1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 1998-2008
5 * Generational garbage collector: evacuation functions
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"
23 #include "MarkStack.h"
26 #include "LdvProfile.h"
28 #if defined(PROF_SPIN) && defined(THREADED_RTS) && defined(PARALLEL_GC)
29 StgWord64 whitehole_spin = 0;
32 #if defined(THREADED_RTS) && !defined(PARALLEL_GC)
33 #define evacuate(p) evacuate1(p)
34 #define HEAP_ALLOCED_GC(p) HEAP_ALLOCED(p)
37 #if !defined(PARALLEL_GC)
38 #define copy_tag_nolock(p, info, src, size, stp, tag) \
39 copy_tag(p, info, src, size, stp, tag)
42 /* Used to avoid long recursion due to selector thunks
44 #define MAX_THUNK_SELECTOR_DEPTH 16
46 static void eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool);
47 STATIC_INLINE void evacuate_large(StgPtr p);
49 /* -----------------------------------------------------------------------------
50 Allocate some space in which to copy an object.
51 -------------------------------------------------------------------------- */
54 alloc_for_copy (nat size, generation *gen)
59 /* Find out where we're going, using the handy "to" pointer in
60 * the gen of the source object. If it turns out we need to
61 * evacuate to an older generation, adjust it here (see comment
64 if (gen < gct->evac_gen) {
65 if (gct->eager_promotion) {
68 gct->failed_to_evac = rtsTrue;
72 ws = &gct->gens[gen->no];
73 // this compiles to a single mem access to gen->abs_no only
75 /* chain a new block onto the to-space for the destination gen if
79 ws->todo_free += size;
80 if (ws->todo_free > ws->todo_lim) {
81 to = todo_block_full(size, ws);
83 ASSERT(ws->todo_free >= ws->todo_bd->free && ws->todo_free <= ws->todo_lim);
88 /* -----------------------------------------------------------------------------
90 -------------------------------------------------------------------------- */
92 STATIC_INLINE GNUC_ATTR_HOT void
93 copy_tag(StgClosure **p, const StgInfoTable *info,
94 StgClosure *src, nat size, generation *gen, StgWord tag)
99 to = alloc_for_copy(size,gen);
103 for (i = 1; i < size; i++) { // unroll for small i
107 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
108 // __builtin_prefetch(to + size + 2, 1);
111 #if defined(PARALLEL_GC)
113 const StgInfoTable *new_info;
114 new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, (W_)info, MK_FORWARDING_PTR(to));
115 if (new_info != info) {
116 return evacuate(p); // does the failed_to_evac stuff
118 *p = TAG_CLOSURE(tag,(StgClosure*)to);
122 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
123 *p = TAG_CLOSURE(tag,(StgClosure*)to);
127 // We store the size of the just evacuated object in the LDV word so that
128 // the profiler can guess the position of the next object later.
129 SET_EVACUAEE_FOR_LDV(from, size);
133 #if defined(PARALLEL_GC)
135 copy_tag_nolock(StgClosure **p, const StgInfoTable *info,
136 StgClosure *src, nat size, generation *gen, StgWord tag)
141 to = alloc_for_copy(size,gen);
145 for (i = 1; i < size; i++) { // unroll for small i
149 // if somebody else reads the forwarding pointer, we better make
150 // sure there's a closure at the end of it.
152 *p = TAG_CLOSURE(tag,(StgClosure*)to);
153 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
155 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
156 // __builtin_prefetch(to + size + 2, 1);
160 // We store the size of the just evacuated object in the LDV word so that
161 // the profiler can guess the position of the next object later.
162 SET_EVACUAEE_FOR_LDV(from, size);
167 /* Special version of copy() for when we only want to copy the info
168 * pointer of an object, but reserve some padding after it. This is
169 * used to optimise evacuation of TSOs.
172 copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve,
173 nat size_to_copy, generation *gen)
179 #if defined(PARALLEL_GC)
181 info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
182 if (info == (W_)&stg_WHITEHOLE_info) {
188 if (IS_FORWARDING_PTR(info)) {
189 src->header.info = (const StgInfoTable *)info;
190 evacuate(p); // does the failed_to_evac stuff
194 info = (W_)src->header.info;
197 to = alloc_for_copy(size_to_reserve, gen);
201 for (i = 1; i < size_to_copy; i++) { // unroll for small i
206 src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(to);
207 *p = (StgClosure *)to;
210 // We store the size of the just evacuated object in the LDV word so that
211 // the profiler can guess the position of the next object later.
212 SET_EVACUAEE_FOR_LDV(from, size_to_reserve);
214 if (size_to_reserve - size_to_copy > 0)
215 LDV_FILL_SLOP(to + size_to_copy, (int)(size_to_reserve - size_to_copy));
222 /* Copy wrappers that don't tag the closure after copying */
223 STATIC_INLINE GNUC_ATTR_HOT void
224 copy(StgClosure **p, const StgInfoTable *info,
225 StgClosure *src, nat size, generation *gen)
227 copy_tag(p,info,src,size,gen,0);
230 /* -----------------------------------------------------------------------------
231 Evacuate a large object
233 This just consists of removing the object from the (doubly-linked)
234 gen->large_objects list, and linking it on to the (singly-linked)
235 gen->new_large_objects list, from where it will be scavenged later.
237 Convention: bd->flags has BF_EVACUATED set for a large object
238 that has been evacuated, or unset otherwise.
239 -------------------------------------------------------------------------- */
242 evacuate_large(StgPtr p)
245 generation *gen, *new_gen;
250 ACQUIRE_SPIN_LOCK(&gen->sync_large_objects);
252 // already evacuated?
253 if (bd->flags & BF_EVACUATED) {
254 /* Don't forget to set the gct->failed_to_evac flag if we didn't get
255 * the desired destination (see comments in evacuate()).
257 if (gen < gct->evac_gen) {
258 gct->failed_to_evac = rtsTrue;
259 TICK_GC_FAILED_PROMOTION();
261 RELEASE_SPIN_LOCK(&gen->sync_large_objects);
265 // remove from large_object list
267 bd->u.back->link = bd->link;
268 } else { // first object in the list
269 gen->large_objects = bd->link;
272 bd->link->u.back = bd->u.back;
275 /* link it on to the evacuated large object list of the destination gen
278 if (new_gen < gct->evac_gen) {
279 if (gct->eager_promotion) {
280 new_gen = gct->evac_gen;
282 gct->failed_to_evac = rtsTrue;
286 ws = &gct->gens[new_gen->no];
288 bd->flags |= BF_EVACUATED;
289 initBdescr(bd, new_gen, new_gen->to);
291 // If this is a block of pinned objects, we don't have to scan
292 // these objects, because they aren't allowed to contain any
293 // pointers. For these blocks, we skip the scavenge stage and put
294 // them straight on the scavenged_large_objects list.
295 if (bd->flags & BF_PINNED) {
296 ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS);
297 if (new_gen != gen) { ACQUIRE_SPIN_LOCK(&new_gen->sync_large_objects); }
298 dbl_link_onto(bd, &new_gen->scavenged_large_objects);
299 new_gen->n_scavenged_large_blocks += bd->blocks;
300 if (new_gen != gen) { RELEASE_SPIN_LOCK(&new_gen->sync_large_objects); }
302 bd->link = ws->todo_large_objects;
303 ws->todo_large_objects = bd;
306 RELEASE_SPIN_LOCK(&gen->sync_large_objects);
309 /* ----------------------------------------------------------------------------
312 This is called (eventually) for every live object in the system.
314 The caller to evacuate specifies a desired generation in the
315 gct->evac_gen thread-local variable. The following conditions apply to
316 evacuating an object which resides in generation M when we're
317 collecting up to generation N
319 if M >= gct->evac_gen
323 if M < gct->evac_gen evac to gct->evac_gen, step 0
325 if the object is already evacuated, then we check which generation
328 if M >= gct->evac_gen do nothing
329 if M < gct->evac_gen set gct->failed_to_evac flag to indicate that we
330 didn't manage to evacuate this object into gct->evac_gen.
335 evacuate() is the single most important function performance-wise
336 in the GC. Various things have been tried to speed it up, but as
337 far as I can tell the code generated by gcc 3.2 with -O2 is about
338 as good as it's going to get. We pass the argument to evacuate()
339 in a register using the 'regparm' attribute (see the prototype for
340 evacuate() near the top of this file).
342 Changing evacuate() to take an (StgClosure **) rather than
343 returning the new pointer seems attractive, because we can avoid
344 writing back the pointer when it hasn't changed (eg. for a static
345 object, or an object in a generation > N). However, I tried it and
346 it doesn't help. One reason is that the (StgClosure **) pointer
347 gets spilled to the stack inside evacuate(), resulting in far more
348 extra reads/writes than we save.
349 ------------------------------------------------------------------------- */
351 REGPARM1 GNUC_ATTR_HOT void
352 evacuate(StgClosure **p)
357 const StgInfoTable *info;
363 /* The tag and the pointer are split, to be merged after evacing */
364 tag = GET_CLOSURE_TAG(q);
365 q = UNTAG_CLOSURE(q);
367 ASSERTM(LOOKS_LIKE_CLOSURE_PTR(q), "invalid closure, info=%p", q->header.info);
369 if (!HEAP_ALLOCED_GC(q)) {
371 if (!major_gc) return;
374 switch (info->type) {
377 if (info->srt_bitmap != 0) {
378 if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
380 *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
381 gct->static_objects = (StgClosure *)q;
384 link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
386 (StgWord)gct->static_objects);
388 gct->static_objects = (StgClosure *)q;
396 if (info->srt_bitmap != 0 &&
397 *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
399 *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
400 gct->static_objects = (StgClosure *)q;
403 link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
405 (StgWord)gct->static_objects);
407 gct->static_objects = (StgClosure *)q;
414 /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
415 * on the CAF list, so don't do anything with it here (we'll
416 * scavenge it later).
418 if (((StgIndStatic *)q)->saved_info == NULL) {
419 if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
421 *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
422 gct->static_objects = (StgClosure *)q;
425 link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
427 (StgWord)gct->static_objects);
429 gct->static_objects = (StgClosure *)q;
437 if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
439 *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
440 gct->static_objects = (StgClosure *)q;
443 link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
445 (StgWord)gct->static_objects);
447 gct->static_objects = (StgClosure *)q;
451 /* I am assuming that static_objects pointers are not
452 * written to other objects, and thus, no need to retag. */
455 case CONSTR_NOCAF_STATIC:
456 /* no need to put these on the static linked list, they don't need
462 barf("evacuate(static): strange closure type %d", (int)(info->type));
468 if ((bd->flags & (BF_LARGE | BF_MARKED | BF_EVACUATED)) != 0) {
470 // pointer into to-space: just return it. It might be a pointer
471 // into a generation that we aren't collecting (> N), or it
472 // might just be a pointer into to-space. The latter doesn't
473 // happen often, but allowing it makes certain things a bit
474 // easier; e.g. scavenging an object is idempotent, so it's OK to
475 // have an object on the mutable list multiple times.
476 if (bd->flags & BF_EVACUATED) {
477 // We aren't copying this object, so we have to check
478 // whether it is already in the target generation. (this is
479 // the write barrier).
480 if (bd->gen < gct->evac_gen) {
481 gct->failed_to_evac = rtsTrue;
482 TICK_GC_FAILED_PROMOTION();
487 /* evacuate large objects by re-linking them onto a different list.
489 if (bd->flags & BF_LARGE) {
491 if (info->type == TSO &&
492 ((StgTSO *)q)->what_next == ThreadRelocated) {
493 q = (StgClosure *)((StgTSO *)q)->_link;
497 evacuate_large((P_)q);
501 /* If the object is in a gen that we're compacting, then we
502 * need to use an alternative evacuate procedure.
504 if (!is_marked((P_)q,bd)) {
506 push_mark_stack((P_)q);
513 info = q->header.info;
514 if (IS_FORWARDING_PTR(info))
516 /* Already evacuated, just return the forwarding address.
517 * HOWEVER: if the requested destination generation (gct->evac_gen) is
518 * older than the actual generation (because the object was
519 * already evacuated to a younger generation) then we have to
520 * set the gct->failed_to_evac flag to indicate that we couldn't
521 * manage to promote the object to the desired generation.
524 * Optimisation: the check is fairly expensive, but we can often
525 * shortcut it if either the required generation is 0, or the
526 * current object (the EVACUATED) is in a high enough generation.
527 * We know that an EVACUATED always points to an object in the
528 * same or an older generation. gen is the lowest generation that the
529 * current object would be evacuated to, so we only do the full
530 * check if gen is too low.
532 StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
533 *p = TAG_CLOSURE(tag,e);
534 if (gen < gct->evac_gen) { // optimisation
535 if (Bdescr((P_)e)->gen < gct->evac_gen) {
536 gct->failed_to_evac = rtsTrue;
537 TICK_GC_FAILED_PROMOTION();
543 switch (INFO_PTR_TO_STRUCT(info)->type) {
552 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen);
555 // For ints and chars of low value, save space by replacing references to
556 // these with closures with references to common, shared ones in the RTS.
558 // * Except when compiling into Windows DLLs which don't support cross-package
559 // data references very well.
563 #if defined(__PIC__) && defined(mingw32_HOST_OS)
564 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen,tag);
566 StgWord w = (StgWord)q->payload[0];
567 if (info == Czh_con_info &&
568 // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
569 (StgChar)w <= MAX_CHARLIKE) {
570 *p = TAG_CLOSURE(tag,
571 (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
574 else if (info == Izh_con_info &&
575 (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
576 *p = TAG_CLOSURE(tag,
577 (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
581 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen,tag);
590 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen,tag);
595 copy(p,info,q,sizeofW(StgThunk)+1,gen);
601 #ifdef NO_PROMOTE_THUNKS
604 copy(p,info,q,sizeofW(StgThunk)+2,gen);
612 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,gen,tag);
616 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,gen,tag);
620 copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen);
625 case IND_OLDGEN_PERM:
627 copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen,tag);
633 const StgInfoTable *i;
634 r = ((StgInd*)q)->indirectee;
635 if (GET_CLOSURE_TAG(r) == 0) {
637 if (IS_FORWARDING_PTR(i)) {
638 r = (StgClosure *)UN_FORWARDING_PTR(i);
641 if (i == &stg_TSO_info
642 || i == &stg_WHITEHOLE_info
643 || i == &stg_BLOCKING_QUEUE_CLEAN_info
644 || i == &stg_BLOCKING_QUEUE_DIRTY_info) {
645 copy(p,info,q,sizeofW(StgInd),gen);
648 ASSERT(i != &stg_IND_info);
659 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen);
663 copy(p,info,q,bco_sizeW((StgBCO *)q),gen);
667 eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
672 // follow chains of indirections, don't evacuate them
673 q = ((StgInd*)q)->indirectee;
684 case CATCH_STM_FRAME:
685 case CATCH_RETRY_FRAME:
686 case ATOMICALLY_FRAME:
687 // shouldn't see these
688 barf("evacuate: stack frame at %p\n", q);
691 copy(p,info,q,pap_sizeW((StgPAP*)q),gen);
695 copy(p,info,q,ap_sizeW((StgAP*)q),gen);
699 copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),gen);
703 // just copy the block
704 copy(p,info,q,arr_words_sizeW((StgArrWords *)q),gen);
707 case MUT_ARR_PTRS_CLEAN:
708 case MUT_ARR_PTRS_DIRTY:
709 case MUT_ARR_PTRS_FROZEN:
710 case MUT_ARR_PTRS_FROZEN0:
711 // just copy the block
712 copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),gen);
717 StgTSO *tso = (StgTSO *)q;
719 /* Deal with redirected TSOs (a TSO that's had its stack enlarged).
721 if (tso->what_next == ThreadRelocated) {
722 q = (StgClosure *)tso->_link;
727 /* To evacuate a small TSO, we need to adjust the stack pointer
734 mine = copyPart(p,(StgClosure *)tso, tso_sizeW(tso),
735 sizeofW(StgTSO), gen);
737 new_tso = (StgTSO *)*p;
738 move_TSO(tso, new_tso);
739 for (r = tso->sp, s = new_tso->sp;
740 r < tso->stack+tso->stack_size;) {
749 copy(p,info,q,sizeofW(StgTRecChunk),gen);
753 barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
759 /* -----------------------------------------------------------------------------
760 Evaluate a THUNK_SELECTOR if possible.
762 p points to a THUNK_SELECTOR that we want to evaluate. The
763 result of "evaluating" it will be evacuated and a pointer to the
764 to-space closure will be returned.
766 If the THUNK_SELECTOR could not be evaluated (its selectee is still
767 a THUNK, for example), then the THUNK_SELECTOR itself will be
769 -------------------------------------------------------------------------- */
771 unchain_thunk_selectors(StgSelector *p, StgClosure *val)
778 ASSERT(p->header.info == &stg_WHITEHOLE_info);
779 // val must be in to-space. Not always: when we recursively
780 // invoke eval_thunk_selector(), the recursive calls will not
781 // evacuate the value (because we want to select on the value,
782 // not evacuate it), so in this case val is in from-space.
783 // ASSERT(!HEAP_ALLOCED_GC(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED));
785 prev = (StgSelector*)((StgClosure *)p)->payload[0];
787 // Update the THUNK_SELECTOR with an indirection to the
788 // value. The value is still in from-space at this stage.
790 // (old note: Why not do upd_evacuee(q,p)? Because we have an
791 // invariant that an EVACUATED closure always points to an
792 // object in the same or an older generation (required by
793 // the short-cut test in the EVACUATED case, below).
794 if ((StgClosure *)p == val) {
795 // must be a loop; just leave a BLACKHOLE in place. This
796 // can happen when we have a chain of selectors that
797 // eventually loops back on itself. We can't leave an
798 // indirection pointing to itself, and we want the program
799 // to deadlock if it ever enters this closure, so
800 // BLACKHOLE is correct.
802 // XXX we do not have BLACKHOLEs any more; replace with
803 // a THUNK_SELECTOR again. This will go into a loop if it is
804 // entered, and should result in a NonTermination exception.
805 ((StgThunk *)p)->payload[0] = val;
807 SET_INFO(p, &stg_sel_0_upd_info);
809 ((StgInd *)p)->indirectee = val;
811 SET_INFO(p, &stg_IND_info);
814 // For the purposes of LDV profiling, we have created an
816 LDV_RECORD_CREATE(p);
823 eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac)
824 // NB. for legacy reasons, p & q are swapped around :(
829 StgClosure *selectee;
830 StgSelector *prev_thunk_selector;
834 prev_thunk_selector = NULL;
835 // this is a chain of THUNK_SELECTORs that we are going to update
836 // to point to the value of the current THUNK_SELECTOR. Each
837 // closure on the chain is a WHITEHOLE, and points to the next in the
838 // chain with payload[0].
842 bd = Bdescr((StgPtr)p);
843 if (HEAP_ALLOCED_GC(p)) {
844 // If the THUNK_SELECTOR is in to-space or in a generation that we
845 // are not collecting, then bale out early. We won't be able to
846 // save any space in any case, and updating with an indirection is
847 // trickier in a non-collected gen: we would have to update the
849 if (bd->flags & BF_EVACUATED) {
850 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
851 *q = (StgClosure *)p;
852 // shortcut, behave as for: if (evac) evacuate(q);
853 if (evac && bd->gen < gct->evac_gen) {
854 gct->failed_to_evac = rtsTrue;
855 TICK_GC_FAILED_PROMOTION();
859 // we don't update THUNK_SELECTORS in the compacted
860 // generation, because compaction does not remove the INDs
861 // that result, this causes confusion later
862 // (scavenge_mark_stack doesn't deal with IND). BEWARE! This
863 // bit is very tricky to get right. If you make changes
864 // around here, test by compiling stage 3 with +RTS -c -RTS.
865 if (bd->flags & BF_MARKED) {
866 // must call evacuate() to mark this closure if evac==rtsTrue
867 *q = (StgClosure *)p;
868 if (evac) evacuate(q);
869 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
875 // WHITEHOLE the selector thunk, since it is now under evaluation.
876 // This is important to stop us going into an infinite loop if
877 // this selector thunk eventually refers to itself.
878 #if defined(THREADED_RTS)
879 // In threaded mode, we'll use WHITEHOLE to lock the selector
880 // thunk while we evaluate it.
883 info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info);
884 } while (info_ptr == (W_)&stg_WHITEHOLE_info);
886 // make sure someone else didn't get here first...
887 if (IS_FORWARDING_PTR(info_ptr) ||
888 INFO_PTR_TO_STRUCT(info_ptr)->type != THUNK_SELECTOR) {
889 // v. tricky now. The THUNK_SELECTOR has been evacuated
890 // by another thread, and is now either a forwarding ptr or IND.
891 // We need to extract ourselves from the current situation
892 // as cleanly as possible.
893 // - unlock the closure
894 // - update *q, we may have done *some* evaluation
895 // - if evac, we need to call evacuate(), because we
896 // need the write-barrier stuff.
897 // - undo the chain we've built to point to p.
898 SET_INFO(p, (const StgInfoTable *)info_ptr);
899 *q = (StgClosure *)p;
900 if (evac) evacuate(q);
901 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
906 // Save the real info pointer (NOTE: not the same as get_itbl()).
907 info_ptr = (StgWord)p->header.info;
908 SET_INFO(p,&stg_WHITEHOLE_info);
911 field = INFO_PTR_TO_STRUCT(info_ptr)->layout.selector_offset;
913 // The selectee might be a constructor closure,
914 // so we untag the pointer.
915 selectee = UNTAG_CLOSURE(p->selectee);
918 // selectee now points to the closure that we're trying to select
919 // a field from. It may or may not be in to-space: we try not to
920 // end up in to-space, but it's impractical to avoid it in
921 // general. The compacting GC scatters to-space pointers in
922 // from-space during marking, for example. We rely on the property
923 // that evacuate() doesn't mind if it gets passed a to-space pointer.
925 info = (StgInfoTable*)selectee->header.info;
927 if (IS_FORWARDING_PTR(info)) {
928 // We don't follow pointers into to-space; the constructor
929 // has already been evacuated, so we won't save any space
930 // leaks by evaluating this selector thunk anyhow.
934 info = INFO_PTR_TO_STRUCT(info);
935 switch (info->type) {
937 goto bale_out; // about to be evacuated by another thread (or a loop).
946 case CONSTR_NOCAF_STATIC:
948 // check that the size is in range
949 ASSERT(field < (StgWord32)(info->layout.payload.ptrs +
950 info->layout.payload.nptrs));
952 // Select the right field from the constructor
953 val = selectee->payload[field];
956 // For the purposes of LDV profiling, we have destroyed
957 // the original selector thunk, p.
958 SET_INFO(p, (StgInfoTable *)info_ptr);
959 LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC((StgClosure *)p);
960 SET_INFO(p, &stg_WHITEHOLE_info);
963 // the closure in val is now the "value" of the
964 // THUNK_SELECTOR in p. However, val may itself be a
965 // THUNK_SELECTOR, in which case we want to continue
966 // evaluating until we find the real value, and then
967 // update the whole chain to point to the value.
969 info_ptr = (StgWord)UNTAG_CLOSURE(val)->header.info;
970 if (!IS_FORWARDING_PTR(info_ptr))
972 info = INFO_PTR_TO_STRUCT(info_ptr);
973 switch (info->type) {
977 case IND_OLDGEN_PERM:
979 val = ((StgInd *)val)->indirectee;
982 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
983 prev_thunk_selector = p;
984 p = (StgSelector*)val;
990 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
991 prev_thunk_selector = p;
995 // update the other selectors in the chain *before*
996 // evacuating the value. This is necessary in the case
997 // where the value turns out to be one of the selectors
998 // in the chain (i.e. we have a loop), and evacuating it
999 // would corrupt the chain.
1000 unchain_thunk_selectors(prev_thunk_selector, val);
1002 // evacuate() cannot recurse through
1003 // eval_thunk_selector(), because we know val is not
1004 // a THUNK_SELECTOR.
1005 if (evac) evacuate(q);
1012 case IND_OLDGEN_PERM:
1014 // Again, we might need to untag a constructor.
1015 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
1021 const StgInfoTable *i;
1022 r = ((StgInd*)selectee)->indirectee;
1024 // establish whether this BH has been updated, and is now an
1025 // indirection, as in evacuate().
1026 if (GET_CLOSURE_TAG(r) == 0) {
1028 if (IS_FORWARDING_PTR(i)) {
1029 r = (StgClosure *)UN_FORWARDING_PTR(i);
1032 if (i == &stg_TSO_info
1033 || i == &stg_WHITEHOLE_info
1034 || i == &stg_BLOCKING_QUEUE_CLEAN_info
1035 || i == &stg_BLOCKING_QUEUE_DIRTY_info) {
1038 ASSERT(i != &stg_IND_info);
1041 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
1045 case THUNK_SELECTOR:
1049 // recursively evaluate this selector. We don't want to
1050 // recurse indefinitely, so we impose a depth bound.
1051 if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) {
1055 gct->thunk_selector_depth++;
1056 // rtsFalse says "don't evacuate the result". It will,
1057 // however, update any THUNK_SELECTORs that are evaluated
1059 eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse);
1060 gct->thunk_selector_depth--;
1062 // did we actually manage to evaluate it?
1063 if (val == selectee) goto bale_out;
1065 // Of course this pointer might be tagged...
1066 selectee = UNTAG_CLOSURE(val);
1079 // not evaluated yet
1083 barf("eval_thunk_selector: strange selectee %d",
1088 // We didn't manage to evaluate this thunk; restore the old info
1089 // pointer. But don't forget: we still need to evacuate the thunk itself.
1090 SET_INFO(p, (const StgInfoTable *)info_ptr);
1091 // THREADED_RTS: we just unlocked the thunk, so another thread
1092 // might get in and update it. copy() will lock it again and
1093 // check whether it was updated in the meantime.
1094 *q = (StgClosure *)p;
1096 copy(q,(const StgInfoTable *)info_ptr,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->dest);
1098 unchain_thunk_selectors(prev_thunk_selector, *q);