comment-out an incorrect assertion
[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 traceEventRunSpark(cap, cap->r.rCurrentTSO);
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 traceEventStealSpark(cap, cap->r.rCurrentTSO, robbed->no);
136
137 return spark;
138 }
139 // otherwise: no success, try next one
140 }
141 } while (retry);
142
143 debugTrace(DEBUG_sched, "No sparks stolen");
144 return NULL;
145 }
146
147 // Returns True if any spark pool is non-empty at this moment in time
148 // The result is only valid for an instant, of course, so in a sense
149 // is immediately invalid, and should not be relied upon for
150 // correctness.
151 rtsBool
152 anySparks (void)
153 {
154 nat i;
155
156 for (i=0; i < n_capabilities; i++) {
157 if (!emptySparkPoolCap(&capabilities[i])) {
158 return rtsTrue;
159 }
160 }
161 return rtsFalse;
162 }
163 #endif
164
165 /* -----------------------------------------------------------------------------
166 * Manage the returning_tasks lists.
167 *
168 * These functions require cap->lock
169 * -------------------------------------------------------------------------- */
170
171 #if defined(THREADED_RTS)
172 STATIC_INLINE void
173 newReturningTask (Capability *cap, Task *task)
174 {
175 ASSERT_LOCK_HELD(&cap->lock);
176 ASSERT(task->return_link == NULL);
177 if (cap->returning_tasks_hd) {
178 ASSERT(cap->returning_tasks_tl->return_link == NULL);
179 cap->returning_tasks_tl->return_link = task;
180 } else {
181 cap->returning_tasks_hd = task;
182 }
183 cap->returning_tasks_tl = task;
184 }
185
186 STATIC_INLINE Task *
187 popReturningTask (Capability *cap)
188 {
189 ASSERT_LOCK_HELD(&cap->lock);
190 Task *task;
191 task = cap->returning_tasks_hd;
192 ASSERT(task);
193 cap->returning_tasks_hd = task->return_link;
194 if (!cap->returning_tasks_hd) {
195 cap->returning_tasks_tl = NULL;
196 }
197 task->return_link = NULL;
198 return task;
199 }
200 #endif
201
202 /* ----------------------------------------------------------------------------
203 * Initialisation
204 *
205 * The Capability is initially marked not free.
206 * ------------------------------------------------------------------------- */
207
208 static void
209 initCapability( Capability *cap, nat i )
210 {
211 nat g;
212
213 cap->no = i;
214 cap->in_haskell = rtsFalse;
215
216 cap->run_queue_hd = END_TSO_QUEUE;
217 cap->run_queue_tl = END_TSO_QUEUE;
218
219 #if defined(THREADED_RTS)
220 initMutex(&cap->lock);
221 cap->running_task = NULL; // indicates cap is free
222 cap->spare_workers = NULL;
223 cap->suspended_ccalling_tasks = NULL;
224 cap->returning_tasks_hd = NULL;
225 cap->returning_tasks_tl = NULL;
226 cap->wakeup_queue_hd = END_TSO_QUEUE;
227 cap->wakeup_queue_tl = END_TSO_QUEUE;
228 cap->sparks_created = 0;
229 cap->sparks_converted = 0;
230 cap->sparks_pruned = 0;
231 #endif
232
233 cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
234 cap->f.stgGCEnter1 = (StgFunPtr)__stg_gc_enter_1;
235 cap->f.stgGCFun = (StgFunPtr)__stg_gc_fun;
236
237 cap->mut_lists = stgMallocBytes(sizeof(bdescr *) *
238 RtsFlags.GcFlags.generations,
239 "initCapability");
240 cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
241 RtsFlags.GcFlags.generations,
242 "initCapability");
243
244 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
245 cap->mut_lists[g] = NULL;
246 }
247
248 cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
249 cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
250 cap->free_trec_chunks = END_STM_CHUNK_LIST;
251 cap->free_trec_headers = NO_TREC;
252 cap->transaction_tokens = 0;
253 cap->context_switch = 0;
254 cap->pinned_object_block = NULL;
255 }
256
257 /* ---------------------------------------------------------------------------
258 * Function: initCapabilities()
259 *
260 * Purpose: set up the Capability handling. For the THREADED_RTS build,
261 * we keep a table of them, the size of which is
262 * controlled by the user via the RTS flag -N.
263 *
264 * ------------------------------------------------------------------------- */
265 void
266 initCapabilities( void )
267 {
268 #if defined(THREADED_RTS)
269 nat i;
270
271 #ifndef REG_Base
272 // We can't support multiple CPUs if BaseReg is not a register
273 if (RtsFlags.ParFlags.nNodes > 1) {
274 errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
275 RtsFlags.ParFlags.nNodes = 1;
276 }
277 #endif
278
279 n_capabilities = RtsFlags.ParFlags.nNodes;
280
281 if (n_capabilities == 1) {
282 capabilities = &MainCapability;
283 // THREADED_RTS must work on builds that don't have a mutable
284 // BaseReg (eg. unregisterised), so in this case
285 // capabilities[0] must coincide with &MainCapability.
286 } else {
287 capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
288 "initCapabilities");
289 }
290
291 for (i = 0; i < n_capabilities; i++) {
292 initCapability(&capabilities[i], i);
293 }
294
295 debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
296
297 #else /* !THREADED_RTS */
298
299 n_capabilities = 1;
300 capabilities = &MainCapability;
301 initCapability(&MainCapability, 0);
302
303 #endif
304
305 // There are no free capabilities to begin with. We will start
306 // a worker Task to each Capability, which will quickly put the
307 // Capability on the free list when it finds nothing to do.
308 last_free_capability = &capabilities[0];
309 }
310
311 /* ----------------------------------------------------------------------------
312 * setContextSwitches: cause all capabilities to context switch as
313 * soon as possible.
314 * ------------------------------------------------------------------------- */
315
316 void setContextSwitches(void)
317 {
318 nat i;
319 for (i=0; i < n_capabilities; i++) {
320 contextSwitchCapability(&capabilities[i]);
321 }
322 }
323
324 /* ----------------------------------------------------------------------------
325 * Give a Capability to a Task. The task must currently be sleeping
326 * on its condition variable.
327 *
328 * Requires cap->lock (modifies cap->running_task).
329 *
330 * When migrating a Task, the migrater must take task->lock before
331 * modifying task->cap, to synchronise with the waking up Task.
332 * Additionally, the migrater should own the Capability (when
333 * migrating the run queue), or cap->lock (when migrating
334 * returning_workers).
335 *
336 * ------------------------------------------------------------------------- */
337
338 #if defined(THREADED_RTS)
339 STATIC_INLINE void
340 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
341 {
342 ASSERT_LOCK_HELD(&cap->lock);
343 ASSERT(task->cap == cap);
344 debugTrace(DEBUG_sched, "passing capability %d to %s %p",
345 cap->no, task->tso ? "bound task" : "worker",
346 (void *)task->id);
347 ACQUIRE_LOCK(&task->lock);
348 task->wakeup = rtsTrue;
349 // the wakeup flag is needed because signalCondition() doesn't
350 // flag the condition if the thread is already runniing, but we want
351 // it to be sticky.
352 signalCondition(&task->cond);
353 RELEASE_LOCK(&task->lock);
354 }
355 #endif
356
357 /* ----------------------------------------------------------------------------
358 * Function: releaseCapability(Capability*)
359 *
360 * Purpose: Letting go of a capability. Causes a
361 * 'returning worker' thread or a 'waiting worker'
362 * to wake up, in that order.
363 * ------------------------------------------------------------------------- */
364
365 #if defined(THREADED_RTS)
366 void
367 releaseCapability_ (Capability* cap,
368 rtsBool always_wakeup)
369 {
370 Task *task;
371
372 task = cap->running_task;
373
374 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
375
376 cap->running_task = NULL;
377
378 // Check to see whether a worker thread can be given
379 // the go-ahead to return the result of an external call..
380 if (cap->returning_tasks_hd != NULL) {
381 giveCapabilityToTask(cap,cap->returning_tasks_hd);
382 // The Task pops itself from the queue (see waitForReturnCapability())
383 return;
384 }
385
386 if (waiting_for_gc == PENDING_GC_SEQ) {
387 last_free_capability = cap; // needed?
388 debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
389 return;
390 }
391
392
393 // If the next thread on the run queue is a bound thread,
394 // give this Capability to the appropriate Task.
395 if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
396 // Make sure we're not about to try to wake ourselves up
397 // ASSERT(task != cap->run_queue_hd->bound);
398 // assertion is false: in schedule() we force a yield after
399 // ThreadBlocked, but the thread may be back on the run queue
400 // by now.
401 task = cap->run_queue_hd->bound;
402 giveCapabilityToTask(cap,task);
403 return;
404 }
405
406 if (!cap->spare_workers) {
407 // Create a worker thread if we don't have one. If the system
408 // is interrupted, we only create a worker task if there
409 // are threads that need to be completed. If the system is
410 // shutting down, we never create a new worker.
411 if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
412 debugTrace(DEBUG_sched,
413 "starting new worker on capability %d", cap->no);
414 startWorkerTask(cap, workerStart);
415 return;
416 }
417 }
418
419 // If we have an unbound thread on the run queue, or if there's
420 // anything else to do, give the Capability to a worker thread.
421 if (always_wakeup ||
422 !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
423 !emptySparkPoolCap(cap) || globalWorkToDo()) {
424 if (cap->spare_workers) {
425 giveCapabilityToTask(cap,cap->spare_workers);
426 // The worker Task pops itself from the queue;
427 return;
428 }
429 }
430
431 last_free_capability = cap;
432 debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
433 }
434
435 void
436 releaseCapability (Capability* cap USED_IF_THREADS)
437 {
438 ACQUIRE_LOCK(&cap->lock);
439 releaseCapability_(cap, rtsFalse);
440 RELEASE_LOCK(&cap->lock);
441 }
442
443 void
444 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
445 {
446 ACQUIRE_LOCK(&cap->lock);
447 releaseCapability_(cap, rtsTrue);
448 RELEASE_LOCK(&cap->lock);
449 }
450
451 static void
452 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
453 {
454 Task *task;
455
456 ACQUIRE_LOCK(&cap->lock);
457
458 task = cap->running_task;
459
460 // If the current task is a worker, save it on the spare_workers
461 // list of this Capability. A worker can mark itself as stopped,
462 // in which case it is not replaced on the spare_worker queue.
463 // This happens when the system is shutting down (see
464 // Schedule.c:workerStart()).
465 // Also, be careful to check that this task hasn't just exited
466 // Haskell to do a foreign call (task->suspended_tso).
467 if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
468 task->next = cap->spare_workers;
469 cap->spare_workers = task;
470 }
471 // Bound tasks just float around attached to their TSOs.
472
473 releaseCapability_(cap,rtsFalse);
474
475 RELEASE_LOCK(&cap->lock);
476 }
477 #endif
478
479 /* ----------------------------------------------------------------------------
480 * waitForReturnCapability( Task *task )
481 *
482 * Purpose: when an OS thread returns from an external call,
483 * it calls waitForReturnCapability() (via Schedule.resumeThread())
484 * to wait for permission to enter the RTS & communicate the
485 * result of the external call back to the Haskell thread that
486 * made it.
487 *
488 * ------------------------------------------------------------------------- */
489 void
490 waitForReturnCapability (Capability **pCap, Task *task)
491 {
492 #if !defined(THREADED_RTS)
493
494 MainCapability.running_task = task;
495 task->cap = &MainCapability;
496 *pCap = &MainCapability;
497
498 #else
499 Capability *cap = *pCap;
500
501 if (cap == NULL) {
502 // Try last_free_capability first
503 cap = last_free_capability;
504 if (cap->running_task) {
505 nat i;
506 // otherwise, search for a free capability
507 cap = NULL;
508 for (i = 0; i < n_capabilities; i++) {
509 if (!capabilities[i].running_task) {
510 cap = &capabilities[i];
511 break;
512 }
513 }
514 if (cap == NULL) {
515 // Can't find a free one, use last_free_capability.
516 cap = last_free_capability;
517 }
518 }
519
520 // record the Capability as the one this Task is now assocated with.
521 task->cap = cap;
522
523 } else {
524 ASSERT(task->cap == cap);
525 }
526
527 ACQUIRE_LOCK(&cap->lock);
528
529 debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
530
531 if (!cap->running_task) {
532 // It's free; just grab it
533 cap->running_task = task;
534 RELEASE_LOCK(&cap->lock);
535 } else {
536 newReturningTask(cap,task);
537 RELEASE_LOCK(&cap->lock);
538
539 for (;;) {
540 ACQUIRE_LOCK(&task->lock);
541 // task->lock held, cap->lock not held
542 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
543 cap = task->cap;
544 task->wakeup = rtsFalse;
545 RELEASE_LOCK(&task->lock);
546
547 // now check whether we should wake up...
548 ACQUIRE_LOCK(&cap->lock);
549 if (cap->running_task == NULL) {
550 if (cap->returning_tasks_hd != task) {
551 giveCapabilityToTask(cap,cap->returning_tasks_hd);
552 RELEASE_LOCK(&cap->lock);
553 continue;
554 }
555 cap->running_task = task;
556 popReturningTask(cap);
557 RELEASE_LOCK(&cap->lock);
558 break;
559 }
560 RELEASE_LOCK(&cap->lock);
561 }
562
563 }
564
565 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
566
567 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
568
569 *pCap = cap;
570 #endif
571 }
572
573 #if defined(THREADED_RTS)
574 /* ----------------------------------------------------------------------------
575 * yieldCapability
576 * ------------------------------------------------------------------------- */
577
578 void
579 yieldCapability (Capability** pCap, Task *task)
580 {
581 Capability *cap = *pCap;
582
583 if (waiting_for_gc == PENDING_GC_PAR) {
584 traceEventGcStart(cap);
585 gcWorkerThread(cap);
586 traceEventGcEnd(cap);
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 traceEventShutdown(cap);
794 RELEASE_LOCK(&cap->lock);
795 break;
796 }
797 // we now have the Capability, its run queue and spare workers
798 // list are both empty.
799
800 // ToDo: we can't drop this mutex, because there might still be
801 // threads performing foreign calls that will eventually try to
802 // return via resumeThread() and attempt to grab cap->lock.
803 // closeMutex(&cap->lock);
804 }
805
806 /* ----------------------------------------------------------------------------
807 * tryGrabCapability
808 *
809 * Attempt to gain control of a Capability if it is free.
810 *
811 * ------------------------------------------------------------------------- */
812
813 rtsBool
814 tryGrabCapability (Capability *cap, Task *task)
815 {
816 if (cap->running_task != NULL) return rtsFalse;
817 ACQUIRE_LOCK(&cap->lock);
818 if (cap->running_task != NULL) {
819 RELEASE_LOCK(&cap->lock);
820 return rtsFalse;
821 }
822 task->cap = cap;
823 cap->running_task = task;
824 RELEASE_LOCK(&cap->lock);
825 return rtsTrue;
826 }
827
828
829 #endif /* THREADED_RTS */
830
831 static void
832 freeCapability (Capability *cap)
833 {
834 stgFree(cap->mut_lists);
835 stgFree(cap->saved_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 evac(user, (StgClosure **)(void *)&task->suspended_tso);
884 }
885
886 #if defined(THREADED_RTS)
887 if (prune_sparks) {
888 pruneSparkQueue (evac, user, cap);
889 } else {
890 traverseSparkQueue (evac, user, cap);
891 }
892 #endif
893 }
894
895 #if !defined(THREADED_RTS)
896 evac(user, (StgClosure **)(void *)&blocked_queue_hd);
897 evac(user, (StgClosure **)(void *)&blocked_queue_tl);
898 evac(user, (StgClosure **)(void *)&sleeping_queue);
899 #endif
900 }
901
902 void
903 markCapabilities (evac_fn evac, void *user)
904 {
905 markSomeCapabilities(evac, user, 0, 1, rtsFalse);
906 }