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 /* extern static volatile StgWord waiting_for_gc;
1409 lives inside capability.c */
1410 rtsBool was_waiting;
1415 // In order to GC, there must be no threads running Haskell code.
1416 // Therefore, the GC thread needs to hold *all* the capabilities,
1417 // and release them after the GC has completed.
1419 // This seems to be the simplest way: previous attempts involved
1420 // making all the threads with capabilities give up their
1421 // capabilities and sleep except for the *last* one, which
1422 // actually did the GC. But it's quite hard to arrange for all
1423 // the other tasks to sleep and stay asleep.
1426 /* Other capabilities are prevented from running yet more Haskell
1427 threads if waiting_for_gc is set. Tested inside
1428 yieldCapability() and releaseCapability() in Capability.c */
1430 was_waiting = cas(&waiting_for_gc, 0, 1);
1433 debugTrace(DEBUG_sched, "someone else is trying to GC...");
1434 if (cap) yieldCapability(&cap,task);
1435 } while (waiting_for_gc);
1436 return cap; // NOTE: task->cap might have changed here
1439 for (i=0; i < n_capabilities; i++) {
1440 debugTrace(DEBUG_sched, "ready_to_gc, grabbing all the capabilies (%d/%d)", i, n_capabilities);
1441 if (cap != &capabilities[i]) {
1442 Capability *pcap = &capabilities[i];
1443 // we better hope this task doesn't get migrated to
1444 // another Capability while we're waiting for this one.
1445 // It won't, because load balancing happens while we have
1446 // all the Capabilities, but even so it's a slightly
1447 // unsavoury invariant.
1450 waitForReturnCapability(&pcap, task);
1451 if (pcap != &capabilities[i]) {
1452 barf("scheduleDoGC: got the wrong capability");
1457 waiting_for_gc = rtsFalse;
1460 // so this happens periodically:
1461 if (cap) scheduleCheckBlackHoles(cap);
1463 IF_DEBUG(scheduler, printAllThreads());
1466 * We now have all the capabilities; if we're in an interrupting
1467 * state, then we should take the opportunity to delete all the
1468 * threads in the system.
1470 if (sched_state >= SCHED_INTERRUPTING) {
1471 deleteAllThreads(&capabilities[0]);
1472 sched_state = SCHED_SHUTTING_DOWN;
1475 heap_census = scheduleNeedHeapProfile(rtsTrue);
1477 /* everybody back, start the GC.
1478 * Could do it in this thread, or signal a condition var
1479 * to do it in another thread. Either way, we need to
1480 * broadcast on gc_pending_cond afterward.
1482 #if defined(THREADED_RTS)
1483 debugTrace(DEBUG_sched, "doing GC");
1485 GarbageCollect(force_major || heap_census);
1488 debugTrace(DEBUG_sched, "performing heap census");
1490 performHeapProfile = rtsFalse;
1493 #if defined(THREADED_RTS)
1494 // release our stash of capabilities.
1495 for (i = 0; i < n_capabilities; i++) {
1496 if (cap != &capabilities[i]) {
1497 task->cap = &capabilities[i];
1498 releaseCapability(&capabilities[i]);
1511 /* ---------------------------------------------------------------------------
1512 * Singleton fork(). Do not copy any running threads.
1513 * ------------------------------------------------------------------------- */
1516 forkProcess(HsStablePtr *entry
1517 #ifndef FORKPROCESS_PRIMOP_SUPPORTED
1522 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
1529 #if defined(THREADED_RTS)
1530 if (RtsFlags.ParFlags.nNodes > 1) {
1531 errorBelch("forking not supported with +RTS -N<n> greater than 1");
1532 stg_exit(EXIT_FAILURE);
1536 debugTrace(DEBUG_sched, "forking!");
1538 // ToDo: for SMP, we should probably acquire *all* the capabilities
1541 // no funny business: hold locks while we fork, otherwise if some
1542 // other thread is holding a lock when the fork happens, the data
1543 // structure protected by the lock will forever be in an
1544 // inconsistent state in the child. See also #1391.
1545 ACQUIRE_LOCK(&sched_mutex);
1546 ACQUIRE_LOCK(&cap->lock);
1547 ACQUIRE_LOCK(&cap->running_task->lock);
1551 if (pid) { // parent
1553 RELEASE_LOCK(&sched_mutex);
1554 RELEASE_LOCK(&cap->lock);
1555 RELEASE_LOCK(&cap->running_task->lock);
1557 // just return the pid
1563 #if defined(THREADED_RTS)
1564 initMutex(&sched_mutex);
1565 initMutex(&cap->lock);
1566 initMutex(&cap->running_task->lock);
1569 // Now, all OS threads except the thread that forked are
1570 // stopped. We need to stop all Haskell threads, including
1571 // those involved in foreign calls. Also we need to delete
1572 // all Tasks, because they correspond to OS threads that are
1575 for (s = 0; s < total_steps; s++) {
1576 for (t = all_steps[s].threads; t != END_TSO_QUEUE; t = next) {
1577 if (t->what_next == ThreadRelocated) {
1580 next = t->global_link;
1581 // don't allow threads to catch the ThreadKilled
1582 // exception, but we do want to raiseAsync() because these
1583 // threads may be evaluating thunks that we need later.
1584 deleteThread_(cap,t);
1589 // Empty the run queue. It seems tempting to let all the
1590 // killed threads stay on the run queue as zombies to be
1591 // cleaned up later, but some of them correspond to bound
1592 // threads for which the corresponding Task does not exist.
1593 cap->run_queue_hd = END_TSO_QUEUE;
1594 cap->run_queue_tl = END_TSO_QUEUE;
1596 // Any suspended C-calling Tasks are no more, their OS threads
1598 cap->suspended_ccalling_tasks = NULL;
1600 // Empty the threads lists. Otherwise, the garbage
1601 // collector may attempt to resurrect some of these threads.
1602 for (s = 0; s < total_steps; s++) {
1603 all_steps[s].threads = END_TSO_QUEUE;
1606 // Wipe the task list, except the current Task.
1607 ACQUIRE_LOCK(&sched_mutex);
1608 for (task = all_tasks; task != NULL; task=task->all_link) {
1609 if (task != cap->running_task) {
1610 #if defined(THREADED_RTS)
1611 initMutex(&task->lock); // see #1391
1616 RELEASE_LOCK(&sched_mutex);
1618 #if defined(THREADED_RTS)
1619 // Wipe our spare workers list, they no longer exist. New
1620 // workers will be created if necessary.
1621 cap->spare_workers = NULL;
1622 cap->returning_tasks_hd = NULL;
1623 cap->returning_tasks_tl = NULL;
1626 // On Unix, all timers are reset in the child, so we need to start
1631 cap = rts_evalStableIO(cap, entry, NULL); // run the action
1632 rts_checkSchedStatus("forkProcess",cap);
1635 hs_exit(); // clean up and exit
1636 stg_exit(EXIT_SUCCESS);
1638 #else /* !FORKPROCESS_PRIMOP_SUPPORTED */
1639 barf("forkProcess#: primop not supported on this platform, sorry!\n");
1644 /* ---------------------------------------------------------------------------
1645 * Delete all the threads in the system
1646 * ------------------------------------------------------------------------- */
1649 deleteAllThreads ( Capability *cap )
1651 // NOTE: only safe to call if we own all capabilities.
1656 debugTrace(DEBUG_sched,"deleting all threads");
1657 for (s = 0; s < total_steps; s++) {
1658 for (t = all_steps[s].threads; t != END_TSO_QUEUE; t = next) {
1659 if (t->what_next == ThreadRelocated) {
1662 next = t->global_link;
1663 deleteThread(cap,t);
1668 // The run queue now contains a bunch of ThreadKilled threads. We
1669 // must not throw these away: the main thread(s) will be in there
1670 // somewhere, and the main scheduler loop has to deal with it.
1671 // Also, the run queue is the only thing keeping these threads from
1672 // being GC'd, and we don't want the "main thread has been GC'd" panic.
1674 #if !defined(THREADED_RTS)
1675 ASSERT(blocked_queue_hd == END_TSO_QUEUE);
1676 ASSERT(sleeping_queue == END_TSO_QUEUE);
1680 /* -----------------------------------------------------------------------------
1681 Managing the suspended_ccalling_tasks list.
1682 Locks required: sched_mutex
1683 -------------------------------------------------------------------------- */
1686 suspendTask (Capability *cap, Task *task)
1688 ASSERT(task->next == NULL && task->prev == NULL);
1689 task->next = cap->suspended_ccalling_tasks;
1691 if (cap->suspended_ccalling_tasks) {
1692 cap->suspended_ccalling_tasks->prev = task;
1694 cap->suspended_ccalling_tasks = task;
1698 recoverSuspendedTask (Capability *cap, Task *task)
1701 task->prev->next = task->next;
1703 ASSERT(cap->suspended_ccalling_tasks == task);
1704 cap->suspended_ccalling_tasks = task->next;
1707 task->next->prev = task->prev;
1709 task->next = task->prev = NULL;
1712 /* ---------------------------------------------------------------------------
1713 * Suspending & resuming Haskell threads.
1715 * When making a "safe" call to C (aka _ccall_GC), the task gives back
1716 * its capability before calling the C function. This allows another
1717 * task to pick up the capability and carry on running Haskell
1718 * threads. It also means that if the C call blocks, it won't lock
1721 * The Haskell thread making the C call is put to sleep for the
1722 * duration of the call, on the susepended_ccalling_threads queue. We
1723 * give out a token to the task, which it can use to resume the thread
1724 * on return from the C function.
1725 * ------------------------------------------------------------------------- */
1728 suspendThread (StgRegTable *reg)
1735 StgWord32 saved_winerror;
1738 saved_errno = errno;
1740 saved_winerror = GetLastError();
1743 /* assume that *reg is a pointer to the StgRegTable part of a Capability.
1745 cap = regTableToCapability(reg);
1747 task = cap->running_task;
1748 tso = cap->r.rCurrentTSO;
1750 debugTrace(DEBUG_sched,
1751 "thread %lu did a safe foreign call",
1752 (unsigned long)cap->r.rCurrentTSO->id);
1754 // XXX this might not be necessary --SDM
1755 tso->what_next = ThreadRunGHC;
1757 threadPaused(cap,tso);
1759 if ((tso->flags & TSO_BLOCKEX) == 0) {
1760 tso->why_blocked = BlockedOnCCall;
1761 tso->flags |= TSO_BLOCKEX;
1762 tso->flags &= ~TSO_INTERRUPTIBLE;
1764 tso->why_blocked = BlockedOnCCall_NoUnblockExc;
1767 // Hand back capability
1768 task->suspended_tso = tso;
1770 ACQUIRE_LOCK(&cap->lock);
1772 suspendTask(cap,task);
1773 cap->in_haskell = rtsFalse;
1774 releaseCapability_(cap);
1776 RELEASE_LOCK(&cap->lock);
1778 #if defined(THREADED_RTS)
1779 /* Preparing to leave the RTS, so ensure there's a native thread/task
1780 waiting to take over.
1782 debugTrace(DEBUG_sched, "thread %lu: leaving RTS", (unsigned long)tso->id);
1785 errno = saved_errno;
1787 SetLastError(saved_winerror);
1793 resumeThread (void *task_)
1800 StgWord32 saved_winerror;
1803 saved_errno = errno;
1805 saved_winerror = GetLastError();
1809 // Wait for permission to re-enter the RTS with the result.
1810 waitForReturnCapability(&cap,task);
1811 // we might be on a different capability now... but if so, our
1812 // entry on the suspended_ccalling_tasks list will also have been
1815 // Remove the thread from the suspended list
1816 recoverSuspendedTask(cap,task);
1818 tso = task->suspended_tso;
1819 task->suspended_tso = NULL;
1820 tso->_link = END_TSO_QUEUE; // no write barrier reqd
1821 debugTrace(DEBUG_sched, "thread %lu: re-entering RTS", (unsigned long)tso->id);
1823 if (tso->why_blocked == BlockedOnCCall) {
1824 awakenBlockedExceptionQueue(cap,tso);
1825 tso->flags &= ~(TSO_BLOCKEX | TSO_INTERRUPTIBLE);
1828 /* Reset blocking status */
1829 tso->why_blocked = NotBlocked;
1831 cap->r.rCurrentTSO = tso;
1832 cap->in_haskell = rtsTrue;
1833 errno = saved_errno;
1835 SetLastError(saved_winerror);
1838 /* We might have GC'd, mark the TSO dirty again */
1841 IF_DEBUG(sanity, checkTSO(tso));
1846 /* ---------------------------------------------------------------------------
1849 * scheduleThread puts a thread on the end of the runnable queue.
1850 * This will usually be done immediately after a thread is created.
1851 * The caller of scheduleThread must create the thread using e.g.
1852 * createThread and push an appropriate closure
1853 * on this thread's stack before the scheduler is invoked.
1854 * ------------------------------------------------------------------------ */
1857 scheduleThread(Capability *cap, StgTSO *tso)
1859 // The thread goes at the *end* of the run-queue, to avoid possible
1860 // starvation of any threads already on the queue.
1861 appendToRunQueue(cap,tso);
1865 scheduleThreadOn(Capability *cap, StgWord cpu USED_IF_THREADS, StgTSO *tso)
1867 #if defined(THREADED_RTS)
1868 tso->flags |= TSO_LOCKED; // we requested explicit affinity; don't
1869 // move this thread from now on.
1870 cpu %= RtsFlags.ParFlags.nNodes;
1871 if (cpu == cap->no) {
1872 appendToRunQueue(cap,tso);
1874 wakeupThreadOnCapability(cap, &capabilities[cpu], tso);
1877 appendToRunQueue(cap,tso);
1882 scheduleWaitThread (StgTSO* tso, /*[out]*/HaskellObj* ret, Capability *cap)
1886 // We already created/initialised the Task
1887 task = cap->running_task;
1889 // This TSO is now a bound thread; make the Task and TSO
1890 // point to each other.
1896 task->stat = NoStatus;
1898 appendToRunQueue(cap,tso);
1900 debugTrace(DEBUG_sched, "new bound thread (%lu)", (unsigned long)tso->id);
1902 cap = schedule(cap,task);
1904 ASSERT(task->stat != NoStatus);
1905 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
1907 debugTrace(DEBUG_sched, "bound thread (%lu) finished", (unsigned long)task->tso->id);
1911 /* ----------------------------------------------------------------------------
1913 * ------------------------------------------------------------------------- */
1915 #if defined(THREADED_RTS)
1917 workerStart(Task *task)
1921 // See startWorkerTask().
1922 ACQUIRE_LOCK(&task->lock);
1924 RELEASE_LOCK(&task->lock);
1926 // set the thread-local pointer to the Task:
1929 // schedule() runs without a lock.
1930 cap = schedule(cap,task);
1932 // On exit from schedule(), we have a Capability.
1933 releaseCapability(cap);
1934 workerTaskStop(task);
1938 /* ---------------------------------------------------------------------------
1941 * Initialise the scheduler. This resets all the queues - if the
1942 * queues contained any threads, they'll be garbage collected at the
1945 * ------------------------------------------------------------------------ */
1950 #if !defined(THREADED_RTS)
1951 blocked_queue_hd = END_TSO_QUEUE;
1952 blocked_queue_tl = END_TSO_QUEUE;
1953 sleeping_queue = END_TSO_QUEUE;
1956 blackhole_queue = END_TSO_QUEUE;
1959 sched_state = SCHED_RUNNING;
1960 recent_activity = ACTIVITY_YES;
1962 #if defined(THREADED_RTS)
1963 /* Initialise the mutex and condition variables used by
1965 initMutex(&sched_mutex);
1968 ACQUIRE_LOCK(&sched_mutex);
1970 /* A capability holds the state a native thread needs in
1971 * order to execute STG code. At least one capability is
1972 * floating around (only THREADED_RTS builds have more than one).
1978 #if defined(THREADED_RTS) || defined(PARALLEL_HASKELL)
1982 #if defined(THREADED_RTS)
1984 * Eagerly start one worker to run each Capability, except for
1985 * Capability 0. The idea is that we're probably going to start a
1986 * bound thread on Capability 0 pretty soon, so we don't want a
1987 * worker task hogging it.
1992 for (i = 1; i < n_capabilities; i++) {
1993 cap = &capabilities[i];
1994 ACQUIRE_LOCK(&cap->lock);
1995 startWorkerTask(cap, workerStart);
1996 RELEASE_LOCK(&cap->lock);
2001 trace(TRACE_sched, "start: %d capabilities", n_capabilities);
2003 RELEASE_LOCK(&sched_mutex);
2008 rtsBool wait_foreign
2009 #if !defined(THREADED_RTS)
2010 __attribute__((unused))
2013 /* see Capability.c, shutdownCapability() */
2017 #if defined(THREADED_RTS)
2018 ACQUIRE_LOCK(&sched_mutex);
2019 task = newBoundTask();
2020 RELEASE_LOCK(&sched_mutex);
2023 // If we haven't killed all the threads yet, do it now.
2024 if (sched_state < SCHED_SHUTTING_DOWN) {
2025 sched_state = SCHED_INTERRUPTING;
2026 scheduleDoGC(NULL,task,rtsFalse);
2028 sched_state = SCHED_SHUTTING_DOWN;
2030 #if defined(THREADED_RTS)
2034 for (i = 0; i < n_capabilities; i++) {
2035 shutdownCapability(&capabilities[i], task, wait_foreign);
2037 boundTaskExiting(task);
2041 freeCapability(&MainCapability);
2046 freeScheduler( void )
2049 if (n_capabilities != 1) {
2050 stgFree(capabilities);
2052 #if defined(THREADED_RTS)
2053 closeMutex(&sched_mutex);
2057 /* -----------------------------------------------------------------------------
2060 This is the interface to the garbage collector from Haskell land.
2061 We provide this so that external C code can allocate and garbage
2062 collect when called from Haskell via _ccall_GC.
2063 -------------------------------------------------------------------------- */
2066 performGC_(rtsBool force_major)
2069 // We must grab a new Task here, because the existing Task may be
2070 // associated with a particular Capability, and chained onto the
2071 // suspended_ccalling_tasks queue.
2072 ACQUIRE_LOCK(&sched_mutex);
2073 task = newBoundTask();
2074 RELEASE_LOCK(&sched_mutex);
2075 scheduleDoGC(NULL,task,force_major);
2076 boundTaskExiting(task);
2082 performGC_(rtsFalse);
2086 performMajorGC(void)
2088 performGC_(rtsTrue);
2091 /* -----------------------------------------------------------------------------
2094 If the thread has reached its maximum stack size, then raise the
2095 StackOverflow exception in the offending thread. Otherwise
2096 relocate the TSO into a larger chunk of memory and adjust its stack
2098 -------------------------------------------------------------------------- */
2101 threadStackOverflow(Capability *cap, StgTSO *tso)
2103 nat new_stack_size, stack_words;
2108 IF_DEBUG(sanity,checkTSO(tso));
2110 // don't allow throwTo() to modify the blocked_exceptions queue
2111 // while we are moving the TSO:
2112 lockClosure((StgClosure *)tso);
2114 if (tso->stack_size >= tso->max_stack_size && !(tso->flags & TSO_BLOCKEX)) {
2115 // NB. never raise a StackOverflow exception if the thread is
2116 // inside Control.Exceptino.block. It is impractical to protect
2117 // against stack overflow exceptions, since virtually anything
2118 // can raise one (even 'catch'), so this is the only sensible
2119 // thing to do here. See bug #767.
2121 debugTrace(DEBUG_gc,
2122 "threadStackOverflow of TSO %ld (%p): stack too large (now %ld; max is %ld)",
2123 (long)tso->id, tso, (long)tso->stack_size, (long)tso->max_stack_size);
2125 /* If we're debugging, just print out the top of the stack */
2126 printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size,
2129 // Send this thread the StackOverflow exception
2131 throwToSingleThreaded(cap, tso, (StgClosure *)stackOverflow_closure);
2135 /* Try to double the current stack size. If that takes us over the
2136 * maximum stack size for this thread, then use the maximum instead.
2137 * Finally round up so the TSO ends up as a whole number of blocks.
2139 new_stack_size = stg_min(tso->stack_size * 2, tso->max_stack_size);
2140 new_tso_size = (lnat)BLOCK_ROUND_UP(new_stack_size * sizeof(W_) +
2141 TSO_STRUCT_SIZE)/sizeof(W_);
2142 new_tso_size = round_to_mblocks(new_tso_size); /* Be MBLOCK-friendly */
2143 new_stack_size = new_tso_size - TSO_STRUCT_SIZEW;
2145 debugTrace(DEBUG_sched,
2146 "increasing stack size from %ld words to %d.",
2147 (long)tso->stack_size, new_stack_size);
2149 dest = (StgTSO *)allocateLocal(cap,new_tso_size);
2150 TICK_ALLOC_TSO(new_stack_size,0);
2152 /* copy the TSO block and the old stack into the new area */
2153 memcpy(dest,tso,TSO_STRUCT_SIZE);
2154 stack_words = tso->stack + tso->stack_size - tso->sp;
2155 new_sp = (P_)dest + new_tso_size - stack_words;
2156 memcpy(new_sp, tso->sp, stack_words * sizeof(W_));
2158 /* relocate the stack pointers... */
2160 dest->stack_size = new_stack_size;
2162 /* Mark the old TSO as relocated. We have to check for relocated
2163 * TSOs in the garbage collector and any primops that deal with TSOs.
2165 * It's important to set the sp value to just beyond the end
2166 * of the stack, so we don't attempt to scavenge any part of the
2169 tso->what_next = ThreadRelocated;
2170 setTSOLink(cap,tso,dest);
2171 tso->sp = (P_)&(tso->stack[tso->stack_size]);
2172 tso->why_blocked = NotBlocked;
2174 IF_PAR_DEBUG(verbose,
2175 debugBelch("@@ threadStackOverflow of TSO %d (now at %p): stack size increased to %ld\n",
2176 tso->id, tso, tso->stack_size);
2177 /* If we're debugging, just print out the top of the stack */
2178 printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size,
2184 IF_DEBUG(sanity,checkTSO(dest));
2186 IF_DEBUG(scheduler,printTSO(dest));
2193 threadStackUnderflow (Task *task STG_UNUSED, StgTSO *tso)
2195 bdescr *bd, *new_bd;
2196 lnat new_tso_size_w, tso_size_w;
2199 tso_size_w = tso_sizeW(tso);
2201 if (tso_size_w < MBLOCK_SIZE_W ||
2202 (nat)(tso->stack + tso->stack_size - tso->sp) > tso->stack_size / 4)
2207 // don't allow throwTo() to modify the blocked_exceptions queue
2208 // while we are moving the TSO:
2209 lockClosure((StgClosure *)tso);
2211 new_tso_size_w = round_to_mblocks(tso_size_w/2);
2213 debugTrace(DEBUG_sched, "thread %ld: reducing TSO size from %lu words to %lu",
2214 tso->id, tso_size_w, new_tso_size_w);
2216 bd = Bdescr((StgPtr)tso);
2217 new_bd = splitLargeBlock(bd, new_tso_size_w / BLOCK_SIZE_W);
2218 new_bd->free = bd->free;
2219 bd->free = bd->start + TSO_STRUCT_SIZEW;
2221 new_tso = (StgTSO *)new_bd->start;
2222 memcpy(new_tso,tso,TSO_STRUCT_SIZE);
2223 new_tso->stack_size = new_tso_size_w - TSO_STRUCT_SIZEW;
2225 tso->what_next = ThreadRelocated;
2226 tso->_link = new_tso; // no write barrier reqd: same generation
2228 // The TSO attached to this Task may have moved, so update the
2230 if (task->tso == tso) {
2231 task->tso = new_tso;
2237 IF_DEBUG(sanity,checkTSO(new_tso));
2242 /* ---------------------------------------------------------------------------
2244 - usually called inside a signal handler so it mustn't do anything fancy.
2245 ------------------------------------------------------------------------ */
2248 interruptStgRts(void)
2250 sched_state = SCHED_INTERRUPTING;
2255 /* -----------------------------------------------------------------------------
2258 This function causes at least one OS thread to wake up and run the
2259 scheduler loop. It is invoked when the RTS might be deadlocked, or
2260 an external event has arrived that may need servicing (eg. a
2261 keyboard interrupt).
2263 In the single-threaded RTS we don't do anything here; we only have
2264 one thread anyway, and the event that caused us to want to wake up
2265 will have interrupted any blocking system call in progress anyway.
2266 -------------------------------------------------------------------------- */
2271 #if defined(THREADED_RTS)
2272 // This forces the IO Manager thread to wakeup, which will
2273 // in turn ensure that some OS thread wakes up and runs the
2274 // scheduler loop, which will cause a GC and deadlock check.
2279 /* -----------------------------------------------------------------------------
2282 * Check the blackhole_queue for threads that can be woken up. We do
2283 * this periodically: before every GC, and whenever the run queue is
2286 * An elegant solution might be to just wake up all the blocked
2287 * threads with awakenBlockedQueue occasionally: they'll go back to
2288 * sleep again if the object is still a BLACKHOLE. Unfortunately this
2289 * doesn't give us a way to tell whether we've actually managed to
2290 * wake up any threads, so we would be busy-waiting.
2292 * -------------------------------------------------------------------------- */
2295 checkBlackHoles (Capability *cap)
2298 rtsBool any_woke_up = rtsFalse;
2301 // blackhole_queue is global:
2302 ASSERT_LOCK_HELD(&sched_mutex);
2304 debugTrace(DEBUG_sched, "checking threads blocked on black holes");
2306 // ASSUMES: sched_mutex
2307 prev = &blackhole_queue;
2308 t = blackhole_queue;
2309 while (t != END_TSO_QUEUE) {
2310 ASSERT(t->why_blocked == BlockedOnBlackHole);
2311 type = get_itbl(UNTAG_CLOSURE(t->block_info.closure))->type;
2312 if (type != BLACKHOLE && type != CAF_BLACKHOLE) {
2313 IF_DEBUG(sanity,checkTSO(t));
2314 t = unblockOne(cap, t);
2316 any_woke_up = rtsTrue;
2326 /* -----------------------------------------------------------------------------
2329 This is used for interruption (^C) and forking, and corresponds to
2330 raising an exception but without letting the thread catch the
2332 -------------------------------------------------------------------------- */
2335 deleteThread (Capability *cap, StgTSO *tso)
2337 // NOTE: must only be called on a TSO that we have exclusive
2338 // access to, because we will call throwToSingleThreaded() below.
2339 // The TSO must be on the run queue of the Capability we own, or
2340 // we must own all Capabilities.
2342 if (tso->why_blocked != BlockedOnCCall &&
2343 tso->why_blocked != BlockedOnCCall_NoUnblockExc) {
2344 throwToSingleThreaded(cap,tso,NULL);
2348 #ifdef FORKPROCESS_PRIMOP_SUPPORTED
2350 deleteThread_(Capability *cap, StgTSO *tso)
2351 { // for forkProcess only:
2352 // like deleteThread(), but we delete threads in foreign calls, too.
2354 if (tso->why_blocked == BlockedOnCCall ||
2355 tso->why_blocked == BlockedOnCCall_NoUnblockExc) {
2356 unblockOne(cap,tso);
2357 tso->what_next = ThreadKilled;
2359 deleteThread(cap,tso);
2364 /* -----------------------------------------------------------------------------
2365 raiseExceptionHelper
2367 This function is called by the raise# primitve, just so that we can
2368 move some of the tricky bits of raising an exception from C-- into
2369 C. Who knows, it might be a useful re-useable thing here too.
2370 -------------------------------------------------------------------------- */
2373 raiseExceptionHelper (StgRegTable *reg, StgTSO *tso, StgClosure *exception)
2375 Capability *cap = regTableToCapability(reg);
2376 StgThunk *raise_closure = NULL;
2378 StgRetInfoTable *info;
2380 // This closure represents the expression 'raise# E' where E
2381 // is the exception raise. It is used to overwrite all the
2382 // thunks which are currently under evaluataion.
2385 // OLD COMMENT (we don't have MIN_UPD_SIZE now):
2386 // LDV profiling: stg_raise_info has THUNK as its closure
2387 // type. Since a THUNK takes at least MIN_UPD_SIZE words in its
2388 // payload, MIN_UPD_SIZE is more approprate than 1. It seems that
2389 // 1 does not cause any problem unless profiling is performed.
2390 // However, when LDV profiling goes on, we need to linearly scan
2391 // small object pool, where raise_closure is stored, so we should
2392 // use MIN_UPD_SIZE.
2394 // raise_closure = (StgClosure *)RET_STGCALL1(P_,allocate,
2395 // sizeofW(StgClosure)+1);
2399 // Walk up the stack, looking for the catch frame. On the way,
2400 // we update any closures pointed to from update frames with the
2401 // raise closure that we just built.
2405 info = get_ret_itbl((StgClosure *)p);
2406 next = p + stack_frame_sizeW((StgClosure *)p);
2407 switch (info->i.type) {
2410 // Only create raise_closure if we need to.
2411 if (raise_closure == NULL) {
2413 (StgThunk *)allocateLocal(cap,sizeofW(StgThunk)+1);
2414 SET_HDR(raise_closure, &stg_raise_info, CCCS);
2415 raise_closure->payload[0] = exception;
2417 UPD_IND(((StgUpdateFrame *)p)->updatee,(StgClosure *)raise_closure);
2421 case ATOMICALLY_FRAME:
2422 debugTrace(DEBUG_stm, "found ATOMICALLY_FRAME at %p", p);
2424 return ATOMICALLY_FRAME;
2430 case CATCH_STM_FRAME:
2431 debugTrace(DEBUG_stm, "found CATCH_STM_FRAME at %p", p);
2433 return CATCH_STM_FRAME;
2439 case CATCH_RETRY_FRAME:
2448 /* -----------------------------------------------------------------------------
2449 findRetryFrameHelper
2451 This function is called by the retry# primitive. It traverses the stack
2452 leaving tso->sp referring to the frame which should handle the retry.
2454 This should either be a CATCH_RETRY_FRAME (if the retry# is within an orElse#)
2455 or should be a ATOMICALLY_FRAME (if the retry# reaches the top level).
2457 We skip CATCH_STM_FRAMEs (aborting and rolling back the nested tx that they
2458 create) because retries are not considered to be exceptions, despite the
2459 similar implementation.
2461 We should not expect to see CATCH_FRAME or STOP_FRAME because those should
2462 not be created within memory transactions.
2463 -------------------------------------------------------------------------- */
2466 findRetryFrameHelper (StgTSO *tso)
2469 StgRetInfoTable *info;
2473 info = get_ret_itbl((StgClosure *)p);
2474 next = p + stack_frame_sizeW((StgClosure *)p);
2475 switch (info->i.type) {
2477 case ATOMICALLY_FRAME:
2478 debugTrace(DEBUG_stm,
2479 "found ATOMICALLY_FRAME at %p during retry", p);
2481 return ATOMICALLY_FRAME;
2483 case CATCH_RETRY_FRAME:
2484 debugTrace(DEBUG_stm,
2485 "found CATCH_RETRY_FRAME at %p during retrry", p);
2487 return CATCH_RETRY_FRAME;
2489 case CATCH_STM_FRAME: {
2490 StgTRecHeader *trec = tso -> trec;
2491 StgTRecHeader *outer = stmGetEnclosingTRec(trec);
2492 debugTrace(DEBUG_stm,
2493 "found CATCH_STM_FRAME at %p during retry", p);
2494 debugTrace(DEBUG_stm, "trec=%p outer=%p", trec, outer);
2495 stmAbortTransaction(tso -> cap, trec);
2496 stmFreeAbortedTRec(tso -> cap, trec);
2497 tso -> trec = outer;
2504 ASSERT(info->i.type != CATCH_FRAME);
2505 ASSERT(info->i.type != STOP_FRAME);
2512 /* -----------------------------------------------------------------------------
2513 resurrectThreads is called after garbage collection on the list of
2514 threads found to be garbage. Each of these threads will be woken
2515 up and sent a signal: BlockedOnDeadMVar if the thread was blocked
2516 on an MVar, or NonTermination if the thread was blocked on a Black
2519 Locks: assumes we hold *all* the capabilities.
2520 -------------------------------------------------------------------------- */
2523 resurrectThreads (StgTSO *threads)
2529 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2530 next = tso->global_link;
2532 step = Bdescr((P_)tso)->step;
2533 tso->global_link = step->threads;
2534 step->threads = tso;
2536 debugTrace(DEBUG_sched, "resurrecting thread %lu", (unsigned long)tso->id);
2538 // Wake up the thread on the Capability it was last on
2541 switch (tso->why_blocked) {
2543 case BlockedOnException:
2544 /* Called by GC - sched_mutex lock is currently held. */
2545 throwToSingleThreaded(cap, tso,
2546 (StgClosure *)blockedOnDeadMVar_closure);
2548 case BlockedOnBlackHole:
2549 throwToSingleThreaded(cap, tso,
2550 (StgClosure *)nonTermination_closure);
2553 throwToSingleThreaded(cap, tso,
2554 (StgClosure *)blockedIndefinitely_closure);
2557 /* This might happen if the thread was blocked on a black hole
2558 * belonging to a thread that we've just woken up (raiseAsync
2559 * can wake up threads, remember...).
2563 barf("resurrectThreads: thread blocked in a strange way");
2568 /* -----------------------------------------------------------------------------
2569 performPendingThrowTos is called after garbage collection, and
2570 passed a list of threads that were found to have pending throwTos
2571 (tso->blocked_exceptions was not empty), and were blocked.
2572 Normally this doesn't happen, because we would deliver the
2573 exception directly if the target thread is blocked, but there are
2574 small windows where it might occur on a multiprocessor (see
2577 NB. we must be holding all the capabilities at this point, just
2578 like resurrectThreads().
2579 -------------------------------------------------------------------------- */
2582 performPendingThrowTos (StgTSO *threads)
2588 for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
2589 next = tso->global_link;
2591 step = Bdescr((P_)tso)->step;
2592 tso->global_link = step->threads;
2593 step->threads = tso;
2595 debugTrace(DEBUG_sched, "performing blocked throwTo to thread %lu", (unsigned long)tso->id);
2598 maybePerformBlockedException(cap, tso);