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.lang.ref.WeakReference; |
10 |
import java.util.AbstractQueue; |
11 |
import java.util.Collection; |
12 |
import java.util.Iterator; |
13 |
import java.util.NoSuchElementException; |
14 |
import java.util.Spliterator; |
15 |
import java.util.Spliterators; |
16 |
import java.util.concurrent.locks.Condition; |
17 |
import java.util.concurrent.locks.ReentrantLock; |
18 |
|
19 |
/** |
20 |
* A bounded {@linkplain BlockingQueue blocking queue} backed by an |
21 |
* array. This queue orders elements FIFO (first-in-first-out). The |
22 |
* <em>head</em> of the queue is that element that has been on the |
23 |
* queue the longest time. The <em>tail</em> of the queue is that |
24 |
* element that has been on the queue the shortest time. New elements |
25 |
* are inserted at the tail of the queue, and the queue retrieval |
26 |
* operations obtain elements at the head of the queue. |
27 |
* |
28 |
* <p>This is a classic "bounded buffer", in which a |
29 |
* fixed-sized array holds elements inserted by producers and |
30 |
* extracted by consumers. Once created, the capacity cannot be |
31 |
* changed. Attempts to {@code put} an element into a full queue |
32 |
* will result in the operation blocking; attempts to {@code take} an |
33 |
* element from an empty queue will similarly block. |
34 |
* |
35 |
* <p>This class supports an optional fairness policy for ordering |
36 |
* waiting producer and consumer threads. By default, this ordering |
37 |
* is not guaranteed. However, a queue constructed with fairness set |
38 |
* to {@code true} grants threads access in FIFO order. Fairness |
39 |
* generally decreases throughput but reduces variability and avoids |
40 |
* starvation. |
41 |
* |
42 |
* <p>This class and its iterator implement all of the |
43 |
* <em>optional</em> methods of the {@link Collection} and {@link |
44 |
* Iterator} interfaces. |
45 |
* |
46 |
* <p>This class is a member of the |
47 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
48 |
* Java Collections Framework</a>. |
49 |
* |
50 |
* @since 1.5 |
51 |
* @author Doug Lea |
52 |
* @param <E> the type of elements held in this queue |
53 |
*/ |
54 |
public class ArrayBlockingQueue<E> extends AbstractQueue<E> |
55 |
implements BlockingQueue<E>, java.io.Serializable { |
56 |
|
57 |
/** |
58 |
* Serialization ID. This class relies on default serialization |
59 |
* even for the items array, which is default-serialized, even if |
60 |
* it is empty. Otherwise it could not be declared final, which is |
61 |
* necessary here. |
62 |
*/ |
63 |
private static final long serialVersionUID = -817911632652898426L; |
64 |
|
65 |
/** The queued items */ |
66 |
final Object[] items; |
67 |
|
68 |
/** items index for next take, poll, peek or remove */ |
69 |
int takeIndex; |
70 |
|
71 |
/** items index for next put, offer, or add */ |
72 |
int putIndex; |
73 |
|
74 |
/** Number of elements in the queue */ |
75 |
int count; |
76 |
|
77 |
/* |
78 |
* Concurrency control uses the classic two-condition algorithm |
79 |
* found in any textbook. |
80 |
*/ |
81 |
|
82 |
/** Main lock guarding all access */ |
83 |
final ReentrantLock lock; |
84 |
|
85 |
/** Condition for waiting takes */ |
86 |
private final Condition notEmpty; |
87 |
|
88 |
/** Condition for waiting puts */ |
89 |
private final Condition notFull; |
90 |
|
91 |
/** |
92 |
* Shared state for currently active iterators, or null if there |
93 |
* are known not to be any. Allows queue operations to update |
94 |
* iterator state. |
95 |
*/ |
96 |
transient Itrs itrs = null; |
97 |
|
98 |
// Internal helper methods |
99 |
|
100 |
/** |
101 |
* Circularly decrements array index i. |
102 |
*/ |
103 |
final int dec(int i) { |
104 |
return ((i == 0) ? items.length : i) - 1; |
105 |
} |
106 |
|
107 |
/** |
108 |
* Returns item at index i. |
109 |
*/ |
110 |
@SuppressWarnings("unchecked") |
111 |
final E itemAt(int i) { |
112 |
return (E) items[i]; |
113 |
} |
114 |
|
115 |
/** |
116 |
* Throws NullPointerException if argument is null. |
117 |
* |
118 |
* @param v the element |
119 |
*/ |
120 |
private static void checkNotNull(Object v) { |
121 |
if (v == null) |
122 |
throw new NullPointerException(); |
123 |
} |
124 |
|
125 |
/** |
126 |
* Inserts element at current put position, advances, and signals. |
127 |
* Call only when holding lock. |
128 |
*/ |
129 |
private void enqueue(E x) { |
130 |
// assert lock.getHoldCount() == 1; |
131 |
// assert items[putIndex] == null; |
132 |
final Object[] items = this.items; |
133 |
items[putIndex] = x; |
134 |
if (++putIndex == items.length) |
135 |
putIndex = 0; |
136 |
count++; |
137 |
notEmpty.signal(); |
138 |
} |
139 |
|
140 |
/** |
141 |
* Extracts element at current take position, advances, and signals. |
142 |
* Call only when holding lock. |
143 |
*/ |
144 |
private E dequeue() { |
145 |
// assert lock.getHoldCount() == 1; |
146 |
// assert items[takeIndex] != null; |
147 |
final Object[] items = this.items; |
148 |
@SuppressWarnings("unchecked") |
149 |
E x = (E) items[takeIndex]; |
150 |
items[takeIndex] = null; |
151 |
if (++takeIndex == items.length) |
152 |
takeIndex = 0; |
153 |
count--; |
154 |
if (itrs != null) |
155 |
itrs.elementDequeued(); |
156 |
notFull.signal(); |
157 |
return x; |
158 |
} |
159 |
|
160 |
/** |
161 |
* Deletes item at array index removeIndex. |
162 |
* Utility for remove(Object) and iterator.remove. |
163 |
* Call only when holding lock. |
164 |
*/ |
165 |
void removeAt(final int removeIndex) { |
166 |
// assert lock.getHoldCount() == 1; |
167 |
// assert items[removeIndex] != null; |
168 |
// assert removeIndex >= 0 && removeIndex < items.length; |
169 |
final Object[] items = this.items; |
170 |
if (removeIndex == takeIndex) { |
171 |
// removing front item; just advance |
172 |
items[takeIndex] = null; |
173 |
if (++takeIndex == items.length) |
174 |
takeIndex = 0; |
175 |
count--; |
176 |
if (itrs != null) |
177 |
itrs.elementDequeued(); |
178 |
} else { |
179 |
// an "interior" remove |
180 |
|
181 |
// slide over all others up through putIndex. |
182 |
final int putIndex = this.putIndex; |
183 |
for (int i = removeIndex;;) { |
184 |
int next = i + 1; |
185 |
if (next == items.length) |
186 |
next = 0; |
187 |
if (next != putIndex) { |
188 |
items[i] = items[next]; |
189 |
i = next; |
190 |
} else { |
191 |
items[i] = null; |
192 |
this.putIndex = i; |
193 |
break; |
194 |
} |
195 |
} |
196 |
count--; |
197 |
if (itrs != null) |
198 |
itrs.removedAt(removeIndex); |
199 |
} |
200 |
notFull.signal(); |
201 |
} |
202 |
|
203 |
/** |
204 |
* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
205 |
* capacity and default access policy. |
206 |
* |
207 |
* @param capacity the capacity of this queue |
208 |
* @throws IllegalArgumentException if {@code capacity < 1} |
209 |
*/ |
210 |
public ArrayBlockingQueue(int capacity) { |
211 |
this(capacity, false); |
212 |
} |
213 |
|
214 |
/** |
215 |
* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
216 |
* capacity and the specified access policy. |
217 |
* |
218 |
* @param capacity the capacity of this queue |
219 |
* @param fair if {@code true} then queue accesses for threads blocked |
220 |
* on insertion or removal, are processed in FIFO order; |
221 |
* if {@code false} the access order is unspecified. |
222 |
* @throws IllegalArgumentException if {@code capacity < 1} |
223 |
*/ |
224 |
public ArrayBlockingQueue(int capacity, boolean fair) { |
225 |
if (capacity <= 0) |
226 |
throw new IllegalArgumentException(); |
227 |
this.items = new Object[capacity]; |
228 |
lock = new ReentrantLock(fair); |
229 |
notEmpty = lock.newCondition(); |
230 |
notFull = lock.newCondition(); |
231 |
} |
232 |
|
233 |
/** |
234 |
* Creates an {@code ArrayBlockingQueue} with the given (fixed) |
235 |
* capacity, the specified access policy and initially containing the |
236 |
* elements of the given collection, |
237 |
* added in traversal order of the collection's iterator. |
238 |
* |
239 |
* @param capacity the capacity of this queue |
240 |
* @param fair if {@code true} then queue accesses for threads blocked |
241 |
* on insertion or removal, are processed in FIFO order; |
242 |
* if {@code false} the access order is unspecified. |
243 |
* @param c the collection of elements to initially contain |
244 |
* @throws IllegalArgumentException if {@code capacity} is less than |
245 |
* {@code c.size()}, or less than 1. |
246 |
* @throws NullPointerException if the specified collection or any |
247 |
* of its elements are null |
248 |
*/ |
249 |
public ArrayBlockingQueue(int capacity, boolean fair, |
250 |
Collection<? extends E> c) { |
251 |
this(capacity, fair); |
252 |
|
253 |
final ReentrantLock lock = this.lock; |
254 |
lock.lock(); // Lock only for visibility, not mutual exclusion |
255 |
try { |
256 |
int i = 0; |
257 |
try { |
258 |
for (E e : c) { |
259 |
checkNotNull(e); |
260 |
items[i++] = e; |
261 |
} |
262 |
} catch (ArrayIndexOutOfBoundsException ex) { |
263 |
throw new IllegalArgumentException(); |
264 |
} |
265 |
count = i; |
266 |
putIndex = (i == capacity) ? 0 : i; |
267 |
} finally { |
268 |
lock.unlock(); |
269 |
} |
270 |
} |
271 |
|
272 |
/** |
273 |
* Inserts the specified element at the tail of this queue if it is |
274 |
* possible to do so immediately without exceeding the queue's capacity, |
275 |
* returning {@code true} upon success and throwing an |
276 |
* {@code IllegalStateException} if this queue is full. |
277 |
* |
278 |
* @param e the element to add |
279 |
* @return {@code true} (as specified by {@link Collection#add}) |
280 |
* @throws IllegalStateException if this queue is full |
281 |
* @throws NullPointerException if the specified element is null |
282 |
*/ |
283 |
public boolean add(E e) { |
284 |
return super.add(e); |
285 |
} |
286 |
|
287 |
/** |
288 |
* Inserts the specified element at the tail of this queue if it is |
289 |
* possible to do so immediately without exceeding the queue's capacity, |
290 |
* returning {@code true} upon success and {@code false} if this queue |
291 |
* is full. This method is generally preferable to method {@link #add}, |
292 |
* which can fail to insert an element only by throwing an exception. |
293 |
* |
294 |
* @throws NullPointerException if the specified element is null |
295 |
*/ |
296 |
public boolean offer(E e) { |
297 |
checkNotNull(e); |
298 |
final ReentrantLock lock = this.lock; |
299 |
lock.lock(); |
300 |
try { |
301 |
if (count == items.length) |
302 |
return false; |
303 |
else { |
304 |
enqueue(e); |
305 |
return true; |
306 |
} |
307 |
} finally { |
308 |
lock.unlock(); |
309 |
} |
310 |
} |
311 |
|
312 |
/** |
313 |
* Inserts the specified element at the tail of this queue, waiting |
314 |
* for space to become available if the queue is full. |
315 |
* |
316 |
* @throws InterruptedException {@inheritDoc} |
317 |
* @throws NullPointerException {@inheritDoc} |
318 |
*/ |
319 |
public void put(E e) throws InterruptedException { |
320 |
checkNotNull(e); |
321 |
final ReentrantLock lock = this.lock; |
322 |
lock.lockInterruptibly(); |
323 |
try { |
324 |
while (count == items.length) |
325 |
notFull.await(); |
326 |
enqueue(e); |
327 |
} finally { |
328 |
lock.unlock(); |
329 |
} |
330 |
} |
331 |
|
332 |
/** |
333 |
* Inserts the specified element at the tail of this queue, waiting |
334 |
* up to the specified wait time for space to become available if |
335 |
* the queue is full. |
336 |
* |
337 |
* @throws InterruptedException {@inheritDoc} |
338 |
* @throws NullPointerException {@inheritDoc} |
339 |
*/ |
340 |
public boolean offer(E e, long timeout, TimeUnit unit) |
341 |
throws InterruptedException { |
342 |
|
343 |
checkNotNull(e); |
344 |
long nanos = unit.toNanos(timeout); |
345 |
final ReentrantLock lock = this.lock; |
346 |
lock.lockInterruptibly(); |
347 |
try { |
348 |
while (count == items.length) { |
349 |
if (nanos <= 0) |
350 |
return false; |
351 |
nanos = notFull.awaitNanos(nanos); |
352 |
} |
353 |
enqueue(e); |
354 |
return true; |
355 |
} finally { |
356 |
lock.unlock(); |
357 |
} |
358 |
} |
359 |
|
360 |
public E poll() { |
361 |
final ReentrantLock lock = this.lock; |
362 |
lock.lock(); |
363 |
try { |
364 |
return (count == 0) ? null : dequeue(); |
365 |
} finally { |
366 |
lock.unlock(); |
367 |
} |
368 |
} |
369 |
|
370 |
public E take() throws InterruptedException { |
371 |
final ReentrantLock lock = this.lock; |
372 |
lock.lockInterruptibly(); |
373 |
try { |
374 |
while (count == 0) |
375 |
notEmpty.await(); |
376 |
return dequeue(); |
377 |
} finally { |
378 |
lock.unlock(); |
379 |
} |
380 |
} |
381 |
|
382 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
383 |
long nanos = unit.toNanos(timeout); |
384 |
final ReentrantLock lock = this.lock; |
385 |
lock.lockInterruptibly(); |
386 |
try { |
387 |
while (count == 0) { |
388 |
if (nanos <= 0) |
389 |
return null; |
390 |
nanos = notEmpty.awaitNanos(nanos); |
391 |
} |
392 |
return dequeue(); |
393 |
} finally { |
394 |
lock.unlock(); |
395 |
} |
396 |
} |
397 |
|
398 |
public E peek() { |
399 |
final ReentrantLock lock = this.lock; |
400 |
lock.lock(); |
401 |
try { |
402 |
return itemAt(takeIndex); // null when queue is empty |
403 |
} finally { |
404 |
lock.unlock(); |
405 |
} |
406 |
} |
407 |
|
408 |
// this doc comment is overridden to remove the reference to collections |
409 |
// greater in size than Integer.MAX_VALUE |
410 |
/** |
411 |
* Returns the number of elements in this queue. |
412 |
* |
413 |
* @return the number of elements in this queue |
414 |
*/ |
415 |
public int size() { |
416 |
final ReentrantLock lock = this.lock; |
417 |
lock.lock(); |
418 |
try { |
419 |
return count; |
420 |
} finally { |
421 |
lock.unlock(); |
422 |
} |
423 |
} |
424 |
|
425 |
// this doc comment is a modified copy of the inherited doc comment, |
426 |
// without the reference to unlimited queues. |
427 |
/** |
428 |
* Returns the number of additional elements that this queue can ideally |
429 |
* (in the absence of memory or resource constraints) accept without |
430 |
* blocking. This is always equal to the initial capacity of this queue |
431 |
* less the current {@code size} of this queue. |
432 |
* |
433 |
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
434 |
* an element will succeed by inspecting {@code remainingCapacity} |
435 |
* because it may be the case that another thread is about to |
436 |
* insert or remove an element. |
437 |
*/ |
438 |
public int remainingCapacity() { |
439 |
final ReentrantLock lock = this.lock; |
440 |
lock.lock(); |
441 |
try { |
442 |
return items.length - count; |
443 |
} finally { |
444 |
lock.unlock(); |
445 |
} |
446 |
} |
447 |
|
448 |
/** |
449 |
* Removes a single instance of the specified element from this queue, |
450 |
* if it is present. More formally, removes an element {@code e} such |
451 |
* that {@code o.equals(e)}, if this queue contains one or more such |
452 |
* elements. |
453 |
* Returns {@code true} if this queue contained the specified element |
454 |
* (or equivalently, if this queue changed as a result of the call). |
455 |
* |
456 |
* <p>Removal of interior elements in circular array based queues |
457 |
* is an intrinsically slow and disruptive operation, so should |
458 |
* be undertaken only in exceptional circumstances, ideally |
459 |
* only when the queue is known not to be accessible by other |
460 |
* threads. |
461 |
* |
462 |
* @param o element to be removed from this queue, if present |
463 |
* @return {@code true} if this queue changed as a result of the call |
464 |
*/ |
465 |
public boolean remove(Object o) { |
466 |
if (o == null) return false; |
467 |
final ReentrantLock lock = this.lock; |
468 |
lock.lock(); |
469 |
try { |
470 |
if (count > 0) { |
471 |
final Object[] items = this.items; |
472 |
final int putIndex = this.putIndex; |
473 |
int i = takeIndex; |
474 |
do { |
475 |
if (o.equals(items[i])) { |
476 |
removeAt(i); |
477 |
return true; |
478 |
} |
479 |
if (++i == items.length) |
480 |
i = 0; |
481 |
} while (i != putIndex); |
482 |
} |
483 |
return false; |
484 |
} finally { |
485 |
lock.unlock(); |
486 |
} |
487 |
} |
488 |
|
489 |
/** |
490 |
* Returns {@code true} if this queue contains the specified element. |
491 |
* More formally, returns {@code true} if and only if this queue contains |
492 |
* at least one element {@code e} such that {@code o.equals(e)}. |
493 |
* |
494 |
* @param o object to be checked for containment in this queue |
495 |
* @return {@code true} if this queue contains the specified element |
496 |
*/ |
497 |
public boolean contains(Object o) { |
498 |
if (o == null) return false; |
499 |
final ReentrantLock lock = this.lock; |
500 |
lock.lock(); |
501 |
try { |
502 |
if (count > 0) { |
503 |
final Object[] items = this.items; |
504 |
final int putIndex = this.putIndex; |
505 |
int i = takeIndex; |
506 |
do { |
507 |
if (o.equals(items[i])) |
508 |
return true; |
509 |
if (++i == items.length) |
510 |
i = 0; |
511 |
} while (i != putIndex); |
512 |
} |
513 |
return false; |
514 |
} finally { |
515 |
lock.unlock(); |
516 |
} |
517 |
} |
518 |
|
519 |
/** |
520 |
* Returns an array containing all of the elements in this queue, in |
521 |
* proper sequence. |
522 |
* |
523 |
* <p>The returned array will be "safe" in that no references to it are |
524 |
* maintained by this queue. (In other words, this method must allocate |
525 |
* a new array). The caller is thus free to modify the returned array. |
526 |
* |
527 |
* <p>This method acts as bridge between array-based and collection-based |
528 |
* APIs. |
529 |
* |
530 |
* @return an array containing all of the elements in this queue |
531 |
*/ |
532 |
public Object[] toArray() { |
533 |
final ReentrantLock lock = this.lock; |
534 |
lock.lock(); |
535 |
try { |
536 |
final int count = this.count; |
537 |
final Object[] a = new Object[count]; |
538 |
int n = items.length - takeIndex; |
539 |
if (count <= n) |
540 |
System.arraycopy(items, takeIndex, a, 0, count); |
541 |
else { |
542 |
System.arraycopy(items, takeIndex, a, 0, n); |
543 |
System.arraycopy(items, 0, a, n, count - n); |
544 |
} |
545 |
return a; |
546 |
} finally { |
547 |
lock.unlock(); |
548 |
} |
549 |
} |
550 |
|
551 |
/** |
552 |
* Returns an array containing all of the elements in this queue, in |
553 |
* proper sequence; the runtime type of the returned array is that of |
554 |
* the specified array. If the queue fits in the specified array, it |
555 |
* is returned therein. Otherwise, a new array is allocated with the |
556 |
* runtime type of the specified array and the size of this queue. |
557 |
* |
558 |
* <p>If this queue fits in the specified array with room to spare |
559 |
* (i.e., the array has more elements than this queue), the element in |
560 |
* the array immediately following the end of the queue is set to |
561 |
* {@code null}. |
562 |
* |
563 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
564 |
* array-based and collection-based APIs. Further, this method allows |
565 |
* precise control over the runtime type of the output array, and may, |
566 |
* under certain circumstances, be used to save allocation costs. |
567 |
* |
568 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
569 |
* The following code can be used to dump the queue into a newly |
570 |
* allocated array of {@code String}: |
571 |
* |
572 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
573 |
* |
574 |
* Note that {@code toArray(new Object[0])} is identical in function to |
575 |
* {@code toArray()}. |
576 |
* |
577 |
* @param a the array into which the elements of the queue are to |
578 |
* be stored, if it is big enough; otherwise, a new array of the |
579 |
* same runtime type is allocated for this purpose |
580 |
* @return an array containing all of the elements in this queue |
581 |
* @throws ArrayStoreException if the runtime type of the specified array |
582 |
* is not a supertype of the runtime type of every element in |
583 |
* this queue |
584 |
* @throws NullPointerException if the specified array is null |
585 |
*/ |
586 |
@SuppressWarnings("unchecked") |
587 |
public <T> T[] toArray(T[] a) { |
588 |
final Object[] items = this.items; |
589 |
final ReentrantLock lock = this.lock; |
590 |
lock.lock(); |
591 |
try { |
592 |
final int count = this.count; |
593 |
final int len = a.length; |
594 |
if (len < count) |
595 |
a = (T[])java.lang.reflect.Array.newInstance( |
596 |
a.getClass().getComponentType(), count); |
597 |
int n = items.length - takeIndex; |
598 |
if (count <= n) |
599 |
System.arraycopy(items, takeIndex, a, 0, count); |
600 |
else { |
601 |
System.arraycopy(items, takeIndex, a, 0, n); |
602 |
System.arraycopy(items, 0, a, n, count - n); |
603 |
} |
604 |
if (len > count) |
605 |
a[count] = null; |
606 |
} finally { |
607 |
lock.unlock(); |
608 |
} |
609 |
return a; |
610 |
} |
611 |
|
612 |
public String toString() { |
613 |
final ReentrantLock lock = this.lock; |
614 |
lock.lock(); |
615 |
try { |
616 |
int k = count; |
617 |
if (k == 0) |
618 |
return "[]"; |
619 |
|
620 |
final Object[] items = this.items; |
621 |
StringBuilder sb = new StringBuilder(); |
622 |
sb.append('['); |
623 |
for (int i = takeIndex; ; ) { |
624 |
Object e = items[i]; |
625 |
sb.append(e == this ? "(this Collection)" : e); |
626 |
if (--k == 0) |
627 |
return sb.append(']').toString(); |
628 |
sb.append(',').append(' '); |
629 |
if (++i == items.length) |
630 |
i = 0; |
631 |
} |
632 |
} finally { |
633 |
lock.unlock(); |
634 |
} |
635 |
} |
636 |
|
637 |
/** |
638 |
* Atomically removes all of the elements from this queue. |
639 |
* The queue will be empty after this call returns. |
640 |
*/ |
641 |
public void clear() { |
642 |
final Object[] items = this.items; |
643 |
final ReentrantLock lock = this.lock; |
644 |
lock.lock(); |
645 |
try { |
646 |
int k = count; |
647 |
if (k > 0) { |
648 |
final int putIndex = this.putIndex; |
649 |
int i = takeIndex; |
650 |
do { |
651 |
items[i] = null; |
652 |
if (++i == items.length) |
653 |
i = 0; |
654 |
} while (i != putIndex); |
655 |
takeIndex = putIndex; |
656 |
count = 0; |
657 |
if (itrs != null) |
658 |
itrs.queueIsEmpty(); |
659 |
for (; k > 0 && lock.hasWaiters(notFull); k--) |
660 |
notFull.signal(); |
661 |
} |
662 |
} finally { |
663 |
lock.unlock(); |
664 |
} |
665 |
} |
666 |
|
667 |
/** |
668 |
* @throws UnsupportedOperationException {@inheritDoc} |
669 |
* @throws ClassCastException {@inheritDoc} |
670 |
* @throws NullPointerException {@inheritDoc} |
671 |
* @throws IllegalArgumentException {@inheritDoc} |
672 |
*/ |
673 |
public int drainTo(Collection<? super E> c) { |
674 |
return drainTo(c, Integer.MAX_VALUE); |
675 |
} |
676 |
|
677 |
/** |
678 |
* @throws UnsupportedOperationException {@inheritDoc} |
679 |
* @throws ClassCastException {@inheritDoc} |
680 |
* @throws NullPointerException {@inheritDoc} |
681 |
* @throws IllegalArgumentException {@inheritDoc} |
682 |
*/ |
683 |
public int drainTo(Collection<? super E> c, int maxElements) { |
684 |
checkNotNull(c); |
685 |
if (c == this) |
686 |
throw new IllegalArgumentException(); |
687 |
if (maxElements <= 0) |
688 |
return 0; |
689 |
final Object[] items = this.items; |
690 |
final ReentrantLock lock = this.lock; |
691 |
lock.lock(); |
692 |
try { |
693 |
int n = Math.min(maxElements, count); |
694 |
int take = takeIndex; |
695 |
int i = 0; |
696 |
try { |
697 |
while (i < n) { |
698 |
@SuppressWarnings("unchecked") |
699 |
E x = (E) items[take]; |
700 |
c.add(x); |
701 |
items[take] = null; |
702 |
if (++take == items.length) |
703 |
take = 0; |
704 |
i++; |
705 |
} |
706 |
return n; |
707 |
} finally { |
708 |
// Restore invariants even if c.add() threw |
709 |
if (i > 0) { |
710 |
count -= i; |
711 |
takeIndex = take; |
712 |
if (itrs != null) { |
713 |
if (count == 0) |
714 |
itrs.queueIsEmpty(); |
715 |
else if (i > take) |
716 |
itrs.takeIndexWrapped(); |
717 |
} |
718 |
for (; i > 0 && lock.hasWaiters(notFull); i--) |
719 |
notFull.signal(); |
720 |
} |
721 |
} |
722 |
} finally { |
723 |
lock.unlock(); |
724 |
} |
725 |
} |
726 |
|
727 |
/** |
728 |
* Returns an iterator over the elements in this queue in proper sequence. |
729 |
* The elements will be returned in order from first (head) to last (tail). |
730 |
* |
731 |
* <p>The returned iterator is |
732 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
733 |
* |
734 |
* @return an iterator over the elements in this queue in proper sequence |
735 |
*/ |
736 |
public Iterator<E> iterator() { |
737 |
return new Itr(); |
738 |
} |
739 |
|
740 |
/** |
741 |
* Shared data between iterators and their queue, allowing queue |
742 |
* modifications to update iterators when elements are removed. |
743 |
* |
744 |
* This adds a lot of complexity for the sake of correctly |
745 |
* handling some uncommon operations, but the combination of |
746 |
* circular-arrays and supporting interior removes (i.e., those |
747 |
* not at head) would cause iterators to sometimes lose their |
748 |
* places and/or (re)report elements they shouldn't. To avoid |
749 |
* this, when a queue has one or more iterators, it keeps iterator |
750 |
* state consistent by: |
751 |
* |
752 |
* (1) keeping track of the number of "cycles", that is, the |
753 |
* number of times takeIndex has wrapped around to 0. |
754 |
* (2) notifying all iterators via the callback removedAt whenever |
755 |
* an interior element is removed (and thus other elements may |
756 |
* be shifted). |
757 |
* |
758 |
* These suffice to eliminate iterator inconsistencies, but |
759 |
* unfortunately add the secondary responsibility of maintaining |
760 |
* the list of iterators. We track all active iterators in a |
761 |
* simple linked list (accessed only when the queue's lock is |
762 |
* held) of weak references to Itr. The list is cleaned up using |
763 |
* 3 different mechanisms: |
764 |
* |
765 |
* (1) Whenever a new iterator is created, do some O(1) checking for |
766 |
* stale list elements. |
767 |
* |
768 |
* (2) Whenever takeIndex wraps around to 0, check for iterators |
769 |
* that have been unused for more than one wrap-around cycle. |
770 |
* |
771 |
* (3) Whenever the queue becomes empty, all iterators are notified |
772 |
* and this entire data structure is discarded. |
773 |
* |
774 |
* So in addition to the removedAt callback that is necessary for |
775 |
* correctness, iterators have the shutdown and takeIndexWrapped |
776 |
* callbacks that help remove stale iterators from the list. |
777 |
* |
778 |
* Whenever a list element is examined, it is expunged if either |
779 |
* the GC has determined that the iterator is discarded, or if the |
780 |
* iterator reports that it is "detached" (does not need any |
781 |
* further state updates). Overhead is maximal when takeIndex |
782 |
* never advances, iterators are discarded before they are |
783 |
* exhausted, and all removals are interior removes, in which case |
784 |
* all stale iterators are discovered by the GC. But even in this |
785 |
* case we don't increase the amortized complexity. |
786 |
* |
787 |
* Care must be taken to keep list sweeping methods from |
788 |
* reentrantly invoking another such method, causing subtle |
789 |
* corruption bugs. |
790 |
*/ |
791 |
class Itrs { |
792 |
|
793 |
/** |
794 |
* Node in a linked list of weak iterator references. |
795 |
*/ |
796 |
private class Node extends WeakReference<Itr> { |
797 |
Node next; |
798 |
|
799 |
Node(Itr iterator, Node next) { |
800 |
super(iterator); |
801 |
this.next = next; |
802 |
} |
803 |
} |
804 |
|
805 |
/** Incremented whenever takeIndex wraps around to 0 */ |
806 |
int cycles; |
807 |
|
808 |
/** Linked list of weak iterator references */ |
809 |
private Node head; |
810 |
|
811 |
/** Used to expunge stale iterators */ |
812 |
private Node sweeper; |
813 |
|
814 |
private static final int SHORT_SWEEP_PROBES = 4; |
815 |
private static final int LONG_SWEEP_PROBES = 16; |
816 |
|
817 |
Itrs(Itr initial) { |
818 |
register(initial); |
819 |
} |
820 |
|
821 |
/** |
822 |
* Sweeps itrs, looking for and expunging stale iterators. |
823 |
* If at least one was found, tries harder to find more. |
824 |
* Called only from iterating thread. |
825 |
* |
826 |
* @param tryHarder whether to start in try-harder mode, because |
827 |
* there is known to be at least one iterator to collect |
828 |
*/ |
829 |
void doSomeSweeping(boolean tryHarder) { |
830 |
// assert lock.getHoldCount() == 1; |
831 |
// assert head != null; |
832 |
int probes = tryHarder ? LONG_SWEEP_PROBES : SHORT_SWEEP_PROBES; |
833 |
Node o, p; |
834 |
final Node sweeper = this.sweeper; |
835 |
boolean passedGo; // to limit search to one full sweep |
836 |
|
837 |
if (sweeper == null) { |
838 |
o = null; |
839 |
p = head; |
840 |
passedGo = true; |
841 |
} else { |
842 |
o = sweeper; |
843 |
p = o.next; |
844 |
passedGo = false; |
845 |
} |
846 |
|
847 |
for (; probes > 0; probes--) { |
848 |
if (p == null) { |
849 |
if (passedGo) |
850 |
break; |
851 |
o = null; |
852 |
p = head; |
853 |
passedGo = true; |
854 |
} |
855 |
final Itr it = p.get(); |
856 |
final Node next = p.next; |
857 |
if (it == null || it.isDetached()) { |
858 |
// found a discarded/exhausted iterator |
859 |
probes = LONG_SWEEP_PROBES; // "try harder" |
860 |
// unlink p |
861 |
p.clear(); |
862 |
p.next = null; |
863 |
if (o == null) { |
864 |
head = next; |
865 |
if (next == null) { |
866 |
// We've run out of iterators to track; retire |
867 |
itrs = null; |
868 |
return; |
869 |
} |
870 |
} |
871 |
else |
872 |
o.next = next; |
873 |
} else { |
874 |
o = p; |
875 |
} |
876 |
p = next; |
877 |
} |
878 |
|
879 |
this.sweeper = (p == null) ? null : o; |
880 |
} |
881 |
|
882 |
/** |
883 |
* Adds a new iterator to the linked list of tracked iterators. |
884 |
*/ |
885 |
void register(Itr itr) { |
886 |
// assert lock.getHoldCount() == 1; |
887 |
head = new Node(itr, head); |
888 |
} |
889 |
|
890 |
/** |
891 |
* Called whenever takeIndex wraps around to 0. |
892 |
* |
893 |
* Notifies all iterators, and expunges any that are now stale. |
894 |
*/ |
895 |
void takeIndexWrapped() { |
896 |
// assert lock.getHoldCount() == 1; |
897 |
cycles++; |
898 |
for (Node o = null, p = head; p != null;) { |
899 |
final Itr it = p.get(); |
900 |
final Node next = p.next; |
901 |
if (it == null || it.takeIndexWrapped()) { |
902 |
// unlink p |
903 |
// assert it == null || it.isDetached(); |
904 |
p.clear(); |
905 |
p.next = null; |
906 |
if (o == null) |
907 |
head = next; |
908 |
else |
909 |
o.next = next; |
910 |
} else { |
911 |
o = p; |
912 |
} |
913 |
p = next; |
914 |
} |
915 |
if (head == null) // no more iterators to track |
916 |
itrs = null; |
917 |
} |
918 |
|
919 |
/** |
920 |
* Called whenever an interior remove (not at takeIndex) occurred. |
921 |
* |
922 |
* Notifies all iterators, and expunges any that are now stale. |
923 |
*/ |
924 |
void removedAt(int removedIndex) { |
925 |
for (Node o = null, p = head; p != null;) { |
926 |
final Itr it = p.get(); |
927 |
final Node next = p.next; |
928 |
if (it == null || it.removedAt(removedIndex)) { |
929 |
// unlink p |
930 |
// assert it == null || it.isDetached(); |
931 |
p.clear(); |
932 |
p.next = null; |
933 |
if (o == null) |
934 |
head = next; |
935 |
else |
936 |
o.next = next; |
937 |
} else { |
938 |
o = p; |
939 |
} |
940 |
p = next; |
941 |
} |
942 |
if (head == null) // no more iterators to track |
943 |
itrs = null; |
944 |
} |
945 |
|
946 |
/** |
947 |
* Called whenever the queue becomes empty. |
948 |
* |
949 |
* Notifies all active iterators that the queue is empty, |
950 |
* clears all weak refs, and unlinks the itrs datastructure. |
951 |
*/ |
952 |
void queueIsEmpty() { |
953 |
// assert lock.getHoldCount() == 1; |
954 |
for (Node p = head; p != null; p = p.next) { |
955 |
Itr it = p.get(); |
956 |
if (it != null) { |
957 |
p.clear(); |
958 |
it.shutdown(); |
959 |
} |
960 |
} |
961 |
head = null; |
962 |
itrs = null; |
963 |
} |
964 |
|
965 |
/** |
966 |
* Called whenever an element has been dequeued (at takeIndex). |
967 |
*/ |
968 |
void elementDequeued() { |
969 |
// assert lock.getHoldCount() == 1; |
970 |
if (count == 0) |
971 |
queueIsEmpty(); |
972 |
else if (takeIndex == 0) |
973 |
takeIndexWrapped(); |
974 |
} |
975 |
} |
976 |
|
977 |
/** |
978 |
* Iterator for ArrayBlockingQueue. |
979 |
* |
980 |
* To maintain weak consistency with respect to puts and takes, we |
981 |
* read ahead one slot, so as to not report hasNext true but then |
982 |
* not have an element to return. |
983 |
* |
984 |
* We switch into "detached" mode (allowing prompt unlinking from |
985 |
* itrs without help from the GC) when all indices are negative, or |
986 |
* when hasNext returns false for the first time. This allows the |
987 |
* iterator to track concurrent updates completely accurately, |
988 |
* except for the corner case of the user calling Iterator.remove() |
989 |
* after hasNext() returned false. Even in this case, we ensure |
990 |
* that we don't remove the wrong element by keeping track of the |
991 |
* expected element to remove, in lastItem. Yes, we may fail to |
992 |
* remove lastItem from the queue if it moved due to an interleaved |
993 |
* interior remove while in detached mode. |
994 |
*/ |
995 |
private class Itr implements Iterator<E> { |
996 |
/** Index to look for new nextItem; NONE at end */ |
997 |
private int cursor; |
998 |
|
999 |
/** Element to be returned by next call to next(); null if none */ |
1000 |
private E nextItem; |
1001 |
|
1002 |
/** Index of nextItem; NONE if none, REMOVED if removed elsewhere */ |
1003 |
private int nextIndex; |
1004 |
|
1005 |
/** Last element returned; null if none or not detached. */ |
1006 |
private E lastItem; |
1007 |
|
1008 |
/** Index of lastItem, NONE if none, REMOVED if removed elsewhere */ |
1009 |
private int lastRet; |
1010 |
|
1011 |
/** Previous value of takeIndex, or DETACHED when detached */ |
1012 |
private int prevTakeIndex; |
1013 |
|
1014 |
/** Previous value of iters.cycles */ |
1015 |
private int prevCycles; |
1016 |
|
1017 |
/** Special index value indicating "not available" or "undefined" */ |
1018 |
private static final int NONE = -1; |
1019 |
|
1020 |
/** |
1021 |
* Special index value indicating "removed elsewhere", that is, |
1022 |
* removed by some operation other than a call to this.remove(). |
1023 |
*/ |
1024 |
private static final int REMOVED = -2; |
1025 |
|
1026 |
/** Special value for prevTakeIndex indicating "detached mode" */ |
1027 |
private static final int DETACHED = -3; |
1028 |
|
1029 |
Itr() { |
1030 |
// assert lock.getHoldCount() == 0; |
1031 |
lastRet = NONE; |
1032 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1033 |
lock.lock(); |
1034 |
try { |
1035 |
if (count == 0) { |
1036 |
// assert itrs == null; |
1037 |
cursor = NONE; |
1038 |
nextIndex = NONE; |
1039 |
prevTakeIndex = DETACHED; |
1040 |
} else { |
1041 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1042 |
prevTakeIndex = takeIndex; |
1043 |
nextItem = itemAt(nextIndex = takeIndex); |
1044 |
cursor = incCursor(takeIndex); |
1045 |
if (itrs == null) { |
1046 |
itrs = new Itrs(this); |
1047 |
} else { |
1048 |
itrs.register(this); // in this order |
1049 |
itrs.doSomeSweeping(false); |
1050 |
} |
1051 |
prevCycles = itrs.cycles; |
1052 |
// assert takeIndex >= 0; |
1053 |
// assert prevTakeIndex == takeIndex; |
1054 |
// assert nextIndex >= 0; |
1055 |
// assert nextItem != null; |
1056 |
} |
1057 |
} finally { |
1058 |
lock.unlock(); |
1059 |
} |
1060 |
} |
1061 |
|
1062 |
boolean isDetached() { |
1063 |
// assert lock.getHoldCount() == 1; |
1064 |
return prevTakeIndex < 0; |
1065 |
} |
1066 |
|
1067 |
private int incCursor(int index) { |
1068 |
// assert lock.getHoldCount() == 1; |
1069 |
if (++index == items.length) |
1070 |
index = 0; |
1071 |
if (index == putIndex) |
1072 |
index = NONE; |
1073 |
return index; |
1074 |
} |
1075 |
|
1076 |
/** |
1077 |
* Returns true if index is invalidated by the given number of |
1078 |
* dequeues, starting from prevTakeIndex. |
1079 |
*/ |
1080 |
private boolean invalidated(int index, int prevTakeIndex, |
1081 |
long dequeues, int length) { |
1082 |
if (index < 0) |
1083 |
return false; |
1084 |
int distance = index - prevTakeIndex; |
1085 |
if (distance < 0) |
1086 |
distance += length; |
1087 |
return dequeues > distance; |
1088 |
} |
1089 |
|
1090 |
/** |
1091 |
* Adjusts indices to incorporate all dequeues since the last |
1092 |
* operation on this iterator. Call only from iterating thread. |
1093 |
*/ |
1094 |
private void incorporateDequeues() { |
1095 |
// assert lock.getHoldCount() == 1; |
1096 |
// assert itrs != null; |
1097 |
// assert !isDetached(); |
1098 |
// assert count > 0; |
1099 |
|
1100 |
final int cycles = itrs.cycles; |
1101 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1102 |
final int prevCycles = this.prevCycles; |
1103 |
final int prevTakeIndex = this.prevTakeIndex; |
1104 |
|
1105 |
if (cycles != prevCycles || takeIndex != prevTakeIndex) { |
1106 |
final int len = items.length; |
1107 |
// how far takeIndex has advanced since the previous |
1108 |
// operation of this iterator |
1109 |
long dequeues = (cycles - prevCycles) * len |
1110 |
+ (takeIndex - prevTakeIndex); |
1111 |
|
1112 |
// Check indices for invalidation |
1113 |
if (invalidated(lastRet, prevTakeIndex, dequeues, len)) |
1114 |
lastRet = REMOVED; |
1115 |
if (invalidated(nextIndex, prevTakeIndex, dequeues, len)) |
1116 |
nextIndex = REMOVED; |
1117 |
if (invalidated(cursor, prevTakeIndex, dequeues, len)) |
1118 |
cursor = takeIndex; |
1119 |
|
1120 |
if (cursor < 0 && nextIndex < 0 && lastRet < 0) |
1121 |
detach(); |
1122 |
else { |
1123 |
this.prevCycles = cycles; |
1124 |
this.prevTakeIndex = takeIndex; |
1125 |
} |
1126 |
} |
1127 |
} |
1128 |
|
1129 |
/** |
1130 |
* Called when itrs should stop tracking this iterator, either |
1131 |
* because there are no more indices to update (cursor < 0 && |
1132 |
* nextIndex < 0 && lastRet < 0) or as a special exception, when |
1133 |
* lastRet >= 0, because hasNext() is about to return false for the |
1134 |
* first time. Call only from iterating thread. |
1135 |
*/ |
1136 |
private void detach() { |
1137 |
// Switch to detached mode |
1138 |
// assert lock.getHoldCount() == 1; |
1139 |
// assert cursor == NONE; |
1140 |
// assert nextIndex < 0; |
1141 |
// assert lastRet < 0 || nextItem == null; |
1142 |
// assert lastRet < 0 ^ lastItem != null; |
1143 |
if (prevTakeIndex >= 0) { |
1144 |
// assert itrs != null; |
1145 |
prevTakeIndex = DETACHED; |
1146 |
// try to unlink from itrs (but not too hard) |
1147 |
itrs.doSomeSweeping(true); |
1148 |
} |
1149 |
} |
1150 |
|
1151 |
/** |
1152 |
* For performance reasons, we would like not to acquire a lock in |
1153 |
* hasNext in the common case. To allow for this, we only access |
1154 |
* fields (i.e. nextItem) that are not modified by update operations |
1155 |
* triggered by queue modifications. |
1156 |
*/ |
1157 |
public boolean hasNext() { |
1158 |
// assert lock.getHoldCount() == 0; |
1159 |
if (nextItem != null) |
1160 |
return true; |
1161 |
noNext(); |
1162 |
return false; |
1163 |
} |
1164 |
|
1165 |
private void noNext() { |
1166 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1167 |
lock.lock(); |
1168 |
try { |
1169 |
// assert cursor == NONE; |
1170 |
// assert nextIndex == NONE; |
1171 |
if (!isDetached()) { |
1172 |
// assert lastRet >= 0; |
1173 |
incorporateDequeues(); // might update lastRet |
1174 |
if (lastRet >= 0) { |
1175 |
lastItem = itemAt(lastRet); |
1176 |
// assert lastItem != null; |
1177 |
detach(); |
1178 |
} |
1179 |
} |
1180 |
// assert isDetached(); |
1181 |
// assert lastRet < 0 ^ lastItem != null; |
1182 |
} finally { |
1183 |
lock.unlock(); |
1184 |
} |
1185 |
} |
1186 |
|
1187 |
public E next() { |
1188 |
// assert lock.getHoldCount() == 0; |
1189 |
final E x = nextItem; |
1190 |
if (x == null) |
1191 |
throw new NoSuchElementException(); |
1192 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1193 |
lock.lock(); |
1194 |
try { |
1195 |
if (!isDetached()) |
1196 |
incorporateDequeues(); |
1197 |
// assert nextIndex != NONE; |
1198 |
// assert lastItem == null; |
1199 |
lastRet = nextIndex; |
1200 |
final int cursor = this.cursor; |
1201 |
if (cursor >= 0) { |
1202 |
nextItem = itemAt(nextIndex = cursor); |
1203 |
// assert nextItem != null; |
1204 |
this.cursor = incCursor(cursor); |
1205 |
} else { |
1206 |
nextIndex = NONE; |
1207 |
nextItem = null; |
1208 |
} |
1209 |
} finally { |
1210 |
lock.unlock(); |
1211 |
} |
1212 |
return x; |
1213 |
} |
1214 |
|
1215 |
public void remove() { |
1216 |
// assert lock.getHoldCount() == 0; |
1217 |
final ReentrantLock lock = ArrayBlockingQueue.this.lock; |
1218 |
lock.lock(); |
1219 |
try { |
1220 |
if (!isDetached()) |
1221 |
incorporateDequeues(); // might update lastRet or detach |
1222 |
final int lastRet = this.lastRet; |
1223 |
this.lastRet = NONE; |
1224 |
if (lastRet >= 0) { |
1225 |
if (!isDetached()) |
1226 |
removeAt(lastRet); |
1227 |
else { |
1228 |
final E lastItem = this.lastItem; |
1229 |
// assert lastItem != null; |
1230 |
this.lastItem = null; |
1231 |
if (itemAt(lastRet) == lastItem) |
1232 |
removeAt(lastRet); |
1233 |
} |
1234 |
} else if (lastRet == NONE) |
1235 |
throw new IllegalStateException(); |
1236 |
// else lastRet == REMOVED and the last returned element was |
1237 |
// previously asynchronously removed via an operation other |
1238 |
// than this.remove(), so nothing to do. |
1239 |
|
1240 |
if (cursor < 0 && nextIndex < 0) |
1241 |
detach(); |
1242 |
} finally { |
1243 |
lock.unlock(); |
1244 |
// assert lastRet == NONE; |
1245 |
// assert lastItem == null; |
1246 |
} |
1247 |
} |
1248 |
|
1249 |
/** |
1250 |
* Called to notify the iterator that the queue is empty, or that it |
1251 |
* has fallen hopelessly behind, so that it should abandon any |
1252 |
* further iteration, except possibly to return one more element |
1253 |
* from next(), as promised by returning true from hasNext(). |
1254 |
*/ |
1255 |
void shutdown() { |
1256 |
// assert lock.getHoldCount() == 1; |
1257 |
cursor = NONE; |
1258 |
if (nextIndex >= 0) |
1259 |
nextIndex = REMOVED; |
1260 |
if (lastRet >= 0) { |
1261 |
lastRet = REMOVED; |
1262 |
lastItem = null; |
1263 |
} |
1264 |
prevTakeIndex = DETACHED; |
1265 |
// Don't set nextItem to null because we must continue to be |
1266 |
// able to return it on next(). |
1267 |
// |
1268 |
// Caller will unlink from itrs when convenient. |
1269 |
} |
1270 |
|
1271 |
private int distance(int index, int prevTakeIndex, int length) { |
1272 |
int distance = index - prevTakeIndex; |
1273 |
if (distance < 0) |
1274 |
distance += length; |
1275 |
return distance; |
1276 |
} |
1277 |
|
1278 |
/** |
1279 |
* Called whenever an interior remove (not at takeIndex) occurred. |
1280 |
* |
1281 |
* @return true if this iterator should be unlinked from itrs |
1282 |
*/ |
1283 |
boolean removedAt(int removedIndex) { |
1284 |
// assert lock.getHoldCount() == 1; |
1285 |
if (isDetached()) |
1286 |
return true; |
1287 |
|
1288 |
final int takeIndex = ArrayBlockingQueue.this.takeIndex; |
1289 |
final int prevTakeIndex = this.prevTakeIndex; |
1290 |
final int len = items.length; |
1291 |
// distance from prevTakeIndex to removedIndex |
1292 |
final int removedDistance = |
1293 |
len * (itrs.cycles - this.prevCycles |
1294 |
+ ((removedIndex < takeIndex) ? 1 : 0)) |
1295 |
+ (removedIndex - prevTakeIndex); |
1296 |
// assert itrs.cycles - this.prevCycles >= 0; |
1297 |
// assert itrs.cycles - this.prevCycles <= 1; |
1298 |
// assert removedDistance > 0; |
1299 |
// assert removedIndex != takeIndex; |
1300 |
int cursor = this.cursor; |
1301 |
if (cursor >= 0) { |
1302 |
int x = distance(cursor, prevTakeIndex, len); |
1303 |
if (x == removedDistance) { |
1304 |
if (cursor == putIndex) |
1305 |
this.cursor = cursor = NONE; |
1306 |
} |
1307 |
else if (x > removedDistance) { |
1308 |
// assert cursor != prevTakeIndex; |
1309 |
this.cursor = cursor = dec(cursor); |
1310 |
} |
1311 |
} |
1312 |
int lastRet = this.lastRet; |
1313 |
if (lastRet >= 0) { |
1314 |
int x = distance(lastRet, prevTakeIndex, len); |
1315 |
if (x == removedDistance) |
1316 |
this.lastRet = lastRet = REMOVED; |
1317 |
else if (x > removedDistance) |
1318 |
this.lastRet = lastRet = dec(lastRet); |
1319 |
} |
1320 |
int nextIndex = this.nextIndex; |
1321 |
if (nextIndex >= 0) { |
1322 |
int x = distance(nextIndex, prevTakeIndex, len); |
1323 |
if (x == removedDistance) |
1324 |
this.nextIndex = nextIndex = REMOVED; |
1325 |
else if (x > removedDistance) |
1326 |
this.nextIndex = nextIndex = dec(nextIndex); |
1327 |
} |
1328 |
if (cursor < 0 && nextIndex < 0 && lastRet < 0) { |
1329 |
this.prevTakeIndex = DETACHED; |
1330 |
return true; |
1331 |
} |
1332 |
return false; |
1333 |
} |
1334 |
|
1335 |
/** |
1336 |
* Called whenever takeIndex wraps around to zero. |
1337 |
* |
1338 |
* @return true if this iterator should be unlinked from itrs |
1339 |
*/ |
1340 |
boolean takeIndexWrapped() { |
1341 |
// assert lock.getHoldCount() == 1; |
1342 |
if (isDetached()) |
1343 |
return true; |
1344 |
if (itrs.cycles - prevCycles > 1) { |
1345 |
// All the elements that existed at the time of the last |
1346 |
// operation are gone, so abandon further iteration. |
1347 |
shutdown(); |
1348 |
return true; |
1349 |
} |
1350 |
return false; |
1351 |
} |
1352 |
|
1353 |
// /** Uncomment for debugging. */ |
1354 |
// public String toString() { |
1355 |
// return ("cursor=" + cursor + " " + |
1356 |
// "nextIndex=" + nextIndex + " " + |
1357 |
// "lastRet=" + lastRet + " " + |
1358 |
// "nextItem=" + nextItem + " " + |
1359 |
// "lastItem=" + lastItem + " " + |
1360 |
// "prevCycles=" + prevCycles + " " + |
1361 |
// "prevTakeIndex=" + prevTakeIndex + " " + |
1362 |
// "size()=" + size() + " " + |
1363 |
// "remainingCapacity()=" + remainingCapacity()); |
1364 |
// } |
1365 |
} |
1366 |
|
1367 |
/** |
1368 |
* Returns a {@link Spliterator} over the elements in this queue. |
1369 |
* |
1370 |
* <p>The returned spliterator is |
1371 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
1372 |
* |
1373 |
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
1374 |
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
1375 |
* |
1376 |
* @implNote |
1377 |
* The {@code Spliterator} implements {@code trySplit} to permit limited |
1378 |
* parallelism. |
1379 |
* |
1380 |
* @return a {@code Spliterator} over the elements in this queue |
1381 |
* @since 1.8 |
1382 |
*/ |
1383 |
public Spliterator<E> spliterator() { |
1384 |
return Spliterators.spliterator |
1385 |
(this, Spliterator.ORDERED | Spliterator.NONNULL | |
1386 |
Spliterator.CONCURRENT); |
1387 |
} |
1388 |
|
1389 |
} |