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 findSpark (Capability *cap)
  59 {
  60   Capability *robbed;
  61   StgClosurePtr spark;
  62   rtsBool retry;
  63   nat i = 0;
  64
  65   if (!emptyRunQueue(cap)) {
  66       // If there are other threads, don't try to run any new
  67       // sparks: sparks might be speculative, we don't want to take
  68       // resources away from the main computation.
  69       return 0;
  70   }
  71
  72   // first try to get a spark from our own pool.
  73   // We should be using reclaimSpark(), because it works without
  74   // needing any atomic instructions:
  75   //   spark = reclaimSpark(cap->sparks);
  76   // However, measurements show that this makes at least one benchmark
  77   // slower (prsa) and doesn't affect the others.
  78   spark = tryStealSpark(cap);
  79   if (spark != NULL) {
  80       cap->sparks_converted++;
  81       return spark;
  82   }
  83
  84   if (n_capabilities == 1) { return NULL; } // makes no sense...
  85
  86   debugTrace(DEBUG_sched,
  87              "cap %d: Trying to steal work from other capabilities",
  88              cap->no);
  89
  90   do {
  91       retry = rtsFalse;
  92
  93       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
  94       start at a random place instead of 0 as well.  */
  95       for ( i=0 ; i < n_capabilities ; i++ ) {
  96           robbed = &capabilities[i];
  97           if (cap == robbed)  // ourselves...
  98               continue;
  99
 100           if (emptySparkPoolCap(robbed)) // nothing to steal here
 101               continue;
 102
 103           spark = tryStealSpark(robbed);
 104           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 105               // we conflicted with another thread while trying to steal;
 106               // try again later.
 107               retry = rtsTrue;
 108           }
 109
 110           if (spark != NULL) {
 111               debugTrace(DEBUG_sched,
 112                  "cap %d: Stole a spark from capability %d",
 113                          cap->no, robbed->no);
 114               cap->sparks_converted++;
 115               return spark;
 116           }
 117           // otherwise: no success, try next one
 118       }
 119   } while (retry);
 120
 121   debugTrace(DEBUG_sched, "No sparks stolen");
 122   return NULL;
 123 }
 124
 125 // Returns True if any spark pool is non-empty at this moment in time
 126 // The result is only valid for an instant, of course, so in a sense
 127 // is immediately invalid, and should not be relied upon for
 128 // correctness.
 129 rtsBool
 130 anySparks (void)
 131 {
 132     nat i;
 133
 134     for (i=0; i < n_capabilities; i++) {
 135         if (!emptySparkPoolCap(&capabilities[i])) {
 136             return rtsTrue;
 137         }
 138     }
 139     return rtsFalse;
 140 }
 141 #endif
 142
 143 /* -----------------------------------------------------------------------------
 144  * Manage the returning_tasks lists.
 145  *
 146  * These functions require cap->lock
 147  * -------------------------------------------------------------------------- */
 148
 149 #if defined(THREADED_RTS)
 150 STATIC_INLINE void
 151 newReturningTask (Capability *cap, Task *task)
 152 {
 153     ASSERT_LOCK_HELD(&cap->lock);
 154     ASSERT(task->return_link == NULL);
 155     if (cap->returning_tasks_hd) {
 156         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 157         cap->returning_tasks_tl->return_link = task;
 158     } else {
 159         cap->returning_tasks_hd = task;
 160     }
 161     cap->returning_tasks_tl = task;
 162 }
 163
 164 STATIC_INLINE Task *
 165 popReturningTask (Capability *cap)
 166 {
 167     ASSERT_LOCK_HELD(&cap->lock);
 168     Task *task;
 169     task = cap->returning_tasks_hd;
 170     ASSERT(task);
 171     cap->returning_tasks_hd = task->return_link;
 172     if (!cap->returning_tasks_hd) {
 173         cap->returning_tasks_tl = NULL;
 174     }
 175     task->return_link = NULL;
 176     return task;
 177 }
 178 #endif
 179
 180 /* ----------------------------------------------------------------------------
 181  * Initialisation
 182  *
 183  * The Capability is initially marked not free.
 184  * ------------------------------------------------------------------------- */
 185
 186 static void
 187 initCapability( Capability *cap, nat i )
 188 {
 189     nat g;
 190
 191     cap->no = i;
 192     cap->in_haskell        = rtsFalse;
 193
 194     cap->run_queue_hd      = END_TSO_QUEUE;
 195     cap->run_queue_tl      = END_TSO_QUEUE;
 196
 197 #if defined(THREADED_RTS)
 198     initMutex(&cap->lock);
 199     cap->running_task      = NULL; // indicates cap is free
 200     cap->spare_workers     = NULL;
 201     cap->suspended_ccalling_tasks = NULL;
 202     cap->returning_tasks_hd = NULL;
 203     cap->returning_tasks_tl = NULL;
 204     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 205     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 206     cap->sparks_created     = 0;
 207     cap->sparks_converted   = 0;
 208     cap->sparks_pruned      = 0;
 209 #endif
 210
 211     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 212     cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
 213     cap->f.stgGCFun        = (F_)__stg_gc_fun;
 214
 215     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 216                                      RtsFlags.GcFlags.generations,
 217                                      "initCapability");
 218
 219     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 220         cap->mut_lists[g] = NULL;
 221     }
 222
 223     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 224     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 225     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 226     cap->free_trec_headers = NO_TREC;
 227     cap->transaction_tokens = 0;
 228     cap->context_switch = 0;
 229 }
 230
 231 /* ---------------------------------------------------------------------------
 232  * Function:  initCapabilities()
 233  *
 234  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 235  *            we keep a table of them, the size of which is
 236  *            controlled by the user via the RTS flag -N.
 237  *
 238  * ------------------------------------------------------------------------- */
 239 void
 240 initCapabilities( void )
 241 {
 242 #if defined(THREADED_RTS)
 243     nat i;
 244
 245 #ifndef REG_Base
 246     // We can't support multiple CPUs if BaseReg is not a register
 247     if (RtsFlags.ParFlags.nNodes > 1) {
 248         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 249         RtsFlags.ParFlags.nNodes = 1;
 250     }
 251 #endif
 252
 253     n_capabilities = RtsFlags.ParFlags.nNodes;
 254
 255     if (n_capabilities == 1) {
 256         capabilities = &MainCapability;
 257         // THREADED_RTS must work on builds that don't have a mutable
 258         // BaseReg (eg. unregisterised), so in this case
 259         // capabilities[0] must coincide with &MainCapability.
 260     } else {
 261         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 262                                       "initCapabilities");
 263     }
 264
 265     for (i = 0; i < n_capabilities; i++) {
 266         initCapability(&capabilities[i], i);
 267     }
 268
 269     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 270
 271 #else /* !THREADED_RTS */
 272
 273     n_capabilities = 1;
 274     capabilities = &MainCapability;
 275     initCapability(&MainCapability, 0);
 276
 277 #endif
 278
 279     // There are no free capabilities to begin with.  We will start
 280     // a worker Task to each Capability, which will quickly put the
 281     // Capability on the free list when it finds nothing to do.
 282     last_free_capability = &capabilities[0];
 283 }
 284
 285 /* ----------------------------------------------------------------------------
 286  * setContextSwitches: cause all capabilities to context switch as
 287  * soon as possible.
 288  * ------------------------------------------------------------------------- */
 289
 290 void setContextSwitches(void)
 291 {
 292   nat i;
 293   for (i=0; i < n_capabilities; i++) {
 294     capabilities[i].context_switch = 1;
 295   }
 296 }
 297
 298 /* ----------------------------------------------------------------------------
 299  * Give a Capability to a Task.  The task must currently be sleeping
 300  * on its condition variable.
 301  *
 302  * Requires cap->lock (modifies cap->running_task).
 303  *
 304  * When migrating a Task, the migrater must take task->lock before
 305  * modifying task->cap, to synchronise with the waking up Task.
 306  * Additionally, the migrater should own the Capability (when
 307  * migrating the run queue), or cap->lock (when migrating
 308  * returning_workers).
 309  *
 310  * ------------------------------------------------------------------------- */
 311
 312 #if defined(THREADED_RTS)
 313 STATIC_INLINE void
 314 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 315 {
 316     ASSERT_LOCK_HELD(&cap->lock);
 317     ASSERT(task->cap == cap);
 318     trace(TRACE_sched | DEBUG_sched,
 319           "passing capability %d to %s %p",
 320           cap->no, task->tso ? "bound task" : "worker",
 321           (void *)task->id);
 322     ACQUIRE_LOCK(&task->lock);
 323     task->wakeup = rtsTrue;
 324     // the wakeup flag is needed because signalCondition() doesn't
 325     // flag the condition if the thread is already runniing, but we want
 326     // it to be sticky.
 327     signalCondition(&task->cond);
 328     RELEASE_LOCK(&task->lock);
 329 }
 330 #endif
 331
 332 /* ----------------------------------------------------------------------------
 333  * Function:  releaseCapability(Capability*)
 334  *
 335  * Purpose:   Letting go of a capability. Causes a
 336  *            'returning worker' thread or a 'waiting worker'
 337  *            to wake up, in that order.
 338  * ------------------------------------------------------------------------- */
 339
 340 #if defined(THREADED_RTS)
 341 void
 342 releaseCapability_ (Capability* cap,
 343                     rtsBool always_wakeup)
 344 {
 345     Task *task;
 346
 347     task = cap->running_task;
 348
 349     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 350
 351     cap->running_task = NULL;
 352
 353     // Check to see whether a worker thread can be given
 354     // the go-ahead to return the result of an external call..
 355     if (cap->returning_tasks_hd != NULL) {
 356         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 357         // The Task pops itself from the queue (see waitForReturnCapability())
 358         return;
 359     }
 360
 361     /* if waiting_for_gc was the reason to release the cap: thread
 362        comes from yieldCap->releaseAndQueueWorker. Unconditionally set
 363        cap. free and return (see default after the if-protected other
 364        special cases). Thread will wait on cond.var and re-acquire the
 365        same cap after GC (GC-triggering cap. calls releaseCap and
 366        enters the spare_workers case)
 367     */
 368     if (waiting_for_gc) {
 369       last_free_capability = cap; // needed?
 370       trace(TRACE_sched | DEBUG_sched,
 371             "GC pending, set capability %d free", cap->no);
 372       return;
 373     }
 374
 375
 376     // If the next thread on the run queue is a bound thread,
 377     // give this Capability to the appropriate Task.
 378     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 379         // Make sure we're not about to try to wake ourselves up
 380         ASSERT(task != cap->run_queue_hd->bound);
 381         task = cap->run_queue_hd->bound;
 382         giveCapabilityToTask(cap,task);
 383         return;
 384     }
 385
 386     if (!cap->spare_workers) {
 387         // Create a worker thread if we don't have one.  If the system
 388         // is interrupted, we only create a worker task if there
 389         // are threads that need to be completed.  If the system is
 390         // shutting down, we never create a new worker.
 391         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 392             debugTrace(DEBUG_sched,
 393                        "starting new worker on capability %d", cap->no);
 394             startWorkerTask(cap, workerStart);
 395             return;
 396         }
 397     }
 398
 399     // If we have an unbound thread on the run queue, or if there's
 400     // anything else to do, give the Capability to a worker thread.
 401     if (always_wakeup ||
 402         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 403         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 404         if (cap->spare_workers) {
 405             giveCapabilityToTask(cap,cap->spare_workers);
 406             // The worker Task pops itself from the queue;
 407             return;
 408         }
 409     }
 410
 411     last_free_capability = cap;
 412     trace(TRACE_sched | DEBUG_sched, "freeing capability %d", cap->no);
 413 }
 414
 415 void
 416 releaseCapability (Capability* cap USED_IF_THREADS)
 417 {
 418     ACQUIRE_LOCK(&cap->lock);
 419     releaseCapability_(cap, rtsFalse);
 420     RELEASE_LOCK(&cap->lock);
 421 }
 422
 423 void
 424 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 425 {
 426     ACQUIRE_LOCK(&cap->lock);
 427     releaseCapability_(cap, rtsTrue);
 428     RELEASE_LOCK(&cap->lock);
 429 }
 430
 431 static void
 432 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 433 {
 434     Task *task;
 435
 436     ACQUIRE_LOCK(&cap->lock);
 437
 438     task = cap->running_task;
 439
 440     // If the current task is a worker, save it on the spare_workers
 441     // list of this Capability.  A worker can mark itself as stopped,
 442     // in which case it is not replaced on the spare_worker queue.
 443     // This happens when the system is shutting down (see
 444     // Schedule.c:workerStart()).
 445     // Also, be careful to check that this task hasn't just exited
 446     // Haskell to do a foreign call (task->suspended_tso).
 447     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 448         task->next = cap->spare_workers;
 449         cap->spare_workers = task;
 450     }
 451     // Bound tasks just float around attached to their TSOs.
 452
 453     releaseCapability_(cap,rtsFalse);
 454
 455     RELEASE_LOCK(&cap->lock);
 456 }
 457 #endif
 458
 459 /* ----------------------------------------------------------------------------
 460  * waitForReturnCapability( Task *task )
 461  *
 462  * Purpose:  when an OS thread returns from an external call,
 463  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 464  * to wait for permission to enter the RTS & communicate the
 465  * result of the external call back to the Haskell thread that
 466  * made it.
 467  *
 468  * ------------------------------------------------------------------------- */
 469 void
 470 waitForReturnCapability (Capability **pCap, Task *task)
 471 {
 472 #if !defined(THREADED_RTS)
 473
 474     MainCapability.running_task = task;
 475     task->cap = &MainCapability;
 476     *pCap = &MainCapability;
 477
 478 #else
 479     Capability *cap = *pCap;
 480
 481     if (cap == NULL) {
 482         // Try last_free_capability first
 483         cap = last_free_capability;
 484         if (!cap->running_task) {
 485             nat i;
 486             // otherwise, search for a free capability
 487             for (i = 0; i < n_capabilities; i++) {
 488                 cap = &capabilities[i];
 489                 if (!cap->running_task) {
 490                     break;
 491                 }
 492             }
 493             // Can't find a free one, use last_free_capability.
 494             cap = last_free_capability;
 495         }
 496
 497         // record the Capability as the one this Task is now assocated with.
 498         task->cap = cap;
 499
 500     } else {
 501         ASSERT(task->cap == cap);
 502     }
 503
 504     ACQUIRE_LOCK(&cap->lock);
 505
 506     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 507
 508     if (!cap->running_task) {
 509         // It's free; just grab it
 510         cap->running_task = task;
 511         RELEASE_LOCK(&cap->lock);
 512     } else {
 513         newReturningTask(cap,task);
 514         RELEASE_LOCK(&cap->lock);
 515
 516         for (;;) {
 517             ACQUIRE_LOCK(&task->lock);
 518             // task->lock held, cap->lock not held
 519             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 520             cap = task->cap;
 521             task->wakeup = rtsFalse;
 522             RELEASE_LOCK(&task->lock);
 523
 524             // now check whether we should wake up...
 525             ACQUIRE_LOCK(&cap->lock);
 526             if (cap->running_task == NULL) {
 527                 if (cap->returning_tasks_hd != task) {
 528                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 529                     RELEASE_LOCK(&cap->lock);
 530                     continue;
 531                 }
 532                 cap->running_task = task;
 533                 popReturningTask(cap);
 534                 RELEASE_LOCK(&cap->lock);
 535                 break;
 536             }
 537             RELEASE_LOCK(&cap->lock);
 538         }
 539
 540     }
 541
 542     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 543
 544     trace(TRACE_sched | DEBUG_sched, "resuming capability %d", cap->no);
 545
 546     *pCap = cap;
 547 #endif
 548 }
 549
 550 #if defined(THREADED_RTS)
 551 /* ----------------------------------------------------------------------------
 552  * yieldCapability
 553  * ------------------------------------------------------------------------- */
 554
 555 void
 556 yieldCapability (Capability** pCap, Task *task)
 557 {
 558     Capability *cap = *pCap;
 559
 560         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 561
 562         // We must now release the capability and wait to be woken up
 563         // again.
 564         task->wakeup = rtsFalse;
 565         releaseCapabilityAndQueueWorker(cap);
 566
 567         for (;;) {
 568             ACQUIRE_LOCK(&task->lock);
 569             // task->lock held, cap->lock not held
 570             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 571             cap = task->cap;
 572             task->wakeup = rtsFalse;
 573             RELEASE_LOCK(&task->lock);
 574
 575             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 576
 577             ACQUIRE_LOCK(&cap->lock);
 578             if (cap->running_task != NULL) {
 579                 debugTrace(DEBUG_sched,
 580                            "capability %d is owned by another task", cap->no);
 581                 RELEASE_LOCK(&cap->lock);
 582                 continue;
 583             }
 584
 585             if (task->tso == NULL) {
 586                 ASSERT(cap->spare_workers != NULL);
 587                 // if we're not at the front of the queue, release it
 588                 // again.  This is unlikely to happen.
 589                 if (cap->spare_workers != task) {
 590                     giveCapabilityToTask(cap,cap->spare_workers);
 591                     RELEASE_LOCK(&cap->lock);
 592                     continue;
 593                 }
 594                 cap->spare_workers = task->next;
 595                 task->next = NULL;
 596             }
 597             cap->running_task = task;
 598             RELEASE_LOCK(&cap->lock);
 599             break;
 600         }
 601
 602         trace(TRACE_sched | DEBUG_sched, "resuming capability %d", cap->no);
 603         ASSERT(cap->running_task == task);
 604
 605     *pCap = cap;
 606
 607     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 608
 609     return;
 610 }
 611
 612 /* ----------------------------------------------------------------------------
 613  * Wake up a thread on a Capability.
 614  *
 615  * This is used when the current Task is running on a Capability and
 616  * wishes to wake up a thread on a different Capability.
 617  * ------------------------------------------------------------------------- */
 618
 619 void
 620 wakeupThreadOnCapability (Capability *my_cap,
 621                           Capability *other_cap,
 622                           StgTSO *tso)
 623 {
 624     ACQUIRE_LOCK(&other_cap->lock);
 625
 626     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 627     if (tso->bound) {
 628         ASSERT(tso->bound->cap == tso->cap);
 629         tso->bound->cap = other_cap;
 630     }
 631     tso->cap = other_cap;
 632
 633     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 634
 635     if (other_cap->running_task == NULL) {
 636         // nobody is running this Capability, we can add our thread
 637         // directly onto the run queue and start up a Task to run it.
 638
 639         other_cap->running_task = myTask();
 640             // precond for releaseCapability_() and appendToRunQueue()
 641
 642         appendToRunQueue(other_cap,tso);
 643
 644         trace(TRACE_sched, "resuming capability %d", other_cap->no);
 645         releaseCapability_(other_cap,rtsFalse);
 646     } else {
 647         appendToWakeupQueue(my_cap,other_cap,tso);
 648         other_cap->context_switch = 1;
 649         // someone is running on this Capability, so it cannot be
 650         // freed without first checking the wakeup queue (see
 651         // releaseCapability_).
 652     }
 653
 654     RELEASE_LOCK(&other_cap->lock);
 655 }
 656
 657 /* ----------------------------------------------------------------------------
 658  * prodCapabilities
 659  *
 660  * Used to indicate that the interrupted flag is now set, or some
 661  * other global condition that might require waking up a Task on each
 662  * Capability.
 663  * ------------------------------------------------------------------------- */
 664
 665 static void
 666 prodCapabilities(rtsBool all)
 667 {
 668     nat i;
 669     Capability *cap;
 670     Task *task;
 671
 672     for (i=0; i < n_capabilities; i++) {
 673         cap = &capabilities[i];
 674         ACQUIRE_LOCK(&cap->lock);
 675         if (!cap->running_task) {
 676             if (cap->spare_workers) {
 677                 trace(TRACE_sched, "resuming capability %d", cap->no);
 678                 task = cap->spare_workers;
 679                 ASSERT(!task->stopped);
 680                 giveCapabilityToTask(cap,task);
 681                 if (!all) {
 682                     RELEASE_LOCK(&cap->lock);
 683                     return;
 684                 }
 685             }
 686         }
 687         RELEASE_LOCK(&cap->lock);
 688     }
 689     return;
 690 }
 691
 692 void
 693 prodAllCapabilities (void)
 694 {
 695     prodCapabilities(rtsTrue);
 696 }
 697
 698 /* ----------------------------------------------------------------------------
 699  * prodOneCapability
 700  *
 701  * Like prodAllCapabilities, but we only require a single Task to wake
 702  * up in order to service some global event, such as checking for
 703  * deadlock after some idle time has passed.
 704  * ------------------------------------------------------------------------- */
 705
 706 void
 707 prodOneCapability (void)
 708 {
 709     prodCapabilities(rtsFalse);
 710 }
 711
 712 /* ----------------------------------------------------------------------------
 713  * shutdownCapability
 714  *
 715  * At shutdown time, we want to let everything exit as cleanly as
 716  * possible.  For each capability, we let its run queue drain, and
 717  * allow the workers to stop.
 718  *
 719  * This function should be called when interrupted and
 720  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 721  * will exit the scheduler and call taskStop(), and any bound thread
 722  * that wakes up will return to its caller.  Runnable threads are
 723  * killed.
 724  *
 725  * ------------------------------------------------------------------------- */
 726
 727 void
 728 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 729 {
 730     nat i;
 731
 732     task->cap = cap;
 733
 734     // Loop indefinitely until all the workers have exited and there
 735     // are no Haskell threads left.  We used to bail out after 50
 736     // iterations of this loop, but that occasionally left a worker
 737     // running which caused problems later (the closeMutex() below
 738     // isn't safe, for one thing).
 739
 740     for (i = 0; /* i < 50 */; i++) {
 741         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 742
 743         debugTrace(DEBUG_sched,
 744                    "shutting down capability %d, attempt %d", cap->no, i);
 745         ACQUIRE_LOCK(&cap->lock);
 746         if (cap->running_task) {
 747             RELEASE_LOCK(&cap->lock);
 748             debugTrace(DEBUG_sched, "not owner, yielding");
 749             yieldThread();
 750             continue;
 751         }
 752         cap->running_task = task;
 753
 754         if (cap->spare_workers) {
 755             // Look for workers that have died without removing
 756             // themselves from the list; this could happen if the OS
 757             // summarily killed the thread, for example.  This
 758             // actually happens on Windows when the system is
 759             // terminating the program, and the RTS is running in a
 760             // DLL.
 761             Task *t, *prev;
 762             prev = NULL;
 763             for (t = cap->spare_workers; t != NULL; t = t->next) {
 764                 if (!osThreadIsAlive(t->id)) {
 765                     debugTrace(DEBUG_sched,
 766                                "worker thread %p has died unexpectedly", (void *)t->id);
 767                         if (!prev) {
 768                             cap->spare_workers = t->next;
 769                         } else {
 770                             prev->next = t->next;
 771                         }
 772                         prev = t;
 773                 }
 774             }
 775         }
 776
 777         if (!emptyRunQueue(cap) || cap->spare_workers) {
 778             debugTrace(DEBUG_sched,
 779                        "runnable threads or workers still alive, yielding");
 780             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 781             RELEASE_LOCK(&cap->lock);
 782             yieldThread();
 783             continue;
 784         }
 785
 786         // If "safe", then busy-wait for any threads currently doing
 787         // foreign calls.  If we're about to unload this DLL, for
 788         // example, we need to be sure that there are no OS threads
 789         // that will try to return to code that has been unloaded.
 790         // We can be a bit more relaxed when this is a standalone
 791         // program that is about to terminate, and let safe=false.
 792         if (cap->suspended_ccalling_tasks && safe) {
 793             debugTrace(DEBUG_sched,
 794                        "thread(s) are involved in foreign calls, yielding");
 795             cap->running_task = NULL;
 796             RELEASE_LOCK(&cap->lock);
 797             yieldThread();
 798             continue;
 799         }
 800
 801         debugTrace(DEBUG_sched, "capability %d is stopped.", cap->no);
 802         RELEASE_LOCK(&cap->lock);
 803         break;
 804     }
 805     // we now have the Capability, its run queue and spare workers
 806     // list are both empty.
 807
 808     // ToDo: we can't drop this mutex, because there might still be
 809     // threads performing foreign calls that will eventually try to
 810     // return via resumeThread() and attempt to grab cap->lock.
 811     // closeMutex(&cap->lock);
 812 }
 813
 814 /* ----------------------------------------------------------------------------
 815  * tryGrabCapability
 816  *
 817  * Attempt to gain control of a Capability if it is free.
 818  *
 819  * ------------------------------------------------------------------------- */
 820
 821 rtsBool
 822 tryGrabCapability (Capability *cap, Task *task)
 823 {
 824     if (cap->running_task != NULL) return rtsFalse;
 825     ACQUIRE_LOCK(&cap->lock);
 826     if (cap->running_task != NULL) {
 827         RELEASE_LOCK(&cap->lock);
 828         return rtsFalse;
 829     }
 830     task->cap = cap;
 831     cap->running_task = task;
 832     RELEASE_LOCK(&cap->lock);
 833     return rtsTrue;
 834 }
 835
 836
 837 #endif /* THREADED_RTS */
 838
 839 static void
 840 freeCapability (Capability *cap)
 841 {
 842     stgFree(cap->mut_lists);
 843 #if defined(THREADED_RTS) || defined(PARALLEL_HASKELL)
 844     freeSparkPool(cap->sparks);
 845 #endif
 846 }
 847
 848 void
 849 freeCapabilities (void)
 850 {
 851 #if defined(THREADED_RTS)
 852     nat i;
 853     for (i=0; i < n_capabilities; i++) {
 854         freeCapability(&capabilities[i]);
 855     }
 856 #else
 857     freeCapability(&MainCapability);
 858 #endif
 859 }
 860
 861 /* ---------------------------------------------------------------------------
 862    Mark everything directly reachable from the Capabilities.  When
 863    using multiple GC threads, each GC thread marks all Capabilities
 864    for which (c `mod` n == 0), for Capability c and thread n.
 865    ------------------------------------------------------------------------ */
 866
 867 void
 868 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 869                       rtsBool prune_sparks USED_IF_THREADS)
 870 {
 871     nat i;
 872     Capability *cap;
 873     Task *task;
 874
 875     // Each GC thread is responsible for following roots from the
 876     // Capability of the same number.  There will usually be the same
 877     // or fewer Capabilities as GC threads, but just in case there
 878     // are more, we mark every Capability whose number is the GC
 879     // thread's index plus a multiple of the number of GC threads.
 880     for (i = i0; i < n_capabilities; i += delta) {
 881         cap = &capabilities[i];
 882         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 883         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 884 #if defined(THREADED_RTS)
 885         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 886         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 887 #endif
 888         for (task = cap->suspended_ccalling_tasks; task != NULL;
 889              task=task->next) {
 890             debugTrace(DEBUG_sched,
 891                        "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
 892             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 893         }
 894
 895 #if defined(THREADED_RTS)
 896         if (prune_sparks) {
 897             pruneSparkQueue (evac, user, cap);
 898         } else {
 899             traverseSparkQueue (evac, user, cap);
 900         }
 901 #endif
 902     }
 903
 904 #if !defined(THREADED_RTS)
 905     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 906     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 907     evac(user, (StgClosure **)(void *)&sleeping_queue);
 908 #endif
 909 }
 910
 911 void
 912 markCapabilities (evac_fn evac, void *user)
 913 {
 914     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 915 }