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 #include "RtsUtils.h"
  22 #include "RtsFlags.h"
  23 #include "STM.h"
  24 #include "OSThreads.h"
  25 #include "Capability.h"
  26 #include "Schedule.h"
  27 #include "Sparks.h"
  28 #include "Trace.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;
  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;
  42
  43 /* GC indicator, in scope for the scheduler, init'ed to false */
  44 volatile StgWord waiting_for_gc = 0;
  45
  46 #if defined(THREADED_RTS)
  47 STATIC_INLINE rtsBool
  48 globalWorkToDo (void)
  49 {
  50     return blackholes_need_checking
  51         || sched_state >= SCHED_INTERRUPTING
  52         ;
  53 }
  54 #endif
  55
  56 #if defined(THREADED_RTS)
  57 StgClosure *
  58 stealWork (Capability *cap)
  59 {
  60   /* use the normal Sparks.h interface (internally modified to enable
  61      concurrent stealing)
  62      and immediately turn the spark into a thread when successful
  63   */
  64   Capability *robbed;
  65   StgClosurePtr spark;
  66   rtsBool retry;
  67   nat i = 0;
  68
  69   debugTrace(DEBUG_sched,
  70              "cap %d: Trying to steal work from other capabilities",
  71              cap->no);
  72
  73   if (n_capabilities == 1) { return NULL; } // makes no sense...
  74
  75   do {
  76       retry = rtsFalse;
  77
  78       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
  79       start at a random place instead of 0 as well.  */
  80       for ( i=0 ; i < n_capabilities ; i++ ) {
  81           robbed = &capabilities[i];
  82           if (cap == robbed)  // ourselves...
  83               continue;
  84
  85           if (emptySparkPoolCap(robbed)) // nothing to steal here
  86               continue;
  87
  88           spark = tryStealSpark(robbed);
  89           if (spark == NULL && !emptySparkPoolCap(robbed)) {
  90               // we conflicted with another thread while trying to steal;
  91               // try again later.
  92               retry = rtsTrue;
  93           }
  94
  95           if (spark != NULL) {
  96               debugTrace(DEBUG_sched,
  97                  "cap %d: Stole a spark from capability %d",
  98                          cap->no, robbed->no);
  99               return spark;
 100           }
 101           // otherwise: no success, try next one
 102       }
 103   } while (retry);
 104
 105   debugTrace(DEBUG_sched, "No sparks stolen");
 106   return NULL;
 107 }
 108
 109 // Returns True if any spark pool is non-empty at this moment in time
 110 // The result is only valid for an instant, of course, so in a sense
 111 // is immediately invalid, and should not be relied upon for
 112 // correctness.
 113 rtsBool
 114 anySparks (void)
 115 {
 116     nat i;
 117
 118     for (i=0; i < n_capabilities; i++) {
 119         if (!emptySparkPoolCap(&capabilities[i])) {
 120             return rtsTrue;
 121         }
 122     }
 123     return rtsFalse;
 124 }
 125 #endif
 126
 127 /* -----------------------------------------------------------------------------
 128  * Manage the returning_tasks lists.
 129  *
 130  * These functions require cap->lock
 131  * -------------------------------------------------------------------------- */
 132
 133 #if defined(THREADED_RTS)
 134 STATIC_INLINE void
 135 newReturningTask (Capability *cap, Task *task)
 136 {
 137     ASSERT_LOCK_HELD(&cap->lock);
 138     ASSERT(task->return_link == NULL);
 139     if (cap->returning_tasks_hd) {
 140         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 141         cap->returning_tasks_tl->return_link = task;
 142     } else {
 143         cap->returning_tasks_hd = task;
 144     }
 145     cap->returning_tasks_tl = task;
 146 }
 147
 148 STATIC_INLINE Task *
 149 popReturningTask (Capability *cap)
 150 {
 151     ASSERT_LOCK_HELD(&cap->lock);
 152     Task *task;
 153     task = cap->returning_tasks_hd;
 154     ASSERT(task);
 155     cap->returning_tasks_hd = task->return_link;
 156     if (!cap->returning_tasks_hd) {
 157         cap->returning_tasks_tl = NULL;
 158     }
 159     task->return_link = NULL;
 160     return task;
 161 }
 162 #endif
 163
 164 /* ----------------------------------------------------------------------------
 165  * Initialisation
 166  *
 167  * The Capability is initially marked not free.
 168  * ------------------------------------------------------------------------- */
 169
 170 static void
 171 initCapability( Capability *cap, nat i )
 172 {
 173     nat g;
 174
 175     cap->no = i;
 176     cap->in_haskell        = rtsFalse;
 177
 178     cap->run_queue_hd      = END_TSO_QUEUE;
 179     cap->run_queue_tl      = END_TSO_QUEUE;
 180
 181 #if defined(THREADED_RTS)
 182     initMutex(&cap->lock);
 183     cap->running_task      = NULL; // indicates cap is free
 184     cap->spare_workers     = NULL;
 185     cap->suspended_ccalling_tasks = NULL;
 186     cap->returning_tasks_hd = NULL;
 187     cap->returning_tasks_tl = NULL;
 188     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 189     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 190     cap->sparks_created     = 0;
 191     cap->sparks_converted   = 0;
 192     cap->sparks_pruned      = 0;
 193 #endif
 194
 195     cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
 196     cap->f.stgGCFun        = (F_)__stg_gc_fun;
 197
 198     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 199                                      RtsFlags.GcFlags.generations,
 200                                      "initCapability");
 201
 202     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 203         cap->mut_lists[g] = NULL;
 204     }
 205
 206     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 207     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 208     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 209     cap->free_trec_headers = NO_TREC;
 210     cap->transaction_tokens = 0;
 211     cap->context_switch = 0;
 212 }
 213
 214 /* ---------------------------------------------------------------------------
 215  * Function:  initCapabilities()
 216  *
 217  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 218  *            we keep a table of them, the size of which is
 219  *            controlled by the user via the RTS flag -N.
 220  *
 221  * ------------------------------------------------------------------------- */
 222 void
 223 initCapabilities( void )
 224 {
 225 #if defined(THREADED_RTS)
 226     nat i;
 227
 228 #ifndef REG_Base
 229     // We can't support multiple CPUs if BaseReg is not a register
 230     if (RtsFlags.ParFlags.nNodes > 1) {
 231         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 232         RtsFlags.ParFlags.nNodes = 1;
 233     }
 234 #endif
 235
 236     n_capabilities = RtsFlags.ParFlags.nNodes;
 237
 238     if (n_capabilities == 1) {
 239         capabilities = &MainCapability;
 240         // THREADED_RTS must work on builds that don't have a mutable
 241         // BaseReg (eg. unregisterised), so in this case
 242         // capabilities[0] must coincide with &MainCapability.
 243     } else {
 244         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 245                                       "initCapabilities");
 246     }
 247
 248     for (i = 0; i < n_capabilities; i++) {
 249         initCapability(&capabilities[i], i);
 250     }
 251
 252     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 253
 254 #else /* !THREADED_RTS */
 255
 256     n_capabilities = 1;
 257     capabilities = &MainCapability;
 258     initCapability(&MainCapability, 0);
 259
 260 #endif
 261
 262     // There are no free capabilities to begin with.  We will start
 263     // a worker Task to each Capability, which will quickly put the
 264     // Capability on the free list when it finds nothing to do.
 265     last_free_capability = &capabilities[0];
 266 }
 267
 268 /* ----------------------------------------------------------------------------
 269  * setContextSwitches: cause all capabilities to context switch as
 270  * soon as possible.
 271  * ------------------------------------------------------------------------- */
 272
 273 void setContextSwitches(void)
 274 {
 275   nat i;
 276   for (i=0; i < n_capabilities; i++) {
 277     capabilities[i].context_switch = 1;
 278   }
 279 }
 280
 281 /* ----------------------------------------------------------------------------
 282  * Give a Capability to a Task.  The task must currently be sleeping
 283  * on its condition variable.
 284  *
 285  * Requires cap->lock (modifies cap->running_task).
 286  *
 287  * When migrating a Task, the migrater must take task->lock before
 288  * modifying task->cap, to synchronise with the waking up Task.
 289  * Additionally, the migrater should own the Capability (when
 290  * migrating the run queue), or cap->lock (when migrating
 291  * returning_workers).
 292  *
 293  * ------------------------------------------------------------------------- */
 294
 295 #if defined(THREADED_RTS)
 296 STATIC_INLINE void
 297 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 298 {
 299     ASSERT_LOCK_HELD(&cap->lock);
 300     ASSERT(task->cap == cap);
 301     trace(TRACE_sched | DEBUG_sched,
 302           "passing capability %d to %s %p",
 303           cap->no, task->tso ? "bound task" : "worker",
 304           (void *)task->id);
 305     ACQUIRE_LOCK(&task->lock);
 306     task->wakeup = rtsTrue;
 307     // the wakeup flag is needed because signalCondition() doesn't
 308     // flag the condition if the thread is already runniing, but we want
 309     // it to be sticky.
 310     signalCondition(&task->cond);
 311     RELEASE_LOCK(&task->lock);
 312 }
 313 #endif
 314
 315 /* ----------------------------------------------------------------------------
 316  * Function:  releaseCapability(Capability*)
 317  *
 318  * Purpose:   Letting go of a capability. Causes a
 319  *            'returning worker' thread or a 'waiting worker'
 320  *            to wake up, in that order.
 321  * ------------------------------------------------------------------------- */
 322
 323 #if defined(THREADED_RTS)
 324 void
 325 releaseCapability_ (Capability* cap,
 326                     rtsBool always_wakeup)
 327 {
 328     Task *task;
 329
 330     task = cap->running_task;
 331
 332     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 333
 334     cap->running_task = NULL;
 335
 336     // Check to see whether a worker thread can be given
 337     // the go-ahead to return the result of an external call..
 338     if (cap->returning_tasks_hd != NULL) {
 339         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 340         // The Task pops itself from the queue (see waitForReturnCapability())
 341         return;
 342     }
 343
 344     /* if waiting_for_gc was the reason to release the cap: thread
 345        comes from yieldCap->releaseAndQueueWorker. Unconditionally set
 346        cap. free and return (see default after the if-protected other
 347        special cases). Thread will wait on cond.var and re-acquire the
 348        same cap after GC (GC-triggering cap. calls releaseCap and
 349        enters the spare_workers case)
 350     */
 351     if (waiting_for_gc) {
 352       last_free_capability = cap; // needed?
 353       trace(TRACE_sched | DEBUG_sched,
 354             "GC pending, set capability %d free", cap->no);
 355       return;
 356     }
 357
 358
 359     // If the next thread on the run queue is a bound thread,
 360     // give this Capability to the appropriate Task.
 361     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 362         // Make sure we're not about to try to wake ourselves up
 363         ASSERT(task != cap->run_queue_hd->bound);
 364         task = cap->run_queue_hd->bound;
 365         giveCapabilityToTask(cap,task);
 366         return;
 367     }
 368
 369     if (!cap->spare_workers) {
 370         // Create a worker thread if we don't have one.  If the system
 371         // is interrupted, we only create a worker task if there
 372         // are threads that need to be completed.  If the system is
 373         // shutting down, we never create a new worker.
 374         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 375             debugTrace(DEBUG_sched,
 376                        "starting new worker on capability %d", cap->no);
 377             startWorkerTask(cap, workerStart);
 378             return;
 379         }
 380     }
 381
 382     // If we have an unbound thread on the run queue, or if there's
 383     // anything else to do, give the Capability to a worker thread.
 384     if (always_wakeup ||
 385         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 386         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 387         if (cap->spare_workers) {
 388             giveCapabilityToTask(cap,cap->spare_workers);
 389             // The worker Task pops itself from the queue;
 390             return;
 391         }
 392     }
 393
 394     last_free_capability = cap;
 395     trace(TRACE_sched | DEBUG_sched, "freeing capability %d", cap->no);
 396 }
 397
 398 void
 399 releaseCapability (Capability* cap USED_IF_THREADS)
 400 {
 401     ACQUIRE_LOCK(&cap->lock);
 402     releaseCapability_(cap, rtsFalse);
 403     RELEASE_LOCK(&cap->lock);
 404 }
 405
 406 void
 407 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 408 {
 409     ACQUIRE_LOCK(&cap->lock);
 410     releaseCapability_(cap, rtsTrue);
 411     RELEASE_LOCK(&cap->lock);
 412 }
 413
 414 static void
 415 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 416 {
 417     Task *task;
 418
 419     ACQUIRE_LOCK(&cap->lock);
 420
 421     task = cap->running_task;
 422
 423     // If the current task is a worker, save it on the spare_workers
 424     // list of this Capability.  A worker can mark itself as stopped,
 425     // in which case it is not replaced on the spare_worker queue.
 426     // This happens when the system is shutting down (see
 427     // Schedule.c:workerStart()).
 428     // Also, be careful to check that this task hasn't just exited
 429     // Haskell to do a foreign call (task->suspended_tso).
 430     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 431         task->next = cap->spare_workers;
 432         cap->spare_workers = task;
 433     }
 434     // Bound tasks just float around attached to their TSOs.
 435
 436     releaseCapability_(cap,rtsFalse);
 437
 438     RELEASE_LOCK(&cap->lock);
 439 }
 440 #endif
 441
 442 /* ----------------------------------------------------------------------------
 443  * waitForReturnCapability( Task *task )
 444  *
 445  * Purpose:  when an OS thread returns from an external call,
 446  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 447  * to wait for permission to enter the RTS & communicate the
 448  * result of the external call back to the Haskell thread that
 449  * made it.
 450  *
 451  * ------------------------------------------------------------------------- */
 452 void
 453 waitForReturnCapability (Capability **pCap, Task *task)
 454 {
 455 #if !defined(THREADED_RTS)
 456
 457     MainCapability.running_task = task;
 458     task->cap = &MainCapability;
 459     *pCap = &MainCapability;
 460
 461 #else
 462     Capability *cap = *pCap;
 463
 464     if (cap == NULL) {
 465         // Try last_free_capability first
 466         cap = last_free_capability;
 467         if (!cap->running_task) {
 468             nat i;
 469             // otherwise, search for a free capability
 470             for (i = 0; i < n_capabilities; i++) {
 471                 cap = &capabilities[i];
 472                 if (!cap->running_task) {
 473                     break;
 474                 }
 475             }
 476             // Can't find a free one, use last_free_capability.
 477             cap = last_free_capability;
 478         }
 479
 480         // record the Capability as the one this Task is now assocated with.
 481         task->cap = cap;
 482
 483     } else {
 484         ASSERT(task->cap == cap);
 485     }
 486
 487     ACQUIRE_LOCK(&cap->lock);
 488
 489     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 490
 491     if (!cap->running_task) {
 492         // It's free; just grab it
 493         cap->running_task = task;
 494         RELEASE_LOCK(&cap->lock);
 495     } else {
 496         newReturningTask(cap,task);
 497         RELEASE_LOCK(&cap->lock);
 498
 499         for (;;) {
 500             ACQUIRE_LOCK(&task->lock);
 501             // task->lock held, cap->lock not held
 502             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 503             cap = task->cap;
 504             task->wakeup = rtsFalse;
 505             RELEASE_LOCK(&task->lock);
 506
 507             // now check whether we should wake up...
 508             ACQUIRE_LOCK(&cap->lock);
 509             if (cap->running_task == NULL) {
 510                 if (cap->returning_tasks_hd != task) {
 511                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 512                     RELEASE_LOCK(&cap->lock);
 513                     continue;
 514                 }
 515                 cap->running_task = task;
 516                 popReturningTask(cap);
 517                 RELEASE_LOCK(&cap->lock);
 518                 break;
 519             }
 520             RELEASE_LOCK(&cap->lock);
 521         }
 522
 523     }
 524
 525     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 526
 527     trace(TRACE_sched | DEBUG_sched, "resuming capability %d", cap->no);
 528
 529     *pCap = cap;
 530 #endif
 531 }
 532
 533 #if defined(THREADED_RTS)
 534 /* ----------------------------------------------------------------------------
 535  * yieldCapability
 536  * ------------------------------------------------------------------------- */
 537
 538 void
 539 yieldCapability (Capability** pCap, Task *task)
 540 {
 541     Capability *cap = *pCap;
 542
 543         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 544
 545         // We must now release the capability and wait to be woken up
 546         // again.
 547         task->wakeup = rtsFalse;
 548         releaseCapabilityAndQueueWorker(cap);
 549
 550         for (;;) {
 551             ACQUIRE_LOCK(&task->lock);
 552             // task->lock held, cap->lock not held
 553             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 554             cap = task->cap;
 555             task->wakeup = rtsFalse;
 556             RELEASE_LOCK(&task->lock);
 557
 558             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 559
 560             ACQUIRE_LOCK(&cap->lock);
 561             if (cap->running_task != NULL) {
 562                 debugTrace(DEBUG_sched,
 563                            "capability %d is owned by another task", cap->no);
 564                 RELEASE_LOCK(&cap->lock);
 565                 continue;
 566             }
 567
 568             if (task->tso == NULL) {
 569                 ASSERT(cap->spare_workers != NULL);
 570                 // if we're not at the front of the queue, release it
 571                 // again.  This is unlikely to happen.
 572                 if (cap->spare_workers != task) {
 573                     giveCapabilityToTask(cap,cap->spare_workers);
 574                     RELEASE_LOCK(&cap->lock);
 575                     continue;
 576                 }
 577                 cap->spare_workers = task->next;
 578                 task->next = NULL;
 579             }
 580             cap->running_task = task;
 581             RELEASE_LOCK(&cap->lock);
 582             break;
 583         }
 584
 585         trace(TRACE_sched | DEBUG_sched, "resuming capability %d", cap->no);
 586         ASSERT(cap->running_task == task);
 587
 588     *pCap = cap;
 589
 590     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 591
 592     return;
 593 }
 594
 595 /* ----------------------------------------------------------------------------
 596  * Wake up a thread on a Capability.
 597  *
 598  * This is used when the current Task is running on a Capability and
 599  * wishes to wake up a thread on a different Capability.
 600  * ------------------------------------------------------------------------- */
 601
 602 void
 603 wakeupThreadOnCapability (Capability *my_cap,
 604                           Capability *other_cap,
 605                           StgTSO *tso)
 606 {
 607     ACQUIRE_LOCK(&other_cap->lock);
 608
 609     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 610     if (tso->bound) {
 611         ASSERT(tso->bound->cap == tso->cap);
 612         tso->bound->cap = other_cap;
 613     }
 614     tso->cap = other_cap;
 615
 616     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 617
 618     if (other_cap->running_task == NULL) {
 619         // nobody is running this Capability, we can add our thread
 620         // directly onto the run queue and start up a Task to run it.
 621
 622         other_cap->running_task = myTask();
 623             // precond for releaseCapability_() and appendToRunQueue()
 624
 625         appendToRunQueue(other_cap,tso);
 626
 627         trace(TRACE_sched, "resuming capability %d", other_cap->no);
 628         releaseCapability_(other_cap,rtsFalse);
 629     } else {
 630         appendToWakeupQueue(my_cap,other_cap,tso);
 631         other_cap->context_switch = 1;
 632         // someone is running on this Capability, so it cannot be
 633         // freed without first checking the wakeup queue (see
 634         // releaseCapability_).
 635     }
 636
 637     RELEASE_LOCK(&other_cap->lock);
 638 }
 639
 640 /* ----------------------------------------------------------------------------
 641  * prodCapabilities
 642  *
 643  * Used to indicate that the interrupted flag is now set, or some
 644  * other global condition that might require waking up a Task on each
 645  * Capability.
 646  * ------------------------------------------------------------------------- */
 647
 648 static void
 649 prodCapabilities(rtsBool all)
 650 {
 651     nat i;
 652     Capability *cap;
 653     Task *task;
 654
 655     for (i=0; i < n_capabilities; i++) {
 656         cap = &capabilities[i];
 657         ACQUIRE_LOCK(&cap->lock);
 658         if (!cap->running_task) {
 659             if (cap->spare_workers) {
 660                 trace(TRACE_sched, "resuming capability %d", cap->no);
 661                 task = cap->spare_workers;
 662                 ASSERT(!task->stopped);
 663                 giveCapabilityToTask(cap,task);
 664                 if (!all) {
 665                     RELEASE_LOCK(&cap->lock);
 666                     return;
 667                 }
 668             }
 669         }
 670         RELEASE_LOCK(&cap->lock);
 671     }
 672     return;
 673 }
 674
 675 void
 676 prodAllCapabilities (void)
 677 {
 678     prodCapabilities(rtsTrue);
 679 }
 680
 681 /* ----------------------------------------------------------------------------
 682  * prodOneCapability
 683  *
 684  * Like prodAllCapabilities, but we only require a single Task to wake
 685  * up in order to service some global event, such as checking for
 686  * deadlock after some idle time has passed.
 687  * ------------------------------------------------------------------------- */
 688
 689 void
 690 prodOneCapability (void)
 691 {
 692     prodCapabilities(rtsFalse);
 693 }
 694
 695 /* ----------------------------------------------------------------------------
 696  * shutdownCapability
 697  *
 698  * At shutdown time, we want to let everything exit as cleanly as
 699  * possible.  For each capability, we let its run queue drain, and
 700  * allow the workers to stop.
 701  *
 702  * This function should be called when interrupted and
 703  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 704  * will exit the scheduler and call taskStop(), and any bound thread
 705  * that wakes up will return to its caller.  Runnable threads are
 706  * killed.
 707  *
 708  * ------------------------------------------------------------------------- */
 709
 710 void
 711 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 712 {
 713     nat i;
 714
 715     ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 716
 717     task->cap = cap;
 718
 719     // Loop indefinitely until all the workers have exited and there
 720     // are no Haskell threads left.  We used to bail out after 50
 721     // iterations of this loop, but that occasionally left a worker
 722     // running which caused problems later (the closeMutex() below
 723     // isn't safe, for one thing).
 724
 725     for (i = 0; /* i < 50 */; i++) {
 726         debugTrace(DEBUG_sched,
 727                    "shutting down capability %d, attempt %d", cap->no, i);
 728         ACQUIRE_LOCK(&cap->lock);
 729         if (cap->running_task) {
 730             RELEASE_LOCK(&cap->lock);
 731             debugTrace(DEBUG_sched, "not owner, yielding");
 732             yieldThread();
 733             continue;
 734         }
 735         cap->running_task = task;
 736
 737         if (cap->spare_workers) {
 738             // Look for workers that have died without removing
 739             // themselves from the list; this could happen if the OS
 740             // summarily killed the thread, for example.  This
 741             // actually happens on Windows when the system is
 742             // terminating the program, and the RTS is running in a
 743             // DLL.
 744             Task *t, *prev;
 745             prev = NULL;
 746             for (t = cap->spare_workers; t != NULL; t = t->next) {
 747                 if (!osThreadIsAlive(t->id)) {
 748                     debugTrace(DEBUG_sched,
 749                                "worker thread %p has died unexpectedly", (void *)t->id);
 750                         if (!prev) {
 751                             cap->spare_workers = t->next;
 752                         } else {
 753                             prev->next = t->next;
 754                         }
 755                         prev = t;
 756                 }
 757             }
 758         }
 759
 760         if (!emptyRunQueue(cap) || cap->spare_workers) {
 761             debugTrace(DEBUG_sched,
 762                        "runnable threads or workers still alive, yielding");
 763             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 764             RELEASE_LOCK(&cap->lock);
 765             yieldThread();
 766             continue;
 767         }
 768
 769         // If "safe", then busy-wait for any threads currently doing
 770         // foreign calls.  If we're about to unload this DLL, for
 771         // example, we need to be sure that there are no OS threads
 772         // that will try to return to code that has been unloaded.
 773         // We can be a bit more relaxed when this is a standalone
 774         // program that is about to terminate, and let safe=false.
 775         if (cap->suspended_ccalling_tasks && safe) {
 776             debugTrace(DEBUG_sched,
 777                        "thread(s) are involved in foreign calls, yielding");
 778             cap->running_task = NULL;
 779             RELEASE_LOCK(&cap->lock);
 780             yieldThread();
 781             continue;
 782         }
 783
 784         debugTrace(DEBUG_sched, "capability %d is stopped.", cap->no);
 785         RELEASE_LOCK(&cap->lock);
 786         break;
 787     }
 788     // we now have the Capability, its run queue and spare workers
 789     // list are both empty.
 790
 791     // ToDo: we can't drop this mutex, because there might still be
 792     // threads performing foreign calls that will eventually try to
 793     // return via resumeThread() and attempt to grab cap->lock.
 794     // closeMutex(&cap->lock);
 795 }
 796
 797 /* ----------------------------------------------------------------------------
 798  * tryGrabCapability
 799  *
 800  * Attempt to gain control of a Capability if it is free.
 801  *
 802  * ------------------------------------------------------------------------- */
 803
 804 rtsBool
 805 tryGrabCapability (Capability *cap, Task *task)
 806 {
 807     if (cap->running_task != NULL) return rtsFalse;
 808     ACQUIRE_LOCK(&cap->lock);
 809     if (cap->running_task != NULL) {
 810         RELEASE_LOCK(&cap->lock);
 811         return rtsFalse;
 812     }
 813     task->cap = cap;
 814     cap->running_task = task;
 815     RELEASE_LOCK(&cap->lock);
 816     return rtsTrue;
 817 }
 818
 819
 820 #endif /* THREADED_RTS */
 821
 822 static void
 823 freeCapability (Capability *cap)
 824 {
 825     stgFree(cap->mut_lists);
 826 #if defined(THREADED_RTS) || defined(PARALLEL_HASKELL)
 827     freeSparkPool(cap->sparks);
 828 #endif
 829 }
 830
 831 void
 832 freeCapabilities (void)
 833 {
 834 #if defined(THREADED_RTS)
 835     nat i;
 836     for (i=0; i < n_capabilities; i++) {
 837         freeCapability(&capabilities[i]);
 838     }
 839 #else
 840     freeCapability(&MainCapability);
 841 #endif
 842 }
 843
 844 /* ---------------------------------------------------------------------------
 845    Mark everything directly reachable from the Capabilities.  When
 846    using multiple GC threads, each GC thread marks all Capabilities
 847    for which (c `mod` n == 0), for Capability c and thread n.
 848    ------------------------------------------------------------------------ */
 849
 850 void
 851 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 852                       rtsBool prune_sparks USED_IF_THREADS)
 853 {
 854     nat i;
 855     Capability *cap;
 856     Task *task;
 857
 858     // Each GC thread is responsible for following roots from the
 859     // Capability of the same number.  There will usually be the same
 860     // or fewer Capabilities as GC threads, but just in case there
 861     // are more, we mark every Capability whose number is the GC
 862     // thread's index plus a multiple of the number of GC threads.
 863     for (i = i0; i < n_capabilities; i += delta) {
 864         cap = &capabilities[i];
 865         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 866         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 867 #if defined(THREADED_RTS)
 868         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 869         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 870 #endif
 871         for (task = cap->suspended_ccalling_tasks; task != NULL;
 872              task=task->next) {
 873             debugTrace(DEBUG_sched,
 874                        "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
 875             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 876         }
 877
 878 #if defined(THREADED_RTS)
 879         if (prune_sparks) {
 880             pruneSparkQueue (evac, user, cap);
 881         } else {
 882             traverseSparkQueue (evac, user, cap);
 883         }
 884 #endif
 885     }
 886
 887 #if !defined(THREADED_RTS)
 888     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 889     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 890     evac(user, (StgClosure **)(void *)&sleeping_queue);
 891 #endif
 892 }
 893
 894 void
 895 markCapabilities (evac_fn evac, void *user)
 896 {
 897     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 898 }