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 sched_state >= SCHED_INTERRUPTING
  66         || recent_activity == ACTIVITY_INACTIVE; // need to check for deadlock
  67 }
  68 #endif
  69
  70 #if defined(THREADED_RTS)
  71 StgClosure *
  72 findSpark (Capability *cap)
  73 {
  74   Capability *robbed;
  75   StgClosurePtr spark;
  76   rtsBool retry;
  77   nat i = 0;
  78
  79   if (!emptyRunQueue(cap) || cap->returning_tasks_hd != NULL) {
  80       // If there are other threads, don't try to run any new
  81       // sparks: sparks might be speculative, we don't want to take
  82       // resources away from the main computation.
  83       return 0;
  84   }
  85
  86   do {
  87       retry = rtsFalse;
  88
  89       // first try to get a spark from our own pool.
  90       // We should be using reclaimSpark(), because it works without
  91       // needing any atomic instructions:
  92       //   spark = reclaimSpark(cap->sparks);
  93       // However, measurements show that this makes at least one benchmark
  94       // slower (prsa) and doesn't affect the others.
  95       spark = tryStealSpark(cap);
  96       if (spark != NULL) {
  97           cap->sparks_converted++;
  98
  99           // Post event for running a spark from capability's own pool.
 100           traceEventRunSpark(cap, cap->r.rCurrentTSO);
 101
 102           return spark;
 103       }
 104       if (!emptySparkPoolCap(cap)) {
 105           retry = rtsTrue;
 106       }
 107
 108       if (n_capabilities == 1) { return NULL; } // makes no sense...
 109
 110       debugTrace(DEBUG_sched,
 111                  "cap %d: Trying to steal work from other capabilities",
 112                  cap->no);
 113
 114       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
 115       start at a random place instead of 0 as well.  */
 116       for ( i=0 ; i < n_capabilities ; i++ ) {
 117           robbed = &capabilities[i];
 118           if (cap == robbed)  // ourselves...
 119               continue;
 120
 121           if (emptySparkPoolCap(robbed)) // nothing to steal here
 122               continue;
 123
 124           spark = tryStealSpark(robbed);
 125           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 126               // we conflicted with another thread while trying to steal;
 127               // try again later.
 128               retry = rtsTrue;
 129           }
 130
 131           if (spark != NULL) {
 132               cap->sparks_converted++;
 133
 134               traceEventStealSpark(cap, cap->r.rCurrentTSO, robbed->no);
 135
 136               return spark;
 137           }
 138           // otherwise: no success, try next one
 139       }
 140   } while (retry);
 141
 142   debugTrace(DEBUG_sched, "No sparks stolen");
 143   return NULL;
 144 }
 145
 146 // Returns True if any spark pool is non-empty at this moment in time
 147 // The result is only valid for an instant, of course, so in a sense
 148 // is immediately invalid, and should not be relied upon for
 149 // correctness.
 150 rtsBool
 151 anySparks (void)
 152 {
 153     nat i;
 154
 155     for (i=0; i < n_capabilities; i++) {
 156         if (!emptySparkPoolCap(&capabilities[i])) {
 157             return rtsTrue;
 158         }
 159     }
 160     return rtsFalse;
 161 }
 162 #endif
 163
 164 /* -----------------------------------------------------------------------------
 165  * Manage the returning_tasks lists.
 166  *
 167  * These functions require cap->lock
 168  * -------------------------------------------------------------------------- */
 169
 170 #if defined(THREADED_RTS)
 171 STATIC_INLINE void
 172 newReturningTask (Capability *cap, Task *task)
 173 {
 174     ASSERT_LOCK_HELD(&cap->lock);
 175     ASSERT(task->next == NULL);
 176     if (cap->returning_tasks_hd) {
 177         ASSERT(cap->returning_tasks_tl->next == NULL);
 178         cap->returning_tasks_tl->next = task;
 179     } else {
 180         cap->returning_tasks_hd = task;
 181     }
 182     cap->returning_tasks_tl = task;
 183 }
 184
 185 STATIC_INLINE Task *
 186 popReturningTask (Capability *cap)
 187 {
 188     ASSERT_LOCK_HELD(&cap->lock);
 189     Task *task;
 190     task = cap->returning_tasks_hd;
 191     ASSERT(task);
 192     cap->returning_tasks_hd = task->next;
 193     if (!cap->returning_tasks_hd) {
 194         cap->returning_tasks_tl = NULL;
 195     }
 196     task->next = NULL;
 197     return task;
 198 }
 199 #endif
 200
 201 /* ----------------------------------------------------------------------------
 202  * Initialisation
 203  *
 204  * The Capability is initially marked not free.
 205  * ------------------------------------------------------------------------- */
 206
 207 static void
 208 initCapability( Capability *cap, nat i )
 209 {
 210     nat g;
 211
 212     cap->no = i;
 213     cap->in_haskell        = rtsFalse;
 214
 215     cap->run_queue_hd      = END_TSO_QUEUE;
 216     cap->run_queue_tl      = END_TSO_QUEUE;
 217
 218 #if defined(THREADED_RTS)
 219     initMutex(&cap->lock);
 220     cap->running_task      = NULL; // indicates cap is free
 221     cap->spare_workers     = NULL;
 222     cap->n_spare_workers   = 0;
 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 Task is stopped, we shouldn't be yielding, we should
 460     // be just exiting.
 461     ASSERT(!task->stopped);
 462
 463     // If the current task is a worker, save it on the spare_workers
 464     // list of this Capability.  A worker can mark itself as stopped,
 465     // in which case it is not replaced on the spare_worker queue.
 466     // This happens when the system is shutting down (see
 467     // Schedule.c:workerStart()).
 468     if (!isBoundTask(task))
 469     {
 470         if (cap->n_spare_workers < MAX_SPARE_WORKERS)
 471         {
 472             task->next = cap->spare_workers;
 473             cap->spare_workers = task;
 474             cap->n_spare_workers++;
 475         }
 476         else
 477         {
 478             debugTrace(DEBUG_sched, "%d spare workers already, exiting",
 479                        cap->n_spare_workers);
 480             releaseCapability_(cap,rtsFalse);
 481             // hold the lock until after workerTaskStop; c.f. scheduleWorker()
 482             workerTaskStop(task);
 483             RELEASE_LOCK(&cap->lock);
 484             shutdownThread();
 485         }
 486     }
 487     // Bound tasks just float around attached to their TSOs.
 488
 489     releaseCapability_(cap,rtsFalse);
 490
 491     RELEASE_LOCK(&cap->lock);
 492 }
 493 #endif
 494
 495 /* ----------------------------------------------------------------------------
 496  * waitForReturnCapability( Task *task )
 497  *
 498  * Purpose:  when an OS thread returns from an external call,
 499  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 500  * to wait for permission to enter the RTS & communicate the
 501  * result of the external call back to the Haskell thread that
 502  * made it.
 503  *
 504  * ------------------------------------------------------------------------- */
 505 void
 506 waitForReturnCapability (Capability **pCap, Task *task)
 507 {
 508 #if !defined(THREADED_RTS)
 509
 510     MainCapability.running_task = task;
 511     task->cap = &MainCapability;
 512     *pCap = &MainCapability;
 513
 514 #else
 515     Capability *cap = *pCap;
 516
 517     if (cap == NULL) {
 518         // Try last_free_capability first
 519         cap = last_free_capability;
 520         if (cap->running_task) {
 521             nat i;
 522             // otherwise, search for a free capability
 523             cap = NULL;
 524             for (i = 0; i < n_capabilities; i++) {
 525                 if (!capabilities[i].running_task) {
 526                     cap = &capabilities[i];
 527                     break;
 528                 }
 529             }
 530             if (cap == NULL) {
 531                 // Can't find a free one, use last_free_capability.
 532                 cap = last_free_capability;
 533             }
 534         }
 535
 536         // record the Capability as the one this Task is now assocated with.
 537         task->cap = cap;
 538
 539     } else {
 540         ASSERT(task->cap == cap);
 541     }
 542
 543     ACQUIRE_LOCK(&cap->lock);
 544
 545     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 546
 547     if (!cap->running_task) {
 548         // It's free; just grab it
 549         cap->running_task = task;
 550         RELEASE_LOCK(&cap->lock);
 551     } else {
 552         newReturningTask(cap,task);
 553         RELEASE_LOCK(&cap->lock);
 554
 555         for (;;) {
 556             ACQUIRE_LOCK(&task->lock);
 557             // task->lock held, cap->lock not held
 558             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 559             cap = task->cap;
 560             task->wakeup = rtsFalse;
 561             RELEASE_LOCK(&task->lock);
 562
 563             // now check whether we should wake up...
 564             ACQUIRE_LOCK(&cap->lock);
 565             if (cap->running_task == NULL) {
 566                 if (cap->returning_tasks_hd != task) {
 567                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 568                     RELEASE_LOCK(&cap->lock);
 569                     continue;
 570                 }
 571                 cap->running_task = task;
 572                 popReturningTask(cap);
 573                 RELEASE_LOCK(&cap->lock);
 574                 break;
 575             }
 576             RELEASE_LOCK(&cap->lock);
 577         }
 578
 579     }
 580
 581     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 582
 583     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 584
 585     *pCap = cap;
 586 #endif
 587 }
 588
 589 #if defined(THREADED_RTS)
 590 /* ----------------------------------------------------------------------------
 591  * yieldCapability
 592  * ------------------------------------------------------------------------- */
 593
 594 void
 595 yieldCapability (Capability** pCap, Task *task)
 596 {
 597     Capability *cap = *pCap;
 598
 599     if (waiting_for_gc == PENDING_GC_PAR) {
 600         traceEventGcStart(cap);
 601         gcWorkerThread(cap);
 602         traceEventGcEnd(cap);
 603         return;
 604     }
 605
 606         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 607
 608         // We must now release the capability and wait to be woken up
 609         // again.
 610         task->wakeup = rtsFalse;
 611         releaseCapabilityAndQueueWorker(cap);
 612
 613         for (;;) {
 614             ACQUIRE_LOCK(&task->lock);
 615             // task->lock held, cap->lock not held
 616             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 617             cap = task->cap;
 618             task->wakeup = rtsFalse;
 619             RELEASE_LOCK(&task->lock);
 620
 621             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 622
 623             ACQUIRE_LOCK(&cap->lock);
 624             if (cap->running_task != NULL) {
 625                 debugTrace(DEBUG_sched,
 626                            "capability %d is owned by another task", cap->no);
 627                 RELEASE_LOCK(&cap->lock);
 628                 continue;
 629             }
 630
 631             if (task->incall->tso == NULL) {
 632                 ASSERT(cap->spare_workers != NULL);
 633                 // if we're not at the front of the queue, release it
 634                 // again.  This is unlikely to happen.
 635                 if (cap->spare_workers != task) {
 636                     giveCapabilityToTask(cap,cap->spare_workers);
 637                     RELEASE_LOCK(&cap->lock);
 638                     continue;
 639                 }
 640                 cap->spare_workers = task->next;
 641                 task->next = NULL;
 642                 cap->n_spare_workers--;
 643             }
 644             cap->running_task = task;
 645             RELEASE_LOCK(&cap->lock);
 646             break;
 647         }
 648
 649         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 650         ASSERT(cap->running_task == task);
 651
 652     *pCap = cap;
 653
 654     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 655
 656     return;
 657 }
 658
 659 /* ----------------------------------------------------------------------------
 660  * prodCapability
 661  *
 662  * If a Capability is currently idle, wake up a Task on it.  Used to
 663  * get every Capability into the GC.
 664  * ------------------------------------------------------------------------- */
 665
 666 void
 667 prodCapability (Capability *cap, Task *task)
 668 {
 669     ACQUIRE_LOCK(&cap->lock);
 670     if (!cap->running_task) {
 671         cap->running_task = task;
 672         releaseCapability_(cap,rtsTrue);
 673     }
 674     RELEASE_LOCK(&cap->lock);
 675 }
 676
 677 /* ----------------------------------------------------------------------------
 678  * shutdownCapability
 679  *
 680  * At shutdown time, we want to let everything exit as cleanly as
 681  * possible.  For each capability, we let its run queue drain, and
 682  * allow the workers to stop.
 683  *
 684  * This function should be called when interrupted and
 685  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 686  * will exit the scheduler and call taskStop(), and any bound thread
 687  * that wakes up will return to its caller.  Runnable threads are
 688  * killed.
 689  *
 690  * ------------------------------------------------------------------------- */
 691
 692 void
 693 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 694 {
 695     nat i;
 696
 697     task->cap = cap;
 698
 699     // Loop indefinitely until all the workers have exited and there
 700     // are no Haskell threads left.  We used to bail out after 50
 701     // iterations of this loop, but that occasionally left a worker
 702     // running which caused problems later (the closeMutex() below
 703     // isn't safe, for one thing).
 704
 705     for (i = 0; /* i < 50 */; i++) {
 706         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 707
 708         debugTrace(DEBUG_sched,
 709                    "shutting down capability %d, attempt %d", cap->no, i);
 710         ACQUIRE_LOCK(&cap->lock);
 711         if (cap->running_task) {
 712             RELEASE_LOCK(&cap->lock);
 713             debugTrace(DEBUG_sched, "not owner, yielding");
 714             yieldThread();
 715             continue;
 716         }
 717         cap->running_task = task;
 718
 719         if (cap->spare_workers) {
 720             // Look for workers that have died without removing
 721             // themselves from the list; this could happen if the OS
 722             // summarily killed the thread, for example.  This
 723             // actually happens on Windows when the system is
 724             // terminating the program, and the RTS is running in a
 725             // DLL.
 726             Task *t, *prev;
 727             prev = NULL;
 728             for (t = cap->spare_workers; t != NULL; t = t->next) {
 729                 if (!osThreadIsAlive(t->id)) {
 730                     debugTrace(DEBUG_sched,
 731                                "worker thread %p has died unexpectedly", (void *)t->id);
 732                     cap->n_spare_workers--;
 733                     if (!prev) {
 734                         cap->spare_workers = t->next;
 735                     } else {
 736                         prev->next = t->next;
 737                     }
 738                     prev = t;
 739                 }
 740             }
 741         }
 742
 743         if (!emptyRunQueue(cap) || cap->spare_workers) {
 744             debugTrace(DEBUG_sched,
 745                        "runnable threads or workers still alive, yielding");
 746             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 747             RELEASE_LOCK(&cap->lock);
 748             yieldThread();
 749             continue;
 750         }
 751
 752         // If "safe", then busy-wait for any threads currently doing
 753         // foreign calls.  If we're about to unload this DLL, for
 754         // example, we need to be sure that there are no OS threads
 755         // that will try to return to code that has been unloaded.
 756         // We can be a bit more relaxed when this is a standalone
 757         // program that is about to terminate, and let safe=false.
 758         if (cap->suspended_ccalls && safe) {
 759             debugTrace(DEBUG_sched,
 760                        "thread(s) are involved in foreign calls, yielding");
 761             cap->running_task = NULL;
 762             RELEASE_LOCK(&cap->lock);
 763             // The IO manager thread might have been slow to start up,
 764             // so the first attempt to kill it might not have
 765             // succeeded.  Just in case, try again - the kill message
 766             // will only be sent once.
 767             //
 768             // To reproduce this deadlock: run ffi002(threaded1)
 769             // repeatedly on a loaded machine.
 770             ioManagerDie();
 771             yieldThread();
 772             continue;
 773         }
 774
 775         traceEventShutdown(cap);
 776         RELEASE_LOCK(&cap->lock);
 777         break;
 778     }
 779     // we now have the Capability, its run queue and spare workers
 780     // list are both empty.
 781
 782     // ToDo: we can't drop this mutex, because there might still be
 783     // threads performing foreign calls that will eventually try to
 784     // return via resumeThread() and attempt to grab cap->lock.
 785     // closeMutex(&cap->lock);
 786 }
 787
 788 /* ----------------------------------------------------------------------------
 789  * tryGrabCapability
 790  *
 791  * Attempt to gain control of a Capability if it is free.
 792  *
 793  * ------------------------------------------------------------------------- */
 794
 795 rtsBool
 796 tryGrabCapability (Capability *cap, Task *task)
 797 {
 798     if (cap->running_task != NULL) return rtsFalse;
 799     ACQUIRE_LOCK(&cap->lock);
 800     if (cap->running_task != NULL) {
 801         RELEASE_LOCK(&cap->lock);
 802         return rtsFalse;
 803     }
 804     task->cap = cap;
 805     cap->running_task = task;
 806     RELEASE_LOCK(&cap->lock);
 807     return rtsTrue;
 808 }
 809
 810
 811 #endif /* THREADED_RTS */
 812
 813 static void
 814 freeCapability (Capability *cap)
 815 {
 816     stgFree(cap->mut_lists);
 817     stgFree(cap->saved_mut_lists);
 818 #if defined(THREADED_RTS)
 819     freeSparkPool(cap->sparks);
 820 #endif
 821 }
 822
 823 void
 824 freeCapabilities (void)
 825 {
 826 #if defined(THREADED_RTS)
 827     nat i;
 828     for (i=0; i < n_capabilities; i++) {
 829         freeCapability(&capabilities[i]);
 830     }
 831 #else
 832     freeCapability(&MainCapability);
 833 #endif
 834 }
 835
 836 /* ---------------------------------------------------------------------------
 837    Mark everything directly reachable from the Capabilities.  When
 838    using multiple GC threads, each GC thread marks all Capabilities
 839    for which (c `mod` n == 0), for Capability c and thread n.
 840    ------------------------------------------------------------------------ */
 841
 842 void
 843 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 844                       rtsBool no_mark_sparks USED_IF_THREADS)
 845 {
 846     nat i;
 847     Capability *cap;
 848     InCall *incall;
 849
 850     // Each GC thread is responsible for following roots from the
 851     // Capability of the same number.  There will usually be the same
 852     // or fewer Capabilities as GC threads, but just in case there
 853     // are more, we mark every Capability whose number is the GC
 854     // thread's index plus a multiple of the number of GC threads.
 855     for (i = i0; i < n_capabilities; i += delta) {
 856         cap = &capabilities[i];
 857         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 858         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 859 #if defined(THREADED_RTS)
 860         evac(user, (StgClosure **)(void *)&cap->inbox);
 861 #endif
 862         for (incall = cap->suspended_ccalls; incall != NULL;
 863              incall=incall->next) {
 864             evac(user, (StgClosure **)(void *)&incall->suspended_tso);
 865         }
 866
 867 #if defined(THREADED_RTS)
 868         if (!no_mark_sparks) {
 869             traverseSparkQueue (evac, user, cap);
 870         }
 871 #endif
 872     }
 873
 874 #if !defined(THREADED_RTS)
 875     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 876     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 877     evac(user, (StgClosure **)(void *)&sleeping_queue);
 878 #endif
 879 }
 880
 881 void
 882 markCapabilities (evac_fn evac, void *user)
 883 {
 884     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 885 }
 886
 887 /* -----------------------------------------------------------------------------
 888    Messages
 889    -------------------------------------------------------------------------- */
 890