1 |
jsr166 |
1.1 |
/* |
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.Spliterator; |
14 |
|
|
import java.util.Spliterators; |
15 |
|
|
import java.util.concurrent.atomic.AtomicInteger; |
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 BlockingQueue blocking queue} based on |
22 |
|
|
* linked nodes. |
23 |
|
|
* This queue orders elements FIFO (first-in-first-out). |
24 |
|
|
* The <em>head</em> of the queue is that element that has been on the |
25 |
|
|
* queue the longest time. |
26 |
|
|
* The <em>tail</em> of the queue is that element that has been on the |
27 |
|
|
* queue the shortest time. New elements |
28 |
|
|
* are inserted at the tail of the queue, and the queue retrieval |
29 |
|
|
* operations obtain elements at the head of the queue. |
30 |
|
|
* Linked queues typically have higher throughput than array-based queues but |
31 |
|
|
* less predictable performance in most concurrent applications. |
32 |
|
|
* |
33 |
|
|
* <p>The optional capacity bound constructor argument serves as a |
34 |
|
|
* way to prevent excessive queue expansion. The capacity, if unspecified, |
35 |
|
|
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
36 |
|
|
* dynamically created upon each insertion unless this would bring the |
37 |
|
|
* queue above capacity. |
38 |
|
|
* |
39 |
|
|
* <p>This class and its iterator implement all of the |
40 |
|
|
* <em>optional</em> methods of the {@link Collection} and {@link |
41 |
|
|
* Iterator} interfaces. |
42 |
|
|
* |
43 |
|
|
* <p>This class is a member of the |
44 |
|
|
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
45 |
|
|
* Java Collections Framework</a>. |
46 |
|
|
* |
47 |
|
|
* @since 1.5 |
48 |
|
|
* @author Doug Lea |
49 |
|
|
* @param <E> the type of elements held in this queue |
50 |
|
|
*/ |
51 |
|
|
public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
52 |
|
|
implements BlockingQueue<E>, java.io.Serializable { |
53 |
|
|
private static final long serialVersionUID = -6903933977591709194L; |
54 |
|
|
|
55 |
|
|
/* |
56 |
|
|
* A variant of the "two lock queue" algorithm. The putLock gates |
57 |
|
|
* entry to put (and offer), and has an associated condition for |
58 |
|
|
* waiting puts. Similarly for the takeLock. The "count" field |
59 |
|
|
* that they both rely on is maintained as an atomic to avoid |
60 |
|
|
* needing to get both locks in most cases. Also, to minimize need |
61 |
|
|
* for puts to get takeLock and vice-versa, cascading notifies are |
62 |
|
|
* used. When a put notices that it has enabled at least one take, |
63 |
|
|
* it signals taker. That taker in turn signals others if more |
64 |
|
|
* items have been entered since the signal. And symmetrically for |
65 |
|
|
* takes signalling puts. Operations such as remove(Object) and |
66 |
|
|
* iterators acquire both locks. |
67 |
|
|
* |
68 |
|
|
* Visibility between writers and readers is provided as follows: |
69 |
|
|
* |
70 |
|
|
* Whenever an element is enqueued, the putLock is acquired and |
71 |
|
|
* count updated. A subsequent reader guarantees visibility to the |
72 |
|
|
* enqueued Node by either acquiring the putLock (via fullyLock) |
73 |
|
|
* or by acquiring the takeLock, and then reading n = count.get(); |
74 |
|
|
* this gives visibility to the first n items. |
75 |
|
|
* |
76 |
|
|
* To implement weakly consistent iterators, it appears we need to |
77 |
|
|
* keep all Nodes GC-reachable from a predecessor dequeued Node. |
78 |
|
|
* That would cause two problems: |
79 |
|
|
* - allow a rogue Iterator to cause unbounded memory retention |
80 |
|
|
* - cause cross-generational linking of old Nodes to new Nodes if |
81 |
|
|
* a Node was tenured while live, which generational GCs have a |
82 |
|
|
* hard time dealing with, causing repeated major collections. |
83 |
|
|
* However, only non-deleted Nodes need to be reachable from |
84 |
|
|
* dequeued Nodes, and reachability does not necessarily have to |
85 |
|
|
* be of the kind understood by the GC. We use the trick of |
86 |
|
|
* linking a Node that has just been dequeued to itself. Such a |
87 |
|
|
* self-link implicitly means to advance to head.next. |
88 |
|
|
*/ |
89 |
|
|
|
90 |
|
|
/** |
91 |
|
|
* Linked list node class. |
92 |
|
|
*/ |
93 |
|
|
static class Node<E> { |
94 |
|
|
E item; |
95 |
|
|
|
96 |
|
|
/** |
97 |
|
|
* One of: |
98 |
|
|
* - the real successor Node |
99 |
|
|
* - this Node, meaning the successor is head.next |
100 |
|
|
* - null, meaning there is no successor (this is the last node) |
101 |
|
|
*/ |
102 |
|
|
Node<E> next; |
103 |
|
|
|
104 |
|
|
Node(E x) { item = x; } |
105 |
|
|
} |
106 |
|
|
|
107 |
|
|
/** The capacity bound, or Integer.MAX_VALUE if none */ |
108 |
|
|
private final int capacity; |
109 |
|
|
|
110 |
|
|
/** Current number of elements */ |
111 |
|
|
private final AtomicInteger count = new AtomicInteger(); |
112 |
|
|
|
113 |
|
|
/** |
114 |
|
|
* Head of linked list. |
115 |
|
|
* Invariant: head.item == null |
116 |
|
|
*/ |
117 |
|
|
transient Node<E> head; |
118 |
|
|
|
119 |
|
|
/** |
120 |
|
|
* Tail of linked list. |
121 |
|
|
* Invariant: last.next == null |
122 |
|
|
*/ |
123 |
|
|
private transient Node<E> last; |
124 |
|
|
|
125 |
|
|
/** Lock held by take, poll, etc */ |
126 |
|
|
private final ReentrantLock takeLock = new ReentrantLock(); |
127 |
|
|
|
128 |
|
|
/** Wait queue for waiting takes */ |
129 |
|
|
private final Condition notEmpty = takeLock.newCondition(); |
130 |
|
|
|
131 |
|
|
/** Lock held by put, offer, etc */ |
132 |
|
|
private final ReentrantLock putLock = new ReentrantLock(); |
133 |
|
|
|
134 |
|
|
/** Wait queue for waiting puts */ |
135 |
|
|
private final Condition notFull = putLock.newCondition(); |
136 |
|
|
|
137 |
|
|
/** |
138 |
|
|
* Signals a waiting take. Called only from put/offer (which do not |
139 |
|
|
* otherwise ordinarily lock takeLock.) |
140 |
|
|
*/ |
141 |
|
|
private void signalNotEmpty() { |
142 |
|
|
final ReentrantLock takeLock = this.takeLock; |
143 |
|
|
takeLock.lock(); |
144 |
|
|
try { |
145 |
|
|
notEmpty.signal(); |
146 |
|
|
} finally { |
147 |
|
|
takeLock.unlock(); |
148 |
|
|
} |
149 |
|
|
} |
150 |
|
|
|
151 |
|
|
/** |
152 |
|
|
* Signals a waiting put. Called only from take/poll. |
153 |
|
|
*/ |
154 |
|
|
private void signalNotFull() { |
155 |
|
|
final ReentrantLock putLock = this.putLock; |
156 |
|
|
putLock.lock(); |
157 |
|
|
try { |
158 |
|
|
notFull.signal(); |
159 |
|
|
} finally { |
160 |
|
|
putLock.unlock(); |
161 |
|
|
} |
162 |
|
|
} |
163 |
|
|
|
164 |
|
|
/** |
165 |
|
|
* Links node at end of queue. |
166 |
|
|
* |
167 |
|
|
* @param node the node |
168 |
|
|
*/ |
169 |
|
|
private void enqueue(Node<E> node) { |
170 |
|
|
// assert putLock.isHeldByCurrentThread(); |
171 |
|
|
// assert last.next == null; |
172 |
|
|
last = last.next = node; |
173 |
|
|
} |
174 |
|
|
|
175 |
|
|
/** |
176 |
|
|
* Removes a node from head of queue. |
177 |
|
|
* |
178 |
|
|
* @return the node |
179 |
|
|
*/ |
180 |
|
|
private E dequeue() { |
181 |
|
|
// assert takeLock.isHeldByCurrentThread(); |
182 |
|
|
// assert head.item == null; |
183 |
|
|
Node<E> h = head; |
184 |
|
|
Node<E> first = h.next; |
185 |
|
|
h.next = h; // help GC |
186 |
|
|
head = first; |
187 |
|
|
E x = first.item; |
188 |
|
|
first.item = null; |
189 |
|
|
return x; |
190 |
|
|
} |
191 |
|
|
|
192 |
|
|
/** |
193 |
|
|
* Locks to prevent both puts and takes. |
194 |
|
|
*/ |
195 |
|
|
void fullyLock() { |
196 |
|
|
putLock.lock(); |
197 |
|
|
takeLock.lock(); |
198 |
|
|
} |
199 |
|
|
|
200 |
|
|
/** |
201 |
|
|
* Unlocks to allow both puts and takes. |
202 |
|
|
*/ |
203 |
|
|
void fullyUnlock() { |
204 |
|
|
takeLock.unlock(); |
205 |
|
|
putLock.unlock(); |
206 |
|
|
} |
207 |
|
|
|
208 |
|
|
// /** |
209 |
|
|
// * Tells whether both locks are held by current thread. |
210 |
|
|
// */ |
211 |
|
|
// boolean isFullyLocked() { |
212 |
|
|
// return (putLock.isHeldByCurrentThread() && |
213 |
|
|
// takeLock.isHeldByCurrentThread()); |
214 |
|
|
// } |
215 |
|
|
|
216 |
|
|
/** |
217 |
|
|
* Creates a {@code LinkedBlockingQueue} with a capacity of |
218 |
|
|
* {@link Integer#MAX_VALUE}. |
219 |
|
|
*/ |
220 |
|
|
public LinkedBlockingQueue() { |
221 |
|
|
this(Integer.MAX_VALUE); |
222 |
|
|
} |
223 |
|
|
|
224 |
|
|
/** |
225 |
|
|
* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. |
226 |
|
|
* |
227 |
|
|
* @param capacity the capacity of this queue |
228 |
|
|
* @throws IllegalArgumentException if {@code capacity} is not greater |
229 |
|
|
* than zero |
230 |
|
|
*/ |
231 |
|
|
public LinkedBlockingQueue(int capacity) { |
232 |
|
|
if (capacity <= 0) throw new IllegalArgumentException(); |
233 |
|
|
this.capacity = capacity; |
234 |
|
|
last = head = new Node<E>(null); |
235 |
|
|
} |
236 |
|
|
|
237 |
|
|
/** |
238 |
|
|
* Creates a {@code LinkedBlockingQueue} with a capacity of |
239 |
|
|
* {@link Integer#MAX_VALUE}, initially containing the elements of the |
240 |
|
|
* given collection, |
241 |
|
|
* added in traversal order of the collection's iterator. |
242 |
|
|
* |
243 |
|
|
* @param c the collection of elements to initially contain |
244 |
|
|
* @throws NullPointerException if the specified collection or any |
245 |
|
|
* of its elements are null |
246 |
|
|
*/ |
247 |
|
|
public LinkedBlockingQueue(Collection<? extends E> c) { |
248 |
|
|
this(Integer.MAX_VALUE); |
249 |
|
|
final ReentrantLock putLock = this.putLock; |
250 |
|
|
putLock.lock(); // Never contended, but necessary for visibility |
251 |
|
|
try { |
252 |
|
|
int n = 0; |
253 |
|
|
for (E e : c) { |
254 |
|
|
if (e == null) |
255 |
|
|
throw new NullPointerException(); |
256 |
|
|
if (n == capacity) |
257 |
|
|
throw new IllegalStateException("Queue full"); |
258 |
|
|
enqueue(new Node<E>(e)); |
259 |
|
|
++n; |
260 |
|
|
} |
261 |
|
|
count.set(n); |
262 |
|
|
} finally { |
263 |
|
|
putLock.unlock(); |
264 |
|
|
} |
265 |
|
|
} |
266 |
|
|
|
267 |
|
|
// this doc comment is overridden to remove the reference to collections |
268 |
|
|
// greater in size than Integer.MAX_VALUE |
269 |
|
|
/** |
270 |
|
|
* Returns the number of elements in this queue. |
271 |
|
|
* |
272 |
|
|
* @return the number of elements in this queue |
273 |
|
|
*/ |
274 |
|
|
public int size() { |
275 |
|
|
return count.get(); |
276 |
|
|
} |
277 |
|
|
|
278 |
|
|
// this doc comment is a modified copy of the inherited doc comment, |
279 |
|
|
// without the reference to unlimited queues. |
280 |
|
|
/** |
281 |
|
|
* Returns the number of additional elements that this queue can ideally |
282 |
|
|
* (in the absence of memory or resource constraints) accept without |
283 |
|
|
* blocking. This is always equal to the initial capacity of this queue |
284 |
|
|
* less the current {@code size} of this queue. |
285 |
|
|
* |
286 |
|
|
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
287 |
|
|
* an element will succeed by inspecting {@code remainingCapacity} |
288 |
|
|
* because it may be the case that another thread is about to |
289 |
|
|
* insert or remove an element. |
290 |
|
|
*/ |
291 |
|
|
public int remainingCapacity() { |
292 |
|
|
return capacity - count.get(); |
293 |
|
|
} |
294 |
|
|
|
295 |
|
|
/** |
296 |
|
|
* Inserts the specified element at the tail of this queue, waiting if |
297 |
|
|
* necessary for space to become available. |
298 |
|
|
* |
299 |
|
|
* @throws InterruptedException {@inheritDoc} |
300 |
|
|
* @throws NullPointerException {@inheritDoc} |
301 |
|
|
*/ |
302 |
|
|
public void put(E e) throws InterruptedException { |
303 |
|
|
if (e == null) throw new NullPointerException(); |
304 |
|
|
// Note: convention in all put/take/etc is to preset local var |
305 |
|
|
// holding count negative to indicate failure unless set. |
306 |
|
|
int c = -1; |
307 |
|
|
Node<E> node = new Node<E>(e); |
308 |
|
|
final ReentrantLock putLock = this.putLock; |
309 |
|
|
final AtomicInteger count = this.count; |
310 |
|
|
putLock.lockInterruptibly(); |
311 |
|
|
try { |
312 |
|
|
/* |
313 |
|
|
* Note that count is used in wait guard even though it is |
314 |
|
|
* not protected by lock. This works because count can |
315 |
|
|
* only decrease at this point (all other puts are shut |
316 |
|
|
* out by lock), and we (or some other waiting put) are |
317 |
|
|
* signalled if it ever changes from capacity. Similarly |
318 |
|
|
* for all other uses of count in other wait guards. |
319 |
|
|
*/ |
320 |
|
|
while (count.get() == capacity) { |
321 |
|
|
notFull.await(); |
322 |
|
|
} |
323 |
|
|
enqueue(node); |
324 |
|
|
c = count.getAndIncrement(); |
325 |
|
|
if (c + 1 < capacity) |
326 |
|
|
notFull.signal(); |
327 |
|
|
} finally { |
328 |
|
|
putLock.unlock(); |
329 |
|
|
} |
330 |
|
|
if (c == 0) |
331 |
|
|
signalNotEmpty(); |
332 |
|
|
} |
333 |
|
|
|
334 |
|
|
/** |
335 |
|
|
* Inserts the specified element at the tail of this queue, waiting if |
336 |
|
|
* necessary up to the specified wait time for space to become available. |
337 |
|
|
* |
338 |
|
|
* @return {@code true} if successful, or {@code false} if |
339 |
|
|
* the specified waiting time elapses before space is available |
340 |
|
|
* @throws InterruptedException {@inheritDoc} |
341 |
|
|
* @throws NullPointerException {@inheritDoc} |
342 |
|
|
*/ |
343 |
|
|
public boolean offer(E e, long timeout, TimeUnit unit) |
344 |
|
|
throws InterruptedException { |
345 |
|
|
|
346 |
|
|
if (e == null) throw new NullPointerException(); |
347 |
|
|
long nanos = unit.toNanos(timeout); |
348 |
|
|
int c = -1; |
349 |
|
|
final ReentrantLock putLock = this.putLock; |
350 |
|
|
final AtomicInteger count = this.count; |
351 |
|
|
putLock.lockInterruptibly(); |
352 |
|
|
try { |
353 |
|
|
while (count.get() == capacity) { |
354 |
|
|
if (nanos <= 0L) |
355 |
|
|
return false; |
356 |
|
|
nanos = notFull.awaitNanos(nanos); |
357 |
|
|
} |
358 |
|
|
enqueue(new Node<E>(e)); |
359 |
|
|
c = count.getAndIncrement(); |
360 |
|
|
if (c + 1 < capacity) |
361 |
|
|
notFull.signal(); |
362 |
|
|
} finally { |
363 |
|
|
putLock.unlock(); |
364 |
|
|
} |
365 |
|
|
if (c == 0) |
366 |
|
|
signalNotEmpty(); |
367 |
|
|
return true; |
368 |
|
|
} |
369 |
|
|
|
370 |
|
|
/** |
371 |
|
|
* Inserts the specified element at the tail of this queue if it is |
372 |
|
|
* possible to do so immediately without exceeding the queue's capacity, |
373 |
|
|
* returning {@code true} upon success and {@code false} if this queue |
374 |
|
|
* is full. |
375 |
|
|
* When using a capacity-restricted queue, this method is generally |
376 |
|
|
* preferable to method {@link BlockingQueue#add add}, which can fail to |
377 |
|
|
* insert an element only by throwing an exception. |
378 |
|
|
* |
379 |
|
|
* @throws NullPointerException if the specified element is null |
380 |
|
|
*/ |
381 |
|
|
public boolean offer(E e) { |
382 |
|
|
if (e == null) throw new NullPointerException(); |
383 |
|
|
final AtomicInteger count = this.count; |
384 |
|
|
if (count.get() == capacity) |
385 |
|
|
return false; |
386 |
|
|
int c = -1; |
387 |
|
|
Node<E> node = new Node<E>(e); |
388 |
|
|
final ReentrantLock putLock = this.putLock; |
389 |
|
|
putLock.lock(); |
390 |
|
|
try { |
391 |
|
|
if (count.get() < capacity) { |
392 |
|
|
enqueue(node); |
393 |
|
|
c = count.getAndIncrement(); |
394 |
|
|
if (c + 1 < capacity) |
395 |
|
|
notFull.signal(); |
396 |
|
|
} |
397 |
|
|
} finally { |
398 |
|
|
putLock.unlock(); |
399 |
|
|
} |
400 |
|
|
if (c == 0) |
401 |
|
|
signalNotEmpty(); |
402 |
|
|
return c >= 0; |
403 |
|
|
} |
404 |
|
|
|
405 |
|
|
public E take() throws InterruptedException { |
406 |
|
|
E x; |
407 |
|
|
int c = -1; |
408 |
|
|
final AtomicInteger count = this.count; |
409 |
|
|
final ReentrantLock takeLock = this.takeLock; |
410 |
|
|
takeLock.lockInterruptibly(); |
411 |
|
|
try { |
412 |
|
|
while (count.get() == 0) { |
413 |
|
|
notEmpty.await(); |
414 |
|
|
} |
415 |
|
|
x = dequeue(); |
416 |
|
|
c = count.getAndDecrement(); |
417 |
|
|
if (c > 1) |
418 |
|
|
notEmpty.signal(); |
419 |
|
|
} finally { |
420 |
|
|
takeLock.unlock(); |
421 |
|
|
} |
422 |
|
|
if (c == capacity) |
423 |
|
|
signalNotFull(); |
424 |
|
|
return x; |
425 |
|
|
} |
426 |
|
|
|
427 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
428 |
|
|
E x = null; |
429 |
|
|
int c = -1; |
430 |
|
|
long nanos = unit.toNanos(timeout); |
431 |
|
|
final AtomicInteger count = this.count; |
432 |
|
|
final ReentrantLock takeLock = this.takeLock; |
433 |
|
|
takeLock.lockInterruptibly(); |
434 |
|
|
try { |
435 |
|
|
while (count.get() == 0) { |
436 |
|
|
if (nanos <= 0L) |
437 |
|
|
return null; |
438 |
|
|
nanos = notEmpty.awaitNanos(nanos); |
439 |
|
|
} |
440 |
|
|
x = dequeue(); |
441 |
|
|
c = count.getAndDecrement(); |
442 |
|
|
if (c > 1) |
443 |
|
|
notEmpty.signal(); |
444 |
|
|
} finally { |
445 |
|
|
takeLock.unlock(); |
446 |
|
|
} |
447 |
|
|
if (c == capacity) |
448 |
|
|
signalNotFull(); |
449 |
|
|
return x; |
450 |
|
|
} |
451 |
|
|
|
452 |
|
|
public E poll() { |
453 |
|
|
final AtomicInteger count = this.count; |
454 |
|
|
if (count.get() == 0) |
455 |
|
|
return null; |
456 |
|
|
E x = null; |
457 |
|
|
int c = -1; |
458 |
|
|
final ReentrantLock takeLock = this.takeLock; |
459 |
|
|
takeLock.lock(); |
460 |
|
|
try { |
461 |
|
|
if (count.get() > 0) { |
462 |
|
|
x = dequeue(); |
463 |
|
|
c = count.getAndDecrement(); |
464 |
|
|
if (c > 1) |
465 |
|
|
notEmpty.signal(); |
466 |
|
|
} |
467 |
|
|
} finally { |
468 |
|
|
takeLock.unlock(); |
469 |
|
|
} |
470 |
|
|
if (c == capacity) |
471 |
|
|
signalNotFull(); |
472 |
|
|
return x; |
473 |
|
|
} |
474 |
|
|
|
475 |
|
|
public E peek() { |
476 |
|
|
if (count.get() == 0) |
477 |
|
|
return null; |
478 |
|
|
final ReentrantLock takeLock = this.takeLock; |
479 |
|
|
takeLock.lock(); |
480 |
|
|
try { |
481 |
|
|
return (count.get() > 0) ? head.next.item : null; |
482 |
|
|
} finally { |
483 |
|
|
takeLock.unlock(); |
484 |
|
|
} |
485 |
|
|
} |
486 |
|
|
|
487 |
|
|
/** |
488 |
|
|
* Unlinks interior Node p with predecessor trail. |
489 |
|
|
*/ |
490 |
|
|
void unlink(Node<E> p, Node<E> trail) { |
491 |
|
|
// assert isFullyLocked(); |
492 |
|
|
// p.next is not changed, to allow iterators that are |
493 |
|
|
// traversing p to maintain their weak-consistency guarantee. |
494 |
|
|
p.item = null; |
495 |
|
|
trail.next = p.next; |
496 |
|
|
if (last == p) |
497 |
|
|
last = trail; |
498 |
|
|
if (count.getAndDecrement() == capacity) |
499 |
|
|
notFull.signal(); |
500 |
|
|
} |
501 |
|
|
|
502 |
|
|
/** |
503 |
|
|
* Removes a single instance of the specified element from this queue, |
504 |
|
|
* if it is present. More formally, removes an element {@code e} such |
505 |
|
|
* that {@code o.equals(e)}, if this queue contains one or more such |
506 |
|
|
* elements. |
507 |
|
|
* Returns {@code true} if this queue contained the specified element |
508 |
|
|
* (or equivalently, if this queue changed as a result of the call). |
509 |
|
|
* |
510 |
|
|
* @param o element to be removed from this queue, if present |
511 |
|
|
* @return {@code true} if this queue changed as a result of the call |
512 |
|
|
*/ |
513 |
|
|
public boolean remove(Object o) { |
514 |
|
|
if (o == null) return false; |
515 |
|
|
fullyLock(); |
516 |
|
|
try { |
517 |
|
|
for (Node<E> trail = head, p = trail.next; |
518 |
|
|
p != null; |
519 |
|
|
trail = p, p = p.next) { |
520 |
|
|
if (o.equals(p.item)) { |
521 |
|
|
unlink(p, trail); |
522 |
|
|
return true; |
523 |
|
|
} |
524 |
|
|
} |
525 |
|
|
return false; |
526 |
|
|
} finally { |
527 |
|
|
fullyUnlock(); |
528 |
|
|
} |
529 |
|
|
} |
530 |
|
|
|
531 |
|
|
/** |
532 |
|
|
* Returns {@code true} if this queue contains the specified element. |
533 |
|
|
* More formally, returns {@code true} if and only if this queue contains |
534 |
|
|
* at least one element {@code e} such that {@code o.equals(e)}. |
535 |
|
|
* |
536 |
|
|
* @param o object to be checked for containment in this queue |
537 |
|
|
* @return {@code true} if this queue contains the specified element |
538 |
|
|
*/ |
539 |
|
|
public boolean contains(Object o) { |
540 |
|
|
if (o == null) return false; |
541 |
|
|
fullyLock(); |
542 |
|
|
try { |
543 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
544 |
|
|
if (o.equals(p.item)) |
545 |
|
|
return true; |
546 |
|
|
return false; |
547 |
|
|
} finally { |
548 |
|
|
fullyUnlock(); |
549 |
|
|
} |
550 |
|
|
} |
551 |
|
|
|
552 |
|
|
/** |
553 |
|
|
* Returns an array containing all of the elements in this queue, in |
554 |
|
|
* proper sequence. |
555 |
|
|
* |
556 |
|
|
* <p>The returned array will be "safe" in that no references to it are |
557 |
|
|
* maintained by this queue. (In other words, this method must allocate |
558 |
|
|
* a new array). The caller is thus free to modify the returned array. |
559 |
|
|
* |
560 |
|
|
* <p>This method acts as bridge between array-based and collection-based |
561 |
|
|
* APIs. |
562 |
|
|
* |
563 |
|
|
* @return an array containing all of the elements in this queue |
564 |
|
|
*/ |
565 |
|
|
public Object[] toArray() { |
566 |
|
|
fullyLock(); |
567 |
|
|
try { |
568 |
|
|
int size = count.get(); |
569 |
|
|
Object[] a = new Object[size]; |
570 |
|
|
int k = 0; |
571 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
572 |
|
|
a[k++] = p.item; |
573 |
|
|
return a; |
574 |
|
|
} finally { |
575 |
|
|
fullyUnlock(); |
576 |
|
|
} |
577 |
|
|
} |
578 |
|
|
|
579 |
|
|
/** |
580 |
|
|
* Returns an array containing all of the elements in this queue, in |
581 |
|
|
* proper sequence; the runtime type of the returned array is that of |
582 |
|
|
* the specified array. If the queue fits in the specified array, it |
583 |
|
|
* is returned therein. Otherwise, a new array is allocated with the |
584 |
|
|
* runtime type of the specified array and the size of this queue. |
585 |
|
|
* |
586 |
|
|
* <p>If this queue fits in the specified array with room to spare |
587 |
|
|
* (i.e., the array has more elements than this queue), the element in |
588 |
|
|
* the array immediately following the end of the queue is set to |
589 |
|
|
* {@code null}. |
590 |
|
|
* |
591 |
|
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
592 |
|
|
* array-based and collection-based APIs. Further, this method allows |
593 |
|
|
* precise control over the runtime type of the output array, and may, |
594 |
|
|
* under certain circumstances, be used to save allocation costs. |
595 |
|
|
* |
596 |
|
|
* <p>Suppose {@code x} is a queue known to contain only strings. |
597 |
|
|
* The following code can be used to dump the queue into a newly |
598 |
|
|
* allocated array of {@code String}: |
599 |
|
|
* |
600 |
|
|
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
601 |
|
|
* |
602 |
|
|
* Note that {@code toArray(new Object[0])} is identical in function to |
603 |
|
|
* {@code toArray()}. |
604 |
|
|
* |
605 |
|
|
* @param a the array into which the elements of the queue are to |
606 |
|
|
* be stored, if it is big enough; otherwise, a new array of the |
607 |
|
|
* same runtime type is allocated for this purpose |
608 |
|
|
* @return an array containing all of the elements in this queue |
609 |
|
|
* @throws ArrayStoreException if the runtime type of the specified array |
610 |
|
|
* is not a supertype of the runtime type of every element in |
611 |
|
|
* this queue |
612 |
|
|
* @throws NullPointerException if the specified array is null |
613 |
|
|
*/ |
614 |
|
|
@SuppressWarnings("unchecked") |
615 |
|
|
public <T> T[] toArray(T[] a) { |
616 |
|
|
fullyLock(); |
617 |
|
|
try { |
618 |
|
|
int size = count.get(); |
619 |
|
|
if (a.length < size) |
620 |
|
|
a = (T[])java.lang.reflect.Array.newInstance |
621 |
|
|
(a.getClass().getComponentType(), size); |
622 |
|
|
|
623 |
|
|
int k = 0; |
624 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
625 |
|
|
a[k++] = (T)p.item; |
626 |
|
|
if (a.length > k) |
627 |
|
|
a[k] = null; |
628 |
|
|
return a; |
629 |
|
|
} finally { |
630 |
|
|
fullyUnlock(); |
631 |
|
|
} |
632 |
|
|
} |
633 |
|
|
|
634 |
|
|
public String toString() { |
635 |
|
|
return Helpers.collectionToString(this); |
636 |
|
|
} |
637 |
|
|
|
638 |
|
|
/** |
639 |
|
|
* Atomically removes all of the elements from this queue. |
640 |
|
|
* The queue will be empty after this call returns. |
641 |
|
|
*/ |
642 |
|
|
public void clear() { |
643 |
|
|
fullyLock(); |
644 |
|
|
try { |
645 |
|
|
for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
646 |
|
|
h.next = h; |
647 |
|
|
p.item = null; |
648 |
|
|
} |
649 |
|
|
head = last; |
650 |
|
|
// assert head.item == null && head.next == null; |
651 |
|
|
if (count.getAndSet(0) == capacity) |
652 |
|
|
notFull.signal(); |
653 |
|
|
} finally { |
654 |
|
|
fullyUnlock(); |
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 |
|
|
if (c == null) |
676 |
|
|
throw new NullPointerException(); |
677 |
|
|
if (c == this) |
678 |
|
|
throw new IllegalArgumentException(); |
679 |
|
|
if (maxElements <= 0) |
680 |
|
|
return 0; |
681 |
|
|
boolean signalNotFull = false; |
682 |
|
|
final ReentrantLock takeLock = this.takeLock; |
683 |
|
|
takeLock.lock(); |
684 |
|
|
try { |
685 |
|
|
int n = Math.min(maxElements, count.get()); |
686 |
|
|
// count.get provides visibility to first n Nodes |
687 |
|
|
Node<E> h = head; |
688 |
|
|
int i = 0; |
689 |
|
|
try { |
690 |
|
|
while (i < n) { |
691 |
|
|
Node<E> p = h.next; |
692 |
|
|
c.add(p.item); |
693 |
|
|
p.item = null; |
694 |
|
|
h.next = h; |
695 |
|
|
h = p; |
696 |
|
|
++i; |
697 |
|
|
} |
698 |
|
|
return n; |
699 |
|
|
} finally { |
700 |
|
|
// Restore invariants even if c.add() threw |
701 |
|
|
if (i > 0) { |
702 |
|
|
// assert h.item == null; |
703 |
|
|
head = h; |
704 |
|
|
signalNotFull = (count.getAndAdd(-i) == capacity); |
705 |
|
|
} |
706 |
|
|
} |
707 |
|
|
} finally { |
708 |
|
|
takeLock.unlock(); |
709 |
|
|
if (signalNotFull) |
710 |
|
|
signalNotFull(); |
711 |
|
|
} |
712 |
|
|
} |
713 |
|
|
|
714 |
|
|
/** |
715 |
|
|
* Returns an iterator over the elements in this queue in proper sequence. |
716 |
|
|
* The elements will be returned in order from first (head) to last (tail). |
717 |
|
|
* |
718 |
|
|
* <p>The returned iterator is |
719 |
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
720 |
|
|
* |
721 |
|
|
* @return an iterator over the elements in this queue in proper sequence |
722 |
|
|
*/ |
723 |
|
|
public Iterator<E> iterator() { |
724 |
|
|
return new Itr(); |
725 |
|
|
} |
726 |
|
|
|
727 |
|
|
private class Itr implements Iterator<E> { |
728 |
|
|
/* |
729 |
|
|
* Basic weakly-consistent iterator. At all times hold the next |
730 |
|
|
* item to hand out so that if hasNext() reports true, we will |
731 |
|
|
* still have it to return even if lost race with a take etc. |
732 |
|
|
*/ |
733 |
|
|
|
734 |
|
|
private Node<E> current; |
735 |
|
|
private Node<E> lastRet; |
736 |
|
|
private E currentElement; |
737 |
|
|
|
738 |
|
|
Itr() { |
739 |
|
|
fullyLock(); |
740 |
|
|
try { |
741 |
|
|
current = head.next; |
742 |
|
|
if (current != null) |
743 |
|
|
currentElement = current.item; |
744 |
|
|
} finally { |
745 |
|
|
fullyUnlock(); |
746 |
|
|
} |
747 |
|
|
} |
748 |
|
|
|
749 |
|
|
public boolean hasNext() { |
750 |
|
|
return current != null; |
751 |
|
|
} |
752 |
|
|
|
753 |
|
|
public E next() { |
754 |
|
|
fullyLock(); |
755 |
|
|
try { |
756 |
|
|
if (current == null) |
757 |
|
|
throw new NoSuchElementException(); |
758 |
|
|
lastRet = current; |
759 |
|
|
E item = null; |
760 |
|
|
// Unlike other traversal methods, iterators must handle both: |
761 |
|
|
// - dequeued nodes (p.next == p) |
762 |
|
|
// - (possibly multiple) interior removed nodes (p.item == null) |
763 |
|
|
for (Node<E> p = current, q;; p = q) { |
764 |
|
|
if ((q = p.next) == p) |
765 |
|
|
q = head.next; |
766 |
|
|
if (q == null || (item = q.item) != null) { |
767 |
|
|
current = q; |
768 |
|
|
E x = currentElement; |
769 |
|
|
currentElement = item; |
770 |
|
|
return x; |
771 |
|
|
} |
772 |
|
|
} |
773 |
|
|
} finally { |
774 |
|
|
fullyUnlock(); |
775 |
|
|
} |
776 |
|
|
} |
777 |
|
|
|
778 |
|
|
public void remove() { |
779 |
|
|
if (lastRet == null) |
780 |
|
|
throw new IllegalStateException(); |
781 |
|
|
fullyLock(); |
782 |
|
|
try { |
783 |
|
|
Node<E> node = lastRet; |
784 |
|
|
lastRet = null; |
785 |
|
|
for (Node<E> trail = head, p = trail.next; |
786 |
|
|
p != null; |
787 |
|
|
trail = p, p = p.next) { |
788 |
|
|
if (p == node) { |
789 |
|
|
unlink(p, trail); |
790 |
|
|
break; |
791 |
|
|
} |
792 |
|
|
} |
793 |
|
|
} finally { |
794 |
|
|
fullyUnlock(); |
795 |
|
|
} |
796 |
|
|
} |
797 |
|
|
} |
798 |
|
|
|
799 |
|
|
/** A customized variant of Spliterators.IteratorSpliterator */ |
800 |
|
|
static final class LBQSpliterator<E> implements Spliterator<E> { |
801 |
|
|
static final int MAX_BATCH = 1 << 25; // max batch array size; |
802 |
|
|
final LinkedBlockingQueue<E> queue; |
803 |
|
|
Node<E> current; // current node; null until initialized |
804 |
|
|
int batch; // batch size for splits |
805 |
|
|
boolean exhausted; // true when no more nodes |
806 |
|
|
long est; // size estimate |
807 |
|
|
LBQSpliterator(LinkedBlockingQueue<E> queue) { |
808 |
|
|
this.queue = queue; |
809 |
|
|
this.est = queue.size(); |
810 |
|
|
} |
811 |
|
|
|
812 |
|
|
public long estimateSize() { return est; } |
813 |
|
|
|
814 |
|
|
public Spliterator<E> trySplit() { |
815 |
|
|
Node<E> h; |
816 |
|
|
final LinkedBlockingQueue<E> q = this.queue; |
817 |
|
|
int b = batch; |
818 |
|
|
int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1; |
819 |
|
|
if (!exhausted && |
820 |
|
|
((h = current) != null || (h = q.head.next) != null) && |
821 |
|
|
h.next != null) { |
822 |
|
|
Object[] a = new Object[n]; |
823 |
|
|
int i = 0; |
824 |
|
|
Node<E> p = current; |
825 |
|
|
q.fullyLock(); |
826 |
|
|
try { |
827 |
|
|
if (p != null || (p = q.head.next) != null) { |
828 |
|
|
do { |
829 |
|
|
if ((a[i] = p.item) != null) |
830 |
|
|
++i; |
831 |
|
|
} while ((p = p.next) != null && i < n); |
832 |
|
|
} |
833 |
|
|
} finally { |
834 |
|
|
q.fullyUnlock(); |
835 |
|
|
} |
836 |
|
|
if ((current = p) == null) { |
837 |
|
|
est = 0L; |
838 |
|
|
exhausted = true; |
839 |
|
|
} |
840 |
|
|
else if ((est -= i) < 0L) |
841 |
|
|
est = 0L; |
842 |
|
|
if (i > 0) { |
843 |
|
|
batch = i; |
844 |
|
|
return Spliterators.spliterator |
845 |
|
|
(a, 0, i, (Spliterator.ORDERED | |
846 |
|
|
Spliterator.NONNULL | |
847 |
|
|
Spliterator.CONCURRENT)); |
848 |
|
|
} |
849 |
|
|
} |
850 |
|
|
return null; |
851 |
|
|
} |
852 |
|
|
|
853 |
|
|
public void forEachRemaining(Consumer<? super E> action) { |
854 |
|
|
if (action == null) throw new NullPointerException(); |
855 |
|
|
final LinkedBlockingQueue<E> q = this.queue; |
856 |
|
|
if (!exhausted) { |
857 |
|
|
exhausted = true; |
858 |
|
|
Node<E> p = current; |
859 |
|
|
do { |
860 |
|
|
E e = null; |
861 |
|
|
q.fullyLock(); |
862 |
|
|
try { |
863 |
|
|
if (p == null) |
864 |
|
|
p = q.head.next; |
865 |
|
|
while (p != null) { |
866 |
|
|
e = p.item; |
867 |
|
|
p = p.next; |
868 |
|
|
if (e != null) |
869 |
|
|
break; |
870 |
|
|
} |
871 |
|
|
} finally { |
872 |
|
|
q.fullyUnlock(); |
873 |
|
|
} |
874 |
|
|
if (e != null) |
875 |
|
|
action.accept(e); |
876 |
|
|
} while (p != null); |
877 |
|
|
} |
878 |
|
|
} |
879 |
|
|
|
880 |
|
|
public boolean tryAdvance(Consumer<? super E> action) { |
881 |
|
|
if (action == null) throw new NullPointerException(); |
882 |
|
|
final LinkedBlockingQueue<E> q = this.queue; |
883 |
|
|
if (!exhausted) { |
884 |
|
|
E e = null; |
885 |
|
|
q.fullyLock(); |
886 |
|
|
try { |
887 |
|
|
if (current == null) |
888 |
|
|
current = q.head.next; |
889 |
|
|
while (current != null) { |
890 |
|
|
e = current.item; |
891 |
|
|
current = current.next; |
892 |
|
|
if (e != null) |
893 |
|
|
break; |
894 |
|
|
} |
895 |
|
|
} finally { |
896 |
|
|
q.fullyUnlock(); |
897 |
|
|
} |
898 |
|
|
if (current == null) |
899 |
|
|
exhausted = true; |
900 |
|
|
if (e != null) { |
901 |
|
|
action.accept(e); |
902 |
|
|
return true; |
903 |
|
|
} |
904 |
|
|
} |
905 |
|
|
return false; |
906 |
|
|
} |
907 |
|
|
|
908 |
|
|
public int characteristics() { |
909 |
|
|
return Spliterator.ORDERED | Spliterator.NONNULL | |
910 |
|
|
Spliterator.CONCURRENT; |
911 |
|
|
} |
912 |
|
|
} |
913 |
|
|
|
914 |
|
|
/** |
915 |
|
|
* Returns a {@link Spliterator} over the elements in this queue. |
916 |
|
|
* |
917 |
|
|
* <p>The returned spliterator is |
918 |
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
919 |
|
|
* |
920 |
|
|
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
921 |
|
|
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
922 |
|
|
* |
923 |
|
|
* @implNote |
924 |
|
|
* The {@code Spliterator} implements {@code trySplit} to permit limited |
925 |
|
|
* parallelism. |
926 |
|
|
* |
927 |
|
|
* @return a {@code Spliterator} over the elements in this queue |
928 |
|
|
* @since 1.8 |
929 |
|
|
*/ |
930 |
|
|
public Spliterator<E> spliterator() { |
931 |
|
|
return new LBQSpliterator<E>(this); |
932 |
|
|
} |
933 |
|
|
|
934 |
|
|
/** |
935 |
|
|
* Saves this queue to a stream (that is, serializes it). |
936 |
|
|
* |
937 |
|
|
* @param s the stream |
938 |
|
|
* @throws java.io.IOException if an I/O error occurs |
939 |
|
|
* @serialData The capacity is emitted (int), followed by all of |
940 |
|
|
* its elements (each an {@code Object}) in the proper order, |
941 |
|
|
* followed by a null |
942 |
|
|
*/ |
943 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
944 |
|
|
throws java.io.IOException { |
945 |
|
|
|
946 |
|
|
fullyLock(); |
947 |
|
|
try { |
948 |
|
|
// Write out any hidden stuff, plus capacity |
949 |
|
|
s.defaultWriteObject(); |
950 |
|
|
|
951 |
|
|
// Write out all elements in the proper order. |
952 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
953 |
|
|
s.writeObject(p.item); |
954 |
|
|
|
955 |
|
|
// Use trailing null as sentinel |
956 |
|
|
s.writeObject(null); |
957 |
|
|
} finally { |
958 |
|
|
fullyUnlock(); |
959 |
|
|
} |
960 |
|
|
} |
961 |
|
|
|
962 |
|
|
/** |
963 |
|
|
* Reconstitutes this queue from a stream (that is, deserializes it). |
964 |
|
|
* @param s the stream |
965 |
|
|
* @throws ClassNotFoundException if the class of a serialized object |
966 |
|
|
* could not be found |
967 |
|
|
* @throws java.io.IOException if an I/O error occurs |
968 |
|
|
*/ |
969 |
|
|
private void readObject(java.io.ObjectInputStream s) |
970 |
|
|
throws java.io.IOException, ClassNotFoundException { |
971 |
|
|
// Read in capacity, and any hidden stuff |
972 |
|
|
s.defaultReadObject(); |
973 |
|
|
|
974 |
|
|
count.set(0); |
975 |
|
|
last = head = new Node<E>(null); |
976 |
|
|
|
977 |
|
|
// Read in all elements and place in queue |
978 |
|
|
for (;;) { |
979 |
|
|
@SuppressWarnings("unchecked") |
980 |
|
|
E item = (E)s.readObject(); |
981 |
|
|
if (item == null) |
982 |
|
|
break; |
983 |
|
|
add(item); |
984 |
|
|
} |
985 |
|
|
} |
986 |
|
|
} |