rts/Capability.c

   1 /* ---------------------------------------------------------------------------
   2  *
   3  * (c) The GHC Team, 2003-2006
   4  *
   5  * Capabilities
   6  *
   7  * A Capability represent the token required to execute STG code,
   8  * and all the state an OS thread/task needs to run Haskell code:
   9  * its STG registers, a pointer to its TSO, a nursery etc. During
  10  * STG execution, a pointer to the capabilitity is kept in a
  11  * register (BaseReg; actually it is a pointer to cap->r).
  12  *
  13  * Only in an THREADED_RTS build will there be multiple capabilities,
  14  * for non-threaded builds there is only one global capability, namely
  15  * MainCapability.
  16  *
  17  * --------------------------------------------------------------------------*/
  18
  19 #include "PosixSource.h"
  20 #include "Rts.h"
  21
  22 #include "Capability.h"
  23 #include "Schedule.h"
  24 #include "Sparks.h"
  25 #include "Trace.h"
  26 #include "sm/GC.h" // for gcWorkerThread()
  27 #include "STM.h"
  28 #include "RtsUtils.h"
  29
  30 // one global capability, this is the Capability for non-threaded
  31 // builds, and for +RTS -N1
  32 Capability MainCapability;
  33
  34 nat n_capabilities = 0;
  35 Capability *capabilities = NULL;
  36
  37 // Holds the Capability which last became free.  This is used so that
  38 // an in-call has a chance of quickly finding a free Capability.
  39 // Maintaining a global free list of Capabilities would require global
  40 // locking, so we don't do that.
  41 Capability *last_free_capability = NULL;
  42
  43 /* GC indicator, in scope for the scheduler, init'ed to false */
  44 volatile StgWord waiting_for_gc = 0;
  45
  46 /* Let foreign code get the current Capability -- assuming there is one!
  47  * This is useful for unsafe foreign calls because they are called with
  48  * the current Capability held, but they are not passed it. For example,
  49  * see see the integer-gmp package which calls allocateLocal() in its
  50  * stgAllocForGMP() function (which gets called by gmp functions).
  51  * */
  52 Capability * rts_unsafeGetMyCapability (void)
  53 {
  54 #if defined(THREADED_RTS)
  55   return myTask()->cap;
  56 #else
  57   return &MainCapability;
  58 #endif
  59 }
  60
  61 #if defined(THREADED_RTS)
  62 STATIC_INLINE rtsBool
  63 globalWorkToDo (void)
  64 {
  65     return blackholes_need_checking
  66         || sched_state >= SCHED_INTERRUPTING
  67         ;
  68 }
  69 #endif
  70
  71 #if defined(THREADED_RTS)
  72 StgClosure *
  73 findSpark (Capability *cap)
  74 {
  75   Capability *robbed;
  76   StgClosurePtr spark;
  77   rtsBool retry;
  78   nat i = 0;
  79
  80   if (!emptyRunQueue(cap) || cap->returning_tasks_hd != NULL) {
  81       // If there are other threads, don't try to run any new
  82       // sparks: sparks might be speculative, we don't want to take
  83       // resources away from the main computation.
  84       return 0;
  85   }
  86
  87   do {
  88       retry = rtsFalse;
  89
  90       // first try to get a spark from our own pool.
  91       // We should be using reclaimSpark(), because it works without
  92       // needing any atomic instructions:
  93       //   spark = reclaimSpark(cap->sparks);
  94       // However, measurements show that this makes at least one benchmark
  95       // slower (prsa) and doesn't affect the others.
  96       spark = tryStealSpark(cap);
  97       if (spark != NULL) {
  98           cap->sparks_converted++;
  99
 100           // Post event for running a spark from capability's own pool.
 101           traceSchedEvent(cap, EVENT_RUN_SPARK, cap->r.rCurrentTSO, 0);
 102
 103           return spark;
 104       }
 105       if (!emptySparkPoolCap(cap)) {
 106           retry = rtsTrue;
 107       }
 108
 109       if (n_capabilities == 1) { return NULL; } // makes no sense...
 110
 111       debugTrace(DEBUG_sched,
 112                  "cap %d: Trying to steal work from other capabilities",
 113                  cap->no);
 114
 115       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
 116       start at a random place instead of 0 as well.  */
 117       for ( i=0 ; i < n_capabilities ; i++ ) {
 118           robbed = &capabilities[i];
 119           if (cap == robbed)  // ourselves...
 120               continue;
 121
 122           if (emptySparkPoolCap(robbed)) // nothing to steal here
 123               continue;
 124
 125           spark = tryStealSpark(robbed);
 126           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 127               // we conflicted with another thread while trying to steal;
 128               // try again later.
 129               retry = rtsTrue;
 130           }
 131
 132           if (spark != NULL) {
 133               cap->sparks_converted++;
 134
 135               traceSchedEvent(cap, EVENT_STEAL_SPARK,
 136                               cap->r.rCurrentTSO, robbed->no);
 137
 138               return spark;
 139           }
 140           // otherwise: no success, try next one
 141       }
 142   } while (retry);
 143
 144   debugTrace(DEBUG_sched, "No sparks stolen");
 145   return NULL;
 146 }
 147
 148 // Returns True if any spark pool is non-empty at this moment in time
 149 // The result is only valid for an instant, of course, so in a sense
 150 // is immediately invalid, and should not be relied upon for
 151 // correctness.
 152 rtsBool
 153 anySparks (void)
 154 {
 155     nat i;
 156
 157     for (i=0; i < n_capabilities; i++) {
 158         if (!emptySparkPoolCap(&capabilities[i])) {
 159             return rtsTrue;
 160         }
 161     }
 162     return rtsFalse;
 163 }
 164 #endif
 165
 166 /* -----------------------------------------------------------------------------
 167  * Manage the returning_tasks lists.
 168  *
 169  * These functions require cap->lock
 170  * -------------------------------------------------------------------------- */
 171
 172 #if defined(THREADED_RTS)
 173 STATIC_INLINE void
 174 newReturningTask (Capability *cap, Task *task)
 175 {
 176     ASSERT_LOCK_HELD(&cap->lock);
 177     ASSERT(task->return_link == NULL);
 178     if (cap->returning_tasks_hd) {
 179         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 180         cap->returning_tasks_tl->return_link = task;
 181     } else {
 182         cap->returning_tasks_hd = task;
 183     }
 184     cap->returning_tasks_tl = task;
 185 }
 186
 187 STATIC_INLINE Task *
 188 popReturningTask (Capability *cap)
 189 {
 190     ASSERT_LOCK_HELD(&cap->lock);
 191     Task *task;
 192     task = cap->returning_tasks_hd;
 193     ASSERT(task);
 194     cap->returning_tasks_hd = task->return_link;
 195     if (!cap->returning_tasks_hd) {
 196         cap->returning_tasks_tl = NULL;
 197     }
 198     task->return_link = NULL;
 199     return task;
 200 }
 201 #endif
 202
 203 /* ----------------------------------------------------------------------------
 204  * Initialisation
 205  *
 206  * The Capability is initially marked not free.
 207  * ------------------------------------------------------------------------- */
 208
 209 static void
 210 initCapability( Capability *cap, nat i )
 211 {
 212     nat g;
 213
 214     cap->no = i;
 215     cap->in_haskell        = rtsFalse;
 216     cap->in_gc             = rtsFalse;
 217
 218     cap->run_queue_hd      = END_TSO_QUEUE;
 219     cap->run_queue_tl      = END_TSO_QUEUE;
 220
 221 #if defined(THREADED_RTS)
 222     initMutex(&cap->lock);
 223     cap->running_task      = NULL; // indicates cap is free
 224     cap->spare_workers     = NULL;
 225     cap->suspended_ccalling_tasks = NULL;
 226     cap->returning_tasks_hd = NULL;
 227     cap->returning_tasks_tl = NULL;
 228     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 229     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 230     cap->sparks_created     = 0;
 231     cap->sparks_converted   = 0;
 232     cap->sparks_pruned      = 0;
 233 #endif
 234
 235     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 236     cap->f.stgGCEnter1     = (StgFunPtr)__stg_gc_enter_1;
 237     cap->f.stgGCFun        = (StgFunPtr)__stg_gc_fun;
 238
 239     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 240                                      RtsFlags.GcFlags.generations,
 241                                      "initCapability");
 242     cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
 243                                           RtsFlags.GcFlags.generations,
 244                                           "initCapability");
 245
 246     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 247         cap->mut_lists[g] = NULL;
 248     }
 249
 250     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 251     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 252     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 253     cap->free_trec_headers = NO_TREC;
 254     cap->transaction_tokens = 0;
 255     cap->context_switch = 0;
 256 }
 257
 258 /* ---------------------------------------------------------------------------
 259  * Function:  initCapabilities()
 260  *
 261  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 262  *            we keep a table of them, the size of which is
 263  *            controlled by the user via the RTS flag -N.
 264  *
 265  * ------------------------------------------------------------------------- */
 266 void
 267 initCapabilities( void )
 268 {
 269 #if defined(THREADED_RTS)
 270     nat i;
 271
 272 #ifndef REG_Base
 273     // We can't support multiple CPUs if BaseReg is not a register
 274     if (RtsFlags.ParFlags.nNodes > 1) {
 275         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 276         RtsFlags.ParFlags.nNodes = 1;
 277     }
 278 #endif
 279
 280     n_capabilities = RtsFlags.ParFlags.nNodes;
 281
 282     if (n_capabilities == 1) {
 283         capabilities = &MainCapability;
 284         // THREADED_RTS must work on builds that don't have a mutable
 285         // BaseReg (eg. unregisterised), so in this case
 286         // capabilities[0] must coincide with &MainCapability.
 287     } else {
 288         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 289                                       "initCapabilities");
 290     }
 291
 292     for (i = 0; i < n_capabilities; i++) {
 293         initCapability(&capabilities[i], i);
 294     }
 295
 296     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 297
 298 #else /* !THREADED_RTS */
 299
 300     n_capabilities = 1;
 301     capabilities = &MainCapability;
 302     initCapability(&MainCapability, 0);
 303
 304 #endif
 305
 306     // There are no free capabilities to begin with.  We will start
 307     // a worker Task to each Capability, which will quickly put the
 308     // Capability on the free list when it finds nothing to do.
 309     last_free_capability = &capabilities[0];
 310 }
 311
 312 /* ----------------------------------------------------------------------------
 313  * setContextSwitches: cause all capabilities to context switch as
 314  * soon as possible.
 315  * ------------------------------------------------------------------------- */
 316
 317 void setContextSwitches(void)
 318 {
 319     nat i;
 320     for (i=0; i < n_capabilities; i++) {
 321         contextSwitchCapability(&capabilities[i]);
 322     }
 323 }
 324
 325 /* ----------------------------------------------------------------------------
 326  * Give a Capability to a Task.  The task must currently be sleeping
 327  * on its condition variable.
 328  *
 329  * Requires cap->lock (modifies cap->running_task).
 330  *
 331  * When migrating a Task, the migrater must take task->lock before
 332  * modifying task->cap, to synchronise with the waking up Task.
 333  * Additionally, the migrater should own the Capability (when
 334  * migrating the run queue), or cap->lock (when migrating
 335  * returning_workers).
 336  *
 337  * ------------------------------------------------------------------------- */
 338
 339 #if defined(THREADED_RTS)
 340 STATIC_INLINE void
 341 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 342 {
 343     ASSERT_LOCK_HELD(&cap->lock);
 344     ASSERT(task->cap == cap);
 345     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 346                cap->no, task->tso ? "bound task" : "worker",
 347                (void *)task->id);
 348     ACQUIRE_LOCK(&task->lock);
 349     task->wakeup = rtsTrue;
 350     // the wakeup flag is needed because signalCondition() doesn't
 351     // flag the condition if the thread is already runniing, but we want
 352     // it to be sticky.
 353     signalCondition(&task->cond);
 354     RELEASE_LOCK(&task->lock);
 355 }
 356 #endif
 357
 358 /* ----------------------------------------------------------------------------
 359  * Function:  releaseCapability(Capability*)
 360  *
 361  * Purpose:   Letting go of a capability. Causes a
 362  *            'returning worker' thread or a 'waiting worker'
 363  *            to wake up, in that order.
 364  * ------------------------------------------------------------------------- */
 365
 366 #if defined(THREADED_RTS)
 367 void
 368 releaseCapability_ (Capability* cap,
 369                     rtsBool always_wakeup)
 370 {
 371     Task *task;
 372
 373     task = cap->running_task;
 374
 375     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 376
 377     cap->running_task = NULL;
 378
 379     // Check to see whether a worker thread can be given
 380     // the go-ahead to return the result of an external call..
 381     if (cap->returning_tasks_hd != NULL) {
 382         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 383         // The Task pops itself from the queue (see waitForReturnCapability())
 384         return;
 385     }
 386
 387     if (waiting_for_gc == PENDING_GC_SEQ) {
 388       last_free_capability = cap; // needed?
 389       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 390       return;
 391     }
 392
 393
 394     // If the next thread on the run queue is a bound thread,
 395     // give this Capability to the appropriate Task.
 396     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 397         // Make sure we're not about to try to wake ourselves up
 398         ASSERT(task != cap->run_queue_hd->bound);
 399         task = cap->run_queue_hd->bound;
 400         giveCapabilityToTask(cap,task);
 401         return;
 402     }
 403
 404     if (!cap->spare_workers) {
 405         // Create a worker thread if we don't have one.  If the system
 406         // is interrupted, we only create a worker task if there
 407         // are threads that need to be completed.  If the system is
 408         // shutting down, we never create a new worker.
 409         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 410             debugTrace(DEBUG_sched,
 411                        "starting new worker on capability %d", cap->no);
 412             startWorkerTask(cap, workerStart);
 413             return;
 414         }
 415     }
 416
 417     // If we have an unbound thread on the run queue, or if there's
 418     // anything else to do, give the Capability to a worker thread.
 419     if (always_wakeup ||
 420         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 421         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 422         if (cap->spare_workers) {
 423             giveCapabilityToTask(cap,cap->spare_workers);
 424             // The worker Task pops itself from the queue;
 425             return;
 426         }
 427     }
 428
 429     last_free_capability = cap;
 430     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 431 }
 432
 433 void
 434 releaseCapability (Capability* cap USED_IF_THREADS)
 435 {
 436     ACQUIRE_LOCK(&cap->lock);
 437     releaseCapability_(cap, rtsFalse);
 438     RELEASE_LOCK(&cap->lock);
 439 }
 440
 441 void
 442 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 443 {
 444     ACQUIRE_LOCK(&cap->lock);
 445     releaseCapability_(cap, rtsTrue);
 446     RELEASE_LOCK(&cap->lock);
 447 }
 448
 449 static void
 450 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 451 {
 452     Task *task;
 453
 454     ACQUIRE_LOCK(&cap->lock);
 455
 456     task = cap->running_task;
 457
 458     // If the current task is a worker, save it on the spare_workers
 459     // list of this Capability.  A worker can mark itself as stopped,
 460     // in which case it is not replaced on the spare_worker queue.
 461     // This happens when the system is shutting down (see
 462     // Schedule.c:workerStart()).
 463     // Also, be careful to check that this task hasn't just exited
 464     // Haskell to do a foreign call (task->suspended_tso).
 465     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 466         task->next = cap->spare_workers;
 467         cap->spare_workers = task;
 468     }
 469     // Bound tasks just float around attached to their TSOs.
 470
 471     releaseCapability_(cap,rtsFalse);
 472
 473     RELEASE_LOCK(&cap->lock);
 474 }
 475 #endif
 476
 477 /* ----------------------------------------------------------------------------
 478  * waitForReturnCapability( Task *task )
 479  *
 480  * Purpose:  when an OS thread returns from an external call,
 481  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 482  * to wait for permission to enter the RTS & communicate the
 483  * result of the external call back to the Haskell thread that
 484  * made it.
 485  *
 486  * ------------------------------------------------------------------------- */
 487 void
 488 waitForReturnCapability (Capability **pCap, Task *task)
 489 {
 490 #if !defined(THREADED_RTS)
 491
 492     MainCapability.running_task = task;
 493     task->cap = &MainCapability;
 494     *pCap = &MainCapability;
 495
 496 #else
 497     Capability *cap = *pCap;
 498
 499     if (cap == NULL) {
 500         // Try last_free_capability first
 501         cap = last_free_capability;
 502         if (cap->running_task) {
 503             nat i;
 504             // otherwise, search for a free capability
 505             cap = NULL;
 506             for (i = 0; i < n_capabilities; i++) {
 507                 if (!capabilities[i].running_task) {
 508                     cap = &capabilities[i];
 509                     break;
 510                 }
 511             }
 512             if (cap == NULL) {
 513                 // Can't find a free one, use last_free_capability.
 514                 cap = last_free_capability;
 515             }
 516         }
 517
 518         // record the Capability as the one this Task is now assocated with.
 519         task->cap = cap;
 520
 521     } else {
 522         ASSERT(task->cap == cap);
 523     }
 524
 525     ACQUIRE_LOCK(&cap->lock);
 526
 527     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 528
 529     if (!cap->running_task) {
 530         // It's free; just grab it
 531         cap->running_task = task;
 532         RELEASE_LOCK(&cap->lock);
 533     } else {
 534         newReturningTask(cap,task);
 535         RELEASE_LOCK(&cap->lock);
 536
 537         for (;;) {
 538             ACQUIRE_LOCK(&task->lock);
 539             // task->lock held, cap->lock not held
 540             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 541             cap = task->cap;
 542             task->wakeup = rtsFalse;
 543             RELEASE_LOCK(&task->lock);
 544
 545             // now check whether we should wake up...
 546             ACQUIRE_LOCK(&cap->lock);
 547             if (cap->running_task == NULL) {
 548                 if (cap->returning_tasks_hd != task) {
 549                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 550                     RELEASE_LOCK(&cap->lock);
 551                     continue;
 552                 }
 553                 cap->running_task = task;
 554                 popReturningTask(cap);
 555                 RELEASE_LOCK(&cap->lock);
 556                 break;
 557             }
 558             RELEASE_LOCK(&cap->lock);
 559         }
 560
 561     }
 562
 563     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 564
 565     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 566
 567     *pCap = cap;
 568 #endif
 569 }
 570
 571 #if defined(THREADED_RTS)
 572 /* ----------------------------------------------------------------------------
 573  * yieldCapability
 574  * ------------------------------------------------------------------------- */
 575
 576 void
 577 yieldCapability (Capability** pCap, Task *task)
 578 {
 579     Capability *cap = *pCap;
 580
 581     if (waiting_for_gc == PENDING_GC_PAR) {
 582         traceSchedEvent(cap, EVENT_GC_START, 0, 0);
 583         gcWorkerThread(cap);
 584         traceSchedEvent(cap, EVENT_GC_END, 0, 0);
 585         return;
 586     }
 587
 588         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 589
 590         // We must now release the capability and wait to be woken up
 591         // again.
 592         task->wakeup = rtsFalse;
 593         releaseCapabilityAndQueueWorker(cap);
 594
 595         for (;;) {
 596             ACQUIRE_LOCK(&task->lock);
 597             // task->lock held, cap->lock not held
 598             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 599             cap = task->cap;
 600             task->wakeup = rtsFalse;
 601             RELEASE_LOCK(&task->lock);
 602
 603             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 604
 605             ACQUIRE_LOCK(&cap->lock);
 606             if (cap->running_task != NULL) {
 607                 debugTrace(DEBUG_sched,
 608                            "capability %d is owned by another task", cap->no);
 609                 RELEASE_LOCK(&cap->lock);
 610                 continue;
 611             }
 612
 613             if (task->tso == NULL) {
 614                 ASSERT(cap->spare_workers != NULL);
 615                 // if we're not at the front of the queue, release it
 616                 // again.  This is unlikely to happen.
 617                 if (cap->spare_workers != task) {
 618                     giveCapabilityToTask(cap,cap->spare_workers);
 619                     RELEASE_LOCK(&cap->lock);
 620                     continue;
 621                 }
 622                 cap->spare_workers = task->next;
 623                 task->next = NULL;
 624             }
 625             cap->running_task = task;
 626             RELEASE_LOCK(&cap->lock);
 627             break;
 628         }
 629
 630         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 631         ASSERT(cap->running_task == task);
 632
 633     *pCap = cap;
 634
 635     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 636
 637     return;
 638 }
 639
 640 /* ----------------------------------------------------------------------------
 641  * Wake up a thread on a Capability.
 642  *
 643  * This is used when the current Task is running on a Capability and
 644  * wishes to wake up a thread on a different Capability.
 645  * ------------------------------------------------------------------------- */
 646
 647 void
 648 wakeupThreadOnCapability (Capability *my_cap,
 649                           Capability *other_cap,
 650                           StgTSO *tso)
 651 {
 652     ACQUIRE_LOCK(&other_cap->lock);
 653
 654     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 655     if (tso->bound) {
 656         ASSERT(tso->bound->cap == tso->cap);
 657         tso->bound->cap = other_cap;
 658     }
 659     tso->cap = other_cap;
 660
 661     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 662
 663     if (other_cap->running_task == NULL) {
 664         // nobody is running this Capability, we can add our thread
 665         // directly onto the run queue and start up a Task to run it.
 666
 667         other_cap->running_task = myTask();
 668             // precond for releaseCapability_() and appendToRunQueue()
 669
 670         appendToRunQueue(other_cap,tso);
 671
 672         releaseCapability_(other_cap,rtsFalse);
 673     } else {
 674         appendToWakeupQueue(my_cap,other_cap,tso);
 675         other_cap->context_switch = 1;
 676         // someone is running on this Capability, so it cannot be
 677         // freed without first checking the wakeup queue (see
 678         // releaseCapability_).
 679     }
 680
 681     RELEASE_LOCK(&other_cap->lock);
 682 }
 683
 684 /* ----------------------------------------------------------------------------
 685  * prodCapability
 686  *
 687  * If a Capability is currently idle, wake up a Task on it.  Used to
 688  * get every Capability into the GC.
 689  * ------------------------------------------------------------------------- */
 690
 691 void
 692 prodCapability (Capability *cap, Task *task)
 693 {
 694     ACQUIRE_LOCK(&cap->lock);
 695     if (!cap->running_task) {
 696         cap->running_task = task;
 697         releaseCapability_(cap,rtsTrue);
 698     }
 699     RELEASE_LOCK(&cap->lock);
 700 }
 701
 702 /* ----------------------------------------------------------------------------
 703  * shutdownCapability
 704  *
 705  * At shutdown time, we want to let everything exit as cleanly as
 706  * possible.  For each capability, we let its run queue drain, and
 707  * allow the workers to stop.
 708  *
 709  * This function should be called when interrupted and
 710  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 711  * will exit the scheduler and call taskStop(), and any bound thread
 712  * that wakes up will return to its caller.  Runnable threads are
 713  * killed.
 714  *
 715  * ------------------------------------------------------------------------- */
 716
 717 void
 718 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 719 {
 720     nat i;
 721
 722     task->cap = cap;
 723
 724     // Loop indefinitely until all the workers have exited and there
 725     // are no Haskell threads left.  We used to bail out after 50
 726     // iterations of this loop, but that occasionally left a worker
 727     // running which caused problems later (the closeMutex() below
 728     // isn't safe, for one thing).
 729
 730     for (i = 0; /* i < 50 */; i++) {
 731         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 732
 733         debugTrace(DEBUG_sched,
 734                    "shutting down capability %d, attempt %d", cap->no, i);
 735         ACQUIRE_LOCK(&cap->lock);
 736         if (cap->running_task) {
 737             RELEASE_LOCK(&cap->lock);
 738             debugTrace(DEBUG_sched, "not owner, yielding");
 739             yieldThread();
 740             continue;
 741         }
 742         cap->running_task = task;
 743
 744         if (cap->spare_workers) {
 745             // Look for workers that have died without removing
 746             // themselves from the list; this could happen if the OS
 747             // summarily killed the thread, for example.  This
 748             // actually happens on Windows when the system is
 749             // terminating the program, and the RTS is running in a
 750             // DLL.
 751             Task *t, *prev;
 752             prev = NULL;
 753             for (t = cap->spare_workers; t != NULL; t = t->next) {
 754                 if (!osThreadIsAlive(t->id)) {
 755                     debugTrace(DEBUG_sched,
 756                                "worker thread %p has died unexpectedly", (void *)t->id);
 757                         if (!prev) {
 758                             cap->spare_workers = t->next;
 759                         } else {
 760                             prev->next = t->next;
 761                         }
 762                         prev = t;
 763                 }
 764             }
 765         }
 766
 767         if (!emptyRunQueue(cap) || cap->spare_workers) {
 768             debugTrace(DEBUG_sched,
 769                        "runnable threads or workers still alive, yielding");
 770             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 771             RELEASE_LOCK(&cap->lock);
 772             yieldThread();
 773             continue;
 774         }
 775
 776         // If "safe", then busy-wait for any threads currently doing
 777         // foreign calls.  If we're about to unload this DLL, for
 778         // example, we need to be sure that there are no OS threads
 779         // that will try to return to code that has been unloaded.
 780         // We can be a bit more relaxed when this is a standalone
 781         // program that is about to terminate, and let safe=false.
 782         if (cap->suspended_ccalling_tasks && safe) {
 783             debugTrace(DEBUG_sched,
 784                        "thread(s) are involved in foreign calls, yielding");
 785             cap->running_task = NULL;
 786             RELEASE_LOCK(&cap->lock);
 787             yieldThread();
 788             continue;
 789         }
 790
 791         traceSchedEvent(cap, EVENT_SHUTDOWN, 0, 0);
 792         RELEASE_LOCK(&cap->lock);
 793         break;
 794     }
 795     // we now have the Capability, its run queue and spare workers
 796     // list are both empty.
 797
 798     // ToDo: we can't drop this mutex, because there might still be
 799     // threads performing foreign calls that will eventually try to
 800     // return via resumeThread() and attempt to grab cap->lock.
 801     // closeMutex(&cap->lock);
 802 }
 803
 804 /* ----------------------------------------------------------------------------
 805  * tryGrabCapability
 806  *
 807  * Attempt to gain control of a Capability if it is free.
 808  *
 809  * ------------------------------------------------------------------------- */
 810
 811 rtsBool
 812 tryGrabCapability (Capability *cap, Task *task)
 813 {
 814     if (cap->running_task != NULL) return rtsFalse;
 815     ACQUIRE_LOCK(&cap->lock);
 816     if (cap->running_task != NULL) {
 817         RELEASE_LOCK(&cap->lock);
 818         return rtsFalse;
 819     }
 820     task->cap = cap;
 821     cap->running_task = task;
 822     RELEASE_LOCK(&cap->lock);
 823     return rtsTrue;
 824 }
 825
 826
 827 #endif /* THREADED_RTS */
 828
 829 static void
 830 freeCapability (Capability *cap)
 831 {
 832     stgFree(cap->mut_lists);
 833     stgFree(cap->saved_mut_lists);
 834 #if defined(THREADED_RTS)
 835     freeSparkPool(cap->sparks);
 836 #endif
 837 }
 838
 839 void
 840 freeCapabilities (void)
 841 {
 842 #if defined(THREADED_RTS)
 843     nat i;
 844     for (i=0; i < n_capabilities; i++) {
 845         freeCapability(&capabilities[i]);
 846     }
 847 #else
 848     freeCapability(&MainCapability);
 849 #endif
 850 }
 851
 852 /* ---------------------------------------------------------------------------
 853    Mark everything directly reachable from the Capabilities.  When
 854    using multiple GC threads, each GC thread marks all Capabilities
 855    for which (c `mod` n == 0), for Capability c and thread n.
 856    ------------------------------------------------------------------------ */
 857
 858 void
 859 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 860                       rtsBool prune_sparks USED_IF_THREADS)
 861 {
 862     nat i;
 863     Capability *cap;
 864     Task *task;
 865
 866     // Each GC thread is responsible for following roots from the
 867     // Capability of the same number.  There will usually be the same
 868     // or fewer Capabilities as GC threads, but just in case there
 869     // are more, we mark every Capability whose number is the GC
 870     // thread's index plus a multiple of the number of GC threads.
 871     for (i = i0; i < n_capabilities; i += delta) {
 872         cap = &capabilities[i];
 873         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 874         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 875 #if defined(THREADED_RTS)
 876         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 877         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 878 #endif
 879         for (task = cap->suspended_ccalling_tasks; task != NULL;
 880              task=task->next) {
 881             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 882         }
 883
 884 #if defined(THREADED_RTS)
 885         if (prune_sparks) {
 886             pruneSparkQueue (evac, user, cap);
 887         } else {
 888             traverseSparkQueue (evac, user, cap);
 889         }
 890 #endif
 891     }
 892
 893 #if !defined(THREADED_RTS)
 894     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 895     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 896     evac(user, (StgClosure **)(void *)&sleeping_queue);
 897 #endif
 898 }
 899
 900 void
 901 markCapabilities (evac_fn evac, void *user)
 902 {
 903     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 904 }