1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 1998-2006
5 * The scheduler and thread-related functionality
7 * --------------------------------------------------------------------------*/
9 #include "PosixSource.h"
10 #define KEEP_LOCKCLOSURE
15 #include "OSThreads.h"
20 #include "StgMiscClosures.h"
21 #include "Interpreter.h"
23 #include "RtsSignals.h"
29 #include "ThreadLabels.h"
30 #include "LdvProfile.h"
32 #include "Proftimer.h"
35 /* PARALLEL_HASKELL includes go here */
38 #include "Capability.h"
40 #include "AwaitEvent.h"
41 #if defined(mingw32_HOST_OS)
42 #include "win32/IOManager.h"
45 #include "RaiseAsync.h"
47 #include "ThrIOManager.h"
49 #ifdef HAVE_SYS_TYPES_H
50 #include <sys/types.h>
64 // Turn off inlining when debugging - it obfuscates things
67 # define STATIC_INLINE static
70 /* -----------------------------------------------------------------------------
72 * -------------------------------------------------------------------------- */
74 #if !defined(THREADED_RTS)
75 // Blocked/sleeping thrads
76 StgTSO *blocked_queue_hd = NULL;
77 StgTSO *blocked_queue_tl = NULL;
78 StgTSO *sleeping_queue = NULL; // perhaps replace with a hash table?
81 /* Threads blocked on blackholes.
82 * LOCK: sched_mutex+capability, or all capabilities
84 StgTSO *blackhole_queue = NULL;
86 /* The blackhole_queue should be checked for threads to wake up. See
87 * Schedule.h for more thorough comment.
88 * LOCK: none (doesn't matter if we miss an update)
90 rtsBool blackholes_need_checking = rtsFalse;
92 /* flag set by signal handler to precipitate a context switch
93 * LOCK: none (just an advisory flag)
95 int context_switch = 0;
97 /* flag that tracks whether we have done any execution in this time slice.
98 * LOCK: currently none, perhaps we should lock (but needs to be
99 * updated in the fast path of the scheduler).
101 nat recent_activity = ACTIVITY_YES;
103 /* if this flag is set as well, give up execution
104 * LOCK: none (changes once, from false->true)
106 rtsBool sched_state = SCHED_RUNNING;
108 /* This is used in `TSO.h' and gcc 2.96 insists that this variable actually
109 * exists - earlier gccs apparently didn't.
115 * Set to TRUE when entering a shutdown state (via shutdownHaskellAndExit()) --
116 * in an MT setting, needed to signal that a worker thread shouldn't hang around
117 * in the scheduler when it is out of work.
119 rtsBool shutting_down_scheduler = rtsFalse;
122 * This mutex protects most of the global scheduler data in
123 * the THREADED_RTS runtime.
125 #if defined(THREADED_RTS)
129 #if !defined(mingw32_HOST_OS)
130 #define FORKPROCESS_PRIMOP_SUPPORTED
133 /* -----------------------------------------------------------------------------
134 * static function prototypes
135 * -------------------------------------------------------------------------- */
137 static Capability *schedule (Capability *initialCapability, Task *task);
140 // These function all encapsulate parts of the scheduler loop, and are
141 // abstracted only to make the structure and control flow of the
142 // scheduler clearer.
144 static void schedulePreLoop (void);
145 #if defined(THREADED_RTS)
146 static void schedulePushWork(Capability *cap, Task *task);
148 static void scheduleStartSignalHandlers (Capability *cap);
149 static void scheduleCheckBlockedThreads (Capability *cap);
150 static void scheduleCheckWakeupThreads(Capability *cap USED_IF_NOT_THREADS);
151 static void scheduleCheckBlackHoles (Capability *cap);
152 static void scheduleDetectDeadlock (Capability *cap, Task *task);
153 #if defined(PARALLEL_HASKELL)
154 static rtsBool scheduleGetRemoteWork(Capability *cap);
155 static void scheduleSendPendingMessages(void);
156 static void scheduleActivateSpark(Capability *cap);
158 static void schedulePostRunThread(StgTSO *t);
159 static rtsBool scheduleHandleHeapOverflow( Capability *cap, StgTSO *t );
160 static void scheduleHandleStackOverflow( Capability *cap, Task *task,
162 static rtsBool scheduleHandleYield( Capability *cap, StgTSO *t,
163 nat prev_what_next );
164 static void scheduleHandleThreadBlocked( StgTSO *t );
165 static rtsBool scheduleHandleThreadFinished( Capability *cap, Task *task,
167 static rtsBool scheduleNeedHeapProfile(rtsBool ready_to_gc);
168 static Capability *scheduleDoGC(Capability *cap, Task *task,
169 rtsBool force_major);
171 static rtsBool checkBlackHoles(Capability *cap);
173 static StgTSO *threadStackOverflow(Capability *cap, StgTSO *tso);
174 static StgTSO *threadStackUnderflow(Task *task, StgTSO *tso);
176 static void deleteThread (Capability *cap, StgTSO *tso);
177 static void deleteAllThreads (Capability *cap);
179 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
180 static void deleteThread_(Capability *cap, StgTSO *tso);
184 static char *whatNext_strs[] = {
194 /* -----------------------------------------------------------------------------
195 * Putting a thread on the run queue: different scheduling policies
196 * -------------------------------------------------------------------------- */
199 addToRunQueue( Capability *cap, StgTSO *t )
201 #if defined(PARALLEL_HASKELL)
202 if (RtsFlags.ParFlags.doFairScheduling) {
203 // this does round-robin scheduling; good for concurrency
204 appendToRunQueue(cap,t);
206 // this does unfair scheduling; good for parallelism
207 pushOnRunQueue(cap,t);
210 // this does round-robin scheduling; good for concurrency
211 appendToRunQueue(cap,t);
215 /* ---------------------------------------------------------------------------
216 Main scheduling loop.
218 We use round-robin scheduling, each thread returning to the
219 scheduler loop when one of these conditions is detected:
222 * timer expires (thread yields)
228 In a GranSim setup this loop iterates over the global event queue.
229 This revolves around the global event queue, which determines what
230 to do next. Therefore, it's more complicated than either the
231 concurrent or the parallel (GUM) setup.
232 This version has been entirely removed (JB 2008/08).
235 GUM iterates over incoming messages.
236 It starts with nothing to do (thus CurrentTSO == END_TSO_QUEUE),
237 and sends out a fish whenever it has nothing to do; in-between
238 doing the actual reductions (shared code below) it processes the
239 incoming messages and deals with delayed operations
240 (see PendingFetches).
241 This is not the ugliest code you could imagine, but it's bloody close.
243 (JB 2008/08) This version was formerly indicated by a PP-Flag PAR,
244 now by PP-flag PARALLEL_HASKELL. The Eden RTS (in GHC-6.x) uses it,
245 as well as future GUM versions. This file has been refurbished to
246 only contain valid code, which is however incomplete, refers to
247 invalid includes etc.
249 ------------------------------------------------------------------------ */
252 schedule (Capability *initialCapability, Task *task)
256 StgThreadReturnCode ret;
257 #if defined(PARALLEL_HASKELL)
258 rtsBool receivedFinish = rtsFalse;
262 #if defined(THREADED_RTS)
263 rtsBool first = rtsTrue;
266 cap = initialCapability;
268 // Pre-condition: this task owns initialCapability.
269 // The sched_mutex is *NOT* held
270 // NB. on return, we still hold a capability.
272 debugTrace (DEBUG_sched,
273 "### NEW SCHEDULER LOOP (task: %p, cap: %p)",
274 task, initialCapability);
278 // -----------------------------------------------------------
279 // Scheduler loop starts here:
281 #if defined(PARALLEL_HASKELL)
282 #define TERMINATION_CONDITION (!receivedFinish)
284 #define TERMINATION_CONDITION rtsTrue
287 while (TERMINATION_CONDITION) {
289 #if defined(THREADED_RTS)
291 // don't yield the first time, we want a chance to run this
292 // thread for a bit, even if there are others banging at the
295 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
297 // Yield the capability to higher-priority tasks if necessary.
298 yieldCapability(&cap, task);
302 #if defined(THREADED_RTS)
303 schedulePushWork(cap,task);
306 // Check whether we have re-entered the RTS from Haskell without
307 // going via suspendThread()/resumeThread (i.e. a 'safe' foreign
309 if (cap->in_haskell) {
310 errorBelch("schedule: re-entered unsafely.\n"
311 " Perhaps a 'foreign import unsafe' should be 'safe'?");
312 stg_exit(EXIT_FAILURE);
315 // The interruption / shutdown sequence.
317 // In order to cleanly shut down the runtime, we want to:
318 // * make sure that all main threads return to their callers
319 // with the state 'Interrupted'.
320 // * clean up all OS threads assocated with the runtime
321 // * free all memory etc.
323 // So the sequence for ^C goes like this:
325 // * ^C handler sets sched_state := SCHED_INTERRUPTING and
326 // arranges for some Capability to wake up
328 // * all threads in the system are halted, and the zombies are
329 // placed on the run queue for cleaning up. We acquire all
330 // the capabilities in order to delete the threads, this is
331 // done by scheduleDoGC() for convenience (because GC already
332 // needs to acquire all the capabilities). We can't kill
333 // threads involved in foreign calls.
335 // * somebody calls shutdownHaskell(), which calls exitScheduler()
337 // * sched_state := SCHED_SHUTTING_DOWN
339 // * all workers exit when the run queue on their capability
340 // drains. All main threads will also exit when their TSO
341 // reaches the head of the run queue and they can return.
343 // * eventually all Capabilities will shut down, and the RTS can
346 // * We might be left with threads blocked in foreign calls,
347 // we should really attempt to kill these somehow (TODO);
349 switch (sched_state) {
352 case SCHED_INTERRUPTING:
353 debugTrace(DEBUG_sched, "SCHED_INTERRUPTING");
354 #if defined(THREADED_RTS)
355 discardSparksCap(cap);
357 /* scheduleDoGC() deletes all the threads */
358 cap = scheduleDoGC(cap,task,rtsFalse);
360 case SCHED_SHUTTING_DOWN:
361 debugTrace(DEBUG_sched, "SCHED_SHUTTING_DOWN");
362 // If we are a worker, just exit. If we're a bound thread
363 // then we will exit below when we've removed our TSO from
365 if (task->tso == NULL && emptyRunQueue(cap)) {
370 barf("sched_state: %d", sched_state);
373 #if defined(THREADED_RTS)
374 // If the run queue is empty, take a spark and turn it into a thread.
376 if (emptyRunQueue(cap)) {
378 spark = findSpark(cap);
380 debugTrace(DEBUG_sched,
381 "turning spark of closure %p into a thread",
382 (StgClosure *)spark);
383 createSparkThread(cap,spark);
387 #endif // THREADED_RTS
389 scheduleStartSignalHandlers(cap);
391 // Only check the black holes here if we've nothing else to do.
392 // During normal execution, the black hole list only gets checked
393 // at GC time, to avoid repeatedly traversing this possibly long
394 // list each time around the scheduler.
395 if (emptyRunQueue(cap)) { scheduleCheckBlackHoles(cap); }
397 scheduleCheckWakeupThreads(cap);
399 scheduleCheckBlockedThreads(cap);
401 #if defined(PARALLEL_HASKELL)
402 /* message processing and work distribution goes here */
404 /* if messages have been buffered... a NOOP in THREADED_RTS */
405 scheduleSendPendingMessages();
407 /* If the run queue is empty,...*/
408 if (emptyRunQueue(cap)) {
409 /* ...take one of our own sparks and turn it into a thread */
410 scheduleActivateSpark(cap);
412 /* if this did not work, try to steal a spark from someone else */
413 if (emptyRunQueue(cap)) {
414 receivedFinish = scheduleGetRemoteWork(cap);
415 continue; // a new round, (hopefully) with new work
417 in GUM, this a) sends out a FISH and returns IF no fish is
419 b) (blocking) awaits and receives messages
421 in Eden, this is only the blocking receive, as b) in GUM.
426 /* since we perform a blocking receive and continue otherwise,
427 either we never reach here or we definitely have work! */
428 // from here: non-empty run queue
429 ASSERT(!emptyRunQueue(cap));
431 if (PacketsWaiting()) { /* now process incoming messages, if any
434 CAUTION: scheduleGetRemoteWork called
435 above, waits for messages as well! */
436 processMessages(cap, &receivedFinish);
438 #endif // PARALLEL_HASKELL
440 scheduleDetectDeadlock(cap,task);
441 #if defined(THREADED_RTS)
442 cap = task->cap; // reload cap, it might have changed
445 // Normally, the only way we can get here with no threads to
446 // run is if a keyboard interrupt received during
447 // scheduleCheckBlockedThreads() or scheduleDetectDeadlock().
448 // Additionally, it is not fatal for the
449 // threaded RTS to reach here with no threads to run.
451 // win32: might be here due to awaitEvent() being abandoned
452 // as a result of a console event having been delivered.
453 if ( emptyRunQueue(cap) ) {
454 #if !defined(THREADED_RTS) && !defined(mingw32_HOST_OS)
455 ASSERT(sched_state >= SCHED_INTERRUPTING);
457 continue; // nothing to do
461 // Get a thread to run
463 t = popRunQueue(cap);
465 // Sanity check the thread we're about to run. This can be
466 // expensive if there is lots of thread switching going on...
467 IF_DEBUG(sanity,checkTSO(t));
469 #if defined(THREADED_RTS)
470 // Check whether we can run this thread in the current task.
471 // If not, we have to pass our capability to the right task.
473 Task *bound = t->bound;
477 debugTrace(DEBUG_sched,
478 "### Running thread %lu in bound thread", (unsigned long)t->id);
479 // yes, the Haskell thread is bound to the current native thread
481 debugTrace(DEBUG_sched,
482 "### thread %lu bound to another OS thread", (unsigned long)t->id);
483 // no, bound to a different Haskell thread: pass to that thread
484 pushOnRunQueue(cap,t);
488 // The thread we want to run is unbound.
490 debugTrace(DEBUG_sched,
491 "### this OS thread cannot run thread %lu", (unsigned long)t->id);
492 // no, the current native thread is bound to a different
493 // Haskell thread, so pass it to any worker thread
494 pushOnRunQueue(cap,t);
501 /* context switches are initiated by the timer signal, unless
502 * the user specified "context switch as often as possible", with
505 if (RtsFlags.ConcFlags.ctxtSwitchTicks == 0
506 && !emptyThreadQueues(cap)) {
512 // CurrentTSO is the thread to run. t might be different if we
513 // loop back to run_thread, so make sure to set CurrentTSO after
515 cap->r.rCurrentTSO = t;
517 debugTrace(DEBUG_sched, "-->> running thread %ld %s ...",
518 (long)t->id, whatNext_strs[t->what_next]);
520 startHeapProfTimer();
522 // Check for exceptions blocked on this thread
523 maybePerformBlockedException (cap, t);
525 // ----------------------------------------------------------------------
526 // Run the current thread
528 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
529 ASSERT(t->cap == cap);
531 prev_what_next = t->what_next;
533 errno = t->saved_errno;
535 SetLastError(t->saved_winerror);
538 cap->in_haskell = rtsTrue;
542 #if defined(THREADED_RTS)
543 if (recent_activity == ACTIVITY_DONE_GC) {
544 // ACTIVITY_DONE_GC means we turned off the timer signal to
545 // conserve power (see #1623). Re-enable it here.
547 prev = xchg((P_)&recent_activity, ACTIVITY_YES);
548 if (prev == ACTIVITY_DONE_GC) {
552 recent_activity = ACTIVITY_YES;
556 switch (prev_what_next) {
560 /* Thread already finished, return to scheduler. */
561 ret = ThreadFinished;
567 r = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
568 cap = regTableToCapability(r);
573 case ThreadInterpret:
574 cap = interpretBCO(cap);
579 barf("schedule: invalid what_next field");
582 cap->in_haskell = rtsFalse;
584 // The TSO might have moved, eg. if it re-entered the RTS and a GC
585 // happened. So find the new location:
586 t = cap->r.rCurrentTSO;
588 // We have run some Haskell code: there might be blackhole-blocked
589 // threads to wake up now.
590 // Lock-free test here should be ok, we're just setting a flag.
591 if ( blackhole_queue != END_TSO_QUEUE ) {
592 blackholes_need_checking = rtsTrue;
595 // And save the current errno in this thread.
596 // XXX: possibly bogus for SMP because this thread might already
597 // be running again, see code below.
598 t->saved_errno = errno;
600 // Similarly for Windows error code
601 t->saved_winerror = GetLastError();
604 #if defined(THREADED_RTS)
605 // If ret is ThreadBlocked, and this Task is bound to the TSO that
606 // blocked, we are in limbo - the TSO is now owned by whatever it
607 // is blocked on, and may in fact already have been woken up,
608 // perhaps even on a different Capability. It may be the case
609 // that task->cap != cap. We better yield this Capability
610 // immediately and return to normaility.
611 if (ret == ThreadBlocked) {
612 debugTrace(DEBUG_sched,
613 "--<< thread %lu (%s) stopped: blocked",
614 (unsigned long)t->id, whatNext_strs[t->what_next]);
619 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
620 ASSERT(t->cap == cap);
622 // ----------------------------------------------------------------------
624 // Costs for the scheduler are assigned to CCS_SYSTEM
626 #if defined(PROFILING)
630 schedulePostRunThread(t);
632 t = threadStackUnderflow(task,t);
634 ready_to_gc = rtsFalse;
638 ready_to_gc = scheduleHandleHeapOverflow(cap,t);
642 scheduleHandleStackOverflow(cap,task,t);
646 if (scheduleHandleYield(cap, t, prev_what_next)) {
647 // shortcut for switching between compiler/interpreter:
653 scheduleHandleThreadBlocked(t);
657 if (scheduleHandleThreadFinished(cap, task, t)) return cap;
658 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
662 barf("schedule: invalid thread return code %d", (int)ret);
665 if (ready_to_gc || scheduleNeedHeapProfile(ready_to_gc)) {
666 cap = scheduleDoGC(cap,task,rtsFalse);
668 } /* end of while() */
671 /* ----------------------------------------------------------------------------
672 * Setting up the scheduler loop
673 * ------------------------------------------------------------------------- */
676 schedulePreLoop(void)
678 // initialisation for scheduler - what cannot go into initScheduler()
681 /* -----------------------------------------------------------------------------
684 * Push work to other Capabilities if we have some.
685 * -------------------------------------------------------------------------- */
687 #if defined(THREADED_RTS)
689 schedulePushWork(Capability *cap USED_IF_THREADS,
690 Task *task USED_IF_THREADS)
692 Capability *free_caps[n_capabilities], *cap0;
695 // migration can be turned off with +RTS -qg
696 if (!RtsFlags.ParFlags.migrate) return;
698 // Check whether we have more threads on our run queue, or sparks
699 // in our pool, that we could hand to another Capability.
700 if ((emptyRunQueue(cap) || cap->run_queue_hd->_link == END_TSO_QUEUE)
701 && sparkPoolSizeCap(cap) < 2) {
705 // First grab as many free Capabilities as we can.
706 for (i=0, n_free_caps=0; i < n_capabilities; i++) {
707 cap0 = &capabilities[i];
708 if (cap != cap0 && tryGrabCapability(cap0,task)) {
709 if (!emptyRunQueue(cap0) || cap->returning_tasks_hd != NULL) {
710 // it already has some work, we just grabbed it at
711 // the wrong moment. Or maybe it's deadlocked!
712 releaseCapability(cap0);
714 free_caps[n_free_caps++] = cap0;
719 // we now have n_free_caps free capabilities stashed in
720 // free_caps[]. Share our run queue equally with them. This is
721 // probably the simplest thing we could do; improvements we might
722 // want to do include:
724 // - giving high priority to moving relatively new threads, on
725 // the gournds that they haven't had time to build up a
726 // working set in the cache on this CPU/Capability.
728 // - giving low priority to moving long-lived threads
730 if (n_free_caps > 0) {
731 StgTSO *prev, *t, *next;
732 rtsBool pushed_to_all;
734 debugTrace(DEBUG_sched, "excess threads on run queue and %d free capabilities, sharing...", n_free_caps);
737 pushed_to_all = rtsFalse;
739 if (cap->run_queue_hd != END_TSO_QUEUE) {
740 prev = cap->run_queue_hd;
742 prev->_link = END_TSO_QUEUE;
743 for (; t != END_TSO_QUEUE; t = next) {
745 t->_link = END_TSO_QUEUE;
746 if (t->what_next == ThreadRelocated
747 || t->bound == task // don't move my bound thread
748 || tsoLocked(t)) { // don't move a locked thread
749 setTSOLink(cap, prev, t);
751 } else if (i == n_free_caps) {
752 pushed_to_all = rtsTrue;
755 setTSOLink(cap, prev, t);
758 debugTrace(DEBUG_sched, "pushing thread %lu to capability %d", (unsigned long)t->id, free_caps[i]->no);
759 appendToRunQueue(free_caps[i],t);
760 if (t->bound) { t->bound->cap = free_caps[i]; }
761 t->cap = free_caps[i];
765 cap->run_queue_tl = prev;
768 // If there are some free capabilities that we didn't push any
769 // threads to, then try to push a spark to each one.
770 if (!pushed_to_all) {
772 // i is the next free capability to push to
773 for (; i < n_free_caps; i++) {
774 if (emptySparkPoolCap(free_caps[i])) {
775 spark = findSpark(cap);
777 debugTrace(DEBUG_sched, "pushing spark %p to capability %d", spark, free_caps[i]->no);
778 newSpark(&(free_caps[i]->r), spark);
784 // release the capabilities
785 for (i = 0; i < n_free_caps; i++) {
786 task->cap = free_caps[i];
787 releaseCapability(free_caps[i]);
790 task->cap = cap; // reset to point to our Capability.
794 /* ----------------------------------------------------------------------------
795 * Start any pending signal handlers
796 * ------------------------------------------------------------------------- */
798 #if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
800 scheduleStartSignalHandlers(Capability *cap)
802 if (RtsFlags.MiscFlags.install_signal_handlers && signals_pending()) {
803 // safe outside the lock
804 startSignalHandlers(cap);
809 scheduleStartSignalHandlers(Capability *cap STG_UNUSED)
814 /* ----------------------------------------------------------------------------
815 * Check for blocked threads that can be woken up.
816 * ------------------------------------------------------------------------- */
819 scheduleCheckBlockedThreads(Capability *cap USED_IF_NOT_THREADS)
821 #if !defined(THREADED_RTS)
823 // Check whether any waiting threads need to be woken up. If the
824 // run queue is empty, and there are no other tasks running, we
825 // can wait indefinitely for something to happen.
827 if ( !emptyQueue(blocked_queue_hd) || !emptyQueue(sleeping_queue) )
829 awaitEvent( emptyRunQueue(cap) && !blackholes_need_checking );
835 /* ----------------------------------------------------------------------------
836 * Check for threads woken up by other Capabilities
837 * ------------------------------------------------------------------------- */
840 scheduleCheckWakeupThreads(Capability *cap USED_IF_THREADS)
842 #if defined(THREADED_RTS)
843 // Any threads that were woken up by other Capabilities get
844 // appended to our run queue.
845 if (!emptyWakeupQueue(cap)) {
846 ACQUIRE_LOCK(&cap->lock);
847 if (emptyRunQueue(cap)) {
848 cap->run_queue_hd = cap->wakeup_queue_hd;
849 cap->run_queue_tl = cap->wakeup_queue_tl;
851 setTSOLink(cap, cap->run_queue_tl, cap->wakeup_queue_hd);
852 cap->run_queue_tl = cap->wakeup_queue_tl;
854 cap->wakeup_queue_hd = cap->wakeup_queue_tl = END_TSO_QUEUE;
855 RELEASE_LOCK(&cap->lock);
860 /* ----------------------------------------------------------------------------
861 * Check for threads blocked on BLACKHOLEs that can be woken up
862 * ------------------------------------------------------------------------- */
864 scheduleCheckBlackHoles (Capability *cap)
866 if ( blackholes_need_checking ) // check without the lock first
868 ACQUIRE_LOCK(&sched_mutex);
869 if ( blackholes_need_checking ) {
870 checkBlackHoles(cap);
871 blackholes_need_checking = rtsFalse;
873 RELEASE_LOCK(&sched_mutex);
877 /* ----------------------------------------------------------------------------
878 * Detect deadlock conditions and attempt to resolve them.
879 * ------------------------------------------------------------------------- */
882 scheduleDetectDeadlock (Capability *cap, Task *task)
885 #if defined(PARALLEL_HASKELL)
886 // ToDo: add deadlock detection in GUM (similar to THREADED_RTS) -- HWL
891 * Detect deadlock: when we have no threads to run, there are no
892 * threads blocked, waiting for I/O, or sleeping, and all the
893 * other tasks are waiting for work, we must have a deadlock of
896 if ( emptyThreadQueues(cap) )
898 #if defined(THREADED_RTS)
900 * In the threaded RTS, we only check for deadlock if there
901 * has been no activity in a complete timeslice. This means
902 * we won't eagerly start a full GC just because we don't have
903 * any threads to run currently.
905 if (recent_activity != ACTIVITY_INACTIVE) return;
908 debugTrace(DEBUG_sched, "deadlocked, forcing major GC...");
910 // Garbage collection can release some new threads due to
911 // either (a) finalizers or (b) threads resurrected because
912 // they are unreachable and will therefore be sent an
913 // exception. Any threads thus released will be immediately
915 cap = scheduleDoGC (cap, task, rtsTrue/*force major GC*/);
917 recent_activity = ACTIVITY_DONE_GC;
918 // disable timer signals (see #1623)
921 if ( !emptyRunQueue(cap) ) return;
923 #if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
924 /* If we have user-installed signal handlers, then wait
925 * for signals to arrive rather then bombing out with a
928 if ( RtsFlags.MiscFlags.install_signal_handlers && anyUserHandlers() ) {
929 debugTrace(DEBUG_sched,
930 "still deadlocked, waiting for signals...");
934 if (signals_pending()) {
935 startSignalHandlers(cap);
938 // either we have threads to run, or we were interrupted:
939 ASSERT(!emptyRunQueue(cap) || sched_state >= SCHED_INTERRUPTING);
945 #if !defined(THREADED_RTS)
946 /* Probably a real deadlock. Send the current main thread the
947 * Deadlock exception.
950 switch (task->tso->why_blocked) {
952 case BlockedOnBlackHole:
953 case BlockedOnException:
955 throwToSingleThreaded(cap, task->tso,
956 (StgClosure *)nonTermination_closure);
959 barf("deadlock: main thread blocked in a strange way");
968 /* ----------------------------------------------------------------------------
969 * Send pending messages (PARALLEL_HASKELL only)
970 * ------------------------------------------------------------------------- */
973 scheduleSendPendingMessages(void)
975 #if defined(PARALLEL_HASKELL)
977 # if defined(PAR) // global Mem.Mgmt., omit for now
978 if (PendingFetches != END_BF_QUEUE) {
983 if (RtsFlags.ParFlags.BufferTime) {
984 // if we use message buffering, we must send away all message
985 // packets which have become too old...
991 /* ----------------------------------------------------------------------------
992 * Activate spark threads (PARALLEL_HASKELL only)
993 * ------------------------------------------------------------------------- */
995 #if defined(PARALLEL_HASKELL)
997 scheduleActivateSpark(Capability *cap)
1001 /* We only want to stay here if the run queue is empty and we want some
1002 work. We try to turn a spark into a thread, and add it to the run
1003 queue, from where it will be picked up in the next iteration of the
1006 if (!emptyRunQueue(cap))
1007 /* In the threaded RTS, another task might have pushed a thread
1008 on our run queue in the meantime ? But would need a lock.. */
1011 spark = findSpark(cap); // defined in Sparks.c
1013 if (spark != NULL) {
1014 debugTrace(DEBUG_sched,
1015 "turning spark of closure %p into a thread",
1016 (StgClosure *)spark);
1017 createSparkThread(cap,spark); // defined in Sparks.c
1020 #endif // PARALLEL_HASKELL
1022 /* ----------------------------------------------------------------------------
1023 * Get work from a remote node (PARALLEL_HASKELL only)
1024 * ------------------------------------------------------------------------- */
1026 #if defined(PARALLEL_HASKELL)
1028 scheduleGetRemoteWork(Capability *cap)
1030 #if defined(PARALLEL_HASKELL)
1031 rtsBool receivedFinish = rtsFalse;
1033 // idle() , i.e. send all buffers, wait for work
1034 if (RtsFlags.ParFlags.BufferTime) {
1035 IF_PAR_DEBUG(verbose,
1036 debugBelch("...send all pending data,"));
1039 for (i=1; i<=nPEs; i++)
1040 sendImmediately(i); // send all messages away immediately
1044 /* this would be the place for fishing in GUM...
1046 if (no-earlier-fish-around)
1047 sendFish(choosePe());
1050 // Eden:just look for incoming messages (blocking receive)
1051 IF_PAR_DEBUG(verbose,
1052 debugBelch("...wait for incoming messages...\n"));
1053 processMessages(cap, &receivedFinish); // blocking receive...
1056 return receivedFinish;
1057 // reenter scheduling look after having received something
1059 #else /* !PARALLEL_HASKELL, i.e. THREADED_RTS */
1061 return rtsFalse; /* return value unused in THREADED_RTS */
1063 #endif /* PARALLEL_HASKELL */
1065 #endif // PARALLEL_HASKELL
1067 /* ----------------------------------------------------------------------------
1068 * After running a thread...
1069 * ------------------------------------------------------------------------- */
1072 schedulePostRunThread (StgTSO *t)
1074 // We have to be able to catch transactions that are in an
1075 // infinite loop as a result of seeing an inconsistent view of
1079 // [a,b] <- mapM readTVar [ta,tb]
1080 // when (a == b) loop
1082 // and a is never equal to b given a consistent view of memory.
1084 if (t -> trec != NO_TREC && t -> why_blocked == NotBlocked) {
1085 if (!stmValidateNestOfTransactions (t -> trec)) {
1086 debugTrace(DEBUG_sched | DEBUG_stm,
1087 "trec %p found wasting its time", t);
1089 // strip the stack back to the
1090 // ATOMICALLY_FRAME, aborting the (nested)
1091 // transaction, and saving the stack of any
1092 // partially-evaluated thunks on the heap.
1093 throwToSingleThreaded_(&capabilities[0], t,
1094 NULL, rtsTrue, NULL);
1096 ASSERT(get_itbl((StgClosure *)t->sp)->type == ATOMICALLY_FRAME);
1100 /* some statistics gathering in the parallel case */
1103 /* -----------------------------------------------------------------------------
1104 * Handle a thread that returned to the scheduler with ThreadHeepOverflow
1105 * -------------------------------------------------------------------------- */
1108 scheduleHandleHeapOverflow( Capability *cap, StgTSO *t )
1110 // did the task ask for a large block?
1111 if (cap->r.rHpAlloc > BLOCK_SIZE) {
1112 // if so, get one and push it on the front of the nursery.
1116 blocks = (lnat)BLOCK_ROUND_UP(cap->r.rHpAlloc) / BLOCK_SIZE;
1118 debugTrace(DEBUG_sched,
1119 "--<< thread %ld (%s) stopped: requesting a large block (size %ld)\n",
1120 (long)t->id, whatNext_strs[t->what_next], blocks);
1122 // don't do this if the nursery is (nearly) full, we'll GC first.
1123 if (cap->r.rCurrentNursery->link != NULL ||
1124 cap->r.rNursery->n_blocks == 1) { // paranoia to prevent infinite loop
1125 // if the nursery has only one block.
1128 bd = allocGroup( blocks );
1130 cap->r.rNursery->n_blocks += blocks;
1132 // link the new group into the list
1133 bd->link = cap->r.rCurrentNursery;
1134 bd->u.back = cap->r.rCurrentNursery->u.back;
1135 if (cap->r.rCurrentNursery->u.back != NULL) {
1136 cap->r.rCurrentNursery->u.back->link = bd;
1138 #if !defined(THREADED_RTS)
1139 ASSERT(g0s0->blocks == cap->r.rCurrentNursery &&
1140 g0s0 == cap->r.rNursery);
1142 cap->r.rNursery->blocks = bd;
1144 cap->r.rCurrentNursery->u.back = bd;
1146 // initialise it as a nursery block. We initialise the
1147 // step, gen_no, and flags field of *every* sub-block in
1148 // this large block, because this is easier than making
1149 // sure that we always find the block head of a large
1150 // block whenever we call Bdescr() (eg. evacuate() and
1151 // isAlive() in the GC would both have to do this, at
1155 for (x = bd; x < bd + blocks; x++) {
1156 x->step = cap->r.rNursery;
1162 // This assert can be a killer if the app is doing lots
1163 // of large block allocations.
1164 IF_DEBUG(sanity, checkNurserySanity(cap->r.rNursery));
1166 // now update the nursery to point to the new block
1167 cap->r.rCurrentNursery = bd;
1169 // we might be unlucky and have another thread get on the
1170 // run queue before us and steal the large block, but in that
1171 // case the thread will just end up requesting another large
1173 pushOnRunQueue(cap,t);
1174 return rtsFalse; /* not actually GC'ing */
1178 debugTrace(DEBUG_sched,
1179 "--<< thread %ld (%s) stopped: HeapOverflow",
1180 (long)t->id, whatNext_strs[t->what_next]);
1182 if (context_switch) {
1183 // Sometimes we miss a context switch, e.g. when calling
1184 // primitives in a tight loop, MAYBE_GC() doesn't check the
1185 // context switch flag, and we end up waiting for a GC.
1186 // See #1984, and concurrent/should_run/1984
1188 addToRunQueue(cap,t);
1190 pushOnRunQueue(cap,t);
1193 /* actual GC is done at the end of the while loop in schedule() */
1196 /* -----------------------------------------------------------------------------
1197 * Handle a thread that returned to the scheduler with ThreadStackOverflow
1198 * -------------------------------------------------------------------------- */
1201 scheduleHandleStackOverflow (Capability *cap, Task *task, StgTSO *t)
1203 debugTrace (DEBUG_sched,
1204 "--<< thread %ld (%s) stopped, StackOverflow",
1205 (long)t->id, whatNext_strs[t->what_next]);
1207 /* just adjust the stack for this thread, then pop it back
1211 /* enlarge the stack */
1212 StgTSO *new_t = threadStackOverflow(cap, t);
1214 /* The TSO attached to this Task may have moved, so update the
1217 if (task->tso == t) {
1220 pushOnRunQueue(cap,new_t);
1224 /* -----------------------------------------------------------------------------
1225 * Handle a thread that returned to the scheduler with ThreadYielding
1226 * -------------------------------------------------------------------------- */
1229 scheduleHandleYield( Capability *cap, StgTSO *t, nat prev_what_next )
1231 // Reset the context switch flag. We don't do this just before
1232 // running the thread, because that would mean we would lose ticks
1233 // during GC, which can lead to unfair scheduling (a thread hogs
1234 // the CPU because the tick always arrives during GC). This way
1235 // penalises threads that do a lot of allocation, but that seems
1236 // better than the alternative.
1239 /* put the thread back on the run queue. Then, if we're ready to
1240 * GC, check whether this is the last task to stop. If so, wake
1241 * up the GC thread. getThread will block during a GC until the
1245 if (t->what_next != prev_what_next) {
1246 debugTrace(DEBUG_sched,
1247 "--<< thread %ld (%s) stopped to switch evaluators",
1248 (long)t->id, whatNext_strs[t->what_next]);
1250 debugTrace(DEBUG_sched,
1251 "--<< thread %ld (%s) stopped, yielding",
1252 (long)t->id, whatNext_strs[t->what_next]);
1257 //debugBelch("&& Doing sanity check on yielding TSO %ld.", t->id);
1259 ASSERT(t->_link == END_TSO_QUEUE);
1261 // Shortcut if we're just switching evaluators: don't bother
1262 // doing stack squeezing (which can be expensive), just run the
1264 if (t->what_next != prev_what_next) {
1268 addToRunQueue(cap,t);
1273 /* -----------------------------------------------------------------------------
1274 * Handle a thread that returned to the scheduler with ThreadBlocked
1275 * -------------------------------------------------------------------------- */
1278 scheduleHandleThreadBlocked( StgTSO *t
1279 #if !defined(GRAN) && !defined(DEBUG)
1285 // We don't need to do anything. The thread is blocked, and it
1286 // has tidied up its stack and placed itself on whatever queue
1287 // it needs to be on.
1289 // ASSERT(t->why_blocked != NotBlocked);
1290 // Not true: for example,
1291 // - in THREADED_RTS, the thread may already have been woken
1292 // up by another Capability. This actually happens: try
1293 // conc023 +RTS -N2.
1294 // - the thread may have woken itself up already, because
1295 // threadPaused() might have raised a blocked throwTo
1296 // exception, see maybePerformBlockedException().
1299 if (traceClass(DEBUG_sched)) {
1300 debugTraceBegin("--<< thread %lu (%s) stopped: ",
1301 (unsigned long)t->id, whatNext_strs[t->what_next]);
1302 printThreadBlockage(t);
1308 /* -----------------------------------------------------------------------------
1309 * Handle a thread that returned to the scheduler with ThreadFinished
1310 * -------------------------------------------------------------------------- */
1313 scheduleHandleThreadFinished (Capability *cap STG_UNUSED, Task *task, StgTSO *t)
1315 /* Need to check whether this was a main thread, and if so,
1316 * return with the return value.
1318 * We also end up here if the thread kills itself with an
1319 * uncaught exception, see Exception.cmm.
1321 debugTrace(DEBUG_sched, "--++ thread %lu (%s) finished",
1322 (unsigned long)t->id, whatNext_strs[t->what_next]);
1325 // Check whether the thread that just completed was a bound
1326 // thread, and if so return with the result.
1328 // There is an assumption here that all thread completion goes
1329 // through this point; we need to make sure that if a thread
1330 // ends up in the ThreadKilled state, that it stays on the run
1331 // queue so it can be dealt with here.
1336 if (t->bound != task) {
1337 #if !defined(THREADED_RTS)
1338 // Must be a bound thread that is not the topmost one. Leave
1339 // it on the run queue until the stack has unwound to the
1340 // point where we can deal with this. Leaving it on the run
1341 // queue also ensures that the garbage collector knows about
1342 // this thread and its return value (it gets dropped from the
1343 // step->threads list so there's no other way to find it).
1344 appendToRunQueue(cap,t);
1347 // this cannot happen in the threaded RTS, because a
1348 // bound thread can only be run by the appropriate Task.
1349 barf("finished bound thread that isn't mine");
1353 ASSERT(task->tso == t);
1355 if (t->what_next == ThreadComplete) {
1357 // NOTE: return val is tso->sp[1] (see StgStartup.hc)
1358 *(task->ret) = (StgClosure *)task->tso->sp[1];
1360 task->stat = Success;
1363 *(task->ret) = NULL;
1365 if (sched_state >= SCHED_INTERRUPTING) {
1366 task->stat = Interrupted;
1368 task->stat = Killed;
1372 removeThreadLabel((StgWord)task->tso->id);
1374 return rtsTrue; // tells schedule() to return
1380 /* -----------------------------------------------------------------------------
1381 * Perform a heap census
1382 * -------------------------------------------------------------------------- */
1385 scheduleNeedHeapProfile( rtsBool ready_to_gc STG_UNUSED )
1387 // When we have +RTS -i0 and we're heap profiling, do a census at
1388 // every GC. This lets us get repeatable runs for debugging.
1389 if (performHeapProfile ||
1390 (RtsFlags.ProfFlags.profileInterval==0 &&
1391 RtsFlags.ProfFlags.doHeapProfile && ready_to_gc)) {
1398 /* -----------------------------------------------------------------------------
1399 * Perform a garbage collection if necessary
1400 * -------------------------------------------------------------------------- */
1403 scheduleDoGC (Capability *cap, Task *task USED_IF_THREADS, rtsBool force_major)
1406 rtsBool heap_census;
1408 static volatile StgWord waiting_for_gc;
1409 rtsBool was_waiting;
1414 // In order to GC, there must be no threads running Haskell code.
1415 // Therefore, the GC thread needs to hold *all* the capabilities,
1416 // and release them after the GC has completed.
1418 // This seems to be the simplest way: previous attempts involved
1419 // making all the threads with capabilities give up their
1420 // capabilities and sleep except for the *last* one, which
1421 // actually did the GC. But it's quite hard to arrange for all
1422 // the other tasks to sleep and stay asleep.
1425 was_waiting = cas(&waiting_for_gc, 0, 1);
1428 debugTrace(DEBUG_sched, "someone else is trying to GC...");
1429 if (cap) yieldCapability(&cap,task);
1430 } while (waiting_for_gc);
1431 return cap; // NOTE: task->cap might have changed here
1434 for (i=0; i < n_capabilities; i++) {
1435 debugTrace(DEBUG_sched, "ready_to_gc, grabbing all the capabilies (%d/%d)", i, n_capabilities);
1436 if (cap != &capabilities[i]) {
1437 Capability *pcap = &capabilities[i];
1438 // we better hope this task doesn't get migrated to
1439 // another Capability while we're waiting for this one.
1440 // It won't, because load balancing happens while we have
1441 // all the Capabilities, but even so it's a slightly
1442 // unsavoury invariant.
1445 waitForReturnCapability(&pcap, task);
1446 if (pcap != &capabilities[i]) {
1447 barf("scheduleDoGC: got the wrong capability");
1452 waiting_for_gc = rtsFalse;
1455 // so this happens periodically:
1456 if (cap) scheduleCheckBlackHoles(cap);
1458 IF_DEBUG(scheduler, printAllThreads());
1461 * We now have all the capabilities; if we're in an interrupting
1462 * state, then we should take the opportunity to delete all the
1463 * threads in the system.
1465 if (sched_state >= SCHED_INTERRUPTING) {
1466 deleteAllThreads(&capabilities[0]);
1467 sched_state = SCHED_SHUTTING_DOWN;
1470 heap_census = scheduleNeedHeapProfile(rtsTrue);
1472 /* everybody back, start the GC.
1473 * Could do it in this thread, or signal a condition var
1474 * to do it in another thread. Either way, we need to
1475 * broadcast on gc_pending_cond afterward.
1477 #if defined(THREADED_RTS)
1478 debugTrace(DEBUG_sched, "doing GC");
1480 GarbageCollect(force_major || heap_census);
1483 debugTrace(DEBUG_sched, "performing heap census");
1485 performHeapProfile = rtsFalse;
1488 #if defined(THREADED_RTS)
1489 // release our stash of capabilities.
1490 for (i = 0; i < n_capabilities; i++) {
1491 if (cap != &capabilities[i]) {
1492 task->cap = &capabilities[i];
1493 releaseCapability(&capabilities[i]);
1506 /* ---------------------------------------------------------------------------
1507 * Singleton fork(). Do not copy any running threads.
1508 * ------------------------------------------------------------------------- */
1511 forkProcess(HsStablePtr *entry
1512 #ifndef FORKPROCESS_PRIMOP_SUPPORTED
1517 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
1524 #if defined(THREADED_RTS)
1525 if (RtsFlags.ParFlags.nNodes > 1) {
1526 errorBelch("forking not supported with +RTS -N<n> greater than 1");
1527 stg_exit(EXIT_FAILURE);
1531 debugTrace(DEBUG_sched, "forking!");
1533 // ToDo: for SMP, we should probably acquire *all* the capabilities
1536 // no funny business: hold locks while we fork, otherwise if some
1537 // other thread is holding a lock when the fork happens, the data
1538 // structure protected by the lock will forever be in an
1539 // inconsistent state in the child. See also #1391.
1540 ACQUIRE_LOCK(&sched_mutex);
1541 ACQUIRE_LOCK(&cap->lock);
1542 ACQUIRE_LOCK(&cap->running_task->lock);
1546 if (pid) { // parent
1548 RELEASE_LOCK(&sched_mutex);
1549 RELEASE_LOCK(&cap->lock);
1550 RELEASE_LOCK(&cap->running_task->lock);
1552 // just return the pid
1558 #if defined(THREADED_RTS)
1559 initMutex(&sched_mutex);
1560 initMutex(&cap->lock);
1561 initMutex(&cap->running_task->lock);
1564 // Now, all OS threads except the thread that forked are
1565 // stopped. We need to stop all Haskell threads, including
1566 // those involved in foreign calls. Also we need to delete
1567 // all Tasks, because they correspond to OS threads that are
1570 for (s = 0; s < total_steps; s++) {
1571 for (t = all_steps[s].threads; t != END_TSO_QUEUE; t = next) {
1572 if (t->what_next == ThreadRelocated) {
1575 next = t->global_link;
1576 // don't allow threads to catch the ThreadKilled
1577 // exception, but we do want to raiseAsync() because these
1578 // threads may be evaluating thunks that we need later.
1579 deleteThread_(cap,t);
1584 // Empty the run queue. It seems tempting to let all the
1585 // killed threads stay on the run queue as zombies to be
1586 // cleaned up later, but some of them correspond to bound
1587 // threads for which the corresponding Task does not exist.
1588 cap->run_queue_hd = END_TSO_QUEUE;
1589 cap->run_queue_tl = END_TSO_QUEUE;
1591 // Any suspended C-calling Tasks are no more, their OS threads
1593 cap->suspended_ccalling_tasks = NULL;
1595 // Empty the threads lists. Otherwise, the garbage
1596 // collector may attempt to resurrect some of these threads.
1597 for (s = 0; s < total_steps; s++) {
1598 all_steps[s].threads = END_TSO_QUEUE;
1601 // Wipe the task list, except the current Task.
1602 ACQUIRE_LOCK(&sched_mutex);
1603 for (task = all_tasks; task != NULL; task=task->all_link) {
1604 if (task != cap->running_task) {
1605 #if defined(THREADED_RTS)
1606 initMutex(&task->lock); // see #1391
1611 RELEASE_LOCK(&sched_mutex);
1613 #if defined(THREADED_RTS)
1614 // Wipe our spare workers list, they no longer exist. New
1615 // workers will be created if necessary.
1616 cap->spare_workers = NULL;
1617 cap->returning_tasks_hd = NULL;
1618 cap->returning_tasks_tl = NULL;
1621 // On Unix, all timers are reset in the child, so we need to start
1626 cap = rts_evalStableIO(cap, entry, NULL); // run the action
1627 rts_checkSchedStatus("forkProcess",cap);
1630 hs_exit(); // clean up and exit
1631 stg_exit(EXIT_SUCCESS);
1633 #else /* !FORKPROCESS_PRIMOP_SUPPORTED */
1634 barf("forkProcess#: primop not supported on this platform, sorry!\n");
1639 /* ---------------------------------------------------------------------------
1640 * Delete all the threads in the system
1641 * ------------------------------------------------------------------------- */
1644 deleteAllThreads ( Capability *cap )
1646 // NOTE: only safe to call if we own all capabilities.
1651 debugTrace(DEBUG_sched,"deleting all threads");
1652 for (s = 0; s < total_steps; s++) {
1653 for (t = all_steps[s].threads; t != END_TSO_QUEUE; t = next) {
1654 if (t->what_next == ThreadRelocated) {
1657 next = t->global_link;
1658 deleteThread(cap,t);
1663 // The run queue now contains a bunch of ThreadKilled threads. We
1664 // must not throw these away: the main thread(s) will be in there
1665 // somewhere, and the main scheduler loop has to deal with it.
1666 // Also, the run queue is the only thing keeping these threads from
1667 // being GC'd, and we don't want the "main thread has been GC'd" panic.
1669 #if !defined(THREADED_RTS)
1670 ASSERT(blocked_queue_hd == END_TSO_QUEUE);
1671 ASSERT(sleeping_queue == END_TSO_QUEUE);
1675 /* -----------------------------------------------------------------------------
1676 Managing the suspended_ccalling_tasks list.
1677 Locks required: sched_mutex
1678 -------------------------------------------------------------------------- */
1681 suspendTask (Capability *cap, Task *task)
1683 ASSERT(task->next == NULL && task->prev == NULL);
1684 task->next = cap->suspended_ccalling_tasks;
1686 if (cap->suspended_ccalling_tasks) {
1687 cap->suspended_ccalling_tasks->prev = task;
1689 cap->suspended_ccalling_tasks = task;
1693 recoverSuspendedTask (Capability *cap, Task *task)
1696 task->prev->next = task->next;
1698 ASSERT(cap->suspended_ccalling_tasks == task);
1699 cap->suspended_ccalling_tasks = task->next;
1702 task->next->prev = task->prev;
1704 task->next = task->prev = NULL;
1707 /* ---------------------------------------------------------------------------
1708 * Suspending & resuming Haskell threads.
1710 * When making a "safe" call to C (aka _ccall_GC), the task gives back
1711 * its capability before calling the C function. This allows another
1712 * task to pick up the capability and carry on running Haskell
1713 * threads. It also means that if the C call blocks, it won't lock
1716 * The Haskell thread making the C call is put to sleep for the
1717 * duration of the call, on the susepended_ccalling_threads queue. We
1718 * give out a token to the task, which it can use to resume the thread
1719 * on return from the C function.
1720 * ------------------------------------------------------------------------- */
1723 suspendThread (StgRegTable *reg)
1730 StgWord32 saved_winerror;
1733 saved_errno = errno;
1735 saved_winerror = GetLastError();
1738 /* assume that *reg is a pointer to the StgRegTable part of a Capability.
1740 cap = regTableToCapability(reg);
1742 task = cap->running_task;
1743 tso = cap->r.rCurrentTSO;
1745 debugTrace(DEBUG_sched,
1746 "thread %lu did a safe foreign call",
1747 (unsigned long)cap->r.rCurrentTSO->id);
1749 // XXX this might not be necessary --SDM
1750 tso->what_next = ThreadRunGHC;
1752 threadPaused(cap,tso);
1754 if ((tso->flags & TSO_BLOCKEX) == 0) {
1755 tso->why_blocked = BlockedOnCCall;
1756 tso->flags |= TSO_BLOCKEX;
1757 tso->flags &= ~TSO_INTERRUPTIBLE;
1759 tso->why_blocked = BlockedOnCCall_NoUnblockExc;
1762 // Hand back capability
1763 task->suspended_tso = tso;
1765 ACQUIRE_LOCK(&cap->lock);
1767 suspendTask(cap,task);
1768 cap->in_haskell = rtsFalse;
1769 releaseCapability_(cap);
1771 RELEASE_LOCK(&cap->lock);
1773 #if defined(THREADED_RTS)
1774 /* Preparing to leave the RTS, so ensure there's a native thread/task
1775 waiting to take over.
1777 debugTrace(DEBUG_sched, "thread %lu: leaving RTS", (unsigned long)tso->id);
1780 errno = saved_errno;
1782 SetLastError(saved_winerror);
1788 resumeThread (void *task_)
1795 StgWord32 saved_winerror;
1798 saved_errno = errno;
1800 saved_winerror = GetLastError();
1804 // Wait for permission to re-enter the RTS with the result.
1805 waitForReturnCapability(&cap,task);
1806 // we might be on a different capability now... but if so, our
1807 // entry on the suspended_ccalling_tasks list will also have been
1810 // Remove the thread from the suspended list
1811 recoverSuspendedTask(cap,task);
1813 tso = task->suspended_tso;
1814 task->suspended_tso = NULL;
1815 tso->_link = END_TSO_QUEUE; // no write barrier reqd
1816 debugTrace(DEBUG_sched, "thread %lu: re-entering RTS", (unsigned long)tso->id);
1818 if (tso->why_blocked == BlockedOnCCall) {
1819 awakenBlockedExceptionQueue(cap,tso);
1820 tso->flags &= ~(TSO_BLOCKEX | TSO_INTERRUPTIBLE);
1823 /* Reset blocking status */
1824 tso->why_blocked = NotBlocked;
1826 cap->r.rCurrentTSO = tso;
1827 cap->in_haskell = rtsTrue;
1828 errno = saved_errno;
1830 SetLastError(saved_winerror);
1833 /* We might have GC'd, mark the TSO dirty again */
1836 IF_DEBUG(sanity, checkTSO(tso));
1841 /* ---------------------------------------------------------------------------
1844 * scheduleThread puts a thread on the end of the runnable queue.
1845 * This will usually be done immediately after a thread is created.
1846 * The caller of scheduleThread must create the thread using e.g.
1847 * createThread and push an appropriate closure
1848 * on this thread's stack before the scheduler is invoked.
1849 * ------------------------------------------------------------------------ */
1852 scheduleThread(Capability *cap, StgTSO *tso)
1854 // The thread goes at the *end* of the run-queue, to avoid possible
1855 // starvation of any threads already on the queue.
1856 appendToRunQueue(cap,tso);
1860 scheduleThreadOn(Capability *cap, StgWord cpu USED_IF_THREADS, StgTSO *tso)
1862 #if defined(THREADED_RTS)
1863 tso->flags |= TSO_LOCKED; // we requested explicit affinity; don't
1864 // move this thread from now on.
1865 cpu %= RtsFlags.ParFlags.nNodes;
1866 if (cpu == cap->no) {
1867 appendToRunQueue(cap,tso);
1869 migrateThreadToCapability_lock(&capabilities[cpu],tso);
1872 appendToRunQueue(cap,tso);
1877 scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability *cap)
1881 // We already created/initialised the Task
1882 task = cap->running_task;
1884 // This TSO is now a bound thread; make the Task and TSO
1885 // point to each other.
1891 task->stat = NoStatus;
1893 appendToRunQueue(cap,tso);
1895 debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)tso->id);
1897 cap = schedule(cap,task);
1899 ASSERT(task->stat != NoStatus);
1900 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
1902 debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)task->tso->id);
1906 /* ----------------------------------------------------------------------------
1908 * ------------------------------------------------------------------------- */
1910 #if defined(THREADED_RTS)
1912 workerStart(Task *task)
1916 // See startWorkerTask().
1917 ACQUIRE_LOCK(&task->lock);
1919 RELEASE_LOCK(&task->lock);
1921 // set the thread-local pointer to the Task:
1924 // schedule() runs without a lock.
1925 cap = schedule(cap,task);
1927 // On exit from schedule(), we have a Capability.
1928 releaseCapability(cap);
1929 workerTaskStop(task);
1933 /* ---------------------------------------------------------------------------
1936 * Initialise the scheduler. This resets all the queues - if the
1937 * queues contained any threads, they'll be garbage collected at the
1940 * ------------------------------------------------------------------------ */
1945 #if !defined(THREADED_RTS)
1946 blocked_queue_hd = END_TSO_QUEUE;
1947 blocked_queue_tl = END_TSO_QUEUE;
1948 sleeping_queue = END_TSO_QUEUE;
1951 blackhole_queue = END_TSO_QUEUE;
1954 sched_state = SCHED_RUNNING;
1955 recent_activity = ACTIVITY_YES;
1957 #if defined(THREADED_RTS)
1958 /* Initialise the mutex and condition variables used by
1960 initMutex(&sched_mutex);
1963 ACQUIRE_LOCK(&sched_mutex);
1965 /* A capability holds the state a native thread needs in
1966 * order to execute STG code. At least one capability is
1967 * floating around (only THREADED_RTS builds have more than one).
1973 #if defined(THREADED_RTS) || defined(PARALLEL_HASKELL)
1977 #if defined(THREADED_RTS)
1979 * Eagerly start one worker to run each Capability, except for
1980 * Capability 0. The idea is that we're probably going to start a
1981 * bound thread on Capability 0 pretty soon, so we don't want a
1982 * worker task hogging it.
1987 for (i = 1; i < n_capabilities; i++) {
1988 cap = &capabilities[i];
1989 ACQUIRE_LOCK(&cap->lock);
1990 startWorkerTask(cap, workerStart);
1991 RELEASE_LOCK(&cap->lock);
1996 trace(TRACE_sched, "start: %d capabilities", n_capabilities);
1998 RELEASE_LOCK(&sched_mutex);
2003 rtsBool wait_foreign
2004 #if !defined(THREADED_RTS)
2005 __attribute__((unused))
2008 /* see Capability.c, shutdownCapability() */
2012 #if defined(THREADED_RTS)
2013 ACQUIRE_LOCK(&sched_mutex);
2014 task = newBoundTask();
2015 RELEASE_LOCK(&sched_mutex);
2018 // If we haven't killed all the threads yet, do it now.
2019 if (sched_state < SCHED_SHUTTING_DOWN) {
2020 sched_state = SCHED_INTERRUPTING;
2021 scheduleDoGC(NULL,task,rtsFalse);
2023 sched_state = SCHED_SHUTTING_DOWN;
2025 #if defined(THREADED_RTS)
2029 for (i = 0; i < n_capabilities; i++) {
2030 shutdownCapability(&capabilities[i], task, wait_foreign);
2032 boundTaskExiting(task);
2036 freeCapability(&MainCapability);
2041 freeScheduler( void )
2044 if (n_capabilities != 1) {
2045 stgFree(capabilities);
2047 #if defined(THREADED_RTS)
2048 closeMutex(&sched_mutex);
2052 /* -----------------------------------------------------------------------------
2055 This is the interface to the garbage collector from Haskell land.
2056 We provide this so that external C code can allocate and garbage
2057 collect when called from Haskell via _ccall_GC.
2058 -------------------------------------------------------------------------- */
2061 performGC_(rtsBool force_major)
2064 // We must grab a new Task here, because the existing Task may be
2065 // associated with a particular Capability, and chained onto the
2066 // suspended_ccalling_tasks queue.
2067 ACQUIRE_LOCK(&sched_mutex);
2068 task = newBoundTask();
2069 RELEASE_LOCK(&sched_mutex);
2070 scheduleDoGC(NULL,task,force_major);
2071 boundTaskExiting(task);
2077 performGC_(rtsFalse);
2081 performMajorGC(void)
2083 performGC_(rtsTrue);
2086 /* -----------------------------------------------------------------------------
2089 If the thread has reached its maximum stack size, then raise the
2090 StackOverflow exception in the offending thread. Otherwise
2091 relocate the TSO into a larger chunk of memory and adjust its stack
2093 -------------------------------------------------------------------------- */
2096 threadStackOverflow(Capability *cap, StgTSO *tso)
2098 nat new_stack_size, stack_words;
2103 IF_DEBUG(sanity,checkTSO(tso));
2105 // don't allow throwTo() to modify the blocked_exceptions queue
2106 // while we are moving the TSO:
2107 lockClosure((StgClosure *)tso);
2109 if (tso->stack_size >= tso->max_stack_size && !(tso->flags & TSO_BLOCKEX)) {
2110 // NB. never raise a StackOverflow exception if the thread is
2111 // inside Control.Exceptino.block. It is impractical to protect
2112 // against stack overflow exceptions, since virtually anything
2113 // can raise one (even 'catch'), so this is the only sensible
2114 // thing to do here. See bug #767.
2116 debugTrace(DEBUG_gc,
2117 "threadStackOverflow of TSO %ld (%p): stack too large (now %ld; max is %ld)",
2118 (long)tso->id, tso, (long)tso->stack_size, (long)tso->max_stack_size);
2120 /* If we're debugging, just print out the top of the stack */
2121 printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size,
2124 // Send this thread the StackOverflow exception
2126 throwToSingleThreaded(cap, tso, (StgClosure *)stackOverflow_closure);
2130 /* Try to double the current stack size. If that takes us over the
2131 * maximum stack size for this thread, then use the maximum instead.
2132 * Finally round up so the TSO ends up as a whole number of blocks.
2134 new_stack_size = stg_min(tso->stack_size * 2, tso->max_stack_size);
2135 new_tso_size = (lnat)BLOCK_ROUND_UP(new_stack_size * sizeof(W_) +
2136 TSO_STRUCT_SIZE)/sizeof(W_);
2137 new_tso_size = round_to_mblocks(new_tso_size); /* Be MBLOCK-friendly */
2138 new_stack_size = new_tso_size - TSO_STRUCT_SIZEW;
2140 debugTrace(DEBUG_sched,
2141 "increasing stack size from %ld words to %d.",
2142 (long)tso->stack_size, new_stack_size);
2144 dest = (StgTSO *)allocateLocal(cap,new_tso_size);
2145 TICK_ALLOC_TSO(new_stack_size,0);
2147 /* copy the TSO block and the old stack into the new area */
2148 memcpy(dest,tso,TSO_STRUCT_SIZE);
2149 stack_words = tso->stack + tso->stack_size - tso->sp;
2150 new_sp = (P_)dest + new_tso_size - stack_words;
2151 memcpy(new_sp, tso->sp, stack_words * sizeof(W_));
2153 /* relocate the stack pointers... */
2155 dest->stack_size = new_stack_size;
2157 /* Mark the old TSO as relocated. We have to check for relocated
2158 * TSOs in the garbage collector and any primops that deal with TSOs.
2160 * It's important to set the sp value to just beyond the end
2161 * of the stack, so we don't attempt to scavenge any part of the
2164 tso->what_next = ThreadRelocated;
2165 setTSOLink(cap,tso,dest);
2166 tso->sp = (P_)&(tso->stack[tso->stack_size]);
2167 tso->why_blocked = NotBlocked;
2169 IF_PAR_DEBUG(verbose,
2170 debugBelch("@@ threadStackOverflow of TSO %d (now at %p): stack size increased to %ld\n",
2171 tso->id, tso, tso->stack_size);
2172 /* If we're debugging, just print out the top of the stack */
2173 printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size,
2179 IF_DEBUG(sanity,checkTSO(dest));
2181 IF_DEBUG(scheduler,printTSO(dest));
2188 threadStackUnderflow (Task *task STG_UNUSED, StgTSO *tso)
2190 bdescr *bd, *new_bd;
2191 lnat new_tso_size_w, tso_size_w;
2194 tso_size_w = tso_sizeW(tso);
2196 if (tso_size_w < MBLOCK_SIZE_W ||
2197 (nat)(tso->stack + tso->stack_size - tso->sp) > tso->stack_size / 4)
2202 // don't allow throwTo() to modify the blocked_exceptions queue
2203 // while we are moving the TSO:
2204 lockClosure((StgClosure *)tso);
2206 new_tso_size_w = round_to_mblocks(tso_size_w/2);
2208 debugTrace(DEBUG_sched, "thread %ld: reducing TSO size from %lu words to %lu",
2209 tso->id, tso_size_w, new_tso_size_w);
2211 bd = Bdescr((StgPtr)tso);
2212 new_bd = splitLargeBlock(bd, new_tso_size_w / BLOCK_SIZE_W);
2213 new_bd->free = bd->free;
2214 bd->free = bd->start + TSO_STRUCT_SIZEW;
2216 new_tso = (StgTSO *)new_bd->start;
2217 memcpy(new_tso,tso,TSO_STRUCT_SIZE);
2218 new_tso->stack_size = new_tso_size_w - TSO_STRUCT_SIZEW;
2220 tso->what_next = ThreadRelocated;
2221 tso->_link = new_tso; // no write barrier reqd: same generation
2223 // The TSO attached to this Task may have moved, so update the
2225 if (task->tso == tso) {
2226 task->tso = new_tso;
2232 IF_DEBUG(sanity,checkTSO(new_tso));
2237 /* ---------------------------------------------------------------------------
2239 - usually called inside a signal handler so it mustn't do anything fancy.
2240 ------------------------------------------------------------------------ */
2243 interruptStgRts(void)
2245 sched_state = SCHED_INTERRUPTING;
2250 /* -----------------------------------------------------------------------------
2253 This function causes at least one OS thread to wake up and run the
2254 scheduler loop. It is invoked when the RTS might be deadlocked, or
2255 an external event has arrived that may need servicing (eg. a
2256 keyboard interrupt).
2258 In the single-threaded RTS we don't do anything here; we only have
2259 one thread anyway, and the event that caused us to want to wake up
2260 will have interrupted any blocking system call in progress anyway.
2261 -------------------------------------------------------------------------- */
2266 #if defined(THREADED_RTS)
2267 // This forces the IO Manager thread to wakeup, which will
2268 // in turn ensure that some OS thread wakes up and runs the
2269 // scheduler loop, which will cause a GC and deadlock check.
2274 /* -----------------------------------------------------------------------------
2277 * Check the blackhole_queue for threads that can be woken up. We do
2278 * this periodically: before every GC, and whenever the run queue is
2281 * An elegant solution might be to just wake up all the blocked
2282 * threads with awakenBlockedQueue occasionally: they'll go back to
2283 * sleep again if the object is still a BLACKHOLE. Unfortunately this
2284 * doesn't give us a way to tell whether we've actually managed to
2285 * wake up any threads, so we would be busy-waiting.
2287 * -------------------------------------------------------------------------- */
2290 checkBlackHoles (Capability *cap)
2293 rtsBool any_woke_up = rtsFalse;
2296 // blackhole_queue is global:
2297 ASSERT_LOCK_HELD(&sched_mutex);
2299 debugTrace(DEBUG_sched, "checking threads blocked on black holes");
2301 // ASSUMES: sched_mutex
2302 prev = &blackhole_queue;
2303 t = blackhole_queue;
2304 while (t != END_TSO_QUEUE) {
2305 ASSERT(t->why_blocked == BlockedOnBlackHole);
2306 type = get_itbl(UNTAG_CLOSURE(t->block_info.closure))->type;
2307 if (type != BLACKHOLE && type != CAF_BLACKHOLE) {
2308 IF_DEBUG(sanity,checkTSO(t));
2309 t = unblockOne(cap, t);
2310 // urk, the threads migrate to the current capability
2311 // here, but we'd like to keep them on the original one.
2313 any_woke_up = rtsTrue;
2323 /* -----------------------------------------------------------------------------
2326 This is used for interruption (^C) and forking, and corresponds to
2327 raising an exception but without letting the thread catch the
2329 -------------------------------------------------------------------------- */
2332 deleteThread (Capability *cap, StgTSO *tso)
2334 // NOTE: must only be called on a TSO that we have exclusive
2335 // access to, because we will call throwToSingleThreaded() below.
2336 // The TSO must be on the run queue of the Capability we own, or
2337 // we must own all Capabilities.
2339 if (tso->why_blocked != BlockedOnCCall &&
2340 tso->why_blocked != BlockedOnCCall_NoUnblockExc) {
2341 throwToSingleThreaded(cap,tso,NULL);
2345 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
2347 deleteThread_(Capability *cap, StgTSO *tso)
2348 { // for forkProcess only:
2349 // like deleteThread(), but we delete threads in foreign calls, too.
2351 if (tso->why_blocked == BlockedOnCCall ||
2352 tso->why_blocked == BlockedOnCCall_NoUnblockExc) {
2353 unblockOne(cap,tso);
2354 tso->what_next = ThreadKilled;
2356 deleteThread(cap,tso);
2361 /* -----------------------------------------------------------------------------
2362 raiseExceptionHelper
2364 This function is called by the raise# primitve, just so that we can
2365 move some of the tricky bits of raising an exception from C-- into
2366 C. Who knows, it might be a useful re-useable thing here too.
2367 -------------------------------------------------------------------------- */
2370 raiseExceptionHelper (StgRegTable *reg, StgTSO *tso, StgClosure *exception)
2372 Capability *cap = regTableToCapability(reg);
2373 StgThunk *raise_closure = NULL;
2375 StgRetInfoTable *info;
2377 // This closure represents the expression 'raise# E' where E
2378 // is the exception raise. It is used to overwrite all the
2379 // thunks which are currently under evaluataion.
2382 // OLD COMMENT (we don't have MIN_UPD_SIZE now):
2383 // LDV profiling: stg_raise_info has THUNK as its closure
2384 // type. Since a THUNK takes at least MIN_UPD_SIZE words in its
2385 // payload, MIN_UPD_SIZE is more approprate than 1. It seems that
2386 // 1 does not cause any problem unless profiling is performed.
2387 // However, when LDV profiling goes on, we need to linearly scan
2388 // small object pool, where raise_closure is stored, so we should
2389 // use MIN_UPD_SIZE.
2391 // raise_closure = (StgClosure *)RET_STGCALL1(P_,allocate,
2392 // sizeofW(StgClosure)+1);
2396 // Walk up the stack, looking for the catch frame. On the way,
2397 // we update any closures pointed to from update frames with the
2398 // raise closure that we just built.
2402 info = get_ret_itbl((StgClosure *)p);
2403 next = p + stack_frame_sizeW((StgClosure *)p);
2404 switch (info->i.type) {
2407 // Only create raise_closure if we need to.
2408 if (raise_closure == NULL) {
2410 (StgThunk *)allocateLocal(cap,sizeofW(StgThunk)+1);
2411 SET_HDR(raise_closure, &stg_raise_info, CCCS);
2412 raise_closure->payload[0] = exception;
2414 UPD_IND(((StgUpdateFrame *)p)->updatee,(StgClosure *)raise_closure);
2418 case ATOMICALLY_FRAME:
2419 debugTrace(DEBUG_stm, "found ATOMICALLY_FRAME at %p", p);
2421 return ATOMICALLY_FRAME;
2427 case CATCH_STM_FRAME:
2428 debugTrace(DEBUG_stm, "found CATCH_STM_FRAME at %p", p);
2430 return CATCH_STM_FRAME;
2436 case CATCH_RETRY_FRAME:
2445 /* -----------------------------------------------------------------------------
2446 findRetryFrameHelper
2448 This function is called by the retry# primitive. It traverses the stack
2449 leaving tso->sp referring to the frame which should handle the retry.
2451 This should either be a CATCH_RETRY_FRAME (if the retry# is within an orElse#)
2452 or should be a ATOMICALLY_FRAME (if the retry# reaches the top level).
2454 We skip CATCH_STM_FRAMEs (aborting and rolling back the nested tx that they
2455 create) because retries are not considered to be exceptions, despite the
2456 similar implementation.
2458 We should not expect to see CATCH_FRAME or STOP_FRAME because those should
2459 not be created within memory transactions.
2460 -------------------------------------------------------------------------- */
2463 findRetryFrameHelper (StgTSO *tso)
2466 StgRetInfoTable *info;
2470 info = get_ret_itbl((StgClosure *)p);
2471 next = p + stack_frame_sizeW((StgClosure *)p);
2472 switch (info->i.type) {
2474 case ATOMICALLY_FRAME:
2475 debugTrace(DEBUG_stm,
2476 "found ATOMICALLY_FRAME at %p during retry", p);
2478 return ATOMICALLY_FRAME;
2480 case CATCH_RETRY_FRAME:
2481 debugTrace(DEBUG_stm,
2482 "found CATCH_RETRY_FRAME at %p during retrry", p);
2484 return CATCH_RETRY_FRAME;
2486 case CATCH_STM_FRAME: {
2487 StgTRecHeader *trec = tso -> trec;
2488 StgTRecHeader *outer = stmGetEnclosingTRec(trec);
2489 debugTrace(DEBUG_stm,
2490 "found CATCH_STM_FRAME at %p during retry", p);
2491 debugTrace(DEBUG_stm, "trec=%p outer=%p", trec, outer);
2492 stmAbortTransaction(tso -> cap, trec);
2493 stmFreeAbortedTRec(tso -> cap, trec);
2494 tso -> trec = outer;
2501 ASSERT(info->i.type != CATCH_FRAME);
2502 ASSERT(info->i.type != STOP_FRAME);
2509 /* -----------------------------------------------------------------------------
2510 resurrectThreads is called after garbage collection on the list of
2511 threads found to be garbage. Each of these threads will be woken
2512 up and sent a signal: BlockedOnDeadMVar if the thread was blocked
2513 on an MVar, or NonTermination if the thread was blocked on a Black
2516 Locks: assumes we hold *all* the capabilities.
2517 -------------------------------------------------------------------------- */
2520 resurrectThreads (StgTSO *threads)
2526 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2527 next = tso->global_link;
2529 step = Bdescr((P_)tso)->step;
2530 tso->global_link = step->threads;
2531 step->threads = tso;
2533 debugTrace(DEBUG_sched, "resurrecting thread %lu", (unsigned long)tso->id);
2535 // Wake up the thread on the Capability it was last on
2538 switch (tso->why_blocked) {
2540 case BlockedOnException:
2541 /* Called by GC - sched_mutex lock is currently held. */
2542 throwToSingleThreaded(cap, tso,
2543 (StgClosure *)blockedOnDeadMVar_closure);
2545 case BlockedOnBlackHole:
2546 throwToSingleThreaded(cap, tso,
2547 (StgClosure *)nonTermination_closure);
2550 throwToSingleThreaded(cap, tso,
2551 (StgClosure *)blockedIndefinitely_closure);
2554 /* This might happen if the thread was blocked on a black hole
2555 * belonging to a thread that we've just woken up (raiseAsync
2556 * can wake up threads, remember...).
2560 barf("resurrectThreads: thread blocked in a strange way");
2565 /* -----------------------------------------------------------------------------
2566 performPendingThrowTos is called after garbage collection, and
2567 passed a list of threads that were found to have pending throwTos
2568 (tso->blocked_exceptions was not empty), and were blocked.
2569 Normally this doesn't happen, because we would deliver the
2570 exception directly if the target thread is blocked, but there are
2571 small windows where it might occur on a multiprocessor (see
2574 NB. we must be holding all the capabilities at this point, just
2575 like resurrectThreads().
2576 -------------------------------------------------------------------------- */
2579 performPendingThrowTos (StgTSO *threads)
2585 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2586 next = tso->global_link;
2588 step = Bdescr((P_)tso)->step;
2589 tso->global_link = step->threads;
2590 step->threads = tso;
2592 debugTrace(DEBUG_sched, "performing blocked throwTo to thread %lu", (unsigned long)tso->id);
2595 maybePerformBlockedException(cap, tso);