110 |
|
* |
111 |
|
* <p>This implementation rejects submitted tasks (that is, by throwing |
112 |
|
* {@link RejectedExecutionException}) only when the pool is shut down |
113 |
< |
* or internal resources have been exhuasted. |
113 |
> |
* or internal resources have been exhausted. |
114 |
|
* |
115 |
|
* @since 1.7 |
116 |
|
* @author Doug Lea |
156 |
|
* ForkJoinWorkerThread.helpJoinTask tracks joining->stealing |
157 |
|
* links to try to find such a task. |
158 |
|
* |
159 |
< |
* Compensating: Unless there are already enough live threads, |
160 |
< |
* creating or or re-activating a spare thread to compensate |
161 |
< |
* for the (blocked) joiner until it unblocks. Spares then |
162 |
< |
* suspend at their next opportunity or eventually die if |
163 |
< |
* unused for too long. See below and the internal |
164 |
< |
* documentation for tryAwaitJoin for more details about |
165 |
< |
* compensation rules. |
159 |
> |
* Compensating: Unless there are already enough live threads, |
160 |
> |
* method helpMaintainParallelism() may create or or |
161 |
> |
* re-activate a spare thread to compensate for blocked |
162 |
> |
* joiners until they unblock. |
163 |
|
* |
164 |
|
* Because the determining existence of conservatively safe |
165 |
|
* helping targets, the availability of already-created spares, |
166 |
|
* and the apparent need to create new spares are all racy and |
167 |
< |
* require heuristic guidance, joins (in |
168 |
< |
* ForkJoinWorkerThread.joinTask) interleave these options until |
169 |
< |
* successful. Creating a new spare always succeeds, but also |
170 |
< |
* increases application footprint, so we try to avoid it, within |
171 |
< |
* reason. |
167 |
> |
* require heuristic guidance, we rely on multiple retries of |
168 |
> |
* each. Further, because it is impossible to keep exactly the |
169 |
> |
* target (parallelism) number of threads running at any given |
170 |
> |
* time, we allow compensation during joins to fail, and enlist |
171 |
> |
* all other threads to help out whenever they are not otherwise |
172 |
> |
* occupied (i.e., mainly in method preStep). |
173 |
|
* |
174 |
< |
* The ManagedBlocker extension API can't use helping so uses a |
175 |
< |
* special version of compensation in method awaitBlocker. |
174 |
> |
* The ManagedBlocker extension API can't use helping so relies |
175 |
> |
* only on compensation in method awaitBlocker. |
176 |
|
* |
177 |
|
* The main throughput advantages of work-stealing stem from |
178 |
|
* decentralized control -- workers mostly steal tasks from each |
205 |
|
* blocked workers. However, all other support code is set up to |
206 |
|
* work with other policies. |
207 |
|
* |
208 |
+ |
* To ensure that we do not hold on to worker references that |
209 |
+ |
* would prevent GC, ALL accesses to workers are via indices into |
210 |
+ |
* the workers array (which is one source of some of the unusual |
211 |
+ |
* code constructions here). In essence, the workers array serves |
212 |
+ |
* as a WeakReference mechanism. Thus for example the event queue |
213 |
+ |
* stores worker indices, not worker references. Access to the |
214 |
+ |
* workers in associated methods (for example releaseEventWaiters) |
215 |
+ |
* must both index-check and null-check the IDs. All such accesses |
216 |
+ |
* ignore bad IDs by returning out early from what they are doing, |
217 |
+ |
* since this can only be associated with shutdown, in which case |
218 |
+ |
* it is OK to give up. On termination, we just clobber these |
219 |
+ |
* data structures without trying to use them. |
220 |
+ |
* |
221 |
|
* 2. Bookkeeping for dynamically adding and removing workers. We |
222 |
|
* aim to approximately maintain the given level of parallelism. |
223 |
|
* When some workers are known to be blocked (on joins or via |
259 |
|
* workers that previously could not find a task to now find one: |
260 |
|
* Submission of a new task to the pool, or another worker pushing |
261 |
|
* a task onto a previously empty queue. (We also use this |
262 |
< |
* mechanism for termination and reconfiguration actions that |
262 |
> |
* mechanism for configuration and termination actions that |
263 |
|
* require wakeups of idle workers). Each worker maintains its |
264 |
|
* last known event count, and blocks when a scan for work did not |
265 |
|
* find a task AND its lastEventCount matches the current |
270 |
|
* a record (field nextEventWaiter) for the next waiting worker. |
271 |
|
* In addition to allowing simpler decisions about need for |
272 |
|
* wakeup, the event count bits in eventWaiters serve the role of |
273 |
< |
* tags to avoid ABA errors in Treiber stacks. To reduce delays |
274 |
< |
* in task diffusion, workers not otherwise occupied may invoke |
275 |
< |
* method releaseWaiters, that removes and signals (unparks) |
276 |
< |
* workers not waiting on current count. To minimize task |
277 |
< |
* production stalls associate with signalling, any worker pushing |
278 |
< |
* a task on an empty queue invokes the weaker method signalWork, |
279 |
< |
* that only releases idle workers until it detects interference |
269 |
< |
* by other threads trying to release, and lets them take |
270 |
< |
* over. The net effect is a tree-like diffusion of signals, where |
271 |
< |
* released threads (and possibly others) help with unparks. To |
272 |
< |
* further reduce contention effects a bit, failed CASes to |
273 |
< |
* increment field eventCount are tolerated without retries. |
273 |
> |
* tags to avoid ABA errors in Treiber stacks. Upon any wakeup, |
274 |
> |
* released threads also try to release others (but give up upon |
275 |
> |
* contention to reduce useless flailing). The net effect is a |
276 |
> |
* tree-like diffusion of signals, where released threads (and |
277 |
> |
* possibly others) help with unparks. To further reduce |
278 |
> |
* contention effects a bit, failed CASes to increment field |
279 |
> |
* eventCount are tolerated without retries in signalWork. |
280 |
|
* Conceptually they are merged into the same event, which is OK |
281 |
|
* when their only purpose is to enable workers to scan for work. |
282 |
|
* |
291 |
|
* spare threads from normal "core" threads: On each call to |
292 |
|
* preStep (the only point at which we can do this) a worker |
293 |
|
* checks to see if there are now too many running workers, and if |
294 |
< |
* so, suspends itself. Methods tryAwaitJoin and awaitBlocker |
295 |
< |
* look for suspended threads to resume before considering |
296 |
< |
* creating a new replacement. We don't need a special data |
297 |
< |
* structure to maintain spares; simply scanning the workers array |
298 |
< |
* looking for worker.isSuspended() is fine because the calling |
299 |
< |
* thread is otherwise not doing anything useful anyway; we are at |
300 |
< |
* least as happy if after locating a spare, the caller doesn't |
301 |
< |
* actually block because the join is ready before we try to |
302 |
< |
* adjust and compensate. Note that this is intrinsically racy. |
303 |
< |
* One thread may become a spare at about the same time as another |
304 |
< |
* is needlessly being created. We counteract this and related |
305 |
< |
* slop in part by requiring resumed spares to immediately recheck |
306 |
< |
* (in preStep) to see whether they they should re-suspend. The |
307 |
< |
* only effective difference between "extra" and "core" threads is |
308 |
< |
* that we allow the "extra" ones to time out and die if they are |
309 |
< |
* not resumed within a keep-alive interval of a few seconds. This |
310 |
< |
* is implemented mainly within ForkJoinWorkerThread, but requires |
311 |
< |
* some coordination (isTrimmed() -- meaning killed while |
312 |
< |
* suspended) to correctly maintain pool counts. |
313 |
< |
* |
314 |
< |
* 6. Deciding when to create new workers. The main dynamic |
315 |
< |
* control in this class is deciding when to create extra threads, |
316 |
< |
* in methods awaitJoin and awaitBlocker. We always need to create |
317 |
< |
* one when the number of running threads would become zero and |
318 |
< |
* all workers are busy. However, this is not easy to detect |
319 |
< |
* reliably in the presence of transients so we use retries and |
320 |
< |
* allow slack (in tryAwaitJoin) to reduce false alarms. These |
321 |
< |
* effectively reduce churn at the price of systematically |
322 |
< |
* undershooting target parallelism when many threads are blocked. |
323 |
< |
* However, biasing toward undeshooting partially compensates for |
324 |
< |
* the above mechanics to suspend extra threads, that normally |
325 |
< |
* lead to overshoot because we can only suspend workers |
326 |
< |
* in-between top-level actions. It also better copes with the |
327 |
< |
* fact that some of the methods in this class tend to never |
328 |
< |
* become compiled (but are interpreted), so some components of |
329 |
< |
* the entire set of controls might execute many times faster than |
330 |
< |
* others. And similarly for cases where the apparent lack of work |
331 |
< |
* is just due to GC stalls and other transient system activity. |
294 |
> |
* so, suspends itself. Method helpMaintainParallelism looks for |
295 |
> |
* suspended threads to resume before considering creating a new |
296 |
> |
* replacement. The spares themselves are encoded on another |
297 |
> |
* variant of a Treiber Stack, headed at field "spareWaiters". |
298 |
> |
* Note that the use of spares is intrinsically racy. One thread |
299 |
> |
* may become a spare at about the same time as another is |
300 |
> |
* needlessly being created. We counteract this and related slop |
301 |
> |
* in part by requiring resumed spares to immediately recheck (in |
302 |
> |
* preStep) to see whether they they should re-suspend. |
303 |
> |
* |
304 |
> |
* 6. Killing off unneeded workers. The Spare and Event queues use |
305 |
> |
* similar mechanisms to shed unused workers: The oldest (first) |
306 |
> |
* waiter uses a timed rather than hard wait. When this wait times |
307 |
> |
* out without a normal wakeup, it tries to shutdown any one (for |
308 |
> |
* convenience the newest) other waiter via tryShutdownSpare or |
309 |
> |
* tryShutdownWaiter, respectively. The wakeup rates for spares |
310 |
> |
* are much shorter than for waiters. Together, they will |
311 |
> |
* eventually reduce the number of worker threads to a minimum of |
312 |
> |
* one after a long enough period without use. |
313 |
> |
* |
314 |
> |
* 7. Deciding when to create new workers. The main dynamic |
315 |
> |
* control in this class is deciding when to create extra threads |
316 |
> |
* in method helpMaintainParallelism. We would like to keep |
317 |
> |
* exactly #parallelism threads running, which is an impossble |
318 |
> |
* task. We always need to create one when the number of running |
319 |
> |
* threads would become zero and all workers are busy. Beyond |
320 |
> |
* this, we must rely on heuristics that work well in the the |
321 |
> |
* presence of transients phenomena such as GC stalls, dynamic |
322 |
> |
* compilation, and wake-up lags. These transients are extremely |
323 |
> |
* common -- we are normally trying to fully saturate the CPUs on |
324 |
> |
* a machine, so almost any activity other than running tasks |
325 |
> |
* impedes accuracy. Our main defense is to allow some slack in |
326 |
> |
* creation thresholds, using rules that reflect the fact that the |
327 |
> |
* more threads we have running, the more likely that we are |
328 |
> |
* underestimating the number running threads. (We also include |
329 |
> |
* some heuristic use of Thread.yield when all workers appear to |
330 |
> |
* be busy, to improve likelihood of counts settling.) The rules |
331 |
> |
* also better cope with the fact that some of the methods in this |
332 |
> |
* class tend to never become compiled (but are interpreted), so |
333 |
> |
* some components of the entire set of controls might execute 100 |
334 |
> |
* times faster than others. And similarly for cases where the |
335 |
> |
* apparent lack of work is just due to GC stalls and other |
336 |
> |
* transient system activity. |
337 |
|
* |
338 |
|
* Beware that there is a lot of representation-level coupling |
339 |
|
* among classes ForkJoinPool, ForkJoinWorkerThread, and |
346 |
|
* |
347 |
|
* Style notes: There are lots of inline assignments (of form |
348 |
|
* "while ((local = field) != 0)") which are usually the simplest |
349 |
< |
* way to ensure read orderings. Also several occurrences of the |
350 |
< |
* unusual "do {} while(!cas...)" which is the simplest way to |
351 |
< |
* force an update of a CAS'ed variable. There are also other |
352 |
< |
* coding oddities that help some methods perform reasonably even |
353 |
< |
* when interpreted (not compiled), at the expense of messiness. |
349 |
> |
* way to ensure the required read orderings (which are sometimes |
350 |
> |
* critical). Also several occurrences of the unusual "do {} |
351 |
> |
* while(!cas...)" which is the simplest way to force an update of |
352 |
> |
* a CAS'ed variable. There are also other coding oddities that |
353 |
> |
* help some methods perform reasonably even when interpreted (not |
354 |
> |
* compiled), at the expense of some messy constructions that |
355 |
> |
* reduce byte code counts. |
356 |
|
* |
357 |
|
* The order of declarations in this file is: (1) statics (2) |
358 |
|
* fields (along with constants used when unpacking some of them) |
420 |
|
new AtomicInteger(); |
421 |
|
|
422 |
|
/** |
423 |
< |
* Absolute bound for parallelism level. Twice this number must |
424 |
< |
* fit into a 16bit field to enable word-packing for some counts. |
423 |
> |
* The wakeup interval (in nanoseconds) for the oldest worker |
424 |
> |
* worker waiting for an event invokes tryShutdownWaiter to shrink |
425 |
> |
* the number of workers. The exact value does not matter too |
426 |
> |
* much, but should be long enough to slowly release resources |
427 |
> |
* during long periods without use without disrupting normal use. |
428 |
> |
*/ |
429 |
> |
private static final long SHRINK_RATE_NANOS = |
430 |
> |
60L * 1000L * 1000L * 1000L; // one minute |
431 |
> |
|
432 |
> |
/** |
433 |
> |
* Absolute bound for parallelism level. Twice this number plus |
434 |
> |
* one (i.e., 0xfff) must fit into a 16bit field to enable |
435 |
> |
* word-packing for some counts and indices. |
436 |
|
*/ |
437 |
< |
private static final int MAX_THREADS = 0x7fff; |
437 |
> |
private static final int MAX_WORKERS = 0x7fff; |
438 |
|
|
439 |
|
/** |
440 |
|
* Array holding all worker threads in the pool. Array size must |
476 |
|
/** |
477 |
|
* Encoded record of top of treiber stack of threads waiting for |
478 |
|
* events. The top 32 bits contain the count being waited for. The |
479 |
< |
* bottom word contains one plus the pool index of waiting worker |
480 |
< |
* thread. |
479 |
> |
* bottom 16 bits contains one plus the pool index of waiting |
480 |
> |
* worker thread. (Bits 16-31 are unused.) |
481 |
|
*/ |
482 |
|
private volatile long eventWaiters; |
483 |
|
|
484 |
|
private static final int EVENT_COUNT_SHIFT = 32; |
485 |
< |
private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L; |
485 |
> |
private static final long WAITER_ID_MASK = (1L << 16) - 1L; |
486 |
|
|
487 |
|
/** |
488 |
|
* A counter for events that may wake up worker threads: |
489 |
|
* - Submission of a new task to the pool |
490 |
|
* - A worker pushing a task on an empty queue |
491 |
< |
* - termination and reconfiguration |
491 |
> |
* - termination |
492 |
|
*/ |
493 |
|
private volatile int eventCount; |
494 |
|
|
495 |
|
/** |
496 |
+ |
* Encoded record of top of treiber stack of spare threads waiting |
497 |
+ |
* for resumption. The top 16 bits contain an arbitrary count to |
498 |
+ |
* avoid ABA effects. The bottom 16bits contains one plus the pool |
499 |
+ |
* index of waiting worker thread. |
500 |
+ |
*/ |
501 |
+ |
private volatile int spareWaiters; |
502 |
+ |
|
503 |
+ |
private static final int SPARE_COUNT_SHIFT = 16; |
504 |
+ |
private static final int SPARE_ID_MASK = (1 << 16) - 1; |
505 |
+ |
|
506 |
+ |
/** |
507 |
|
* Lifecycle control. The low word contains the number of workers |
508 |
|
* that are (probably) executing tasks. This value is atomically |
509 |
|
* incremented before a worker gets a task to run, and decremented |
514 |
|
* These are bundled together to ensure consistent read for |
515 |
|
* termination checks (i.e., that runLevel is at least SHUTDOWN |
516 |
|
* and active threads is zero). |
517 |
+ |
* |
518 |
+ |
* Notes: Most direct CASes are dependent on these bitfield |
519 |
+ |
* positions. Also, this field is non-private to enable direct |
520 |
+ |
* performance-sensitive CASes in ForkJoinWorkerThread. |
521 |
|
*/ |
522 |
< |
private volatile int runState; |
522 |
> |
volatile int runState; |
523 |
|
|
524 |
|
// Note: The order among run level values matters. |
525 |
|
private static final int RUNLEVEL_SHIFT = 16; |
527 |
|
private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1); |
528 |
|
private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2); |
529 |
|
private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1; |
491 |
– |
private static final int ONE_ACTIVE = 1; // active update delta |
530 |
|
|
531 |
|
/** |
532 |
|
* Holds number of total (i.e., created and not yet terminated) |
567 |
|
*/ |
568 |
|
private final int poolNumber; |
569 |
|
|
570 |
< |
// Utilities for CASing fields. Note that several of these |
571 |
< |
// are manually inlined by callers |
570 |
> |
|
571 |
> |
// Utilities for CASing fields. Note that most of these |
572 |
> |
// are usually manually inlined by callers |
573 |
|
|
574 |
|
/** |
575 |
< |
* Increments running count. Also used by ForkJoinTask. |
575 |
> |
* Increments running count part of workerCounts |
576 |
|
*/ |
577 |
|
final void incrementRunningCount() { |
578 |
|
int c; |
593 |
|
} |
594 |
|
|
595 |
|
/** |
596 |
< |
* Tries to increment running count |
596 |
> |
* Forces decrement of encoded workerCounts, awaiting nonzero if |
597 |
> |
* (rarely) necessary when other count updates lag. |
598 |
> |
* |
599 |
> |
* @param dr -- either zero or ONE_RUNNING |
600 |
> |
* @param dt == either zero or ONE_TOTAL |
601 |
|
*/ |
602 |
< |
final boolean tryIncrementRunningCount() { |
603 |
< |
int wc; |
604 |
< |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
605 |
< |
wc = workerCounts, wc + ONE_RUNNING); |
602 |
> |
private void decrementWorkerCounts(int dr, int dt) { |
603 |
> |
for (;;) { |
604 |
> |
int wc = workerCounts; |
605 |
> |
if ((wc & RUNNING_COUNT_MASK) - dr < 0 || |
606 |
> |
(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) { |
607 |
> |
if ((runState & TERMINATED) != 0) |
608 |
> |
return; // lagging termination on a backout |
609 |
> |
Thread.yield(); |
610 |
> |
} |
611 |
> |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
612 |
> |
wc, wc - (dr + dt))) |
613 |
> |
return; |
614 |
> |
} |
615 |
> |
} |
616 |
> |
|
617 |
> |
/** |
618 |
> |
* Increments event count |
619 |
> |
*/ |
620 |
> |
private void advanceEventCount() { |
621 |
> |
int c; |
622 |
> |
do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset, |
623 |
> |
c = eventCount, c+1)); |
624 |
|
} |
625 |
|
|
626 |
|
/** |
632 |
|
final boolean tryIncrementActiveCount() { |
633 |
|
int c; |
634 |
|
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
635 |
< |
c = runState, c + ONE_ACTIVE); |
635 |
> |
c = runState, c + 1); |
636 |
|
} |
637 |
|
|
638 |
|
/** |
642 |
|
final boolean tryDecrementActiveCount() { |
643 |
|
int c; |
644 |
|
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
645 |
< |
c = runState, c - ONE_ACTIVE); |
645 |
> |
c = runState, c - 1); |
646 |
|
} |
647 |
|
|
648 |
|
/** |
671 |
|
lock.lock(); |
672 |
|
try { |
673 |
|
ForkJoinWorkerThread[] ws = workers; |
674 |
< |
int nws = ws.length; |
675 |
< |
if (k < 0 || k >= nws || ws[k] != null) { |
676 |
< |
for (k = 0; k < nws && ws[k] != null; ++k) |
674 |
> |
int n = ws.length; |
675 |
> |
if (k < 0 || k >= n || ws[k] != null) { |
676 |
> |
for (k = 0; k < n && ws[k] != null; ++k) |
677 |
|
; |
678 |
< |
if (k == nws) |
679 |
< |
ws = Arrays.copyOf(ws, nws << 1); |
678 |
> |
if (k == n) |
679 |
> |
ws = Arrays.copyOf(ws, n << 1); |
680 |
|
} |
681 |
|
ws[k] = w; |
682 |
|
workers = ws; // volatile array write ensures slot visibility |
710 |
|
* are already updated to accommodate the worker, so adjusts on |
711 |
|
* failure. |
712 |
|
* |
713 |
< |
* @return new worker or null if creation failed |
713 |
> |
* @return the worker, or null on failure |
714 |
|
*/ |
715 |
|
private ForkJoinWorkerThread addWorker() { |
716 |
|
ForkJoinWorkerThread w = null; |
717 |
|
try { |
718 |
|
w = factory.newThread(this); |
719 |
|
} finally { // Adjust on either null or exceptional factory return |
720 |
< |
if (w == null) |
721 |
< |
onWorkerCreationFailure(); |
720 |
> |
if (w == null) { |
721 |
> |
decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL); |
722 |
> |
tryTerminate(false); // in case of failure during shutdown |
723 |
> |
} |
724 |
|
} |
725 |
< |
if (w != null) |
725 |
> |
if (w != null) { |
726 |
|
w.start(recordWorker(w), ueh); |
727 |
+ |
advanceEventCount(); |
728 |
+ |
} |
729 |
|
return w; |
730 |
|
} |
731 |
|
|
732 |
|
/** |
733 |
< |
* Adjusts counts upon failure to create worker |
733 |
> |
* Final callback from terminating worker. Removes record of |
734 |
> |
* worker from array, and adjusts counts. If pool is shutting |
735 |
> |
* down, tries to complete terminatation. |
736 |
> |
* |
737 |
> |
* @param w the worker |
738 |
|
*/ |
739 |
< |
private void onWorkerCreationFailure() { |
740 |
< |
for (;;) { |
741 |
< |
int wc = workerCounts; |
742 |
< |
int rc = wc & RUNNING_COUNT_MASK; |
743 |
< |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
744 |
< |
if (rc == 0 || wc == 0) |
745 |
< |
Thread.yield(); // must wait for other counts to settle |
746 |
< |
else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
747 |
< |
wc - (ONE_RUNNING|ONE_TOTAL))) |
739 |
> |
final void workerTerminated(ForkJoinWorkerThread w) { |
740 |
> |
forgetWorker(w); |
741 |
> |
decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL); |
742 |
> |
while (w.stealCount != 0) // collect final count |
743 |
> |
tryAccumulateStealCount(w); |
744 |
> |
tryTerminate(false); |
745 |
> |
} |
746 |
> |
|
747 |
> |
// Waiting for and signalling events |
748 |
> |
|
749 |
> |
/** |
750 |
> |
* Releases workers blocked on a count not equal to current count. |
751 |
> |
* Normally called after precheck that eventWaiters isn't zero to |
752 |
> |
* avoid wasted array checks. Gives up upon a change in count or |
753 |
> |
* contention, letting other workers take over. |
754 |
> |
*/ |
755 |
> |
private void releaseEventWaiters() { |
756 |
> |
ForkJoinWorkerThread[] ws = workers; |
757 |
> |
int n = ws.length; |
758 |
> |
long h = eventWaiters; |
759 |
> |
int ec = eventCount; |
760 |
> |
ForkJoinWorkerThread w; int id; |
761 |
> |
while ((int)(h >>> EVENT_COUNT_SHIFT) != ec && |
762 |
> |
(id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 && |
763 |
> |
id < n && (w = ws[id]) != null && |
764 |
> |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
765 |
> |
h, h = w.nextWaiter)) { |
766 |
> |
LockSupport.unpark(w); |
767 |
> |
if (eventWaiters != h || eventCount != ec) |
768 |
|
break; |
769 |
|
} |
681 |
– |
tryTerminate(false); // in case of failure during shutdown |
770 |
|
} |
771 |
|
|
772 |
|
/** |
773 |
< |
* Creates enough total workers to establish target parallelism, |
774 |
< |
* giving up if terminating or addWorker fails |
773 |
> |
* Tries to advance eventCount and releases waiters. Called only |
774 |
> |
* from workers. |
775 |
|
*/ |
776 |
< |
private void ensureEnoughTotalWorkers() { |
777 |
< |
int wc; |
778 |
< |
while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism && |
779 |
< |
runState < TERMINATING) { |
780 |
< |
if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
781 |
< |
wc, wc + (ONE_RUNNING|ONE_TOTAL)) && |
782 |
< |
addWorker() == null)) |
776 |
> |
final void signalWork() { |
777 |
> |
int c; // try to increment event count -- CAS failure OK |
778 |
> |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1); |
779 |
> |
if (eventWaiters != 0L) |
780 |
> |
releaseEventWaiters(); |
781 |
> |
} |
782 |
> |
|
783 |
> |
/** |
784 |
> |
* Adds the given worker to event queue and blocks until |
785 |
> |
* terminating or event count advances from the workers |
786 |
> |
* lastEventCount value |
787 |
> |
* |
788 |
> |
* @param w the calling worker thread |
789 |
> |
*/ |
790 |
> |
private void eventSync(ForkJoinWorkerThread w) { |
791 |
> |
int ec = w.lastEventCount; |
792 |
> |
long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1)); |
793 |
> |
long h; |
794 |
> |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
795 |
> |
(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 || |
796 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) == ec) && |
797 |
> |
eventCount == ec) { |
798 |
> |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
799 |
> |
w.nextWaiter = h, nh)) { |
800 |
> |
awaitEvent(w, ec); |
801 |
|
break; |
802 |
+ |
} |
803 |
|
} |
804 |
|
} |
805 |
|
|
806 |
|
/** |
807 |
< |
* Final callback from terminating worker. Removes record of |
808 |
< |
* worker from array, and adjusts counts. If pool is shutting |
809 |
< |
* down, tries to complete terminatation, else possibly replaces |
810 |
< |
* the worker. |
807 |
> |
* Blocks the given worker (that has already been entered as an |
808 |
> |
* event waiter) until terminating or event count advances from |
809 |
> |
* the given value. The oldest (first) waiter uses a timed wait to |
810 |
> |
* occasionally one-by-one shrink the number of workers (to a |
811 |
> |
* minumum of one) if the pool has not been used for extended |
812 |
> |
* periods. |
813 |
|
* |
814 |
< |
* @param w the worker |
814 |
> |
* @param w the calling worker thread |
815 |
> |
* @param ec the count |
816 |
|
*/ |
817 |
< |
final void workerTerminated(ForkJoinWorkerThread w) { |
818 |
< |
if (w.active) { // force inactive |
819 |
< |
w.active = false; |
820 |
< |
do {} while (!tryDecrementActiveCount()); |
817 |
> |
private void awaitEvent(ForkJoinWorkerThread w, int ec) { |
818 |
> |
while (eventCount == ec) { |
819 |
> |
if (tryAccumulateStealCount(w)) { // transfer while idle |
820 |
> |
boolean untimed = (w.nextWaiter != 0L || |
821 |
> |
(workerCounts & RUNNING_COUNT_MASK) <= 1); |
822 |
> |
long startTime = untimed? 0 : System.nanoTime(); |
823 |
> |
Thread.interrupted(); // clear/ignore interrupt |
824 |
> |
if (eventCount != ec || !w.isRunning() || |
825 |
> |
runState >= TERMINATING) // recheck after clear |
826 |
> |
break; |
827 |
> |
if (untimed) |
828 |
> |
LockSupport.park(w); |
829 |
> |
else { |
830 |
> |
LockSupport.parkNanos(w, SHRINK_RATE_NANOS); |
831 |
> |
if (eventCount != ec || !w.isRunning() || |
832 |
> |
runState >= TERMINATING) |
833 |
> |
break; |
834 |
> |
if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS) |
835 |
> |
tryShutdownWaiter(ec); |
836 |
> |
} |
837 |
> |
} |
838 |
|
} |
839 |
< |
forgetWorker(w); |
839 |
> |
} |
840 |
|
|
841 |
< |
// Decrement total count, and if was running, running count |
842 |
< |
// Spin (waiting for other updates) if either would be negative |
843 |
< |
int nr = w.isTrimmed() ? 0 : ONE_RUNNING; |
844 |
< |
int unit = ONE_TOTAL + nr; |
845 |
< |
for (;;) { |
846 |
< |
int wc = workerCounts; |
847 |
< |
int rc = wc & RUNNING_COUNT_MASK; |
848 |
< |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
849 |
< |
if (rc - nr < 0 || tc == 0) |
850 |
< |
Thread.yield(); // back off if waiting for other updates |
851 |
< |
else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
852 |
< |
wc, wc - unit)) |
853 |
< |
break; |
841 |
> |
/** |
842 |
> |
* Callback from the oldest waiter in awaitEvent waking up after a |
843 |
> |
* period of non-use. Tries (once) to shutdown an event waiter (or |
844 |
> |
* a spare, if one exists). Note that we don't need CAS or locks |
845 |
> |
* here because the method is called only from one thread |
846 |
> |
* occasionally waking (and even misfires are OK). Note that |
847 |
> |
* until the shutdown worker fully terminates, workerCounts |
848 |
> |
* will overestimate total count, which is tolerable. |
849 |
> |
* |
850 |
> |
* @param ec the event count waited on by caller (to abort |
851 |
> |
* attempt if count has since changed). |
852 |
> |
*/ |
853 |
> |
private void tryShutdownWaiter(int ec) { |
854 |
> |
if (spareWaiters != 0) { // prefer killing spares |
855 |
> |
tryShutdownSpare(); |
856 |
> |
return; |
857 |
|
} |
858 |
+ |
ForkJoinWorkerThread[] ws = workers; |
859 |
+ |
int n = ws.length; |
860 |
+ |
long h = eventWaiters; |
861 |
+ |
ForkJoinWorkerThread w; int id; long nh; |
862 |
+ |
if (runState == 0 && |
863 |
+ |
submissionQueue.isEmpty() && |
864 |
+ |
eventCount == ec && |
865 |
+ |
(id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 && |
866 |
+ |
id < n && (w = ws[id]) != null && |
867 |
+ |
(nh = w.nextWaiter) != 0L && // keep at least one worker |
868 |
+ |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh)) { |
869 |
+ |
w.shutdown(); |
870 |
+ |
LockSupport.unpark(w); |
871 |
+ |
} |
872 |
+ |
releaseEventWaiters(); |
873 |
+ |
} |
874 |
+ |
|
875 |
+ |
// Maintaining spares |
876 |
|
|
877 |
< |
accumulateStealCount(w); // collect final count |
878 |
< |
if (!tryTerminate(false)) |
879 |
< |
ensureEnoughTotalWorkers(); |
877 |
> |
/** |
878 |
> |
* Pushes worker onto the spare stack |
879 |
> |
*/ |
880 |
> |
final void pushSpare(ForkJoinWorkerThread w) { |
881 |
> |
int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1); |
882 |
> |
do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
883 |
> |
w.nextSpare = spareWaiters,ns)); |
884 |
|
} |
885 |
|
|
886 |
< |
// Waiting for and signalling events |
886 |
> |
/** |
887 |
> |
* Callback from oldest spare occasionally waking up. Tries |
888 |
> |
* (once) to shutdown a spare. Same idea as tryShutdownWaiter. |
889 |
> |
*/ |
890 |
> |
final void tryShutdownSpare() { |
891 |
> |
int sw, id; |
892 |
> |
ForkJoinWorkerThread w; |
893 |
> |
ForkJoinWorkerThread[] ws; |
894 |
> |
if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
895 |
> |
id < (ws = workers).length && (w = ws[id]) != null && |
896 |
> |
(workerCounts & RUNNING_COUNT_MASK) >= parallelism && |
897 |
> |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
898 |
> |
sw, w.nextSpare)) { |
899 |
> |
w.shutdown(); |
900 |
> |
LockSupport.unpark(w); |
901 |
> |
advanceEventCount(); |
902 |
> |
} |
903 |
> |
} |
904 |
|
|
905 |
|
/** |
906 |
< |
* Releases workers blocked on a count not equal to current count. |
907 |
< |
* @return true if any released |
906 |
> |
* Tries (once) to resume a spare if worker counts match |
907 |
> |
* the given count. |
908 |
> |
* |
909 |
> |
* @param wc workerCounts value on invocation of this method |
910 |
|
*/ |
911 |
< |
private void releaseWaiters() { |
912 |
< |
long top; |
913 |
< |
while ((top = eventWaiters) != 0L) { |
914 |
< |
ForkJoinWorkerThread[] ws = workers; |
915 |
< |
int n = ws.length; |
916 |
< |
for (;;) { |
917 |
< |
int i = ((int)(top & WAITER_ID_MASK)) - 1; |
918 |
< |
int e = (int)(top >>> EVENT_COUNT_SHIFT); |
919 |
< |
if (i < 0 || e == eventCount) |
920 |
< |
return; |
921 |
< |
ForkJoinWorkerThread w; |
922 |
< |
if (i < n && (w = ws[i]) != null && |
923 |
< |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
924 |
< |
top, w.nextWaiter)) { |
911 |
> |
private void tryResumeSpare(int wc) { |
912 |
> |
ForkJoinWorkerThread[] ws = workers; |
913 |
> |
int n = ws.length; |
914 |
> |
int sw, id, rs; ForkJoinWorkerThread w; |
915 |
> |
if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
916 |
> |
id < n && (w = ws[id]) != null && |
917 |
> |
(rs = runState) < TERMINATING && |
918 |
> |
eventWaiters == 0L && workerCounts == wc) { |
919 |
> |
// In case all workers busy, heuristically back off to let settle |
920 |
> |
Thread.yield(); |
921 |
> |
if (eventWaiters == 0L && runState == rs && // recheck |
922 |
> |
workerCounts == wc && spareWaiters == sw && |
923 |
> |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
924 |
> |
sw, w.nextSpare)) { |
925 |
> |
int c; // increment running count before resume |
926 |
> |
do {} while(!UNSAFE.compareAndSwapInt |
927 |
> |
(this, workerCountsOffset, |
928 |
> |
c = workerCounts, c + ONE_RUNNING)); |
929 |
> |
if (w.tryUnsuspend()) |
930 |
|
LockSupport.unpark(w); |
931 |
< |
top = eventWaiters; |
932 |
< |
} |
757 |
< |
else |
758 |
< |
break; // possibly stale; reread |
931 |
> |
else // back out if w was shutdown |
932 |
> |
decrementWorkerCounts(ONE_RUNNING, 0); |
933 |
|
} |
934 |
|
} |
935 |
|
} |
936 |
|
|
937 |
+ |
// adding workers on demand |
938 |
+ |
|
939 |
|
/** |
940 |
< |
* Ensures eventCount on exit is different (mod 2^32) than on |
941 |
< |
* entry and wakes up all waiters |
940 |
> |
* Adds one or more workers if needed to establish target parallelism. |
941 |
> |
* Retries upon contention. |
942 |
|
*/ |
943 |
< |
private void signalEvent() { |
944 |
< |
int c; |
945 |
< |
do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset, |
946 |
< |
c = eventCount, c+1)); |
947 |
< |
releaseWaiters(); |
943 |
> |
private void addWorkerIfBelowTarget() { |
944 |
> |
int pc = parallelism; |
945 |
> |
int wc; |
946 |
> |
while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < pc && |
947 |
> |
runState < TERMINATING) { |
948 |
> |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
949 |
> |
wc + (ONE_RUNNING|ONE_TOTAL))) { |
950 |
> |
if (addWorker() == null) |
951 |
> |
break; |
952 |
> |
} |
953 |
> |
} |
954 |
|
} |
955 |
|
|
956 |
|
/** |
957 |
< |
* Advances eventCount and releases waiters until interference by |
958 |
< |
* other releasing threads is detected. |
957 |
> |
* Tries (once) to add a new worker if all existing workers are |
958 |
> |
* busy, and there are either no running workers or the deficit is |
959 |
> |
* at least twice the surplus. |
960 |
> |
* |
961 |
> |
* @param wc workerCounts value on invocation of this method |
962 |
|
*/ |
963 |
< |
final void signalWork() { |
964 |
< |
int c; |
965 |
< |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1); |
966 |
< |
long top; |
967 |
< |
while ((top = eventWaiters) != 0L) { |
968 |
< |
int ec = eventCount; |
969 |
< |
ForkJoinWorkerThread[] ws = workers; |
970 |
< |
int n = ws.length; |
971 |
< |
for (;;) { |
972 |
< |
int i = ((int)(top & WAITER_ID_MASK)) - 1; |
973 |
< |
int e = (int)(top >>> EVENT_COUNT_SHIFT); |
974 |
< |
if (i < 0 || e == ec) |
975 |
< |
return; |
976 |
< |
ForkJoinWorkerThread w; |
977 |
< |
if (i < n && (w = ws[i]) != null && |
793 |
< |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
794 |
< |
top, top = w.nextWaiter)) { |
795 |
< |
LockSupport.unpark(w); |
796 |
< |
if (top != eventWaiters) // let someone else take over |
797 |
< |
return; |
798 |
< |
} |
799 |
< |
else |
800 |
< |
break; // possibly stale; reread |
801 |
< |
} |
963 |
> |
private void tryAddWorkerIfBusy(int wc) { |
964 |
> |
int tc, rc, rs; |
965 |
> |
int pc = parallelism; |
966 |
> |
if ((tc = wc >>> TOTAL_COUNT_SHIFT) < MAX_WORKERS && |
967 |
> |
((rc = wc & RUNNING_COUNT_MASK) == 0 || |
968 |
> |
rc < pc - ((tc - pc) << 1)) && |
969 |
> |
(rs = runState) < TERMINATING && |
970 |
> |
(rs & ACTIVE_COUNT_MASK) == tc) { |
971 |
> |
// Since all workers busy, heuristically back off to let settle |
972 |
> |
Thread.yield(); |
973 |
> |
if (eventWaiters == 0L && spareWaiters == 0 && // recheck |
974 |
> |
runState == rs && workerCounts == wc && |
975 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
976 |
> |
wc + (ONE_RUNNING|ONE_TOTAL))) |
977 |
> |
addWorker(); |
978 |
|
} |
979 |
|
} |
980 |
|
|
981 |
|
/** |
982 |
< |
* Blockss worker until terminating or event count |
807 |
< |
* advances from last value held by worker |
982 |
> |
* Does at most one of: |
983 |
|
* |
984 |
< |
* @param w the calling worker thread |
985 |
< |
*/ |
986 |
< |
private void eventSync(ForkJoinWorkerThread w) { |
987 |
< |
int wec = w.lastEventCount; |
988 |
< |
long nextTop = (((long)wec << EVENT_COUNT_SHIFT) | |
989 |
< |
((long)(w.poolIndex + 1))); |
990 |
< |
long top; |
991 |
< |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
992 |
< |
(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 || |
993 |
< |
(int)(top >>> EVENT_COUNT_SHIFT) == wec) && |
994 |
< |
eventCount == wec) { |
995 |
< |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
996 |
< |
w.nextWaiter = top, nextTop)) { |
997 |
< |
accumulateStealCount(w); // transfer steals while idle |
998 |
< |
Thread.interrupted(); // clear/ignore interrupt |
999 |
< |
while (eventCount == wec) |
1000 |
< |
w.doPark(); |
1001 |
< |
break; |
1002 |
< |
} |
984 |
> |
* 1. Help wake up existing workers waiting for work via |
985 |
> |
* releaseEventWaiters. (If any exist, then it doesn't |
986 |
> |
* matter right now if under target parallelism level.) |
987 |
> |
* |
988 |
> |
* 2. If a spare exists, try (once) to resume it via tryResumeSpare. |
989 |
> |
* |
990 |
> |
* 3. If there are not enough total workers, add some |
991 |
> |
* via addWorkerIfBelowTarget; |
992 |
> |
* |
993 |
> |
* 4. Try (once) to add a new worker if all existing workers |
994 |
> |
* are busy, via tryAddWorkerIfBusy |
995 |
> |
*/ |
996 |
> |
private void helpMaintainParallelism() { |
997 |
> |
long h; int pc, wc; |
998 |
> |
if (((int)((h = eventWaiters) & WAITER_ID_MASK)) != 0) { |
999 |
> |
if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount) |
1000 |
> |
releaseEventWaiters(); // avoid useless call |
1001 |
> |
} |
1002 |
> |
else if ((pc = parallelism) > |
1003 |
> |
((wc = workerCounts) & RUNNING_COUNT_MASK)) { |
1004 |
> |
if (spareWaiters != 0) |
1005 |
> |
tryResumeSpare(wc); |
1006 |
> |
else if ((wc >>> TOTAL_COUNT_SHIFT) < pc) |
1007 |
> |
addWorkerIfBelowTarget(); |
1008 |
> |
else |
1009 |
> |
tryAddWorkerIfBusy(wc); |
1010 |
|
} |
829 |
– |
w.lastEventCount = eventCount; |
1011 |
|
} |
1012 |
|
|
1013 |
|
/** |
1014 |
|
* Callback from workers invoked upon each top-level action (i.e., |
1015 |
< |
* stealing a task or taking a submission and running |
1016 |
< |
* it). Performs one or both of the following: |
1015 |
> |
* stealing a task or taking a submission and running it). |
1016 |
> |
* Performs one or more of the following: |
1017 |
|
* |
1018 |
< |
* * If the worker cannot find work, updates its active status to |
1019 |
< |
* inactive and updates activeCount unless there is contention, in |
1020 |
< |
* which case it may try again (either in this or a subsequent |
1021 |
< |
* call). Additionally, awaits the next task event and/or helps |
1022 |
< |
* wake up other releasable waiters. |
1023 |
< |
* |
1024 |
< |
* * If there are too many running threads, suspends this worker |
1025 |
< |
* (first forcing inactivation if necessary). If it is not |
1026 |
< |
* resumed before a keepAlive elapses, the worker may be "trimmed" |
1027 |
< |
* -- killed while suspended within suspendAsSpare. Otherwise, |
1028 |
< |
* upon resume it rechecks to make sure that it is still needed. |
1018 |
> |
* 1. If the worker is active, try to set its active status to |
1019 |
> |
* inactive and update activeCount. On contention, we may try |
1020 |
> |
* again on this or subsequent call. |
1021 |
> |
* |
1022 |
> |
* 2. Release any existing event waiters that are now relesable |
1023 |
> |
* |
1024 |
> |
* 3. If there are too many running threads, suspend this worker |
1025 |
> |
* (first forcing inactive if necessary). If it is not |
1026 |
> |
* needed, it may be killed while suspended via |
1027 |
> |
* tryShutdownSpare. Otherwise, upon resume it rechecks to make |
1028 |
> |
* sure that it is still needed. |
1029 |
> |
* |
1030 |
> |
* 4. If more than 1 miss, await the next task event via |
1031 |
> |
* eventSync (first forcing inactivation if necessary), upon |
1032 |
> |
* which worker may also be killed, via tryShutdownWaiter. |
1033 |
> |
* |
1034 |
> |
* 5. Help reactivate other workers via helpMaintainParallelism |
1035 |
|
* |
1036 |
|
* @param w the worker |
1037 |
< |
* @param retries the number of scans by caller failing to find work |
1038 |
< |
* find any (in which case it may block waiting for work). |
1037 |
> |
* @param misses the number of scans by caller failing to find work |
1038 |
> |
* (saturating at 2 to avoid wraparound) |
1039 |
|
*/ |
1040 |
< |
final void preStep(ForkJoinWorkerThread w, int retries) { |
1040 |
> |
final void preStep(ForkJoinWorkerThread w, int misses) { |
1041 |
|
boolean active = w.active; |
1042 |
< |
boolean inactivate = active && retries > 0; |
1042 |
> |
int pc = parallelism; |
1043 |
|
for (;;) { |
1044 |
< |
int rs, wc; |
1045 |
< |
if (inactivate && |
1046 |
< |
UNSAFE.compareAndSwapInt(this, runStateOffset, |
1047 |
< |
rs = runState, rs - ONE_ACTIVE)) |
1048 |
< |
inactivate = active = w.active = false; |
1049 |
< |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) { |
1050 |
< |
if (retries > 0) { |
1051 |
< |
if (retries > 1 && !active) |
1044 |
> |
int rs, wc, rc, ec; long h; |
1045 |
> |
if (active && UNSAFE.compareAndSwapInt(this, runStateOffset, |
1046 |
> |
rs = runState, rs - 1)) |
1047 |
> |
active = w.active = false; |
1048 |
> |
if (((int)((h = eventWaiters) & WAITER_ID_MASK)) != 0 && |
1049 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) != eventCount) { |
1050 |
> |
releaseEventWaiters(); |
1051 |
> |
if (misses > 1) |
1052 |
> |
continue; // clear before sync below |
1053 |
> |
} |
1054 |
> |
if ((rc = ((wc = workerCounts) & RUNNING_COUNT_MASK)) > pc) { |
1055 |
> |
if (!active && // must inactivate to suspend |
1056 |
> |
workerCounts == wc && // try to suspend as spare |
1057 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1058 |
> |
wc, wc - ONE_RUNNING)) { |
1059 |
> |
w.suspendAsSpare(); |
1060 |
> |
if (!w.isRunning()) |
1061 |
> |
break; // was killed while spare |
1062 |
> |
} |
1063 |
> |
continue; |
1064 |
> |
} |
1065 |
> |
if (misses > 0) { |
1066 |
> |
if ((ec = eventCount) == w.lastEventCount && misses > 1) { |
1067 |
> |
if (!active) { // must inactivate to sync |
1068 |
|
eventSync(w); |
1069 |
< |
releaseWaiters(); |
1069 |
> |
if (w.isRunning()) |
1070 |
> |
misses = 1; // don't re-sync |
1071 |
> |
else |
1072 |
> |
break; // was killed while waiting |
1073 |
> |
} |
1074 |
> |
continue; |
1075 |
|
} |
1076 |
< |
break; |
1076 |
> |
w.lastEventCount = ec; |
1077 |
|
} |
1078 |
< |
if (!(inactivate |= active) && // must inactivate to suspend |
1079 |
< |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1080 |
< |
wc, wc - ONE_RUNNING) && |
873 |
< |
!w.suspendAsSpare()) // false if trimmed |
874 |
< |
break; |
1078 |
> |
if (rc < pc) |
1079 |
> |
helpMaintainParallelism(); |
1080 |
> |
break; |
1081 |
|
} |
1082 |
|
} |
1083 |
|
|
1084 |
|
/** |
1085 |
< |
* Awaits join of the given task if enough threads, or can resume |
1086 |
< |
* or create a spare. Fails (in which case the given task might |
1087 |
< |
* not be done) upon contention or lack of decision about |
1088 |
< |
* blocking. |
1089 |
< |
* |
884 |
< |
* We allow blocking if: |
885 |
< |
* |
886 |
< |
* 1. There would still be at least as many running threads as |
887 |
< |
* parallelism level if this thread blocks. |
888 |
< |
* |
889 |
< |
* 2. A spare is resumed to replace this worker. We tolerate |
890 |
< |
* races in the decision to replace when a spare is found. |
891 |
< |
* This may release too many, but if so, the superfluous ones |
892 |
< |
* will re-suspend via preStep(). |
893 |
< |
* |
894 |
< |
* 3. After #spares repeated retries, there are fewer than #spare |
895 |
< |
* threads not running. We allow this slack to avoid hysteresis |
896 |
< |
* and as a hedge against lag/uncertainty of running count |
897 |
< |
* estimates when signalling or unblocking stalls. |
898 |
< |
* |
899 |
< |
* 4. All existing workers are busy (as rechecked via #spares |
900 |
< |
* repeated retries by caller) and a new spare is created. |
901 |
< |
* |
902 |
< |
* If none of the above hold, we escape out by re-incrementing |
903 |
< |
* count and returning to caller, which can retry later. |
1085 |
> |
* Helps and/or blocks awaiting join of the given task. |
1086 |
> |
* Alternates between helpJoinTask() and helpMaintainParallelism() |
1087 |
> |
* as many times as there is a deficit in running count (or longer |
1088 |
> |
* if running count would become zero), then blocks if task still |
1089 |
> |
* not done. |
1090 |
|
* |
1091 |
|
* @param joinMe the task to join |
906 |
– |
* @param retries the number of calls to this method for this join |
1092 |
|
*/ |
1093 |
< |
final void tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) { |
1094 |
< |
int pc = parallelism; |
1095 |
< |
boolean running = true; // false when running count decremented |
1096 |
< |
outer:while (joinMe.status >= 0) { |
1097 |
< |
int wc = workerCounts; |
1098 |
< |
int rc = wc & RUNNING_COUNT_MASK; |
1099 |
< |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1100 |
< |
if (running) { // replace with spare or decrement count |
1101 |
< |
if (rc <= pc && tc > pc && |
1102 |
< |
(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) { |
1103 |
< |
ForkJoinWorkerThread[] ws = workers; // search for spare |
1104 |
< |
int nws = ws.length; |
1105 |
< |
for (int i = 0; i < nws; ++i) { |
921 |
< |
ForkJoinWorkerThread w = ws[i]; |
922 |
< |
if (w != null && w.isSuspended()) { |
923 |
< |
if ((workerCounts & RUNNING_COUNT_MASK) > pc) |
924 |
< |
continue outer; |
925 |
< |
if (joinMe.status < 0) |
926 |
< |
break outer; |
927 |
< |
if (w.tryResumeSpare()) { |
928 |
< |
running = false; |
929 |
< |
break outer; |
930 |
< |
} |
931 |
< |
continue outer; // rescan on failure to resume |
932 |
< |
} |
933 |
< |
} |
934 |
< |
} |
935 |
< |
if ((rc <= pc && (rc == 0 || --retries < 0)) || // no retry |
936 |
< |
joinMe.status < 0) |
937 |
< |
break; |
938 |
< |
if (workerCounts == wc && |
939 |
< |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
940 |
< |
wc, wc - ONE_RUNNING)) |
941 |
< |
running = false; |
1093 |
> |
final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) { |
1094 |
> |
int threshold = parallelism; // descend blocking thresholds |
1095 |
> |
while (joinMe.status >= 0) { |
1096 |
> |
boolean block; int wc; |
1097 |
> |
worker.helpJoinTask(joinMe); |
1098 |
> |
if (joinMe.status < 0) |
1099 |
> |
break; |
1100 |
> |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
1101 |
> |
if (threshold > 0) |
1102 |
> |
--threshold; |
1103 |
> |
else |
1104 |
> |
advanceEventCount(); // force release |
1105 |
> |
block = false; |
1106 |
|
} |
1107 |
< |
else { // allow blocking if enough threads |
1108 |
< |
int sc = tc - pc + 1; // = spares, plus the one to add |
1109 |
< |
if (sc > 0 && rc > 0 && rc >= pc - sc && rc > pc - retries) |
1110 |
< |
break; |
1111 |
< |
if (--retries > sc && tc < MAX_THREADS && |
1112 |
< |
tc == (runState & ACTIVE_COUNT_MASK) && |
1113 |
< |
workerCounts == wc && |
1114 |
< |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
1115 |
< |
wc + (ONE_RUNNING|ONE_TOTAL))) { |
1116 |
< |
addWorker(); |
1117 |
< |
break; |
954 |
< |
} |
955 |
< |
if (workerCounts == wc && |
956 |
< |
UNSAFE.compareAndSwapInt (this, workerCountsOffset, |
957 |
< |
wc, wc + ONE_RUNNING)) { |
958 |
< |
running = true; // back out; allow retry |
959 |
< |
break; |
960 |
< |
} |
1107 |
> |
else |
1108 |
> |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1109 |
> |
wc, wc - ONE_RUNNING); |
1110 |
> |
helpMaintainParallelism(); |
1111 |
> |
if (block) { |
1112 |
> |
int c; |
1113 |
> |
joinMe.internalAwaitDone(); |
1114 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
1115 |
> |
(this, workerCountsOffset, |
1116 |
> |
c = workerCounts, c + ONE_RUNNING)); |
1117 |
> |
break; |
1118 |
|
} |
1119 |
|
} |
963 |
– |
if (!running) { // can block |
964 |
– |
int c; // to inline incrementRunningCount |
965 |
– |
joinMe.internalAwaitDone(); |
966 |
– |
do {} while (!UNSAFE.compareAndSwapInt |
967 |
– |
(this, workerCountsOffset, |
968 |
– |
c = workerCounts, c + ONE_RUNNING)); |
969 |
– |
} |
1120 |
|
} |
1121 |
|
|
1122 |
|
/** |
1123 |
< |
* Same idea as (and shares many code snippets with) tryAwaitJoin, |
974 |
< |
* but self-contained because there are no caller retries. |
975 |
< |
* TODO: Rework to use simpler API. |
1123 |
> |
* Same idea as awaitJoin, but no helping |
1124 |
|
*/ |
1125 |
|
final void awaitBlocker(ManagedBlocker blocker) |
1126 |
|
throws InterruptedException { |
1127 |
< |
int pc = parallelism; |
1128 |
< |
boolean running = true; |
1129 |
< |
int retries = 0; |
1130 |
< |
boolean done; |
1131 |
< |
outer:while (!(done = blocker.isReleasable())) { |
1132 |
< |
int wc = workerCounts; |
1133 |
< |
int rc = wc & RUNNING_COUNT_MASK; |
1134 |
< |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1135 |
< |
if (running) { |
988 |
< |
if (rc <= pc && tc > pc && |
989 |
< |
(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) { |
990 |
< |
ForkJoinWorkerThread[] ws = workers; |
991 |
< |
int nws = ws.length; |
992 |
< |
for (int i = 0; i < nws; ++i) { |
993 |
< |
ForkJoinWorkerThread w = ws[i]; |
994 |
< |
if (w != null && w.isSuspended()) { |
995 |
< |
if ((workerCounts & RUNNING_COUNT_MASK) > pc) |
996 |
< |
continue outer; |
997 |
< |
if (done = blocker.isReleasable()) |
998 |
< |
break outer; |
999 |
< |
if (w.tryResumeSpare()) { |
1000 |
< |
running = false; |
1001 |
< |
break outer; |
1002 |
< |
} |
1003 |
< |
continue outer; |
1004 |
< |
} |
1005 |
< |
} |
1006 |
< |
if (done = blocker.isReleasable()) |
1007 |
< |
break; |
1008 |
< |
} |
1009 |
< |
if (rc > 0 && workerCounts == wc && |
1010 |
< |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1011 |
< |
wc, wc - ONE_RUNNING)) { |
1012 |
< |
running = false; |
1013 |
< |
if (rc > pc) |
1014 |
< |
break; |
1015 |
< |
} |
1127 |
> |
int threshold = parallelism; |
1128 |
> |
while (!blocker.isReleasable()) { |
1129 |
> |
boolean block; int wc; |
1130 |
> |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
1131 |
> |
if (threshold > 0) |
1132 |
> |
--threshold; |
1133 |
> |
else |
1134 |
> |
advanceEventCount(); |
1135 |
> |
block = false; |
1136 |
|
} |
1137 |
< |
else if (rc >= pc) |
1138 |
< |
break; |
1139 |
< |
else if (tc < MAX_THREADS && |
1140 |
< |
tc == (runState & ACTIVE_COUNT_MASK) && |
1141 |
< |
workerCounts == wc && |
1142 |
< |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
1143 |
< |
wc + (ONE_RUNNING|ONE_TOTAL))) { |
1144 |
< |
addWorker(); |
1137 |
> |
else |
1138 |
> |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1139 |
> |
wc, wc - ONE_RUNNING); |
1140 |
> |
helpMaintainParallelism(); |
1141 |
> |
if (block) { |
1142 |
> |
try { |
1143 |
> |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1144 |
> |
} finally { |
1145 |
> |
int c; |
1146 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
1147 |
> |
(this, workerCountsOffset, |
1148 |
> |
c = workerCounts, c + ONE_RUNNING)); |
1149 |
> |
} |
1150 |
|
break; |
1151 |
|
} |
1027 |
– |
else if (workerCounts == wc && |
1028 |
– |
UNSAFE.compareAndSwapInt (this, workerCountsOffset, |
1029 |
– |
wc, wc + ONE_RUNNING)) { |
1030 |
– |
Thread.yield(); |
1031 |
– |
++retries; |
1032 |
– |
running = true; // allow rescan |
1033 |
– |
} |
1034 |
– |
} |
1035 |
– |
|
1036 |
– |
try { |
1037 |
– |
if (!done) |
1038 |
– |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1039 |
– |
} finally { |
1040 |
– |
if (!running) { |
1041 |
– |
int c; |
1042 |
– |
do {} while (!UNSAFE.compareAndSwapInt |
1043 |
– |
(this, workerCountsOffset, |
1044 |
– |
c = workerCounts, c + ONE_RUNNING)); |
1045 |
– |
} |
1152 |
|
} |
1153 |
|
} |
1154 |
|
|
1180 |
|
|
1181 |
|
/** |
1182 |
|
* Actions on transition to TERMINATING |
1183 |
+ |
* |
1184 |
+ |
* Runs up to four passes through workers: (0) shutting down each |
1185 |
+ |
* (without waking up if parked) to quickly spread notifications |
1186 |
+ |
* without unnecessary bouncing around event queues etc (1) wake |
1187 |
+ |
* up and help cancel tasks (2) interrupt (3) mop up races with |
1188 |
+ |
* interrupted workers |
1189 |
|
*/ |
1190 |
|
private void startTerminating() { |
1191 |
< |
for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers |
1192 |
< |
cancelSubmissions(); |
1193 |
< |
shutdownWorkers(); |
1194 |
< |
cancelWorkerTasks(); |
1195 |
< |
signalEvent(); |
1196 |
< |
interruptWorkers(); |
1191 |
> |
cancelSubmissions(); |
1192 |
> |
for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) { |
1193 |
> |
advanceEventCount(); |
1194 |
> |
eventWaiters = 0L; // clobber lists |
1195 |
> |
spareWaiters = 0; |
1196 |
> |
ForkJoinWorkerThread[] ws = workers; |
1197 |
> |
int n = ws.length; |
1198 |
> |
for (int i = 0; i < n; ++i) { |
1199 |
> |
ForkJoinWorkerThread w = ws[i]; |
1200 |
> |
if (w != null) { |
1201 |
> |
w.shutdown(); |
1202 |
> |
if (passes > 0 && !w.isTerminated()) { |
1203 |
> |
w.cancelTasks(); |
1204 |
> |
LockSupport.unpark(w); |
1205 |
> |
if (passes > 1) { |
1206 |
> |
try { |
1207 |
> |
w.interrupt(); |
1208 |
> |
} catch (SecurityException ignore) { |
1209 |
> |
} |
1210 |
> |
} |
1211 |
> |
} |
1212 |
> |
} |
1213 |
> |
} |
1214 |
|
} |
1215 |
|
} |
1216 |
|
|
1227 |
|
} |
1228 |
|
} |
1229 |
|
|
1101 |
– |
/** |
1102 |
– |
* Sets all worker run states to at least shutdown, |
1103 |
– |
* also resuming suspended workers |
1104 |
– |
*/ |
1105 |
– |
private void shutdownWorkers() { |
1106 |
– |
ForkJoinWorkerThread[] ws = workers; |
1107 |
– |
int nws = ws.length; |
1108 |
– |
for (int i = 0; i < nws; ++i) { |
1109 |
– |
ForkJoinWorkerThread w = ws[i]; |
1110 |
– |
if (w != null) |
1111 |
– |
w.shutdown(); |
1112 |
– |
} |
1113 |
– |
} |
1114 |
– |
|
1115 |
– |
/** |
1116 |
– |
* Clears out and cancels all locally queued tasks |
1117 |
– |
*/ |
1118 |
– |
private void cancelWorkerTasks() { |
1119 |
– |
ForkJoinWorkerThread[] ws = workers; |
1120 |
– |
int nws = ws.length; |
1121 |
– |
for (int i = 0; i < nws; ++i) { |
1122 |
– |
ForkJoinWorkerThread w = ws[i]; |
1123 |
– |
if (w != null) |
1124 |
– |
w.cancelTasks(); |
1125 |
– |
} |
1126 |
– |
} |
1127 |
– |
|
1128 |
– |
/** |
1129 |
– |
* Unsticks all workers blocked on joins etc |
1130 |
– |
*/ |
1131 |
– |
private void interruptWorkers() { |
1132 |
– |
ForkJoinWorkerThread[] ws = workers; |
1133 |
– |
int nws = ws.length; |
1134 |
– |
for (int i = 0; i < nws; ++i) { |
1135 |
– |
ForkJoinWorkerThread w = ws[i]; |
1136 |
– |
if (w != null && !w.isTerminated()) { |
1137 |
– |
try { |
1138 |
– |
w.interrupt(); |
1139 |
– |
} catch (SecurityException ignore) { |
1140 |
– |
} |
1141 |
– |
} |
1142 |
– |
} |
1143 |
– |
} |
1144 |
– |
|
1230 |
|
// misc support for ForkJoinWorkerThread |
1231 |
|
|
1232 |
|
/** |
1237 |
|
} |
1238 |
|
|
1239 |
|
/** |
1240 |
< |
* Accumulates steal count from a worker, clearing |
1241 |
< |
* the worker's value |
1240 |
> |
* Tries to accumulates steal count from a worker, clearing |
1241 |
> |
* the worker's value. |
1242 |
> |
* |
1243 |
> |
* @return true if worker steal count now zero |
1244 |
|
*/ |
1245 |
< |
final void accumulateStealCount(ForkJoinWorkerThread w) { |
1245 |
> |
final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) { |
1246 |
|
int sc = w.stealCount; |
1247 |
< |
if (sc != 0) { |
1248 |
< |
long c; |
1249 |
< |
w.stealCount = 0; |
1250 |
< |
do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset, |
1251 |
< |
c = stealCount, c + sc)); |
1247 |
> |
long c = stealCount; |
1248 |
> |
// CAS even if zero, for fence effects |
1249 |
> |
if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) { |
1250 |
> |
if (sc != 0) |
1251 |
> |
w.stealCount = 0; |
1252 |
> |
return true; |
1253 |
|
} |
1254 |
+ |
return sc == 0; |
1255 |
|
} |
1256 |
|
|
1257 |
|
/** |
1334 |
|
checkPermission(); |
1335 |
|
if (factory == null) |
1336 |
|
throw new NullPointerException(); |
1337 |
< |
if (parallelism <= 0 || parallelism > MAX_THREADS) |
1337 |
> |
if (parallelism <= 0 || parallelism > MAX_WORKERS) |
1338 |
|
throw new IllegalArgumentException(); |
1339 |
|
this.parallelism = parallelism; |
1340 |
|
this.factory = factory; |
1353 |
|
* @param pc the initial parallelism level |
1354 |
|
*/ |
1355 |
|
private static int initialArraySizeFor(int pc) { |
1356 |
< |
// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16) |
1357 |
< |
int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS; |
1356 |
> |
// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16) |
1357 |
> |
int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS; |
1358 |
|
size |= size >>> 1; |
1359 |
|
size |= size >>> 2; |
1360 |
|
size |= size >>> 4; |
1373 |
|
if (runState >= SHUTDOWN) |
1374 |
|
throw new RejectedExecutionException(); |
1375 |
|
submissionQueue.offer(task); |
1376 |
< |
signalEvent(); |
1377 |
< |
ensureEnoughTotalWorkers(); |
1376 |
> |
advanceEventCount(); |
1377 |
> |
if (eventWaiters != 0L) |
1378 |
> |
releaseEventWaiters(); |
1379 |
> |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism) |
1380 |
> |
addWorkerIfBelowTarget(); |
1381 |
|
} |
1382 |
|
|
1383 |
|
/** |
1384 |
|
* Performs the given task, returning its result upon completion. |
1293 |
– |
* If the caller is already engaged in a fork/join computation in |
1294 |
– |
* the current pool, this method is equivalent in effect to |
1295 |
– |
* {@link ForkJoinTask#invoke}. |
1385 |
|
* |
1386 |
|
* @param task the task |
1387 |
|
* @return the task's result |
1396 |
|
|
1397 |
|
/** |
1398 |
|
* Arranges for (asynchronous) execution of the given task. |
1310 |
– |
* If the caller is already engaged in a fork/join computation in |
1311 |
– |
* the current pool, this method is equivalent in effect to |
1312 |
– |
* {@link ForkJoinTask#fork}. |
1399 |
|
* |
1400 |
|
* @param task the task |
1401 |
|
* @throws NullPointerException if the task is null |
1424 |
|
|
1425 |
|
/** |
1426 |
|
* Submits a ForkJoinTask for execution. |
1341 |
– |
* If the caller is already engaged in a fork/join computation in |
1342 |
– |
* the current pool, this method is equivalent in effect to |
1343 |
– |
* {@link ForkJoinTask#fork}. |
1427 |
|
* |
1428 |
|
* @param task the task to submit |
1429 |
|
* @return the task |
1615 |
|
public long getQueuedTaskCount() { |
1616 |
|
long count = 0; |
1617 |
|
ForkJoinWorkerThread[] ws = workers; |
1618 |
< |
int nws = ws.length; |
1619 |
< |
for (int i = 0; i < nws; ++i) { |
1618 |
> |
int n = ws.length; |
1619 |
> |
for (int i = 0; i < n; ++i) { |
1620 |
|
ForkJoinWorkerThread w = ws[i]; |
1621 |
|
if (w != null) |
1622 |
|
count += w.getQueueSize(); |
1674 |
|
* @return the number of elements transferred |
1675 |
|
*/ |
1676 |
|
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1677 |
< |
int n = submissionQueue.drainTo(c); |
1595 |
< |
ForkJoinWorkerThread[] ws = workers; |
1596 |
< |
int nws = ws.length; |
1597 |
< |
for (int i = 0; i < nws; ++i) { |
1598 |
< |
ForkJoinWorkerThread w = ws[i]; |
1599 |
< |
if (w != null) |
1600 |
< |
n += w.drainTasksTo(c); |
1601 |
< |
} |
1602 |
< |
return n; |
1603 |
< |
} |
1604 |
< |
|
1605 |
< |
/** |
1606 |
< |
* Returns count of total parks by existing workers. |
1607 |
< |
* Used during development only since not meaningful to users. |
1608 |
< |
*/ |
1609 |
< |
private int collectParkCount() { |
1610 |
< |
int count = 0; |
1677 |
> |
int count = submissionQueue.drainTo(c); |
1678 |
|
ForkJoinWorkerThread[] ws = workers; |
1679 |
< |
int nws = ws.length; |
1680 |
< |
for (int i = 0; i < nws; ++i) { |
1679 |
> |
int n = ws.length; |
1680 |
> |
for (int i = 0; i < n; ++i) { |
1681 |
|
ForkJoinWorkerThread w = ws[i]; |
1682 |
|
if (w != null) |
1683 |
< |
count += w.parkCount; |
1683 |
> |
count += w.drainTasksTo(c); |
1684 |
|
} |
1685 |
|
return count; |
1686 |
|
} |
1702 |
|
int pc = parallelism; |
1703 |
|
int rs = runState; |
1704 |
|
int ac = rs & ACTIVE_COUNT_MASK; |
1638 |
– |
// int pk = collectParkCount(); |
1705 |
|
return super.toString() + |
1706 |
|
"[" + runLevelToString(rs) + |
1707 |
|
", parallelism = " + pc + |
1711 |
|
", steals = " + st + |
1712 |
|
", tasks = " + qt + |
1713 |
|
", submissions = " + qs + |
1648 |
– |
// ", parks = " + pk + |
1714 |
|
"]"; |
1715 |
|
} |
1716 |
|
|
1817 |
|
* Interface for extending managed parallelism for tasks running |
1818 |
|
* in {@link ForkJoinPool}s. |
1819 |
|
* |
1820 |
< |
* <p>A {@code ManagedBlocker} provides two methods. |
1821 |
< |
* Method {@code isReleasable} must return {@code true} if |
1822 |
< |
* blocking is not necessary. Method {@code block} blocks the |
1823 |
< |
* current thread if necessary (perhaps internally invoking |
1824 |
< |
* {@code isReleasable} before actually blocking). |
1820 |
> |
* <p>A {@code ManagedBlocker} provides two methods. Method |
1821 |
> |
* {@code isReleasable} must return {@code true} if blocking is |
1822 |
> |
* not necessary. Method {@code block} blocks the current thread |
1823 |
> |
* if necessary (perhaps internally invoking {@code isReleasable} |
1824 |
> |
* before actually blocking). The unusual methods in this API |
1825 |
> |
* accommodate synchronizers that may, but don't usually, block |
1826 |
> |
* for long periods. Similarly, they allow more efficient internal |
1827 |
> |
* handling of cases in which additional workers may be, but |
1828 |
> |
* usually are not, needed to ensure sufficient parallelism. |
1829 |
> |
* Toward this end, implementations of method {@code isReleasable} |
1830 |
> |
* must be amenable to repeated invocation. |
1831 |
|
* |
1832 |
|
* <p>For example, here is a ManagedBlocker based on a |
1833 |
|
* ReentrantLock: |
1845 |
|
* return hasLock || (hasLock = lock.tryLock()); |
1846 |
|
* } |
1847 |
|
* }}</pre> |
1848 |
+ |
* |
1849 |
+ |
* <p>Here is a class that possibly blocks waiting for an |
1850 |
+ |
* item on a given queue: |
1851 |
+ |
* <pre> {@code |
1852 |
+ |
* class QueueTaker<E> implements ManagedBlocker { |
1853 |
+ |
* final BlockingQueue<E> queue; |
1854 |
+ |
* volatile E item = null; |
1855 |
+ |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
1856 |
+ |
* public boolean block() throws InterruptedException { |
1857 |
+ |
* if (item == null) |
1858 |
+ |
* item = queue.take |
1859 |
+ |
* return true; |
1860 |
+ |
* } |
1861 |
+ |
* public boolean isReleasable() { |
1862 |
+ |
* return item != null || (item = queue.poll) != null; |
1863 |
+ |
* } |
1864 |
+ |
* public E getItem() { // call after pool.managedBlock completes |
1865 |
+ |
* return item; |
1866 |
+ |
* } |
1867 |
+ |
* }}</pre> |
1868 |
|
*/ |
1869 |
|
public static interface ManagedBlocker { |
1870 |
|
/** |
1907 |
|
public static void managedBlock(ManagedBlocker blocker) |
1908 |
|
throws InterruptedException { |
1909 |
|
Thread t = Thread.currentThread(); |
1910 |
< |
if (t instanceof ForkJoinWorkerThread) |
1911 |
< |
((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker); |
1910 |
> |
if (t instanceof ForkJoinWorkerThread) { |
1911 |
> |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
1912 |
> |
w.pool.awaitBlocker(blocker); |
1913 |
> |
} |
1914 |
|
else { |
1915 |
|
do {} while (!blocker.isReleasable() && !blocker.block()); |
1916 |
|
} |
1941 |
|
objectFieldOffset("eventWaiters",ForkJoinPool.class); |
1942 |
|
private static final long stealCountOffset = |
1943 |
|
objectFieldOffset("stealCount",ForkJoinPool.class); |
1944 |
+ |
private static final long spareWaitersOffset = |
1945 |
+ |
objectFieldOffset("spareWaiters",ForkJoinPool.class); |
1946 |
|
|
1947 |
|
private static long objectFieldOffset(String field, Class<?> klazz) { |
1948 |
|
try { |