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--- old/src/share/classes/java/util/concurrent/PriorityBlockingQueue.java
+++ new/src/share/classes/java/util/concurrent/PriorityBlockingQueue.java
1 1 /*
2 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 3 *
4 4 * This code is free software; you can redistribute it and/or modify it
5 5 * under the terms of the GNU General Public License version 2 only, as
6 6 * published by the Free Software Foundation. Oracle designates this
7 7 * particular file as subject to the "Classpath" exception as provided
8 8 * by Oracle in the LICENSE file that accompanied this code.
9 9 *
10 10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 13 * version 2 for more details (a copy is included in the LICENSE file that
14 14 * accompanied this code).
15 15 *
16 16 * You should have received a copy of the GNU General Public License version
17 17 * 2 along with this work; if not, write to the Free Software Foundation,
18 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 19 *
20 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 21 * or visit www.oracle.com if you need additional information or have any
22 22 * questions.
23 23 */
24 24
25 25 /*
26 26 * This file is available under and governed by the GNU General Public
27 27 * License version 2 only, as published by the Free Software Foundation.
28 28 * However, the following notice accompanied the original version of this
29 29 * file:
30 30 *
31 31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 32 * Expert Group and released to the public domain, as explained at
33 33 * http://creativecommons.org/licenses/publicdomain
34 34 */
35 35
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35 lines elided |
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36 36 package java.util.concurrent;
37 37
38 38 import java.util.concurrent.locks.*;
39 39 import java.util.*;
40 40
41 41 /**
42 42 * An unbounded {@linkplain BlockingQueue blocking queue} that uses
43 43 * the same ordering rules as class {@link PriorityQueue} and supplies
44 44 * blocking retrieval operations. While this queue is logically
45 45 * unbounded, attempted additions may fail due to resource exhaustion
46 - * (causing <tt>OutOfMemoryError</tt>). This class does not permit
47 - * <tt>null</tt> elements. A priority queue relying on {@linkplain
46 + * (causing {@code OutOfMemoryError}). This class does not permit
47 + * {@code null} elements. A priority queue relying on {@linkplain
48 48 * Comparable natural ordering} also does not permit insertion of
49 49 * non-comparable objects (doing so results in
50 - * <tt>ClassCastException</tt>).
50 + * {@code ClassCastException}).
51 51 *
52 52 * <p>This class and its iterator implement all of the
53 53 * <em>optional</em> methods of the {@link Collection} and {@link
54 54 * Iterator} interfaces. The Iterator provided in method {@link
55 55 * #iterator()} is <em>not</em> guaranteed to traverse the elements of
56 56 * the PriorityBlockingQueue in any particular order. If you need
57 57 * ordered traversal, consider using
58 - * <tt>Arrays.sort(pq.toArray())</tt>. Also, method <tt>drainTo</tt>
58 + * {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo}
59 59 * can be used to <em>remove</em> some or all elements in priority
60 60 * order and place them in another collection.
61 61 *
62 62 * <p>Operations on this class make no guarantees about the ordering
63 63 * of elements with equal priority. If you need to enforce an
64 64 * ordering, you can define custom classes or comparators that use a
65 65 * secondary key to break ties in primary priority values. For
66 66 * example, here is a class that applies first-in-first-out
67 67 * tie-breaking to comparable elements. To use it, you would insert a
68 - * <tt>new FIFOEntry(anEntry)</tt> instead of a plain entry object.
68 + * {@code new FIFOEntry(anEntry)} instead of a plain entry object.
69 69 *
70 - * <pre>
71 - * class FIFOEntry<E extends Comparable<? super E>>
72 - * implements Comparable<FIFOEntry<E>> {
73 - * final static AtomicLong seq = new AtomicLong();
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 74 * final long seqNum;
75 75 * final E entry;
76 76 * public FIFOEntry(E entry) {
77 77 * seqNum = seq.getAndIncrement();
78 78 * this.entry = entry;
79 79 * }
80 80 * public E getEntry() { return entry; }
81 - * public int compareTo(FIFOEntry<E> other) {
81 + * public int compareTo(FIFOEntry<E> other) {
82 82 * int res = entry.compareTo(other.entry);
83 - * if (res == 0 && other.entry != this.entry)
84 - * res = (seqNum < other.seqNum ? -1 : 1);
83 + * if (res == 0 && other.entry != this.entry)
84 + * res = (seqNum < other.seqNum ? -1 : 1);
85 85 * return res;
86 86 * }
87 - * }</pre>
87 + * }}</pre>
88 88 *
89 89 * <p>This class is a member of the
90 90 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
91 91 * Java Collections Framework</a>.
92 92 *
93 93 * @since 1.5
94 94 * @author Doug Lea
95 95 * @param <E> the type of elements held in this collection
96 96 */
97 97 public class PriorityBlockingQueue<E> extends AbstractQueue<E>
98 98 implements BlockingQueue<E>, java.io.Serializable {
99 99 private static final long serialVersionUID = 5595510919245408276L;
100 100
101 - private final PriorityQueue<E> q;
102 - private final ReentrantLock lock = new ReentrantLock(true);
103 - private final Condition notEmpty = lock.newCondition();
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 + */
104 116
105 117 /**
106 - * Creates a <tt>PriorityBlockingQueue</tt> with the default
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
107 175 * initial capacity (11) that orders its elements according to
108 176 * their {@linkplain Comparable natural ordering}.
109 177 */
110 178 public PriorityBlockingQueue() {
111 - q = new PriorityQueue<E>();
179 + this(DEFAULT_INITIAL_CAPACITY, null);
112 180 }
113 181
114 182 /**
115 - * Creates a <tt>PriorityBlockingQueue</tt> with the specified
183 + * Creates a {@code PriorityBlockingQueue} with the specified
116 184 * initial capacity that orders its elements according to their
117 185 * {@linkplain Comparable natural ordering}.
118 186 *
119 187 * @param initialCapacity the initial capacity for this priority queue
120 - * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
188 + * @throws IllegalArgumentException if {@code initialCapacity} is less
121 189 * than 1
122 190 */
123 191 public PriorityBlockingQueue(int initialCapacity) {
124 - q = new PriorityQueue<E>(initialCapacity, null);
192 + this(initialCapacity, null);
125 193 }
126 194
127 195 /**
128 - * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
196 + * Creates a {@code PriorityBlockingQueue} with the specified initial
129 197 * capacity that orders its elements according to the specified
130 198 * comparator.
131 199 *
132 200 * @param initialCapacity the initial capacity for this priority queue
133 201 * @param comparator the comparator that will be used to order this
134 202 * priority queue. If {@code null}, the {@linkplain Comparable
135 203 * natural ordering} of the elements will be used.
136 - * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
204 + * @throws IllegalArgumentException if {@code initialCapacity} is less
137 205 * than 1
138 206 */
139 207 public PriorityBlockingQueue(int initialCapacity,
140 208 Comparator<? super E> comparator) {
141 - q = new PriorityQueue<E>(initialCapacity, 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];
142 215 }
143 216
144 217 /**
145 - * Creates a <tt>PriorityBlockingQueue</tt> containing the elements
218 + * Creates a {@code PriorityBlockingQueue} containing the elements
146 219 * in the specified collection. If the specified collection is a
147 220 * {@link SortedSet} or a {@link PriorityQueue}, this
148 221 * priority queue will be ordered according to the same ordering.
149 222 * Otherwise, this priority queue will be ordered according to the
150 223 * {@linkplain Comparable natural ordering} of its elements.
151 224 *
152 225 * @param c the collection whose elements are to be placed
153 226 * into this priority queue
154 227 * @throws ClassCastException if elements of the specified collection
155 228 * cannot be compared to one another according to the priority
156 229 * queue's ordering
157 230 * @throws NullPointerException if the specified collection or any
158 231 * of its elements are null
159 232 */
160 233 public PriorityBlockingQueue(Collection<? extends E> c) {
161 - q = new PriorityQueue<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();
162 265 }
163 266
164 267 /**
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 + /**
165 439 * Inserts the specified element into this priority queue.
166 440 *
167 441 * @param e the element to add
168 - * @return <tt>true</tt> (as specified by {@link Collection#add})
442 + * @return {@code true} (as specified by {@link Collection#add})
169 443 * @throws ClassCastException if the specified element cannot be compared
170 444 * with elements currently in the priority queue according to the
171 445 * priority queue's ordering
172 446 * @throws NullPointerException if the specified element is null
173 447 */
174 448 public boolean add(E e) {
175 449 return offer(e);
176 450 }
177 451
178 452 /**
179 453 * Inserts the specified element into this priority queue.
454 + * As the queue is unbounded, this method will never return {@code false}.
180 455 *
181 456 * @param e the element to add
182 - * @return <tt>true</tt> (as specified by {@link Queue#offer})
457 + * @return {@code true} (as specified by {@link Queue#offer})
183 458 * @throws ClassCastException if the specified element cannot be compared
184 459 * with elements currently in the priority queue according to the
185 460 * priority queue's ordering
186 461 * @throws NullPointerException if the specified element is null
187 462 */
188 463 public boolean offer(E e) {
464 + if (e == null)
465 + throw new NullPointerException();
189 466 final ReentrantLock lock = this.lock;
190 467 lock.lock();
468 + int n, cap;
469 + Object[] array;
470 + while ((n = size) >= (cap = (array = queue).length))
471 + tryGrow(array, cap);
191 472 try {
192 - boolean ok = q.offer(e);
193 - assert ok;
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;
194 479 notEmpty.signal();
195 - return true;
196 480 } finally {
197 481 lock.unlock();
198 482 }
483 + return true;
199 484 }
200 485
201 486 /**
202 - * Inserts the specified element into this priority queue. As the queue is
203 - * unbounded this method will never block.
487 + * Inserts the specified element into this priority queue.
488 + * As the queue is unbounded, this method will never block.
204 489 *
205 490 * @param e the element to add
206 491 * @throws ClassCastException if the specified element cannot be compared
207 492 * with elements currently in the priority queue according to the
208 493 * priority queue's ordering
209 494 * @throws NullPointerException if the specified element is null
210 495 */
211 496 public void put(E e) {
212 497 offer(e); // never need to block
213 498 }
214 499
215 500 /**
216 - * Inserts the specified element into this priority queue. As the queue is
217 - * unbounded this method will never block.
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}.
218 504 *
219 505 * @param e the element to add
220 506 * @param timeout This parameter is ignored as the method never blocks
221 507 * @param unit This parameter is ignored as the method never blocks
222 - * @return <tt>true</tt>
508 + * @return {@code true} (as specified by
509 + * {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
223 510 * @throws ClassCastException if the specified element cannot be compared
224 511 * with elements currently in the priority queue according to the
225 512 * priority queue's ordering
226 513 * @throws NullPointerException if the specified element is null
227 514 */
228 515 public boolean offer(E e, long timeout, TimeUnit unit) {
229 516 return offer(e); // never need to block
230 517 }
231 518
232 519 public E poll() {
233 520 final ReentrantLock lock = this.lock;
234 521 lock.lock();
522 + E result;
235 523 try {
236 - return q.poll();
524 + result = extract();
237 525 } finally {
238 526 lock.unlock();
239 527 }
528 + return result;
240 529 }
241 530
242 531 public E take() throws InterruptedException {
243 532 final ReentrantLock lock = this.lock;
244 533 lock.lockInterruptibly();
534 + E result;
245 535 try {
246 - try {
247 - while (q.size() == 0)
248 - notEmpty.await();
249 - } catch (InterruptedException ie) {
250 - notEmpty.signal(); // propagate to non-interrupted thread
251 - throw ie;
252 - }
253 - E x = q.poll();
254 - assert x != null;
255 - return x;
536 + while ( (result = extract()) == null)
537 + notEmpty.await();
256 538 } finally {
257 539 lock.unlock();
258 540 }
541 + return result;
259 542 }
260 543
261 544 public E poll(long timeout, TimeUnit unit) throws InterruptedException {
262 545 long nanos = unit.toNanos(timeout);
263 546 final ReentrantLock lock = this.lock;
264 547 lock.lockInterruptibly();
548 + E result;
265 549 try {
266 - for (;;) {
267 - E x = q.poll();
268 - if (x != null)
269 - return x;
270 - if (nanos <= 0)
271 - return null;
272 - try {
273 - nanos = notEmpty.awaitNanos(nanos);
274 - } catch (InterruptedException ie) {
275 - notEmpty.signal(); // propagate to non-interrupted thread
276 - throw ie;
277 - }
278 - }
550 + while ( (result = extract()) == null && nanos > 0)
551 + nanos = notEmpty.awaitNanos(nanos);
279 552 } finally {
280 553 lock.unlock();
281 554 }
555 + return result;
282 556 }
283 557
284 558 public E peek() {
285 559 final ReentrantLock lock = this.lock;
286 560 lock.lock();
561 + E result;
287 562 try {
288 - return q.peek();
563 + result = size > 0 ? (E) queue[0] : null;
289 564 } finally {
290 565 lock.unlock();
291 566 }
567 + return result;
292 568 }
293 569
294 570 /**
295 571 * Returns the comparator used to order the elements in this queue,
296 - * or <tt>null</tt> if this queue uses the {@linkplain Comparable
572 + * or {@code null} if this queue uses the {@linkplain Comparable
297 573 * natural ordering} of its elements.
298 574 *
299 575 * @return the comparator used to order the elements in this queue,
300 - * or <tt>null</tt> if this queue uses the natural
576 + * or {@code null} if this queue uses the natural
301 577 * ordering of its elements
302 578 */
303 579 public Comparator<? super E> comparator() {
304 - return q.comparator();
580 + return comparator;
305 581 }
306 582
307 583 public int size() {
308 584 final ReentrantLock lock = this.lock;
309 585 lock.lock();
310 586 try {
311 - return q.size();
587 + return size;
312 588 } finally {
313 589 lock.unlock();
314 590 }
315 591 }
316 592
317 593 /**
318 - * Always returns <tt>Integer.MAX_VALUE</tt> because
319 - * a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
320 - * @return <tt>Integer.MAX_VALUE</tt>
594 + * Always returns {@code Integer.MAX_VALUE} because
595 + * a {@code PriorityBlockingQueue} is not capacity constrained.
596 + * @return {@code Integer.MAX_VALUE} always
321 597 */
322 598 public int remainingCapacity() {
323 599 return Integer.MAX_VALUE;
324 600 }
325 601
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 +
326 613 /**
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 + /**
327 640 * Removes a single instance of the specified element from this queue,
328 641 * if it is present. More formally, removes an element {@code e} such
329 642 * that {@code o.equals(e)}, if this queue contains one or more such
330 643 * elements. Returns {@code true} if and only if this queue contained
331 644 * the specified element (or equivalently, if this queue changed as a
332 645 * result of the call).
333 646 *
334 647 * @param o element to be removed from this queue, if present
335 - * @return <tt>true</tt> if this queue changed as a result of the call
648 + * @return {@code true} if this queue changed as a result of the call
336 649 */
337 650 public boolean remove(Object o) {
651 + boolean removed = false;
338 652 final ReentrantLock lock = this.lock;
339 653 lock.lock();
340 654 try {
341 - return q.remove(o);
655 + int i = indexOf(o);
656 + if (i != -1) {
657 + removeAt(i);
658 + removed = true;
659 + }
342 660 } finally {
343 661 lock.unlock();
344 662 }
663 + return removed;
345 664 }
346 665
666 +
347 667 /**
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 + /**
348 688 * Returns {@code true} if this queue contains the specified element.
349 689 * More formally, returns {@code true} if and only if this queue contains
350 690 * at least one element {@code e} such that {@code o.equals(e)}.
351 691 *
352 692 * @param o object to be checked for containment in this queue
353 - * @return <tt>true</tt> if this queue contains the specified element
693 + * @return {@code true} if this queue contains the specified element
354 694 */
355 695 public boolean contains(Object o) {
696 + int index;
356 697 final ReentrantLock lock = this.lock;
357 698 lock.lock();
358 699 try {
359 - return q.contains(o);
700 + index = indexOf(o);
360 701 } finally {
361 702 lock.unlock();
362 703 }
704 + return index != -1;
363 705 }
364 706
365 707 /**
366 708 * Returns an array containing all of the elements in this queue.
367 709 * The returned array elements are in no particular order.
368 710 *
369 711 * <p>The returned array will be "safe" in that no references to it are
370 712 * maintained by this queue. (In other words, this method must allocate
371 713 * a new array). The caller is thus free to modify the returned array.
372 714 *
373 715 * <p>This method acts as bridge between array-based and collection-based
374 716 * APIs.
375 717 *
376 718 * @return an array containing all of the elements in this queue
377 719 */
378 720 public Object[] toArray() {
379 721 final ReentrantLock lock = this.lock;
380 722 lock.lock();
381 723 try {
382 - return q.toArray();
724 + return Arrays.copyOf(queue, size);
383 725 } finally {
384 726 lock.unlock();
385 727 }
386 728 }
387 729
388 730
389 731 public String toString() {
390 732 final ReentrantLock lock = this.lock;
391 733 lock.lock();
392 734 try {
393 - return q.toString();
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();
394 747 } finally {
395 748 lock.unlock();
396 749 }
397 750 }
398 751
399 752 /**
400 753 * @throws UnsupportedOperationException {@inheritDoc}
401 754 * @throws ClassCastException {@inheritDoc}
402 755 * @throws NullPointerException {@inheritDoc}
403 756 * @throws IllegalArgumentException {@inheritDoc}
404 757 */
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405 758 public int drainTo(Collection<? super E> c) {
406 759 if (c == null)
407 760 throw new NullPointerException();
408 761 if (c == this)
409 762 throw new IllegalArgumentException();
410 763 final ReentrantLock lock = this.lock;
411 764 lock.lock();
412 765 try {
413 766 int n = 0;
414 767 E e;
415 - while ( (e = q.poll()) != null) {
768 + while ( (e = extract()) != null) {
416 769 c.add(e);
417 770 ++n;
418 771 }
419 772 return n;
420 773 } finally {
421 774 lock.unlock();
422 775 }
423 776 }
424 777
425 778 /**
426 779 * @throws UnsupportedOperationException {@inheritDoc}
427 780 * @throws ClassCastException {@inheritDoc}
428 781 * @throws NullPointerException {@inheritDoc}
429 782 * @throws IllegalArgumentException {@inheritDoc}
430 783 */
431 784 public int drainTo(Collection<? super E> c, int maxElements) {
432 785 if (c == null)
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433 786 throw new NullPointerException();
434 787 if (c == this)
435 788 throw new IllegalArgumentException();
436 789 if (maxElements <= 0)
437 790 return 0;
438 791 final ReentrantLock lock = this.lock;
439 792 lock.lock();
440 793 try {
441 794 int n = 0;
442 795 E e;
443 - while (n < maxElements && (e = q.poll()) != null) {
796 + while (n < maxElements && (e = extract()) != null) {
444 797 c.add(e);
445 798 ++n;
446 799 }
447 800 return n;
448 801 } finally {
449 802 lock.unlock();
450 803 }
451 804 }
452 805
453 806 /**
454 807 * Atomically removes all of the elements from this queue.
455 808 * The queue will be empty after this call returns.
456 809 */
457 810 public void clear() {
458 811 final ReentrantLock lock = this.lock;
459 812 lock.lock();
460 813 try {
461 - q.clear();
814 + Object[] array = queue;
815 + int n = size;
816 + size = 0;
817 + for (int i = 0; i < n; i++)
818 + array[i] = null;
462 819 } finally {
463 820 lock.unlock();
464 821 }
465 822 }
466 823
467 824 /**
468 825 * Returns an array containing all of the elements in this queue; the
469 826 * runtime type of the returned array is that of the specified array.
470 827 * The returned array elements are in no particular order.
471 828 * If the queue fits in the specified array, it is returned therein.
472 829 * Otherwise, a new array is allocated with the runtime type of the
473 830 * specified array and the size of this queue.
474 831 *
475 832 * <p>If this queue fits in the specified array with room to spare
476 833 * (i.e., the array has more elements than this queue), the element in
477 834 * the array immediately following the end of the queue is set to
478 - * <tt>null</tt>.
835 + * {@code null}.
479 836 *
480 837 * <p>Like the {@link #toArray()} method, this method acts as bridge between
481 838 * array-based and collection-based APIs. Further, this method allows
482 839 * precise control over the runtime type of the output array, and may,
483 840 * under certain circumstances, be used to save allocation costs.
484 841 *
485 - * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
842 + * <p>Suppose {@code x} is a queue known to contain only strings.
486 843 * The following code can be used to dump the queue into a newly
487 - * allocated array of <tt>String</tt>:
844 + * allocated array of {@code String}:
488 845 *
489 846 * <pre>
490 847 * String[] y = x.toArray(new String[0]);</pre>
491 848 *
492 - * Note that <tt>toArray(new Object[0])</tt> is identical in function to
493 - * <tt>toArray()</tt>.
849 + * Note that {@code toArray(new Object[0])} is identical in function to
850 + * {@code toArray()}.
494 851 *
495 852 * @param a the array into which the elements of the queue are to
496 853 * be stored, if it is big enough; otherwise, a new array of the
497 854 * same runtime type is allocated for this purpose
498 855 * @return an array containing all of the elements in this queue
499 856 * @throws ArrayStoreException if the runtime type of the specified array
500 857 * is not a supertype of the runtime type of every element in
501 858 * this queue
502 859 * @throws NullPointerException if the specified array is null
503 860 */
504 861 public <T> T[] toArray(T[] a) {
505 862 final ReentrantLock lock = this.lock;
506 863 lock.lock();
507 864 try {
508 - return q.toArray(a);
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;
509 873 } finally {
510 874 lock.unlock();
511 875 }
512 876 }
513 877
514 878 /**
515 879 * Returns an iterator over the elements in this queue. The
516 880 * iterator does not return the elements in any particular order.
517 - * The returned <tt>Iterator</tt> is a "weakly consistent"
518 - * iterator that will never throw {@link
881 + *
882 + * <p>The returned iterator is a "weakly consistent" iterator that
883 + * will never throw {@link java.util.ConcurrentModificationException
519 884 * ConcurrentModificationException}, and guarantees to traverse
520 885 * elements as they existed upon construction of the iterator, and
521 886 * may (but is not guaranteed to) reflect any modifications
522 887 * subsequent to construction.
523 888 *
524 889 * @return an iterator over the elements in this queue
525 890 */
526 891 public Iterator<E> iterator() {
527 892 return new Itr(toArray());
528 893 }
529 894
530 895 /**
531 896 * Snapshot iterator that works off copy of underlying q array.
532 897 */
533 - private class Itr implements Iterator<E> {
898 + final class Itr implements Iterator<E> {
534 899 final Object[] array; // Array of all elements
535 900 int cursor; // index of next element to return;
536 901 int lastRet; // index of last element, or -1 if no such
537 902
538 903 Itr(Object[] array) {
539 904 lastRet = -1;
540 905 this.array = array;
541 906 }
542 907
543 908 public boolean hasNext() {
544 909 return cursor < array.length;
545 910 }
546 911
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547 912 public E next() {
548 913 if (cursor >= array.length)
549 914 throw new NoSuchElementException();
550 915 lastRet = cursor;
551 916 return (E)array[cursor++];
552 917 }
553 918
554 919 public void remove() {
555 920 if (lastRet < 0)
556 921 throw new IllegalStateException();
557 - Object x = array[lastRet];
922 + removeEQ(array[lastRet]);
558 923 lastRet = -1;
559 - // Traverse underlying queue to find == element,
560 - // not just a .equals element.
561 - lock.lock();
562 - try {
563 - for (Iterator it = q.iterator(); it.hasNext(); ) {
564 - if (it.next() == x) {
565 - it.remove();
566 - return;
567 - }
568 - }
569 - } finally {
570 - lock.unlock();
571 - }
572 924 }
573 925 }
574 926
575 927 /**
576 - * Saves the state to a stream (that is, serializes it). This
577 - * merely wraps default serialization within lock. The
578 - * serialization strategy for items is left to underlying
579 - * Queue. Note that locking is not needed on deserialization, so
580 - * readObject is not defined, just relying on default.
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.
581 932 */
582 933 private void writeObject(java.io.ObjectOutputStream s)
583 934 throws java.io.IOException {
584 935 lock.lock();
585 936 try {
937 + int n = size; // avoid zero capacity argument
938 + q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator);
939 + q.addAll(this);
586 940 s.defaultWriteObject();
587 941 } finally {
942 + q = null;
588 943 lock.unlock();
589 944 }
590 945 }
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 = sun.misc.Unsafe.getUnsafe();
967 + private static final long allocationSpinLockOffset =
968 + objectFieldOffset(UNSAFE, "allocationSpinLock",
969 + PriorityBlockingQueue.class);
970 +
971 + static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
972 + String field, Class<?> klazz) {
973 + try {
974 + return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
975 + } catch (NoSuchFieldException e) {
976 + // Convert Exception to corresponding Error
977 + NoSuchFieldError error = new NoSuchFieldError(field);
978 + error.initCause(e);
979 + throw error;
980 + }
981 + }
591 982
592 983 }
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