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, step *stp)
59 /* Find out where we're going, using the handy "to" pointer in
60 * the step of the source object. If it turns out we need to
61 * evacuate to an older generation, adjust it here (see comment
64 if (stp < gct->evac_step) {
65 if (gct->eager_promotion) {
68 gct->failed_to_evac = rtsTrue;
72 ws = &gct->steps[stp->abs_no];
73 // this compiles to a single mem access to stp->abs_no only
75 /* chain a new block onto the to-space for the destination step 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, step *stp, StgWord tag)
99 to = alloc_for_copy(size,stp);
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, step *stp, StgWord tag)
141 to = alloc_for_copy(size,stp);
142 *p = TAG_CLOSURE(tag,(StgClosure*)to);
143 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
147 for (i = 1; i < size; i++) { // unroll for small i
151 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
152 // __builtin_prefetch(to + size + 2, 1);
156 // We store the size of the just evacuated object in the LDV word so that
157 // the profiler can guess the position of the next object later.
158 SET_EVACUAEE_FOR_LDV(from, size);
163 /* Special version of copy() for when we only want to copy the info
164 * pointer of an object, but reserve some padding after it. This is
165 * used to optimise evacuation of BLACKHOLEs.
168 copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp)
174 #if defined(PARALLEL_GC)
176 info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
177 if (info == (W_)&stg_WHITEHOLE_info) {
183 if (IS_FORWARDING_PTR(info)) {
184 src->header.info = (const StgInfoTable *)info;
185 evacuate(p); // does the failed_to_evac stuff
189 info = (W_)src->header.info;
192 to = alloc_for_copy(size_to_reserve, stp);
193 *p = (StgClosure *)to;
197 for (i = 1; i < size_to_copy; i++) { // unroll for small i
201 #if defined(PARALLEL_GC)
204 src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(to);
207 // We store the size of the just evacuated object in the LDV word so that
208 // the profiler can guess the position of the next object later.
209 SET_EVACUAEE_FOR_LDV(from, size_to_reserve);
211 if (size_to_reserve - size_to_copy > 0)
212 LDV_FILL_SLOP(to + size_to_copy, (int)(size_to_reserve - size_to_copy));
219 /* Copy wrappers that don't tag the closure after copying */
220 STATIC_INLINE GNUC_ATTR_HOT void
221 copy(StgClosure **p, const StgInfoTable *info,
222 StgClosure *src, nat size, step *stp)
224 copy_tag(p,info,src,size,stp,0);
227 /* -----------------------------------------------------------------------------
228 Evacuate a large object
230 This just consists of removing the object from the (doubly-linked)
231 step->large_objects list, and linking it on to the (singly-linked)
232 step->new_large_objects list, from where it will be scavenged later.
234 Convention: bd->flags has BF_EVACUATED set for a large object
235 that has been evacuated, or unset otherwise.
236 -------------------------------------------------------------------------- */
239 evacuate_large(StgPtr p)
241 bdescr *bd = Bdescr(p);
246 ACQUIRE_SPIN_LOCK(&stp->sync_large_objects);
248 // already evacuated?
249 if (bd->flags & BF_EVACUATED) {
250 /* Don't forget to set the gct->failed_to_evac flag if we didn't get
251 * the desired destination (see comments in evacuate()).
253 if (stp < gct->evac_step) {
254 gct->failed_to_evac = rtsTrue;
255 TICK_GC_FAILED_PROMOTION();
257 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
261 // remove from large_object list
263 bd->u.back->link = bd->link;
264 } else { // first object in the list
265 stp->large_objects = bd->link;
268 bd->link->u.back = bd->u.back;
271 /* link it on to the evacuated large object list of the destination step
274 if (new_stp < gct->evac_step) {
275 if (gct->eager_promotion) {
276 new_stp = gct->evac_step;
278 gct->failed_to_evac = rtsTrue;
282 ws = &gct->steps[new_stp->abs_no];
284 bd->flags |= BF_EVACUATED;
285 initBdescr(bd, new_stp);
287 // If this is a block of pinned objects, we don't have to scan
288 // these objects, because they aren't allowed to contain any
289 // pointers. For these blocks, we skip the scavenge stage and put
290 // them straight on the scavenged_large_objects list.
291 if (bd->flags & BF_PINNED) {
292 ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS);
293 if (new_stp != stp) { ACQUIRE_SPIN_LOCK(&new_stp->sync_large_objects); }
294 dbl_link_onto(bd, &new_stp->scavenged_large_objects);
295 new_stp->n_scavenged_large_blocks += bd->blocks;
296 if (new_stp != stp) { RELEASE_SPIN_LOCK(&new_stp->sync_large_objects); }
298 bd->link = ws->todo_large_objects;
299 ws->todo_large_objects = bd;
302 RELEASE_SPIN_LOCK(&stp->sync_large_objects);
305 /* ----------------------------------------------------------------------------
308 This is called (eventually) for every live object in the system.
310 The caller to evacuate specifies a desired generation in the
311 gct->evac_step thread-local variable. The following conditions apply to
312 evacuating an object which resides in generation M when we're
313 collecting up to generation N
315 if M >= gct->evac_step
317 else evac to step->to
319 if M < gct->evac_step evac to gct->evac_step, step 0
321 if the object is already evacuated, then we check which generation
324 if M >= gct->evac_step do nothing
325 if M < gct->evac_step set gct->failed_to_evac flag to indicate that we
326 didn't manage to evacuate this object into gct->evac_step.
331 evacuate() is the single most important function performance-wise
332 in the GC. Various things have been tried to speed it up, but as
333 far as I can tell the code generated by gcc 3.2 with -O2 is about
334 as good as it's going to get. We pass the argument to evacuate()
335 in a register using the 'regparm' attribute (see the prototype for
336 evacuate() near the top of this file).
338 Changing evacuate() to take an (StgClosure **) rather than
339 returning the new pointer seems attractive, because we can avoid
340 writing back the pointer when it hasn't changed (eg. for a static
341 object, or an object in a generation > N). However, I tried it and
342 it doesn't help. One reason is that the (StgClosure **) pointer
343 gets spilled to the stack inside evacuate(), resulting in far more
344 extra reads/writes than we save.
345 ------------------------------------------------------------------------- */
347 REGPARM1 GNUC_ATTR_HOT void
348 evacuate(StgClosure **p)
353 const StgInfoTable *info;
359 /* The tag and the pointer are split, to be merged after evacing */
360 tag = GET_CLOSURE_TAG(q);
361 q = UNTAG_CLOSURE(q);
363 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
365 if (!HEAP_ALLOCED_GC(q)) {
367 if (!major_gc) return;
370 switch (info->type) {
373 if (info->srt_bitmap != 0) {
374 if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
376 *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
377 gct->static_objects = (StgClosure *)q;
380 link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
382 (StgWord)gct->static_objects);
384 gct->static_objects = (StgClosure *)q;
392 if (info->srt_bitmap != 0 &&
393 *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
395 *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
396 gct->static_objects = (StgClosure *)q;
399 link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
401 (StgWord)gct->static_objects);
403 gct->static_objects = (StgClosure *)q;
410 /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
411 * on the CAF list, so don't do anything with it here (we'll
412 * scavenge it later).
414 if (((StgIndStatic *)q)->saved_info == NULL) {
415 if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
417 *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
418 gct->static_objects = (StgClosure *)q;
421 link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
423 (StgWord)gct->static_objects);
425 gct->static_objects = (StgClosure *)q;
433 if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
435 *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
436 gct->static_objects = (StgClosure *)q;
439 link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
441 (StgWord)gct->static_objects);
443 gct->static_objects = (StgClosure *)q;
447 /* I am assuming that static_objects pointers are not
448 * written to other objects, and thus, no need to retag. */
451 case CONSTR_NOCAF_STATIC:
452 /* no need to put these on the static linked list, they don't need
458 barf("evacuate(static): strange closure type %d", (int)(info->type));
464 if ((bd->flags & (BF_LARGE | BF_MARKED | BF_EVACUATED)) != 0) {
466 // pointer into to-space: just return it. It might be a pointer
467 // into a generation that we aren't collecting (> N), or it
468 // might just be a pointer into to-space. The latter doesn't
469 // happen often, but allowing it makes certain things a bit
470 // easier; e.g. scavenging an object is idempotent, so it's OK to
471 // have an object on the mutable list multiple times.
472 if (bd->flags & BF_EVACUATED) {
473 // We aren't copying this object, so we have to check
474 // whether it is already in the target generation. (this is
475 // the write barrier).
476 if (bd->step < gct->evac_step) {
477 gct->failed_to_evac = rtsTrue;
478 TICK_GC_FAILED_PROMOTION();
483 /* evacuate large objects by re-linking them onto a different list.
485 if (bd->flags & BF_LARGE) {
487 if (info->type == TSO &&
488 ((StgTSO *)q)->what_next == ThreadRelocated) {
489 q = (StgClosure *)((StgTSO *)q)->_link;
493 evacuate_large((P_)q);
497 /* If the object is in a step that we're compacting, then we
498 * need to use an alternative evacuate procedure.
500 if (!is_marked((P_)q,bd)) {
502 push_mark_stack((P_)q);
509 info = q->header.info;
510 if (IS_FORWARDING_PTR(info))
512 /* Already evacuated, just return the forwarding address.
513 * HOWEVER: if the requested destination generation (gct->evac_step) is
514 * older than the actual generation (because the object was
515 * already evacuated to a younger generation) then we have to
516 * set the gct->failed_to_evac flag to indicate that we couldn't
517 * manage to promote the object to the desired generation.
520 * Optimisation: the check is fairly expensive, but we can often
521 * shortcut it if either the required generation is 0, or the
522 * current object (the EVACUATED) is in a high enough generation.
523 * We know that an EVACUATED always points to an object in the
524 * same or an older generation. stp is the lowest step that the
525 * current object would be evacuated to, so we only do the full
526 * check if stp is too low.
528 StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
529 *p = TAG_CLOSURE(tag,e);
530 if (stp < gct->evac_step) { // optimisation
531 if (Bdescr((P_)e)->step < gct->evac_step) {
532 gct->failed_to_evac = rtsTrue;
533 TICK_GC_FAILED_PROMOTION();
539 switch (INFO_PTR_TO_STRUCT(info)->type) {
548 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
551 // For ints and chars of low value, save space by replacing references to
552 // these with closures with references to common, shared ones in the RTS.
554 // * Except when compiling into Windows DLLs which don't support cross-package
555 // data references very well.
559 #if defined(__PIC__) && defined(mingw32_HOST_OS)
560 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
562 StgWord w = (StgWord)q->payload[0];
563 if (info == Czh_con_info &&
564 // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
565 (StgChar)w <= MAX_CHARLIKE) {
566 *p = TAG_CLOSURE(tag,
567 (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
570 else if (info == Izh_con_info &&
571 (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
572 *p = TAG_CLOSURE(tag,
573 (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
577 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
586 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
591 copy(p,info,q,sizeofW(StgThunk)+1,stp);
597 #ifdef NO_PROMOTE_THUNKS
598 if (bd->gen_no == 0 &&
600 bd->step->no == generations[bd->gen_no].n_steps-1) {
604 copy(p,info,q,sizeofW(StgThunk)+2,stp);
612 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
616 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
620 copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
625 case IND_OLDGEN_PERM:
627 copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
632 copy_tag(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
636 copy(p,info,q,bco_sizeW((StgBCO *)q),stp);
641 copyPart(p,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
645 eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
650 // follow chains of indirections, don't evacuate them
651 q = ((StgInd*)q)->indirectee;
662 case CATCH_STM_FRAME:
663 case CATCH_RETRY_FRAME:
664 case ATOMICALLY_FRAME:
665 // shouldn't see these
666 barf("evacuate: stack frame at %p\n", q);
669 copy(p,info,q,pap_sizeW((StgPAP*)q),stp);
673 copy(p,info,q,ap_sizeW((StgAP*)q),stp);
677 copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),stp);
681 // just copy the block
682 copy(p,info,q,arr_words_sizeW((StgArrWords *)q),stp);
685 case MUT_ARR_PTRS_CLEAN:
686 case MUT_ARR_PTRS_DIRTY:
687 case MUT_ARR_PTRS_FROZEN:
688 case MUT_ARR_PTRS_FROZEN0:
689 // just copy the block
690 copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),stp);
695 StgTSO *tso = (StgTSO *)q;
697 /* Deal with redirected TSOs (a TSO that's had its stack enlarged).
699 if (tso->what_next == ThreadRelocated) {
700 q = (StgClosure *)tso->_link;
705 /* To evacuate a small TSO, we need to adjust the stack pointer
712 mine = copyPart(p,(StgClosure *)tso, tso_sizeW(tso),
713 sizeofW(StgTSO), stp);
715 new_tso = (StgTSO *)*p;
716 move_TSO(tso, new_tso);
717 for (r = tso->sp, s = new_tso->sp;
718 r < tso->stack+tso->stack_size;) {
727 copy(p,info,q,sizeofW(StgTRecHeader),stp);
730 case TVAR_WATCH_QUEUE:
731 copy(p,info,q,sizeofW(StgTVarWatchQueue),stp);
735 copy(p,info,q,sizeofW(StgTVar),stp);
739 copy(p,info,q,sizeofW(StgTRecChunk),stp);
742 case ATOMIC_INVARIANT:
743 copy(p,info,q,sizeofW(StgAtomicInvariant),stp);
746 case INVARIANT_CHECK_QUEUE:
747 copy(p,info,q,sizeofW(StgInvariantCheckQueue),stp);
751 barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
757 /* -----------------------------------------------------------------------------
758 Evaluate a THUNK_SELECTOR if possible.
760 p points to a THUNK_SELECTOR that we want to evaluate. The
761 result of "evaluating" it will be evacuated and a pointer to the
762 to-space closure will be returned.
764 If the THUNK_SELECTOR could not be evaluated (its selectee is still
765 a THUNK, for example), then the THUNK_SELECTOR itself will be
767 -------------------------------------------------------------------------- */
769 unchain_thunk_selectors(StgSelector *p, StgClosure *val)
777 ASSERT(p->header.info == &stg_WHITEHOLE_info);
779 ASSERT(p->header.info == &stg_BLACKHOLE_info);
781 // val must be in to-space. Not always: when we recursively
782 // invoke eval_thunk_selector(), the recursive calls will not
783 // evacuate the value (because we want to select on the value,
784 // not evacuate it), so in this case val is in from-space.
785 // ASSERT(!HEAP_ALLOCED_GC(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED));
787 prev = (StgSelector*)((StgClosure *)p)->payload[0];
789 // Update the THUNK_SELECTOR with an indirection to the
790 // value. The value is still in from-space at this stage.
792 // (old note: Why not do upd_evacuee(q,p)? Because we have an
793 // invariant that an EVACUATED closure always points to an
794 // object in the same or an older generation (required by
795 // the short-cut test in the EVACUATED case, below).
796 if ((StgClosure *)p == val) {
797 // must be a loop; just leave a BLACKHOLE in place. This
798 // can happen when we have a chain of selectors that
799 // eventually loops back on itself. We can't leave an
800 // indirection pointing to itself, and we want the program
801 // to deadlock if it ever enters this closure, so
802 // BLACKHOLE is correct.
803 SET_INFO(p, &stg_BLACKHOLE_info);
805 ((StgInd *)p)->indirectee = val;
807 SET_INFO(p, &stg_IND_info);
810 // For the purposes of LDV profiling, we have created an
812 LDV_RECORD_CREATE(p);
819 eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac)
820 // NB. for legacy reasons, p & q are swapped around :(
825 StgClosure *selectee;
826 StgSelector *prev_thunk_selector;
830 prev_thunk_selector = NULL;
831 // this is a chain of THUNK_SELECTORs that we are going to update
832 // to point to the value of the current THUNK_SELECTOR. Each
833 // closure on the chain is a BLACKHOLE, and points to the next in the
834 // chain with payload[0].
838 bd = Bdescr((StgPtr)p);
839 if (HEAP_ALLOCED_GC(p)) {
840 // If the THUNK_SELECTOR is in to-space or in a generation that we
841 // are not collecting, then bale out early. We won't be able to
842 // save any space in any case, and updating with an indirection is
843 // trickier in a non-collected gen: we would have to update the
845 if (bd->flags & BF_EVACUATED) {
846 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
847 *q = (StgClosure *)p;
848 // shortcut, behave as for: if (evac) evacuate(q);
849 if (evac && bd->step < gct->evac_step) {
850 gct->failed_to_evac = rtsTrue;
851 TICK_GC_FAILED_PROMOTION();
855 // we don't update THUNK_SELECTORS in the compacted
856 // generation, because compaction does not remove the INDs
857 // that result, this causes confusion later
858 // (scavenge_mark_stack doesn't deal with IND). BEWARE! This
859 // bit is very tricky to get right. If you make changes
860 // around here, test by compiling stage 3 with +RTS -c -RTS.
861 if (bd->flags & BF_MARKED) {
862 // must call evacuate() to mark this closure if evac==rtsTrue
863 *q = (StgClosure *)p;
864 if (evac) evacuate(q);
865 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
871 // BLACKHOLE the selector thunk, since it is now under evaluation.
872 // This is important to stop us going into an infinite loop if
873 // this selector thunk eventually refers to itself.
874 #if defined(THREADED_RTS)
875 // In threaded mode, we'll use WHITEHOLE to lock the selector
876 // thunk while we evaluate it.
879 info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info);
880 } while (info_ptr == (W_)&stg_WHITEHOLE_info);
882 // make sure someone else didn't get here first...
883 if (IS_FORWARDING_PTR(p) ||
884 INFO_PTR_TO_STRUCT(info_ptr)->type != THUNK_SELECTOR) {
885 // v. tricky now. The THUNK_SELECTOR has been evacuated
886 // by another thread, and is now either a forwarding ptr or IND.
887 // We need to extract ourselves from the current situation
888 // as cleanly as possible.
889 // - unlock the closure
890 // - update *q, we may have done *some* evaluation
891 // - if evac, we need to call evacuate(), because we
892 // need the write-barrier stuff.
893 // - undo the chain we've built to point to p.
894 SET_INFO(p, (const StgInfoTable *)info_ptr);
895 *q = (StgClosure *)p;
896 if (evac) evacuate(q);
897 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
902 // Save the real info pointer (NOTE: not the same as get_itbl()).
903 info_ptr = (StgWord)p->header.info;
904 SET_INFO(p,&stg_BLACKHOLE_info);
907 field = INFO_PTR_TO_STRUCT(info_ptr)->layout.selector_offset;
909 // The selectee might be a constructor closure,
910 // so we untag the pointer.
911 selectee = UNTAG_CLOSURE(p->selectee);
914 // selectee now points to the closure that we're trying to select
915 // a field from. It may or may not be in to-space: we try not to
916 // end up in to-space, but it's impractical to avoid it in
917 // general. The compacting GC scatters to-space pointers in
918 // from-space during marking, for example. We rely on the property
919 // that evacuate() doesn't mind if it gets passed a to-space pointer.
921 info = (StgInfoTable*)selectee->header.info;
923 if (IS_FORWARDING_PTR(info)) {
924 // We don't follow pointers into to-space; the constructor
925 // has already been evacuated, so we won't save any space
926 // leaks by evaluating this selector thunk anyhow.
930 info = INFO_PTR_TO_STRUCT(info);
931 switch (info->type) {
933 goto bale_out; // about to be evacuated by another thread (or a loop).
942 case CONSTR_NOCAF_STATIC:
944 // check that the size is in range
945 ASSERT(field < (StgWord32)(info->layout.payload.ptrs +
946 info->layout.payload.nptrs));
948 // Select the right field from the constructor
949 val = selectee->payload[field];
952 // For the purposes of LDV profiling, we have destroyed
953 // the original selector thunk, p.
954 SET_INFO(p, (StgInfoTable *)info_ptr);
955 LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC((StgClosure *)p);
956 #if defined(THREADED_RTS)
957 SET_INFO(p, &stg_WHITEHOLE_info);
959 SET_INFO(p, &stg_BLACKHOLE_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 );
1018 case THUNK_SELECTOR:
1022 // recursively evaluate this selector. We don't want to
1023 // recurse indefinitely, so we impose a depth bound.
1024 if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) {
1028 gct->thunk_selector_depth++;
1029 // rtsFalse says "don't evacuate the result". It will,
1030 // however, update any THUNK_SELECTORs that are evaluated
1032 eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse);
1033 gct->thunk_selector_depth--;
1035 // did we actually manage to evaluate it?
1036 if (val == selectee) goto bale_out;
1038 // Of course this pointer might be tagged...
1039 selectee = UNTAG_CLOSURE(val);
1054 // not evaluated yet
1058 barf("eval_thunk_selector: strange selectee %d",
1063 // We didn't manage to evaluate this thunk; restore the old info
1064 // pointer. But don't forget: we still need to evacuate the thunk itself.
1065 SET_INFO(p, (const StgInfoTable *)info_ptr);
1066 // THREADED_RTS: we just unlocked the thunk, so another thread
1067 // might get in and update it. copy() will lock it again and
1068 // check whether it was updated in the meantime.
1069 *q = (StgClosure *)p;
1071 copy(q,(const StgInfoTable *)info_ptr,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->dest);
1073 unchain_thunk_selectors(prev_thunk_selector, *q);