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       traceSchedEvent(cap, EVENT_RUN_SPARK, cap->r.rCurrentTSO, 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               cap->sparks_converted++;
 131
 132               traceSchedEvent(cap, EVENT_STEAL_SPARK,
 133                               cap->r.rCurrentTSO, robbed->no);
 134
 135               return spark;
 136           }
 137           // otherwise: no success, try next one
 138       }
 139   } while (retry);
 140
 141   debugTrace(DEBUG_sched, "No sparks stolen");
 142   return NULL;
 143 }
 144
 145 // Returns True if any spark pool is non-empty at this moment in time
 146 // The result is only valid for an instant, of course, so in a sense
 147 // is immediately invalid, and should not be relied upon for
 148 // correctness.
 149 rtsBool
 150 anySparks (void)
 151 {
 152     nat i;
 153
 154     for (i=0; i < n_capabilities; i++) {
 155         if (!emptySparkPoolCap(&capabilities[i])) {
 156             return rtsTrue;
 157         }
 158     }
 159     return rtsFalse;
 160 }
 161 #endif
 162
 163 /* -----------------------------------------------------------------------------
 164  * Manage the returning_tasks lists.
 165  *
 166  * These functions require cap->lock
 167  * -------------------------------------------------------------------------- */
 168
 169 #if defined(THREADED_RTS)
 170 STATIC_INLINE void
 171 newReturningTask (Capability *cap, Task *task)
 172 {
 173     ASSERT_LOCK_HELD(&cap->lock);
 174     ASSERT(task->return_link == NULL);
 175     if (cap->returning_tasks_hd) {
 176         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 177         cap->returning_tasks_tl->return_link = task;
 178     } else {
 179         cap->returning_tasks_hd = task;
 180     }
 181     cap->returning_tasks_tl = task;
 182 }
 183
 184 STATIC_INLINE Task *
 185 popReturningTask (Capability *cap)
 186 {
 187     ASSERT_LOCK_HELD(&cap->lock);
 188     Task *task;
 189     task = cap->returning_tasks_hd;
 190     ASSERT(task);
 191     cap->returning_tasks_hd = task->return_link;
 192     if (!cap->returning_tasks_hd) {
 193         cap->returning_tasks_tl = NULL;
 194     }
 195     task->return_link = NULL;
 196     return task;
 197 }
 198 #endif
 199
 200 /* ----------------------------------------------------------------------------
 201  * Initialisation
 202  *
 203  * The Capability is initially marked not free.
 204  * ------------------------------------------------------------------------- */
 205
 206 static void
 207 initCapability( Capability *cap, nat i )
 208 {
 209     nat g;
 210
 211     cap->no = i;
 212     cap->in_haskell        = rtsFalse;
 213     cap->in_gc             = 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->suspended_ccalling_tasks = NULL;
 223     cap->returning_tasks_hd = NULL;
 224     cap->returning_tasks_tl = NULL;
 225     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 226     cap->wakeup_queue_tl    = 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 }
 254
 255 /* ---------------------------------------------------------------------------
 256  * Function:  initCapabilities()
 257  *
 258  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 259  *            we keep a table of them, the size of which is
 260  *            controlled by the user via the RTS flag -N.
 261  *
 262  * ------------------------------------------------------------------------- */
 263 void
 264 initCapabilities( void )
 265 {
 266 #if defined(THREADED_RTS)
 267     nat i;
 268
 269 #ifndef REG_Base
 270     // We can't support multiple CPUs if BaseReg is not a register
 271     if (RtsFlags.ParFlags.nNodes > 1) {
 272         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 273         RtsFlags.ParFlags.nNodes = 1;
 274     }
 275 #endif
 276
 277     n_capabilities = RtsFlags.ParFlags.nNodes;
 278
 279     if (n_capabilities == 1) {
 280         capabilities = &MainCapability;
 281         // THREADED_RTS must work on builds that don't have a mutable
 282         // BaseReg (eg. unregisterised), so in this case
 283         // capabilities[0] must coincide with &MainCapability.
 284     } else {
 285         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 286                                       "initCapabilities");
 287     }
 288
 289     for (i = 0; i < n_capabilities; i++) {
 290         initCapability(&capabilities[i], i);
 291     }
 292
 293     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 294
 295 #else /* !THREADED_RTS */
 296
 297     n_capabilities = 1;
 298     capabilities = &MainCapability;
 299     initCapability(&MainCapability, 0);
 300
 301 #endif
 302
 303     // There are no free capabilities to begin with.  We will start
 304     // a worker Task to each Capability, which will quickly put the
 305     // Capability on the free list when it finds nothing to do.
 306     last_free_capability = &capabilities[0];
 307 }
 308
 309 /* ----------------------------------------------------------------------------
 310  * setContextSwitches: cause all capabilities to context switch as
 311  * soon as possible.
 312  * ------------------------------------------------------------------------- */
 313
 314 void setContextSwitches(void)
 315 {
 316     nat i;
 317     for (i=0; i < n_capabilities; i++) {
 318         contextSwitchCapability(&capabilities[i]);
 319     }
 320 }
 321
 322 /* ----------------------------------------------------------------------------
 323  * Give a Capability to a Task.  The task must currently be sleeping
 324  * on its condition variable.
 325  *
 326  * Requires cap->lock (modifies cap->running_task).
 327  *
 328  * When migrating a Task, the migrater must take task->lock before
 329  * modifying task->cap, to synchronise with the waking up Task.
 330  * Additionally, the migrater should own the Capability (when
 331  * migrating the run queue), or cap->lock (when migrating
 332  * returning_workers).
 333  *
 334  * ------------------------------------------------------------------------- */
 335
 336 #if defined(THREADED_RTS)
 337 STATIC_INLINE void
 338 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 339 {
 340     ASSERT_LOCK_HELD(&cap->lock);
 341     ASSERT(task->cap == cap);
 342     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 343                cap->no, task->tso ? "bound task" : "worker",
 344                (void *)task->id);
 345     ACQUIRE_LOCK(&task->lock);
 346     task->wakeup = rtsTrue;
 347     // the wakeup flag is needed because signalCondition() doesn't
 348     // flag the condition if the thread is already runniing, but we want
 349     // it to be sticky.
 350     signalCondition(&task->cond);
 351     RELEASE_LOCK(&task->lock);
 352 }
 353 #endif
 354
 355 /* ----------------------------------------------------------------------------
 356  * Function:  releaseCapability(Capability*)
 357  *
 358  * Purpose:   Letting go of a capability. Causes a
 359  *            'returning worker' thread or a 'waiting worker'
 360  *            to wake up, in that order.
 361  * ------------------------------------------------------------------------- */
 362
 363 #if defined(THREADED_RTS)
 364 void
 365 releaseCapability_ (Capability* cap,
 366                     rtsBool always_wakeup)
 367 {
 368     Task *task;
 369
 370     task = cap->running_task;
 371
 372     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 373
 374     cap->running_task = NULL;
 375
 376     // Check to see whether a worker thread can be given
 377     // the go-ahead to return the result of an external call..
 378     if (cap->returning_tasks_hd != NULL) {
 379         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 380         // The Task pops itself from the queue (see waitForReturnCapability())
 381         return;
 382     }
 383
 384     if (waiting_for_gc == PENDING_GC_SEQ) {
 385       last_free_capability = cap; // needed?
 386       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 387       return;
 388     }
 389
 390
 391     // If the next thread on the run queue is a bound thread,
 392     // give this Capability to the appropriate Task.
 393     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 394         // Make sure we're not about to try to wake ourselves up
 395         ASSERT(task != cap->run_queue_hd->bound);
 396         task = cap->run_queue_hd->bound;
 397         giveCapabilityToTask(cap,task);
 398         return;
 399     }
 400
 401     if (!cap->spare_workers) {
 402         // Create a worker thread if we don't have one.  If the system
 403         // is interrupted, we only create a worker task if there
 404         // are threads that need to be completed.  If the system is
 405         // shutting down, we never create a new worker.
 406         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 407             debugTrace(DEBUG_sched,
 408                        "starting new worker on capability %d", cap->no);
 409             startWorkerTask(cap, workerStart);
 410             return;
 411         }
 412     }
 413
 414     // If we have an unbound thread on the run queue, or if there's
 415     // anything else to do, give the Capability to a worker thread.
 416     if (always_wakeup ||
 417         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 418         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 419         if (cap->spare_workers) {
 420             giveCapabilityToTask(cap,cap->spare_workers);
 421             // The worker Task pops itself from the queue;
 422             return;
 423         }
 424     }
 425
 426     last_free_capability = cap;
 427     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 428 }
 429
 430 void
 431 releaseCapability (Capability* cap USED_IF_THREADS)
 432 {
 433     ACQUIRE_LOCK(&cap->lock);
 434     releaseCapability_(cap, rtsFalse);
 435     RELEASE_LOCK(&cap->lock);
 436 }
 437
 438 void
 439 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 440 {
 441     ACQUIRE_LOCK(&cap->lock);
 442     releaseCapability_(cap, rtsTrue);
 443     RELEASE_LOCK(&cap->lock);
 444 }
 445
 446 static void
 447 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 448 {
 449     Task *task;
 450
 451     ACQUIRE_LOCK(&cap->lock);
 452
 453     task = cap->running_task;
 454
 455     // If the current task is a worker, save it on the spare_workers
 456     // list of this Capability.  A worker can mark itself as stopped,
 457     // in which case it is not replaced on the spare_worker queue.
 458     // This happens when the system is shutting down (see
 459     // Schedule.c:workerStart()).
 460     // Also, be careful to check that this task hasn't just exited
 461     // Haskell to do a foreign call (task->suspended_tso).
 462     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 463         task->next = cap->spare_workers;
 464         cap->spare_workers = task;
 465     }
 466     // Bound tasks just float around attached to their TSOs.
 467
 468     releaseCapability_(cap,rtsFalse);
 469
 470     RELEASE_LOCK(&cap->lock);
 471 }
 472 #endif
 473
 474 /* ----------------------------------------------------------------------------
 475  * waitForReturnCapability( Task *task )
 476  *
 477  * Purpose:  when an OS thread returns from an external call,
 478  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 479  * to wait for permission to enter the RTS & communicate the
 480  * result of the external call back to the Haskell thread that
 481  * made it.
 482  *
 483  * ------------------------------------------------------------------------- */
 484 void
 485 waitForReturnCapability (Capability **pCap, Task *task)
 486 {
 487 #if !defined(THREADED_RTS)
 488
 489     MainCapability.running_task = task;
 490     task->cap = &MainCapability;
 491     *pCap = &MainCapability;
 492
 493 #else
 494     Capability *cap = *pCap;
 495
 496     if (cap == NULL) {
 497         // Try last_free_capability first
 498         cap = last_free_capability;
 499         if (cap->running_task) {
 500             nat i;
 501             // otherwise, search for a free capability
 502             cap = NULL;
 503             for (i = 0; i < n_capabilities; i++) {
 504                 if (!capabilities[i].running_task) {
 505                     cap = &capabilities[i];
 506                     break;
 507                 }
 508             }
 509             if (cap == NULL) {
 510                 // Can't find a free one, use last_free_capability.
 511                 cap = last_free_capability;
 512             }
 513         }
 514
 515         // record the Capability as the one this Task is now assocated with.
 516         task->cap = cap;
 517
 518     } else {
 519         ASSERT(task->cap == cap);
 520     }
 521
 522     ACQUIRE_LOCK(&cap->lock);
 523
 524     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 525
 526     if (!cap->running_task) {
 527         // It's free; just grab it
 528         cap->running_task = task;
 529         RELEASE_LOCK(&cap->lock);
 530     } else {
 531         newReturningTask(cap,task);
 532         RELEASE_LOCK(&cap->lock);
 533
 534         for (;;) {
 535             ACQUIRE_LOCK(&task->lock);
 536             // task->lock held, cap->lock not held
 537             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 538             cap = task->cap;
 539             task->wakeup = rtsFalse;
 540             RELEASE_LOCK(&task->lock);
 541
 542             // now check whether we should wake up...
 543             ACQUIRE_LOCK(&cap->lock);
 544             if (cap->running_task == NULL) {
 545                 if (cap->returning_tasks_hd != task) {
 546                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 547                     RELEASE_LOCK(&cap->lock);
 548                     continue;
 549                 }
 550                 cap->running_task = task;
 551                 popReturningTask(cap);
 552                 RELEASE_LOCK(&cap->lock);
 553                 break;
 554             }
 555             RELEASE_LOCK(&cap->lock);
 556         }
 557
 558     }
 559
 560     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 561
 562     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 563
 564     *pCap = cap;
 565 #endif
 566 }
 567
 568 #if defined(THREADED_RTS)
 569 /* ----------------------------------------------------------------------------
 570  * yieldCapability
 571  * ------------------------------------------------------------------------- */
 572
 573 void
 574 yieldCapability (Capability** pCap, Task *task)
 575 {
 576     Capability *cap = *pCap;
 577
 578     if (waiting_for_gc == PENDING_GC_PAR) {
 579         traceSchedEvent(cap, EVENT_GC_START, 0, 0);
 580         gcWorkerThread(cap);
 581         traceSchedEvent(cap, EVENT_GC_END, 0, 0);
 582         return;
 583     }
 584
 585         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 586
 587         // We must now release the capability and wait to be woken up
 588         // again.
 589         task->wakeup = rtsFalse;
 590         releaseCapabilityAndQueueWorker(cap);
 591
 592         for (;;) {
 593             ACQUIRE_LOCK(&task->lock);
 594             // task->lock held, cap->lock not held
 595             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 596             cap = task->cap;
 597             task->wakeup = rtsFalse;
 598             RELEASE_LOCK(&task->lock);
 599
 600             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 601
 602             ACQUIRE_LOCK(&cap->lock);
 603             if (cap->running_task != NULL) {
 604                 debugTrace(DEBUG_sched,
 605                            "capability %d is owned by another task", cap->no);
 606                 RELEASE_LOCK(&cap->lock);
 607                 continue;
 608             }
 609
 610             if (task->tso == NULL) {
 611                 ASSERT(cap->spare_workers != NULL);
 612                 // if we're not at the front of the queue, release it
 613                 // again.  This is unlikely to happen.
 614                 if (cap->spare_workers != task) {
 615                     giveCapabilityToTask(cap,cap->spare_workers);
 616                     RELEASE_LOCK(&cap->lock);
 617                     continue;
 618                 }
 619                 cap->spare_workers = task->next;
 620                 task->next = NULL;
 621             }
 622             cap->running_task = task;
 623             RELEASE_LOCK(&cap->lock);
 624             break;
 625         }
 626
 627         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 628         ASSERT(cap->running_task == task);
 629
 630     *pCap = cap;
 631
 632     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 633
 634     return;
 635 }
 636
 637 /* ----------------------------------------------------------------------------
 638  * Wake up a thread on a Capability.
 639  *
 640  * This is used when the current Task is running on a Capability and
 641  * wishes to wake up a thread on a different Capability.
 642  * ------------------------------------------------------------------------- */
 643
 644 void
 645 wakeupThreadOnCapability (Capability *my_cap,
 646                           Capability *other_cap,
 647                           StgTSO *tso)
 648 {
 649     ACQUIRE_LOCK(&other_cap->lock);
 650
 651     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 652     if (tso->bound) {
 653         ASSERT(tso->bound->cap == tso->cap);
 654         tso->bound->cap = other_cap;
 655     }
 656     tso->cap = other_cap;
 657
 658     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 659
 660     if (other_cap->running_task == NULL) {
 661         // nobody is running this Capability, we can add our thread
 662         // directly onto the run queue and start up a Task to run it.
 663
 664         other_cap->running_task = myTask();
 665             // precond for releaseCapability_() and appendToRunQueue()
 666
 667         appendToRunQueue(other_cap,tso);
 668
 669         releaseCapability_(other_cap,rtsFalse);
 670     } else {
 671         appendToWakeupQueue(my_cap,other_cap,tso);
 672         other_cap->context_switch = 1;
 673         // someone is running on this Capability, so it cannot be
 674         // freed without first checking the wakeup queue (see
 675         // releaseCapability_).
 676     }
 677
 678     RELEASE_LOCK(&other_cap->lock);
 679 }
 680
 681 /* ----------------------------------------------------------------------------
 682  * prodCapability
 683  *
 684  * If a Capability is currently idle, wake up a Task on it.  Used to
 685  * get every Capability into the GC.
 686  * ------------------------------------------------------------------------- */
 687
 688 void
 689 prodCapability (Capability *cap, Task *task)
 690 {
 691     ACQUIRE_LOCK(&cap->lock);
 692     if (!cap->running_task) {
 693         cap->running_task = task;
 694         releaseCapability_(cap,rtsTrue);
 695     }
 696     RELEASE_LOCK(&cap->lock);
 697 }
 698
 699 /* ----------------------------------------------------------------------------
 700  * shutdownCapability
 701  *
 702  * At shutdown time, we want to let everything exit as cleanly as
 703  * possible.  For each capability, we let its run queue drain, and
 704  * allow the workers to stop.
 705  *
 706  * This function should be called when interrupted and
 707  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 708  * will exit the scheduler and call taskStop(), and any bound thread
 709  * that wakes up will return to its caller.  Runnable threads are
 710  * killed.
 711  *
 712  * ------------------------------------------------------------------------- */
 713
 714 void
 715 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 716 {
 717     nat i;
 718
 719     task->cap = cap;
 720
 721     // Loop indefinitely until all the workers have exited and there
 722     // are no Haskell threads left.  We used to bail out after 50
 723     // iterations of this loop, but that occasionally left a worker
 724     // running which caused problems later (the closeMutex() below
 725     // isn't safe, for one thing).
 726
 727     for (i = 0; /* i < 50 */; i++) {
 728         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 729
 730         debugTrace(DEBUG_sched,
 731                    "shutting down capability %d, attempt %d", cap->no, i);
 732         ACQUIRE_LOCK(&cap->lock);
 733         if (cap->running_task) {
 734             RELEASE_LOCK(&cap->lock);
 735             debugTrace(DEBUG_sched, "not owner, yielding");
 736             yieldThread();
 737             continue;
 738         }
 739         cap->running_task = task;
 740
 741         if (cap->spare_workers) {
 742             // Look for workers that have died without removing
 743             // themselves from the list; this could happen if the OS
 744             // summarily killed the thread, for example.  This
 745             // actually happens on Windows when the system is
 746             // terminating the program, and the RTS is running in a
 747             // DLL.
 748             Task *t, *prev;
 749             prev = NULL;
 750             for (t = cap->spare_workers; t != NULL; t = t->next) {
 751                 if (!osThreadIsAlive(t->id)) {
 752                     debugTrace(DEBUG_sched,
 753                                "worker thread %p has died unexpectedly", (void *)t->id);
 754                         if (!prev) {
 755                             cap->spare_workers = t->next;
 756                         } else {
 757                             prev->next = t->next;
 758                         }
 759                         prev = t;
 760                 }
 761             }
 762         }
 763
 764         if (!emptyRunQueue(cap) || cap->spare_workers) {
 765             debugTrace(DEBUG_sched,
 766                        "runnable threads or workers still alive, yielding");
 767             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 768             RELEASE_LOCK(&cap->lock);
 769             yieldThread();
 770             continue;
 771         }
 772
 773         // If "safe", then busy-wait for any threads currently doing
 774         // foreign calls.  If we're about to unload this DLL, for
 775         // example, we need to be sure that there are no OS threads
 776         // that will try to return to code that has been unloaded.
 777         // We can be a bit more relaxed when this is a standalone
 778         // program that is about to terminate, and let safe=false.
 779         if (cap->suspended_ccalling_tasks && safe) {
 780             debugTrace(DEBUG_sched,
 781                        "thread(s) are involved in foreign calls, yielding");
 782             cap->running_task = NULL;
 783             RELEASE_LOCK(&cap->lock);
 784             yieldThread();
 785             continue;
 786         }
 787
 788         traceSchedEvent(cap, EVENT_SHUTDOWN, 0, 0);
 789         RELEASE_LOCK(&cap->lock);
 790         break;
 791     }
 792     // we now have the Capability, its run queue and spare workers
 793     // list are both empty.
 794
 795     // ToDo: we can't drop this mutex, because there might still be
 796     // threads performing foreign calls that will eventually try to
 797     // return via resumeThread() and attempt to grab cap->lock.
 798     // closeMutex(&cap->lock);
 799 }
 800
 801 /* ----------------------------------------------------------------------------
 802  * tryGrabCapability
 803  *
 804  * Attempt to gain control of a Capability if it is free.
 805  *
 806  * ------------------------------------------------------------------------- */
 807
 808 rtsBool
 809 tryGrabCapability (Capability *cap, Task *task)
 810 {
 811     if (cap->running_task != NULL) return rtsFalse;
 812     ACQUIRE_LOCK(&cap->lock);
 813     if (cap->running_task != NULL) {
 814         RELEASE_LOCK(&cap->lock);
 815         return rtsFalse;
 816     }
 817     task->cap = cap;
 818     cap->running_task = task;
 819     RELEASE_LOCK(&cap->lock);
 820     return rtsTrue;
 821 }
 822
 823
 824 #endif /* THREADED_RTS */
 825
 826 static void
 827 freeCapability (Capability *cap)
 828 {
 829     stgFree(cap->mut_lists);
 830 #if defined(THREADED_RTS)
 831     freeSparkPool(cap->sparks);
 832 #endif
 833 }
 834
 835 void
 836 freeCapabilities (void)
 837 {
 838 #if defined(THREADED_RTS)
 839     nat i;
 840     for (i=0; i < n_capabilities; i++) {
 841         freeCapability(&capabilities[i]);
 842     }
 843 #else
 844     freeCapability(&MainCapability);
 845 #endif
 846 }
 847
 848 /* ---------------------------------------------------------------------------
 849    Mark everything directly reachable from the Capabilities.  When
 850    using multiple GC threads, each GC thread marks all Capabilities
 851    for which (c `mod` n == 0), for Capability c and thread n.
 852    ------------------------------------------------------------------------ */
 853
 854 void
 855 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 856                       rtsBool prune_sparks USED_IF_THREADS)
 857 {
 858     nat i;
 859     Capability *cap;
 860     Task *task;
 861
 862     // Each GC thread is responsible for following roots from the
 863     // Capability of the same number.  There will usually be the same
 864     // or fewer Capabilities as GC threads, but just in case there
 865     // are more, we mark every Capability whose number is the GC
 866     // thread's index plus a multiple of the number of GC threads.
 867     for (i = i0; i < n_capabilities; i += delta) {
 868         cap = &capabilities[i];
 869         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 870         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 871 #if defined(THREADED_RTS)
 872         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 873         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 874 #endif
 875         for (task = cap->suspended_ccalling_tasks; task != NULL;
 876              task=task->next) {
 877             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 878         }
 879
 880 #if defined(THREADED_RTS)
 881         if (prune_sparks) {
 882             pruneSparkQueue (evac, user, cap);
 883         } else {
 884             traverseSparkQueue (evac, user, cap);
 885         }
 886 #endif
 887     }
 888
 889 #if !defined(THREADED_RTS)
 890     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 891     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 892     evac(user, (StgClosure **)(void *)&sleeping_queue);
 893 #endif
 894 }
 895
 896 void
 897 markCapabilities (evac_fn evac, void *user)
 898 {
 899     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 900 }