1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2003-2006
7 * A Capability represent the token required to execute STG code,
8 * and all the state an OS thread/task needs to run Haskell code:
9 * its STG registers, a pointer to its TSO, a nursery etc. During
10 * STG execution, a pointer to the capabilitity is kept in a
11 * register (BaseReg; actually it is a pointer to cap->r).
13 * Only in an THREADED_RTS build will there be multiple capabilities,
14 * for non-threaded builds there is only one global capability, namely
17 * --------------------------------------------------------------------------*/
19 #include "PosixSource.h"
22 #include "Capability.h"
26 #include "sm/GC.h" // for gcWorkerThread()
30 // one global capability, this is the Capability for non-threaded
31 // builds, and for +RTS -N1
32 Capability MainCapability;
34 nat n_capabilities = 0;
35 Capability *capabilities = NULL;
37 // Holds the Capability which last became free. This is used so that
38 // an in-call has a chance of quickly finding a free Capability.
39 // Maintaining a global free list of Capabilities would require global
40 // locking, so we don't do that.
41 Capability *last_free_capability = NULL;
43 /* GC indicator, in scope for the scheduler, init'ed to false */
44 volatile StgWord waiting_for_gc = 0;
46 /* Let foreign code get the current Capability -- assuming there is one!
47 * This is useful for unsafe foreign calls because they are called with
48 * the current Capability held, but they are not passed it. For example,
49 * see see the integer-gmp package which calls allocateLocal() in its
50 * stgAllocForGMP() function (which gets called by gmp functions).
52 Capability * rts_unsafeGetMyCapability (void)
54 #if defined(THREADED_RTS)
57 return &MainCapability;
61 #if defined(THREADED_RTS)
65 return sched_state >= SCHED_INTERRUPTING
66 || recent_activity == ACTIVITY_INACTIVE; // need to check for deadlock
70 #if defined(THREADED_RTS)
72 findSpark (Capability *cap)
79 if (!emptyRunQueue(cap) || cap->returning_tasks_hd != NULL) {
80 // If there are other threads, don't try to run any new
81 // sparks: sparks might be speculative, we don't want to take
82 // resources away from the main computation.
89 // first try to get a spark from our own pool.
90 // We should be using reclaimSpark(), because it works without
91 // needing any atomic instructions:
92 // spark = reclaimSpark(cap->sparks);
93 // However, measurements show that this makes at least one benchmark
94 // slower (prsa) and doesn't affect the others.
95 spark = tryStealSpark(cap);
97 cap->sparks_converted++;
99 // Post event for running a spark from capability's own pool.
100 traceEventRunSpark(cap, cap->r.rCurrentTSO);
104 if (!emptySparkPoolCap(cap)) {
108 if (n_capabilities == 1) { return NULL; } // makes no sense...
110 debugTrace(DEBUG_sched,
111 "cap %d: Trying to steal work from other capabilities",
114 /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
115 start at a random place instead of 0 as well. */
116 for ( i=0 ; i < n_capabilities ; i++ ) {
117 robbed = &capabilities[i];
118 if (cap == robbed) // ourselves...
121 if (emptySparkPoolCap(robbed)) // nothing to steal here
124 spark = tryStealSpark(robbed);
125 if (spark == NULL && !emptySparkPoolCap(robbed)) {
126 // we conflicted with another thread while trying to steal;
132 cap->sparks_converted++;
134 traceEventStealSpark(cap, cap->r.rCurrentTSO, robbed->no);
138 // otherwise: no success, try next one
142 debugTrace(DEBUG_sched, "No sparks stolen");
146 // Returns True if any spark pool is non-empty at this moment in time
147 // The result is only valid for an instant, of course, so in a sense
148 // is immediately invalid, and should not be relied upon for
155 for (i=0; i < n_capabilities; i++) {
156 if (!emptySparkPoolCap(&capabilities[i])) {
164 /* -----------------------------------------------------------------------------
165 * Manage the returning_tasks lists.
167 * These functions require cap->lock
168 * -------------------------------------------------------------------------- */
170 #if defined(THREADED_RTS)
172 newReturningTask (Capability *cap, Task *task)
174 ASSERT_LOCK_HELD(&cap->lock);
175 ASSERT(task->next == NULL);
176 if (cap->returning_tasks_hd) {
177 ASSERT(cap->returning_tasks_tl->next == NULL);
178 cap->returning_tasks_tl->next = task;
180 cap->returning_tasks_hd = task;
182 cap->returning_tasks_tl = task;
186 popReturningTask (Capability *cap)
188 ASSERT_LOCK_HELD(&cap->lock);
190 task = cap->returning_tasks_hd;
192 cap->returning_tasks_hd = task->next;
193 if (!cap->returning_tasks_hd) {
194 cap->returning_tasks_tl = NULL;
201 /* ----------------------------------------------------------------------------
204 * The Capability is initially marked not free.
205 * ------------------------------------------------------------------------- */
208 initCapability( Capability *cap, nat i )
213 cap->in_haskell = rtsFalse;
215 cap->run_queue_hd = END_TSO_QUEUE;
216 cap->run_queue_tl = END_TSO_QUEUE;
218 #if defined(THREADED_RTS)
219 initMutex(&cap->lock);
220 cap->running_task = NULL; // indicates cap is free
221 cap->spare_workers = NULL;
222 cap->suspended_ccalls = NULL;
223 cap->returning_tasks_hd = NULL;
224 cap->returning_tasks_tl = NULL;
225 cap->inbox = (Message*)END_TSO_QUEUE;
226 cap->sparks_created = 0;
227 cap->sparks_converted = 0;
228 cap->sparks_pruned = 0;
231 cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
232 cap->f.stgGCEnter1 = (StgFunPtr)__stg_gc_enter_1;
233 cap->f.stgGCFun = (StgFunPtr)__stg_gc_fun;
235 cap->mut_lists = stgMallocBytes(sizeof(bdescr *) *
236 RtsFlags.GcFlags.generations,
238 cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
239 RtsFlags.GcFlags.generations,
242 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
243 cap->mut_lists[g] = NULL;
246 cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
247 cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
248 cap->free_trec_chunks = END_STM_CHUNK_LIST;
249 cap->free_trec_headers = NO_TREC;
250 cap->transaction_tokens = 0;
251 cap->context_switch = 0;
252 cap->pinned_object_block = NULL;
255 /* ---------------------------------------------------------------------------
256 * Function: initCapabilities()
258 * Purpose: set up the Capability handling. For the THREADED_RTS build,
259 * we keep a table of them, the size of which is
260 * controlled by the user via the RTS flag -N.
262 * ------------------------------------------------------------------------- */
264 initCapabilities( void )
266 #if defined(THREADED_RTS)
270 // We can't support multiple CPUs if BaseReg is not a register
271 if (RtsFlags.ParFlags.nNodes > 1) {
272 errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
273 RtsFlags.ParFlags.nNodes = 1;
277 n_capabilities = RtsFlags.ParFlags.nNodes;
279 if (n_capabilities == 1) {
280 capabilities = &MainCapability;
281 // THREADED_RTS must work on builds that don't have a mutable
282 // BaseReg (eg. unregisterised), so in this case
283 // capabilities[0] must coincide with &MainCapability.
285 capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
289 for (i = 0; i < n_capabilities; i++) {
290 initCapability(&capabilities[i], i);
293 debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
295 #else /* !THREADED_RTS */
298 capabilities = &MainCapability;
299 initCapability(&MainCapability, 0);
303 // There are no free capabilities to begin with. We will start
304 // a worker Task to each Capability, which will quickly put the
305 // Capability on the free list when it finds nothing to do.
306 last_free_capability = &capabilities[0];
309 /* ----------------------------------------------------------------------------
310 * setContextSwitches: cause all capabilities to context switch as
312 * ------------------------------------------------------------------------- */
314 void setContextSwitches(void)
317 for (i=0; i < n_capabilities; i++) {
318 contextSwitchCapability(&capabilities[i]);
322 /* ----------------------------------------------------------------------------
323 * Give a Capability to a Task. The task must currently be sleeping
324 * on its condition variable.
326 * Requires cap->lock (modifies cap->running_task).
328 * When migrating a Task, the migrater must take task->lock before
329 * modifying task->cap, to synchronise with the waking up Task.
330 * Additionally, the migrater should own the Capability (when
331 * migrating the run queue), or cap->lock (when migrating
332 * returning_workers).
334 * ------------------------------------------------------------------------- */
336 #if defined(THREADED_RTS)
338 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
340 ASSERT_LOCK_HELD(&cap->lock);
341 ASSERT(task->cap == cap);
342 debugTrace(DEBUG_sched, "passing capability %d to %s %p",
343 cap->no, task->incall->tso ? "bound task" : "worker",
345 ACQUIRE_LOCK(&task->lock);
346 task->wakeup = rtsTrue;
347 // the wakeup flag is needed because signalCondition() doesn't
348 // flag the condition if the thread is already runniing, but we want
350 signalCondition(&task->cond);
351 RELEASE_LOCK(&task->lock);
355 /* ----------------------------------------------------------------------------
356 * Function: releaseCapability(Capability*)
358 * Purpose: Letting go of a capability. Causes a
359 * 'returning worker' thread or a 'waiting worker'
360 * to wake up, in that order.
361 * ------------------------------------------------------------------------- */
363 #if defined(THREADED_RTS)
365 releaseCapability_ (Capability* cap,
366 rtsBool always_wakeup)
370 task = cap->running_task;
372 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
374 cap->running_task = NULL;
376 // Check to see whether a worker thread can be given
377 // the go-ahead to return the result of an external call..
378 if (cap->returning_tasks_hd != NULL) {
379 giveCapabilityToTask(cap,cap->returning_tasks_hd);
380 // The Task pops itself from the queue (see waitForReturnCapability())
384 if (waiting_for_gc == PENDING_GC_SEQ) {
385 last_free_capability = cap; // needed?
386 debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
391 // If the next thread on the run queue is a bound thread,
392 // give this Capability to the appropriate Task.
393 if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
394 // Make sure we're not about to try to wake ourselves up
395 // ASSERT(task != cap->run_queue_hd->bound);
396 // assertion is false: in schedule() we force a yield after
397 // ThreadBlocked, but the thread may be back on the run queue
399 task = cap->run_queue_hd->bound->task;
400 giveCapabilityToTask(cap,task);
404 if (!cap->spare_workers) {
405 // Create a worker thread if we don't have one. If the system
406 // is interrupted, we only create a worker task if there
407 // are threads that need to be completed. If the system is
408 // shutting down, we never create a new worker.
409 if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
410 debugTrace(DEBUG_sched,
411 "starting new worker on capability %d", cap->no);
412 startWorkerTask(cap);
417 // If we have an unbound thread on the run queue, or if there's
418 // anything else to do, give the Capability to a worker thread.
420 !emptyRunQueue(cap) || !emptyInbox(cap) ||
421 !emptySparkPoolCap(cap) || globalWorkToDo()) {
422 if (cap->spare_workers) {
423 giveCapabilityToTask(cap,cap->spare_workers);
424 // The worker Task pops itself from the queue;
429 last_free_capability = cap;
430 debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
434 releaseCapability (Capability* cap USED_IF_THREADS)
436 ACQUIRE_LOCK(&cap->lock);
437 releaseCapability_(cap, rtsFalse);
438 RELEASE_LOCK(&cap->lock);
442 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
444 ACQUIRE_LOCK(&cap->lock);
445 releaseCapability_(cap, rtsTrue);
446 RELEASE_LOCK(&cap->lock);
450 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
454 ACQUIRE_LOCK(&cap->lock);
456 task = cap->running_task;
458 // If the current task is a worker, save it on the spare_workers
459 // list of this Capability. A worker can mark itself as stopped,
460 // in which case it is not replaced on the spare_worker queue.
461 // This happens when the system is shutting down (see
462 // Schedule.c:workerStart()).
463 if (!isBoundTask(task) && !task->stopped) {
464 task->next = cap->spare_workers;
465 cap->spare_workers = task;
467 // Bound tasks just float around attached to their TSOs.
469 releaseCapability_(cap,rtsFalse);
471 RELEASE_LOCK(&cap->lock);
475 /* ----------------------------------------------------------------------------
476 * waitForReturnCapability( Task *task )
478 * Purpose: when an OS thread returns from an external call,
479 * it calls waitForReturnCapability() (via Schedule.resumeThread())
480 * to wait for permission to enter the RTS & communicate the
481 * result of the external call back to the Haskell thread that
484 * ------------------------------------------------------------------------- */
486 waitForReturnCapability (Capability **pCap, Task *task)
488 #if !defined(THREADED_RTS)
490 MainCapability.running_task = task;
491 task->cap = &MainCapability;
492 *pCap = &MainCapability;
495 Capability *cap = *pCap;
498 // Try last_free_capability first
499 cap = last_free_capability;
500 if (cap->running_task) {
502 // otherwise, search for a free capability
504 for (i = 0; i < n_capabilities; i++) {
505 if (!capabilities[i].running_task) {
506 cap = &capabilities[i];
511 // Can't find a free one, use last_free_capability.
512 cap = last_free_capability;
516 // record the Capability as the one this Task is now assocated with.
520 ASSERT(task->cap == cap);
523 ACQUIRE_LOCK(&cap->lock);
525 debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
527 if (!cap->running_task) {
528 // It's free; just grab it
529 cap->running_task = task;
530 RELEASE_LOCK(&cap->lock);
532 newReturningTask(cap,task);
533 RELEASE_LOCK(&cap->lock);
536 ACQUIRE_LOCK(&task->lock);
537 // task->lock held, cap->lock not held
538 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
540 task->wakeup = rtsFalse;
541 RELEASE_LOCK(&task->lock);
543 // now check whether we should wake up...
544 ACQUIRE_LOCK(&cap->lock);
545 if (cap->running_task == NULL) {
546 if (cap->returning_tasks_hd != task) {
547 giveCapabilityToTask(cap,cap->returning_tasks_hd);
548 RELEASE_LOCK(&cap->lock);
551 cap->running_task = task;
552 popReturningTask(cap);
553 RELEASE_LOCK(&cap->lock);
556 RELEASE_LOCK(&cap->lock);
561 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
563 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
569 #if defined(THREADED_RTS)
570 /* ----------------------------------------------------------------------------
572 * ------------------------------------------------------------------------- */
575 yieldCapability (Capability** pCap, Task *task)
577 Capability *cap = *pCap;
579 if (waiting_for_gc == PENDING_GC_PAR) {
580 traceEventGcStart(cap);
582 traceEventGcEnd(cap);
586 debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
588 // We must now release the capability and wait to be woken up
590 task->wakeup = rtsFalse;
591 releaseCapabilityAndQueueWorker(cap);
594 ACQUIRE_LOCK(&task->lock);
595 // task->lock held, cap->lock not held
596 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
598 task->wakeup = rtsFalse;
599 RELEASE_LOCK(&task->lock);
601 debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
603 ACQUIRE_LOCK(&cap->lock);
604 if (cap->running_task != NULL) {
605 debugTrace(DEBUG_sched,
606 "capability %d is owned by another task", cap->no);
607 RELEASE_LOCK(&cap->lock);
611 if (task->incall->tso == NULL) {
612 ASSERT(cap->spare_workers != NULL);
613 // if we're not at the front of the queue, release it
614 // again. This is unlikely to happen.
615 if (cap->spare_workers != task) {
616 giveCapabilityToTask(cap,cap->spare_workers);
617 RELEASE_LOCK(&cap->lock);
620 cap->spare_workers = task->next;
623 cap->running_task = task;
624 RELEASE_LOCK(&cap->lock);
628 debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
629 ASSERT(cap->running_task == task);
633 ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
638 /* ----------------------------------------------------------------------------
641 * If a Capability is currently idle, wake up a Task on it. Used to
642 * get every Capability into the GC.
643 * ------------------------------------------------------------------------- */
646 prodCapability (Capability *cap, Task *task)
648 ACQUIRE_LOCK(&cap->lock);
649 if (!cap->running_task) {
650 cap->running_task = task;
651 releaseCapability_(cap,rtsTrue);
653 RELEASE_LOCK(&cap->lock);
656 /* ----------------------------------------------------------------------------
659 * At shutdown time, we want to let everything exit as cleanly as
660 * possible. For each capability, we let its run queue drain, and
661 * allow the workers to stop.
663 * This function should be called when interrupted and
664 * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
665 * will exit the scheduler and call taskStop(), and any bound thread
666 * that wakes up will return to its caller. Runnable threads are
669 * ------------------------------------------------------------------------- */
672 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
678 // Loop indefinitely until all the workers have exited and there
679 // are no Haskell threads left. We used to bail out after 50
680 // iterations of this loop, but that occasionally left a worker
681 // running which caused problems later (the closeMutex() below
682 // isn't safe, for one thing).
684 for (i = 0; /* i < 50 */; i++) {
685 ASSERT(sched_state == SCHED_SHUTTING_DOWN);
687 debugTrace(DEBUG_sched,
688 "shutting down capability %d, attempt %d", cap->no, i);
689 ACQUIRE_LOCK(&cap->lock);
690 if (cap->running_task) {
691 RELEASE_LOCK(&cap->lock);
692 debugTrace(DEBUG_sched, "not owner, yielding");
696 cap->running_task = task;
698 if (cap->spare_workers) {
699 // Look for workers that have died without removing
700 // themselves from the list; this could happen if the OS
701 // summarily killed the thread, for example. This
702 // actually happens on Windows when the system is
703 // terminating the program, and the RTS is running in a
707 for (t = cap->spare_workers; t != NULL; t = t->next) {
708 if (!osThreadIsAlive(t->id)) {
709 debugTrace(DEBUG_sched,
710 "worker thread %p has died unexpectedly", (void *)t->id);
712 cap->spare_workers = t->next;
714 prev->next = t->next;
721 if (!emptyRunQueue(cap) || cap->spare_workers) {
722 debugTrace(DEBUG_sched,
723 "runnable threads or workers still alive, yielding");
724 releaseCapability_(cap,rtsFalse); // this will wake up a worker
725 RELEASE_LOCK(&cap->lock);
730 // If "safe", then busy-wait for any threads currently doing
731 // foreign calls. If we're about to unload this DLL, for
732 // example, we need to be sure that there are no OS threads
733 // that will try to return to code that has been unloaded.
734 // We can be a bit more relaxed when this is a standalone
735 // program that is about to terminate, and let safe=false.
736 if (cap->suspended_ccalls && safe) {
737 debugTrace(DEBUG_sched,
738 "thread(s) are involved in foreign calls, yielding");
739 cap->running_task = NULL;
740 RELEASE_LOCK(&cap->lock);
741 // The IO manager thread might have been slow to start up,
742 // so the first attempt to kill it might not have
743 // succeeded. Just in case, try again - the kill message
744 // will only be sent once.
746 // To reproduce this deadlock: run ffi002(threaded1)
747 // repeatedly on a loaded machine.
753 traceEventShutdown(cap);
754 RELEASE_LOCK(&cap->lock);
757 // we now have the Capability, its run queue and spare workers
758 // list are both empty.
760 // ToDo: we can't drop this mutex, because there might still be
761 // threads performing foreign calls that will eventually try to
762 // return via resumeThread() and attempt to grab cap->lock.
763 // closeMutex(&cap->lock);
766 /* ----------------------------------------------------------------------------
769 * Attempt to gain control of a Capability if it is free.
771 * ------------------------------------------------------------------------- */
774 tryGrabCapability (Capability *cap, Task *task)
776 if (cap->running_task != NULL) return rtsFalse;
777 ACQUIRE_LOCK(&cap->lock);
778 if (cap->running_task != NULL) {
779 RELEASE_LOCK(&cap->lock);
783 cap->running_task = task;
784 RELEASE_LOCK(&cap->lock);
789 #endif /* THREADED_RTS */
792 freeCapability (Capability *cap)
794 stgFree(cap->mut_lists);
795 stgFree(cap->saved_mut_lists);
796 #if defined(THREADED_RTS)
797 freeSparkPool(cap->sparks);
802 freeCapabilities (void)
804 #if defined(THREADED_RTS)
806 for (i=0; i < n_capabilities; i++) {
807 freeCapability(&capabilities[i]);
810 freeCapability(&MainCapability);
814 /* ---------------------------------------------------------------------------
815 Mark everything directly reachable from the Capabilities. When
816 using multiple GC threads, each GC thread marks all Capabilities
817 for which (c `mod` n == 0), for Capability c and thread n.
818 ------------------------------------------------------------------------ */
821 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
822 rtsBool no_mark_sparks USED_IF_THREADS)
828 // Each GC thread is responsible for following roots from the
829 // Capability of the same number. There will usually be the same
830 // or fewer Capabilities as GC threads, but just in case there
831 // are more, we mark every Capability whose number is the GC
832 // thread's index plus a multiple of the number of GC threads.
833 for (i = i0; i < n_capabilities; i += delta) {
834 cap = &capabilities[i];
835 evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
836 evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
837 #if defined(THREADED_RTS)
838 evac(user, (StgClosure **)(void *)&cap->inbox);
840 for (incall = cap->suspended_ccalls; incall != NULL;
841 incall=incall->next) {
842 evac(user, (StgClosure **)(void *)&incall->suspended_tso);
845 #if defined(THREADED_RTS)
846 if (!no_mark_sparks) {
847 traverseSparkQueue (evac, user, cap);
852 #if !defined(THREADED_RTS)
853 evac(user, (StgClosure **)(void *)&blocked_queue_hd);
854 evac(user, (StgClosure **)(void *)&blocked_queue_tl);
855 evac(user, (StgClosure **)(void *)&sleeping_queue);
860 markCapabilities (evac_fn evac, void *user)
862 markSomeCapabilities(evac, user, 0, 1, rtsFalse);
865 /* -----------------------------------------------------------------------------
867 -------------------------------------------------------------------------- */