waitForReturnCapability: fix logic bug
[ghc.git] / rts / Capability.c
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 2003-2006
4 *
5 * Capabilities
6 *
7 * A Capability represent the token required to execute STG code,
8 * and all the state an OS thread/task needs to run Haskell code:
9 * its STG registers, a pointer to its TSO, a nursery etc. During
10 * STG execution, a pointer to the capabilitity is kept in a
11 * register (BaseReg; actually it is a pointer to cap->r).
12 *
13 * Only in an THREADED_RTS build will there be multiple capabilities,
14 * for non-threaded builds there is only one global capability, namely
15 * MainCapability.
16 *
17 * --------------------------------------------------------------------------*/
18
19 #include "PosixSource.h"
20 #include "Rts.h"
21
22 #include "Capability.h"
23 #include "Schedule.h"
24 #include "Sparks.h"
25 #include "Trace.h"
26 #include "sm/GC.h" // for gcWorkerThread()
27 #include "STM.h"
28 #include "RtsUtils.h"
29
30 // one global capability, this is the Capability for non-threaded
31 // builds, and for +RTS -N1
32 Capability MainCapability;
33
34 nat n_capabilities = 0;
35 Capability *capabilities = NULL;
36
37 // Holds the Capability which last became free. This is used so that
38 // an in-call has a chance of quickly finding a free Capability.
39 // Maintaining a global free list of Capabilities would require global
40 // locking, so we don't do that.
41 Capability *last_free_capability = NULL;
42
43 /* GC indicator, in scope for the scheduler, init'ed to false */
44 volatile StgWord waiting_for_gc = 0;
45
46 /* Let foreign code get the current Capability -- assuming there is one!
47 * This is useful for unsafe foreign calls because they are called with
48 * the current Capability held, but they are not passed it. For example,
49 * see see the integer-gmp package which calls allocateLocal() in its
50 * stgAllocForGMP() function (which gets called by gmp functions).
51 * */
52 Capability * rts_unsafeGetMyCapability (void)
53 {
54 #if defined(THREADED_RTS)
55 return myTask()->cap;
56 #else
57 return &MainCapability;
58 #endif
59 }
60
61 #if defined(THREADED_RTS)
62 STATIC_INLINE rtsBool
63 globalWorkToDo (void)
64 {
65 return blackholes_need_checking
66 || sched_state >= SCHED_INTERRUPTING
67 ;
68 }
69 #endif
70
71 #if defined(THREADED_RTS)
72 StgClosure *
73 findSpark (Capability *cap)
74 {
75 Capability *robbed;
76 StgClosurePtr spark;
77 rtsBool retry;
78 nat i = 0;
79
80 if (!emptyRunQueue(cap)) {
81 // If there are other threads, don't try to run any new
82 // sparks: sparks might be speculative, we don't want to take
83 // resources away from the main computation.
84 return 0;
85 }
86
87 // first try to get a spark from our own pool.
88 // We should be using reclaimSpark(), because it works without
89 // needing any atomic instructions:
90 // spark = reclaimSpark(cap->sparks);
91 // However, measurements show that this makes at least one benchmark
92 // slower (prsa) and doesn't affect the others.
93 spark = tryStealSpark(cap);
94 if (spark != NULL) {
95 cap->sparks_converted++;
96
97 // Post event for running a spark from capability's own pool.
98 postEvent(cap, EVENT_RUN_SPARK, cap->r.rCurrentTSO->id, 0);
99
100 return spark;
101 }
102
103 if (n_capabilities == 1) { return NULL; } // makes no sense...
104
105 debugTrace(DEBUG_sched,
106 "cap %d: Trying to steal work from other capabilities",
107 cap->no);
108
109 do {
110 retry = rtsFalse;
111
112 /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
113 start at a random place instead of 0 as well. */
114 for ( i=0 ; i < n_capabilities ; i++ ) {
115 robbed = &capabilities[i];
116 if (cap == robbed) // ourselves...
117 continue;
118
119 if (emptySparkPoolCap(robbed)) // nothing to steal here
120 continue;
121
122 spark = tryStealSpark(robbed);
123 if (spark == NULL && !emptySparkPoolCap(robbed)) {
124 // we conflicted with another thread while trying to steal;
125 // try again later.
126 retry = rtsTrue;
127 }
128
129 if (spark != NULL) {
130 debugTrace(DEBUG_sched,
131 "cap %d: Stole a spark from capability %d",
132 cap->no, robbed->no);
133 cap->sparks_converted++;
134
135 postEvent(cap, EVENT_STEAL_SPARK,
136 cap->r.rCurrentTSO->id, robbed->no);
137
138
139 return spark;
140 }
141 // otherwise: no success, try next one
142 }
143 } while (retry);
144
145 debugTrace(DEBUG_sched, "No sparks stolen");
146 return NULL;
147 }
148
149 // Returns True if any spark pool is non-empty at this moment in time
150 // The result is only valid for an instant, of course, so in a sense
151 // is immediately invalid, and should not be relied upon for
152 // correctness.
153 rtsBool
154 anySparks (void)
155 {
156 nat i;
157
158 for (i=0; i < n_capabilities; i++) {
159 if (!emptySparkPoolCap(&capabilities[i])) {
160 return rtsTrue;
161 }
162 }
163 return rtsFalse;
164 }
165 #endif
166
167 /* -----------------------------------------------------------------------------
168 * Manage the returning_tasks lists.
169 *
170 * These functions require cap->lock
171 * -------------------------------------------------------------------------- */
172
173 #if defined(THREADED_RTS)
174 STATIC_INLINE void
175 newReturningTask (Capability *cap, Task *task)
176 {
177 ASSERT_LOCK_HELD(&cap->lock);
178 ASSERT(task->return_link == NULL);
179 if (cap->returning_tasks_hd) {
180 ASSERT(cap->returning_tasks_tl->return_link == NULL);
181 cap->returning_tasks_tl->return_link = task;
182 } else {
183 cap->returning_tasks_hd = task;
184 }
185 cap->returning_tasks_tl = task;
186 }
187
188 STATIC_INLINE Task *
189 popReturningTask (Capability *cap)
190 {
191 ASSERT_LOCK_HELD(&cap->lock);
192 Task *task;
193 task = cap->returning_tasks_hd;
194 ASSERT(task);
195 cap->returning_tasks_hd = task->return_link;
196 if (!cap->returning_tasks_hd) {
197 cap->returning_tasks_tl = NULL;
198 }
199 task->return_link = NULL;
200 return task;
201 }
202 #endif
203
204 /* ----------------------------------------------------------------------------
205 * Initialisation
206 *
207 * The Capability is initially marked not free.
208 * ------------------------------------------------------------------------- */
209
210 static void
211 initCapability( Capability *cap, nat i )
212 {
213 nat g;
214
215 cap->no = i;
216 cap->in_haskell = rtsFalse;
217 cap->in_gc = rtsFalse;
218
219 cap->run_queue_hd = END_TSO_QUEUE;
220 cap->run_queue_tl = END_TSO_QUEUE;
221
222 #if defined(THREADED_RTS)
223 initMutex(&cap->lock);
224 cap->running_task = NULL; // indicates cap is free
225 cap->spare_workers = NULL;
226 cap->suspended_ccalling_tasks = NULL;
227 cap->returning_tasks_hd = NULL;
228 cap->returning_tasks_tl = NULL;
229 cap->wakeup_queue_hd = END_TSO_QUEUE;
230 cap->wakeup_queue_tl = END_TSO_QUEUE;
231 cap->sparks_created = 0;
232 cap->sparks_converted = 0;
233 cap->sparks_pruned = 0;
234 #endif
235
236 cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
237 cap->f.stgGCEnter1 = (StgFunPtr)__stg_gc_enter_1;
238 cap->f.stgGCFun = (StgFunPtr)__stg_gc_fun;
239
240 cap->mut_lists = stgMallocBytes(sizeof(bdescr *) *
241 RtsFlags.GcFlags.generations,
242 "initCapability");
243 cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
244 RtsFlags.GcFlags.generations,
245 "initCapability");
246
247 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
248 cap->mut_lists[g] = NULL;
249 }
250
251 cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
252 cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
253 cap->free_trec_chunks = END_STM_CHUNK_LIST;
254 cap->free_trec_headers = NO_TREC;
255 cap->transaction_tokens = 0;
256 cap->context_switch = 0;
257 }
258
259 /* ---------------------------------------------------------------------------
260 * Function: initCapabilities()
261 *
262 * Purpose: set up the Capability handling. For the THREADED_RTS build,
263 * we keep a table of them, the size of which is
264 * controlled by the user via the RTS flag -N.
265 *
266 * ------------------------------------------------------------------------- */
267 void
268 initCapabilities( void )
269 {
270 #if defined(THREADED_RTS)
271 nat i;
272
273 #ifndef REG_Base
274 // We can't support multiple CPUs if BaseReg is not a register
275 if (RtsFlags.ParFlags.nNodes > 1) {
276 errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
277 RtsFlags.ParFlags.nNodes = 1;
278 }
279 #endif
280
281 n_capabilities = RtsFlags.ParFlags.nNodes;
282
283 if (n_capabilities == 1) {
284 capabilities = &MainCapability;
285 // THREADED_RTS must work on builds that don't have a mutable
286 // BaseReg (eg. unregisterised), so in this case
287 // capabilities[0] must coincide with &MainCapability.
288 } else {
289 capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
290 "initCapabilities");
291 }
292
293 for (i = 0; i < n_capabilities; i++) {
294 initCapability(&capabilities[i], i);
295 }
296
297 debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
298
299 #else /* !THREADED_RTS */
300
301 n_capabilities = 1;
302 capabilities = &MainCapability;
303 initCapability(&MainCapability, 0);
304
305 #endif
306
307 // There are no free capabilities to begin with. We will start
308 // a worker Task to each Capability, which will quickly put the
309 // Capability on the free list when it finds nothing to do.
310 last_free_capability = &capabilities[0];
311 }
312
313 /* ----------------------------------------------------------------------------
314 * setContextSwitches: cause all capabilities to context switch as
315 * soon as possible.
316 * ------------------------------------------------------------------------- */
317
318 void setContextSwitches(void)
319 {
320 nat i;
321 for (i=0; i < n_capabilities; i++) {
322 contextSwitchCapability(&capabilities[i]);
323 }
324 }
325
326 /* ----------------------------------------------------------------------------
327 * Give a Capability to a Task. The task must currently be sleeping
328 * on its condition variable.
329 *
330 * Requires cap->lock (modifies cap->running_task).
331 *
332 * When migrating a Task, the migrater must take task->lock before
333 * modifying task->cap, to synchronise with the waking up Task.
334 * Additionally, the migrater should own the Capability (when
335 * migrating the run queue), or cap->lock (when migrating
336 * returning_workers).
337 *
338 * ------------------------------------------------------------------------- */
339
340 #if defined(THREADED_RTS)
341 STATIC_INLINE void
342 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
343 {
344 ASSERT_LOCK_HELD(&cap->lock);
345 ASSERT(task->cap == cap);
346 debugTrace(DEBUG_sched, "passing capability %d to %s %p",
347 cap->no, task->tso ? "bound task" : "worker",
348 (void *)task->id);
349 ACQUIRE_LOCK(&task->lock);
350 task->wakeup = rtsTrue;
351 // the wakeup flag is needed because signalCondition() doesn't
352 // flag the condition if the thread is already runniing, but we want
353 // it to be sticky.
354 signalCondition(&task->cond);
355 RELEASE_LOCK(&task->lock);
356 }
357 #endif
358
359 /* ----------------------------------------------------------------------------
360 * Function: releaseCapability(Capability*)
361 *
362 * Purpose: Letting go of a capability. Causes a
363 * 'returning worker' thread or a 'waiting worker'
364 * to wake up, in that order.
365 * ------------------------------------------------------------------------- */
366
367 #if defined(THREADED_RTS)
368 void
369 releaseCapability_ (Capability* cap,
370 rtsBool always_wakeup)
371 {
372 Task *task;
373
374 task = cap->running_task;
375
376 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
377
378 cap->running_task = NULL;
379
380 // Check to see whether a worker thread can be given
381 // the go-ahead to return the result of an external call..
382 if (cap->returning_tasks_hd != NULL) {
383 giveCapabilityToTask(cap,cap->returning_tasks_hd);
384 // The Task pops itself from the queue (see waitForReturnCapability())
385 return;
386 }
387
388 if (waiting_for_gc == PENDING_GC_SEQ) {
389 last_free_capability = cap; // needed?
390 debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
391 return;
392 }
393
394
395 // If the next thread on the run queue is a bound thread,
396 // give this Capability to the appropriate Task.
397 if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
398 // Make sure we're not about to try to wake ourselves up
399 ASSERT(task != cap->run_queue_hd->bound);
400 task = cap->run_queue_hd->bound;
401 giveCapabilityToTask(cap,task);
402 return;
403 }
404
405 if (!cap->spare_workers) {
406 // Create a worker thread if we don't have one. If the system
407 // is interrupted, we only create a worker task if there
408 // are threads that need to be completed. If the system is
409 // shutting down, we never create a new worker.
410 if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
411 debugTrace(DEBUG_sched,
412 "starting new worker on capability %d", cap->no);
413 startWorkerTask(cap, workerStart);
414 return;
415 }
416 }
417
418 // If we have an unbound thread on the run queue, or if there's
419 // anything else to do, give the Capability to a worker thread.
420 if (always_wakeup ||
421 !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
422 !emptySparkPoolCap(cap) || globalWorkToDo()) {
423 if (cap->spare_workers) {
424 giveCapabilityToTask(cap,cap->spare_workers);
425 // The worker Task pops itself from the queue;
426 return;
427 }
428 }
429
430 last_free_capability = cap;
431 debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
432 }
433
434 void
435 releaseCapability (Capability* cap USED_IF_THREADS)
436 {
437 ACQUIRE_LOCK(&cap->lock);
438 releaseCapability_(cap, rtsFalse);
439 RELEASE_LOCK(&cap->lock);
440 }
441
442 void
443 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
444 {
445 ACQUIRE_LOCK(&cap->lock);
446 releaseCapability_(cap, rtsTrue);
447 RELEASE_LOCK(&cap->lock);
448 }
449
450 static void
451 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
452 {
453 Task *task;
454
455 ACQUIRE_LOCK(&cap->lock);
456
457 task = cap->running_task;
458
459 // If the current task is a worker, save it on the spare_workers
460 // list of this Capability. A worker can mark itself as stopped,
461 // in which case it is not replaced on the spare_worker queue.
462 // This happens when the system is shutting down (see
463 // Schedule.c:workerStart()).
464 // Also, be careful to check that this task hasn't just exited
465 // Haskell to do a foreign call (task->suspended_tso).
466 if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
467 task->next = cap->spare_workers;
468 cap->spare_workers = task;
469 }
470 // Bound tasks just float around attached to their TSOs.
471
472 releaseCapability_(cap,rtsFalse);
473
474 RELEASE_LOCK(&cap->lock);
475 }
476 #endif
477
478 /* ----------------------------------------------------------------------------
479 * waitForReturnCapability( Task *task )
480 *
481 * Purpose: when an OS thread returns from an external call,
482 * it calls waitForReturnCapability() (via Schedule.resumeThread())
483 * to wait for permission to enter the RTS & communicate the
484 * result of the external call back to the Haskell thread that
485 * made it.
486 *
487 * ------------------------------------------------------------------------- */
488 void
489 waitForReturnCapability (Capability **pCap, Task *task)
490 {
491 #if !defined(THREADED_RTS)
492
493 MainCapability.running_task = task;
494 task->cap = &MainCapability;
495 *pCap = &MainCapability;
496
497 #else
498 Capability *cap = *pCap;
499
500 if (cap == NULL) {
501 // Try last_free_capability first
502 cap = last_free_capability;
503 if (cap->running_task) {
504 nat i;
505 // otherwise, search for a free capability
506 cap = NULL;
507 for (i = 0; i < n_capabilities; i++) {
508 if (!capabilities[i].running_task) {
509 cap = &capabilities[i];
510 break;
511 }
512 }
513 if (cap == NULL) {
514 // Can't find a free one, use last_free_capability.
515 cap = last_free_capability;
516 }
517 }
518
519 // record the Capability as the one this Task is now assocated with.
520 task->cap = cap;
521
522 } else {
523 ASSERT(task->cap == cap);
524 }
525
526 ACQUIRE_LOCK(&cap->lock);
527
528 debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
529
530 if (!cap->running_task) {
531 // It's free; just grab it
532 cap->running_task = task;
533 RELEASE_LOCK(&cap->lock);
534 } else {
535 newReturningTask(cap,task);
536 RELEASE_LOCK(&cap->lock);
537
538 for (;;) {
539 ACQUIRE_LOCK(&task->lock);
540 // task->lock held, cap->lock not held
541 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
542 cap = task->cap;
543 task->wakeup = rtsFalse;
544 RELEASE_LOCK(&task->lock);
545
546 // now check whether we should wake up...
547 ACQUIRE_LOCK(&cap->lock);
548 if (cap->running_task == NULL) {
549 if (cap->returning_tasks_hd != task) {
550 giveCapabilityToTask(cap,cap->returning_tasks_hd);
551 RELEASE_LOCK(&cap->lock);
552 continue;
553 }
554 cap->running_task = task;
555 popReturningTask(cap);
556 RELEASE_LOCK(&cap->lock);
557 break;
558 }
559 RELEASE_LOCK(&cap->lock);
560 }
561
562 }
563
564 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
565
566 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
567
568 *pCap = cap;
569 #endif
570 }
571
572 #if defined(THREADED_RTS)
573 /* ----------------------------------------------------------------------------
574 * yieldCapability
575 * ------------------------------------------------------------------------- */
576
577 void
578 yieldCapability (Capability** pCap, Task *task)
579 {
580 Capability *cap = *pCap;
581
582 if (waiting_for_gc == PENDING_GC_PAR) {
583 debugTrace(DEBUG_sched, "capability %d: becoming a GC thread", cap->no);
584 postEvent(cap, EVENT_GC_START, 0, 0);
585 gcWorkerThread(cap);
586 postEvent(cap, EVENT_GC_END, 0, 0);
587 return;
588 }
589
590 debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
591
592 // We must now release the capability and wait to be woken up
593 // again.
594 task->wakeup = rtsFalse;
595 releaseCapabilityAndQueueWorker(cap);
596
597 for (;;) {
598 ACQUIRE_LOCK(&task->lock);
599 // task->lock held, cap->lock not held
600 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
601 cap = task->cap;
602 task->wakeup = rtsFalse;
603 RELEASE_LOCK(&task->lock);
604
605 debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
606
607 ACQUIRE_LOCK(&cap->lock);
608 if (cap->running_task != NULL) {
609 debugTrace(DEBUG_sched,
610 "capability %d is owned by another task", cap->no);
611 RELEASE_LOCK(&cap->lock);
612 continue;
613 }
614
615 if (task->tso == NULL) {
616 ASSERT(cap->spare_workers != NULL);
617 // if we're not at the front of the queue, release it
618 // again. This is unlikely to happen.
619 if (cap->spare_workers != task) {
620 giveCapabilityToTask(cap,cap->spare_workers);
621 RELEASE_LOCK(&cap->lock);
622 continue;
623 }
624 cap->spare_workers = task->next;
625 task->next = NULL;
626 }
627 cap->running_task = task;
628 RELEASE_LOCK(&cap->lock);
629 break;
630 }
631
632 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
633 ASSERT(cap->running_task == task);
634
635 *pCap = cap;
636
637 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
638
639 return;
640 }
641
642 /* ----------------------------------------------------------------------------
643 * Wake up a thread on a Capability.
644 *
645 * This is used when the current Task is running on a Capability and
646 * wishes to wake up a thread on a different Capability.
647 * ------------------------------------------------------------------------- */
648
649 void
650 wakeupThreadOnCapability (Capability *my_cap,
651 Capability *other_cap,
652 StgTSO *tso)
653 {
654 ACQUIRE_LOCK(&other_cap->lock);
655
656 // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
657 if (tso->bound) {
658 ASSERT(tso->bound->cap == tso->cap);
659 tso->bound->cap = other_cap;
660 }
661 tso->cap = other_cap;
662
663 ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
664
665 if (other_cap->running_task == NULL) {
666 // nobody is running this Capability, we can add our thread
667 // directly onto the run queue and start up a Task to run it.
668
669 other_cap->running_task = myTask();
670 // precond for releaseCapability_() and appendToRunQueue()
671
672 appendToRunQueue(other_cap,tso);
673
674 releaseCapability_(other_cap,rtsFalse);
675 } else {
676 appendToWakeupQueue(my_cap,other_cap,tso);
677 other_cap->context_switch = 1;
678 // someone is running on this Capability, so it cannot be
679 // freed without first checking the wakeup queue (see
680 // releaseCapability_).
681 }
682
683 RELEASE_LOCK(&other_cap->lock);
684 }
685
686 /* ----------------------------------------------------------------------------
687 * prodCapability
688 *
689 * If a Capability is currently idle, wake up a Task on it. Used to
690 * get every Capability into the GC.
691 * ------------------------------------------------------------------------- */
692
693 void
694 prodCapability (Capability *cap, Task *task)
695 {
696 ACQUIRE_LOCK(&cap->lock);
697 if (!cap->running_task) {
698 cap->running_task = task;
699 releaseCapability_(cap,rtsTrue);
700 }
701 RELEASE_LOCK(&cap->lock);
702 }
703
704 /* ----------------------------------------------------------------------------
705 * shutdownCapability
706 *
707 * At shutdown time, we want to let everything exit as cleanly as
708 * possible. For each capability, we let its run queue drain, and
709 * allow the workers to stop.
710 *
711 * This function should be called when interrupted and
712 * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
713 * will exit the scheduler and call taskStop(), and any bound thread
714 * that wakes up will return to its caller. Runnable threads are
715 * killed.
716 *
717 * ------------------------------------------------------------------------- */
718
719 void
720 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
721 {
722 nat i;
723
724 task->cap = cap;
725
726 // Loop indefinitely until all the workers have exited and there
727 // are no Haskell threads left. We used to bail out after 50
728 // iterations of this loop, but that occasionally left a worker
729 // running which caused problems later (the closeMutex() below
730 // isn't safe, for one thing).
731
732 for (i = 0; /* i < 50 */; i++) {
733 ASSERT(sched_state == SCHED_SHUTTING_DOWN);
734
735 debugTrace(DEBUG_sched,
736 "shutting down capability %d, attempt %d", cap->no, i);
737 ACQUIRE_LOCK(&cap->lock);
738 if (cap->running_task) {
739 RELEASE_LOCK(&cap->lock);
740 debugTrace(DEBUG_sched, "not owner, yielding");
741 yieldThread();
742 continue;
743 }
744 cap->running_task = task;
745
746 if (cap->spare_workers) {
747 // Look for workers that have died without removing
748 // themselves from the list; this could happen if the OS
749 // summarily killed the thread, for example. This
750 // actually happens on Windows when the system is
751 // terminating the program, and the RTS is running in a
752 // DLL.
753 Task *t, *prev;
754 prev = NULL;
755 for (t = cap->spare_workers; t != NULL; t = t->next) {
756 if (!osThreadIsAlive(t->id)) {
757 debugTrace(DEBUG_sched,
758 "worker thread %p has died unexpectedly", (void *)t->id);
759 if (!prev) {
760 cap->spare_workers = t->next;
761 } else {
762 prev->next = t->next;
763 }
764 prev = t;
765 }
766 }
767 }
768
769 if (!emptyRunQueue(cap) || cap->spare_workers) {
770 debugTrace(DEBUG_sched,
771 "runnable threads or workers still alive, yielding");
772 releaseCapability_(cap,rtsFalse); // this will wake up a worker
773 RELEASE_LOCK(&cap->lock);
774 yieldThread();
775 continue;
776 }
777
778 // If "safe", then busy-wait for any threads currently doing
779 // foreign calls. If we're about to unload this DLL, for
780 // example, we need to be sure that there are no OS threads
781 // that will try to return to code that has been unloaded.
782 // We can be a bit more relaxed when this is a standalone
783 // program that is about to terminate, and let safe=false.
784 if (cap->suspended_ccalling_tasks && safe) {
785 debugTrace(DEBUG_sched,
786 "thread(s) are involved in foreign calls, yielding");
787 cap->running_task = NULL;
788 RELEASE_LOCK(&cap->lock);
789 yieldThread();
790 continue;
791 }
792
793 postEvent(cap, EVENT_SHUTDOWN, 0, 0);
794 debugTrace(DEBUG_sched, "capability %d is stopped.", cap->no);
795 RELEASE_LOCK(&cap->lock);
796 break;
797 }
798 // we now have the Capability, its run queue and spare workers
799 // list are both empty.
800
801 // ToDo: we can't drop this mutex, because there might still be
802 // threads performing foreign calls that will eventually try to
803 // return via resumeThread() and attempt to grab cap->lock.
804 // closeMutex(&cap->lock);
805 }
806
807 /* ----------------------------------------------------------------------------
808 * tryGrabCapability
809 *
810 * Attempt to gain control of a Capability if it is free.
811 *
812 * ------------------------------------------------------------------------- */
813
814 rtsBool
815 tryGrabCapability (Capability *cap, Task *task)
816 {
817 if (cap->running_task != NULL) return rtsFalse;
818 ACQUIRE_LOCK(&cap->lock);
819 if (cap->running_task != NULL) {
820 RELEASE_LOCK(&cap->lock);
821 return rtsFalse;
822 }
823 task->cap = cap;
824 cap->running_task = task;
825 RELEASE_LOCK(&cap->lock);
826 return rtsTrue;
827 }
828
829
830 #endif /* THREADED_RTS */
831
832 static void
833 freeCapability (Capability *cap)
834 {
835 stgFree(cap->mut_lists);
836 #if defined(THREADED_RTS)
837 freeSparkPool(cap->sparks);
838 #endif
839 }
840
841 void
842 freeCapabilities (void)
843 {
844 #if defined(THREADED_RTS)
845 nat i;
846 for (i=0; i < n_capabilities; i++) {
847 freeCapability(&capabilities[i]);
848 }
849 #else
850 freeCapability(&MainCapability);
851 #endif
852 }
853
854 /* ---------------------------------------------------------------------------
855 Mark everything directly reachable from the Capabilities. When
856 using multiple GC threads, each GC thread marks all Capabilities
857 for which (c `mod` n == 0), for Capability c and thread n.
858 ------------------------------------------------------------------------ */
859
860 void
861 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
862 rtsBool prune_sparks USED_IF_THREADS)
863 {
864 nat i;
865 Capability *cap;
866 Task *task;
867
868 // Each GC thread is responsible for following roots from the
869 // Capability of the same number. There will usually be the same
870 // or fewer Capabilities as GC threads, but just in case there
871 // are more, we mark every Capability whose number is the GC
872 // thread's index plus a multiple of the number of GC threads.
873 for (i = i0; i < n_capabilities; i += delta) {
874 cap = &capabilities[i];
875 evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
876 evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
877 #if defined(THREADED_RTS)
878 evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
879 evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
880 #endif
881 for (task = cap->suspended_ccalling_tasks; task != NULL;
882 task=task->next) {
883 debugTrace(DEBUG_sched,
884 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
885 evac(user, (StgClosure **)(void *)&task->suspended_tso);
886 }
887
888 #if defined(THREADED_RTS)
889 if (prune_sparks) {
890 pruneSparkQueue (evac, user, cap);
891 } else {
892 traverseSparkQueue (evac, user, cap);
893 }
894 #endif
895 }
896
897 #if !defined(THREADED_RTS)
898 evac(user, (StgClosure **)(void *)&blocked_queue_hd);
899 evac(user, (StgClosure **)(void *)&blocked_queue_tl);
900 evac(user, (StgClosure **)(void *)&sleeping_queue);
901 #endif
902 }
903
904 void
905 markCapabilities (evac_fn evac, void *user)
906 {
907 markSomeCapabilities(evac, user, 0, 1, rtsFalse);
908 }