X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fsm%2FEvac.c;h=b0b7ef56545464b39cdd078fb62e439198a42d66;hb=f86e7206ea94b48b94fb61007a1c5d55b8c60f45;hp=6ca7d85fc2ce9a211683897bbd936166679f35da;hpb=9cd54893c0097b5b763dc9657e3c228492cdb87f;p=ghc-hetmet.git diff --git a/rts/sm/Evac.c b/rts/sm/Evac.c index 6ca7d85..b0b7ef5 100644 --- a/rts/sm/Evac.c +++ b/rts/sm/Evac.c @@ -16,173 +16,71 @@ #include "MBlock.h" #include "Evac.h" #include "GC.h" +#include "GCThread.h" #include "GCUtils.h" #include "Compact.h" #include "Prelude.h" #include "LdvProfile.h" -/* Used to avoid long recursion due to selector thunks - */ -lnat thunk_selector_depth = 0; -#define MAX_THUNK_SELECTOR_DEPTH 8 - -static StgClosure * eval_thunk_selector ( nat field, StgSelector * p ); - -STATIC_INLINE void -upd_evacuee(StgClosure *p, StgClosure *dest) -{ - // not true: (ToDo: perhaps it should be) - // ASSERT(Bdescr((P_)dest)->flags & BF_EVACUATED); - SET_INFO(p, &stg_EVACUATED_info); - ((StgEvacuated *)p)->evacuee = dest; -} - - -STATIC_INLINE StgClosure * -copy(StgClosure *src, nat size, step *stp) -{ - StgPtr to, from; - nat i; -#ifdef PROFILING - // @LDV profiling - nat size_org = size; +#if defined(PROF_SPIN) && defined(THREADED_RTS) +StgWord64 whitehole_spin = 0; #endif - TICK_GC_WORDS_COPIED(size); - /* Find out where we're going, using the handy "to" pointer in - * the step of the source object. If it turns out we need to - * evacuate to an older generation, adjust it here (see comment - * by evacuate()). - */ - if (stp->gen_no < evac_gen) { - if (eager_promotion) { - stp = &generations[evac_gen].steps[0]; - } else { - failed_to_evac = rtsTrue; - } - } - - /* chain a new block onto the to-space for the destination step if - * necessary. - */ - if (stp->hp + size >= stp->hpLim) { - gc_alloc_block(stp); - } +/* Used to avoid long recursion due to selector thunks + */ +#define MAX_THUNK_SELECTOR_DEPTH 16 - to = stp->hp; - from = (StgPtr)src; - stp->hp = to + size; - for (i = 0; i < size; i++) { // unroll for small i - to[i] = from[i]; - } - upd_evacuee((StgClosure *)from,(StgClosure *)to); +static void eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool); +STATIC_INLINE void evacuate_large(StgPtr p); -#ifdef PROFILING - // We store the size of the just evacuated object in the LDV word so that - // the profiler can guess the position of the next object later. - SET_EVACUAEE_FOR_LDV(from, size_org); -#endif - return (StgClosure *)to; -} +/* ----------------------------------------------------------------------------- + Allocate some space in which to copy an object. + -------------------------------------------------------------------------- */ -// Same as copy() above, except the object will be allocated in memory -// that will not be scavenged. Used for object that have no pointer -// fields. -STATIC_INLINE StgClosure * -copy_noscav(StgClosure *src, nat size, step *stp) +STATIC_INLINE StgPtr +alloc_for_copy (nat size, step *stp) { - StgPtr to, from; - nat i; -#ifdef PROFILING - // @LDV profiling - nat size_org = size; -#endif + StgPtr to; + step_workspace *ws; - TICK_GC_WORDS_COPIED(size); - /* Find out where we're going, using the handy "to" pointer in - * the step of the source object. If it turns out we need to - * evacuate to an older generation, adjust it here (see comment - * by evacuate()). - */ - if (stp->gen_no < evac_gen) { - if (eager_promotion) { - stp = &generations[evac_gen].steps[0]; - } else { - failed_to_evac = rtsTrue; - } - } - - /* chain a new block onto the to-space for the destination step if - * necessary. - */ - if (stp->scavd_hp + size >= stp->scavd_hpLim) { - gc_alloc_scavd_block(stp); - } - - to = stp->scavd_hp; - from = (StgPtr)src; - stp->scavd_hp = to + size; - for (i = 0; i < size; i++) { // unroll for small i - to[i] = from[i]; - } - upd_evacuee((StgClosure *)from,(StgClosure *)to); + /* Find out where we're going, using the handy "to" pointer in + * the step of the source object. If it turns out we need to + * evacuate to an older generation, adjust it here (see comment + * by evacuate()). + */ + if (stp < gct->evac_step) { + if (gct->eager_promotion) { + stp = gct->evac_step; + } else { + gct->failed_to_evac = rtsTrue; + } + } + + ws = &gct->steps[stp->abs_no]; + // this compiles to a single mem access to stp->abs_no only + + /* chain a new block onto the to-space for the destination step if + * necessary. + */ + to = ws->todo_free; + if (to + size > ws->todo_lim) { + to = todo_block_full(size, ws); + } + ws->todo_free = to + size; + ASSERT(ws->todo_free >= ws->todo_bd->free && ws->todo_free <= ws->todo_lim); -#ifdef PROFILING - // We store the size of the just evacuated object in the LDV word so that - // the profiler can guess the position of the next object later. - SET_EVACUAEE_FOR_LDV(from, size_org); -#endif - return (StgClosure *)to; + return to; } -/* Special version of copy() for when we only want to copy the info - * pointer of an object, but reserve some padding after it. This is - * used to optimise evacuation of BLACKHOLEs. - */ - - -static StgClosure * -copyPart(StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp) -{ - P_ dest, to, from; -#ifdef PROFILING - // @LDV profiling - nat size_to_copy_org = size_to_copy; -#endif - - TICK_GC_WORDS_COPIED(size_to_copy); - if (stp->gen_no < evac_gen) { - if (eager_promotion) { - stp = &generations[evac_gen].steps[0]; - } else { - failed_to_evac = rtsTrue; - } - } - - if (stp->hp + size_to_reserve >= stp->hpLim) { - gc_alloc_block(stp); - } +/* ----------------------------------------------------------------------------- + The evacuate() code + -------------------------------------------------------------------------- */ - for(to = stp->hp, from = (P_)src; size_to_copy>0; --size_to_copy) { - *to++ = *from++; - } - - dest = stp->hp; - stp->hp += size_to_reserve; - upd_evacuee(src,(StgClosure *)dest); -#ifdef PROFILING - // We store the size of the just evacuated object in the LDV word so that - // the profiler can guess the position of the next object later. - // size_to_copy_org is wrong because the closure already occupies size_to_reserve - // words. - SET_EVACUAEE_FOR_LDV(src, size_to_reserve); - // fill the slop - if (size_to_reserve - size_to_copy_org > 0) - LDV_FILL_SLOP(stp->hp - 1, (int)(size_to_reserve - size_to_copy_org)); -#endif - return (StgClosure *)dest; -} +#define PARALLEL_GC +#include "Evac.c-inc" +#undef PARALLEL_GC +#include "Evac.c-inc" /* ----------------------------------------------------------------------------- Evacuate a large object @@ -195,12 +93,15 @@ copyPart(StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp) that has been evacuated, or unset otherwise. -------------------------------------------------------------------------- */ - STATIC_INLINE void evacuate_large(StgPtr p) { bdescr *bd = Bdescr(p); - step *stp; + step *stp, *new_stp; + step_workspace *ws; + + stp = bd->step; + ACQUIRE_SPIN_LOCK(&stp->sync_large_objects); // object must be at the beginning of the block (or be a ByteArray) ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS || @@ -208,17 +109,17 @@ evacuate_large(StgPtr p) // already evacuated? if (bd->flags & BF_EVACUATED) { - /* Don't forget to set the failed_to_evac flag if we didn't get + /* Don't forget to set the gct->failed_to_evac flag if we didn't get * the desired destination (see comments in evacuate()). */ - if (bd->gen_no < evac_gen) { - failed_to_evac = rtsTrue; - TICK_GC_FAILED_PROMOTION(); + if (stp < gct->evac_step) { + gct->failed_to_evac = rtsTrue; + TICK_GC_FAILED_PROMOTION(); } + RELEASE_SPIN_LOCK(&stp->sync_large_objects); return; } - stp = bd->step; // remove from large_object list if (bd->u.back) { bd->u.back->link = bd->link; @@ -231,570 +132,177 @@ evacuate_large(StgPtr p) /* link it on to the evacuated large object list of the destination step */ - stp = bd->step->to; - if (stp->gen_no < evac_gen) { - if (eager_promotion) { - stp = &generations[evac_gen].steps[0]; + new_stp = stp->to; + if (new_stp < gct->evac_step) { + if (gct->eager_promotion) { + new_stp = gct->evac_step; } else { - failed_to_evac = rtsTrue; + gct->failed_to_evac = rtsTrue; } } - bd->step = stp; - bd->gen_no = stp->gen_no; - bd->link = stp->new_large_objects; - stp->new_large_objects = bd; + ws = &gct->steps[new_stp->abs_no]; bd->flags |= BF_EVACUATED; + bd->step = new_stp; + bd->gen_no = new_stp->gen_no; + bd->link = ws->todo_large_objects; + ws->todo_large_objects = bd; + + RELEASE_SPIN_LOCK(&stp->sync_large_objects); } /* ----------------------------------------------------------------------------- - Evacuate - - This is called (eventually) for every live object in the system. - - The caller to evacuate specifies a desired generation in the - evac_gen global variable. The following conditions apply to - evacuating an object which resides in generation M when we're - collecting up to generation N - - if M >= evac_gen - if M > N do nothing - else evac to step->to - - if M < evac_gen evac to evac_gen, step 0 - - if the object is already evacuated, then we check which generation - it now resides in. - - if M >= evac_gen do nothing - if M < evac_gen set failed_to_evac flag to indicate that we - didn't manage to evacuate this object into evac_gen. - - - OPTIMISATION NOTES: + Evaluate a THUNK_SELECTOR if possible. - evacuate() is the single most important function performance-wise - in the GC. Various things have been tried to speed it up, but as - far as I can tell the code generated by gcc 3.2 with -O2 is about - as good as it's going to get. We pass the argument to evacuate() - in a register using the 'regparm' attribute (see the prototype for - evacuate() near the top of this file). + p points to a THUNK_SELECTOR that we want to evaluate. The + result of "evaluating" it will be evacuated and a pointer to the + to-space closure will be returned. - Changing evacuate() to take an (StgClosure **) rather than - returning the new pointer seems attractive, because we can avoid - writing back the pointer when it hasn't changed (eg. for a static - object, or an object in a generation > N). However, I tried it and - it doesn't help. One reason is that the (StgClosure **) pointer - gets spilled to the stack inside evacuate(), resulting in far more - extra reads/writes than we save. + If the THUNK_SELECTOR could not be evaluated (its selectee is still + a THUNK, for example), then the THUNK_SELECTOR itself will be + evacuated. -------------------------------------------------------------------------- */ - -REGPARM1 StgClosure * -evacuate(StgClosure *q) +static void +unchain_thunk_selectors(StgSelector *p, StgClosure *val) { - bdescr *bd = NULL; - step *stp; - const StgInfoTable *info; - -loop: - ASSERT(LOOKS_LIKE_CLOSURE_PTR(q)); - - if (!HEAP_ALLOCED(q)) { - - if (!major_gc) return q; - - info = get_itbl(q); - switch (info->type) { - - case THUNK_STATIC: - if (info->srt_bitmap != 0 && - *THUNK_STATIC_LINK((StgClosure *)q) == NULL) { - *THUNK_STATIC_LINK((StgClosure *)q) = static_objects; - static_objects = (StgClosure *)q; - } - return q; - - case FUN_STATIC: - if (info->srt_bitmap != 0 && - *FUN_STATIC_LINK((StgClosure *)q) == NULL) { - *FUN_STATIC_LINK((StgClosure *)q) = static_objects; - static_objects = (StgClosure *)q; - } - return q; - - case IND_STATIC: - /* If q->saved_info != NULL, then it's a revertible CAF - it'll be - * on the CAF list, so don't do anything with it here (we'll - * scavenge it later). - */ - if (((StgIndStatic *)q)->saved_info == NULL - && *IND_STATIC_LINK((StgClosure *)q) == NULL) { - *IND_STATIC_LINK((StgClosure *)q) = static_objects; - static_objects = (StgClosure *)q; - } - return q; - - case CONSTR_STATIC: - if (*STATIC_LINK(info,(StgClosure *)q) == NULL) { - *STATIC_LINK(info,(StgClosure *)q) = static_objects; - static_objects = (StgClosure *)q; - } - return q; - - case CONSTR_NOCAF_STATIC: - /* no need to put these on the static linked list, they don't need - * to be scavenged. - */ - return q; - - default: - barf("evacuate(static): strange closure type %d", (int)(info->type)); - } - } - - bd = Bdescr((P_)q); - - if (bd->gen_no > N) { - /* Can't evacuate this object, because it's in a generation - * older than the ones we're collecting. Let's hope that it's - * in evac_gen or older, or we will have to arrange to track - * this pointer using the mutable list. - */ - if (bd->gen_no < evac_gen) { - // nope - failed_to_evac = rtsTrue; - TICK_GC_FAILED_PROMOTION(); - } - return q; - } + StgSelector *prev; - if ((bd->flags & (BF_LARGE | BF_COMPACTED | BF_EVACUATED)) != 0) { - - /* pointer into to-space: just return it. This normally - * shouldn't happen, but alllowing it makes certain things - * slightly easier (eg. the mutable list can contain the same - * object twice, for example). - */ - if (bd->flags & BF_EVACUATED) { - if (bd->gen_no < evac_gen) { - failed_to_evac = rtsTrue; - TICK_GC_FAILED_PROMOTION(); - } - return q; - } - - /* evacuate large objects by re-linking them onto a different list. - */ - if (bd->flags & BF_LARGE) { - info = get_itbl(q); - if (info->type == TSO && - ((StgTSO *)q)->what_next == ThreadRelocated) { - q = (StgClosure *)((StgTSO *)q)->link; - goto loop; - } - evacuate_large((P_)q); - return q; - } - - /* If the object is in a step that we're compacting, then we - * need to use an alternative evacuate procedure. - */ - if (bd->flags & BF_COMPACTED) { - if (!is_marked((P_)q,bd)) { - mark((P_)q,bd); - if (mark_stack_full()) { - mark_stack_overflowed = rtsTrue; - reset_mark_stack(); - } - push_mark_stack((P_)q); - } - return q; - } - } - - stp = bd->step->to; - - info = get_itbl(q); - - switch (info->type) { - - case MUT_VAR_CLEAN: - case MUT_VAR_DIRTY: - case MVAR: - return copy(q,sizeW_fromITBL(info),stp); - - case CONSTR_0_1: - { - StgWord w = (StgWord)q->payload[0]; - if (q->header.info == Czh_con_info && - // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE && - (StgChar)w <= MAX_CHARLIKE) { - return (StgClosure *)CHARLIKE_CLOSURE((StgChar)w); - } - if (q->header.info == Izh_con_info && - (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) { - return (StgClosure *)INTLIKE_CLOSURE((StgInt)w); - } - // else - return copy_noscav(q,sizeofW(StgHeader)+1,stp); - } - - case FUN_0_1: - case FUN_1_0: - case CONSTR_1_0: - return copy(q,sizeofW(StgHeader)+1,stp); - - case THUNK_1_0: - case THUNK_0_1: - return copy(q,sizeofW(StgThunk)+1,stp); - - case THUNK_1_1: - case THUNK_2_0: - case THUNK_0_2: -#ifdef NO_PROMOTE_THUNKS - if (bd->gen_no == 0 && - bd->step->no != 0 && - bd->step->no == generations[bd->gen_no].n_steps-1) { - stp = bd->step; - } -#endif - return copy(q,sizeofW(StgThunk)+2,stp); - - case FUN_1_1: - case FUN_2_0: - case CONSTR_1_1: - case CONSTR_2_0: - case FUN_0_2: - return copy(q,sizeofW(StgHeader)+2,stp); - - case CONSTR_0_2: - return copy_noscav(q,sizeofW(StgHeader)+2,stp); - - case THUNK: - return copy(q,thunk_sizeW_fromITBL(info),stp); - - case FUN: - case CONSTR: - case IND_PERM: - case IND_OLDGEN_PERM: - case WEAK: - case STABLE_NAME: - return copy(q,sizeW_fromITBL(info),stp); - - case BCO: - return copy(q,bco_sizeW((StgBCO *)q),stp); - - case CAF_BLACKHOLE: - case SE_CAF_BLACKHOLE: - case SE_BLACKHOLE: - case BLACKHOLE: - return copyPart(q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp); - - case THUNK_SELECTOR: + prev = NULL; + while (p) { - StgClosure *p; - const StgInfoTable *info_ptr; - - if (thunk_selector_depth > MAX_THUNK_SELECTOR_DEPTH) { - return copy(q,THUNK_SELECTOR_sizeW(),stp); - } - - // stashed away for LDV profiling, see below - info_ptr = q->header.info; - - p = eval_thunk_selector(info->layout.selector_offset, - (StgSelector *)q); - - if (p == NULL) { - return copy(q,THUNK_SELECTOR_sizeW(),stp); - } else { - StgClosure *val; - // q is still BLACKHOLE'd. - thunk_selector_depth++; - val = evacuate(p); - thunk_selector_depth--; - -#ifdef PROFILING - // For the purposes of LDV profiling, we have destroyed - // the original selector thunk. - SET_INFO(q, info_ptr); - LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC(q); +#ifdef THREADED_RTS + ASSERT(p->header.info == &stg_WHITEHOLE_info); +#else + ASSERT(p->header.info == &stg_BLACKHOLE_info); #endif - - // Update the THUNK_SELECTOR with an indirection to the - // EVACUATED closure now at p. Why do this rather than - // upd_evacuee(q,p)? Because we have an invariant that an - // EVACUATED closure always points to an object in the - // same or an older generation (required by the short-cut - // test in the EVACUATED case, below). - SET_INFO(q, &stg_IND_info); - ((StgInd *)q)->indirectee = p; - - // For the purposes of LDV profiling, we have created an - // indirection. - LDV_RECORD_CREATE(q); - - return val; - } + // val must be in to-space. Not always: when we recursively + // invoke eval_thunk_selector(), the recursive calls will not + // evacuate the value (because we want to select on the value, + // not evacuate it), so in this case val is in from-space. + // ASSERT(!HEAP_ALLOCED(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED)); + + prev = (StgSelector*)((StgClosure *)p)->payload[0]; + + // Update the THUNK_SELECTOR with an indirection to the + // EVACUATED closure now at p. Why do this rather than + // upd_evacuee(q,p)? Because we have an invariant that an + // EVACUATED closure always points to an object in the + // same or an older generation (required by the short-cut + // test in the EVACUATED case, below). + ((StgInd *)p)->indirectee = val; + write_barrier(); + SET_INFO(p, &stg_IND_info); + + // For the purposes of LDV profiling, we have created an + // indirection. + LDV_RECORD_CREATE(p); + + p = prev; } - - case IND: - case IND_OLDGEN: - // follow chains of indirections, don't evacuate them - q = ((StgInd*)q)->indirectee; - goto loop; - - case RET_BCO: - case RET_SMALL: - case RET_VEC_SMALL: - case RET_BIG: - case RET_VEC_BIG: - case RET_DYN: - case UPDATE_FRAME: - case STOP_FRAME: - case CATCH_FRAME: - case CATCH_STM_FRAME: - case CATCH_RETRY_FRAME: - case ATOMICALLY_FRAME: - // shouldn't see these - barf("evacuate: stack frame at %p\n", q); - - case PAP: - return copy(q,pap_sizeW((StgPAP*)q),stp); - - case AP: - return copy(q,ap_sizeW((StgAP*)q),stp); - - case AP_STACK: - return copy(q,ap_stack_sizeW((StgAP_STACK*)q),stp); - - case EVACUATED: - /* Already evacuated, just return the forwarding address. - * HOWEVER: if the requested destination generation (evac_gen) is - * older than the actual generation (because the object was - * already evacuated to a younger generation) then we have to - * set the failed_to_evac flag to indicate that we couldn't - * manage to promote the object to the desired generation. - */ - /* - * Optimisation: the check is fairly expensive, but we can often - * shortcut it if either the required generation is 0, or the - * current object (the EVACUATED) is in a high enough generation. - * We know that an EVACUATED always points to an object in the - * same or an older generation. stp is the lowest step that the - * current object would be evacuated to, so we only do the full - * check if stp is too low. - */ - if (evac_gen > 0 && stp->gen_no < evac_gen) { // optimisation - StgClosure *p = ((StgEvacuated*)q)->evacuee; - if (HEAP_ALLOCED(p) && Bdescr((P_)p)->gen_no < evac_gen) { - failed_to_evac = rtsTrue; - TICK_GC_FAILED_PROMOTION(); - } - } - return ((StgEvacuated*)q)->evacuee; - - case ARR_WORDS: - // just copy the block - return copy_noscav(q,arr_words_sizeW((StgArrWords *)q),stp); - - case MUT_ARR_PTRS_CLEAN: - case MUT_ARR_PTRS_DIRTY: - case MUT_ARR_PTRS_FROZEN: - case MUT_ARR_PTRS_FROZEN0: - // just copy the block - return copy(q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),stp); - - case TSO: - { - StgTSO *tso = (StgTSO *)q; - - /* Deal with redirected TSOs (a TSO that's had its stack enlarged). - */ - if (tso->what_next == ThreadRelocated) { - q = (StgClosure *)tso->link; - goto loop; - } - - /* To evacuate a small TSO, we need to relocate the update frame - * list it contains. - */ - { - StgTSO *new_tso; - StgPtr p, q; - - new_tso = (StgTSO *)copyPart((StgClosure *)tso, - tso_sizeW(tso), - sizeofW(StgTSO), stp); - move_TSO(tso, new_tso); - for (p = tso->sp, q = new_tso->sp; - p < tso->stack+tso->stack_size;) { - *q++ = *p++; - } - - return (StgClosure *)new_tso; - } - } - - case TREC_HEADER: - return copy(q,sizeofW(StgTRecHeader),stp); - - case TVAR_WATCH_QUEUE: - return copy(q,sizeofW(StgTVarWatchQueue),stp); - - case TVAR: - return copy(q,sizeofW(StgTVar),stp); - - case TREC_CHUNK: - return copy(q,sizeofW(StgTRecChunk),stp); - - case ATOMIC_INVARIANT: - return copy(q,sizeofW(StgAtomicInvariant),stp); - - case INVARIANT_CHECK_QUEUE: - return copy(q,sizeofW(StgInvariantCheckQueue),stp); - - default: - barf("evacuate: strange closure type %d", (int)(info->type)); - } - - barf("evacuate"); } -/* ----------------------------------------------------------------------------- - Evaluate a THUNK_SELECTOR if possible. - - returns: NULL if we couldn't evaluate this THUNK_SELECTOR, or - a closure pointer if we evaluated it and this is the result. Note - that "evaluating" the THUNK_SELECTOR doesn't necessarily mean - reducing it to HNF, just that we have eliminated the selection. - The result might be another thunk, or even another THUNK_SELECTOR. - - If the return value is non-NULL, the original selector thunk has - been BLACKHOLE'd, and should be updated with an indirection or a - forwarding pointer. If the return value is NULL, then the selector - thunk is unchanged. - - *** - ToDo: the treatment of THUNK_SELECTORS could be improved in the - following way (from a suggestion by Ian Lynagh): - - We can have a chain like this: - - sel_0 --> (a,b) - | - |-----> sel_0 --> (a,b) - | - |-----> sel_0 --> ... - - and the depth limit means we don't go all the way to the end of the - chain, which results in a space leak. This affects the recursive - call to evacuate() in the THUNK_SELECTOR case in evacuate(): *not* - the recursive call to eval_thunk_selector() in - eval_thunk_selector(). - - We could eliminate the depth bound in this case, in the following - way: - - - traverse the chain once to discover the *value* of the - THUNK_SELECTOR. Mark all THUNK_SELECTORS that we - visit on the way as having been visited already (somehow). - - - in a second pass, traverse the chain again updating all - THUNK_SEELCTORS that we find on the way with indirections to - the value. - - - if we encounter a "marked" THUNK_SELECTOR in a normal - evacuate(), we konw it can't be updated so just evac it. - - Program that illustrates the problem: - - foo [] = ([], []) - foo (x:xs) = let (ys, zs) = foo xs - in if x >= 0 then (x:ys, zs) else (ys, x:zs) - - main = bar [1..(100000000::Int)] - bar xs = (\(ys, zs) -> print ys >> print zs) (foo xs) - - -------------------------------------------------------------------------- */ - -static inline rtsBool -is_to_space ( StgClosure *p ) -{ - bdescr *bd; - - bd = Bdescr((StgPtr)p); - if (HEAP_ALLOCED(p) && - ((bd->flags & BF_EVACUATED) - || ((bd->flags & BF_COMPACTED) && - is_marked((P_)p,bd)))) { - return rtsTrue; - } else { - return rtsFalse; - } -} - -static StgClosure * -eval_thunk_selector( nat field, StgSelector * p ) +static void +eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac) + // NB. for legacy reasons, p & q are swapped around :( { + nat field; StgInfoTable *info; - const StgInfoTable *info_ptr; + StgWord info_ptr; StgClosure *selectee; + StgSelector *prev_thunk_selector; + bdescr *bd; + StgClosure *val; - selectee = p->selectee; + prev_thunk_selector = NULL; + // this is a chain of THUNK_SELECTORs that we are going to update + // to point to the value of the current THUNK_SELECTOR. Each + // closure on the chain is a BLACKHOLE, and points to the next in the + // chain with payload[0]. - // Save the real info pointer (NOTE: not the same as get_itbl()). - info_ptr = p->header.info; - - // If the THUNK_SELECTOR is in a generation that we are not - // collecting, then bail out early. We won't be able to save any - // space in any case, and updating with an indirection is trickier - // in an old gen. - if (Bdescr((StgPtr)p)->gen_no > N) { - return NULL; +selector_chain: + + bd = Bdescr((StgPtr)p); + if (HEAP_ALLOCED(p)) { + // If the THUNK_SELECTOR is in to-space or in a generation that we + // are not collecting, then bale out early. We won't be able to + // save any space in any case, and updating with an indirection is + // trickier in a non-collected gen: we would have to update the + // mutable list. + if ((bd->gen_no > N) || (bd->flags & BF_EVACUATED)) { + unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p); + *q = (StgClosure *)p; + return; + } + // we don't update THUNK_SELECTORS in the compacted + // generation, because compaction does not remove the INDs + // that result, this causes confusion later + // (scavenge_mark_stack doesn't deal with IND). BEWARE! This + // bit is very tricky to get right. If you make changes + // around here, test by compiling stage 3 with +RTS -c -RTS. + if (bd->flags & BF_COMPACTED) { + // must call evacuate() to mark this closure if evac==rtsTrue + *q = (StgClosure *)p; + if (evac) evacuate(q); + unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p); + return; + } } + // BLACKHOLE the selector thunk, since it is now under evaluation. // This is important to stop us going into an infinite loop if // this selector thunk eventually refers to itself. +#if defined(THREADED_RTS) + // In threaded mode, we'll use WHITEHOLE to lock the selector + // thunk while we evaluate it. + { + do { + info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info); + } while (info_ptr == (W_)&stg_WHITEHOLE_info); + + // make sure someone else didn't get here first... + if (INFO_PTR_TO_STRUCT(info_ptr)->type != THUNK_SELECTOR) { + // v. tricky now. The THUNK_SELECTOR has been evacuated + // by another thread, and is now either EVACUATED or IND. + // We need to extract ourselves from the current situation + // as cleanly as possible. + // - unlock the closure + // - update *q, we may have done *some* evaluation + // - if evac, we need to call evacuate(), because we + // need the write-barrier stuff. + // - undo the chain we've built to point to p. + SET_INFO(p, (const StgInfoTable *)info_ptr); + *q = (StgClosure *)p; + if (evac) evacuate(q); + unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p); + return; + } + } +#else + // Save the real info pointer (NOTE: not the same as get_itbl()). + info_ptr = (StgWord)p->header.info; SET_INFO(p,&stg_BLACKHOLE_info); +#endif -selector_loop: + field = INFO_PTR_TO_STRUCT(info_ptr)->layout.selector_offset; - // We don't want to end up in to-space, because this causes - // problems when the GC later tries to evacuate the result of - // eval_thunk_selector(). There are various ways this could - // happen: - // - // 1. following an IND_STATIC - // - // 2. when the old generation is compacted, the mark phase updates - // from-space pointers to be to-space pointers, and we can't - // reliably tell which we're following (eg. from an IND_STATIC). - // - // 3. compacting GC again: if we're looking at a constructor in - // the compacted generation, it might point directly to objects - // in to-space. We must bale out here, otherwise doing the selection - // will result in a to-space pointer being returned. - // - // (1) is dealt with using a BF_EVACUATED test on the - // selectee. (2) and (3): we can tell if we're looking at an - // object in the compacted generation that might point to - // to-space objects by testing that (a) it is BF_COMPACTED, (b) - // the compacted generation is being collected, and (c) the - // object is marked. Only a marked object may have pointers that - // point to to-space objects, because that happens when - // scavenging. - // - // The to-space test is now embodied in the in_to_space() inline - // function, as it is re-used below. - // - if (is_to_space(selectee)) { - goto bale_out; - } + // The selectee might be a constructor closure, + // so we untag the pointer. + selectee = UNTAG_CLOSURE(p->selectee); + +selector_loop: + // selectee now points to the closure that we're trying to select + // a field from. It may or may not be in to-space: we try not to + // end up in to-space, but it's impractical to avoid it in + // general. The compacting GC scatters to-space pointers in + // from-space during marking, for example. We rely on the property + // that evacuate() doesn't mind if it gets passed a to-space pointer. info = get_itbl(selectee); switch (info->type) { + case WHITEHOLE: + goto bale_out; // about to be evacuated by another thread (or a loop). + case CONSTR: case CONSTR_1_0: case CONSTR_0_1: @@ -803,88 +311,95 @@ selector_loop: case CONSTR_0_2: case CONSTR_STATIC: case CONSTR_NOCAF_STATIC: - // check that the size is in range - ASSERT(field < (StgWord32)(info->layout.payload.ptrs + - info->layout.payload.nptrs)); + { + // check that the size is in range + ASSERT(field < (StgWord32)(info->layout.payload.ptrs + + info->layout.payload.nptrs)); - // Select the right field from the constructor, and check - // that the result isn't in to-space. It might be in - // to-space if, for example, this constructor contains - // pointers to younger-gen objects (and is on the mut-once - // list). - // - { - StgClosure *q; - q = selectee->payload[field]; - if (is_to_space(q)) { - goto bale_out; - } else { - return q; - } - } + // Select the right field from the constructor + val = selectee->payload[field]; + +#ifdef PROFILING + // For the purposes of LDV profiling, we have destroyed + // the original selector thunk, p. + SET_INFO(p, (StgInfoTable *)info_ptr); + LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC((StgClosure *)p); + SET_INFO(p, &stg_BLACKHOLE_info); +#endif + + // the closure in val is now the "value" of the + // THUNK_SELECTOR in p. However, val may itself be a + // THUNK_SELECTOR, in which case we want to continue + // evaluating until we find the real value, and then + // update the whole chain to point to the value. + val_loop: + info = get_itbl(UNTAG_CLOSURE(val)); + switch (info->type) { + case IND: + case IND_PERM: + case IND_OLDGEN: + case IND_OLDGEN_PERM: + case IND_STATIC: + val = ((StgInd *)val)->indirectee; + goto val_loop; + case THUNK_SELECTOR: + ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector; + prev_thunk_selector = p; + p = (StgSelector*)val; + goto selector_chain; + default: + ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector; + prev_thunk_selector = p; + + *q = val; + if (evac) evacuate(q); + val = *q; + // evacuate() cannot recurse through + // eval_thunk_selector(), because we know val is not + // a THUNK_SELECTOR. + unchain_thunk_selectors(prev_thunk_selector, val); + return; + } + } case IND: case IND_PERM: case IND_OLDGEN: case IND_OLDGEN_PERM: case IND_STATIC: - selectee = ((StgInd *)selectee)->indirectee; + // Again, we might need to untag a constructor. + selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee ); goto selector_loop; case EVACUATED: // We don't follow pointers into to-space; the constructor // has already been evacuated, so we won't save any space // leaks by evaluating this selector thunk anyhow. - break; + goto bale_out; case THUNK_SELECTOR: { StgClosure *val; - // check that we don't recurse too much, re-using the - // depth bound also used in evacuate(). - if (thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) { - break; + // recursively evaluate this selector. We don't want to + // recurse indefinitely, so we impose a depth bound. + if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) { + goto bale_out; } - // we don't update THUNK_SELECTORS in the compacted - // generation, because compaction does not remove the INDs - // that result, this causes confusion later. - if (Bdescr((P_)selectee)->flags && BF_COMPACTED) { - break; - } + gct->thunk_selector_depth++; + // rtsFalse says "don't evacuate the result". It will, + // however, update any THUNK_SELECTORs that are evaluated + // along the way. + eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse); + gct->thunk_selector_depth--; - thunk_selector_depth++; + // did we actually manage to evaluate it? + if (val == selectee) goto bale_out; - val = eval_thunk_selector(info->layout.selector_offset, - (StgSelector *)selectee); - - thunk_selector_depth--; - - if (val == NULL) { - break; - } else { - // We evaluated this selector thunk, so update it with - // an indirection. NOTE: we don't use UPD_IND here, - // because we are guaranteed that p is in a generation - // that we are collecting, and we never want to put the - // indirection on a mutable list. -#ifdef PROFILING - // For the purposes of LDV profiling, we have destroyed - // the original selector thunk. - SET_INFO(p, info_ptr); - LDV_RECORD_DEAD_FILL_SLOP_DYNAMIC(selectee); -#endif - ((StgInd *)selectee)->indirectee = val; - SET_INFO(selectee,&stg_IND_info); - - // For the purposes of LDV profiling, we have created an - // indirection. - LDV_RECORD_CREATE(selectee); - - selectee = val; - goto selector_loop; - } + // Of course this pointer might be tagged... + selectee = UNTAG_CLOSURE(val); + goto selector_loop; } case AP: @@ -901,7 +416,7 @@ selector_loop: case SE_BLACKHOLE: case BLACKHOLE: // not evaluated yet - break; + goto bale_out; default: barf("eval_thunk_selector: strange selectee %d", @@ -909,9 +424,18 @@ selector_loop: } bale_out: - // We didn't manage to evaluate this thunk; restore the old info pointer - SET_INFO(p, info_ptr); - return NULL; + // We didn't manage to evaluate this thunk; restore the old info + // pointer. But don't forget: we still need to evacuate the thunk itself. + SET_INFO(p, (const StgInfoTable *)info_ptr); + // THREADED_RTS: we just unlocked the thunk, so another thread + // might get in and update it. copy() will lock it again and + // check whether it was updated in the meantime. + *q = (StgClosure *)p; + if (evac) { + copy(q,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->step->to); + } + unchain_thunk_selectors(prev_thunk_selector, *q); + return; } /* -----------------------------------------------------------------------------