Use message-passing to implement throwTo in the RTS
[ghc.git] / rts / sm / Compact.c
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 2001-2008
4 *
5 * Compacting garbage collector
6 *
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
9 *
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
11 *
12 * ---------------------------------------------------------------------------*/
13
14 #include "PosixSource.h"
15 #include "Rts.h"
16
17 #include "Storage.h"
18 #include "RtsUtils.h"
19 #include "BlockAlloc.h"
20 #include "GC.h"
21 #include "Compact.h"
22 #include "Schedule.h"
23 #include "Apply.h"
24 #include "Trace.h"
25 #include "Weak.h"
26 #include "MarkWeak.h"
27 #include "Stable.h"
28
29 // Turn off inlining when debugging - it obfuscates things
30 #ifdef DEBUG
31 # undef STATIC_INLINE
32 # define STATIC_INLINE static
33 #endif
34
35 /* ----------------------------------------------------------------------------
36 Threading / unthreading pointers.
37
38 The basic idea here is to chain together all the fields pointing at
39 a particular object, with the root of the chain in the object's
40 info table field. The original contents of the info pointer goes
41 at the end of the chain.
42
43 Adding a new field to the chain is a matter of swapping the
44 contents of the field with the contents of the object's info table
45 field.
46
47 To unthread the chain, we walk down it updating all the fields on
48 the chain with the new location of the object. We stop when we
49 reach the info pointer at the end.
50
51 The main difficulty here is that we need to be able to identify the
52 info pointer at the end of the chain. We can't use the low bits of
53 the pointer for this; they are already being used for
54 pointer-tagging. What's more, we need to retain the
55 pointer-tagging tag bits on each pointer during the
56 threading/unthreading process.
57
58 Our solution is as follows:
59 - an info pointer (chain length zero) is identified by having tag 0
60 - in a threaded chain of length > 0:
61 - the pointer-tagging tag bits are attached to the info pointer
62 - the first entry in the chain has tag 1
63 - second and subsequent entries in the chain have tag 2
64
65 This exploits the fact that the tag on each pointer to a given
66 closure is normally the same (if they are not the same, then
67 presumably the tag is not essential and it therefore doesn't matter
68 if we throw away some of the tags).
69 ------------------------------------------------------------------------- */
70
71 STATIC_INLINE void
72 thread (StgClosure **p)
73 {
74 StgClosure *q0;
75 StgPtr q;
76 StgWord iptr;
77 bdescr *bd;
78
79 q0 = *p;
80 q = (StgPtr)UNTAG_CLOSURE(q0);
81
82 // It doesn't look like a closure at the moment, because the info
83 // ptr is possibly threaded:
84 // ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
85
86 if (HEAP_ALLOCED(q)) {
87 bd = Bdescr(q);
88
89 if (bd->flags & BF_MARKED)
90 {
91 iptr = *q;
92 switch (GET_CLOSURE_TAG((StgClosure *)iptr))
93 {
94 case 0:
95 // this is the info pointer; we are creating a new chain.
96 // save the original tag at the end of the chain.
97 *p = (StgClosure *)((StgWord)iptr + GET_CLOSURE_TAG(q0));
98 *q = (StgWord)p + 1;
99 break;
100 case 1:
101 case 2:
102 // this is a chain of length 1 or more
103 *p = (StgClosure *)iptr;
104 *q = (StgWord)p + 2;
105 break;
106 }
107 }
108 }
109 }
110
111 static void
112 thread_root (void *user STG_UNUSED, StgClosure **p)
113 {
114 thread(p);
115 }
116
117 // This version of thread() takes a (void *), used to circumvent
118 // warnings from gcc about pointer punning and strict aliasing.
119 STATIC_INLINE void thread_ (void *p) { thread((StgClosure **)p); }
120
121 STATIC_INLINE void
122 unthread( StgPtr p, StgWord free )
123 {
124 StgWord q, r;
125 StgPtr q0;
126
127 q = *p;
128 loop:
129 switch (GET_CLOSURE_TAG((StgClosure *)q))
130 {
131 case 0:
132 // nothing to do; the chain is length zero
133 return;
134 case 1:
135 q0 = (StgPtr)(q-1);
136 r = *q0; // r is the info ptr, tagged with the pointer-tag
137 *q0 = free;
138 *p = (StgWord)UNTAG_CLOSURE((StgClosure *)r);
139 return;
140 case 2:
141 q0 = (StgPtr)(q-2);
142 r = *q0;
143 *q0 = free;
144 q = r;
145 goto loop;
146 default:
147 barf("unthread");
148 }
149 }
150
151 // Traverse a threaded chain and pull out the info pointer at the end.
152 // The info pointer is also tagged with the appropriate pointer tag
153 // for this closure, which should be attached to the pointer
154 // subsequently passed to unthread().
155 STATIC_INLINE StgWord
156 get_threaded_info( StgPtr p )
157 {
158 StgWord q;
159
160 q = (W_)GET_INFO(UNTAG_CLOSURE((StgClosure *)p));
161
162 loop:
163 switch (GET_CLOSURE_TAG((StgClosure *)q))
164 {
165 case 0:
166 ASSERT(LOOKS_LIKE_INFO_PTR(q));
167 return q;
168 case 1:
169 {
170 StgWord r = *(StgPtr)(q-1);
171 ASSERT(LOOKS_LIKE_INFO_PTR((StgWord)UNTAG_CLOSURE((StgClosure *)r)));
172 return r;
173 }
174 case 2:
175 q = *(StgPtr)(q-2);
176 goto loop;
177 default:
178 barf("get_threaded_info");
179 }
180 }
181
182 // A word-aligned memmove will be faster for small objects than libc's or gcc's.
183 // Remember, the two regions *might* overlap, but: to <= from.
184 STATIC_INLINE void
185 move(StgPtr to, StgPtr from, nat size)
186 {
187 for(; size > 0; --size) {
188 *to++ = *from++;
189 }
190 }
191
192 static void
193 thread_static( StgClosure* p )
194 {
195 const StgInfoTable *info;
196
197 // keep going until we've threaded all the objects on the linked
198 // list...
199 while (p != END_OF_STATIC_LIST) {
200
201 info = get_itbl(p);
202 switch (info->type) {
203
204 case IND_STATIC:
205 thread(&((StgInd *)p)->indirectee);
206 p = *IND_STATIC_LINK(p);
207 continue;
208
209 case THUNK_STATIC:
210 p = *THUNK_STATIC_LINK(p);
211 continue;
212 case FUN_STATIC:
213 p = *FUN_STATIC_LINK(p);
214 continue;
215 case CONSTR_STATIC:
216 p = *STATIC_LINK(info,p);
217 continue;
218
219 default:
220 barf("thread_static: strange closure %d", (int)(info->type));
221 }
222
223 }
224 }
225
226 STATIC_INLINE void
227 thread_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size )
228 {
229 nat i, b;
230 StgWord bitmap;
231
232 b = 0;
233 bitmap = large_bitmap->bitmap[b];
234 for (i = 0; i < size; ) {
235 if ((bitmap & 1) == 0) {
236 thread((StgClosure **)p);
237 }
238 i++;
239 p++;
240 if (i % BITS_IN(W_) == 0) {
241 b++;
242 bitmap = large_bitmap->bitmap[b];
243 } else {
244 bitmap = bitmap >> 1;
245 }
246 }
247 }
248
249 STATIC_INLINE StgPtr
250 thread_arg_block (StgFunInfoTable *fun_info, StgClosure **args)
251 {
252 StgPtr p;
253 StgWord bitmap;
254 nat size;
255
256 p = (StgPtr)args;
257 switch (fun_info->f.fun_type) {
258 case ARG_GEN:
259 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
260 size = BITMAP_SIZE(fun_info->f.b.bitmap);
261 goto small_bitmap;
262 case ARG_GEN_BIG:
263 size = GET_FUN_LARGE_BITMAP(fun_info)->size;
264 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
265 p += size;
266 break;
267 default:
268 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
269 size = BITMAP_SIZE(stg_arg_bitmaps[fun_info->f.fun_type]);
270 small_bitmap:
271 while (size > 0) {
272 if ((bitmap & 1) == 0) {
273 thread((StgClosure **)p);
274 }
275 p++;
276 bitmap = bitmap >> 1;
277 size--;
278 }
279 break;
280 }
281 return p;
282 }
283
284 static void
285 thread_stack(StgPtr p, StgPtr stack_end)
286 {
287 const StgRetInfoTable* info;
288 StgWord bitmap;
289 nat size;
290
291 // highly similar to scavenge_stack, but we do pointer threading here.
292
293 while (p < stack_end) {
294
295 // *p must be the info pointer of an activation
296 // record. All activation records have 'bitmap' style layout
297 // info.
298 //
299 info = get_ret_itbl((StgClosure *)p);
300
301 switch (info->i.type) {
302
303 // Dynamic bitmap: the mask is stored on the stack
304 case RET_DYN:
305 {
306 StgWord dyn;
307 dyn = ((StgRetDyn *)p)->liveness;
308
309 // traverse the bitmap first
310 bitmap = RET_DYN_LIVENESS(dyn);
311 p = (P_)&((StgRetDyn *)p)->payload[0];
312 size = RET_DYN_BITMAP_SIZE;
313 while (size > 0) {
314 if ((bitmap & 1) == 0) {
315 thread((StgClosure **)p);
316 }
317 p++;
318 bitmap = bitmap >> 1;
319 size--;
320 }
321
322 // skip over the non-ptr words
323 p += RET_DYN_NONPTRS(dyn) + RET_DYN_NONPTR_REGS_SIZE;
324
325 // follow the ptr words
326 for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
327 thread((StgClosure **)p);
328 p++;
329 }
330 continue;
331 }
332
333 // small bitmap (<= 32 entries, or 64 on a 64-bit machine)
334 case CATCH_RETRY_FRAME:
335 case CATCH_STM_FRAME:
336 case ATOMICALLY_FRAME:
337 case UPDATE_FRAME:
338 case STOP_FRAME:
339 case CATCH_FRAME:
340 case RET_SMALL:
341 bitmap = BITMAP_BITS(info->i.layout.bitmap);
342 size = BITMAP_SIZE(info->i.layout.bitmap);
343 p++;
344 // NOTE: the payload starts immediately after the info-ptr, we
345 // don't have an StgHeader in the same sense as a heap closure.
346 while (size > 0) {
347 if ((bitmap & 1) == 0) {
348 thread((StgClosure **)p);
349 }
350 p++;
351 bitmap = bitmap >> 1;
352 size--;
353 }
354 continue;
355
356 case RET_BCO: {
357 StgBCO *bco;
358 nat size;
359
360 p++;
361 bco = (StgBCO *)*p;
362 thread((StgClosure **)p);
363 p++;
364 size = BCO_BITMAP_SIZE(bco);
365 thread_large_bitmap(p, BCO_BITMAP(bco), size);
366 p += size;
367 continue;
368 }
369
370 // large bitmap (> 32 entries, or 64 on a 64-bit machine)
371 case RET_BIG:
372 p++;
373 size = GET_LARGE_BITMAP(&info->i)->size;
374 thread_large_bitmap(p, GET_LARGE_BITMAP(&info->i), size);
375 p += size;
376 continue;
377
378 case RET_FUN:
379 {
380 StgRetFun *ret_fun = (StgRetFun *)p;
381 StgFunInfoTable *fun_info;
382
383 fun_info = FUN_INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)
384 get_threaded_info((StgPtr)ret_fun->fun)));
385 // *before* threading it!
386 thread(&ret_fun->fun);
387 p = thread_arg_block(fun_info, ret_fun->payload);
388 continue;
389 }
390
391 default:
392 barf("thread_stack: weird activation record found on stack: %d",
393 (int)(info->i.type));
394 }
395 }
396 }
397
398 STATIC_INLINE StgPtr
399 thread_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
400 {
401 StgPtr p;
402 StgWord bitmap;
403 StgFunInfoTable *fun_info;
404
405 fun_info = FUN_INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)
406 get_threaded_info((StgPtr)fun)));
407 ASSERT(fun_info->i.type != PAP);
408
409 p = (StgPtr)payload;
410
411 switch (fun_info->f.fun_type) {
412 case ARG_GEN:
413 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
414 goto small_bitmap;
415 case ARG_GEN_BIG:
416 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
417 p += size;
418 break;
419 case ARG_BCO:
420 thread_large_bitmap((StgPtr)payload, BCO_BITMAP(fun), size);
421 p += size;
422 break;
423 default:
424 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
425 small_bitmap:
426 while (size > 0) {
427 if ((bitmap & 1) == 0) {
428 thread((StgClosure **)p);
429 }
430 p++;
431 bitmap = bitmap >> 1;
432 size--;
433 }
434 break;
435 }
436
437 return p;
438 }
439
440 STATIC_INLINE StgPtr
441 thread_PAP (StgPAP *pap)
442 {
443 StgPtr p;
444 p = thread_PAP_payload(pap->fun, pap->payload, pap->n_args);
445 thread(&pap->fun);
446 return p;
447 }
448
449 STATIC_INLINE StgPtr
450 thread_AP (StgAP *ap)
451 {
452 StgPtr p;
453 p = thread_PAP_payload(ap->fun, ap->payload, ap->n_args);
454 thread(&ap->fun);
455 return p;
456 }
457
458 STATIC_INLINE StgPtr
459 thread_AP_STACK (StgAP_STACK *ap)
460 {
461 thread(&ap->fun);
462 thread_stack((P_)ap->payload, (P_)ap->payload + ap->size);
463 return (P_)ap + sizeofW(StgAP_STACK) + ap->size;
464 }
465
466 static StgPtr
467 thread_TSO (StgTSO *tso)
468 {
469 thread_(&tso->_link);
470 thread_(&tso->global_link);
471
472 if ( tso->why_blocked == BlockedOnMVar
473 || tso->why_blocked == BlockedOnBlackHole
474 || tso->why_blocked == BlockedOnMsgThrowTo
475 || tso->why_blocked == BlockedOnMsgWakeup
476 ) {
477 thread_(&tso->block_info.closure);
478 }
479 thread_(&tso->blocked_exceptions);
480
481 thread_(&tso->trec);
482
483 thread_stack(tso->sp, &(tso->stack[tso->stack_size]));
484 return (StgPtr)tso + tso_sizeW(tso);
485 }
486
487
488 static void
489 update_fwd_large( bdescr *bd )
490 {
491 StgPtr p;
492 const StgInfoTable* info;
493
494 for (; bd != NULL; bd = bd->link) {
495
496 // nothing to do in a pinned block; it might not even have an object
497 // at the beginning.
498 if (bd->flags & BF_PINNED) continue;
499
500 p = bd->start;
501 info = get_itbl((StgClosure *)p);
502
503 switch (info->type) {
504
505 case ARR_WORDS:
506 // nothing to follow
507 continue;
508
509 case MUT_ARR_PTRS_CLEAN:
510 case MUT_ARR_PTRS_DIRTY:
511 case MUT_ARR_PTRS_FROZEN:
512 case MUT_ARR_PTRS_FROZEN0:
513 // follow everything
514 {
515 StgMutArrPtrs *a;
516
517 a = (StgMutArrPtrs*)p;
518 for (p = (P_)a->payload; p < (P_)&a->payload[a->ptrs]; p++) {
519 thread((StgClosure **)p);
520 }
521 continue;
522 }
523
524 case TSO:
525 thread_TSO((StgTSO *)p);
526 continue;
527
528 case AP_STACK:
529 thread_AP_STACK((StgAP_STACK *)p);
530 continue;
531
532 case PAP:
533 thread_PAP((StgPAP *)p);
534 continue;
535
536 case TREC_CHUNK:
537 {
538 StgWord i;
539 StgTRecChunk *tc = (StgTRecChunk *)p;
540 TRecEntry *e = &(tc -> entries[0]);
541 thread_(&tc->prev_chunk);
542 for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
543 thread_(&e->tvar);
544 thread(&e->expected_value);
545 thread(&e->new_value);
546 }
547 continue;
548 }
549
550 default:
551 barf("update_fwd_large: unknown/strange object %d", (int)(info->type));
552 }
553 }
554 }
555
556 // ToDo: too big to inline
557 static /* STATIC_INLINE */ StgPtr
558 thread_obj (StgInfoTable *info, StgPtr p)
559 {
560 switch (info->type) {
561 case THUNK_0_1:
562 return p + sizeofW(StgThunk) + 1;
563
564 case FUN_0_1:
565 case CONSTR_0_1:
566 return p + sizeofW(StgHeader) + 1;
567
568 case FUN_1_0:
569 case CONSTR_1_0:
570 thread(&((StgClosure *)p)->payload[0]);
571 return p + sizeofW(StgHeader) + 1;
572
573 case THUNK_1_0:
574 thread(&((StgThunk *)p)->payload[0]);
575 return p + sizeofW(StgThunk) + 1;
576
577 case THUNK_0_2:
578 return p + sizeofW(StgThunk) + 2;
579
580 case FUN_0_2:
581 case CONSTR_0_2:
582 return p + sizeofW(StgHeader) + 2;
583
584 case THUNK_1_1:
585 thread(&((StgThunk *)p)->payload[0]);
586 return p + sizeofW(StgThunk) + 2;
587
588 case FUN_1_1:
589 case CONSTR_1_1:
590 thread(&((StgClosure *)p)->payload[0]);
591 return p + sizeofW(StgHeader) + 2;
592
593 case THUNK_2_0:
594 thread(&((StgThunk *)p)->payload[0]);
595 thread(&((StgThunk *)p)->payload[1]);
596 return p + sizeofW(StgThunk) + 2;
597
598 case FUN_2_0:
599 case CONSTR_2_0:
600 thread(&((StgClosure *)p)->payload[0]);
601 thread(&((StgClosure *)p)->payload[1]);
602 return p + sizeofW(StgHeader) + 2;
603
604 case BCO: {
605 StgBCO *bco = (StgBCO *)p;
606 thread_(&bco->instrs);
607 thread_(&bco->literals);
608 thread_(&bco->ptrs);
609 return p + bco_sizeW(bco);
610 }
611
612 case THUNK:
613 {
614 StgPtr end;
615
616 end = (P_)((StgThunk *)p)->payload +
617 info->layout.payload.ptrs;
618 for (p = (P_)((StgThunk *)p)->payload; p < end; p++) {
619 thread((StgClosure **)p);
620 }
621 return p + info->layout.payload.nptrs;
622 }
623
624 case FUN:
625 case CONSTR:
626 case PRIM:
627 case MUT_PRIM:
628 case IND_PERM:
629 case MUT_VAR_CLEAN:
630 case MUT_VAR_DIRTY:
631 case CAF_BLACKHOLE:
632 case BLACKHOLE:
633 {
634 StgPtr end;
635
636 end = (P_)((StgClosure *)p)->payload +
637 info->layout.payload.ptrs;
638 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
639 thread((StgClosure **)p);
640 }
641 return p + info->layout.payload.nptrs;
642 }
643
644 case WEAK:
645 {
646 StgWeak *w = (StgWeak *)p;
647 thread(&w->cfinalizer);
648 thread(&w->key);
649 thread(&w->value);
650 thread(&w->finalizer);
651 if (w->link != NULL) {
652 thread_(&w->link);
653 }
654 return p + sizeofW(StgWeak);
655 }
656
657 case MVAR_CLEAN:
658 case MVAR_DIRTY:
659 {
660 StgMVar *mvar = (StgMVar *)p;
661 thread_(&mvar->head);
662 thread_(&mvar->tail);
663 thread(&mvar->value);
664 return p + sizeofW(StgMVar);
665 }
666
667 case IND_OLDGEN:
668 case IND_OLDGEN_PERM:
669 thread(&((StgInd *)p)->indirectee);
670 return p + sizeofW(StgInd);
671
672 case THUNK_SELECTOR:
673 {
674 StgSelector *s = (StgSelector *)p;
675 thread(&s->selectee);
676 return p + THUNK_SELECTOR_sizeW();
677 }
678
679 case AP_STACK:
680 return thread_AP_STACK((StgAP_STACK *)p);
681
682 case PAP:
683 return thread_PAP((StgPAP *)p);
684
685 case AP:
686 return thread_AP((StgAP *)p);
687
688 case ARR_WORDS:
689 return p + arr_words_sizeW((StgArrWords *)p);
690
691 case MUT_ARR_PTRS_CLEAN:
692 case MUT_ARR_PTRS_DIRTY:
693 case MUT_ARR_PTRS_FROZEN:
694 case MUT_ARR_PTRS_FROZEN0:
695 // follow everything
696 {
697 StgMutArrPtrs *a;
698
699 a = (StgMutArrPtrs *)p;
700 for (p = (P_)a->payload; p < (P_)&a->payload[a->ptrs]; p++) {
701 thread((StgClosure **)p);
702 }
703
704 return (StgPtr)a + mut_arr_ptrs_sizeW(a);
705 }
706
707 case TSO:
708 return thread_TSO((StgTSO *)p);
709
710 case TREC_CHUNK:
711 {
712 StgWord i;
713 StgTRecChunk *tc = (StgTRecChunk *)p;
714 TRecEntry *e = &(tc -> entries[0]);
715 thread_(&tc->prev_chunk);
716 for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
717 thread_(&e->tvar);
718 thread(&e->expected_value);
719 thread(&e->new_value);
720 }
721 return p + sizeofW(StgTRecChunk);
722 }
723
724 default:
725 barf("update_fwd: unknown/strange object %d", (int)(info->type));
726 return NULL;
727 }
728 }
729
730 static void
731 update_fwd( bdescr *blocks )
732 {
733 StgPtr p;
734 bdescr *bd;
735 StgInfoTable *info;
736
737 bd = blocks;
738
739 // cycle through all the blocks in the step
740 for (; bd != NULL; bd = bd->link) {
741 p = bd->start;
742
743 // linearly scan the objects in this block
744 while (p < bd->free) {
745 ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
746 info = get_itbl((StgClosure *)p);
747 p = thread_obj(info, p);
748 }
749 }
750 }
751
752 static void
753 update_fwd_compact( bdescr *blocks )
754 {
755 StgPtr p, q, free;
756 #if 0
757 StgWord m;
758 #endif
759 bdescr *bd, *free_bd;
760 StgInfoTable *info;
761 nat size;
762 StgWord iptr;
763
764 bd = blocks;
765 free_bd = blocks;
766 free = free_bd->start;
767
768 // cycle through all the blocks in the step
769 for (; bd != NULL; bd = bd->link) {
770 p = bd->start;
771
772 while (p < bd->free ) {
773
774 while ( p < bd->free && !is_marked(p,bd) ) {
775 p++;
776 }
777 if (p >= bd->free) {
778 break;
779 }
780
781 #if 0
782 next:
783 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
784 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
785
786 while ( p < bd->free ) {
787
788 if ((m & 1) == 0) {
789 m >>= 1;
790 p++;
791 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
792 goto next;
793 } else {
794 continue;
795 }
796 }
797 #endif
798
799 // Problem: we need to know the destination for this cell
800 // in order to unthread its info pointer. But we can't
801 // know the destination without the size, because we may
802 // spill into the next block. So we have to run down the
803 // threaded list and get the info ptr first.
804 //
805 // ToDo: one possible avenue of attack is to use the fact
806 // that if (p&BLOCK_MASK) >= (free&BLOCK_MASK), then we
807 // definitely have enough room. Also see bug #1147.
808 iptr = get_threaded_info(p);
809 info = INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)iptr));
810
811 q = p;
812
813 p = thread_obj(info, p);
814
815 size = p - q;
816 if (free + size > free_bd->start + BLOCK_SIZE_W) {
817 // set the next bit in the bitmap to indicate that
818 // this object needs to be pushed into the next
819 // block. This saves us having to run down the
820 // threaded info pointer list twice during the next pass.
821 mark(q+1,bd);
822 free_bd = free_bd->link;
823 free = free_bd->start;
824 } else {
825 ASSERT(!is_marked(q+1,bd));
826 }
827
828 unthread(q,(StgWord)free + GET_CLOSURE_TAG((StgClosure *)iptr));
829 free += size;
830 #if 0
831 goto next;
832 #endif
833 }
834 }
835 }
836
837 static nat
838 update_bkwd_compact( generation *gen )
839 {
840 StgPtr p, free;
841 #if 0
842 StgWord m;
843 #endif
844 bdescr *bd, *free_bd;
845 StgInfoTable *info;
846 nat size, free_blocks;
847 StgWord iptr;
848
849 bd = free_bd = gen->old_blocks;
850 free = free_bd->start;
851 free_blocks = 1;
852
853 // cycle through all the blocks in the step
854 for (; bd != NULL; bd = bd->link) {
855 p = bd->start;
856
857 while (p < bd->free ) {
858
859 while ( p < bd->free && !is_marked(p,bd) ) {
860 p++;
861 }
862 if (p >= bd->free) {
863 break;
864 }
865
866 #if 0
867 next:
868 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
869 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
870
871 while ( p < bd->free ) {
872
873 if ((m & 1) == 0) {
874 m >>= 1;
875 p++;
876 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
877 goto next;
878 } else {
879 continue;
880 }
881 }
882 #endif
883
884 if (is_marked(p+1,bd)) {
885 // don't forget to update the free ptr in the block desc.
886 free_bd->free = free;
887 free_bd = free_bd->link;
888 free = free_bd->start;
889 free_blocks++;
890 }
891
892 iptr = get_threaded_info(p);
893 unthread(p, (StgWord)free + GET_CLOSURE_TAG((StgClosure *)iptr));
894 ASSERT(LOOKS_LIKE_INFO_PTR((StgWord)((StgClosure *)p)->header.info));
895 info = get_itbl((StgClosure *)p);
896 size = closure_sizeW_((StgClosure *)p,info);
897
898 if (free != p) {
899 move(free,p,size);
900 }
901
902 // relocate TSOs
903 if (info->type == TSO) {
904 move_TSO((StgTSO *)p, (StgTSO *)free);
905 }
906
907 free += size;
908 p += size;
909 #if 0
910 goto next;
911 #endif
912 }
913 }
914
915 // free the remaining blocks and count what's left.
916 free_bd->free = free;
917 if (free_bd->link != NULL) {
918 freeChain(free_bd->link);
919 free_bd->link = NULL;
920 }
921
922 return free_blocks;
923 }
924
925 void
926 compact(StgClosure *static_objects)
927 {
928 nat g, blocks;
929 generation *gen;
930
931 // 1. thread the roots
932 markCapabilities((evac_fn)thread_root, NULL);
933
934 // the weak pointer lists...
935 if (weak_ptr_list != NULL) {
936 thread((void *)&weak_ptr_list);
937 }
938 if (old_weak_ptr_list != NULL) {
939 thread((void *)&old_weak_ptr_list); // tmp
940 }
941
942 // mutable lists
943 for (g = 1; g < RtsFlags.GcFlags.generations; g++) {
944 bdescr *bd;
945 StgPtr p;
946 nat n;
947 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
948 for (p = bd->start; p < bd->free; p++) {
949 thread((StgClosure **)p);
950 }
951 }
952 for (n = 0; n < n_capabilities; n++) {
953 for (bd = capabilities[n].mut_lists[g];
954 bd != NULL; bd = bd->link) {
955 for (p = bd->start; p < bd->free; p++) {
956 thread((StgClosure **)p);
957 }
958 }
959 }
960 }
961
962 // the global thread list
963 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
964 thread((void *)&generations[g].threads);
965 }
966
967 // any threads resurrected during this GC
968 thread((void *)&resurrected_threads);
969
970 // the blackhole queue
971 thread((void *)&blackhole_queue);
972
973 // the task list
974 {
975 Task *task;
976 InCall *incall;
977 for (task = all_tasks; task != NULL; task = task->all_link) {
978 for (incall = task->incall; incall != NULL;
979 incall = incall->prev_stack) {
980 if (incall->tso) {
981 thread_(&incall->tso);
982 }
983 }
984 }
985 }
986
987 // the static objects
988 thread_static(static_objects /* ToDo: ok? */);
989
990 // the stable pointer table
991 threadStablePtrTable((evac_fn)thread_root, NULL);
992
993 // the CAF list (used by GHCi)
994 markCAFs((evac_fn)thread_root, NULL);
995
996 // 2. update forward ptrs
997 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
998 gen = &generations[g];
999 debugTrace(DEBUG_gc, "update_fwd: %d", g);
1000
1001 update_fwd(gen->blocks);
1002 update_fwd_large(gen->scavenged_large_objects);
1003 if (g == RtsFlags.GcFlags.generations-1 && gen->old_blocks != NULL) {
1004 debugTrace(DEBUG_gc, "update_fwd: %d (compact)", g);
1005 update_fwd_compact(gen->old_blocks);
1006 }
1007 }
1008
1009 // 3. update backward ptrs
1010 gen = oldest_gen;
1011 if (gen->old_blocks != NULL) {
1012 blocks = update_bkwd_compact(gen);
1013 debugTrace(DEBUG_gc,
1014 "update_bkwd: %d (compact, old: %d blocks, now %d blocks)",
1015 gen->no, gen->n_old_blocks, blocks);
1016 gen->n_old_blocks = blocks;
1017 }
1018 }