d562e33680c278c3eb44899db498409d3e2c88aa
[ghc.git] / rts / RaiseAsync.c
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 1998-2006
4 *
5 * Asynchronous exceptions
6 *
7 * --------------------------------------------------------------------------*/
8
9 #include "PosixSource.h"
10 #include "Rts.h"
11 #include "Threads.h"
12 #include "Trace.h"
13 #include "RaiseAsync.h"
14 #include "SMP.h"
15 #include "Schedule.h"
16 #include "LdvProfile.h"
17 #include "Updates.h"
18 #include "STM.h"
19 #include "Sanity.h"
20 #include "Profiling.h"
21 #if defined(mingw32_HOST_OS)
22 #include "win32/IOManager.h"
23 #endif
24
25 static void raiseAsync (Capability *cap,
26 StgTSO *tso,
27 StgClosure *exception,
28 rtsBool stop_at_atomically,
29 StgPtr stop_here);
30
31 static void removeFromQueues(Capability *cap, StgTSO *tso);
32
33 static void blockedThrowTo (StgTSO *source, StgTSO *target);
34
35 static void performBlockedException (Capability *cap,
36 StgTSO *source, StgTSO *target);
37
38 /* -----------------------------------------------------------------------------
39 throwToSingleThreaded
40
41 This version of throwTo is safe to use if and only if one of the
42 following holds:
43
44 - !THREADED_RTS
45
46 - all the other threads in the system are stopped (eg. during GC).
47
48 - we surely own the target TSO (eg. we just took it from the
49 run queue of the current capability, or we are running it).
50
51 It doesn't cater for blocking the source thread until the exception
52 has been raised.
53 -------------------------------------------------------------------------- */
54
55 void
56 throwToSingleThreaded(Capability *cap, StgTSO *tso, StgClosure *exception)
57 {
58 throwToSingleThreaded_(cap, tso, exception, rtsFalse, NULL);
59 }
60
61 void
62 throwToSingleThreaded_(Capability *cap, StgTSO *tso, StgClosure *exception,
63 rtsBool stop_at_atomically, StgPtr stop_here)
64 {
65 // Thread already dead?
66 if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
67 return;
68 }
69
70 // Remove it from any blocking queues
71 removeFromQueues(cap,tso);
72
73 raiseAsync(cap, tso, exception, stop_at_atomically, stop_here);
74 }
75
76 void
77 suspendComputation(Capability *cap, StgTSO *tso, StgPtr stop_here)
78 {
79 // Thread already dead?
80 if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
81 return;
82 }
83
84 // Remove it from any blocking queues
85 removeFromQueues(cap,tso);
86
87 raiseAsync(cap, tso, NULL, rtsFalse, stop_here);
88 }
89
90 /* -----------------------------------------------------------------------------
91 throwTo
92
93 This function may be used to throw an exception from one thread to
94 another, during the course of normal execution. This is a tricky
95 task: the target thread might be running on another CPU, or it
96 may be blocked and could be woken up at any point by another CPU.
97 We have some delicate synchronisation to do.
98
99 There is a completely safe fallback scheme: it is always possible
100 to just block the source TSO on the target TSO's blocked_exceptions
101 queue. This queue is locked using lockTSO()/unlockTSO(). It is
102 checked at regular intervals: before and after running a thread
103 (schedule() and threadPaused() respectively), and just before GC
104 (scheduleDoGC()). Activating a thread on this queue should be done
105 using maybePerformBlockedException(): this is done in the context
106 of the target thread, so the exception can be raised eagerly.
107
108 This fallback scheme works even if the target thread is complete or
109 killed: scheduleDoGC() will discover the blocked thread before the
110 target is GC'd.
111
112 Blocking the source thread on the target thread's blocked_exception
113 queue is also employed when the target thread is currently blocking
114 exceptions (ie. inside Control.Exception.block).
115
116 We could use the safe fallback scheme exclusively, but that
117 wouldn't be ideal: most calls to throwTo would block immediately,
118 possibly until the next GC, which might require the deadlock
119 detection mechanism to kick in. So we try to provide promptness
120 wherever possible.
121
122 We can promptly deliver the exception if the target thread is:
123
124 - runnable, on the same Capability as the source thread (because
125 we own the run queue and therefore the target thread).
126
127 - blocked, and we can obtain exclusive access to it. Obtaining
128 exclusive access to the thread depends on how it is blocked.
129
130 We must also be careful to not trip over threadStackOverflow(),
131 which might be moving the TSO to enlarge its stack.
132 lockTSO()/unlockTSO() are used here too.
133
134 Returns:
135
136 THROWTO_SUCCESS exception was raised, ok to continue
137
138 THROWTO_BLOCKED exception was not raised; block the source
139 thread then call throwToReleaseTarget() when
140 the source thread is properly tidied away.
141
142 -------------------------------------------------------------------------- */
143
144 nat
145 throwTo (Capability *cap, // the Capability we hold
146 StgTSO *source, // the TSO sending the exception
147 StgTSO *target, // the TSO receiving the exception
148 StgClosure *exception, // the exception closure
149 /*[out]*/ void **out USED_IF_THREADS)
150 {
151 StgWord status;
152
153 // follow ThreadRelocated links in the target first
154 while (target->what_next == ThreadRelocated) {
155 target = target->link;
156 // No, it might be a WHITEHOLE:
157 // ASSERT(get_itbl(target)->type == TSO);
158 }
159
160 debugTrace(DEBUG_sched, "throwTo: from thread %lu to thread %lu",
161 (unsigned long)source->id, (unsigned long)target->id);
162
163 #ifdef DEBUG
164 if (traceClass(DEBUG_sched)) {
165 debugTraceBegin("throwTo: target");
166 printThreadStatus(target);
167 debugTraceEnd();
168 }
169 #endif
170
171 goto check_target;
172 retry:
173 debugTrace(DEBUG_sched, "throwTo: retrying...");
174
175 check_target:
176 // Thread already dead?
177 if (target->what_next == ThreadComplete
178 || target->what_next == ThreadKilled) {
179 return THROWTO_SUCCESS;
180 }
181
182 status = target->why_blocked;
183
184 switch (status) {
185 case NotBlocked:
186 /* if status==NotBlocked, and target->cap == cap, then
187 we own this TSO and can raise the exception.
188
189 How do we establish this condition? Very carefully.
190
191 Let
192 P = (status == NotBlocked)
193 Q = (tso->cap == cap)
194
195 Now, if P & Q are true, then the TSO is locked and owned by
196 this capability. No other OS thread can steal it.
197
198 If P==0 and Q==1: the TSO is blocked, but attached to this
199 capabilty, and it can be stolen by another capability.
200
201 If P==1 and Q==0: the TSO is runnable on another
202 capability. At any time, the TSO may change from runnable
203 to blocked and vice versa, while it remains owned by
204 another capability.
205
206 Suppose we test like this:
207
208 p = P
209 q = Q
210 if (p && q) ...
211
212 this is defeated by another capability stealing a blocked
213 TSO from us to wake it up (Schedule.c:unblockOne()). The
214 other thread is doing
215
216 Q = 0
217 P = 1
218
219 assuming arbitrary reordering, we could see this
220 interleaving:
221
222 start: P==0 && Q==1
223 P = 1
224 p = P
225 q = Q
226 Q = 0
227 if (p && q) ...
228
229 so we need a memory barrier:
230
231 p = P
232 mb()
233 q = Q
234 if (p && q) ...
235
236 this avoids the problematic case. There are other cases
237 to consider, but this is the tricky one.
238
239 Note that we must be sure that unblockOne() does the
240 writes in the correct order: Q before P. The memory
241 barrier ensures that if we have seen the write to P, we
242 have also seen the write to Q.
243 */
244 {
245 Capability *target_cap;
246
247 write_barrier();
248 target_cap = target->cap;
249 if (target_cap == cap && (target->flags & TSO_BLOCKEX) == 0) {
250 // It's on our run queue and not blocking exceptions
251 raiseAsync(cap, target, exception, rtsFalse, NULL);
252 return THROWTO_SUCCESS;
253 } else {
254 // Otherwise, just block on the blocked_exceptions queue
255 // of the target thread. The queue will get looked at
256 // soon enough: it is checked before and after running a
257 // thread, and during GC.
258 lockTSO(target);
259
260 // Avoid race with threadStackOverflow, which may have
261 // just moved this TSO.
262 if (target->what_next == ThreadRelocated) {
263 unlockTSO(target);
264 target = target->link;
265 goto retry;
266 }
267 blockedThrowTo(source,target);
268 *out = target;
269 return THROWTO_BLOCKED;
270 }
271 }
272
273 case BlockedOnMVar:
274 {
275 /*
276 To establish ownership of this TSO, we need to acquire a
277 lock on the MVar that it is blocked on.
278 */
279 StgMVar *mvar;
280 StgInfoTable *info USED_IF_THREADS;
281
282 mvar = (StgMVar *)target->block_info.closure;
283
284 // ASSUMPTION: tso->block_info must always point to a
285 // closure. In the threaded RTS it does.
286 switch (get_itbl(mvar)->type) {
287 case MVAR_CLEAN:
288 case MVAR_DIRTY:
289 break;
290 default:
291 goto retry;
292 }
293
294 info = lockClosure((StgClosure *)mvar);
295
296 if (target->what_next == ThreadRelocated) {
297 target = target->link;
298 unlockClosure((StgClosure *)mvar,info);
299 goto retry;
300 }
301 // we have the MVar, let's check whether the thread
302 // is still blocked on the same MVar.
303 if (target->why_blocked != BlockedOnMVar
304 || (StgMVar *)target->block_info.closure != mvar) {
305 unlockClosure((StgClosure *)mvar, info);
306 goto retry;
307 }
308
309 if ((target->flags & TSO_BLOCKEX) &&
310 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
311 lockClosure((StgClosure *)target);
312 blockedThrowTo(source,target);
313 unlockClosure((StgClosure *)mvar, info);
314 *out = target;
315 return THROWTO_BLOCKED; // caller releases TSO
316 } else {
317 removeThreadFromMVarQueue(mvar, target);
318 raiseAsync(cap, target, exception, rtsFalse, NULL);
319 unblockOne(cap, target);
320 unlockClosure((StgClosure *)mvar, info);
321 return THROWTO_SUCCESS;
322 }
323 }
324
325 case BlockedOnBlackHole:
326 {
327 ACQUIRE_LOCK(&sched_mutex);
328 // double checking the status after the memory barrier:
329 if (target->why_blocked != BlockedOnBlackHole) {
330 RELEASE_LOCK(&sched_mutex);
331 goto retry;
332 }
333
334 if (target->flags & TSO_BLOCKEX) {
335 lockTSO(target);
336 blockedThrowTo(source,target);
337 RELEASE_LOCK(&sched_mutex);
338 *out = target;
339 return THROWTO_BLOCKED; // caller releases TSO
340 } else {
341 removeThreadFromQueue(&blackhole_queue, target);
342 raiseAsync(cap, target, exception, rtsFalse, NULL);
343 unblockOne(cap, target);
344 RELEASE_LOCK(&sched_mutex);
345 return THROWTO_SUCCESS;
346 }
347 }
348
349 case BlockedOnException:
350 {
351 StgTSO *target2;
352 StgInfoTable *info;
353
354 /*
355 To obtain exclusive access to a BlockedOnException thread,
356 we must call lockClosure() on the TSO on which it is blocked.
357 Since the TSO might change underneath our feet, after we
358 call lockClosure() we must check that
359
360 (a) the closure we locked is actually a TSO
361 (b) the original thread is still BlockedOnException,
362 (c) the original thread is still blocked on the TSO we locked
363 and (d) the target thread has not been relocated.
364
365 We synchronise with threadStackOverflow() (which relocates
366 threads) using lockClosure()/unlockClosure().
367 */
368 target2 = target->block_info.tso;
369
370 info = lockClosure((StgClosure *)target2);
371 if (info != &stg_TSO_info) {
372 unlockClosure((StgClosure *)target2, info);
373 goto retry;
374 }
375 if (target->what_next == ThreadRelocated) {
376 target = target->link;
377 unlockTSO(target2);
378 goto retry;
379 }
380 if (target2->what_next == ThreadRelocated) {
381 target->block_info.tso = target2->link;
382 unlockTSO(target2);
383 goto retry;
384 }
385 if (target->why_blocked != BlockedOnException
386 || target->block_info.tso != target2) {
387 unlockTSO(target2);
388 goto retry;
389 }
390
391 /*
392 Now we have exclusive rights to the target TSO...
393
394 If it is blocking exceptions, add the source TSO to its
395 blocked_exceptions queue. Otherwise, raise the exception.
396 */
397 if ((target->flags & TSO_BLOCKEX) &&
398 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
399 lockTSO(target);
400 blockedThrowTo(source,target);
401 unlockTSO(target2);
402 *out = target;
403 return THROWTO_BLOCKED;
404 } else {
405 removeThreadFromQueue(&target2->blocked_exceptions, target);
406 raiseAsync(cap, target, exception, rtsFalse, NULL);
407 unblockOne(cap, target);
408 unlockTSO(target2);
409 return THROWTO_SUCCESS;
410 }
411 }
412
413 case BlockedOnSTM:
414 lockTSO(target);
415 // Unblocking BlockedOnSTM threads requires the TSO to be
416 // locked; see STM.c:unpark_tso().
417 if (target->why_blocked != BlockedOnSTM) {
418 goto retry;
419 }
420 if ((target->flags & TSO_BLOCKEX) &&
421 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
422 blockedThrowTo(source,target);
423 *out = target;
424 return THROWTO_BLOCKED;
425 } else {
426 raiseAsync(cap, target, exception, rtsFalse, NULL);
427 unblockOne(cap, target);
428 unlockTSO(target);
429 return THROWTO_SUCCESS;
430 }
431
432 case BlockedOnCCall:
433 case BlockedOnCCall_NoUnblockExc:
434 // I don't think it's possible to acquire ownership of a
435 // BlockedOnCCall thread. We just assume that the target
436 // thread is blocking exceptions, and block on its
437 // blocked_exception queue.
438 lockTSO(target);
439 blockedThrowTo(source,target);
440 *out = target;
441 return THROWTO_BLOCKED;
442
443 #ifndef THREADEDED_RTS
444 case BlockedOnRead:
445 case BlockedOnWrite:
446 case BlockedOnDelay:
447 #if defined(mingw32_HOST_OS)
448 case BlockedOnDoProc:
449 #endif
450 if ((target->flags & TSO_BLOCKEX) &&
451 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
452 blockedThrowTo(source,target);
453 return THROWTO_BLOCKED;
454 } else {
455 removeFromQueues(cap,target);
456 raiseAsync(cap, target, exception, rtsFalse, NULL);
457 return THROWTO_SUCCESS;
458 }
459 #endif
460
461 default:
462 barf("throwTo: unrecognised why_blocked value");
463 }
464 barf("throwTo");
465 }
466
467 // Block a TSO on another TSO's blocked_exceptions queue.
468 // Precondition: we hold an exclusive lock on the target TSO (this is
469 // complex to achieve as there's no single lock on a TSO; see
470 // throwTo()).
471 static void
472 blockedThrowTo (StgTSO *source, StgTSO *target)
473 {
474 debugTrace(DEBUG_sched, "throwTo: blocking on thread %lu", (unsigned long)target->id);
475 source->link = target->blocked_exceptions;
476 target->blocked_exceptions = source;
477 dirtyTSO(target); // we modified the blocked_exceptions queue
478
479 source->block_info.tso = target;
480 write_barrier(); // throwTo_exception *must* be visible if BlockedOnException is.
481 source->why_blocked = BlockedOnException;
482 }
483
484
485 #ifdef THREADED_RTS
486 void
487 throwToReleaseTarget (void *tso)
488 {
489 unlockTSO((StgTSO *)tso);
490 }
491 #endif
492
493 /* -----------------------------------------------------------------------------
494 Waking up threads blocked in throwTo
495
496 There are two ways to do this: maybePerformBlockedException() will
497 perform the throwTo() for the thread at the head of the queue
498 immediately, and leave the other threads on the queue.
499 maybePerformBlockedException() also checks the TSO_BLOCKEX flag
500 before raising an exception.
501
502 awakenBlockedExceptionQueue() will wake up all the threads in the
503 queue, but not perform any throwTo() immediately. This might be
504 more appropriate when the target thread is the one actually running
505 (see Exception.cmm).
506
507 Returns: non-zero if an exception was raised, zero otherwise.
508 -------------------------------------------------------------------------- */
509
510 int
511 maybePerformBlockedException (Capability *cap, StgTSO *tso)
512 {
513 StgTSO *source;
514
515 if (tso->blocked_exceptions != END_TSO_QUEUE
516 && ((tso->flags & TSO_BLOCKEX) == 0
517 || ((tso->flags & TSO_INTERRUPTIBLE) && interruptible(tso)))) {
518
519 // Lock the TSO, this gives us exclusive access to the queue
520 lockTSO(tso);
521
522 // Check the queue again; it might have changed before we
523 // locked it.
524 if (tso->blocked_exceptions == END_TSO_QUEUE) {
525 unlockTSO(tso);
526 return 0;
527 }
528
529 // We unblock just the first thread on the queue, and perform
530 // its throw immediately.
531 source = tso->blocked_exceptions;
532 performBlockedException(cap, source, tso);
533 tso->blocked_exceptions = unblockOne_(cap, source,
534 rtsFalse/*no migrate*/);
535 unlockTSO(tso);
536 return 1;
537 }
538 return 0;
539 }
540
541 void
542 awakenBlockedExceptionQueue (Capability *cap, StgTSO *tso)
543 {
544 if (tso->blocked_exceptions != END_TSO_QUEUE) {
545 lockTSO(tso);
546 awakenBlockedQueue(cap, tso->blocked_exceptions);
547 tso->blocked_exceptions = END_TSO_QUEUE;
548 unlockTSO(tso);
549 }
550 }
551
552 static void
553 performBlockedException (Capability *cap, StgTSO *source, StgTSO *target)
554 {
555 StgClosure *exception;
556
557 ASSERT(source->why_blocked == BlockedOnException);
558 ASSERT(source->block_info.tso->id == target->id);
559 ASSERT(source->sp[0] == (StgWord)&stg_block_throwto_info);
560 ASSERT(((StgTSO *)source->sp[1])->id == target->id);
561 // check ids not pointers, because the thread might be relocated
562
563 exception = (StgClosure *)source->sp[2];
564 throwToSingleThreaded(cap, target, exception);
565 source->sp += 3;
566 }
567
568 /* -----------------------------------------------------------------------------
569 Remove a thread from blocking queues.
570
571 This is for use when we raise an exception in another thread, which
572 may be blocked.
573 This has nothing to do with the UnblockThread event in GranSim. -- HWL
574 -------------------------------------------------------------------------- */
575
576 #if defined(GRAN) || defined(PARALLEL_HASKELL)
577 /*
578 NB: only the type of the blocking queue is different in GranSim and GUM
579 the operations on the queue-elements are the same
580 long live polymorphism!
581
582 Locks: sched_mutex is held upon entry and exit.
583
584 */
585 static void
586 removeFromQueues(Capability *cap, StgTSO *tso)
587 {
588 StgBlockingQueueElement *t, **last;
589
590 switch (tso->why_blocked) {
591
592 case NotBlocked:
593 return; /* not blocked */
594
595 case BlockedOnSTM:
596 // Be careful: nothing to do here! We tell the scheduler that the thread
597 // is runnable and we leave it to the stack-walking code to abort the
598 // transaction while unwinding the stack. We should perhaps have a debugging
599 // test to make sure that this really happens and that the 'zombie' transaction
600 // does not get committed.
601 goto done;
602
603 case BlockedOnMVar:
604 ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
605 {
606 StgBlockingQueueElement *last_tso = END_BQ_QUEUE;
607 StgMVar *mvar = (StgMVar *)(tso->block_info.closure);
608
609 last = (StgBlockingQueueElement **)&mvar->head;
610 for (t = (StgBlockingQueueElement *)mvar->head;
611 t != END_BQ_QUEUE;
612 last = &t->link, last_tso = t, t = t->link) {
613 if (t == (StgBlockingQueueElement *)tso) {
614 *last = (StgBlockingQueueElement *)tso->link;
615 if (mvar->tail == tso) {
616 mvar->tail = (StgTSO *)last_tso;
617 }
618 goto done;
619 }
620 }
621 barf("removeFromQueues (MVAR): TSO not found");
622 }
623
624 case BlockedOnBlackHole:
625 ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
626 {
627 StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);
628
629 last = &bq->blocking_queue;
630 for (t = bq->blocking_queue;
631 t != END_BQ_QUEUE;
632 last = &t->link, t = t->link) {
633 if (t == (StgBlockingQueueElement *)tso) {
634 *last = (StgBlockingQueueElement *)tso->link;
635 goto done;
636 }
637 }
638 barf("removeFromQueues (BLACKHOLE): TSO not found");
639 }
640
641 case BlockedOnException:
642 {
643 StgTSO *target = tso->block_info.tso;
644
645 ASSERT(get_itbl(target)->type == TSO);
646
647 while (target->what_next == ThreadRelocated) {
648 target = target2->link;
649 ASSERT(get_itbl(target)->type == TSO);
650 }
651
652 last = (StgBlockingQueueElement **)&target->blocked_exceptions;
653 for (t = (StgBlockingQueueElement *)target->blocked_exceptions;
654 t != END_BQ_QUEUE;
655 last = &t->link, t = t->link) {
656 ASSERT(get_itbl(t)->type == TSO);
657 if (t == (StgBlockingQueueElement *)tso) {
658 *last = (StgBlockingQueueElement *)tso->link;
659 goto done;
660 }
661 }
662 barf("removeFromQueues (Exception): TSO not found");
663 }
664
665 case BlockedOnRead:
666 case BlockedOnWrite:
667 #if defined(mingw32_HOST_OS)
668 case BlockedOnDoProc:
669 #endif
670 {
671 /* take TSO off blocked_queue */
672 StgBlockingQueueElement *prev = NULL;
673 for (t = (StgBlockingQueueElement *)blocked_queue_hd; t != END_BQ_QUEUE;
674 prev = t, t = t->link) {
675 if (t == (StgBlockingQueueElement *)tso) {
676 if (prev == NULL) {
677 blocked_queue_hd = (StgTSO *)t->link;
678 if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
679 blocked_queue_tl = END_TSO_QUEUE;
680 }
681 } else {
682 prev->link = t->link;
683 if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
684 blocked_queue_tl = (StgTSO *)prev;
685 }
686 }
687 #if defined(mingw32_HOST_OS)
688 /* (Cooperatively) signal that the worker thread should abort
689 * the request.
690 */
691 abandonWorkRequest(tso->block_info.async_result->reqID);
692 #endif
693 goto done;
694 }
695 }
696 barf("removeFromQueues (I/O): TSO not found");
697 }
698
699 case BlockedOnDelay:
700 {
701 /* take TSO off sleeping_queue */
702 StgBlockingQueueElement *prev = NULL;
703 for (t = (StgBlockingQueueElement *)sleeping_queue; t != END_BQ_QUEUE;
704 prev = t, t = t->link) {
705 if (t == (StgBlockingQueueElement *)tso) {
706 if (prev == NULL) {
707 sleeping_queue = (StgTSO *)t->link;
708 } else {
709 prev->link = t->link;
710 }
711 goto done;
712 }
713 }
714 barf("removeFromQueues (delay): TSO not found");
715 }
716
717 default:
718 barf("removeFromQueues: %d", tso->why_blocked);
719 }
720
721 done:
722 tso->link = END_TSO_QUEUE;
723 tso->why_blocked = NotBlocked;
724 tso->block_info.closure = NULL;
725 pushOnRunQueue(cap,tso);
726 }
727 #else
728 static void
729 removeFromQueues(Capability *cap, StgTSO *tso)
730 {
731 switch (tso->why_blocked) {
732
733 case NotBlocked:
734 return;
735
736 case BlockedOnSTM:
737 // Be careful: nothing to do here! We tell the scheduler that the
738 // thread is runnable and we leave it to the stack-walking code to
739 // abort the transaction while unwinding the stack. We should
740 // perhaps have a debugging test to make sure that this really
741 // happens and that the 'zombie' transaction does not get
742 // committed.
743 goto done;
744
745 case BlockedOnMVar:
746 removeThreadFromMVarQueue((StgMVar *)tso->block_info.closure, tso);
747 goto done;
748
749 case BlockedOnBlackHole:
750 removeThreadFromQueue(&blackhole_queue, tso);
751 goto done;
752
753 case BlockedOnException:
754 {
755 StgTSO *target = tso->block_info.tso;
756
757 // NO: when called by threadPaused(), we probably have this
758 // TSO already locked (WHITEHOLEd) because we just placed
759 // ourselves on its queue.
760 // ASSERT(get_itbl(target)->type == TSO);
761
762 while (target->what_next == ThreadRelocated) {
763 target = target->link;
764 }
765
766 removeThreadFromQueue(&target->blocked_exceptions, tso);
767 goto done;
768 }
769
770 #if !defined(THREADED_RTS)
771 case BlockedOnRead:
772 case BlockedOnWrite:
773 #if defined(mingw32_HOST_OS)
774 case BlockedOnDoProc:
775 #endif
776 removeThreadFromDeQueue(&blocked_queue_hd, &blocked_queue_tl, tso);
777 #if defined(mingw32_HOST_OS)
778 /* (Cooperatively) signal that the worker thread should abort
779 * the request.
780 */
781 abandonWorkRequest(tso->block_info.async_result->reqID);
782 #endif
783 goto done;
784
785 case BlockedOnDelay:
786 removeThreadFromQueue(&sleeping_queue, tso);
787 goto done;
788 #endif
789
790 default:
791 barf("removeFromQueues: %d", tso->why_blocked);
792 }
793
794 done:
795 tso->link = END_TSO_QUEUE;
796 tso->why_blocked = NotBlocked;
797 tso->block_info.closure = NULL;
798 appendToRunQueue(cap,tso);
799
800 // We might have just migrated this TSO to our Capability:
801 if (tso->bound) {
802 tso->bound->cap = cap;
803 }
804 tso->cap = cap;
805 }
806 #endif
807
808 /* -----------------------------------------------------------------------------
809 * raiseAsync()
810 *
811 * The following function implements the magic for raising an
812 * asynchronous exception in an existing thread.
813 *
814 * We first remove the thread from any queue on which it might be
815 * blocked. The possible blockages are MVARs and BLACKHOLE_BQs.
816 *
817 * We strip the stack down to the innermost CATCH_FRAME, building
818 * thunks in the heap for all the active computations, so they can
819 * be restarted if necessary. When we reach a CATCH_FRAME, we build
820 * an application of the handler to the exception, and push it on
821 * the top of the stack.
822 *
823 * How exactly do we save all the active computations? We create an
824 * AP_STACK for every UpdateFrame on the stack. Entering one of these
825 * AP_STACKs pushes everything from the corresponding update frame
826 * upwards onto the stack. (Actually, it pushes everything up to the
827 * next update frame plus a pointer to the next AP_STACK object.
828 * Entering the next AP_STACK object pushes more onto the stack until we
829 * reach the last AP_STACK object - at which point the stack should look
830 * exactly as it did when we killed the TSO and we can continue
831 * execution by entering the closure on top of the stack.
832 *
833 * We can also kill a thread entirely - this happens if either (a) the
834 * exception passed to raiseAsync is NULL, or (b) there's no
835 * CATCH_FRAME on the stack. In either case, we strip the entire
836 * stack and replace the thread with a zombie.
837 *
838 * ToDo: in THREADED_RTS mode, this function is only safe if either
839 * (a) we hold all the Capabilities (eg. in GC, or if there is only
840 * one Capability), or (b) we own the Capability that the TSO is
841 * currently blocked on or on the run queue of.
842 *
843 * -------------------------------------------------------------------------- */
844
845 static void
846 raiseAsync(Capability *cap, StgTSO *tso, StgClosure *exception,
847 rtsBool stop_at_atomically, StgPtr stop_here)
848 {
849 StgRetInfoTable *info;
850 StgPtr sp, frame;
851 nat i;
852
853 debugTrace(DEBUG_sched,
854 "raising exception in thread %ld.", (long)tso->id);
855
856 #if defined(PROFILING)
857 /*
858 * Debugging tool: on raising an exception, show where we are.
859 * See also Exception.cmm:raisezh_fast.
860 * This wasn't done for asynchronous exceptions originally; see #1450
861 */
862 if (RtsFlags.ProfFlags.showCCSOnException)
863 {
864 fprintCCS_stderr(tso->prof.CCCS);
865 }
866 #endif
867
868 // mark it dirty; we're about to change its stack.
869 dirtyTSO(tso);
870
871 sp = tso->sp;
872
873 // ASSUMES: the thread is not already complete or dead. Upper
874 // layers should deal with that.
875 ASSERT(tso->what_next != ThreadComplete && tso->what_next != ThreadKilled);
876
877 // The stack freezing code assumes there's a closure pointer on
878 // the top of the stack, so we have to arrange that this is the case...
879 //
880 if (sp[0] == (W_)&stg_enter_info) {
881 sp++;
882 } else {
883 sp--;
884 sp[0] = (W_)&stg_dummy_ret_closure;
885 }
886
887 frame = sp + 1;
888 while (stop_here == NULL || frame < stop_here) {
889
890 // 1. Let the top of the stack be the "current closure"
891 //
892 // 2. Walk up the stack until we find either an UPDATE_FRAME or a
893 // CATCH_FRAME.
894 //
895 // 3. If it's an UPDATE_FRAME, then make an AP_STACK containing the
896 // current closure applied to the chunk of stack up to (but not
897 // including) the update frame. This closure becomes the "current
898 // closure". Go back to step 2.
899 //
900 // 4. If it's a CATCH_FRAME, then leave the exception handler on
901 // top of the stack applied to the exception.
902 //
903 // 5. If it's a STOP_FRAME, then kill the thread.
904 //
905 // NB: if we pass an ATOMICALLY_FRAME then abort the associated
906 // transaction
907
908 info = get_ret_itbl((StgClosure *)frame);
909
910 switch (info->i.type) {
911
912 case UPDATE_FRAME:
913 {
914 StgAP_STACK * ap;
915 nat words;
916
917 // First build an AP_STACK consisting of the stack chunk above the
918 // current update frame, with the top word on the stack as the
919 // fun field.
920 //
921 words = frame - sp - 1;
922 ap = (StgAP_STACK *)allocateLocal(cap,AP_STACK_sizeW(words));
923
924 ap->size = words;
925 ap->fun = (StgClosure *)sp[0];
926 sp++;
927 for(i=0; i < (nat)words; ++i) {
928 ap->payload[i] = (StgClosure *)*sp++;
929 }
930
931 SET_HDR(ap,&stg_AP_STACK_info,
932 ((StgClosure *)frame)->header.prof.ccs /* ToDo */);
933 TICK_ALLOC_UP_THK(words+1,0);
934
935 //IF_DEBUG(scheduler,
936 // debugBelch("sched: Updating ");
937 // printPtr((P_)((StgUpdateFrame *)frame)->updatee);
938 // debugBelch(" with ");
939 // printObj((StgClosure *)ap);
940 // );
941
942 // Replace the updatee with an indirection
943 //
944 // Warning: if we're in a loop, more than one update frame on
945 // the stack may point to the same object. Be careful not to
946 // overwrite an IND_OLDGEN in this case, because we'll screw
947 // up the mutable lists. To be on the safe side, don't
948 // overwrite any kind of indirection at all. See also
949 // threadSqueezeStack in GC.c, where we have to make a similar
950 // check.
951 //
952 if (!closure_IND(((StgUpdateFrame *)frame)->updatee)) {
953 // revert the black hole
954 UPD_IND_NOLOCK(((StgUpdateFrame *)frame)->updatee,
955 (StgClosure *)ap);
956 }
957 sp += sizeofW(StgUpdateFrame) - 1;
958 sp[0] = (W_)ap; // push onto stack
959 frame = sp + 1;
960 continue; //no need to bump frame
961 }
962
963 case STOP_FRAME:
964 {
965 // We've stripped the entire stack, the thread is now dead.
966 tso->what_next = ThreadKilled;
967 tso->sp = frame + sizeofW(StgStopFrame);
968 return;
969 }
970
971 case CATCH_FRAME:
972 // If we find a CATCH_FRAME, and we've got an exception to raise,
973 // then build the THUNK raise(exception), and leave it on
974 // top of the CATCH_FRAME ready to enter.
975 //
976 {
977 #ifdef PROFILING
978 StgCatchFrame *cf = (StgCatchFrame *)frame;
979 #endif
980 StgThunk *raise;
981
982 if (exception == NULL) break;
983
984 // we've got an exception to raise, so let's pass it to the
985 // handler in this frame.
986 //
987 raise = (StgThunk *)allocateLocal(cap,sizeofW(StgThunk)+1);
988 TICK_ALLOC_SE_THK(1,0);
989 SET_HDR(raise,&stg_raise_info,cf->header.prof.ccs);
990 raise->payload[0] = exception;
991
992 // throw away the stack from Sp up to the CATCH_FRAME.
993 //
994 sp = frame - 1;
995
996 /* Ensure that async excpetions are blocked now, so we don't get
997 * a surprise exception before we get around to executing the
998 * handler.
999 */
1000 tso->flags |= TSO_BLOCKEX | TSO_INTERRUPTIBLE;
1001
1002 /* Put the newly-built THUNK on top of the stack, ready to execute
1003 * when the thread restarts.
1004 */
1005 sp[0] = (W_)raise;
1006 sp[-1] = (W_)&stg_enter_info;
1007 tso->sp = sp-1;
1008 tso->what_next = ThreadRunGHC;
1009 IF_DEBUG(sanity, checkTSO(tso));
1010 return;
1011 }
1012
1013 case ATOMICALLY_FRAME:
1014 if (stop_at_atomically) {
1015 ASSERT(stmGetEnclosingTRec(tso->trec) == NO_TREC);
1016 stmCondemnTransaction(cap, tso -> trec);
1017 #ifdef REG_R1
1018 tso->sp = frame;
1019 #else
1020 // R1 is not a register: the return convention for IO in
1021 // this case puts the return value on the stack, so we
1022 // need to set up the stack to return to the atomically
1023 // frame properly...
1024 tso->sp = frame - 2;
1025 tso->sp[1] = (StgWord) &stg_NO_FINALIZER_closure; // why not?
1026 tso->sp[0] = (StgWord) &stg_ut_1_0_unreg_info;
1027 #endif
1028 tso->what_next = ThreadRunGHC;
1029 return;
1030 }
1031 // Not stop_at_atomically... fall through and abort the
1032 // transaction.
1033
1034 case CATCH_RETRY_FRAME:
1035 // IF we find an ATOMICALLY_FRAME then we abort the
1036 // current transaction and propagate the exception. In
1037 // this case (unlike ordinary exceptions) we do not care
1038 // whether the transaction is valid or not because its
1039 // possible validity cannot have caused the exception
1040 // and will not be visible after the abort.
1041
1042 {
1043 StgTRecHeader *trec = tso -> trec;
1044 StgTRecHeader *outer = stmGetEnclosingTRec(trec);
1045 debugTrace(DEBUG_stm,
1046 "found atomically block delivering async exception");
1047 stmAbortTransaction(cap, trec);
1048 stmFreeAbortedTRec(cap, trec);
1049 tso -> trec = outer;
1050 break;
1051 };
1052
1053 default:
1054 break;
1055 }
1056
1057 // move on to the next stack frame
1058 frame += stack_frame_sizeW((StgClosure *)frame);
1059 }
1060
1061 // if we got here, then we stopped at stop_here
1062 ASSERT(stop_here != NULL);
1063 }
1064
1065