1 /* -----------------------------------------------------------------------------
2 * $Id: GC.c,v 1.41 1999/02/24 17:24:07 simonm Exp $
4 * (c) The GHC Team 1998-1999
6 * Generational garbage collector
8 * ---------------------------------------------------------------------------*/
14 #include "StoragePriv.h"
17 #include "SchedAPI.h" /* for ReverCAFs prototype */
20 #include "BlockAlloc.h"
22 #include "DebugProf.h"
25 #include "StablePriv.h"
29 /* STATIC OBJECT LIST.
32 * We maintain a linked list of static objects that are still live.
33 * The requirements for this list are:
35 * - we need to scan the list while adding to it, in order to
36 * scavenge all the static objects (in the same way that
37 * breadth-first scavenging works for dynamic objects).
39 * - we need to be able to tell whether an object is already on
40 * the list, to break loops.
42 * Each static object has a "static link field", which we use for
43 * linking objects on to the list. We use a stack-type list, consing
44 * objects on the front as they are added (this means that the
45 * scavenge phase is depth-first, not breadth-first, but that
48 * A separate list is kept for objects that have been scavenged
49 * already - this is so that we can zero all the marks afterwards.
51 * An object is on the list if its static link field is non-zero; this
52 * means that we have to mark the end of the list with '1', not NULL.
54 * Extra notes for generational GC:
56 * Each generation has a static object list associated with it. When
57 * collecting generations up to N, we treat the static object lists
58 * from generations > N as roots.
60 * We build up a static object list while collecting generations 0..N,
61 * which is then appended to the static object list of generation N+1.
63 StgClosure* static_objects; /* live static objects */
64 StgClosure* scavenged_static_objects; /* static objects scavenged so far */
66 /* N is the oldest generation being collected, where the generations
67 * are numbered starting at 0. A major GC (indicated by the major_gc
68 * flag) is when we're collecting all generations. We only attempt to
69 * deal with static objects and GC CAFs when doing a major GC.
72 static rtsBool major_gc;
74 /* Youngest generation that objects should be evacuated to in
75 * evacuate(). (Logically an argument to evacuate, but it's static
76 * a lot of the time so we optimise it into a global variable).
82 static StgWeak *old_weak_ptr_list; /* also pending finaliser list */
83 static rtsBool weak_done; /* all done for this pass */
85 /* Flag indicating failure to evacuate an object to the desired
88 static rtsBool failed_to_evac;
90 /* Old to-space (used for two-space collector only)
94 /* Data used for allocation area sizing.
96 lnat new_blocks; /* blocks allocated during this GC */
97 lnat g0s0_pcnt_kept = 30; /* percentage of g0s0 live at last minor GC */
99 /* -----------------------------------------------------------------------------
100 Static function declarations
101 -------------------------------------------------------------------------- */
103 static StgClosure *evacuate(StgClosure *q);
104 static void zeroStaticObjectList(StgClosure* first_static);
105 static rtsBool traverse_weak_ptr_list(void);
106 static void zeroMutableList(StgMutClosure *first);
107 static void revertDeadCAFs(void);
109 static void scavenge_stack(StgPtr p, StgPtr stack_end);
110 static void scavenge_large(step *step);
111 static void scavenge(step *step);
112 static void scavenge_static(void);
113 static void scavenge_mutable_list(generation *g);
114 static void scavenge_mut_once_list(generation *g);
117 static void gcCAFs(void);
120 /* -----------------------------------------------------------------------------
123 For garbage collecting generation N (and all younger generations):
125 - follow all pointers in the root set. the root set includes all
126 mutable objects in all steps in all generations.
128 - for each pointer, evacuate the object it points to into either
129 + to-space in the next higher step in that generation, if one exists,
130 + if the object's generation == N, then evacuate it to the next
131 generation if one exists, or else to-space in the current
133 + if the object's generation < N, then evacuate it to to-space
134 in the next generation.
136 - repeatedly scavenge to-space from each step in each generation
137 being collected until no more objects can be evacuated.
139 - free from-space in each step, and set from-space = to-space.
141 -------------------------------------------------------------------------- */
143 void GarbageCollect(void (*get_roots)(void))
147 lnat live, allocated, collected = 0, copied = 0;
151 CostCentreStack *prev_CCS;
154 /* tell the stats department that we've started a GC */
157 /* attribute any costs to CCS_GC */
163 /* We might have been called from Haskell land by _ccall_GC, in
164 * which case we need to call threadPaused() because the scheduler
165 * won't have done it.
167 if (CurrentTSO) { threadPaused(CurrentTSO); }
169 /* Approximate how much we allocated: number of blocks in the
170 * nursery + blocks allocated via allocate() - unused nusery blocks.
171 * This leaves a little slop at the end of each block, and doesn't
172 * take into account large objects (ToDo).
174 allocated = (nursery_blocks * BLOCK_SIZE_W) + allocated_bytes();
175 for ( bd = current_nursery->link; bd != NULL; bd = bd->link ) {
176 allocated -= BLOCK_SIZE_W;
179 /* Figure out which generation to collect
182 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
183 if (generations[g].steps[0].n_blocks >= generations[g].max_blocks) {
187 major_gc = (N == RtsFlags.GcFlags.generations-1);
189 /* check stack sanity *before* GC (ToDo: check all threads) */
190 /*IF_DEBUG(sanity, checkTSO(MainTSO,0)); */
191 IF_DEBUG(sanity, checkFreeListSanity());
193 /* Initialise the static object lists
195 static_objects = END_OF_STATIC_LIST;
196 scavenged_static_objects = END_OF_STATIC_LIST;
198 /* zero the mutable list for the oldest generation (see comment by
199 * zeroMutableList below).
202 zeroMutableList(generations[RtsFlags.GcFlags.generations-1].mut_once_list);
205 /* Save the old to-space if we're doing a two-space collection
207 if (RtsFlags.GcFlags.generations == 1) {
208 old_to_space = g0s0->to_space;
209 g0s0->to_space = NULL;
212 /* Keep a count of how many new blocks we allocated during this GC
213 * (used for resizing the allocation area, later).
217 /* Initialise to-space in all the generations/steps that we're
220 for (g = 0; g <= N; g++) {
221 generations[g].mut_once_list = END_MUT_LIST;
222 generations[g].mut_list = END_MUT_LIST;
224 for (s = 0; s < generations[g].n_steps; s++) {
226 /* generation 0, step 0 doesn't need to-space */
227 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
231 /* Get a free block for to-space. Extra blocks will be chained on
235 step = &generations[g].steps[s];
236 ASSERT(step->gen->no == g);
237 ASSERT(step->hp ? Bdescr(step->hp)->step == step : rtsTrue);
238 bd->gen = &generations[g];
241 bd->evacuated = 1; /* it's a to-space block */
242 step->hp = bd->start;
243 step->hpLim = step->hp + BLOCK_SIZE_W;
247 step->scan = bd->start;
249 step->new_large_objects = NULL;
250 step->scavenged_large_objects = NULL;
252 /* mark the large objects as not evacuated yet */
253 for (bd = step->large_objects; bd; bd = bd->link) {
259 /* make sure the older generations have at least one block to
260 * allocate into (this makes things easier for copy(), see below.
262 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
263 for (s = 0; s < generations[g].n_steps; s++) {
264 step = &generations[g].steps[s];
265 if (step->hp_bd == NULL) {
267 bd->gen = &generations[g];
270 bd->evacuated = 0; /* *not* a to-space block */
271 step->hp = bd->start;
272 step->hpLim = step->hp + BLOCK_SIZE_W;
278 /* Set the scan pointer for older generations: remember we
279 * still have to scavenge objects that have been promoted. */
280 step->scan = step->hp;
281 step->scan_bd = step->hp_bd;
282 step->to_space = NULL;
284 step->new_large_objects = NULL;
285 step->scavenged_large_objects = NULL;
289 /* -----------------------------------------------------------------------
290 * follow all the roots that we know about:
291 * - mutable lists from each generation > N
292 * we want to *scavenge* these roots, not evacuate them: they're not
293 * going to move in this GC.
294 * Also: do them in reverse generation order. This is because we
295 * often want to promote objects that are pointed to by older
296 * generations early, so we don't have to repeatedly copy them.
297 * Doing the generations in reverse order ensures that we don't end
298 * up in the situation where we want to evac an object to gen 3 and
299 * it has already been evaced to gen 2.
303 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
304 generations[g].saved_mut_list = generations[g].mut_list;
305 generations[g].mut_list = END_MUT_LIST;
308 /* Do the mut-once lists first */
309 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
310 scavenge_mut_once_list(&generations[g]);
312 for (st = generations[g].n_steps-1; st >= 0; st--) {
313 scavenge(&generations[g].steps[st]);
317 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
318 scavenge_mutable_list(&generations[g]);
320 for (st = generations[g].n_steps-1; st >= 0; st--) {
321 scavenge(&generations[g].steps[st]);
326 /* follow all the roots that the application knows about.
331 /* And don't forget to mark the TSO if we got here direct from
334 CurrentTSO = (StgTSO *)MarkRoot((StgClosure *)CurrentTSO);
337 /* Mark the weak pointer list, and prepare to detect dead weak
341 old_weak_ptr_list = weak_ptr_list;
342 weak_ptr_list = NULL;
343 weak_done = rtsFalse;
345 /* Mark the stable pointer table.
347 markStablePtrTable(major_gc);
351 /* ToDo: To fix the caf leak, we need to make the commented out
352 * parts of this code do something sensible - as described in
355 extern void markHugsObjects(void);
357 /* ToDo: This (undefined) function should contain the scavenge
358 * loop immediately below this block of code - but I'm not sure
359 * enough of the details to do this myself.
361 scavengeEverything();
362 /* revert dead CAFs and update enteredCAFs list */
367 /* This will keep the CAFs and the attached BCOs alive
368 * but the values will have been reverted
370 scavengeEverything();
375 /* -------------------------------------------------------------------------
376 * Repeatedly scavenge all the areas we know about until there's no
377 * more scavenging to be done.
384 /* scavenge static objects */
385 if (major_gc && static_objects != END_OF_STATIC_LIST) {
389 /* When scavenging the older generations: Objects may have been
390 * evacuated from generations <= N into older generations, and we
391 * need to scavenge these objects. We're going to try to ensure that
392 * any evacuations that occur move the objects into at least the
393 * same generation as the object being scavenged, otherwise we
394 * have to create new entries on the mutable list for the older
398 /* scavenge each step in generations 0..maxgen */
402 for (gen = RtsFlags.GcFlags.generations-1; gen >= 0; gen--) {
403 for (st = generations[gen].n_steps-1; st >= 0 ; st--) {
404 if (gen == 0 && st == 0 && RtsFlags.GcFlags.generations > 1) {
407 step = &generations[gen].steps[st];
409 if (step->hp_bd != step->scan_bd || step->scan < step->hp) {
414 if (step->new_large_objects != NULL) {
415 scavenge_large(step);
422 if (flag) { goto loop; }
424 /* must be last... */
425 if (traverse_weak_ptr_list()) { /* returns rtsTrue if evaced something */
430 /* Now see which stable names are still alive
432 gcStablePtrTable(major_gc);
434 /* Set the maximum blocks for the oldest generation, based on twice
435 * the amount of live data now, adjusted to fit the maximum heap
438 * This is an approximation, since in the worst case we'll need
439 * twice the amount of live data plus whatever space the other
442 if (RtsFlags.GcFlags.generations > 1) {
444 oldest_gen->max_blocks =
445 stg_max(oldest_gen->steps[0].to_blocks * RtsFlags.GcFlags.oldGenFactor,
446 RtsFlags.GcFlags.minOldGenSize);
447 if (oldest_gen->max_blocks > RtsFlags.GcFlags.maxHeapSize / 2) {
448 oldest_gen->max_blocks = RtsFlags.GcFlags.maxHeapSize / 2;
449 if (((int)oldest_gen->max_blocks -
450 (int)oldest_gen->steps[0].to_blocks) <
451 (RtsFlags.GcFlags.pcFreeHeap *
452 RtsFlags.GcFlags.maxHeapSize / 200)) {
459 /* run through all the generations/steps and tidy up
461 copied = new_blocks * BLOCK_SIZE_W;
462 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
465 generations[g].collections++; /* for stats */
468 for (s = 0; s < generations[g].n_steps; s++) {
470 step = &generations[g].steps[s];
472 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
473 /* Tidy the end of the to-space chains */
474 step->hp_bd->free = step->hp;
475 step->hp_bd->link = NULL;
476 /* stats information: how much we copied */
478 copied -= step->hp_bd->start + BLOCK_SIZE_W -
483 /* for generations we collected... */
486 collected += step->n_blocks * BLOCK_SIZE_W; /* for stats */
488 /* free old memory and shift to-space into from-space for all
489 * the collected steps (except the allocation area). These
490 * freed blocks will probaby be quickly recycled.
492 if (!(g == 0 && s == 0)) {
493 freeChain(step->blocks);
494 step->blocks = step->to_space;
495 step->n_blocks = step->to_blocks;
496 step->to_space = NULL;
498 for (bd = step->blocks; bd != NULL; bd = bd->link) {
499 bd->evacuated = 0; /* now from-space */
503 /* LARGE OBJECTS. The current live large objects are chained on
504 * scavenged_large, having been moved during garbage
505 * collection from large_objects. Any objects left on
506 * large_objects list are therefore dead, so we free them here.
508 for (bd = step->large_objects; bd != NULL; bd = next) {
513 for (bd = step->scavenged_large_objects; bd != NULL; bd = bd->link) {
516 step->large_objects = step->scavenged_large_objects;
518 /* Set the maximum blocks for this generation, interpolating
519 * between the maximum size of the oldest and youngest
522 * max_blocks = oldgen_max_blocks * G
523 * ----------------------
528 generations[g].max_blocks = (oldest_gen->max_blocks * g)
529 / (RtsFlags.GcFlags.generations-1);
531 generations[g].max_blocks = oldest_gen->max_blocks;
534 /* for older generations... */
537 /* For older generations, we need to append the
538 * scavenged_large_object list (i.e. large objects that have been
539 * promoted during this GC) to the large_object list for that step.
541 for (bd = step->scavenged_large_objects; bd; bd = next) {
544 dbl_link_onto(bd, &step->large_objects);
547 /* add the new blocks we promoted during this GC */
548 step->n_blocks += step->to_blocks;
553 /* Guess the amount of live data for stats. */
556 /* Free the small objects allocated via allocate(), since this will
557 * all have been copied into G0S1 now.
559 if (small_alloc_list != NULL) {
560 freeChain(small_alloc_list);
562 small_alloc_list = NULL;
566 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
568 /* Two-space collector:
569 * Free the old to-space, and estimate the amount of live data.
571 if (RtsFlags.GcFlags.generations == 1) {
574 if (old_to_space != NULL) {
575 freeChain(old_to_space);
577 for (bd = g0s0->to_space; bd != NULL; bd = bd->link) {
578 bd->evacuated = 0; /* now from-space */
581 /* For a two-space collector, we need to resize the nursery. */
583 /* set up a new nursery. Allocate a nursery size based on a
584 * function of the amount of live data (currently a factor of 2,
585 * should be configurable (ToDo)). Use the blocks from the old
586 * nursery if possible, freeing up any left over blocks.
588 * If we get near the maximum heap size, then adjust our nursery
589 * size accordingly. If the nursery is the same size as the live
590 * data (L), then we need 3L bytes. We can reduce the size of the
591 * nursery to bring the required memory down near 2L bytes.
593 * A normal 2-space collector would need 4L bytes to give the same
594 * performance we get from 3L bytes, reducing to the same
595 * performance at 2L bytes.
597 blocks = g0s0->to_blocks;
599 if ( blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
600 RtsFlags.GcFlags.maxHeapSize ) {
601 int adjusted_blocks; /* signed on purpose */
604 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
605 IF_DEBUG(gc, fprintf(stderr, "Near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %d\n", RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks));
606 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
607 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even be < 0 */ {
610 blocks = adjusted_blocks;
613 blocks *= RtsFlags.GcFlags.oldGenFactor;
614 if (blocks < RtsFlags.GcFlags.minAllocAreaSize) {
615 blocks = RtsFlags.GcFlags.minAllocAreaSize;
618 resizeNursery(blocks);
621 /* Generational collector:
622 * If the user has given us a suggested heap size, adjust our
623 * allocation area to make best use of the memory available.
626 if (RtsFlags.GcFlags.heapSizeSuggestion) {
628 nat needed = calcNeeded(); /* approx blocks needed at next GC */
630 /* Guess how much will be live in generation 0 step 0 next time.
631 * A good approximation is the obtained by finding the
632 * percentage of g0s0 that was live at the last minor GC.
635 g0s0_pcnt_kept = (new_blocks * 100) / g0s0->n_blocks;
638 /* Estimate a size for the allocation area based on the
639 * information available. We might end up going slightly under
640 * or over the suggested heap size, but we should be pretty
643 * Formula: suggested - needed
644 * ----------------------------
645 * 1 + g0s0_pcnt_kept/100
647 * where 'needed' is the amount of memory needed at the next
648 * collection for collecting all steps except g0s0.
651 (((int)RtsFlags.GcFlags.heapSizeSuggestion - (int)needed) * 100) /
652 (100 + (int)g0s0_pcnt_kept);
654 if (blocks < (int)RtsFlags.GcFlags.minAllocAreaSize) {
655 blocks = RtsFlags.GcFlags.minAllocAreaSize;
658 resizeNursery((nat)blocks);
662 /* revert dead CAFs and update enteredCAFs list */
665 /* mark the garbage collected CAFs as dead */
667 if (major_gc) { gcCAFs(); }
670 /* zero the scavenged static object list */
672 zeroStaticObjectList(scavenged_static_objects);
677 for (bd = g0s0->blocks; bd; bd = bd->link) {
678 bd->free = bd->start;
679 ASSERT(bd->gen == g0);
680 ASSERT(bd->step == g0s0);
681 IF_DEBUG(sanity,memset(bd->start, 0xaa, BLOCK_SIZE));
683 current_nursery = g0s0->blocks;
685 /* start any pending finalizers */
686 scheduleFinalizers(old_weak_ptr_list);
688 /* check sanity after GC */
689 IF_DEBUG(sanity, checkSanity(N));
691 /* extra GC trace info */
692 IF_DEBUG(gc, stat_describe_gens());
695 /* symbol-table based profiling */
696 /* heapCensus(to_space); */ /* ToDo */
699 /* restore enclosing cost centre */
704 /* check for memory leaks if sanity checking is on */
705 IF_DEBUG(sanity, memInventory());
707 /* ok, GC over: tell the stats department what happened. */
708 stat_endGC(allocated, collected, live, copied, N);
711 /* -----------------------------------------------------------------------------
714 traverse_weak_ptr_list is called possibly many times during garbage
715 collection. It returns a flag indicating whether it did any work
716 (i.e. called evacuate on any live pointers).
718 Invariant: traverse_weak_ptr_list is called when the heap is in an
719 idempotent state. That means that there are no pending
720 evacuate/scavenge operations. This invariant helps the weak
721 pointer code decide which weak pointers are dead - if there are no
722 new live weak pointers, then all the currently unreachable ones are
725 For generational GC: we just don't try to finalize weak pointers in
726 older generations than the one we're collecting. This could
727 probably be optimised by keeping per-generation lists of weak
728 pointers, but for a few weak pointers this scheme will work.
729 -------------------------------------------------------------------------- */
732 traverse_weak_ptr_list(void)
734 StgWeak *w, **last_w, *next_w;
736 rtsBool flag = rtsFalse;
738 if (weak_done) { return rtsFalse; }
740 /* doesn't matter where we evacuate values/finalizers to, since
741 * these pointers are treated as roots (iff the keys are alive).
745 last_w = &old_weak_ptr_list;
746 for (w = old_weak_ptr_list; w; w = next_w) {
748 if ((new = isAlive(w->key))) {
750 /* evacuate the value and finalizer */
751 w->value = evacuate(w->value);
752 w->finalizer = evacuate(w->finalizer);
753 /* remove this weak ptr from the old_weak_ptr list */
755 /* and put it on the new weak ptr list */
757 w->link = weak_ptr_list;
760 IF_DEBUG(weak, fprintf(stderr,"Weak pointer still alive at %p -> %p\n", w, w->key));
770 /* If we didn't make any changes, then we can go round and kill all
771 * the dead weak pointers. The old_weak_ptr list is used as a list
772 * of pending finalizers later on.
774 if (flag == rtsFalse) {
775 for (w = old_weak_ptr_list; w; w = w->link) {
776 w->value = evacuate(w->value);
777 w->finalizer = evacuate(w->finalizer);
785 /* -----------------------------------------------------------------------------
786 isAlive determines whether the given closure is still alive (after
787 a garbage collection) or not. It returns the new address of the
788 closure if it is alive, or NULL otherwise.
789 -------------------------------------------------------------------------- */
792 isAlive(StgClosure *p)
800 /* ToDo: for static closures, check the static link field.
801 * Problem here is that we sometimes don't set the link field, eg.
802 * for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
805 /* ignore closures in generations that we're not collecting. */
806 if (LOOKS_LIKE_STATIC(p) || Bdescr((P_)p)->gen->no > N) {
810 switch (info->type) {
815 case IND_OLDGEN: /* rely on compatible layout with StgInd */
816 case IND_OLDGEN_PERM:
817 /* follow indirections */
818 p = ((StgInd *)p)->indirectee;
823 return ((StgEvacuated *)p)->evacuee;
833 MarkRoot(StgClosure *root)
835 return evacuate(root);
838 static void addBlock(step *step)
840 bdescr *bd = allocBlock();
844 if (step->gen->no <= N) {
850 step->hp_bd->free = step->hp;
851 step->hp_bd->link = bd;
852 step->hp = bd->start;
853 step->hpLim = step->hp + BLOCK_SIZE_W;
859 static __inline__ StgClosure *
860 copy(StgClosure *src, nat size, step *step)
864 TICK_GC_WORDS_COPIED(size);
865 /* Find out where we're going, using the handy "to" pointer in
866 * the step of the source object. If it turns out we need to
867 * evacuate to an older generation, adjust it here (see comment
870 if (step->gen->no < evac_gen) {
871 #ifdef NO_EAGER_PROMOTION
872 failed_to_evac = rtsTrue;
874 step = &generations[evac_gen].steps[0];
878 /* chain a new block onto the to-space for the destination step if
881 if (step->hp + size >= step->hpLim) {
885 for(to = step->hp, from = (P_)src; size>0; --size) {
891 return (StgClosure *)dest;
894 /* Special version of copy() for when we only want to copy the info
895 * pointer of an object, but reserve some padding after it. This is
896 * used to optimise evacuation of BLACKHOLEs.
899 static __inline__ StgClosure *
900 copyPart(StgClosure *src, nat size_to_reserve, nat size_to_copy, step *step)
904 TICK_GC_WORDS_COPIED(size_to_copy);
905 if (step->gen->no < evac_gen) {
906 #ifdef NO_EAGER_PROMOTION
907 failed_to_evac = rtsTrue;
909 step = &generations[evac_gen].steps[0];
913 if (step->hp + size_to_reserve >= step->hpLim) {
917 for(to = step->hp, from = (P_)src; size_to_copy>0; --size_to_copy) {
922 step->hp += size_to_reserve;
923 return (StgClosure *)dest;
926 static __inline__ void
927 upd_evacuee(StgClosure *p, StgClosure *dest)
929 StgEvacuated *q = (StgEvacuated *)p;
931 SET_INFO(q,&EVACUATED_info);
935 /* -----------------------------------------------------------------------------
936 Evacuate a large object
938 This just consists of removing the object from the (doubly-linked)
939 large_alloc_list, and linking it on to the (singly-linked)
940 new_large_objects list, from where it will be scavenged later.
942 Convention: bd->evacuated is /= 0 for a large object that has been
943 evacuated, or 0 otherwise.
944 -------------------------------------------------------------------------- */
947 evacuate_large(StgPtr p, rtsBool mutable)
949 bdescr *bd = Bdescr(p);
952 /* should point to the beginning of the block */
953 ASSERT(((W_)p & BLOCK_MASK) == 0);
955 /* already evacuated? */
957 /* Don't forget to set the failed_to_evac flag if we didn't get
958 * the desired destination (see comments in evacuate()).
960 if (bd->gen->no < evac_gen) {
961 failed_to_evac = rtsTrue;
962 TICK_GC_FAILED_PROMOTION();
968 /* remove from large_object list */
970 bd->back->link = bd->link;
971 } else { /* first object in the list */
972 step->large_objects = bd->link;
975 bd->link->back = bd->back;
978 /* link it on to the evacuated large object list of the destination step
981 if (step->gen->no < evac_gen) {
982 #ifdef NO_EAGER_PROMOTION
983 failed_to_evac = rtsTrue;
985 step = &generations[evac_gen].steps[0];
991 bd->link = step->new_large_objects;
992 step->new_large_objects = bd;
996 recordMutable((StgMutClosure *)p);
1000 /* -----------------------------------------------------------------------------
1001 Adding a MUT_CONS to an older generation.
1003 This is necessary from time to time when we end up with an
1004 old-to-new generation pointer in a non-mutable object. We defer
1005 the promotion until the next GC.
1006 -------------------------------------------------------------------------- */
1009 mkMutCons(StgClosure *ptr, generation *gen)
1014 step = &gen->steps[0];
1016 /* chain a new block onto the to-space for the destination step if
1019 if (step->hp + sizeofW(StgIndOldGen) >= step->hpLim) {
1023 q = (StgMutVar *)step->hp;
1024 step->hp += sizeofW(StgMutVar);
1026 SET_HDR(q,&MUT_CONS_info,CCS_GC);
1028 recordOldToNewPtrs((StgMutClosure *)q);
1030 return (StgClosure *)q;
1033 /* -----------------------------------------------------------------------------
1036 This is called (eventually) for every live object in the system.
1038 The caller to evacuate specifies a desired generation in the
1039 evac_gen global variable. The following conditions apply to
1040 evacuating an object which resides in generation M when we're
1041 collecting up to generation N
1045 else evac to step->to
1047 if M < evac_gen evac to evac_gen, step 0
1049 if the object is already evacuated, then we check which generation
1052 if M >= evac_gen do nothing
1053 if M < evac_gen set failed_to_evac flag to indicate that we
1054 didn't manage to evacuate this object into evac_gen.
1056 -------------------------------------------------------------------------- */
1060 evacuate(StgClosure *q)
1065 const StgInfoTable *info;
1068 if (!LOOKS_LIKE_STATIC(q)) {
1070 if (bd->gen->no > N) {
1071 /* Can't evacuate this object, because it's in a generation
1072 * older than the ones we're collecting. Let's hope that it's
1073 * in evac_gen or older, or we will have to make an IND_OLDGEN object.
1075 if (bd->gen->no < evac_gen) {
1077 failed_to_evac = rtsTrue;
1078 TICK_GC_FAILED_PROMOTION();
1082 step = bd->step->to;
1085 /* make sure the info pointer is into text space */
1086 ASSERT(q && (LOOKS_LIKE_GHC_INFO(GET_INFO(q))
1087 || IS_HUGS_CONSTR_INFO(GET_INFO(q))));
1090 switch (info -> type) {
1093 to = copy(q,bco_sizeW(stgCast(StgBCO*,q)),step);
1098 ASSERT(q->header.info != &MUT_CONS_info);
1100 to = copy(q,sizeW_fromITBL(info),step);
1102 recordMutable((StgMutClosure *)to);
1106 stable_ptr_table[((StgStableName *)q)->sn].keep = rtsTrue;
1107 to = copy(q,sizeofW(StgStableName),step);
1115 to = copy(q,sizeofW(StgHeader)+1,step);
1119 case THUNK_1_0: /* here because of MIN_UPD_SIZE */
1130 to = copy(q,sizeofW(StgHeader)+2,step);
1138 case IND_OLDGEN_PERM:
1143 to = copy(q,sizeW_fromITBL(info),step);
1149 to = copyPart(q,BLACKHOLE_sizeW(),sizeofW(StgHeader),step);
1154 to = copy(q,BLACKHOLE_sizeW(),step);
1156 recordMutable((StgMutClosure *)to);
1159 case THUNK_SELECTOR:
1161 const StgInfoTable* selectee_info;
1162 StgClosure* selectee = ((StgSelector*)q)->selectee;
1165 selectee_info = get_itbl(selectee);
1166 switch (selectee_info->type) {
1175 StgNat32 offset = info->layout.selector_offset;
1177 /* check that the size is in range */
1179 (StgNat32)(selectee_info->layout.payload.ptrs +
1180 selectee_info->layout.payload.nptrs));
1182 /* perform the selection! */
1183 q = selectee->payload[offset];
1185 /* if we're already in to-space, there's no need to continue
1186 * with the evacuation, just update the source address with
1187 * a pointer to the (evacuated) constructor field.
1189 if (IS_USER_PTR(q)) {
1190 bdescr *bd = Bdescr((P_)q);
1191 if (bd->evacuated) {
1192 if (bd->gen->no < evac_gen) {
1193 failed_to_evac = rtsTrue;
1194 TICK_GC_FAILED_PROMOTION();
1200 /* otherwise, carry on and evacuate this constructor field,
1201 * (but not the constructor itself)
1210 case IND_OLDGEN_PERM:
1211 selectee = stgCast(StgInd *,selectee)->indirectee;
1215 selectee = stgCast(StgCAF *,selectee)->value;
1219 selectee = stgCast(StgEvacuated*,selectee)->evacuee;
1229 case THUNK_SELECTOR:
1230 /* aargh - do recursively???? */
1235 /* not evaluated yet */
1239 barf("evacuate: THUNK_SELECTOR: strange selectee");
1242 to = copy(q,THUNK_SELECTOR_sizeW(),step);
1248 /* follow chains of indirections, don't evacuate them */
1249 q = ((StgInd*)q)->indirectee;
1252 /* ToDo: optimise STATIC_LINK for known cases.
1253 - FUN_STATIC : payload[0]
1254 - THUNK_STATIC : payload[1]
1255 - IND_STATIC : payload[1]
1259 if (info->srt_len == 0) { /* small optimisation */
1265 /* don't want to evacuate these, but we do want to follow pointers
1266 * from SRTs - see scavenge_static.
1269 /* put the object on the static list, if necessary.
1271 if (major_gc && STATIC_LINK(info,(StgClosure *)q) == NULL) {
1272 STATIC_LINK(info,(StgClosure *)q) = static_objects;
1273 static_objects = (StgClosure *)q;
1277 case CONSTR_INTLIKE:
1278 case CONSTR_CHARLIKE:
1279 case CONSTR_NOCAF_STATIC:
1280 /* no need to put these on the static linked list, they don't need
1295 /* shouldn't see these */
1296 barf("evacuate: stack frame\n");
1300 /* these are special - the payload is a copy of a chunk of stack,
1302 to = copy(q,pap_sizeW(stgCast(StgPAP*,q)),step);
1307 /* Already evacuated, just return the forwarding address.
1308 * HOWEVER: if the requested destination generation (evac_gen) is
1309 * older than the actual generation (because the object was
1310 * already evacuated to a younger generation) then we have to
1311 * set the failed_to_evac flag to indicate that we couldn't
1312 * manage to promote the object to the desired generation.
1314 if (evac_gen > 0) { /* optimisation */
1315 StgClosure *p = ((StgEvacuated*)q)->evacuee;
1316 if (Bdescr((P_)p)->gen->no < evac_gen) {
1317 /* fprintf(stderr,"evac failed!\n");*/
1318 failed_to_evac = rtsTrue;
1319 TICK_GC_FAILED_PROMOTION();
1322 return ((StgEvacuated*)q)->evacuee;
1326 nat size = arr_words_sizeW(stgCast(StgArrWords*,q));
1328 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1329 evacuate_large((P_)q, rtsFalse);
1332 /* just copy the block */
1333 to = copy(q,size,step);
1340 case MUT_ARR_PTRS_FROZEN:
1342 nat size = mut_arr_ptrs_sizeW(stgCast(StgMutArrPtrs*,q));
1344 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1345 evacuate_large((P_)q, info->type == MUT_ARR_PTRS);
1348 /* just copy the block */
1349 to = copy(q,size,step);
1351 if (info->type == MUT_ARR_PTRS) {
1352 recordMutable((StgMutClosure *)to);
1360 StgTSO *tso = stgCast(StgTSO *,q);
1361 nat size = tso_sizeW(tso);
1364 /* Large TSOs don't get moved, so no relocation is required.
1366 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1367 evacuate_large((P_)q, rtsTrue);
1370 /* To evacuate a small TSO, we need to relocate the update frame
1374 StgTSO *new_tso = (StgTSO *)copy((StgClosure *)tso,tso_sizeW(tso),step);
1376 diff = (StgPtr)new_tso - (StgPtr)tso; /* In *words* */
1378 /* relocate the stack pointers... */
1379 new_tso->su = (StgUpdateFrame *) ((StgPtr)new_tso->su + diff);
1380 new_tso->sp = (StgPtr)new_tso->sp + diff;
1381 new_tso->splim = (StgPtr)new_tso->splim + diff;
1383 relocate_TSO(tso, new_tso);
1384 upd_evacuee(q,(StgClosure *)new_tso);
1386 recordMutable((StgMutClosure *)new_tso);
1387 return (StgClosure *)new_tso;
1393 fprintf(stderr,"evacuate: unimplemented/strange closure type\n");
1397 barf("evacuate: strange closure type");
1403 /* -----------------------------------------------------------------------------
1404 relocate_TSO is called just after a TSO has been copied from src to
1405 dest. It adjusts the update frame list for the new location.
1406 -------------------------------------------------------------------------- */
1409 relocate_TSO(StgTSO *src, StgTSO *dest)
1416 diff = (StgPtr)dest->sp - (StgPtr)src->sp; /* In *words* */
1420 while ((P_)su < dest->stack + dest->stack_size) {
1421 switch (get_itbl(su)->type) {
1423 /* GCC actually manages to common up these three cases! */
1426 su->link = (StgUpdateFrame *) ((StgPtr)su->link + diff);
1431 cf = (StgCatchFrame *)su;
1432 cf->link = (StgUpdateFrame *) ((StgPtr)cf->link + diff);
1437 sf = (StgSeqFrame *)su;
1438 sf->link = (StgUpdateFrame *) ((StgPtr)sf->link + diff);
1447 barf("relocate_TSO");
1456 scavenge_srt(const StgInfoTable *info)
1458 StgClosure **srt, **srt_end;
1460 /* evacuate the SRT. If srt_len is zero, then there isn't an
1461 * srt field in the info table. That's ok, because we'll
1462 * never dereference it.
1464 srt = stgCast(StgClosure **,info->srt);
1465 srt_end = srt + info->srt_len;
1466 for (; srt < srt_end; srt++) {
1471 /* -----------------------------------------------------------------------------
1472 Scavenge a given step until there are no more objects in this step
1475 evac_gen is set by the caller to be either zero (for a step in a
1476 generation < N) or G where G is the generation of the step being
1479 We sometimes temporarily change evac_gen back to zero if we're
1480 scavenging a mutable object where early promotion isn't such a good
1482 -------------------------------------------------------------------------- */
1486 scavenge(step *step)
1489 const StgInfoTable *info;
1491 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
1496 failed_to_evac = rtsFalse;
1498 /* scavenge phase - standard breadth-first scavenging of the
1502 while (bd != step->hp_bd || p < step->hp) {
1504 /* If we're at the end of this block, move on to the next block */
1505 if (bd != step->hp_bd && p == bd->free) {
1511 q = p; /* save ptr to object */
1513 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO((StgClosure *)p))
1514 || IS_HUGS_CONSTR_INFO(GET_INFO((StgClosure *)p))));
1516 info = get_itbl((StgClosure *)p);
1517 switch (info -> type) {
1521 StgBCO* bco = stgCast(StgBCO*,p);
1523 for (i = 0; i < bco->n_ptrs; i++) {
1524 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
1526 p += bco_sizeW(bco);
1531 /* treat MVars specially, because we don't want to evacuate the
1532 * mut_link field in the middle of the closure.
1535 StgMVar *mvar = ((StgMVar *)p);
1537 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
1538 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
1539 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
1540 p += sizeofW(StgMVar);
1541 evac_gen = saved_evac_gen;
1549 ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
1550 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1551 p += sizeofW(StgHeader) + 2;
1556 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1557 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1563 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1564 p += sizeofW(StgHeader) + 1;
1569 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1575 p += sizeofW(StgHeader) + 1;
1582 p += sizeofW(StgHeader) + 2;
1589 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1590 p += sizeofW(StgHeader) + 2;
1603 case IND_OLDGEN_PERM:
1609 end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
1610 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
1611 (StgClosure *)*p = evacuate((StgClosure *)*p);
1613 p += info->layout.payload.nptrs;
1618 /* ignore MUT_CONSs */
1619 if (((StgMutVar *)p)->header.info != &MUT_CONS_info) {
1621 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
1622 evac_gen = saved_evac_gen;
1624 p += sizeofW(StgMutVar);
1629 p += BLACKHOLE_sizeW();
1634 StgBlockingQueue *bh = (StgBlockingQueue *)p;
1635 (StgClosure *)bh->blocking_queue =
1636 evacuate((StgClosure *)bh->blocking_queue);
1637 if (failed_to_evac) {
1638 failed_to_evac = rtsFalse;
1639 recordMutable((StgMutClosure *)bh);
1641 p += BLACKHOLE_sizeW();
1645 case THUNK_SELECTOR:
1647 StgSelector *s = (StgSelector *)p;
1648 s->selectee = evacuate(s->selectee);
1649 p += THUNK_SELECTOR_sizeW();
1655 barf("scavenge:IND???\n");
1657 case CONSTR_INTLIKE:
1658 case CONSTR_CHARLIKE:
1660 case CONSTR_NOCAF_STATIC:
1664 /* Shouldn't see a static object here. */
1665 barf("scavenge: STATIC object\n");
1677 /* Shouldn't see stack frames here. */
1678 barf("scavenge: stack frame\n");
1680 case AP_UPD: /* same as PAPs */
1682 /* Treat a PAP just like a section of stack, not forgetting to
1683 * evacuate the function pointer too...
1686 StgPAP* pap = stgCast(StgPAP*,p);
1688 pap->fun = evacuate(pap->fun);
1689 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1690 p += pap_sizeW(pap);
1695 /* nothing to follow */
1696 p += arr_words_sizeW(stgCast(StgArrWords*,p));
1700 /* follow everything */
1704 evac_gen = 0; /* repeatedly mutable */
1705 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1706 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1707 (StgClosure *)*p = evacuate((StgClosure *)*p);
1709 evac_gen = saved_evac_gen;
1713 case MUT_ARR_PTRS_FROZEN:
1714 /* follow everything */
1716 StgPtr start = p, next;
1718 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1719 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1720 (StgClosure *)*p = evacuate((StgClosure *)*p);
1722 if (failed_to_evac) {
1723 /* we can do this easier... */
1724 recordMutable((StgMutClosure *)start);
1725 failed_to_evac = rtsFalse;
1736 /* chase the link field for any TSOs on the same queue */
1737 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
1738 /* scavenge this thread's stack */
1739 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
1740 evac_gen = saved_evac_gen;
1741 p += tso_sizeW(tso);
1748 barf("scavenge: unimplemented/strange closure type\n");
1754 /* If we didn't manage to promote all the objects pointed to by
1755 * the current object, then we have to designate this object as
1756 * mutable (because it contains old-to-new generation pointers).
1758 if (failed_to_evac) {
1759 mkMutCons((StgClosure *)q, &generations[evac_gen]);
1760 failed_to_evac = rtsFalse;
1768 /* -----------------------------------------------------------------------------
1769 Scavenge one object.
1771 This is used for objects that are temporarily marked as mutable
1772 because they contain old-to-new generation pointers. Only certain
1773 objects can have this property.
1774 -------------------------------------------------------------------------- */
1776 scavenge_one(StgClosure *p)
1781 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1782 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1786 switch (info -> type) {
1789 case FUN_1_0: /* hardly worth specialising these guys */
1809 case IND_OLDGEN_PERM:
1815 end = (P_)p->payload + info->layout.payload.ptrs;
1816 for (q = (P_)p->payload; q < end; q++) {
1817 (StgClosure *)*q = evacuate((StgClosure *)*q);
1826 case THUNK_SELECTOR:
1828 StgSelector *s = (StgSelector *)p;
1829 s->selectee = evacuate(s->selectee);
1833 case AP_UPD: /* same as PAPs */
1835 /* Treat a PAP just like a section of stack, not forgetting to
1836 * evacuate the function pointer too...
1839 StgPAP* pap = (StgPAP *)p;
1841 pap->fun = evacuate(pap->fun);
1842 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1847 /* This might happen if for instance a MUT_CONS was pointing to a
1848 * THUNK which has since been updated. The IND_OLDGEN will
1849 * be on the mutable list anyway, so we don't need to do anything
1855 barf("scavenge_one: strange object");
1858 no_luck = failed_to_evac;
1859 failed_to_evac = rtsFalse;
1864 /* -----------------------------------------------------------------------------
1865 Scavenging mutable lists.
1867 We treat the mutable list of each generation > N (i.e. all the
1868 generations older than the one being collected) as roots. We also
1869 remove non-mutable objects from the mutable list at this point.
1870 -------------------------------------------------------------------------- */
1873 scavenge_mut_once_list(generation *gen)
1876 StgMutClosure *p, *next, *new_list;
1878 p = gen->mut_once_list;
1879 new_list = END_MUT_LIST;
1883 failed_to_evac = rtsFalse;
1885 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
1887 /* make sure the info pointer is into text space */
1888 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1889 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1892 switch(info->type) {
1895 case IND_OLDGEN_PERM:
1897 /* Try to pull the indirectee into this generation, so we can
1898 * remove the indirection from the mutable list.
1900 ((StgIndOldGen *)p)->indirectee =
1901 evacuate(((StgIndOldGen *)p)->indirectee);
1904 /* Debugging code to print out the size of the thing we just
1908 StgPtr start = gen->steps[0].scan;
1909 bdescr *start_bd = gen->steps[0].scan_bd;
1911 scavenge(&gen->steps[0]);
1912 if (start_bd != gen->steps[0].scan_bd) {
1913 size += (P_)BLOCK_ROUND_UP(start) - start;
1914 start_bd = start_bd->link;
1915 while (start_bd != gen->steps[0].scan_bd) {
1916 size += BLOCK_SIZE_W;
1917 start_bd = start_bd->link;
1919 size += gen->steps[0].scan -
1920 (P_)BLOCK_ROUND_DOWN(gen->steps[0].scan);
1922 size = gen->steps[0].scan - start;
1924 fprintf(stderr,"evac IND_OLDGEN: %d bytes\n", size * sizeof(W_));
1928 /* failed_to_evac might happen if we've got more than two
1929 * generations, we're collecting only generation 0, the
1930 * indirection resides in generation 2 and the indirectee is
1933 if (failed_to_evac) {
1934 failed_to_evac = rtsFalse;
1935 p->mut_link = new_list;
1938 /* the mut_link field of an IND_STATIC is overloaded as the
1939 * static link field too (it just so happens that we don't need
1940 * both at the same time), so we need to NULL it out when
1941 * removing this object from the mutable list because the static
1942 * link fields are all assumed to be NULL before doing a major
1950 /* MUT_CONS is a kind of MUT_VAR, except it that we try to remove
1951 * it from the mutable list if possible by promoting whatever it
1954 ASSERT(p->header.info == &MUT_CONS_info);
1955 if (scavenge_one(((StgMutVar *)p)->var) == rtsTrue) {
1956 /* didn't manage to promote everything, so put the
1957 * MUT_CONS back on the list.
1959 p->mut_link = new_list;
1965 /* shouldn't have anything else on the mutables list */
1966 barf("scavenge_mut_once_list: strange object?");
1970 gen->mut_once_list = new_list;
1975 scavenge_mutable_list(generation *gen)
1978 StgMutClosure *p, *next;
1980 p = gen->saved_mut_list;
1984 failed_to_evac = rtsFalse;
1986 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
1988 /* make sure the info pointer is into text space */
1989 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1990 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1993 switch(info->type) {
1995 case MUT_ARR_PTRS_FROZEN:
1996 /* remove this guy from the mutable list, but follow the ptrs
1997 * anyway (and make sure they get promoted to this gen).
2002 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2004 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
2005 (StgClosure *)*q = evacuate((StgClosure *)*q);
2009 if (failed_to_evac) {
2010 failed_to_evac = rtsFalse;
2011 p->mut_link = gen->mut_list;
2018 /* follow everything */
2019 p->mut_link = gen->mut_list;
2024 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2025 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
2026 (StgClosure *)*q = evacuate((StgClosure *)*q);
2032 /* MUT_CONS is a kind of MUT_VAR, except that we try to remove
2033 * it from the mutable list if possible by promoting whatever it
2036 ASSERT(p->header.info != &MUT_CONS_info);
2037 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
2038 p->mut_link = gen->mut_list;
2044 StgMVar *mvar = (StgMVar *)p;
2045 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
2046 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
2047 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
2048 p->mut_link = gen->mut_list;
2054 /* follow ptrs and remove this from the mutable list */
2056 StgTSO *tso = (StgTSO *)p;
2058 /* Don't bother scavenging if this thread is dead
2060 if (!(tso->whatNext == ThreadComplete ||
2061 tso->whatNext == ThreadKilled)) {
2062 /* Don't need to chase the link field for any TSOs on the
2063 * same queue. Just scavenge this thread's stack
2065 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2068 /* Don't take this TSO off the mutable list - it might still
2069 * point to some younger objects (because we set evac_gen to 0
2072 tso->mut_link = gen->mut_list;
2073 gen->mut_list = (StgMutClosure *)tso;
2079 StgBlockingQueue *bh = (StgBlockingQueue *)p;
2080 (StgClosure *)bh->blocking_queue =
2081 evacuate((StgClosure *)bh->blocking_queue);
2082 p->mut_link = gen->mut_list;
2088 /* shouldn't have anything else on the mutables list */
2089 barf("scavenge_mut_list: strange object?");
2095 scavenge_static(void)
2097 StgClosure* p = static_objects;
2098 const StgInfoTable *info;
2100 /* Always evacuate straight to the oldest generation for static
2102 evac_gen = oldest_gen->no;
2104 /* keep going until we've scavenged all the objects on the linked
2106 while (p != END_OF_STATIC_LIST) {
2110 /* make sure the info pointer is into text space */
2111 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
2112 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
2114 /* Take this object *off* the static_objects list,
2115 * and put it on the scavenged_static_objects list.
2117 static_objects = STATIC_LINK(info,p);
2118 STATIC_LINK(info,p) = scavenged_static_objects;
2119 scavenged_static_objects = p;
2121 switch (info -> type) {
2125 StgInd *ind = (StgInd *)p;
2126 ind->indirectee = evacuate(ind->indirectee);
2128 /* might fail to evacuate it, in which case we have to pop it
2129 * back on the mutable list (and take it off the
2130 * scavenged_static list because the static link and mut link
2131 * pointers are one and the same).
2133 if (failed_to_evac) {
2134 failed_to_evac = rtsFalse;
2135 scavenged_static_objects = STATIC_LINK(info,p);
2136 ((StgMutClosure *)ind)->mut_link = oldest_gen->mut_once_list;
2137 oldest_gen->mut_once_list = (StgMutClosure *)ind;
2151 next = (P_)p->payload + info->layout.payload.ptrs;
2152 /* evacuate the pointers */
2153 for (q = (P_)p->payload; q < next; q++) {
2154 (StgClosure *)*q = evacuate((StgClosure *)*q);
2160 barf("scavenge_static");
2163 ASSERT(failed_to_evac == rtsFalse);
2165 /* get the next static object from the list. Remeber, there might
2166 * be more stuff on this list now that we've done some evacuating!
2167 * (static_objects is a global)
2173 /* -----------------------------------------------------------------------------
2174 scavenge_stack walks over a section of stack and evacuates all the
2175 objects pointed to by it. We can use the same code for walking
2176 PAPs, since these are just sections of copied stack.
2177 -------------------------------------------------------------------------- */
2180 scavenge_stack(StgPtr p, StgPtr stack_end)
2183 const StgInfoTable* info;
2187 * Each time around this loop, we are looking at a chunk of stack
2188 * that starts with either a pending argument section or an
2189 * activation record.
2192 while (p < stack_end) {
2193 q = *stgCast(StgPtr*,p);
2195 /* If we've got a tag, skip over that many words on the stack */
2196 if (IS_ARG_TAG(stgCast(StgWord,q))) {
2201 /* Is q a pointer to a closure?
2203 if (! LOOKS_LIKE_GHC_INFO(q)) {
2206 if (LOOKS_LIKE_STATIC(q)) { /* Is it a static closure? */
2207 ASSERT(closure_STATIC(stgCast(StgClosure*,q)));
2209 /* otherwise, must be a pointer into the allocation space.
2213 (StgClosure *)*p = evacuate((StgClosure *)q);
2219 * Otherwise, q must be the info pointer of an activation
2220 * record. All activation records have 'bitmap' style layout
2223 info = get_itbl(stgCast(StgClosure*,p));
2225 switch (info->type) {
2227 /* Dynamic bitmap: the mask is stored on the stack */
2229 bitmap = stgCast(StgRetDyn*,p)->liveness;
2230 p = &payloadWord(stgCast(StgRetDyn*,p),0);
2233 /* probably a slow-entry point return address: */
2239 /* Specialised code for update frames, since they're so common.
2240 * We *know* the updatee points to a BLACKHOLE, CAF_BLACKHOLE,
2241 * or BLACKHOLE_BQ, so just inline the code to evacuate it here.
2245 StgUpdateFrame *frame = (StgUpdateFrame *)p;
2247 StgClosureType type = get_itbl(frame->updatee)->type;
2249 p += sizeofW(StgUpdateFrame);
2250 if (type == EVACUATED) {
2251 frame->updatee = evacuate(frame->updatee);
2254 bdescr *bd = Bdescr((P_)frame->updatee);
2256 if (bd->gen->no > N) {
2257 if (bd->gen->no < evac_gen) {
2258 failed_to_evac = rtsTrue;
2263 /* Don't promote blackholes */
2265 if (!(step->gen->no == 0 &&
2267 step->no == step->gen->n_steps-1)) {
2274 to = copyPart(frame->updatee, BLACKHOLE_sizeW(),
2275 sizeofW(StgHeader), step);
2276 upd_evacuee(frame->updatee,to);
2277 frame->updatee = to;
2280 to = copy(frame->updatee, BLACKHOLE_sizeW(), step);
2281 upd_evacuee(frame->updatee,to);
2282 frame->updatee = to;
2283 recordMutable((StgMutClosure *)to);
2286 barf("scavenge_stack: UPDATE_FRAME updatee");
2291 /* small bitmap (< 32 entries, or 64 on a 64-bit machine) */
2298 bitmap = info->layout.bitmap;
2301 while (bitmap != 0) {
2302 if ((bitmap & 1) == 0) {
2303 (StgClosure *)*p = evacuate((StgClosure *)*p);
2306 bitmap = bitmap >> 1;
2313 /* large bitmap (> 32 entries) */
2318 StgLargeBitmap *large_bitmap;
2321 large_bitmap = info->layout.large_bitmap;
2324 for (i=0; i<large_bitmap->size; i++) {
2325 bitmap = large_bitmap->bitmap[i];
2326 q = p + sizeof(W_) * 8;
2327 while (bitmap != 0) {
2328 if ((bitmap & 1) == 0) {
2329 (StgClosure *)*p = evacuate((StgClosure *)*p);
2332 bitmap = bitmap >> 1;
2334 if (i+1 < large_bitmap->size) {
2336 (StgClosure *)*p = evacuate((StgClosure *)*p);
2342 /* and don't forget to follow the SRT */
2347 barf("scavenge_stack: weird activation record found on stack.\n");
2352 /*-----------------------------------------------------------------------------
2353 scavenge the large object list.
2355 evac_gen set by caller; similar games played with evac_gen as with
2356 scavenge() - see comment at the top of scavenge(). Most large
2357 objects are (repeatedly) mutable, so most of the time evac_gen will
2359 --------------------------------------------------------------------------- */
2362 scavenge_large(step *step)
2366 const StgInfoTable* info;
2367 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
2369 evac_gen = 0; /* most objects are mutable */
2370 bd = step->new_large_objects;
2372 for (; bd != NULL; bd = step->new_large_objects) {
2374 /* take this object *off* the large objects list and put it on
2375 * the scavenged large objects list. This is so that we can
2376 * treat new_large_objects as a stack and push new objects on
2377 * the front when evacuating.
2379 step->new_large_objects = bd->link;
2380 dbl_link_onto(bd, &step->scavenged_large_objects);
2383 info = get_itbl(stgCast(StgClosure*,p));
2385 switch (info->type) {
2387 /* only certain objects can be "large"... */
2390 /* nothing to follow */
2394 /* follow everything */
2398 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2399 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2400 (StgClosure *)*p = evacuate((StgClosure *)*p);
2405 case MUT_ARR_PTRS_FROZEN:
2406 /* follow everything */
2408 StgPtr start = p, next;
2410 evac_gen = saved_evac_gen; /* not really mutable */
2411 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2412 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2413 (StgClosure *)*p = evacuate((StgClosure *)*p);
2416 if (failed_to_evac) {
2417 recordMutable((StgMutClosure *)start);
2424 StgBCO* bco = stgCast(StgBCO*,p);
2426 evac_gen = saved_evac_gen;
2427 for (i = 0; i < bco->n_ptrs; i++) {
2428 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
2439 /* chase the link field for any TSOs on the same queue */
2440 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
2441 /* scavenge this thread's stack */
2442 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2447 barf("scavenge_large: unknown/strange object");
2453 zeroStaticObjectList(StgClosure* first_static)
2457 const StgInfoTable *info;
2459 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
2461 link = STATIC_LINK(info, p);
2462 STATIC_LINK(info,p) = NULL;
2466 /* This function is only needed because we share the mutable link
2467 * field with the static link field in an IND_STATIC, so we have to
2468 * zero the mut_link field before doing a major GC, which needs the
2469 * static link field.
2471 * It doesn't do any harm to zero all the mutable link fields on the
2475 zeroMutableList(StgMutClosure *first)
2477 StgMutClosure *next, *c;
2479 for (c = first; c != END_MUT_LIST; c = next) {
2485 /* -----------------------------------------------------------------------------
2487 -------------------------------------------------------------------------- */
2489 void RevertCAFs(void)
2491 while (enteredCAFs != END_CAF_LIST) {
2492 StgCAF* caf = enteredCAFs;
2494 enteredCAFs = caf->link;
2495 ASSERT(get_itbl(caf)->type == CAF_ENTERED);
2496 SET_INFO(caf,&CAF_UNENTERED_info);
2497 caf->value = stgCast(StgClosure*,0xdeadbeef);
2498 caf->link = stgCast(StgCAF*,0xdeadbeef);
2502 void revertDeadCAFs(void)
2504 StgCAF* caf = enteredCAFs;
2505 enteredCAFs = END_CAF_LIST;
2506 while (caf != END_CAF_LIST) {
2507 StgCAF* next = caf->link;
2509 switch(GET_INFO(caf)->type) {
2512 /* This object has been evacuated, it must be live. */
2513 StgCAF* new = stgCast(StgCAF*,stgCast(StgEvacuated*,caf)->evacuee);
2514 new->link = enteredCAFs;
2520 SET_INFO(caf,&CAF_UNENTERED_info);
2521 caf->value = stgCast(StgClosure*,0xdeadbeef);
2522 caf->link = stgCast(StgCAF*,0xdeadbeef);
2526 barf("revertDeadCAFs: enteredCAFs list corrupted");
2532 /* -----------------------------------------------------------------------------
2533 Sanity code for CAF garbage collection.
2535 With DEBUG turned on, we manage a CAF list in addition to the SRT
2536 mechanism. After GC, we run down the CAF list and blackhole any
2537 CAFs which have been garbage collected. This means we get an error
2538 whenever the program tries to enter a garbage collected CAF.
2540 Any garbage collected CAFs are taken off the CAF list at the same
2542 -------------------------------------------------------------------------- */
2550 const StgInfoTable *info;
2561 ASSERT(info->type == IND_STATIC);
2563 if (STATIC_LINK(info,p) == NULL) {
2564 IF_DEBUG(gccafs, fprintf(stderr, "CAF gc'd at 0x%04x\n", (int)p));
2566 SET_INFO(p,&BLACKHOLE_info);
2567 p = STATIC_LINK2(info,p);
2571 pp = &STATIC_LINK2(info,p);
2578 /* fprintf(stderr, "%d CAFs live\n", i); */
2582 /* -----------------------------------------------------------------------------
2585 Whenever a thread returns to the scheduler after possibly doing
2586 some work, we have to run down the stack and black-hole all the
2587 closures referred to by update frames.
2588 -------------------------------------------------------------------------- */
2591 threadLazyBlackHole(StgTSO *tso)
2593 StgUpdateFrame *update_frame;
2594 StgBlockingQueue *bh;
2597 stack_end = &tso->stack[tso->stack_size];
2598 update_frame = tso->su;
2601 switch (get_itbl(update_frame)->type) {
2604 update_frame = stgCast(StgCatchFrame*,update_frame)->link;
2608 bh = (StgBlockingQueue *)update_frame->updatee;
2610 /* if the thunk is already blackholed, it means we've also
2611 * already blackholed the rest of the thunks on this stack,
2612 * so we can stop early.
2614 * The blackhole made for a CAF is a CAF_BLACKHOLE, so they
2615 * don't interfere with this optimisation.
2617 if (bh->header.info == &BLACKHOLE_info) {
2621 if (bh->header.info != &BLACKHOLE_BQ_info &&
2622 bh->header.info != &CAF_BLACKHOLE_info) {
2623 SET_INFO(bh,&BLACKHOLE_info);
2626 update_frame = update_frame->link;
2630 update_frame = stgCast(StgSeqFrame*,update_frame)->link;
2636 barf("threadPaused");
2641 /* -----------------------------------------------------------------------------
2644 * Code largely pinched from old RTS, then hacked to bits. We also do
2645 * lazy black holing here.
2647 * -------------------------------------------------------------------------- */
2650 threadSqueezeStack(StgTSO *tso)
2652 lnat displacement = 0;
2653 StgUpdateFrame *frame;
2654 StgUpdateFrame *next_frame; /* Temporally next */
2655 StgUpdateFrame *prev_frame; /* Temporally previous */
2657 rtsBool prev_was_update_frame;
2659 bottom = &(tso->stack[tso->stack_size]);
2662 /* There must be at least one frame, namely the STOP_FRAME.
2664 ASSERT((P_)frame < bottom);
2666 /* Walk down the stack, reversing the links between frames so that
2667 * we can walk back up as we squeeze from the bottom. Note that
2668 * next_frame and prev_frame refer to next and previous as they were
2669 * added to the stack, rather than the way we see them in this
2670 * walk. (It makes the next loop less confusing.)
2672 * Stop if we find an update frame pointing to a black hole
2673 * (see comment in threadLazyBlackHole()).
2677 while ((P_)frame < bottom - 1) { /* bottom - 1 is the STOP_FRAME */
2678 prev_frame = frame->link;
2679 frame->link = next_frame;
2682 if (get_itbl(frame)->type == UPDATE_FRAME
2683 && frame->updatee->header.info == &BLACKHOLE_info) {
2688 /* Now, we're at the bottom. Frame points to the lowest update
2689 * frame on the stack, and its link actually points to the frame
2690 * above. We have to walk back up the stack, squeezing out empty
2691 * update frames and turning the pointers back around on the way
2694 * The bottom-most frame (the STOP_FRAME) has not been altered, and
2695 * we never want to eliminate it anyway. Just walk one step up
2696 * before starting to squeeze. When you get to the topmost frame,
2697 * remember that there are still some words above it that might have
2704 prev_was_update_frame = (get_itbl(prev_frame)->type == UPDATE_FRAME);
2707 * Loop through all of the frames (everything except the very
2708 * bottom). Things are complicated by the fact that we have
2709 * CATCH_FRAMEs and SEQ_FRAMEs interspersed with the update frames.
2710 * We can only squeeze when there are two consecutive UPDATE_FRAMEs.
2712 while (frame != NULL) {
2714 StgPtr frame_bottom = (P_)frame + sizeofW(StgUpdateFrame);
2715 rtsBool is_update_frame;
2717 next_frame = frame->link;
2718 is_update_frame = (get_itbl(frame)->type == UPDATE_FRAME);
2721 * 1. both the previous and current frame are update frames
2722 * 2. the current frame is empty
2724 if (prev_was_update_frame && is_update_frame &&
2725 (P_)prev_frame == frame_bottom + displacement) {
2727 /* Now squeeze out the current frame */
2728 StgClosure *updatee_keep = prev_frame->updatee;
2729 StgClosure *updatee_bypass = frame->updatee;
2732 fprintf(stderr, "squeezing frame at %p\n", frame);
2735 /* Deal with blocking queues. If both updatees have blocked
2736 * threads, then we should merge the queues into the update
2737 * frame that we're keeping.
2739 * Alternatively, we could just wake them up: they'll just go
2740 * straight to sleep on the proper blackhole! This is less code
2741 * and probably less bug prone, although it's probably much
2744 #if 0 /* do it properly... */
2745 if (GET_INFO(updatee_bypass) == BLACKHOLE_BQ_info) {
2746 /* Sigh. It has one. Don't lose those threads! */
2747 if (GET_INFO(updatee_keep) == BLACKHOLE_BQ_info) {
2748 /* Urgh. Two queues. Merge them. */
2749 P_ keep_tso = ((StgBlockingQueue *)updatee_keep)->blocking_queue;
2751 while (keep_tso->link != END_TSO_QUEUE) {
2752 keep_tso = keep_tso->link;
2754 keep_tso->link = ((StgBlockingQueue *)updatee_bypass)->blocking_queue;
2757 /* For simplicity, just swap the BQ for the BH */
2758 P_ temp = updatee_keep;
2760 updatee_keep = updatee_bypass;
2761 updatee_bypass = temp;
2763 /* Record the swap in the kept frame (below) */
2764 prev_frame->updatee = updatee_keep;
2769 TICK_UPD_SQUEEZED();
2770 UPD_IND(updatee_bypass, updatee_keep); /* this wakes the threads up */
2772 sp = (P_)frame - 1; /* sp = stuff to slide */
2773 displacement += sizeofW(StgUpdateFrame);
2776 /* No squeeze for this frame */
2777 sp = frame_bottom - 1; /* Keep the current frame */
2779 /* Do lazy black-holing.
2781 if (is_update_frame) {
2782 StgBlockingQueue *bh = (StgBlockingQueue *)frame->updatee;
2783 if (bh->header.info != &BLACKHOLE_BQ_info &&
2784 bh->header.info != &CAF_BLACKHOLE_info) {
2785 SET_INFO(bh,&BLACKHOLE_info);
2789 /* Fix the link in the current frame (should point to the frame below) */
2790 frame->link = prev_frame;
2791 prev_was_update_frame = is_update_frame;
2794 /* Now slide all words from sp up to the next frame */
2796 if (displacement > 0) {
2797 P_ next_frame_bottom;
2799 if (next_frame != NULL)
2800 next_frame_bottom = (P_)next_frame + sizeofW(StgUpdateFrame);
2802 next_frame_bottom = tso->sp - 1;
2805 fprintf(stderr, "sliding [%p, %p] by %ld\n", sp, next_frame_bottom,
2809 while (sp >= next_frame_bottom) {
2810 sp[displacement] = *sp;
2814 (P_)prev_frame = (P_)frame + displacement;
2818 tso->sp += displacement;
2819 tso->su = prev_frame;
2822 /* -----------------------------------------------------------------------------
2825 * We have to prepare for GC - this means doing lazy black holing
2826 * here. We also take the opportunity to do stack squeezing if it's
2828 * -------------------------------------------------------------------------- */
2831 threadPaused(StgTSO *tso)
2833 if ( RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue )
2834 threadSqueezeStack(tso); /* does black holing too */
2836 threadLazyBlackHole(tso);