1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 2001
5 * Compacting garbage collector
7 * ---------------------------------------------------------------------------*/
9 #include "PosixSource.h"
13 #include "OSThreads.h"
15 #include "BlockAlloc.h"
17 #include "GCCompact.h"
21 // Turn off inlining when debugging - it obfuscates things
24 # define STATIC_INLINE static
27 /* -----------------------------------------------------------------------------
28 Threading / unthreading pointers.
30 The basic idea here is to chain together all the fields pointing at
31 a particular object, with the root of the chain in the object's
32 info table field. The original contents of the info pointer goes
33 at the end of the chain.
35 Adding a new field to the chain is a matter of swapping the
36 contents of the field with the contents of the object's info table
39 To unthread the chain, we walk down it updating all the fields on
40 the chain with the new location of the object. We stop when we
41 reach the info pointer at the end.
43 We use a trick to identify the info pointer: when swapping pointers
44 for threading, we set the low bit of the original pointer, with the
45 result that all the pointers in the chain have their low bits set
46 except for the info pointer.
47 -------------------------------------------------------------------------- */
52 StgPtr q = (StgPtr)*p;
55 // It doesn't look like a closure at the moment, because the info
56 // ptr is possibly threaded:
57 // ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
59 if (HEAP_ALLOCED(q)) {
61 // a handy way to discover whether the ptr is into the
62 // compacted area of the old gen, is that the EVACUATED flag
63 // is zero (it's non-zero for all the other areas of live
65 if ((bd->flags & BF_EVACUATED) == 0) {
67 *q = (StgWord)p + 1; // set the low bit
73 unthread( StgPtr p, StgPtr free )
77 while ((q & 1) != 0) {
78 q -= 1; // unset the low bit again
80 *((StgPtr)q) = (StgWord)free;
86 STATIC_INLINE StgInfoTable *
87 get_threaded_info( StgPtr p )
89 StgPtr q = (P_)GET_INFO((StgClosure *)p);
91 while (((StgWord)q & 1) != 0) {
92 q = (P_)*((StgPtr)((StgWord)q-1));
95 ASSERT(LOOKS_LIKE_INFO_PTR(q));
96 return INFO_PTR_TO_STRUCT((StgInfoTable *)q);
99 // A word-aligned memmove will be faster for small objects than libc's or gcc's.
100 // Remember, the two regions *might* overlap, but: to <= from.
102 move(StgPtr to, StgPtr from, nat size)
104 for(; size > 0; --size) {
110 obj_sizeW( StgClosure *p, StgInfoTable *info )
112 switch (info->type) {
115 return sizeofW(StgThunk) + 1;
120 return sizeofW(StgHeader) + 1;
124 return sizeofW(StgThunk) + 2;
131 return sizeofW(StgHeader) + 2;
133 return THUNK_SELECTOR_sizeW();
135 return ap_stack_sizeW((StgAP_STACK *)p);
138 return pap_sizeW((StgPAP *)p);
140 return arr_words_sizeW((StgArrWords *)p);
142 case MUT_ARR_PTRS_FROZEN:
143 case MUT_ARR_PTRS_FROZEN0:
144 return mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
146 return tso_sizeW((StgTSO *)p);
148 return bco_sizeW((StgBCO *)p);
149 case TVAR_WAIT_QUEUE:
150 return sizeofW(StgTVarWaitQueue);
152 return sizeofW(StgTVar);
154 return sizeofW(StgTRecChunk);
156 return sizeofW(StgTRecHeader);
158 return sizeW_fromITBL(info);
163 thread_static( StgClosure* p )
165 const StgInfoTable *info;
167 // keep going until we've threaded all the objects on the linked
169 while (p != END_OF_STATIC_LIST) {
172 switch (info->type) {
175 thread((StgPtr)&((StgInd *)p)->indirectee);
176 p = *IND_STATIC_LINK(p);
180 p = *THUNK_STATIC_LINK(p);
183 p = *FUN_STATIC_LINK(p);
186 p = *STATIC_LINK(info,p);
190 barf("thread_static: strange closure %d", (int)(info->type));
197 thread_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size )
203 bitmap = large_bitmap->bitmap[b];
204 for (i = 0; i < size; ) {
205 if ((bitmap & 1) == 0) {
210 if (i % BITS_IN(W_) == 0) {
212 bitmap = large_bitmap->bitmap[b];
214 bitmap = bitmap >> 1;
220 thread_arg_block (StgFunInfoTable *fun_info, StgClosure **args)
227 switch (fun_info->f.fun_type) {
229 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
230 size = BITMAP_SIZE(fun_info->f.b.bitmap);
233 size = GET_FUN_LARGE_BITMAP(fun_info)->size;
234 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
238 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
239 size = BITMAP_SIZE(stg_arg_bitmaps[fun_info->f.fun_type]);
242 if ((bitmap & 1) == 0) {
246 bitmap = bitmap >> 1;
255 thread_stack(StgPtr p, StgPtr stack_end)
257 const StgRetInfoTable* info;
261 // highly similar to scavenge_stack, but we do pointer threading here.
263 while (p < stack_end) {
265 // *p must be the info pointer of an activation
266 // record. All activation records have 'bitmap' style layout
269 info = get_ret_itbl((StgClosure *)p);
271 switch (info->i.type) {
273 // Dynamic bitmap: the mask is stored on the stack
277 dyn = ((StgRetDyn *)p)->liveness;
279 // traverse the bitmap first
280 bitmap = RET_DYN_LIVENESS(dyn);
281 p = (P_)&((StgRetDyn *)p)->payload[0];
282 size = RET_DYN_BITMAP_SIZE;
284 if ((bitmap & 1) == 0) {
288 bitmap = bitmap >> 1;
292 // skip over the non-ptr words
293 p += RET_DYN_NONPTRS(dyn) + RET_DYN_NONPTR_REGS_SIZE;
295 // follow the ptr words
296 for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
303 // small bitmap (<= 32 entries, or 64 on a 64-bit machine)
304 case CATCH_RETRY_FRAME:
305 case CATCH_STM_FRAME:
306 case ATOMICALLY_FRAME:
312 bitmap = BITMAP_BITS(info->i.layout.bitmap);
313 size = BITMAP_SIZE(info->i.layout.bitmap);
315 // NOTE: the payload starts immediately after the info-ptr, we
316 // don't have an StgHeader in the same sense as a heap closure.
318 if ((bitmap & 1) == 0) {
322 bitmap = bitmap >> 1;
335 size = BCO_BITMAP_SIZE(bco);
336 thread_large_bitmap(p, BCO_BITMAP(bco), size);
341 // large bitmap (> 32 entries, or 64 on a 64-bit machine)
345 size = GET_LARGE_BITMAP(&info->i)->size;
346 thread_large_bitmap(p, GET_LARGE_BITMAP(&info->i), size);
352 StgRetFun *ret_fun = (StgRetFun *)p;
353 StgFunInfoTable *fun_info;
355 fun_info = itbl_to_fun_itbl(
356 get_threaded_info((StgPtr)ret_fun->fun));
357 // *before* threading it!
358 thread((StgPtr)&ret_fun->fun);
359 p = thread_arg_block(fun_info, ret_fun->payload);
364 barf("thread_stack: weird activation record found on stack: %d",
365 (int)(info->i.type));
371 thread_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
375 StgFunInfoTable *fun_info;
377 fun_info = itbl_to_fun_itbl(get_threaded_info((StgPtr)fun));
378 ASSERT(fun_info->i.type != PAP);
382 switch (fun_info->f.fun_type) {
384 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
387 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
391 thread_large_bitmap((StgPtr)payload, BCO_BITMAP(fun), size);
395 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
398 if ((bitmap & 1) == 0) {
402 bitmap = bitmap >> 1;
412 thread_PAP (StgPAP *pap)
415 p = thread_PAP_payload(pap->fun, pap->payload, pap->n_args);
416 thread((StgPtr)&pap->fun);
421 thread_AP (StgAP *ap)
424 p = thread_PAP_payload(ap->fun, ap->payload, ap->n_args);
425 thread((StgPtr)&ap->fun);
430 thread_AP_STACK (StgAP_STACK *ap)
432 thread((StgPtr)&ap->fun);
433 thread_stack((P_)ap->payload, (P_)ap->payload + ap->size);
434 return (P_)ap + sizeofW(StgAP_STACK) + ap->size;
438 thread_TSO (StgTSO *tso)
440 thread((StgPtr)&tso->link);
441 thread((StgPtr)&tso->global_link);
443 if ( tso->why_blocked == BlockedOnMVar
444 || tso->why_blocked == BlockedOnBlackHole
445 || tso->why_blocked == BlockedOnException
447 || tso->why_blocked == BlockedOnGA
448 || tso->why_blocked == BlockedOnGA_NoSend
451 thread((StgPtr)&tso->block_info.closure);
453 if ( tso->blocked_exceptions != NULL ) {
454 thread((StgPtr)&tso->blocked_exceptions);
457 thread((StgPtr)&tso->trec);
459 thread_stack(tso->sp, &(tso->stack[tso->stack_size]));
460 return (StgPtr)tso + tso_sizeW(tso);
465 update_fwd_large( bdescr *bd )
468 const StgInfoTable* info;
470 for (; bd != NULL; bd = bd->link) {
473 info = get_itbl((StgClosure *)p);
475 switch (info->type) {
482 case MUT_ARR_PTRS_FROZEN:
483 case MUT_ARR_PTRS_FROZEN0:
488 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
489 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
496 thread_TSO((StgTSO *)p);
500 thread_AP_STACK((StgAP_STACK *)p);
504 thread_PAP((StgPAP *)p);
508 barf("update_fwd_large: unknown/strange object %d", (int)(info->type));
514 thread_obj (StgInfoTable *info, StgPtr p)
516 switch (info->type) {
518 return p + sizeofW(StgThunk) + 1;
522 return p + sizeofW(StgHeader) + 1;
526 thread((StgPtr)&((StgClosure *)p)->payload[0]);
527 return p + sizeofW(StgHeader) + 1;
530 thread((StgPtr)&((StgThunk *)p)->payload[0]);
531 return p + sizeofW(StgThunk) + 1;
534 return p + sizeofW(StgThunk) + 2;
538 return p + sizeofW(StgHeader) + 2;
541 thread((StgPtr)&((StgThunk *)p)->payload[0]);
542 return p + sizeofW(StgThunk) + 2;
546 thread((StgPtr)&((StgClosure *)p)->payload[0]);
547 return p + sizeofW(StgHeader) + 2;
550 thread((StgPtr)&((StgThunk *)p)->payload[0]);
551 thread((StgPtr)&((StgThunk *)p)->payload[1]);
552 return p + sizeofW(StgThunk) + 2;
556 thread((StgPtr)&((StgClosure *)p)->payload[0]);
557 thread((StgPtr)&((StgClosure *)p)->payload[1]);
558 return p + sizeofW(StgHeader) + 2;
561 StgBCO *bco = (StgBCO *)p;
562 thread((StgPtr)&bco->instrs);
563 thread((StgPtr)&bco->literals);
564 thread((StgPtr)&bco->ptrs);
565 thread((StgPtr)&bco->itbls);
566 return p + bco_sizeW(bco);
573 end = (P_)((StgThunk *)p)->payload +
574 info->layout.payload.ptrs;
575 for (p = (P_)((StgThunk *)p)->payload; p < end; p++) {
578 return p + info->layout.payload.nptrs;
588 case SE_CAF_BLACKHOLE:
594 end = (P_)((StgClosure *)p)->payload +
595 info->layout.payload.ptrs;
596 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
599 return p + info->layout.payload.nptrs;
604 StgWeak *w = (StgWeak *)p;
605 thread((StgPtr)&w->key);
606 thread((StgPtr)&w->value);
607 thread((StgPtr)&w->finalizer);
608 if (w->link != NULL) {
609 thread((StgPtr)&w->link);
611 return p + sizeofW(StgWeak);
616 StgMVar *mvar = (StgMVar *)p;
617 thread((StgPtr)&mvar->head);
618 thread((StgPtr)&mvar->tail);
619 thread((StgPtr)&mvar->value);
620 return p + sizeofW(StgMVar);
624 case IND_OLDGEN_PERM:
625 thread((StgPtr)&((StgInd *)p)->indirectee);
626 return p + sizeofW(StgInd);
630 StgSelector *s = (StgSelector *)p;
631 thread((StgPtr)&s->selectee);
632 return p + THUNK_SELECTOR_sizeW();
636 return thread_AP_STACK((StgAP_STACK *)p);
639 return thread_PAP((StgPAP *)p);
642 return thread_AP((StgAP *)p);
645 return p + arr_words_sizeW((StgArrWords *)p);
648 case MUT_ARR_PTRS_FROZEN:
649 case MUT_ARR_PTRS_FROZEN0:
654 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
655 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
662 return thread_TSO((StgTSO *)p);
664 case TVAR_WAIT_QUEUE:
666 StgTVarWaitQueue *wq = (StgTVarWaitQueue *)p;
667 thread((StgPtr)&wq->waiting_tso);
668 thread((StgPtr)&wq->next_queue_entry);
669 thread((StgPtr)&wq->prev_queue_entry);
670 return p + sizeofW(StgTVarWaitQueue);
675 StgTVar *tvar = (StgTVar *)p;
676 thread((StgPtr)&tvar->current_value);
677 thread((StgPtr)&tvar->first_wait_queue_entry);
678 thread((StgPtr)&tvar->last_update_by);
679 return p + sizeofW(StgTVar);
684 StgTRecHeader *trec = (StgTRecHeader *)p;
685 thread((StgPtr)&trec->enclosing_trec);
686 thread((StgPtr)&trec->current_chunk);
687 return p + sizeofW(StgTRecHeader);
693 StgTRecChunk *tc = (StgTRecChunk *)p;
694 TRecEntry *e = &(tc -> entries[0]);
695 thread((StgPtr)&tc->prev_chunk);
696 for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
697 thread((StgPtr)&e->tvar);
698 thread((StgPtr)&e->expected_value);
699 thread((StgPtr)&e->new_value);
701 return p + sizeofW(StgTRecChunk);
705 barf("update_fwd: unknown/strange object %d", (int)(info->type));
711 update_fwd( bdescr *blocks )
720 barf("update_fwd: ToDo");
723 // cycle through all the blocks in the step
724 for (; bd != NULL; bd = bd->link) {
727 // linearly scan the objects in this block
728 while (p < bd->free) {
729 ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
730 info = get_itbl((StgClosure *)p);
731 p = thread_obj(info, p);
737 update_fwd_compact( bdescr *blocks )
743 bdescr *bd, *free_bd;
749 free = free_bd->start;
752 barf("update_fwd: ToDo");
755 // cycle through all the blocks in the step
756 for (; bd != NULL; bd = bd->link) {
759 while (p < bd->free ) {
761 while ( p < bd->free && !is_marked(p,bd) ) {
770 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
771 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
773 while ( p < bd->free ) {
778 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
786 // Problem: we need to know the destination for this cell
787 // in order to unthread its info pointer. But we can't
788 // know the destination without the size, because we may
789 // spill into the next block. So we have to run down the
790 // threaded list and get the info ptr first.
791 info = get_threaded_info(p);
795 p = thread_obj(info, p);
798 if (free + size > free_bd->start + BLOCK_SIZE_W) {
799 // unset the next bit in the bitmap to indicate that
800 // this object needs to be pushed into the next
801 // block. This saves us having to run down the
802 // threaded info pointer list twice during the next pass.
804 free_bd = free_bd->link;
805 free = free_bd->start;
807 ASSERT(is_marked(q+1,bd));
820 update_bkwd_compact( step *stp )
826 bdescr *bd, *free_bd;
828 nat size, free_blocks;
830 bd = free_bd = stp->blocks;
831 free = free_bd->start;
835 barf("update_bkwd: ToDo");
838 // cycle through all the blocks in the step
839 for (; bd != NULL; bd = bd->link) {
842 while (p < bd->free ) {
844 while ( p < bd->free && !is_marked(p,bd) ) {
853 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
854 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
856 while ( p < bd->free ) {
861 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
869 if (!is_marked(p+1,bd)) {
870 // don't forget to update the free ptr in the block desc.
871 free_bd->free = free;
872 free_bd = free_bd->link;
873 free = free_bd->start;
878 ASSERT(LOOKS_LIKE_INFO_PTR(((StgClosure *)p)->header.info));
879 info = get_itbl((StgClosure *)p);
880 size = obj_sizeW((StgClosure *)p,info);
887 if (info->type == TSO) {
888 move_TSO((StgTSO *)p, (StgTSO *)free);
899 // free the remaining blocks and count what's left.
900 free_bd->free = free;
901 if (free_bd->link != NULL) {
902 freeChain(free_bd->link);
903 free_bd->link = NULL;
905 stp->n_blocks = free_blocks;
911 compact( void (*get_roots)(evac_fn) )
916 // 1. thread the roots
917 get_roots((evac_fn)thread);
919 // the weak pointer lists...
920 if (weak_ptr_list != NULL) {
921 thread((StgPtr)&weak_ptr_list);
923 if (old_weak_ptr_list != NULL) {
924 thread((StgPtr)&old_weak_ptr_list); // tmp
928 for (g = 1; g < RtsFlags.GcFlags.generations; g++) {
931 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
932 for (p = bd->start; p < bd->free; p++) {
938 // the global thread list
939 thread((StgPtr)&all_threads);
941 // any threads resurrected during this GC
942 thread((StgPtr)&resurrected_threads);
944 // the main threads list
947 for (m = main_threads; m != NULL; m = m->link) {
948 thread((StgPtr)&m->tso);
952 // the static objects
953 thread_static(scavenged_static_objects);
955 // the stable pointer table
956 threadStablePtrTable((evac_fn)thread);
958 // the CAF list (used by GHCi)
959 markCAFs((evac_fn)thread);
961 // 2. update forward ptrs
962 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
963 for (s = 0; s < generations[g].n_steps; s++) {
964 stp = &generations[g].steps[s];
965 IF_DEBUG(gc, debugBelch("update_fwd: %d.%d\n", stp->gen->no, stp->no););
967 update_fwd(stp->to_blocks);
968 update_fwd_large(stp->scavenged_large_objects);
969 if (g == RtsFlags.GcFlags.generations-1 && stp->blocks != NULL) {
970 IF_DEBUG(gc, debugBelch("update_fwd: %d.%d (compact)\n", stp->gen->no, stp->no););
971 update_fwd_compact(stp->blocks);
976 // 3. update backward ptrs
977 stp = &oldest_gen->steps[0];
978 if (stp->blocks != NULL) {
979 blocks = update_bkwd_compact(stp);
980 IF_DEBUG(gc, debugBelch("update_bkwd: %d.%d (compact, old: %d blocks, now %d blocks)\n",
981 stp->gen->no, stp->no,
982 stp->n_blocks, blocks););
983 stp->n_blocks = blocks;