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->next == NULL);
 177     if (cap->returning_tasks_hd) {
 178         ASSERT(cap->returning_tasks_tl->next == NULL);
 179         cap->returning_tasks_tl->next = 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->next;
 194     if (!cap->returning_tasks_hd) {
 195         cap->returning_tasks_tl = NULL;
 196     }
 197     task->next = 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_ccalls  = NULL;
 224     cap->returning_tasks_hd = NULL;
 225     cap->returning_tasks_tl = NULL;
 226     cap->inbox              = (Message*)END_TSO_QUEUE;
 227     cap->sparks_created     = 0;
 228     cap->sparks_converted   = 0;
 229     cap->sparks_pruned      = 0;
 230 #endif
 231
 232     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 233     cap->f.stgGCEnter1     = (StgFunPtr)__stg_gc_enter_1;
 234     cap->f.stgGCFun        = (StgFunPtr)__stg_gc_fun;
 235
 236     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 237                                      RtsFlags.GcFlags.generations,
 238                                      "initCapability");
 239     cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
 240                                           RtsFlags.GcFlags.generations,
 241                                           "initCapability");
 242
 243     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 244         cap->mut_lists[g] = NULL;
 245     }
 246
 247     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 248     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 249     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 250     cap->free_trec_headers = NO_TREC;
 251     cap->transaction_tokens = 0;
 252     cap->context_switch = 0;
 253     cap->pinned_object_block = NULL;
 254 }
 255
 256 /* ---------------------------------------------------------------------------
 257  * Function:  initCapabilities()
 258  *
 259  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 260  *            we keep a table of them, the size of which is
 261  *            controlled by the user via the RTS flag -N.
 262  *
 263  * ------------------------------------------------------------------------- */
 264 void
 265 initCapabilities( void )
 266 {
 267 #if defined(THREADED_RTS)
 268     nat i;
 269
 270 #ifndef REG_Base
 271     // We can't support multiple CPUs if BaseReg is not a register
 272     if (RtsFlags.ParFlags.nNodes > 1) {
 273         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 274         RtsFlags.ParFlags.nNodes = 1;
 275     }
 276 #endif
 277
 278     n_capabilities = RtsFlags.ParFlags.nNodes;
 279
 280     if (n_capabilities == 1) {
 281         capabilities = &MainCapability;
 282         // THREADED_RTS must work on builds that don't have a mutable
 283         // BaseReg (eg. unregisterised), so in this case
 284         // capabilities[0] must coincide with &MainCapability.
 285     } else {
 286         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 287                                       "initCapabilities");
 288     }
 289
 290     for (i = 0; i < n_capabilities; i++) {
 291         initCapability(&capabilities[i], i);
 292     }
 293
 294     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 295
 296 #else /* !THREADED_RTS */
 297
 298     n_capabilities = 1;
 299     capabilities = &MainCapability;
 300     initCapability(&MainCapability, 0);
 301
 302 #endif
 303
 304     // There are no free capabilities to begin with.  We will start
 305     // a worker Task to each Capability, which will quickly put the
 306     // Capability on the free list when it finds nothing to do.
 307     last_free_capability = &capabilities[0];
 308 }
 309
 310 /* ----------------------------------------------------------------------------
 311  * setContextSwitches: cause all capabilities to context switch as
 312  * soon as possible.
 313  * ------------------------------------------------------------------------- */
 314
 315 void setContextSwitches(void)
 316 {
 317     nat i;
 318     for (i=0; i < n_capabilities; i++) {
 319         contextSwitchCapability(&capabilities[i]);
 320     }
 321 }
 322
 323 /* ----------------------------------------------------------------------------
 324  * Give a Capability to a Task.  The task must currently be sleeping
 325  * on its condition variable.
 326  *
 327  * Requires cap->lock (modifies cap->running_task).
 328  *
 329  * When migrating a Task, the migrater must take task->lock before
 330  * modifying task->cap, to synchronise with the waking up Task.
 331  * Additionally, the migrater should own the Capability (when
 332  * migrating the run queue), or cap->lock (when migrating
 333  * returning_workers).
 334  *
 335  * ------------------------------------------------------------------------- */
 336
 337 #if defined(THREADED_RTS)
 338 STATIC_INLINE void
 339 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 340 {
 341     ASSERT_LOCK_HELD(&cap->lock);
 342     ASSERT(task->cap == cap);
 343     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 344                cap->no, task->incall->tso ? "bound task" : "worker",
 345                (void *)task->id);
 346     ACQUIRE_LOCK(&task->lock);
 347     task->wakeup = rtsTrue;
 348     // the wakeup flag is needed because signalCondition() doesn't
 349     // flag the condition if the thread is already runniing, but we want
 350     // it to be sticky.
 351     signalCondition(&task->cond);
 352     RELEASE_LOCK(&task->lock);
 353 }
 354 #endif
 355
 356 /* ----------------------------------------------------------------------------
 357  * Function:  releaseCapability(Capability*)
 358  *
 359  * Purpose:   Letting go of a capability. Causes a
 360  *            'returning worker' thread or a 'waiting worker'
 361  *            to wake up, in that order.
 362  * ------------------------------------------------------------------------- */
 363
 364 #if defined(THREADED_RTS)
 365 void
 366 releaseCapability_ (Capability* cap,
 367                     rtsBool always_wakeup)
 368 {
 369     Task *task;
 370
 371     task = cap->running_task;
 372
 373     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 374
 375     cap->running_task = NULL;
 376
 377     // Check to see whether a worker thread can be given
 378     // the go-ahead to return the result of an external call..
 379     if (cap->returning_tasks_hd != NULL) {
 380         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 381         // The Task pops itself from the queue (see waitForReturnCapability())
 382         return;
 383     }
 384
 385     if (waiting_for_gc == PENDING_GC_SEQ) {
 386       last_free_capability = cap; // needed?
 387       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 388       return;
 389     }
 390
 391
 392     // If the next thread on the run queue is a bound thread,
 393     // give this Capability to the appropriate Task.
 394     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 395         // Make sure we're not about to try to wake ourselves up
 396         // ASSERT(task != cap->run_queue_hd->bound);
 397         // assertion is false: in schedule() we force a yield after
 398         // ThreadBlocked, but the thread may be back on the run queue
 399         // by now.
 400         task = cap->run_queue_hd->bound->task;
 401         giveCapabilityToTask(cap,task);
 402         return;
 403     }
 404
 405     if (!cap->spare_workers) {
 406         // Create a worker thread if we don't have one.  If the system
 407         // is interrupted, we only create a worker task if there
 408         // are threads that need to be completed.  If the system is
 409         // shutting down, we never create a new worker.
 410         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 411             debugTrace(DEBUG_sched,
 412                        "starting new worker on capability %d", cap->no);
 413             startWorkerTask(cap);
 414             return;
 415         }
 416     }
 417
 418     // If we have an unbound thread on the run queue, or if there's
 419     // anything else to do, give the Capability to a worker thread.
 420     if (always_wakeup ||
 421         !emptyRunQueue(cap) || !emptyInbox(cap) ||
 422         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 423         if (cap->spare_workers) {
 424             giveCapabilityToTask(cap,cap->spare_workers);
 425             // The worker Task pops itself from the queue;
 426             return;
 427         }
 428     }
 429
 430     last_free_capability = cap;
 431     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 432 }
 433
 434 void
 435 releaseCapability (Capability* cap USED_IF_THREADS)
 436 {
 437     ACQUIRE_LOCK(&cap->lock);
 438     releaseCapability_(cap, rtsFalse);
 439     RELEASE_LOCK(&cap->lock);
 440 }
 441
 442 void
 443 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 444 {
 445     ACQUIRE_LOCK(&cap->lock);
 446     releaseCapability_(cap, rtsTrue);
 447     RELEASE_LOCK(&cap->lock);
 448 }
 449
 450 static void
 451 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 452 {
 453     Task *task;
 454
 455     ACQUIRE_LOCK(&cap->lock);
 456
 457     task = cap->running_task;
 458
 459     // If the current task is a worker, save it on the spare_workers
 460     // list of this Capability.  A worker can mark itself as stopped,
 461     // in which case it is not replaced on the spare_worker queue.
 462     // This happens when the system is shutting down (see
 463     // Schedule.c:workerStart()).
 464     if (!isBoundTask(task) && !task->stopped) {
 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->incall->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 *cap,
 648                           Capability *other_cap,
 649                           StgTSO *tso)
 650 {
 651     MessageWakeup *msg;
 652
 653     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 654     if (tso->bound) {
 655         ASSERT(tso->bound->task->cap == tso->cap);
 656         tso->bound->task->cap = other_cap;
 657     }
 658     tso->cap = other_cap;
 659
 660     ASSERT(tso->why_blocked != BlockedOnMsgWakeup ||
 661            tso->block_info.closure->header.info == &stg_IND_info);
 662
 663     ASSERT(tso->block_info.closure->header.info != &stg_MSG_WAKEUP_info);
 664
 665     msg = (MessageWakeup*) allocate(cap, sizeofW(MessageWakeup));
 666     msg->header.info = &stg_MSG_WAKEUP_info;
 667     msg->tso = tso;
 668     tso->block_info.closure = (StgClosure *)msg;
 669     dirty_TSO(cap, tso);
 670     write_barrier();
 671     tso->why_blocked = BlockedOnMsgWakeup;
 672
 673     sendMessage(other_cap, (Message*)msg);
 674 }
 675
 676 /* ----------------------------------------------------------------------------
 677  * prodCapability
 678  *
 679  * If a Capability is currently idle, wake up a Task on it.  Used to
 680  * get every Capability into the GC.
 681  * ------------------------------------------------------------------------- */
 682
 683 void
 684 prodCapability (Capability *cap, Task *task)
 685 {
 686     ACQUIRE_LOCK(&cap->lock);
 687     if (!cap->running_task) {
 688         cap->running_task = task;
 689         releaseCapability_(cap,rtsTrue);
 690     }
 691     RELEASE_LOCK(&cap->lock);
 692 }
 693
 694 /* ----------------------------------------------------------------------------
 695  * shutdownCapability
 696  *
 697  * At shutdown time, we want to let everything exit as cleanly as
 698  * possible.  For each capability, we let its run queue drain, and
 699  * allow the workers to stop.
 700  *
 701  * This function should be called when interrupted and
 702  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 703  * will exit the scheduler and call taskStop(), and any bound thread
 704  * that wakes up will return to its caller.  Runnable threads are
 705  * killed.
 706  *
 707  * ------------------------------------------------------------------------- */
 708
 709 void
 710 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 711 {
 712     nat i;
 713
 714     task->cap = cap;
 715
 716     // Loop indefinitely until all the workers have exited and there
 717     // are no Haskell threads left.  We used to bail out after 50
 718     // iterations of this loop, but that occasionally left a worker
 719     // running which caused problems later (the closeMutex() below
 720     // isn't safe, for one thing).
 721
 722     for (i = 0; /* i < 50 */; i++) {
 723         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 724
 725         debugTrace(DEBUG_sched,
 726                    "shutting down capability %d, attempt %d", cap->no, i);
 727         ACQUIRE_LOCK(&cap->lock);
 728         if (cap->running_task) {
 729             RELEASE_LOCK(&cap->lock);
 730             debugTrace(DEBUG_sched, "not owner, yielding");
 731             yieldThread();
 732             continue;
 733         }
 734         cap->running_task = task;
 735
 736         if (cap->spare_workers) {
 737             // Look for workers that have died without removing
 738             // themselves from the list; this could happen if the OS
 739             // summarily killed the thread, for example.  This
 740             // actually happens on Windows when the system is
 741             // terminating the program, and the RTS is running in a
 742             // DLL.
 743             Task *t, *prev;
 744             prev = NULL;
 745             for (t = cap->spare_workers; t != NULL; t = t->next) {
 746                 if (!osThreadIsAlive(t->id)) {
 747                     debugTrace(DEBUG_sched,
 748                                "worker thread %p has died unexpectedly", (void *)t->id);
 749                         if (!prev) {
 750                             cap->spare_workers = t->next;
 751                         } else {
 752                             prev->next = t->next;
 753                         }
 754                         prev = t;
 755                 }
 756             }
 757         }
 758
 759         if (!emptyRunQueue(cap) || cap->spare_workers) {
 760             debugTrace(DEBUG_sched,
 761                        "runnable threads or workers still alive, yielding");
 762             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 763             RELEASE_LOCK(&cap->lock);
 764             yieldThread();
 765             continue;
 766         }
 767
 768         // If "safe", then busy-wait for any threads currently doing
 769         // foreign calls.  If we're about to unload this DLL, for
 770         // example, we need to be sure that there are no OS threads
 771         // that will try to return to code that has been unloaded.
 772         // We can be a bit more relaxed when this is a standalone
 773         // program that is about to terminate, and let safe=false.
 774         if (cap->suspended_ccalls && safe) {
 775             debugTrace(DEBUG_sched,
 776                        "thread(s) are involved in foreign calls, yielding");
 777             cap->running_task = NULL;
 778             RELEASE_LOCK(&cap->lock);
 779             // The IO manager thread might have been slow to start up,
 780             // so the first attempt to kill it might not have
 781             // succeeded.  Just in case, try again - the kill message
 782             // will only be sent once.
 783             //
 784             // To reproduce this deadlock: run ffi002(threaded1)
 785             // repeatedly on a loaded machine.
 786             ioManagerDie();
 787             yieldThread();
 788             continue;
 789         }
 790
 791         traceEventShutdown(cap);
 792         RELEASE_LOCK(&cap->lock);
 793         break;
 794     }
 795     // we now have the Capability, its run queue and spare workers
 796     // list are both empty.
 797
 798     // ToDo: we can't drop this mutex, because there might still be
 799     // threads performing foreign calls that will eventually try to
 800     // return via resumeThread() and attempt to grab cap->lock.
 801     // closeMutex(&cap->lock);
 802 }
 803
 804 /* ----------------------------------------------------------------------------
 805  * tryGrabCapability
 806  *
 807  * Attempt to gain control of a Capability if it is free.
 808  *
 809  * ------------------------------------------------------------------------- */
 810
 811 rtsBool
 812 tryGrabCapability (Capability *cap, Task *task)
 813 {
 814     if (cap->running_task != NULL) return rtsFalse;
 815     ACQUIRE_LOCK(&cap->lock);
 816     if (cap->running_task != NULL) {
 817         RELEASE_LOCK(&cap->lock);
 818         return rtsFalse;
 819     }
 820     task->cap = cap;
 821     cap->running_task = task;
 822     RELEASE_LOCK(&cap->lock);
 823     return rtsTrue;
 824 }
 825
 826
 827 #endif /* THREADED_RTS */
 828
 829 static void
 830 freeCapability (Capability *cap)
 831 {
 832     stgFree(cap->mut_lists);
 833     stgFree(cap->saved_mut_lists);
 834 #if defined(THREADED_RTS)
 835     freeSparkPool(cap->sparks);
 836 #endif
 837 }
 838
 839 void
 840 freeCapabilities (void)
 841 {
 842 #if defined(THREADED_RTS)
 843     nat i;
 844     for (i=0; i < n_capabilities; i++) {
 845         freeCapability(&capabilities[i]);
 846     }
 847 #else
 848     freeCapability(&MainCapability);
 849 #endif
 850 }
 851
 852 /* ---------------------------------------------------------------------------
 853    Mark everything directly reachable from the Capabilities.  When
 854    using multiple GC threads, each GC thread marks all Capabilities
 855    for which (c `mod` n == 0), for Capability c and thread n.
 856    ------------------------------------------------------------------------ */
 857
 858 void
 859 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 860                       rtsBool prune_sparks USED_IF_THREADS)
 861 {
 862     nat i;
 863     Capability *cap;
 864     InCall *incall;
 865
 866     // Each GC thread is responsible for following roots from the
 867     // Capability of the same number.  There will usually be the same
 868     // or fewer Capabilities as GC threads, but just in case there
 869     // are more, we mark every Capability whose number is the GC
 870     // thread's index plus a multiple of the number of GC threads.
 871     for (i = i0; i < n_capabilities; i += delta) {
 872         cap = &capabilities[i];
 873         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 874         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 875 #if defined(THREADED_RTS)
 876         evac(user, (StgClosure **)(void *)&cap->inbox);
 877 #endif
 878         for (incall = cap->suspended_ccalls; incall != NULL;
 879              incall=incall->next) {
 880             evac(user, (StgClosure **)(void *)&incall->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 }
 904
 905 /* -----------------------------------------------------------------------------
 906    Messages
 907    -------------------------------------------------------------------------- */
 908
 909 #ifdef THREADED_RTS
 910
 911 void sendMessage(Capability *cap, Message *msg)
 912 {
 913     ACQUIRE_LOCK(&cap->lock);
 914
 915     msg->link = cap->inbox;
 916     cap->inbox = msg;
 917
 918     if (cap->running_task == NULL) {
 919         cap->running_task = myTask();
 920             // precond for releaseCapability_()
 921         releaseCapability_(cap,rtsFalse);
 922     } else {
 923         contextSwitchCapability(cap);
 924     }
 925
 926     RELEASE_LOCK(&cap->lock);
 927 }
 928
 929 #endif // THREADED_RTS