1 |
dl |
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.concurrent.atomic.AtomicInteger; |
10 |
|
|
import java.util.concurrent.locks.Condition; |
11 |
|
|
import java.util.concurrent.locks.ReentrantLock; |
12 |
|
|
import java.util.AbstractQueue; |
13 |
|
|
import java.util.Collection; |
14 |
|
|
import java.util.Iterator; |
15 |
|
|
import java.util.NoSuchElementException; |
16 |
|
|
|
17 |
|
|
/** |
18 |
|
|
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
19 |
|
|
* linked nodes. |
20 |
|
|
* This queue orders elements FIFO (first-in-first-out). |
21 |
|
|
* The <em>head</em> of the queue is that element that has been on the |
22 |
|
|
* queue the longest time. |
23 |
|
|
* The <em>tail</em> of the queue is that element that has been on the |
24 |
|
|
* queue the shortest time. New elements |
25 |
|
|
* are inserted at the tail of the queue, and the queue retrieval |
26 |
|
|
* operations obtain elements at the head of the queue. |
27 |
|
|
* Linked queues typically have higher throughput than array-based queues but |
28 |
|
|
* less predictable performance in most concurrent applications. |
29 |
|
|
* |
30 |
|
|
* <p>The optional capacity bound constructor argument serves as a |
31 |
|
|
* way to prevent excessive queue expansion. The capacity, if unspecified, |
32 |
|
|
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
33 |
|
|
* dynamically created upon each insertion unless this would bring the |
34 |
|
|
* queue above capacity. |
35 |
|
|
* |
36 |
|
|
* <p>This class and its iterator implement all of the |
37 |
|
|
* <em>optional</em> methods of the {@link Collection} and {@link |
38 |
|
|
* Iterator} interfaces. |
39 |
|
|
* |
40 |
|
|
* <p>This class is a member of the |
41 |
|
|
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
42 |
|
|
* Java Collections Framework</a>. |
43 |
|
|
* |
44 |
|
|
* @since 1.5 |
45 |
|
|
* @author Doug Lea |
46 |
|
|
* @param <E> the type of elements held in this collection |
47 |
|
|
*/ |
48 |
|
|
public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
49 |
|
|
implements BlockingQueue<E>, java.io.Serializable { |
50 |
|
|
private static final long serialVersionUID = -6903933977591709194L; |
51 |
|
|
|
52 |
|
|
/* |
53 |
|
|
* A variant of the "two lock queue" algorithm. The putLock gates |
54 |
|
|
* entry to put (and offer), and has an associated condition for |
55 |
|
|
* waiting puts. Similarly for the takeLock. The "count" field |
56 |
|
|
* that they both rely on is maintained as an atomic to avoid |
57 |
|
|
* needing to get both locks in most cases. Also, to minimize need |
58 |
|
|
* for puts to get takeLock and vice-versa, cascading notifies are |
59 |
|
|
* used. When a put notices that it has enabled at least one take, |
60 |
|
|
* it signals taker. That taker in turn signals others if more |
61 |
|
|
* items have been entered since the signal. And symmetrically for |
62 |
|
|
* takes signalling puts. Operations such as remove(Object) and |
63 |
|
|
* iterators acquire both locks. |
64 |
|
|
* |
65 |
|
|
* Visibility between writers and readers is provided as follows: |
66 |
|
|
* |
67 |
|
|
* Whenever an element is enqueued, the putLock is acquired and |
68 |
|
|
* count updated. A subsequent reader guarantees visibility to the |
69 |
|
|
* enqueued Node by either acquiring the putLock (via fullyLock) |
70 |
|
|
* or by acquiring the takeLock, and then reading n = count.get(); |
71 |
|
|
* this gives visibility to the first n items. |
72 |
|
|
* |
73 |
|
|
* To implement weakly consistent iterators, it appears we need to |
74 |
|
|
* keep all Nodes GC-reachable from a predecessor dequeued Node. |
75 |
|
|
* That would cause two problems: |
76 |
|
|
* - allow a rogue Iterator to cause unbounded memory retention |
77 |
|
|
* - cause cross-generational linking of old Nodes to new Nodes if |
78 |
|
|
* a Node was tenured while live, which generational GCs have a |
79 |
|
|
* hard time dealing with, causing repeated major collections. |
80 |
|
|
* However, only non-deleted Nodes need to be reachable from |
81 |
|
|
* dequeued Nodes, and reachability does not necessarily have to |
82 |
|
|
* be of the kind understood by the GC. We use the trick of |
83 |
|
|
* linking a Node that has just been dequeued to itself. Such a |
84 |
|
|
* self-link implicitly means to advance to head.next. |
85 |
|
|
*/ |
86 |
|
|
|
87 |
|
|
/** |
88 |
|
|
* Linked list node class |
89 |
|
|
*/ |
90 |
|
|
static class Node<E> { |
91 |
|
|
E item; |
92 |
|
|
|
93 |
|
|
/** |
94 |
|
|
* One of: |
95 |
|
|
* - the real successor Node |
96 |
|
|
* - this Node, meaning the successor is head.next |
97 |
|
|
* - null, meaning there is no successor (this is the last node) |
98 |
|
|
*/ |
99 |
|
|
Node<E> next; |
100 |
|
|
|
101 |
|
|
Node(E x) { item = x; } |
102 |
|
|
} |
103 |
|
|
|
104 |
|
|
/** The capacity bound, or Integer.MAX_VALUE if none */ |
105 |
|
|
private final int capacity; |
106 |
|
|
|
107 |
|
|
/** Current number of elements */ |
108 |
|
|
private final AtomicInteger count = new AtomicInteger(); |
109 |
|
|
|
110 |
|
|
/** |
111 |
|
|
* Head of linked list. |
112 |
|
|
* Invariant: head.item == null |
113 |
|
|
*/ |
114 |
|
|
transient Node<E> head; |
115 |
|
|
|
116 |
|
|
/** |
117 |
|
|
* Tail of linked list. |
118 |
|
|
* Invariant: last.next == null |
119 |
|
|
*/ |
120 |
|
|
private transient Node<E> last; |
121 |
|
|
|
122 |
|
|
/** Lock held by take, poll, etc */ |
123 |
|
|
private final ReentrantLock takeLock = new ReentrantLock(); |
124 |
|
|
|
125 |
|
|
/** Wait queue for waiting takes */ |
126 |
|
|
private final Condition notEmpty = takeLock.newCondition(); |
127 |
|
|
|
128 |
|
|
/** Lock held by put, offer, etc */ |
129 |
|
|
private final ReentrantLock putLock = new ReentrantLock(); |
130 |
|
|
|
131 |
|
|
/** Wait queue for waiting puts */ |
132 |
|
|
private final Condition notFull = putLock.newCondition(); |
133 |
|
|
|
134 |
|
|
/** |
135 |
|
|
* Signals a waiting take. Called only from put/offer (which do not |
136 |
|
|
* otherwise ordinarily lock takeLock.) |
137 |
|
|
*/ |
138 |
|
|
private void signalNotEmpty() { |
139 |
|
|
final ReentrantLock takeLock = this.takeLock; |
140 |
|
|
takeLock.lock(); |
141 |
|
|
try { |
142 |
|
|
notEmpty.signal(); |
143 |
|
|
} finally { |
144 |
|
|
takeLock.unlock(); |
145 |
|
|
} |
146 |
|
|
} |
147 |
|
|
|
148 |
|
|
/** |
149 |
|
|
* Signals a waiting put. Called only from take/poll. |
150 |
|
|
*/ |
151 |
|
|
private void signalNotFull() { |
152 |
|
|
final ReentrantLock putLock = this.putLock; |
153 |
|
|
putLock.lock(); |
154 |
|
|
try { |
155 |
|
|
notFull.signal(); |
156 |
|
|
} finally { |
157 |
|
|
putLock.unlock(); |
158 |
|
|
} |
159 |
|
|
} |
160 |
|
|
|
161 |
|
|
/** |
162 |
|
|
* Links node at end of queue. |
163 |
|
|
* |
164 |
|
|
* @param node the node |
165 |
|
|
*/ |
166 |
|
|
private void enqueue(Node<E> node) { |
167 |
|
|
// assert putLock.isHeldByCurrentThread(); |
168 |
|
|
// assert last.next == null; |
169 |
|
|
last = last.next = node; |
170 |
|
|
} |
171 |
|
|
|
172 |
|
|
/** |
173 |
|
|
* Removes a node from head of queue. |
174 |
|
|
* |
175 |
|
|
* @return the node |
176 |
|
|
*/ |
177 |
|
|
private E dequeue() { |
178 |
|
|
// assert takeLock.isHeldByCurrentThread(); |
179 |
|
|
// assert head.item == null; |
180 |
|
|
Node<E> h = head; |
181 |
|
|
Node<E> first = h.next; |
182 |
|
|
h.next = h; // help GC |
183 |
|
|
head = first; |
184 |
|
|
E x = first.item; |
185 |
|
|
first.item = null; |
186 |
|
|
return x; |
187 |
|
|
} |
188 |
|
|
|
189 |
|
|
/** |
190 |
jsr166 |
1.2 |
* Locks to prevent both puts and takes. |
191 |
dl |
1.1 |
*/ |
192 |
|
|
void fullyLock() { |
193 |
|
|
putLock.lock(); |
194 |
|
|
takeLock.lock(); |
195 |
|
|
} |
196 |
|
|
|
197 |
|
|
/** |
198 |
jsr166 |
1.2 |
* Unlocks to allow both puts and takes. |
199 |
dl |
1.1 |
*/ |
200 |
|
|
void fullyUnlock() { |
201 |
|
|
takeLock.unlock(); |
202 |
|
|
putLock.unlock(); |
203 |
|
|
} |
204 |
|
|
|
205 |
|
|
// /** |
206 |
|
|
// * Tells whether both locks are held by current thread. |
207 |
|
|
// */ |
208 |
|
|
// boolean isFullyLocked() { |
209 |
|
|
// return (putLock.isHeldByCurrentThread() && |
210 |
|
|
// takeLock.isHeldByCurrentThread()); |
211 |
|
|
// } |
212 |
|
|
|
213 |
|
|
/** |
214 |
|
|
* Creates a {@code LinkedBlockingQueue} with a capacity of |
215 |
|
|
* {@link Integer#MAX_VALUE}. |
216 |
|
|
*/ |
217 |
|
|
public LinkedBlockingQueue() { |
218 |
|
|
this(Integer.MAX_VALUE); |
219 |
|
|
} |
220 |
|
|
|
221 |
|
|
/** |
222 |
|
|
* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. |
223 |
|
|
* |
224 |
|
|
* @param capacity the capacity of this queue |
225 |
|
|
* @throws IllegalArgumentException if {@code capacity} is not greater |
226 |
|
|
* than zero |
227 |
|
|
*/ |
228 |
|
|
public LinkedBlockingQueue(int capacity) { |
229 |
|
|
if (capacity <= 0) throw new IllegalArgumentException(); |
230 |
|
|
this.capacity = capacity; |
231 |
|
|
last = head = new Node<E>(null); |
232 |
|
|
} |
233 |
|
|
|
234 |
|
|
/** |
235 |
|
|
* Creates a {@code LinkedBlockingQueue} with a capacity of |
236 |
|
|
* {@link Integer#MAX_VALUE}, initially containing the elements of the |
237 |
|
|
* given collection, |
238 |
|
|
* added in traversal order of the collection's iterator. |
239 |
|
|
* |
240 |
|
|
* @param c the collection of elements to initially contain |
241 |
|
|
* @throws NullPointerException if the specified collection or any |
242 |
|
|
* of its elements are null |
243 |
|
|
*/ |
244 |
|
|
public LinkedBlockingQueue(Collection<? extends E> c) { |
245 |
|
|
this(Integer.MAX_VALUE); |
246 |
|
|
final ReentrantLock putLock = this.putLock; |
247 |
|
|
putLock.lock(); // Never contended, but necessary for visibility |
248 |
|
|
try { |
249 |
|
|
int n = 0; |
250 |
|
|
for (E e : c) { |
251 |
|
|
if (e == null) |
252 |
|
|
throw new NullPointerException(); |
253 |
|
|
if (n == capacity) |
254 |
|
|
throw new IllegalStateException("Queue full"); |
255 |
|
|
enqueue(new Node<E>(e)); |
256 |
|
|
++n; |
257 |
|
|
} |
258 |
|
|
count.set(n); |
259 |
|
|
} finally { |
260 |
|
|
putLock.unlock(); |
261 |
|
|
} |
262 |
|
|
} |
263 |
|
|
|
264 |
|
|
// this doc comment is overridden to remove the reference to collections |
265 |
|
|
// greater in size than Integer.MAX_VALUE |
266 |
|
|
/** |
267 |
|
|
* Returns the number of elements in this queue. |
268 |
|
|
* |
269 |
|
|
* @return the number of elements in this queue |
270 |
|
|
*/ |
271 |
|
|
public int size() { |
272 |
|
|
return count.get(); |
273 |
|
|
} |
274 |
|
|
|
275 |
|
|
// this doc comment is a modified copy of the inherited doc comment, |
276 |
|
|
// without the reference to unlimited queues. |
277 |
|
|
/** |
278 |
|
|
* Returns the number of additional elements that this queue can ideally |
279 |
|
|
* (in the absence of memory or resource constraints) accept without |
280 |
|
|
* blocking. This is always equal to the initial capacity of this queue |
281 |
|
|
* less the current {@code size} of this queue. |
282 |
|
|
* |
283 |
|
|
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
284 |
|
|
* an element will succeed by inspecting {@code remainingCapacity} |
285 |
|
|
* because it may be the case that another thread is about to |
286 |
|
|
* insert or remove an element. |
287 |
|
|
*/ |
288 |
|
|
public int remainingCapacity() { |
289 |
|
|
return capacity - count.get(); |
290 |
|
|
} |
291 |
|
|
|
292 |
|
|
/** |
293 |
|
|
* Inserts the specified element at the tail of this queue, waiting if |
294 |
|
|
* necessary for space to become available. |
295 |
|
|
* |
296 |
|
|
* @throws InterruptedException {@inheritDoc} |
297 |
|
|
* @throws NullPointerException {@inheritDoc} |
298 |
|
|
*/ |
299 |
|
|
public void put(E e) throws InterruptedException { |
300 |
|
|
if (e == null) throw new NullPointerException(); |
301 |
|
|
// Note: convention in all put/take/etc is to preset local var |
302 |
|
|
// holding count negative to indicate failure unless set. |
303 |
|
|
int c = -1; |
304 |
|
|
Node<E> node = new Node<E>(e); |
305 |
|
|
final ReentrantLock putLock = this.putLock; |
306 |
|
|
final AtomicInteger count = this.count; |
307 |
|
|
putLock.lockInterruptibly(); |
308 |
|
|
try { |
309 |
|
|
/* |
310 |
|
|
* Note that count is used in wait guard even though it is |
311 |
|
|
* not protected by lock. This works because count can |
312 |
|
|
* only decrease at this point (all other puts are shut |
313 |
|
|
* out by lock), and we (or some other waiting put) are |
314 |
|
|
* signalled if it ever changes from capacity. Similarly |
315 |
|
|
* for all other uses of count in other wait guards. |
316 |
|
|
*/ |
317 |
|
|
while (count.get() == capacity) { |
318 |
|
|
notFull.await(); |
319 |
|
|
} |
320 |
|
|
enqueue(node); |
321 |
|
|
c = count.getAndIncrement(); |
322 |
|
|
if (c + 1 < capacity) |
323 |
|
|
notFull.signal(); |
324 |
|
|
} finally { |
325 |
|
|
putLock.unlock(); |
326 |
|
|
} |
327 |
|
|
if (c == 0) |
328 |
|
|
signalNotEmpty(); |
329 |
|
|
} |
330 |
|
|
|
331 |
|
|
/** |
332 |
|
|
* Inserts the specified element at the tail of this queue, waiting if |
333 |
|
|
* necessary up to the specified wait time for space to become available. |
334 |
|
|
* |
335 |
|
|
* @return {@code true} if successful, or {@code false} if |
336 |
|
|
* the specified waiting time elapses before space is available. |
337 |
|
|
* @throws InterruptedException {@inheritDoc} |
338 |
|
|
* @throws NullPointerException {@inheritDoc} |
339 |
|
|
*/ |
340 |
|
|
public boolean offer(E e, long timeout, TimeUnit unit) |
341 |
|
|
throws InterruptedException { |
342 |
|
|
|
343 |
|
|
if (e == null) throw new NullPointerException(); |
344 |
|
|
long nanos = unit.toNanos(timeout); |
345 |
|
|
int c = -1; |
346 |
|
|
final ReentrantLock putLock = this.putLock; |
347 |
|
|
final AtomicInteger count = this.count; |
348 |
|
|
putLock.lockInterruptibly(); |
349 |
|
|
try { |
350 |
|
|
while (count.get() == capacity) { |
351 |
|
|
if (nanos <= 0) |
352 |
|
|
return false; |
353 |
|
|
nanos = notFull.awaitNanos(nanos); |
354 |
|
|
} |
355 |
|
|
enqueue(new Node<E>(e)); |
356 |
|
|
c = count.getAndIncrement(); |
357 |
|
|
if (c + 1 < capacity) |
358 |
|
|
notFull.signal(); |
359 |
|
|
} finally { |
360 |
|
|
putLock.unlock(); |
361 |
|
|
} |
362 |
|
|
if (c == 0) |
363 |
|
|
signalNotEmpty(); |
364 |
|
|
return true; |
365 |
|
|
} |
366 |
|
|
|
367 |
|
|
/** |
368 |
|
|
* Inserts the specified element at the tail of this queue if it is |
369 |
|
|
* possible to do so immediately without exceeding the queue's capacity, |
370 |
|
|
* returning {@code true} upon success and {@code false} if this queue |
371 |
|
|
* is full. |
372 |
|
|
* When using a capacity-restricted queue, this method is generally |
373 |
|
|
* preferable to method {@link BlockingQueue#add add}, which can fail to |
374 |
|
|
* insert an element only by throwing an exception. |
375 |
|
|
* |
376 |
|
|
* @throws NullPointerException if the specified element is null |
377 |
|
|
*/ |
378 |
|
|
public boolean offer(E e) { |
379 |
|
|
if (e == null) throw new NullPointerException(); |
380 |
|
|
final AtomicInteger count = this.count; |
381 |
|
|
if (count.get() == capacity) |
382 |
|
|
return false; |
383 |
|
|
int c = -1; |
384 |
|
|
Node<E> node = new Node<E>(e); |
385 |
|
|
final ReentrantLock putLock = this.putLock; |
386 |
|
|
putLock.lock(); |
387 |
|
|
try { |
388 |
|
|
if (count.get() < capacity) { |
389 |
|
|
enqueue(node); |
390 |
|
|
c = count.getAndIncrement(); |
391 |
|
|
if (c + 1 < capacity) |
392 |
|
|
notFull.signal(); |
393 |
|
|
} |
394 |
|
|
} finally { |
395 |
|
|
putLock.unlock(); |
396 |
|
|
} |
397 |
|
|
if (c == 0) |
398 |
|
|
signalNotEmpty(); |
399 |
|
|
return c >= 0; |
400 |
|
|
} |
401 |
|
|
|
402 |
|
|
public E take() throws InterruptedException { |
403 |
|
|
E x; |
404 |
|
|
int c = -1; |
405 |
|
|
final AtomicInteger count = this.count; |
406 |
|
|
final ReentrantLock takeLock = this.takeLock; |
407 |
|
|
takeLock.lockInterruptibly(); |
408 |
|
|
try { |
409 |
|
|
while (count.get() == 0) { |
410 |
|
|
notEmpty.await(); |
411 |
|
|
} |
412 |
|
|
x = dequeue(); |
413 |
|
|
c = count.getAndDecrement(); |
414 |
|
|
if (c > 1) |
415 |
|
|
notEmpty.signal(); |
416 |
|
|
} finally { |
417 |
|
|
takeLock.unlock(); |
418 |
|
|
} |
419 |
|
|
if (c == capacity) |
420 |
|
|
signalNotFull(); |
421 |
|
|
return x; |
422 |
|
|
} |
423 |
|
|
|
424 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
425 |
|
|
E x = null; |
426 |
|
|
int c = -1; |
427 |
|
|
long nanos = unit.toNanos(timeout); |
428 |
|
|
final AtomicInteger count = this.count; |
429 |
|
|
final ReentrantLock takeLock = this.takeLock; |
430 |
|
|
takeLock.lockInterruptibly(); |
431 |
|
|
try { |
432 |
|
|
while (count.get() == 0) { |
433 |
|
|
if (nanos <= 0) |
434 |
|
|
return null; |
435 |
|
|
nanos = notEmpty.awaitNanos(nanos); |
436 |
|
|
} |
437 |
|
|
x = dequeue(); |
438 |
|
|
c = count.getAndDecrement(); |
439 |
|
|
if (c > 1) |
440 |
|
|
notEmpty.signal(); |
441 |
|
|
} finally { |
442 |
|
|
takeLock.unlock(); |
443 |
|
|
} |
444 |
|
|
if (c == capacity) |
445 |
|
|
signalNotFull(); |
446 |
|
|
return x; |
447 |
|
|
} |
448 |
|
|
|
449 |
|
|
public E poll() { |
450 |
|
|
final AtomicInteger count = this.count; |
451 |
|
|
if (count.get() == 0) |
452 |
|
|
return null; |
453 |
|
|
E x = null; |
454 |
|
|
int c = -1; |
455 |
|
|
final ReentrantLock takeLock = this.takeLock; |
456 |
|
|
takeLock.lock(); |
457 |
|
|
try { |
458 |
|
|
if (count.get() > 0) { |
459 |
|
|
x = dequeue(); |
460 |
|
|
c = count.getAndDecrement(); |
461 |
|
|
if (c > 1) |
462 |
|
|
notEmpty.signal(); |
463 |
|
|
} |
464 |
|
|
} finally { |
465 |
|
|
takeLock.unlock(); |
466 |
|
|
} |
467 |
|
|
if (c == capacity) |
468 |
|
|
signalNotFull(); |
469 |
|
|
return x; |
470 |
|
|
} |
471 |
|
|
|
472 |
|
|
public E peek() { |
473 |
|
|
if (count.get() == 0) |
474 |
|
|
return null; |
475 |
|
|
final ReentrantLock takeLock = this.takeLock; |
476 |
|
|
takeLock.lock(); |
477 |
|
|
try { |
478 |
|
|
Node<E> first = head.next; |
479 |
|
|
if (first == null) |
480 |
|
|
return null; |
481 |
|
|
else |
482 |
|
|
return first.item; |
483 |
|
|
} finally { |
484 |
|
|
takeLock.unlock(); |
485 |
|
|
} |
486 |
|
|
} |
487 |
|
|
|
488 |
|
|
/** |
489 |
|
|
* Unlinks interior Node p with predecessor trail. |
490 |
|
|
*/ |
491 |
|
|
void unlink(Node<E> p, Node<E> trail) { |
492 |
|
|
// assert isFullyLocked(); |
493 |
|
|
// p.next is not changed, to allow iterators that are |
494 |
|
|
// traversing p to maintain their weak-consistency guarantee. |
495 |
|
|
p.item = null; |
496 |
|
|
trail.next = p.next; |
497 |
|
|
if (last == p) |
498 |
|
|
last = trail; |
499 |
|
|
if (count.getAndDecrement() == capacity) |
500 |
|
|
notFull.signal(); |
501 |
|
|
} |
502 |
|
|
|
503 |
|
|
/** |
504 |
|
|
* Removes a single instance of the specified element from this queue, |
505 |
|
|
* if it is present. More formally, removes an element {@code e} such |
506 |
|
|
* that {@code o.equals(e)}, if this queue contains one or more such |
507 |
|
|
* elements. |
508 |
|
|
* Returns {@code true} if this queue contained the specified element |
509 |
|
|
* (or equivalently, if this queue changed as a result of the call). |
510 |
|
|
* |
511 |
|
|
* @param o element to be removed from this queue, if present |
512 |
|
|
* @return {@code true} if this queue changed as a result of the call |
513 |
|
|
*/ |
514 |
|
|
public boolean remove(Object o) { |
515 |
|
|
if (o == null) return false; |
516 |
|
|
fullyLock(); |
517 |
|
|
try { |
518 |
|
|
for (Node<E> trail = head, p = trail.next; |
519 |
|
|
p != null; |
520 |
|
|
trail = p, p = p.next) { |
521 |
|
|
if (o.equals(p.item)) { |
522 |
|
|
unlink(p, trail); |
523 |
|
|
return true; |
524 |
|
|
} |
525 |
|
|
} |
526 |
|
|
return false; |
527 |
|
|
} finally { |
528 |
|
|
fullyUnlock(); |
529 |
|
|
} |
530 |
|
|
} |
531 |
|
|
|
532 |
|
|
/** |
533 |
|
|
* Returns {@code true} if this queue contains the specified element. |
534 |
|
|
* More formally, returns {@code true} if and only if this queue contains |
535 |
|
|
* at least one element {@code e} such that {@code o.equals(e)}. |
536 |
|
|
* |
537 |
|
|
* @param o object to be checked for containment in this queue |
538 |
|
|
* @return {@code true} if this queue contains the specified element |
539 |
|
|
*/ |
540 |
|
|
public boolean contains(Object o) { |
541 |
|
|
if (o == null) return false; |
542 |
|
|
fullyLock(); |
543 |
|
|
try { |
544 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
545 |
|
|
if (o.equals(p.item)) |
546 |
|
|
return true; |
547 |
|
|
return false; |
548 |
|
|
} finally { |
549 |
|
|
fullyUnlock(); |
550 |
|
|
} |
551 |
|
|
} |
552 |
|
|
|
553 |
|
|
/** |
554 |
|
|
* Returns an array containing all of the elements in this queue, in |
555 |
|
|
* proper sequence. |
556 |
|
|
* |
557 |
|
|
* <p>The returned array will be "safe" in that no references to it are |
558 |
|
|
* maintained by this queue. (In other words, this method must allocate |
559 |
|
|
* a new array). The caller is thus free to modify the returned array. |
560 |
|
|
* |
561 |
|
|
* <p>This method acts as bridge between array-based and collection-based |
562 |
|
|
* APIs. |
563 |
|
|
* |
564 |
|
|
* @return an array containing all of the elements in this queue |
565 |
|
|
*/ |
566 |
|
|
public Object[] toArray() { |
567 |
|
|
fullyLock(); |
568 |
|
|
try { |
569 |
|
|
int size = count.get(); |
570 |
|
|
Object[] a = new Object[size]; |
571 |
|
|
int k = 0; |
572 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
573 |
|
|
a[k++] = p.item; |
574 |
|
|
return a; |
575 |
|
|
} finally { |
576 |
|
|
fullyUnlock(); |
577 |
|
|
} |
578 |
|
|
} |
579 |
|
|
|
580 |
|
|
/** |
581 |
|
|
* Returns an array containing all of the elements in this queue, in |
582 |
|
|
* proper sequence; the runtime type of the returned array is that of |
583 |
|
|
* the specified array. If the queue fits in the specified array, it |
584 |
|
|
* is returned therein. Otherwise, a new array is allocated with the |
585 |
|
|
* runtime type of the specified array and the size of this queue. |
586 |
|
|
* |
587 |
|
|
* <p>If this queue fits in the specified array with room to spare |
588 |
|
|
* (i.e., the array has more elements than this queue), the element in |
589 |
|
|
* the array immediately following the end of the queue is set to |
590 |
|
|
* {@code null}. |
591 |
|
|
* |
592 |
|
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
593 |
|
|
* array-based and collection-based APIs. Further, this method allows |
594 |
|
|
* precise control over the runtime type of the output array, and may, |
595 |
|
|
* under certain circumstances, be used to save allocation costs. |
596 |
|
|
* |
597 |
|
|
* <p>Suppose {@code x} is a queue known to contain only strings. |
598 |
|
|
* The following code can be used to dump the queue into a newly |
599 |
|
|
* allocated array of {@code String}: |
600 |
|
|
* |
601 |
|
|
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
602 |
|
|
* |
603 |
|
|
* Note that {@code toArray(new Object[0])} is identical in function to |
604 |
|
|
* {@code toArray()}. |
605 |
|
|
* |
606 |
|
|
* @param a the array into which the elements of the queue are to |
607 |
|
|
* be stored, if it is big enough; otherwise, a new array of the |
608 |
|
|
* same runtime type is allocated for this purpose |
609 |
|
|
* @return an array containing all of the elements in this queue |
610 |
|
|
* @throws ArrayStoreException if the runtime type of the specified array |
611 |
|
|
* is not a supertype of the runtime type of every element in |
612 |
|
|
* this queue |
613 |
|
|
* @throws NullPointerException if the specified array is null |
614 |
|
|
*/ |
615 |
|
|
@SuppressWarnings("unchecked") |
616 |
|
|
public <T> T[] toArray(T[] a) { |
617 |
|
|
fullyLock(); |
618 |
|
|
try { |
619 |
|
|
int size = count.get(); |
620 |
|
|
if (a.length < size) |
621 |
|
|
a = (T[])java.lang.reflect.Array.newInstance |
622 |
|
|
(a.getClass().getComponentType(), size); |
623 |
|
|
|
624 |
|
|
int k = 0; |
625 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
626 |
|
|
a[k++] = (T)p.item; |
627 |
|
|
if (a.length > k) |
628 |
|
|
a[k] = null; |
629 |
|
|
return a; |
630 |
|
|
} finally { |
631 |
|
|
fullyUnlock(); |
632 |
|
|
} |
633 |
|
|
} |
634 |
|
|
|
635 |
|
|
public String toString() { |
636 |
|
|
fullyLock(); |
637 |
|
|
try { |
638 |
|
|
Node<E> p = head.next; |
639 |
|
|
if (p == null) |
640 |
|
|
return "[]"; |
641 |
|
|
|
642 |
|
|
StringBuilder sb = new StringBuilder(); |
643 |
|
|
sb.append('['); |
644 |
|
|
for (;;) { |
645 |
|
|
E e = p.item; |
646 |
|
|
sb.append(e == this ? "(this Collection)" : e); |
647 |
|
|
p = p.next; |
648 |
|
|
if (p == null) |
649 |
|
|
return sb.append(']').toString(); |
650 |
|
|
sb.append(',').append(' '); |
651 |
|
|
} |
652 |
|
|
} finally { |
653 |
|
|
fullyUnlock(); |
654 |
|
|
} |
655 |
|
|
} |
656 |
|
|
|
657 |
|
|
/** |
658 |
|
|
* Atomically removes all of the elements from this queue. |
659 |
|
|
* The queue will be empty after this call returns. |
660 |
|
|
*/ |
661 |
|
|
public void clear() { |
662 |
|
|
fullyLock(); |
663 |
|
|
try { |
664 |
|
|
for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
665 |
|
|
h.next = h; |
666 |
|
|
p.item = null; |
667 |
|
|
} |
668 |
|
|
head = last; |
669 |
|
|
// assert head.item == null && head.next == null; |
670 |
|
|
if (count.getAndSet(0) == capacity) |
671 |
|
|
notFull.signal(); |
672 |
|
|
} finally { |
673 |
|
|
fullyUnlock(); |
674 |
|
|
} |
675 |
|
|
} |
676 |
|
|
|
677 |
|
|
/** |
678 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
679 |
|
|
* @throws ClassCastException {@inheritDoc} |
680 |
|
|
* @throws NullPointerException {@inheritDoc} |
681 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
682 |
|
|
*/ |
683 |
|
|
public int drainTo(Collection<? super E> c) { |
684 |
|
|
return drainTo(c, Integer.MAX_VALUE); |
685 |
|
|
} |
686 |
|
|
|
687 |
|
|
/** |
688 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
689 |
|
|
* @throws ClassCastException {@inheritDoc} |
690 |
|
|
* @throws NullPointerException {@inheritDoc} |
691 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
692 |
|
|
*/ |
693 |
|
|
public int drainTo(Collection<? super E> c, int maxElements) { |
694 |
|
|
if (c == null) |
695 |
|
|
throw new NullPointerException(); |
696 |
|
|
if (c == this) |
697 |
|
|
throw new IllegalArgumentException(); |
698 |
|
|
if (maxElements <= 0) |
699 |
|
|
return 0; |
700 |
|
|
boolean signalNotFull = false; |
701 |
|
|
final ReentrantLock takeLock = this.takeLock; |
702 |
|
|
takeLock.lock(); |
703 |
|
|
try { |
704 |
|
|
int n = Math.min(maxElements, count.get()); |
705 |
|
|
// count.get provides visibility to first n Nodes |
706 |
|
|
Node<E> h = head; |
707 |
|
|
int i = 0; |
708 |
|
|
try { |
709 |
|
|
while (i < n) { |
710 |
|
|
Node<E> p = h.next; |
711 |
|
|
c.add(p.item); |
712 |
|
|
p.item = null; |
713 |
|
|
h.next = h; |
714 |
|
|
h = p; |
715 |
|
|
++i; |
716 |
|
|
} |
717 |
|
|
return n; |
718 |
|
|
} finally { |
719 |
|
|
// Restore invariants even if c.add() threw |
720 |
|
|
if (i > 0) { |
721 |
|
|
// assert h.item == null; |
722 |
|
|
head = h; |
723 |
|
|
signalNotFull = (count.getAndAdd(-i) == capacity); |
724 |
|
|
} |
725 |
|
|
} |
726 |
|
|
} finally { |
727 |
|
|
takeLock.unlock(); |
728 |
|
|
if (signalNotFull) |
729 |
|
|
signalNotFull(); |
730 |
|
|
} |
731 |
|
|
} |
732 |
|
|
|
733 |
|
|
/** |
734 |
|
|
* Returns an iterator over the elements in this queue in proper sequence. |
735 |
|
|
* The elements will be returned in order from first (head) to last (tail). |
736 |
|
|
* |
737 |
|
|
* <p>The returned iterator is a "weakly consistent" iterator that |
738 |
|
|
* will never throw {@link java.util.ConcurrentModificationException |
739 |
|
|
* ConcurrentModificationException}, and guarantees to traverse |
740 |
|
|
* elements as they existed upon construction of the iterator, and |
741 |
|
|
* may (but is not guaranteed to) reflect any modifications |
742 |
|
|
* subsequent to construction. |
743 |
|
|
* |
744 |
|
|
* @return an iterator over the elements in this queue in proper sequence |
745 |
|
|
*/ |
746 |
|
|
public Iterator<E> iterator() { |
747 |
|
|
return new Itr(); |
748 |
|
|
} |
749 |
|
|
|
750 |
|
|
private class Itr implements Iterator<E> { |
751 |
|
|
/* |
752 |
|
|
* Basic weakly-consistent iterator. At all times hold the next |
753 |
|
|
* item to hand out so that if hasNext() reports true, we will |
754 |
|
|
* still have it to return even if lost race with a take etc. |
755 |
|
|
*/ |
756 |
jsr166 |
1.3 |
|
757 |
dl |
1.1 |
private Node<E> current; |
758 |
|
|
private Node<E> lastRet; |
759 |
|
|
private E currentElement; |
760 |
|
|
|
761 |
|
|
Itr() { |
762 |
|
|
fullyLock(); |
763 |
|
|
try { |
764 |
|
|
current = head.next; |
765 |
|
|
if (current != null) |
766 |
|
|
currentElement = current.item; |
767 |
|
|
} finally { |
768 |
|
|
fullyUnlock(); |
769 |
|
|
} |
770 |
|
|
} |
771 |
|
|
|
772 |
|
|
public boolean hasNext() { |
773 |
|
|
return current != null; |
774 |
|
|
} |
775 |
|
|
|
776 |
|
|
/** |
777 |
|
|
* Returns the next live successor of p, or null if no such. |
778 |
|
|
* |
779 |
|
|
* Unlike other traversal methods, iterators need to handle both: |
780 |
|
|
* - dequeued nodes (p.next == p) |
781 |
|
|
* - (possibly multiple) interior removed nodes (p.item == null) |
782 |
|
|
*/ |
783 |
|
|
private Node<E> nextNode(Node<E> p) { |
784 |
|
|
for (;;) { |
785 |
|
|
Node<E> s = p.next; |
786 |
|
|
if (s == p) |
787 |
|
|
return head.next; |
788 |
|
|
if (s == null || s.item != null) |
789 |
|
|
return s; |
790 |
|
|
p = s; |
791 |
|
|
} |
792 |
|
|
} |
793 |
|
|
|
794 |
|
|
public E next() { |
795 |
|
|
fullyLock(); |
796 |
|
|
try { |
797 |
|
|
if (current == null) |
798 |
|
|
throw new NoSuchElementException(); |
799 |
|
|
E x = currentElement; |
800 |
|
|
lastRet = current; |
801 |
|
|
current = nextNode(current); |
802 |
|
|
currentElement = (current == null) ? null : current.item; |
803 |
|
|
return x; |
804 |
|
|
} finally { |
805 |
|
|
fullyUnlock(); |
806 |
|
|
} |
807 |
|
|
} |
808 |
|
|
|
809 |
|
|
public void remove() { |
810 |
|
|
if (lastRet == null) |
811 |
|
|
throw new IllegalStateException(); |
812 |
|
|
fullyLock(); |
813 |
|
|
try { |
814 |
|
|
Node<E> node = lastRet; |
815 |
|
|
lastRet = null; |
816 |
|
|
for (Node<E> trail = head, p = trail.next; |
817 |
|
|
p != null; |
818 |
|
|
trail = p, p = p.next) { |
819 |
|
|
if (p == node) { |
820 |
|
|
unlink(p, trail); |
821 |
|
|
break; |
822 |
|
|
} |
823 |
|
|
} |
824 |
|
|
} finally { |
825 |
|
|
fullyUnlock(); |
826 |
|
|
} |
827 |
|
|
} |
828 |
|
|
} |
829 |
|
|
|
830 |
|
|
/** |
831 |
|
|
* Saves this queue to a stream (that is, serializes it). |
832 |
|
|
* |
833 |
|
|
* @serialData The capacity is emitted (int), followed by all of |
834 |
|
|
* its elements (each an {@code Object}) in the proper order, |
835 |
|
|
* followed by a null |
836 |
|
|
*/ |
837 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
838 |
|
|
throws java.io.IOException { |
839 |
|
|
|
840 |
|
|
fullyLock(); |
841 |
|
|
try { |
842 |
|
|
// Write out any hidden stuff, plus capacity |
843 |
|
|
s.defaultWriteObject(); |
844 |
|
|
|
845 |
|
|
// Write out all elements in the proper order. |
846 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
847 |
|
|
s.writeObject(p.item); |
848 |
|
|
|
849 |
|
|
// Use trailing null as sentinel |
850 |
|
|
s.writeObject(null); |
851 |
|
|
} finally { |
852 |
|
|
fullyUnlock(); |
853 |
|
|
} |
854 |
|
|
} |
855 |
|
|
|
856 |
|
|
/** |
857 |
|
|
* Reconstitutes this queue from a stream (that is, deserializes it). |
858 |
|
|
*/ |
859 |
|
|
private void readObject(java.io.ObjectInputStream s) |
860 |
|
|
throws java.io.IOException, ClassNotFoundException { |
861 |
|
|
// Read in capacity, and any hidden stuff |
862 |
|
|
s.defaultReadObject(); |
863 |
|
|
|
864 |
|
|
count.set(0); |
865 |
|
|
last = head = new Node<E>(null); |
866 |
|
|
|
867 |
|
|
// Read in all elements and place in queue |
868 |
|
|
for (;;) { |
869 |
|
|
@SuppressWarnings("unchecked") |
870 |
|
|
E item = (E)s.readObject(); |
871 |
|
|
if (item == null) |
872 |
|
|
break; |
873 |
|
|
add(item); |
874 |
|
|
} |
875 |
|
|
} |
876 |
|
|
} |