Merge branch 'master' of darcs.haskell.org:/home/darcs/ghc
[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(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. t 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 throwToSingleThreaded(cap, task->incall->tso,
951 (StgClosure *)nonTermination_closure);
952 return;
953 default:
954 barf("deadlock: main thread blocked in a strange way");
955 }
956 }
957 return;
958 #endif
959 }
960 }
961
962
963 /* ----------------------------------------------------------------------------
964 * Send pending messages (PARALLEL_HASKELL only)
965 * ------------------------------------------------------------------------- */
966
967 #if defined(PARALLEL_HASKELL)
968 static void
969 scheduleSendPendingMessages(void)
970 {
971
972 # if defined(PAR) // global Mem.Mgmt., omit for now
973 if (PendingFetches != END_BF_QUEUE) {
974 processFetches();
975 }
976 # endif
977
978 if (RtsFlags.ParFlags.BufferTime) {
979 // if we use message buffering, we must send away all message
980 // packets which have become too old...
981 sendOldBuffers();
982 }
983 }
984 #endif
985
986 /* ----------------------------------------------------------------------------
987 * Process message in the current Capability's inbox
988 * ------------------------------------------------------------------------- */
989
990 static void
991 scheduleProcessInbox (Capability **pcap USED_IF_THREADS)
992 {
993 #if defined(THREADED_RTS)
994 Message *m, *next;
995 int r;
996 Capability *cap = *pcap;
997
998 while (!emptyInbox(cap)) {
999 if (cap->r.rCurrentNursery->link == NULL ||
1000 g0->n_new_large_words >= large_alloc_lim) {
1001 scheduleDoGC(pcap, cap->running_task, rtsFalse);
1002 cap = *pcap;
1003 }
1004
1005 // don't use a blocking acquire; if the lock is held by
1006 // another thread then just carry on. This seems to avoid
1007 // getting stuck in a message ping-pong situation with other
1008 // processors. We'll check the inbox again later anyway.
1009 //
1010 // We should really use a more efficient queue data structure
1011 // here. The trickiness is that we must ensure a Capability
1012 // never goes idle if the inbox is non-empty, which is why we
1013 // use cap->lock (cap->lock is released as the last thing
1014 // before going idle; see Capability.c:releaseCapability()).
1015 r = TRY_ACQUIRE_LOCK(&cap->lock);
1016 if (r != 0) return;
1017
1018 m = cap->inbox;
1019 cap->inbox = (Message*)END_TSO_QUEUE;
1020
1021 RELEASE_LOCK(&cap->lock);
1022
1023 while (m != (Message*)END_TSO_QUEUE) {
1024 next = m->link;
1025 executeMessage(cap, m);
1026 m = next;
1027 }
1028 }
1029 #endif
1030 }
1031
1032 /* ----------------------------------------------------------------------------
1033 * Activate spark threads (PARALLEL_HASKELL and THREADED_RTS)
1034 * ------------------------------------------------------------------------- */
1035
1036 #if defined(THREADED_RTS)
1037 static void
1038 scheduleActivateSpark(Capability *cap)
1039 {
1040 if (anySparks() && !cap->disabled)
1041 {
1042 createSparkThread(cap);
1043 debugTrace(DEBUG_sched, "creating a spark thread");
1044 }
1045 }
1046 #endif // PARALLEL_HASKELL || THREADED_RTS
1047
1048 /* ----------------------------------------------------------------------------
1049 * After running a thread...
1050 * ------------------------------------------------------------------------- */
1051
1052 static void
1053 schedulePostRunThread (Capability *cap, StgTSO *t)
1054 {
1055 // We have to be able to catch transactions that are in an
1056 // infinite loop as a result of seeing an inconsistent view of
1057 // memory, e.g.
1058 //
1059 // atomically $ do
1060 // [a,b] <- mapM readTVar [ta,tb]
1061 // when (a == b) loop
1062 //
1063 // and a is never equal to b given a consistent view of memory.
1064 //
1065 if (t -> trec != NO_TREC && t -> why_blocked == NotBlocked) {
1066 if (!stmValidateNestOfTransactions(cap, t -> trec)) {
1067 debugTrace(DEBUG_sched | DEBUG_stm,
1068 "trec %p found wasting its time", t);
1069
1070 // strip the stack back to the
1071 // ATOMICALLY_FRAME, aborting the (nested)
1072 // transaction, and saving the stack of any
1073 // partially-evaluated thunks on the heap.
1074 throwToSingleThreaded_(cap, t, NULL, rtsTrue);
1075
1076 // ASSERT(get_itbl((StgClosure *)t->sp)->type == ATOMICALLY_FRAME);
1077 }
1078 }
1079
1080 /* some statistics gathering in the parallel case */
1081 }
1082
1083 /* -----------------------------------------------------------------------------
1084 * Handle a thread that returned to the scheduler with ThreadHeepOverflow
1085 * -------------------------------------------------------------------------- */
1086
1087 static rtsBool
1088 scheduleHandleHeapOverflow( Capability *cap, StgTSO *t )
1089 {
1090 // did the task ask for a large block?
1091 if (cap->r.rHpAlloc > BLOCK_SIZE) {
1092 // if so, get one and push it on the front of the nursery.
1093 bdescr *bd;
1094 W_ blocks;
1095
1096 blocks = (W_)BLOCK_ROUND_UP(cap->r.rHpAlloc) / BLOCK_SIZE;
1097
1098 if (blocks > BLOCKS_PER_MBLOCK) {
1099 barf("allocation of %ld bytes too large (GHC should have complained at compile-time)", (long)cap->r.rHpAlloc);
1100 }
1101
1102 debugTrace(DEBUG_sched,
1103 "--<< thread %ld (%s) stopped: requesting a large block (size %ld)\n",
1104 (long)t->id, what_next_strs[t->what_next], blocks);
1105
1106 // don't do this if the nursery is (nearly) full, we'll GC first.
1107 if (cap->r.rCurrentNursery->link != NULL ||
1108 cap->r.rNursery->n_blocks == 1) { // paranoia to prevent infinite loop
1109 // if the nursery has only one block.
1110
1111 bd = allocGroup_lock(blocks);
1112 cap->r.rNursery->n_blocks += blocks;
1113
1114 // link the new group into the list
1115 bd->link = cap->r.rCurrentNursery;
1116 bd->u.back = cap->r.rCurrentNursery->u.back;
1117 if (cap->r.rCurrentNursery->u.back != NULL) {
1118 cap->r.rCurrentNursery->u.back->link = bd;
1119 } else {
1120 cap->r.rNursery->blocks = bd;
1121 }
1122 cap->r.rCurrentNursery->u.back = bd;
1123
1124 // initialise it as a nursery block. We initialise the
1125 // step, gen_no, and flags field of *every* sub-block in
1126 // this large block, because this is easier than making
1127 // sure that we always find the block head of a large
1128 // block whenever we call Bdescr() (eg. evacuate() and
1129 // isAlive() in the GC would both have to do this, at
1130 // least).
1131 {
1132 bdescr *x;
1133 for (x = bd; x < bd + blocks; x++) {
1134 initBdescr(x,g0,g0);
1135 x->free = x->start;
1136 x->flags = 0;
1137 }
1138 }
1139
1140 // This assert can be a killer if the app is doing lots
1141 // of large block allocations.
1142 IF_DEBUG(sanity, checkNurserySanity(cap->r.rNursery));
1143
1144 // now update the nursery to point to the new block
1145 cap->r.rCurrentNursery = bd;
1146
1147 // we might be unlucky and have another thread get on the
1148 // run queue before us and steal the large block, but in that
1149 // case the thread will just end up requesting another large
1150 // block.
1151 pushOnRunQueue(cap,t);
1152 return rtsFalse; /* not actually GC'ing */
1153 }
1154 }
1155
1156 if (cap->r.rHpLim == NULL || cap->context_switch) {
1157 // Sometimes we miss a context switch, e.g. when calling
1158 // primitives in a tight loop, MAYBE_GC() doesn't check the
1159 // context switch flag, and we end up waiting for a GC.
1160 // See #1984, and concurrent/should_run/1984
1161 cap->context_switch = 0;
1162 appendToRunQueue(cap,t);
1163 } else {
1164 pushOnRunQueue(cap,t);
1165 }
1166 return rtsTrue;
1167 /* actual GC is done at the end of the while loop in schedule() */
1168 }
1169
1170 /* -----------------------------------------------------------------------------
1171 * Handle a thread that returned to the scheduler with ThreadYielding
1172 * -------------------------------------------------------------------------- */
1173
1174 static rtsBool
1175 scheduleHandleYield( Capability *cap, StgTSO *t, nat prev_what_next )
1176 {
1177 /* put the thread back on the run queue. Then, if we're ready to
1178 * GC, check whether this is the last task to stop. If so, wake
1179 * up the GC thread. getThread will block during a GC until the
1180 * GC is finished.
1181 */
1182
1183 ASSERT(t->_link == END_TSO_QUEUE);
1184
1185 // Shortcut if we're just switching evaluators: don't bother
1186 // doing stack squeezing (which can be expensive), just run the
1187 // thread.
1188 if (cap->context_switch == 0 && t->what_next != prev_what_next) {
1189 debugTrace(DEBUG_sched,
1190 "--<< thread %ld (%s) stopped to switch evaluators",
1191 (long)t->id, what_next_strs[t->what_next]);
1192 return rtsTrue;
1193 }
1194
1195 // Reset the context switch flag. We don't do this just before
1196 // running the thread, because that would mean we would lose ticks
1197 // during GC, which can lead to unfair scheduling (a thread hogs
1198 // the CPU because the tick always arrives during GC). This way
1199 // penalises threads that do a lot of allocation, but that seems
1200 // better than the alternative.
1201 if (cap->context_switch != 0) {
1202 cap->context_switch = 0;
1203 appendToRunQueue(cap,t);
1204 } else {
1205 pushOnRunQueue(cap,t);
1206 }
1207
1208 IF_DEBUG(sanity,
1209 //debugBelch("&& Doing sanity check on yielding TSO %ld.", t->id);
1210 checkTSO(t));
1211
1212 return rtsFalse;
1213 }
1214
1215 /* -----------------------------------------------------------------------------
1216 * Handle a thread that returned to the scheduler with ThreadBlocked
1217 * -------------------------------------------------------------------------- */
1218
1219 static void
1220 scheduleHandleThreadBlocked( StgTSO *t
1221 #if !defined(DEBUG)
1222 STG_UNUSED
1223 #endif
1224 )
1225 {
1226
1227 // We don't need to do anything. The thread is blocked, and it
1228 // has tidied up its stack and placed itself on whatever queue
1229 // it needs to be on.
1230
1231 // ASSERT(t->why_blocked != NotBlocked);
1232 // Not true: for example,
1233 // - the thread may have woken itself up already, because
1234 // threadPaused() might have raised a blocked throwTo
1235 // exception, see maybePerformBlockedException().
1236
1237 #ifdef DEBUG
1238 traceThreadStatus(DEBUG_sched, t);
1239 #endif
1240 }
1241
1242 /* -----------------------------------------------------------------------------
1243 * Handle a thread that returned to the scheduler with ThreadFinished
1244 * -------------------------------------------------------------------------- */
1245
1246 static rtsBool
1247 scheduleHandleThreadFinished (Capability *cap STG_UNUSED, Task *task, StgTSO *t)
1248 {
1249 /* Need to check whether this was a main thread, and if so,
1250 * return with the return value.
1251 *
1252 * We also end up here if the thread kills itself with an
1253 * uncaught exception, see Exception.cmm.
1254 */
1255
1256 // blocked exceptions can now complete, even if the thread was in
1257 // blocked mode (see #2910).
1258 awakenBlockedExceptionQueue (cap, t);
1259
1260 //
1261 // Check whether the thread that just completed was a bound
1262 // thread, and if so return with the result.
1263 //
1264 // There is an assumption here that all thread completion goes
1265 // through this point; we need to make sure that if a thread
1266 // ends up in the ThreadKilled state, that it stays on the run
1267 // queue so it can be dealt with here.
1268 //
1269
1270 if (t->bound) {
1271
1272 if (t->bound != task->incall) {
1273 #if !defined(THREADED_RTS)
1274 // Must be a bound thread that is not the topmost one. Leave
1275 // it on the run queue until the stack has unwound to the
1276 // point where we can deal with this. Leaving it on the run
1277 // queue also ensures that the garbage collector knows about
1278 // this thread and its return value (it gets dropped from the
1279 // step->threads list so there's no other way to find it).
1280 appendToRunQueue(cap,t);
1281 return rtsFalse;
1282 #else
1283 // this cannot happen in the threaded RTS, because a
1284 // bound thread can only be run by the appropriate Task.
1285 barf("finished bound thread that isn't mine");
1286 #endif
1287 }
1288
1289 ASSERT(task->incall->tso == t);
1290
1291 if (t->what_next == ThreadComplete) {
1292 if (task->incall->ret) {
1293 // NOTE: return val is stack->sp[1] (see StgStartup.hc)
1294 *(task->incall->ret) = (StgClosure *)task->incall->tso->stackobj->sp[1];
1295 }
1296 task->incall->stat = Success;
1297 } else {
1298 if (task->incall->ret) {
1299 *(task->incall->ret) = NULL;
1300 }
1301 if (sched_state >= SCHED_INTERRUPTING) {
1302 if (heap_overflow) {
1303 task->incall->stat = HeapExhausted;
1304 } else {
1305 task->incall->stat = Interrupted;
1306 }
1307 } else {
1308 task->incall->stat = Killed;
1309 }
1310 }
1311 #ifdef DEBUG
1312 removeThreadLabel((StgWord)task->incall->tso->id);
1313 #endif
1314
1315 // We no longer consider this thread and task to be bound to
1316 // each other. The TSO lives on until it is GC'd, but the
1317 // task is about to be released by the caller, and we don't
1318 // want anyone following the pointer from the TSO to the
1319 // defunct task (which might have already been
1320 // re-used). This was a real bug: the GC updated
1321 // tso->bound->tso which lead to a deadlock.
1322 t->bound = NULL;
1323 task->incall->tso = NULL;
1324
1325 return rtsTrue; // tells schedule() to return
1326 }
1327
1328 return rtsFalse;
1329 }
1330
1331 /* -----------------------------------------------------------------------------
1332 * Perform a heap census
1333 * -------------------------------------------------------------------------- */
1334
1335 static rtsBool
1336 scheduleNeedHeapProfile( rtsBool ready_to_gc STG_UNUSED )
1337 {
1338 // When we have +RTS -i0 and we're heap profiling, do a census at
1339 // every GC. This lets us get repeatable runs for debugging.
1340 if (performHeapProfile ||
1341 (RtsFlags.ProfFlags.heapProfileInterval==0 &&
1342 RtsFlags.ProfFlags.doHeapProfile && ready_to_gc)) {
1343 return rtsTrue;
1344 } else {
1345 return rtsFalse;
1346 }
1347 }
1348
1349 /* -----------------------------------------------------------------------------
1350 * Start a synchronisation of all capabilities
1351 * -------------------------------------------------------------------------- */
1352
1353 // Returns:
1354 // 0 if we successfully got a sync
1355 // non-0 if there was another sync request in progress,
1356 // and we yielded to it. The value returned is the
1357 // type of the other sync request.
1358 //
1359 #if defined(THREADED_RTS)
1360 static nat requestSync (Capability **pcap, Task *task, nat sync_type)
1361 {
1362 nat prev_pending_sync;
1363
1364 prev_pending_sync = cas(&pending_sync, 0, sync_type);
1365
1366 if (prev_pending_sync)
1367 {
1368 do {
1369 debugTrace(DEBUG_sched, "someone else is trying to sync (%d)...",
1370 prev_pending_sync);
1371 ASSERT(*pcap);
1372 yieldCapability(pcap,task,rtsTrue);
1373 } while (pending_sync);
1374 return prev_pending_sync; // NOTE: task->cap might have changed now
1375 }
1376 else
1377 {
1378 return 0;
1379 }
1380 }
1381
1382 //
1383 // Grab all the capabilities except the one we already hold. Used
1384 // when synchronising before a single-threaded GC (SYNC_SEQ_GC), and
1385 // before a fork (SYNC_OTHER).
1386 //
1387 // Only call this after requestSync(), otherwise a deadlock might
1388 // ensue if another thread is trying to synchronise.
1389 //
1390 static void acquireAllCapabilities(Capability *cap, Task *task)
1391 {
1392 Capability *tmpcap;
1393 nat i;
1394
1395 for (i=0; i < n_capabilities; i++) {
1396 debugTrace(DEBUG_sched, "grabbing all the capabilies (%d/%d)", i, n_capabilities);
1397 tmpcap = &capabilities[i];
1398 if (tmpcap != cap) {
1399 // we better hope this task doesn't get migrated to
1400 // another Capability while we're waiting for this one.
1401 // It won't, because load balancing happens while we have
1402 // all the Capabilities, but even so it's a slightly
1403 // unsavoury invariant.
1404 task->cap = tmpcap;
1405 waitForReturnCapability(&tmpcap, task);
1406 if (tmpcap->no != i) {
1407 barf("acquireAllCapabilities: got the wrong capability");
1408 }
1409 }
1410 }
1411 task->cap = cap;
1412 }
1413
1414 static void releaseAllCapabilities(Capability *cap, Task *task)
1415 {
1416 nat i;
1417
1418 for (i = 0; i < n_capabilities; i++) {
1419 if (cap->no != i) {
1420 task->cap = &capabilities[i];
1421 releaseCapability(&capabilities[i]);
1422 }
1423 }
1424 task->cap = cap;
1425 }
1426 #endif
1427
1428 /* -----------------------------------------------------------------------------
1429 * Perform a garbage collection if necessary
1430 * -------------------------------------------------------------------------- */
1431
1432 static void
1433 scheduleDoGC (Capability **pcap, Task *task USED_IF_THREADS,
1434 rtsBool force_major)
1435 {
1436 Capability *cap = *pcap;
1437 rtsBool heap_census;
1438 nat collect_gen;
1439 #ifdef THREADED_RTS
1440 rtsBool idle_cap[n_capabilities];
1441 rtsBool 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 interruptAllCapabilities();
1503
1504 // The final shutdown GC is always single-threaded, because it's
1505 // possible that some of the Capabilities have no worker threads.
1506
1507 if (gc_type == SYNC_GC_SEQ)
1508 {
1509 traceEventRequestSeqGc(cap);
1510 }
1511 else
1512 {
1513 traceEventRequestParGc(cap);
1514 debugTrace(DEBUG_sched, "ready_to_gc, grabbing GC threads");
1515 }
1516
1517 if (gc_type == SYNC_GC_SEQ)
1518 {
1519 // single-threaded GC: grab all the capabilities
1520 acquireAllCapabilities(cap,task);
1521 }
1522 else
1523 {
1524 // If we are load-balancing collections in this
1525 // generation, then we require all GC threads to participate
1526 // in the collection. Otherwise, we only require active
1527 // threads to participate, and we set gc_threads[i]->idle for
1528 // any idle capabilities. The rationale here is that waking
1529 // up an idle Capability takes much longer than just doing any
1530 // GC work on its behalf.
1531
1532 if (RtsFlags.ParFlags.parGcNoSyncWithIdle == 0
1533 || (RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
1534 collect_gen >= RtsFlags.ParFlags.parGcLoadBalancingGen)) {
1535 for (i=0; i < n_capabilities; i++) {
1536 if (capabilities[i].disabled) {
1537 idle_cap[i] = tryGrabCapability(&capabilities[i], task);
1538 } else {
1539 idle_cap[i] = rtsFalse;
1540 }
1541 }
1542 } else {
1543 for (i=0; i < n_capabilities; i++) {
1544 if (capabilities[i].disabled) {
1545 idle_cap[i] = tryGrabCapability(&capabilities[i], task);
1546 } else if (i == cap->no ||
1547 capabilities[i].idle < RtsFlags.ParFlags.parGcNoSyncWithIdle) {
1548 idle_cap[i] = rtsFalse;
1549 } else {
1550 idle_cap[i] = tryGrabCapability(&capabilities[i], task);
1551 if (!idle_cap[i]) {
1552 n_failed_trygrab_idles++;
1553 } else {
1554 n_idle_caps++;
1555 }
1556 }
1557 }
1558 }
1559
1560 // We set the gc_thread[i]->idle flag if that
1561 // capability/thread is not participating in this collection.
1562 // We also keep a local record of which capabilities are idle
1563 // in idle_cap[], because scheduleDoGC() is re-entrant:
1564 // another thread might start a GC as soon as we've finished
1565 // this one, and thus the gc_thread[]->idle flags are invalid
1566 // as soon as we release any threads after GC. Getting this
1567 // wrong leads to a rare and hard to debug deadlock!
1568
1569 for (i=0; i < n_capabilities; i++) {
1570 gc_threads[i]->idle = idle_cap[i];
1571 capabilities[i].idle++;
1572 }
1573
1574 // For all capabilities participating in this GC, wait until
1575 // they have stopped mutating and are standing by for GC.
1576 waitForGcThreads(cap);
1577
1578 #if defined(THREADED_RTS)
1579 // Stable point where we can do a global check on our spark counters
1580 ASSERT(checkSparkCountInvariant());
1581 #endif
1582 }
1583
1584 #endif
1585
1586 IF_DEBUG(scheduler, printAllThreads());
1587
1588 delete_threads_and_gc:
1589 /*
1590 * We now have all the capabilities; if we're in an interrupting
1591 * state, then we should take the opportunity to delete all the
1592 * threads in the system.
1593 */
1594 if (sched_state == SCHED_INTERRUPTING) {
1595 deleteAllThreads(cap);
1596 #if defined(THREADED_RTS)
1597 // Discard all the sparks from every Capability. Why?
1598 // They'll probably be GC'd anyway since we've killed all the
1599 // threads. It just avoids the GC having to do any work to
1600 // figure out that any remaining sparks are garbage.
1601 for (i = 0; i < n_capabilities; i++) {
1602 capabilities[i].spark_stats.gcd +=
1603 sparkPoolSize(capabilities[i].sparks);
1604 // No race here since all Caps are stopped.
1605 discardSparksCap(&capabilities[i]);
1606 }
1607 #endif
1608 sched_state = SCHED_SHUTTING_DOWN;
1609 }
1610
1611 /*
1612 * When there are disabled capabilities, we want to migrate any
1613 * threads away from them. Normally this happens in the
1614 * scheduler's loop, but only for unbound threads - it's really
1615 * hard for a bound thread to migrate itself. So we have another
1616 * go here.
1617 */
1618 #if defined(THREADED_RTS)
1619 for (i = enabled_capabilities; i < n_capabilities; i++) {
1620 Capability *tmp_cap, *dest_cap;
1621 tmp_cap = &capabilities[i];
1622 ASSERT(tmp_cap->disabled);
1623 if (i != cap->no) {
1624 dest_cap = &capabilities[i % enabled_capabilities];
1625 while (!emptyRunQueue(tmp_cap)) {
1626 tso = popRunQueue(tmp_cap);
1627 migrateThread(tmp_cap, tso, dest_cap);
1628 if (tso->bound) {
1629 traceTaskMigrate(tso->bound->task,
1630 tso->bound->task->cap,
1631 dest_cap);
1632 tso->bound->task->cap = dest_cap;
1633 }
1634 }
1635 }
1636 }
1637 #endif
1638
1639 #if defined(THREADED_RTS)
1640 // reset pending_sync *before* GC, so that when the GC threads
1641 // emerge they don't immediately re-enter the GC.
1642 pending_sync = 0;
1643 GarbageCollect(collect_gen, heap_census, gc_type, cap);
1644 #else
1645 GarbageCollect(collect_gen, heap_census, 0, cap);
1646 #endif
1647
1648 traceSparkCounters(cap);
1649
1650 switch (recent_activity) {
1651 case ACTIVITY_INACTIVE:
1652 if (force_major) {
1653 // We are doing a GC because the system has been idle for a
1654 // timeslice and we need to check for deadlock. Record the
1655 // fact that we've done a GC and turn off the timer signal;
1656 // it will get re-enabled if we run any threads after the GC.
1657 recent_activity = ACTIVITY_DONE_GC;
1658 #ifndef PROFILING
1659 stopTimer();
1660 #endif
1661 break;
1662 }
1663 // fall through...
1664
1665 case ACTIVITY_MAYBE_NO:
1666 // the GC might have taken long enough for the timer to set
1667 // recent_activity = ACTIVITY_MAYBE_NO or ACTIVITY_INACTIVE,
1668 // but we aren't necessarily deadlocked:
1669 recent_activity = ACTIVITY_YES;
1670 break;
1671
1672 case ACTIVITY_DONE_GC:
1673 // If we are actually active, the scheduler will reset the
1674 // recent_activity flag and re-enable the timer.
1675 break;
1676 }
1677
1678 #if defined(THREADED_RTS)
1679 // Stable point where we can do a global check on our spark counters
1680 ASSERT(checkSparkCountInvariant());
1681 #endif
1682
1683 // The heap census itself is done during GarbageCollect().
1684 if (heap_census) {
1685 performHeapProfile = rtsFalse;
1686 }
1687
1688 #if defined(THREADED_RTS)
1689 if (gc_type == SYNC_GC_PAR)
1690 {
1691 releaseGCThreads(cap);
1692 for (i = 0; i < n_capabilities; i++) {
1693 if (i != cap->no) {
1694 if (idle_cap[i]) {
1695 ASSERT(capabilities[i].running_task == task);
1696 task->cap = &capabilities[i];
1697 releaseCapability(&capabilities[i]);
1698 } else {
1699 ASSERT(capabilities[i].running_task != task);
1700 }
1701 }
1702 }
1703 task->cap = cap;
1704 }
1705 #endif
1706
1707 if (heap_overflow && sched_state < SCHED_INTERRUPTING) {
1708 // GC set the heap_overflow flag, so we should proceed with
1709 // an orderly shutdown now. Ultimately we want the main
1710 // thread to return to its caller with HeapExhausted, at which
1711 // point the caller should call hs_exit(). The first step is
1712 // to delete all the threads.
1713 //
1714 // Another way to do this would be to raise an exception in
1715 // the main thread, which we really should do because it gives
1716 // the program a chance to clean up. But how do we find the
1717 // main thread? It should presumably be the same one that
1718 // gets ^C exceptions, but that's all done on the Haskell side
1719 // (GHC.TopHandler).
1720 sched_state = SCHED_INTERRUPTING;
1721 goto delete_threads_and_gc;
1722 }
1723
1724 #ifdef SPARKBALANCE
1725 /* JB
1726 Once we are all together... this would be the place to balance all
1727 spark pools. No concurrent stealing or adding of new sparks can
1728 occur. Should be defined in Sparks.c. */
1729 balanceSparkPoolsCaps(n_capabilities, capabilities);
1730 #endif
1731
1732 #if defined(THREADED_RTS)
1733 if (gc_type == SYNC_GC_SEQ) {
1734 // release our stash of capabilities.
1735 releaseAllCapabilities(cap, task);
1736 }
1737 #endif
1738
1739 return;
1740 }
1741
1742 /* ---------------------------------------------------------------------------
1743 * Singleton fork(). Do not copy any running threads.
1744 * ------------------------------------------------------------------------- */
1745
1746 pid_t
1747 forkProcess(HsStablePtr *entry
1748 #ifndef FORKPROCESS_PRIMOP_SUPPORTED
1749 STG_UNUSED
1750 #endif
1751 )
1752 {
1753 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
1754 pid_t pid;
1755 StgTSO* t,*next;
1756 Capability *cap;
1757 nat g;
1758 Task *task = NULL;
1759 nat i;
1760 #ifdef THREADED_RTS
1761 nat sync;
1762 #endif
1763
1764 debugTrace(DEBUG_sched, "forking!");
1765
1766 task = newBoundTask();
1767
1768 cap = NULL;
1769 waitForReturnCapability(&cap, task);
1770
1771 #ifdef THREADED_RTS
1772 do {
1773 sync = requestSync(&cap, task, SYNC_OTHER);
1774 } while (sync);
1775
1776 acquireAllCapabilities(cap,task);
1777
1778 pending_sync = 0;
1779 #endif
1780
1781 // no funny business: hold locks while we fork, otherwise if some
1782 // other thread is holding a lock when the fork happens, the data
1783 // structure protected by the lock will forever be in an
1784 // inconsistent state in the child. See also #1391.
1785 ACQUIRE_LOCK(&sched_mutex);
1786 ACQUIRE_LOCK(&sm_mutex);
1787 ACQUIRE_LOCK(&stable_mutex);
1788 ACQUIRE_LOCK(&task->lock);
1789
1790 for (i=0; i < n_capabilities; i++) {
1791 ACQUIRE_LOCK(&capabilities[i].lock);
1792 }
1793
1794 stopTimer(); // See #4074
1795
1796 #if defined(TRACING)
1797 flushEventLog(); // so that child won't inherit dirty file buffers
1798 #endif
1799
1800 pid = fork();
1801
1802 if (pid) { // parent
1803
1804 startTimer(); // #4074
1805
1806 RELEASE_LOCK(&sched_mutex);
1807 RELEASE_LOCK(&sm_mutex);
1808 RELEASE_LOCK(&stable_mutex);
1809 RELEASE_LOCK(&task->lock);
1810
1811 for (i=0; i < n_capabilities; i++) {
1812 releaseCapability_(&capabilities[i],rtsFalse);
1813 RELEASE_LOCK(&capabilities[i].lock);
1814 }
1815 boundTaskExiting(task);
1816
1817 // just return the pid
1818 return pid;
1819
1820 } else { // child
1821
1822 #if defined(THREADED_RTS)
1823 initMutex(&sched_mutex);
1824 initMutex(&sm_mutex);
1825 initMutex(&stable_mutex);
1826 initMutex(&task->lock);
1827
1828 for (i=0; i < n_capabilities; i++) {
1829 initMutex(&capabilities[i].lock);
1830 }
1831 #endif
1832
1833 #ifdef TRACING
1834 resetTracing();
1835 #endif
1836
1837 // Now, all OS threads except the thread that forked are
1838 // stopped. We need to stop all Haskell threads, including
1839 // those involved in foreign calls. Also we need to delete
1840 // all Tasks, because they correspond to OS threads that are
1841 // now gone.
1842
1843 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1844 for (t = generations[g].threads; t != END_TSO_QUEUE; t = next) {
1845 next = t->global_link;
1846 // don't allow threads to catch the ThreadKilled
1847 // exception, but we do want to raiseAsync() because these
1848 // threads may be evaluating thunks that we need later.
1849 deleteThread_(t->cap,t);
1850
1851 // stop the GC from updating the InCall to point to
1852 // the TSO. This is only necessary because the
1853 // OSThread bound to the TSO has been killed, and
1854 // won't get a chance to exit in the usual way (see
1855 // also scheduleHandleThreadFinished).
1856 t->bound = NULL;
1857 }
1858 }
1859
1860 discardTasksExcept(task);
1861
1862 for (i=0; i < n_capabilities; i++) {
1863 cap = &capabilities[i];
1864
1865 // Empty the run queue. It seems tempting to let all the
1866 // killed threads stay on the run queue as zombies to be
1867 // cleaned up later, but some of them may correspond to
1868 // bound threads for which the corresponding Task does not
1869 // exist.
1870 truncateRunQueue(cap);
1871
1872 // Any suspended C-calling Tasks are no more, their OS threads
1873 // don't exist now:
1874 cap->suspended_ccalls = NULL;
1875
1876 #if defined(THREADED_RTS)
1877 // Wipe our spare workers list, they no longer exist. New
1878 // workers will be created if necessary.
1879 cap->spare_workers = NULL;
1880 cap->n_spare_workers = 0;
1881 cap->returning_tasks_hd = NULL;
1882 cap->returning_tasks_tl = NULL;
1883 #endif
1884
1885 // Release all caps except 0, we'll use that for starting
1886 // the IO manager and running the client action below.
1887 if (cap->no != 0) {
1888 task->cap = cap;
1889 releaseCapability(cap);
1890 }
1891 }
1892 cap = &capabilities[0];
1893 task->cap = cap;
1894
1895 // Empty the threads lists. Otherwise, the garbage
1896 // collector may attempt to resurrect some of these threads.
1897 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1898 generations[g].threads = END_TSO_QUEUE;
1899 }
1900
1901 // On Unix, all timers are reset in the child, so we need to start
1902 // the timer again.
1903 initTimer();
1904 startTimer();
1905
1906 // TODO: need to trace various other things in the child
1907 // like startup event, capabilities, process info etc
1908 traceTaskCreate(task, cap);
1909
1910 #if defined(THREADED_RTS)
1911 ioManagerStartCap(&cap);
1912 #endif
1913
1914 rts_evalStableIO(&cap, entry, NULL); // run the action
1915 rts_checkSchedStatus("forkProcess",cap);
1916
1917 rts_unlock(cap);
1918 hs_exit(); // clean up and exit
1919 stg_exit(EXIT_SUCCESS);
1920 }
1921 #else /* !FORKPROCESS_PRIMOP_SUPPORTED */
1922 barf("forkProcess#: primop not supported on this platform, sorry!\n");
1923 #endif
1924 }
1925
1926 /* ---------------------------------------------------------------------------
1927 * Changing the number of Capabilities
1928 *
1929 * Changing the number of Capabilities is very tricky! We can only do
1930 * it with the system fully stopped, so we do a full sync with
1931 * requestSync(SYNC_OTHER) and grab all the capabilities.
1932 *
1933 * Then we resize the appropriate data structures, and update all
1934 * references to the old data structures which have now moved.
1935 * Finally we release the Capabilities we are holding, and start
1936 * worker Tasks on the new Capabilities we created.
1937 *
1938 * ------------------------------------------------------------------------- */
1939
1940 void
1941 setNumCapabilities (nat new_n_capabilities USED_IF_THREADS)
1942 {
1943 #if !defined(THREADED_RTS)
1944 if (new_n_capabilities != 1) {
1945 errorBelch("setNumCapabilities: not supported in the non-threaded RTS");
1946 }
1947 return;
1948 #elif defined(NOSMP)
1949 if (new_n_capabilities != 1) {
1950 errorBelch("setNumCapabilities: not supported on this platform");
1951 }
1952 return;
1953 #else
1954 Task *task;
1955 Capability *cap;
1956 nat sync;
1957 StgTSO* t;
1958 nat g, n;
1959 Capability *old_capabilities = NULL;
1960
1961 if (new_n_capabilities == enabled_capabilities) return;
1962
1963 debugTrace(DEBUG_sched, "changing the number of Capabilities from %d to %d",
1964 enabled_capabilities, new_n_capabilities);
1965
1966 cap = rts_lock();
1967 task = cap->running_task;
1968
1969 do {
1970 sync = requestSync(&cap, task, SYNC_OTHER);
1971 } while (sync);
1972
1973 acquireAllCapabilities(cap,task);
1974
1975 pending_sync = 0;
1976
1977 if (new_n_capabilities < enabled_capabilities)
1978 {
1979 // Reducing the number of capabilities: we do not actually
1980 // remove the extra capabilities, we just mark them as
1981 // "disabled". This has the following effects:
1982 //
1983 // - threads on a disabled capability are migrated away by the
1984 // scheduler loop
1985 //
1986 // - disabled capabilities do not participate in GC
1987 // (see scheduleDoGC())
1988 //
1989 // - No spark threads are created on this capability
1990 // (see scheduleActivateSpark())
1991 //
1992 // - We do not attempt to migrate threads *to* a disabled
1993 // capability (see schedulePushWork()).
1994 //
1995 // but in other respects, a disabled capability remains
1996 // alive. Threads may be woken up on a disabled capability,
1997 // but they will be immediately migrated away.
1998 //
1999 // This approach is much easier than trying to actually remove
2000 // the capability; we don't have to worry about GC data
2001 // structures, the nursery, etc.
2002 //
2003 for (n = new_n_capabilities; n < enabled_capabilities; n++) {
2004 capabilities[n].disabled = rtsTrue;
2005 traceCapDisable(&capabilities[n]);
2006 }
2007 enabled_capabilities = new_n_capabilities;
2008 }
2009 else
2010 {
2011 // Increasing the number of enabled capabilities.
2012 //
2013 // enable any disabled capabilities, up to the required number
2014 for (n = enabled_capabilities;
2015 n < new_n_capabilities && n < n_capabilities; n++) {
2016 capabilities[n].disabled = rtsFalse;
2017 traceCapEnable(&capabilities[n]);
2018 }
2019 enabled_capabilities = n;
2020
2021 if (new_n_capabilities > n_capabilities) {
2022 #if defined(TRACING)
2023 // Allocate eventlog buffers for the new capabilities. Note this
2024 // must be done before calling moreCapabilities(), because that
2025 // will emit events about creating the new capabilities and adding
2026 // them to existing capsets.
2027 tracingAddCapapilities(n_capabilities, new_n_capabilities);
2028 #endif
2029
2030 // Resize the capabilities array
2031 // NB. after this, capabilities points somewhere new. Any pointers
2032 // of type (Capability *) are now invalid.
2033 old_capabilities = moreCapabilities(n_capabilities, new_n_capabilities);
2034
2035 // update our own cap pointer
2036 cap = &capabilities[cap->no];
2037
2038 // Resize and update storage manager data structures
2039 storageAddCapabilities(n_capabilities, new_n_capabilities);
2040
2041 // Update (Capability *) refs in the Task manager.
2042 updateCapabilityRefs();
2043
2044 // Update (Capability *) refs from TSOs
2045 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
2046 for (t = generations[g].threads; t != END_TSO_QUEUE; t = t->global_link) {
2047 t->cap = &capabilities[t->cap->no];
2048 }
2049 }
2050 }
2051 }
2052
2053 // We're done: release the original Capabilities
2054 releaseAllCapabilities(cap,task);
2055
2056 // Start worker tasks on the new Capabilities
2057 startWorkerTasks(n_capabilities, new_n_capabilities);
2058
2059 // finally, update n_capabilities
2060 if (new_n_capabilities > n_capabilities) {
2061 n_capabilities = enabled_capabilities = new_n_capabilities;
2062 }
2063
2064 // We can't free the old array until now, because we access it
2065 // while updating pointers in updateCapabilityRefs().
2066 if (old_capabilities) {
2067 stgFree(old_capabilities);
2068 }
2069
2070 // Notify IO manager that the number of capabilities has changed.
2071 rts_evalIO(
2072 &cap,
2073 &base_GHCziConcziIO_ioManagerCapabilitiesChanged_closure,
2074 NULL);
2075
2076 rts_unlock(cap);
2077
2078 #endif // THREADED_RTS
2079 }
2080
2081
2082
2083 /* ---------------------------------------------------------------------------
2084 * Delete all the threads in the system
2085 * ------------------------------------------------------------------------- */
2086
2087 static void
2088 deleteAllThreads ( Capability *cap )
2089 {
2090 // NOTE: only safe to call if we own all capabilities.
2091
2092 StgTSO* t, *next;
2093 nat g;
2094
2095 debugTrace(DEBUG_sched,"deleting all threads");
2096 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
2097 for (t = generations[g].threads; t != END_TSO_QUEUE; t = next) {
2098 next = t->global_link;
2099 deleteThread(cap,t);
2100 }
2101 }
2102
2103 // The run queue now contains a bunch of ThreadKilled threads. We
2104 // must not throw these away: the main thread(s) will be in there
2105 // somewhere, and the main scheduler loop has to deal with it.
2106 // Also, the run queue is the only thing keeping these threads from
2107 // being GC'd, and we don't want the "main thread has been GC'd" panic.
2108
2109 #if !defined(THREADED_RTS)
2110 ASSERT(blocked_queue_hd == END_TSO_QUEUE);
2111 ASSERT(sleeping_queue == END_TSO_QUEUE);
2112 #endif
2113 }
2114
2115 /* -----------------------------------------------------------------------------
2116 Managing the suspended_ccalls list.
2117 Locks required: sched_mutex
2118 -------------------------------------------------------------------------- */
2119
2120 STATIC_INLINE void
2121 suspendTask (Capability *cap, Task *task)
2122 {
2123 InCall *incall;
2124
2125 incall = task->incall;
2126 ASSERT(incall->next == NULL && incall->prev == NULL);
2127 incall->next = cap->suspended_ccalls;
2128 incall->prev = NULL;
2129 if (cap->suspended_ccalls) {
2130 cap->suspended_ccalls->prev = incall;
2131 }
2132 cap->suspended_ccalls = incall;
2133 }
2134
2135 STATIC_INLINE void
2136 recoverSuspendedTask (Capability *cap, Task *task)
2137 {
2138 InCall *incall;
2139
2140 incall = task->incall;
2141 if (incall->prev) {
2142 incall->prev->next = incall->next;
2143 } else {
2144 ASSERT(cap->suspended_ccalls == incall);
2145 cap->suspended_ccalls = incall->next;
2146 }
2147 if (incall->next) {
2148 incall->next->prev = incall->prev;
2149 }
2150 incall->next = incall->prev = NULL;
2151 }
2152
2153 /* ---------------------------------------------------------------------------
2154 * Suspending & resuming Haskell threads.
2155 *
2156 * When making a "safe" call to C (aka _ccall_GC), the task gives back
2157 * its capability before calling the C function. This allows another
2158 * task to pick up the capability and carry on running Haskell
2159 * threads. It also means that if the C call blocks, it won't lock
2160 * the whole system.
2161 *
2162 * The Haskell thread making the C call is put to sleep for the
2163 * duration of the call, on the suspended_ccalling_threads queue. We
2164 * give out a token to the task, which it can use to resume the thread
2165 * on return from the C function.
2166 *
2167 * If this is an interruptible C call, this means that the FFI call may be
2168 * unceremoniously terminated and should be scheduled on an
2169 * unbound worker thread.
2170 * ------------------------------------------------------------------------- */
2171
2172 void *
2173 suspendThread (StgRegTable *reg, rtsBool interruptible)
2174 {
2175 Capability *cap;
2176 int saved_errno;
2177 StgTSO *tso;
2178 Task *task;
2179 #if mingw32_HOST_OS
2180 StgWord32 saved_winerror;
2181 #endif
2182
2183 saved_errno = errno;
2184 #if mingw32_HOST_OS
2185 saved_winerror = GetLastError();
2186 #endif
2187
2188 /* assume that *reg is a pointer to the StgRegTable part of a Capability.
2189 */
2190 cap = regTableToCapability(reg);
2191
2192 task = cap->running_task;
2193 tso = cap->r.rCurrentTSO;
2194
2195 traceEventStopThread(cap, tso, THREAD_SUSPENDED_FOREIGN_CALL, 0);
2196
2197 // XXX this might not be necessary --SDM
2198 tso->what_next = ThreadRunGHC;
2199
2200 threadPaused(cap,tso);
2201
2202 if (interruptible) {
2203 tso->why_blocked = BlockedOnCCall_Interruptible;
2204 } else {
2205 tso->why_blocked = BlockedOnCCall;
2206 }
2207
2208 // Hand back capability
2209 task->incall->suspended_tso = tso;
2210 task->incall->suspended_cap = cap;
2211
2212 ACQUIRE_LOCK(&cap->lock);
2213
2214 suspendTask(cap,task);
2215 cap->in_haskell = rtsFalse;
2216 releaseCapability_(cap,rtsFalse);
2217
2218 RELEASE_LOCK(&cap->lock);
2219
2220 errno = saved_errno;
2221 #if mingw32_HOST_OS
2222 SetLastError(saved_winerror);
2223 #endif
2224 return task;
2225 }
2226
2227 StgRegTable *
2228 resumeThread (void *task_)
2229 {
2230 StgTSO *tso;
2231 InCall *incall;
2232 Capability *cap;
2233 Task *task = task_;
2234 int saved_errno;
2235 #if mingw32_HOST_OS
2236 StgWord32 saved_winerror;
2237 #endif
2238
2239 saved_errno = errno;
2240 #if mingw32_HOST_OS
2241 saved_winerror = GetLastError();
2242 #endif
2243
2244 incall = task->incall;
2245 cap = incall->suspended_cap;
2246 task->cap = cap;
2247
2248 // Wait for permission to re-enter the RTS with the result.
2249 waitForReturnCapability(&cap,task);
2250 // we might be on a different capability now... but if so, our
2251 // entry on the suspended_ccalls list will also have been
2252 // migrated.
2253
2254 // Remove the thread from the suspended list
2255 recoverSuspendedTask(cap,task);
2256
2257 tso = incall->suspended_tso;
2258 incall->suspended_tso = NULL;
2259 incall->suspended_cap = NULL;
2260 tso->_link = END_TSO_QUEUE; // no write barrier reqd
2261
2262 traceEventRunThread(cap, tso);
2263
2264 /* Reset blocking status */
2265 tso->why_blocked = NotBlocked;
2266
2267 if ((tso->flags & TSO_BLOCKEX) == 0) {
2268 // avoid locking the TSO if we don't have to
2269 if (tso->blocked_exceptions != END_BLOCKED_EXCEPTIONS_QUEUE) {
2270 maybePerformBlockedException(cap,tso);
2271 }
2272 }
2273
2274 cap->r.rCurrentTSO = tso;
2275 cap->in_haskell = rtsTrue;
2276 errno = saved_errno;
2277 #if mingw32_HOST_OS
2278 SetLastError(saved_winerror);
2279 #endif
2280
2281 /* We might have GC'd, mark the TSO dirty again */
2282 dirty_TSO(cap,tso);
2283 dirty_STACK(cap,tso->stackobj);
2284
2285 IF_DEBUG(sanity, checkTSO(tso));
2286
2287 return &cap->r;
2288 }
2289
2290 /* ---------------------------------------------------------------------------
2291 * scheduleThread()
2292 *
2293 * scheduleThread puts a thread on the end of the runnable queue.
2294 * This will usually be done immediately after a thread is created.
2295 * The caller of scheduleThread must create the thread using e.g.
2296 * createThread and push an appropriate closure
2297 * on this thread's stack before the scheduler is invoked.
2298 * ------------------------------------------------------------------------ */
2299
2300 void
2301 scheduleThread(Capability *cap, StgTSO *tso)
2302 {
2303 // The thread goes at the *end* of the run-queue, to avoid possible
2304 // starvation of any threads already on the queue.
2305 appendToRunQueue(cap,tso);
2306 }
2307
2308 void
2309 scheduleThreadOn(Capability *cap, StgWord cpu USED_IF_THREADS, StgTSO *tso)
2310 {
2311 tso->flags |= TSO_LOCKED; // we requested explicit affinity; don't
2312 // move this thread from now on.
2313 #if defined(THREADED_RTS)
2314 cpu %= enabled_capabilities;
2315 if (cpu == cap->no) {
2316 appendToRunQueue(cap,tso);
2317 } else {
2318 migrateThread(cap, tso, &capabilities[cpu]);
2319 }
2320 #else
2321 appendToRunQueue(cap,tso);
2322 #endif
2323 }
2324
2325 void
2326 scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability **pcap)
2327 {
2328 Task *task;
2329 DEBUG_ONLY( StgThreadID id );
2330 Capability *cap;
2331
2332 cap = *pcap;
2333
2334 // We already created/initialised the Task
2335 task = cap->running_task;
2336
2337 // This TSO is now a bound thread; make the Task and TSO
2338 // point to each other.
2339 tso->bound = task->incall;
2340 tso->cap = cap;
2341
2342 task->incall->tso = tso;
2343 task->incall->ret = ret;
2344 task->incall->stat = NoStatus;
2345
2346 appendToRunQueue(cap,tso);
2347
2348 DEBUG_ONLY( id = tso->id );
2349 debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)id);
2350
2351 cap = schedule(cap,task);
2352
2353 ASSERT(task->incall->stat != NoStatus);
2354 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
2355
2356 debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)id);
2357 *pcap = cap;
2358 }
2359
2360 /* ----------------------------------------------------------------------------
2361 * Starting Tasks
2362 * ------------------------------------------------------------------------- */
2363
2364 #if defined(THREADED_RTS)
2365 void scheduleWorker (Capability *cap, Task *task)
2366 {
2367 // schedule() runs without a lock.
2368 cap = schedule(cap,task);
2369
2370 // On exit from schedule(), we have a Capability, but possibly not
2371 // the same one we started with.
2372
2373 // During shutdown, the requirement is that after all the
2374 // Capabilities are shut down, all workers that are shutting down
2375 // have finished workerTaskStop(). This is why we hold on to
2376 // cap->lock until we've finished workerTaskStop() below.
2377 //
2378 // There may be workers still involved in foreign calls; those
2379 // will just block in waitForReturnCapability() because the
2380 // Capability has been shut down.
2381 //
2382 ACQUIRE_LOCK(&cap->lock);
2383 releaseCapability_(cap,rtsFalse);
2384 workerTaskStop(task);
2385 RELEASE_LOCK(&cap->lock);
2386 }
2387 #endif
2388
2389 /* ---------------------------------------------------------------------------
2390 * Start new worker tasks on Capabilities from--to
2391 * -------------------------------------------------------------------------- */
2392
2393 static void
2394 startWorkerTasks (nat from USED_IF_THREADS, nat to USED_IF_THREADS)
2395 {
2396 #if defined(THREADED_RTS)
2397 nat i;
2398 Capability *cap;
2399
2400 for (i = from; i < to; i++) {
2401 cap = &capabilities[i];
2402 ACQUIRE_LOCK(&cap->lock);
2403 startWorkerTask(cap);
2404 RELEASE_LOCK(&cap->lock);
2405 }
2406 #endif
2407 }
2408
2409 /* ---------------------------------------------------------------------------
2410 * initScheduler()
2411 *
2412 * Initialise the scheduler. This resets all the queues - if the
2413 * queues contained any threads, they'll be garbage collected at the
2414 * next pass.
2415 *
2416 * ------------------------------------------------------------------------ */
2417
2418 void
2419 initScheduler(void)
2420 {
2421 #if !defined(THREADED_RTS)
2422 blocked_queue_hd = END_TSO_QUEUE;
2423 blocked_queue_tl = END_TSO_QUEUE;
2424 sleeping_queue = END_TSO_QUEUE;
2425 #endif
2426
2427 sched_state = SCHED_RUNNING;
2428 recent_activity = ACTIVITY_YES;
2429
2430 #if defined(THREADED_RTS)
2431 /* Initialise the mutex and condition variables used by
2432 * the scheduler. */
2433 initMutex(&sched_mutex);
2434 #endif
2435
2436 ACQUIRE_LOCK(&sched_mutex);
2437
2438 /* A capability holds the state a native thread needs in
2439 * order to execute STG code. At least one capability is
2440 * floating around (only THREADED_RTS builds have more than one).
2441 */
2442 initCapabilities();
2443
2444 initTaskManager();
2445
2446 /*
2447 * Eagerly start one worker to run each Capability, except for
2448 * Capability 0. The idea is that we're probably going to start a
2449 * bound thread on Capability 0 pretty soon, so we don't want a
2450 * worker task hogging it.
2451 */
2452 startWorkerTasks(1, n_capabilities);
2453
2454 RELEASE_LOCK(&sched_mutex);
2455
2456 }
2457
2458 void
2459 exitScheduler (rtsBool wait_foreign USED_IF_THREADS)
2460 /* see Capability.c, shutdownCapability() */
2461 {
2462 Task *task = NULL;
2463
2464 task = newBoundTask();
2465
2466 // If we haven't killed all the threads yet, do it now.
2467 if (sched_state < SCHED_SHUTTING_DOWN) {
2468 sched_state = SCHED_INTERRUPTING;
2469 Capability *cap = task->cap;
2470 waitForReturnCapability(&cap,task);
2471 scheduleDoGC(&cap,task,rtsTrue);
2472 ASSERT(task->incall->tso == NULL);
2473 releaseCapability(cap);
2474 }
2475 sched_state = SCHED_SHUTTING_DOWN;
2476
2477 shutdownCapabilities(task, wait_foreign);
2478
2479 // debugBelch("n_failed_trygrab_idles = %d, n_idle_caps = %d\n",
2480 // n_failed_trygrab_idles, n_idle_caps);
2481
2482 boundTaskExiting(task);
2483 }
2484
2485 void
2486 freeScheduler( void )
2487 {
2488 nat still_running;
2489
2490 ACQUIRE_LOCK(&sched_mutex);
2491 still_running = freeTaskManager();
2492 // We can only free the Capabilities if there are no Tasks still
2493 // running. We might have a Task about to return from a foreign
2494 // call into waitForReturnCapability(), for example (actually,
2495 // this should be the *only* thing that a still-running Task can
2496 // do at this point, and it will block waiting for the
2497 // Capability).
2498 if (still_running == 0) {
2499 freeCapabilities();
2500 if (n_capabilities != 1) {
2501 stgFree(capabilities);
2502 }
2503 }
2504 RELEASE_LOCK(&sched_mutex);
2505 #if defined(THREADED_RTS)
2506 closeMutex(&sched_mutex);
2507 #endif
2508 }
2509
2510 void markScheduler (evac_fn evac USED_IF_NOT_THREADS,
2511 void *user USED_IF_NOT_THREADS)
2512 {
2513 #if !defined(THREADED_RTS)
2514 evac(user, (StgClosure **)(void *)&blocked_queue_hd);
2515 evac(user, (StgClosure **)(void *)&blocked_queue_tl);
2516 evac(user, (StgClosure **)(void *)&sleeping_queue);
2517 #endif
2518 }
2519
2520 /* -----------------------------------------------------------------------------
2521 performGC
2522
2523 This is the interface to the garbage collector from Haskell land.
2524 We provide this so that external C code can allocate and garbage
2525 collect when called from Haskell via _ccall_GC.
2526 -------------------------------------------------------------------------- */
2527
2528 static void
2529 performGC_(rtsBool force_major)
2530 {
2531 Task *task;
2532 Capability *cap = NULL;
2533
2534 // We must grab a new Task here, because the existing Task may be
2535 // associated with a particular Capability, and chained onto the
2536 // suspended_ccalls queue.
2537 task = newBoundTask();
2538
2539 // TODO: do we need to traceTask*() here?
2540
2541 waitForReturnCapability(&cap,task);
2542 scheduleDoGC(&cap,task,force_major);
2543 releaseCapability(cap);
2544 boundTaskExiting(task);
2545 }
2546
2547 void
2548 performGC(void)
2549 {
2550 performGC_(rtsFalse);
2551 }
2552
2553 void
2554 performMajorGC(void)
2555 {
2556 performGC_(rtsTrue);
2557 }
2558
2559 /* ---------------------------------------------------------------------------
2560 Interrupt execution
2561 - usually called inside a signal handler so it mustn't do anything fancy.
2562 ------------------------------------------------------------------------ */
2563
2564 void
2565 interruptStgRts(void)
2566 {
2567 sched_state = SCHED_INTERRUPTING;
2568 interruptAllCapabilities();
2569 #if defined(THREADED_RTS)
2570 wakeUpRts();
2571 #endif
2572 }
2573
2574 /* -----------------------------------------------------------------------------
2575 Wake up the RTS
2576
2577 This function causes at least one OS thread to wake up and run the
2578 scheduler loop. It is invoked when the RTS might be deadlocked, or
2579 an external event has arrived that may need servicing (eg. a
2580 keyboard interrupt).
2581
2582 In the single-threaded RTS we don't do anything here; we only have
2583 one thread anyway, and the event that caused us to want to wake up
2584 will have interrupted any blocking system call in progress anyway.
2585 -------------------------------------------------------------------------- */
2586
2587 #if defined(THREADED_RTS)
2588 void wakeUpRts(void)
2589 {
2590 // This forces the IO Manager thread to wakeup, which will
2591 // in turn ensure that some OS thread wakes up and runs the
2592 // scheduler loop, which will cause a GC and deadlock check.
2593 ioManagerWakeup();
2594 }
2595 #endif
2596
2597 /* -----------------------------------------------------------------------------
2598 Deleting threads
2599
2600 This is used for interruption (^C) and forking, and corresponds to
2601 raising an exception but without letting the thread catch the
2602 exception.
2603 -------------------------------------------------------------------------- */
2604
2605 static void
2606 deleteThread (Capability *cap STG_UNUSED, StgTSO *tso)
2607 {
2608 // NOTE: must only be called on a TSO that we have exclusive
2609 // access to, because we will call throwToSingleThreaded() below.
2610 // The TSO must be on the run queue of the Capability we own, or
2611 // we must own all Capabilities.
2612
2613 if (tso->why_blocked != BlockedOnCCall &&
2614 tso->why_blocked != BlockedOnCCall_Interruptible) {
2615 throwToSingleThreaded(tso->cap,tso,NULL);
2616 }
2617 }
2618
2619 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
2620 static void
2621 deleteThread_(Capability *cap, StgTSO *tso)
2622 { // for forkProcess only:
2623 // like deleteThread(), but we delete threads in foreign calls, too.
2624
2625 if (tso->why_blocked == BlockedOnCCall ||
2626 tso->why_blocked == BlockedOnCCall_Interruptible) {
2627 tso->what_next = ThreadKilled;
2628 appendToRunQueue(tso->cap, tso);
2629 } else {
2630 deleteThread(cap,tso);
2631 }
2632 }
2633 #endif
2634
2635 /* -----------------------------------------------------------------------------
2636 raiseExceptionHelper
2637
2638 This function is called by the raise# primitve, just so that we can
2639 move some of the tricky bits of raising an exception from C-- into
2640 C. Who knows, it might be a useful re-useable thing here too.
2641 -------------------------------------------------------------------------- */
2642
2643 StgWord
2644 raiseExceptionHelper (StgRegTable *reg, StgTSO *tso, StgClosure *exception)
2645 {
2646 Capability *cap = regTableToCapability(reg);
2647 StgThunk *raise_closure = NULL;
2648 StgPtr p, next;
2649 StgRetInfoTable *info;
2650 //
2651 // This closure represents the expression 'raise# E' where E
2652 // is the exception raise. It is used to overwrite all the
2653 // thunks which are currently under evaluataion.
2654 //
2655
2656 // OLD COMMENT (we don't have MIN_UPD_SIZE now):
2657 // LDV profiling: stg_raise_info has THUNK as its closure
2658 // type. Since a THUNK takes at least MIN_UPD_SIZE words in its
2659 // payload, MIN_UPD_SIZE is more approprate than 1. It seems that
2660 // 1 does not cause any problem unless profiling is performed.
2661 // However, when LDV profiling goes on, we need to linearly scan
2662 // small object pool, where raise_closure is stored, so we should
2663 // use MIN_UPD_SIZE.
2664 //
2665 // raise_closure = (StgClosure *)RET_STGCALL1(P_,allocate,
2666 // sizeofW(StgClosure)+1);
2667 //
2668
2669 //
2670 // Walk up the stack, looking for the catch frame. On the way,
2671 // we update any closures pointed to from update frames with the
2672 // raise closure that we just built.
2673 //
2674 p = tso->stackobj->sp;
2675 while(1) {
2676 info = get_ret_itbl((StgClosure *)p);
2677 next = p + stack_frame_sizeW((StgClosure *)p);
2678 switch (info->i.type) {
2679
2680 case UPDATE_FRAME:
2681 // Only create raise_closure if we need to.
2682 if (raise_closure == NULL) {
2683 raise_closure =
2684 (StgThunk *)allocate(cap,sizeofW(StgThunk)+1);
2685 SET_HDR(raise_closure, &stg_raise_info, cap->r.rCCCS);
2686 raise_closure->payload[0] = exception;
2687 }
2688 updateThunk(cap, tso, ((StgUpdateFrame *)p)->updatee,
2689 (StgClosure *)raise_closure);
2690 p = next;
2691 continue;
2692
2693 case ATOMICALLY_FRAME:
2694 debugTrace(DEBUG_stm, "found ATOMICALLY_FRAME at %p", p);
2695 tso->stackobj->sp = p;
2696 return ATOMICALLY_FRAME;
2697
2698 case CATCH_FRAME:
2699 tso->stackobj->sp = p;
2700 return CATCH_FRAME;
2701
2702 case CATCH_STM_FRAME:
2703 debugTrace(DEBUG_stm, "found CATCH_STM_FRAME at %p", p);
2704 tso->stackobj->sp = p;
2705 return CATCH_STM_FRAME;
2706
2707 case UNDERFLOW_FRAME:
2708 tso->stackobj->sp = p;
2709 threadStackUnderflow(cap,tso);
2710 p = tso->stackobj->sp;
2711 continue;
2712
2713 case STOP_FRAME:
2714 tso->stackobj->sp = p;
2715 return STOP_FRAME;
2716
2717 case CATCH_RETRY_FRAME:
2718 default:
2719 p = next;
2720 continue;
2721 }
2722 }
2723 }
2724
2725
2726 /* -----------------------------------------------------------------------------
2727 findRetryFrameHelper
2728
2729 This function is called by the retry# primitive. It traverses the stack
2730 leaving tso->sp referring to the frame which should handle the retry.
2731
2732 This should either be a CATCH_RETRY_FRAME (if the retry# is within an orElse#)
2733 or should be a ATOMICALLY_FRAME (if the retry# reaches the top level).
2734
2735 We skip CATCH_STM_FRAMEs (aborting and rolling back the nested tx that they
2736 create) because retries are not considered to be exceptions, despite the
2737 similar implementation.
2738
2739 We should not expect to see CATCH_FRAME or STOP_FRAME because those should
2740 not be created within memory transactions.
2741 -------------------------------------------------------------------------- */
2742
2743 StgWord
2744 findRetryFrameHelper (Capability *cap, StgTSO *tso)
2745 {
2746 StgPtr p, next;
2747 StgRetInfoTable *info;
2748
2749 p = tso->stackobj->sp;
2750 while (1) {
2751 info = get_ret_itbl((StgClosure *)p);
2752 next = p + stack_frame_sizeW((StgClosure *)p);
2753 switch (info->i.type) {
2754
2755 case ATOMICALLY_FRAME:
2756 debugTrace(DEBUG_stm,
2757 "found ATOMICALLY_FRAME at %p during retry", p);
2758 tso->stackobj->sp = p;
2759 return ATOMICALLY_FRAME;
2760
2761 case CATCH_RETRY_FRAME:
2762 debugTrace(DEBUG_stm,
2763 "found CATCH_RETRY_FRAME at %p during retry", p);
2764 tso->stackobj->sp = p;
2765 return CATCH_RETRY_FRAME;
2766
2767 case CATCH_STM_FRAME: {
2768 StgTRecHeader *trec = tso -> trec;
2769 StgTRecHeader *outer = trec -> enclosing_trec;
2770 debugTrace(DEBUG_stm,
2771 "found CATCH_STM_FRAME at %p during retry", p);
2772 debugTrace(DEBUG_stm, "trec=%p outer=%p", trec, outer);
2773 stmAbortTransaction(cap, trec);
2774 stmFreeAbortedTRec(cap, trec);
2775 tso -> trec = outer;
2776 p = next;
2777 continue;
2778 }
2779
2780 case UNDERFLOW_FRAME:
2781 tso->stackobj->sp = p;
2782 threadStackUnderflow(cap,tso);
2783 p = tso->stackobj->sp;
2784 continue;
2785
2786 default:
2787 ASSERT(info->i.type != CATCH_FRAME);
2788 ASSERT(info->i.type != STOP_FRAME);
2789 p = next;
2790 continue;
2791 }
2792 }
2793 }
2794
2795 /* -----------------------------------------------------------------------------
2796 resurrectThreads is called after garbage collection on the list of
2797 threads found to be garbage. Each of these threads will be woken
2798 up and sent a signal: BlockedOnDeadMVar if the thread was blocked
2799 on an MVar, or NonTermination if the thread was blocked on a Black
2800 Hole.
2801
2802 Locks: assumes we hold *all* the capabilities.
2803 -------------------------------------------------------------------------- */
2804
2805 void
2806 resurrectThreads (StgTSO *threads)
2807 {
2808 StgTSO *tso, *next;
2809 Capability *cap;
2810 generation *gen;
2811
2812 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2813 next = tso->global_link;
2814
2815 gen = Bdescr((P_)tso)->gen;
2816 tso->global_link = gen->threads;
2817 gen->threads = tso;
2818
2819 debugTrace(DEBUG_sched, "resurrecting thread %lu", (unsigned long)tso->id);
2820
2821 // Wake up the thread on the Capability it was last on
2822 cap = tso->cap;
2823
2824 switch (tso->why_blocked) {
2825 case BlockedOnMVar:
2826 /* Called by GC - sched_mutex lock is currently held. */
2827 throwToSingleThreaded(cap, tso,
2828 (StgClosure *)blockedIndefinitelyOnMVar_closure);
2829 break;
2830 case BlockedOnBlackHole:
2831 throwToSingleThreaded(cap, tso,
2832 (StgClosure *)nonTermination_closure);
2833 break;
2834 case BlockedOnSTM:
2835 throwToSingleThreaded(cap, tso,
2836 (StgClosure *)blockedIndefinitelyOnSTM_closure);
2837 break;
2838 case NotBlocked:
2839 /* This might happen if the thread was blocked on a black hole
2840 * belonging to a thread that we've just woken up (raiseAsync
2841 * can wake up threads, remember...).
2842 */
2843 continue;
2844 case BlockedOnMsgThrowTo:
2845 // This can happen if the target is masking, blocks on a
2846 // black hole, and then is found to be unreachable. In
2847 // this case, we want to let the target wake up and carry
2848 // on, and do nothing to this thread.
2849 continue;
2850 default:
2851 barf("resurrectThreads: thread blocked in a strange way: %d",
2852 tso->why_blocked);
2853 }
2854 }
2855 }