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