Default to infinite stack size (#8189)
[ghc.git] / rts / Schedule.c
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 1998-2006
4 *
5 * The scheduler and thread-related functionality
6 *
7 * --------------------------------------------------------------------------*/
8
9 #include "PosixSource.h"
10 #define KEEP_LOCKCLOSURE
11 #include "Rts.h"
12
13 #include "sm/Storage.h"
14 #include "RtsUtils.h"
15 #include "StgRun.h"
16 #include "Schedule.h"
17 #include "Interpreter.h"
18 #include "Printer.h"
19 #include "RtsSignals.h"
20 #include "sm/Sanity.h"
21 #include "Stats.h"
22 #include "STM.h"
23 #include "Prelude.h"
24 #include "ThreadLabels.h"
25 #include "Updates.h"
26 #include "Proftimer.h"
27 #include "ProfHeap.h"
28 #include "Weak.h"
29 #include "sm/GC.h" // waitForGcThreads, releaseGCThreads, N
30 #include "sm/GCThread.h"
31 #include "Sparks.h"
32 #include "Capability.h"
33 #include "Task.h"
34 #include "AwaitEvent.h"
35 #if defined(mingw32_HOST_OS)
36 #include "win32/IOManager.h"
37 #endif
38 #include "Trace.h"
39 #include "RaiseAsync.h"
40 #include "Threads.h"
41 #include "Timer.h"
42 #include "ThreadPaused.h"
43 #include "Messages.h"
44 #include "Stable.h"
45
46 #ifdef HAVE_SYS_TYPES_H
47 #include <sys/types.h>
48 #endif
49 #ifdef HAVE_UNISTD_H
50 #include <unistd.h>
51 #endif
52
53 #include <string.h>
54 #include <stdlib.h>
55 #include <stdarg.h>
56
57 #ifdef HAVE_ERRNO_H
58 #include <errno.h>
59 #endif
60
61 #ifdef TRACING
62 #include "eventlog/EventLog.h"
63 #endif
64 /* -----------------------------------------------------------------------------
65 * Global variables
66 * -------------------------------------------------------------------------- */
67
68 #if !defined(THREADED_RTS)
69 // Blocked/sleeping thrads
70 StgTSO *blocked_queue_hd = NULL;
71 StgTSO *blocked_queue_tl = NULL;
72 StgTSO *sleeping_queue = NULL; // perhaps replace with a hash table?
73 #endif
74
75 /* Set to true when the latest garbage collection failed to reclaim
76 * enough space, and the runtime should proceed to shut itself down in
77 * an orderly fashion (emitting profiling info etc.)
78 */
79 rtsBool heap_overflow = rtsFalse;
80
81 /* flag that tracks whether we have done any execution in this time slice.
82 * LOCK: currently none, perhaps we should lock (but needs to be
83 * updated in the fast path of the scheduler).
84 *
85 * NB. must be StgWord, we do xchg() on it.
86 */
87 volatile StgWord recent_activity = ACTIVITY_YES;
88
89 /* if this flag is set as well, give up execution
90 * LOCK: none (changes monotonically)
91 */
92 volatile StgWord sched_state = SCHED_RUNNING;
93
94 /* This is used in `TSO.h' and gcc 2.96 insists that this variable actually
95 * exists - earlier gccs apparently didn't.
96 * -= chak
97 */
98 StgTSO dummy_tso;
99
100 /*
101 * This mutex protects most of the global scheduler data in
102 * the THREADED_RTS runtime.
103 */
104 #if defined(THREADED_RTS)
105 Mutex sched_mutex;
106 #endif
107
108 #if !defined(mingw32_HOST_OS)
109 #define FORKPROCESS_PRIMOP_SUPPORTED
110 #endif
111
112 // Local stats
113 #ifdef THREADED_RTS
114 static nat n_failed_trygrab_idles = 0, n_idle_caps = 0;
115 #endif
116
117 /* -----------------------------------------------------------------------------
118 * static function prototypes
119 * -------------------------------------------------------------------------- */
120
121 static Capability *schedule (Capability *initialCapability, Task *task);
122
123 //
124 // These functions all encapsulate parts of the scheduler loop, and are
125 // abstracted only to make the structure and control flow of the
126 // scheduler clearer.
127 //
128 static void schedulePreLoop (void);
129 static void scheduleFindWork (Capability **pcap);
130 #if defined(THREADED_RTS)
131 static void scheduleYield (Capability **pcap, Task *task);
132 #endif
133 #if defined(THREADED_RTS)
134 static nat requestSync (Capability **pcap, Task *task, nat sync_type);
135 static void acquireAllCapabilities(Capability *cap, Task *task);
136 static void releaseAllCapabilities(nat n, Capability *cap, Task *task);
137 static void startWorkerTasks (nat from USED_IF_THREADS, nat to USED_IF_THREADS);
138 #endif
139 static void scheduleStartSignalHandlers (Capability *cap);
140 static void scheduleCheckBlockedThreads (Capability *cap);
141 static void scheduleProcessInbox(Capability **cap);
142 static void scheduleDetectDeadlock (Capability **pcap, Task *task);
143 static void schedulePushWork(Capability *cap, Task *task);
144 #if defined(THREADED_RTS)
145 static void scheduleActivateSpark(Capability *cap);
146 #endif
147 static void schedulePostRunThread(Capability *cap, StgTSO *t);
148 static rtsBool scheduleHandleHeapOverflow( Capability *cap, StgTSO *t );
149 static rtsBool scheduleHandleYield( Capability *cap, StgTSO *t,
150 nat prev_what_next );
151 static void scheduleHandleThreadBlocked( StgTSO *t );
152 static rtsBool scheduleHandleThreadFinished( Capability *cap, Task *task,
153 StgTSO *t );
154 static rtsBool scheduleNeedHeapProfile(rtsBool ready_to_gc);
155 static void scheduleDoGC(Capability **pcap, Task *task, rtsBool force_major);
156
157 static void deleteThread (Capability *cap, StgTSO *tso);
158 static void deleteAllThreads (Capability *cap);
159
160 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
161 static void deleteThread_(Capability *cap, StgTSO *tso);
162 #endif
163
164 /* ---------------------------------------------------------------------------
165 Main scheduling loop.
166
167 We use round-robin scheduling, each thread returning to the
168 scheduler loop when one of these conditions is detected:
169
170 * out of heap space
171 * timer expires (thread yields)
172 * thread blocks
173 * thread ends
174 * stack overflow
175
176 ------------------------------------------------------------------------ */
177
178 static Capability *
179 schedule (Capability *initialCapability, Task *task)
180 {
181 StgTSO *t;
182 Capability *cap;
183 StgThreadReturnCode ret;
184 nat prev_what_next;
185 rtsBool ready_to_gc;
186 #if defined(THREADED_RTS)
187 rtsBool first = rtsTrue;
188 #endif
189
190 cap = initialCapability;
191
192 // Pre-condition: this task owns initialCapability.
193 // The sched_mutex is *NOT* held
194 // NB. on return, we still hold a capability.
195
196 debugTrace (DEBUG_sched, "cap %d: schedule()", initialCapability->no);
197
198 schedulePreLoop();
199
200 // -----------------------------------------------------------
201 // Scheduler loop starts here:
202
203 while (1) {
204
205 // Check whether we have re-entered the RTS from Haskell without
206 // going via suspendThread()/resumeThread (i.e. a 'safe' foreign
207 // call).
208 if (cap->in_haskell) {
209 errorBelch("schedule: re-entered unsafely.\n"
210 " Perhaps a 'foreign import unsafe' should be 'safe'?");
211 stg_exit(EXIT_FAILURE);
212 }
213
214 // The interruption / shutdown sequence.
215 //
216 // In order to cleanly shut down the runtime, we want to:
217 // * make sure that all main threads return to their callers
218 // with the state 'Interrupted'.
219 // * clean up all OS threads assocated with the runtime
220 // * free all memory etc.
221 //
222 // So the sequence for ^C goes like this:
223 //
224 // * ^C handler sets sched_state := SCHED_INTERRUPTING and
225 // arranges for some Capability to wake up
226 //
227 // * all threads in the system are halted, and the zombies are
228 // placed on the run queue for cleaning up. We acquire all
229 // the capabilities in order to delete the threads, this is
230 // done by scheduleDoGC() for convenience (because GC already
231 // needs to acquire all the capabilities). We can't kill
232 // threads involved in foreign calls.
233 //
234 // * somebody calls shutdownHaskell(), which calls exitScheduler()
235 //
236 // * sched_state := SCHED_SHUTTING_DOWN
237 //
238 // * all workers exit when the run queue on their capability
239 // drains. All main threads will also exit when their TSO
240 // reaches the head of the run queue and they can return.
241 //
242 // * eventually all Capabilities will shut down, and the RTS can
243 // exit.
244 //
245 // * We might be left with threads blocked in foreign calls,
246 // we should really attempt to kill these somehow (TODO);
247
248 switch (sched_state) {
249 case SCHED_RUNNING:
250 break;
251 case SCHED_INTERRUPTING:
252 debugTrace(DEBUG_sched, "SCHED_INTERRUPTING");
253 /* scheduleDoGC() deletes all the threads */
254 scheduleDoGC(&cap,task,rtsFalse);
255
256 // after scheduleDoGC(), we must be shutting down. Either some
257 // other Capability did the final GC, or we did it above,
258 // either way we can fall through to the SCHED_SHUTTING_DOWN
259 // case now.
260 ASSERT(sched_state == SCHED_SHUTTING_DOWN);
261 // fall through
262
263 case SCHED_SHUTTING_DOWN:
264 debugTrace(DEBUG_sched, "SCHED_SHUTTING_DOWN");
265 // If we are a worker, just exit. If we're a bound thread
266 // then we will exit below when we've removed our TSO from
267 // the run queue.
268 if (!isBoundTask(task) && emptyRunQueue(cap)) {
269 return cap;
270 }
271 break;
272 default:
273 barf("sched_state: %d", sched_state);
274 }
275
276 scheduleFindWork(&cap);
277
278 /* work pushing, currently relevant only for THREADED_RTS:
279 (pushes threads, wakes up idle capabilities for stealing) */
280 schedulePushWork(cap,task);
281
282 scheduleDetectDeadlock(&cap,task);
283
284 // Normally, the only way we can get here with no threads to
285 // run is if a keyboard interrupt received during
286 // scheduleCheckBlockedThreads() or scheduleDetectDeadlock().
287 // Additionally, it is not fatal for the
288 // threaded RTS to reach here with no threads to run.
289 //
290 // win32: might be here due to awaitEvent() being abandoned
291 // as a result of a console event having been delivered.
292
293 #if defined(THREADED_RTS)
294 if (first)
295 {
296 // XXX: ToDo
297 // // don't yield the first time, we want a chance to run this
298 // // thread for a bit, even if there are others banging at the
299 // // door.
300 // first = rtsFalse;
301 // ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
302 }
303
304 scheduleYield(&cap,task);
305
306 if (emptyRunQueue(cap)) continue; // look for work again
307 #endif
308
309 #if !defined(THREADED_RTS) && !defined(mingw32_HOST_OS)
310 if ( emptyRunQueue(cap) ) {
311 ASSERT(sched_state >= SCHED_INTERRUPTING);
312 }
313 #endif
314
315 //
316 // Get a thread to run
317 //
318 t = popRunQueue(cap);
319
320 // Sanity check the thread we're about to run. This can be
321 // expensive if there is lots of thread switching going on...
322 IF_DEBUG(sanity,checkTSO(t));
323
324 #if defined(THREADED_RTS)
325 // Check whether we can run this thread in the current task.
326 // If not, we have to pass our capability to the right task.
327 {
328 InCall *bound = t->bound;
329
330 if (bound) {
331 if (bound->task == task) {
332 // yes, the Haskell thread is bound to the current native thread
333 } else {
334 debugTrace(DEBUG_sched,
335 "thread %lu bound to another OS thread",
336 (unsigned long)t->id);
337 // no, bound to a different Haskell thread: pass to that thread
338 pushOnRunQueue(cap,t);
339 continue;
340 }
341 } else {
342 // The thread we want to run is unbound.
343 if (task->incall->tso) {
344 debugTrace(DEBUG_sched,
345 "this OS thread cannot run thread %lu",
346 (unsigned long)t->id);
347 // no, the current native thread is bound to a different
348 // Haskell thread, so pass it to any worker thread
349 pushOnRunQueue(cap,t);
350 continue;
351 }
352 }
353 }
354 #endif
355
356 // If we're shutting down, and this thread has not yet been
357 // killed, kill it now. This sometimes happens when a finalizer
358 // thread is created by the final GC, or a thread previously
359 // in a foreign call returns.
360 if (sched_state >= SCHED_INTERRUPTING &&
361 !(t->what_next == ThreadComplete || t->what_next == ThreadKilled)) {
362 deleteThread(cap,t);
363 }
364
365 // If this capability is disabled, migrate the thread away rather
366 // than running it. NB. but not if the thread is bound: it is
367 // really hard for a bound thread to migrate itself. Believe me,
368 // I tried several ways and couldn't find a way to do it.
369 // Instead, when everything is stopped for GC, we migrate all the
370 // threads on the run queue then (see scheduleDoGC()).
371 //
372 // ToDo: what about TSO_LOCKED? Currently we're migrating those
373 // when the number of capabilities drops, but we never migrate
374 // them back if it rises again. Presumably we should, but after
375 // the thread has been migrated we no longer know what capability
376 // it was originally on.
377 #ifdef THREADED_RTS
378 if (cap->disabled && !t->bound) {
379 Capability *dest_cap = capabilities[cap->no % enabled_capabilities];
380 migrateThread(cap, t, dest_cap);
381 continue;
382 }
383 #endif
384
385 /* context switches are initiated by the timer signal, unless
386 * the user specified "context switch as often as possible", with
387 * +RTS -C0
388 */
389 if (RtsFlags.ConcFlags.ctxtSwitchTicks == 0
390 && !emptyThreadQueues(cap)) {
391 cap->context_switch = 1;
392 }
393
394 run_thread:
395
396 // CurrentTSO is the thread to run. It might be different if we
397 // loop back to run_thread, so make sure to set CurrentTSO after
398 // that.
399 cap->r.rCurrentTSO = t;
400
401 startHeapProfTimer();
402
403 // ----------------------------------------------------------------------
404 // Run the current thread
405
406 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
407 ASSERT(t->cap == cap);
408 ASSERT(t->bound ? t->bound->task->cap == cap : 1);
409
410 prev_what_next = t->what_next;
411
412 errno = t->saved_errno;
413 #if mingw32_HOST_OS
414 SetLastError(t->saved_winerror);
415 #endif
416
417 // reset the interrupt flag before running Haskell code
418 cap->interrupt = 0;
419
420 cap->in_haskell = rtsTrue;
421 cap->idle = 0;
422
423 dirty_TSO(cap,t);
424 dirty_STACK(cap,t->stackobj);
425
426 switch (recent_activity)
427 {
428 case ACTIVITY_DONE_GC: {
429 // ACTIVITY_DONE_GC means we turned off the timer signal to
430 // conserve power (see #1623). Re-enable it here.
431 nat prev;
432 prev = xchg((P_)&recent_activity, ACTIVITY_YES);
433 if (prev == ACTIVITY_DONE_GC) {
434 #ifndef PROFILING
435 startTimer();
436 #endif
437 }
438 break;
439 }
440 case ACTIVITY_INACTIVE:
441 // If we reached ACTIVITY_INACTIVE, then don't reset it until
442 // we've done the GC. The thread running here might just be
443 // the IO manager thread that handle_tick() woke up via
444 // wakeUpRts().
445 break;
446 default:
447 recent_activity = ACTIVITY_YES;
448 }
449
450 traceEventRunThread(cap, t);
451
452 switch (prev_what_next) {
453
454 case ThreadKilled:
455 case ThreadComplete:
456 /* Thread already finished, return to scheduler. */
457 ret = ThreadFinished;
458 break;
459
460 case ThreadRunGHC:
461 {
462 StgRegTable *r;
463 r = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
464 cap = regTableToCapability(r);
465 ret = r->rRet;
466 break;
467 }
468
469 case ThreadInterpret:
470 cap = interpretBCO(cap);
471 ret = cap->r.rRet;
472 break;
473
474 default:
475 barf("schedule: invalid what_next field");
476 }
477
478 cap->in_haskell = rtsFalse;
479
480 // The TSO might have moved, eg. if it re-entered the RTS and a GC
481 // happened. So find the new location:
482 t = cap->r.rCurrentTSO;
483
484 // And save the current errno in this thread.
485 // XXX: possibly bogus for SMP because this thread might already
486 // be running again, see code below.
487 t->saved_errno = errno;
488 #if mingw32_HOST_OS
489 // Similarly for Windows error code
490 t->saved_winerror = GetLastError();
491 #endif
492
493 if (ret == ThreadBlocked) {
494 if (t->why_blocked == BlockedOnBlackHole) {
495 StgTSO *owner = blackHoleOwner(t->block_info.bh->bh);
496 traceEventStopThread(cap, t, t->why_blocked + 6,
497 owner != NULL ? owner->id : 0);
498 } else {
499 traceEventStopThread(cap, t, t->why_blocked + 6, 0);
500 }
501 } else {
502 traceEventStopThread(cap, t, ret, 0);
503 }
504
505 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
506 ASSERT(t->cap == cap);
507
508 // ----------------------------------------------------------------------
509
510 // Costs for the scheduler are assigned to CCS_SYSTEM
511 stopHeapProfTimer();
512 #if defined(PROFILING)
513 cap->r.rCCCS = CCS_SYSTEM;
514 #endif
515
516 schedulePostRunThread(cap,t);
517
518 ready_to_gc = rtsFalse;
519
520 switch (ret) {
521 case HeapOverflow:
522 ready_to_gc = scheduleHandleHeapOverflow(cap,t);
523 break;
524
525 case StackOverflow:
526 // just adjust the stack for this thread, then pop it back
527 // on the run queue.
528 threadStackOverflow(cap, t);
529 pushOnRunQueue(cap,t);
530 break;
531
532 case ThreadYielding:
533 if (scheduleHandleYield(cap, t, prev_what_next)) {
534 // shortcut for switching between compiler/interpreter:
535 goto run_thread;
536 }
537 break;
538
539 case ThreadBlocked:
540 scheduleHandleThreadBlocked(t);
541 break;
542
543 case ThreadFinished:
544 if (scheduleHandleThreadFinished(cap, task, t)) return cap;
545 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
546 break;
547
548 default:
549 barf("schedule: invalid thread return code %d", (int)ret);
550 }
551
552 if (ready_to_gc || scheduleNeedHeapProfile(ready_to_gc)) {
553 scheduleDoGC(&cap,task,rtsFalse);
554 }
555 } /* end of while() */
556 }
557
558 /* -----------------------------------------------------------------------------
559 * Run queue operations
560 * -------------------------------------------------------------------------- */
561
562 void
563 removeFromRunQueue (Capability *cap, StgTSO *tso)
564 {
565 if (tso->block_info.prev == END_TSO_QUEUE) {
566 ASSERT(cap->run_queue_hd == tso);
567 cap->run_queue_hd = tso->_link;
568 } else {
569 setTSOLink(cap, tso->block_info.prev, tso->_link);
570 }
571 if (tso->_link == END_TSO_QUEUE) {
572 ASSERT(cap->run_queue_tl == tso);
573 cap->run_queue_tl = tso->block_info.prev;
574 } else {
575 setTSOPrev(cap, tso->_link, tso->block_info.prev);
576 }
577 tso->_link = tso->block_info.prev = END_TSO_QUEUE;
578
579 IF_DEBUG(sanity, checkRunQueue(cap));
580 }
581
582 void
583 promoteInRunQueue (Capability *cap, StgTSO *tso)
584 {
585 removeFromRunQueue(cap, tso);
586 pushOnRunQueue(cap, tso);
587 }
588
589 /* ----------------------------------------------------------------------------
590 * Setting up the scheduler loop
591 * ------------------------------------------------------------------------- */
592
593 static void
594 schedulePreLoop(void)
595 {
596 // initialisation for scheduler - what cannot go into initScheduler()
597
598 #if defined(mingw32_HOST_OS) && !defined(USE_MINIINTERPRETER)
599 win32AllocStack();
600 #endif
601 }
602
603 /* -----------------------------------------------------------------------------
604 * scheduleFindWork()
605 *
606 * Search for work to do, and handle messages from elsewhere.
607 * -------------------------------------------------------------------------- */
608
609 static void
610 scheduleFindWork (Capability **pcap)
611 {
612 scheduleStartSignalHandlers(*pcap);
613
614 scheduleProcessInbox(pcap);
615
616 scheduleCheckBlockedThreads(*pcap);
617
618 #if defined(THREADED_RTS)
619 if (emptyRunQueue(*pcap)) { scheduleActivateSpark(*pcap); }
620 #endif
621 }
622
623 #if defined(THREADED_RTS)
624 STATIC_INLINE rtsBool
625 shouldYieldCapability (Capability *cap, Task *task, rtsBool didGcLast)
626 {
627 // we need to yield this capability to someone else if..
628 // - another thread is initiating a GC, and we didn't just do a GC
629 // (see Note [GC livelock])
630 // - another Task is returning from a foreign call
631 // - the thread at the head of the run queue cannot be run
632 // by this Task (it is bound to another Task, or it is unbound
633 // and this task it bound).
634 //
635 // Note [GC livelock]
636 //
637 // If we are interrupted to do a GC, then we do not immediately do
638 // another one. This avoids a starvation situation where one
639 // Capability keeps forcing a GC and the other Capabilities make no
640 // progress at all.
641
642 return ((pending_sync && !didGcLast) ||
643 cap->returning_tasks_hd != NULL ||
644 (!emptyRunQueue(cap) && (task->incall->tso == NULL
645 ? peekRunQueue(cap)->bound != NULL
646 : peekRunQueue(cap)->bound != task->incall)));
647 }
648
649 // This is the single place where a Task goes to sleep. There are
650 // two reasons it might need to sleep:
651 // - there are no threads to run
652 // - we need to yield this Capability to someone else
653 // (see shouldYieldCapability())
654 //
655 // Careful: the scheduler loop is quite delicate. Make sure you run
656 // the tests in testsuite/concurrent (all ways) after modifying this,
657 // and also check the benchmarks in nofib/parallel for regressions.
658
659 static void
660 scheduleYield (Capability **pcap, Task *task)
661 {
662 Capability *cap = *pcap;
663 int didGcLast = rtsFalse;
664
665 // if we have work, and we don't need to give up the Capability, continue.
666 //
667 if (!shouldYieldCapability(cap,task,rtsFalse) &&
668 (!emptyRunQueue(cap) ||
669 !emptyInbox(cap) ||
670 sched_state >= SCHED_INTERRUPTING)) {
671 return;
672 }
673
674 // otherwise yield (sleep), and keep yielding if necessary.
675 do {
676 didGcLast = yieldCapability(&cap,task, !didGcLast);
677 }
678 while (shouldYieldCapability(cap,task,didGcLast));
679
680 // note there may still be no threads on the run queue at this
681 // point, the caller has to check.
682
683 *pcap = cap;
684 return;
685 }
686 #endif
687
688 /* -----------------------------------------------------------------------------
689 * schedulePushWork()
690 *
691 * Push work to other Capabilities if we have some.
692 * -------------------------------------------------------------------------- */
693
694 static void
695 schedulePushWork(Capability *cap USED_IF_THREADS,
696 Task *task USED_IF_THREADS)
697 {
698 /* following code not for PARALLEL_HASKELL. I kept the call general,
699 future GUM versions might use pushing in a distributed setup */
700 #if defined(THREADED_RTS)
701
702 Capability *free_caps[n_capabilities], *cap0;
703 nat i, n_free_caps;
704
705 // migration can be turned off with +RTS -qm
706 if (!RtsFlags.ParFlags.migrate) return;
707
708 // Check whether we have more threads on our run queue, or sparks
709 // in our pool, that we could hand to another Capability.
710 if (emptyRunQueue(cap)) {
711 if (sparkPoolSizeCap(cap) < 2) return;
712 } else {
713 if (singletonRunQueue(cap) &&
714 sparkPoolSizeCap(cap) < 1) return;
715 }
716
717 // First grab as many free Capabilities as we can.
718 for (i=0, n_free_caps=0; i < n_capabilities; i++) {
719 cap0 = capabilities[i];
720 if (cap != cap0 && !cap0->disabled && tryGrabCapability(cap0,task)) {
721 if (!emptyRunQueue(cap0)
722 || cap0->returning_tasks_hd != NULL
723 || cap0->inbox != (Message*)END_TSO_QUEUE) {
724 // it already has some work, we just grabbed it at
725 // the wrong moment. Or maybe it's deadlocked!
726 releaseCapability(cap0);
727 } else {
728 free_caps[n_free_caps++] = cap0;
729 }
730 }
731 }
732
733 // we now have n_free_caps free capabilities stashed in
734 // free_caps[]. Share our run queue equally with them. This is
735 // probably the simplest thing we could do; improvements we might
736 // want to do include:
737 //
738 // - giving high priority to moving relatively new threads, on
739 // the gournds that they haven't had time to build up a
740 // working set in the cache on this CPU/Capability.
741 //
742 // - giving low priority to moving long-lived threads
743
744 if (n_free_caps > 0) {
745 StgTSO *prev, *t, *next;
746 #ifdef SPARK_PUSHING
747 rtsBool pushed_to_all;
748 #endif
749
750 debugTrace(DEBUG_sched,
751 "cap %d: %s and %d free capabilities, sharing...",
752 cap->no,
753 (!emptyRunQueue(cap) && !singletonRunQueue(cap))?
754 "excess threads on run queue":"sparks to share (>=2)",
755 n_free_caps);
756
757 i = 0;
758 #ifdef SPARK_PUSHING
759 pushed_to_all = rtsFalse;
760 #endif
761
762 if (cap->run_queue_hd != END_TSO_QUEUE) {
763 prev = cap->run_queue_hd;
764 t = prev->_link;
765 prev->_link = END_TSO_QUEUE;
766 for (; t != END_TSO_QUEUE; t = next) {
767 next = t->_link;
768 t->_link = END_TSO_QUEUE;
769 if (t->bound == task->incall // don't move my bound thread
770 || tsoLocked(t)) { // don't move a locked thread
771 setTSOLink(cap, prev, t);
772 setTSOPrev(cap, t, prev);
773 prev = t;
774 } else if (i == n_free_caps) {
775 #ifdef SPARK_PUSHING
776 pushed_to_all = rtsTrue;
777 #endif
778 i = 0;
779 // keep one for us
780 setTSOLink(cap, prev, t);
781 setTSOPrev(cap, t, prev);
782 prev = t;
783 } else {
784 appendToRunQueue(free_caps[i],t);
785
786 traceEventMigrateThread (cap, t, free_caps[i]->no);
787
788 if (t->bound) { t->bound->task->cap = free_caps[i]; }
789 t->cap = free_caps[i];
790 i++;
791 }
792 }
793 cap->run_queue_tl = prev;
794
795 IF_DEBUG(sanity, checkRunQueue(cap));
796 }
797
798 #ifdef SPARK_PUSHING
799 /* JB I left this code in place, it would work but is not necessary */
800
801 // If there are some free capabilities that we didn't push any
802 // threads to, then try to push a spark to each one.
803 if (!pushed_to_all) {
804 StgClosure *spark;
805 // i is the next free capability to push to
806 for (; i < n_free_caps; i++) {
807 if (emptySparkPoolCap(free_caps[i])) {
808 spark = tryStealSpark(cap->sparks);
809 if (spark != NULL) {
810 /* TODO: if anyone wants to re-enable this code then
811 * they must consider the fizzledSpark(spark) case
812 * and update the per-cap spark statistics.
813 */
814 debugTrace(DEBUG_sched, "pushing spark %p to capability %d", spark, free_caps[i]->no);
815
816 traceEventStealSpark(free_caps[i], t, cap->no);
817
818 newSpark(&(free_caps[i]->r), spark);
819 }
820 }
821 }
822 }
823 #endif /* SPARK_PUSHING */
824
825 // release the capabilities
826 for (i = 0; i < n_free_caps; i++) {
827 task->cap = free_caps[i];
828 releaseAndWakeupCapability(free_caps[i]);
829 }
830 }
831 task->cap = cap; // reset to point to our Capability.
832
833 #endif /* THREADED_RTS */
834
835 }
836
837 /* ----------------------------------------------------------------------------
838 * Start any pending signal handlers
839 * ------------------------------------------------------------------------- */
840
841 #if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
842 static void
843 scheduleStartSignalHandlers(Capability *cap)
844 {
845 if (RtsFlags.MiscFlags.install_signal_handlers && signals_pending()) {
846 // safe outside the lock
847 startSignalHandlers(cap);
848 }
849 }
850 #else
851 static void
852 scheduleStartSignalHandlers(Capability *cap STG_UNUSED)
853 {
854 }
855 #endif
856
857 /* ----------------------------------------------------------------------------
858 * Check for blocked threads that can be woken up.
859 * ------------------------------------------------------------------------- */
860
861 static void
862 scheduleCheckBlockedThreads(Capability *cap USED_IF_NOT_THREADS)
863 {
864 #if !defined(THREADED_RTS)
865 //
866 // Check whether any waiting threads need to be woken up. If the
867 // run queue is empty, and there are no other tasks running, we
868 // can wait indefinitely for something to happen.
869 //
870 if ( !emptyQueue(blocked_queue_hd) || !emptyQueue(sleeping_queue) )
871 {
872 awaitEvent (emptyRunQueue(cap));
873 }
874 #endif
875 }
876
877 /* ----------------------------------------------------------------------------
878 * Detect deadlock conditions and attempt to resolve them.
879 * ------------------------------------------------------------------------- */
880
881 static void
882 scheduleDetectDeadlock (Capability **pcap, Task *task)
883 {
884 Capability *cap = *pcap;
885 /*
886 * Detect deadlock: when we have no threads to run, there are no
887 * threads blocked, waiting for I/O, or sleeping, and all the
888 * other tasks are waiting for work, we must have a deadlock of
889 * some description.
890 */
891 if ( emptyThreadQueues(cap) )
892 {
893 #if defined(THREADED_RTS)
894 /*
895 * In the threaded RTS, we only check for deadlock if there
896 * has been no activity in a complete timeslice. This means
897 * we won't eagerly start a full GC just because we don't have
898 * any threads to run currently.
899 */
900 if (recent_activity != ACTIVITY_INACTIVE) return;
901 #endif
902
903 debugTrace(DEBUG_sched, "deadlocked, forcing major GC...");
904
905 // Garbage collection can release some new threads due to
906 // either (a) finalizers or (b) threads resurrected because
907 // they are unreachable and will therefore be sent an
908 // exception. Any threads thus released will be immediately
909 // runnable.
910 scheduleDoGC (pcap, task, rtsTrue/*force major GC*/);
911 cap = *pcap;
912 // when force_major == rtsTrue. scheduleDoGC sets
913 // recent_activity to ACTIVITY_DONE_GC and turns off the timer
914 // signal.
915
916 if ( !emptyRunQueue(cap) ) return;
917
918 #if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
919 /* If we have user-installed signal handlers, then wait
920 * for signals to arrive rather then bombing out with a
921 * deadlock.
922 */
923 if ( RtsFlags.MiscFlags.install_signal_handlers && anyUserHandlers() ) {
924 debugTrace(DEBUG_sched,
925 "still deadlocked, waiting for signals...");
926
927 awaitUserSignals();
928
929 if (signals_pending()) {
930 startSignalHandlers(cap);
931 }
932
933 // either we have threads to run, or we were interrupted:
934 ASSERT(!emptyRunQueue(cap) || sched_state >= SCHED_INTERRUPTING);
935
936 return;
937 }
938 #endif
939
940 #if !defined(THREADED_RTS)
941 /* Probably a real deadlock. Send the current main thread the
942 * Deadlock exception.
943 */
944 if (task->incall->tso) {
945 switch (task->incall->tso->why_blocked) {
946 case BlockedOnSTM:
947 case BlockedOnBlackHole:
948 case BlockedOnMsgThrowTo:
949 case BlockedOnMVar:
950 case BlockedOnMVarRead:
951 throwToSingleThreaded(cap, task->incall->tso,
952 (StgClosure *)nonTermination_closure);
953 return;
954 default:
955 barf("deadlock: main thread blocked in a strange way");
956 }
957 }
958 return;
959 #endif
960 }
961 }
962
963
964 /* ----------------------------------------------------------------------------
965 * Send pending messages (PARALLEL_HASKELL only)
966 * ------------------------------------------------------------------------- */
967
968 #if defined(PARALLEL_HASKELL)
969 static void
970 scheduleSendPendingMessages(void)
971 {
972
973 # if defined(PAR) // global Mem.Mgmt., omit for now
974 if (PendingFetches != END_BF_QUEUE) {
975 processFetches();
976 }
977 # endif
978
979 if (RtsFlags.ParFlags.BufferTime) {
980 // if we use message buffering, we must send away all message
981 // packets which have become too old...
982 sendOldBuffers();
983 }
984 }
985 #endif
986
987 /* ----------------------------------------------------------------------------
988 * Process message in the current Capability's inbox
989 * ------------------------------------------------------------------------- */
990
991 static void
992 scheduleProcessInbox (Capability **pcap USED_IF_THREADS)
993 {
994 #if defined(THREADED_RTS)
995 Message *m, *next;
996 int r;
997 Capability *cap = *pcap;
998
999 while (!emptyInbox(cap)) {
1000 if (cap->r.rCurrentNursery->link == NULL ||
1001 g0->n_new_large_words >= large_alloc_lim) {
1002 scheduleDoGC(pcap, cap->running_task, rtsFalse);
1003 cap = *pcap;
1004 }
1005
1006 // don't use a blocking acquire; if the lock is held by
1007 // another thread then just carry on. This seems to avoid
1008 // getting stuck in a message ping-pong situation with other
1009 // processors. We'll check the inbox again later anyway.
1010 //
1011 // We should really use a more efficient queue data structure
1012 // here. The trickiness is that we must ensure a Capability
1013 // never goes idle if the inbox is non-empty, which is why we
1014 // use cap->lock (cap->lock is released as the last thing
1015 // before going idle; see Capability.c:releaseCapability()).
1016 r = TRY_ACQUIRE_LOCK(&cap->lock);
1017 if (r != 0) return;
1018
1019 m = cap->inbox;
1020 cap->inbox = (Message*)END_TSO_QUEUE;
1021
1022 RELEASE_LOCK(&cap->lock);
1023
1024 while (m != (Message*)END_TSO_QUEUE) {
1025 next = m->link;
1026 executeMessage(cap, m);
1027 m = next;
1028 }
1029 }
1030 #endif
1031 }
1032
1033 /* ----------------------------------------------------------------------------
1034 * Activate spark threads (PARALLEL_HASKELL and THREADED_RTS)
1035 * ------------------------------------------------------------------------- */
1036
1037 #if defined(THREADED_RTS)
1038 static void
1039 scheduleActivateSpark(Capability *cap)
1040 {
1041 if (anySparks() && !cap->disabled)
1042 {
1043 createSparkThread(cap);
1044 debugTrace(DEBUG_sched, "creating a spark thread");
1045 }
1046 }
1047 #endif // PARALLEL_HASKELL || THREADED_RTS
1048
1049 /* ----------------------------------------------------------------------------
1050 * After running a thread...
1051 * ------------------------------------------------------------------------- */
1052
1053 static void
1054 schedulePostRunThread (Capability *cap, StgTSO *t)
1055 {
1056 // We have to be able to catch transactions that are in an
1057 // infinite loop as a result of seeing an inconsistent view of
1058 // memory, e.g.
1059 //
1060 // atomically $ do
1061 // [a,b] <- mapM readTVar [ta,tb]
1062 // when (a == b) loop
1063 //
1064 // and a is never equal to b given a consistent view of memory.
1065 //
1066 if (t -> trec != NO_TREC && t -> why_blocked == NotBlocked) {
1067 if (!stmValidateNestOfTransactions(cap, t -> trec)) {
1068 debugTrace(DEBUG_sched | DEBUG_stm,
1069 "trec %p found wasting its time", t);
1070
1071 // strip the stack back to the
1072 // ATOMICALLY_FRAME, aborting the (nested)
1073 // transaction, and saving the stack of any
1074 // partially-evaluated thunks on the heap.
1075 throwToSingleThreaded_(cap, t, NULL, rtsTrue);
1076
1077 // ASSERT(get_itbl((StgClosure *)t->sp)->type == ATOMICALLY_FRAME);
1078 }
1079 }
1080
1081 /* some statistics gathering in the parallel case */
1082 }
1083
1084 /* -----------------------------------------------------------------------------
1085 * Handle a thread that returned to the scheduler with ThreadHeepOverflow
1086 * -------------------------------------------------------------------------- */
1087
1088 static rtsBool
1089 scheduleHandleHeapOverflow( Capability *cap, StgTSO *t )
1090 {
1091 // did the task ask for a large block?
1092 if (cap->r.rHpAlloc > BLOCK_SIZE) {
1093 // if so, get one and push it on the front of the nursery.
1094 bdescr *bd;
1095 W_ blocks;
1096
1097 blocks = (W_)BLOCK_ROUND_UP(cap->r.rHpAlloc) / BLOCK_SIZE;
1098
1099 if (blocks > BLOCKS_PER_MBLOCK) {
1100 barf("allocation of %ld bytes too large (GHC should have complained at compile-time)", (long)cap->r.rHpAlloc);
1101 }
1102
1103 debugTrace(DEBUG_sched,
1104 "--<< thread %ld (%s) stopped: requesting a large block (size %ld)\n",
1105 (long)t->id, what_next_strs[t->what_next], blocks);
1106
1107 // don't do this if the nursery is (nearly) full, we'll GC first.
1108 if (cap->r.rCurrentNursery->link != NULL ||
1109 cap->r.rNursery->n_blocks == 1) { // paranoia to prevent infinite loop
1110 // if the nursery has only one block.
1111
1112 bd = allocGroup_lock(blocks);
1113 cap->r.rNursery->n_blocks += blocks;
1114
1115 // link the new group into the list
1116 bd->link = cap->r.rCurrentNursery;
1117 bd->u.back = cap->r.rCurrentNursery->u.back;
1118 if (cap->r.rCurrentNursery->u.back != NULL) {
1119 cap->r.rCurrentNursery->u.back->link = bd;
1120 } else {
1121 cap->r.rNursery->blocks = bd;
1122 }
1123 cap->r.rCurrentNursery->u.back = bd;
1124
1125 // initialise it as a nursery block. We initialise the
1126 // step, gen_no, and flags field of *every* sub-block in
1127 // this large block, because this is easier than making
1128 // sure that we always find the block head of a large
1129 // block whenever we call Bdescr() (eg. evacuate() and
1130 // isAlive() in the GC would both have to do this, at
1131 // least).
1132 {
1133 bdescr *x;
1134 for (x = bd; x < bd + blocks; x++) {
1135 initBdescr(x,g0,g0);
1136 x->free = x->start;
1137 x->flags = 0;
1138 }
1139 }
1140
1141 // This assert can be a killer if the app is doing lots
1142 // of large block allocations.
1143 IF_DEBUG(sanity, checkNurserySanity(cap->r.rNursery));
1144
1145 // now update the nursery to point to the new block
1146 cap->r.rCurrentNursery = bd;
1147
1148 // we might be unlucky and have another thread get on the
1149 // run queue before us and steal the large block, but in that
1150 // case the thread will just end up requesting another large
1151 // block.
1152 pushOnRunQueue(cap,t);
1153 return rtsFalse; /* not actually GC'ing */
1154 }
1155 }
1156
1157 if (cap->r.rHpLim == NULL || cap->context_switch) {
1158 // Sometimes we miss a context switch, e.g. when calling
1159 // primitives in a tight loop, MAYBE_GC() doesn't check the
1160 // context switch flag, and we end up waiting for a GC.
1161 // See #1984, and concurrent/should_run/1984
1162 cap->context_switch = 0;
1163 appendToRunQueue(cap,t);
1164 } else {
1165 pushOnRunQueue(cap,t);
1166 }
1167 return rtsTrue;
1168 /* actual GC is done at the end of the while loop in schedule() */
1169 }
1170
1171 /* -----------------------------------------------------------------------------
1172 * Handle a thread that returned to the scheduler with ThreadYielding
1173 * -------------------------------------------------------------------------- */
1174
1175 static rtsBool
1176 scheduleHandleYield( Capability *cap, StgTSO *t, nat prev_what_next )
1177 {
1178 /* put the thread back on the run queue. Then, if we're ready to
1179 * GC, check whether this is the last task to stop. If so, wake
1180 * up the GC thread. getThread will block during a GC until the
1181 * GC is finished.
1182 */
1183
1184 ASSERT(t->_link == END_TSO_QUEUE);
1185
1186 // Shortcut if we're just switching evaluators: don't bother
1187 // doing stack squeezing (which can be expensive), just run the
1188 // thread.
1189 if (cap->context_switch == 0 && t->what_next != prev_what_next) {
1190 debugTrace(DEBUG_sched,
1191 "--<< thread %ld (%s) stopped to switch evaluators",
1192 (long)t->id, what_next_strs[t->what_next]);
1193 return rtsTrue;
1194 }
1195
1196 // Reset the context switch flag. We don't do this just before
1197 // running the thread, because that would mean we would lose ticks
1198 // during GC, which can lead to unfair scheduling (a thread hogs
1199 // the CPU because the tick always arrives during GC). This way
1200 // penalises threads that do a lot of allocation, but that seems
1201 // better than the alternative.
1202 if (cap->context_switch != 0) {
1203 cap->context_switch = 0;
1204 appendToRunQueue(cap,t);
1205 } else {
1206 pushOnRunQueue(cap,t);
1207 }
1208
1209 IF_DEBUG(sanity,
1210 //debugBelch("&& Doing sanity check on yielding TSO %ld.", t->id);
1211 checkTSO(t));
1212
1213 return rtsFalse;
1214 }
1215
1216 /* -----------------------------------------------------------------------------
1217 * Handle a thread that returned to the scheduler with ThreadBlocked
1218 * -------------------------------------------------------------------------- */
1219
1220 static void
1221 scheduleHandleThreadBlocked( StgTSO *t
1222 #if !defined(DEBUG)
1223 STG_UNUSED
1224 #endif
1225 )
1226 {
1227
1228 // We don't need to do anything. The thread is blocked, and it
1229 // has tidied up its stack and placed itself on whatever queue
1230 // it needs to be on.
1231
1232 // ASSERT(t->why_blocked != NotBlocked);
1233 // Not true: for example,
1234 // - the thread may have woken itself up already, because
1235 // threadPaused() might have raised a blocked throwTo
1236 // exception, see maybePerformBlockedException().
1237
1238 #ifdef DEBUG
1239 traceThreadStatus(DEBUG_sched, t);
1240 #endif
1241 }
1242
1243 /* -----------------------------------------------------------------------------
1244 * Handle a thread that returned to the scheduler with ThreadFinished
1245 * -------------------------------------------------------------------------- */
1246
1247 static rtsBool
1248 scheduleHandleThreadFinished (Capability *cap STG_UNUSED, Task *task, StgTSO *t)
1249 {
1250 /* Need to check whether this was a main thread, and if so,
1251 * return with the return value.
1252 *
1253 * We also end up here if the thread kills itself with an
1254 * uncaught exception, see Exception.cmm.
1255 */
1256
1257 // blocked exceptions can now complete, even if the thread was in
1258 // blocked mode (see #2910).
1259 awakenBlockedExceptionQueue (cap, t);
1260
1261 //
1262 // Check whether the thread that just completed was a bound
1263 // thread, and if so return with the result.
1264 //
1265 // There is an assumption here that all thread completion goes
1266 // through this point; we need to make sure that if a thread
1267 // ends up in the ThreadKilled state, that it stays on the run
1268 // queue so it can be dealt with here.
1269 //
1270
1271 if (t->bound) {
1272
1273 if (t->bound != task->incall) {
1274 #if !defined(THREADED_RTS)
1275 // Must be a bound thread that is not the topmost one. Leave
1276 // it on the run queue until the stack has unwound to the
1277 // point where we can deal with this. Leaving it on the run
1278 // queue also ensures that the garbage collector knows about
1279 // this thread and its return value (it gets dropped from the
1280 // step->threads list so there's no other way to find it).
1281 appendToRunQueue(cap,t);
1282 return rtsFalse;
1283 #else
1284 // this cannot happen in the threaded RTS, because a
1285 // bound thread can only be run by the appropriate Task.
1286 barf("finished bound thread that isn't mine");
1287 #endif
1288 }
1289
1290 ASSERT(task->incall->tso == t);
1291
1292 if (t->what_next == ThreadComplete) {
1293 if (task->incall->ret) {
1294 // NOTE: return val is stack->sp[1] (see StgStartup.hc)
1295 *(task->incall->ret) = (StgClosure *)task->incall->tso->stackobj->sp[1];
1296 }
1297 task->incall->stat = Success;
1298 } else {
1299 if (task->incall->ret) {
1300 *(task->incall->ret) = NULL;
1301 }
1302 if (sched_state >= SCHED_INTERRUPTING) {
1303 if (heap_overflow) {
1304 task->incall->stat = HeapExhausted;
1305 } else {
1306 task->incall->stat = Interrupted;
1307 }
1308 } else {
1309 task->incall->stat = Killed;
1310 }
1311 }
1312 #ifdef DEBUG
1313 removeThreadLabel((StgWord)task->incall->tso->id);
1314 #endif
1315
1316 // We no longer consider this thread and task to be bound to
1317 // each other. The TSO lives on until it is GC'd, but the
1318 // task is about to be released by the caller, and we don't
1319 // want anyone following the pointer from the TSO to the
1320 // defunct task (which might have already been
1321 // re-used). This was a real bug: the GC updated
1322 // tso->bound->tso which lead to a deadlock.
1323 t->bound = NULL;
1324 task->incall->tso = NULL;
1325
1326 return rtsTrue; // tells schedule() to return
1327 }
1328
1329 return rtsFalse;
1330 }
1331
1332 /* -----------------------------------------------------------------------------
1333 * Perform a heap census
1334 * -------------------------------------------------------------------------- */
1335
1336 static rtsBool
1337 scheduleNeedHeapProfile( rtsBool ready_to_gc STG_UNUSED )
1338 {
1339 // When we have +RTS -i0 and we're heap profiling, do a census at
1340 // every GC. This lets us get repeatable runs for debugging.
1341 if (performHeapProfile ||
1342 (RtsFlags.ProfFlags.heapProfileInterval==0 &&
1343 RtsFlags.ProfFlags.doHeapProfile && ready_to_gc)) {
1344 return rtsTrue;
1345 } else {
1346 return rtsFalse;
1347 }
1348 }
1349
1350 /* -----------------------------------------------------------------------------
1351 * Start a synchronisation of all capabilities
1352 * -------------------------------------------------------------------------- */
1353
1354 // Returns:
1355 // 0 if we successfully got a sync
1356 // non-0 if there was another sync request in progress,
1357 // and we yielded to it. The value returned is the
1358 // type of the other sync request.
1359 //
1360 #if defined(THREADED_RTS)
1361 static nat requestSync (Capability **pcap, Task *task, nat sync_type)
1362 {
1363 nat prev_pending_sync;
1364
1365 prev_pending_sync = cas(&pending_sync, 0, sync_type);
1366
1367 if (prev_pending_sync)
1368 {
1369 do {
1370 debugTrace(DEBUG_sched, "someone else is trying to sync (%d)...",
1371 prev_pending_sync);
1372 ASSERT(*pcap);
1373 yieldCapability(pcap,task,rtsTrue);
1374 } while (pending_sync);
1375 return prev_pending_sync; // NOTE: task->cap might have changed now
1376 }
1377 else
1378 {
1379 return 0;
1380 }
1381 }
1382
1383 //
1384 // Grab all the capabilities except the one we already hold. Used
1385 // when synchronising before a single-threaded GC (SYNC_SEQ_GC), and
1386 // before a fork (SYNC_OTHER).
1387 //
1388 // Only call this after requestSync(), otherwise a deadlock might
1389 // ensue if another thread is trying to synchronise.
1390 //
1391 static void acquireAllCapabilities(Capability *cap, Task *task)
1392 {
1393 Capability *tmpcap;
1394 nat i;
1395
1396 for (i=0; i < n_capabilities; i++) {
1397 debugTrace(DEBUG_sched, "grabbing all the capabilies (%d/%d)", i, n_capabilities);
1398 tmpcap = capabilities[i];
1399 if (tmpcap != cap) {
1400 // we better hope this task doesn't get migrated to
1401 // another Capability while we're waiting for this one.
1402 // It won't, because load balancing happens while we have
1403 // all the Capabilities, but even so it's a slightly
1404 // unsavoury invariant.
1405 task->cap = tmpcap;
1406 waitForReturnCapability(&tmpcap, task);
1407 if (tmpcap->no != i) {
1408 barf("acquireAllCapabilities: got the wrong capability");
1409 }
1410 }
1411 }
1412 task->cap = cap;
1413 }
1414
1415 static void releaseAllCapabilities(nat n, Capability *cap, Task *task)
1416 {
1417 nat i;
1418
1419 for (i = 0; i < n; i++) {
1420 if (cap->no != i) {
1421 task->cap = capabilities[i];
1422 releaseCapability(capabilities[i]);
1423 }
1424 }
1425 task->cap = cap;
1426 }
1427 #endif
1428
1429 /* -----------------------------------------------------------------------------
1430 * Perform a garbage collection if necessary
1431 * -------------------------------------------------------------------------- */
1432
1433 static void
1434 scheduleDoGC (Capability **pcap, Task *task USED_IF_THREADS,
1435 rtsBool force_major)
1436 {
1437 Capability *cap = *pcap;
1438 rtsBool heap_census;
1439 nat collect_gen;
1440 #ifdef THREADED_RTS
1441 StgWord8 gc_type;
1442 nat i, sync;
1443 StgTSO *tso;
1444 #endif
1445
1446 if (sched_state == SCHED_SHUTTING_DOWN) {
1447 // The final GC has already been done, and the system is
1448 // shutting down. We'll probably deadlock if we try to GC
1449 // now.
1450 return;
1451 }
1452
1453 heap_census = scheduleNeedHeapProfile(rtsTrue);
1454
1455 // Figure out which generation we are collecting, so that we can
1456 // decide whether this is a parallel GC or not.
1457 collect_gen = calcNeeded(force_major || heap_census, NULL);
1458
1459 #ifdef THREADED_RTS
1460 if (sched_state < SCHED_INTERRUPTING
1461 && RtsFlags.ParFlags.parGcEnabled
1462 && collect_gen >= RtsFlags.ParFlags.parGcGen
1463 && ! oldest_gen->mark)
1464 {
1465 gc_type = SYNC_GC_PAR;
1466 } else {
1467 gc_type = SYNC_GC_SEQ;
1468 }
1469
1470 // In order to GC, there must be no threads running Haskell code.
1471 // Therefore, the GC thread needs to hold *all* the capabilities,
1472 // and release them after the GC has completed.
1473 //
1474 // This seems to be the simplest way: previous attempts involved
1475 // making all the threads with capabilities give up their
1476 // capabilities and sleep except for the *last* one, which
1477 // actually did the GC. But it's quite hard to arrange for all
1478 // the other tasks to sleep and stay asleep.
1479 //
1480
1481 /* Other capabilities are prevented from running yet more Haskell
1482 threads if pending_sync is set. Tested inside
1483 yieldCapability() and releaseCapability() in Capability.c */
1484
1485 do {
1486 sync = requestSync(pcap, task, gc_type);
1487 cap = *pcap;
1488 if (sync == SYNC_GC_SEQ || sync == SYNC_GC_PAR) {
1489 // someone else had a pending sync request for a GC, so
1490 // let's assume GC has been done and we don't need to GC
1491 // again.
1492 return;
1493 }
1494 if (sched_state == SCHED_SHUTTING_DOWN) {
1495 // The scheduler might now be shutting down. We tested
1496 // this above, but it might have become true since then as
1497 // we yielded the capability in requestSync().
1498 return;
1499 }
1500 } while (sync);
1501
1502 // don't declare this until after we have sync'd, because
1503 // n_capabilities may change.
1504 rtsBool idle_cap[n_capabilities];
1505 #ifdef DEBUG
1506 unsigned int old_n_capabilities = n_capabilities;
1507 #endif
1508
1509 interruptAllCapabilities();
1510
1511 // The final shutdown GC is always single-threaded, because it's
1512 // possible that some of the Capabilities have no worker threads.
1513
1514 if (gc_type == SYNC_GC_SEQ)
1515 {
1516 traceEventRequestSeqGc(cap);
1517 }
1518 else
1519 {
1520 traceEventRequestParGc(cap);
1521 debugTrace(DEBUG_sched, "ready_to_gc, grabbing GC threads");
1522 }
1523
1524 if (gc_type == SYNC_GC_SEQ)
1525 {
1526 // single-threaded GC: grab all the capabilities
1527 acquireAllCapabilities(cap,task);
1528 }
1529 else
1530 {
1531 // If we are load-balancing collections in this
1532 // generation, then we require all GC threads to participate
1533 // in the collection. Otherwise, we only require active
1534 // threads to participate, and we set gc_threads[i]->idle for
1535 // any idle capabilities. The rationale here is that waking
1536 // up an idle Capability takes much longer than just doing any
1537 // GC work on its behalf.
1538
1539 if (RtsFlags.ParFlags.parGcNoSyncWithIdle == 0
1540 || (RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
1541 collect_gen >= RtsFlags.ParFlags.parGcLoadBalancingGen)) {
1542 for (i=0; i < n_capabilities; i++) {
1543 if (capabilities[i]->disabled) {
1544 idle_cap[i] = tryGrabCapability(capabilities[i], task);
1545 } else {
1546 idle_cap[i] = rtsFalse;
1547 }
1548 }
1549 } else {
1550 for (i=0; i < n_capabilities; i++) {
1551 if (capabilities[i]->disabled) {
1552 idle_cap[i] = tryGrabCapability(capabilities[i], task);
1553 } else if (i == cap->no ||
1554 capabilities[i]->idle < RtsFlags.ParFlags.parGcNoSyncWithIdle) {
1555 idle_cap[i] = rtsFalse;
1556 } else {
1557 idle_cap[i] = tryGrabCapability(capabilities[i], task);
1558 if (!idle_cap[i]) {
1559 n_failed_trygrab_idles++;
1560 } else {
1561 n_idle_caps++;
1562 }
1563 }
1564 }
1565 }
1566
1567 // We set the gc_thread[i]->idle flag if that
1568 // capability/thread is not participating in this collection.
1569 // We also keep a local record of which capabilities are idle
1570 // in idle_cap[], because scheduleDoGC() is re-entrant:
1571 // another thread might start a GC as soon as we've finished
1572 // this one, and thus the gc_thread[]->idle flags are invalid
1573 // as soon as we release any threads after GC. Getting this
1574 // wrong leads to a rare and hard to debug deadlock!
1575
1576 for (i=0; i < n_capabilities; i++) {
1577 gc_threads[i]->idle = idle_cap[i];
1578 capabilities[i]->idle++;
1579 }
1580
1581 // For all capabilities participating in this GC, wait until
1582 // they have stopped mutating and are standing by for GC.
1583 waitForGcThreads(cap);
1584
1585 #if defined(THREADED_RTS)
1586 // Stable point where we can do a global check on our spark counters
1587 ASSERT(checkSparkCountInvariant());
1588 #endif
1589 }
1590
1591 #endif
1592
1593 IF_DEBUG(scheduler, printAllThreads());
1594
1595 delete_threads_and_gc:
1596 /*
1597 * We now have all the capabilities; if we're in an interrupting
1598 * state, then we should take the opportunity to delete all the
1599 * threads in the system.
1600 */
1601 if (sched_state == SCHED_INTERRUPTING) {
1602 deleteAllThreads(cap);
1603 #if defined(THREADED_RTS)
1604 // Discard all the sparks from every Capability. Why?
1605 // They'll probably be GC'd anyway since we've killed all the
1606 // threads. It just avoids the GC having to do any work to
1607 // figure out that any remaining sparks are garbage.
1608 for (i = 0; i < n_capabilities; i++) {
1609 capabilities[i]->spark_stats.gcd +=
1610 sparkPoolSize(capabilities[i]->sparks);
1611 // No race here since all Caps are stopped.
1612 discardSparksCap(capabilities[i]);
1613 }
1614 #endif
1615 sched_state = SCHED_SHUTTING_DOWN;
1616 }
1617
1618 /*
1619 * When there are disabled capabilities, we want to migrate any
1620 * threads away from them. Normally this happens in the
1621 * scheduler's loop, but only for unbound threads - it's really
1622 * hard for a bound thread to migrate itself. So we have another
1623 * go here.
1624 */
1625 #if defined(THREADED_RTS)
1626 for (i = enabled_capabilities; i < n_capabilities; i++) {
1627 Capability *tmp_cap, *dest_cap;
1628 tmp_cap = capabilities[i];
1629 ASSERT(tmp_cap->disabled);
1630 if (i != cap->no) {
1631 dest_cap = capabilities[i % enabled_capabilities];
1632 while (!emptyRunQueue(tmp_cap)) {
1633 tso = popRunQueue(tmp_cap);
1634 migrateThread(tmp_cap, tso, dest_cap);
1635 if (tso->bound) {
1636 traceTaskMigrate(tso->bound->task,
1637 tso->bound->task->cap,
1638 dest_cap);
1639 tso->bound->task->cap = dest_cap;
1640 }
1641 }
1642 }
1643 }
1644 #endif
1645
1646 #if defined(THREADED_RTS)
1647 // reset pending_sync *before* GC, so that when the GC threads
1648 // emerge they don't immediately re-enter the GC.
1649 pending_sync = 0;
1650 GarbageCollect(collect_gen, heap_census, gc_type, cap);
1651 #else
1652 GarbageCollect(collect_gen, heap_census, 0, cap);
1653 #endif
1654
1655 traceSparkCounters(cap);
1656
1657 switch (recent_activity) {
1658 case ACTIVITY_INACTIVE:
1659 if (force_major) {
1660 // We are doing a GC because the system has been idle for a
1661 // timeslice and we need to check for deadlock. Record the
1662 // fact that we've done a GC and turn off the timer signal;
1663 // it will get re-enabled if we run any threads after the GC.
1664 recent_activity = ACTIVITY_DONE_GC;
1665 #ifndef PROFILING
1666 stopTimer();
1667 #endif
1668 break;
1669 }
1670 // fall through...
1671
1672 case ACTIVITY_MAYBE_NO:
1673 // the GC might have taken long enough for the timer to set
1674 // recent_activity = ACTIVITY_MAYBE_NO or ACTIVITY_INACTIVE,
1675 // but we aren't necessarily deadlocked:
1676 recent_activity = ACTIVITY_YES;
1677 break;
1678
1679 case ACTIVITY_DONE_GC:
1680 // If we are actually active, the scheduler will reset the
1681 // recent_activity flag and re-enable the timer.
1682 break;
1683 }
1684
1685 #if defined(THREADED_RTS)
1686 // Stable point where we can do a global check on our spark counters
1687 ASSERT(checkSparkCountInvariant());
1688 #endif
1689
1690 // The heap census itself is done during GarbageCollect().
1691 if (heap_census) {
1692 performHeapProfile = rtsFalse;
1693 }
1694
1695 #if defined(THREADED_RTS)
1696
1697 // If n_capabilities has changed during GC, we're in trouble.
1698 ASSERT(n_capabilities == old_n_capabilities);
1699
1700 if (gc_type == SYNC_GC_PAR)
1701 {
1702 releaseGCThreads(cap);
1703 for (i = 0; i < n_capabilities; i++) {
1704 if (i != cap->no) {
1705 if (idle_cap[i]) {
1706 ASSERT(capabilities[i]->running_task == task);
1707 task->cap = capabilities[i];
1708 releaseCapability(capabilities[i]);
1709 } else {
1710 ASSERT(capabilities[i]->running_task != task);
1711 }
1712 }
1713 }
1714 task->cap = cap;
1715 }
1716 #endif
1717
1718 if (heap_overflow && sched_state < SCHED_INTERRUPTING) {
1719 // GC set the heap_overflow flag, so we should proceed with
1720 // an orderly shutdown now. Ultimately we want the main
1721 // thread to return to its caller with HeapExhausted, at which
1722 // point the caller should call hs_exit(). The first step is
1723 // to delete all the threads.
1724 //
1725 // Another way to do this would be to raise an exception in
1726 // the main thread, which we really should do because it gives
1727 // the program a chance to clean up. But how do we find the
1728 // main thread? It should presumably be the same one that
1729 // gets ^C exceptions, but that's all done on the Haskell side
1730 // (GHC.TopHandler).
1731 sched_state = SCHED_INTERRUPTING;
1732 goto delete_threads_and_gc;
1733 }
1734
1735 #ifdef SPARKBALANCE
1736 /* JB
1737 Once we are all together... this would be the place to balance all
1738 spark pools. No concurrent stealing or adding of new sparks can
1739 occur. Should be defined in Sparks.c. */
1740 balanceSparkPoolsCaps(n_capabilities, capabilities);
1741 #endif
1742
1743 #if defined(THREADED_RTS)
1744 if (gc_type == SYNC_GC_SEQ) {
1745 // release our stash of capabilities.
1746 releaseAllCapabilities(n_capabilities, cap, task);
1747 }
1748 #endif
1749
1750 return;
1751 }
1752
1753 /* ---------------------------------------------------------------------------
1754 * Singleton fork(). Do not copy any running threads.
1755 * ------------------------------------------------------------------------- */
1756
1757 pid_t
1758 forkProcess(HsStablePtr *entry
1759 #ifndef FORKPROCESS_PRIMOP_SUPPORTED
1760 STG_UNUSED
1761 #endif
1762 )
1763 {
1764 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
1765 pid_t pid;
1766 StgTSO* t,*next;
1767 Capability *cap;
1768 nat g;
1769 Task *task = NULL;
1770 nat i;
1771 #ifdef THREADED_RTS
1772 nat sync;
1773 #endif
1774
1775 debugTrace(DEBUG_sched, "forking!");
1776
1777 task = newBoundTask();
1778
1779 cap = NULL;
1780 waitForReturnCapability(&cap, task);
1781
1782 #ifdef THREADED_RTS
1783 do {
1784 sync = requestSync(&cap, task, SYNC_OTHER);
1785 } while (sync);
1786
1787 acquireAllCapabilities(cap,task);
1788
1789 pending_sync = 0;
1790 #endif
1791
1792 // no funny business: hold locks while we fork, otherwise if some
1793 // other thread is holding a lock when the fork happens, the data
1794 // structure protected by the lock will forever be in an
1795 // inconsistent state in the child. See also #1391.
1796 ACQUIRE_LOCK(&sched_mutex);
1797 ACQUIRE_LOCK(&sm_mutex);
1798 ACQUIRE_LOCK(&stable_mutex);
1799 ACQUIRE_LOCK(&task->lock);
1800
1801 for (i=0; i < n_capabilities; i++) {
1802 ACQUIRE_LOCK(&capabilities[i]->lock);
1803 }
1804
1805 stopTimer(); // See #4074
1806
1807 #if defined(TRACING)
1808 flushEventLog(); // so that child won't inherit dirty file buffers
1809 #endif
1810
1811 pid = fork();
1812
1813 if (pid) { // parent
1814
1815 startTimer(); // #4074
1816
1817 RELEASE_LOCK(&sched_mutex);
1818 RELEASE_LOCK(&sm_mutex);
1819 RELEASE_LOCK(&stable_mutex);
1820 RELEASE_LOCK(&task->lock);
1821
1822 for (i=0; i < n_capabilities; i++) {
1823 releaseCapability_(capabilities[i],rtsFalse);
1824 RELEASE_LOCK(&capabilities[i]->lock);
1825 }
1826 boundTaskExiting(task);
1827
1828 // just return the pid
1829 return pid;
1830
1831 } else { // child
1832
1833 #if defined(THREADED_RTS)
1834 initMutex(&sched_mutex);
1835 initMutex(&sm_mutex);
1836 initMutex(&stable_mutex);
1837 initMutex(&task->lock);
1838
1839 for (i=0; i < n_capabilities; i++) {
1840 initMutex(&capabilities[i]->lock);
1841 }
1842 #endif
1843
1844 #ifdef TRACING
1845 resetTracing();
1846 #endif
1847
1848 // Now, all OS threads except the thread that forked are
1849 // stopped. We need to stop all Haskell threads, including
1850 // those involved in foreign calls. Also we need to delete
1851 // all Tasks, because they correspond to OS threads that are
1852 // now gone.
1853
1854 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1855 for (t = generations[g].threads; t != END_TSO_QUEUE; t = next) {
1856 next = t->global_link;
1857 // don't allow threads to catch the ThreadKilled
1858 // exception, but we do want to raiseAsync() because these
1859 // threads may be evaluating thunks that we need later.
1860 deleteThread_(t->cap,t);
1861
1862 // stop the GC from updating the InCall to point to
1863 // the TSO. This is only necessary because the
1864 // OSThread bound to the TSO has been killed, and
1865 // won't get a chance to exit in the usual way (see
1866 // also scheduleHandleThreadFinished).
1867 t->bound = NULL;
1868 }
1869 }
1870
1871 discardTasksExcept(task);
1872
1873 for (i=0; i < n_capabilities; i++) {
1874 cap = capabilities[i];
1875
1876 // Empty the run queue. It seems tempting to let all the
1877 // killed threads stay on the run queue as zombies to be
1878 // cleaned up later, but some of them may correspond to
1879 // bound threads for which the corresponding Task does not
1880 // exist.
1881 truncateRunQueue(cap);
1882
1883 // Any suspended C-calling Tasks are no more, their OS threads
1884 // don't exist now:
1885 cap->suspended_ccalls = NULL;
1886
1887 #if defined(THREADED_RTS)
1888 // Wipe our spare workers list, they no longer exist. New
1889 // workers will be created if necessary.
1890 cap->spare_workers = NULL;
1891 cap->n_spare_workers = 0;
1892 cap->returning_tasks_hd = NULL;
1893 cap->returning_tasks_tl = NULL;
1894 #endif
1895
1896 // Release all caps except 0, we'll use that for starting
1897 // the IO manager and running the client action below.
1898 if (cap->no != 0) {
1899 task->cap = cap;
1900 releaseCapability(cap);
1901 }
1902 }
1903 cap = capabilities[0];
1904 task->cap = cap;
1905
1906 // Empty the threads lists. Otherwise, the garbage
1907 // collector may attempt to resurrect some of these threads.
1908 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1909 generations[g].threads = END_TSO_QUEUE;
1910 }
1911
1912 // On Unix, all timers are reset in the child, so we need to start
1913 // the timer again.
1914 initTimer();
1915 startTimer();
1916
1917 // TODO: need to trace various other things in the child
1918 // like startup event, capabilities, process info etc
1919 traceTaskCreate(task, cap);
1920
1921 #if defined(THREADED_RTS)
1922 ioManagerStartCap(&cap);
1923 #endif
1924
1925 rts_evalStableIO(&cap, entry, NULL); // run the action
1926 rts_checkSchedStatus("forkProcess",cap);
1927
1928 rts_unlock(cap);
1929 hs_exit(); // clean up and exit
1930 stg_exit(EXIT_SUCCESS);
1931 }
1932 #else /* !FORKPROCESS_PRIMOP_SUPPORTED */
1933 barf("forkProcess#: primop not supported on this platform, sorry!\n");
1934 #endif
1935 }
1936
1937 /* ---------------------------------------------------------------------------
1938 * Changing the number of Capabilities
1939 *
1940 * Changing the number of Capabilities is very tricky! We can only do
1941 * it with the system fully stopped, so we do a full sync with
1942 * requestSync(SYNC_OTHER) and grab all the capabilities.
1943 *
1944 * Then we resize the appropriate data structures, and update all
1945 * references to the old data structures which have now moved.
1946 * Finally we release the Capabilities we are holding, and start
1947 * worker Tasks on the new Capabilities we created.
1948 *
1949 * ------------------------------------------------------------------------- */
1950
1951 void
1952 setNumCapabilities (nat new_n_capabilities USED_IF_THREADS)
1953 {
1954 #if !defined(THREADED_RTS)
1955 if (new_n_capabilities != 1) {
1956 errorBelch("setNumCapabilities: not supported in the non-threaded RTS");
1957 }
1958 return;
1959 #elif defined(NOSMP)
1960 if (new_n_capabilities != 1) {
1961 errorBelch("setNumCapabilities: not supported on this platform");
1962 }
1963 return;
1964 #else
1965 Task *task;
1966 Capability *cap;
1967 nat sync;
1968 nat n;
1969 Capability *old_capabilities = NULL;
1970 nat old_n_capabilities = n_capabilities;
1971
1972 if (new_n_capabilities == enabled_capabilities) return;
1973
1974 debugTrace(DEBUG_sched, "changing the number of Capabilities from %d to %d",
1975 enabled_capabilities, new_n_capabilities);
1976
1977 cap = rts_lock();
1978 task = cap->running_task;
1979
1980 do {
1981 sync = requestSync(&cap, task, SYNC_OTHER);
1982 } while (sync);
1983
1984 acquireAllCapabilities(cap,task);
1985
1986 pending_sync = 0;
1987
1988 if (new_n_capabilities < enabled_capabilities)
1989 {
1990 // Reducing the number of capabilities: we do not actually
1991 // remove the extra capabilities, we just mark them as
1992 // "disabled". This has the following effects:
1993 //
1994 // - threads on a disabled capability are migrated away by the
1995 // scheduler loop
1996 //
1997 // - disabled capabilities do not participate in GC
1998 // (see scheduleDoGC())
1999 //
2000 // - No spark threads are created on this capability
2001 // (see scheduleActivateSpark())
2002 //
2003 // - We do not attempt to migrate threads *to* a disabled
2004 // capability (see schedulePushWork()).
2005 //
2006 // but in other respects, a disabled capability remains
2007 // alive. Threads may be woken up on a disabled capability,
2008 // but they will be immediately migrated away.
2009 //
2010 // This approach is much easier than trying to actually remove
2011 // the capability; we don't have to worry about GC data
2012 // structures, the nursery, etc.
2013 //
2014 for (n = new_n_capabilities; n < enabled_capabilities; n++) {
2015 capabilities[n]->disabled = rtsTrue;
2016 traceCapDisable(capabilities[n]);
2017 }
2018 enabled_capabilities = new_n_capabilities;
2019 }
2020 else
2021 {
2022 // Increasing the number of enabled capabilities.
2023 //
2024 // enable any disabled capabilities, up to the required number
2025 for (n = enabled_capabilities;
2026 n < new_n_capabilities && n < n_capabilities; n++) {
2027 capabilities[n]->disabled = rtsFalse;
2028 traceCapEnable(capabilities[n]);
2029 }
2030 enabled_capabilities = n;
2031
2032 if (new_n_capabilities > n_capabilities) {
2033 #if defined(TRACING)
2034 // Allocate eventlog buffers for the new capabilities. Note this
2035 // must be done before calling moreCapabilities(), because that
2036 // will emit events about creating the new capabilities and adding
2037 // them to existing capsets.
2038 tracingAddCapapilities(n_capabilities, new_n_capabilities);
2039 #endif
2040
2041 // Resize the capabilities array
2042 // NB. after this, capabilities points somewhere new. Any pointers
2043 // of type (Capability *) are now invalid.
2044 moreCapabilities(n_capabilities, new_n_capabilities);
2045
2046 // Resize and update storage manager data structures
2047 storageAddCapabilities(n_capabilities, new_n_capabilities);
2048 }
2049 }
2050
2051 // update n_capabilities before things start running
2052 if (new_n_capabilities > n_capabilities) {
2053 n_capabilities = enabled_capabilities = new_n_capabilities;
2054 }
2055
2056 // Start worker tasks on the new Capabilities
2057 startWorkerTasks(old_n_capabilities, new_n_capabilities);
2058
2059 // We're done: release the original Capabilities
2060 releaseAllCapabilities(old_n_capabilities, cap,task);
2061
2062 // We can't free the old array until now, because we access it
2063 // while updating pointers in updateCapabilityRefs().
2064 if (old_capabilities) {
2065 stgFree(old_capabilities);
2066 }
2067
2068 // Notify IO manager that the number of capabilities has changed.
2069 rts_evalIO(&cap, ioManagerCapabilitiesChanged_closure, NULL);
2070
2071 rts_unlock(cap);
2072
2073 #endif // THREADED_RTS
2074 }
2075
2076
2077
2078 /* ---------------------------------------------------------------------------
2079 * Delete all the threads in the system
2080 * ------------------------------------------------------------------------- */
2081
2082 static void
2083 deleteAllThreads ( Capability *cap )
2084 {
2085 // NOTE: only safe to call if we own all capabilities.
2086
2087 StgTSO* t, *next;
2088 nat g;
2089
2090 debugTrace(DEBUG_sched,"deleting all threads");
2091 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
2092 for (t = generations[g].threads; t != END_TSO_QUEUE; t = next) {
2093 next = t->global_link;
2094 deleteThread(cap,t);
2095 }
2096 }
2097
2098 // The run queue now contains a bunch of ThreadKilled threads. We
2099 // must not throw these away: the main thread(s) will be in there
2100 // somewhere, and the main scheduler loop has to deal with it.
2101 // Also, the run queue is the only thing keeping these threads from
2102 // being GC'd, and we don't want the "main thread has been GC'd" panic.
2103
2104 #if !defined(THREADED_RTS)
2105 ASSERT(blocked_queue_hd == END_TSO_QUEUE);
2106 ASSERT(sleeping_queue == END_TSO_QUEUE);
2107 #endif
2108 }
2109
2110 /* -----------------------------------------------------------------------------
2111 Managing the suspended_ccalls list.
2112 Locks required: sched_mutex
2113 -------------------------------------------------------------------------- */
2114
2115 STATIC_INLINE void
2116 suspendTask (Capability *cap, Task *task)
2117 {
2118 InCall *incall;
2119
2120 incall = task->incall;
2121 ASSERT(incall->next == NULL && incall->prev == NULL);
2122 incall->next = cap->suspended_ccalls;
2123 incall->prev = NULL;
2124 if (cap->suspended_ccalls) {
2125 cap->suspended_ccalls->prev = incall;
2126 }
2127 cap->suspended_ccalls = incall;
2128 }
2129
2130 STATIC_INLINE void
2131 recoverSuspendedTask (Capability *cap, Task *task)
2132 {
2133 InCall *incall;
2134
2135 incall = task->incall;
2136 if (incall->prev) {
2137 incall->prev->next = incall->next;
2138 } else {
2139 ASSERT(cap->suspended_ccalls == incall);
2140 cap->suspended_ccalls = incall->next;
2141 }
2142 if (incall->next) {
2143 incall->next->prev = incall->prev;
2144 }
2145 incall->next = incall->prev = NULL;
2146 }
2147
2148 /* ---------------------------------------------------------------------------
2149 * Suspending & resuming Haskell threads.
2150 *
2151 * When making a "safe" call to C (aka _ccall_GC), the task gives back
2152 * its capability before calling the C function. This allows another
2153 * task to pick up the capability and carry on running Haskell
2154 * threads. It also means that if the C call blocks, it won't lock
2155 * the whole system.
2156 *
2157 * The Haskell thread making the C call is put to sleep for the
2158 * duration of the call, on the suspended_ccalling_threads queue. We
2159 * give out a token to the task, which it can use to resume the thread
2160 * on return from the C function.
2161 *
2162 * If this is an interruptible C call, this means that the FFI call may be
2163 * unceremoniously terminated and should be scheduled on an
2164 * unbound worker thread.
2165 * ------------------------------------------------------------------------- */
2166
2167 void *
2168 suspendThread (StgRegTable *reg, rtsBool interruptible)
2169 {
2170 Capability *cap;
2171 int saved_errno;
2172 StgTSO *tso;
2173 Task *task;
2174 #if mingw32_HOST_OS
2175 StgWord32 saved_winerror;
2176 #endif
2177
2178 saved_errno = errno;
2179 #if mingw32_HOST_OS
2180 saved_winerror = GetLastError();
2181 #endif
2182
2183 /* assume that *reg is a pointer to the StgRegTable part of a Capability.
2184 */
2185 cap = regTableToCapability(reg);
2186
2187 task = cap->running_task;
2188 tso = cap->r.rCurrentTSO;
2189
2190 traceEventStopThread(cap, tso, THREAD_SUSPENDED_FOREIGN_CALL, 0);
2191
2192 // XXX this might not be necessary --SDM
2193 tso->what_next = ThreadRunGHC;
2194
2195 threadPaused(cap,tso);
2196
2197 if (interruptible) {
2198 tso->why_blocked = BlockedOnCCall_Interruptible;
2199 } else {
2200 tso->why_blocked = BlockedOnCCall;
2201 }
2202
2203 // Hand back capability
2204 task->incall->suspended_tso = tso;
2205 task->incall->suspended_cap = cap;
2206
2207 ACQUIRE_LOCK(&cap->lock);
2208
2209 suspendTask(cap,task);
2210 cap->in_haskell = rtsFalse;
2211 releaseCapability_(cap,rtsFalse);
2212
2213 RELEASE_LOCK(&cap->lock);
2214
2215 errno = saved_errno;
2216 #if mingw32_HOST_OS
2217 SetLastError(saved_winerror);
2218 #endif
2219 return task;
2220 }
2221
2222 StgRegTable *
2223 resumeThread (void *task_)
2224 {
2225 StgTSO *tso;
2226 InCall *incall;
2227 Capability *cap;
2228 Task *task = task_;
2229 int saved_errno;
2230 #if mingw32_HOST_OS
2231 StgWord32 saved_winerror;
2232 #endif
2233
2234 saved_errno = errno;
2235 #if mingw32_HOST_OS
2236 saved_winerror = GetLastError();
2237 #endif
2238
2239 incall = task->incall;
2240 cap = incall->suspended_cap;
2241 task->cap = cap;
2242
2243 // Wait for permission to re-enter the RTS with the result.
2244 waitForReturnCapability(&cap,task);
2245 // we might be on a different capability now... but if so, our
2246 // entry on the suspended_ccalls list will also have been
2247 // migrated.
2248
2249 // Remove the thread from the suspended list
2250 recoverSuspendedTask(cap,task);
2251
2252 tso = incall->suspended_tso;
2253 incall->suspended_tso = NULL;
2254 incall->suspended_cap = NULL;
2255 tso->_link = END_TSO_QUEUE; // no write barrier reqd
2256
2257 traceEventRunThread(cap, tso);
2258
2259 /* Reset blocking status */
2260 tso->why_blocked = NotBlocked;
2261
2262 if ((tso->flags & TSO_BLOCKEX) == 0) {
2263 // avoid locking the TSO if we don't have to
2264 if (tso->blocked_exceptions != END_BLOCKED_EXCEPTIONS_QUEUE) {
2265 maybePerformBlockedException(cap,tso);
2266 }
2267 }
2268
2269 cap->r.rCurrentTSO = tso;
2270 cap->in_haskell = rtsTrue;
2271 errno = saved_errno;
2272 #if mingw32_HOST_OS
2273 SetLastError(saved_winerror);
2274 #endif
2275
2276 /* We might have GC'd, mark the TSO dirty again */
2277 dirty_TSO(cap,tso);
2278 dirty_STACK(cap,tso->stackobj);
2279
2280 IF_DEBUG(sanity, checkTSO(tso));
2281
2282 return &cap->r;
2283 }
2284
2285 /* ---------------------------------------------------------------------------
2286 * scheduleThread()
2287 *
2288 * scheduleThread puts a thread on the end of the runnable queue.
2289 * This will usually be done immediately after a thread is created.
2290 * The caller of scheduleThread must create the thread using e.g.
2291 * createThread and push an appropriate closure
2292 * on this thread's stack before the scheduler is invoked.
2293 * ------------------------------------------------------------------------ */
2294
2295 void
2296 scheduleThread(Capability *cap, StgTSO *tso)
2297 {
2298 // The thread goes at the *end* of the run-queue, to avoid possible
2299 // starvation of any threads already on the queue.
2300 appendToRunQueue(cap,tso);
2301 }
2302
2303 void
2304 scheduleThreadOn(Capability *cap, StgWord cpu USED_IF_THREADS, StgTSO *tso)
2305 {
2306 tso->flags |= TSO_LOCKED; // we requested explicit affinity; don't
2307 // move this thread from now on.
2308 #if defined(THREADED_RTS)
2309 cpu %= enabled_capabilities;
2310 if (cpu == cap->no) {
2311 appendToRunQueue(cap,tso);
2312 } else {
2313 migrateThread(cap, tso, capabilities[cpu]);
2314 }
2315 #else
2316 appendToRunQueue(cap,tso);
2317 #endif
2318 }
2319
2320 void
2321 scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability **pcap)
2322 {
2323 Task *task;
2324 DEBUG_ONLY( StgThreadID id );
2325 Capability *cap;
2326
2327 cap = *pcap;
2328
2329 // We already created/initialised the Task
2330 task = cap->running_task;
2331
2332 // This TSO is now a bound thread; make the Task and TSO
2333 // point to each other.
2334 tso->bound = task->incall;
2335 tso->cap = cap;
2336
2337 task->incall->tso = tso;
2338 task->incall->ret = ret;
2339 task->incall->stat = NoStatus;
2340
2341 appendToRunQueue(cap,tso);
2342
2343 DEBUG_ONLY( id = tso->id );
2344 debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)id);
2345
2346 cap = schedule(cap,task);
2347
2348 ASSERT(task->incall->stat != NoStatus);
2349 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
2350
2351 debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)id);
2352 *pcap = cap;
2353 }
2354
2355 /* ----------------------------------------------------------------------------
2356 * Starting Tasks
2357 * ------------------------------------------------------------------------- */
2358
2359 #if defined(THREADED_RTS)
2360 void scheduleWorker (Capability *cap, Task *task)
2361 {
2362 // schedule() runs without a lock.
2363 cap = schedule(cap,task);
2364
2365 // On exit from schedule(), we have a Capability, but possibly not
2366 // the same one we started with.
2367
2368 // During shutdown, the requirement is that after all the
2369 // Capabilities are shut down, all workers that are shutting down
2370 // have finished workerTaskStop(). This is why we hold on to
2371 // cap->lock until we've finished workerTaskStop() below.
2372 //
2373 // There may be workers still involved in foreign calls; those
2374 // will just block in waitForReturnCapability() because the
2375 // Capability has been shut down.
2376 //
2377 ACQUIRE_LOCK(&cap->lock);
2378 releaseCapability_(cap,rtsFalse);
2379 workerTaskStop(task);
2380 RELEASE_LOCK(&cap->lock);
2381 }
2382 #endif
2383
2384 /* ---------------------------------------------------------------------------
2385 * Start new worker tasks on Capabilities from--to
2386 * -------------------------------------------------------------------------- */
2387
2388 static void
2389 startWorkerTasks (nat from USED_IF_THREADS, nat to USED_IF_THREADS)
2390 {
2391 #if defined(THREADED_RTS)
2392 nat i;
2393 Capability *cap;
2394
2395 for (i = from; i < to; i++) {
2396 cap = capabilities[i];
2397 ACQUIRE_LOCK(&cap->lock);
2398 startWorkerTask(cap);
2399 RELEASE_LOCK(&cap->lock);
2400 }
2401 #endif
2402 }
2403
2404 /* ---------------------------------------------------------------------------
2405 * initScheduler()
2406 *
2407 * Initialise the scheduler. This resets all the queues - if the
2408 * queues contained any threads, they'll be garbage collected at the
2409 * next pass.
2410 *
2411 * ------------------------------------------------------------------------ */
2412
2413 void
2414 initScheduler(void)
2415 {
2416 #if !defined(THREADED_RTS)
2417 blocked_queue_hd = END_TSO_QUEUE;
2418 blocked_queue_tl = END_TSO_QUEUE;
2419 sleeping_queue = END_TSO_QUEUE;
2420 #endif
2421
2422 sched_state = SCHED_RUNNING;
2423 recent_activity = ACTIVITY_YES;
2424
2425 #if defined(THREADED_RTS)
2426 /* Initialise the mutex and condition variables used by
2427 * the scheduler. */
2428 initMutex(&sched_mutex);
2429 #endif
2430
2431 ACQUIRE_LOCK(&sched_mutex);
2432
2433 /* A capability holds the state a native thread needs in
2434 * order to execute STG code. At least one capability is
2435 * floating around (only THREADED_RTS builds have more than one).
2436 */
2437 initCapabilities();
2438
2439 initTaskManager();
2440
2441 /*
2442 * Eagerly start one worker to run each Capability, except for
2443 * Capability 0. The idea is that we're probably going to start a
2444 * bound thread on Capability 0 pretty soon, so we don't want a
2445 * worker task hogging it.
2446 */
2447 startWorkerTasks(1, n_capabilities);
2448
2449 RELEASE_LOCK(&sched_mutex);
2450
2451 }
2452
2453 void
2454 exitScheduler (rtsBool wait_foreign USED_IF_THREADS)
2455 /* see Capability.c, shutdownCapability() */
2456 {
2457 Task *task = NULL;
2458
2459 task = newBoundTask();
2460
2461 // If we haven't killed all the threads yet, do it now.
2462 if (sched_state < SCHED_SHUTTING_DOWN) {
2463 sched_state = SCHED_INTERRUPTING;
2464 Capability *cap = task->cap;
2465 waitForReturnCapability(&cap,task);
2466 scheduleDoGC(&cap,task,rtsTrue);
2467 ASSERT(task->incall->tso == NULL);
2468 releaseCapability(cap);
2469 }
2470 sched_state = SCHED_SHUTTING_DOWN;
2471
2472 shutdownCapabilities(task, wait_foreign);
2473
2474 // debugBelch("n_failed_trygrab_idles = %d, n_idle_caps = %d\n",
2475 // n_failed_trygrab_idles, n_idle_caps);
2476
2477 boundTaskExiting(task);
2478 }
2479
2480 void
2481 freeScheduler( void )
2482 {
2483 nat still_running;
2484
2485 ACQUIRE_LOCK(&sched_mutex);
2486 still_running = freeTaskManager();
2487 // We can only free the Capabilities if there are no Tasks still
2488 // running. We might have a Task about to return from a foreign
2489 // call into waitForReturnCapability(), for example (actually,
2490 // this should be the *only* thing that a still-running Task can
2491 // do at this point, and it will block waiting for the
2492 // Capability).
2493 if (still_running == 0) {
2494 freeCapabilities();
2495 }
2496 RELEASE_LOCK(&sched_mutex);
2497 #if defined(THREADED_RTS)
2498 closeMutex(&sched_mutex);
2499 #endif
2500 }
2501
2502 void markScheduler (evac_fn evac USED_IF_NOT_THREADS,
2503 void *user USED_IF_NOT_THREADS)
2504 {
2505 #if !defined(THREADED_RTS)
2506 evac(user, (StgClosure **)(void *)&blocked_queue_hd);
2507 evac(user, (StgClosure **)(void *)&blocked_queue_tl);
2508 evac(user, (StgClosure **)(void *)&sleeping_queue);
2509 #endif
2510 }
2511
2512 /* -----------------------------------------------------------------------------
2513 performGC
2514
2515 This is the interface to the garbage collector from Haskell land.
2516 We provide this so that external C code can allocate and garbage
2517 collect when called from Haskell via _ccall_GC.
2518 -------------------------------------------------------------------------- */
2519
2520 static void
2521 performGC_(rtsBool force_major)
2522 {
2523 Task *task;
2524 Capability *cap = NULL;
2525
2526 // We must grab a new Task here, because the existing Task may be
2527 // associated with a particular Capability, and chained onto the
2528 // suspended_ccalls queue.
2529 task = newBoundTask();
2530
2531 // TODO: do we need to traceTask*() here?
2532
2533 waitForReturnCapability(&cap,task);
2534 scheduleDoGC(&cap,task,force_major);
2535 releaseCapability(cap);
2536 boundTaskExiting(task);
2537 }
2538
2539 void
2540 performGC(void)
2541 {
2542 performGC_(rtsFalse);
2543 }
2544
2545 void
2546 performMajorGC(void)
2547 {
2548 performGC_(rtsTrue);
2549 }
2550
2551 /* ---------------------------------------------------------------------------
2552 Interrupt execution
2553 - usually called inside a signal handler so it mustn't do anything fancy.
2554 ------------------------------------------------------------------------ */
2555
2556 void
2557 interruptStgRts(void)
2558 {
2559 sched_state = SCHED_INTERRUPTING;
2560 interruptAllCapabilities();
2561 #if defined(THREADED_RTS)
2562 wakeUpRts();
2563 #endif
2564 }
2565
2566 /* -----------------------------------------------------------------------------
2567 Wake up the RTS
2568
2569 This function causes at least one OS thread to wake up and run the
2570 scheduler loop. It is invoked when the RTS might be deadlocked, or
2571 an external event has arrived that may need servicing (eg. a
2572 keyboard interrupt).
2573
2574 In the single-threaded RTS we don't do anything here; we only have
2575 one thread anyway, and the event that caused us to want to wake up
2576 will have interrupted any blocking system call in progress anyway.
2577 -------------------------------------------------------------------------- */
2578
2579 #if defined(THREADED_RTS)
2580 void wakeUpRts(void)
2581 {
2582 // This forces the IO Manager thread to wakeup, which will
2583 // in turn ensure that some OS thread wakes up and runs the
2584 // scheduler loop, which will cause a GC and deadlock check.
2585 ioManagerWakeup();
2586 }
2587 #endif
2588
2589 /* -----------------------------------------------------------------------------
2590 Deleting threads
2591
2592 This is used for interruption (^C) and forking, and corresponds to
2593 raising an exception but without letting the thread catch the
2594 exception.
2595 -------------------------------------------------------------------------- */
2596
2597 static void
2598 deleteThread (Capability *cap STG_UNUSED, StgTSO *tso)
2599 {
2600 // NOTE: must only be called on a TSO that we have exclusive
2601 // access to, because we will call throwToSingleThreaded() below.
2602 // The TSO must be on the run queue of the Capability we own, or
2603 // we must own all Capabilities.
2604
2605 if (tso->why_blocked != BlockedOnCCall &&
2606 tso->why_blocked != BlockedOnCCall_Interruptible) {
2607 throwToSingleThreaded(tso->cap,tso,NULL);
2608 }
2609 }
2610
2611 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
2612 static void
2613 deleteThread_(Capability *cap, StgTSO *tso)
2614 { // for forkProcess only:
2615 // like deleteThread(), but we delete threads in foreign calls, too.
2616
2617 if (tso->why_blocked == BlockedOnCCall ||
2618 tso->why_blocked == BlockedOnCCall_Interruptible) {
2619 tso->what_next = ThreadKilled;
2620 appendToRunQueue(tso->cap, tso);
2621 } else {
2622 deleteThread(cap,tso);
2623 }
2624 }
2625 #endif
2626
2627 /* -----------------------------------------------------------------------------
2628 raiseExceptionHelper
2629
2630 This function is called by the raise# primitve, just so that we can
2631 move some of the tricky bits of raising an exception from C-- into
2632 C. Who knows, it might be a useful re-useable thing here too.
2633 -------------------------------------------------------------------------- */
2634
2635 StgWord
2636 raiseExceptionHelper (StgRegTable *reg, StgTSO *tso, StgClosure *exception)
2637 {
2638 Capability *cap = regTableToCapability(reg);
2639 StgThunk *raise_closure = NULL;
2640 StgPtr p, next;
2641 StgRetInfoTable *info;
2642 //
2643 // This closure represents the expression 'raise# E' where E
2644 // is the exception raise. It is used to overwrite all the
2645 // thunks which are currently under evaluataion.
2646 //
2647
2648 // OLD COMMENT (we don't have MIN_UPD_SIZE now):
2649 // LDV profiling: stg_raise_info has THUNK as its closure
2650 // type. Since a THUNK takes at least MIN_UPD_SIZE words in its
2651 // payload, MIN_UPD_SIZE is more approprate than 1. It seems that
2652 // 1 does not cause any problem unless profiling is performed.
2653 // However, when LDV profiling goes on, we need to linearly scan
2654 // small object pool, where raise_closure is stored, so we should
2655 // use MIN_UPD_SIZE.
2656 //
2657 // raise_closure = (StgClosure *)RET_STGCALL1(P_,allocate,
2658 // sizeofW(StgClosure)+1);
2659 //
2660
2661 //
2662 // Walk up the stack, looking for the catch frame. On the way,
2663 // we update any closures pointed to from update frames with the
2664 // raise closure that we just built.
2665 //
2666 p = tso->stackobj->sp;
2667 while(1) {
2668 info = get_ret_itbl((StgClosure *)p);
2669 next = p + stack_frame_sizeW((StgClosure *)p);
2670 switch (info->i.type) {
2671
2672 case UPDATE_FRAME:
2673 // Only create raise_closure if we need to.
2674 if (raise_closure == NULL) {
2675 raise_closure =
2676 (StgThunk *)allocate(cap,sizeofW(StgThunk)+1);
2677 SET_HDR(raise_closure, &stg_raise_info, cap->r.rCCCS);
2678 raise_closure->payload[0] = exception;
2679 }
2680 updateThunk(cap, tso, ((StgUpdateFrame *)p)->updatee,
2681 (StgClosure *)raise_closure);
2682 p = next;
2683 continue;
2684
2685 case ATOMICALLY_FRAME:
2686 debugTrace(DEBUG_stm, "found ATOMICALLY_FRAME at %p", p);
2687 tso->stackobj->sp = p;
2688 return ATOMICALLY_FRAME;
2689
2690 case CATCH_FRAME:
2691 tso->stackobj->sp = p;
2692 return CATCH_FRAME;
2693
2694 case CATCH_STM_FRAME:
2695 debugTrace(DEBUG_stm, "found CATCH_STM_FRAME at %p", p);
2696 tso->stackobj->sp = p;
2697 return CATCH_STM_FRAME;
2698
2699 case UNDERFLOW_FRAME:
2700 tso->stackobj->sp = p;
2701 threadStackUnderflow(cap,tso);
2702 p = tso->stackobj->sp;
2703 continue;
2704
2705 case STOP_FRAME:
2706 tso->stackobj->sp = p;
2707 return STOP_FRAME;
2708
2709 case CATCH_RETRY_FRAME: {
2710 StgTRecHeader *trec = tso -> trec;
2711 StgTRecHeader *outer = trec -> enclosing_trec;
2712 debugTrace(DEBUG_stm,
2713 "found CATCH_RETRY_FRAME at %p during raise", p);
2714 debugTrace(DEBUG_stm, "trec=%p outer=%p", trec, outer);
2715 stmAbortTransaction(cap, trec);
2716 stmFreeAbortedTRec(cap, trec);
2717 tso -> trec = outer;
2718 p = next;
2719 continue;
2720 }
2721
2722 default:
2723 p = next;
2724 continue;
2725 }
2726 }
2727 }
2728
2729
2730 /* -----------------------------------------------------------------------------
2731 findRetryFrameHelper
2732
2733 This function is called by the retry# primitive. It traverses the stack
2734 leaving tso->sp referring to the frame which should handle the retry.
2735
2736 This should either be a CATCH_RETRY_FRAME (if the retry# is within an orElse#)
2737 or should be a ATOMICALLY_FRAME (if the retry# reaches the top level).
2738
2739 We skip CATCH_STM_FRAMEs (aborting and rolling back the nested tx that they
2740 create) because retries are not considered to be exceptions, despite the
2741 similar implementation.
2742
2743 We should not expect to see CATCH_FRAME or STOP_FRAME because those should
2744 not be created within memory transactions.
2745 -------------------------------------------------------------------------- */
2746
2747 StgWord
2748 findRetryFrameHelper (Capability *cap, StgTSO *tso)
2749 {
2750 StgPtr p, next;
2751 StgRetInfoTable *info;
2752
2753 p = tso->stackobj->sp;
2754 while (1) {
2755 info = get_ret_itbl((StgClosure *)p);
2756 next = p + stack_frame_sizeW((StgClosure *)p);
2757 switch (info->i.type) {
2758
2759 case ATOMICALLY_FRAME:
2760 debugTrace(DEBUG_stm,
2761 "found ATOMICALLY_FRAME at %p during retry", p);
2762 tso->stackobj->sp = p;
2763 return ATOMICALLY_FRAME;
2764
2765 case CATCH_RETRY_FRAME:
2766 debugTrace(DEBUG_stm,
2767 "found CATCH_RETRY_FRAME at %p during retry", p);
2768 tso->stackobj->sp = p;
2769 return CATCH_RETRY_FRAME;
2770
2771 case CATCH_STM_FRAME: {
2772 StgTRecHeader *trec = tso -> trec;
2773 StgTRecHeader *outer = trec -> enclosing_trec;
2774 debugTrace(DEBUG_stm,
2775 "found CATCH_STM_FRAME at %p during retry", p);
2776 debugTrace(DEBUG_stm, "trec=%p outer=%p", trec, outer);
2777 stmAbortTransaction(cap, trec);
2778 stmFreeAbortedTRec(cap, trec);
2779 tso -> trec = outer;
2780 p = next;
2781 continue;
2782 }
2783
2784 case UNDERFLOW_FRAME:
2785 tso->stackobj->sp = p;
2786 threadStackUnderflow(cap,tso);
2787 p = tso->stackobj->sp;
2788 continue;
2789
2790 default:
2791 ASSERT(info->i.type != CATCH_FRAME);
2792 ASSERT(info->i.type != STOP_FRAME);
2793 p = next;
2794 continue;
2795 }
2796 }
2797 }
2798
2799 /* -----------------------------------------------------------------------------
2800 resurrectThreads is called after garbage collection on the list of
2801 threads found to be garbage. Each of these threads will be woken
2802 up and sent a signal: BlockedOnDeadMVar if the thread was blocked
2803 on an MVar, or NonTermination if the thread was blocked on a Black
2804 Hole.
2805
2806 Locks: assumes we hold *all* the capabilities.
2807 -------------------------------------------------------------------------- */
2808
2809 void
2810 resurrectThreads (StgTSO *threads)
2811 {
2812 StgTSO *tso, *next;
2813 Capability *cap;
2814 generation *gen;
2815
2816 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2817 next = tso->global_link;
2818
2819 gen = Bdescr((P_)tso)->gen;
2820 tso->global_link = gen->threads;
2821 gen->threads = tso;
2822
2823 debugTrace(DEBUG_sched, "resurrecting thread %lu", (unsigned long)tso->id);
2824
2825 // Wake up the thread on the Capability it was last on
2826 cap = tso->cap;
2827
2828 switch (tso->why_blocked) {
2829 case BlockedOnMVar:
2830 case BlockedOnMVarRead:
2831 /* Called by GC - sched_mutex lock is currently held. */
2832 throwToSingleThreaded(cap, tso,
2833 (StgClosure *)blockedIndefinitelyOnMVar_closure);
2834 break;
2835 case BlockedOnBlackHole:
2836 throwToSingleThreaded(cap, tso,
2837 (StgClosure *)nonTermination_closure);
2838 break;
2839 case BlockedOnSTM:
2840 throwToSingleThreaded(cap, tso,
2841 (StgClosure *)blockedIndefinitelyOnSTM_closure);
2842 break;
2843 case NotBlocked:
2844 /* This might happen if the thread was blocked on a black hole
2845 * belonging to a thread that we've just woken up (raiseAsync
2846 * can wake up threads, remember...).
2847 */
2848 continue;
2849 case BlockedOnMsgThrowTo:
2850 // This can happen if the target is masking, blocks on a
2851 // black hole, and then is found to be unreachable. In
2852 // this case, we want to let the target wake up and carry
2853 // on, and do nothing to this thread.
2854 continue;
2855 default:
2856 barf("resurrectThreads: thread blocked in a strange way: %d",
2857 tso->why_blocked);
2858 }
2859 }
2860 }