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.ArrayList; |
10 |
import java.util.List; |
11 |
import java.util.concurrent.locks.LockSupport; |
12 |
import java.util.function.BiPredicate; |
13 |
import java.util.function.Function; |
14 |
import java.util.function.Supplier; |
15 |
|
16 |
/** |
17 |
* A {@link Flow.Publisher} that asynchronously issues submitted |
18 |
* (non-null) items to current subscribers until it is closed. Each |
19 |
* current subscriber receives newly submitted items in the same order |
20 |
* unless drops or exceptions are encountered. Using a |
21 |
* SubmissionPublisher allows item generators to act as Publishers |
22 |
* relying on drop handling and/or blocking for flow control. |
23 |
* |
24 |
* <p>A SubmissionPublisher uses the {@link Executor} supplied in its |
25 |
* constructor for delivery to subscribers. The best choice of |
26 |
* Executor depends on expected usage. If the generator(s) of |
27 |
* submitted items run in separate threads, and the number of |
28 |
* subscribers can be estimated, consider using a {@link |
29 |
* Executors#newFixedThreadPool}. Otherwise consider using a |
30 |
* work-stealing pool (including {@link ForkJoinPool#commonPool}). |
31 |
* |
32 |
* <p>Buffering allows producers and consumers to transiently operate |
33 |
* at different rates. Each subscriber uses an independent buffer. |
34 |
* Buffers are created upon first use and expanded as needed up to the |
35 |
* given maximum. (the enforced capacity may be rounded up to the |
36 |
* nearest power of two and/or bounded by the largest value supported |
37 |
* by this implementation.) Invocations of {@link |
38 |
* Flow.Subscription#request} do not directly result in buffer |
39 |
* expansion, but risk saturation if unfilled requests exceed the |
40 |
* maximum capacity. Choices of buffer parameters rely on expected |
41 |
* rates, resources, and usages, that usually benefit from empirical |
42 |
* testing. As a first guess, consider a value of 64. |
43 |
* |
44 |
* <p>Publication methods support different policies about what to do |
45 |
* when buffers are saturated. Method {@link #submit} blocks until |
46 |
* resources are available. This is simplest, but least |
47 |
* responsive. The {@code offer} methods may drop items (either |
48 |
* immediately or with bounded timeout), but provide an opportunity to |
49 |
* interpose a handler and then retry. |
50 |
* |
51 |
* <p>If any Subscriber method throws an exception, its subscription |
52 |
* is cancelled. If the supplied Executor throws |
53 |
* RejectedExecutionException (or any other RuntimeException or Error) |
54 |
* when attempting to execute a task, or a drop handler throws an |
55 |
* exception when processing a dropped item, then the exception is |
56 |
* rethrown. In these cases, some but not all subscribers may have |
57 |
* received items. It is usually good practice to {@link |
58 |
* #closeExceptionally closeExceptionally} in these cases. |
59 |
* |
60 |
* <p>This class may also serve as a convenient base for subclasses |
61 |
* that generate items, and use the methods in this class to publish |
62 |
* them. For example here is a class that periodically publishes the |
63 |
* items generated from a supplier. (In practice you might add methods |
64 |
* to independently start and stop generation, to share schedulers |
65 |
* among publishers, and so on, or instead use a SubmissionPublisher |
66 |
* as a component rather than a superclass.) |
67 |
* |
68 |
* <pre> {@code |
69 |
* class PeriodicPublisher<T> extends SubmissionPublisher<T> { |
70 |
* final ScheduledFuture<?> periodicTask; |
71 |
* final ScheduledExecutorService scheduler; |
72 |
* PeriodicPublisher(Executor executor, int maxBufferCapacity, |
73 |
* Supplier<? extends T> supplier, |
74 |
* long period, TimeUnit unit) { |
75 |
* super(executor, maxBufferCapacity); |
76 |
* scheduler = new ScheduledThreadPoolExecutor(1); |
77 |
* periodicTask = scheduler.scheduleAtFixedRate( |
78 |
* () -> submit(supplier.get()), 0, period, unit); |
79 |
* } |
80 |
* public void close() { |
81 |
* periodicTask.cancel(false); |
82 |
* scheduler.shutdown(); |
83 |
* super.close(); |
84 |
* } |
85 |
* }}</pre> |
86 |
* |
87 |
* <p>Here is an example of a {@link Flow.Processor} implementation. |
88 |
* It uses single-step requests to its publisher for simplicity of |
89 |
* illustration. A more adaptive version could monitor flow using the |
90 |
* lag estimate returned from {@code submit} and/or other utility |
91 |
* methods. |
92 |
* |
93 |
* <pre> {@code |
94 |
* class TransformProcessor<S,T> extends SubmissionPublisher<T> |
95 |
* implements Flow.Processor<S,T> { |
96 |
* final Function<? super S, ? extends T> function; |
97 |
* Flow.Subscription subscription; |
98 |
* TransformProcessor(Executor executor, int maxBufferCapacity, |
99 |
* Function<? super S, ? extends T> function) { |
100 |
* super(executor, maxBufferCapacity); |
101 |
* this.function = function; |
102 |
* } |
103 |
* public void onSubscribe(Flow.Subscription subscription) { |
104 |
* (this.subscription = subscription).request(1); |
105 |
* } |
106 |
* public void onNext(S item) { |
107 |
* subscription.request(1); |
108 |
* submit(function.apply(item)); |
109 |
* } |
110 |
* public void onError(Throwable ex) { closeExceptionally(ex); } |
111 |
* public void onComplete() { close(); } |
112 |
* }}</pre> |
113 |
* |
114 |
* @param <T> the published item type |
115 |
* @author Doug Lea |
116 |
* @since 1.9 |
117 |
*/ |
118 |
public class SubmissionPublisher<T> implements Flow.Publisher<T>, |
119 |
AutoCloseable { |
120 |
/* |
121 |
* Most mechanics are handled by BufferedSubscription. This class |
122 |
* mainly tracks subscribers and ensures sequentiality, by using |
123 |
* built-in synchronization locks across public methods. (Using |
124 |
* built-in locks works well in the most typical case in which |
125 |
* only one thread submits items). |
126 |
*/ |
127 |
|
128 |
// Ensuring that all arrays have power of two length |
129 |
|
130 |
static final int MAXIMUM_BUFFER_CAPACITY = 1 << 30; |
131 |
static final int roundCapacity(int cap) { // to nearest power of 2 |
132 |
int n = cap - 1; |
133 |
n |= n >>> 1; |
134 |
n |= n >>> 2; |
135 |
n |= n >>> 4; |
136 |
n |= n >>> 8; |
137 |
n |= n >>> 16; |
138 |
return (n <= 0) ? 2 : // at least 2 |
139 |
(n >= MAXIMUM_BUFFER_CAPACITY) ? MAXIMUM_BUFFER_CAPACITY : n + 1; |
140 |
} |
141 |
|
142 |
/** |
143 |
* Clients (BufferedSubscriptions) are maintained in a linked list |
144 |
* (via their "next" fields). This works well for publish loops. |
145 |
* It requires O(n) traversal to check for duplicate subscribers, |
146 |
* but we expect that subscribing is much less common than |
147 |
* publishing. Unsubscribing occurs only during traversal loops, |
148 |
* when BufferedSubscription methods or status checks return |
149 |
* negative values signifying that they have been disabled. |
150 |
*/ |
151 |
BufferedSubscription<T> clients; |
152 |
|
153 |
/** Run status, updated only within locks */ |
154 |
volatile boolean closed; |
155 |
|
156 |
// Parameters for constructing BufferedSubscriptions |
157 |
final Executor executor; |
158 |
final int maxBufferCapacity; |
159 |
|
160 |
/** |
161 |
* Creates a new SubmissionPublisher using the given Executor for |
162 |
* async delivery to subscribers, and with the given maximum |
163 |
* buffer size for each subscriber. In the absence of other |
164 |
* constraints, consider using {@code ForkJoinPool.commonPool(), |
165 |
* 64}. |
166 |
* |
167 |
* @param executor the executor to use for async delivery, |
168 |
* supporting creation of at least one independent thread |
169 |
* @param maxBufferCapacity the maximum capacity for each |
170 |
* subscriber's buffer (the enforced capacity may be rounded up to |
171 |
* the nearest power of two and/or bounded by the largest value |
172 |
* supported by this implementation; method {@link #getMaxBufferCapacity} |
173 |
* returns the actual value) |
174 |
* @throws NullPointerException if executor is null |
175 |
* @throws IllegalArgumentException if maxBufferCapacity not |
176 |
* positive |
177 |
*/ |
178 |
public SubmissionPublisher(Executor executor, int maxBufferCapacity) { |
179 |
if (executor == null) |
180 |
throw new NullPointerException(); |
181 |
if (maxBufferCapacity <= 0) |
182 |
throw new IllegalArgumentException("capacity must be positive"); |
183 |
this.executor = executor; |
184 |
this.maxBufferCapacity = roundCapacity(maxBufferCapacity); |
185 |
} |
186 |
|
187 |
/** |
188 |
* Adds the given Subscriber unless already subscribed. If |
189 |
* already subscribed, the Subscriber's onError method is invoked |
190 |
* with an IllegalStateException. Otherwise, upon success, the |
191 |
* Subscriber's onSubscribe method is invoked with a new |
192 |
* Subscription. If onSubscribe throws an exception, the |
193 |
* subscription is cancelled. Otherwise, if this |
194 |
* SubmissionPublisher is closed, the subscriber's onComplete |
195 |
* method is then invoked. Subscribers may enable receiving items |
196 |
* by invoking the {@code request} method of the new Subscription, |
197 |
* and may unsubscribe by invoking its cancel method. |
198 |
* |
199 |
* @param subscriber the subscriber |
200 |
* @throws NullPointerException if subscriber is null |
201 |
*/ |
202 |
public void subscribe(Flow.Subscriber<? super T> subscriber) { |
203 |
if (subscriber == null) throw new NullPointerException(); |
204 |
BufferedSubscription<T> subscription = |
205 |
new BufferedSubscription<T>(subscriber, executor, maxBufferCapacity); |
206 |
boolean present = false, complete; |
207 |
synchronized (this) { |
208 |
complete = closed; |
209 |
BufferedSubscription<T> pred = null, next; |
210 |
for (BufferedSubscription<T> b = clients; ; b = next) { |
211 |
if (b == null) { |
212 |
if (pred == null) |
213 |
clients = subscription; |
214 |
else |
215 |
pred.next = subscription; |
216 |
subscription.onSubscribe(); |
217 |
break; |
218 |
} |
219 |
next = b.next; |
220 |
if (b.isDisabled()) { // remove |
221 |
if (pred == null) |
222 |
clients = next; |
223 |
else |
224 |
pred.next = next; |
225 |
} |
226 |
else if (subscriber.equals(b.subscriber)) { |
227 |
present = true; |
228 |
break; |
229 |
} |
230 |
pred = b; |
231 |
} |
232 |
} |
233 |
if (present) |
234 |
subscriber.onError(new IllegalStateException("Already subscribed")); |
235 |
else if (complete) |
236 |
subscription.onComplete(); |
237 |
} |
238 |
|
239 |
/** |
240 |
* Publishes the given item to each current subscriber by |
241 |
* asynchronously invoking its onNext method, blocking |
242 |
* uninterruptibly while resources for any subscriber are |
243 |
* unavailable. This method returns an estimate of the maximum lag |
244 |
* (number of items submitted but not yet consumed) among all |
245 |
* current subscribers. This value is at least one (accounting for |
246 |
* this submitted item) if there are any subscribers, else zero. |
247 |
* |
248 |
* <p>If the Executor for this publisher throws a |
249 |
* RejectedExecutionException (or any other RuntimeException or |
250 |
* Error) when attempting to asynchronously notify subscribers, |
251 |
* then this exception is rethrown. |
252 |
* |
253 |
* @param item the (non-null) item to publish |
254 |
* @return the estimated maximum lag among subscribers |
255 |
* @throws IllegalStateException if closed |
256 |
* @throws NullPointerException if item is null |
257 |
* @throws RejectedExecutionException if thrown by Executor |
258 |
*/ |
259 |
public int submit(T item) { |
260 |
if (item == null) throw new NullPointerException(); |
261 |
int lag = 0; |
262 |
synchronized (this) { |
263 |
if (closed) |
264 |
throw new IllegalStateException("Closed"); |
265 |
/* |
266 |
* To reduce head-of-line blocking, try offer() on each, |
267 |
* place saturated ones in retries list, and later wait |
268 |
* them out. |
269 |
*/ |
270 |
BufferedSubscription<T> b = clients, retries = null, |
271 |
rtail = null, pred = null, next; |
272 |
for ( ; b != null; b = next) { |
273 |
int stat; |
274 |
next = b.next; |
275 |
if ((stat = b.offer(item)) < 0) { |
276 |
if (pred == null) |
277 |
clients = next; |
278 |
else |
279 |
pred.next = next; |
280 |
} |
281 |
else { |
282 |
if (stat == 0) { |
283 |
if (rtail == null) |
284 |
retries = b; |
285 |
else |
286 |
rtail.nextRetry = b; |
287 |
rtail = b; |
288 |
stat = maxBufferCapacity; |
289 |
} |
290 |
if (stat > lag) |
291 |
lag = stat; |
292 |
pred = b; |
293 |
} |
294 |
} |
295 |
if (retries != null) |
296 |
retrySubmit(retries, item); |
297 |
} |
298 |
return lag; |
299 |
} |
300 |
|
301 |
/** |
302 |
* Calls submit on each subscription on retry list. |
303 |
*/ |
304 |
private void retrySubmit(BufferedSubscription<T> retries, T item) { |
305 |
for (BufferedSubscription<T> r = retries; r != null;) { |
306 |
BufferedSubscription<T> nextRetry = r.nextRetry; |
307 |
r.nextRetry = null; |
308 |
r.submit(item); |
309 |
r = nextRetry; |
310 |
} |
311 |
} |
312 |
|
313 |
/** |
314 |
* Publishes the given item, if possible, to each current |
315 |
* subscriber by asynchronously invoking its onNext method. The |
316 |
* item may be dropped by one or more subscribers if resource |
317 |
* limits are exceeded, in which case the given handler (if |
318 |
* non-null) is invoked, and if it returns true, retried once. |
319 |
* Other calls to methods in this class by other threads are |
320 |
* blocked while the handler is invoked. Unless recovery is |
321 |
* assured, options are usually limited to logging the error |
322 |
* and/or issuing an onError signal to the subscriber. |
323 |
* |
324 |
* <p>This method returns a status indicator: If negative, it |
325 |
* represents the (negative) number of drops (failed attempts to |
326 |
* issue the item to a subscriber). Otherwise it is an estimate of |
327 |
* the maximum lag (number of items submitted but not yet |
328 |
* consumed) among all current subscribers. This value is at least |
329 |
* one (accounting for this submitted item) if there are any |
330 |
* subscribers, else zero. |
331 |
* |
332 |
* <p>If the Executor for this publisher throws a |
333 |
* RejectedExecutionException (or any other RuntimeException or |
334 |
* Error) when attempting to asynchronously notify subscribers, or |
335 |
* the drop handler throws an exception when processing a dropped |
336 |
* item, then this exception is rethrown. |
337 |
* |
338 |
* @param item the (non-null) item to publish |
339 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
340 |
* subscriber, with arguments of the subscriber and item; if it |
341 |
* returns true, an offer is re-attempted (once) |
342 |
* @return if negative, the (negative) number of drops; otherwise |
343 |
* an estimate of maximum lag |
344 |
* @throws IllegalStateException if closed |
345 |
* @throws NullPointerException if item is null |
346 |
* @throws RejectedExecutionException if thrown by Executor |
347 |
*/ |
348 |
public int offer(T item, |
349 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
350 |
if (item == null) throw new NullPointerException(); |
351 |
int ret = 0; |
352 |
synchronized (this) { |
353 |
if (closed) |
354 |
throw new IllegalStateException("Closed"); |
355 |
BufferedSubscription<T> pred = null, next; |
356 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
357 |
int stat; |
358 |
next = b.next; |
359 |
if ((stat = b.offer(item)) == 0 && |
360 |
onDrop != null && |
361 |
onDrop.test(b.subscriber, item)) |
362 |
stat = b.offer(item); |
363 |
if (stat < 0) { |
364 |
if (pred == null) |
365 |
clients = next; |
366 |
else |
367 |
pred.next = next; |
368 |
} |
369 |
else { |
370 |
pred = b; |
371 |
if (stat == 0) |
372 |
ret = (ret >= 0) ? -1 : ret - 1; |
373 |
else if (ret >= 0 && stat > ret) |
374 |
ret = stat; |
375 |
} |
376 |
} |
377 |
return ret; |
378 |
} |
379 |
} |
380 |
|
381 |
/** |
382 |
* Publishes the given item, if possible, to each current |
383 |
* subscriber by asynchronously invoking its onNext method, |
384 |
* blocking while resources for any subscription are unavailable, |
385 |
* up to the specified timeout or the caller thread is |
386 |
* interrupted, at which point the given handler (if non-null) is |
387 |
* invoked, and if it returns true, retried once. (The drop |
388 |
* handler may distinguish timeouts from interrupts by checking |
389 |
* whether the current thread is interrupted.) Other calls to |
390 |
* methods in this class by other threads are blocked while the |
391 |
* handler is invoked. Unless recovery is assured, options are |
392 |
* usually limited to logging the error and/or issuing an onError |
393 |
* signal to the subscriber. |
394 |
* |
395 |
* <p>This method returns a status indicator: If negative, it |
396 |
* represents the (negative) number of drops (failed attempts to |
397 |
* issue the item to a subscriber). Otherwise it is an estimate of |
398 |
* the maximum lag (number of items submitted but not yet |
399 |
* consumed) among all current subscribers. This value is at least |
400 |
* one (accounting for this submitted item) if there are any |
401 |
* subscribers, else zero. |
402 |
* |
403 |
* <p>If the Executor for this publisher throws a |
404 |
* RejectedExecutionException (or any other RuntimeException or |
405 |
* Error) when attempting to asynchronously notify subscribers, or |
406 |
* the drop handler throws an exception when processing a dropped |
407 |
* item, then this exception is rethrown. |
408 |
* |
409 |
* @param item the (non-null) item to publish |
410 |
* @param timeout how long to wait for resources for any subscriber |
411 |
* before giving up, in units of {@code unit} |
412 |
* @param unit a {@code TimeUnit} determining how to interpret the |
413 |
* {@code timeout} parameter |
414 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
415 |
* subscriber, with arguments of the subscriber and item; if it |
416 |
* returns true, an offer is re-attempted (once) |
417 |
* @return if negative, the (negative) number of drops; otherwise |
418 |
* an estimate of maximum lag |
419 |
* @throws IllegalStateException if closed |
420 |
* @throws NullPointerException if item is null |
421 |
* @throws RejectedExecutionException if thrown by Executor |
422 |
*/ |
423 |
public int offer(T item, long timeout, TimeUnit unit, |
424 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
425 |
if (item == null) throw new NullPointerException(); |
426 |
long nanos = unit.toNanos(timeout); |
427 |
int ret = 0; |
428 |
synchronized (this) { |
429 |
if (closed) |
430 |
throw new IllegalStateException("Closed"); |
431 |
BufferedSubscription<T> pred = null, next; |
432 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
433 |
int stat; |
434 |
next = b.next; |
435 |
if ((stat = b.offerNanos(item, nanos)) == 0 && |
436 |
onDrop != null && onDrop.test(b.subscriber, item)) |
437 |
stat = b.offer(item); |
438 |
if (stat < 0) { |
439 |
if (pred == null) |
440 |
clients = next; |
441 |
else |
442 |
pred.next = next; |
443 |
} |
444 |
else { |
445 |
pred = b; |
446 |
if (stat == 0) |
447 |
ret = (ret >= 0) ? -1 : ret - 1; |
448 |
else if (ret >= 0 && stat > ret) |
449 |
ret = stat; |
450 |
} |
451 |
} |
452 |
} |
453 |
return ret; |
454 |
} |
455 |
|
456 |
/** |
457 |
* Unless already closed, issues onComplete signals to current |
458 |
* subscribers, and disallows subsequent attempts to publish. |
459 |
*/ |
460 |
public void close() { |
461 |
if (!closed) { |
462 |
BufferedSubscription<T> b, next; |
463 |
synchronized (this) { |
464 |
b = clients; |
465 |
clients = null; |
466 |
closed = true; |
467 |
} |
468 |
while (b != null) { |
469 |
next = b.next; |
470 |
b.onComplete(); |
471 |
b = next; |
472 |
} |
473 |
} |
474 |
} |
475 |
|
476 |
/** |
477 |
* Unless already closed, issues onError signals to current |
478 |
* subscribers with the given error, and disallows subsequent |
479 |
* attempts to publish. |
480 |
* |
481 |
* @param error the onError argument sent to subscribers |
482 |
* @throws NullPointerException if error is null |
483 |
*/ |
484 |
public void closeExceptionally(Throwable error) { |
485 |
if (error == null) |
486 |
throw new NullPointerException(); |
487 |
if (!closed) { |
488 |
BufferedSubscription<T> b, next; |
489 |
synchronized (this) { |
490 |
b = clients; |
491 |
clients = null; |
492 |
closed = true; |
493 |
} |
494 |
while (b != null) { |
495 |
next = b.next; |
496 |
b.onError(error); |
497 |
b = next; |
498 |
} |
499 |
} |
500 |
} |
501 |
|
502 |
/** |
503 |
* Returns true if this publisher is not accepting submissions. |
504 |
* |
505 |
* @return true if closed |
506 |
*/ |
507 |
public boolean isClosed() { |
508 |
return closed; |
509 |
} |
510 |
|
511 |
/** |
512 |
* Returns true if this publisher has any subscribers. |
513 |
* |
514 |
* @return true if this publisher has any subscribers |
515 |
*/ |
516 |
public boolean hasSubscribers() { |
517 |
boolean nonEmpty = false; |
518 |
if (!closed) { |
519 |
synchronized (this) { |
520 |
BufferedSubscription<T> pred = null, next; |
521 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
522 |
next = b.next; |
523 |
if (b.isDisabled()) { |
524 |
if (pred == null) |
525 |
clients = next; |
526 |
else |
527 |
pred.next = next; |
528 |
} |
529 |
else { |
530 |
nonEmpty = true; |
531 |
break; |
532 |
} |
533 |
} |
534 |
} |
535 |
} |
536 |
return nonEmpty; |
537 |
} |
538 |
|
539 |
/** |
540 |
* Returns the number of current subscribers. |
541 |
* |
542 |
* @return the number of current subscribers |
543 |
*/ |
544 |
public int getNumberOfSubscribers() { |
545 |
int count = 0; |
546 |
if (!closed) { |
547 |
synchronized (this) { |
548 |
BufferedSubscription<T> pred = null, next; |
549 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
550 |
next = b.next; |
551 |
if (b.isDisabled()) { |
552 |
if (pred == null) |
553 |
clients = next; |
554 |
else |
555 |
pred.next = next; |
556 |
} |
557 |
else { |
558 |
pred = b; |
559 |
++count; |
560 |
} |
561 |
} |
562 |
} |
563 |
} |
564 |
return count; |
565 |
} |
566 |
|
567 |
/** |
568 |
* Returns the Executor used for asynchronous delivery. |
569 |
* |
570 |
* @return the Executor used for asynchronous delivery |
571 |
*/ |
572 |
public Executor getExecutor() { |
573 |
return executor; |
574 |
} |
575 |
|
576 |
/** |
577 |
* Returns the maximum per-subscriber buffer capacity. |
578 |
* |
579 |
* @return the maximum per-subscriber buffer capacity |
580 |
*/ |
581 |
public int getMaxBufferCapacity() { |
582 |
return maxBufferCapacity; |
583 |
} |
584 |
|
585 |
/** |
586 |
* Returns a list of current subscribers. |
587 |
* |
588 |
* @return list of current subscribers |
589 |
*/ |
590 |
public List<Flow.Subscriber<? super T>> getSubscribers() { |
591 |
ArrayList<Flow.Subscriber<? super T>> subs = new ArrayList<>(); |
592 |
synchronized (this) { |
593 |
BufferedSubscription<T> pred = null, next; |
594 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
595 |
next = b.next; |
596 |
if (b.isDisabled()) { |
597 |
if (pred == null) |
598 |
clients = next; |
599 |
else |
600 |
pred.next = next; |
601 |
} |
602 |
else |
603 |
subs.add(b.subscriber); |
604 |
} |
605 |
} |
606 |
return subs; |
607 |
} |
608 |
|
609 |
/** |
610 |
* Returns true if the given Subscriber is currently subscribed. |
611 |
* |
612 |
* @param subscriber the subscriber |
613 |
* @return true if currently subscribed |
614 |
* @throws NullPointerException if subscriber is null |
615 |
*/ |
616 |
public boolean isSubscribed(Flow.Subscriber<? super T> subscriber) { |
617 |
if (subscriber == null) throw new NullPointerException(); |
618 |
if (!closed) { |
619 |
synchronized (this) { |
620 |
BufferedSubscription<T> pred = null, next; |
621 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
622 |
next = b.next; |
623 |
if (b.isDisabled()) { |
624 |
if (pred == null) |
625 |
clients = next; |
626 |
else |
627 |
pred.next = next; |
628 |
} |
629 |
else if (subscriber.equals(b.subscriber)) |
630 |
return true; |
631 |
else |
632 |
pred = b; |
633 |
} |
634 |
} |
635 |
} |
636 |
return false; |
637 |
} |
638 |
|
639 |
/** |
640 |
* Returns an estimate of the minimum number of items requested |
641 |
* (via {@link Flow.Subscription#request}) but not yet produced, |
642 |
* among all current subscribers. |
643 |
* |
644 |
* @return the estimate, or zero if no subscribers |
645 |
*/ |
646 |
public long estimateMinimumDemand() { |
647 |
long min = Long.MAX_VALUE; |
648 |
boolean nonEmpty = false; |
649 |
synchronized (this) { |
650 |
BufferedSubscription<T> pred = null, next; |
651 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
652 |
int n; long d; |
653 |
next = b.next; |
654 |
if ((n = b.estimateLag()) < 0) { |
655 |
if (pred == null) |
656 |
clients = next; |
657 |
else |
658 |
pred.next = next; |
659 |
} |
660 |
else { |
661 |
if ((d = b.demand - n) < min) |
662 |
min = d; |
663 |
nonEmpty = true; |
664 |
} |
665 |
} |
666 |
} |
667 |
return nonEmpty ? min : 0; |
668 |
} |
669 |
|
670 |
/** |
671 |
* Returns an estimate of the maximum number of items produced but |
672 |
* not yet consumed among all current subscribers. |
673 |
* |
674 |
* @return the estimate |
675 |
*/ |
676 |
public int estimateMaximumLag() { |
677 |
int max = 0; |
678 |
synchronized (this) { |
679 |
BufferedSubscription<T> pred = null, next; |
680 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
681 |
int n; |
682 |
next = b.next; |
683 |
if ((n = b.estimateLag()) < 0) { |
684 |
if (pred == null) |
685 |
clients = next; |
686 |
else |
687 |
pred.next = next; |
688 |
} |
689 |
else if (n > max) |
690 |
max = n; |
691 |
} |
692 |
} |
693 |
return max; |
694 |
} |
695 |
|
696 |
/** |
697 |
* A bounded (ring) buffer with integrated control to start a |
698 |
* consumer task whenever items are available. The buffer |
699 |
* algorithm is similar to one used inside ForkJoinPool, |
700 |
* specialized for the case of at most one concurrent producer and |
701 |
* consumer, and power of two buffer sizes. This allows methods to |
702 |
* operate without locks even while supporting resizing, blocking, |
703 |
* task-triggering, and garbage-free buffers (nulling out elements |
704 |
* when consumed), although supporting these does impose a bit of |
705 |
* overhead compared to plain fixed-size ring buffers. |
706 |
* |
707 |
* The publisher guarantees a single producer via its lock. We |
708 |
* ensure in this class that there is at most one consumer. The |
709 |
* request and cancel methods must be fully thread-safe but are |
710 |
* coded to exploit the most common case in which they are only |
711 |
* called by consumers (usually within onNext). |
712 |
* |
713 |
* This class also serves as its own consumer task, consuming as |
714 |
* many items/signals as possible before terminating, at which |
715 |
* point it is re-executed when needed. (The dual Runnable and |
716 |
* ForkJoinTask declaration saves overhead when executed by |
717 |
* ForkJoinPools, without impacting other kinds of Executors.) |
718 |
* Execution control is managed using the ACTIVE ctl bit. We |
719 |
* ensure that a task is active when consumable items (and |
720 |
* usually, SUBSCRIBE, ERROR or COMPLETE signals) are present and |
721 |
* there is demand (unfilled requests). This is complicated on |
722 |
* the creation side by the possibility of exceptions when trying |
723 |
* to execute tasks. These eventually force DISABLED state, but |
724 |
* sometimes not directly. On the task side, termination (clearing |
725 |
* ACTIVE) may race with producers or request() calls, so in some |
726 |
* cases requires a re-check, re-activating if possible. |
727 |
* |
728 |
* The ctl field also manages run state. When DISABLED, no further |
729 |
* updates are possible. Disabling may be preceded by setting |
730 |
* ERROR or COMPLETE (or both -- ERROR has precedence), in which |
731 |
* case the associated Subscriber methods are invoked, possibly |
732 |
* synchronously if there is no active consumer task (including |
733 |
* cases where execute() failed). The cancel() method is supported |
734 |
* by treating as ERROR but suppressing onError signal. |
735 |
* |
736 |
* Support for blocking also exploits the fact that there is only |
737 |
* one possible waiter. ManagedBlocker-compatible control fields |
738 |
* are placed in this class itself rather than in wait-nodes. |
739 |
* Blocking control relies on the "waiter" field. Producers set |
740 |
* the field before trying to block, but must then recheck (via |
741 |
* offer) before parking. Signalling then just unparks and clears |
742 |
* waiter field. If the producer and consumer are both in the same |
743 |
* ForkJoinPool, the producer attempts to help run consumer tasks |
744 |
* that it forked before blocking. |
745 |
* |
746 |
* This class uses @Contended and heuristic field declaration |
747 |
* ordering to reduce memory contention on BufferedSubscription |
748 |
* itself, but it does not currently attempt to avoid memory |
749 |
* contention (especially including card-marks) among buffer |
750 |
* elements, that can significantly slow down some usages. |
751 |
* Addressing this may require allocating substantially more space |
752 |
* than users expect. |
753 |
*/ |
754 |
@SuppressWarnings("serial") |
755 |
@sun.misc.Contended |
756 |
static final class BufferedSubscription<T> extends ForkJoinTask<Void> |
757 |
implements Runnable, Flow.Subscription, ForkJoinPool.ManagedBlocker { |
758 |
// Order-sensitive field declarations |
759 |
long timeout; // > 0 if timed wait |
760 |
volatile long demand; // # unfilled requests |
761 |
int maxCapacity; // reduced on OOME |
762 |
int putStat; // offer result for ManagedBlocker |
763 |
volatile int ctl; // atomic run state flags |
764 |
volatile int head; // next position to take |
765 |
volatile int tail; // next position to put |
766 |
volatile Object[] array; // buffer: null if disabled |
767 |
Flow.Subscriber<? super T> subscriber; // null if disabled |
768 |
Executor executor; // null if disabled |
769 |
volatile Throwable pendingError; // holds until onError issued |
770 |
volatile Thread waiter; // blocked producer thread |
771 |
T putItem; // for offer within ManagedBlocker |
772 |
BufferedSubscription<T> next; // used only by publisher |
773 |
BufferedSubscription<T> nextRetry;// used only by publisher |
774 |
|
775 |
// ctl values |
776 |
static final int ACTIVE = 0x01; // consumer task active |
777 |
static final int DISABLED = 0x02; // final state |
778 |
static final int ERROR = 0x04; // signal onError then disable |
779 |
static final int SUBSCRIBE = 0x08; // signal onSubscribe |
780 |
static final int COMPLETE = 0x10; // signal onComplete when done |
781 |
|
782 |
static final long INTERRUPTED = -1L; // timeout vs interrupt sentinel |
783 |
|
784 |
/** |
785 |
* Initial/Minimum buffer capacity. Must be a power of two, at least 2. |
786 |
*/ |
787 |
static final int MINCAP = 8; |
788 |
|
789 |
BufferedSubscription(Flow.Subscriber<? super T> subscriber, |
790 |
Executor executor, int maxBufferCapacity) { |
791 |
this.subscriber = subscriber; |
792 |
this.executor = executor; |
793 |
this.maxCapacity = maxBufferCapacity; |
794 |
} |
795 |
|
796 |
final boolean isDisabled() { |
797 |
return ctl == DISABLED; |
798 |
} |
799 |
|
800 |
/** |
801 |
* Returns estimated number of buffered items, or -1 if |
802 |
* disabled |
803 |
*/ |
804 |
final int estimateLag() { |
805 |
int n; |
806 |
return (ctl == DISABLED) ? -1 : ((n = tail - head) > 0) ? n : 0; |
807 |
} |
808 |
|
809 |
/** |
810 |
* Tries to add item and start consumer task if necessary. |
811 |
* @return -1 if disabled, 0 if dropped, else estimated lag |
812 |
*/ |
813 |
final int offer(T item) { |
814 |
Object[] a = array; |
815 |
int t = tail, stat = t + 1 - head, n, i; |
816 |
if (a != null && (n = a.length) >= stat && (i = t & (n - 1)) >= 0) { |
817 |
a[i] = item; |
818 |
U.putOrderedInt(this, TAIL, t + 1); |
819 |
} |
820 |
else if ((stat = growAndAdd(a, item)) <= 0) |
821 |
return stat; |
822 |
for (int c;;) { // possibly start task |
823 |
Executor e; |
824 |
if (((c = ctl) & ACTIVE) != 0) |
825 |
break; |
826 |
else if (c == DISABLED || (e = executor) == null) |
827 |
return -1; |
828 |
else if (demand == 0L || tail == head) |
829 |
break; |
830 |
else if (U.compareAndSwapInt(this, CTL, c, c | ACTIVE)) { |
831 |
try { |
832 |
e.execute(this); |
833 |
break; |
834 |
} catch (RuntimeException | Error ex) { // back out |
835 |
do {} while ((c = ctl) >= 0 && |
836 |
(c & ACTIVE) != 0 && |
837 |
!U.compareAndSwapInt(this, CTL, c, |
838 |
c & ~ACTIVE)); |
839 |
throw ex; |
840 |
} |
841 |
} |
842 |
} |
843 |
return stat; |
844 |
} |
845 |
|
846 |
/** |
847 |
* Tries to create or expand buffer, then adds item if possible |
848 |
*/ |
849 |
final int growAndAdd(Object[] oldArray, T item) { |
850 |
int oldLen, newLen; |
851 |
if (oldArray == null) { |
852 |
oldLen = 0; |
853 |
newLen = (maxCapacity >= MINCAP ? MINCAP : |
854 |
maxCapacity >= 2 ? maxCapacity : 2); |
855 |
} |
856 |
else if ((oldLen = oldArray.length) >= maxCapacity || |
857 |
(newLen = oldLen << 1) <= 0) |
858 |
return 0; // cannot grow |
859 |
if (ctl == DISABLED) |
860 |
return -1; |
861 |
Object[] newArray; |
862 |
try { |
863 |
newArray = new Object[newLen]; |
864 |
} catch (Throwable ex) { // try to cope with OOME |
865 |
if (oldLen > 0) |
866 |
maxCapacity = oldLen; // avoid continuous failure |
867 |
return 0; |
868 |
} |
869 |
array = newArray; |
870 |
int t = tail, oldMask = oldLen - 1, newMask = newLen - 1; |
871 |
if (oldArray != null && oldMask >= 0 && newMask >= oldMask) { |
872 |
for (int j = head; j != t; ++j) { // races with consumer |
873 |
Object x; |
874 |
int i = j & oldMask; |
875 |
if ((x = oldArray[i]) != null && |
876 |
U.compareAndSwapObject(oldArray, |
877 |
(((long)i) << ASHIFT) + ABASE, |
878 |
x, null)) |
879 |
newArray[j & newMask] = x; |
880 |
} |
881 |
} |
882 |
newArray[t & newMask] = item; |
883 |
tail = t + 1; |
884 |
return oldLen + 1; |
885 |
} |
886 |
|
887 |
/** |
888 |
* Spins/helps/blocks while offer returns 0 |
889 |
*/ |
890 |
final int submit(T item) { |
891 |
int stat; |
892 |
if ((stat = offer(item)) == 0) { |
893 |
Thread thread = Thread.currentThread(); |
894 |
if ((thread instanceof ForkJoinWorkerThread) && |
895 |
((ForkJoinWorkerThread)thread).getPool() == executor) { |
896 |
for (ForkJoinTask<?> t;;) { // try helping |
897 |
if ((t = ForkJoinTask.peekNextLocalTask()) == null || |
898 |
!(t instanceof BufferedSubscription)) |
899 |
break; |
900 |
if (t.tryUnfork()) |
901 |
((BufferedSubscription<?>)t).exec(); |
902 |
if ((stat = offer(item)) != 0) |
903 |
break; |
904 |
} |
905 |
} |
906 |
if (stat == 0) { |
907 |
putItem = item; |
908 |
timeout = 0L; |
909 |
try { |
910 |
ForkJoinPool.managedBlock(this); |
911 |
} catch (InterruptedException ie) { |
912 |
timeout = INTERRUPTED; |
913 |
} |
914 |
stat = putStat; |
915 |
if (timeout < 0L) |
916 |
Thread.currentThread().interrupt(); |
917 |
} |
918 |
} |
919 |
return stat; |
920 |
} |
921 |
|
922 |
/** |
923 |
* Timeout version of offer |
924 |
*/ |
925 |
final int offerNanos(T item, long nanos) { |
926 |
int stat; |
927 |
if ((stat = offer(item)) == 0 && nanos > 0L) { |
928 |
Thread thread = Thread.currentThread(); |
929 |
if ((thread instanceof ForkJoinWorkerThread) && |
930 |
((ForkJoinWorkerThread)thread).getPool() == executor) { |
931 |
long deadline = System.nanoTime() + nanos; |
932 |
for (ForkJoinTask<?> t;;) { // similar to above |
933 |
if ((t = ForkJoinTask.peekNextLocalTask()) == null || |
934 |
!(t instanceof BufferedSubscription)) |
935 |
break; |
936 |
if (t.tryUnfork()) |
937 |
((BufferedSubscription<?>)t).exec(); |
938 |
if ((stat = offer(item)) != 0 || |
939 |
(nanos = deadline - System.nanoTime()) <= 0L) |
940 |
break; |
941 |
} |
942 |
} |
943 |
if (stat == 0 && (timeout = nanos) > 0L) { |
944 |
putItem = item; |
945 |
try { |
946 |
ForkJoinPool.managedBlock(this); |
947 |
} catch (InterruptedException ie) { |
948 |
timeout = INTERRUPTED; |
949 |
} |
950 |
stat = putStat; |
951 |
if (timeout < 0L) |
952 |
Thread.currentThread().interrupt(); |
953 |
} |
954 |
} |
955 |
return stat; |
956 |
} |
957 |
|
958 |
/** |
959 |
* Nulls out most fields, mainly to avoid garbage retention |
960 |
* until publisher unsubscribes, but also to help cleanly stop |
961 |
* upon error by nulling required components. |
962 |
*/ |
963 |
final void detach() { |
964 |
pendingError = null; |
965 |
subscriber = null; |
966 |
executor = null; |
967 |
array = null; |
968 |
Thread w = waiter; |
969 |
if (w != null) { |
970 |
waiter = null; |
971 |
LockSupport.unpark(w); // force wakeup |
972 |
} |
973 |
} |
974 |
|
975 |
/** |
976 |
* Issues error signal, asynchronously if a task is running, |
977 |
* else synchronously |
978 |
*/ |
979 |
final void onError(Throwable ex) { |
980 |
for (int c;;) { |
981 |
if ((c = ctl) == DISABLED) |
982 |
break; |
983 |
else if ((c & ACTIVE) != 0) { |
984 |
pendingError = ex; |
985 |
if (U.compareAndSwapInt(this, CTL, c, c | ERROR)) |
986 |
break; // cause consumer task to exit |
987 |
} |
988 |
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) { |
989 |
Flow.Subscriber<? super T> s = subscriber; |
990 |
if (s != null && ex != null) { |
991 |
try { |
992 |
s.onError(ex); |
993 |
} catch (Throwable ignore) { |
994 |
} |
995 |
} |
996 |
detach(); |
997 |
break; |
998 |
} |
999 |
} |
1000 |
} |
1001 |
|
1002 |
/** |
1003 |
* Tries to start consumer task upon a signal or request; |
1004 |
* disables on failure. |
1005 |
*/ |
1006 |
final void startOrDisable() { |
1007 |
Executor e; // skip if already disabled |
1008 |
if ((e = executor) != null) { |
1009 |
try { |
1010 |
e.execute(this); |
1011 |
} catch (Throwable ex) { // back out and force signal |
1012 |
for (int c;;) { |
1013 |
if ((c = ctl) == DISABLED || (c & ACTIVE) == 0) |
1014 |
break; |
1015 |
if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE)) { |
1016 |
onError(ex); |
1017 |
break; |
1018 |
} |
1019 |
} |
1020 |
} |
1021 |
} |
1022 |
} |
1023 |
|
1024 |
final void onComplete() { |
1025 |
for (int c;;) { |
1026 |
if ((c = ctl) == DISABLED) |
1027 |
break; |
1028 |
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | COMPLETE))) { |
1029 |
if ((c & ACTIVE) == 0) |
1030 |
startOrDisable(); |
1031 |
break; |
1032 |
} |
1033 |
} |
1034 |
} |
1035 |
|
1036 |
final void onSubscribe() { |
1037 |
for (int c;;) { |
1038 |
if ((c = ctl) == DISABLED) |
1039 |
break; |
1040 |
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | SUBSCRIBE))) { |
1041 |
if ((c & ACTIVE) == 0) |
1042 |
startOrDisable(); |
1043 |
break; |
1044 |
} |
1045 |
} |
1046 |
} |
1047 |
|
1048 |
/** |
1049 |
* Causes consumer task to exit if active (without reporting |
1050 |
* onError unless there is already a pending error), and |
1051 |
* disables. |
1052 |
*/ |
1053 |
public void cancel() { |
1054 |
for (int c;;) { |
1055 |
if ((c = ctl) == DISABLED) |
1056 |
break; |
1057 |
else if ((c & ACTIVE) != 0) { |
1058 |
if (U.compareAndSwapInt(this, CTL, c, c | ERROR)) |
1059 |
break; |
1060 |
} |
1061 |
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) { |
1062 |
detach(); |
1063 |
break; |
1064 |
} |
1065 |
} |
1066 |
} |
1067 |
|
1068 |
/** |
1069 |
* Adds to demand and possibly starts task. |
1070 |
*/ |
1071 |
public void request(long n) { |
1072 |
if (n > 0L) { |
1073 |
for (;;) { |
1074 |
long prev = demand, d; |
1075 |
if ((d = prev + n) < prev) // saturate |
1076 |
d = Long.MAX_VALUE; |
1077 |
if (U.compareAndSwapLong(this, DEMAND, prev, d)) { |
1078 |
for (int c, h;;) { |
1079 |
if (((c = ctl) & (ACTIVE | DISABLED)) != 0 || |
1080 |
demand == 0L) |
1081 |
break; |
1082 |
if ((h = head) != tail) { |
1083 |
if (U.compareAndSwapInt(this, CTL, c, |
1084 |
c | ACTIVE)) { |
1085 |
startOrDisable(); |
1086 |
break; |
1087 |
} |
1088 |
} |
1089 |
else if (head == h && tail == h) |
1090 |
break; |
1091 |
} |
1092 |
break; |
1093 |
} |
1094 |
} |
1095 |
} |
1096 |
else if (n < 0L) |
1097 |
onError(new IllegalArgumentException( |
1098 |
"negative subscription request")); |
1099 |
} |
1100 |
|
1101 |
public final boolean isReleasable() { // for ManagedBlocker |
1102 |
T item = putItem; |
1103 |
if (item != null) { |
1104 |
if ((putStat = offer(item)) == 0) |
1105 |
return false; |
1106 |
putItem = null; |
1107 |
} |
1108 |
return true; |
1109 |
} |
1110 |
|
1111 |
public final boolean block() { // for ManagedBlocker |
1112 |
T item = putItem; |
1113 |
if (item != null) { |
1114 |
putItem = null; |
1115 |
long nanos = timeout; |
1116 |
long deadline = (nanos > 0L) ? System.nanoTime() + nanos : 0L; |
1117 |
while ((putStat = offer(item)) == 0) { |
1118 |
if (Thread.interrupted()) { |
1119 |
timeout = INTERRUPTED; |
1120 |
if (nanos > 0L) |
1121 |
break; |
1122 |
} |
1123 |
else if (nanos > 0L && |
1124 |
(nanos = deadline - System.nanoTime()) <= 0L) |
1125 |
break; |
1126 |
else if (waiter == null) |
1127 |
waiter = Thread.currentThread(); |
1128 |
else { |
1129 |
if (nanos > 0L) |
1130 |
LockSupport.parkNanos(this, nanos); |
1131 |
else |
1132 |
LockSupport.park(this); |
1133 |
waiter = null; |
1134 |
} |
1135 |
} |
1136 |
} |
1137 |
waiter = null; |
1138 |
return true; |
1139 |
} |
1140 |
|
1141 |
/** |
1142 |
* Consumer task loop; supports resubmission when used as |
1143 |
* ForkJoinTask. |
1144 |
*/ |
1145 |
public final boolean exec() { |
1146 |
Flow.Subscriber<? super T> s; |
1147 |
if ((s = subscriber) != null) { // else disabled |
1148 |
for (;;) { |
1149 |
long d = demand; // read volatile fields in acceptable order |
1150 |
int c = ctl; |
1151 |
int h = head; |
1152 |
int t = tail; |
1153 |
Object[] a = array; |
1154 |
int i, n; Object x; Thread w; |
1155 |
if ((c & (ERROR | SUBSCRIBE | DISABLED)) != 0) { |
1156 |
if ((c & ERROR) != 0) { |
1157 |
Throwable ex = pendingError; |
1158 |
ctl = DISABLED; // no need for CAS |
1159 |
if (ex != null) { |
1160 |
try { |
1161 |
s.onError(ex); |
1162 |
} catch (Throwable ignore) { |
1163 |
} |
1164 |
} |
1165 |
} |
1166 |
else if ((c & SUBSCRIBE) != 0) { |
1167 |
if (U.compareAndSwapInt(this, CTL, c, |
1168 |
c & ~SUBSCRIBE)) { |
1169 |
try { |
1170 |
s.onSubscribe(this); |
1171 |
} catch (Throwable ex) { |
1172 |
ctl = DISABLED; // disable on throw |
1173 |
} |
1174 |
} |
1175 |
} |
1176 |
else { |
1177 |
detach(); |
1178 |
break; |
1179 |
} |
1180 |
} |
1181 |
else if (h == t) { // empty |
1182 |
if (h == tail && |
1183 |
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE)) { |
1184 |
if (h != tail || c != (c = ctl)) { // recheck |
1185 |
if ((c & (ACTIVE | DISABLED)) != 0 || |
1186 |
!U.compareAndSwapInt(this, CTL, c, |
1187 |
c | ACTIVE)) |
1188 |
break; |
1189 |
} |
1190 |
else if ((c & COMPLETE) != 0) { |
1191 |
ctl = DISABLED; |
1192 |
try { |
1193 |
s.onComplete(); |
1194 |
} catch (Throwable ignore) { |
1195 |
} |
1196 |
} |
1197 |
else |
1198 |
break; |
1199 |
} |
1200 |
} |
1201 |
else if (a == null || (n = a.length) == 0 || |
1202 |
(x = a[i = h & (n - 1)]) == null) |
1203 |
; // stale; retry |
1204 |
else if (d == 0L) { // can't take |
1205 |
if (demand == 0L && |
1206 |
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE) && |
1207 |
((demand == 0L && c == (c = ctl)) || // recheck |
1208 |
(c & (ACTIVE | DISABLED)) != 0 || |
1209 |
!U.compareAndSwapInt(this, CTL, c, c | ACTIVE))) |
1210 |
break; |
1211 |
} |
1212 |
else if (U.compareAndSwapObject( |
1213 |
a, (((long)i) << ASHIFT) + ABASE, x, null)) { |
1214 |
U.putOrderedInt(this, HEAD, h + 1); |
1215 |
while (!U.compareAndSwapLong(this, DEMAND, d, d - 1L)) |
1216 |
d = demand; // almost never fails |
1217 |
if ((w = waiter) != null) { |
1218 |
waiter = null; |
1219 |
LockSupport.unpark(w); // release producer |
1220 |
} |
1221 |
try { |
1222 |
@SuppressWarnings("unchecked") T y = (T) x; |
1223 |
s.onNext(y); |
1224 |
} catch (Throwable ex) { // disable on throw |
1225 |
ctl = DISABLED; |
1226 |
} |
1227 |
} |
1228 |
} |
1229 |
} |
1230 |
return false; // resubmittable; never joined |
1231 |
} |
1232 |
|
1233 |
// Runnable and FJ support |
1234 |
public final void run() { exec(); } |
1235 |
public final Void getRawResult() { return null; } |
1236 |
public final void setRawResult(Void v) {} |
1237 |
|
1238 |
// Unsafe mechanics |
1239 |
private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); |
1240 |
private static final long CTL; |
1241 |
private static final long TAIL; |
1242 |
private static final long HEAD; |
1243 |
private static final long DEMAND; |
1244 |
private static final int ABASE; |
1245 |
private static final int ASHIFT; |
1246 |
|
1247 |
static { |
1248 |
try { |
1249 |
CTL = U.objectFieldOffset |
1250 |
(BufferedSubscription.class.getDeclaredField("ctl")); |
1251 |
TAIL = U.objectFieldOffset |
1252 |
(BufferedSubscription.class.getDeclaredField("tail")); |
1253 |
HEAD = U.objectFieldOffset |
1254 |
(BufferedSubscription.class.getDeclaredField("head")); |
1255 |
DEMAND = U.objectFieldOffset |
1256 |
(BufferedSubscription.class.getDeclaredField("demand")); |
1257 |
|
1258 |
ABASE = U.arrayBaseOffset(Object[].class); |
1259 |
int scale = U.arrayIndexScale(Object[].class); |
1260 |
if ((scale & (scale - 1)) != 0) |
1261 |
throw new Error("data type scale not a power of two"); |
1262 |
ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
1263 |
} catch (ReflectiveOperationException e) { |
1264 |
throw new Error(e); |
1265 |
} |
1266 |
} |
1267 |
} |
1268 |
} |