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 #include "GC.h"
  30
  31 // one global capability, this is the Capability for non-threaded
  32 // builds, and for +RTS -N1
  33 Capability MainCapability;
  34
  35 nat n_capabilities;
  36 Capability *capabilities = NULL;
  37
  38 // Holds the Capability which last became free.  This is used so that
  39 // an in-call has a chance of quickly finding a free Capability.
  40 // Maintaining a global free list of Capabilities would require global
  41 // locking, so we don't do that.
  42 Capability *last_free_capability;
  43
  44 /* GC indicator, in scope for the scheduler, init'ed to false */
  45 volatile StgWord waiting_for_gc = 0;
  46
  47 /* Let foreign code get the current Capability -- assuming there is one!
  48  * This is useful for unsafe foreign calls because they are called with
  49  * the current Capability held, but they are not passed it. For example,
  50  * see see the integer-gmp package which calls allocateLocal() in its
  51  * stgAllocForGMP() function (which gets called by gmp functions).
  52  * */
  53 Capability * rts_unsafeGetMyCapability (void)
  54 {
  55 #if defined(THREADED_RTS)
  56   return myTask()->cap;
  57 #else
  58   return &MainCapability;
  59 #endif
  60 }
  61
  62 #if defined(THREADED_RTS)
  63 STATIC_INLINE rtsBool
  64 globalWorkToDo (void)
  65 {
  66     return blackholes_need_checking
  67         || sched_state >= SCHED_INTERRUPTING
  68         ;
  69 }
  70 #endif
  71
  72 #if defined(THREADED_RTS)
  73 StgClosure *
  74 findSpark (Capability *cap)
  75 {
  76   Capability *robbed;
  77   StgClosurePtr spark;
  78   rtsBool retry;
  79   nat i = 0;
  80
  81   if (!emptyRunQueue(cap)) {
  82       // If there are other threads, don't try to run any new
  83       // sparks: sparks might be speculative, we don't want to take
  84       // resources away from the main computation.
  85       return 0;
  86   }
  87
  88   // first try to get a spark from our own pool.
  89   // We should be using reclaimSpark(), because it works without
  90   // needing any atomic instructions:
  91   //   spark = reclaimSpark(cap->sparks);
  92   // However, measurements show that this makes at least one benchmark
  93   // slower (prsa) and doesn't affect the others.
  94   spark = tryStealSpark(cap);
  95   if (spark != NULL) {
  96       cap->sparks_converted++;
  97
  98       // Post event for running a spark from capability's own pool.
  99       postEvent(cap, EVENT_RUN_SPARK, cap->r.rCurrentTSO->id, 0);
 100
 101       return spark;
 102   }
 103
 104   if (n_capabilities == 1) { return NULL; } // makes no sense...
 105
 106   debugTrace(DEBUG_sched,
 107              "cap %d: Trying to steal work from other capabilities",
 108              cap->no);
 109
 110   do {
 111       retry = rtsFalse;
 112
 113       /* visit cap.s 0..n-1 in sequence until a theft succeeds. We could
 114       start at a random place instead of 0 as well.  */
 115       for ( i=0 ; i < n_capabilities ; i++ ) {
 116           robbed = &capabilities[i];
 117           if (cap == robbed)  // ourselves...
 118               continue;
 119
 120           if (emptySparkPoolCap(robbed)) // nothing to steal here
 121               continue;
 122
 123           spark = tryStealSpark(robbed);
 124           if (spark == NULL && !emptySparkPoolCap(robbed)) {
 125               // we conflicted with another thread while trying to steal;
 126               // try again later.
 127               retry = rtsTrue;
 128           }
 129
 130           if (spark != NULL) {
 131               debugTrace(DEBUG_sched,
 132                  "cap %d: Stole a spark from capability %d",
 133                          cap->no, robbed->no);
 134               cap->sparks_converted++;
 135
 136               postEvent(cap, EVENT_STEAL_SPARK,
 137                         cap->r.rCurrentTSO->id, robbed->no);
 138
 139
 140               return spark;
 141           }
 142           // otherwise: no success, try next one
 143       }
 144   } while (retry);
 145
 146   debugTrace(DEBUG_sched, "No sparks stolen");
 147   return NULL;
 148 }
 149
 150 // Returns True if any spark pool is non-empty at this moment in time
 151 // The result is only valid for an instant, of course, so in a sense
 152 // is immediately invalid, and should not be relied upon for
 153 // correctness.
 154 rtsBool
 155 anySparks (void)
 156 {
 157     nat i;
 158
 159     for (i=0; i < n_capabilities; i++) {
 160         if (!emptySparkPoolCap(&capabilities[i])) {
 161             return rtsTrue;
 162         }
 163     }
 164     return rtsFalse;
 165 }
 166 #endif
 167
 168 /* -----------------------------------------------------------------------------
 169  * Manage the returning_tasks lists.
 170  *
 171  * These functions require cap->lock
 172  * -------------------------------------------------------------------------- */
 173
 174 #if defined(THREADED_RTS)
 175 STATIC_INLINE void
 176 newReturningTask (Capability *cap, Task *task)
 177 {
 178     ASSERT_LOCK_HELD(&cap->lock);
 179     ASSERT(task->return_link == NULL);
 180     if (cap->returning_tasks_hd) {
 181         ASSERT(cap->returning_tasks_tl->return_link == NULL);
 182         cap->returning_tasks_tl->return_link = task;
 183     } else {
 184         cap->returning_tasks_hd = task;
 185     }
 186     cap->returning_tasks_tl = task;
 187 }
 188
 189 STATIC_INLINE Task *
 190 popReturningTask (Capability *cap)
 191 {
 192     ASSERT_LOCK_HELD(&cap->lock);
 193     Task *task;
 194     task = cap->returning_tasks_hd;
 195     ASSERT(task);
 196     cap->returning_tasks_hd = task->return_link;
 197     if (!cap->returning_tasks_hd) {
 198         cap->returning_tasks_tl = NULL;
 199     }
 200     task->return_link = NULL;
 201     return task;
 202 }
 203 #endif
 204
 205 /* ----------------------------------------------------------------------------
 206  * Initialisation
 207  *
 208  * The Capability is initially marked not free.
 209  * ------------------------------------------------------------------------- */
 210
 211 static void
 212 initCapability( Capability *cap, nat i )
 213 {
 214     nat g;
 215
 216     cap->no = i;
 217     cap->in_haskell        = rtsFalse;
 218     cap->in_gc             = rtsFalse;
 219
 220     cap->run_queue_hd      = END_TSO_QUEUE;
 221     cap->run_queue_tl      = END_TSO_QUEUE;
 222
 223 #if defined(THREADED_RTS)
 224     initMutex(&cap->lock);
 225     cap->running_task      = NULL; // indicates cap is free
 226     cap->spare_workers     = NULL;
 227     cap->suspended_ccalling_tasks = NULL;
 228     cap->returning_tasks_hd = NULL;
 229     cap->returning_tasks_tl = NULL;
 230     cap->wakeup_queue_hd    = END_TSO_QUEUE;
 231     cap->wakeup_queue_tl    = END_TSO_QUEUE;
 232     cap->sparks_created     = 0;
 233     cap->sparks_converted   = 0;
 234     cap->sparks_pruned      = 0;
 235 #endif
 236
 237     cap->f.stgEagerBlackholeInfo = (W_)&__stg_EAGER_BLACKHOLE_info;
 238     cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
 239     cap->f.stgGCFun        = (F_)__stg_gc_fun;
 240
 241     cap->mut_lists  = stgMallocBytes(sizeof(bdescr *) *
 242                                      RtsFlags.GcFlags.generations,
 243                                      "initCapability");
 244     cap->saved_mut_lists = stgMallocBytes(sizeof(bdescr *) *
 245                                           RtsFlags.GcFlags.generations,
 246                                           "initCapability");
 247
 248     for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
 249         cap->mut_lists[g] = NULL;
 250     }
 251
 252     cap->free_tvar_watch_queues = END_STM_WATCH_QUEUE;
 253     cap->free_invariant_check_queues = END_INVARIANT_CHECK_QUEUE;
 254     cap->free_trec_chunks = END_STM_CHUNK_LIST;
 255     cap->free_trec_headers = NO_TREC;
 256     cap->transaction_tokens = 0;
 257     cap->context_switch = 0;
 258 }
 259
 260 /* ---------------------------------------------------------------------------
 261  * Function:  initCapabilities()
 262  *
 263  * Purpose:   set up the Capability handling. For the THREADED_RTS build,
 264  *            we keep a table of them, the size of which is
 265  *            controlled by the user via the RTS flag -N.
 266  *
 267  * ------------------------------------------------------------------------- */
 268 void
 269 initCapabilities( void )
 270 {
 271 #if defined(THREADED_RTS)
 272     nat i;
 273
 274 #ifndef REG_Base
 275     // We can't support multiple CPUs if BaseReg is not a register
 276     if (RtsFlags.ParFlags.nNodes > 1) {
 277         errorBelch("warning: multiple CPUs not supported in this build, reverting to 1");
 278         RtsFlags.ParFlags.nNodes = 1;
 279     }
 280 #endif
 281
 282     n_capabilities = RtsFlags.ParFlags.nNodes;
 283
 284     if (n_capabilities == 1) {
 285         capabilities = &MainCapability;
 286         // THREADED_RTS must work on builds that don't have a mutable
 287         // BaseReg (eg. unregisterised), so in this case
 288         // capabilities[0] must coincide with &MainCapability.
 289     } else {
 290         capabilities = stgMallocBytes(n_capabilities * sizeof(Capability),
 291                                       "initCapabilities");
 292     }
 293
 294     for (i = 0; i < n_capabilities; i++) {
 295         initCapability(&capabilities[i], i);
 296     }
 297
 298     debugTrace(DEBUG_sched, "allocated %d capabilities", n_capabilities);
 299
 300 #else /* !THREADED_RTS */
 301
 302     n_capabilities = 1;
 303     capabilities = &MainCapability;
 304     initCapability(&MainCapability, 0);
 305
 306 #endif
 307
 308     // There are no free capabilities to begin with.  We will start
 309     // a worker Task to each Capability, which will quickly put the
 310     // Capability on the free list when it finds nothing to do.
 311     last_free_capability = &capabilities[0];
 312 }
 313
 314 /* ----------------------------------------------------------------------------
 315  * setContextSwitches: cause all capabilities to context switch as
 316  * soon as possible.
 317  * ------------------------------------------------------------------------- */
 318
 319 void setContextSwitches(void)
 320 {
 321     nat i;
 322     for (i=0; i < n_capabilities; i++) {
 323         contextSwitchCapability(&capabilities[i]);
 324     }
 325 }
 326
 327 /* ----------------------------------------------------------------------------
 328  * Give a Capability to a Task.  The task must currently be sleeping
 329  * on its condition variable.
 330  *
 331  * Requires cap->lock (modifies cap->running_task).
 332  *
 333  * When migrating a Task, the migrater must take task->lock before
 334  * modifying task->cap, to synchronise with the waking up Task.
 335  * Additionally, the migrater should own the Capability (when
 336  * migrating the run queue), or cap->lock (when migrating
 337  * returning_workers).
 338  *
 339  * ------------------------------------------------------------------------- */
 340
 341 #if defined(THREADED_RTS)
 342 STATIC_INLINE void
 343 giveCapabilityToTask (Capability *cap USED_IF_DEBUG, Task *task)
 344 {
 345     ASSERT_LOCK_HELD(&cap->lock);
 346     ASSERT(task->cap == cap);
 347     debugTrace(DEBUG_sched, "passing capability %d to %s %p",
 348                cap->no, task->tso ? "bound task" : "worker",
 349                (void *)task->id);
 350     ACQUIRE_LOCK(&task->lock);
 351     task->wakeup = rtsTrue;
 352     // the wakeup flag is needed because signalCondition() doesn't
 353     // flag the condition if the thread is already runniing, but we want
 354     // it to be sticky.
 355     signalCondition(&task->cond);
 356     RELEASE_LOCK(&task->lock);
 357 }
 358 #endif
 359
 360 /* ----------------------------------------------------------------------------
 361  * Function:  releaseCapability(Capability*)
 362  *
 363  * Purpose:   Letting go of a capability. Causes a
 364  *            'returning worker' thread or a 'waiting worker'
 365  *            to wake up, in that order.
 366  * ------------------------------------------------------------------------- */
 367
 368 #if defined(THREADED_RTS)
 369 void
 370 releaseCapability_ (Capability* cap,
 371                     rtsBool always_wakeup)
 372 {
 373     Task *task;
 374
 375     task = cap->running_task;
 376
 377     ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task);
 378
 379     cap->running_task = NULL;
 380
 381     // Check to see whether a worker thread can be given
 382     // the go-ahead to return the result of an external call..
 383     if (cap->returning_tasks_hd != NULL) {
 384         giveCapabilityToTask(cap,cap->returning_tasks_hd);
 385         // The Task pops itself from the queue (see waitForReturnCapability())
 386         return;
 387     }
 388
 389     if (waiting_for_gc == PENDING_GC_SEQ) {
 390       last_free_capability = cap; // needed?
 391       debugTrace(DEBUG_sched, "GC pending, set capability %d free", cap->no);
 392       return;
 393     }
 394
 395
 396     // If the next thread on the run queue is a bound thread,
 397     // give this Capability to the appropriate Task.
 398     if (!emptyRunQueue(cap) && cap->run_queue_hd->bound) {
 399         // Make sure we're not about to try to wake ourselves up
 400         ASSERT(task != cap->run_queue_hd->bound);
 401         task = cap->run_queue_hd->bound;
 402         giveCapabilityToTask(cap,task);
 403         return;
 404     }
 405
 406     if (!cap->spare_workers) {
 407         // Create a worker thread if we don't have one.  If the system
 408         // is interrupted, we only create a worker task if there
 409         // are threads that need to be completed.  If the system is
 410         // shutting down, we never create a new worker.
 411         if (sched_state < SCHED_SHUTTING_DOWN || !emptyRunQueue(cap)) {
 412             debugTrace(DEBUG_sched,
 413                        "starting new worker on capability %d", cap->no);
 414             startWorkerTask(cap, workerStart);
 415             return;
 416         }
 417     }
 418
 419     // If we have an unbound thread on the run queue, or if there's
 420     // anything else to do, give the Capability to a worker thread.
 421     if (always_wakeup ||
 422         !emptyRunQueue(cap) || !emptyWakeupQueue(cap) ||
 423         !emptySparkPoolCap(cap) || globalWorkToDo()) {
 424         if (cap->spare_workers) {
 425             giveCapabilityToTask(cap,cap->spare_workers);
 426             // The worker Task pops itself from the queue;
 427             return;
 428         }
 429     }
 430
 431     last_free_capability = cap;
 432     debugTrace(DEBUG_sched, "freeing capability %d", cap->no);
 433 }
 434
 435 void
 436 releaseCapability (Capability* cap USED_IF_THREADS)
 437 {
 438     ACQUIRE_LOCK(&cap->lock);
 439     releaseCapability_(cap, rtsFalse);
 440     RELEASE_LOCK(&cap->lock);
 441 }
 442
 443 void
 444 releaseAndWakeupCapability (Capability* cap USED_IF_THREADS)
 445 {
 446     ACQUIRE_LOCK(&cap->lock);
 447     releaseCapability_(cap, rtsTrue);
 448     RELEASE_LOCK(&cap->lock);
 449 }
 450
 451 static void
 452 releaseCapabilityAndQueueWorker (Capability* cap USED_IF_THREADS)
 453 {
 454     Task *task;
 455
 456     ACQUIRE_LOCK(&cap->lock);
 457
 458     task = cap->running_task;
 459
 460     // If the current task is a worker, save it on the spare_workers
 461     // list of this Capability.  A worker can mark itself as stopped,
 462     // in which case it is not replaced on the spare_worker queue.
 463     // This happens when the system is shutting down (see
 464     // Schedule.c:workerStart()).
 465     // Also, be careful to check that this task hasn't just exited
 466     // Haskell to do a foreign call (task->suspended_tso).
 467     if (!isBoundTask(task) && !task->stopped && !task->suspended_tso) {
 468         task->next = cap->spare_workers;
 469         cap->spare_workers = task;
 470     }
 471     // Bound tasks just float around attached to their TSOs.
 472
 473     releaseCapability_(cap,rtsFalse);
 474
 475     RELEASE_LOCK(&cap->lock);
 476 }
 477 #endif
 478
 479 /* ----------------------------------------------------------------------------
 480  * waitForReturnCapability( Task *task )
 481  *
 482  * Purpose:  when an OS thread returns from an external call,
 483  * it calls waitForReturnCapability() (via Schedule.resumeThread())
 484  * to wait for permission to enter the RTS & communicate the
 485  * result of the external call back to the Haskell thread that
 486  * made it.
 487  *
 488  * ------------------------------------------------------------------------- */
 489 void
 490 waitForReturnCapability (Capability **pCap, Task *task)
 491 {
 492 #if !defined(THREADED_RTS)
 493
 494     MainCapability.running_task = task;
 495     task->cap = &MainCapability;
 496     *pCap = &MainCapability;
 497
 498 #else
 499     Capability *cap = *pCap;
 500
 501     if (cap == NULL) {
 502         // Try last_free_capability first
 503         cap = last_free_capability;
 504         if (!cap->running_task) {
 505             nat i;
 506             // otherwise, search for a free capability
 507             cap = NULL;
 508             for (i = 0; i < n_capabilities; i++) {
 509                 if (!capabilities[i].running_task) {
 510                     cap = &capabilities[i];
 511                     break;
 512                 }
 513             }
 514             if (cap == NULL) {
 515                 // Can't find a free one, use last_free_capability.
 516                 cap = last_free_capability;
 517             }
 518         }
 519
 520         // record the Capability as the one this Task is now assocated with.
 521         task->cap = cap;
 522
 523     } else {
 524         ASSERT(task->cap == cap);
 525     }
 526
 527     ACQUIRE_LOCK(&cap->lock);
 528
 529     debugTrace(DEBUG_sched, "returning; I want capability %d", cap->no);
 530
 531     if (!cap->running_task) {
 532         // It's free; just grab it
 533         cap->running_task = task;
 534         RELEASE_LOCK(&cap->lock);
 535     } else {
 536         newReturningTask(cap,task);
 537         RELEASE_LOCK(&cap->lock);
 538
 539         for (;;) {
 540             ACQUIRE_LOCK(&task->lock);
 541             // task->lock held, cap->lock not held
 542             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 543             cap = task->cap;
 544             task->wakeup = rtsFalse;
 545             RELEASE_LOCK(&task->lock);
 546
 547             // now check whether we should wake up...
 548             ACQUIRE_LOCK(&cap->lock);
 549             if (cap->running_task == NULL) {
 550                 if (cap->returning_tasks_hd != task) {
 551                     giveCapabilityToTask(cap,cap->returning_tasks_hd);
 552                     RELEASE_LOCK(&cap->lock);
 553                     continue;
 554                 }
 555                 cap->running_task = task;
 556                 popReturningTask(cap);
 557                 RELEASE_LOCK(&cap->lock);
 558                 break;
 559             }
 560             RELEASE_LOCK(&cap->lock);
 561         }
 562
 563     }
 564
 565     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 566
 567     debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 568
 569     *pCap = cap;
 570 #endif
 571 }
 572
 573 #if defined(THREADED_RTS)
 574 /* ----------------------------------------------------------------------------
 575  * yieldCapability
 576  * ------------------------------------------------------------------------- */
 577
 578 void
 579 yieldCapability (Capability** pCap, Task *task)
 580 {
 581     Capability *cap = *pCap;
 582
 583     if (waiting_for_gc == PENDING_GC_PAR) {
 584         debugTrace(DEBUG_sched, "capability %d: becoming a GC thread", cap->no);
 585         postEvent(cap, EVENT_GC_START, 0, 0);
 586         gcWorkerThread(cap);
 587         postEvent(cap, EVENT_GC_END, 0, 0);
 588         return;
 589     }
 590
 591         debugTrace(DEBUG_sched, "giving up capability %d", cap->no);
 592
 593         // We must now release the capability and wait to be woken up
 594         // again.
 595         task->wakeup = rtsFalse;
 596         releaseCapabilityAndQueueWorker(cap);
 597
 598         for (;;) {
 599             ACQUIRE_LOCK(&task->lock);
 600             // task->lock held, cap->lock not held
 601             if (!task->wakeup) waitCondition(&task->cond, &task->lock);
 602             cap = task->cap;
 603             task->wakeup = rtsFalse;
 604             RELEASE_LOCK(&task->lock);
 605
 606             debugTrace(DEBUG_sched, "woken up on capability %d", cap->no);
 607
 608             ACQUIRE_LOCK(&cap->lock);
 609             if (cap->running_task != NULL) {
 610                 debugTrace(DEBUG_sched,
 611                            "capability %d is owned by another task", cap->no);
 612                 RELEASE_LOCK(&cap->lock);
 613                 continue;
 614             }
 615
 616             if (task->tso == NULL) {
 617                 ASSERT(cap->spare_workers != NULL);
 618                 // if we're not at the front of the queue, release it
 619                 // again.  This is unlikely to happen.
 620                 if (cap->spare_workers != task) {
 621                     giveCapabilityToTask(cap,cap->spare_workers);
 622                     RELEASE_LOCK(&cap->lock);
 623                     continue;
 624                 }
 625                 cap->spare_workers = task->next;
 626                 task->next = NULL;
 627             }
 628             cap->running_task = task;
 629             RELEASE_LOCK(&cap->lock);
 630             break;
 631         }
 632
 633         debugTrace(DEBUG_sched, "resuming capability %d", cap->no);
 634         ASSERT(cap->running_task == task);
 635
 636     *pCap = cap;
 637
 638     ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
 639
 640     return;
 641 }
 642
 643 /* ----------------------------------------------------------------------------
 644  * Wake up a thread on a Capability.
 645  *
 646  * This is used when the current Task is running on a Capability and
 647  * wishes to wake up a thread on a different Capability.
 648  * ------------------------------------------------------------------------- */
 649
 650 void
 651 wakeupThreadOnCapability (Capability *my_cap,
 652                           Capability *other_cap,
 653                           StgTSO *tso)
 654 {
 655     ACQUIRE_LOCK(&other_cap->lock);
 656
 657     // ASSUMES: cap->lock is held (asserted in wakeupThreadOnCapability)
 658     if (tso->bound) {
 659         ASSERT(tso->bound->cap == tso->cap);
 660         tso->bound->cap = other_cap;
 661     }
 662     tso->cap = other_cap;
 663
 664     ASSERT(tso->bound ? tso->bound->cap == other_cap : 1);
 665
 666     if (other_cap->running_task == NULL) {
 667         // nobody is running this Capability, we can add our thread
 668         // directly onto the run queue and start up a Task to run it.
 669
 670         other_cap->running_task = myTask();
 671             // precond for releaseCapability_() and appendToRunQueue()
 672
 673         appendToRunQueue(other_cap,tso);
 674
 675         releaseCapability_(other_cap,rtsFalse);
 676     } else {
 677         appendToWakeupQueue(my_cap,other_cap,tso);
 678         other_cap->context_switch = 1;
 679         // someone is running on this Capability, so it cannot be
 680         // freed without first checking the wakeup queue (see
 681         // releaseCapability_).
 682     }
 683
 684     RELEASE_LOCK(&other_cap->lock);
 685 }
 686
 687 /* ----------------------------------------------------------------------------
 688  * prodCapability
 689  *
 690  * If a Capability is currently idle, wake up a Task on it.  Used to
 691  * get every Capability into the GC.
 692  * ------------------------------------------------------------------------- */
 693
 694 void
 695 prodCapability (Capability *cap, Task *task)
 696 {
 697     ACQUIRE_LOCK(&cap->lock);
 698     if (!cap->running_task) {
 699         cap->running_task = task;
 700         releaseCapability_(cap,rtsTrue);
 701     }
 702     RELEASE_LOCK(&cap->lock);
 703 }
 704
 705 /* ----------------------------------------------------------------------------
 706  * shutdownCapability
 707  *
 708  * At shutdown time, we want to let everything exit as cleanly as
 709  * possible.  For each capability, we let its run queue drain, and
 710  * allow the workers to stop.
 711  *
 712  * This function should be called when interrupted and
 713  * shutting_down_scheduler = rtsTrue, thus any worker that wakes up
 714  * will exit the scheduler and call taskStop(), and any bound thread
 715  * that wakes up will return to its caller.  Runnable threads are
 716  * killed.
 717  *
 718  * ------------------------------------------------------------------------- */
 719
 720 void
 721 shutdownCapability (Capability *cap, Task *task, rtsBool safe)
 722 {
 723     nat i;
 724
 725     task->cap = cap;
 726
 727     // Loop indefinitely until all the workers have exited and there
 728     // are no Haskell threads left.  We used to bail out after 50
 729     // iterations of this loop, but that occasionally left a worker
 730     // running which caused problems later (the closeMutex() below
 731     // isn't safe, for one thing).
 732
 733     for (i = 0; /* i < 50 */; i++) {
 734         ASSERT(sched_state == SCHED_SHUTTING_DOWN);
 735
 736         debugTrace(DEBUG_sched,
 737                    "shutting down capability %d, attempt %d", cap->no, i);
 738         ACQUIRE_LOCK(&cap->lock);
 739         if (cap->running_task) {
 740             RELEASE_LOCK(&cap->lock);
 741             debugTrace(DEBUG_sched, "not owner, yielding");
 742             yieldThread();
 743             continue;
 744         }
 745         cap->running_task = task;
 746
 747         if (cap->spare_workers) {
 748             // Look for workers that have died without removing
 749             // themselves from the list; this could happen if the OS
 750             // summarily killed the thread, for example.  This
 751             // actually happens on Windows when the system is
 752             // terminating the program, and the RTS is running in a
 753             // DLL.
 754             Task *t, *prev;
 755             prev = NULL;
 756             for (t = cap->spare_workers; t != NULL; t = t->next) {
 757                 if (!osThreadIsAlive(t->id)) {
 758                     debugTrace(DEBUG_sched,
 759                                "worker thread %p has died unexpectedly", (void *)t->id);
 760                         if (!prev) {
 761                             cap->spare_workers = t->next;
 762                         } else {
 763                             prev->next = t->next;
 764                         }
 765                         prev = t;
 766                 }
 767             }
 768         }
 769
 770         if (!emptyRunQueue(cap) || cap->spare_workers) {
 771             debugTrace(DEBUG_sched,
 772                        "runnable threads or workers still alive, yielding");
 773             releaseCapability_(cap,rtsFalse); // this will wake up a worker
 774             RELEASE_LOCK(&cap->lock);
 775             yieldThread();
 776             continue;
 777         }
 778
 779         // If "safe", then busy-wait for any threads currently doing
 780         // foreign calls.  If we're about to unload this DLL, for
 781         // example, we need to be sure that there are no OS threads
 782         // that will try to return to code that has been unloaded.
 783         // We can be a bit more relaxed when this is a standalone
 784         // program that is about to terminate, and let safe=false.
 785         if (cap->suspended_ccalling_tasks && safe) {
 786             debugTrace(DEBUG_sched,
 787                        "thread(s) are involved in foreign calls, yielding");
 788             cap->running_task = NULL;
 789             RELEASE_LOCK(&cap->lock);
 790             yieldThread();
 791             continue;
 792         }
 793
 794         postEvent(cap, EVENT_SHUTDOWN, 0, 0);
 795         debugTrace(DEBUG_sched, "capability %d is stopped.", cap->no);
 796         RELEASE_LOCK(&cap->lock);
 797         break;
 798     }
 799     // we now have the Capability, its run queue and spare workers
 800     // list are both empty.
 801
 802     // ToDo: we can't drop this mutex, because there might still be
 803     // threads performing foreign calls that will eventually try to
 804     // return via resumeThread() and attempt to grab cap->lock.
 805     // closeMutex(&cap->lock);
 806 }
 807
 808 /* ----------------------------------------------------------------------------
 809  * tryGrabCapability
 810  *
 811  * Attempt to gain control of a Capability if it is free.
 812  *
 813  * ------------------------------------------------------------------------- */
 814
 815 rtsBool
 816 tryGrabCapability (Capability *cap, Task *task)
 817 {
 818     if (cap->running_task != NULL) return rtsFalse;
 819     ACQUIRE_LOCK(&cap->lock);
 820     if (cap->running_task != NULL) {
 821         RELEASE_LOCK(&cap->lock);
 822         return rtsFalse;
 823     }
 824     task->cap = cap;
 825     cap->running_task = task;
 826     RELEASE_LOCK(&cap->lock);
 827     return rtsTrue;
 828 }
 829
 830
 831 #endif /* THREADED_RTS */
 832
 833 static void
 834 freeCapability (Capability *cap)
 835 {
 836     stgFree(cap->mut_lists);
 837 #if defined(THREADED_RTS)
 838     freeSparkPool(cap->sparks);
 839 #endif
 840 }
 841
 842 void
 843 freeCapabilities (void)
 844 {
 845 #if defined(THREADED_RTS)
 846     nat i;
 847     for (i=0; i < n_capabilities; i++) {
 848         freeCapability(&capabilities[i]);
 849     }
 850 #else
 851     freeCapability(&MainCapability);
 852 #endif
 853 }
 854
 855 /* ---------------------------------------------------------------------------
 856    Mark everything directly reachable from the Capabilities.  When
 857    using multiple GC threads, each GC thread marks all Capabilities
 858    for which (c `mod` n == 0), for Capability c and thread n.
 859    ------------------------------------------------------------------------ */
 860
 861 void
 862 markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
 863                       rtsBool prune_sparks USED_IF_THREADS)
 864 {
 865     nat i;
 866     Capability *cap;
 867     Task *task;
 868
 869     // Each GC thread is responsible for following roots from the
 870     // Capability of the same number.  There will usually be the same
 871     // or fewer Capabilities as GC threads, but just in case there
 872     // are more, we mark every Capability whose number is the GC
 873     // thread's index plus a multiple of the number of GC threads.
 874     for (i = i0; i < n_capabilities; i += delta) {
 875         cap = &capabilities[i];
 876         evac(user, (StgClosure **)(void *)&cap->run_queue_hd);
 877         evac(user, (StgClosure **)(void *)&cap->run_queue_tl);
 878 #if defined(THREADED_RTS)
 879         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_hd);
 880         evac(user, (StgClosure **)(void *)&cap->wakeup_queue_tl);
 881 #endif
 882         for (task = cap->suspended_ccalling_tasks; task != NULL;
 883              task=task->next) {
 884             debugTrace(DEBUG_sched,
 885                        "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
 886             evac(user, (StgClosure **)(void *)&task->suspended_tso);
 887         }
 888
 889 #if defined(THREADED_RTS)
 890         if (prune_sparks) {
 891             pruneSparkQueue (evac, user, cap);
 892         } else {
 893             traverseSparkQueue (evac, user, cap);
 894         }
 895 #endif
 896     }
 897
 898 #if !defined(THREADED_RTS)
 899     evac(user, (StgClosure **)(void *)&blocked_queue_hd);
 900     evac(user, (StgClosure **)(void *)&blocked_queue_tl);
 901     evac(user, (StgClosure **)(void *)&sleeping_queue);
 902 #endif
 903 }
 904
 905 void
 906 markCapabilities (evac_fn evac, void *user)
 907 {
 908     markSomeCapabilities(evac, user, 0, 1, rtsFalse);
 909 }