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         // assertion is false: in schedule() we force a yield after
 399         // ThreadBlocked, but the thread may be back on the run queue
 400         // by now.
 401         task = cap->run_queue_hd->bound;
 402         giveCapabilityToTask(cap,task);
 403         return;
 404     }
 405
 406     if (!cap->spare_workers) {
 407         // Create a worker thread if we don't have one.  If the system
 408         // is interrupted, we only create a worker task if there
 409         // are threads that need to be completed.  If the system is
 410         // shutting down, we never create a new worker.
 411         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 412             debugTrace(DEBUG_sched,
 413                        "starting new worker on capability %d", cap->no);
 414             startWorkerTask(cap, workerStart);
 415             return;
 416         }
 417     }
 418
 419     // If we have an unbound thread on the run queue, or if there's
 420     // anything else to do, give the Capability to a worker thread.
 421     if (always_wakeup ||
 422         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 423         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 424         if (cap->spare_workers) {
 425             giveCapabilityToTask(cap,cap->spare_workers);
 426             // The worker Task pops itself from the queue;
 427             return;
 428         }
 429     }
 430
 431     last_free_capability = cap;
 432     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 433 }
 434
 435 void
 436 releaseCapability (Capability* cap USED_IF_THREADS)
 437 {
 438     ACQUIRE_LOCK(&cap->lock);
 439     releaseCapability_(cap, rtsFalse);
 440     RELEASE_LOCK(&cap->lock);
 441 }
 442
 443 void
 444 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 445 {
 446     ACQUIRE_LOCK(&cap->lock);
 447     releaseCapability_(cap, rtsTrue);
 448     RELEASE_LOCK(&cap->lock);
 449 }
 450
 451 static void
 452 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 453 {
 454     Task *task;
 455
 456     ACQUIRE_LOCK(&cap->lock);
 457
 458     task = cap->running_task;
 459
 460     // If the current task is a worker, save it on the spare_workers
 461     // list of this Capability.  A worker can mark itself as stopped,
 462     // in which case it is not replaced on the spare_worker queue.
 463     // This happens when the system is shutting down (see
 464     // Schedule.c:workerStart()).
 465     // Also, be careful to check that this task hasn't just exited
 466     // Haskell to do a foreign call (task->suspended_tso).
 467     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 468         task->next = cap->spare_workers;
 469         cap->spare_workers = task;
 470     }
 471     // Bound tasks just float around attached to their TSOs.
 472
 473     releaseCapability_(cap,rtsFalse);
 474
 475     RELEASE_LOCK(&cap->lock);
 476 }
 477 #endif
 478
 479 /* ----------------------------------------------------------------------------
 480  * waitForReturnCapability( Task *task )
 481  *
 482  * Purpose:  when an OS thread returns from an external call,
 483  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 484  * to wait for permission to enter the RTS & communicate the
 485  * result of the external call back to the Haskell thread that
 486  * made it.
 487  *
 488  * ------------------------------------------------------------------------- */
 489 void
 490 waitForReturnCapability (Capability **pCap, Task *task)
 491 {
 492 #if !defined(THREADED_RTS)
 493
 494     MainCapability.running_task = task;
 495     task->cap = &MainCapability;
 496     *pCap = &MainCapability;
 497
 498 #else
 499     Capability *cap = *pCap;
 500
 501     if (cap == NULL) {
 502         // Try last_free_capability first
 503         cap = last_free_capability;
 504         if (cap->running_task) {
 505             nat i;
 506             // otherwise, search for a free capability
 507             cap = NULL;
 508             for (i = 0; i < n_capabilities; i++) {
 509                 if (!capabilities[i].running_task) {
 510                     cap = &capabilities[i];
 511                     break;
 512                 }
 513             }
 514             if (cap == NULL) {
 515                 // Can't find a free one, use last_free_capability.
 516                 cap = last_free_capability;
 517             }
 518         }
 519
 520         // record the Capability as the one this Task is now assocated with.
 521         task->cap = cap;
 522
 523     } else {
 524         ASSERT(task->cap == cap);
 525     }
 526
 527     ACQUIRE_LOCK(&cap->lock);
 528
 529     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 530
 531     if (!cap->running_task) {
 532         // It's free; just grab it
 533         cap->running_task = task;
 534         RELEASE_LOCK(&cap->lock);
 535     } else {
 536         newReturningTask(cap,task);
 537         RELEASE_LOCK(&cap->lock);
 538
 539         for (;;) {
 540             ACQUIRE_LOCK(&task->lock);
 541             // task->lock held, cap->lock not held
 542             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 543             cap = task->cap;
 544             task->wakeup = rtsFalse;
 545             RELEASE_LOCK(&task->lock);
 546
 547             // now check whether we should wake up...
 548             ACQUIRE_LOCK(&cap->lock);
 549             if (cap->running_task == NULL) {
 550                 if (cap->returning_tasks_hd != task) {
 551                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 552                     RELEASE_LOCK(&cap->lock);
 553                     continue;
 554                 }
 555                 cap->running_task = task;
 556                 popReturningTask(cap);
 557                 RELEASE_LOCK(&cap->lock);
 558                 break;
 559             }
 560             RELEASE_LOCK(&cap->lock);
 561         }
 562
 563     }
 564
 565     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 566
 567     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 568
 569     *pCap = cap;
 570 #endif
 571 }
 572
 573 #if defined(THREADED_RTS)
 574 /* ----------------------------------------------------------------------------
 575  * yieldCapability
 576  * ------------------------------------------------------------------------- */
 577
 578 void
 579 yieldCapability (Capability** pCap, Task *task)
 580 {
 581     Capability *cap = *pCap;
 582
 583     if (waiting_for_gc == PENDING_GC_PAR) {
 584         traceEventGcStart(cap);
 585         gcWorkerThread(cap);
 586         traceEventGcEnd(cap);
 587         return;
 588     }
 589
 590         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 591
 592         // We must now release the capability and wait to be woken up
 593         // again.
 594         task->wakeup = rtsFalse;
 595         releaseCapabilityAndQueueWorker(cap);
 596
 597         for (;;) {
 598             ACQUIRE_LOCK(&task->lock);
 599             // task->lock held, cap->lock not held
 600             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 601             cap = task->cap;
 602             task->wakeup = rtsFalse;
 603             RELEASE_LOCK(&task->lock);
 604
 605             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 606
 607             ACQUIRE_LOCK(&cap->lock);
 608             if (cap->running_task != NULL) {
 609                 debugTrace(DEBUG_sched,
 610                            "capability %d is owned by another task", cap->no);
 611                 RELEASE_LOCK(&cap->lock);
 612                 continue;
 613             }
 614
 615             if (task->tso == NULL) {
 616                 ASSERT(cap->spare_workers != NULL);
 617                 // if we're not at the front of the queue, release it
 618                 // again.  This is unlikely to happen.
 619                 if (cap->spare_workers != task) {
 620                     giveCapabilityToTask(cap,cap->spare_workers);
 621                     RELEASE_LOCK(&cap->lock);
 622                     continue;
 623                 }
 624                 cap->spare_workers = task->next;
 625                 task->next = NULL;
 626             }
 627             cap->running_task = task;
 628             RELEASE_LOCK(&cap->lock);
 629             break;
 630         }
 631
 632         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 633         ASSERT(cap->running_task == task);
 634
 635     *pCap = cap;
 636
 637     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 638
 639     return;
 640 }
 641
 642 /* ----------------------------------------------------------------------------
 643  * Wake up a thread on a Capability.
 644  *
 645  * This is used when the current Task is running on a Capability and
 646  * wishes to wake up a thread on a different Capability.
 647  * ------------------------------------------------------------------------- */
 648
 649 void
 650 wakeupThreadOnCapability (Capability *my_cap,
 651                           Capability *other_cap,
 652                           StgTSO *tso)
 653 {
 654     ACQUIRE_LOCK(&other_cap->lock);
 655
 656     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 657     if (tso->bound) {
 658         ASSERT(tso->bound->cap == tso->cap);
 659         tso->bound->cap = other_cap;
 660     }
 661     tso->cap = other_cap;
 662
 663     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 664
 665     if (other_cap->running_task == NULL) {
 666         // nobody is running this Capability, we can add our thread
 667         // directly onto the run queue and start up a Task to run it.
 668
 669         other_cap->running_task = myTask();
 670             // precond for releaseCapability_() and appendToRunQueue()
 671
 672         appendToRunQueue(other_cap,tso);
 673
 674         releaseCapability_(other_cap,rtsFalse);
 675     } else {
 676         appendToWakeupQueue(my_cap,other_cap,tso);
 677         other_cap->context_switch = 1;
 678         // someone is running on this Capability, so it cannot be
 679         // freed without first checking the wakeup queue (see
 680         // releaseCapability_).
 681     }
 682
 683     RELEASE_LOCK(&other_cap->lock);
 684 }
 685
 686 /* ----------------------------------------------------------------------------
 687  * prodCapability
 688  *
 689  * If a Capability is currently idle, wake up a Task on it.  Used to
 690  * get every Capability into the GC.
 691  * ------------------------------------------------------------------------- */
 692
 693 void
 694 prodCapability (Capability *cap, Task *task)
 695 {
 696     ACQUIRE_LOCK(&cap->lock);
 697     if (!cap->running_task) {
 698         cap->running_task = task;
 699         releaseCapability_(cap,rtsTrue);
 700     }
 701     RELEASE_LOCK(&cap->lock);
 702 }
 703
 704 /* ----------------------------------------------------------------------------
 705  * shutdownCapability
 706  *
 707  * At shutdown time, we want to let everything exit as cleanly as
 708  * possible.  For each capability, we let its run queue drain, and
 709  * allow the workers to stop.
 710  *
 711  * This function should be called when interrupted and
 712  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 713  * will exit the scheduler and call taskStop(), and any bound thread
 714  * that wakes up will return to its caller.  Runnable threads are
 715  * killed.
 716  *
 717  * ------------------------------------------------------------------------- */
 718
 719 void
 720 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 721 {
 722     nat i;
 723
 724     task->cap = cap;
 725
 726     // Loop indefinitely until all the workers have exited and there
 727     // are no Haskell threads left.  We used to bail out after 50
 728     // iterations of this loop, but that occasionally left a worker
 729     // running which caused problems later (the closeMutex() below
 730     // isn't safe, for one thing).
 731
 732     for (i = 0; /* i < 50 */; i++) {
 733         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 734
 735         debugTrace(DEBUG_sched,
 736                    "shutting down capability %d, attempt %d", cap->no, i);
 737         ACQUIRE_LOCK(&cap->lock);
 738         if (cap->running_task) {
 739             RELEASE_LOCK(&cap->lock);
 740             debugTrace(DEBUG_sched, "not owner, yielding");
 741             yieldThread();
 742             continue;
 743         }
 744         cap->running_task = task;
 745
 746         if (cap->spare_workers) {
 747             // Look for workers that have died without removing
 748             // themselves from the list; this could happen if the OS
 749             // summarily killed the thread, for example.  This
 750             // actually happens on Windows when the system is
 751             // terminating the program, and the RTS is running in a
 752             // DLL.
 753             Task *t, *prev;
 754             prev = NULL;
 755             for (t = cap->spare_workers; t != NULL; t = t->next) {
 756                 if (!osThreadIsAlive(t->id)) {
 757                     debugTrace(DEBUG_sched,
 758                                "worker thread %p has died unexpectedly", (void *)t->id);
 759                         if (!prev) {
 760                             cap->spare_workers = t->next;
 761                         } else {
 762                             prev->next = t->next;
 763                         }
 764                         prev = t;
 765                 }
 766             }
 767         }
 768
 769         if (!emptyRunQueue(cap) || cap->spare_workers) {
 770             debugTrace(DEBUG_sched,
 771                        "runnable threads or workers still alive, yielding");
 772             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 773             RELEASE_LOCK(&cap->lock);
 774             yieldThread();
 775             continue;
 776         }
 777
 778         // If "safe", then busy-wait for any threads currently doing
 779         // foreign calls.  If we're about to unload this DLL, for
 780         // example, we need to be sure that there are no OS threads
 781         // that will try to return to code that has been unloaded.
 782         // We can be a bit more relaxed when this is a standalone
 783         // program that is about to terminate, and let safe=false.
 784         if (cap->suspended_ccalling_tasks && safe) {
 785             debugTrace(DEBUG_sched,
 786                        "thread(s) are involved in foreign calls, yielding");
 787             cap->running_task = NULL;
 788             RELEASE_LOCK(&cap->lock);
 789             // The IO manager thread might have been slow to start up,
 790             // so the first attempt to kill it might not have
 791             // succeeded.  Just in case, try again - the kill message
 792             // will only be sent once.
 793             //
 794             // To reproduce this deadlock: run ffi002(threaded1)
 795             // repeatedly on a loaded machine.
 796             ioManagerDie();
 797             yieldThread();
 798             continue;
 799         }
 800
 801         traceEventShutdown(cap);
 802         RELEASE_LOCK(&cap->lock);
 803         break;
 804     }
 805     // we now have the Capability, its run queue and spare workers
 806     // list are both empty.
 807
 808     // ToDo: we can't drop this mutex, because there might still be
 809     // threads performing foreign calls that will eventually try to
 810     // return via resumeThread() and attempt to grab cap->lock.
 811     // closeMutex(&cap->lock);
 812 }
 813
 814 /* ----------------------------------------------------------------------------
 815  * tryGrabCapability
 816  *
 817  * Attempt to gain control of a Capability if it is free.
 818  *
 819  * ------------------------------------------------------------------------- */
 820
 821 rtsBool
 822 tryGrabCapability (Capability *cap, Task *task)
 823 {
 824     if (cap->running_task != NULL) return rtsFalse;
 825     ACQUIRE_LOCK(&cap->lock);
 826     if (cap->running_task != NULL) {
 827         RELEASE_LOCK(&cap->lock);
 828         return rtsFalse;
 829     }
 830     task->cap = cap;
 831     cap->running_task = task;
 832     RELEASE_LOCK(&cap->lock);
 833     return rtsTrue;
 834 }
 835
 836
 837 #endif /* THREADED_RTS */
 838
 839 static void
 840 freeCapability (Capability *cap)
 841 {
 842     stgFree(cap->mut_lists);
 843     stgFree(cap->saved_mut_lists);
 844 #if defined(THREADED_RTS)
 845     freeSparkPool(cap->sparks);
 846 #endif
 847 }
 848
 849 void
 850 freeCapabilities (void)
 851 {
 852 #if defined(THREADED_RTS)
 853     nat i;
 854     for (i=0; i < n_capabilities; i++) {
 855         freeCapability(&capabilities[i]);
 856     }
 857 #else
 858     freeCapability(&MainCapability);
 859 #endif
 860 }
 861
 862 /* ---------------------------------------------------------------------------
 863    Mark everything directly reachable from the Capabilities.  When
 864    using multiple GC threads, each GC thread marks all Capabilities
 865    for which (c `mod` n == 0), for Capability c and thread n.
 866    ------------------------------------------------------------------------ */
 867
 868 void
 869 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 870                       rtsBool prune_sparks USED_IF_THREADS)
 871 {
 872     nat i;
 873     Capability *cap;
 874     Task *task;
 875
 876     // Each GC thread is responsible for following roots from the
 877     // Capability of the same number.  There will usually be the same
 878     // or fewer Capabilities as GC threads, but just in case there
 879     // are more, we mark every Capability whose number is the GC
 880     // thread's index plus a multiple of the number of GC threads.
 881     for (i = i0; i < n_capabilities; i += delta) {
 882         cap = &capabilities[i];
 883         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 884         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 885 #if defined(THREADED_RTS)
 886         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 887         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 888 #endif
 889         for (task = cap->suspended_ccalling_tasks; task != NULL;
 890              task=task->next) {
 891             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 892         }
 893
 894 #if defined(THREADED_RTS)
 895         if (prune_sparks) {
 896             pruneSparkQueue (evac, user, cap);
 897         } else {
 898             traverseSparkQueue (evac, user, cap);
 899         }
 900 #endif
 901     }
 902
 903 #if !defined(THREADED_RTS)
 904     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 905     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 906     evac(user, (StgClosure **)(void *)&sleeping_queue);
 907 #endif
 908 }
 909
 910 void
 911 markCapabilities (evac_fn evac, void *user)
 912 {
 913     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 914 }