summaryrefslogtreecommitdiff
path: root/rts/RtsAPI.c
blob: 26433ac209ba19aa13c1e6fd9d91899f254069db (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
/* ----------------------------------------------------------------------------
 *
 * (c) The GHC Team, 1998-2001
 *
 * API for invoking Haskell functions via the RTS
 *
 * --------------------------------------------------------------------------*/

#include "PosixSource.h"
#include "Rts.h"
#include "RtsAPI.h"
#include "HsFFI.h"

#include "RtsUtils.h"
#include "Prelude.h"
#include "Schedule.h"
#include "Capability.h"
#include "StablePtr.h"
#include "Threads.h"
#include "Weak.h"

/* ----------------------------------------------------------------------------
   Building Haskell objects from C datatypes.

   TODO: Currently this code does not tag created pointers,
         however it is not unsafe (the constructor code will do it)
         just inefficient.
   ------------------------------------------------------------------------- */
HaskellObj
rts_mkChar (Capability *cap, HsChar c)
{
  StgClosure *p = (StgClosure *)allocate(cap, CONSTR_sizeW(0,1));
  SET_HDR(p, Czh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgWord)(StgChar)c;
  return p;
}

HaskellObj
rts_mkInt (Capability *cap, HsInt i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, Izh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgInt)i;
  return p;
}

HaskellObj
rts_mkInt8 (Capability *cap, HsInt8 i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, I8zh_con_info, CCS_SYSTEM);
  /* Make sure we mask out the bits above the lowest 8 */
  p->payload[0]  = (StgClosure *)(StgInt)i;
  return p;
}

HaskellObj
rts_mkInt16 (Capability *cap, HsInt16 i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, I16zh_con_info, CCS_SYSTEM);
  /* Make sure we mask out the relevant bits */
  p->payload[0]  = (StgClosure *)(StgInt)i;
  return p;
}

HaskellObj
rts_mkInt32 (Capability *cap, HsInt32 i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, I32zh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgInt)i;
  return p;
}

HaskellObj
rts_mkInt64 (Capability *cap, HsInt64 i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,2));
  SET_HDR(p, I64zh_con_info, CCS_SYSTEM);
  ASSIGN_Int64((P_)&(p->payload[0]), i);
  return p;
}

HaskellObj
rts_mkWord (Capability *cap, HsWord i)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, Wzh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgWord)i;
  return p;
}

HaskellObj
rts_mkWord8 (Capability *cap, HsWord8 w)
{
  /* see rts_mkInt* comments */
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, W8zh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgWord)(w & 0xff);
  return p;
}

HaskellObj
rts_mkWord16 (Capability *cap, HsWord16 w)
{
  /* see rts_mkInt* comments */
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, W16zh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgWord)(w & 0xffff);
  return p;
}

HaskellObj
rts_mkWord32 (Capability *cap, HsWord32 w)
{
  /* see rts_mkInt* comments */
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, W32zh_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)(StgWord)(w & 0xffffffff);
  return p;
}

HaskellObj
rts_mkWord64 (Capability *cap, HsWord64 w)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,2));
  /* see mk_Int8 comment */
  SET_HDR(p, W64zh_con_info, CCS_SYSTEM);
  ASSIGN_Word64((P_)&(p->payload[0]), w);
  return p;
}


HaskellObj
rts_mkFloat (Capability *cap, HsFloat f)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,1));
  SET_HDR(p, Fzh_con_info, CCS_SYSTEM);
  ASSIGN_FLT((P_)p->payload, (StgFloat)f);
  return p;
}

HaskellObj
rts_mkDouble (Capability *cap, HsDouble d)
{
  StgClosure *p = (StgClosure *)allocate(cap,CONSTR_sizeW(0,sizeofW(StgDouble)));
  SET_HDR(p, Dzh_con_info, CCS_SYSTEM);
  ASSIGN_DBL((P_)p->payload, (StgDouble)d);
  return p;
}

HaskellObj
rts_mkStablePtr (Capability *cap, HsStablePtr s)
{
  StgClosure *p = (StgClosure *)allocate(cap,sizeofW(StgHeader)+1);
  SET_HDR(p, StablePtr_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)s;
  return p;
}

HaskellObj
rts_mkPtr (Capability *cap, HsPtr a)
{
  StgClosure *p = (StgClosure *)allocate(cap,sizeofW(StgHeader)+1);
  SET_HDR(p, Ptr_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)a;
  return p;
}

HaskellObj
rts_mkFunPtr (Capability *cap, HsFunPtr a)
{
  StgClosure *p = (StgClosure *)allocate(cap,sizeofW(StgHeader)+1);
  SET_HDR(p, FunPtr_con_info, CCS_SYSTEM);
  p->payload[0]  = (StgClosure *)a;
  return p;
}

HaskellObj
rts_mkBool (Capability *cap STG_UNUSED, HsBool b)
{
  if (b) {
    return (StgClosure *)True_closure;
  } else {
    return (StgClosure *)False_closure;
  }
}

HaskellObj
rts_mkString (Capability *cap, char *s)
{
  return rts_apply(cap, (StgClosure *)unpackCString_closure, rts_mkPtr(cap,s));
}

HaskellObj
rts_apply (Capability *cap, HaskellObj f, HaskellObj arg)
{
    StgThunk *ap;

    ap = (StgThunk *)allocate(cap,sizeofW(StgThunk) + 2);
    // Here we don't want to use CCS_SYSTEM, because it's a hidden cost centre,
    // and evaluating Haskell code under a hidden cost centre leads to
    // confusing profiling output. (#7753)
    SET_HDR(ap, (StgInfoTable *)&stg_ap_2_upd_info, CCS_MAIN);
    ap->payload[0] = f;
    ap->payload[1] = arg;
    return (StgClosure *)ap;
}

/* ----------------------------------------------------------------------------
   Deconstructing Haskell objects

   We would like to assert that we have the right kind of object in
   each case, but this is problematic because in GHCi the info table
   for the D# constructor (say) might be dynamically loaded.  Hence we
   omit these assertions for now.
   ------------------------------------------------------------------------- */

HsChar
rts_getChar (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Czh_con_info ||
    //        p->header.info == Czh_static_info);
    return (StgChar)(StgWord)(UNTAG_CLOSURE(p)->payload[0]);
}

HsInt
rts_getInt (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Izh_con_info ||
    //        p->header.info == Izh_static_info);
    return (HsInt)(UNTAG_CLOSURE(p)->payload[0]);
}

HsInt8
rts_getInt8 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == I8zh_con_info ||
    //        p->header.info == I8zh_static_info);
    return (HsInt8)(HsInt)(UNTAG_CLOSURE(p)->payload[0]);
}

HsInt16
rts_getInt16 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == I16zh_con_info ||
    //        p->header.info == I16zh_static_info);
    return (HsInt16)(HsInt)(UNTAG_CLOSURE(p)->payload[0]);
}

HsInt32
rts_getInt32 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == I32zh_con_info ||
    //        p->header.info == I32zh_static_info);
  return (HsInt32)(HsInt)(UNTAG_CLOSURE(p)->payload[0]);
}

HsInt64
rts_getInt64 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == I64zh_con_info ||
    //        p->header.info == I64zh_static_info);
    return PK_Int64((P_)&(UNTAG_CLOSURE(p)->payload[0]));
}

HsWord
rts_getWord (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Wzh_con_info ||
    //        p->header.info == Wzh_static_info);
    return (HsWord)(UNTAG_CLOSURE(p)->payload[0]);
}

HsWord8
rts_getWord8 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == W8zh_con_info ||
    //        p->header.info == W8zh_static_info);
    return (HsWord8)(HsWord)(UNTAG_CLOSURE(p)->payload[0]);
}

HsWord16
rts_getWord16 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == W16zh_con_info ||
    //        p->header.info == W16zh_static_info);
    return (HsWord16)(HsWord)(UNTAG_CLOSURE(p)->payload[0]);
}

HsWord32
rts_getWord32 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == W32zh_con_info ||
    //        p->header.info == W32zh_static_info);
    return (HsWord32)(HsWord)(UNTAG_CLOSURE(p)->payload[0]);
}

HsWord64
rts_getWord64 (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == W64zh_con_info ||
    //        p->header.info == W64zh_static_info);
    return PK_Word64((P_)&(UNTAG_CLOSURE(p)->payload[0]));
}

HsFloat
rts_getFloat (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Fzh_con_info ||
    //        p->header.info == Fzh_static_info);
    return (float)(PK_FLT((P_)UNTAG_CLOSURE(p)->payload));
}

HsDouble
rts_getDouble (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Dzh_con_info ||
    //        p->header.info == Dzh_static_info);
    return (double)(PK_DBL((P_)UNTAG_CLOSURE(p)->payload));
}

HsStablePtr
rts_getStablePtr (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == StablePtr_con_info ||
    //        p->header.info == StablePtr_static_info);
    return (StgStablePtr)(UNTAG_CLOSURE(p)->payload[0]);
}

HsPtr
rts_getPtr (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == Ptr_con_info ||
    //        p->header.info == Ptr_static_info);
    return (Capability *)(UNTAG_CLOSURE(p)->payload[0]);
}

HsFunPtr
rts_getFunPtr (HaskellObj p)
{
    // See comment above:
    // ASSERT(p->header.info == FunPtr_con_info ||
    //        p->header.info == FunPtr_static_info);
    return (void *)(UNTAG_CLOSURE(p)->payload[0]);
}

HsBool
rts_getBool (HaskellObj p)
{
    const StgInfoTable *info;

    info = get_itbl((const StgClosure *)UNTAG_CONST_CLOSURE(p));
    if (info->srt == 0) { // srt is the constructor tag
        return 0;
    } else {
        return 1;
    }
}

/* -----------------------------------------------------------------------------
   Creating threads
   -------------------------------------------------------------------------- */

INLINE_HEADER void pushClosure   (StgTSO *tso, StgWord c) {
  tso->stackobj->sp--;
  tso->stackobj->sp[0] = (W_) c;
}

StgTSO *
createGenThread (Capability *cap, W_ stack_size,  StgClosure *closure)
{
  StgTSO *t;
  t = createThread (cap, stack_size);
  pushClosure(t, (W_)closure);
  pushClosure(t, (W_)&stg_enter_info);
  return t;
}

StgTSO *
createIOThread (Capability *cap, W_ stack_size,  StgClosure *closure)
{
  StgTSO *t;
  t = createThread (cap, stack_size);
  pushClosure(t, (W_)&stg_ap_v_info);
  pushClosure(t, (W_)closure);
  pushClosure(t, (W_)&stg_enter_info);
  return t;
}

/*
 * Same as above, but also evaluate the result of the IO action
 * to whnf while we're at it.
 */

StgTSO *
createStrictIOThread(Capability *cap, W_ stack_size,  StgClosure *closure)
{
  StgTSO *t;
  t = createThread(cap, stack_size);
  pushClosure(t, (W_)&stg_forceIO_info);
  pushClosure(t, (W_)&stg_ap_v_info);
  pushClosure(t, (W_)closure);
  pushClosure(t, (W_)&stg_enter_info);
  return t;
}

/* ----------------------------------------------------------------------------
   Evaluating Haskell expressions
   ------------------------------------------------------------------------- */

void rts_eval (/* inout */ Capability **cap,
               /* in    */ HaskellObj p,
               /* out */   HaskellObj *ret)
{
    StgTSO *tso;

    tso = createGenThread(*cap, RtsFlags.GcFlags.initialStkSize, p);
    scheduleWaitThread(tso,ret,cap);
}

void rts_eval_ (/* inout */ Capability **cap,
                /* in    */ HaskellObj p,
                /* in    */ unsigned int stack_size,
                /* out   */ HaskellObj *ret)
{
    StgTSO *tso;

    tso = createGenThread(*cap, stack_size, p);
    scheduleWaitThread(tso,ret,cap);
}

/*
 * rts_evalIO() evaluates a value of the form (IO a), forcing the action's
 * result to WHNF before returning.
 */
void rts_evalIO (/* inout */ Capability **cap,
                 /* in    */ HaskellObj p,
                 /* out */   HaskellObj *ret)
{
    StgTSO* tso;

    tso = createStrictIOThread(*cap, RtsFlags.GcFlags.initialStkSize, p);
    scheduleWaitThread(tso,ret,cap);
}

/*
 * rts_evalStableIOMain() is suitable for calling main Haskell thread
 * stored in (StablePtr (IO a)) it calls rts_evalStableIO but wraps
 * function in GHC.TopHandler.runMainIO that installs top_handlers.
 * See #12903.
 */
void rts_evalStableIOMain(/* inout */ Capability **cap,
                          /* in    */ HsStablePtr s,
                          /* out   */ HsStablePtr *ret)
{
    StgTSO* tso;
    StgClosure *p, *r, *w;
    SchedulerStatus stat;

    p = (StgClosure *)deRefStablePtr(s);
    w = rts_apply(*cap, &base_GHCziTopHandler_runMainIO_closure, p);
    tso = createStrictIOThread(*cap, RtsFlags.GcFlags.initialStkSize, w);
    // async exceptions are always blocked by default in the created
    // thread.  See #1048.
    tso->flags |= TSO_BLOCKEX | TSO_INTERRUPTIBLE;
    scheduleWaitThread(tso,&r,cap);
    stat = rts_getSchedStatus(*cap);

    if (stat == Success && ret != NULL) {
        ASSERT(r != NULL);
        *ret = getStablePtr((StgPtr)r);
    }
}

/*
 * rts_evalStableIO() is suitable for calling from Haskell.  It
 * evaluates a value of the form (StablePtr (IO a)), forcing the
 * action's result to WHNF before returning.  The result is returned
 * in a StablePtr.
 */
void rts_evalStableIO (/* inout */ Capability **cap,
                       /* in    */ HsStablePtr s,
                       /* out */   HsStablePtr *ret)
{
    StgTSO* tso;
    StgClosure *p, *r;
    SchedulerStatus stat;

    p = (StgClosure *)deRefStablePtr(s);
    tso = createStrictIOThread(*cap, RtsFlags.GcFlags.initialStkSize, p);
    // async exceptions are always blocked by default in the created
    // thread.  See #1048.
    tso->flags |= TSO_BLOCKEX | TSO_INTERRUPTIBLE;
    scheduleWaitThread(tso,&r,cap);
    stat = rts_getSchedStatus(*cap);

    if (stat == Success && ret != NULL) {
        ASSERT(r != NULL);
        *ret = getStablePtr((StgPtr)r);
    }
}

/*
 * Like rts_evalIO(), but doesn't force the action's result.
 */
void rts_evalLazyIO (/* inout */ Capability **cap,
                     /* in    */ HaskellObj p,
                     /* out */   HaskellObj *ret)
{
    StgTSO *tso;

    tso = createIOThread(*cap, RtsFlags.GcFlags.initialStkSize, p);
    scheduleWaitThread(tso,ret,cap);
}

void rts_evalLazyIO_ (/* inout */ Capability **cap,
                      /* in    */ HaskellObj p,
                      /* in    */ unsigned int stack_size,
                      /* out   */ HaskellObj *ret)
{
    StgTSO *tso;

    tso = createIOThread(*cap, stack_size, p);
    scheduleWaitThread(tso,ret,cap);
}

/* Convenience function for decoding the returned status. */

void
rts_checkSchedStatus (char* site, Capability *cap)
{
    SchedulerStatus rc = cap->running_task->incall->rstat;
    switch (rc) {
    case Success:
        return;
    case Killed:
        errorBelch("%s: uncaught exception",site);
        stg_exit(EXIT_FAILURE);
    case Interrupted:
        errorBelch("%s: interrupted", site);
#if defined(THREADED_RTS)
        // The RTS is shutting down, and the process will probably
        // soon exit.  We don't want to preempt the shutdown
        // by exiting the whole process here, so we just terminate the
        // current thread.  Don't forget to release the cap first though.
        rts_unlock(cap);
        shutdownThread();
#else
        stg_exit(EXIT_FAILURE);
#endif
    default:
        errorBelch("%s: Return code (%d) not ok",(site),(rc));
        stg_exit(EXIT_FAILURE);
    }
}

SchedulerStatus
rts_getSchedStatus (Capability *cap)
{
    return cap->running_task->incall->rstat;
}

Capability *
rts_lock (void)
{
    Capability *cap;
    Task *task;

    task = newBoundTask();

    if (task->running_finalizers) {
        errorBelch("error: a C finalizer called back into Haskell.\n"
                   "   This was previously allowed, but is disallowed in GHC 6.10.2 and later.\n"
                   "   To create finalizers that may call back into Haskell, use\n"
                   "   Foreign.Concurrent.newForeignPtr instead of Foreign.newForeignPtr.");
        stg_exit(EXIT_FAILURE);
    }

    cap = NULL;
    waitForCapability(&cap, task);

    if (task->incall->prev_stack == NULL) {
      // This is a new outermost call from C into Haskell land.
      // Until the corresponding call to rts_unlock, this task
      // is doing work on behalf of the RTS.
      traceTaskCreate(task, cap);
    }

    return (Capability *)cap;
}

// Exiting the RTS: we hold a Capability that is not necessarily the
// same one that was originally returned by rts_lock(), because
// rts_evalIO() etc. may return a new one.  Now that we have
// investigated the return value, we can release the Capability,
// and free the Task (in that order).

void
rts_unlock (Capability *cap)
{
    Task *task;

    task = cap->running_task;
    ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);

    // Now release the Capability.  With the capability released, GC
    // may happen.  NB. does not try to put the current Task on the
    // worker queue.
    // NB. keep cap->lock held while we call boundTaskExiting().  This
    // is necessary during shutdown, where we want the invariant that
    // after shutdownCapability(), all the Tasks associated with the
    // Capability have completed their shutdown too.  Otherwise we
    // could have boundTaskExiting()/workerTaskStop() running at some
    // random point in the future, which causes problems for
    // freeTaskManager().
    ACQUIRE_LOCK(&cap->lock);
    releaseCapability_(cap,false);

    // Finally, we can release the Task to the free list.
    boundTaskExiting(task);
    RELEASE_LOCK(&cap->lock);

    if (task->incall == NULL) {
      // This is the end of an outermost call from C into Haskell land.
      // From here on, the task goes back to C land and we should not count
      // it as doing work on behalf of the RTS.
      traceTaskDelete(task);
    }
}

void rts_done (void)
{
    freeMyTask();
}

/* -----------------------------------------------------------------------------
   tryPutMVar from outside Haskell

   The C call

      hs_try_putmvar(cap, mvar)

   is equivalent to the Haskell call

      tryPutMVar mvar ()

   but it is

     * non-blocking: takes a bounded, short, amount of time
     * asynchronous: the actual putMVar may be performed after the
       call returns.  That's why hs_try_putmvar() doesn't return a
       result to say whether the put succeeded.

   NOTE: this call transfers ownership of the StablePtr to the RTS, which will
   free it after the tryPutMVar has taken place.  The reason is that otherwise,
   it would be very difficult for the caller to arrange to free the StablePtr
   in all circumstances.

   For more details, see the section "Waking up Haskell threads from C" in the
   User's Guide.
   -------------------------------------------------------------------------- */

void hs_try_putmvar (/* in */ int capability,
                     /* in */ HsStablePtr mvar)
{
    Task *task = getTask();
    Capability *cap;

    if (capability < 0) {
        capability = task->preferred_capability;
        if (capability < 0) {
            capability = 0;
        }
    }
    cap = capabilities[capability % enabled_capabilities];

#if !defined(THREADED_RTS)

    performTryPutMVar(cap, (StgMVar*)deRefStablePtr(mvar), Unit_closure);
    freeStablePtr(mvar);

#else

    ACQUIRE_LOCK(&cap->lock);
    // If the capability is free, we can perform the tryPutMVar immediately
    if (cap->running_task == NULL) {
        cap->running_task = task;
        task->cap = cap;
        RELEASE_LOCK(&cap->lock);

        performTryPutMVar(cap, (StgMVar*)deRefStablePtr(mvar), Unit_closure);

        freeStablePtr(mvar);

        // Wake up the capability, which will start running the thread that we
        // just awoke (if there was one).
        releaseCapability(cap);
    } else {
        PutMVar *p = stgMallocBytes(sizeof(PutMVar),"hs_try_putmvar");
        // We cannot deref the StablePtr if we don't have a capability,
        // so we have to store it and deref it later.
        p->mvar = mvar;
        p->link = cap->putMVars;
        cap->putMVars = p;
        RELEASE_LOCK(&cap->lock);
    }

#endif
}