 | * <p>If this queue fits in the specified array with room to spare | ||
| 541 | * (i.e., the array has more elements than this queue), the element in | ||
| 542 | * the array immediately following the end of the queue is set to | ||
| 543 | * {@code null}. | ||
| 544 | * | ||
| 545 | * <p>Like the {@link #toArray()} method, this method acts as bridge between | ||
| 546 | * array-based and collection-based APIs. Further, this method allows | ||
| 547 | * precise control over the runtime type of the output array, and may, | ||
| 548 | * under certain circumstances, be used to save allocation costs. | ||
| 549 | * | ||
| 550 | * <p>Suppose {@code x} is a queue known to contain only strings. | ||
| 551 | * The following code can be used to dump the queue into a newly | ||
| 552 | * allocated array of {@code String}: | ||
| 553 | * | ||
| 554 | * <pre> | ||
| 555 | * String[] y = x.toArray(new String[0]);</pre> | ||
| 556 | * | ||
| 557 | * Note that {@code toArray(new Object[0])} is identical in function to | ||
| 558 | * {@code toArray()}. | ||
| 559 | * | ||
| 560 | * @param a the array into which the elements of the queue are to | ||
| 561 | * be stored, if it is big enough; otherwise, a new array of the | ||
| 562 | * same runtime type is allocated for this purpose | ||
| 563 | * @return an array containing all of the elements in this queue | ||
| 564 | * @throws ArrayStoreException if the runtime type of the specified array | ||
| 565 | * is not a supertype of the runtime type of every element in | ||
| 566 | * this queue | ||
| 567 | * @throws NullPointerException if the specified array is null | ||
| 568 | */ | ||
| 569 | @SuppressWarnings("unchecked") | ||
| 570 | public <T> T[] toArray(T[] a) { | ||
| 571 | final Object[] items = this.items; | ||
| 572 | final ReentrantLock lock = this.lock; | ||
| 573 | lock.lock(); | ||
| 574 | try { | ||
| 575 | final int count = this.count; | ||
| 576 | final int len = a.length; | ||
| 577 | if (len < count) | ||
| 578 | a = (T[])java.lang.reflect.Array.newInstance( | ||
| 579 | a.getClass().getComponentType(), count); | ||
| 580 | for (int i = takeIndex, k = 0; k < count; i = inc(i), k++) | ||
| 581 | a[k] = (T) items[i]; | ||
| 582 | if (len > count) | ||
| 583 | a[count] = null; | ||
| 584 | return a; | ||
| 585 | } finally { | ||
| 586 | lock.unlock(); | ||
| 587 | } | ||
| 588 | } | ||
| 589 | |||
| 590 | public String toString() { | ||
| 591 | final ReentrantLock lock = this.lock; | ||
| 592 | lock.lock(); | ||
| 593 | try { | ||
| 594 | int k = count; | ||
| 595 | if (k == 0) | ||
| 596 | return "[]"; | ||
| 597 | |||
| 598 | StringBuilder sb = new StringBuilder(); | ||
| 599 | sb.append('['); | ||
| 600 | for (int i = takeIndex; ; i = inc(i)) { | ||
| 601 | Object e = items[i]; | ||
| 602 | sb.append(e == this ? "(this Collection)" : e); | ||
| 603 | if (--k == 0) | ||
| 604 | return sb.append(']').toString(); | ||
| 605 | sb.append(',').append(' '); | ||
| 606 | } | ||
| 607 | } finally { | ||
| 608 | lock.unlock(); | ||
| 609 | } | ||
| 610 | } | ||
| 611 | |||
| 612 | /** | ||
| 613 | * Atomically removes all of the elements from this queue. | ||
| 614 | * The queue will be empty after this call returns. | ||
| 615 | */ | ||
| 616 | public void clear() { | ||
| 617 | final Object[] items = this.items; | ||
| 618 | final ReentrantLock lock = this.lock; | ||
| 619 | lock.lock(); | ||
| 620 | try { | ||
| 621 | for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) | ||
| 622 | items[i] = null; | ||
| 623 | count = 0; | ||
| 624 | putIndex = 0; | ||
| 625 | takeIndex = 0; | ||
| 626 | notFull.signalAll(); | ||
| 627 | } finally { | ||
| 628 | lock.unlock(); | ||
| 629 | } | ||
| 630 | } | ||
| 631 | |||
| 632 | /** | ||
| 633 | * @throws UnsupportedOperationException {@inheritDoc} | ||
| 634 | * @throws ClassCastException {@inheritDoc} | ||
| 635 | * @throws NullPointerException {@inheritDoc} | ||
| 636 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 637 | */ | ||
| 638 | public int drainTo(Collection<? super E> c) { | ||
| 639 | checkNotNull(c); | ||
| 640 | if (c == this) | ||
| 641 | throw new IllegalArgumentException(); | ||
| 642 | final Object[] items = this.items; | ||
| 643 | final ReentrantLock lock = this.lock; | ||
| 644 | lock.lock(); | ||
| 645 | try { | ||
| 646 | int i = takeIndex; | ||
| 647 | int n = 0; | ||
| 648 | int max = count; | ||
| 649 | while (n < max) { | ||
| 650 | c.add(this.<E>cast(items[i])); | ||
| 651 | items[i] = null; | ||
| 652 | i = inc(i); | ||
| 653 | ++n; | ||
| 654 | } | ||
| 655 | if (n > 0) { | ||
| 656 | count = 0; | ||
| 657 | putIndex = 0; | ||
| 658 | takeIndex = 0; | ||
| 659 | notFull.signalAll(); | ||
| 660 | } | ||
| 661 | return n; | ||
| 662 | } finally { | ||
| 663 | lock.unlock(); | ||
| 664 | } | ||
| 665 | } | ||
| 666 | |||
| 667 | /** | ||
| 668 | * @throws UnsupportedOperationException {@inheritDoc} | ||
| 669 | * @throws ClassCastException {@inheritDoc} | ||
| 670 | * @throws NullPointerException {@inheritDoc} | ||
| 671 | * @throws IllegalArgumentException {@inheritDoc} | ||
| 672 | */ | ||
| 673 | public int drainTo(Collection<? super E> c, int maxElements) { | ||
| 674 | checkNotNull(c); | ||
| 675 | if (c == this) | ||
| 676 | throw new IllegalArgumentException(); | ||
| 677 | if (maxElements <= 0) | ||
| 678 | return 0; | ||
| 679 | final Object[] items = this.items; | ||
| 680 | final ReentrantLock lock = this.lock; | ||
| 681 | lock.lock(); | ||
| 682 | try { | ||
| 683 | int i = takeIndex; | ||
| 684 | int n = 0; | ||
| 685 | int max = (maxElements < count) ? maxElements : count; | ||
| 686 | while (n < max) { | ||
| 687 | c.add(this.<E>cast(items[i])); | ||
| 688 | items[i] = null; | ||
| 689 | i = inc(i); | ||
| 690 | ++n; | ||
| 691 | } | ||
| 692 | if (n > 0) { | ||
| 693 | count -= n; | ||
| 694 | takeIndex = i; | ||
| 695 | notFull.signalAll(); | ||
| 696 | } | ||
| 697 | return n; | ||
| 698 | } finally { | ||
| 699 | lock.unlock(); | ||
| 700 | } | ||
| 701 | } | ||
| 702 | |||
| 703 | /** | ||
| 704 | * Returns an iterator over the elements in this queue in proper sequence. | ||
| 705 | * The elements will be returned in order from first (head) to last (tail). | ||
| 706 | * | ||
| 707 | * <p>The returned {@code Iterator} is a "weakly consistent" iterator that | ||
| 708 | * will never throw {@link java.util.ConcurrentModificationException | ||
| 709 | * ConcurrentModificationException}, | ||
| 710 | * and guarantees to traverse elements as they existed upon | ||
| 711 | * construction of the iterator, and may (but is not guaranteed to) | ||
| 712 | * reflect any modifications subsequent to construction. | ||
| 713 | * | ||
| 714 | * @return an iterator over the elements in this queue in proper sequence | ||
| 715 | */ | ||
| 716 | public Iterator<E> iterator() { | ||
| 717 | return new Itr(); | ||
| 718 | } | ||
| 719 | |||
| 720 | /** | ||
| 721 | * Iterator for ArrayBlockingQueue. To maintain weak consistency | ||
| 722 | * with respect to puts and takes, we (1) read ahead one slot, so | ||
| 723 | * as to not report hasNext true but then not have an element to | ||
| 724 | * return -- however we later recheck this slot to use the most | ||
| 725 | * current value; (2) ensure that each array slot is traversed at | ||
| 726 | * most once (by tracking "remaining" elements); (3) skip over | ||
| 727 | * null slots, which can occur if takes race ahead of iterators. | ||
| 728 | * However, for circular array-based queues, we cannot rely on any | ||
| 729 | * well established definition of what it means to be weakly | ||
| 730 | * consistent with respect to interior removes since these may | ||
| 731 | * require slot overwrites in the process of sliding elements to | ||
| 732 | * cover gaps. So we settle for resiliency, operating on | ||
| 733 | * established apparent nexts, which may miss some elements that | ||
| 734 | * have moved between calls to next. | ||
| 735 | */ | ||
| 736 | private class Itr implements Iterator<E> { | ||
| 737 | private int remaining; // Number of elements yet to be returned | ||
| 738 | private int nextIndex; // Index of element to be returned by next | ||
| 739 | private E nextItem; // Element to be returned by next call to next | ||
| 740 | private E lastItem; // Element returned by last call to next | ||
| 741 | private int lastRet; // Index of last element returned, or -1 if none | ||
| 742 | |||
| 743 | Itr() { | ||
| 744 | final ReentrantLock lock = ArrayBlockingQueue.this.lock; | ||
| 745 | lock.lock(); | ||
| 746 | try { | ||
| 747 | lastRet = -1; | ||
| 748 | if ((remaining = count) > 0) | ||
| 749 | nextItem = itemAt(nextIndex = takeIndex); | ||
| 750 | } finally { | ||
| 751 | lock.unlock(); | ||
| 752 | } | ||
| 753 | } | ||
| 754 | |||
| 755 | public boolean hasNext() { | ||
| 756 | return remaining > 0; | ||
| 757 | } | ||
| 758 | |||
| 759 | public E next() { | ||
| 760 | final ReentrantLock lock = ArrayBlockingQueue.this.lock; | ||
| 761 | lock.lock(); | ||
| 762 | try { | ||
| 763 | if (remaining <= 0) | ||
| 764 | throw new NoSuchElementException(); | ||
| 765 | lastRet = nextIndex; | ||
| 766 | E x = itemAt(nextIndex); // check for fresher value | ||
| 767 | if (x == null) { | ||
| 768 | x = nextItem; // we are forced to report old value | ||
| 769 | lastItem = null; // but ensure remove fails | ||
| 770 | } | ||
| 771 | else | ||
| 772 | lastItem = x; | ||
| 773 | while (--remaining > 0 && // skip over nulls | ||
| 774 | (nextItem = itemAt(nextIndex = inc(nextIndex))) == null) | ||
| 775 | ; | ||
| 776 | return x; | ||
| 777 | } finally { | ||
| 778 | lock.unlock(); | ||
| 779 | } | ||
| 780 | } | ||
| 781 | |||
| 782 | public void remove() { | ||
| 783 | final ReentrantLock lock = ArrayBlockingQueue.this.lock; | ||
| 784 | lock.lock(); | ||
| 785 | try { | ||
| 786 | int i = lastRet; | ||
| 787 | if (i == -1) | ||
| 788 | throw new IllegalStateException(); | ||
| 789 | lastRet = -1; | ||
| 790 | E x = lastItem; | ||
| 791 | lastItem = null; | ||
| 792 | // only remove if item still at index | ||
| 793 | if (x != null && x == items[i]) { | ||
| 794 | boolean removingHead = (i == takeIndex); | ||
| 795 | removeAt(i); | ||
| 796 | if (!removingHead) | ||
| 797 | nextIndex = dec(nextIndex); | ||
| 798 | } | ||
| 799 | } finally { | ||
| 800 | lock.unlock(); | ||
| 801 | } | ||
| 802 | } | ||
| 803 | } | ||
| 804 | |||
| 805 | } | ||