1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 1998-2006
5 * Asynchronous exceptions
7 * --------------------------------------------------------------------------*/
9 #include "PosixSource.h"
13 #include "RaiseAsync.h"
17 #include "LdvProfile.h"
21 #if defined(mingw32_HOST_OS)
22 #include "win32/IOManager.h"
25 static void raiseAsync (Capability *cap,
27 StgClosure *exception,
28 rtsBool stop_at_atomically,
31 static void removeFromQueues(Capability *cap, StgTSO *tso);
33 static void blockedThrowTo (StgTSO *source, StgTSO *target);
35 static void performBlockedException (Capability *cap,
36 StgTSO *source, StgTSO *target);
38 /* -----------------------------------------------------------------------------
41 This version of throwTo is safe to use if and only if one of the
46 - all the other threads in the system are stopped (eg. during GC).
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).
51 It doesn't cater for blocking the source thread until the exception
53 -------------------------------------------------------------------------- */
56 throwToSingleThreaded(Capability *cap, StgTSO *tso, StgClosure *exception)
58 throwToSingleThreaded_(cap, tso, exception, rtsFalse, NULL);
62 throwToSingleThreaded_(Capability *cap, StgTSO *tso, StgClosure *exception,
63 rtsBool stop_at_atomically, StgPtr stop_here)
65 // Thread already dead?
66 if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
70 // Remove it from any blocking queues
71 removeFromQueues(cap,tso);
73 raiseAsync(cap, tso, exception, stop_at_atomically, stop_here);
77 suspendComputation(Capability *cap, StgTSO *tso, StgPtr stop_here)
79 // Thread already dead?
80 if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
84 // Remove it from any blocking queues
85 removeFromQueues(cap,tso);
87 raiseAsync(cap, tso, NULL, rtsFalse, stop_here);
90 /* -----------------------------------------------------------------------------
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.
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.
108 This fallback scheme works even if the target thread is complete or
109 killed: scheduleDoGC() will discover the blocked thread before the
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).
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
122 We can promptly deliver the exception if the target thread is:
124 - runnable, on the same Capability as the source thread (because
125 we own the run queue and therefore the target thread).
127 - blocked, and we can obtain exclusive access to it. Obtaining
128 exclusive access to the thread depends on how it is blocked.
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.
136 THROWTO_SUCCESS exception was raised, ok to continue
138 THROWTO_BLOCKED exception was not raised; block the source
139 thread then call throwToReleaseTarget() when
140 the source thread is properly tidied away.
142 -------------------------------------------------------------------------- */
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)
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);
160 debugTrace(DEBUG_sched, "throwTo: from thread %lu to thread %lu",
161 (unsigned long)source->id, (unsigned long)target->id);
164 if (traceClass(DEBUG_sched)) {
165 debugTraceBegin("throwTo: target");
166 printThreadStatus(target);
173 debugTrace(DEBUG_sched, "throwTo: retrying...");
176 // Thread already dead?
177 if (target->what_next == ThreadComplete
178 || target->what_next == ThreadKilled) {
179 return THROWTO_SUCCESS;
182 status = target->why_blocked;
186 /* if status==NotBlocked, and target->cap == cap, then
187 we own this TSO and can raise the exception.
189 How do we establish this condition? Very carefully.
192 P = (status == NotBlocked)
193 Q = (tso->cap == cap)
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.
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.
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
206 Suppose we test like this:
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
219 assuming arbitrary reordering, we could see this
229 so we need a memory barrier:
236 this avoids the problematic case. There are other cases
237 to consider, but this is the tricky one.
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.
245 Capability *target_cap;
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;
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.
260 // Avoid race with threadStackOverflow, which may have
261 // just moved this TSO.
262 if (target->what_next == ThreadRelocated) {
264 target = target->link;
267 blockedThrowTo(source,target);
269 return THROWTO_BLOCKED;
276 To establish ownership of this TSO, we need to acquire a
277 lock on the MVar that it is blocked on.
280 StgInfoTable *info USED_IF_THREADS;
282 mvar = (StgMVar *)target->block_info.closure;
284 // ASSUMPTION: tso->block_info must always point to a
285 // closure. In the threaded RTS it does.
286 if (get_itbl(mvar)->type != MVAR) goto retry;
288 info = lockClosure((StgClosure *)mvar);
290 if (target->what_next == ThreadRelocated) {
291 target = target->link;
292 unlockClosure((StgClosure *)mvar,info);
295 // we have the MVar, let's check whether the thread
296 // is still blocked on the same MVar.
297 if (target->why_blocked != BlockedOnMVar
298 || (StgMVar *)target->block_info.closure != mvar) {
299 unlockClosure((StgClosure *)mvar, info);
303 if ((target->flags & TSO_BLOCKEX) &&
304 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
305 lockClosure((StgClosure *)target);
306 blockedThrowTo(source,target);
307 unlockClosure((StgClosure *)mvar, info);
309 return THROWTO_BLOCKED; // caller releases TSO
311 removeThreadFromMVarQueue(mvar, target);
312 raiseAsync(cap, target, exception, rtsFalse, NULL);
313 unblockOne(cap, target);
314 unlockClosure((StgClosure *)mvar, info);
315 return THROWTO_SUCCESS;
319 case BlockedOnBlackHole:
321 ACQUIRE_LOCK(&sched_mutex);
322 // double checking the status after the memory barrier:
323 if (target->why_blocked != BlockedOnBlackHole) {
324 RELEASE_LOCK(&sched_mutex);
328 if (target->flags & TSO_BLOCKEX) {
330 blockedThrowTo(source,target);
331 RELEASE_LOCK(&sched_mutex);
333 return THROWTO_BLOCKED; // caller releases TSO
335 removeThreadFromQueue(&blackhole_queue, target);
336 raiseAsync(cap, target, exception, rtsFalse, NULL);
337 unblockOne(cap, target);
338 RELEASE_LOCK(&sched_mutex);
339 return THROWTO_SUCCESS;
343 case BlockedOnException:
349 To obtain exclusive access to a BlockedOnException thread,
350 we must call lockClosure() on the TSO on which it is blocked.
351 Since the TSO might change underneath our feet, after we
352 call lockClosure() we must check that
354 (a) the closure we locked is actually a TSO
355 (b) the original thread is still BlockedOnException,
356 (c) the original thread is still blocked on the TSO we locked
357 and (d) the target thread has not been relocated.
359 We synchronise with threadStackOverflow() (which relocates
360 threads) using lockClosure()/unlockClosure().
362 target2 = target->block_info.tso;
364 info = lockClosure((StgClosure *)target2);
365 if (info != &stg_TSO_info) {
366 unlockClosure((StgClosure *)target2, info);
369 if (target->what_next == ThreadRelocated) {
370 target = target->link;
374 if (target2->what_next == ThreadRelocated) {
375 target->block_info.tso = target2->link;
379 if (target->why_blocked != BlockedOnException
380 || target->block_info.tso != target2) {
386 Now we have exclusive rights to the target TSO...
388 If it is blocking exceptions, add the source TSO to its
389 blocked_exceptions queue. Otherwise, raise the exception.
391 if ((target->flags & TSO_BLOCKEX) &&
392 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
394 blockedThrowTo(source,target);
397 return THROWTO_BLOCKED;
399 removeThreadFromQueue(&target2->blocked_exceptions, target);
400 raiseAsync(cap, target, exception, rtsFalse, NULL);
401 unblockOne(cap, target);
403 return THROWTO_SUCCESS;
409 // Unblocking BlockedOnSTM threads requires the TSO to be
410 // locked; see STM.c:unpark_tso().
411 if (target->why_blocked != BlockedOnSTM) {
414 if ((target->flags & TSO_BLOCKEX) &&
415 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
416 blockedThrowTo(source,target);
418 return THROWTO_BLOCKED;
420 raiseAsync(cap, target, exception, rtsFalse, NULL);
421 unblockOne(cap, target);
423 return THROWTO_SUCCESS;
427 case BlockedOnCCall_NoUnblockExc:
428 // I don't think it's possible to acquire ownership of a
429 // BlockedOnCCall thread. We just assume that the target
430 // thread is blocking exceptions, and block on its
431 // blocked_exception queue.
433 blockedThrowTo(source,target);
435 return THROWTO_BLOCKED;
437 #ifndef THREADEDED_RTS
441 if ((target->flags & TSO_BLOCKEX) &&
442 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
443 blockedThrowTo(source,target);
444 return THROWTO_BLOCKED;
446 removeFromQueues(cap,target);
447 raiseAsync(cap, target, exception, rtsFalse, NULL);
448 return THROWTO_SUCCESS;
453 barf("throwTo: unrecognised why_blocked value");
458 // Block a TSO on another TSO's blocked_exceptions queue.
459 // Precondition: we hold an exclusive lock on the target TSO (this is
460 // complex to achieve as there's no single lock on a TSO; see
463 blockedThrowTo (StgTSO *source, StgTSO *target)
465 debugTrace(DEBUG_sched, "throwTo: blocking on thread %lu", (unsigned long)target->id);
466 source->link = target->blocked_exceptions;
467 target->blocked_exceptions = source;
468 dirtyTSO(target); // we modified the blocked_exceptions queue
470 source->block_info.tso = target;
471 write_barrier(); // throwTo_exception *must* be visible if BlockedOnException is.
472 source->why_blocked = BlockedOnException;
478 throwToReleaseTarget (void *tso)
480 unlockTSO((StgTSO *)tso);
484 /* -----------------------------------------------------------------------------
485 Waking up threads blocked in throwTo
487 There are two ways to do this: maybePerformBlockedException() will
488 perform the throwTo() for the thread at the head of the queue
489 immediately, and leave the other threads on the queue.
490 maybePerformBlockedException() also checks the TSO_BLOCKEX flag
491 before raising an exception.
493 awakenBlockedExceptionQueue() will wake up all the threads in the
494 queue, but not perform any throwTo() immediately. This might be
495 more appropriate when the target thread is the one actually running
497 -------------------------------------------------------------------------- */
500 maybePerformBlockedException (Capability *cap, StgTSO *tso)
504 if (tso->blocked_exceptions != END_TSO_QUEUE
505 && ((tso->flags & TSO_BLOCKEX) == 0
506 || ((tso->flags & TSO_INTERRUPTIBLE) && interruptible(tso)))) {
508 // Lock the TSO, this gives us exclusive access to the queue
511 // Check the queue again; it might have changed before we
513 if (tso->blocked_exceptions == END_TSO_QUEUE) {
518 // We unblock just the first thread on the queue, and perform
519 // its throw immediately.
520 source = tso->blocked_exceptions;
521 performBlockedException(cap, source, tso);
522 tso->blocked_exceptions = unblockOne_(cap, source,
523 rtsFalse/*no migrate*/);
529 awakenBlockedExceptionQueue (Capability *cap, StgTSO *tso)
531 if (tso->blocked_exceptions != END_TSO_QUEUE) {
533 awakenBlockedQueue(cap, tso->blocked_exceptions);
534 tso->blocked_exceptions = END_TSO_QUEUE;
540 performBlockedException (Capability *cap, StgTSO *source, StgTSO *target)
542 StgClosure *exception;
544 ASSERT(source->why_blocked == BlockedOnException);
545 ASSERT(source->block_info.tso->id == target->id);
546 ASSERT(source->sp[0] == (StgWord)&stg_block_throwto_info);
547 ASSERT(((StgTSO *)source->sp[1])->id == target->id);
548 // check ids not pointers, because the thread might be relocated
550 exception = (StgClosure *)source->sp[2];
551 throwToSingleThreaded(cap, target, exception);
555 /* -----------------------------------------------------------------------------
556 Remove a thread from blocking queues.
558 This is for use when we raise an exception in another thread, which
560 This has nothing to do with the UnblockThread event in GranSim. -- HWL
561 -------------------------------------------------------------------------- */
563 #if defined(GRAN) || defined(PARALLEL_HASKELL)
565 NB: only the type of the blocking queue is different in GranSim and GUM
566 the operations on the queue-elements are the same
567 long live polymorphism!
569 Locks: sched_mutex is held upon entry and exit.
573 removeFromQueues(Capability *cap, StgTSO *tso)
575 StgBlockingQueueElement *t, **last;
577 switch (tso->why_blocked) {
580 return; /* not blocked */
583 // Be careful: nothing to do here! We tell the scheduler that the thread
584 // is runnable and we leave it to the stack-walking code to abort the
585 // transaction while unwinding the stack. We should perhaps have a debugging
586 // test to make sure that this really happens and that the 'zombie' transaction
587 // does not get committed.
591 ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
593 StgBlockingQueueElement *last_tso = END_BQ_QUEUE;
594 StgMVar *mvar = (StgMVar *)(tso->block_info.closure);
596 last = (StgBlockingQueueElement **)&mvar->head;
597 for (t = (StgBlockingQueueElement *)mvar->head;
599 last = &t->link, last_tso = t, t = t->link) {
600 if (t == (StgBlockingQueueElement *)tso) {
601 *last = (StgBlockingQueueElement *)tso->link;
602 if (mvar->tail == tso) {
603 mvar->tail = (StgTSO *)last_tso;
608 barf("removeFromQueues (MVAR): TSO not found");
611 case BlockedOnBlackHole:
612 ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
614 StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);
616 last = &bq->blocking_queue;
617 for (t = bq->blocking_queue;
619 last = &t->link, t = t->link) {
620 if (t == (StgBlockingQueueElement *)tso) {
621 *last = (StgBlockingQueueElement *)tso->link;
625 barf("removeFromQueues (BLACKHOLE): TSO not found");
628 case BlockedOnException:
630 StgTSO *target = tso->block_info.tso;
632 ASSERT(get_itbl(target)->type == TSO);
634 while (target->what_next == ThreadRelocated) {
635 target = target2->link;
636 ASSERT(get_itbl(target)->type == TSO);
639 last = (StgBlockingQueueElement **)&target->blocked_exceptions;
640 for (t = (StgBlockingQueueElement *)target->blocked_exceptions;
642 last = &t->link, t = t->link) {
643 ASSERT(get_itbl(t)->type == TSO);
644 if (t == (StgBlockingQueueElement *)tso) {
645 *last = (StgBlockingQueueElement *)tso->link;
649 barf("removeFromQueues (Exception): TSO not found");
654 #if defined(mingw32_HOST_OS)
655 case BlockedOnDoProc:
658 /* take TSO off blocked_queue */
659 StgBlockingQueueElement *prev = NULL;
660 for (t = (StgBlockingQueueElement *)blocked_queue_hd; t != END_BQ_QUEUE;
661 prev = t, t = t->link) {
662 if (t == (StgBlockingQueueElement *)tso) {
664 blocked_queue_hd = (StgTSO *)t->link;
665 if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
666 blocked_queue_tl = END_TSO_QUEUE;
669 prev->link = t->link;
670 if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
671 blocked_queue_tl = (StgTSO *)prev;
674 #if defined(mingw32_HOST_OS)
675 /* (Cooperatively) signal that the worker thread should abort
678 abandonWorkRequest(tso->block_info.async_result->reqID);
683 barf("removeFromQueues (I/O): TSO not found");
688 /* take TSO off sleeping_queue */
689 StgBlockingQueueElement *prev = NULL;
690 for (t = (StgBlockingQueueElement *)sleeping_queue; t != END_BQ_QUEUE;
691 prev = t, t = t->link) {
692 if (t == (StgBlockingQueueElement *)tso) {
694 sleeping_queue = (StgTSO *)t->link;
696 prev->link = t->link;
701 barf("removeFromQueues (delay): TSO not found");
705 barf("removeFromQueues");
709 tso->link = END_TSO_QUEUE;
710 tso->why_blocked = NotBlocked;
711 tso->block_info.closure = NULL;
712 pushOnRunQueue(cap,tso);
716 removeFromQueues(Capability *cap, StgTSO *tso)
718 switch (tso->why_blocked) {
724 // Be careful: nothing to do here! We tell the scheduler that the
725 // thread is runnable and we leave it to the stack-walking code to
726 // abort the transaction while unwinding the stack. We should
727 // perhaps have a debugging test to make sure that this really
728 // happens and that the 'zombie' transaction does not get
733 removeThreadFromMVarQueue((StgMVar *)tso->block_info.closure, tso);
736 case BlockedOnBlackHole:
737 removeThreadFromQueue(&blackhole_queue, tso);
740 case BlockedOnException:
742 StgTSO *target = tso->block_info.tso;
744 // NO: when called by threadPaused(), we probably have this
745 // TSO already locked (WHITEHOLEd) because we just placed
746 // ourselves on its queue.
747 // ASSERT(get_itbl(target)->type == TSO);
749 while (target->what_next == ThreadRelocated) {
750 target = target->link;
753 removeThreadFromQueue(&target->blocked_exceptions, tso);
757 #if !defined(THREADED_RTS)
760 #if defined(mingw32_HOST_OS)
761 case BlockedOnDoProc:
763 removeThreadFromDeQueue(&blocked_queue_hd, &blocked_queue_tl, tso);
764 #if defined(mingw32_HOST_OS)
765 /* (Cooperatively) signal that the worker thread should abort
768 abandonWorkRequest(tso->block_info.async_result->reqID);
773 removeThreadFromQueue(&sleeping_queue, tso);
778 barf("removeFromQueues");
782 tso->link = END_TSO_QUEUE;
783 tso->why_blocked = NotBlocked;
784 tso->block_info.closure = NULL;
785 appendToRunQueue(cap,tso);
787 // We might have just migrated this TSO to our Capability:
789 tso->bound->cap = cap;
795 /* -----------------------------------------------------------------------------
798 * The following function implements the magic for raising an
799 * asynchronous exception in an existing thread.
801 * We first remove the thread from any queue on which it might be
802 * blocked. The possible blockages are MVARs and BLACKHOLE_BQs.
804 * We strip the stack down to the innermost CATCH_FRAME, building
805 * thunks in the heap for all the active computations, so they can
806 * be restarted if necessary. When we reach a CATCH_FRAME, we build
807 * an application of the handler to the exception, and push it on
808 * the top of the stack.
810 * How exactly do we save all the active computations? We create an
811 * AP_STACK for every UpdateFrame on the stack. Entering one of these
812 * AP_STACKs pushes everything from the corresponding update frame
813 * upwards onto the stack. (Actually, it pushes everything up to the
814 * next update frame plus a pointer to the next AP_STACK object.
815 * Entering the next AP_STACK object pushes more onto the stack until we
816 * reach the last AP_STACK object - at which point the stack should look
817 * exactly as it did when we killed the TSO and we can continue
818 * execution by entering the closure on top of the stack.
820 * We can also kill a thread entirely - this happens if either (a) the
821 * exception passed to raiseAsync is NULL, or (b) there's no
822 * CATCH_FRAME on the stack. In either case, we strip the entire
823 * stack and replace the thread with a zombie.
825 * ToDo: in THREADED_RTS mode, this function is only safe if either
826 * (a) we hold all the Capabilities (eg. in GC, or if there is only
827 * one Capability), or (b) we own the Capability that the TSO is
828 * currently blocked on or on the run queue of.
830 * -------------------------------------------------------------------------- */
833 raiseAsync(Capability *cap, StgTSO *tso, StgClosure *exception,
834 rtsBool stop_at_atomically, StgPtr stop_here)
836 StgRetInfoTable *info;
840 debugTrace(DEBUG_sched,
841 "raising exception in thread %ld.", (long)tso->id);
843 // mark it dirty; we're about to change its stack.
848 // ASSUMES: the thread is not already complete or dead. Upper
849 // layers should deal with that.
850 ASSERT(tso->what_next != ThreadComplete && tso->what_next != ThreadKilled);
852 // The stack freezing code assumes there's a closure pointer on
853 // the top of the stack, so we have to arrange that this is the case...
855 if (sp[0] == (W_)&stg_enter_info) {
859 sp[0] = (W_)&stg_dummy_ret_closure;
863 while (stop_here == NULL || frame < stop_here) {
865 // 1. Let the top of the stack be the "current closure"
867 // 2. Walk up the stack until we find either an UPDATE_FRAME or a
870 // 3. If it's an UPDATE_FRAME, then make an AP_STACK containing the
871 // current closure applied to the chunk of stack up to (but not
872 // including) the update frame. This closure becomes the "current
873 // closure". Go back to step 2.
875 // 4. If it's a CATCH_FRAME, then leave the exception handler on
876 // top of the stack applied to the exception.
878 // 5. If it's a STOP_FRAME, then kill the thread.
880 // NB: if we pass an ATOMICALLY_FRAME then abort the associated
883 info = get_ret_itbl((StgClosure *)frame);
885 switch (info->i.type) {
892 // First build an AP_STACK consisting of the stack chunk above the
893 // current update frame, with the top word on the stack as the
896 words = frame - sp - 1;
897 ap = (StgAP_STACK *)allocateLocal(cap,AP_STACK_sizeW(words));
900 ap->fun = (StgClosure *)sp[0];
902 for(i=0; i < (nat)words; ++i) {
903 ap->payload[i] = (StgClosure *)*sp++;
906 SET_HDR(ap,&stg_AP_STACK_info,
907 ((StgClosure *)frame)->header.prof.ccs /* ToDo */);
908 TICK_ALLOC_UP_THK(words+1,0);
910 //IF_DEBUG(scheduler,
911 // debugBelch("sched: Updating ");
912 // printPtr((P_)((StgUpdateFrame *)frame)->updatee);
913 // debugBelch(" with ");
914 // printObj((StgClosure *)ap);
917 // Replace the updatee with an indirection
919 // Warning: if we're in a loop, more than one update frame on
920 // the stack may point to the same object. Be careful not to
921 // overwrite an IND_OLDGEN in this case, because we'll screw
922 // up the mutable lists. To be on the safe side, don't
923 // overwrite any kind of indirection at all. See also
924 // threadSqueezeStack in GC.c, where we have to make a similar
927 if (!closure_IND(((StgUpdateFrame *)frame)->updatee)) {
928 // revert the black hole
929 UPD_IND_NOLOCK(((StgUpdateFrame *)frame)->updatee,
932 sp += sizeofW(StgUpdateFrame) - 1;
933 sp[0] = (W_)ap; // push onto stack
935 continue; //no need to bump frame
939 // We've stripped the entire stack, the thread is now dead.
940 tso->what_next = ThreadKilled;
941 tso->sp = frame + sizeofW(StgStopFrame);
945 // If we find a CATCH_FRAME, and we've got an exception to raise,
946 // then build the THUNK raise(exception), and leave it on
947 // top of the CATCH_FRAME ready to enter.
951 StgCatchFrame *cf = (StgCatchFrame *)frame;
955 if (exception == NULL) break;
957 // we've got an exception to raise, so let's pass it to the
958 // handler in this frame.
960 raise = (StgThunk *)allocateLocal(cap,sizeofW(StgThunk)+1);
961 TICK_ALLOC_SE_THK(1,0);
962 SET_HDR(raise,&stg_raise_info,cf->header.prof.ccs);
963 raise->payload[0] = exception;
965 // throw away the stack from Sp up to the CATCH_FRAME.
969 /* Ensure that async excpetions are blocked now, so we don't get
970 * a surprise exception before we get around to executing the
973 tso->flags |= TSO_BLOCKEX | TSO_INTERRUPTIBLE;
975 /* Put the newly-built THUNK on top of the stack, ready to execute
976 * when the thread restarts.
979 sp[-1] = (W_)&stg_enter_info;
981 tso->what_next = ThreadRunGHC;
982 IF_DEBUG(sanity, checkTSO(tso));
986 case ATOMICALLY_FRAME:
987 if (stop_at_atomically) {
988 ASSERT(stmGetEnclosingTRec(tso->trec) == NO_TREC);
989 stmCondemnTransaction(cap, tso -> trec);
993 // R1 is not a register: the return convention for IO in
994 // this case puts the return value on the stack, so we
995 // need to set up the stack to return to the atomically
998 tso->sp[1] = (StgWord) &stg_NO_FINALIZER_closure; // why not?
999 tso->sp[0] = (StgWord) &stg_ut_1_0_unreg_info;
1001 tso->what_next = ThreadRunGHC;
1004 // Not stop_at_atomically... fall through and abort the
1007 case CATCH_RETRY_FRAME:
1008 // IF we find an ATOMICALLY_FRAME then we abort the
1009 // current transaction and propagate the exception. In
1010 // this case (unlike ordinary exceptions) we do not care
1011 // whether the transaction is valid or not because its
1012 // possible validity cannot have caused the exception
1013 // and will not be visible after the abort.
1014 debugTrace(DEBUG_stm,
1015 "found atomically block delivering async exception");
1017 StgTRecHeader *trec = tso -> trec;
1018 StgTRecHeader *outer = stmGetEnclosingTRec(trec);
1019 stmAbortTransaction(cap, trec);
1020 tso -> trec = outer;
1027 // move on to the next stack frame
1028 frame += stack_frame_sizeW((StgClosure *)frame);
1031 // if we got here, then we stopped at stop_here
1032 ASSERT(stop_here != NULL);