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