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.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 | * increased. Attempts to <tt>put</tt> an element into a full queue |
| 53 | * will result in the operation blocking; attempts to <tt>take</tt> 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 <tt>true</tt> 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 | private final E[] items; |
| 88 | /** items index for next take, poll or remove */ |
| 89 | private int takeIndex; |
| 90 | /** items index for next put, offer, or add. */ |
| 91 | private int putIndex; |
| 92 | /** Number of items in the queue */ |
| 93 | private int count; |
| 94 | |
| 95 | /* |
| 96 | * Concurrency control uses the classic two-condition algorithm |
| 97 | * found in any textbook. |
| 98 | */ |
| 99 | |
| 100 | /** Main lock guarding all access */ |
| 101 | private final ReentrantLock lock; |
| 102 | /** Condition for waiting takes */ |
| 103 | private final Condition notEmpty; |
| 104 | /** Condition for waiting puts */ |
| 105 | private final Condition notFull; |
| 106 | |
| 107 | // Internal helper methods |
| 108 | |
| 109 | /** |
| 110 | * Circularly increment i. |
| 111 | */ |
| 112 | final int inc(int i) { |
| 113 | return (++i == items.length)? 0 : i; |
| 114 | } |
| 115 | |
| 116 | /** |
| 117 | * Inserts element at current put position, advances, and signals. |
| 118 | * Call only when holding lock. |
| 119 | */ |
| 120 | private void insert(E x) { |
| 121 | items[putIndex] = x; |
| 122 | putIndex = inc(putIndex); |
| 123 | ++count; |
| 124 | notEmpty.signal(); |
| 125 | } |
| 126 | |
| 127 | /** |
| 128 | * Extracts element at current take position, advances, and signals. |
| 129 | * Call only when holding lock. |
| 130 | */ |
| 131 | private E extract() { |
| 132 | final E[] items = this.items; |
| 133 | E x = items[takeIndex]; |
| 134 | items[takeIndex] = null; |
| 135 | takeIndex = inc(takeIndex); |
| 136 | --count; |
| 137 | notFull.signal(); |
| 138 | return x; |
| 139 | } |
| 140 | |
| 141 | /** |
| 142 | * Utility for remove and iterator.remove: Delete item at position i. |
| 143 | * Call only when holding lock. |
| 144 | */ |
| 145 | void removeAt(int i) { |
| 146 | final E[] items = this.items; |
| 147 | // if removing front item, just advance |
| 148 | if (i == takeIndex) { |
| 149 | items[takeIndex] = null; |
| 150 | takeIndex = inc(takeIndex); |
| 151 | } else { |
| 152 | // slide over all others up through putIndex. |
| 153 | for (;;) { |
| 154 | int nexti = inc(i); |
| 155 | if (nexti != putIndex) { |
| 156 | items[i] = items[nexti]; |
| 157 | i = nexti; |
| 158 | } else { |
| 159 | items[i] = null; |
| 160 | putIndex = i; |
| 161 | break; |
| 162 | } |
| 163 | } |
| 164 | } |
| 165 | --count; |
| 166 | notFull.signal(); |
| 167 | } |
| 168 | |
| 169 | /** |
| 170 | * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed) |
| 171 | * capacity and default access policy. |
| 172 | * |
| 173 | * @param capacity the capacity of this queue |
| 174 | * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1 |
| 175 | */ |
| 176 | public ArrayBlockingQueue(int capacity) { |
| 177 | this(capacity, false); |
| 178 | } |
| 179 | |
| 180 | /** |
| 181 | * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed) |
| 182 | * capacity and the specified access policy. |
| 183 | * |
| 184 | * @param capacity the capacity of this queue |
| 185 | * @param fair if <tt>true</tt> then queue accesses for threads blocked |
| 186 | * on insertion or removal, are processed in FIFO order; |
| 187 | * if <tt>false</tt> the access order is unspecified. |
| 188 | * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1 |
| 189 | */ |
| 190 | public ArrayBlockingQueue(int capacity, boolean fair) { |
| 191 | if (capacity <= 0) |
| 192 | throw new IllegalArgumentException(); |
| 193 | this.items = (E[]) new Object[capacity]; |
| 194 | lock = new ReentrantLock(fair); |
| 195 | notEmpty = lock.newCondition(); |
| 196 | notFull = lock.newCondition(); |
| 197 | } |
| 198 | |
| 199 | /** |
| 200 | * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed) |
| 201 | * capacity, the specified access policy and initially containing the |
| 202 | * elements of the given collection, |
| 203 | * added in traversal order of the collection's iterator. |
| 204 | * |
| 205 | * @param capacity the capacity of this queue |
| 206 | * @param fair if <tt>true</tt> then queue accesses for threads blocked |
| 207 | * on insertion or removal, are processed in FIFO order; |
| 208 | * if <tt>false</tt> the access order is unspecified. |
| 209 | * @param c the collection of elements to initially contain |
| 210 | * @throws IllegalArgumentException if <tt>capacity</tt> is less than |
| 211 | * <tt>c.size()</tt>, or less than 1. |
| 212 | * @throws NullPointerException if the specified collection or any |
| 213 | * of its elements are null |
| 214 | */ |
| 215 | public ArrayBlockingQueue(int capacity, boolean fair, |
| 216 | Collection<? extends E> c) { |
| 217 | this(capacity, fair); |
| 218 | if (capacity < c.size()) |
| 219 | throw new IllegalArgumentException(); |
| 220 | |
| 221 | for (Iterator<? extends E> it = c.iterator(); it.hasNext();) |
| 222 | add(it.next()); |
| 223 | } |
| 224 | |
| 225 | /** |
| 226 | * Inserts the specified element at the tail of this queue if it is |
| 227 | * possible to do so immediately without exceeding the queue's capacity, |
| 228 | * returning <tt>true</tt> upon success and throwing an |
| 229 | * <tt>IllegalStateException</tt> if this queue is full. |
| 230 | * |
| 231 | * @param e the element to add |
| 232 | * @return <tt>true</tt> (as specified by {@link Collection#add}) |
| 233 | * @throws IllegalStateException if this queue is full |
| 234 | * @throws NullPointerException if the specified element is null |
| 235 | */ |
| 236 | public boolean add(E e) { |
| 237 | return super.add(e); |
| 238 | } |
| 239 | |
| 240 | /** |
| 241 | * Inserts the specified element at the tail of this queue if it is |
| 242 | * possible to do so immediately without exceeding the queue's capacity, |
| 243 | * returning <tt>true</tt> upon success and <tt>false</tt> if this queue |
| 244 | * is full. This method is generally preferable to method {@link #add}, |
| 245 | * which can fail to insert an element only by throwing an exception. |
| 246 | * |
| 247 | * @throws NullPointerException if the specified element is null |
| 248 | */ |
| 249 | public boolean offer(E e) { |
| 250 | if (e == null) throw new NullPointerException(); |
| 251 | final ReentrantLock lock = this.lock; |
| 252 | lock.lock(); |
| 253 | try { |
| 254 | if (count == items.length) |
| 255 | return false; |
| 256 | else { |
| 257 | insert(e); |
| 258 | return true; |
| 259 | } |
| 260 | } finally { |
| 261 | lock.unlock(); |
| 262 | } |
| 263 | } |
| 264 | |
| 265 | /** |
| 266 | * Inserts the specified element at the tail of this queue, waiting |
| 267 | * for space to become available if the queue is full. |
| 268 | * |
| 269 | * @throws InterruptedException {@inheritDoc} |
| 270 | * @throws NullPointerException {@inheritDoc} |
| 271 | */ |
| 272 | public void put(E e) throws InterruptedException { |
| 273 | if (e == null) throw new NullPointerException(); |
| 274 | final E[] items = this.items; |
| 275 | final ReentrantLock lock = this.lock; |
| 276 | lock.lockInterruptibly(); |
| 277 | try { |
| 278 | try { |
| 279 | while (count == items.length) |
| 280 | notFull.await(); |
| 281 | } catch (InterruptedException ie) { |
| 282 | notFull.signal(); // propagate to non-interrupted thread |
| 283 | throw ie; |
| 284 | } |
| 285 | insert(e); |
| 286 | } finally { |
| 287 | lock.unlock(); |
| 288 | } |
| 289 | } |
| 290 | |
| 291 | /** |
| 292 | * Inserts the specified element at the tail of this queue, waiting |
| 293 | * up to the specified wait time for space to become available if |
| 294 | * the queue is full. |
| 295 | * |
| 296 | * @throws InterruptedException {@inheritDoc} |
| 297 | * @throws NullPointerException {@inheritDoc} |
| 298 | */ |
| 299 | public boolean offer(E e, long timeout, TimeUnit unit) |
| 300 | throws InterruptedException { |
| 301 | |
| 302 | if (e == null) throw new NullPointerException(); |
| 303 | long nanos = unit.toNanos(timeout); |
| 304 | final ReentrantLock lock = this.lock; |
| 305 | lock.lockInterruptibly(); |
| 306 | try { |
| 307 | for (;;) { |
| 308 | if (count != items.length) { |
| 309 | insert(e); |
| 310 | return true; |
| 311 | } |
| 312 | if (nanos <= 0) |
| 313 | return false; |
| 314 | try { |
| 315 | nanos = notFull.awaitNanos(nanos); |
| 316 | } catch (InterruptedException ie) { |
| 317 | notFull.signal(); // propagate to non-interrupted thread |
| 318 | throw ie; |
| 319 | } |
| 320 | } |
| 321 | } finally { |
| 322 | lock.unlock(); |
| 323 | } |
| 324 | } |
| 325 | |
| 326 | public E poll() { |
| 327 | final ReentrantLock lock = this.lock; |
| 328 | lock.lock(); |
| 329 | try { |
| 330 | if (count == 0) |
| 331 | return null; |
| 332 | E x = extract(); |
| 333 | return x; |
| 334 | } finally { |
| 335 | lock.unlock(); |
| 336 | } |
| 337 | } |
| 338 | |
| 339 | public E take() throws InterruptedException { |
| 340 | final ReentrantLock lock = this.lock; |
| 341 | lock.lockInterruptibly(); |
| 342 | try { |
| 343 | try { |
| 344 | while (count == 0) |
| 345 | notEmpty.await(); |
| 346 | } catch (InterruptedException ie) { |
| 347 | notEmpty.signal(); // propagate to non-interrupted thread |
| 348 | throw ie; |
| 349 | } |
| 350 | E x = extract(); |
| 351 | return x; |
| 352 | } finally { |
| 353 | lock.unlock(); |
| 354 | } |
| 355 | } |
| 356 | |
| 357 | public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
| 358 | long nanos = unit.toNanos(timeout); |
| 359 | final ReentrantLock lock = this.lock; |
| 360 | lock.lockInterruptibly(); |
| 361 | try { |
| 362 | for (;;) { |
| 363 | if (count != 0) { |
| 364 | E x = extract(); |
| 365 | return x; |
| 366 | } |
| 367 | if (nanos <= 0) |
| 368 | return null; |
| 369 | try { |
| 370 | nanos = notEmpty.awaitNanos(nanos); |
| 371 | } catch (InterruptedException ie) { |
| 372 | notEmpty.signal(); // propagate to non-interrupted thread |
| 373 | throw ie; |
| 374 | } |
| 375 | |
| 376 | } |
| 377 | } finally { |
| 378 | lock.unlock(); |
| 379 | } |
| 380 | } |
| 381 | |
| 382 | public E peek() { |
| 383 | final ReentrantLock lock = this.lock; |
| 384 | lock.lock(); |
| 385 | try { |
| 386 | return (count == 0) ? null : items[takeIndex]; |
| 387 | } finally { |
| 388 | lock.unlock(); |
| 389 | } |
| 390 | } |
| 391 | |
| 392 | // this doc comment is overridden to remove the reference to collections |
| 393 | // greater in size than Integer.MAX_VALUE |
| 394 | /** |
| 395 | * Returns the number of elements in this queue. |
| 396 | * |
| 397 | * @return the number of elements in this queue |
| 398 | */ |
| 399 | public int size() { |
| 400 | final ReentrantLock lock = this.lock; |
| 401 | lock.lock(); |
| 402 | try { |
| 403 | return count; |
| 404 | } finally { |
| 405 | lock.unlock(); |
| 406 | } |
| 407 | } |
| 408 | |
| 409 | // this doc comment is a modified copy of the inherited doc comment, |
| 410 | // without the reference to unlimited queues. |
| 411 | /** |
| 412 | * Returns the number of additional elements that this queue can ideally |
| 413 | * (in the absence of memory or resource constraints) accept without |
| 414 | * blocking. This is always equal to the initial capacity of this queue |
| 415 | * less the current <tt>size</tt> of this queue. |
| 416 | * |
| 417 | * <p>Note that you <em>cannot</em> always tell if an attempt to insert |
| 418 | * an element will succeed by inspecting <tt>remainingCapacity</tt> |
| 419 | * because it may be the case that another thread is about to |
| 420 | * insert or remove an element. |
| 421 | */ |
| 422 | public int remainingCapacity() { |
| 423 | final ReentrantLock lock = this.lock; |
| 424 | lock.lock(); |
| 425 | try { |
| 426 | return items.length - count; |
| 427 | } finally { |
| 428 | lock.unlock(); |
| 429 | } |
| 430 | } |
| 431 | |
| 432 | /** |
| 433 | * Removes a single instance of the specified element from this queue, |
| 434 | * if it is present. More formally, removes an element <tt>e</tt> such |
| 435 | * that <tt>o.equals(e)</tt>, if this queue contains one or more such |
| 436 | * elements. |
| 437 | * Returns <tt>true</tt> if this queue contained the specified element |
| 438 | * (or equivalently, if this queue changed as a result of the call). |
| 439 | * |
| 440 | * @param o element to be removed from this queue, if present |
| 441 | * @return <tt>true</tt> if this queue changed as a result of the call |
| 442 | */ |
| 443 | public boolean remove(Object o) { |
| 444 | if (o == null) return false; |
| 445 | final E[] items = this.items; |
| 446 | final ReentrantLock lock = this.lock; |
| 447 | lock.lock(); |
| 448 | try { |
| 449 | int i = takeIndex; |
| 450 | int k = 0; |
| 451 | for (;;) { |
| 452 | if (k++ >= count) |
| 453 | return false; |
| 454 | if (o.equals(items[i])) { |
| 455 | removeAt(i); |
| 456 | return true; |
| 457 | } |
| 458 | i = inc(i); |
| 459 | } |
| 460 | |
| 461 | } finally { |
| 462 | lock.unlock(); |
| 463 | } |
| 464 | } |
| 465 | |
| 466 | /** |
| 467 | * Returns <tt>true</tt> if this queue contains the specified element. |
| 468 | * More formally, returns <tt>true</tt> if and only if this queue contains |
| 469 | * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
| 470 | * |
| 471 | * @param o object to be checked for containment in this queue |
| 472 | * @return <tt>true</tt> if this queue contains the specified element |
| 473 | */ |
| 474 | public boolean contains(Object o) { |
| 475 | if (o == null) return false; |
| 476 | final E[] items = this.items; |
| 477 | final ReentrantLock lock = this.lock; |
| 478 | lock.lock(); |
| 479 | try { |
| 480 | int i = takeIndex; |
| 481 | int k = 0; |
| 482 | while (k++ < count) { |
| 483 | if (o.equals(items[i])) |
| 484 | return true; |
| 485 | i = inc(i); |
| 486 | } |
| 487 | return false; |
| 488 | } finally { |
| 489 | lock.unlock(); |
| 490 | } |
| 491 | } |
| 492 | |
| 493 | /** |
| 494 | * Returns an array containing all of the elements in this queue, in |
| 495 | * proper sequence. |
| 496 | * |
| 497 | * <p>The returned array will be "safe" in that no references to it are |
| 498 | * maintained by this queue. (In other words, this method must allocate |
| 499 | * a new array). The caller is thus free to modify the returned array. |
| 500 | * |
| 501 | * <p>This method acts as bridge between array-based and collection-based |
| 502 | * APIs. |
| 503 | * |
| 504 | * @return an array containing all of the elements in this queue |
| 505 | */ |
| 506 | public Object[] toArray() { |
| 507 | final E[] items = this.items; |
| 508 | final ReentrantLock lock = this.lock; |
| 509 | lock.lock(); |
| 510 | try { |
| 511 | Object[] a = new Object[count]; |
| 512 | int k = 0; |
| 513 | int i = takeIndex; |
| 514 | while (k < count) { |
| 515 | a[k++] = items[i]; |
| 516 | i = inc(i); |
| 517 | } |
| 518 | return a; |
| 519 | } finally { |
| 520 | lock.unlock(); |
| 521 | } |
| 522 | } |
| 523 | |
| 524 | /** |
| 525 | * Returns an array containing all of the elements in this queue, in |
| 526 | * proper sequence; the runtime type of the returned array is that of |
| 527 | * the specified array. If the queue fits in the specified array, it |
| 528 | * is returned therein. Otherwise, a new array is allocated with the |
| 529 | * runtime type of the specified array and the size of this queue. |
| 530 | * |
| 531 | * <p>If this queue fits in the specified array with room to spare |
| 532 | * (i.e., the array has more elements than this queue), the element in |
| 533 | * the array immediately following the end of the queue is set to |
| 534 | * <tt>null</tt>. |
| 535 | * |
| 536 | * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| 537 | * array-based and collection-based APIs. Further, this method allows |
| 538 | * precise control over the runtime type of the output array, and may, |
| 539 | * under certain circumstances, be used to save allocation costs. |
| 540 | * |
| 541 | * <p>Suppose <tt>x</tt> is a queue known to contain only strings. |
| 542 | * The following code can be used to dump the queue into a newly |
| 543 | * allocated array of <tt>String</tt>: |
| 544 | * |
| 545 | * <pre> |
| 546 | * String[] y = x.toArray(new String[0]);</pre> |
| 547 | * |
| 548 | * Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| 549 | * <tt>toArray()</tt>. |
| 550 | * |
| 551 | * @param a the array into which the elements of the queue are to |
| 552 | * be stored, if it is big enough; otherwise, a new array of the |
| 553 | * same runtime type is allocated for this purpose |
| 554 | * @return an array containing all of the elements in this queue |
| 555 | * @throws ArrayStoreException if the runtime type of the specified array |
| 556 | * is not a supertype of the runtime type of every element in |
| 557 | * this queue |
| 558 | * @throws NullPointerException if the specified array is null |
| 559 | */ |
| 560 | public <T> T[] toArray(T[] a) { |
| 561 | final E[] items = this.items; |
| 562 | final ReentrantLock lock = this.lock; |
| 563 | lock.lock(); |
| 564 | try { |
| 565 | if (a.length < count) |
| 566 | a = (T[])java.lang.reflect.Array.newInstance( |
| 567 | a.getClass().getComponentType(), |
| 568 | count |
| 569 | ); |
| 570 | |
| 571 | int k = 0; |
| 572 | int i = takeIndex; |
| 573 | while (k < count) { |
| 574 | a[k++] = (T)items[i]; |
| 575 | i = inc(i); |
| 576 | } |
| 577 | if (a.length > count) |
| 578 | a[count] = null; |
| 579 | return a; |
| 580 | } finally { |
| 581 | lock.unlock(); |
| 582 | } |
| 583 | } |
| 584 | |
| 585 | public String toString() { |
| 586 | final ReentrantLock lock = this.lock; |
| 587 | lock.lock(); |
| 588 | try { |
| 589 | return super.toString(); |
| 590 | } finally { |
| 591 | lock.unlock(); |
| 592 | } |
| 593 | } |
| 594 | |
| 595 | /** |
| 596 | * Atomically removes all of the elements from this queue. |
| 597 | * The queue will be empty after this call returns. |
| 598 | */ |
| 599 | public void clear() { |
| 600 | final E[] items = this.items; |
| 601 | final ReentrantLock lock = this.lock; |
| 602 | lock.lock(); |
| 603 | try { |
| 604 | int i = takeIndex; |
| 605 | int k = count; |
| 606 | while (k-- > 0) { |
| 607 | items[i] = null; |
| 608 | i = inc(i); |
| 609 | } |
| 610 | count = 0; |
| 611 | putIndex = 0; |
| 612 | takeIndex = 0; |
| 613 | notFull.signalAll(); |
| 614 | } finally { |
| 615 | lock.unlock(); |
| 616 | } |
| 617 | } |
| 618 | |
| 619 | /** |
| 620 | * @throws UnsupportedOperationException {@inheritDoc} |
| 621 | * @throws ClassCastException {@inheritDoc} |
| 622 | * @throws NullPointerException {@inheritDoc} |
| 623 | * @throws IllegalArgumentException {@inheritDoc} |
| 624 | */ |
| 625 | public int drainTo(Collection<? super E> c) { |
| 626 | if (c == null) |
| 627 | throw new NullPointerException(); |
| 628 | if (c == this) |
| 629 | throw new IllegalArgumentException(); |
| 630 | final E[] items = this.items; |
| 631 | final ReentrantLock lock = this.lock; |
| 632 | lock.lock(); |
| 633 | try { |
| 634 | int i = takeIndex; |
| 635 | int n = 0; |
| 636 | int max = count; |
| 637 | while (n < max) { |
| 638 | c.add(items[i]); |
| 639 | items[i] = null; |
| 640 | i = inc(i); |
| 641 | ++n; |
| 642 | } |
| 643 | if (n > 0) { |
| 644 | count = 0; |
| 645 | putIndex = 0; |
| 646 | takeIndex = 0; |
| 647 | notFull.signalAll(); |
| 648 | } |
| 649 | return n; |
| 650 | } finally { |
| 651 | lock.unlock(); |
| 652 | } |
| 653 | } |
| 654 | |
| 655 | /** |
| 656 | * @throws UnsupportedOperationException {@inheritDoc} |
| 657 | * @throws ClassCastException {@inheritDoc} |
| 658 | * @throws NullPointerException {@inheritDoc} |
| 659 | * @throws IllegalArgumentException {@inheritDoc} |
| 660 | */ |
| 661 | public int drainTo(Collection<? super E> c, int maxElements) { |
| 662 | if (c == null) |
| 663 | throw new NullPointerException(); |
| 664 | if (c == this) |
| 665 | throw new IllegalArgumentException(); |
| 666 | if (maxElements <= 0) |
| 667 | return 0; |
| 668 | final E[] items = this.items; |
| 669 | final ReentrantLock lock = this.lock; |
| 670 | lock.lock(); |
| 671 | try { |
| 672 | int i = takeIndex; |
| 673 | int n = 0; |
| 674 | int sz = count; |
| 675 | int max = (maxElements < count)? maxElements : count; |
| 676 | while (n < max) { |
| 677 | c.add(items[i]); |
| 678 | items[i] = null; |
| 679 | i = inc(i); |
| 680 | ++n; |
| 681 | } |
| 682 | if (n > 0) { |
| 683 | count -= n; |
| 684 | takeIndex = i; |
| 685 | notFull.signalAll(); |
| 686 | } |
| 687 | return n; |
| 688 | } finally { |
| 689 | lock.unlock(); |
| 690 | } |
| 691 | } |
| 692 | |
| 693 | |
| 694 | /** |
| 695 | * Returns an iterator over the elements in this queue in proper sequence. |
| 696 | * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
| 697 | * will never throw {@link ConcurrentModificationException}, |
| 698 | * and guarantees to traverse elements as they existed upon |
| 699 | * construction of the iterator, and may (but is not guaranteed to) |
| 700 | * reflect any modifications subsequent to construction. |
| 701 | * |
| 702 | * @return an iterator over the elements in this queue in proper sequence |
| 703 | */ |
| 704 | public Iterator<E> iterator() { |
| 705 | final ReentrantLock lock = this.lock; |
| 706 | lock.lock(); |
| 707 | try { |
| 708 | return new Itr(); |
| 709 | } finally { |
| 710 | lock.unlock(); |
| 711 | } |
| 712 | } |
| 713 | |
| 714 | /** |
| 715 | * Iterator for ArrayBlockingQueue |
| 716 | */ |
| 717 | private class Itr implements Iterator<E> { |
| 718 | /** |
| 719 | * Index of element to be returned by next, |
| 720 | * or a negative number if no such. |
| 721 | */ |
| 722 | private int nextIndex; |
| 723 | |
| 724 | /** |
| 725 | * nextItem holds on to item fields because once we claim |
| 726 | * that an element exists in hasNext(), we must return it in |
| 727 | * the following next() call even if it was in the process of |
| 728 | * being removed when hasNext() was called. |
| 729 | */ |
| 730 | private E nextItem; |
| 731 | |
| 732 | /** |
| 733 | * Index of element returned by most recent call to next. |
| 734 | * Reset to -1 if this element is deleted by a call to remove. |
| 735 | */ |
| 736 | private int lastRet; |
| 737 | |
| 738 | Itr() { |
| 739 | lastRet = -1; |
| 740 | if (count == 0) |
| 741 | nextIndex = -1; |
| 742 | else { |
| 743 | nextIndex = takeIndex; |
| 744 | nextItem = items[takeIndex]; |
| 745 | } |
| 746 | } |
| 747 | |
| 748 | public boolean hasNext() { |
| 749 | /* |
| 750 | * No sync. We can return true by mistake here |
| 751 | * only if this iterator passed across threads, |
| 752 | * which we don't support anyway. |
| 753 | */ |
| 754 | return nextIndex >= 0; |
| 755 | } |
| 756 | |
| 757 | /** |
| 758 | * Checks whether nextIndex is valid; if so setting nextItem. |
| 759 | * Stops iterator when either hits putIndex or sees null item. |
| 760 | */ |
| 761 | private void checkNext() { |
| 762 | if (nextIndex == putIndex) { |
| 763 | nextIndex = -1; |
| 764 | nextItem = null; |
| 765 | } else { |
| 766 | nextItem = items[nextIndex]; |
| 767 | if (nextItem == null) |
| 768 | nextIndex = -1; |
| 769 | } |
| 770 | } |
| 771 | |
| 772 | public E next() { |
| 773 | final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
| 774 | lock.lock(); |
| 775 | try { |
| 776 | if (nextIndex < 0) |
| 777 | throw new NoSuchElementException(); |
| 778 | lastRet = nextIndex; |
| 779 | E x = nextItem; |
| 780 | nextIndex = inc(nextIndex); |
| 781 | checkNext(); |
| 782 | return x; |
| 783 | } finally { |
| 784 | lock.unlock(); |
| 785 | } |
| 786 | } |
| 787 | |
| 788 | public void remove() { |
| 789 | final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
| 790 | lock.lock(); |
| 791 | try { |
| 792 | int i = lastRet; |
| 793 | if (i == -1) |
| 794 | throw new IllegalStateException(); |
| 795 | lastRet = -1; |
| 796 | |
| 797 | int ti = takeIndex; |
| 798 | removeAt(i); |
| 799 | // back up cursor (reset to front if was first element) |
| 800 | nextIndex = (i == ti) ? takeIndex : i; |
| 801 | checkNext(); |
| 802 | } finally { |
| 803 | lock.unlock(); |
| 804 | } |
| 805 | } |
| 806 | } |
| 807 | } |