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.AbstractQueue; |
10 |
import java.util.Collection; |
11 |
import java.util.Iterator; |
12 |
import java.util.NoSuchElementException; |
13 |
import java.util.Objects; |
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 |
import java.util.function.Consumer; |
19 |
|
20 |
/** |
21 |
* An optionally-bounded {@linkplain BlockingDeque blocking deque} based on |
22 |
* linked nodes. |
23 |
* |
24 |
* <p>The optional capacity bound constructor argument serves as a |
25 |
* way to prevent excessive expansion. The capacity, if unspecified, |
26 |
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
27 |
* dynamically created upon each insertion unless this would bring the |
28 |
* deque above capacity. |
29 |
* |
30 |
* <p>Most operations run in constant time (ignoring time spent |
31 |
* blocking). Exceptions include {@link #remove(Object) remove}, |
32 |
* {@link #removeFirstOccurrence removeFirstOccurrence}, {@link |
33 |
* #removeLastOccurrence removeLastOccurrence}, {@link #contains |
34 |
* contains}, {@link #iterator iterator.remove()}, and the bulk |
35 |
* operations, all of which run in linear time. |
36 |
* |
37 |
* <p>This class and its iterator implement all of the |
38 |
* <em>optional</em> methods of the {@link Collection} and {@link |
39 |
* Iterator} interfaces. |
40 |
* |
41 |
* <p>This class is a member of the |
42 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
43 |
* Java Collections Framework</a>. |
44 |
* |
45 |
* @since 1.6 |
46 |
* @author Doug Lea |
47 |
* @param <E> the type of elements held in this deque |
48 |
*/ |
49 |
public class LinkedBlockingDeque<E> |
50 |
extends AbstractQueue<E> |
51 |
implements BlockingDeque<E>, java.io.Serializable { |
52 |
|
53 |
/* |
54 |
* Implemented as a simple doubly-linked list protected by a |
55 |
* single lock and using conditions to manage blocking. |
56 |
* |
57 |
* To implement weakly consistent iterators, it appears we need to |
58 |
* keep all Nodes GC-reachable from a predecessor dequeued Node. |
59 |
* That would cause two problems: |
60 |
* - allow a rogue Iterator to cause unbounded memory retention |
61 |
* - cause cross-generational linking of old Nodes to new Nodes if |
62 |
* a Node was tenured while live, which generational GCs have a |
63 |
* hard time dealing with, causing repeated major collections. |
64 |
* However, only non-deleted Nodes need to be reachable from |
65 |
* dequeued Nodes, and reachability does not necessarily have to |
66 |
* be of the kind understood by the GC. We use the trick of |
67 |
* linking a Node that has just been dequeued to itself. Such a |
68 |
* self-link implicitly means to jump to "first" (for next links) |
69 |
* or "last" (for prev links). |
70 |
*/ |
71 |
|
72 |
/* |
73 |
* We have "diamond" multiple interface/abstract class inheritance |
74 |
* here, and that introduces ambiguities. Often we want the |
75 |
* BlockingDeque javadoc combined with the AbstractQueue |
76 |
* implementation, so a lot of method specs are duplicated here. |
77 |
*/ |
78 |
|
79 |
private static final long serialVersionUID = -387911632671998426L; |
80 |
|
81 |
/** Doubly-linked list node class */ |
82 |
static final class Node<E> { |
83 |
/** |
84 |
* The item, or null if this node has been removed. |
85 |
*/ |
86 |
E item; |
87 |
|
88 |
/** |
89 |
* One of: |
90 |
* - the real predecessor Node |
91 |
* - this Node, meaning the predecessor is tail |
92 |
* - null, meaning there is no predecessor |
93 |
*/ |
94 |
Node<E> prev; |
95 |
|
96 |
/** |
97 |
* One of: |
98 |
* - the real successor Node |
99 |
* - this Node, meaning the successor is head |
100 |
* - null, meaning there is no successor |
101 |
*/ |
102 |
Node<E> next; |
103 |
|
104 |
Node(E x) { |
105 |
item = x; |
106 |
} |
107 |
} |
108 |
|
109 |
/** |
110 |
* Pointer to first node. |
111 |
* Invariant: (first == null && last == null) || |
112 |
* (first.prev == null && first.item != null) |
113 |
*/ |
114 |
transient Node<E> first; |
115 |
|
116 |
/** |
117 |
* Pointer to last node. |
118 |
* Invariant: (first == null && last == null) || |
119 |
* (last.next == null && last.item != null) |
120 |
*/ |
121 |
transient Node<E> last; |
122 |
|
123 |
/** Number of items in the deque */ |
124 |
private transient int count; |
125 |
|
126 |
/** Maximum number of items in the deque */ |
127 |
private final int capacity; |
128 |
|
129 |
/** Main lock guarding all access */ |
130 |
final ReentrantLock lock = new ReentrantLock(); |
131 |
|
132 |
/** Condition for waiting takes */ |
133 |
private final Condition notEmpty = lock.newCondition(); |
134 |
|
135 |
/** Condition for waiting puts */ |
136 |
private final Condition notFull = lock.newCondition(); |
137 |
|
138 |
/** |
139 |
* Creates a {@code LinkedBlockingDeque} with a capacity of |
140 |
* {@link Integer#MAX_VALUE}. |
141 |
*/ |
142 |
public LinkedBlockingDeque() { |
143 |
this(Integer.MAX_VALUE); |
144 |
} |
145 |
|
146 |
/** |
147 |
* Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity. |
148 |
* |
149 |
* @param capacity the capacity of this deque |
150 |
* @throws IllegalArgumentException if {@code capacity} is less than 1 |
151 |
*/ |
152 |
public LinkedBlockingDeque(int capacity) { |
153 |
if (capacity <= 0) throw new IllegalArgumentException(); |
154 |
this.capacity = capacity; |
155 |
} |
156 |
|
157 |
/** |
158 |
* Creates a {@code LinkedBlockingDeque} with a capacity of |
159 |
* {@link Integer#MAX_VALUE}, initially containing the elements of |
160 |
* the given collection, added in traversal order of the |
161 |
* collection's iterator. |
162 |
* |
163 |
* @param c the collection of elements to initially contain |
164 |
* @throws NullPointerException if the specified collection or any |
165 |
* of its elements are null |
166 |
*/ |
167 |
public LinkedBlockingDeque(Collection<? extends E> c) { |
168 |
this(Integer.MAX_VALUE); |
169 |
final ReentrantLock lock = this.lock; |
170 |
lock.lock(); // Never contended, but necessary for visibility |
171 |
try { |
172 |
for (E e : c) { |
173 |
if (e == null) |
174 |
throw new NullPointerException(); |
175 |
if (!linkLast(new Node<E>(e))) |
176 |
throw new IllegalStateException("Deque full"); |
177 |
} |
178 |
} finally { |
179 |
// checkInvariants(); |
180 |
lock.unlock(); |
181 |
} |
182 |
} |
183 |
|
184 |
|
185 |
// Basic linking and unlinking operations, called only while holding lock |
186 |
|
187 |
/** |
188 |
* Links node as first element, or returns false if full. |
189 |
*/ |
190 |
private boolean linkFirst(Node<E> node) { |
191 |
// assert lock.isHeldByCurrentThread(); |
192 |
if (count >= capacity) |
193 |
return false; |
194 |
Node<E> f = first; |
195 |
node.next = f; |
196 |
first = node; |
197 |
if (last == null) |
198 |
last = node; |
199 |
else |
200 |
f.prev = node; |
201 |
++count; |
202 |
notEmpty.signal(); |
203 |
return true; |
204 |
} |
205 |
|
206 |
/** |
207 |
* Links node as last element, or returns false if full. |
208 |
*/ |
209 |
private boolean linkLast(Node<E> node) { |
210 |
// assert lock.isHeldByCurrentThread(); |
211 |
if (count >= capacity) |
212 |
return false; |
213 |
Node<E> l = last; |
214 |
node.prev = l; |
215 |
last = node; |
216 |
if (first == null) |
217 |
first = node; |
218 |
else |
219 |
l.next = node; |
220 |
++count; |
221 |
notEmpty.signal(); |
222 |
return true; |
223 |
} |
224 |
|
225 |
/** |
226 |
* Removes and returns first element, or null if empty. |
227 |
*/ |
228 |
private E unlinkFirst() { |
229 |
// assert lock.isHeldByCurrentThread(); |
230 |
Node<E> f = first; |
231 |
if (f == null) |
232 |
return null; |
233 |
Node<E> n = f.next; |
234 |
E item = f.item; |
235 |
f.item = null; |
236 |
f.next = f; // help GC |
237 |
first = n; |
238 |
if (n == null) |
239 |
last = null; |
240 |
else |
241 |
n.prev = null; |
242 |
--count; |
243 |
notFull.signal(); |
244 |
return item; |
245 |
} |
246 |
|
247 |
/** |
248 |
* Removes and returns last element, or null if empty. |
249 |
*/ |
250 |
private E unlinkLast() { |
251 |
// assert lock.isHeldByCurrentThread(); |
252 |
Node<E> l = last; |
253 |
if (l == null) |
254 |
return null; |
255 |
Node<E> p = l.prev; |
256 |
E item = l.item; |
257 |
l.item = null; |
258 |
l.prev = l; // help GC |
259 |
last = p; |
260 |
if (p == null) |
261 |
first = null; |
262 |
else |
263 |
p.next = null; |
264 |
--count; |
265 |
notFull.signal(); |
266 |
return item; |
267 |
} |
268 |
|
269 |
/** |
270 |
* Unlinks x. |
271 |
*/ |
272 |
void unlink(Node<E> x) { |
273 |
// assert lock.isHeldByCurrentThread(); |
274 |
Node<E> p = x.prev; |
275 |
Node<E> n = x.next; |
276 |
if (p == null) { |
277 |
unlinkFirst(); |
278 |
} else if (n == null) { |
279 |
unlinkLast(); |
280 |
} else { |
281 |
p.next = n; |
282 |
n.prev = p; |
283 |
x.item = null; |
284 |
// Don't mess with x's links. They may still be in use by |
285 |
// an iterator. |
286 |
--count; |
287 |
notFull.signal(); |
288 |
} |
289 |
} |
290 |
|
291 |
// BlockingDeque methods |
292 |
|
293 |
/** |
294 |
* @throws IllegalStateException if this deque is full |
295 |
* @throws NullPointerException {@inheritDoc} |
296 |
*/ |
297 |
public void addFirst(E e) { |
298 |
if (!offerFirst(e)) |
299 |
throw new IllegalStateException("Deque full"); |
300 |
} |
301 |
|
302 |
/** |
303 |
* @throws IllegalStateException if this deque is full |
304 |
* @throws NullPointerException {@inheritDoc} |
305 |
*/ |
306 |
public void addLast(E e) { |
307 |
if (!offerLast(e)) |
308 |
throw new IllegalStateException("Deque full"); |
309 |
} |
310 |
|
311 |
/** |
312 |
* @throws NullPointerException {@inheritDoc} |
313 |
*/ |
314 |
public boolean offerFirst(E e) { |
315 |
if (e == null) throw new NullPointerException(); |
316 |
Node<E> node = new Node<E>(e); |
317 |
final ReentrantLock lock = this.lock; |
318 |
lock.lock(); |
319 |
try { |
320 |
return linkFirst(node); |
321 |
} finally { |
322 |
// checkInvariants(); |
323 |
lock.unlock(); |
324 |
} |
325 |
} |
326 |
|
327 |
/** |
328 |
* @throws NullPointerException {@inheritDoc} |
329 |
*/ |
330 |
public boolean offerLast(E e) { |
331 |
if (e == null) throw new NullPointerException(); |
332 |
Node<E> node = new Node<E>(e); |
333 |
final ReentrantLock lock = this.lock; |
334 |
lock.lock(); |
335 |
try { |
336 |
return linkLast(node); |
337 |
} finally { |
338 |
// checkInvariants(); |
339 |
lock.unlock(); |
340 |
} |
341 |
} |
342 |
|
343 |
/** |
344 |
* @throws NullPointerException {@inheritDoc} |
345 |
* @throws InterruptedException {@inheritDoc} |
346 |
*/ |
347 |
public void putFirst(E e) throws InterruptedException { |
348 |
if (e == null) throw new NullPointerException(); |
349 |
Node<E> node = new Node<E>(e); |
350 |
final ReentrantLock lock = this.lock; |
351 |
lock.lock(); |
352 |
try { |
353 |
while (!linkFirst(node)) |
354 |
notFull.await(); |
355 |
} finally { |
356 |
// checkInvariants(); |
357 |
lock.unlock(); |
358 |
} |
359 |
} |
360 |
|
361 |
/** |
362 |
* @throws NullPointerException {@inheritDoc} |
363 |
* @throws InterruptedException {@inheritDoc} |
364 |
*/ |
365 |
public void putLast(E e) throws InterruptedException { |
366 |
if (e == null) throw new NullPointerException(); |
367 |
Node<E> node = new Node<E>(e); |
368 |
final ReentrantLock lock = this.lock; |
369 |
lock.lock(); |
370 |
try { |
371 |
while (!linkLast(node)) |
372 |
notFull.await(); |
373 |
} finally { |
374 |
// checkInvariants(); |
375 |
lock.unlock(); |
376 |
} |
377 |
} |
378 |
|
379 |
/** |
380 |
* @throws NullPointerException {@inheritDoc} |
381 |
* @throws InterruptedException {@inheritDoc} |
382 |
*/ |
383 |
public boolean offerFirst(E e, long timeout, TimeUnit unit) |
384 |
throws InterruptedException { |
385 |
if (e == null) throw new NullPointerException(); |
386 |
Node<E> node = new Node<E>(e); |
387 |
long nanos = unit.toNanos(timeout); |
388 |
final ReentrantLock lock = this.lock; |
389 |
lock.lockInterruptibly(); |
390 |
try { |
391 |
while (!linkFirst(node)) { |
392 |
if (nanos <= 0L) |
393 |
return false; |
394 |
nanos = notFull.awaitNanos(nanos); |
395 |
} |
396 |
return true; |
397 |
} finally { |
398 |
// checkInvariants(); |
399 |
lock.unlock(); |
400 |
} |
401 |
} |
402 |
|
403 |
/** |
404 |
* @throws NullPointerException {@inheritDoc} |
405 |
* @throws InterruptedException {@inheritDoc} |
406 |
*/ |
407 |
public boolean offerLast(E e, long timeout, TimeUnit unit) |
408 |
throws InterruptedException { |
409 |
if (e == null) throw new NullPointerException(); |
410 |
Node<E> node = new Node<E>(e); |
411 |
long nanos = unit.toNanos(timeout); |
412 |
final ReentrantLock lock = this.lock; |
413 |
lock.lockInterruptibly(); |
414 |
try { |
415 |
while (!linkLast(node)) { |
416 |
if (nanos <= 0L) |
417 |
return false; |
418 |
nanos = notFull.awaitNanos(nanos); |
419 |
} |
420 |
return true; |
421 |
} finally { |
422 |
// checkInvariants(); |
423 |
lock.unlock(); |
424 |
} |
425 |
} |
426 |
|
427 |
/** |
428 |
* @throws NoSuchElementException {@inheritDoc} |
429 |
*/ |
430 |
public E removeFirst() { |
431 |
E x = pollFirst(); |
432 |
if (x == null) throw new NoSuchElementException(); |
433 |
return x; |
434 |
} |
435 |
|
436 |
/** |
437 |
* @throws NoSuchElementException {@inheritDoc} |
438 |
*/ |
439 |
public E removeLast() { |
440 |
E x = pollLast(); |
441 |
if (x == null) throw new NoSuchElementException(); |
442 |
return x; |
443 |
} |
444 |
|
445 |
public E pollFirst() { |
446 |
final ReentrantLock lock = this.lock; |
447 |
lock.lock(); |
448 |
try { |
449 |
return unlinkFirst(); |
450 |
} finally { |
451 |
// checkInvariants(); |
452 |
lock.unlock(); |
453 |
} |
454 |
} |
455 |
|
456 |
public E pollLast() { |
457 |
final ReentrantLock lock = this.lock; |
458 |
lock.lock(); |
459 |
try { |
460 |
return unlinkLast(); |
461 |
} finally { |
462 |
// checkInvariants(); |
463 |
lock.unlock(); |
464 |
} |
465 |
} |
466 |
|
467 |
public E takeFirst() throws InterruptedException { |
468 |
final ReentrantLock lock = this.lock; |
469 |
lock.lock(); |
470 |
try { |
471 |
E x; |
472 |
while ( (x = unlinkFirst()) == null) |
473 |
notEmpty.await(); |
474 |
return x; |
475 |
} finally { |
476 |
// checkInvariants(); |
477 |
lock.unlock(); |
478 |
} |
479 |
} |
480 |
|
481 |
public E takeLast() throws InterruptedException { |
482 |
final ReentrantLock lock = this.lock; |
483 |
lock.lock(); |
484 |
try { |
485 |
E x; |
486 |
while ( (x = unlinkLast()) == null) |
487 |
notEmpty.await(); |
488 |
return x; |
489 |
} finally { |
490 |
// checkInvariants(); |
491 |
lock.unlock(); |
492 |
} |
493 |
} |
494 |
|
495 |
public E pollFirst(long timeout, TimeUnit unit) |
496 |
throws InterruptedException { |
497 |
long nanos = unit.toNanos(timeout); |
498 |
final ReentrantLock lock = this.lock; |
499 |
lock.lockInterruptibly(); |
500 |
try { |
501 |
E x; |
502 |
while ( (x = unlinkFirst()) == null) { |
503 |
if (nanos <= 0L) |
504 |
return null; |
505 |
nanos = notEmpty.awaitNanos(nanos); |
506 |
} |
507 |
return x; |
508 |
} finally { |
509 |
// checkInvariants(); |
510 |
lock.unlock(); |
511 |
} |
512 |
} |
513 |
|
514 |
public E pollLast(long timeout, TimeUnit unit) |
515 |
throws InterruptedException { |
516 |
long nanos = unit.toNanos(timeout); |
517 |
final ReentrantLock lock = this.lock; |
518 |
lock.lockInterruptibly(); |
519 |
try { |
520 |
E x; |
521 |
while ( (x = unlinkLast()) == null) { |
522 |
if (nanos <= 0L) |
523 |
return null; |
524 |
nanos = notEmpty.awaitNanos(nanos); |
525 |
} |
526 |
return x; |
527 |
} finally { |
528 |
// checkInvariants(); |
529 |
lock.unlock(); |
530 |
} |
531 |
} |
532 |
|
533 |
/** |
534 |
* @throws NoSuchElementException {@inheritDoc} |
535 |
*/ |
536 |
public E getFirst() { |
537 |
E x = peekFirst(); |
538 |
if (x == null) throw new NoSuchElementException(); |
539 |
return x; |
540 |
} |
541 |
|
542 |
/** |
543 |
* @throws NoSuchElementException {@inheritDoc} |
544 |
*/ |
545 |
public E getLast() { |
546 |
E x = peekLast(); |
547 |
if (x == null) throw new NoSuchElementException(); |
548 |
return x; |
549 |
} |
550 |
|
551 |
public E peekFirst() { |
552 |
final ReentrantLock lock = this.lock; |
553 |
lock.lock(); |
554 |
try { |
555 |
return (first == null) ? null : first.item; |
556 |
} finally { |
557 |
// checkInvariants(); |
558 |
lock.unlock(); |
559 |
} |
560 |
} |
561 |
|
562 |
public E peekLast() { |
563 |
final ReentrantLock lock = this.lock; |
564 |
lock.lock(); |
565 |
try { |
566 |
return (last == null) ? null : last.item; |
567 |
} finally { |
568 |
// checkInvariants(); |
569 |
lock.unlock(); |
570 |
} |
571 |
} |
572 |
|
573 |
public boolean removeFirstOccurrence(Object o) { |
574 |
if (o == null) return false; |
575 |
final ReentrantLock lock = this.lock; |
576 |
lock.lock(); |
577 |
try { |
578 |
for (Node<E> p = first; p != null; p = p.next) { |
579 |
if (o.equals(p.item)) { |
580 |
unlink(p); |
581 |
return true; |
582 |
} |
583 |
} |
584 |
return false; |
585 |
} finally { |
586 |
// checkInvariants(); |
587 |
lock.unlock(); |
588 |
} |
589 |
} |
590 |
|
591 |
public boolean removeLastOccurrence(Object o) { |
592 |
if (o == null) return false; |
593 |
final ReentrantLock lock = this.lock; |
594 |
lock.lock(); |
595 |
try { |
596 |
for (Node<E> p = last; p != null; p = p.prev) { |
597 |
if (o.equals(p.item)) { |
598 |
unlink(p); |
599 |
return true; |
600 |
} |
601 |
} |
602 |
return false; |
603 |
} finally { |
604 |
// checkInvariants(); |
605 |
lock.unlock(); |
606 |
} |
607 |
} |
608 |
|
609 |
// BlockingQueue methods |
610 |
|
611 |
/** |
612 |
* Inserts the specified element at the end of this deque unless it would |
613 |
* violate capacity restrictions. When using a capacity-restricted deque, |
614 |
* it is generally preferable to use method {@link #offer(Object) offer}. |
615 |
* |
616 |
* <p>This method is equivalent to {@link #addLast}. |
617 |
* |
618 |
* @throws IllegalStateException if this deque is full |
619 |
* @throws NullPointerException if the specified element is null |
620 |
*/ |
621 |
public boolean add(E e) { |
622 |
addLast(e); |
623 |
return true; |
624 |
} |
625 |
|
626 |
/** |
627 |
* @throws NullPointerException if the specified element is null |
628 |
*/ |
629 |
public boolean offer(E e) { |
630 |
return offerLast(e); |
631 |
} |
632 |
|
633 |
/** |
634 |
* @throws NullPointerException {@inheritDoc} |
635 |
* @throws InterruptedException {@inheritDoc} |
636 |
*/ |
637 |
public void put(E e) throws InterruptedException { |
638 |
putLast(e); |
639 |
} |
640 |
|
641 |
/** |
642 |
* @throws NullPointerException {@inheritDoc} |
643 |
* @throws InterruptedException {@inheritDoc} |
644 |
*/ |
645 |
public boolean offer(E e, long timeout, TimeUnit unit) |
646 |
throws InterruptedException { |
647 |
return offerLast(e, timeout, unit); |
648 |
} |
649 |
|
650 |
/** |
651 |
* Retrieves and removes the head of the queue represented by this deque. |
652 |
* This method differs from {@link #poll poll} only in that it throws an |
653 |
* exception if this deque is empty. |
654 |
* |
655 |
* <p>This method is equivalent to {@link #removeFirst() removeFirst}. |
656 |
* |
657 |
* @return the head of the queue represented by this deque |
658 |
* @throws NoSuchElementException if this deque is empty |
659 |
*/ |
660 |
public E remove() { |
661 |
return removeFirst(); |
662 |
} |
663 |
|
664 |
public E poll() { |
665 |
return pollFirst(); |
666 |
} |
667 |
|
668 |
public E take() throws InterruptedException { |
669 |
return takeFirst(); |
670 |
} |
671 |
|
672 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
673 |
return pollFirst(timeout, unit); |
674 |
} |
675 |
|
676 |
/** |
677 |
* Retrieves, but does not remove, the head of the queue represented by |
678 |
* this deque. This method differs from {@link #peek peek} only in that |
679 |
* it throws an exception if this deque is empty. |
680 |
* |
681 |
* <p>This method is equivalent to {@link #getFirst() getFirst}. |
682 |
* |
683 |
* @return the head of the queue represented by this deque |
684 |
* @throws NoSuchElementException if this deque is empty |
685 |
*/ |
686 |
public E element() { |
687 |
return getFirst(); |
688 |
} |
689 |
|
690 |
public E peek() { |
691 |
return peekFirst(); |
692 |
} |
693 |
|
694 |
/** |
695 |
* Returns the number of additional elements that this deque can ideally |
696 |
* (in the absence of memory or resource constraints) accept without |
697 |
* blocking. This is always equal to the initial capacity of this deque |
698 |
* less the current {@code size} of this deque. |
699 |
* |
700 |
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
701 |
* an element will succeed by inspecting {@code remainingCapacity} |
702 |
* because it may be the case that another thread is about to |
703 |
* insert or remove an element. |
704 |
*/ |
705 |
public int remainingCapacity() { |
706 |
final ReentrantLock lock = this.lock; |
707 |
lock.lock(); |
708 |
try { |
709 |
return capacity - count; |
710 |
} finally { |
711 |
// checkInvariants(); |
712 |
lock.unlock(); |
713 |
} |
714 |
} |
715 |
|
716 |
/** |
717 |
* @throws UnsupportedOperationException {@inheritDoc} |
718 |
* @throws ClassCastException {@inheritDoc} |
719 |
* @throws NullPointerException {@inheritDoc} |
720 |
* @throws IllegalArgumentException {@inheritDoc} |
721 |
*/ |
722 |
public int drainTo(Collection<? super E> c) { |
723 |
return drainTo(c, Integer.MAX_VALUE); |
724 |
} |
725 |
|
726 |
/** |
727 |
* @throws UnsupportedOperationException {@inheritDoc} |
728 |
* @throws ClassCastException {@inheritDoc} |
729 |
* @throws NullPointerException {@inheritDoc} |
730 |
* @throws IllegalArgumentException {@inheritDoc} |
731 |
*/ |
732 |
public int drainTo(Collection<? super E> c, int maxElements) { |
733 |
Objects.requireNonNull(c); |
734 |
if (c == this) |
735 |
throw new IllegalArgumentException(); |
736 |
if (maxElements <= 0) |
737 |
return 0; |
738 |
final ReentrantLock lock = this.lock; |
739 |
lock.lock(); |
740 |
try { |
741 |
int n = Math.min(maxElements, count); |
742 |
for (int i = 0; i < n; i++) { |
743 |
c.add(first.item); // In this order, in case add() throws. |
744 |
unlinkFirst(); |
745 |
} |
746 |
return n; |
747 |
} finally { |
748 |
// checkInvariants(); |
749 |
lock.unlock(); |
750 |
} |
751 |
} |
752 |
|
753 |
// Stack methods |
754 |
|
755 |
/** |
756 |
* @throws IllegalStateException if this deque is full |
757 |
* @throws NullPointerException {@inheritDoc} |
758 |
*/ |
759 |
public void push(E e) { |
760 |
addFirst(e); |
761 |
} |
762 |
|
763 |
/** |
764 |
* @throws NoSuchElementException {@inheritDoc} |
765 |
*/ |
766 |
public E pop() { |
767 |
return removeFirst(); |
768 |
} |
769 |
|
770 |
// Collection methods |
771 |
|
772 |
/** |
773 |
* Removes the first occurrence of the specified element from this deque. |
774 |
* If the deque does not contain the element, it is unchanged. |
775 |
* More formally, removes the first element {@code e} such that |
776 |
* {@code o.equals(e)} (if such an element exists). |
777 |
* Returns {@code true} if this deque contained the specified element |
778 |
* (or equivalently, if this deque changed as a result of the call). |
779 |
* |
780 |
* <p>This method is equivalent to |
781 |
* {@link #removeFirstOccurrence(Object) removeFirstOccurrence}. |
782 |
* |
783 |
* @param o element to be removed from this deque, if present |
784 |
* @return {@code true} if this deque changed as a result of the call |
785 |
*/ |
786 |
public boolean remove(Object o) { |
787 |
return removeFirstOccurrence(o); |
788 |
} |
789 |
|
790 |
/** |
791 |
* Returns the number of elements in this deque. |
792 |
* |
793 |
* @return the number of elements in this deque |
794 |
*/ |
795 |
public int size() { |
796 |
final ReentrantLock lock = this.lock; |
797 |
lock.lock(); |
798 |
try { |
799 |
return count; |
800 |
} finally { |
801 |
// checkInvariants(); |
802 |
lock.unlock(); |
803 |
} |
804 |
} |
805 |
|
806 |
/** |
807 |
* Returns {@code true} if this deque contains the specified element. |
808 |
* More formally, returns {@code true} if and only if this deque contains |
809 |
* at least one element {@code e} such that {@code o.equals(e)}. |
810 |
* |
811 |
* @param o object to be checked for containment in this deque |
812 |
* @return {@code true} if this deque contains the specified element |
813 |
*/ |
814 |
public boolean contains(Object o) { |
815 |
if (o == null) return false; |
816 |
final ReentrantLock lock = this.lock; |
817 |
lock.lock(); |
818 |
try { |
819 |
for (Node<E> p = first; p != null; p = p.next) |
820 |
if (o.equals(p.item)) |
821 |
return true; |
822 |
return false; |
823 |
} finally { |
824 |
// checkInvariants(); |
825 |
lock.unlock(); |
826 |
} |
827 |
} |
828 |
|
829 |
/* |
830 |
* TODO: Add support for more efficient bulk operations. |
831 |
* |
832 |
* We don't want to acquire the lock for every iteration, but we |
833 |
* also want other threads a chance to interact with the |
834 |
* collection, especially when count is close to capacity. |
835 |
*/ |
836 |
|
837 |
// /** |
838 |
// * Adds all of the elements in the specified collection to this |
839 |
// * queue. Attempts to addAll of a queue to itself result in |
840 |
// * {@code IllegalArgumentException}. Further, the behavior of |
841 |
// * this operation is undefined if the specified collection is |
842 |
// * modified while the operation is in progress. |
843 |
// * |
844 |
// * @param c collection containing elements to be added to this queue |
845 |
// * @return {@code true} if this queue changed as a result of the call |
846 |
// * @throws ClassCastException {@inheritDoc} |
847 |
// * @throws NullPointerException {@inheritDoc} |
848 |
// * @throws IllegalArgumentException {@inheritDoc} |
849 |
// * @throws IllegalStateException if this deque is full |
850 |
// * @see #add(Object) |
851 |
// */ |
852 |
// public boolean addAll(Collection<? extends E> c) { |
853 |
// if (c == null) |
854 |
// throw new NullPointerException(); |
855 |
// if (c == this) |
856 |
// throw new IllegalArgumentException(); |
857 |
// final ReentrantLock lock = this.lock; |
858 |
// lock.lock(); |
859 |
// try { |
860 |
// boolean modified = false; |
861 |
// for (E e : c) |
862 |
// if (linkLast(e)) |
863 |
// modified = true; |
864 |
// return modified; |
865 |
// } finally { |
866 |
// lock.unlock(); |
867 |
// } |
868 |
// } |
869 |
|
870 |
/** |
871 |
* Returns an array containing all of the elements in this deque, in |
872 |
* proper sequence (from first to last element). |
873 |
* |
874 |
* <p>The returned array will be "safe" in that no references to it are |
875 |
* maintained by this deque. (In other words, this method must allocate |
876 |
* a new array). The caller is thus free to modify the returned array. |
877 |
* |
878 |
* <p>This method acts as bridge between array-based and collection-based |
879 |
* APIs. |
880 |
* |
881 |
* @return an array containing all of the elements in this deque |
882 |
*/ |
883 |
@SuppressWarnings("unchecked") |
884 |
public Object[] toArray() { |
885 |
final ReentrantLock lock = this.lock; |
886 |
lock.lock(); |
887 |
try { |
888 |
Object[] a = new Object[count]; |
889 |
int k = 0; |
890 |
for (Node<E> p = first; p != null; p = p.next) |
891 |
a[k++] = p.item; |
892 |
return a; |
893 |
} finally { |
894 |
// checkInvariants(); |
895 |
lock.unlock(); |
896 |
} |
897 |
} |
898 |
|
899 |
/** |
900 |
* Returns an array containing all of the elements in this deque, in |
901 |
* proper sequence; the runtime type of the returned array is that of |
902 |
* the specified array. If the deque fits in the specified array, it |
903 |
* is returned therein. Otherwise, a new array is allocated with the |
904 |
* runtime type of the specified array and the size of this deque. |
905 |
* |
906 |
* <p>If this deque fits in the specified array with room to spare |
907 |
* (i.e., the array has more elements than this deque), the element in |
908 |
* the array immediately following the end of the deque is set to |
909 |
* {@code null}. |
910 |
* |
911 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
912 |
* array-based and collection-based APIs. Further, this method allows |
913 |
* precise control over the runtime type of the output array, and may, |
914 |
* under certain circumstances, be used to save allocation costs. |
915 |
* |
916 |
* <p>Suppose {@code x} is a deque known to contain only strings. |
917 |
* The following code can be used to dump the deque into a newly |
918 |
* allocated array of {@code String}: |
919 |
* |
920 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
921 |
* |
922 |
* Note that {@code toArray(new Object[0])} is identical in function to |
923 |
* {@code toArray()}. |
924 |
* |
925 |
* @param a the array into which the elements of the deque are to |
926 |
* be stored, if it is big enough; otherwise, a new array of the |
927 |
* same runtime type is allocated for this purpose |
928 |
* @return an array containing all of the elements in this deque |
929 |
* @throws ArrayStoreException if the runtime type of the specified array |
930 |
* is not a supertype of the runtime type of every element in |
931 |
* this deque |
932 |
* @throws NullPointerException if the specified array is null |
933 |
*/ |
934 |
@SuppressWarnings("unchecked") |
935 |
public <T> T[] toArray(T[] a) { |
936 |
final ReentrantLock lock = this.lock; |
937 |
lock.lock(); |
938 |
try { |
939 |
if (a.length < count) |
940 |
a = (T[])java.lang.reflect.Array.newInstance |
941 |
(a.getClass().getComponentType(), count); |
942 |
|
943 |
int k = 0; |
944 |
for (Node<E> p = first; p != null; p = p.next) |
945 |
a[k++] = (T)p.item; |
946 |
if (a.length > k) |
947 |
a[k] = null; |
948 |
return a; |
949 |
} finally { |
950 |
// checkInvariants(); |
951 |
lock.unlock(); |
952 |
} |
953 |
} |
954 |
|
955 |
public String toString() { |
956 |
return Helpers.collectionToString(this); |
957 |
} |
958 |
|
959 |
/** |
960 |
* Atomically removes all of the elements from this deque. |
961 |
* The deque will be empty after this call returns. |
962 |
*/ |
963 |
public void clear() { |
964 |
final ReentrantLock lock = this.lock; |
965 |
lock.lock(); |
966 |
try { |
967 |
for (Node<E> f = first; f != null; ) { |
968 |
f.item = null; |
969 |
Node<E> n = f.next; |
970 |
f.prev = null; |
971 |
f.next = null; |
972 |
f = n; |
973 |
} |
974 |
first = last = null; |
975 |
count = 0; |
976 |
notFull.signalAll(); |
977 |
} finally { |
978 |
// checkInvariants(); |
979 |
lock.unlock(); |
980 |
} |
981 |
} |
982 |
|
983 |
/** |
984 |
* Used for any element traversal that is not entirely under lock. |
985 |
* Such traversals must handle both: |
986 |
* - dequeued nodes (p.next == p) |
987 |
* - (possibly multiple) interior removed nodes (p.item == null) |
988 |
*/ |
989 |
Node<E> succ(Node<E> p) { |
990 |
return (p == (p = p.next)) ? first : p; |
991 |
} |
992 |
|
993 |
/** |
994 |
* Returns an iterator over the elements in this deque in proper sequence. |
995 |
* The elements will be returned in order from first (head) to last (tail). |
996 |
* |
997 |
* <p>The returned iterator is |
998 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
999 |
* |
1000 |
* @return an iterator over the elements in this deque in proper sequence |
1001 |
*/ |
1002 |
public Iterator<E> iterator() { |
1003 |
return new Itr(); |
1004 |
} |
1005 |
|
1006 |
/** |
1007 |
* Returns an iterator over the elements in this deque in reverse |
1008 |
* sequential order. The elements will be returned in order from |
1009 |
* last (tail) to first (head). |
1010 |
* |
1011 |
* <p>The returned iterator is |
1012 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
1013 |
* |
1014 |
* @return an iterator over the elements in this deque in reverse order |
1015 |
*/ |
1016 |
public Iterator<E> descendingIterator() { |
1017 |
return new DescendingItr(); |
1018 |
} |
1019 |
|
1020 |
/** |
1021 |
* Base class for LinkedBlockingDeque iterators. |
1022 |
*/ |
1023 |
private abstract class AbstractItr implements Iterator<E> { |
1024 |
/** |
1025 |
* The next node to return in next(). |
1026 |
*/ |
1027 |
Node<E> next; |
1028 |
|
1029 |
/** |
1030 |
* nextItem holds on to item fields because once we claim that |
1031 |
* an element exists in hasNext(), we must return item read |
1032 |
* under lock even if it was in the process of being removed |
1033 |
* when hasNext() was called. |
1034 |
*/ |
1035 |
E nextItem; |
1036 |
|
1037 |
/** |
1038 |
* Node returned by most recent call to next. Needed by remove. |
1039 |
* Reset to null if this element is deleted by a call to remove. |
1040 |
*/ |
1041 |
private Node<E> lastRet; |
1042 |
|
1043 |
abstract Node<E> firstNode(); |
1044 |
abstract Node<E> nextNode(Node<E> n); |
1045 |
|
1046 |
private Node<E> succ(Node<E> p) { |
1047 |
return (p == (p = nextNode(p))) ? firstNode() : p; |
1048 |
} |
1049 |
|
1050 |
AbstractItr() { |
1051 |
// set to initial position |
1052 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1053 |
lock.lock(); |
1054 |
try { |
1055 |
if ((next = firstNode()) != null) |
1056 |
nextItem = next.item; |
1057 |
} finally { |
1058 |
// checkInvariants(); |
1059 |
lock.unlock(); |
1060 |
} |
1061 |
} |
1062 |
|
1063 |
public boolean hasNext() { |
1064 |
return next != null; |
1065 |
} |
1066 |
|
1067 |
public E next() { |
1068 |
Node<E> p; |
1069 |
if ((p = next) == null) |
1070 |
throw new NoSuchElementException(); |
1071 |
E ret = nextItem, e = null; |
1072 |
lastRet = p; |
1073 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1074 |
lock.lock(); |
1075 |
try { |
1076 |
for (p = nextNode(p); p != null; p = succ(p)) |
1077 |
if ((e = p.item) != null) |
1078 |
break; |
1079 |
} finally { |
1080 |
// checkInvariants(); |
1081 |
lock.unlock(); |
1082 |
} |
1083 |
next = p; |
1084 |
nextItem = e; |
1085 |
return ret; |
1086 |
} |
1087 |
|
1088 |
public void forEachRemaining(Consumer<? super E> action) { |
1089 |
// A variant of forEachFrom |
1090 |
Objects.requireNonNull(action); |
1091 |
Node<E> p; |
1092 |
if ((p = next) == null) return; |
1093 |
lastRet = next; |
1094 |
next = null; |
1095 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1096 |
final int batchSize = 32; |
1097 |
Object[] es = null; |
1098 |
int n, len = 1; |
1099 |
do { |
1100 |
lock.lock(); |
1101 |
try { |
1102 |
if (es == null) { |
1103 |
p = nextNode(p); |
1104 |
for (Node<E> q = p; q != null; q = succ(q)) |
1105 |
if (q.item != null && ++len == batchSize) |
1106 |
break; |
1107 |
es = new Object[len]; |
1108 |
es[0] = nextItem; |
1109 |
nextItem = null; |
1110 |
n = 1; |
1111 |
} else |
1112 |
n = 0; |
1113 |
for (; p != null && n < len; p = succ(p)) |
1114 |
if ((es[n] = p.item) != null) { |
1115 |
lastRet = p; |
1116 |
n++; |
1117 |
} |
1118 |
} finally { |
1119 |
// checkInvariants(); |
1120 |
lock.unlock(); |
1121 |
} |
1122 |
for (int i = 0; i < n; i++) { |
1123 |
@SuppressWarnings("unchecked") E e = (E) es[i]; |
1124 |
action.accept(e); |
1125 |
} |
1126 |
} while (n > 0 && p != null); |
1127 |
} |
1128 |
|
1129 |
public void remove() { |
1130 |
Node<E> n = lastRet; |
1131 |
if (n == null) |
1132 |
throw new IllegalStateException(); |
1133 |
lastRet = null; |
1134 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1135 |
lock.lock(); |
1136 |
try { |
1137 |
if (n.item != null) |
1138 |
unlink(n); |
1139 |
} finally { |
1140 |
// checkInvariants(); |
1141 |
lock.unlock(); |
1142 |
} |
1143 |
} |
1144 |
} |
1145 |
|
1146 |
/** Forward iterator */ |
1147 |
private class Itr extends AbstractItr { |
1148 |
Node<E> firstNode() { return first; } |
1149 |
Node<E> nextNode(Node<E> n) { return n.next; } |
1150 |
} |
1151 |
|
1152 |
/** Descending iterator */ |
1153 |
private class DescendingItr extends AbstractItr { |
1154 |
Node<E> firstNode() { return last; } |
1155 |
Node<E> nextNode(Node<E> n) { return n.prev; } |
1156 |
} |
1157 |
|
1158 |
/** |
1159 |
* A customized variant of Spliterators.IteratorSpliterator. |
1160 |
* Keep this class in sync with (very similar) LBQSpliterator. |
1161 |
*/ |
1162 |
private final class LBDSpliterator implements Spliterator<E> { |
1163 |
static final int MAX_BATCH = 1 << 25; // max batch array size; |
1164 |
Node<E> current; // current node; null until initialized |
1165 |
int batch; // batch size for splits |
1166 |
boolean exhausted; // true when no more nodes |
1167 |
long est = size(); // size estimate |
1168 |
|
1169 |
LBDSpliterator() {} |
1170 |
|
1171 |
public long estimateSize() { return est; } |
1172 |
|
1173 |
public Spliterator<E> trySplit() { |
1174 |
Node<E> h; |
1175 |
int b = batch; |
1176 |
int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1; |
1177 |
if (!exhausted && |
1178 |
((h = current) != null || (h = first) != null) |
1179 |
&& h.next != null) { |
1180 |
Object[] a = new Object[n]; |
1181 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1182 |
int i = 0; |
1183 |
Node<E> p = current; |
1184 |
lock.lock(); |
1185 |
try { |
1186 |
if (p != null || (p = first) != null) |
1187 |
for (; p != null && i < n; p = succ(p)) |
1188 |
if ((a[i] = p.item) != null) |
1189 |
i++; |
1190 |
} finally { |
1191 |
// checkInvariants(); |
1192 |
lock.unlock(); |
1193 |
} |
1194 |
if ((current = p) == null) { |
1195 |
est = 0L; |
1196 |
exhausted = true; |
1197 |
} |
1198 |
else if ((est -= i) < 0L) |
1199 |
est = 0L; |
1200 |
if (i > 0) { |
1201 |
batch = i; |
1202 |
return Spliterators.spliterator |
1203 |
(a, 0, i, (Spliterator.ORDERED | |
1204 |
Spliterator.NONNULL | |
1205 |
Spliterator.CONCURRENT)); |
1206 |
} |
1207 |
} |
1208 |
return null; |
1209 |
} |
1210 |
|
1211 |
public boolean tryAdvance(Consumer<? super E> action) { |
1212 |
Objects.requireNonNull(action); |
1213 |
if (!exhausted) { |
1214 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
1215 |
Node<E> p = current; |
1216 |
E e = null; |
1217 |
lock.lock(); |
1218 |
try { |
1219 |
if (p != null || (p = first) != null) |
1220 |
do { |
1221 |
e = p.item; |
1222 |
p = succ(p); |
1223 |
} while (e == null && p != null); |
1224 |
} finally { |
1225 |
// checkInvariants(); |
1226 |
lock.unlock(); |
1227 |
} |
1228 |
exhausted = ((current = p) == null); |
1229 |
if (e != null) { |
1230 |
action.accept(e); |
1231 |
return true; |
1232 |
} |
1233 |
} |
1234 |
return false; |
1235 |
} |
1236 |
|
1237 |
public void forEachRemaining(Consumer<? super E> action) { |
1238 |
Objects.requireNonNull(action); |
1239 |
if (!exhausted) { |
1240 |
exhausted = true; |
1241 |
Node<E> p = current; |
1242 |
current = null; |
1243 |
forEachFrom(action, p); |
1244 |
} |
1245 |
} |
1246 |
|
1247 |
public int characteristics() { |
1248 |
return (Spliterator.ORDERED | |
1249 |
Spliterator.NONNULL | |
1250 |
Spliterator.CONCURRENT); |
1251 |
} |
1252 |
} |
1253 |
|
1254 |
/** |
1255 |
* Returns a {@link Spliterator} over the elements in this deque. |
1256 |
* |
1257 |
* <p>The returned spliterator is |
1258 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
1259 |
* |
1260 |
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
1261 |
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
1262 |
* |
1263 |
* @implNote |
1264 |
* The {@code Spliterator} implements {@code trySplit} to permit limited |
1265 |
* parallelism. |
1266 |
* |
1267 |
* @return a {@code Spliterator} over the elements in this deque |
1268 |
* @since 1.8 |
1269 |
*/ |
1270 |
public Spliterator<E> spliterator() { |
1271 |
return new LBDSpliterator(); |
1272 |
} |
1273 |
|
1274 |
/** |
1275 |
* @throws NullPointerException {@inheritDoc} |
1276 |
*/ |
1277 |
public void forEach(Consumer<? super E> action) { |
1278 |
Objects.requireNonNull(action); |
1279 |
forEachFrom(action, null); |
1280 |
} |
1281 |
|
1282 |
/** |
1283 |
* Runs action on each element found during a traversal starting at p. |
1284 |
* If p is null, traversal starts at head. |
1285 |
*/ |
1286 |
void forEachFrom(Consumer<? super E> action, Node<E> p) { |
1287 |
// Extract batches of elements while holding the lock; then |
1288 |
// run the action on the elements while not |
1289 |
final ReentrantLock lock = this.lock; |
1290 |
final int batchSize = 32; // max number of elements per batch |
1291 |
Object[] es = null; // container for batch of elements |
1292 |
int n, len = 0; |
1293 |
do { |
1294 |
lock.lock(); |
1295 |
try { |
1296 |
if (es == null) { |
1297 |
if (p == null) p = first; |
1298 |
for (Node<E> q = p; q != null; q = succ(q)) |
1299 |
if (q.item != null && ++len == batchSize) |
1300 |
break; |
1301 |
es = new Object[len]; |
1302 |
} |
1303 |
for (n = 0; p != null && n < len; p = succ(p)) |
1304 |
if ((es[n] = p.item) != null) |
1305 |
n++; |
1306 |
} finally { |
1307 |
// checkInvariants(); |
1308 |
lock.unlock(); |
1309 |
} |
1310 |
for (int i = 0; i < n; i++) { |
1311 |
@SuppressWarnings("unchecked") E e = (E) es[i]; |
1312 |
action.accept(e); |
1313 |
} |
1314 |
} while (n > 0 && p != null); |
1315 |
} |
1316 |
|
1317 |
/** |
1318 |
* Saves this deque to a stream (that is, serializes it). |
1319 |
* |
1320 |
* @param s the stream |
1321 |
* @throws java.io.IOException if an I/O error occurs |
1322 |
* @serialData The capacity (int), followed by elements (each an |
1323 |
* {@code Object}) in the proper order, followed by a null |
1324 |
*/ |
1325 |
private void writeObject(java.io.ObjectOutputStream s) |
1326 |
throws java.io.IOException { |
1327 |
final ReentrantLock lock = this.lock; |
1328 |
lock.lock(); |
1329 |
try { |
1330 |
// Write out capacity and any hidden stuff |
1331 |
s.defaultWriteObject(); |
1332 |
// Write out all elements in the proper order. |
1333 |
for (Node<E> p = first; p != null; p = p.next) |
1334 |
s.writeObject(p.item); |
1335 |
// Use trailing null as sentinel |
1336 |
s.writeObject(null); |
1337 |
} finally { |
1338 |
// checkInvariants(); |
1339 |
lock.unlock(); |
1340 |
} |
1341 |
} |
1342 |
|
1343 |
/** |
1344 |
* Reconstitutes this deque from a stream (that is, deserializes it). |
1345 |
* @param s the stream |
1346 |
* @throws ClassNotFoundException if the class of a serialized object |
1347 |
* could not be found |
1348 |
* @throws java.io.IOException if an I/O error occurs |
1349 |
*/ |
1350 |
private void readObject(java.io.ObjectInputStream s) |
1351 |
throws java.io.IOException, ClassNotFoundException { |
1352 |
s.defaultReadObject(); |
1353 |
count = 0; |
1354 |
first = null; |
1355 |
last = null; |
1356 |
// Read in all elements and place in queue |
1357 |
for (;;) { |
1358 |
@SuppressWarnings("unchecked") E item = (E)s.readObject(); |
1359 |
if (item == null) |
1360 |
break; |
1361 |
add(item); |
1362 |
} |
1363 |
} |
1364 |
|
1365 |
void checkInvariants() { |
1366 |
// assert lock.isHeldByCurrentThread(); |
1367 |
// Nodes may get self-linked or lose their item, but only |
1368 |
// after being unlinked and becoming unreachable from first. |
1369 |
for (Node<E> p = first; p != null; p = p.next) { |
1370 |
// assert p.next != p; |
1371 |
// assert p.item != null; |
1372 |
} |
1373 |
} |
1374 |
|
1375 |
} |