1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2003-2005
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 SMP build will there be multiple capabilities, for
14 * the threaded RTS and other non-threaded builds, there is only
15 * one global capability, namely MainCapability.
17 * --------------------------------------------------------------------------*/
19 #include "PosixSource.h"
23 #include "OSThreads.h"
24 #include "Capability.h"
28 Capability MainCapability; // for non-SMP, we have one global capability
32 Capability *capabilities = NULL;
34 // Holds the Capability which last became free. This is used so that
35 // an in-call has a chance of quickly finding a free Capability.
36 // Maintaining a global free list of Capabilities would require global
37 // locking, so we don't do that.
38 Capability *last_free_capability;
41 #define UNUSED_IF_NOT_SMP
43 #define UNUSED_IF_NOT_SMP STG_UNUSED
46 #ifdef RTS_USER_SIGNALS
47 #define UNUSED_IF_NOT_THREADS
49 #define UNUSED_IF_NOT_THREADS STG_UNUSED
56 return blackholes_need_checking
58 #if defined(RTS_USER_SIGNALS)
64 #if defined(THREADED_RTS)
66 anyWorkForMe( Capability *cap, Task *task )
68 // If the run queue is not empty, then we only wake up the guy who
69 // can run the thread at the head, even if there is some other
70 // reason for this task to run (eg. interrupted=rtsTrue).
71 if (!emptyRunQueue(cap)) {
72 if (cap->run_queue_hd->bound == NULL) {
73 return (task->tso == NULL);
75 return (cap->run_queue_hd->bound == task);
78 return globalWorkToDo();
82 /* -----------------------------------------------------------------------------
83 * Manage the returning_tasks lists.
85 * These functions require cap->lock
86 * -------------------------------------------------------------------------- */
88 #if defined(THREADED_RTS)
90 newReturningTask (Capability *cap, Task *task)
92 ASSERT_LOCK_HELD(&cap->lock);
93 ASSERT(task->return_link == NULL);
94 if (cap->returning_tasks_hd) {
95 ASSERT(cap->returning_tasks_tl->return_link == NULL);
96 cap->returning_tasks_tl->return_link = task;
98 cap->returning_tasks_hd = task;
100 cap->returning_tasks_tl = task;
104 popReturningTask (Capability *cap)
106 ASSERT_LOCK_HELD(&cap->lock);
108 task = cap->returning_tasks_hd;
110 cap->returning_tasks_hd = task->return_link;
111 if (!cap->returning_tasks_hd) {
112 cap->returning_tasks_tl = NULL;
114 task->return_link = NULL;
119 /* ----------------------------------------------------------------------------
122 * The Capability is initially marked not free.
123 * ------------------------------------------------------------------------- */
126 initCapability( Capability *cap, nat i )
129 cap->in_haskell = rtsFalse;
131 cap->run_queue_hd = END_TSO_QUEUE;
132 cap->run_queue_tl = END_TSO_QUEUE;
134 #if defined(THREADED_RTS)
135 initMutex(&cap->lock);
136 cap->running_task = NULL; // indicates cap is free
137 cap->spare_workers = NULL;
138 cap->suspended_ccalling_tasks = NULL;
139 cap->returning_tasks_hd = NULL;
140 cap->returning_tasks_tl = NULL;
145 cap->f.stgGCEnter1 = (F_)__stg_gc_enter_1;
146 cap->f.stgGCFun = (F_)__stg_gc_fun;
149 /* ---------------------------------------------------------------------------
150 * Function: initCapabilities()
152 * Purpose: set up the Capability handling. For the SMP build,
153 * we keep a table of them, the size of which is
154 * controlled by the user via the RTS flag -N.
156 * ------------------------------------------------------------------------- */
158 initCapabilities( void )
163 n_capabilities = n = RtsFlags.ParFlags.nNodes;
164 capabilities = stgMallocBytes(n * sizeof(Capability), "initCapabilities");
166 for (i = 0; i < n; i++) {
167 initCapability(&capabilities[i], i);
170 IF_DEBUG(scheduler, sched_belch("allocated %d capabilities", n));
173 capabilities = &MainCapability;
174 initCapability(&MainCapability, 0);
177 // There are no free capabilities to begin with. We will start
178 // a worker Task to each Capability, which will quickly put the
179 // Capability on the free list when it finds nothing to do.
180 last_free_capability = &capabilities[0];
183 /* ----------------------------------------------------------------------------
184 * Give a Capability to a Task. The task must currently be sleeping
185 * on its condition variable.
187 * Requires cap->lock (modifies cap->running_task).
189 * When migrating a Task, the migrater must take task->lock before
190 * modifying task->cap, to synchronise with the waking up Task.
191 * Additionally, the migrater should own the Capability (when
192 * migrating the run queue), or cap->lock (when migrating
193 * returning_workers).
195 * ------------------------------------------------------------------------- */
197 #if defined(THREADED_RTS)
199 giveCapabilityToTask (Capability *cap, Task *task)
201 ASSERT_LOCK_HELD(&cap->lock);
202 ASSERT(task->cap == cap);
203 // We are not modifying task->cap, so we do not need to take task->lock.
205 sched_belch("passing capability %d to %s %p",
206 cap->no, task->tso ? "bound task" : "worker",
208 ACQUIRE_LOCK(&task->lock);
209 task->wakeup = rtsTrue;
210 // the wakeup flag is needed because signalCondition() doesn't
211 // flag the condition if the thread is already runniing, but we want
213 signalCondition(&task->cond);
214 RELEASE_LOCK(&task->lock);
218 /* ----------------------------------------------------------------------------
219 * Function: releaseCapability(Capability*)
221 * Purpose: Letting go of a capability. Causes a
222 * 'returning worker' thread or a 'waiting worker'
223 * to wake up, in that order.
224 * ------------------------------------------------------------------------- */
226 #if defined(THREADED_RTS)
228 releaseCapability_ (Capability* cap)
232 ASSERT(cap->running_task != NULL && myTask() == cap->running_task);
234 task = cap->running_task;
235 cap->running_task = NULL;
237 ASSERT(task->id == osThreadId());
239 // Check to see whether a worker thread can be given
240 // the go-ahead to return the result of an external call..
241 if (cap->returning_tasks_hd != NULL) {
242 giveCapabilityToTask(cap,cap->returning_tasks_hd);
243 // The Task pops itself from the queue (see waitForReturnCapability())
247 // If the next thread on the run queue is a bound thread,
248 // give this Capability to the appropriate Task.
249 if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
250 // Make sure we're not about to try to wake ourselves up
251 ASSERT(task != cap->run_queue_hd->bound);
252 task = cap->run_queue_hd->bound;
253 giveCapabilityToTask(cap,task);
257 // If we have an unbound thread on the run queue, or if there's
258 // anything else to do, give the Capability to a worker thread.
259 if (!emptyRunQueue(cap) || globalWorkToDo()) {
260 if (cap->spare_workers) {
261 giveCapabilityToTask(cap,cap->spare_workers);
262 // The worker Task pops itself from the queue;
266 // Create a worker thread if we don't have one. If the system
267 // is interrupted, we only create a worker task if there
268 // are threads that need to be completed. If the system is
269 // shutting down, we never create a new worker.
270 if (!shutting_down_scheduler) {
272 sched_belch("starting new worker on capability %d", cap->no));
273 startWorkerTask(cap, workerStart);
278 last_free_capability = cap;
279 IF_DEBUG(scheduler, sched_belch("freeing capability %d", cap->no));
283 releaseCapability (Capability* cap UNUSED_IF_NOT_THREADS)
285 ACQUIRE_LOCK(&cap->lock);
286 releaseCapability_(cap);
287 RELEASE_LOCK(&cap->lock);
291 releaseCapabilityAndQueueWorker (Capability* cap UNUSED_IF_NOT_THREADS)
295 ACQUIRE_LOCK(&cap->lock);
297 task = cap->running_task;
299 // If the current task is a worker, save it on the spare_workers
300 // list of this Capability. A worker can mark itself as stopped,
301 // in which case it is not replaced on the spare_worker queue.
302 // This happens when the system is shutting down (see
303 // Schedule.c:workerStart()).
304 // Also, be careful to check that this task hasn't just exited
305 // Haskell to do a foreign call (task->suspended_tso).
306 if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
307 task->next = cap->spare_workers;
308 cap->spare_workers = task;
310 // Bound tasks just float around attached to their TSOs.
312 releaseCapability_(cap);
314 RELEASE_LOCK(&cap->lock);
318 /* ----------------------------------------------------------------------------
319 * waitForReturnCapability( Task *task )
321 * Purpose: when an OS thread returns from an external call,
322 * it calls waitForReturnCapability() (via Schedule.resumeThread())
323 * to wait for permission to enter the RTS & communicate the
324 * result of the external call back to the Haskell thread that
327 * ------------------------------------------------------------------------- */
329 waitForReturnCapability (Capability **pCap,
330 Task *task UNUSED_IF_NOT_THREADS)
332 #if !defined(THREADED_RTS)
334 MainCapability.running_task = task;
335 task->cap = &MainCapability;
336 *pCap = &MainCapability;
339 Capability *cap = *pCap;
342 // Try last_free_capability first
343 cap = last_free_capability;
344 if (!cap->running_task) {
346 // otherwise, search for a free capability
347 for (i = 0; i < n_capabilities; i++) {
348 cap = &capabilities[i];
349 if (!cap->running_task) {
353 // Can't find a free one, use last_free_capability.
354 cap = last_free_capability;
357 // record the Capability as the one this Task is now assocated with.
361 ASSERT(task->cap == cap);
364 ACQUIRE_LOCK(&cap->lock);
367 sched_belch("returning; I want capability %d", cap->no));
369 if (!cap->running_task) {
370 // It's free; just grab it
371 cap->running_task = task;
372 RELEASE_LOCK(&cap->lock);
374 newReturningTask(cap,task);
375 RELEASE_LOCK(&cap->lock);
378 ACQUIRE_LOCK(&task->lock);
379 // task->lock held, cap->lock not held
380 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
382 task->wakeup = rtsFalse;
383 RELEASE_LOCK(&task->lock);
385 // now check whether we should wake up...
386 ACQUIRE_LOCK(&cap->lock);
387 if (cap->running_task == NULL) {
388 if (cap->returning_tasks_hd != task) {
389 giveCapabilityToTask(cap,cap->returning_tasks_hd);
390 RELEASE_LOCK(&cap->lock);
393 cap->running_task = task;
394 popReturningTask(cap);
395 RELEASE_LOCK(&cap->lock);
398 RELEASE_LOCK(&cap->lock);
403 ASSERT(cap->running_task == task);
406 sched_belch("returning; got capability %d", cap->no));
412 #if defined(THREADED_RTS)
413 /* ----------------------------------------------------------------------------
415 * ------------------------------------------------------------------------- */
418 yieldCapability (Capability** pCap, Task *task)
420 Capability *cap = *pCap;
422 // The fast path; no locking
423 if ( cap->returning_tasks_hd == NULL && anyWorkForMe(cap,task) )
426 while ( cap->returning_tasks_hd != NULL || !anyWorkForMe(cap,task) ) {
427 IF_DEBUG(scheduler, sched_belch("giving up capability %d", cap->no));
429 // We must now release the capability and wait to be woken up
431 releaseCapabilityAndQueueWorker(cap);
434 ACQUIRE_LOCK(&task->lock);
435 // task->lock held, cap->lock not held
436 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
438 task->wakeup = rtsFalse;
439 RELEASE_LOCK(&task->lock);
441 IF_DEBUG(scheduler, sched_belch("woken up on capability %d", cap->no));
442 ACQUIRE_LOCK(&cap->lock);
443 if (cap->running_task != NULL) {
444 RELEASE_LOCK(&cap->lock);
448 if (task->tso == NULL) {
449 ASSERT(cap->spare_workers != NULL);
450 // if we're not at the front of the queue, release it
451 // again. This is unlikely to happen.
452 if (cap->spare_workers != task) {
453 giveCapabilityToTask(cap,cap->spare_workers);
454 RELEASE_LOCK(&cap->lock);
457 cap->spare_workers = task->next;
460 cap->running_task = task;
461 RELEASE_LOCK(&cap->lock);
465 IF_DEBUG(scheduler, sched_belch("got capability %d", cap->no));
466 ASSERT(cap->running_task == task);
473 /* ----------------------------------------------------------------------------
476 * Used to indicate that the interrupted flag is now set, or some
477 * other global condition that might require waking up a Task on each
479 * ------------------------------------------------------------------------- */
482 prodCapabilities(rtsBool all)
488 for (i=0; i < n_capabilities; i++) {
489 cap = &capabilities[i];
490 ACQUIRE_LOCK(&cap->lock);
491 if (!cap->running_task) {
492 if (cap->spare_workers) {
493 task = cap->spare_workers;
494 ASSERT(!task->stopped);
495 giveCapabilityToTask(cap,task);
497 RELEASE_LOCK(&cap->lock);
502 RELEASE_LOCK(&cap->lock);
507 prodAllCapabilities (void)
509 prodCapabilities(rtsTrue);
512 /* ----------------------------------------------------------------------------
515 * Like prodAllCapabilities, but we only require a single Task to wake
516 * up in order to service some global event, such as checking for
517 * deadlock after some idle time has passed.
518 * ------------------------------------------------------------------------- */
521 prodOneCapability (void)
523 prodCapabilities(rtsFalse);
526 /* ----------------------------------------------------------------------------
529 * At shutdown time, we want to let everything exit as cleanly as
530 * possible. For each capability, we let its run queue drain, and
531 * allow the workers to stop.
533 * This function should be called when interrupted and
534 * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
535 * will exit the scheduler and call taskStop(), and any bound thread
536 * that wakes up will return to its caller. Runnable threads are
539 * ------------------------------------------------------------------------- */
542 shutdownCapability (Capability *cap, Task *task)
546 ASSERT(interrupted && shutting_down_scheduler);
550 for (i = 0; i < 50; i++) {
551 IF_DEBUG(scheduler, sched_belch("shutting down capability %d, attempt %d", cap->no, i));
552 ACQUIRE_LOCK(&cap->lock);
553 if (cap->running_task) {
554 RELEASE_LOCK(&cap->lock);
555 IF_DEBUG(scheduler, sched_belch("not owner, yielding"));
559 cap->running_task = task;
560 if (!emptyRunQueue(cap) || cap->spare_workers) {
561 IF_DEBUG(scheduler, sched_belch("runnable threads or workers still alive, yielding"));
562 releaseCapability_(cap); // this will wake up a worker
563 RELEASE_LOCK(&cap->lock);
567 IF_DEBUG(scheduler, sched_belch("capability %d is stopped.", cap->no));
568 RELEASE_LOCK(&cap->lock);
571 // we now have the Capability, its run queue and spare workers
572 // list are both empty.
575 #endif /* THREADED_RTS */