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