1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 2001-2008
5 * Compacting garbage collector
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
12 * ---------------------------------------------------------------------------*/
14 #include "PosixSource.h"
18 #include "OSThreads.h"
19 #include "BlockAlloc.h"
27 // Turn off inlining when debugging - it obfuscates things
30 # define STATIC_INLINE static
33 /* ----------------------------------------------------------------------------
34 Threading / unthreading pointers.
36 The basic idea here is to chain together all the fields pointing at
37 a particular object, with the root of the chain in the object's
38 info table field. The original contents of the info pointer goes
39 at the end of the chain.
41 Adding a new field to the chain is a matter of swapping the
42 contents of the field with the contents of the object's info table
45 To unthread the chain, we walk down it updating all the fields on
46 the chain with the new location of the object. We stop when we
47 reach the info pointer at the end.
49 The main difficulty here is that we need to be able to identify the
50 info pointer at the end of the chain. We can't use the low bits of
51 the pointer for this; they are already being used for
52 pointer-tagging. What's more, we need to retain the
53 pointer-tagging tag bits on each pointer during the
54 threading/unthreading process.
56 Our solution is as follows:
57 - an info pointer (chain length zero) is identified by having tag 0
58 - in a threaded chain of length > 0:
59 - the pointer-tagging tag bits are attached to the info pointer
60 - the first entry in the chain has tag 1
61 - second and subsequent entries in the chain have tag 2
63 This exploits the fact that the tag on each pointer to a given
64 closure is normally the same (if they are not the same, then
65 presumably the tag is not essential and it therefore doesn't matter
66 if we throw away some of the tags).
67 ------------------------------------------------------------------------- */
70 thread (StgClosure **p)
78 q = (StgPtr)UNTAG_CLOSURE(q0);
80 // It doesn't look like a closure at the moment, because the info
81 // ptr is possibly threaded:
82 // ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
84 if (HEAP_ALLOCED(q)) {
87 if (bd->flags & BF_MARKED)
90 switch (GET_CLOSURE_TAG((StgClosure *)iptr))
93 // this is the info pointer; we are creating a new chain.
94 // save the original tag at the end of the chain.
95 *p = (StgClosure *)((StgWord)iptr + GET_CLOSURE_TAG(q0));
100 // this is a chain of length 1 or more
101 *p = (StgClosure *)iptr;
110 thread_root (void *user STG_UNUSED, StgClosure **p)
115 // This version of thread() takes a (void *), used to circumvent
116 // warnings from gcc about pointer punning and strict aliasing.
117 STATIC_INLINE void thread_ (void *p) { thread((StgClosure **)p); }
120 unthread( StgPtr p, StgWord free )
127 switch (GET_CLOSURE_TAG((StgClosure *)q))
130 // nothing to do; the chain is length zero
134 r = *q0; // r is the info ptr, tagged with the pointer-tag
136 *p = (StgWord)UNTAG_CLOSURE((StgClosure *)r);
149 // Traverse a threaded chain and pull out the info pointer at the end.
150 // The info pointer is also tagged with the appropriate pointer tag
151 // for this closure, which should be attached to the pointer
152 // subsequently passed to unthread().
153 STATIC_INLINE StgWord
154 get_threaded_info( StgPtr p )
158 q = (W_)GET_INFO(UNTAG_CLOSURE((StgClosure *)p));
161 switch (GET_CLOSURE_TAG((StgClosure *)q))
164 ASSERT(LOOKS_LIKE_INFO_PTR(q));
168 StgWord r = *(StgPtr)(q-1);
169 ASSERT(LOOKS_LIKE_INFO_PTR(UNTAG_CLOSURE((StgClosure *)r)));
176 barf("get_threaded_info");
180 // A word-aligned memmove will be faster for small objects than libc's or gcc's.
181 // Remember, the two regions *might* overlap, but: to <= from.
183 move(StgPtr to, StgPtr from, nat size)
185 for(; size > 0; --size) {
191 thread_static( StgClosure* p )
193 const StgInfoTable *info;
195 // keep going until we've threaded all the objects on the linked
197 while (p != END_OF_STATIC_LIST) {
200 switch (info->type) {
203 thread(&((StgInd *)p)->indirectee);
204 p = *IND_STATIC_LINK(p);
208 p = *THUNK_STATIC_LINK(p);
211 p = *FUN_STATIC_LINK(p);
214 p = *STATIC_LINK(info,p);
218 barf("thread_static: strange closure %d", (int)(info->type));
225 thread_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size )
231 bitmap = large_bitmap->bitmap[b];
232 for (i = 0; i < size; ) {
233 if ((bitmap & 1) == 0) {
234 thread((StgClosure **)p);
238 if (i % BITS_IN(W_) == 0) {
240 bitmap = large_bitmap->bitmap[b];
242 bitmap = bitmap >> 1;
248 thread_arg_block (StgFunInfoTable *fun_info, StgClosure **args)
255 switch (fun_info->f.fun_type) {
257 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
258 size = BITMAP_SIZE(fun_info->f.b.bitmap);
261 size = GET_FUN_LARGE_BITMAP(fun_info)->size;
262 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
266 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
267 size = BITMAP_SIZE(stg_arg_bitmaps[fun_info->f.fun_type]);
270 if ((bitmap & 1) == 0) {
271 thread((StgClosure **)p);
274 bitmap = bitmap >> 1;
283 thread_stack(StgPtr p, StgPtr stack_end)
285 const StgRetInfoTable* info;
289 // highly similar to scavenge_stack, but we do pointer threading here.
291 while (p < stack_end) {
293 // *p must be the info pointer of an activation
294 // record. All activation records have 'bitmap' style layout
297 info = get_ret_itbl((StgClosure *)p);
299 switch (info->i.type) {
301 // Dynamic bitmap: the mask is stored on the stack
305 dyn = ((StgRetDyn *)p)->liveness;
307 // traverse the bitmap first
308 bitmap = RET_DYN_LIVENESS(dyn);
309 p = (P_)&((StgRetDyn *)p)->payload[0];
310 size = RET_DYN_BITMAP_SIZE;
312 if ((bitmap & 1) == 0) {
313 thread((StgClosure **)p);
316 bitmap = bitmap >> 1;
320 // skip over the non-ptr words
321 p += RET_DYN_NONPTRS(dyn) + RET_DYN_NONPTR_REGS_SIZE;
323 // follow the ptr words
324 for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
325 thread((StgClosure **)p);
331 // small bitmap (<= 32 entries, or 64 on a 64-bit machine)
332 case CATCH_RETRY_FRAME:
333 case CATCH_STM_FRAME:
334 case ATOMICALLY_FRAME:
339 bitmap = BITMAP_BITS(info->i.layout.bitmap);
340 size = BITMAP_SIZE(info->i.layout.bitmap);
342 // NOTE: the payload starts immediately after the info-ptr, we
343 // don't have an StgHeader in the same sense as a heap closure.
345 if ((bitmap & 1) == 0) {
346 thread((StgClosure **)p);
349 bitmap = bitmap >> 1;
360 thread((StgClosure **)p);
362 size = BCO_BITMAP_SIZE(bco);
363 thread_large_bitmap(p, BCO_BITMAP(bco), size);
368 // large bitmap (> 32 entries, or 64 on a 64-bit machine)
371 size = GET_LARGE_BITMAP(&info->i)->size;
372 thread_large_bitmap(p, GET_LARGE_BITMAP(&info->i), size);
378 StgRetFun *ret_fun = (StgRetFun *)p;
379 StgFunInfoTable *fun_info;
381 fun_info = FUN_INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)
382 get_threaded_info((StgPtr)ret_fun->fun)));
383 // *before* threading it!
384 thread(&ret_fun->fun);
385 p = thread_arg_block(fun_info, ret_fun->payload);
390 barf("thread_stack: weird activation record found on stack: %d",
391 (int)(info->i.type));
397 thread_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
401 StgFunInfoTable *fun_info;
403 fun_info = FUN_INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)
404 get_threaded_info((StgPtr)fun)));
405 ASSERT(fun_info->i.type != PAP);
409 switch (fun_info->f.fun_type) {
411 bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
414 thread_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size);
418 thread_large_bitmap((StgPtr)payload, BCO_BITMAP(fun), size);
422 bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
425 if ((bitmap & 1) == 0) {
426 thread((StgClosure **)p);
429 bitmap = bitmap >> 1;
439 thread_PAP (StgPAP *pap)
442 p = thread_PAP_payload(pap->fun, pap->payload, pap->n_args);
448 thread_AP (StgAP *ap)
451 p = thread_PAP_payload(ap->fun, ap->payload, ap->n_args);
457 thread_AP_STACK (StgAP_STACK *ap)
460 thread_stack((P_)ap->payload, (P_)ap->payload + ap->size);
461 return (P_)ap + sizeofW(StgAP_STACK) + ap->size;
465 thread_TSO (StgTSO *tso)
467 thread_(&tso->_link);
468 thread_(&tso->global_link);
470 if ( tso->why_blocked == BlockedOnMVar
471 || tso->why_blocked == BlockedOnBlackHole
472 || tso->why_blocked == BlockedOnException
474 thread_(&tso->block_info.closure);
476 thread_(&tso->blocked_exceptions);
480 thread_stack(tso->sp, &(tso->stack[tso->stack_size]));
481 return (StgPtr)tso + tso_sizeW(tso);
486 update_fwd_large( bdescr *bd )
489 const StgInfoTable* info;
491 for (; bd != NULL; bd = bd->link) {
493 // nothing to do in a pinned block; it might not even have an object
495 if (bd->flags & BF_PINNED) continue;
498 info = get_itbl((StgClosure *)p);
500 switch (info->type) {
506 case MUT_ARR_PTRS_CLEAN:
507 case MUT_ARR_PTRS_DIRTY:
508 case MUT_ARR_PTRS_FROZEN:
509 case MUT_ARR_PTRS_FROZEN0:
514 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
515 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
516 thread((StgClosure **)p);
522 thread_TSO((StgTSO *)p);
526 thread_AP_STACK((StgAP_STACK *)p);
530 thread_PAP((StgPAP *)p);
536 StgTRecChunk *tc = (StgTRecChunk *)p;
537 TRecEntry *e = &(tc -> entries[0]);
538 thread_(&tc->prev_chunk);
539 for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
541 thread(&e->expected_value);
542 thread(&e->new_value);
548 barf("update_fwd_large: unknown/strange object %d", (int)(info->type));
553 // ToDo: too big to inline
554 static /* STATIC_INLINE */ StgPtr
555 thread_obj (StgInfoTable *info, StgPtr p)
557 switch (info->type) {
559 return p + sizeofW(StgThunk) + 1;
563 return p + sizeofW(StgHeader) + 1;
567 thread(&((StgClosure *)p)->payload[0]);
568 return p + sizeofW(StgHeader) + 1;
571 thread(&((StgThunk *)p)->payload[0]);
572 return p + sizeofW(StgThunk) + 1;
575 return p + sizeofW(StgThunk) + 2;
579 return p + sizeofW(StgHeader) + 2;
582 thread(&((StgThunk *)p)->payload[0]);
583 return p + sizeofW(StgThunk) + 2;
587 thread(&((StgClosure *)p)->payload[0]);
588 return p + sizeofW(StgHeader) + 2;
591 thread(&((StgThunk *)p)->payload[0]);
592 thread(&((StgThunk *)p)->payload[1]);
593 return p + sizeofW(StgThunk) + 2;
597 thread(&((StgClosure *)p)->payload[0]);
598 thread(&((StgClosure *)p)->payload[1]);
599 return p + sizeofW(StgHeader) + 2;
602 StgBCO *bco = (StgBCO *)p;
603 thread_(&bco->instrs);
604 thread_(&bco->literals);
606 return p + bco_sizeW(bco);
613 end = (P_)((StgThunk *)p)->payload +
614 info->layout.payload.ptrs;
615 for (p = (P_)((StgThunk *)p)->payload; p < end; p++) {
616 thread((StgClosure **)p);
618 return p + info->layout.payload.nptrs;
632 end = (P_)((StgClosure *)p)->payload +
633 info->layout.payload.ptrs;
634 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
635 thread((StgClosure **)p);
637 return p + info->layout.payload.nptrs;
642 StgWeak *w = (StgWeak *)p;
643 thread(&w->cfinalizer);
646 thread(&w->finalizer);
647 if (w->link != NULL) {
650 return p + sizeofW(StgWeak);
656 StgMVar *mvar = (StgMVar *)p;
657 thread_(&mvar->head);
658 thread_(&mvar->tail);
659 thread(&mvar->value);
660 return p + sizeofW(StgMVar);
664 case IND_OLDGEN_PERM:
665 thread(&((StgInd *)p)->indirectee);
666 return p + sizeofW(StgInd);
670 StgSelector *s = (StgSelector *)p;
671 thread(&s->selectee);
672 return p + THUNK_SELECTOR_sizeW();
676 return thread_AP_STACK((StgAP_STACK *)p);
679 return thread_PAP((StgPAP *)p);
682 return thread_AP((StgAP *)p);
685 return p + arr_words_sizeW((StgArrWords *)p);
687 case MUT_ARR_PTRS_CLEAN:
688 case MUT_ARR_PTRS_DIRTY:
689 case MUT_ARR_PTRS_FROZEN:
690 case MUT_ARR_PTRS_FROZEN0:
695 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
696 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
697 thread((StgClosure **)p);
703 return thread_TSO((StgTSO *)p);
705 case TVAR_WATCH_QUEUE:
707 StgTVarWatchQueue *wq = (StgTVarWatchQueue *)p;
708 thread_(&wq->closure);
709 thread_(&wq->next_queue_entry);
710 thread_(&wq->prev_queue_entry);
711 return p + sizeofW(StgTVarWatchQueue);
716 StgTVar *tvar = (StgTVar *)p;
717 thread((void *)&tvar->current_value);
718 thread((void *)&tvar->first_watch_queue_entry);
719 return p + sizeofW(StgTVar);
724 StgTRecHeader *trec = (StgTRecHeader *)p;
725 thread_(&trec->enclosing_trec);
726 thread_(&trec->current_chunk);
727 thread_(&trec->invariants_to_check);
728 return p + sizeofW(StgTRecHeader);
734 StgTRecChunk *tc = (StgTRecChunk *)p;
735 TRecEntry *e = &(tc -> entries[0]);
736 thread_(&tc->prev_chunk);
737 for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
739 thread(&e->expected_value);
740 thread(&e->new_value);
742 return p + sizeofW(StgTRecChunk);
745 case ATOMIC_INVARIANT:
747 StgAtomicInvariant *invariant = (StgAtomicInvariant *)p;
748 thread_(&invariant->code);
749 thread_(&invariant->last_execution);
750 return p + sizeofW(StgAtomicInvariant);
753 case INVARIANT_CHECK_QUEUE:
755 StgInvariantCheckQueue *queue = (StgInvariantCheckQueue *)p;
756 thread_(&queue->invariant);
757 thread_(&queue->my_execution);
758 thread_(&queue->next_queue_entry);
759 return p + sizeofW(StgInvariantCheckQueue);
763 barf("update_fwd: unknown/strange object %d", (int)(info->type));
769 update_fwd( bdescr *blocks )
777 // cycle through all the blocks in the step
778 for (; bd != NULL; bd = bd->link) {
781 // linearly scan the objects in this block
782 while (p < bd->free) {
783 ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
784 info = get_itbl((StgClosure *)p);
785 p = thread_obj(info, p);
791 update_fwd_compact( bdescr *blocks )
797 bdescr *bd, *free_bd;
804 free = free_bd->start;
806 // cycle through all the blocks in the step
807 for (; bd != NULL; bd = bd->link) {
810 while (p < bd->free ) {
812 while ( p < bd->free && !is_marked(p,bd) ) {
821 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
822 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
824 while ( p < bd->free ) {
829 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
837 // Problem: we need to know the destination for this cell
838 // in order to unthread its info pointer. But we can't
839 // know the destination without the size, because we may
840 // spill into the next block. So we have to run down the
841 // threaded list and get the info ptr first.
843 // ToDo: one possible avenue of attack is to use the fact
844 // that if (p&BLOCK_MASK) >= (free&BLOCK_MASK), then we
845 // definitely have enough room. Also see bug #1147.
846 iptr = get_threaded_info(p);
847 info = INFO_PTR_TO_STRUCT(UNTAG_CLOSURE((StgClosure *)iptr));
851 p = thread_obj(info, p);
854 if (free + size > free_bd->start + BLOCK_SIZE_W) {
855 // unset the next bit in the bitmap to indicate that
856 // this object needs to be pushed into the next
857 // block. This saves us having to run down the
858 // threaded info pointer list twice during the next pass.
860 free_bd = free_bd->link;
861 free = free_bd->start;
863 ASSERT(is_marked(q+1,bd));
866 unthread(q,(StgWord)free + GET_CLOSURE_TAG((StgClosure *)iptr));
876 update_bkwd_compact( step *stp )
882 bdescr *bd, *free_bd;
884 nat size, free_blocks;
887 bd = free_bd = stp->old_blocks;
888 free = free_bd->start;
891 // cycle through all the blocks in the step
892 for (; bd != NULL; bd = bd->link) {
895 while (p < bd->free ) {
897 while ( p < bd->free && !is_marked(p,bd) ) {
906 m = * ((StgPtr)bd->u.bitmap + ((p - bd->start) / (BITS_IN(StgWord))));
907 m >>= ((p - bd->start) & (BITS_IN(StgWord) - 1));
909 while ( p < bd->free ) {
914 if (((StgWord)p & (sizeof(W_) * BITS_IN(StgWord))) == 0) {
922 if (!is_marked(p+1,bd)) {
923 // don't forget to update the free ptr in the block desc.
924 free_bd->free = free;
925 free_bd = free_bd->link;
926 free = free_bd->start;
930 iptr = get_threaded_info(p);
931 unthread(p, (StgWord)free + GET_CLOSURE_TAG((StgClosure *)iptr));
932 ASSERT(LOOKS_LIKE_INFO_PTR(((StgClosure *)p)->header.info));
933 info = get_itbl((StgClosure *)p);
934 size = closure_sizeW_((StgClosure *)p,info);
941 if (info->type == TSO) {
942 move_TSO((StgTSO *)p, (StgTSO *)free);
953 // free the remaining blocks and count what's left.
954 free_bd->free = free;
955 if (free_bd->link != NULL) {
956 freeChain(free_bd->link);
957 free_bd->link = NULL;
964 compact(StgClosure *static_objects)
969 // 1. thread the roots
970 markCapabilities((evac_fn)thread_root, NULL);
972 // the weak pointer lists...
973 if (weak_ptr_list != NULL) {
974 thread((void *)&weak_ptr_list);
976 if (old_weak_ptr_list != NULL) {
977 thread((void *)&old_weak_ptr_list); // tmp
981 for (g = 1; g < RtsFlags.GcFlags.generations; g++) {
985 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
986 for (p = bd->start; p < bd->free; p++) {
987 thread((StgClosure **)p);
990 for (n = 0; n < n_capabilities; n++) {
991 for (bd = capabilities[n].mut_lists[g];
992 bd != NULL; bd = bd->link) {
993 for (p = bd->start; p < bd->free; p++) {
994 thread((StgClosure **)p);
1000 // the global thread list
1001 for (s = 0; s < total_steps; s++) {
1002 thread((void *)&all_steps[s].threads);
1005 // any threads resurrected during this GC
1006 thread((void *)&resurrected_threads);
1008 // the blackhole queue
1009 thread((void *)&blackhole_queue);
1014 for (task = all_tasks; task != NULL; task = task->all_link) {
1016 thread_(&task->tso);
1021 // the static objects
1022 thread_static(static_objects /* ToDo: ok? */);
1024 // the stable pointer table
1025 threadStablePtrTable((evac_fn)thread_root, NULL);
1027 // the CAF list (used by GHCi)
1028 markCAFs((evac_fn)thread_root, NULL);
1030 // 2. update forward ptrs
1031 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1032 for (s = 0; s < generations[g].n_steps; s++) {
1033 if (g==0 && s ==0) continue;
1034 stp = &generations[g].steps[s];
1035 debugTrace(DEBUG_gc, "update_fwd: %d.%d",
1036 stp->gen->no, stp->no);
1038 update_fwd(stp->blocks);
1039 update_fwd_large(stp->scavenged_large_objects);
1040 if (g == RtsFlags.GcFlags.generations-1 && stp->old_blocks != NULL) {
1041 debugTrace(DEBUG_gc, "update_fwd: %d.%d (compact)",
1042 stp->gen->no, stp->no);
1043 update_fwd_compact(stp->old_blocks);
1048 // 3. update backward ptrs
1049 stp = &oldest_gen->steps[0];
1050 if (stp->old_blocks != NULL) {
1051 blocks = update_bkwd_compact(stp);
1052 debugTrace(DEBUG_gc,
1053 "update_bkwd: %d.%d (compact, old: %d blocks, now %d blocks)",
1054 stp->gen->no, stp->no,
1055 stp->n_old_blocks, blocks);
1056 stp->n_old_blocks = blocks;