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My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

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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
36package java.util.concurrent;
37
38import java.util.concurrent.locks.*;
39import java.util.*;
40
41/**
42 * An unbounded {@linkplain BlockingQueue blocking queue} that uses
43 * the same ordering rules as class {@link PriorityQueue} and supplies
44 * blocking retrieval operations. While this queue is logically
45 * unbounded, attempted additions may fail due to resource exhaustion
46 * (causing {@code OutOfMemoryError}). This class does not permit
47 * {@code null} elements. A priority queue relying on {@linkplain
48 * Comparable natural ordering} also does not permit insertion of
49 * non-comparable objects (doing so results in
50 * {@code ClassCastException}).
51 *
52 * <p>This class and its iterator implement all of the
53 * <em>optional</em> methods of the {@link Collection} and {@link
54 * Iterator} interfaces. The Iterator provided in method {@link
55 * #iterator()} is <em>not</em> guaranteed to traverse the elements of
56 * the PriorityBlockingQueue in any particular order. If you need
57 * ordered traversal, consider using
58 * {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo}
59 * can be used to <em>remove</em> some or all elements in priority
60 * order and place them in another collection.
61 *
62 * <p>Operations on this class make no guarantees about the ordering
63 * of elements with equal priority. If you need to enforce an
64 * ordering, you can define custom classes or comparators that use a
65 * secondary key to break ties in primary priority values. For
66 * example, here is a class that applies first-in-first-out
67 * tie-breaking to comparable elements. To use it, you would insert a
68 * {@code new FIFOEntry(anEntry)} instead of a plain entry object.
69 *
70 * <pre> {@code
71 * class FIFOEntry<E extends Comparable<? super E>>
72 * implements Comparable<FIFOEntry<E>> {
73 * static final AtomicLong seq = new AtomicLong(0);
74 * final long seqNum;
75 * final E entry;
76 * public FIFOEntry(E entry) {
77 * seqNum = seq.getAndIncrement();
78 * this.entry = entry;
79 * }
80 * public E getEntry() { return entry; }
81 * public int compareTo(FIFOEntry<E> other) {
82 * int res = entry.compareTo(other.entry);
83 * if (res == 0 && other.entry != this.entry)
84 * res = (seqNum < other.seqNum ? -1 : 1);
85 * return res;
86 * }
87 * }}</pre>
88 *
89 * <p>This class is a member of the
90 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
91 * Java Collections Framework</a>.
92 *
93 * @since 1.5
94 * @author Doug Lea
95 * @param <E> the type of elements held in this collection
96 */
97public class PriorityBlockingQueue<E> extends AbstractQueue<E>
98 implements BlockingQueue<E>, java.io.Serializable {
99 private static final long serialVersionUID = 5595510919245408276L;
100
101 /*
102 * The implementation uses an array-based binary heap, with public
103 * operations protected with a single lock. However, allocation
104 * during resizing uses a simple spinlock (used only while not
105 * holding main lock) in order to allow takes to operate
106 * concurrently with allocation. This avoids repeated
107 * postponement of waiting consumers and consequent element
108 * build-up. The need to back away from lock during allocation
109 * makes it impossible to simply wrap delegated
110 * java.util.PriorityQueue operations within a lock, as was done
111 * in a previous version of this class. To maintain
112 * interoperability, a plain PriorityQueue is still used during
113 * serialization, which maintains compatibility at the espense of
114 * transiently doubling overhead.
115 */
116
117 /**
118 * Default array capacity.
119 */
120 private static final int DEFAULT_INITIAL_CAPACITY = 11;
121
122 /**
123 * The maximum size of array to allocate.
124 * Some VMs reserve some header words in an array.
125 * Attempts to allocate larger arrays may result in
126 * OutOfMemoryError: Requested array size exceeds VM limit
127 */
128 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
129
130 /**
131 * Priority queue represented as a balanced binary heap: the two
132 * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
133 * priority queue is ordered by comparator, or by the elements'
134 * natural ordering, if comparator is null: For each node n in the
135 * heap and each descendant d of n, n <= d. The element with the
136 * lowest value is in queue[0], assuming the queue is nonempty.
137 */
138 private transient Object[] queue;
139
140 /**
141 * The number of elements in the priority queue.
142 */
143 private transient int size;
144
145 /**
146 * The comparator, or null if priority queue uses elements'
147 * natural ordering.
148 */
149 private transient Comparator<? super E> comparator;
150
151 /**
152 * Lock used for all public operations
153 */
154 private final ReentrantLock lock;
155
156 /**
157 * Condition for blocking when empty
158 */
159 private final Condition notEmpty;
160
161 /**
162 * Spinlock for allocation, acquired via CAS.
163 */
164 private transient volatile int allocationSpinLock;
165
166 /**
167 * A plain PriorityQueue used only for serialization,
168 * to maintain compatibility with previous versions
169 * of this class. Non-null only during serialization/deserialization.
170 */
171 private PriorityQueue q;
172
173 /**
174 * Creates a {@code PriorityBlockingQueue} with the default
175 * initial capacity (11) that orders its elements according to
176 * their {@linkplain Comparable natural ordering}.
177 */
178 public PriorityBlockingQueue() {
179 this(DEFAULT_INITIAL_CAPACITY, null);
180 }
181
182 /**
183 * Creates a {@code PriorityBlockingQueue} with the specified
184 * initial capacity that orders its elements according to their
185 * {@linkplain Comparable natural ordering}.
186 *
187 * @param initialCapacity the initial capacity for this priority queue
188 * @throws IllegalArgumentException if {@code initialCapacity} is less
189 * than 1
190 */
191 public PriorityBlockingQueue(int initialCapacity) {
192 this(initialCapacity, null);
193 }
194
195 /**
196 * Creates a {@code PriorityBlockingQueue} with the specified initial
197 * capacity that orders its elements according to the specified
198 * comparator.
199 *
200 * @param initialCapacity the initial capacity for this priority queue
201 * @param comparator the comparator that will be used to order this
202 * priority queue. If {@code null}, the {@linkplain Comparable
203 * natural ordering} of the elements will be used.
204 * @throws IllegalArgumentException if {@code initialCapacity} is less
205 * than 1
206 */
207 public PriorityBlockingQueue(int initialCapacity,
208 Comparator<? super E> comparator) {
209 if (initialCapacity < 1)
210 throw new IllegalArgumentException();
211 this.lock = new ReentrantLock();
212 this.notEmpty = lock.newCondition();
213 this.comparator = comparator;
214 this.queue = new Object[initialCapacity];
215 }
216
217 /**
218 * Creates a {@code PriorityBlockingQueue} containing the elements
219 * in the specified collection. If the specified collection is a
220 * {@link SortedSet} or a {@link PriorityQueue}, this
221 * priority queue will be ordered according to the same ordering.
222 * Otherwise, this priority queue will be ordered according to the
223 * {@linkplain Comparable natural ordering} of its elements.
224 *
225 * @param c the collection whose elements are to be placed
226 * into this priority queue
227 * @throws ClassCastException if elements of the specified collection
228 * cannot be compared to one another according to the priority
229 * queue's ordering
230 * @throws NullPointerException if the specified collection or any
231 * of its elements are null
232 */
233 public PriorityBlockingQueue(Collection<? extends E> c) {
234 this.lock = new ReentrantLock();
235 this.notEmpty = lock.newCondition();
236 boolean heapify = true; // true if not known to be in heap order
237 boolean screen = true; // true if must screen for nulls
238 if (c instanceof SortedSet<?>) {
239 SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
240 this.comparator = (Comparator<? super E>) ss.comparator();
241 heapify = false;
242 }
243 else if (c instanceof PriorityBlockingQueue<?>) {
244 PriorityBlockingQueue<? extends E> pq =
245 (PriorityBlockingQueue<? extends E>) c;
246 this.comparator = (Comparator<? super E>) pq.comparator();
247 screen = false;
248 if (pq.getClass() == PriorityBlockingQueue.class) // exact match
249 heapify = false;
250 }
251 Object[] a = c.toArray();
252 int n = a.length;
253 // If c.toArray incorrectly doesn't return Object[], copy it.
254 if (a.getClass() != Object[].class)
255 a = Arrays.copyOf(a, n, Object[].class);
256 if (screen && (n == 1 || this.comparator != null)) {
257 for (int i = 0; i < n; ++i)
258 if (a[i] == null)
259 throw new NullPointerException();
260 }
261 this.queue = a;
262 this.size = n;
263 if (heapify)
264 heapify();
265 }
266
267 /**
268 * Tries to grow array to accommodate at least one more element
269 * (but normally expand by about 50%), giving up (allowing retry)
270 * on contention (which we expect to be rare). Call only while
271 * holding lock.
272 *
273 * @param array the heap array
274 * @param oldCap the length of the array
275 */
276 private void tryGrow(Object[] array, int oldCap) {
277 lock.unlock(); // must release and then re-acquire main lock
278 Object[] newArray = null;
279 if (allocationSpinLock == 0 &&
280 UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset,
281 0, 1)) {
282 try {
283 int newCap = oldCap + ((oldCap < 64) ?
284 (oldCap + 2) : // grow faster if small
285 (oldCap >> 1));
286 if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow
287 int minCap = oldCap + 1;
288 if (minCap < 0 || minCap > MAX_ARRAY_SIZE)
289 throw new OutOfMemoryError();
290 newCap = MAX_ARRAY_SIZE;
291 }
292 if (newCap > oldCap && queue == array)
293 newArray = new Object[newCap];
294 } finally {
295 allocationSpinLock = 0;
296 }
297 }
298 if (newArray == null) // back off if another thread is allocating
299 Thread.yield();
300 lock.lock();
301 if (newArray != null && queue == array) {
302 queue = newArray;
303 System.arraycopy(array, 0, newArray, 0, oldCap);
304 }
305 }
306
307 /**
308 * Mechanics for poll(). Call only while holding lock.
309 */
310 private E extract() {
311 E result;
312 int n = size - 1;
313 if (n < 0)
314 result = null;
315 else {
316 Object[] array = queue;
317 result = (E) array[0];
318 E x = (E) array[n];
319 array[n] = null;
320 Comparator<? super E> cmp = comparator;
321 if (cmp == null)
322 siftDownComparable(0, x, array, n);
323 else
324 siftDownUsingComparator(0, x, array, n, cmp);
325 size = n;
326 }
327 return result;
328 }
329
330 /**
331 * Inserts item x at position k, maintaining heap invariant by
332 * promoting x up the tree until it is greater than or equal to
333 * its parent, or is the root.
334 *
335 * To simplify and speed up coercions and comparisons. the
336 * Comparable and Comparator versions are separated into different
337 * methods that are otherwise identical. (Similarly for siftDown.)
338 * These methods are static, with heap state as arguments, to
339 * simplify use in light of possible comparator exceptions.
340 *
341 * @param k the position to fill
342 * @param x the item to insert
343 * @param array the heap array
344 * @param n heap size
345 */
346 private static <T> void siftUpComparable(int k, T x, Object[] array) {
347 Comparable<? super T> key = (Comparable<? super T>) x;
348 while (k > 0) {
349 int parent = (k - 1) >>> 1;
350 Object e = array[parent];
351 if (key.compareTo((T) e) >= 0)
352 break;
353 array[k] = e;
354 k = parent;
355 }
356 array[k] = key;
357 }
358
359 private static <T> void siftUpUsingComparator(int k, T x, Object[] array,
360 Comparator<? super T> cmp) {
361 while (k > 0) {
362 int parent = (k - 1) >>> 1;
363 Object e = array[parent];
364 if (cmp.compare(x, (T) e) >= 0)
365 break;
366 array[k] = e;
367 k = parent;
368 }
369 array[k] = x;
370 }
371
372 /**
373 * Inserts item x at position k, maintaining heap invariant by
374 * demoting x down the tree repeatedly until it is less than or
375 * equal to its children or is a leaf.
376 *
377 * @param k the position to fill
378 * @param x the item to insert
379 * @param array the heap array
380 * @param n heap size
381 */
382 private static <T> void siftDownComparable(int k, T x, Object[] array,
383 int n) {
384 Comparable<? super T> key = (Comparable<? super T>)x;
385 int half = n >>> 1; // loop while a non-leaf
386 while (k < half) {
387 int child = (k << 1) + 1; // assume left child is least
388 Object c = array[child];
389 int right = child + 1;
390 if (right < n &&
391 ((Comparable<? super T>) c).compareTo((T) array[right]) > 0)
392 c = array[child = right];
393 if (key.compareTo((T) c) <= 0)
394 break;
395 array[k] = c;
396 k = child;
397 }
398 array[k] = key;
399 }
400
401 private static <T> void siftDownUsingComparator(int k, T x, Object[] array,
402 int n,
403 Comparator<? super T> cmp) {
404 int half = n >>> 1;
405 while (k < half) {
406 int child = (k << 1) + 1;
407 Object c = array[child];
408 int right = child + 1;
409 if (right < n && cmp.compare((T) c, (T) array[right]) > 0)
410 c = array[child = right];
411 if (cmp.compare(x, (T) c) <= 0)
412 break;
413 array[k] = c;
414 k = child;
415 }
416 array[k] = x;
417 }
418
419 /**
420 * Establishes the heap invariant (described above) in the entire tree,
421 * assuming nothing about the order of the elements prior to the call.
422 */
423 private void heapify() {
424 Object[] array = queue;
425 int n = size;
426 int half = (n >>> 1) - 1;
427 Comparator<? super E> cmp = comparator;
428 if (cmp == null) {
429 for (int i = half; i >= 0; i--)
430 siftDownComparable(i, (E) array[i], array, n);
431 }
432 else {
433 for (int i = half; i >= 0; i--)
434 siftDownUsingComparator(i, (E) array[i], array, n, cmp);
435 }
436 }
437
438 /**
439 * Inserts the specified element into this priority queue.
440 *
441 * @param e the element to add
442 * @return {@code true} (as specified by {@link Collection#add})
443 * @throws ClassCastException if the specified element cannot be compared
444 * with elements currently in the priority queue according to the
445 * priority queue's ordering
446 * @throws NullPointerException if the specified element is null
447 */
448 public boolean add(E e) {
449 return offer(e);
450 }
451
452 /**
453 * Inserts the specified element into this priority queue.
454 * As the queue is unbounded, this method will never return {@code false}.
455 *
456 * @param e the element to add
457 * @return {@code true} (as specified by {@link Queue#offer})
458 * @throws ClassCastException if the specified element cannot be compared
459 * with elements currently in the priority queue according to the
460 * priority queue's ordering
461 * @throws NullPointerException if the specified element is null
462 */
463 public boolean offer(E e) {
464 if (e == null)
465 throw new NullPointerException();
466 final ReentrantLock lock = this.lock;
467 lock.lock();
468 int n, cap;
469 Object[] array;
470 while ((n = size) >= (cap = (array = queue).length))
471 tryGrow(array, cap);
472 try {
473 Comparator<? super E> cmp = comparator;
474 if (cmp == null)
475 siftUpComparable(n, e, array);
476 else
477 siftUpUsingComparator(n, e, array, cmp);
478 size = n + 1;
479 notEmpty.signal();
480 } finally {
481 lock.unlock();
482 }
483 return true;
484 }
485
486 /**
487 * Inserts the specified element into this priority queue.
488 * As the queue is unbounded, this method will never block.
489 *
490 * @param e the element to add
491 * @throws ClassCastException if the specified element cannot be compared
492 * with elements currently in the priority queue according to the
493 * priority queue's ordering
494 * @throws NullPointerException if the specified element is null
495 */
496 public void put(E e) {
497 offer(e); // never need to block
498 }
499
500 /**
501 * Inserts the specified element into this priority queue.
502 * As the queue is unbounded, this method will never block or
503 * return {@code false}.
504 *
505 * @param e the element to add
506 * @param timeout This parameter is ignored as the method never blocks
507 * @param unit This parameter is ignored as the method never blocks
508 * @return {@code true} (as specified by
509 * {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
510 * @throws ClassCastException if the specified element cannot be compared
511 * with elements currently in the priority queue according to the
512 * priority queue's ordering
513 * @throws NullPointerException if the specified element is null
514 */
515 public boolean offer(E e, long timeout, TimeUnit unit) {
516 return offer(e); // never need to block
517 }
518
519 public E poll() {
520 final ReentrantLock lock = this.lock;
521 lock.lock();
522 E result;
523 try {
524 result = extract();
525 } finally {
526 lock.unlock();
527 }
528 return result;
529 }
530
531 public E take() throws InterruptedException {
532 final ReentrantLock lock = this.lock;
533 lock.lockInterruptibly();
534 E result;
535 try {
536 while ( (result = extract()) == null)
537 notEmpty.await();
538 } finally {
539 lock.unlock();
540 }
541 return result;
542 }
543
544 public E poll(long timeout, TimeUnit unit) throws InterruptedException {
545 long nanos = unit.toNanos(timeout);
546 final ReentrantLock lock = this.lock;
547 lock.lockInterruptibly();
548 E result;
549 try {
550 while ( (result = extract()) == null && nanos > 0)
551 nanos = notEmpty.awaitNanos(nanos);
552 } finally {
553 lock.unlock();
554 }
555 return result;
556 }
557
558 public E peek() {
559 final ReentrantLock lock = this.lock;
560 lock.lock();
561 E result;
562 try {
563 result = size > 0 ? (E) queue[0] : null;
564 } finally {
565 lock.unlock();
566 }
567 return result;
568 }
569
570 /**
571 * Returns the comparator used to order the elements in this queue,
572 * or {@code null} if this queue uses the {@linkplain Comparable
573 * natural ordering} of its elements.
574 *
575 * @return the comparator used to order the elements in this queue,
576 * or {@code null} if this queue uses the natural
577 * ordering of its elements
578 */
579 public Comparator<? super E> comparator() {
580 return comparator;
581 }
582
583 public int size() {
584 final ReentrantLock lock = this.lock;
585 lock.lock();
586 try {
587 return size;
588 } finally {
589 lock.unlock();
590 }
591 }
592
593 /**
594 * Always returns {@code Integer.MAX_VALUE} because
595 * a {@code PriorityBlockingQueue} is not capacity constrained.
596 * @return {@code Integer.MAX_VALUE} always
597 */
598 public int remainingCapacity() {
599 return Integer.MAX_VALUE;
600 }
601
602 private int indexOf(Object o) {
603 if (o != null) {
604 Object[] array = queue;
605 int n = size;
606 for (int i = 0; i < n; i++)
607 if (o.equals(array[i]))
608 return i;
609 }
610 return -1;
611 }
612
613 /**
614 * Removes the ith element from queue.
615 */
616 private void removeAt(int i) {
617 Object[] array = queue;
618 int n = size - 1;
619 if (n == i) // removed last element
620 array[i] = null;
621 else {
622 E moved = (E) array[n];
623 array[n] = null;
624 Comparator<? super E> cmp = comparator;
625 if (cmp == null)
626 siftDownComparable(i, moved, array, n);
627 else
628 siftDownUsingComparator(i, moved, array, n, cmp);
629 if (array[i] == moved) {
630 if (cmp == null)
631 siftUpComparable(i, moved, array);
632 else
633 siftUpUsingComparator(i, moved, array, cmp);
634 }
635 }
636 size = n;
637 }
638
639 /**
640 * Removes a single instance of the specified element from this queue,
641 * if it is present. More formally, removes an element {@code e} such
642 * that {@code o.equals(e)}, if this queue contains one or more such
643 * elements. Returns {@code true} if and only if this queue contained
644 * the specified element (or equivalently, if this queue changed as a
645 * result of the call).
646 *
647 * @param o element to be removed from this queue, if present
648 * @return {@code true} if this queue changed as a result of the call
649 */
650 public boolean remove(Object o) {
651 boolean removed = false;
652 final ReentrantLock lock = this.lock;
653 lock.lock();
654 try {
655 int i = indexOf(o);
656 if (i != -1) {
657 removeAt(i);
658 removed = true;
659 }
660 } finally {
661 lock.unlock();
662 }
663 return removed;
664 }
665
666
667 /**
668 * Identity-based version for use in Itr.remove
669 */
670 private void removeEQ(Object o) {
671 final ReentrantLock lock = this.lock;
672 lock.lock();
673 try {
674 Object[] array = queue;
675 int n = size;
676 for (int i = 0; i < n; i++) {
677 if (o == array[i]) {
678 removeAt(i);
679 break;
680 }
681 }
682 } finally {
683 lock.unlock();
684 }
685 }
686
687 /**
688 * Returns {@code true} if this queue contains the specified element.
689 * More formally, returns {@code true} if and only if this queue contains
690 * at least one element {@code e} such that {@code o.equals(e)}.
691 *
692 * @param o object to be checked for containment in this queue
693 * @return {@code true} if this queue contains the specified element
694 */
695 public boolean contains(Object o) {
696 int index;
697 final ReentrantLock lock = this.lock;
698 lock.lock();
699 try {
700 index = indexOf(o);
701 } finally {
702 lock.unlock();
703 }
704 return index != -1;
705 }
706
707 /**
708 * Returns an array containing all of the elements in this queue.
709 * The returned array elements are in no particular order.
710 *
711 * <p>The returned array will be "safe" in that no references to it are
712 * maintained by this queue. (In other words, this method must allocate
713 * a new array). The caller is thus free to modify the returned array.
714 *
715 * <p>This method acts as bridge between array-based and collection-based
716 * APIs.
717 *
718 * @return an array containing all of the elements in this queue
719 */
720 public Object[] toArray() {
721 final ReentrantLock lock = this.lock;
722 lock.lock();
723 try {
724 return Arrays.copyOf(queue, size);
725 } finally {
726 lock.unlock();
727 }
728 }
729
730
731 public String toString() {
732 final ReentrantLock lock = this.lock;
733 lock.lock();
734 try {
735 int n = size;
736 if (n == 0)
737 return "[]";
738 StringBuilder sb = new StringBuilder();
739 sb.append('[');
740 for (int i = 0; i < n; ++i) {
741 E e = (E)queue[i];
742 sb.append(e == this ? "(this Collection)" : e);
743 if (i != n - 1)
744 sb.append(',').append(' ');
745 }
746 return sb.append(']').toString();
747 } finally {
748 lock.unlock();
749 }
750 }
751
752 /**
753 * @throws UnsupportedOperationException {@inheritDoc}
754 * @throws ClassCastException {@inheritDoc}
755 * @throws NullPointerException {@inheritDoc}
756 * @throws IllegalArgumentException {@inheritDoc}
757 */
758 public int drainTo(Collection<? super E> c) {
759 if (c == null)
760 throw new NullPointerException();
761 if (c == this)
762 throw new IllegalArgumentException();
763 final ReentrantLock lock = this.lock;
764 lock.lock();
765 try {
766 int n = 0;
767 E e;
768 while ( (e = extract()) != null) {
769 c.add(e);
770 ++n;
771 }
772 return n;
773 } finally {
774 lock.unlock();
775 }
776 }
777
778 /**
779 * @throws UnsupportedOperationException {@inheritDoc}
780 * @throws ClassCastException {@inheritDoc}
781 * @throws NullPointerException {@inheritDoc}
782 * @throws IllegalArgumentException {@inheritDoc}
783 */
784 public int drainTo(Collection<? super E> c, int maxElements) {
785 if (c == null)
786 throw new NullPointerException();
787 if (c == this)
788 throw new IllegalArgumentException();
789 if (maxElements <= 0)
790 return 0;
791 final ReentrantLock lock = this.lock;
792 lock.lock();
793 try {
794 int n = 0;
795 E e;
796 while (n < maxElements && (e = extract()) != null) {
797 c.add(e);
798 ++n;
799 }
800 return n;
801 } finally {
802 lock.unlock();
803 }
804 }
805
806 /**
807 * Atomically removes all of the elements from this queue.
808 * The queue will be empty after this call returns.
809 */
810 public void clear() {
811 final ReentrantLock lock = this.lock;
812 lock.lock();
813 try {
814 Object[] array = queue;
815 int n = size;
816 size = 0;
817 for (int i = 0; i < n; i++)
818 array[i] = null;
819 } finally {
820 lock.unlock();
821 }
822 }
823
824 /**
825 * Returns an array containing all of the elements in this queue; the
826 * runtime type of the returned array is that of the specified array.
827 * The returned array elements are in no particular order.
828 * If the queue fits in the specified array, it is returned therein.
829 * Otherwise, a new array is allocated with the runtime type of the
830 * specified array and the size of this queue.
831 *
832 * <p>If this queue fits in the specified array with room to spare
833 * (i.e., the array has more elements than this queue), the element in
834 * the array immediately following the end of the queue is set to
835 * {@code null}.
836 *
837 * <p>Like the {@link #toArray()} method, this method acts as bridge between
838 * array-based and collection-based APIs. Further, this method allows
839 * precise control over the runtime type of the output array, and may,
840 * under certain circumstances, be used to save allocation costs.
841 *
842 * <p>Suppose {@code x} is a queue known to contain only strings.
843 * The following code can be used to dump the queue into a newly
844 * allocated array of {@code String}:
845 *
846 * <pre>
847 * String[] y = x.toArray(new String[0]);</pre>
848 *
849 * Note that {@code toArray(new Object[0])} is identical in function to
850 * {@code toArray()}.
851 *
852 * @param a the array into which the elements of the queue are to
853 * be stored, if it is big enough; otherwise, a new array of the
854 * same runtime type is allocated for this purpose
855 * @return an array containing all of the elements in this queue
856 * @throws ArrayStoreException if the runtime type of the specified array
857 * is not a supertype of the runtime type of every element in
858 * this queue
859 * @throws NullPointerException if the specified array is null
860 */
861 public <T> T[] toArray(T[] a) {
862 final ReentrantLock lock = this.lock;
863 lock.lock();
864 try {
865 int n = size;
866 if (a.length < n)
867 // Make a new array of a's runtime type, but my contents:
868 return (T[]) Arrays.copyOf(queue, size, a.getClass());
869 System.arraycopy(queue, 0, a, 0, n);
870 if (a.length > n)
871 a[n] = null;
872 return a;
873 } finally {
874 lock.unlock();
875 }
876 }
877
878 /**
879 * Returns an iterator over the elements in this queue. The
880 * iterator does not return the elements in any particular order.
881 *
882 * <p>The returned iterator is a "weakly consistent" iterator that
883 * will never throw {@link java.util.ConcurrentModificationException
884 * ConcurrentModificationException}, and guarantees to traverse
885 * elements as they existed upon construction of the iterator, and
886 * may (but is not guaranteed to) reflect any modifications
887 * subsequent to construction.
888 *
889 * @return an iterator over the elements in this queue
890 */
891 public Iterator<E> iterator() {
892 return new Itr(toArray());
893 }
894
895 /**
896 * Snapshot iterator that works off copy of underlying q array.
897 */
898 final class Itr implements Iterator<E> {
899 final Object[] array; // Array of all elements
900 int cursor; // index of next element to return;
901 int lastRet; // index of last element, or -1 if no such
902
903 Itr(Object[] array) {
904 lastRet = -1;
905 this.array = array;
906 }
907
908 public boolean hasNext() {
909 return cursor < array.length;
910 }
911
912 public E next() {
913 if (cursor >= array.length)
914 throw new NoSuchElementException();
915 lastRet = cursor;
916 return (E)array[cursor++];
917 }
918
919 public void remove() {
920 if (lastRet < 0)
921 throw new IllegalStateException();
922 removeEQ(array[lastRet]);
923 lastRet = -1;
924 }
925 }
926
927 /**
928 * Saves the state to a stream (that is, serializes it). For
929 * compatibility with previous version of this class,
930 * elements are first copied to a java.util.PriorityQueue,
931 * which is then serialized.
932 */
933 private void writeObject(java.io.ObjectOutputStream s)
934 throws java.io.IOException {
935 lock.lock();
936 try {
937 int n = size; // avoid zero capacity argument
938 q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator);
939 q.addAll(this);
940 s.defaultWriteObject();
941 } finally {
942 q = null;
943 lock.unlock();
944 }
945 }
946
947 /**
948 * Reconstitutes the {@code PriorityBlockingQueue} instance from a stream
949 * (that is, deserializes it).
950 *
951 * @param s the stream
952 */
953 private void readObject(java.io.ObjectInputStream s)
954 throws java.io.IOException, ClassNotFoundException {
955 try {
956 s.defaultReadObject();
957 this.queue = new Object[q.size()];
958 comparator = q.comparator();
959 addAll(q);
960 } finally {
961 q = null;
962 }
963 }
964
965 // Unsafe mechanics
966 private static final sun.misc.Unsafe UNSAFE;
967 private static final long allocationSpinLockOffset;
968 static {
969 try {
970 UNSAFE = sun.misc.Unsafe.getUnsafe();
971 Class k = PriorityBlockingQueue.class;
972 allocationSpinLockOffset = UNSAFE.objectFieldOffset
973 (k.getDeclaredField("allocationSpinLock"));
974 } catch (Exception e) {
975 throw new Error(e);
976 }
977 }
978}