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));
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, step *stp)
227 copy_tag(p,info,src,size,stp,0);
230 /* -----------------------------------------------------------------------------
231 Evacuate a large object
233 This just consists of removing the object from the (doubly-linked)
234 step->large_objects list, and linking it on to the (singly-linked)
235 step->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)
244 bdescr *bd = Bdescr(p);
249 ACQUIRE_SPIN_LOCK(&stp->sync_large_objects);
251 // object must be at the beginning of the block (or be a ByteArray)
252 ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS ||
253 (((W_)p & BLOCK_MASK) == 0));
255 // already evacuated?
256 if (bd->flags & BF_EVACUATED) {
257 /* Don't forget to set the gct->failed_to_evac flag if we didn't get
258 * the desired destination (see comments in evacuate()).
260 if (stp < gct->evac_step) {
261 gct->failed_to_evac = rtsTrue;
262 TICK_GC_FAILED_PROMOTION();
264 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
268 // remove from large_object list
270 bd->u.back->link = bd->link;
271 } else { // first object in the list
272 stp->large_objects = bd->link;
275 bd->link->u.back = bd->u.back;
278 /* link it on to the evacuated large object list of the destination step
281 if (new_stp < gct->evac_step) {
282 if (gct->eager_promotion) {
283 new_stp = gct->evac_step;
285 gct->failed_to_evac = rtsTrue;
289 ws = &gct->steps[new_stp->abs_no];
290 bd->flags |= BF_EVACUATED;
292 bd->gen_no = new_stp->gen_no;
293 bd->link = ws->todo_large_objects;
294 ws->todo_large_objects = bd;
296 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
299 /* ----------------------------------------------------------------------------
302 This is called (eventually) for every live object in the system.
304 The caller to evacuate specifies a desired generation in the
305 gct->evac_step thread-local variable. The following conditions apply to
306 evacuating an object which resides in generation M when we're
307 collecting up to generation N
309 if M >= gct->evac_step
311 else evac to step->to
313 if M < gct->evac_step evac to gct->evac_step, step 0
315 if the object is already evacuated, then we check which generation
318 if M >= gct->evac_step do nothing
319 if M < gct->evac_step set gct->failed_to_evac flag to indicate that we
320 didn't manage to evacuate this object into gct->evac_step.
325 evacuate() is the single most important function performance-wise
326 in the GC. Various things have been tried to speed it up, but as
327 far as I can tell the code generated by gcc 3.2 with -O2 is about
328 as good as it's going to get. We pass the argument to evacuate()
329 in a register using the 'regparm' attribute (see the prototype for
330 evacuate() near the top of this file).
332 Changing evacuate() to take an (StgClosure **) rather than
333 returning the new pointer seems attractive, because we can avoid
334 writing back the pointer when it hasn't changed (eg. for a static
335 object, or an object in a generation > N). However, I tried it and
336 it doesn't help. One reason is that the (StgClosure **) pointer
337 gets spilled to the stack inside evacuate(), resulting in far more
338 extra reads/writes than we save.
339 ------------------------------------------------------------------------- */
341 REGPARM1 GNUC_ATTR_HOT void
342 evacuate(StgClosure **p)
347 const StgInfoTable *info;
353 /* The tag and the pointer are split, to be merged after evacing */
354 tag = GET_CLOSURE_TAG(q);
355 q = UNTAG_CLOSURE(q);
357 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
359 if (!HEAP_ALLOCED(q)) {
361 if (!major_gc) return;
364 switch (info->type) {
367 if (info->srt_bitmap != 0) {
368 if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
370 *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
371 gct->static_objects = (StgClosure *)q;
374 link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
376 (StgWord)gct->static_objects);
378 gct->static_objects = (StgClosure *)q;
386 if (info->srt_bitmap != 0 &&
387 *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
389 *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
390 gct->static_objects = (StgClosure *)q;
393 link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
395 (StgWord)gct->static_objects);
397 gct->static_objects = (StgClosure *)q;
404 /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
405 * on the CAF list, so don't do anything with it here (we'll
406 * scavenge it later).
408 if (((StgIndStatic *)q)->saved_info == NULL) {
409 if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
411 *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
412 gct->static_objects = (StgClosure *)q;
415 link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
417 (StgWord)gct->static_objects);
419 gct->static_objects = (StgClosure *)q;
427 if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
429 *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
430 gct->static_objects = (StgClosure *)q;
433 link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
435 (StgWord)gct->static_objects);
437 gct->static_objects = (StgClosure *)q;
441 /* I am assuming that static_objects pointers are not
442 * written to other objects, and thus, no need to retag. */
445 case CONSTR_NOCAF_STATIC:
446 /* no need to put these on the static linked list, they don't need
452 barf("evacuate(static): strange closure type %d", (int)(info->type));
458 if ((bd->flags & (BF_LARGE | BF_MARKED | BF_EVACUATED)) != 0) {
460 // pointer into to-space: just return it. It might be a pointer
461 // into a generation that we aren't collecting (> N), or it
462 // might just be a pointer into to-space. The latter doesn't
463 // happen often, but allowing it makes certain things a bit
464 // easier; e.g. scavenging an object is idempotent, so it's OK to
465 // have an object on the mutable list multiple times.
466 if (bd->flags & BF_EVACUATED) {
467 // We aren't copying this object, so we have to check
468 // whether it is already in the target generation. (this is
469 // the write barrier).
470 if (bd->step < gct->evac_step) {
471 gct->failed_to_evac = rtsTrue;
472 TICK_GC_FAILED_PROMOTION();
477 /* evacuate large objects by re-linking them onto a different list.
479 if (bd->flags & BF_LARGE) {
481 if (info->type == TSO &&
482 ((StgTSO *)q)->what_next == ThreadRelocated) {
483 q = (StgClosure *)((StgTSO *)q)->_link;
487 evacuate_large((P_)q);
491 /* If the object is in a step that we're compacting, then we
492 * need to use an alternative evacuate procedure.
494 if (!is_marked((P_)q,bd)) {
496 if (mark_stack_full()) {
497 debugTrace(DEBUG_gc,"mark stack overflowed");
498 mark_stack_overflowed = rtsTrue;
501 push_mark_stack((P_)q);
508 info = q->header.info;
509 if (IS_FORWARDING_PTR(info))
511 /* Already evacuated, just return the forwarding address.
512 * HOWEVER: if the requested destination generation (gct->evac_step) is
513 * older than the actual generation (because the object was
514 * already evacuated to a younger generation) then we have to
515 * set the gct->failed_to_evac flag to indicate that we couldn't
516 * manage to promote the object to the desired generation.
519 * Optimisation: the check is fairly expensive, but we can often
520 * shortcut it if either the required generation is 0, or the
521 * current object (the EVACUATED) is in a high enough generation.
522 * We know that an EVACUATED always points to an object in the
523 * same or an older generation. stp is the lowest step that the
524 * current object would be evacuated to, so we only do the full
525 * check if stp is too low.
527 StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
528 *p = TAG_CLOSURE(tag,e);
529 if (stp < gct->evac_step) { // optimisation
530 if (Bdescr((P_)e)->step < gct->evac_step) {
531 gct->failed_to_evac = rtsTrue;
532 TICK_GC_FAILED_PROMOTION();
538 switch (INFO_PTR_TO_STRUCT(info)->type) {
547 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
552 StgWord w = (StgWord)q->payload[0];
553 if (info == Czh_con_info &&
554 // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
555 (StgChar)w <= MAX_CHARLIKE) {
556 *p = TAG_CLOSURE(tag,
557 (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
560 else if (info == Izh_con_info &&
561 (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
562 *p = TAG_CLOSURE(tag,
563 (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
567 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
575 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
580 copy(p,info,q,sizeofW(StgThunk)+1,stp);
586 #ifdef NO_PROMOTE_THUNKS
587 if (bd->gen_no == 0 &&
589 bd->step->no == generations[bd->gen_no].n_steps-1) {
593 copy(p,info,q,sizeofW(StgThunk)+2,stp);
601 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
605 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
609 copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
614 case IND_OLDGEN_PERM:
616 copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
621 copy_tag(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
625 copy(p,info,q,bco_sizeW((StgBCO *)q),stp);
629 case SE_CAF_BLACKHOLE:
632 copyPart(p,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
636 eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
641 // follow chains of indirections, don't evacuate them
642 q = ((StgInd*)q)->indirectee;
653 case CATCH_STM_FRAME:
654 case CATCH_RETRY_FRAME:
655 case ATOMICALLY_FRAME:
656 // shouldn't see these
657 barf("evacuate: stack frame at %p\n", q);
660 copy(p,info,q,pap_sizeW((StgPAP*)q),stp);
664 copy(p,info,q,ap_sizeW((StgAP*)q),stp);
668 copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),stp);
672 // just copy the block
673 copy(p,info,q,arr_words_sizeW((StgArrWords *)q),stp);
676 case MUT_ARR_PTRS_CLEAN:
677 case MUT_ARR_PTRS_DIRTY:
678 case MUT_ARR_PTRS_FROZEN:
679 case MUT_ARR_PTRS_FROZEN0:
680 // just copy the block
681 copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),stp);
686 StgTSO *tso = (StgTSO *)q;
688 /* Deal with redirected TSOs (a TSO that's had its stack enlarged).
690 if (tso->what_next == ThreadRelocated) {
691 q = (StgClosure *)tso->_link;
696 /* To evacuate a small TSO, we need to relocate the update frame
704 mine = copyPart(p,(StgClosure *)tso, tso_sizeW(tso),
705 sizeofW(StgTSO), stp);
707 new_tso = (StgTSO *)*p;
708 move_TSO(tso, new_tso);
709 for (r = tso->sp, s = new_tso->sp;
710 r < tso->stack+tso->stack_size;) {
719 copy(p,info,q,sizeofW(StgTRecHeader),stp);
722 case TVAR_WATCH_QUEUE:
723 copy(p,info,q,sizeofW(StgTVarWatchQueue),stp);
727 copy(p,info,q,sizeofW(StgTVar),stp);
731 copy(p,info,q,sizeofW(StgTRecChunk),stp);
734 case ATOMIC_INVARIANT:
735 copy(p,info,q,sizeofW(StgAtomicInvariant),stp);
738 case INVARIANT_CHECK_QUEUE:
739 copy(p,info,q,sizeofW(StgInvariantCheckQueue),stp);
743 barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
749 /* -----------------------------------------------------------------------------
750 Evaluate a THUNK_SELECTOR if possible.
752 p points to a THUNK_SELECTOR that we want to evaluate. The
753 result of "evaluating" it will be evacuated and a pointer to the
754 to-space closure will be returned.
756 If the THUNK_SELECTOR could not be evaluated (its selectee is still
757 a THUNK, for example), then the THUNK_SELECTOR itself will be
759 -------------------------------------------------------------------------- */
761 unchain_thunk_selectors(StgSelector *p, StgClosure *val)
769 ASSERT(p->header.info == &stg_WHITEHOLE_info);
771 ASSERT(p->header.info == &stg_BLACKHOLE_info);
773 // val must be in to-space. Not always: when we recursively
774 // invoke eval_thunk_selector(), the recursive calls will not
775 // evacuate the value (because we want to select on the value,
776 // not evacuate it), so in this case val is in from-space.
777 // ASSERT(!HEAP_ALLOCED(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED));
779 prev = (StgSelector*)((StgClosure *)p)->payload[0];
781 // Update the THUNK_SELECTOR with an indirection to the
782 // value. The value is still in from-space at this stage.
784 // (old note: Why not do upd_evacuee(q,p)? Because we have an
785 // invariant that an EVACUATED closure always points to an
786 // object in the same or an older generation (required by
787 // the short-cut test in the EVACUATED case, below).
788 if ((StgClosure *)p == val) {
789 // must be a loop; just leave a BLACKHOLE in place. This
790 // can happen when we have a chain of selectors that
791 // eventually loops back on itself. We can't leave an
792 // indirection pointing to itself, and we want the program
793 // to deadlock if it ever enters this closure, so
794 // BLACKHOLE is correct.
795 SET_INFO(p, &stg_BLACKHOLE_info);
797 ((StgInd *)p)->indirectee = val;
799 SET_INFO(p, &stg_IND_info);
802 // For the purposes of LDV profiling, we have created an
804 LDV_RECORD_CREATE(p);
811 eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac)
812 // NB. for legacy reasons, p & q are swapped around :(
817 StgClosure *selectee;
818 StgSelector *prev_thunk_selector;
822 prev_thunk_selector = NULL;
823 // this is a chain of THUNK_SELECTORs that we are going to update
824 // to point to the value of the current THUNK_SELECTOR. Each
825 // closure on the chain is a BLACKHOLE, and points to the next in the
826 // chain with payload[0].
830 bd = Bdescr((StgPtr)p);
831 if (HEAP_ALLOCED(p)) {
832 // If the THUNK_SELECTOR is in to-space or in a generation that we
833 // are not collecting, then bale out early. We won't be able to
834 // save any space in any case, and updating with an indirection is
835 // trickier in a non-collected gen: we would have to update the
837 if (bd->flags & BF_EVACUATED) {
838 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
839 *q = (StgClosure *)p;
842 // we don't update THUNK_SELECTORS in the compacted
843 // generation, because compaction does not remove the INDs
844 // that result, this causes confusion later
845 // (scavenge_mark_stack doesn't deal with IND). BEWARE! This
846 // bit is very tricky to get right. If you make changes
847 // around here, test by compiling stage 3 with +RTS -c -RTS.
848 if (bd->flags & BF_MARKED) {
849 // must call evacuate() to mark this closure if evac==rtsTrue
850 *q = (StgClosure *)p;
851 if (evac) evacuate(q);
852 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
858 // BLACKHOLE the selector thunk, since it is now under evaluation.
859 // This is important to stop us going into an infinite loop if
860 // this selector thunk eventually refers to itself.
861 #if defined(THREADED_RTS)
862 // In threaded mode, we'll use WHITEHOLE to lock the selector
863 // thunk while we evaluate it.
866 info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info);
867 } while (info_ptr == (W_)&stg_WHITEHOLE_info);
869 // make sure someone else didn't get here first...
870 if (IS_FORWARDING_PTR(p) ||
871 INFO_PTR_TO_STRUCT(info_ptr)->type != THUNK_SELECTOR) {
872 // v. tricky now. The THUNK_SELECTOR has been evacuated
873 // by another thread, and is now either a forwarding ptr or IND.
874 // We need to extract ourselves from the current situation
875 // as cleanly as possible.
876 // - unlock the closure
877 // - update *q, we may have done *some* evaluation
878 // - if evac, we need to call evacuate(), because we
879 // need the write-barrier stuff.
880 // - undo the chain we've built to point to p.
881 SET_INFO(p, (const StgInfoTable *)info_ptr);
882 *q = (StgClosure *)p;
883 if (evac) evacuate(q);
884 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
889 // Save the real info pointer (NOTE: not the same as get_itbl()).
890 info_ptr = (StgWord)p->header.info;
891 SET_INFO(p,&stg_BLACKHOLE_info);
894 field = INFO_PTR_TO_STRUCT(info_ptr)->layout.selector_offset;
896 // The selectee might be a constructor closure,
897 // so we untag the pointer.
898 selectee = UNTAG_CLOSURE(p->selectee);
901 // selectee now points to the closure that we're trying to select
902 // a field from. It may or may not be in to-space: we try not to
903 // end up in to-space, but it's impractical to avoid it in
904 // general. The compacting GC scatters to-space pointers in
905 // from-space during marking, for example. We rely on the property
906 // that evacuate() doesn't mind if it gets passed a to-space pointer.
908 info = (StgInfoTable*)selectee->header.info;
910 if (IS_FORWARDING_PTR(info)) {
911 // We don't follow pointers into to-space; the constructor
912 // has already been evacuated, so we won't save any space
913 // leaks by evaluating this selector thunk anyhow.
917 info = INFO_PTR_TO_STRUCT(info);
918 switch (info->type) {
920 goto bale_out; // about to be evacuated by another thread (or a loop).
929 case CONSTR_NOCAF_STATIC:
931 // check that the size is in range
932 ASSERT(field < (StgWord32)(info->layout.payload.ptrs +
933 info->layout.payload.nptrs));
935 // Select the right field from the constructor
936 val = selectee->payload[field];
939 // For the purposes of LDV profiling, we have destroyed
940 // the original selector thunk, p.
941 SET_INFO(p, (StgInfoTable *)info_ptr);
942 LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC((StgClosure *)p);
943 SET_INFO(p, &stg_BLACKHOLE_info);
946 // the closure in val is now the "value" of the
947 // THUNK_SELECTOR in p. However, val may itself be a
948 // THUNK_SELECTOR, in which case we want to continue
949 // evaluating until we find the real value, and then
950 // update the whole chain to point to the value.
952 info_ptr = (StgWord)UNTAG_CLOSURE(val)->header.info;
953 if (!IS_FORWARDING_PTR(info_ptr))
955 info = INFO_PTR_TO_STRUCT(info_ptr);
956 switch (info->type) {
960 case IND_OLDGEN_PERM:
962 val = ((StgInd *)val)->indirectee;
965 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
966 prev_thunk_selector = p;
967 p = (StgSelector*)val;
973 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
974 prev_thunk_selector = p;
978 // update the other selectors in the chain *before*
979 // evacuating the value. This is necessary in the case
980 // where the value turns out to be one of the selectors
981 // in the chain (i.e. we have a loop), and evacuating it
982 // would corrupt the chain.
983 unchain_thunk_selectors(prev_thunk_selector, val);
985 // evacuate() cannot recurse through
986 // eval_thunk_selector(), because we know val is not
988 if (evac) evacuate(q);
995 case IND_OLDGEN_PERM:
997 // Again, we might need to untag a constructor.
998 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
1001 case THUNK_SELECTOR:
1005 // recursively evaluate this selector. We don't want to
1006 // recurse indefinitely, so we impose a depth bound.
1007 if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) {
1011 gct->thunk_selector_depth++;
1012 // rtsFalse says "don't evacuate the result". It will,
1013 // however, update any THUNK_SELECTORs that are evaluated
1015 eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse);
1016 gct->thunk_selector_depth--;
1018 // did we actually manage to evaluate it?
1019 if (val == selectee) goto bale_out;
1021 // Of course this pointer might be tagged...
1022 selectee = UNTAG_CLOSURE(val);
1036 case SE_CAF_BLACKHOLE:
1039 // not evaluated yet
1043 barf("eval_thunk_selector: strange selectee %d",
1048 // We didn't manage to evaluate this thunk; restore the old info
1049 // pointer. But don't forget: we still need to evacuate the thunk itself.
1050 SET_INFO(p, (const StgInfoTable *)info_ptr);
1051 // THREADED_RTS: we just unlocked the thunk, so another thread
1052 // might get in and update it. copy() will lock it again and
1053 // check whether it was updated in the meantime.
1054 *q = (StgClosure *)p;
1056 copy(q,(const StgInfoTable *)info_ptr,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->step->to);
1058 unchain_thunk_selectors(prev_thunk_selector, *q);