1 /* -----------------------------------------------------------------------------
2 * $Id: GC.c,v 1.39 1999/02/24 16:25:40 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 step = &generations[evac_gen].steps[0];
874 /* chain a new block onto the to-space for the destination step if
877 if (step->hp + size >= step->hpLim) {
881 for(to = step->hp, from = (P_)src; size>0; --size) {
887 return (StgClosure *)dest;
890 /* Special version of copy() for when we only want to copy the info
891 * pointer of an object, but reserve some padding after it. This is
892 * used to optimise evacuation of BLACKHOLEs.
895 static __inline__ StgClosure *
896 copyPart(StgClosure *src, nat size_to_reserve, nat size_to_copy, step *step)
900 TICK_GC_WORDS_COPIED(size_to_copy);
901 if (step->gen->no < evac_gen) {
902 step = &generations[evac_gen].steps[0];
905 if (step->hp + size_to_reserve >= step->hpLim) {
909 for(to = step->hp, from = (P_)src; size_to_copy>0; --size_to_copy) {
914 step->hp += size_to_reserve;
915 return (StgClosure *)dest;
918 static __inline__ void
919 upd_evacuee(StgClosure *p, StgClosure *dest)
921 StgEvacuated *q = (StgEvacuated *)p;
923 SET_INFO(q,&EVACUATED_info);
927 /* -----------------------------------------------------------------------------
928 Evacuate a large object
930 This just consists of removing the object from the (doubly-linked)
931 large_alloc_list, and linking it on to the (singly-linked)
932 new_large_objects list, from where it will be scavenged later.
934 Convention: bd->evacuated is /= 0 for a large object that has been
935 evacuated, or 0 otherwise.
936 -------------------------------------------------------------------------- */
939 evacuate_large(StgPtr p, rtsBool mutable)
941 bdescr *bd = Bdescr(p);
944 /* should point to the beginning of the block */
945 ASSERT(((W_)p & BLOCK_MASK) == 0);
947 /* already evacuated? */
949 /* Don't forget to set the failed_to_evac flag if we didn't get
950 * the desired destination (see comments in evacuate()).
952 if (bd->gen->no < evac_gen) {
953 failed_to_evac = rtsTrue;
954 TICK_GC_FAILED_PROMOTION();
960 /* remove from large_object list */
962 bd->back->link = bd->link;
963 } else { /* first object in the list */
964 step->large_objects = bd->link;
967 bd->link->back = bd->back;
970 /* link it on to the evacuated large object list of the destination step
973 if (step->gen->no < evac_gen) {
974 step = &generations[evac_gen].steps[0];
979 bd->link = step->new_large_objects;
980 step->new_large_objects = bd;
984 recordMutable((StgMutClosure *)p);
988 /* -----------------------------------------------------------------------------
989 Adding a MUT_CONS to an older generation.
991 This is necessary from time to time when we end up with an
992 old-to-new generation pointer in a non-mutable object. We defer
993 the promotion until the next GC.
994 -------------------------------------------------------------------------- */
997 mkMutCons(StgClosure *ptr, generation *gen)
1002 step = &gen->steps[0];
1004 /* chain a new block onto the to-space for the destination step if
1007 if (step->hp + sizeofW(StgIndOldGen) >= step->hpLim) {
1011 q = (StgMutVar *)step->hp;
1012 step->hp += sizeofW(StgMutVar);
1014 SET_HDR(q,&MUT_CONS_info,CCS_GC);
1016 recordOldToNewPtrs((StgMutClosure *)q);
1018 return (StgClosure *)q;
1021 /* -----------------------------------------------------------------------------
1024 This is called (eventually) for every live object in the system.
1026 The caller to evacuate specifies a desired generation in the
1027 evac_gen global variable. The following conditions apply to
1028 evacuating an object which resides in generation M when we're
1029 collecting up to generation N
1033 else evac to step->to
1035 if M < evac_gen evac to evac_gen, step 0
1037 if the object is already evacuated, then we check which generation
1040 if M >= evac_gen do nothing
1041 if M < evac_gen set failed_to_evac flag to indicate that we
1042 didn't manage to evacuate this object into evac_gen.
1044 -------------------------------------------------------------------------- */
1048 evacuate(StgClosure *q)
1053 const StgInfoTable *info;
1056 if (!LOOKS_LIKE_STATIC(q)) {
1058 if (bd->gen->no > N) {
1059 /* Can't evacuate this object, because it's in a generation
1060 * older than the ones we're collecting. Let's hope that it's
1061 * in evac_gen or older, or we will have to make an IND_OLDGEN object.
1063 if (bd->gen->no < evac_gen) {
1065 failed_to_evac = rtsTrue;
1066 TICK_GC_FAILED_PROMOTION();
1070 step = bd->step->to;
1073 /* make sure the info pointer is into text space */
1074 ASSERT(q && (LOOKS_LIKE_GHC_INFO(GET_INFO(q))
1075 || IS_HUGS_CONSTR_INFO(GET_INFO(q))));
1078 switch (info -> type) {
1081 to = copy(q,bco_sizeW(stgCast(StgBCO*,q)),step);
1086 ASSERT(q->header.info != &MUT_CONS_info);
1088 to = copy(q,sizeW_fromITBL(info),step);
1090 recordMutable((StgMutClosure *)to);
1094 stable_ptr_table[((StgStableName *)q)->sn].keep = rtsTrue;
1095 to = copy(q,sizeofW(StgStableName),step);
1103 to = copy(q,sizeofW(StgHeader)+1,step);
1107 case THUNK_1_0: /* here because of MIN_UPD_SIZE */
1118 to = copy(q,sizeofW(StgHeader)+2,step);
1126 case IND_OLDGEN_PERM:
1131 to = copy(q,sizeW_fromITBL(info),step);
1137 to = copyPart(q,BLACKHOLE_sizeW(),sizeofW(StgHeader),step);
1142 to = copy(q,BLACKHOLE_sizeW(),step);
1144 recordMutable((StgMutClosure *)to);
1147 case THUNK_SELECTOR:
1149 const StgInfoTable* selectee_info;
1150 StgClosure* selectee = ((StgSelector*)q)->selectee;
1153 selectee_info = get_itbl(selectee);
1154 switch (selectee_info->type) {
1163 StgNat32 offset = info->layout.selector_offset;
1165 /* check that the size is in range */
1167 (StgNat32)(selectee_info->layout.payload.ptrs +
1168 selectee_info->layout.payload.nptrs));
1170 /* perform the selection! */
1171 q = selectee->payload[offset];
1173 /* if we're already in to-space, there's no need to continue
1174 * with the evacuation, just update the source address with
1175 * a pointer to the (evacuated) constructor field.
1177 if (IS_USER_PTR(q)) {
1178 bdescr *bd = Bdescr((P_)q);
1179 if (bd->evacuated) {
1180 if (bd->gen->no < evac_gen) {
1181 failed_to_evac = rtsTrue;
1182 TICK_GC_FAILED_PROMOTION();
1188 /* otherwise, carry on and evacuate this constructor field,
1189 * (but not the constructor itself)
1198 case IND_OLDGEN_PERM:
1199 selectee = stgCast(StgInd *,selectee)->indirectee;
1203 selectee = stgCast(StgCAF *,selectee)->value;
1207 selectee = stgCast(StgEvacuated*,selectee)->evacuee;
1217 case THUNK_SELECTOR:
1218 /* aargh - do recursively???? */
1223 /* not evaluated yet */
1227 barf("evacuate: THUNK_SELECTOR: strange selectee");
1230 to = copy(q,THUNK_SELECTOR_sizeW(),step);
1236 /* follow chains of indirections, don't evacuate them */
1237 q = ((StgInd*)q)->indirectee;
1240 /* ToDo: optimise STATIC_LINK for known cases.
1241 - FUN_STATIC : payload[0]
1242 - THUNK_STATIC : payload[1]
1243 - IND_STATIC : payload[1]
1247 if (info->srt_len == 0) { /* small optimisation */
1253 /* don't want to evacuate these, but we do want to follow pointers
1254 * from SRTs - see scavenge_static.
1257 /* put the object on the static list, if necessary.
1259 if (major_gc && STATIC_LINK(info,(StgClosure *)q) == NULL) {
1260 STATIC_LINK(info,(StgClosure *)q) = static_objects;
1261 static_objects = (StgClosure *)q;
1265 case CONSTR_INTLIKE:
1266 case CONSTR_CHARLIKE:
1267 case CONSTR_NOCAF_STATIC:
1268 /* no need to put these on the static linked list, they don't need
1283 /* shouldn't see these */
1284 barf("evacuate: stack frame\n");
1288 /* these are special - the payload is a copy of a chunk of stack,
1290 to = copy(q,pap_sizeW(stgCast(StgPAP*,q)),step);
1295 /* Already evacuated, just return the forwarding address.
1296 * HOWEVER: if the requested destination generation (evac_gen) is
1297 * older than the actual generation (because the object was
1298 * already evacuated to a younger generation) then we have to
1299 * set the failed_to_evac flag to indicate that we couldn't
1300 * manage to promote the object to the desired generation.
1302 if (evac_gen > 0) { /* optimisation */
1303 StgClosure *p = ((StgEvacuated*)q)->evacuee;
1304 if (Bdescr((P_)p)->gen->no < evac_gen) {
1305 /* fprintf(stderr,"evac failed!\n");*/
1306 failed_to_evac = rtsTrue;
1307 TICK_GC_FAILED_PROMOTION();
1310 return ((StgEvacuated*)q)->evacuee;
1314 nat size = arr_words_sizeW(stgCast(StgArrWords*,q));
1316 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1317 evacuate_large((P_)q, rtsFalse);
1320 /* just copy the block */
1321 to = copy(q,size,step);
1328 case MUT_ARR_PTRS_FROZEN:
1330 nat size = mut_arr_ptrs_sizeW(stgCast(StgMutArrPtrs*,q));
1332 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1333 evacuate_large((P_)q, info->type == MUT_ARR_PTRS);
1336 /* just copy the block */
1337 to = copy(q,size,step);
1339 if (info->type == MUT_ARR_PTRS) {
1340 recordMutable((StgMutClosure *)to);
1348 StgTSO *tso = stgCast(StgTSO *,q);
1349 nat size = tso_sizeW(tso);
1352 /* Large TSOs don't get moved, so no relocation is required.
1354 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1355 evacuate_large((P_)q, rtsTrue);
1358 /* To evacuate a small TSO, we need to relocate the update frame
1362 StgTSO *new_tso = (StgTSO *)copy((StgClosure *)tso,tso_sizeW(tso),step);
1364 diff = (StgPtr)new_tso - (StgPtr)tso; /* In *words* */
1366 /* relocate the stack pointers... */
1367 new_tso->su = (StgUpdateFrame *) ((StgPtr)new_tso->su + diff);
1368 new_tso->sp = (StgPtr)new_tso->sp + diff;
1369 new_tso->splim = (StgPtr)new_tso->splim + diff;
1371 relocate_TSO(tso, new_tso);
1372 upd_evacuee(q,(StgClosure *)new_tso);
1374 recordMutable((StgMutClosure *)new_tso);
1375 return (StgClosure *)new_tso;
1381 fprintf(stderr,"evacuate: unimplemented/strange closure type\n");
1385 barf("evacuate: strange closure type");
1391 /* -----------------------------------------------------------------------------
1392 relocate_TSO is called just after a TSO has been copied from src to
1393 dest. It adjusts the update frame list for the new location.
1394 -------------------------------------------------------------------------- */
1397 relocate_TSO(StgTSO *src, StgTSO *dest)
1404 diff = (StgPtr)dest->sp - (StgPtr)src->sp; /* In *words* */
1408 while ((P_)su < dest->stack + dest->stack_size) {
1409 switch (get_itbl(su)->type) {
1411 /* GCC actually manages to common up these three cases! */
1414 su->link = (StgUpdateFrame *) ((StgPtr)su->link + diff);
1419 cf = (StgCatchFrame *)su;
1420 cf->link = (StgUpdateFrame *) ((StgPtr)cf->link + diff);
1425 sf = (StgSeqFrame *)su;
1426 sf->link = (StgUpdateFrame *) ((StgPtr)sf->link + diff);
1435 barf("relocate_TSO");
1444 scavenge_srt(const StgInfoTable *info)
1446 StgClosure **srt, **srt_end;
1448 /* evacuate the SRT. If srt_len is zero, then there isn't an
1449 * srt field in the info table. That's ok, because we'll
1450 * never dereference it.
1452 srt = stgCast(StgClosure **,info->srt);
1453 srt_end = srt + info->srt_len;
1454 for (; srt < srt_end; srt++) {
1459 /* -----------------------------------------------------------------------------
1460 Scavenge a given step until there are no more objects in this step
1463 evac_gen is set by the caller to be either zero (for a step in a
1464 generation < N) or G where G is the generation of the step being
1467 We sometimes temporarily change evac_gen back to zero if we're
1468 scavenging a mutable object where early promotion isn't such a good
1470 -------------------------------------------------------------------------- */
1474 scavenge(step *step)
1477 const StgInfoTable *info;
1479 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
1484 failed_to_evac = rtsFalse;
1486 /* scavenge phase - standard breadth-first scavenging of the
1490 while (bd != step->hp_bd || p < step->hp) {
1492 /* If we're at the end of this block, move on to the next block */
1493 if (bd != step->hp_bd && p == bd->free) {
1499 q = p; /* save ptr to object */
1501 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO((StgClosure *)p))
1502 || IS_HUGS_CONSTR_INFO(GET_INFO((StgClosure *)p))));
1504 info = get_itbl((StgClosure *)p);
1505 switch (info -> type) {
1509 StgBCO* bco = stgCast(StgBCO*,p);
1511 for (i = 0; i < bco->n_ptrs; i++) {
1512 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
1514 p += bco_sizeW(bco);
1519 /* treat MVars specially, because we don't want to evacuate the
1520 * mut_link field in the middle of the closure.
1523 StgMVar *mvar = ((StgMVar *)p);
1525 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
1526 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
1527 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
1528 p += sizeofW(StgMVar);
1529 evac_gen = saved_evac_gen;
1537 ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
1538 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1539 p += sizeofW(StgHeader) + 2;
1544 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1545 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1551 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1552 p += sizeofW(StgHeader) + 1;
1557 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1563 p += sizeofW(StgHeader) + 1;
1570 p += sizeofW(StgHeader) + 2;
1577 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1578 p += sizeofW(StgHeader) + 2;
1591 case IND_OLDGEN_PERM:
1597 end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
1598 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
1599 (StgClosure *)*p = evacuate((StgClosure *)*p);
1601 p += info->layout.payload.nptrs;
1606 /* ignore MUT_CONSs */
1607 if (((StgMutVar *)p)->header.info != &MUT_CONS_info) {
1609 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
1610 evac_gen = saved_evac_gen;
1612 p += sizeofW(StgMutVar);
1617 p += BLACKHOLE_sizeW();
1622 StgBlockingQueue *bh = (StgBlockingQueue *)p;
1623 (StgClosure *)bh->blocking_queue =
1624 evacuate((StgClosure *)bh->blocking_queue);
1625 if (failed_to_evac) {
1626 failed_to_evac = rtsFalse;
1627 recordMutable((StgMutClosure *)bh);
1629 p += BLACKHOLE_sizeW();
1633 case THUNK_SELECTOR:
1635 StgSelector *s = (StgSelector *)p;
1636 s->selectee = evacuate(s->selectee);
1637 p += THUNK_SELECTOR_sizeW();
1643 barf("scavenge:IND???\n");
1645 case CONSTR_INTLIKE:
1646 case CONSTR_CHARLIKE:
1648 case CONSTR_NOCAF_STATIC:
1652 /* Shouldn't see a static object here. */
1653 barf("scavenge: STATIC object\n");
1665 /* Shouldn't see stack frames here. */
1666 barf("scavenge: stack frame\n");
1668 case AP_UPD: /* same as PAPs */
1670 /* Treat a PAP just like a section of stack, not forgetting to
1671 * evacuate the function pointer too...
1674 StgPAP* pap = stgCast(StgPAP*,p);
1676 pap->fun = evacuate(pap->fun);
1677 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1678 p += pap_sizeW(pap);
1683 /* nothing to follow */
1684 p += arr_words_sizeW(stgCast(StgArrWords*,p));
1688 /* follow everything */
1692 evac_gen = 0; /* repeatedly mutable */
1693 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1694 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1695 (StgClosure *)*p = evacuate((StgClosure *)*p);
1697 evac_gen = saved_evac_gen;
1701 case MUT_ARR_PTRS_FROZEN:
1702 /* follow everything */
1704 StgPtr start = p, next;
1706 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1707 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1708 (StgClosure *)*p = evacuate((StgClosure *)*p);
1710 if (failed_to_evac) {
1711 /* we can do this easier... */
1712 recordMutable((StgMutClosure *)start);
1713 failed_to_evac = rtsFalse;
1724 /* chase the link field for any TSOs on the same queue */
1725 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
1726 /* scavenge this thread's stack */
1727 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
1728 evac_gen = saved_evac_gen;
1729 p += tso_sizeW(tso);
1736 barf("scavenge: unimplemented/strange closure type\n");
1742 /* If we didn't manage to promote all the objects pointed to by
1743 * the current object, then we have to designate this object as
1744 * mutable (because it contains old-to-new generation pointers).
1746 if (failed_to_evac) {
1747 mkMutCons((StgClosure *)q, &generations[evac_gen]);
1748 failed_to_evac = rtsFalse;
1756 /* -----------------------------------------------------------------------------
1757 Scavenge one object.
1759 This is used for objects that are temporarily marked as mutable
1760 because they contain old-to-new generation pointers. Only certain
1761 objects can have this property.
1762 -------------------------------------------------------------------------- */
1764 scavenge_one(StgClosure *p)
1769 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1770 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1774 switch (info -> type) {
1777 case FUN_1_0: /* hardly worth specialising these guys */
1797 case IND_OLDGEN_PERM:
1803 end = (P_)p->payload + info->layout.payload.ptrs;
1804 for (q = (P_)p->payload; q < end; q++) {
1805 (StgClosure *)*q = evacuate((StgClosure *)*q);
1814 case THUNK_SELECTOR:
1816 StgSelector *s = (StgSelector *)p;
1817 s->selectee = evacuate(s->selectee);
1821 case AP_UPD: /* same as PAPs */
1823 /* Treat a PAP just like a section of stack, not forgetting to
1824 * evacuate the function pointer too...
1827 StgPAP* pap = (StgPAP *)p;
1829 pap->fun = evacuate(pap->fun);
1830 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1835 /* This might happen if for instance a MUT_CONS was pointing to a
1836 * THUNK which has since been updated. The IND_OLDGEN will
1837 * be on the mutable list anyway, so we don't need to do anything
1843 barf("scavenge_one: strange object");
1846 no_luck = failed_to_evac;
1847 failed_to_evac = rtsFalse;
1852 /* -----------------------------------------------------------------------------
1853 Scavenging mutable lists.
1855 We treat the mutable list of each generation > N (i.e. all the
1856 generations older than the one being collected) as roots. We also
1857 remove non-mutable objects from the mutable list at this point.
1858 -------------------------------------------------------------------------- */
1861 scavenge_mut_once_list(generation *gen)
1864 StgMutClosure *p, *next, *new_list;
1866 p = gen->mut_once_list;
1867 new_list = END_MUT_LIST;
1871 failed_to_evac = rtsFalse;
1873 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
1875 /* make sure the info pointer is into text space */
1876 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1877 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1880 switch(info->type) {
1883 case IND_OLDGEN_PERM:
1885 /* Try to pull the indirectee into this generation, so we can
1886 * remove the indirection from the mutable list.
1888 ((StgIndOldGen *)p)->indirectee =
1889 evacuate(((StgIndOldGen *)p)->indirectee);
1892 /* Debugging code to print out the size of the thing we just
1896 StgPtr start = gen->steps[0].scan;
1897 bdescr *start_bd = gen->steps[0].scan_bd;
1899 scavenge(&gen->steps[0]);
1900 if (start_bd != gen->steps[0].scan_bd) {
1901 size += (P_)BLOCK_ROUND_UP(start) - start;
1902 start_bd = start_bd->link;
1903 while (start_bd != gen->steps[0].scan_bd) {
1904 size += BLOCK_SIZE_W;
1905 start_bd = start_bd->link;
1907 size += gen->steps[0].scan -
1908 (P_)BLOCK_ROUND_DOWN(gen->steps[0].scan);
1910 size = gen->steps[0].scan - start;
1912 fprintf(stderr,"evac IND_OLDGEN: %d bytes\n", size * sizeof(W_));
1916 /* failed_to_evac might happen if we've got more than two
1917 * generations, we're collecting only generation 0, the
1918 * indirection resides in generation 2 and the indirectee is
1921 if (failed_to_evac) {
1922 failed_to_evac = rtsFalse;
1923 p->mut_link = new_list;
1926 /* the mut_link field of an IND_STATIC is overloaded as the
1927 * static link field too (it just so happens that we don't need
1928 * both at the same time), so we need to NULL it out when
1929 * removing this object from the mutable list because the static
1930 * link fields are all assumed to be NULL before doing a major
1938 /* MUT_CONS is a kind of MUT_VAR, except it that we try to remove
1939 * it from the mutable list if possible by promoting whatever it
1942 ASSERT(p->header.info == &MUT_CONS_info);
1943 if (scavenge_one(((StgMutVar *)p)->var) == rtsTrue) {
1944 /* didn't manage to promote everything, so put the
1945 * MUT_CONS back on the list.
1947 p->mut_link = new_list;
1953 /* shouldn't have anything else on the mutables list */
1954 barf("scavenge_mut_once_list: strange object?");
1958 gen->mut_once_list = new_list;
1963 scavenge_mutable_list(generation *gen)
1966 StgMutClosure *p, *next;
1968 p = gen->saved_mut_list;
1972 failed_to_evac = rtsFalse;
1974 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
1976 /* make sure the info pointer is into text space */
1977 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1978 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1981 switch(info->type) {
1983 case MUT_ARR_PTRS_FROZEN:
1984 /* remove this guy from the mutable list, but follow the ptrs
1985 * anyway (and make sure they get promoted to this gen).
1990 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1992 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
1993 (StgClosure *)*q = evacuate((StgClosure *)*q);
1997 if (failed_to_evac) {
1998 failed_to_evac = rtsFalse;
1999 p->mut_link = gen->mut_list;
2006 /* follow everything */
2007 p->mut_link = gen->mut_list;
2012 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2013 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
2014 (StgClosure *)*q = evacuate((StgClosure *)*q);
2020 /* MUT_CONS is a kind of MUT_VAR, except that we try to remove
2021 * it from the mutable list if possible by promoting whatever it
2024 ASSERT(p->header.info != &MUT_CONS_info);
2025 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
2026 p->mut_link = gen->mut_list;
2032 StgMVar *mvar = (StgMVar *)p;
2033 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
2034 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
2035 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
2036 p->mut_link = gen->mut_list;
2042 /* follow ptrs and remove this from the mutable list */
2044 StgTSO *tso = (StgTSO *)p;
2046 /* Don't bother scavenging if this thread is dead
2048 if (!(tso->whatNext == ThreadComplete ||
2049 tso->whatNext == ThreadKilled)) {
2050 /* Don't need to chase the link field for any TSOs on the
2051 * same queue. Just scavenge this thread's stack
2053 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2056 /* Don't take this TSO off the mutable list - it might still
2057 * point to some younger objects (because we set evac_gen to 0
2060 tso->mut_link = gen->mut_list;
2061 gen->mut_list = (StgMutClosure *)tso;
2067 StgBlockingQueue *bh = (StgBlockingQueue *)p;
2068 (StgClosure *)bh->blocking_queue =
2069 evacuate((StgClosure *)bh->blocking_queue);
2070 p->mut_link = gen->mut_list;
2076 /* shouldn't have anything else on the mutables list */
2077 barf("scavenge_mut_list: strange object?");
2083 scavenge_static(void)
2085 StgClosure* p = static_objects;
2086 const StgInfoTable *info;
2088 /* Always evacuate straight to the oldest generation for static
2090 evac_gen = oldest_gen->no;
2092 /* keep going until we've scavenged all the objects on the linked
2094 while (p != END_OF_STATIC_LIST) {
2098 /* make sure the info pointer is into text space */
2099 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
2100 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
2102 /* Take this object *off* the static_objects list,
2103 * and put it on the scavenged_static_objects list.
2105 static_objects = STATIC_LINK(info,p);
2106 STATIC_LINK(info,p) = scavenged_static_objects;
2107 scavenged_static_objects = p;
2109 switch (info -> type) {
2113 StgInd *ind = (StgInd *)p;
2114 ind->indirectee = evacuate(ind->indirectee);
2116 /* might fail to evacuate it, in which case we have to pop it
2117 * back on the mutable list (and take it off the
2118 * scavenged_static list because the static link and mut link
2119 * pointers are one and the same).
2121 if (failed_to_evac) {
2122 failed_to_evac = rtsFalse;
2123 scavenged_static_objects = STATIC_LINK(info,p);
2124 ((StgMutClosure *)ind)->mut_link = oldest_gen->mut_once_list;
2125 oldest_gen->mut_once_list = (StgMutClosure *)ind;
2139 next = (P_)p->payload + info->layout.payload.ptrs;
2140 /* evacuate the pointers */
2141 for (q = (P_)p->payload; q < next; q++) {
2142 (StgClosure *)*q = evacuate((StgClosure *)*q);
2148 barf("scavenge_static");
2151 ASSERT(failed_to_evac == rtsFalse);
2153 /* get the next static object from the list. Remeber, there might
2154 * be more stuff on this list now that we've done some evacuating!
2155 * (static_objects is a global)
2161 /* -----------------------------------------------------------------------------
2162 scavenge_stack walks over a section of stack and evacuates all the
2163 objects pointed to by it. We can use the same code for walking
2164 PAPs, since these are just sections of copied stack.
2165 -------------------------------------------------------------------------- */
2168 scavenge_stack(StgPtr p, StgPtr stack_end)
2171 const StgInfoTable* info;
2175 * Each time around this loop, we are looking at a chunk of stack
2176 * that starts with either a pending argument section or an
2177 * activation record.
2180 while (p < stack_end) {
2181 q = *stgCast(StgPtr*,p);
2183 /* If we've got a tag, skip over that many words on the stack */
2184 if (IS_ARG_TAG(stgCast(StgWord,q))) {
2189 /* Is q a pointer to a closure?
2191 if (! LOOKS_LIKE_GHC_INFO(q)) {
2194 if (LOOKS_LIKE_STATIC(q)) { /* Is it a static closure? */
2195 ASSERT(closure_STATIC(stgCast(StgClosure*,q)));
2197 /* otherwise, must be a pointer into the allocation space.
2201 (StgClosure *)*p = evacuate((StgClosure *)q);
2207 * Otherwise, q must be the info pointer of an activation
2208 * record. All activation records have 'bitmap' style layout
2211 info = get_itbl(stgCast(StgClosure*,p));
2213 switch (info->type) {
2215 /* Dynamic bitmap: the mask is stored on the stack */
2217 bitmap = stgCast(StgRetDyn*,p)->liveness;
2218 p = &payloadWord(stgCast(StgRetDyn*,p),0);
2221 /* probably a slow-entry point return address: */
2227 /* Specialised code for update frames, since they're so common.
2228 * We *know* the updatee points to a BLACKHOLE, CAF_BLACKHOLE,
2229 * or BLACKHOLE_BQ, so just inline the code to evacuate it here.
2233 StgUpdateFrame *frame = (StgUpdateFrame *)p;
2235 StgClosureType type = get_itbl(frame->updatee)->type;
2237 p += sizeofW(StgUpdateFrame);
2238 if (type == EVACUATED) {
2239 frame->updatee = evacuate(frame->updatee);
2242 bdescr *bd = Bdescr((P_)frame->updatee);
2244 if (bd->gen->no > N) {
2245 if (bd->gen->no < evac_gen) {
2246 failed_to_evac = rtsTrue;
2250 step = bd->step->to;
2254 to = copyPart(frame->updatee, BLACKHOLE_sizeW(),
2255 sizeofW(StgHeader), step);
2256 upd_evacuee(frame->updatee,to);
2257 frame->updatee = to;
2260 to = copy(frame->updatee, BLACKHOLE_sizeW(), step);
2261 upd_evacuee(frame->updatee,to);
2262 frame->updatee = to;
2263 recordMutable((StgMutClosure *)to);
2266 barf("scavenge_stack: UPDATE_FRAME updatee");
2271 /* small bitmap (< 32 entries, or 64 on a 64-bit machine) */
2278 bitmap = info->layout.bitmap;
2281 while (bitmap != 0) {
2282 if ((bitmap & 1) == 0) {
2283 (StgClosure *)*p = evacuate((StgClosure *)*p);
2286 bitmap = bitmap >> 1;
2293 /* large bitmap (> 32 entries) */
2298 StgLargeBitmap *large_bitmap;
2301 large_bitmap = info->layout.large_bitmap;
2304 for (i=0; i<large_bitmap->size; i++) {
2305 bitmap = large_bitmap->bitmap[i];
2306 q = p + sizeof(W_) * 8;
2307 while (bitmap != 0) {
2308 if ((bitmap & 1) == 0) {
2309 (StgClosure *)*p = evacuate((StgClosure *)*p);
2312 bitmap = bitmap >> 1;
2314 if (i+1 < large_bitmap->size) {
2316 (StgClosure *)*p = evacuate((StgClosure *)*p);
2322 /* and don't forget to follow the SRT */
2327 barf("scavenge_stack: weird activation record found on stack.\n");
2332 /*-----------------------------------------------------------------------------
2333 scavenge the large object list.
2335 evac_gen set by caller; similar games played with evac_gen as with
2336 scavenge() - see comment at the top of scavenge(). Most large
2337 objects are (repeatedly) mutable, so most of the time evac_gen will
2339 --------------------------------------------------------------------------- */
2342 scavenge_large(step *step)
2346 const StgInfoTable* info;
2347 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
2349 evac_gen = 0; /* most objects are mutable */
2350 bd = step->new_large_objects;
2352 for (; bd != NULL; bd = step->new_large_objects) {
2354 /* take this object *off* the large objects list and put it on
2355 * the scavenged large objects list. This is so that we can
2356 * treat new_large_objects as a stack and push new objects on
2357 * the front when evacuating.
2359 step->new_large_objects = bd->link;
2360 dbl_link_onto(bd, &step->scavenged_large_objects);
2363 info = get_itbl(stgCast(StgClosure*,p));
2365 switch (info->type) {
2367 /* only certain objects can be "large"... */
2370 /* nothing to follow */
2374 /* follow everything */
2378 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2379 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2380 (StgClosure *)*p = evacuate((StgClosure *)*p);
2385 case MUT_ARR_PTRS_FROZEN:
2386 /* follow everything */
2388 StgPtr start = p, next;
2390 evac_gen = saved_evac_gen; /* not really mutable */
2391 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2392 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2393 (StgClosure *)*p = evacuate((StgClosure *)*p);
2396 if (failed_to_evac) {
2397 recordMutable((StgMutClosure *)start);
2404 StgBCO* bco = stgCast(StgBCO*,p);
2406 evac_gen = saved_evac_gen;
2407 for (i = 0; i < bco->n_ptrs; i++) {
2408 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
2419 /* chase the link field for any TSOs on the same queue */
2420 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
2421 /* scavenge this thread's stack */
2422 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2427 barf("scavenge_large: unknown/strange object");
2433 zeroStaticObjectList(StgClosure* first_static)
2437 const StgInfoTable *info;
2439 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
2441 link = STATIC_LINK(info, p);
2442 STATIC_LINK(info,p) = NULL;
2446 /* This function is only needed because we share the mutable link
2447 * field with the static link field in an IND_STATIC, so we have to
2448 * zero the mut_link field before doing a major GC, which needs the
2449 * static link field.
2451 * It doesn't do any harm to zero all the mutable link fields on the
2455 zeroMutableList(StgMutClosure *first)
2457 StgMutClosure *next, *c;
2459 for (c = first; c != END_MUT_LIST; c = next) {
2465 /* -----------------------------------------------------------------------------
2467 -------------------------------------------------------------------------- */
2469 void RevertCAFs(void)
2471 while (enteredCAFs != END_CAF_LIST) {
2472 StgCAF* caf = enteredCAFs;
2474 enteredCAFs = caf->link;
2475 ASSERT(get_itbl(caf)->type == CAF_ENTERED);
2476 SET_INFO(caf,&CAF_UNENTERED_info);
2477 caf->value = stgCast(StgClosure*,0xdeadbeef);
2478 caf->link = stgCast(StgCAF*,0xdeadbeef);
2482 void revertDeadCAFs(void)
2484 StgCAF* caf = enteredCAFs;
2485 enteredCAFs = END_CAF_LIST;
2486 while (caf != END_CAF_LIST) {
2487 StgCAF* next = caf->link;
2489 switch(GET_INFO(caf)->type) {
2492 /* This object has been evacuated, it must be live. */
2493 StgCAF* new = stgCast(StgCAF*,stgCast(StgEvacuated*,caf)->evacuee);
2494 new->link = enteredCAFs;
2500 SET_INFO(caf,&CAF_UNENTERED_info);
2501 caf->value = stgCast(StgClosure*,0xdeadbeef);
2502 caf->link = stgCast(StgCAF*,0xdeadbeef);
2506 barf("revertDeadCAFs: enteredCAFs list corrupted");
2512 /* -----------------------------------------------------------------------------
2513 Sanity code for CAF garbage collection.
2515 With DEBUG turned on, we manage a CAF list in addition to the SRT
2516 mechanism. After GC, we run down the CAF list and blackhole any
2517 CAFs which have been garbage collected. This means we get an error
2518 whenever the program tries to enter a garbage collected CAF.
2520 Any garbage collected CAFs are taken off the CAF list at the same
2522 -------------------------------------------------------------------------- */
2530 const StgInfoTable *info;
2541 ASSERT(info->type == IND_STATIC);
2543 if (STATIC_LINK(info,p) == NULL) {
2544 IF_DEBUG(gccafs, fprintf(stderr, "CAF gc'd at 0x%04x\n", (int)p));
2546 SET_INFO(p,&BLACKHOLE_info);
2547 p = STATIC_LINK2(info,p);
2551 pp = &STATIC_LINK2(info,p);
2558 /* fprintf(stderr, "%d CAFs live\n", i); */
2562 /* -----------------------------------------------------------------------------
2565 Whenever a thread returns to the scheduler after possibly doing
2566 some work, we have to run down the stack and black-hole all the
2567 closures referred to by update frames.
2568 -------------------------------------------------------------------------- */
2571 threadLazyBlackHole(StgTSO *tso)
2573 StgUpdateFrame *update_frame;
2574 StgBlockingQueue *bh;
2577 stack_end = &tso->stack[tso->stack_size];
2578 update_frame = tso->su;
2581 switch (get_itbl(update_frame)->type) {
2584 update_frame = stgCast(StgCatchFrame*,update_frame)->link;
2588 bh = (StgBlockingQueue *)update_frame->updatee;
2590 /* if the thunk is already blackholed, it means we've also
2591 * already blackholed the rest of the thunks on this stack,
2592 * so we can stop early.
2594 * The blackhole made for a CAF is a CAF_BLACKHOLE, so they
2595 * don't interfere with this optimisation.
2597 if (bh->header.info == &BLACKHOLE_info) {
2601 if (bh->header.info != &BLACKHOLE_BQ_info &&
2602 bh->header.info != &CAF_BLACKHOLE_info) {
2603 SET_INFO(bh,&BLACKHOLE_info);
2606 update_frame = update_frame->link;
2610 update_frame = stgCast(StgSeqFrame*,update_frame)->link;
2616 barf("threadPaused");
2621 /* -----------------------------------------------------------------------------
2624 * Code largely pinched from old RTS, then hacked to bits. We also do
2625 * lazy black holing here.
2627 * -------------------------------------------------------------------------- */
2630 threadSqueezeStack(StgTSO *tso)
2632 lnat displacement = 0;
2633 StgUpdateFrame *frame;
2634 StgUpdateFrame *next_frame; /* Temporally next */
2635 StgUpdateFrame *prev_frame; /* Temporally previous */
2637 rtsBool prev_was_update_frame;
2639 bottom = &(tso->stack[tso->stack_size]);
2642 /* There must be at least one frame, namely the STOP_FRAME.
2644 ASSERT((P_)frame < bottom);
2646 /* Walk down the stack, reversing the links between frames so that
2647 * we can walk back up as we squeeze from the bottom. Note that
2648 * next_frame and prev_frame refer to next and previous as they were
2649 * added to the stack, rather than the way we see them in this
2650 * walk. (It makes the next loop less confusing.)
2652 * Stop if we find an update frame pointing to a black hole
2653 * (see comment in threadLazyBlackHole()).
2657 while ((P_)frame < bottom - 1) { /* bottom - 1 is the STOP_FRAME */
2658 prev_frame = frame->link;
2659 frame->link = next_frame;
2662 if (get_itbl(frame)->type == UPDATE_FRAME
2663 && frame->updatee->header.info == &BLACKHOLE_info) {
2668 /* Now, we're at the bottom. Frame points to the lowest update
2669 * frame on the stack, and its link actually points to the frame
2670 * above. We have to walk back up the stack, squeezing out empty
2671 * update frames and turning the pointers back around on the way
2674 * The bottom-most frame (the STOP_FRAME) has not been altered, and
2675 * we never want to eliminate it anyway. Just walk one step up
2676 * before starting to squeeze. When you get to the topmost frame,
2677 * remember that there are still some words above it that might have
2684 prev_was_update_frame = (get_itbl(prev_frame)->type == UPDATE_FRAME);
2687 * Loop through all of the frames (everything except the very
2688 * bottom). Things are complicated by the fact that we have
2689 * CATCH_FRAMEs and SEQ_FRAMEs interspersed with the update frames.
2690 * We can only squeeze when there are two consecutive UPDATE_FRAMEs.
2692 while (frame != NULL) {
2694 StgPtr frame_bottom = (P_)frame + sizeofW(StgUpdateFrame);
2695 rtsBool is_update_frame;
2697 next_frame = frame->link;
2698 is_update_frame = (get_itbl(frame)->type == UPDATE_FRAME);
2701 * 1. both the previous and current frame are update frames
2702 * 2. the current frame is empty
2704 if (prev_was_update_frame && is_update_frame &&
2705 (P_)prev_frame == frame_bottom + displacement) {
2707 /* Now squeeze out the current frame */
2708 StgClosure *updatee_keep = prev_frame->updatee;
2709 StgClosure *updatee_bypass = frame->updatee;
2712 fprintf(stderr, "squeezing frame at %p\n", frame);
2715 /* Deal with blocking queues. If both updatees have blocked
2716 * threads, then we should merge the queues into the update
2717 * frame that we're keeping.
2719 * Alternatively, we could just wake them up: they'll just go
2720 * straight to sleep on the proper blackhole! This is less code
2721 * and probably less bug prone, although it's probably much
2724 #if 0 /* do it properly... */
2725 if (GET_INFO(updatee_bypass) == BLACKHOLE_BQ_info) {
2726 /* Sigh. It has one. Don't lose those threads! */
2727 if (GET_INFO(updatee_keep) == BLACKHOLE_BQ_info) {
2728 /* Urgh. Two queues. Merge them. */
2729 P_ keep_tso = ((StgBlockingQueue *)updatee_keep)->blocking_queue;
2731 while (keep_tso->link != END_TSO_QUEUE) {
2732 keep_tso = keep_tso->link;
2734 keep_tso->link = ((StgBlockingQueue *)updatee_bypass)->blocking_queue;
2737 /* For simplicity, just swap the BQ for the BH */
2738 P_ temp = updatee_keep;
2740 updatee_keep = updatee_bypass;
2741 updatee_bypass = temp;
2743 /* Record the swap in the kept frame (below) */
2744 prev_frame->updatee = updatee_keep;
2749 TICK_UPD_SQUEEZED();
2750 UPD_IND(updatee_bypass, updatee_keep); /* this wakes the threads up */
2752 sp = (P_)frame - 1; /* sp = stuff to slide */
2753 displacement += sizeofW(StgUpdateFrame);
2756 /* No squeeze for this frame */
2757 sp = frame_bottom - 1; /* Keep the current frame */
2759 /* Do lazy black-holing.
2761 if (is_update_frame) {
2762 StgBlockingQueue *bh = (StgBlockingQueue *)frame->updatee;
2763 if (bh->header.info != &BLACKHOLE_BQ_info &&
2764 bh->header.info != &CAF_BLACKHOLE_info) {
2765 SET_INFO(bh,&BLACKHOLE_info);
2769 /* Fix the link in the current frame (should point to the frame below) */
2770 frame->link = prev_frame;
2771 prev_was_update_frame = is_update_frame;
2774 /* Now slide all words from sp up to the next frame */
2776 if (displacement > 0) {
2777 P_ next_frame_bottom;
2779 if (next_frame != NULL)
2780 next_frame_bottom = (P_)next_frame + sizeofW(StgUpdateFrame);
2782 next_frame_bottom = tso->sp - 1;
2785 fprintf(stderr, "sliding [%p, %p] by %ld\n", sp, next_frame_bottom,
2789 while (sp >= next_frame_bottom) {
2790 sp[displacement] = *sp;
2794 (P_)prev_frame = (P_)frame + displacement;
2798 tso->sp += displacement;
2799 tso->su = prev_frame;
2802 /* -----------------------------------------------------------------------------
2805 * We have to prepare for GC - this means doing lazy black holing
2806 * here. We also take the opportunity to do stack squeezing if it's
2808 * -------------------------------------------------------------------------- */
2811 threadPaused(StgTSO *tso)
2813 if ( RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue )
2814 threadSqueezeStack(tso); /* does black holing too */
2816 threadLazyBlackHole(tso);