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 * ---------------------------------------------------------------------------*/
23 #include "LdvProfile.h"
26 #if defined(PROF_SPIN) && defined(THREADED_RTS) && defined(PARALLEL_GC)
27 StgWord64 whitehole_spin = 0;
30 #if defined(THREADED_RTS) && !defined(PARALLEL_GC)
31 #define evacuate(p) evacuate1(p)
34 #if !defined(PARALLEL_GC)
35 #define copy_tag_nolock(p, info, src, size, stp, tag) \
36 copy_tag(p, info, src, size, stp, tag)
39 /* Used to avoid long recursion due to selector thunks
41 #define MAX_THUNK_SELECTOR_DEPTH 16
43 static void eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool);
44 STATIC_INLINE void evacuate_large(StgPtr p);
46 /* -----------------------------------------------------------------------------
47 Allocate some space in which to copy an object.
48 -------------------------------------------------------------------------- */
51 alloc_for_copy (nat size, step *stp)
56 /* Find out where we're going, using the handy "to" pointer in
57 * the step of the source object. If it turns out we need to
58 * evacuate to an older generation, adjust it here (see comment
61 if (stp < gct->evac_step) {
62 if (gct->eager_promotion) {
65 gct->failed_to_evac = rtsTrue;
69 ws = &gct->steps[stp->abs_no];
70 // this compiles to a single mem access to stp->abs_no only
72 /* chain a new block onto the to-space for the destination step if
76 if (to + size > ws->todo_lim) {
77 to = todo_block_full(size, ws);
79 ws->todo_free = to + size;
80 ASSERT(ws->todo_free >= ws->todo_bd->free && ws->todo_free <= ws->todo_lim);
85 /* -----------------------------------------------------------------------------
87 -------------------------------------------------------------------------- */
89 STATIC_INLINE GNUC_ATTR_HOT void
90 copy_tag(StgClosure **p, const StgInfoTable *info,
91 StgClosure *src, nat size, step *stp, StgWord tag)
96 to = alloc_for_copy(size,stp);
98 TICK_GC_WORDS_COPIED(size);
102 for (i = 1; i < size; i++) { // unroll for small i
106 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
107 // __builtin_prefetch(to + size + 2, 1);
110 #if defined(PARALLEL_GC)
112 const StgInfoTable *new_info;
113 new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, (W_)info, MK_FORWARDING_PTR(to));
114 if (new_info != info) {
115 return evacuate(p); // does the failed_to_evac stuff
117 *p = TAG_CLOSURE(tag,(StgClosure*)to);
121 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
122 *p = TAG_CLOSURE(tag,(StgClosure*)to);
126 // We store the size of the just evacuated object in the LDV word so that
127 // the profiler can guess the position of the next object later.
128 SET_EVACUAEE_FOR_LDV(from, size);
132 #if defined(PARALLEL_GC)
134 copy_tag_nolock(StgClosure **p, const StgInfoTable *info,
135 StgClosure *src, nat size, step *stp, StgWord tag)
140 to = alloc_for_copy(size,stp);
141 *p = TAG_CLOSURE(tag,(StgClosure*)to);
142 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
144 TICK_GC_WORDS_COPIED(size);
148 for (i = 1; i < size; i++) { // unroll for small i
152 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
153 // __builtin_prefetch(to + size + 2, 1);
157 // We store the size of the just evacuated object in the LDV word so that
158 // the profiler can guess the position of the next object later.
159 SET_EVACUAEE_FOR_LDV(from, size);
164 /* Special version of copy() for when we only want to copy the info
165 * pointer of an object, but reserve some padding after it. This is
166 * used to optimise evacuation of BLACKHOLEs.
169 copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp)
175 #if defined(PARALLEL_GC)
177 info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
178 if (info == (W_)&stg_WHITEHOLE_info) {
184 if (IS_FORWARDING_PTR(info)) {
185 src->header.info = (const StgInfoTable *)info;
186 evacuate(p); // does the failed_to_evac stuff
190 info = (W_)src->header.info;
193 to = alloc_for_copy(size_to_reserve, stp);
194 *p = (StgClosure *)to;
196 TICK_GC_WORDS_COPIED(size_to_copy);
200 for (i = 1; i < size_to_copy; i++) { // unroll for small i
204 #if defined(PARALLEL_GC)
207 src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(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 - 1, (int)(size_to_reserve - size_to_copy));
220 /* Copy wrappers that don't tag the closure after copying */
221 STATIC_INLINE GNUC_ATTR_HOT void
222 copy(StgClosure **p, const StgInfoTable *info,
223 StgClosure *src, nat size, step *stp)
225 copy_tag(p,info,src,size,stp,0);
228 /* ----------------------------------------------------------------------------
231 This is called (eventually) for every live object in the system.
233 The caller to evacuate specifies a desired generation in the
234 gct->evac_step thread-local variable. The following conditions apply to
235 evacuating an object which resides in generation M when we're
236 collecting up to generation N
238 if M >= gct->evac_step
240 else evac to step->to
242 if M < gct->evac_step evac to gct->evac_step, step 0
244 if the object is already evacuated, then we check which generation
247 if M >= gct->evac_step do nothing
248 if M < gct->evac_step set gct->failed_to_evac flag to indicate that we
249 didn't manage to evacuate this object into gct->evac_step.
254 evacuate() is the single most important function performance-wise
255 in the GC. Various things have been tried to speed it up, but as
256 far as I can tell the code generated by gcc 3.2 with -O2 is about
257 as good as it's going to get. We pass the argument to evacuate()
258 in a register using the 'regparm' attribute (see the prototype for
259 evacuate() near the top of this file).
261 Changing evacuate() to take an (StgClosure **) rather than
262 returning the new pointer seems attractive, because we can avoid
263 writing back the pointer when it hasn't changed (eg. for a static
264 object, or an object in a generation > N). However, I tried it and
265 it doesn't help. One reason is that the (StgClosure **) pointer
266 gets spilled to the stack inside evacuate(), resulting in far more
267 extra reads/writes than we save.
268 ------------------------------------------------------------------------- */
270 REGPARM1 GNUC_ATTR_HOT void
271 evacuate(StgClosure **p)
276 const StgInfoTable *info;
282 /* The tag and the pointer are split, to be merged after evacing */
283 tag = GET_CLOSURE_TAG(q);
284 q = UNTAG_CLOSURE(q);
286 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
288 if (!HEAP_ALLOCED(q)) {
290 if (!major_gc) return;
293 switch (info->type) {
296 if (info->srt_bitmap != 0) {
297 if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
299 *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
300 gct->static_objects = (StgClosure *)q;
303 link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
305 (StgWord)gct->static_objects);
307 gct->static_objects = (StgClosure *)q;
315 if (info->srt_bitmap != 0 &&
316 *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
318 *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
319 gct->static_objects = (StgClosure *)q;
322 link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
324 (StgWord)gct->static_objects);
326 gct->static_objects = (StgClosure *)q;
333 /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
334 * on the CAF list, so don't do anything with it here (we'll
335 * scavenge it later).
337 if (((StgIndStatic *)q)->saved_info == NULL) {
338 if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
340 *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
341 gct->static_objects = (StgClosure *)q;
344 link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
346 (StgWord)gct->static_objects);
348 gct->static_objects = (StgClosure *)q;
356 if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
358 *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
359 gct->static_objects = (StgClosure *)q;
362 link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
364 (StgWord)gct->static_objects);
366 gct->static_objects = (StgClosure *)q;
370 /* I am assuming that static_objects pointers are not
371 * written to other objects, and thus, no need to retag. */
374 case CONSTR_NOCAF_STATIC:
375 /* no need to put these on the static linked list, they don't need
381 barf("evacuate(static): strange closure type %d", (int)(info->type));
387 if ((bd->flags & (BF_LARGE | BF_MARKED | BF_EVACUATED)) != 0) {
389 // pointer into to-space: just return it. It might be a pointer
390 // into a generation that we aren't collecting (> N), or it
391 // might just be a pointer into to-space. The latter doesn't
392 // happen often, but allowing it makes certain things a bit
393 // easier; e.g. scavenging an object is idempotent, so it's OK to
394 // have an object on the mutable list multiple times.
395 if (bd->flags & BF_EVACUATED) {
396 // We aren't copying this object, so we have to check
397 // whether it is already in the target generation. (this is
398 // the write barrier).
399 if (bd->step < gct->evac_step) {
400 gct->failed_to_evac = rtsTrue;
401 TICK_GC_FAILED_PROMOTION();
406 /* evacuate large objects by re-linking them onto a different list.
408 if (bd->flags & BF_LARGE) {
410 if (info->type == TSO &&
411 ((StgTSO *)q)->what_next == ThreadRelocated) {
412 q = (StgClosure *)((StgTSO *)q)->_link;
416 evacuate_large((P_)q);
420 /* If the object is in a step that we're compacting, then we
421 * need to use an alternative evacuate procedure.
423 if (!is_marked((P_)q,bd)) {
425 if (mark_stack_full()) {
426 debugTrace(DEBUG_gc,"mark stack overflowed");
427 mark_stack_overflowed = rtsTrue;
430 push_mark_stack((P_)q);
437 info = q->header.info;
438 if (IS_FORWARDING_PTR(info))
440 /* Already evacuated, just return the forwarding address.
441 * HOWEVER: if the requested destination generation (gct->evac_step) is
442 * older than the actual generation (because the object was
443 * already evacuated to a younger generation) then we have to
444 * set the gct->failed_to_evac flag to indicate that we couldn't
445 * manage to promote the object to the desired generation.
448 * Optimisation: the check is fairly expensive, but we can often
449 * shortcut it if either the required generation is 0, or the
450 * current object (the EVACUATED) is in a high enough generation.
451 * We know that an EVACUATED always points to an object in the
452 * same or an older generation. stp is the lowest step that the
453 * current object would be evacuated to, so we only do the full
454 * check if stp is too low.
456 StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
457 *p = TAG_CLOSURE(tag,e);
458 if (stp < gct->evac_step) { // optimisation
459 if (Bdescr((P_)e)->step < gct->evac_step) {
460 gct->failed_to_evac = rtsTrue;
461 TICK_GC_FAILED_PROMOTION();
467 switch (INFO_PTR_TO_STRUCT(info)->type) {
476 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
481 StgWord w = (StgWord)q->payload[0];
482 if (info == Czh_con_info &&
483 // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
484 (StgChar)w <= MAX_CHARLIKE) {
485 *p = TAG_CLOSURE(tag,
486 (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
489 else if (info == Izh_con_info &&
490 (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
491 *p = TAG_CLOSURE(tag,
492 (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
496 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
504 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
509 copy(p,info,q,sizeofW(StgThunk)+1,stp);
515 #ifdef NO_PROMOTE_THUNKS
516 if (bd->gen_no == 0 &&
518 bd->step->no == generations[bd->gen_no].n_steps-1) {
522 copy(p,info,q,sizeofW(StgThunk)+2,stp);
530 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
534 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
538 copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
543 case IND_OLDGEN_PERM:
545 copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
550 copy_tag(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
554 copy(p,info,q,bco_sizeW((StgBCO *)q),stp);
558 case SE_CAF_BLACKHOLE:
561 copyPart(p,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
565 eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
570 // follow chains of indirections, don't evacuate them
571 q = ((StgInd*)q)->indirectee;
582 case CATCH_STM_FRAME:
583 case CATCH_RETRY_FRAME:
584 case ATOMICALLY_FRAME:
585 // shouldn't see these
586 barf("evacuate: stack frame at %p\n", q);
589 copy(p,info,q,pap_sizeW((StgPAP*)q),stp);
593 copy(p,info,q,ap_sizeW((StgAP*)q),stp);
597 copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),stp);
601 // just copy the block
602 copy(p,info,q,arr_words_sizeW((StgArrWords *)q),stp);
605 case MUT_ARR_PTRS_CLEAN:
606 case MUT_ARR_PTRS_DIRTY:
607 case MUT_ARR_PTRS_FROZEN:
608 case MUT_ARR_PTRS_FROZEN0:
609 // just copy the block
610 copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),stp);
615 StgTSO *tso = (StgTSO *)q;
617 /* Deal with redirected TSOs (a TSO that's had its stack enlarged).
619 if (tso->what_next == ThreadRelocated) {
620 q = (StgClosure *)tso->_link;
625 /* To evacuate a small TSO, we need to relocate the update frame
632 copyPart(p,(StgClosure *)tso, tso_sizeW(tso), sizeofW(StgTSO), stp);
633 new_tso = (StgTSO *)*p;
634 move_TSO(tso, new_tso);
635 for (r = tso->sp, s = new_tso->sp;
636 r < tso->stack+tso->stack_size;) {
644 copy(p,info,q,sizeofW(StgTRecHeader),stp);
647 case TVAR_WATCH_QUEUE:
648 copy(p,info,q,sizeofW(StgTVarWatchQueue),stp);
652 copy(p,info,q,sizeofW(StgTVar),stp);
656 copy(p,info,q,sizeofW(StgTRecChunk),stp);
659 case ATOMIC_INVARIANT:
660 copy(p,info,q,sizeofW(StgAtomicInvariant),stp);
663 case INVARIANT_CHECK_QUEUE:
664 copy(p,info,q,sizeofW(StgInvariantCheckQueue),stp);
668 barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
674 /* -----------------------------------------------------------------------------
675 Evacuate a large object
677 This just consists of removing the object from the (doubly-linked)
678 step->large_objects list, and linking it on to the (singly-linked)
679 step->new_large_objects list, from where it will be scavenged later.
681 Convention: bd->flags has BF_EVACUATED set for a large object
682 that has been evacuated, or unset otherwise.
683 -------------------------------------------------------------------------- */
686 evacuate_large(StgPtr p)
688 bdescr *bd = Bdescr(p);
693 ACQUIRE_SPIN_LOCK(&stp->sync_large_objects);
695 // object must be at the beginning of the block (or be a ByteArray)
696 ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS ||
697 (((W_)p & BLOCK_MASK) == 0));
699 // already evacuated?
700 if (bd->flags & BF_EVACUATED) {
701 /* Don't forget to set the gct->failed_to_evac flag if we didn't get
702 * the desired destination (see comments in evacuate()).
704 if (stp < gct->evac_step) {
705 gct->failed_to_evac = rtsTrue;
706 TICK_GC_FAILED_PROMOTION();
708 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
712 // remove from large_object list
714 bd->u.back->link = bd->link;
715 } else { // first object in the list
716 stp->large_objects = bd->link;
719 bd->link->u.back = bd->u.back;
722 /* link it on to the evacuated large object list of the destination step
725 if (new_stp < gct->evac_step) {
726 if (gct->eager_promotion) {
727 new_stp = gct->evac_step;
729 gct->failed_to_evac = rtsTrue;
733 ws = &gct->steps[new_stp->abs_no];
734 bd->flags |= BF_EVACUATED;
736 bd->gen_no = new_stp->gen_no;
737 bd->link = ws->todo_large_objects;
738 ws->todo_large_objects = bd;
740 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
743 /* -----------------------------------------------------------------------------
744 Evaluate a THUNK_SELECTOR if possible.
746 p points to a THUNK_SELECTOR that we want to evaluate. The
747 result of "evaluating" it will be evacuated and a pointer to the
748 to-space closure will be returned.
750 If the THUNK_SELECTOR could not be evaluated (its selectee is still
751 a THUNK, for example), then the THUNK_SELECTOR itself will be
753 -------------------------------------------------------------------------- */
755 unchain_thunk_selectors(StgSelector *p, StgClosure *val)
763 ASSERT(p->header.info == &stg_WHITEHOLE_info);
765 ASSERT(p->header.info == &stg_BLACKHOLE_info);
767 // val must be in to-space. Not always: when we recursively
768 // invoke eval_thunk_selector(), the recursive calls will not
769 // evacuate the value (because we want to select on the value,
770 // not evacuate it), so in this case val is in from-space.
771 // ASSERT(!HEAP_ALLOCED(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED));
773 prev = (StgSelector*)((StgClosure *)p)->payload[0];
775 // Update the THUNK_SELECTOR with an indirection to the
776 // EVACUATED closure now at p. Why do this rather than
777 // upd_evacuee(q,p)? Because we have an invariant that an
778 // EVACUATED closure always points to an object in the
779 // same or an older generation (required by the short-cut
780 // test in the EVACUATED case, below).
781 ((StgInd *)p)->indirectee = val;
783 SET_INFO(p, &stg_IND_info);
785 // For the purposes of LDV profiling, we have created an
787 LDV_RECORD_CREATE(p);
794 eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac)
795 // NB. for legacy reasons, p & q are swapped around :(
800 StgClosure *selectee;
801 StgSelector *prev_thunk_selector;
805 prev_thunk_selector = NULL;
806 // this is a chain of THUNK_SELECTORs that we are going to update
807 // to point to the value of the current THUNK_SELECTOR. Each
808 // closure on the chain is a BLACKHOLE, and points to the next in the
809 // chain with payload[0].
813 bd = Bdescr((StgPtr)p);
814 if (HEAP_ALLOCED(p)) {
815 // If the THUNK_SELECTOR is in to-space or in a generation that we
816 // are not collecting, then bale out early. We won't be able to
817 // save any space in any case, and updating with an indirection is
818 // trickier in a non-collected gen: we would have to update the
820 if (bd->flags & BF_EVACUATED) {
821 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
822 *q = (StgClosure *)p;
825 // we don't update THUNK_SELECTORS in the compacted
826 // generation, because compaction does not remove the INDs
827 // that result, this causes confusion later
828 // (scavenge_mark_stack doesn't deal with IND). BEWARE! This
829 // bit is very tricky to get right. If you make changes
830 // around here, test by compiling stage 3 with +RTS -c -RTS.
831 if (bd->flags & BF_MARKED) {
832 // must call evacuate() to mark this closure if evac==rtsTrue
833 *q = (StgClosure *)p;
834 if (evac) evacuate(q);
835 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
841 // BLACKHOLE the selector thunk, since it is now under evaluation.
842 // This is important to stop us going into an infinite loop if
843 // this selector thunk eventually refers to itself.
844 #if defined(THREADED_RTS)
845 // In threaded mode, we'll use WHITEHOLE to lock the selector
846 // thunk while we evaluate it.
849 info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info);
850 } while (info_ptr == (W_)&stg_WHITEHOLE_info);
852 // make sure someone else didn't get here first...
853 if (IS_FORWARDING_PTR(p) ||
854 INFO_PTR_TO_STRUCT(info_ptr)->type != THUNK_SELECTOR) {
855 // v. tricky now. The THUNK_SELECTOR has been evacuated
856 // by another thread, and is now either a forwarding ptr or IND.
857 // We need to extract ourselves from the current situation
858 // as cleanly as possible.
859 // - unlock the closure
860 // - update *q, we may have done *some* evaluation
861 // - if evac, we need to call evacuate(), because we
862 // need the write-barrier stuff.
863 // - undo the chain we've built to point to p.
864 SET_INFO(p, (const StgInfoTable *)info_ptr);
865 *q = (StgClosure *)p;
866 if (evac) evacuate(q);
867 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
872 // Save the real info pointer (NOTE: not the same as get_itbl()).
873 info_ptr = (StgWord)p->header.info;
874 SET_INFO(p,&stg_BLACKHOLE_info);
877 field = INFO_PTR_TO_STRUCT(info_ptr)->layout.selector_offset;
879 // The selectee might be a constructor closure,
880 // so we untag the pointer.
881 selectee = UNTAG_CLOSURE(p->selectee);
884 // selectee now points to the closure that we're trying to select
885 // a field from. It may or may not be in to-space: we try not to
886 // end up in to-space, but it's impractical to avoid it in
887 // general. The compacting GC scatters to-space pointers in
888 // from-space during marking, for example. We rely on the property
889 // that evacuate() doesn't mind if it gets passed a to-space pointer.
891 info = (StgInfoTable*)selectee->header.info;
893 if (IS_FORWARDING_PTR(info)) {
894 // We don't follow pointers into to-space; the constructor
895 // has already been evacuated, so we won't save any space
896 // leaks by evaluating this selector thunk anyhow.
900 info = INFO_PTR_TO_STRUCT(info);
901 switch (info->type) {
903 goto bale_out; // about to be evacuated by another thread (or a loop).
912 case CONSTR_NOCAF_STATIC:
914 // check that the size is in range
915 ASSERT(field < (StgWord32)(info->layout.payload.ptrs +
916 info->layout.payload.nptrs));
918 // Select the right field from the constructor
919 val = selectee->payload[field];
922 // For the purposes of LDV profiling, we have destroyed
923 // the original selector thunk, p.
924 SET_INFO(p, (StgInfoTable *)info_ptr);
925 LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC((StgClosure *)p);
926 SET_INFO(p, &stg_BLACKHOLE_info);
929 // the closure in val is now the "value" of the
930 // THUNK_SELECTOR in p. However, val may itself be a
931 // THUNK_SELECTOR, in which case we want to continue
932 // evaluating until we find the real value, and then
933 // update the whole chain to point to the value.
935 info_ptr = (StgWord)UNTAG_CLOSURE(val)->header.info;
936 if (!IS_FORWARDING_PTR(info_ptr))
938 info = INFO_PTR_TO_STRUCT(info_ptr);
939 switch (info->type) {
943 case IND_OLDGEN_PERM:
945 val = ((StgInd *)val)->indirectee;
948 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
949 prev_thunk_selector = p;
950 p = (StgSelector*)val;
956 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
957 prev_thunk_selector = p;
960 if (evac) evacuate(q);
962 // evacuate() cannot recurse through
963 // eval_thunk_selector(), because we know val is not
965 unchain_thunk_selectors(prev_thunk_selector, val);
972 case IND_OLDGEN_PERM:
974 // Again, we might need to untag a constructor.
975 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
982 // recursively evaluate this selector. We don't want to
983 // recurse indefinitely, so we impose a depth bound.
984 if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) {
988 gct->thunk_selector_depth++;
989 // rtsFalse says "don't evacuate the result". It will,
990 // however, update any THUNK_SELECTORs that are evaluated
992 eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse);
993 gct->thunk_selector_depth--;
995 // did we actually manage to evaluate it?
996 if (val == selectee) goto bale_out;
998 // Of course this pointer might be tagged...
999 selectee = UNTAG_CLOSURE(val);
1013 case SE_CAF_BLACKHOLE:
1016 // not evaluated yet
1020 barf("eval_thunk_selector: strange selectee %d",
1025 // We didn't manage to evaluate this thunk; restore the old info
1026 // pointer. But don't forget: we still need to evacuate the thunk itself.
1027 SET_INFO(p, (const StgInfoTable *)info_ptr);
1028 // THREADED_RTS: we just unlocked the thunk, so another thread
1029 // might get in and update it. copy() will lock it again and
1030 // check whether it was updated in the meantime.
1031 *q = (StgClosure *)p;
1033 copy(q,(const StgInfoTable *)info_ptr,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->step->to);
1035 unchain_thunk_selectors(prev_thunk_selector, *q);