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