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;
143 cap->f.stgGCEnter1 = (F_)__stg_gc_enter_1;
144 cap->f.stgGCFun = (F_)__stg_gc_fun;
147 /* ---------------------------------------------------------------------------
148 * Function: initCapabilities()
150 * Purpose: set up the Capability handling. For the SMP build,
151 * we keep a table of them, the size of which is
152 * controlled by the user via the RTS flag -N.
154 * ------------------------------------------------------------------------- */
156 initCapabilities( void )
161 n_capabilities = n = RtsFlags.ParFlags.nNodes;
162 capabilities = stgMallocBytes(n * sizeof(Capability), "initCapabilities");
164 for (i = 0; i < n; i++) {
165 initCapability(&capabilities[i], i);
168 IF_DEBUG(scheduler, sched_belch("allocated %d capabilities", n));
171 capabilities = &MainCapability;
172 initCapability(&MainCapability, 0);
175 // There are no free capabilities to begin with. We will start
176 // a worker Task to each Capability, which will quickly put the
177 // Capability on the free list when it finds nothing to do.
178 last_free_capability = &capabilities[0];
181 /* ----------------------------------------------------------------------------
182 * Give a Capability to a Task. The task must currently be sleeping
183 * on its condition variable.
185 * Requires cap->lock (modifies cap->running_task).
187 * When migrating a Task, the migrater must take task->lock before
188 * modifying task->cap, to synchronise with the waking up Task.
189 * Additionally, the migrater should own the Capability (when
190 * migrating the run queue), or cap->lock (when migrating
191 * returning_workers).
193 * ------------------------------------------------------------------------- */
195 #if defined(THREADED_RTS)
197 giveCapabilityToTask (Capability *cap, Task *task)
199 ASSERT_LOCK_HELD(&cap->lock);
200 ASSERT(task->cap == cap);
201 // We are not modifying task->cap, so we do not need to take task->lock.
203 sched_belch("passing capability %d to %s %p",
204 cap->no, task->tso ? "bound task" : "worker",
206 ACQUIRE_LOCK(&task->lock);
207 task->wakeup = rtsTrue;
208 // the wakeup flag is needed because signalCondition() doesn't
209 // flag the condition if the thread is already runniing, but we want
211 signalCondition(&task->cond);
212 RELEASE_LOCK(&task->lock);
216 /* ----------------------------------------------------------------------------
217 * Function: releaseCapability(Capability*)
219 * Purpose: Letting go of a capability. Causes a
220 * 'returning worker' thread or a 'waiting worker'
221 * to wake up, in that order.
222 * ------------------------------------------------------------------------- */
224 #if defined(THREADED_RTS)
226 releaseCapability_ (Capability* cap)
230 ASSERT(cap->running_task != NULL && myTask() == cap->running_task);
232 task = cap->running_task;
233 cap->running_task = NULL;
235 ASSERT(task->id == osThreadId());
237 // Check to see whether a worker thread can be given
238 // the go-ahead to return the result of an external call..
239 if (cap->returning_tasks_hd != NULL) {
240 giveCapabilityToTask(cap,cap->returning_tasks_hd);
241 // The Task pops itself from the queue (see waitForReturnCapability())
245 // If the next thread on the run queue is a bound thread,
246 // give this Capability to the appropriate Task.
247 if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
248 // Make sure we're not about to try to wake ourselves up
249 ASSERT(task != cap->run_queue_hd->bound);
250 task = cap->run_queue_hd->bound;
251 giveCapabilityToTask(cap,task);
255 // If we have an unbound thread on the run queue, or if there's
256 // anything else to do, give the Capability to a worker thread.
257 if (!emptyRunQueue(cap) || globalWorkToDo()) {
258 if (cap->spare_workers) {
259 giveCapabilityToTask(cap,cap->spare_workers);
260 // The worker Task pops itself from the queue;
264 // Create a worker thread if we don't have one. If the system
265 // is interrupted, we only create a worker task if there
266 // are threads that need to be completed. If the system is
267 // shutting down, we never create a new worker.
268 if (!shutting_down_scheduler) {
270 sched_belch("starting new worker on capability %d", cap->no));
271 startWorkerTask(cap, workerStart);
276 last_free_capability = cap;
277 IF_DEBUG(scheduler, sched_belch("freeing capability %d", cap->no));
281 releaseCapability (Capability* cap UNUSED_IF_NOT_THREADS)
283 ACQUIRE_LOCK(&cap->lock);
284 releaseCapability_(cap);
285 RELEASE_LOCK(&cap->lock);
289 releaseCapabilityAndQueueWorker (Capability* cap UNUSED_IF_NOT_THREADS)
293 ACQUIRE_LOCK(&cap->lock);
295 task = cap->running_task;
297 // If the current task is a worker, save it on the spare_workers
298 // list of this Capability. A worker can mark itself as stopped,
299 // in which case it is not replaced on the spare_worker queue.
300 // This happens when the system is shutting down (see
301 // Schedule.c:workerStart()).
302 // Also, be careful to check that this task hasn't just exited
303 // Haskell to do a foreign call (task->suspended_tso).
304 if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
305 task->next = cap->spare_workers;
306 cap->spare_workers = task;
308 // Bound tasks just float around attached to their TSOs.
310 releaseCapability_(cap);
312 RELEASE_LOCK(&cap->lock);
316 /* ----------------------------------------------------------------------------
317 * waitForReturnCapability( Task *task )
319 * Purpose: when an OS thread returns from an external call,
320 * it calls waitForReturnCapability() (via Schedule.resumeThread())
321 * to wait for permission to enter the RTS & communicate the
322 * result of the external call back to the Haskell thread that
325 * ------------------------------------------------------------------------- */
327 waitForReturnCapability (Capability **pCap,
328 Task *task UNUSED_IF_NOT_THREADS)
330 #if !defined(THREADED_RTS)
332 MainCapability.running_task = task;
333 task->cap = &MainCapability;
334 *pCap = &MainCapability;
337 Capability *cap = *pCap;
340 // Try last_free_capability first
341 cap = last_free_capability;
342 if (!cap->running_task) {
344 // otherwise, search for a free capability
345 for (i = 0; i < n_capabilities; i++) {
346 cap = &capabilities[i];
347 if (!cap->running_task) {
351 // Can't find a free one, use last_free_capability.
352 cap = last_free_capability;
355 // record the Capability as the one this Task is now assocated with.
359 ASSERT(task->cap == cap);
362 ACQUIRE_LOCK(&cap->lock);
365 sched_belch("returning; I want capability %d", cap->no));
367 if (!cap->running_task) {
368 // It's free; just grab it
369 cap->running_task = task;
370 RELEASE_LOCK(&cap->lock);
372 newReturningTask(cap,task);
373 RELEASE_LOCK(&cap->lock);
376 ACQUIRE_LOCK(&task->lock);
377 // task->lock held, cap->lock not held
378 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
380 task->wakeup = rtsFalse;
381 RELEASE_LOCK(&task->lock);
383 // now check whether we should wake up...
384 ACQUIRE_LOCK(&cap->lock);
385 if (cap->running_task == NULL) {
386 if (cap->returning_tasks_hd != task) {
387 giveCapabilityToTask(cap,cap->returning_tasks_hd);
388 RELEASE_LOCK(&cap->lock);
391 cap->running_task = task;
392 popReturningTask(cap);
393 RELEASE_LOCK(&cap->lock);
396 RELEASE_LOCK(&cap->lock);
401 ASSERT(cap->running_task == task);
404 sched_belch("returning; got capability %d", cap->no));
410 #if defined(THREADED_RTS)
411 /* ----------------------------------------------------------------------------
413 * ------------------------------------------------------------------------- */
416 yieldCapability (Capability** pCap, Task *task)
418 Capability *cap = *pCap;
420 // The fast path; no locking
421 if ( cap->returning_tasks_hd == NULL && anyWorkForMe(cap,task) )
424 while ( cap->returning_tasks_hd != NULL || !anyWorkForMe(cap,task) ) {
425 IF_DEBUG(scheduler, sched_belch("giving up capability %d", cap->no));
427 // We must now release the capability and wait to be woken up
429 releaseCapabilityAndQueueWorker(cap);
432 ACQUIRE_LOCK(&task->lock);
433 // task->lock held, cap->lock not held
434 if (!task->wakeup) waitCondition(&task->cond, &task->lock);
436 task->wakeup = rtsFalse;
437 RELEASE_LOCK(&task->lock);
439 IF_DEBUG(scheduler, sched_belch("woken up on capability %d", cap->no));
440 ACQUIRE_LOCK(&cap->lock);
441 if (cap->running_task != NULL) {
442 RELEASE_LOCK(&cap->lock);
446 if (task->tso == NULL) {
447 ASSERT(cap->spare_workers != NULL);
448 // if we're not at the front of the queue, release it
449 // again. This is unlikely to happen.
450 if (cap->spare_workers != task) {
451 giveCapabilityToTask(cap,cap->spare_workers);
452 RELEASE_LOCK(&cap->lock);
455 cap->spare_workers = task->next;
458 cap->running_task = task;
459 RELEASE_LOCK(&cap->lock);
463 IF_DEBUG(scheduler, sched_belch("got capability %d", cap->no));
464 ASSERT(cap->running_task == task);
471 /* ----------------------------------------------------------------------------
474 * Used to indicate that the interrupted flag is now set, or some
475 * other global condition that might require waking up a Task on each
477 * ------------------------------------------------------------------------- */
480 prodCapabilities(rtsBool all)
486 for (i=0; i < n_capabilities; i++) {
487 cap = &capabilities[i];
488 ACQUIRE_LOCK(&cap->lock);
489 if (!cap->running_task) {
490 if (cap->spare_workers) {
491 task = cap->spare_workers;
492 ASSERT(!task->stopped);
493 giveCapabilityToTask(cap,task);
495 RELEASE_LOCK(&cap->lock);
500 RELEASE_LOCK(&cap->lock);
505 prodAllCapabilities (void)
507 prodCapabilities(rtsTrue);
510 /* ----------------------------------------------------------------------------
513 * Like prodAllCapabilities, but we only require a single Task to wake
514 * up in order to service some global event, such as checking for
515 * deadlock after some idle time has passed.
516 * ------------------------------------------------------------------------- */
519 prodOneCapability (void)
521 prodCapabilities(rtsFalse);
524 /* ----------------------------------------------------------------------------
527 * At shutdown time, we want to let everything exit as cleanly as
528 * possible. For each capability, we let its run queue drain, and
529 * allow the workers to stop.
531 * This function should be called when interrupted and
532 * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
533 * will exit the scheduler and call taskStop(), and any bound thread
534 * that wakes up will return to its caller. Runnable threads are
537 * ------------------------------------------------------------------------- */
540 shutdownCapability (Capability *cap, Task *task)
544 ASSERT(interrupted && shutting_down_scheduler);
548 for (i = 0; i < 50; i++) {
549 IF_DEBUG(scheduler, sched_belch("shutting down capability %d, attempt %d", cap->no, i));
550 ACQUIRE_LOCK(&cap->lock);
551 if (cap->running_task) {
552 RELEASE_LOCK(&cap->lock);
553 IF_DEBUG(scheduler, sched_belch("not owner, yielding"));
557 cap->running_task = task;
558 if (!emptyRunQueue(cap) || cap->spare_workers) {
559 IF_DEBUG(scheduler, sched_belch("runnable threads or workers still alive, yielding"));
560 releaseCapability_(cap); // this will wake up a worker
561 RELEASE_LOCK(&cap->lock);
565 IF_DEBUG(scheduler, sched_belch("capability %d is stopped.", cap->no));
566 RELEASE_LOCK(&cap->lock);
569 // we now have the Capability, its run queue and spare workers
570 // list are both empty.
573 #endif /* THREADED_RTS */