Revert "Add capability sets to the event system. Contains code from Duncan Coutts."
[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 sched_state >= SCHED_INTERRUPTING
66 || recent_activity == ACTIVITY_INACTIVE; // need to check for deadlock
67 }
68 #endif
69
70 #if defined(THREADED_RTS)
71 StgClosure *
72 findSpark (Capability *cap)
73 {
74 Capability *robbed;
75 StgClosurePtr spark;
76 rtsBool retry;
77 nat i = 0;
78
79 if (!emptyRunQueue(cap) || cap->returning_tasks_hd != NULL) {
80 // If there are other threads, don't try to run any new
81 // sparks: sparks might be speculative, we don't want to take
82 // resources away from the main computation.
83 return 0;
84 }
85
86 do {
87 retry = rtsFalse;
88
89 // first try to get a spark from our own pool.
90 // We should be using reclaimSpark(), because it works without
91 // needing any atomic instructions:
92 // spark = reclaimSpark(cap->sparks);
93 // However, measurements show that this makes at least one benchmark
94 // slower (prsa) and doesn't affect the others.
95 spark = tryStealSpark(cap);
96 if (spark != NULL) {
97 cap->sparks_converted++;
98
99 // Post event for running a spark from capability's own pool.
100 traceEventRunSpark(cap, cap->r.rCurrentTSO);
101
102 return spark;
103 }
104 if (!emptySparkPoolCap(cap)) {
105 retry = rtsTrue;
106 }
107
108 if (n_capabilities == 1) { return NULL; } // makes no sense...
109
110 debugTrace(DEBUG_sched,
111 "cap %d: Trying to steal work from other capabilities",
112 cap->no);
113
114 /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
115 start at a random place instead of 0 as well. */
116 for ( i=0 ; i < n_capabilities ; i++ ) {
117 robbed = &capabilities[i];
118 if (cap == robbed) // ourselves...
119 continue;
120
121 if (emptySparkPoolCap(robbed)) // nothing to steal here
122 continue;
123
124 spark = tryStealSpark(robbed);
125 if (spark == NULL && !emptySparkPoolCap(robbed)) {
126 // we conflicted with another thread while trying to steal;
127 // try again later.
128 retry = rtsTrue;
129 }
130
131 if (spark != NULL) {
132 cap->sparks_converted++;
133
134 traceEventStealSpark(cap, cap->r.rCurrentTSO, robbed->no);
135
136 return spark;
137 }
138 // otherwise: no success, try next one
139 }
140 } while (retry);
141
142 debugTrace(DEBUG_sched, "No sparks stolen");
143 return NULL;
144 }
145
146 // Returns True if any spark pool is non-empty at this moment in time
147 // The result is only valid for an instant, of course, so in a sense
148 // is immediately invalid, and should not be relied upon for
149 // correctness.
150 rtsBool
151 anySparks (void)
152 {
153 nat i;
154
155 for (i=0; i < n_capabilities; i++) {
156 if (!emptySparkPoolCap(&capabilities[i])) {
157 return rtsTrue;
158 }
159 }
160 return rtsFalse;
161 }
162 #endif
163
164 /* -----------------------------------------------------------------------------
165 * Manage the returning_tasks lists.
166 *
167 * These functions require cap->lock
168 * -------------------------------------------------------------------------- */
169
170 #if defined(THREADED_RTS)
171 STATIC_INLINE void
172 newReturningTask (Capability *cap, Task *task)
173 {
174 ASSERT_LOCK_HELD(&cap->lock);
175 ASSERT(task->next == NULL);
176 if (cap->returning_tasks_hd) {
177 ASSERT(cap->returning_tasks_tl->next == NULL);
178 cap->returning_tasks_tl->next = task;
179 } else {
180 cap->returning_tasks_hd = task;
181 }
182 cap->returning_tasks_tl = task;
183 }
184
185 STATIC_INLINE Task *
186 popReturningTask (Capability *cap)
187 {
188 ASSERT_LOCK_HELD(&cap->lock);
189 Task *task;
190 task = cap->returning_tasks_hd;
191 ASSERT(task);
192 cap->returning_tasks_hd = task->next;
193 if (!cap->returning_tasks_hd) {
194 cap->returning_tasks_tl = NULL;
195 }
196 task->next = NULL;
197 return task;
198 }
199 #endif
200
201 /* ----------------------------------------------------------------------------
202 * Initialisation
203 *
204 * The Capability is initially marked not free.
205 * ------------------------------------------------------------------------- */
206
207 static void
208 initCapability( Capability *cap, nat i )
209 {
210 nat g;
211
212 cap->no = i;
213 cap->in_haskell = rtsFalse;
214
215 cap->run_queue_hd = END_TSO_QUEUE;
216 cap->run_queue_tl = END_TSO_QUEUE;
217
218 #if defined(THREADED_RTS)
219 initMutex(&cap->lock);
220 cap->running_task = NULL; // indicates cap is free
221 cap->spare_workers = NULL;
222 cap->n_spare_workers = 0;
223 cap->suspended_ccalls = NULL;
224 cap->returning_tasks_hd = NULL;
225 cap->returning_tasks_tl = NULL;
226 cap->inbox = (Message*)END_TSO_QUEUE;
227 cap->sparks_created = 0;
228 cap->sparks_dud = 0;
229 cap->sparks_converted = 0;
230 cap->sparks_gcd = 0;
231 cap->sparks_fizzled = 0;
232 #endif
233
234 cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
235 cap->f.stgGCEnter1 = (StgFunPtr)__stg_gc_enter_1;
236 cap->f.stgGCFun = (StgFunPtr)__stg_gc_fun;
237
238 cap->mut_lists = stgMallocBytes(sizeof(bdescr *) *
239 RtsFlags.GcFlags.generations,
240 "initCapability");
241 cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
242 RtsFlags.GcFlags.generations,
243 "initCapability");
244
245 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
246 cap->mut_lists[g] = NULL;
247 }
248
249 cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
250 cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
251 cap->free_trec_chunks = END_STM_CHUNK_LIST;
252 cap->free_trec_headers = NO_TREC;
253 cap->transaction_tokens = 0;
254 cap->context_switch = 0;
255 cap->pinned_object_block = NULL;
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->incall->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 // assertion is false: in schedule() we force a yield after
400 // ThreadBlocked, but the thread may be back on the run queue
401 // by now.
402 task = cap->run_queue_hd->bound->task;
403 giveCapabilityToTask(cap,task);
404 return;
405 }
406
407 if (!cap->spare_workers) {
408 // Create a worker thread if we don't have one. If the system
409 // is interrupted, we only create a worker task if there
410 // are threads that need to be completed. If the system is
411 // shutting down, we never create a new worker.
412 if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
413 debugTrace(DEBUG_sched,
414 "starting new worker on capability %d", cap->no);
415 startWorkerTask(cap);
416 return;
417 }
418 }
419
420 // If we have an unbound thread on the run queue, or if there's
421 // anything else to do, give the Capability to a worker thread.
422 if (always_wakeup ||
423 !emptyRunQueue(cap) || !emptyInbox(cap) ||
424 !emptySparkPoolCap(cap) || globalWorkToDo()) {
425 if (cap->spare_workers) {
426 giveCapabilityToTask(cap,cap->spare_workers);
427 // The worker Task pops itself from the queue;
428 return;
429 }
430 }
431
432 last_free_capability = cap;
433 debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
434 }
435
436 void
437 releaseCapability (Capability* cap USED_IF_THREADS)
438 {
439 ACQUIRE_LOCK(&cap->lock);
440 releaseCapability_(cap, rtsFalse);
441 RELEASE_LOCK(&cap->lock);
442 }
443
444 void
445 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
446 {
447 ACQUIRE_LOCK(&cap->lock);
448 releaseCapability_(cap, rtsTrue);
449 RELEASE_LOCK(&cap->lock);
450 }
451
452 static void
453 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
454 {
455 Task *task;
456
457 ACQUIRE_LOCK(&cap->lock);
458
459 task = cap->running_task;
460
461 // If the Task is stopped, we shouldn't be yielding, we should
462 // be just exiting.
463 ASSERT(!task->stopped);
464
465 // If the current task is a worker, save it on the spare_workers
466 // list of this Capability. A worker can mark itself as stopped,
467 // in which case it is not replaced on the spare_worker queue.
468 // This happens when the system is shutting down (see
469 // Schedule.c:workerStart()).
470 if (!isBoundTask(task))
471 {
472 if (cap->n_spare_workers < MAX_SPARE_WORKERS)
473 {
474 task->next = cap->spare_workers;
475 cap->spare_workers = task;
476 cap->n_spare_workers++;
477 }
478 else
479 {
480 debugTrace(DEBUG_sched, "%d spare workers already, exiting",
481 cap->n_spare_workers);
482 releaseCapability_(cap,rtsFalse);
483 // hold the lock until after workerTaskStop; c.f. scheduleWorker()
484 workerTaskStop(task);
485 RELEASE_LOCK(&cap->lock);
486 shutdownThread();
487 }
488 }
489 // Bound tasks just float around attached to their TSOs.
490
491 releaseCapability_(cap,rtsFalse);
492
493 RELEASE_LOCK(&cap->lock);
494 }
495 #endif
496
497 /* ----------------------------------------------------------------------------
498 * waitForReturnCapability( Task *task )
499 *
500 * Purpose: when an OS thread returns from an external call,
501 * it calls waitForReturnCapability() (via Schedule.resumeThread())
502 * to wait for permission to enter the RTS & communicate the
503 * result of the external call back to the Haskell thread that
504 * made it.
505 *
506 * ------------------------------------------------------------------------- */
507 void
508 waitForReturnCapability (Capability **pCap, Task *task)
509 {
510 #if !defined(THREADED_RTS)
511
512 MainCapability.running_task = task;
513 task->cap = &MainCapability;
514 *pCap = &MainCapability;
515
516 #else
517 Capability *cap = *pCap;
518
519 if (cap == NULL) {
520 // Try last_free_capability first
521 cap = last_free_capability;
522 if (cap->running_task) {
523 nat i;
524 // otherwise, search for a free capability
525 cap = NULL;
526 for (i = 0; i < n_capabilities; i++) {
527 if (!capabilities[i].running_task) {
528 cap = &capabilities[i];
529 break;
530 }
531 }
532 if (cap == NULL) {
533 // Can't find a free one, use last_free_capability.
534 cap = last_free_capability;
535 }
536 }
537
538 // record the Capability as the one this Task is now assocated with.
539 task->cap = cap;
540
541 } else {
542 ASSERT(task->cap == cap);
543 }
544
545 ACQUIRE_LOCK(&cap->lock);
546
547 debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
548
549 if (!cap->running_task) {
550 // It's free; just grab it
551 cap->running_task = task;
552 RELEASE_LOCK(&cap->lock);
553 } else {
554 newReturningTask(cap,task);
555 RELEASE_LOCK(&cap->lock);
556
557 for (;;) {
558 ACQUIRE_LOCK(&task->lock);
559 // task->lock held, cap->lock not held
560 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
561 cap = task->cap;
562 task->wakeup = rtsFalse;
563 RELEASE_LOCK(&task->lock);
564
565 // now check whether we should wake up...
566 ACQUIRE_LOCK(&cap->lock);
567 if (cap->running_task == NULL) {
568 if (cap->returning_tasks_hd != task) {
569 giveCapabilityToTask(cap,cap->returning_tasks_hd);
570 RELEASE_LOCK(&cap->lock);
571 continue;
572 }
573 cap->running_task = task;
574 popReturningTask(cap);
575 RELEASE_LOCK(&cap->lock);
576 break;
577 }
578 RELEASE_LOCK(&cap->lock);
579 }
580
581 }
582
583 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
584
585 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
586
587 *pCap = cap;
588 #endif
589 }
590
591 #if defined(THREADED_RTS)
592 /* ----------------------------------------------------------------------------
593 * yieldCapability
594 * ------------------------------------------------------------------------- */
595
596 void
597 yieldCapability (Capability** pCap, Task *task)
598 {
599 Capability *cap = *pCap;
600
601 if (waiting_for_gc == PENDING_GC_PAR) {
602 traceEventGcStart(cap);
603 gcWorkerThread(cap);
604 traceEventGcEnd(cap);
605 return;
606 }
607
608 debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
609
610 // We must now release the capability and wait to be woken up
611 // again.
612 task->wakeup = rtsFalse;
613 releaseCapabilityAndQueueWorker(cap);
614
615 for (;;) {
616 ACQUIRE_LOCK(&task->lock);
617 // task->lock held, cap->lock not held
618 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
619 cap = task->cap;
620 task->wakeup = rtsFalse;
621 RELEASE_LOCK(&task->lock);
622
623 debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
624
625 ACQUIRE_LOCK(&cap->lock);
626 if (cap->running_task != NULL) {
627 debugTrace(DEBUG_sched,
628 "capability %d is owned by another task", cap->no);
629 RELEASE_LOCK(&cap->lock);
630 continue;
631 }
632
633 if (task->incall->tso == NULL) {
634 ASSERT(cap->spare_workers != NULL);
635 // if we're not at the front of the queue, release it
636 // again. This is unlikely to happen.
637 if (cap->spare_workers != task) {
638 giveCapabilityToTask(cap,cap->spare_workers);
639 RELEASE_LOCK(&cap->lock);
640 continue;
641 }
642 cap->spare_workers = task->next;
643 task->next = NULL;
644 cap->n_spare_workers--;
645 }
646 cap->running_task = task;
647 RELEASE_LOCK(&cap->lock);
648 break;
649 }
650
651 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
652 ASSERT(cap->running_task == task);
653
654 *pCap = cap;
655
656 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
657
658 return;
659 }
660
661 /* ----------------------------------------------------------------------------
662 * prodCapability
663 *
664 * If a Capability is currently idle, wake up a Task on it. Used to
665 * get every Capability into the GC.
666 * ------------------------------------------------------------------------- */
667
668 void
669 prodCapability (Capability *cap, Task *task)
670 {
671 ACQUIRE_LOCK(&cap->lock);
672 if (!cap->running_task) {
673 cap->running_task = task;
674 releaseCapability_(cap,rtsTrue);
675 }
676 RELEASE_LOCK(&cap->lock);
677 }
678
679 /* ----------------------------------------------------------------------------
680 * shutdownCapability
681 *
682 * At shutdown time, we want to let everything exit as cleanly as
683 * possible. For each capability, we let its run queue drain, and
684 * allow the workers to stop.
685 *
686 * This function should be called when interrupted and
687 * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
688 * will exit the scheduler and call taskStop(), and any bound thread
689 * that wakes up will return to its caller. Runnable threads are
690 * killed.
691 *
692 * ------------------------------------------------------------------------- */
693
694 void
695 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
696 {
697 nat i;
698
699 task->cap = cap;
700
701 // Loop indefinitely until all the workers have exited and there
702 // are no Haskell threads left. We used to bail out after 50
703 // iterations of this loop, but that occasionally left a worker
704 // running which caused problems later (the closeMutex() below
705 // isn't safe, for one thing).
706
707 for (i = 0; /* i < 50 */; i++) {
708 ASSERT(sched_state == SCHED_SHUTTING_DOWN);
709
710 debugTrace(DEBUG_sched,
711 "shutting down capability %d, attempt %d", cap->no, i);
712 ACQUIRE_LOCK(&cap->lock);
713 if (cap->running_task) {
714 RELEASE_LOCK(&cap->lock);
715 debugTrace(DEBUG_sched, "not owner, yielding");
716 yieldThread();
717 continue;
718 }
719 cap->running_task = task;
720
721 if (cap->spare_workers) {
722 // Look for workers that have died without removing
723 // themselves from the list; this could happen if the OS
724 // summarily killed the thread, for example. This
725 // actually happens on Windows when the system is
726 // terminating the program, and the RTS is running in a
727 // DLL.
728 Task *t, *prev;
729 prev = NULL;
730 for (t = cap->spare_workers; t != NULL; t = t->next) {
731 if (!osThreadIsAlive(t->id)) {
732 debugTrace(DEBUG_sched,
733 "worker thread %p has died unexpectedly", (void *)t->id);
734 cap->n_spare_workers--;
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_ccalls && 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 // The IO manager thread might have been slow to start up,
766 // so the first attempt to kill it might not have
767 // succeeded. Just in case, try again - the kill message
768 // will only be sent once.
769 //
770 // To reproduce this deadlock: run ffi002(threaded1)
771 // repeatedly on a loaded machine.
772 ioManagerDie();
773 yieldThread();
774 continue;
775 }
776
777 traceEventShutdown(cap);
778 RELEASE_LOCK(&cap->lock);
779 break;
780 }
781 // we now have the Capability, its run queue and spare workers
782 // list are both empty.
783
784 // ToDo: we can't drop this mutex, because there might still be
785 // threads performing foreign calls that will eventually try to
786 // return via resumeThread() and attempt to grab cap->lock.
787 // closeMutex(&cap->lock);
788 }
789
790 /* ----------------------------------------------------------------------------
791 * tryGrabCapability
792 *
793 * Attempt to gain control of a Capability if it is free.
794 *
795 * ------------------------------------------------------------------------- */
796
797 rtsBool
798 tryGrabCapability (Capability *cap, Task *task)
799 {
800 if (cap->running_task != NULL) return rtsFalse;
801 ACQUIRE_LOCK(&cap->lock);
802 if (cap->running_task != NULL) {
803 RELEASE_LOCK(&cap->lock);
804 return rtsFalse;
805 }
806 task->cap = cap;
807 cap->running_task = task;
808 RELEASE_LOCK(&cap->lock);
809 return rtsTrue;
810 }
811
812
813 #endif /* THREADED_RTS */
814
815 static void
816 freeCapability (Capability *cap)
817 {
818 stgFree(cap->mut_lists);
819 stgFree(cap->saved_mut_lists);
820 #if defined(THREADED_RTS)
821 freeSparkPool(cap->sparks);
822 #endif
823 }
824
825 void
826 freeCapabilities (void)
827 {
828 #if defined(THREADED_RTS)
829 nat i;
830 for (i=0; i < n_capabilities; i++) {
831 freeCapability(&capabilities[i]);
832 }
833 #else
834 freeCapability(&MainCapability);
835 #endif
836 }
837
838 /* ---------------------------------------------------------------------------
839 Mark everything directly reachable from the Capabilities. When
840 using multiple GC threads, each GC thread marks all Capabilities
841 for which (c `mod` n == 0), for Capability c and thread n.
842 ------------------------------------------------------------------------ */
843
844 void
845 markCapability (evac_fn evac, void *user, Capability *cap,
846 rtsBool no_mark_sparks USED_IF_THREADS)
847 {
848 InCall *incall;
849
850 // Each GC thread is responsible for following roots from the
851 // Capability of the same number. There will usually be the same
852 // or fewer Capabilities as GC threads, but just in case there
853 // are more, we mark every Capability whose number is the GC
854 // thread's index plus a multiple of the number of GC threads.
855 evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
856 evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
857 #if defined(THREADED_RTS)
858 evac(user, (StgClosure **)(void *)&cap->inbox);
859 #endif
860 for (incall = cap->suspended_ccalls; incall != NULL;
861 incall=incall->next) {
862 evac(user, (StgClosure **)(void *)&incall->suspended_tso);
863 }
864
865 #if defined(THREADED_RTS)
866 if (!no_mark_sparks) {
867 traverseSparkQueue (evac, user, cap);
868 }
869 #endif
870
871 // Free STM structures for this Capability
872 stmPreGCHook(cap);
873 }
874
875 void
876 markCapabilities (evac_fn evac, void *user)
877 {
878 nat n;
879 for (n = 0; n < n_capabilities; n++) {
880 markCapability(evac, user, &capabilities[n], rtsFalse);
881 }
882 }