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