1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 1998-2006
5 * Asynchronous exceptions
7 * --------------------------------------------------------------------------*/
9 #include "PosixSource.h"
12 #include "sm/Storage.h"
15 #include "RaiseAsync.h"
19 #include "sm/Sanity.h"
20 #include "Profiling.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,
29 StgUpdateFrame *stop_here);
31 static void removeFromQueues(Capability *cap, StgTSO *tso);
33 static void blockedThrowTo (Capability *cap, 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);
62 throwToSingleThreaded_(Capability *cap, StgTSO *tso, StgClosure *exception,
63 rtsBool stop_at_atomically)
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, NULL);
77 suspendComputation(Capability *cap, StgTSO *tso, StgUpdateFrame *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 ASSERT(target != END_TSO_QUEUE);
155 // follow ThreadRelocated links in the target first
156 while (target->what_next == ThreadRelocated) {
157 target = target->_link;
158 // No, it might be a WHITEHOLE:
159 // ASSERT(get_itbl(target)->type == TSO);
162 debugTrace(DEBUG_sched, "throwTo: from thread %lu to thread %lu",
163 (unsigned long)source->id, (unsigned long)target->id);
166 traceThreadStatus(DEBUG_sched, target);
171 debugTrace(DEBUG_sched, "throwTo: retrying...");
174 ASSERT(target != END_TSO_QUEUE);
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 // check again for ThreadComplete and ThreadKilled. This
268 // cooperates with scheduleHandleThreadFinished to ensure
269 // that we never miss any threads that are throwing an
270 // exception to a thread in the process of terminating.
271 if (target->what_next == ThreadComplete
272 || target->what_next == ThreadKilled) {
274 return THROWTO_SUCCESS;
276 blockedThrowTo(cap,source,target);
278 return THROWTO_BLOCKED;
285 To establish ownership of this TSO, we need to acquire a
286 lock on the MVar that it is blocked on.
289 StgInfoTable *info USED_IF_THREADS;
291 mvar = (StgMVar *)target->block_info.closure;
293 // ASSUMPTION: tso->block_info must always point to a
294 // closure. In the threaded RTS it does.
295 switch (get_itbl(mvar)->type) {
303 info = lockClosure((StgClosure *)mvar);
305 if (target->what_next == ThreadRelocated) {
306 target = target->_link;
307 unlockClosure((StgClosure *)mvar,info);
310 // we have the MVar, let's check whether the thread
311 // is still blocked on the same MVar.
312 if (target->why_blocked != BlockedOnMVar
313 || (StgMVar *)target->block_info.closure != mvar) {
314 unlockClosure((StgClosure *)mvar, info);
318 if ((target->flags & TSO_BLOCKEX) &&
319 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
320 lockClosure((StgClosure *)target);
321 blockedThrowTo(cap,source,target);
322 unlockClosure((StgClosure *)mvar, info);
324 return THROWTO_BLOCKED; // caller releases TSO
326 removeThreadFromMVarQueue(cap, mvar, target);
327 raiseAsync(cap, target, exception, rtsFalse, NULL);
328 unblockOne(cap, target);
329 unlockClosure((StgClosure *)mvar, info);
330 return THROWTO_SUCCESS;
334 case BlockedOnBlackHole:
336 ACQUIRE_LOCK(&sched_mutex);
337 // double checking the status after the memory barrier:
338 if (target->why_blocked != BlockedOnBlackHole) {
339 RELEASE_LOCK(&sched_mutex);
343 if (target->flags & TSO_BLOCKEX) {
345 blockedThrowTo(cap,source,target);
346 RELEASE_LOCK(&sched_mutex);
348 return THROWTO_BLOCKED; // caller releases TSO
350 removeThreadFromQueue(cap, &blackhole_queue, target);
351 raiseAsync(cap, target, exception, rtsFalse, NULL);
352 unblockOne(cap, target);
353 RELEASE_LOCK(&sched_mutex);
354 return THROWTO_SUCCESS;
358 case BlockedOnException:
364 To obtain exclusive access to a BlockedOnException thread,
365 we must call lockClosure() on the TSO on which it is blocked.
366 Since the TSO might change underneath our feet, after we
367 call lockClosure() we must check that
369 (a) the closure we locked is actually a TSO
370 (b) the original thread is still BlockedOnException,
371 (c) the original thread is still blocked on the TSO we locked
372 and (d) the target thread has not been relocated.
374 We synchronise with threadStackOverflow() (which relocates
375 threads) using lockClosure()/unlockClosure().
377 target2 = target->block_info.tso;
379 info = lockClosure((StgClosure *)target2);
380 if (info != &stg_TSO_info) {
381 unlockClosure((StgClosure *)target2, info);
384 if (target->what_next == ThreadRelocated) {
385 target = target->_link;
389 if (target2->what_next == ThreadRelocated) {
390 target->block_info.tso = target2->_link;
394 if (target->why_blocked != BlockedOnException
395 || target->block_info.tso != target2) {
401 Now we have exclusive rights to the target TSO...
403 If it is blocking exceptions, add the source TSO to its
404 blocked_exceptions queue. Otherwise, raise the exception.
406 if ((target->flags & TSO_BLOCKEX) &&
407 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
409 blockedThrowTo(cap,source,target);
412 return THROWTO_BLOCKED;
414 removeThreadFromQueue(cap, &target2->blocked_exceptions, target);
415 raiseAsync(cap, target, exception, rtsFalse, NULL);
416 unblockOne(cap, target);
418 return THROWTO_SUCCESS;
424 // Unblocking BlockedOnSTM threads requires the TSO to be
425 // locked; see STM.c:unpark_tso().
426 if (target->why_blocked != BlockedOnSTM) {
430 if ((target->flags & TSO_BLOCKEX) &&
431 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
432 blockedThrowTo(cap,source,target);
434 return THROWTO_BLOCKED;
436 raiseAsync(cap, target, exception, rtsFalse, NULL);
437 unblockOne(cap, target);
439 return THROWTO_SUCCESS;
443 case BlockedOnCCall_NoUnblockExc:
444 // I don't think it's possible to acquire ownership of a
445 // BlockedOnCCall thread. We just assume that the target
446 // thread is blocking exceptions, and block on its
447 // blocked_exception queue.
449 if (target->why_blocked != BlockedOnCCall &&
450 target->why_blocked != BlockedOnCCall_NoUnblockExc) {
454 blockedThrowTo(cap,source,target);
456 return THROWTO_BLOCKED;
458 #ifndef THREADEDED_RTS
462 #if defined(mingw32_HOST_OS)
463 case BlockedOnDoProc:
465 if ((target->flags & TSO_BLOCKEX) &&
466 ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
467 blockedThrowTo(cap,source,target);
468 return THROWTO_BLOCKED;
470 removeFromQueues(cap,target);
471 raiseAsync(cap, target, exception, rtsFalse, NULL);
472 return THROWTO_SUCCESS;
477 barf("throwTo: unrecognised why_blocked value");
482 // Block a TSO on another TSO's blocked_exceptions queue.
483 // Precondition: we hold an exclusive lock on the target TSO (this is
484 // complex to achieve as there's no single lock on a TSO; see
487 blockedThrowTo (Capability *cap, StgTSO *source, StgTSO *target)
489 debugTrace(DEBUG_sched, "throwTo: blocking on thread %lu", (unsigned long)target->id);
490 setTSOLink(cap, source, target->blocked_exceptions);
491 target->blocked_exceptions = source;
492 dirty_TSO(cap,target); // we modified the blocked_exceptions queue
494 source->block_info.tso = target;
495 write_barrier(); // throwTo_exception *must* be visible if BlockedOnException is.
496 source->why_blocked = BlockedOnException;
502 throwToReleaseTarget (void *tso)
504 unlockTSO((StgTSO *)tso);
508 /* -----------------------------------------------------------------------------
509 Waking up threads blocked in throwTo
511 There are two ways to do this: maybePerformBlockedException() will
512 perform the throwTo() for the thread at the head of the queue
513 immediately, and leave the other threads on the queue.
514 maybePerformBlockedException() also checks the TSO_BLOCKEX flag
515 before raising an exception.
517 awakenBlockedExceptionQueue() will wake up all the threads in the
518 queue, but not perform any throwTo() immediately. This might be
519 more appropriate when the target thread is the one actually running
522 Returns: non-zero if an exception was raised, zero otherwise.
523 -------------------------------------------------------------------------- */
526 maybePerformBlockedException (Capability *cap, StgTSO *tso)
530 if (tso->what_next == ThreadComplete || tso->what_next == ThreadFinished) {
531 if (tso->blocked_exceptions != END_TSO_QUEUE) {
532 awakenBlockedExceptionQueue(cap,tso);
539 if (tso->blocked_exceptions != END_TSO_QUEUE &&
540 (tso->flags & TSO_BLOCKEX) != 0) {
541 debugTrace(DEBUG_sched, "throwTo: thread %lu has blocked exceptions but is inside block", (unsigned long)tso->id);
544 if (tso->blocked_exceptions != END_TSO_QUEUE
545 && ((tso->flags & TSO_BLOCKEX) == 0
546 || ((tso->flags & TSO_INTERRUPTIBLE) && interruptible(tso)))) {
548 // Lock the TSO, this gives us exclusive access to the queue
551 // Check the queue again; it might have changed before we
553 if (tso->blocked_exceptions == END_TSO_QUEUE) {
558 // We unblock just the first thread on the queue, and perform
559 // its throw immediately.
560 source = tso->blocked_exceptions;
561 performBlockedException(cap, source, tso);
562 tso->blocked_exceptions = unblockOne_(cap, source,
563 rtsFalse/*no migrate*/);
570 // awakenBlockedExceptionQueue(): Just wake up the whole queue of
571 // blocked exceptions and let them try again.
574 awakenBlockedExceptionQueue (Capability *cap, StgTSO *tso)
577 awakenBlockedQueue(cap, tso->blocked_exceptions);
578 tso->blocked_exceptions = END_TSO_QUEUE;
583 performBlockedException (Capability *cap, StgTSO *source, StgTSO *target)
585 StgClosure *exception;
587 ASSERT(source->why_blocked == BlockedOnException);
588 ASSERT(source->block_info.tso->id == target->id);
589 ASSERT(source->sp[0] == (StgWord)&stg_block_throwto_info);
590 ASSERT(((StgTSO *)source->sp[1])->id == target->id);
591 // check ids not pointers, because the thread might be relocated
593 exception = (StgClosure *)source->sp[2];
594 throwToSingleThreaded(cap, target, exception);
598 /* -----------------------------------------------------------------------------
599 Remove a thread from blocking queues.
601 This is for use when we raise an exception in another thread, which
604 Precondition: we have exclusive access to the TSO, via the same set
605 of conditions as throwToSingleThreaded() (c.f.).
606 -------------------------------------------------------------------------- */
609 removeFromQueues(Capability *cap, StgTSO *tso)
611 switch (tso->why_blocked) {
617 // Be careful: nothing to do here! We tell the scheduler that the
618 // thread is runnable and we leave it to the stack-walking code to
619 // abort the transaction while unwinding the stack. We should
620 // perhaps have a debugging test to make sure that this really
621 // happens and that the 'zombie' transaction does not get
626 removeThreadFromMVarQueue(cap, (StgMVar *)tso->block_info.closure, tso);
629 case BlockedOnBlackHole:
630 removeThreadFromQueue(cap, &blackhole_queue, tso);
633 case BlockedOnException:
635 StgTSO *target = tso->block_info.tso;
637 // NO: when called by threadPaused(), we probably have this
638 // TSO already locked (WHITEHOLEd) because we just placed
639 // ourselves on its queue.
640 // ASSERT(get_itbl(target)->type == TSO);
642 while (target->what_next == ThreadRelocated) {
643 target = target->_link;
646 removeThreadFromQueue(cap, &target->blocked_exceptions, tso);
650 #if !defined(THREADED_RTS)
653 #if defined(mingw32_HOST_OS)
654 case BlockedOnDoProc:
656 removeThreadFromDeQueue(cap, &blocked_queue_hd, &blocked_queue_tl, tso);
657 #if defined(mingw32_HOST_OS)
658 /* (Cooperatively) signal that the worker thread should abort
661 abandonWorkRequest(tso->block_info.async_result->reqID);
666 removeThreadFromQueue(cap, &sleeping_queue, tso);
671 barf("removeFromQueues: %d", tso->why_blocked);
675 unblockOne(cap, tso);
678 /* -----------------------------------------------------------------------------
681 * The following function implements the magic for raising an
682 * asynchronous exception in an existing thread.
684 * We first remove the thread from any queue on which it might be
685 * blocked. The possible blockages are MVARs and BLACKHOLE_BQs.
687 * We strip the stack down to the innermost CATCH_FRAME, building
688 * thunks in the heap for all the active computations, so they can
689 * be restarted if necessary. When we reach a CATCH_FRAME, we build
690 * an application of the handler to the exception, and push it on
691 * the top of the stack.
693 * How exactly do we save all the active computations? We create an
694 * AP_STACK for every UpdateFrame on the stack. Entering one of these
695 * AP_STACKs pushes everything from the corresponding update frame
696 * upwards onto the stack. (Actually, it pushes everything up to the
697 * next update frame plus a pointer to the next AP_STACK object.
698 * Entering the next AP_STACK object pushes more onto the stack until we
699 * reach the last AP_STACK object - at which point the stack should look
700 * exactly as it did when we killed the TSO and we can continue
701 * execution by entering the closure on top of the stack.
703 * We can also kill a thread entirely - this happens if either (a) the
704 * exception passed to raiseAsync is NULL, or (b) there's no
705 * CATCH_FRAME on the stack. In either case, we strip the entire
706 * stack and replace the thread with a zombie.
708 * ToDo: in THREADED_RTS mode, this function is only safe if either
709 * (a) we hold all the Capabilities (eg. in GC, or if there is only
710 * one Capability), or (b) we own the Capability that the TSO is
711 * currently blocked on or on the run queue of.
713 * -------------------------------------------------------------------------- */
716 raiseAsync(Capability *cap, StgTSO *tso, StgClosure *exception,
717 rtsBool stop_at_atomically, StgUpdateFrame *stop_here)
719 StgRetInfoTable *info;
724 debugTrace(DEBUG_sched,
725 "raising exception in thread %ld.", (long)tso->id);
727 #if defined(PROFILING)
729 * Debugging tool: on raising an exception, show where we are.
730 * See also Exception.cmm:stg_raisezh.
731 * This wasn't done for asynchronous exceptions originally; see #1450
733 if (RtsFlags.ProfFlags.showCCSOnException)
735 fprintCCS_stderr(tso->prof.CCCS);
739 // mark it dirty; we're about to change its stack.
744 // ASSUMES: the thread is not already complete or dead. Upper
745 // layers should deal with that.
746 ASSERT(tso->what_next != ThreadComplete && tso->what_next != ThreadKilled);
748 if (stop_here != NULL) {
749 updatee = stop_here->updatee;
754 // The stack freezing code assumes there's a closure pointer on
755 // the top of the stack, so we have to arrange that this is the case...
757 if (sp[0] == (W_)&stg_enter_info) {
761 sp[0] = (W_)&stg_dummy_ret_closure;
765 while (stop_here == NULL || frame < (StgPtr)stop_here) {
767 // 1. Let the top of the stack be the "current closure"
769 // 2. Walk up the stack until we find either an UPDATE_FRAME or a
772 // 3. If it's an UPDATE_FRAME, then make an AP_STACK containing the
773 // current closure applied to the chunk of stack up to (but not
774 // including) the update frame. This closure becomes the "current
775 // closure". Go back to step 2.
777 // 4. If it's a CATCH_FRAME, then leave the exception handler on
778 // top of the stack applied to the exception.
780 // 5. If it's a STOP_FRAME, then kill the thread.
782 // NB: if we pass an ATOMICALLY_FRAME then abort the associated
785 info = get_ret_itbl((StgClosure *)frame);
787 switch (info->i.type) {
794 // First build an AP_STACK consisting of the stack chunk above the
795 // current update frame, with the top word on the stack as the
798 words = frame - sp - 1;
799 ap = (StgAP_STACK *)allocate(cap,AP_STACK_sizeW(words));
802 ap->fun = (StgClosure *)sp[0];
804 for(i=0; i < (nat)words; ++i) {
805 ap->payload[i] = (StgClosure *)*sp++;
808 SET_HDR(ap,&stg_AP_STACK_info,
809 ((StgClosure *)frame)->header.prof.ccs /* ToDo */);
810 TICK_ALLOC_UP_THK(words+1,0);
812 //IF_DEBUG(scheduler,
813 // debugBelch("sched: Updating ");
814 // printPtr((P_)((StgUpdateFrame *)frame)->updatee);
815 // debugBelch(" with ");
816 // printObj((StgClosure *)ap);
819 if (((StgUpdateFrame *)frame)->updatee == updatee) {
820 // If this update frame points to the same closure as
821 // the update frame further down the stack
822 // (stop_here), then don't perform the update. We
823 // want to keep the blackhole in this case, so we can
824 // detect and report the loop (#2783).
825 ap = (StgAP_STACK*)updatee;
827 // Perform the update
828 // TODO: this may waste some work, if the thunk has
829 // already been updated by another thread.
830 UPD_IND(((StgUpdateFrame *)frame)->updatee, (StgClosure *)ap);
833 sp += sizeofW(StgUpdateFrame) - 1;
834 sp[0] = (W_)ap; // push onto stack
836 continue; //no need to bump frame
841 // We've stripped the entire stack, the thread is now dead.
842 tso->what_next = ThreadKilled;
843 tso->sp = frame + sizeofW(StgStopFrame);
848 // If we find a CATCH_FRAME, and we've got an exception to raise,
849 // then build the THUNK raise(exception), and leave it on
850 // top of the CATCH_FRAME ready to enter.
854 StgCatchFrame *cf = (StgCatchFrame *)frame;
858 if (exception == NULL) break;
860 // we've got an exception to raise, so let's pass it to the
861 // handler in this frame.
863 raise = (StgThunk *)allocate(cap,sizeofW(StgThunk)+1);
864 TICK_ALLOC_SE_THK(1,0);
865 SET_HDR(raise,&stg_raise_info,cf->header.prof.ccs);
866 raise->payload[0] = exception;
868 // throw away the stack from Sp up to the CATCH_FRAME.
872 /* Ensure that async excpetions are blocked now, so we don't get
873 * a surprise exception before we get around to executing the
876 tso->flags |= TSO_BLOCKEX | TSO_INTERRUPTIBLE;
878 /* Put the newly-built THUNK on top of the stack, ready to execute
879 * when the thread restarts.
882 sp[-1] = (W_)&stg_enter_info;
884 tso->what_next = ThreadRunGHC;
885 IF_DEBUG(sanity, checkTSO(tso));
889 case ATOMICALLY_FRAME:
890 if (stop_at_atomically) {
891 ASSERT(tso->trec->enclosing_trec == NO_TREC);
892 stmCondemnTransaction(cap, tso -> trec);
894 // The ATOMICALLY_FRAME expects to be returned a
895 // result from the transaction, which it stores in the
896 // stack frame. Hence we arrange to return a dummy
897 // result, so that the GC doesn't get upset (#3578).
898 // Perhaps a better way would be to have a different
899 // ATOMICALLY_FRAME instance for condemned
900 // transactions, but I don't fully understand the
901 // interaction with STM invariants.
902 tso->sp[1] = (W_)&stg_NO_TREC_closure;
903 tso->sp[0] = (W_)&stg_gc_unpt_r1_info;
904 tso->what_next = ThreadRunGHC;
907 // Not stop_at_atomically... fall through and abort the
910 case CATCH_STM_FRAME:
911 case CATCH_RETRY_FRAME:
912 // IF we find an ATOMICALLY_FRAME then we abort the
913 // current transaction and propagate the exception. In
914 // this case (unlike ordinary exceptions) we do not care
915 // whether the transaction is valid or not because its
916 // possible validity cannot have caused the exception
917 // and will not be visible after the abort.
920 StgTRecHeader *trec = tso -> trec;
921 StgTRecHeader *outer = trec -> enclosing_trec;
922 debugTrace(DEBUG_stm,
923 "found atomically block delivering async exception");
924 stmAbortTransaction(cap, trec);
925 stmFreeAbortedTRec(cap, trec);
934 // move on to the next stack frame
935 frame += stack_frame_sizeW((StgClosure *)frame);
938 // if we got here, then we stopped at stop_here
939 ASSERT(stop_here != NULL);