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)) {
  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   // first try to get a spark from our own pool.
  88   // We should be using reclaimSpark(), because it works without
  89   // needing any atomic instructions:
  90   //   spark = reclaimSpark(cap->sparks);
  91   // However, measurements show that this makes at least one benchmark
  92   // slower (prsa) and doesn't affect the others.
  93   spark = tryStealSpark(cap);
  94   if (spark != NULL) {
  95       cap->sparks_converted++;
  96
  97       // Post event for running a spark from capability's own pool.
  98       postEvent(cap, EVENT_RUN_SPARK, cap->r.rCurrentTSO->id, 0);
  99
 100       return spark;
 101   }
 102
 103   if (n_capabilities == 1) { return NULL; } // makes no sense...
 104
 105   debugTrace(DEBUG_sched,
 106              "cap %d: Trying to steal work from other capabilities",
 107              cap->no);
 108
 109   do {
 110       retry = rtsFalse;
 111
 112       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
 113       start at a random place instead of 0 as well.  */
 114       for ( i=0 ; i < n_capabilities ; i++ ) {
 115           robbed = &capabilities[i];
 116           if (cap == robbed)  // ourselves...
 117               continue;
 118
 119           if (emptySparkPoolCap(robbed)) // nothing to steal here
 120               continue;
 121
 122           spark = tryStealSpark(robbed);
 123           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 124               // we conflicted with another thread while trying to steal;
 125               // try again later.
 126               retry = rtsTrue;
 127           }
 128
 129           if (spark != NULL) {
 130               debugTrace(DEBUG_sched,
 131                  "cap %d: Stole a spark from capability %d",
 132                          cap->no, robbed->no);
 133               cap->sparks_converted++;
 134
 135               postEvent(cap, EVENT_STEAL_SPARK,
 136                         cap->r.rCurrentTSO->id, robbed->no);
 137
 138
 139               return spark;
 140           }
 141           // otherwise: no success, try next one
 142       }
 143   } while (retry);
 144
 145   debugTrace(DEBUG_sched, "No sparks stolen");
 146   return NULL;
 147 }
 148
 149 // Returns True if any spark pool is non-empty at this moment in time
 150 // The result is only valid for an instant, of course, so in a sense
 151 // is immediately invalid, and should not be relied upon for
 152 // correctness.
 153 rtsBool
 154 anySparks (void)
 155 {
 156     nat i;
 157
 158     for (i=0; i < n_capabilities; i++) {
 159         if (!emptySparkPoolCap(&capabilities[i])) {
 160             return rtsTrue;
 161         }
 162     }
 163     return rtsFalse;
 164 }
 165 #endif
 166
 167 /* -----------------------------------------------------------------------------
 168  * Manage the returning_tasks lists.
 169  *
 170  * These functions require cap->lock
 171  * -------------------------------------------------------------------------- */
 172
 173 #if defined(THREADED_RTS)
 174 STATIC_INLINE void
 175 newReturningTask (Capability *cap, Task *task)
 176 {
 177     ASSERT_LOCK_HELD(&cap->lock);
 178     ASSERT(task->return_link == NULL);
 179     if (cap->returning_tasks_hd) {
 180         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 181         cap->returning_tasks_tl->return_link = task;
 182     } else {
 183         cap->returning_tasks_hd = task;
 184     }
 185     cap->returning_tasks_tl = task;
 186 }
 187
 188 STATIC_INLINE Task *
 189 popReturningTask (Capability *cap)
 190 {
 191     ASSERT_LOCK_HELD(&cap->lock);
 192     Task *task;
 193     task = cap->returning_tasks_hd;
 194     ASSERT(task);
 195     cap->returning_tasks_hd = task->return_link;
 196     if (!cap->returning_tasks_hd) {
 197         cap->returning_tasks_tl = NULL;
 198     }
 199     task->return_link = NULL;
 200     return task;
 201 }
 202 #endif
 203
 204 /* ----------------------------------------------------------------------------
 205  * Initialisation
 206  *
 207  * The Capability is initially marked not free.
 208  * ------------------------------------------------------------------------- */
 209
 210 static void
 211 initCapability( Capability *cap, nat i )
 212 {
 213     nat g;
 214
 215     cap->no = i;
 216     cap->in_haskell        = rtsFalse;
 217     cap->in_gc             = rtsFalse;
 218
 219     cap->run_queue_hd      = END_TSO_QUEUE;
 220     cap->run_queue_tl      = END_TSO_QUEUE;
 221
 222 #if defined(THREADED_RTS)
 223     initMutex(&cap->lock);
 224     cap->running_task      = NULL; // indicates cap is free
 225     cap->spare_workers     = NULL;
 226     cap->suspended_ccalling_tasks = NULL;
 227     cap->returning_tasks_hd = NULL;
 228     cap->returning_tasks_tl = NULL;
 229     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 230     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 231     cap->sparks_created     = 0;
 232     cap->sparks_converted   = 0;
 233     cap->sparks_pruned      = 0;
 234 #endif
 235
 236     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 237     cap->f.stgGCEnter1     = (StgFunPtr)__stg_gc_enter_1;
 238     cap->f.stgGCFun        = (StgFunPtr)__stg_gc_fun;
 239
 240     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 241                                      RtsFlags.GcFlags.generations,
 242                                      "initCapability");
 243     cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
 244                                           RtsFlags.GcFlags.generations,
 245                                           "initCapability");
 246
 247     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 248         cap->mut_lists[g] = NULL;
 249     }
 250
 251     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 252     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 253     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 254     cap->free_trec_headers = NO_TREC;
 255     cap->transaction_tokens = 0;
 256     cap->context_switch = 0;
 257 }
 258
 259 /* ---------------------------------------------------------------------------
 260  * Function:  initCapabilities()
 261  *
 262  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 263  *            we keep a table of them, the size of which is
 264  *            controlled by the user via the RTS flag -N.
 265  *
 266  * ------------------------------------------------------------------------- */
 267 void
 268 initCapabilities( void )
 269 {
 270 #if defined(THREADED_RTS)
 271     nat i;
 272
 273 #ifndef REG_Base
 274     // We can't support multiple CPUs if BaseReg is not a register
 275     if (RtsFlags.ParFlags.nNodes > 1) {
 276         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 277         RtsFlags.ParFlags.nNodes = 1;
 278     }
 279 #endif
 280
 281     n_capabilities = RtsFlags.ParFlags.nNodes;
 282
 283     if (n_capabilities == 1) {
 284         capabilities = &MainCapability;
 285         // THREADED_RTS must work on builds that don't have a mutable
 286         // BaseReg (eg. unregisterised), so in this case
 287         // capabilities[0] must coincide with &MainCapability.
 288     } else {
 289         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 290                                       "initCapabilities");
 291     }
 292
 293     for (i = 0; i < n_capabilities; i++) {
 294         initCapability(&capabilities[i], i);
 295     }
 296
 297     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 298
 299 #else /* !THREADED_RTS */
 300
 301     n_capabilities = 1;
 302     capabilities = &MainCapability;
 303     initCapability(&MainCapability, 0);
 304
 305 #endif
 306
 307     // There are no free capabilities to begin with.  We will start
 308     // a worker Task to each Capability, which will quickly put the
 309     // Capability on the free list when it finds nothing to do.
 310     last_free_capability = &capabilities[0];
 311 }
 312
 313 /* ----------------------------------------------------------------------------
 314  * setContextSwitches: cause all capabilities to context switch as
 315  * soon as possible.
 316  * ------------------------------------------------------------------------- */
 317
 318 void setContextSwitches(void)
 319 {
 320     nat i;
 321     for (i=0; i < n_capabilities; i++) {
 322         contextSwitchCapability(&capabilities[i]);
 323     }
 324 }
 325
 326 /* ----------------------------------------------------------------------------
 327  * Give a Capability to a Task.  The task must currently be sleeping
 328  * on its condition variable.
 329  *
 330  * Requires cap->lock (modifies cap->running_task).
 331  *
 332  * When migrating a Task, the migrater must take task->lock before
 333  * modifying task->cap, to synchronise with the waking up Task.
 334  * Additionally, the migrater should own the Capability (when
 335  * migrating the run queue), or cap->lock (when migrating
 336  * returning_workers).
 337  *
 338  * ------------------------------------------------------------------------- */
 339
 340 #if defined(THREADED_RTS)
 341 STATIC_INLINE void
 342 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 343 {
 344     ASSERT_LOCK_HELD(&cap->lock);
 345     ASSERT(task->cap == cap);
 346     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 347                cap->no, task->tso ? "bound task" : "worker",
 348                (void *)task->id);
 349     ACQUIRE_LOCK(&task->lock);
 350     task->wakeup = rtsTrue;
 351     // the wakeup flag is needed because signalCondition() doesn't
 352     // flag the condition if the thread is already runniing, but we want
 353     // it to be sticky.
 354     signalCondition(&task->cond);
 355     RELEASE_LOCK(&task->lock);
 356 }
 357 #endif
 358
 359 /* ----------------------------------------------------------------------------
 360  * Function:  releaseCapability(Capability*)
 361  *
 362  * Purpose:   Letting go of a capability. Causes a
 363  *            'returning worker' thread or a 'waiting worker'
 364  *            to wake up, in that order.
 365  * ------------------------------------------------------------------------- */
 366
 367 #if defined(THREADED_RTS)
 368 void
 369 releaseCapability_ (Capability* cap,
 370                     rtsBool always_wakeup)
 371 {
 372     Task *task;
 373
 374     task = cap->running_task;
 375
 376     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 377
 378     cap->running_task = NULL;
 379
 380     // Check to see whether a worker thread can be given
 381     // the go-ahead to return the result of an external call..
 382     if (cap->returning_tasks_hd != NULL) {
 383         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 384         // The Task pops itself from the queue (see waitForReturnCapability())
 385         return;
 386     }
 387
 388     if (waiting_for_gc == PENDING_GC_SEQ) {
 389       last_free_capability = cap; // needed?
 390       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 391       return;
 392     }
 393
 394
 395     // If the next thread on the run queue is a bound thread,
 396     // give this Capability to the appropriate Task.
 397     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 398         // Make sure we're not about to try to wake ourselves up
 399         ASSERT(task != cap->run_queue_hd->bound);
 400         task = cap->run_queue_hd->bound;
 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, workerStart);
 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) || !emptyWakeupQueue(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     // Also, be careful to check that this task hasn't just exited
 465     // Haskell to do a foreign call (task->suspended_tso).
 466     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 467         task->next = cap->spare_workers;
 468         cap->spare_workers = task;
 469     }
 470     // Bound tasks just float around attached to their TSOs.
 471
 472     releaseCapability_(cap,rtsFalse);
 473
 474     RELEASE_LOCK(&cap->lock);
 475 }
 476 #endif
 477
 478 /* ----------------------------------------------------------------------------
 479  * waitForReturnCapability( Task *task )
 480  *
 481  * Purpose:  when an OS thread returns from an external call,
 482  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 483  * to wait for permission to enter the RTS & communicate the
 484  * result of the external call back to the Haskell thread that
 485  * made it.
 486  *
 487  * ------------------------------------------------------------------------- */
 488 void
 489 waitForReturnCapability (Capability **pCap, Task *task)
 490 {
 491 #if !defined(THREADED_RTS)
 492
 493     MainCapability.running_task = task;
 494     task->cap = &MainCapability;
 495     *pCap = &MainCapability;
 496
 497 #else
 498     Capability *cap = *pCap;
 499
 500     if (cap == NULL) {
 501         // Try last_free_capability first
 502         cap = last_free_capability;
 503         if (cap->running_task) {
 504             nat i;
 505             // otherwise, search for a free capability
 506             cap = NULL;
 507             for (i = 0; i < n_capabilities; i++) {
 508                 if (!capabilities[i].running_task) {
 509                     cap = &capabilities[i];
 510                     break;
 511                 }
 512             }
 513             if (cap == NULL) {
 514                 // Can't find a free one, use last_free_capability.
 515                 cap = last_free_capability;
 516             }
 517         }
 518
 519         // record the Capability as the one this Task is now assocated with.
 520         task->cap = cap;
 521
 522     } else {
 523         ASSERT(task->cap == cap);
 524     }
 525
 526     ACQUIRE_LOCK(&cap->lock);
 527
 528     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 529
 530     if (!cap->running_task) {
 531         // It's free; just grab it
 532         cap->running_task = task;
 533         RELEASE_LOCK(&cap->lock);
 534     } else {
 535         newReturningTask(cap,task);
 536         RELEASE_LOCK(&cap->lock);
 537
 538         for (;;) {
 539             ACQUIRE_LOCK(&task->lock);
 540             // task->lock held, cap->lock not held
 541             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 542             cap = task->cap;
 543             task->wakeup = rtsFalse;
 544             RELEASE_LOCK(&task->lock);
 545
 546             // now check whether we should wake up...
 547             ACQUIRE_LOCK(&cap->lock);
 548             if (cap->running_task == NULL) {
 549                 if (cap->returning_tasks_hd != task) {
 550                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 551                     RELEASE_LOCK(&cap->lock);
 552                     continue;
 553                 }
 554                 cap->running_task = task;
 555                 popReturningTask(cap);
 556                 RELEASE_LOCK(&cap->lock);
 557                 break;
 558             }
 559             RELEASE_LOCK(&cap->lock);
 560         }
 561
 562     }
 563
 564     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 565
 566     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 567
 568     *pCap = cap;
 569 #endif
 570 }
 571
 572 #if defined(THREADED_RTS)
 573 /* ----------------------------------------------------------------------------
 574  * yieldCapability
 575  * ------------------------------------------------------------------------- */
 576
 577 void
 578 yieldCapability (Capability** pCap, Task *task)
 579 {
 580     Capability *cap = *pCap;
 581
 582     if (waiting_for_gc == PENDING_GC_PAR) {
 583         debugTrace(DEBUG_sched, "capability %d: becoming a GC thread", cap->no);
 584         postEvent(cap, EVENT_GC_START, 0, 0);
 585         gcWorkerThread(cap);
 586         postEvent(cap, EVENT_GC_END, 0, 0);
 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             yieldThread();
 790             continue;
 791         }
 792
 793         postEvent(cap, EVENT_SHUTDOWN, 0, 0);
 794         debugTrace(DEBUG_sched, "capability %d is stopped.", cap->no);
 795         RELEASE_LOCK(&cap->lock);
 796         break;
 797     }
 798     // we now have the Capability, its run queue and spare workers
 799     // list are both empty.
 800
 801     // ToDo: we can't drop this mutex, because there might still be
 802     // threads performing foreign calls that will eventually try to
 803     // return via resumeThread() and attempt to grab cap->lock.
 804     // closeMutex(&cap->lock);
 805 }
 806
 807 /* ----------------------------------------------------------------------------
 808  * tryGrabCapability
 809  *
 810  * Attempt to gain control of a Capability if it is free.
 811  *
 812  * ------------------------------------------------------------------------- */
 813
 814 rtsBool
 815 tryGrabCapability (Capability *cap, Task *task)
 816 {
 817     if (cap->running_task != NULL) return rtsFalse;
 818     ACQUIRE_LOCK(&cap->lock);
 819     if (cap->running_task != NULL) {
 820         RELEASE_LOCK(&cap->lock);
 821         return rtsFalse;
 822     }
 823     task->cap = cap;
 824     cap->running_task = task;
 825     RELEASE_LOCK(&cap->lock);
 826     return rtsTrue;
 827 }
 828
 829
 830 #endif /* THREADED_RTS */
 831
 832 static void
 833 freeCapability (Capability *cap)
 834 {
 835     stgFree(cap->mut_lists);
 836 #if defined(THREADED_RTS)
 837     freeSparkPool(cap->sparks);
 838 #endif
 839 }
 840
 841 void
 842 freeCapabilities (void)
 843 {
 844 #if defined(THREADED_RTS)
 845     nat i;
 846     for (i=0; i < n_capabilities; i++) {
 847         freeCapability(&capabilities[i]);
 848     }
 849 #else
 850     freeCapability(&MainCapability);
 851 #endif
 852 }
 853
 854 /* ---------------------------------------------------------------------------
 855    Mark everything directly reachable from the Capabilities.  When
 856    using multiple GC threads, each GC thread marks all Capabilities
 857    for which (c `mod` n == 0), for Capability c and thread n.
 858    ------------------------------------------------------------------------ */
 859
 860 void
 861 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 862                       rtsBool prune_sparks USED_IF_THREADS)
 863 {
 864     nat i;
 865     Capability *cap;
 866     Task *task;
 867
 868     // Each GC thread is responsible for following roots from the
 869     // Capability of the same number.  There will usually be the same
 870     // or fewer Capabilities as GC threads, but just in case there
 871     // are more, we mark every Capability whose number is the GC
 872     // thread's index plus a multiple of the number of GC threads.
 873     for (i = i0; i < n_capabilities; i += delta) {
 874         cap = &capabilities[i];
 875         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 876         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 877 #if defined(THREADED_RTS)
 878         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 879         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 880 #endif
 881         for (task = cap->suspended_ccalling_tasks; task != NULL;
 882              task=task->next) {
 883             debugTrace(DEBUG_sched,
 884                        "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
 885             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 886         }
 887
 888 #if defined(THREADED_RTS)
 889         if (prune_sparks) {
 890             pruneSparkQueue (evac, user, cap);
 891         } else {
 892             traverseSparkQueue (evac, user, cap);
 893         }
 894 #endif
 895     }
 896
 897 #if !defined(THREADED_RTS)
 898     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 899     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 900     evac(user, (StgClosure **)(void *)&sleeping_queue);
 901 #endif
 902 }
 903
 904 void
 905 markCapabilities (evac_fn evac, void *user)
 906 {
 907     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 908 }