rts/Capability.c

   1 /* ---------------------------------------------------------------------------
   2  *
   3  * (c) The GHC Team, 2003-2006
   4  *
   5  * Capabilities
   6  *
   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).
  12  *
  13  * Only in an THREADED_RTS build will there be multiple capabilities,
  14  * for non-threaded builds there is only one global capability, namely
  15  * MainCapability.
  16  *
  17  * --------------------------------------------------------------------------*/
  18
  19 #include "PosixSource.h"
  20 #include "Rts.h"
  21
  22 #include "Capability.h"
  23 #include "Schedule.h"
  24 #include "Sparks.h"
  25 #include "Trace.h"
  26 #include "sm/GC.h" // for gcWorkerThread()
  27 #include "STM.h"
  28 #include "RtsUtils.h"
  29
  30 // one global capability, this is the Capability for non-threaded
  31 // builds, and for +RTS -N1
  32 Capability MainCapability;
  33
  34 nat n_capabilities = 0;
  35 Capability *capabilities = NULL;
  36
  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;
  42
  43 /* GC indicator, in scope for the scheduler, init'ed to false */
  44 volatile StgWord waiting_for_gc = 0;
  45
  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).
  51  * */
  52 Capability * rts_unsafeGetMyCapability (void)
  53 {
  54 #if defined(THREADED_RTS)
  55   return myTask()->cap;
  56 #else
  57   return &MainCapability;
  58 #endif
  59 }
  60
  61 #if defined(THREADED_RTS)
  62 STATIC_INLINE rtsBool
  63 globalWorkToDo (void)
  64 {
  65     return blackholes_need_checking
  66         || sched_state >= SCHED_INTERRUPTING
  67         ;
  68 }
  69 #endif
  70
  71 #if defined(THREADED_RTS)
  72 StgClosure *
  73 findSpark (Capability *cap)
  74 {
  75   Capability *robbed;
  76   StgClosurePtr spark;
  77   rtsBool retry;
  78   nat i = 0;
  79
  80   if (!emptyRunQueue(cap) || cap->returning_tasks_hd != NULL) {
  81       // If there are other threads, don't try to run any new
  82       // sparks: sparks might be speculative, we don't want to take
  83       // resources away from the main computation.
  84       return 0;
  85   }
  86
  87   do {
  88       retry = rtsFalse;
  89
  90       // first try to get a spark from our own pool.
  91       // We should be using reclaimSpark(), because it works without
  92       // needing any atomic instructions:
  93       //   spark = reclaimSpark(cap->sparks);
  94       // However, measurements show that this makes at least one benchmark
  95       // slower (prsa) and doesn't affect the others.
  96       spark = tryStealSpark(cap);
  97       if (spark != NULL) {
  98           cap->sparks_converted++;
  99
 100           // Post event for running a spark from capability's own pool.
 101           traceEventRunSpark(cap, cap->r.rCurrentTSO);
 102
 103           return spark;
 104       }
 105       if (!emptySparkPoolCap(cap)) {
 106           retry = rtsTrue;
 107       }
 108
 109       if (n_capabilities == 1) { return NULL; } // makes no sense...
 110
 111       debugTrace(DEBUG_sched,
 112                  "cap %d: Trying to steal work from other capabilities",
 113                  cap->no);
 114
 115       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
 116       start at a random place instead of 0 as well.  */
 117       for ( i=0 ; i < n_capabilities ; i++ ) {
 118           robbed = &capabilities[i];
 119           if (cap == robbed)  // ourselves...
 120               continue;
 121
 122           if (emptySparkPoolCap(robbed)) // nothing to steal here
 123               continue;
 124
 125           spark = tryStealSpark(robbed);
 126           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 127               // we conflicted with another thread while trying to steal;
 128               // try again later.
 129               retry = rtsTrue;
 130           }
 131
 132           if (spark != NULL) {
 133               cap->sparks_converted++;
 134
 135               traceEventStealSpark(cap, cap->r.rCurrentTSO, robbed->no);
 136
 137               return spark;
 138           }
 139           // otherwise: no success, try next one
 140       }
 141   } while (retry);
 142
 143   debugTrace(DEBUG_sched, "No sparks stolen");
 144   return NULL;
 145 }
 146
 147 // Returns True if any spark pool is non-empty at this moment in time
 148 // The result is only valid for an instant, of course, so in a sense
 149 // is immediately invalid, and should not be relied upon for
 150 // correctness.
 151 rtsBool
 152 anySparks (void)
 153 {
 154     nat i;
 155
 156     for (i=0; i < n_capabilities; i++) {
 157         if (!emptySparkPoolCap(&capabilities[i])) {
 158             return rtsTrue;
 159         }
 160     }
 161     return rtsFalse;
 162 }
 163 #endif
 164
 165 /* -----------------------------------------------------------------------------
 166  * Manage the returning_tasks lists.
 167  *
 168  * These functions require cap->lock
 169  * -------------------------------------------------------------------------- */
 170
 171 #if defined(THREADED_RTS)
 172 STATIC_INLINE void
 173 newReturningTask (Capability *cap, Task *task)
 174 {
 175     ASSERT_LOCK_HELD(&cap->lock);
 176     ASSERT(task->return_link == NULL);
 177     if (cap->returning_tasks_hd) {
 178         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 179         cap->returning_tasks_tl->return_link = task;
 180     } else {
 181         cap->returning_tasks_hd = task;
 182     }
 183     cap->returning_tasks_tl = task;
 184 }
 185
 186 STATIC_INLINE Task *
 187 popReturningTask (Capability *cap)
 188 {
 189     ASSERT_LOCK_HELD(&cap->lock);
 190     Task *task;
 191     task = cap->returning_tasks_hd;
 192     ASSERT(task);
 193     cap->returning_tasks_hd = task->return_link;
 194     if (!cap->returning_tasks_hd) {
 195         cap->returning_tasks_tl = NULL;
 196     }
 197     task->return_link = NULL;
 198     return task;
 199 }
 200 #endif
 201
 202 /* ----------------------------------------------------------------------------
 203  * Initialisation
 204  *
 205  * The Capability is initially marked not free.
 206  * ------------------------------------------------------------------------- */
 207
 208 static void
 209 initCapability( Capability *cap, nat i )
 210 {
 211     nat g;
 212
 213     cap->no = i;
 214     cap->in_haskell        = rtsFalse;
 215
 216     cap->run_queue_hd      = END_TSO_QUEUE;
 217     cap->run_queue_tl      = END_TSO_QUEUE;
 218
 219 #if defined(THREADED_RTS)
 220     initMutex(&cap->lock);
 221     cap->running_task      = NULL; // indicates cap is free
 222     cap->spare_workers     = NULL;
 223     cap->suspended_ccalling_tasks = NULL;
 224     cap->returning_tasks_hd = NULL;
 225     cap->returning_tasks_tl = NULL;
 226     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 227     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 228     cap->sparks_created     = 0;
 229     cap->sparks_converted   = 0;
 230     cap->sparks_pruned      = 0;
 231 #endif
 232
 233     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 234     cap->f.stgGCEnter1     = (StgFunPtr)__stg_gc_enter_1;
 235     cap->f.stgGCFun        = (StgFunPtr)__stg_gc_fun;
 236
 237     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 238                                      RtsFlags.GcFlags.generations,
 239                                      "initCapability");
 240     cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
 241                                           RtsFlags.GcFlags.generations,
 242                                           "initCapability");
 243
 244     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 245         cap->mut_lists[g] = NULL;
 246     }
 247
 248     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 249     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 250     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 251     cap->free_trec_headers = NO_TREC;
 252     cap->transaction_tokens = 0;
 253     cap->context_switch = 0;
 254     cap->pinned_object_block = NULL;
 255 }
 256
 257 /* ---------------------------------------------------------------------------
 258  * Function:  initCapabilities()
 259  *
 260  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 261  *            we keep a table of them, the size of which is
 262  *            controlled by the user via the RTS flag -N.
 263  *
 264  * ------------------------------------------------------------------------- */
 265 void
 266 initCapabilities( void )
 267 {
 268 #if defined(THREADED_RTS)
 269     nat i;
 270
 271 #ifndef REG_Base
 272     // We can't support multiple CPUs if BaseReg is not a register
 273     if (RtsFlags.ParFlags.nNodes > 1) {
 274         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 275         RtsFlags.ParFlags.nNodes = 1;
 276     }
 277 #endif
 278
 279     n_capabilities = RtsFlags.ParFlags.nNodes;
 280
 281     if (n_capabilities == 1) {
 282         capabilities = &MainCapability;
 283         // THREADED_RTS must work on builds that don't have a mutable
 284         // BaseReg (eg. unregisterised), so in this case
 285         // capabilities[0] must coincide with &MainCapability.
 286     } else {
 287         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 288                                       "initCapabilities");
 289     }
 290
 291     for (i = 0; i < n_capabilities; i++) {
 292         initCapability(&capabilities[i], i);
 293     }
 294
 295     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 296
 297 #else /* !THREADED_RTS */
 298
 299     n_capabilities = 1;
 300     capabilities = &MainCapability;
 301     initCapability(&MainCapability, 0);
 302
 303 #endif
 304
 305     // There are no free capabilities to begin with.  We will start
 306     // a worker Task to each Capability, which will quickly put the
 307     // Capability on the free list when it finds nothing to do.
 308     last_free_capability = &capabilities[0];
 309 }
 310
 311 /* ----------------------------------------------------------------------------
 312  * setContextSwitches: cause all capabilities to context switch as
 313  * soon as possible.
 314  * ------------------------------------------------------------------------- */
 315
 316 void setContextSwitches(void)
 317 {
 318     nat i;
 319     for (i=0; i < n_capabilities; i++) {
 320         contextSwitchCapability(&capabilities[i]);
 321     }
 322 }
 323
 324 /* ----------------------------------------------------------------------------
 325  * Give a Capability to a Task.  The task must currently be sleeping
 326  * on its condition variable.
 327  *
 328  * Requires cap->lock (modifies cap->running_task).
 329  *
 330  * When migrating a Task, the migrater must take task->lock before
 331  * modifying task->cap, to synchronise with the waking up Task.
 332  * Additionally, the migrater should own the Capability (when
 333  * migrating the run queue), or cap->lock (when migrating
 334  * returning_workers).
 335  *
 336  * ------------------------------------------------------------------------- */
 337
 338 #if defined(THREADED_RTS)
 339 STATIC_INLINE void
 340 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 341 {
 342     ASSERT_LOCK_HELD(&cap->lock);
 343     ASSERT(task->cap == cap);
 344     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 345                cap->no, task->tso ? "bound task" : "worker",
 346                (void *)task->id);
 347     ACQUIRE_LOCK(&task->lock);
 348     task->wakeup = rtsTrue;
 349     // the wakeup flag is needed because signalCondition() doesn't
 350     // flag the condition if the thread is already runniing, but we want
 351     // it to be sticky.
 352     signalCondition(&task->cond);
 353     RELEASE_LOCK(&task->lock);
 354 }
 355 #endif
 356
 357 /* ----------------------------------------------------------------------------
 358  * Function:  releaseCapability(Capability*)
 359  *
 360  * Purpose:   Letting go of a capability. Causes a
 361  *            'returning worker' thread or a 'waiting worker'
 362  *            to wake up, in that order.
 363  * ------------------------------------------------------------------------- */
 364
 365 #if defined(THREADED_RTS)
 366 void
 367 releaseCapability_ (Capability* cap,
 368                     rtsBool always_wakeup)
 369 {
 370     Task *task;
 371
 372     task = cap->running_task;
 373
 374     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 375
 376     cap->running_task = NULL;
 377
 378     // Check to see whether a worker thread can be given
 379     // the go-ahead to return the result of an external call..
 380     if (cap->returning_tasks_hd != NULL) {
 381         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 382         // The Task pops itself from the queue (see waitForReturnCapability())
 383         return;
 384     }
 385
 386     if (waiting_for_gc == PENDING_GC_SEQ) {
 387       last_free_capability = cap; // needed?
 388       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 389       return;
 390     }
 391
 392
 393     // If the next thread on the run queue is a bound thread,
 394     // give this Capability to the appropriate Task.
 395     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 396         // Make sure we're not about to try to wake ourselves up
 397         ASSERT(task != cap->run_queue_hd->bound);
 398         task = cap->run_queue_hd->bound;
 399         giveCapabilityToTask(cap,task);
 400         return;
 401     }
 402
 403     if (!cap->spare_workers) {
 404         // Create a worker thread if we don't have one.  If the system
 405         // is interrupted, we only create a worker task if there
 406         // are threads that need to be completed.  If the system is
 407         // shutting down, we never create a new worker.
 408         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 409             debugTrace(DEBUG_sched,
 410                        "starting new worker on capability %d", cap->no);
 411             startWorkerTask(cap, workerStart);
 412             return;
 413         }
 414     }
 415
 416     // If we have an unbound thread on the run queue, or if there's
 417     // anything else to do, give the Capability to a worker thread.
 418     if (always_wakeup ||
 419         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 420         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 421         if (cap->spare_workers) {
 422             giveCapabilityToTask(cap,cap->spare_workers);
 423             // The worker Task pops itself from the queue;
 424             return;
 425         }
 426     }
 427
 428     last_free_capability = cap;
 429     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 430 }
 431
 432 void
 433 releaseCapability (Capability* cap USED_IF_THREADS)
 434 {
 435     ACQUIRE_LOCK(&cap->lock);
 436     releaseCapability_(cap, rtsFalse);
 437     RELEASE_LOCK(&cap->lock);
 438 }
 439
 440 void
 441 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 442 {
 443     ACQUIRE_LOCK(&cap->lock);
 444     releaseCapability_(cap, rtsTrue);
 445     RELEASE_LOCK(&cap->lock);
 446 }
 447
 448 static void
 449 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 450 {
 451     Task *task;
 452
 453     ACQUIRE_LOCK(&cap->lock);
 454
 455     task = cap->running_task;
 456
 457     // If the current task is a worker, save it on the spare_workers
 458     // list of this Capability.  A worker can mark itself as stopped,
 459     // in which case it is not replaced on the spare_worker queue.
 460     // This happens when the system is shutting down (see
 461     // Schedule.c:workerStart()).
 462     // Also, be careful to check that this task hasn't just exited
 463     // Haskell to do a foreign call (task->suspended_tso).
 464     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 465         task->next = cap->spare_workers;
 466         cap->spare_workers = task;
 467     }
 468     // Bound tasks just float around attached to their TSOs.
 469
 470     releaseCapability_(cap,rtsFalse);
 471
 472     RELEASE_LOCK(&cap->lock);
 473 }
 474 #endif
 475
 476 /* ----------------------------------------------------------------------------
 477  * waitForReturnCapability( Task *task )
 478  *
 479  * Purpose:  when an OS thread returns from an external call,
 480  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 481  * to wait for permission to enter the RTS & communicate the
 482  * result of the external call back to the Haskell thread that
 483  * made it.
 484  *
 485  * ------------------------------------------------------------------------- */
 486 void
 487 waitForReturnCapability (Capability **pCap, Task *task)
 488 {
 489 #if !defined(THREADED_RTS)
 490
 491     MainCapability.running_task = task;
 492     task->cap = &MainCapability;
 493     *pCap = &MainCapability;
 494
 495 #else
 496     Capability *cap = *pCap;
 497
 498     if (cap == NULL) {
 499         // Try last_free_capability first
 500         cap = last_free_capability;
 501         if (cap->running_task) {
 502             nat i;
 503             // otherwise, search for a free capability
 504             cap = NULL;
 505             for (i = 0; i < n_capabilities; i++) {
 506                 if (!capabilities[i].running_task) {
 507                     cap = &capabilities[i];
 508                     break;
 509                 }
 510             }
 511             if (cap == NULL) {
 512                 // Can't find a free one, use last_free_capability.
 513                 cap = last_free_capability;
 514             }
 515         }
 516
 517         // record the Capability as the one this Task is now assocated with.
 518         task->cap = cap;
 519
 520     } else {
 521         ASSERT(task->cap == cap);
 522     }
 523
 524     ACQUIRE_LOCK(&cap->lock);
 525
 526     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 527
 528     if (!cap->running_task) {
 529         // It's free; just grab it
 530         cap->running_task = task;
 531         RELEASE_LOCK(&cap->lock);
 532     } else {
 533         newReturningTask(cap,task);
 534         RELEASE_LOCK(&cap->lock);
 535
 536         for (;;) {
 537             ACQUIRE_LOCK(&task->lock);
 538             // task->lock held, cap->lock not held
 539             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 540             cap = task->cap;
 541             task->wakeup = rtsFalse;
 542             RELEASE_LOCK(&task->lock);
 543
 544             // now check whether we should wake up...
 545             ACQUIRE_LOCK(&cap->lock);
 546             if (cap->running_task == NULL) {
 547                 if (cap->returning_tasks_hd != task) {
 548                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 549                     RELEASE_LOCK(&cap->lock);
 550                     continue;
 551                 }
 552                 cap->running_task = task;
 553                 popReturningTask(cap);
 554                 RELEASE_LOCK(&cap->lock);
 555                 break;
 556             }
 557             RELEASE_LOCK(&cap->lock);
 558         }
 559
 560     }
 561
 562     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 563
 564     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 565
 566     *pCap = cap;
 567 #endif
 568 }
 569
 570 #if defined(THREADED_RTS)
 571 /* ----------------------------------------------------------------------------
 572  * yieldCapability
 573  * ------------------------------------------------------------------------- */
 574
 575 void
 576 yieldCapability (Capability** pCap, Task *task)
 577 {
 578     Capability *cap = *pCap;
 579
 580     if (waiting_for_gc == PENDING_GC_PAR) {
 581         traceEventGcStart(cap);
 582         gcWorkerThread(cap);
 583         traceEventGcEnd(cap);
 584         return;
 585     }
 586
 587         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 588
 589         // We must now release the capability and wait to be woken up
 590         // again.
 591         task->wakeup = rtsFalse;
 592         releaseCapabilityAndQueueWorker(cap);
 593
 594         for (;;) {
 595             ACQUIRE_LOCK(&task->lock);
 596             // task->lock held, cap->lock not held
 597             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 598             cap = task->cap;
 599             task->wakeup = rtsFalse;
 600             RELEASE_LOCK(&task->lock);
 601
 602             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 603
 604             ACQUIRE_LOCK(&cap->lock);
 605             if (cap->running_task != NULL) {
 606                 debugTrace(DEBUG_sched,
 607                            "capability %d is owned by another task", cap->no);
 608                 RELEASE_LOCK(&cap->lock);
 609                 continue;
 610             }
 611
 612             if (task->tso == NULL) {
 613                 ASSERT(cap->spare_workers != NULL);
 614                 // if we're not at the front of the queue, release it
 615                 // again.  This is unlikely to happen.
 616                 if (cap->spare_workers != task) {
 617                     giveCapabilityToTask(cap,cap->spare_workers);
 618                     RELEASE_LOCK(&cap->lock);
 619                     continue;
 620                 }
 621                 cap->spare_workers = task->next;
 622                 task->next = NULL;
 623             }
 624             cap->running_task = task;
 625             RELEASE_LOCK(&cap->lock);
 626             break;
 627         }
 628
 629         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 630         ASSERT(cap->running_task == task);
 631
 632     *pCap = cap;
 633
 634     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 635
 636     return;
 637 }
 638
 639 /* ----------------------------------------------------------------------------
 640  * Wake up a thread on a Capability.
 641  *
 642  * This is used when the current Task is running on a Capability and
 643  * wishes to wake up a thread on a different Capability.
 644  * ------------------------------------------------------------------------- */
 645
 646 void
 647 wakeupThreadOnCapability (Capability *my_cap,
 648                           Capability *other_cap,
 649                           StgTSO *tso)
 650 {
 651     ACQUIRE_LOCK(&other_cap->lock);
 652
 653     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 654     if (tso->bound) {
 655         ASSERT(tso->bound->cap == tso->cap);
 656         tso->bound->cap = other_cap;
 657     }
 658     tso->cap = other_cap;
 659
 660     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 661
 662     if (other_cap->running_task == NULL) {
 663         // nobody is running this Capability, we can add our thread
 664         // directly onto the run queue and start up a Task to run it.
 665
 666         other_cap->running_task = myTask();
 667             // precond for releaseCapability_() and appendToRunQueue()
 668
 669         appendToRunQueue(other_cap,tso);
 670
 671         releaseCapability_(other_cap,rtsFalse);
 672     } else {
 673         appendToWakeupQueue(my_cap,other_cap,tso);
 674         other_cap->context_switch = 1;
 675         // someone is running on this Capability, so it cannot be
 676         // freed without first checking the wakeup queue (see
 677         // releaseCapability_).
 678     }
 679
 680     RELEASE_LOCK(&other_cap->lock);
 681 }
 682
 683 /* ----------------------------------------------------------------------------
 684  * prodCapability
 685  *
 686  * If a Capability is currently idle, wake up a Task on it.  Used to
 687  * get every Capability into the GC.
 688  * ------------------------------------------------------------------------- */
 689
 690 void
 691 prodCapability (Capability *cap, Task *task)
 692 {
 693     ACQUIRE_LOCK(&cap->lock);
 694     if (!cap->running_task) {
 695         cap->running_task = task;
 696         releaseCapability_(cap,rtsTrue);
 697     }
 698     RELEASE_LOCK(&cap->lock);
 699 }
 700
 701 /* ----------------------------------------------------------------------------
 702  * shutdownCapability
 703  *
 704  * At shutdown time, we want to let everything exit as cleanly as
 705  * possible.  For each capability, we let its run queue drain, and
 706  * allow the workers to stop.
 707  *
 708  * This function should be called when interrupted and
 709  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 710  * will exit the scheduler and call taskStop(), and any bound thread
 711  * that wakes up will return to its caller.  Runnable threads are
 712  * killed.
 713  *
 714  * ------------------------------------------------------------------------- */
 715
 716 void
 717 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 718 {
 719     nat i;
 720
 721     task->cap = cap;
 722
 723     // Loop indefinitely until all the workers have exited and there
 724     // are no Haskell threads left.  We used to bail out after 50
 725     // iterations of this loop, but that occasionally left a worker
 726     // running which caused problems later (the closeMutex() below
 727     // isn't safe, for one thing).
 728
 729     for (i = 0; /* i < 50 */; i++) {
 730         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 731
 732         debugTrace(DEBUG_sched,
 733                    "shutting down capability %d, attempt %d", cap->no, i);
 734         ACQUIRE_LOCK(&cap->lock);
 735         if (cap->running_task) {
 736             RELEASE_LOCK(&cap->lock);
 737             debugTrace(DEBUG_sched, "not owner, yielding");
 738             yieldThread();
 739             continue;
 740         }
 741         cap->running_task = task;
 742
 743         if (cap->spare_workers) {
 744             // Look for workers that have died without removing
 745             // themselves from the list; this could happen if the OS
 746             // summarily killed the thread, for example.  This
 747             // actually happens on Windows when the system is
 748             // terminating the program, and the RTS is running in a
 749             // DLL.
 750             Task *t, *prev;
 751             prev = NULL;
 752             for (t = cap->spare_workers; t != NULL; t = t->next) {
 753                 if (!osThreadIsAlive(t->id)) {
 754                     debugTrace(DEBUG_sched,
 755                                "worker thread %p has died unexpectedly", (void *)t->id);
 756                         if (!prev) {
 757                             cap->spare_workers = t->next;
 758                         } else {
 759                             prev->next = t->next;
 760                         }
 761                         prev = t;
 762                 }
 763             }
 764         }
 765
 766         if (!emptyRunQueue(cap) || cap->spare_workers) {
 767             debugTrace(DEBUG_sched,
 768                        "runnable threads or workers still alive, yielding");
 769             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 770             RELEASE_LOCK(&cap->lock);
 771             yieldThread();
 772             continue;
 773         }
 774
 775         // If "safe", then busy-wait for any threads currently doing
 776         // foreign calls.  If we're about to unload this DLL, for
 777         // example, we need to be sure that there are no OS threads
 778         // that will try to return to code that has been unloaded.
 779         // We can be a bit more relaxed when this is a standalone
 780         // program that is about to terminate, and let safe=false.
 781         if (cap->suspended_ccalling_tasks && safe) {
 782             debugTrace(DEBUG_sched,
 783                        "thread(s) are involved in foreign calls, yielding");
 784             cap->running_task = NULL;
 785             RELEASE_LOCK(&cap->lock);
 786             yieldThread();
 787             continue;
 788         }
 789
 790         traceEventShutdown(cap);
 791         RELEASE_LOCK(&cap->lock);
 792         break;
 793     }
 794     // we now have the Capability, its run queue and spare workers
 795     // list are both empty.
 796
 797     // ToDo: we can't drop this mutex, because there might still be
 798     // threads performing foreign calls that will eventually try to
 799     // return via resumeThread() and attempt to grab cap->lock.
 800     // closeMutex(&cap->lock);
 801 }
 802
 803 /* ----------------------------------------------------------------------------
 804  * tryGrabCapability
 805  *
 806  * Attempt to gain control of a Capability if it is free.
 807  *
 808  * ------------------------------------------------------------------------- */
 809
 810 rtsBool
 811 tryGrabCapability (Capability *cap, Task *task)
 812 {
 813     if (cap->running_task != NULL) return rtsFalse;
 814     ACQUIRE_LOCK(&cap->lock);
 815     if (cap->running_task != NULL) {
 816         RELEASE_LOCK(&cap->lock);
 817         return rtsFalse;
 818     }
 819     task->cap = cap;
 820     cap->running_task = task;
 821     RELEASE_LOCK(&cap->lock);
 822     return rtsTrue;
 823 }
 824
 825
 826 #endif /* THREADED_RTS */
 827
 828 static void
 829 freeCapability (Capability *cap)
 830 {
 831     stgFree(cap->mut_lists);
 832     stgFree(cap->saved_mut_lists);
 833 #if defined(THREADED_RTS)
 834     freeSparkPool(cap->sparks);
 835 #endif
 836 }
 837
 838 void
 839 freeCapabilities (void)
 840 {
 841 #if defined(THREADED_RTS)
 842     nat i;
 843     for (i=0; i < n_capabilities; i++) {
 844         freeCapability(&capabilities[i]);
 845     }
 846 #else
 847     freeCapability(&MainCapability);
 848 #endif
 849 }
 850
 851 /* ---------------------------------------------------------------------------
 852    Mark everything directly reachable from the Capabilities.  When
 853    using multiple GC threads, each GC thread marks all Capabilities
 854    for which (c `mod` n == 0), for Capability c and thread n.
 855    ------------------------------------------------------------------------ */
 856
 857 void
 858 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 859                       rtsBool prune_sparks USED_IF_THREADS)
 860 {
 861     nat i;
 862     Capability *cap;
 863     Task *task;
 864
 865     // Each GC thread is responsible for following roots from the
 866     // Capability of the same number.  There will usually be the same
 867     // or fewer Capabilities as GC threads, but just in case there
 868     // are more, we mark every Capability whose number is the GC
 869     // thread's index plus a multiple of the number of GC threads.
 870     for (i = i0; i < n_capabilities; i += delta) {
 871         cap = &capabilities[i];
 872         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 873         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 874 #if defined(THREADED_RTS)
 875         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 876         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 877 #endif
 878         for (task = cap->suspended_ccalling_tasks; task != NULL;
 879              task=task->next) {
 880             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 881         }
 882
 883 #if defined(THREADED_RTS)
 884         if (prune_sparks) {
 885             pruneSparkQueue (evac, user, cap);
 886         } else {
 887             traverseSparkQueue (evac, user, cap);
 888         }
 889 #endif
 890     }
 891
 892 #if !defined(THREADED_RTS)
 893     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 894     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 895     evac(user, (StgClosure **)(void *)&sleeping_queue);
 896 #endif
 897 }
 898
 899 void
 900 markCapabilities (evac_fn evac, void *user)
 901 {
 902     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 903 }