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.atomic.AtomicInteger; |
17 |
import java.util.concurrent.locks.Condition; |
18 |
import java.util.concurrent.locks.ReentrantLock; |
19 |
import java.util.function.Consumer; |
20 |
|
21 |
/** |
22 |
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
23 |
* linked nodes. |
24 |
* This queue orders elements FIFO (first-in-first-out). |
25 |
* The <em>head</em> of the queue is that element that has been on the |
26 |
* queue the longest time. |
27 |
* The <em>tail</em> of the queue is that element that has been on the |
28 |
* queue the shortest time. New elements |
29 |
* are inserted at the tail of the queue, and the queue retrieval |
30 |
* operations obtain elements at the head of the queue. |
31 |
* Linked queues typically have higher throughput than array-based queues but |
32 |
* less predictable performance in most concurrent applications. |
33 |
* |
34 |
* <p>The optional capacity bound constructor argument serves as a |
35 |
* way to prevent excessive queue expansion. The capacity, if unspecified, |
36 |
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
37 |
* dynamically created upon each insertion unless this would bring the |
38 |
* queue above capacity. |
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 queue |
51 |
*/ |
52 |
public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
53 |
implements BlockingQueue<E>, java.io.Serializable { |
54 |
private static final long serialVersionUID = -6903933977591709194L; |
55 |
|
56 |
/* |
57 |
* A variant of the "two lock queue" algorithm. The putLock gates |
58 |
* entry to put (and offer), and has an associated condition for |
59 |
* waiting puts. Similarly for the takeLock. The "count" field |
60 |
* that they both rely on is maintained as an atomic to avoid |
61 |
* needing to get both locks in most cases. Also, to minimize need |
62 |
* for puts to get takeLock and vice-versa, cascading notifies are |
63 |
* used. When a put notices that it has enabled at least one take, |
64 |
* it signals taker. That taker in turn signals others if more |
65 |
* items have been entered since the signal. And symmetrically for |
66 |
* takes signalling puts. Operations such as remove(Object) and |
67 |
* iterators acquire both locks. |
68 |
* |
69 |
* Visibility between writers and readers is provided as follows: |
70 |
* |
71 |
* Whenever an element is enqueued, the putLock is acquired and |
72 |
* count updated. A subsequent reader guarantees visibility to the |
73 |
* enqueued Node by either acquiring the putLock (via fullyLock) |
74 |
* or by acquiring the takeLock, and then reading n = count.get(); |
75 |
* this gives visibility to the first n items. |
76 |
* |
77 |
* To implement weakly consistent iterators, it appears we need to |
78 |
* keep all Nodes GC-reachable from a predecessor dequeued Node. |
79 |
* That would cause two problems: |
80 |
* - allow a rogue Iterator to cause unbounded memory retention |
81 |
* - cause cross-generational linking of old Nodes to new Nodes if |
82 |
* a Node was tenured while live, which generational GCs have a |
83 |
* hard time dealing with, causing repeated major collections. |
84 |
* However, only non-deleted Nodes need to be reachable from |
85 |
* dequeued Nodes, and reachability does not necessarily have to |
86 |
* be of the kind understood by the GC. We use the trick of |
87 |
* linking a Node that has just been dequeued to itself. Such a |
88 |
* self-link implicitly means to advance to head.next. |
89 |
*/ |
90 |
|
91 |
/** |
92 |
* Linked list node class. |
93 |
*/ |
94 |
static class Node<E> { |
95 |
E item; |
96 |
|
97 |
/** |
98 |
* One of: |
99 |
* - the real successor Node |
100 |
* - this Node, meaning the successor is head.next |
101 |
* - null, meaning there is no successor (this is the last node) |
102 |
*/ |
103 |
Node<E> next; |
104 |
|
105 |
Node(E x) { item = x; } |
106 |
} |
107 |
|
108 |
/** The capacity bound, or Integer.MAX_VALUE if none */ |
109 |
private final int capacity; |
110 |
|
111 |
/** Current number of elements */ |
112 |
private final AtomicInteger count = new AtomicInteger(); |
113 |
|
114 |
/** |
115 |
* Head of linked list. |
116 |
* Invariant: head.item == null |
117 |
*/ |
118 |
transient Node<E> head; |
119 |
|
120 |
/** |
121 |
* Tail of linked list. |
122 |
* Invariant: last.next == null |
123 |
*/ |
124 |
private transient Node<E> last; |
125 |
|
126 |
/** Lock held by take, poll, etc */ |
127 |
private final ReentrantLock takeLock = new ReentrantLock(); |
128 |
|
129 |
/** Wait queue for waiting takes */ |
130 |
private final Condition notEmpty = takeLock.newCondition(); |
131 |
|
132 |
/** Lock held by put, offer, etc */ |
133 |
private final ReentrantLock putLock = new ReentrantLock(); |
134 |
|
135 |
/** Wait queue for waiting puts */ |
136 |
private final Condition notFull = putLock.newCondition(); |
137 |
|
138 |
/** |
139 |
* Signals a waiting take. Called only from put/offer (which do not |
140 |
* otherwise ordinarily lock takeLock.) |
141 |
*/ |
142 |
private void signalNotEmpty() { |
143 |
final ReentrantLock takeLock = this.takeLock; |
144 |
takeLock.lock(); |
145 |
try { |
146 |
notEmpty.signal(); |
147 |
} finally { |
148 |
takeLock.unlock(); |
149 |
} |
150 |
} |
151 |
|
152 |
/** |
153 |
* Signals a waiting put. Called only from take/poll. |
154 |
*/ |
155 |
private void signalNotFull() { |
156 |
final ReentrantLock putLock = this.putLock; |
157 |
putLock.lock(); |
158 |
try { |
159 |
notFull.signal(); |
160 |
} finally { |
161 |
putLock.unlock(); |
162 |
} |
163 |
} |
164 |
|
165 |
/** |
166 |
* Links node at end of queue. |
167 |
* |
168 |
* @param node the node |
169 |
*/ |
170 |
private void enqueue(Node<E> node) { |
171 |
// assert putLock.isHeldByCurrentThread(); |
172 |
// assert last.next == null; |
173 |
last = last.next = node; |
174 |
} |
175 |
|
176 |
/** |
177 |
* Removes a node from head of queue. |
178 |
* |
179 |
* @return the node |
180 |
*/ |
181 |
private E dequeue() { |
182 |
// assert takeLock.isHeldByCurrentThread(); |
183 |
// assert head.item == null; |
184 |
Node<E> h = head; |
185 |
Node<E> first = h.next; |
186 |
h.next = h; // help GC |
187 |
head = first; |
188 |
E x = first.item; |
189 |
first.item = null; |
190 |
return x; |
191 |
} |
192 |
|
193 |
/** |
194 |
* Locks to prevent both puts and takes. |
195 |
*/ |
196 |
void fullyLock() { |
197 |
putLock.lock(); |
198 |
takeLock.lock(); |
199 |
} |
200 |
|
201 |
/** |
202 |
* Unlocks to allow both puts and takes. |
203 |
*/ |
204 |
void fullyUnlock() { |
205 |
takeLock.unlock(); |
206 |
putLock.unlock(); |
207 |
} |
208 |
|
209 |
/** |
210 |
* Creates a {@code LinkedBlockingQueue} with a capacity of |
211 |
* {@link Integer#MAX_VALUE}. |
212 |
*/ |
213 |
public LinkedBlockingQueue() { |
214 |
this(Integer.MAX_VALUE); |
215 |
} |
216 |
|
217 |
/** |
218 |
* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. |
219 |
* |
220 |
* @param capacity the capacity of this queue |
221 |
* @throws IllegalArgumentException if {@code capacity} is not greater |
222 |
* than zero |
223 |
*/ |
224 |
public LinkedBlockingQueue(int capacity) { |
225 |
if (capacity <= 0) throw new IllegalArgumentException(); |
226 |
this.capacity = capacity; |
227 |
last = head = new Node<E>(null); |
228 |
} |
229 |
|
230 |
/** |
231 |
* Creates a {@code LinkedBlockingQueue} with a capacity of |
232 |
* {@link Integer#MAX_VALUE}, initially containing the elements of the |
233 |
* given collection, |
234 |
* added in traversal order of the collection's iterator. |
235 |
* |
236 |
* @param c the collection of elements to initially contain |
237 |
* @throws NullPointerException if the specified collection or any |
238 |
* of its elements are null |
239 |
*/ |
240 |
public LinkedBlockingQueue(Collection<? extends E> c) { |
241 |
this(Integer.MAX_VALUE); |
242 |
final ReentrantLock putLock = this.putLock; |
243 |
putLock.lock(); // Never contended, but necessary for visibility |
244 |
try { |
245 |
int n = 0; |
246 |
for (E e : c) { |
247 |
if (e == null) |
248 |
throw new NullPointerException(); |
249 |
if (n == capacity) |
250 |
throw new IllegalStateException("Queue full"); |
251 |
enqueue(new Node<E>(e)); |
252 |
++n; |
253 |
} |
254 |
count.set(n); |
255 |
} finally { |
256 |
putLock.unlock(); |
257 |
} |
258 |
} |
259 |
|
260 |
// this doc comment is overridden to remove the reference to collections |
261 |
// greater in size than Integer.MAX_VALUE |
262 |
/** |
263 |
* Returns the number of elements in this queue. |
264 |
* |
265 |
* @return the number of elements in this queue |
266 |
*/ |
267 |
public int size() { |
268 |
return count.get(); |
269 |
} |
270 |
|
271 |
// this doc comment is a modified copy of the inherited doc comment, |
272 |
// without the reference to unlimited queues. |
273 |
/** |
274 |
* Returns the number of additional elements that this queue can ideally |
275 |
* (in the absence of memory or resource constraints) accept without |
276 |
* blocking. This is always equal to the initial capacity of this queue |
277 |
* less the current {@code size} of this queue. |
278 |
* |
279 |
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
280 |
* an element will succeed by inspecting {@code remainingCapacity} |
281 |
* because it may be the case that another thread is about to |
282 |
* insert or remove an element. |
283 |
*/ |
284 |
public int remainingCapacity() { |
285 |
return capacity - count.get(); |
286 |
} |
287 |
|
288 |
/** |
289 |
* Inserts the specified element at the tail of this queue, waiting if |
290 |
* necessary for space to become available. |
291 |
* |
292 |
* @throws InterruptedException {@inheritDoc} |
293 |
* @throws NullPointerException {@inheritDoc} |
294 |
*/ |
295 |
public void put(E e) throws InterruptedException { |
296 |
if (e == null) throw new NullPointerException(); |
297 |
// Note: convention in all put/take/etc is to preset local var |
298 |
// holding count negative to indicate failure unless set. |
299 |
int c = -1; |
300 |
Node<E> node = new Node<E>(e); |
301 |
final ReentrantLock putLock = this.putLock; |
302 |
final AtomicInteger count = this.count; |
303 |
putLock.lockInterruptibly(); |
304 |
try { |
305 |
/* |
306 |
* Note that count is used in wait guard even though it is |
307 |
* not protected by lock. This works because count can |
308 |
* only decrease at this point (all other puts are shut |
309 |
* out by lock), and we (or some other waiting put) are |
310 |
* signalled if it ever changes from capacity. Similarly |
311 |
* for all other uses of count in other wait guards. |
312 |
*/ |
313 |
while (count.get() == capacity) { |
314 |
notFull.await(); |
315 |
} |
316 |
enqueue(node); |
317 |
c = count.getAndIncrement(); |
318 |
if (c + 1 < capacity) |
319 |
notFull.signal(); |
320 |
} finally { |
321 |
putLock.unlock(); |
322 |
} |
323 |
if (c == 0) |
324 |
signalNotEmpty(); |
325 |
} |
326 |
|
327 |
/** |
328 |
* Inserts the specified element at the tail of this queue, waiting if |
329 |
* necessary up to the specified wait time for space to become available. |
330 |
* |
331 |
* @return {@code true} if successful, or {@code false} if |
332 |
* the specified waiting time elapses before space is available |
333 |
* @throws InterruptedException {@inheritDoc} |
334 |
* @throws NullPointerException {@inheritDoc} |
335 |
*/ |
336 |
public boolean offer(E e, long timeout, TimeUnit unit) |
337 |
throws InterruptedException { |
338 |
|
339 |
if (e == null) throw new NullPointerException(); |
340 |
long nanos = unit.toNanos(timeout); |
341 |
int c = -1; |
342 |
final ReentrantLock putLock = this.putLock; |
343 |
final AtomicInteger count = this.count; |
344 |
putLock.lockInterruptibly(); |
345 |
try { |
346 |
while (count.get() == capacity) { |
347 |
if (nanos <= 0L) |
348 |
return false; |
349 |
nanos = notFull.awaitNanos(nanos); |
350 |
} |
351 |
enqueue(new Node<E>(e)); |
352 |
c = count.getAndIncrement(); |
353 |
if (c + 1 < capacity) |
354 |
notFull.signal(); |
355 |
} finally { |
356 |
putLock.unlock(); |
357 |
} |
358 |
if (c == 0) |
359 |
signalNotEmpty(); |
360 |
return true; |
361 |
} |
362 |
|
363 |
/** |
364 |
* Inserts the specified element at the tail of this queue if it is |
365 |
* possible to do so immediately without exceeding the queue's capacity, |
366 |
* returning {@code true} upon success and {@code false} if this queue |
367 |
* is full. |
368 |
* When using a capacity-restricted queue, this method is generally |
369 |
* preferable to method {@link BlockingQueue#add add}, which can fail to |
370 |
* insert an element only by throwing an exception. |
371 |
* |
372 |
* @throws NullPointerException if the specified element is null |
373 |
*/ |
374 |
public boolean offer(E e) { |
375 |
if (e == null) throw new NullPointerException(); |
376 |
final AtomicInteger count = this.count; |
377 |
if (count.get() == capacity) |
378 |
return false; |
379 |
int c = -1; |
380 |
Node<E> node = new Node<E>(e); |
381 |
final ReentrantLock putLock = this.putLock; |
382 |
putLock.lock(); |
383 |
try { |
384 |
if (count.get() < capacity) { |
385 |
enqueue(node); |
386 |
c = count.getAndIncrement(); |
387 |
if (c + 1 < capacity) |
388 |
notFull.signal(); |
389 |
} |
390 |
} finally { |
391 |
putLock.unlock(); |
392 |
} |
393 |
if (c == 0) |
394 |
signalNotEmpty(); |
395 |
return c >= 0; |
396 |
} |
397 |
|
398 |
public E take() throws InterruptedException { |
399 |
E x; |
400 |
int c = -1; |
401 |
final AtomicInteger count = this.count; |
402 |
final ReentrantLock takeLock = this.takeLock; |
403 |
takeLock.lockInterruptibly(); |
404 |
try { |
405 |
while (count.get() == 0) { |
406 |
notEmpty.await(); |
407 |
} |
408 |
x = dequeue(); |
409 |
c = count.getAndDecrement(); |
410 |
if (c > 1) |
411 |
notEmpty.signal(); |
412 |
} finally { |
413 |
takeLock.unlock(); |
414 |
} |
415 |
if (c == capacity) |
416 |
signalNotFull(); |
417 |
return x; |
418 |
} |
419 |
|
420 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
421 |
E x = null; |
422 |
int c = -1; |
423 |
long nanos = unit.toNanos(timeout); |
424 |
final AtomicInteger count = this.count; |
425 |
final ReentrantLock takeLock = this.takeLock; |
426 |
takeLock.lockInterruptibly(); |
427 |
try { |
428 |
while (count.get() == 0) { |
429 |
if (nanos <= 0L) |
430 |
return null; |
431 |
nanos = notEmpty.awaitNanos(nanos); |
432 |
} |
433 |
x = dequeue(); |
434 |
c = count.getAndDecrement(); |
435 |
if (c > 1) |
436 |
notEmpty.signal(); |
437 |
} finally { |
438 |
takeLock.unlock(); |
439 |
} |
440 |
if (c == capacity) |
441 |
signalNotFull(); |
442 |
return x; |
443 |
} |
444 |
|
445 |
public E poll() { |
446 |
final AtomicInteger count = this.count; |
447 |
if (count.get() == 0) |
448 |
return null; |
449 |
E x = null; |
450 |
int c = -1; |
451 |
final ReentrantLock takeLock = this.takeLock; |
452 |
takeLock.lock(); |
453 |
try { |
454 |
if (count.get() > 0) { |
455 |
x = dequeue(); |
456 |
c = count.getAndDecrement(); |
457 |
if (c > 1) |
458 |
notEmpty.signal(); |
459 |
} |
460 |
} finally { |
461 |
takeLock.unlock(); |
462 |
} |
463 |
if (c == capacity) |
464 |
signalNotFull(); |
465 |
return x; |
466 |
} |
467 |
|
468 |
public E peek() { |
469 |
if (count.get() == 0) |
470 |
return null; |
471 |
final ReentrantLock takeLock = this.takeLock; |
472 |
takeLock.lock(); |
473 |
try { |
474 |
return (count.get() > 0) ? head.next.item : null; |
475 |
} finally { |
476 |
takeLock.unlock(); |
477 |
} |
478 |
} |
479 |
|
480 |
/** |
481 |
* Unlinks interior Node p with predecessor trail. |
482 |
*/ |
483 |
void unlink(Node<E> p, Node<E> trail) { |
484 |
// assert putLock.isHeldByCurrentThread(); |
485 |
// assert takeLock.isHeldByCurrentThread(); |
486 |
// p.next is not changed, to allow iterators that are |
487 |
// traversing p to maintain their weak-consistency guarantee. |
488 |
p.item = null; |
489 |
trail.next = p.next; |
490 |
if (last == p) |
491 |
last = trail; |
492 |
if (count.getAndDecrement() == capacity) |
493 |
notFull.signal(); |
494 |
} |
495 |
|
496 |
/** |
497 |
* Removes a single instance of the specified element from this queue, |
498 |
* if it is present. More formally, removes an element {@code e} such |
499 |
* that {@code o.equals(e)}, if this queue contains one or more such |
500 |
* elements. |
501 |
* Returns {@code true} if this queue contained the specified element |
502 |
* (or equivalently, if this queue changed as a result of the call). |
503 |
* |
504 |
* @param o element to be removed from this queue, if present |
505 |
* @return {@code true} if this queue changed as a result of the call |
506 |
*/ |
507 |
public boolean remove(Object o) { |
508 |
if (o == null) return false; |
509 |
fullyLock(); |
510 |
try { |
511 |
for (Node<E> trail = head, p = trail.next; |
512 |
p != null; |
513 |
trail = p, p = p.next) { |
514 |
if (o.equals(p.item)) { |
515 |
unlink(p, trail); |
516 |
return true; |
517 |
} |
518 |
} |
519 |
return false; |
520 |
} finally { |
521 |
fullyUnlock(); |
522 |
} |
523 |
} |
524 |
|
525 |
/** |
526 |
* Returns {@code true} if this queue contains the specified element. |
527 |
* More formally, returns {@code true} if and only if this queue contains |
528 |
* at least one element {@code e} such that {@code o.equals(e)}. |
529 |
* |
530 |
* @param o object to be checked for containment in this queue |
531 |
* @return {@code true} if this queue contains the specified element |
532 |
*/ |
533 |
public boolean contains(Object o) { |
534 |
if (o == null) return false; |
535 |
fullyLock(); |
536 |
try { |
537 |
for (Node<E> p = head.next; p != null; p = p.next) |
538 |
if (o.equals(p.item)) |
539 |
return true; |
540 |
return false; |
541 |
} finally { |
542 |
fullyUnlock(); |
543 |
} |
544 |
} |
545 |
|
546 |
/** |
547 |
* Returns an array containing all of the elements in this queue, in |
548 |
* proper sequence. |
549 |
* |
550 |
* <p>The returned array will be "safe" in that no references to it are |
551 |
* maintained by this queue. (In other words, this method must allocate |
552 |
* a new array). The caller is thus free to modify the returned array. |
553 |
* |
554 |
* <p>This method acts as bridge between array-based and collection-based |
555 |
* APIs. |
556 |
* |
557 |
* @return an array containing all of the elements in this queue |
558 |
*/ |
559 |
public Object[] toArray() { |
560 |
fullyLock(); |
561 |
try { |
562 |
int size = count.get(); |
563 |
Object[] a = new Object[size]; |
564 |
int k = 0; |
565 |
for (Node<E> p = head.next; p != null; p = p.next) |
566 |
a[k++] = p.item; |
567 |
return a; |
568 |
} finally { |
569 |
fullyUnlock(); |
570 |
} |
571 |
} |
572 |
|
573 |
/** |
574 |
* Returns an array containing all of the elements in this queue, in |
575 |
* proper sequence; the runtime type of the returned array is that of |
576 |
* the specified array. If the queue fits in the specified array, it |
577 |
* is returned therein. Otherwise, a new array is allocated with the |
578 |
* runtime type of the specified array and the size of this queue. |
579 |
* |
580 |
* <p>If this queue fits in the specified array with room to spare |
581 |
* (i.e., the array has more elements than this queue), the element in |
582 |
* the array immediately following the end of the queue is set to |
583 |
* {@code null}. |
584 |
* |
585 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
586 |
* array-based and collection-based APIs. Further, this method allows |
587 |
* precise control over the runtime type of the output array, and may, |
588 |
* under certain circumstances, be used to save allocation costs. |
589 |
* |
590 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
591 |
* The following code can be used to dump the queue into a newly |
592 |
* allocated array of {@code String}: |
593 |
* |
594 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
595 |
* |
596 |
* Note that {@code toArray(new Object[0])} is identical in function to |
597 |
* {@code toArray()}. |
598 |
* |
599 |
* @param a the array into which the elements of the queue are to |
600 |
* be stored, if it is big enough; otherwise, a new array of the |
601 |
* same runtime type is allocated for this purpose |
602 |
* @return an array containing all of the elements in this queue |
603 |
* @throws ArrayStoreException if the runtime type of the specified array |
604 |
* is not a supertype of the runtime type of every element in |
605 |
* this queue |
606 |
* @throws NullPointerException if the specified array is null |
607 |
*/ |
608 |
@SuppressWarnings("unchecked") |
609 |
public <T> T[] toArray(T[] a) { |
610 |
fullyLock(); |
611 |
try { |
612 |
int size = count.get(); |
613 |
if (a.length < size) |
614 |
a = (T[])java.lang.reflect.Array.newInstance |
615 |
(a.getClass().getComponentType(), size); |
616 |
|
617 |
int k = 0; |
618 |
for (Node<E> p = head.next; p != null; p = p.next) |
619 |
a[k++] = (T)p.item; |
620 |
if (a.length > k) |
621 |
a[k] = null; |
622 |
return a; |
623 |
} finally { |
624 |
fullyUnlock(); |
625 |
} |
626 |
} |
627 |
|
628 |
public String toString() { |
629 |
return Helpers.collectionToString(this); |
630 |
} |
631 |
|
632 |
/** |
633 |
* Atomically removes all of the elements from this queue. |
634 |
* The queue will be empty after this call returns. |
635 |
*/ |
636 |
public void clear() { |
637 |
fullyLock(); |
638 |
try { |
639 |
for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
640 |
h.next = h; |
641 |
p.item = null; |
642 |
} |
643 |
head = last; |
644 |
// assert head.item == null && head.next == null; |
645 |
if (count.getAndSet(0) == capacity) |
646 |
notFull.signal(); |
647 |
} finally { |
648 |
fullyUnlock(); |
649 |
} |
650 |
} |
651 |
|
652 |
/** |
653 |
* @throws UnsupportedOperationException {@inheritDoc} |
654 |
* @throws ClassCastException {@inheritDoc} |
655 |
* @throws NullPointerException {@inheritDoc} |
656 |
* @throws IllegalArgumentException {@inheritDoc} |
657 |
*/ |
658 |
public int drainTo(Collection<? super E> c) { |
659 |
return drainTo(c, Integer.MAX_VALUE); |
660 |
} |
661 |
|
662 |
/** |
663 |
* @throws UnsupportedOperationException {@inheritDoc} |
664 |
* @throws ClassCastException {@inheritDoc} |
665 |
* @throws NullPointerException {@inheritDoc} |
666 |
* @throws IllegalArgumentException {@inheritDoc} |
667 |
*/ |
668 |
public int drainTo(Collection<? super E> c, int maxElements) { |
669 |
Objects.requireNonNull(c); |
670 |
if (c == this) |
671 |
throw new IllegalArgumentException(); |
672 |
if (maxElements <= 0) |
673 |
return 0; |
674 |
boolean signalNotFull = false; |
675 |
final ReentrantLock takeLock = this.takeLock; |
676 |
takeLock.lock(); |
677 |
try { |
678 |
int n = Math.min(maxElements, count.get()); |
679 |
// count.get provides visibility to first n Nodes |
680 |
Node<E> h = head; |
681 |
int i = 0; |
682 |
try { |
683 |
while (i < n) { |
684 |
Node<E> p = h.next; |
685 |
c.add(p.item); |
686 |
p.item = null; |
687 |
h.next = h; |
688 |
h = p; |
689 |
++i; |
690 |
} |
691 |
return n; |
692 |
} finally { |
693 |
// Restore invariants even if c.add() threw |
694 |
if (i > 0) { |
695 |
// assert h.item == null; |
696 |
head = h; |
697 |
signalNotFull = (count.getAndAdd(-i) == capacity); |
698 |
} |
699 |
} |
700 |
} finally { |
701 |
takeLock.unlock(); |
702 |
if (signalNotFull) |
703 |
signalNotFull(); |
704 |
} |
705 |
} |
706 |
|
707 |
/** |
708 |
* Used for any element traversal that is not entirely under lock. |
709 |
* Such traversals must handle both: |
710 |
* - dequeued nodes (p.next == p) |
711 |
* - (possibly multiple) interior removed nodes (p.item == null) |
712 |
*/ |
713 |
Node<E> succ(Node<E> p) { |
714 |
return (p == (p = p.next)) ? head.next : p; |
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 |
722 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
723 |
* |
724 |
* @return an iterator over the elements in this queue in proper sequence |
725 |
*/ |
726 |
public Iterator<E> iterator() { |
727 |
return new Itr(); |
728 |
} |
729 |
|
730 |
private class Itr implements Iterator<E> { |
731 |
/* |
732 |
* Basic weakly-consistent iterator. At all times hold the next |
733 |
* item to hand out so that if hasNext() reports true, we will |
734 |
* still have it to return even if lost race with a take etc. |
735 |
*/ |
736 |
|
737 |
private Node<E> current; |
738 |
private Node<E> lastRet; |
739 |
private E currentElement; |
740 |
|
741 |
Itr() { |
742 |
fullyLock(); |
743 |
try { |
744 |
if ((current = head.next) != null) |
745 |
currentElement = current.item; |
746 |
} finally { |
747 |
fullyUnlock(); |
748 |
} |
749 |
} |
750 |
|
751 |
public boolean hasNext() { |
752 |
return current != null; |
753 |
} |
754 |
|
755 |
public E next() { |
756 |
Node<E> p; |
757 |
if ((p = current) == null) |
758 |
throw new NoSuchElementException(); |
759 |
E ret = currentElement, e = null; |
760 |
lastRet = p; |
761 |
fullyLock(); |
762 |
try { |
763 |
for (p = p.next; p != null; p = succ(p)) |
764 |
if ((e = p.item) != null) |
765 |
break; |
766 |
} finally { |
767 |
fullyUnlock(); |
768 |
} |
769 |
current = p; |
770 |
currentElement = e; |
771 |
return ret; |
772 |
} |
773 |
|
774 |
public void forEachRemaining(Consumer<? super E> action) { |
775 |
// A variant of forEachFrom |
776 |
Objects.requireNonNull(action); |
777 |
Node<E> p; |
778 |
if ((p = current) == null) return; |
779 |
lastRet = current; |
780 |
current = null; |
781 |
final int batchSize = 32; |
782 |
Object[] es = null; |
783 |
int n, len = 1; |
784 |
do { |
785 |
fullyLock(); |
786 |
try { |
787 |
if (es == null) { |
788 |
p = p.next; |
789 |
for (Node<E> q = p; q != null; q = succ(q)) |
790 |
if (q.item != null && ++len == batchSize) |
791 |
break; |
792 |
es = new Object[len]; |
793 |
es[0] = currentElement; |
794 |
currentElement = null; |
795 |
n = 1; |
796 |
} else |
797 |
n = 0; |
798 |
for (; p != null && n < len; p = succ(p)) |
799 |
if ((es[n] = p.item) != null) { |
800 |
lastRet = p; |
801 |
n++; |
802 |
} |
803 |
} finally { |
804 |
fullyUnlock(); |
805 |
} |
806 |
for (int i = 0; i < n; i++) { |
807 |
@SuppressWarnings("unchecked") E e = (E) es[i]; |
808 |
action.accept(e); |
809 |
} |
810 |
} while (n > 0 && p != null); |
811 |
} |
812 |
|
813 |
public void remove() { |
814 |
if (lastRet == null) |
815 |
throw new IllegalStateException(); |
816 |
fullyLock(); |
817 |
try { |
818 |
Node<E> node = lastRet; |
819 |
lastRet = null; |
820 |
for (Node<E> trail = head, p = trail.next; |
821 |
p != null; |
822 |
trail = p, p = p.next) { |
823 |
if (p == node) { |
824 |
unlink(p, trail); |
825 |
break; |
826 |
} |
827 |
} |
828 |
} finally { |
829 |
fullyUnlock(); |
830 |
} |
831 |
} |
832 |
} |
833 |
|
834 |
/** |
835 |
* A customized variant of Spliterators.IteratorSpliterator. |
836 |
* Keep this class in sync with (very similar) LBDSpliterator. |
837 |
*/ |
838 |
private final class LBQSpliterator implements Spliterator<E> { |
839 |
static final int MAX_BATCH = 1 << 25; // max batch array size; |
840 |
Node<E> current; // current node; null until initialized |
841 |
int batch; // batch size for splits |
842 |
boolean exhausted; // true when no more nodes |
843 |
long est = size(); // size estimate |
844 |
|
845 |
LBQSpliterator() {} |
846 |
|
847 |
public long estimateSize() { return est; } |
848 |
|
849 |
public Spliterator<E> trySplit() { |
850 |
Node<E> h; |
851 |
int b = batch; |
852 |
int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1; |
853 |
if (!exhausted && |
854 |
((h = current) != null || (h = head.next) != null) |
855 |
&& h.next != null) { |
856 |
Object[] a = new Object[n]; |
857 |
int i = 0; |
858 |
Node<E> p = current; |
859 |
fullyLock(); |
860 |
try { |
861 |
if (p != null || (p = head.next) != null) |
862 |
for (; p != null && i < n; p = succ(p)) |
863 |
if ((a[i] = p.item) != null) |
864 |
i++; |
865 |
} finally { |
866 |
fullyUnlock(); |
867 |
} |
868 |
if ((current = p) == null) { |
869 |
est = 0L; |
870 |
exhausted = true; |
871 |
} |
872 |
else if ((est -= i) < 0L) |
873 |
est = 0L; |
874 |
if (i > 0) { |
875 |
batch = i; |
876 |
return Spliterators.spliterator |
877 |
(a, 0, i, (Spliterator.ORDERED | |
878 |
Spliterator.NONNULL | |
879 |
Spliterator.CONCURRENT)); |
880 |
} |
881 |
} |
882 |
return null; |
883 |
} |
884 |
|
885 |
public boolean tryAdvance(Consumer<? super E> action) { |
886 |
Objects.requireNonNull(action); |
887 |
if (!exhausted) { |
888 |
Node<E> p = current; |
889 |
E e = null; |
890 |
fullyLock(); |
891 |
try { |
892 |
if (p != null || (p = head.next) != null) |
893 |
do { |
894 |
e = p.item; |
895 |
p = succ(p); |
896 |
} while (e == null && p != null); |
897 |
} finally { |
898 |
fullyUnlock(); |
899 |
} |
900 |
exhausted = ((current = p) == null); |
901 |
if (e != null) { |
902 |
action.accept(e); |
903 |
return true; |
904 |
} |
905 |
} |
906 |
return false; |
907 |
} |
908 |
|
909 |
public void forEachRemaining(Consumer<? super E> action) { |
910 |
Objects.requireNonNull(action); |
911 |
if (!exhausted) { |
912 |
exhausted = true; |
913 |
Node<E> p = current; |
914 |
current = null; |
915 |
forEachFrom(action, p); |
916 |
} |
917 |
} |
918 |
|
919 |
public int characteristics() { |
920 |
return (Spliterator.ORDERED | |
921 |
Spliterator.NONNULL | |
922 |
Spliterator.CONCURRENT); |
923 |
} |
924 |
} |
925 |
|
926 |
/** |
927 |
* Returns a {@link Spliterator} over the elements in this queue. |
928 |
* |
929 |
* <p>The returned spliterator is |
930 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
931 |
* |
932 |
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
933 |
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
934 |
* |
935 |
* @implNote |
936 |
* The {@code Spliterator} implements {@code trySplit} to permit limited |
937 |
* parallelism. |
938 |
* |
939 |
* @return a {@code Spliterator} over the elements in this queue |
940 |
* @since 1.8 |
941 |
*/ |
942 |
public Spliterator<E> spliterator() { |
943 |
return new LBQSpliterator(); |
944 |
} |
945 |
|
946 |
/** |
947 |
* @throws NullPointerException {@inheritDoc} |
948 |
*/ |
949 |
public void forEach(Consumer<? super E> action) { |
950 |
Objects.requireNonNull(action); |
951 |
forEachFrom(action, null); |
952 |
} |
953 |
|
954 |
/** |
955 |
* Runs action on each element found during a traversal starting at p. |
956 |
* If p is null, traversal starts at head. |
957 |
*/ |
958 |
void forEachFrom(Consumer<? super E> action, Node<E> p) { |
959 |
// Extract batches of elements while holding the lock; then |
960 |
// run the action on the elements while not |
961 |
final int batchSize = 32; // max number of elements per batch |
962 |
Object[] es = null; // container for batch of elements |
963 |
int n, len = 0; |
964 |
do { |
965 |
fullyLock(); |
966 |
try { |
967 |
if (es == null) { |
968 |
if (p == null) p = head.next; |
969 |
for (Node<E> q = p; q != null; q = succ(q)) |
970 |
if (q.item != null && ++len == batchSize) |
971 |
break; |
972 |
es = new Object[len]; |
973 |
} |
974 |
for (n = 0; p != null && n < len; p = succ(p)) |
975 |
if ((es[n] = p.item) != null) |
976 |
n++; |
977 |
} finally { |
978 |
fullyUnlock(); |
979 |
} |
980 |
for (int i = 0; i < n; i++) { |
981 |
@SuppressWarnings("unchecked") E e = (E) es[i]; |
982 |
action.accept(e); |
983 |
} |
984 |
} while (n > 0 && p != null); |
985 |
} |
986 |
|
987 |
/** |
988 |
* Saves this queue to a stream (that is, serializes it). |
989 |
* |
990 |
* @param s the stream |
991 |
* @throws java.io.IOException if an I/O error occurs |
992 |
* @serialData The capacity is emitted (int), followed by all of |
993 |
* its elements (each an {@code Object}) in the proper order, |
994 |
* followed by a null |
995 |
*/ |
996 |
private void writeObject(java.io.ObjectOutputStream s) |
997 |
throws java.io.IOException { |
998 |
|
999 |
fullyLock(); |
1000 |
try { |
1001 |
// Write out any hidden stuff, plus capacity |
1002 |
s.defaultWriteObject(); |
1003 |
|
1004 |
// Write out all elements in the proper order. |
1005 |
for (Node<E> p = head.next; p != null; p = p.next) |
1006 |
s.writeObject(p.item); |
1007 |
|
1008 |
// Use trailing null as sentinel |
1009 |
s.writeObject(null); |
1010 |
} finally { |
1011 |
fullyUnlock(); |
1012 |
} |
1013 |
} |
1014 |
|
1015 |
/** |
1016 |
* Reconstitutes this queue from a stream (that is, deserializes it). |
1017 |
* @param s the stream |
1018 |
* @throws ClassNotFoundException if the class of a serialized object |
1019 |
* could not be found |
1020 |
* @throws java.io.IOException if an I/O error occurs |
1021 |
*/ |
1022 |
private void readObject(java.io.ObjectInputStream s) |
1023 |
throws java.io.IOException, ClassNotFoundException { |
1024 |
// Read in capacity, and any hidden stuff |
1025 |
s.defaultReadObject(); |
1026 |
|
1027 |
count.set(0); |
1028 |
last = head = new Node<E>(null); |
1029 |
|
1030 |
// Read in all elements and place in queue |
1031 |
for (;;) { |
1032 |
@SuppressWarnings("unchecked") |
1033 |
E item = (E)s.readObject(); |
1034 |
if (item == null) |
1035 |
break; |
1036 |
add(item); |
1037 |
} |
1038 |
} |
1039 |
} |