1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain, as explained at |
4 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
5 |
*/ |
6 |
|
7 |
package java.util.concurrent; |
8 |
|
9 |
import java.util.concurrent.locks.*; |
10 |
import java.util.*; |
11 |
|
12 |
/** |
13 |
* An unbounded {@linkplain BlockingQueue blocking queue} that uses |
14 |
* the same ordering rules as class {@link PriorityQueue} and supplies |
15 |
* blocking retrieval operations. While this queue is logically |
16 |
* unbounded, attempted additions may fail due to resource exhaustion |
17 |
* (causing {@code OutOfMemoryError}). This class does not permit |
18 |
* {@code null} elements. A priority queue relying on {@linkplain |
19 |
* Comparable natural ordering} also does not permit insertion of |
20 |
* non-comparable objects (doing so results in |
21 |
* {@code ClassCastException}). |
22 |
* |
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* <p>This class and its iterator implement all of the |
24 |
* <em>optional</em> methods of the {@link Collection} and {@link |
25 |
* Iterator} interfaces. The Iterator provided in method {@link |
26 |
* #iterator()} is <em>not</em> guaranteed to traverse the elements of |
27 |
* the PriorityBlockingQueue in any particular order. If you need |
28 |
* ordered traversal, consider using |
29 |
* {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo} |
30 |
* can be used to <em>remove</em> some or all elements in priority |
31 |
* order and place them in another collection. |
32 |
* |
33 |
* <p>Operations on this class make no guarantees about the ordering |
34 |
* of elements with equal priority. If you need to enforce an |
35 |
* ordering, you can define custom classes or comparators that use a |
36 |
* secondary key to break ties in primary priority values. For |
37 |
* example, here is a class that applies first-in-first-out |
38 |
* tie-breaking to comparable elements. To use it, you would insert a |
39 |
* {@code new FIFOEntry(anEntry)} instead of a plain entry object. |
40 |
* |
41 |
* <pre> {@code |
42 |
* class FIFOEntry<E extends Comparable<? super E>> |
43 |
* implements Comparable<FIFOEntry<E>> { |
44 |
* static final AtomicLong seq = new AtomicLong(0); |
45 |
* final long seqNum; |
46 |
* final E entry; |
47 |
* public FIFOEntry(E entry) { |
48 |
* seqNum = seq.getAndIncrement(); |
49 |
* this.entry = entry; |
50 |
* } |
51 |
* public E getEntry() { return entry; } |
52 |
* public int compareTo(FIFOEntry<E> other) { |
53 |
* int res = entry.compareTo(other.entry); |
54 |
* if (res == 0 && other.entry != this.entry) |
55 |
* res = (seqNum < other.seqNum ? -1 : 1); |
56 |
* return res; |
57 |
* } |
58 |
* }}</pre> |
59 |
* |
60 |
* <p>This class is a member of the |
61 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
62 |
* Java Collections Framework</a>. |
63 |
* |
64 |
* @since 1.5 |
65 |
* @author Doug Lea |
66 |
* @param <E> the type of elements held in this collection |
67 |
*/ |
68 |
public class PriorityBlockingQueue<E> extends AbstractQueue<E> |
69 |
implements BlockingQueue<E>, java.io.Serializable { |
70 |
private static final long serialVersionUID = 5595510919245408276L; |
71 |
|
72 |
/* |
73 |
* The implementation uses an array-based binary heap, with public |
74 |
* operations protected with a single lock. However, allocation |
75 |
* during resizing uses a simple spinlock (used only while not |
76 |
* holding main lock) in order to allow takes to operate |
77 |
* concurrently with allocation. This avoids repeated |
78 |
* postponement of waiting consumers and consequent element |
79 |
* build-up. The need to back away from lock during allocation |
80 |
* makes it impossible to simply wrap delegated |
81 |
* java.util.PriorityQueue operations within a lock, as was done |
82 |
* in a previous version of this class. To maintain |
83 |
* interoperability, a plain PriorityQueue is still used during |
84 |
* serialization, which maintains compatibility at the espense of |
85 |
* transiently doubling overhead. |
86 |
*/ |
87 |
|
88 |
/** |
89 |
* Default array capacity. |
90 |
*/ |
91 |
private static final int DEFAULT_INITIAL_CAPACITY = 11; |
92 |
|
93 |
/** |
94 |
* The maximum size of array to allocate. |
95 |
* Some VMs reserve some header words in an array. |
96 |
* Attempts to allocate larger arrays may result in |
97 |
* OutOfMemoryError: Requested array size exceeds VM limit |
98 |
*/ |
99 |
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; |
100 |
|
101 |
/** |
102 |
* Priority queue represented as a balanced binary heap: the two |
103 |
* children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The |
104 |
* priority queue is ordered by comparator, or by the elements' |
105 |
* natural ordering, if comparator is null: For each node n in the |
106 |
* heap and each descendant d of n, n <= d. The element with the |
107 |
* lowest value is in queue[0], assuming the queue is nonempty. |
108 |
*/ |
109 |
private transient Object[] queue; |
110 |
|
111 |
/** |
112 |
* The number of elements in the priority queue. |
113 |
*/ |
114 |
private transient int size; |
115 |
|
116 |
/** |
117 |
* The comparator, or null if priority queue uses elements' |
118 |
* natural ordering. |
119 |
*/ |
120 |
private transient Comparator<? super E> comparator; |
121 |
|
122 |
/** |
123 |
* Lock used for all public operations |
124 |
*/ |
125 |
private final ReentrantLock lock; |
126 |
|
127 |
/** |
128 |
* Condition for blocking when empty |
129 |
*/ |
130 |
private final Condition notEmpty; |
131 |
|
132 |
/** |
133 |
* Spinlock for allocation, acquired via CAS. |
134 |
*/ |
135 |
private transient volatile int allocationSpinLock; |
136 |
|
137 |
/** |
138 |
* A plain PriorityQueue used only for serialization, |
139 |
* to maintain compatibility with previous versions |
140 |
* of this class. Non-null only during serialization/deserialization. |
141 |
*/ |
142 |
private PriorityQueue<E> q; |
143 |
|
144 |
/** |
145 |
* Creates a {@code PriorityBlockingQueue} with the default |
146 |
* initial capacity (11) that orders its elements according to |
147 |
* their {@linkplain Comparable natural ordering}. |
148 |
*/ |
149 |
public PriorityBlockingQueue() { |
150 |
this(DEFAULT_INITIAL_CAPACITY, null); |
151 |
} |
152 |
|
153 |
/** |
154 |
* Creates a {@code PriorityBlockingQueue} with the specified |
155 |
* initial capacity that orders its elements according to their |
156 |
* {@linkplain Comparable natural ordering}. |
157 |
* |
158 |
* @param initialCapacity the initial capacity for this priority queue |
159 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
160 |
* than 1 |
161 |
*/ |
162 |
public PriorityBlockingQueue(int initialCapacity) { |
163 |
this(initialCapacity, null); |
164 |
} |
165 |
|
166 |
/** |
167 |
* Creates a {@code PriorityBlockingQueue} with the specified initial |
168 |
* capacity that orders its elements according to the specified |
169 |
* comparator. |
170 |
* |
171 |
* @param initialCapacity the initial capacity for this priority queue |
172 |
* @param comparator the comparator that will be used to order this |
173 |
* priority queue. If {@code null}, the {@linkplain Comparable |
174 |
* natural ordering} of the elements will be used. |
175 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
176 |
* than 1 |
177 |
*/ |
178 |
public PriorityBlockingQueue(int initialCapacity, |
179 |
Comparator<? super E> comparator) { |
180 |
if (initialCapacity < 1) |
181 |
throw new IllegalArgumentException(); |
182 |
this.lock = new ReentrantLock(); |
183 |
this.notEmpty = lock.newCondition(); |
184 |
this.comparator = comparator; |
185 |
this.queue = new Object[initialCapacity]; |
186 |
} |
187 |
|
188 |
/** |
189 |
* Creates a {@code PriorityBlockingQueue} containing the elements |
190 |
* in the specified collection. If the specified collection is a |
191 |
* {@link SortedSet} or a {@link PriorityQueue}, this |
192 |
* priority queue will be ordered according to the same ordering. |
193 |
* Otherwise, this priority queue will be ordered according to the |
194 |
* {@linkplain Comparable natural ordering} of its elements. |
195 |
* |
196 |
* @param c the collection whose elements are to be placed |
197 |
* into this priority queue |
198 |
* @throws ClassCastException if elements of the specified collection |
199 |
* cannot be compared to one another according to the priority |
200 |
* queue's ordering |
201 |
* @throws NullPointerException if the specified collection or any |
202 |
* of its elements are null |
203 |
*/ |
204 |
public PriorityBlockingQueue(Collection<? extends E> c) { |
205 |
this.lock = new ReentrantLock(); |
206 |
this.notEmpty = lock.newCondition(); |
207 |
boolean heapify = true; // true if not known to be in heap order |
208 |
boolean screen = true; // true if must screen for nulls |
209 |
if (c instanceof SortedSet<?>) { |
210 |
SortedSet<? extends E> ss = (SortedSet<? extends E>) c; |
211 |
this.comparator = (Comparator<? super E>) ss.comparator(); |
212 |
heapify = false; |
213 |
} |
214 |
else if (c instanceof PriorityBlockingQueue<?>) { |
215 |
PriorityBlockingQueue<? extends E> pq = |
216 |
(PriorityBlockingQueue<? extends E>) c; |
217 |
this.comparator = (Comparator<? super E>) pq.comparator(); |
218 |
screen = false; |
219 |
if (pq.getClass() == PriorityBlockingQueue.class) // exact match |
220 |
heapify = false; |
221 |
} |
222 |
Object[] a = c.toArray(); |
223 |
int n = a.length; |
224 |
// If c.toArray incorrectly doesn't return Object[], copy it. |
225 |
if (a.getClass() != Object[].class) |
226 |
a = Arrays.copyOf(a, n, Object[].class); |
227 |
if (screen && (n == 1 || this.comparator != null)) { |
228 |
for (int i = 0; i < n; ++i) |
229 |
if (a[i] == null) |
230 |
throw new NullPointerException(); |
231 |
} |
232 |
this.queue = a; |
233 |
this.size = n; |
234 |
if (heapify) |
235 |
heapify(); |
236 |
} |
237 |
|
238 |
/** |
239 |
* Tries to grow array to accommodate at least one more element |
240 |
* (but normally expand by about 50%), giving up (allowing retry) |
241 |
* on contention (which we expect to be rare). Call only while |
242 |
* holding lock. |
243 |
* |
244 |
* @param array the heap array |
245 |
* @param oldCap the length of the array |
246 |
*/ |
247 |
private void tryGrow(Object[] array, int oldCap) { |
248 |
lock.unlock(); // must release and then re-acquire main lock |
249 |
Object[] newArray = null; |
250 |
if (allocationSpinLock == 0 && |
251 |
UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset, |
252 |
0, 1)) { |
253 |
try { |
254 |
int newCap = oldCap + ((oldCap < 64) ? |
255 |
(oldCap + 2) : // grow faster if small |
256 |
(oldCap >> 1)); |
257 |
if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow |
258 |
int minCap = oldCap + 1; |
259 |
if (minCap < 0 || minCap > MAX_ARRAY_SIZE) |
260 |
throw new OutOfMemoryError(); |
261 |
newCap = MAX_ARRAY_SIZE; |
262 |
} |
263 |
if (newCap > oldCap && queue == array) |
264 |
newArray = new Object[newCap]; |
265 |
} finally { |
266 |
allocationSpinLock = 0; |
267 |
} |
268 |
} |
269 |
if (newArray == null) // back off if another thread is allocating |
270 |
Thread.yield(); |
271 |
lock.lock(); |
272 |
if (newArray != null && queue == array) { |
273 |
queue = newArray; |
274 |
System.arraycopy(array, 0, newArray, 0, oldCap); |
275 |
} |
276 |
} |
277 |
|
278 |
/** |
279 |
* Mechanics for poll(). Call only while holding lock. |
280 |
*/ |
281 |
private E extract() { |
282 |
int n = size - 1; |
283 |
if (n < 0) |
284 |
return null; |
285 |
else { |
286 |
Object[] array = queue; |
287 |
E result = (E) array[0]; |
288 |
E x = (E) array[n]; |
289 |
array[n] = null; |
290 |
Comparator<? super E> cmp = comparator; |
291 |
if (cmp == null) |
292 |
siftDownComparable(0, x, array, n); |
293 |
else |
294 |
siftDownUsingComparator(0, x, array, n, cmp); |
295 |
size = n; |
296 |
return result; |
297 |
} |
298 |
} |
299 |
|
300 |
/** |
301 |
* Inserts item x at position k, maintaining heap invariant by |
302 |
* promoting x up the tree until it is greater than or equal to |
303 |
* its parent, or is the root. |
304 |
* |
305 |
* To simplify and speed up coercions and comparisons. the |
306 |
* Comparable and Comparator versions are separated into different |
307 |
* methods that are otherwise identical. (Similarly for siftDown.) |
308 |
* These methods are static, with heap state as arguments, to |
309 |
* simplify use in light of possible comparator exceptions. |
310 |
* |
311 |
* @param k the position to fill |
312 |
* @param x the item to insert |
313 |
* @param array the heap array |
314 |
* @param n heap size |
315 |
*/ |
316 |
private static <T> void siftUpComparable(int k, T x, Object[] array) { |
317 |
Comparable<? super T> key = (Comparable<? super T>) x; |
318 |
while (k > 0) { |
319 |
int parent = (k - 1) >>> 1; |
320 |
Object e = array[parent]; |
321 |
if (key.compareTo((T) e) >= 0) |
322 |
break; |
323 |
array[k] = e; |
324 |
k = parent; |
325 |
} |
326 |
array[k] = key; |
327 |
} |
328 |
|
329 |
private static <T> void siftUpUsingComparator(int k, T x, Object[] array, |
330 |
Comparator<? super T> cmp) { |
331 |
while (k > 0) { |
332 |
int parent = (k - 1) >>> 1; |
333 |
Object e = array[parent]; |
334 |
if (cmp.compare(x, (T) e) >= 0) |
335 |
break; |
336 |
array[k] = e; |
337 |
k = parent; |
338 |
} |
339 |
array[k] = x; |
340 |
} |
341 |
|
342 |
/** |
343 |
* Inserts item x at position k, maintaining heap invariant by |
344 |
* demoting x down the tree repeatedly until it is less than or |
345 |
* equal to its children or is a leaf. |
346 |
* |
347 |
* @param k the position to fill |
348 |
* @param x the item to insert |
349 |
* @param array the heap array |
350 |
* @param n heap size |
351 |
*/ |
352 |
private static <T> void siftDownComparable(int k, T x, Object[] array, |
353 |
int n) { |
354 |
Comparable<? super T> key = (Comparable<? super T>)x; |
355 |
int half = n >>> 1; // loop while a non-leaf |
356 |
while (k < half) { |
357 |
int child = (k << 1) + 1; // assume left child is least |
358 |
Object c = array[child]; |
359 |
int right = child + 1; |
360 |
if (right < n && |
361 |
((Comparable<? super T>) c).compareTo((T) array[right]) > 0) |
362 |
c = array[child = right]; |
363 |
if (key.compareTo((T) c) <= 0) |
364 |
break; |
365 |
array[k] = c; |
366 |
k = child; |
367 |
} |
368 |
array[k] = key; |
369 |
} |
370 |
|
371 |
private static <T> void siftDownUsingComparator(int k, T x, Object[] array, |
372 |
int n, |
373 |
Comparator<? super T> cmp) { |
374 |
int half = n >>> 1; |
375 |
while (k < half) { |
376 |
int child = (k << 1) + 1; |
377 |
Object c = array[child]; |
378 |
int right = child + 1; |
379 |
if (right < n && cmp.compare((T) c, (T) array[right]) > 0) |
380 |
c = array[child = right]; |
381 |
if (cmp.compare(x, (T) c) <= 0) |
382 |
break; |
383 |
array[k] = c; |
384 |
k = child; |
385 |
} |
386 |
array[k] = x; |
387 |
} |
388 |
|
389 |
/** |
390 |
* Establishes the heap invariant (described above) in the entire tree, |
391 |
* assuming nothing about the order of the elements prior to the call. |
392 |
*/ |
393 |
private void heapify() { |
394 |
Object[] array = queue; |
395 |
int n = size; |
396 |
int half = (n >>> 1) - 1; |
397 |
Comparator<? super E> cmp = comparator; |
398 |
if (cmp == null) { |
399 |
for (int i = half; i >= 0; i--) |
400 |
siftDownComparable(i, (E) array[i], array, n); |
401 |
} |
402 |
else { |
403 |
for (int i = half; i >= 0; i--) |
404 |
siftDownUsingComparator(i, (E) array[i], array, n, cmp); |
405 |
} |
406 |
} |
407 |
|
408 |
/** |
409 |
* Inserts the specified element into this priority queue. |
410 |
* |
411 |
* @param e the element to add |
412 |
* @return {@code true} (as specified by {@link Collection#add}) |
413 |
* @throws ClassCastException if the specified element cannot be compared |
414 |
* with elements currently in the priority queue according to the |
415 |
* priority queue's ordering |
416 |
* @throws NullPointerException if the specified element is null |
417 |
*/ |
418 |
public boolean add(E e) { |
419 |
return offer(e); |
420 |
} |
421 |
|
422 |
/** |
423 |
* Inserts the specified element into this priority queue. |
424 |
* As the queue is unbounded, this method will never return {@code false}. |
425 |
* |
426 |
* @param e the element to add |
427 |
* @return {@code true} (as specified by {@link Queue#offer}) |
428 |
* @throws ClassCastException if the specified element cannot be compared |
429 |
* with elements currently in the priority queue according to the |
430 |
* priority queue's ordering |
431 |
* @throws NullPointerException if the specified element is null |
432 |
*/ |
433 |
public boolean offer(E e) { |
434 |
if (e == null) |
435 |
throw new NullPointerException(); |
436 |
final ReentrantLock lock = this.lock; |
437 |
lock.lock(); |
438 |
int n, cap; |
439 |
Object[] array; |
440 |
while ((n = size) >= (cap = (array = queue).length)) |
441 |
tryGrow(array, cap); |
442 |
try { |
443 |
Comparator<? super E> cmp = comparator; |
444 |
if (cmp == null) |
445 |
siftUpComparable(n, e, array); |
446 |
else |
447 |
siftUpUsingComparator(n, e, array, cmp); |
448 |
size = n + 1; |
449 |
notEmpty.signal(); |
450 |
} finally { |
451 |
lock.unlock(); |
452 |
} |
453 |
return true; |
454 |
} |
455 |
|
456 |
/** |
457 |
* Inserts the specified element into this priority queue. |
458 |
* As the queue is unbounded, this method will never block. |
459 |
* |
460 |
* @param e the element to add |
461 |
* @throws ClassCastException if the specified element cannot be compared |
462 |
* with elements currently in the priority queue according to the |
463 |
* priority queue's ordering |
464 |
* @throws NullPointerException if the specified element is null |
465 |
*/ |
466 |
public void put(E e) { |
467 |
offer(e); // never need to block |
468 |
} |
469 |
|
470 |
/** |
471 |
* Inserts the specified element into this priority queue. |
472 |
* As the queue is unbounded, this method will never block or |
473 |
* return {@code false}. |
474 |
* |
475 |
* @param e the element to add |
476 |
* @param timeout This parameter is ignored as the method never blocks |
477 |
* @param unit This parameter is ignored as the method never blocks |
478 |
* @return {@code true} (as specified by |
479 |
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
480 |
* @throws ClassCastException if the specified element cannot be compared |
481 |
* with elements currently in the priority queue according to the |
482 |
* priority queue's ordering |
483 |
* @throws NullPointerException if the specified element is null |
484 |
*/ |
485 |
public boolean offer(E e, long timeout, TimeUnit unit) { |
486 |
return offer(e); // never need to block |
487 |
} |
488 |
|
489 |
public E poll() { |
490 |
final ReentrantLock lock = this.lock; |
491 |
lock.lock(); |
492 |
try { |
493 |
return extract(); |
494 |
} finally { |
495 |
lock.unlock(); |
496 |
} |
497 |
} |
498 |
|
499 |
public E take() throws InterruptedException { |
500 |
final ReentrantLock lock = this.lock; |
501 |
lock.lockInterruptibly(); |
502 |
E result; |
503 |
try { |
504 |
while ( (result = extract()) == null) |
505 |
notEmpty.await(); |
506 |
} finally { |
507 |
lock.unlock(); |
508 |
} |
509 |
return result; |
510 |
} |
511 |
|
512 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
513 |
long nanos = unit.toNanos(timeout); |
514 |
final ReentrantLock lock = this.lock; |
515 |
lock.lockInterruptibly(); |
516 |
E result; |
517 |
try { |
518 |
while ( (result = extract()) == null && nanos > 0) |
519 |
nanos = notEmpty.awaitNanos(nanos); |
520 |
} finally { |
521 |
lock.unlock(); |
522 |
} |
523 |
return result; |
524 |
} |
525 |
|
526 |
public E peek() { |
527 |
final ReentrantLock lock = this.lock; |
528 |
lock.lock(); |
529 |
try { |
530 |
return (size == 0) ? null : (E) queue[0]; |
531 |
} finally { |
532 |
lock.unlock(); |
533 |
} |
534 |
} |
535 |
|
536 |
/** |
537 |
* Returns the comparator used to order the elements in this queue, |
538 |
* or {@code null} if this queue uses the {@linkplain Comparable |
539 |
* natural ordering} of its elements. |
540 |
* |
541 |
* @return the comparator used to order the elements in this queue, |
542 |
* or {@code null} if this queue uses the natural |
543 |
* ordering of its elements |
544 |
*/ |
545 |
public Comparator<? super E> comparator() { |
546 |
return comparator; |
547 |
} |
548 |
|
549 |
public int size() { |
550 |
final ReentrantLock lock = this.lock; |
551 |
lock.lock(); |
552 |
try { |
553 |
return size; |
554 |
} finally { |
555 |
lock.unlock(); |
556 |
} |
557 |
} |
558 |
|
559 |
/** |
560 |
* Always returns {@code Integer.MAX_VALUE} because |
561 |
* a {@code PriorityBlockingQueue} is not capacity constrained. |
562 |
* @return {@code Integer.MAX_VALUE} always |
563 |
*/ |
564 |
public int remainingCapacity() { |
565 |
return Integer.MAX_VALUE; |
566 |
} |
567 |
|
568 |
private int indexOf(Object o) { |
569 |
if (o != null) { |
570 |
Object[] array = queue; |
571 |
int n = size; |
572 |
for (int i = 0; i < n; i++) |
573 |
if (o.equals(array[i])) |
574 |
return i; |
575 |
} |
576 |
return -1; |
577 |
} |
578 |
|
579 |
/** |
580 |
* Removes the ith element from queue. |
581 |
*/ |
582 |
private void removeAt(int i) { |
583 |
Object[] array = queue; |
584 |
int n = size - 1; |
585 |
if (n == i) // removed last element |
586 |
array[i] = null; |
587 |
else { |
588 |
E moved = (E) array[n]; |
589 |
array[n] = null; |
590 |
Comparator<? super E> cmp = comparator; |
591 |
if (cmp == null) |
592 |
siftDownComparable(i, moved, array, n); |
593 |
else |
594 |
siftDownUsingComparator(i, moved, array, n, cmp); |
595 |
if (array[i] == moved) { |
596 |
if (cmp == null) |
597 |
siftUpComparable(i, moved, array); |
598 |
else |
599 |
siftUpUsingComparator(i, moved, array, cmp); |
600 |
} |
601 |
} |
602 |
size = n; |
603 |
} |
604 |
|
605 |
/** |
606 |
* Removes a single instance of the specified element from this queue, |
607 |
* if it is present. More formally, removes an element {@code e} such |
608 |
* that {@code o.equals(e)}, if this queue contains one or more such |
609 |
* elements. Returns {@code true} if and only if this queue contained |
610 |
* the specified element (or equivalently, if this queue changed as a |
611 |
* result of the call). |
612 |
* |
613 |
* @param o element to be removed from this queue, if present |
614 |
* @return {@code true} if this queue changed as a result of the call |
615 |
*/ |
616 |
public boolean remove(Object o) { |
617 |
boolean removed = false; |
618 |
final ReentrantLock lock = this.lock; |
619 |
lock.lock(); |
620 |
try { |
621 |
int i = indexOf(o); |
622 |
if (i != -1) { |
623 |
removeAt(i); |
624 |
removed = true; |
625 |
} |
626 |
} finally { |
627 |
lock.unlock(); |
628 |
} |
629 |
return removed; |
630 |
} |
631 |
|
632 |
|
633 |
/** |
634 |
* Identity-based version for use in Itr.remove |
635 |
*/ |
636 |
private void removeEQ(Object o) { |
637 |
final ReentrantLock lock = this.lock; |
638 |
lock.lock(); |
639 |
try { |
640 |
Object[] array = queue; |
641 |
int n = size; |
642 |
for (int i = 0; i < n; i++) { |
643 |
if (o == array[i]) { |
644 |
removeAt(i); |
645 |
break; |
646 |
} |
647 |
} |
648 |
} finally { |
649 |
lock.unlock(); |
650 |
} |
651 |
} |
652 |
|
653 |
/** |
654 |
* Returns {@code true} if this queue contains the specified element. |
655 |
* More formally, returns {@code true} if and only if this queue contains |
656 |
* at least one element {@code e} such that {@code o.equals(e)}. |
657 |
* |
658 |
* @param o object to be checked for containment in this queue |
659 |
* @return {@code true} if this queue contains the specified element |
660 |
*/ |
661 |
public boolean contains(Object o) { |
662 |
int index; |
663 |
final ReentrantLock lock = this.lock; |
664 |
lock.lock(); |
665 |
try { |
666 |
index = indexOf(o); |
667 |
} finally { |
668 |
lock.unlock(); |
669 |
} |
670 |
return index != -1; |
671 |
} |
672 |
|
673 |
/** |
674 |
* Returns an array containing all of the elements in this queue. |
675 |
* The returned array elements are in no particular order. |
676 |
* |
677 |
* <p>The returned array will be "safe" in that no references to it are |
678 |
* maintained by this queue. (In other words, this method must allocate |
679 |
* a new array). The caller is thus free to modify the returned array. |
680 |
* |
681 |
* <p>This method acts as bridge between array-based and collection-based |
682 |
* APIs. |
683 |
* |
684 |
* @return an array containing all of the elements in this queue |
685 |
*/ |
686 |
public Object[] toArray() { |
687 |
final ReentrantLock lock = this.lock; |
688 |
lock.lock(); |
689 |
try { |
690 |
return Arrays.copyOf(queue, size); |
691 |
} finally { |
692 |
lock.unlock(); |
693 |
} |
694 |
} |
695 |
|
696 |
|
697 |
public String toString() { |
698 |
final ReentrantLock lock = this.lock; |
699 |
lock.lock(); |
700 |
try { |
701 |
int n = size; |
702 |
if (n == 0) |
703 |
return "[]"; |
704 |
StringBuilder sb = new StringBuilder(); |
705 |
sb.append('['); |
706 |
for (int i = 0; i < n; ++i) { |
707 |
Object e = queue[i]; |
708 |
sb.append(e == this ? "(this Collection)" : e); |
709 |
if (i != n - 1) |
710 |
sb.append(',').append(' '); |
711 |
} |
712 |
return sb.append(']').toString(); |
713 |
} finally { |
714 |
lock.unlock(); |
715 |
} |
716 |
} |
717 |
|
718 |
/** |
719 |
* @throws UnsupportedOperationException {@inheritDoc} |
720 |
* @throws ClassCastException {@inheritDoc} |
721 |
* @throws NullPointerException {@inheritDoc} |
722 |
* @throws IllegalArgumentException {@inheritDoc} |
723 |
*/ |
724 |
public int drainTo(Collection<? super E> c) { |
725 |
if (c == null) |
726 |
throw new NullPointerException(); |
727 |
if (c == this) |
728 |
throw new IllegalArgumentException(); |
729 |
final ReentrantLock lock = this.lock; |
730 |
lock.lock(); |
731 |
try { |
732 |
int n = 0; |
733 |
for (E e; (e = extract()) != null;) { |
734 |
c.add(e); |
735 |
++n; |
736 |
} |
737 |
return n; |
738 |
} finally { |
739 |
lock.unlock(); |
740 |
} |
741 |
} |
742 |
|
743 |
/** |
744 |
* @throws UnsupportedOperationException {@inheritDoc} |
745 |
* @throws ClassCastException {@inheritDoc} |
746 |
* @throws NullPointerException {@inheritDoc} |
747 |
* @throws IllegalArgumentException {@inheritDoc} |
748 |
*/ |
749 |
public int drainTo(Collection<? super E> c, int maxElements) { |
750 |
if (c == null) |
751 |
throw new NullPointerException(); |
752 |
if (c == this) |
753 |
throw new IllegalArgumentException(); |
754 |
if (maxElements <= 0) |
755 |
return 0; |
756 |
final ReentrantLock lock = this.lock; |
757 |
lock.lock(); |
758 |
try { |
759 |
int n = 0; |
760 |
for (E e; n < maxElements && (e = extract()) != null;) { |
761 |
c.add(e); |
762 |
++n; |
763 |
} |
764 |
return n; |
765 |
} finally { |
766 |
lock.unlock(); |
767 |
} |
768 |
} |
769 |
|
770 |
/** |
771 |
* Atomically removes all of the elements from this queue. |
772 |
* The queue will be empty after this call returns. |
773 |
*/ |
774 |
public void clear() { |
775 |
final ReentrantLock lock = this.lock; |
776 |
lock.lock(); |
777 |
try { |
778 |
Object[] array = queue; |
779 |
int n = size; |
780 |
size = 0; |
781 |
for (int i = 0; i < n; i++) |
782 |
array[i] = null; |
783 |
} finally { |
784 |
lock.unlock(); |
785 |
} |
786 |
} |
787 |
|
788 |
/** |
789 |
* Returns an array containing all of the elements in this queue; the |
790 |
* runtime type of the returned array is that of the specified array. |
791 |
* The returned array elements are in no particular order. |
792 |
* If the queue fits in the specified array, it is returned therein. |
793 |
* Otherwise, a new array is allocated with the runtime type of the |
794 |
* specified array and the size of this queue. |
795 |
* |
796 |
* <p>If this queue fits in the specified array with room to spare |
797 |
* (i.e., the array has more elements than this queue), the element in |
798 |
* the array immediately following the end of the queue is set to |
799 |
* {@code null}. |
800 |
* |
801 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
802 |
* array-based and collection-based APIs. Further, this method allows |
803 |
* precise control over the runtime type of the output array, and may, |
804 |
* under certain circumstances, be used to save allocation costs. |
805 |
* |
806 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
807 |
* The following code can be used to dump the queue into a newly |
808 |
* allocated array of {@code String}: |
809 |
* |
810 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
811 |
* |
812 |
* Note that {@code toArray(new Object[0])} is identical in function to |
813 |
* {@code toArray()}. |
814 |
* |
815 |
* @param a the array into which the elements of the queue are to |
816 |
* be stored, if it is big enough; otherwise, a new array of the |
817 |
* same runtime type is allocated for this purpose |
818 |
* @return an array containing all of the elements in this queue |
819 |
* @throws ArrayStoreException if the runtime type of the specified array |
820 |
* is not a supertype of the runtime type of every element in |
821 |
* this queue |
822 |
* @throws NullPointerException if the specified array is null |
823 |
*/ |
824 |
public <T> T[] toArray(T[] a) { |
825 |
final ReentrantLock lock = this.lock; |
826 |
lock.lock(); |
827 |
try { |
828 |
int n = size; |
829 |
if (a.length < n) |
830 |
// Make a new array of a's runtime type, but my contents: |
831 |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
832 |
System.arraycopy(queue, 0, a, 0, n); |
833 |
if (a.length > n) |
834 |
a[n] = null; |
835 |
return a; |
836 |
} finally { |
837 |
lock.unlock(); |
838 |
} |
839 |
} |
840 |
|
841 |
/** |
842 |
* Returns an iterator over the elements in this queue. The |
843 |
* iterator does not return the elements in any particular order. |
844 |
* |
845 |
* <p>The returned iterator is a "weakly consistent" iterator that |
846 |
* will never throw {@link java.util.ConcurrentModificationException |
847 |
* ConcurrentModificationException}, and guarantees to traverse |
848 |
* elements as they existed upon construction of the iterator, and |
849 |
* may (but is not guaranteed to) reflect any modifications |
850 |
* subsequent to construction. |
851 |
* |
852 |
* @return an iterator over the elements in this queue |
853 |
*/ |
854 |
public Iterator<E> iterator() { |
855 |
return new Itr(toArray()); |
856 |
} |
857 |
|
858 |
/** |
859 |
* Snapshot iterator that works off copy of underlying q array. |
860 |
*/ |
861 |
final class Itr implements Iterator<E> { |
862 |
final Object[] array; // Array of all elements |
863 |
int cursor; // index of next element to return; |
864 |
int lastRet; // index of last element, or -1 if no such |
865 |
|
866 |
Itr(Object[] array) { |
867 |
lastRet = -1; |
868 |
this.array = array; |
869 |
} |
870 |
|
871 |
public boolean hasNext() { |
872 |
return cursor < array.length; |
873 |
} |
874 |
|
875 |
public E next() { |
876 |
if (cursor >= array.length) |
877 |
throw new NoSuchElementException(); |
878 |
lastRet = cursor; |
879 |
return (E)array[cursor++]; |
880 |
} |
881 |
|
882 |
public void remove() { |
883 |
if (lastRet < 0) |
884 |
throw new IllegalStateException(); |
885 |
removeEQ(array[lastRet]); |
886 |
lastRet = -1; |
887 |
} |
888 |
} |
889 |
|
890 |
/** |
891 |
* Saves the state to a stream (that is, serializes it). For |
892 |
* compatibility with previous version of this class, |
893 |
* elements are first copied to a java.util.PriorityQueue, |
894 |
* which is then serialized. |
895 |
*/ |
896 |
private void writeObject(java.io.ObjectOutputStream s) |
897 |
throws java.io.IOException { |
898 |
lock.lock(); |
899 |
try { |
900 |
int n = size; // avoid zero capacity argument |
901 |
q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator); |
902 |
q.addAll(this); |
903 |
s.defaultWriteObject(); |
904 |
} finally { |
905 |
q = null; |
906 |
lock.unlock(); |
907 |
} |
908 |
} |
909 |
|
910 |
/** |
911 |
* Reconstitutes the {@code PriorityBlockingQueue} instance from a stream |
912 |
* (that is, deserializes it). |
913 |
* |
914 |
* @param s the stream |
915 |
*/ |
916 |
private void readObject(java.io.ObjectInputStream s) |
917 |
throws java.io.IOException, ClassNotFoundException { |
918 |
try { |
919 |
s.defaultReadObject(); |
920 |
this.queue = new Object[q.size()]; |
921 |
comparator = q.comparator(); |
922 |
addAll(q); |
923 |
} finally { |
924 |
q = null; |
925 |
} |
926 |
} |
927 |
|
928 |
// Unsafe mechanics |
929 |
private static final sun.misc.Unsafe UNSAFE; |
930 |
private static final long allocationSpinLockOffset; |
931 |
static { |
932 |
try { |
933 |
UNSAFE = sun.misc.Unsafe.getUnsafe(); |
934 |
Class<?> k = PriorityBlockingQueue.class; |
935 |
allocationSpinLockOffset = UNSAFE.objectFieldOffset |
936 |
(k.getDeclaredField("allocationSpinLock")); |
937 |
} catch (Exception e) { |
938 |
throw new Error(e); |
939 |
} |
940 |
} |
941 |
} |