1 /* -----------------------------------------------------------------------------
2 * $Id: GC.c,v 1.58 1999/05/04 10:19:14 sof 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 zero_static_object_list ( StgClosure* first_static );
105 static void zero_mutable_list ( StgMutClosure *first );
106 static void revert_dead_CAFs ( void );
108 static rtsBool traverse_weak_ptr_list ( void );
109 static void cleanup_weak_ptr_list ( StgWeak **list );
111 static void scavenge_stack ( StgPtr p, StgPtr stack_end );
112 static void scavenge_large ( step *step );
113 static void scavenge ( step *step );
114 static void scavenge_static ( void );
115 static void scavenge_mutable_list ( generation *g );
116 static void scavenge_mut_once_list ( generation *g );
119 static void gcCAFs ( void );
122 /* -----------------------------------------------------------------------------
125 For garbage collecting generation N (and all younger generations):
127 - follow all pointers in the root set. the root set includes all
128 mutable objects in all steps in all generations.
130 - for each pointer, evacuate the object it points to into either
131 + to-space in the next higher step in that generation, if one exists,
132 + if the object's generation == N, then evacuate it to the next
133 generation if one exists, or else to-space in the current
135 + if the object's generation < N, then evacuate it to to-space
136 in the next generation.
138 - repeatedly scavenge to-space from each step in each generation
139 being collected until no more objects can be evacuated.
141 - free from-space in each step, and set from-space = to-space.
143 -------------------------------------------------------------------------- */
145 void GarbageCollect(void (*get_roots)(void))
149 lnat live, allocated, collected = 0, copied = 0;
153 CostCentreStack *prev_CCS;
156 /* tell the stats department that we've started a GC */
159 /* attribute any costs to CCS_GC */
165 /* We might have been called from Haskell land by _ccall_GC, in
166 * which case we need to call threadPaused() because the scheduler
167 * won't have done it.
169 if (CurrentTSO) { threadPaused(CurrentTSO); }
171 /* Approximate how much we allocated: number of blocks in the
172 * nursery + blocks allocated via allocate() - unused nusery blocks.
173 * This leaves a little slop at the end of each block, and doesn't
174 * take into account large objects (ToDo).
176 allocated = (nursery_blocks * BLOCK_SIZE_W) + allocated_bytes();
177 for ( bd = current_nursery->link; bd != NULL; bd = bd->link ) {
178 allocated -= BLOCK_SIZE_W;
180 if (current_nursery->free < current_nursery->start + BLOCK_SIZE_W) {
181 allocated -= (current_nursery->start + BLOCK_SIZE_W)
182 - current_nursery->free;
185 /* Figure out which generation to collect
188 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
189 if (generations[g].steps[0].n_blocks >= generations[g].max_blocks) {
193 major_gc = (N == RtsFlags.GcFlags.generations-1);
195 /* check stack sanity *before* GC (ToDo: check all threads) */
196 /*IF_DEBUG(sanity, checkTSO(MainTSO,0)); */
197 IF_DEBUG(sanity, checkFreeListSanity());
199 /* Initialise the static object lists
201 static_objects = END_OF_STATIC_LIST;
202 scavenged_static_objects = END_OF_STATIC_LIST;
204 /* zero the mutable list for the oldest generation (see comment by
205 * zero_mutable_list below).
208 zero_mutable_list(generations[RtsFlags.GcFlags.generations-1].mut_once_list);
211 /* Save the old to-space if we're doing a two-space collection
213 if (RtsFlags.GcFlags.generations == 1) {
214 old_to_space = g0s0->to_space;
215 g0s0->to_space = NULL;
218 /* Keep a count of how many new blocks we allocated during this GC
219 * (used for resizing the allocation area, later).
223 /* Initialise to-space in all the generations/steps that we're
226 for (g = 0; g <= N; g++) {
227 generations[g].mut_once_list = END_MUT_LIST;
228 generations[g].mut_list = END_MUT_LIST;
230 for (s = 0; s < generations[g].n_steps; s++) {
232 /* generation 0, step 0 doesn't need to-space */
233 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
237 /* Get a free block for to-space. Extra blocks will be chained on
241 step = &generations[g].steps[s];
242 ASSERT(step->gen->no == g);
243 ASSERT(step->hp ? Bdescr(step->hp)->step == step : rtsTrue);
244 bd->gen = &generations[g];
247 bd->evacuated = 1; /* it's a to-space block */
248 step->hp = bd->start;
249 step->hpLim = step->hp + BLOCK_SIZE_W;
253 step->scan = bd->start;
255 step->new_large_objects = NULL;
256 step->scavenged_large_objects = NULL;
258 /* mark the large objects as not evacuated yet */
259 for (bd = step->large_objects; bd; bd = bd->link) {
265 /* make sure the older generations have at least one block to
266 * allocate into (this makes things easier for copy(), see below.
268 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
269 for (s = 0; s < generations[g].n_steps; s++) {
270 step = &generations[g].steps[s];
271 if (step->hp_bd == NULL) {
273 bd->gen = &generations[g];
276 bd->evacuated = 0; /* *not* a to-space block */
277 step->hp = bd->start;
278 step->hpLim = step->hp + BLOCK_SIZE_W;
284 /* Set the scan pointer for older generations: remember we
285 * still have to scavenge objects that have been promoted. */
286 step->scan = step->hp;
287 step->scan_bd = step->hp_bd;
288 step->to_space = NULL;
290 step->new_large_objects = NULL;
291 step->scavenged_large_objects = NULL;
295 /* -----------------------------------------------------------------------
296 * follow all the roots that we know about:
297 * - mutable lists from each generation > N
298 * we want to *scavenge* these roots, not evacuate them: they're not
299 * going to move in this GC.
300 * Also: do them in reverse generation order. This is because we
301 * often want to promote objects that are pointed to by older
302 * generations early, so we don't have to repeatedly copy them.
303 * Doing the generations in reverse order ensures that we don't end
304 * up in the situation where we want to evac an object to gen 3 and
305 * it has already been evaced to gen 2.
309 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
310 generations[g].saved_mut_list = generations[g].mut_list;
311 generations[g].mut_list = END_MUT_LIST;
314 /* Do the mut-once lists first */
315 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
316 scavenge_mut_once_list(&generations[g]);
318 for (st = generations[g].n_steps-1; st >= 0; st--) {
319 scavenge(&generations[g].steps[st]);
323 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
324 scavenge_mutable_list(&generations[g]);
326 for (st = generations[g].n_steps-1; st >= 0; st--) {
327 scavenge(&generations[g].steps[st]);
332 /* follow all the roots that the application knows about.
337 /* And don't forget to mark the TSO if we got here direct from
340 CurrentTSO = (StgTSO *)MarkRoot((StgClosure *)CurrentTSO);
343 /* Mark the weak pointer list, and prepare to detect dead weak
346 old_weak_ptr_list = weak_ptr_list;
347 weak_ptr_list = NULL;
348 weak_done = rtsFalse;
350 /* Mark the stable pointer table.
352 markStablePtrTable(major_gc);
356 /* ToDo: To fix the caf leak, we need to make the commented out
357 * parts of this code do something sensible - as described in
360 extern void markHugsObjects(void);
365 /* -------------------------------------------------------------------------
366 * Repeatedly scavenge all the areas we know about until there's no
367 * more scavenging to be done.
374 /* scavenge static objects */
375 if (major_gc && static_objects != END_OF_STATIC_LIST) {
379 /* When scavenging the older generations: Objects may have been
380 * evacuated from generations <= N into older generations, and we
381 * need to scavenge these objects. We're going to try to ensure that
382 * any evacuations that occur move the objects into at least the
383 * same generation as the object being scavenged, otherwise we
384 * have to create new entries on the mutable list for the older
388 /* scavenge each step in generations 0..maxgen */
392 for (gen = RtsFlags.GcFlags.generations-1; gen >= 0; gen--) {
393 for (st = generations[gen].n_steps-1; st >= 0 ; st--) {
394 if (gen == 0 && st == 0 && RtsFlags.GcFlags.generations > 1) {
397 step = &generations[gen].steps[st];
399 if (step->hp_bd != step->scan_bd || step->scan < step->hp) {
404 if (step->new_large_objects != NULL) {
405 scavenge_large(step);
412 if (flag) { goto loop; }
414 /* must be last... */
415 if (traverse_weak_ptr_list()) { /* returns rtsTrue if evaced something */
420 /* Final traversal of the weak pointer list (see comment by
421 * cleanUpWeakPtrList below).
423 cleanup_weak_ptr_list(&weak_ptr_list);
425 /* Now see which stable names are still alive.
427 gcStablePtrTable(major_gc);
429 /* revert dead CAFs and update enteredCAFs list */
432 /* Set the maximum blocks for the oldest generation, based on twice
433 * the amount of live data now, adjusted to fit the maximum heap
436 * This is an approximation, since in the worst case we'll need
437 * twice the amount of live data plus whatever space the other
440 if (RtsFlags.GcFlags.generations > 1) {
442 oldest_gen->max_blocks =
443 stg_max(oldest_gen->steps[0].to_blocks * RtsFlags.GcFlags.oldGenFactor,
444 RtsFlags.GcFlags.minOldGenSize);
445 if (oldest_gen->max_blocks > RtsFlags.GcFlags.maxHeapSize / 2) {
446 oldest_gen->max_blocks = RtsFlags.GcFlags.maxHeapSize / 2;
447 if (((int)oldest_gen->max_blocks -
448 (int)oldest_gen->steps[0].to_blocks) <
449 (RtsFlags.GcFlags.pcFreeHeap *
450 RtsFlags.GcFlags.maxHeapSize / 200)) {
457 /* run through all the generations/steps and tidy up
459 copied = new_blocks * BLOCK_SIZE_W;
460 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
463 generations[g].collections++; /* for stats */
466 for (s = 0; s < generations[g].n_steps; s++) {
468 step = &generations[g].steps[s];
470 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
471 /* Tidy the end of the to-space chains */
472 step->hp_bd->free = step->hp;
473 step->hp_bd->link = NULL;
474 /* stats information: how much we copied */
476 copied -= step->hp_bd->start + BLOCK_SIZE_W -
481 /* for generations we collected... */
484 collected += step->n_blocks * BLOCK_SIZE_W; /* for stats */
486 /* free old memory and shift to-space into from-space for all
487 * the collected steps (except the allocation area). These
488 * freed blocks will probaby be quickly recycled.
490 if (!(g == 0 && s == 0)) {
491 freeChain(step->blocks);
492 step->blocks = step->to_space;
493 step->n_blocks = step->to_blocks;
494 step->to_space = NULL;
496 for (bd = step->blocks; bd != NULL; bd = bd->link) {
497 bd->evacuated = 0; /* now from-space */
501 /* LARGE OBJECTS. The current live large objects are chained on
502 * scavenged_large, having been moved during garbage
503 * collection from large_objects. Any objects left on
504 * large_objects list are therefore dead, so we free them here.
506 for (bd = step->large_objects; bd != NULL; bd = next) {
511 for (bd = step->scavenged_large_objects; bd != NULL; bd = bd->link) {
514 step->large_objects = step->scavenged_large_objects;
516 /* Set the maximum blocks for this generation, interpolating
517 * between the maximum size of the oldest and youngest
520 * max_blocks = oldgen_max_blocks * G
521 * ----------------------
526 generations[g].max_blocks = (oldest_gen->max_blocks * g)
527 / (RtsFlags.GcFlags.generations-1);
529 generations[g].max_blocks = oldest_gen->max_blocks;
532 /* for older generations... */
535 /* For older generations, we need to append the
536 * scavenged_large_object list (i.e. large objects that have been
537 * promoted during this GC) to the large_object list for that step.
539 for (bd = step->scavenged_large_objects; bd; bd = next) {
542 dbl_link_onto(bd, &step->large_objects);
545 /* add the new blocks we promoted during this GC */
546 step->n_blocks += step->to_blocks;
551 /* Guess the amount of live data for stats. */
554 /* Free the small objects allocated via allocate(), since this will
555 * all have been copied into G0S1 now.
557 if (small_alloc_list != NULL) {
558 freeChain(small_alloc_list);
560 small_alloc_list = NULL;
564 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
566 /* Two-space collector:
567 * Free the old to-space, and estimate the amount of live data.
569 if (RtsFlags.GcFlags.generations == 1) {
572 if (old_to_space != NULL) {
573 freeChain(old_to_space);
575 for (bd = g0s0->to_space; bd != NULL; bd = bd->link) {
576 bd->evacuated = 0; /* now from-space */
579 /* For a two-space collector, we need to resize the nursery. */
581 /* set up a new nursery. Allocate a nursery size based on a
582 * function of the amount of live data (currently a factor of 2,
583 * should be configurable (ToDo)). Use the blocks from the old
584 * nursery if possible, freeing up any left over blocks.
586 * If we get near the maximum heap size, then adjust our nursery
587 * size accordingly. If the nursery is the same size as the live
588 * data (L), then we need 3L bytes. We can reduce the size of the
589 * nursery to bring the required memory down near 2L bytes.
591 * A normal 2-space collector would need 4L bytes to give the same
592 * performance we get from 3L bytes, reducing to the same
593 * performance at 2L bytes.
595 blocks = g0s0->to_blocks;
597 if ( blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
598 RtsFlags.GcFlags.maxHeapSize ) {
599 int adjusted_blocks; /* signed on purpose */
602 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
603 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));
604 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
605 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even be < 0 */ {
608 blocks = adjusted_blocks;
611 blocks *= RtsFlags.GcFlags.oldGenFactor;
612 if (blocks < RtsFlags.GcFlags.minAllocAreaSize) {
613 blocks = RtsFlags.GcFlags.minAllocAreaSize;
616 resizeNursery(blocks);
619 /* Generational collector:
620 * If the user has given us a suggested heap size, adjust our
621 * allocation area to make best use of the memory available.
624 if (RtsFlags.GcFlags.heapSizeSuggestion) {
626 nat needed = calcNeeded(); /* approx blocks needed at next GC */
628 /* Guess how much will be live in generation 0 step 0 next time.
629 * A good approximation is the obtained by finding the
630 * percentage of g0s0 that was live at the last minor GC.
633 g0s0_pcnt_kept = (new_blocks * 100) / g0s0->n_blocks;
636 /* Estimate a size for the allocation area based on the
637 * information available. We might end up going slightly under
638 * or over the suggested heap size, but we should be pretty
641 * Formula: suggested - needed
642 * ----------------------------
643 * 1 + g0s0_pcnt_kept/100
645 * where 'needed' is the amount of memory needed at the next
646 * collection for collecting all steps except g0s0.
649 (((int)RtsFlags.GcFlags.heapSizeSuggestion - (int)needed) * 100) /
650 (100 + (int)g0s0_pcnt_kept);
652 if (blocks < (int)RtsFlags.GcFlags.minAllocAreaSize) {
653 blocks = RtsFlags.GcFlags.minAllocAreaSize;
656 resizeNursery((nat)blocks);
660 /* mark the garbage collected CAFs as dead */
662 if (major_gc) { gcCAFs(); }
665 /* zero the scavenged static object list */
667 zero_static_object_list(scavenged_static_objects);
672 for (bd = g0s0->blocks; bd; bd = bd->link) {
673 bd->free = bd->start;
674 ASSERT(bd->gen == g0);
675 ASSERT(bd->step == g0s0);
676 IF_DEBUG(sanity,memset(bd->start, 0xaa, BLOCK_SIZE));
678 current_nursery = g0s0->blocks;
680 /* start any pending finalizers */
681 scheduleFinalizers(old_weak_ptr_list);
683 /* check sanity after GC */
684 IF_DEBUG(sanity, checkSanity(N));
686 /* extra GC trace info */
687 IF_DEBUG(gc, stat_describe_gens());
690 /* symbol-table based profiling */
691 /* heapCensus(to_space); */ /* ToDo */
694 /* restore enclosing cost centre */
699 /* check for memory leaks if sanity checking is on */
700 IF_DEBUG(sanity, memInventory());
702 /* ok, GC over: tell the stats department what happened. */
703 stat_endGC(allocated, collected, live, copied, N);
706 /* -----------------------------------------------------------------------------
709 traverse_weak_ptr_list is called possibly many times during garbage
710 collection. It returns a flag indicating whether it did any work
711 (i.e. called evacuate on any live pointers).
713 Invariant: traverse_weak_ptr_list is called when the heap is in an
714 idempotent state. That means that there are no pending
715 evacuate/scavenge operations. This invariant helps the weak
716 pointer code decide which weak pointers are dead - if there are no
717 new live weak pointers, then all the currently unreachable ones are
720 For generational GC: we just don't try to finalize weak pointers in
721 older generations than the one we're collecting. This could
722 probably be optimised by keeping per-generation lists of weak
723 pointers, but for a few weak pointers this scheme will work.
724 -------------------------------------------------------------------------- */
727 traverse_weak_ptr_list(void)
729 StgWeak *w, **last_w, *next_w;
731 rtsBool flag = rtsFalse;
733 if (weak_done) { return rtsFalse; }
735 /* doesn't matter where we evacuate values/finalizers to, since
736 * these pointers are treated as roots (iff the keys are alive).
740 last_w = &old_weak_ptr_list;
741 for (w = old_weak_ptr_list; w; w = next_w) {
743 /* First, this weak pointer might have been evacuated. If so,
744 * remove the forwarding pointer from the weak_ptr_list.
746 if (get_itbl(w)->type == EVACUATED) {
747 w = (StgWeak *)((StgEvacuated *)w)->evacuee;
751 /* There might be a DEAD_WEAK on the list if finalizeWeak# was
752 * called on a live weak pointer object. Just remove it.
754 if (w->header.info == &DEAD_WEAK_info) {
755 next_w = ((StgDeadWeak *)w)->link;
760 ASSERT(get_itbl(w)->type == WEAK);
762 /* Now, check whether the key is reachable.
764 if ((new = isAlive(w->key))) {
766 /* evacuate the value and finalizer */
767 w->value = evacuate(w->value);
768 w->finalizer = evacuate(w->finalizer);
769 /* remove this weak ptr from the old_weak_ptr list */
771 /* and put it on the new weak ptr list */
773 w->link = weak_ptr_list;
776 IF_DEBUG(weak, fprintf(stderr,"Weak pointer still alive at %p -> %p\n", w, w->key));
786 /* If we didn't make any changes, then we can go round and kill all
787 * the dead weak pointers. The old_weak_ptr list is used as a list
788 * of pending finalizers later on.
790 if (flag == rtsFalse) {
791 cleanup_weak_ptr_list(&old_weak_ptr_list);
792 for (w = old_weak_ptr_list; w; w = w->link) {
793 w->finalizer = evacuate(w->finalizer);
801 /* -----------------------------------------------------------------------------
802 After GC, the live weak pointer list may have forwarding pointers
803 on it, because a weak pointer object was evacuated after being
804 moved to the live weak pointer list. We remove those forwarding
807 Also, we don't consider weak pointer objects to be reachable, but
808 we must nevertheless consider them to be "live" and retain them.
809 Therefore any weak pointer objects which haven't as yet been
810 evacuated need to be evacuated now.
811 -------------------------------------------------------------------------- */
814 cleanup_weak_ptr_list ( StgWeak **list )
816 StgWeak *w, **last_w;
819 for (w = *list; w; w = w->link) {
821 if (get_itbl(w)->type == EVACUATED) {
822 w = (StgWeak *)((StgEvacuated *)w)->evacuee;
826 if (Bdescr((P_)w)->evacuated == 0) {
827 (StgClosure *)w = evacuate((StgClosure *)w);
834 /* -----------------------------------------------------------------------------
835 isAlive determines whether the given closure is still alive (after
836 a garbage collection) or not. It returns the new address of the
837 closure if it is alive, or NULL otherwise.
838 -------------------------------------------------------------------------- */
841 isAlive(StgClosure *p)
849 /* ToDo: for static closures, check the static link field.
850 * Problem here is that we sometimes don't set the link field, eg.
851 * for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
854 /* ignore closures in generations that we're not collecting. */
855 if (LOOKS_LIKE_STATIC(p) || Bdescr((P_)p)->gen->no > N) {
859 switch (info->type) {
864 case IND_OLDGEN: /* rely on compatible layout with StgInd */
865 case IND_OLDGEN_PERM:
866 /* follow indirections */
867 p = ((StgInd *)p)->indirectee;
872 return ((StgEvacuated *)p)->evacuee;
882 MarkRoot(StgClosure *root)
884 return evacuate(root);
887 static void addBlock(step *step)
889 bdescr *bd = allocBlock();
893 if (step->gen->no <= N) {
899 step->hp_bd->free = step->hp;
900 step->hp_bd->link = bd;
901 step->hp = bd->start;
902 step->hpLim = step->hp + BLOCK_SIZE_W;
908 static __inline__ void
909 upd_evacuee(StgClosure *p, StgClosure *dest)
911 p->header.info = &EVACUATED_info;
912 ((StgEvacuated *)p)->evacuee = dest;
915 static __inline__ StgClosure *
916 copy(StgClosure *src, nat size, step *step)
920 TICK_GC_WORDS_COPIED(size);
921 /* Find out where we're going, using the handy "to" pointer in
922 * the step of the source object. If it turns out we need to
923 * evacuate to an older generation, adjust it here (see comment
926 if (step->gen->no < evac_gen) {
927 #ifdef NO_EAGER_PROMOTION
928 failed_to_evac = rtsTrue;
930 step = &generations[evac_gen].steps[0];
934 /* chain a new block onto the to-space for the destination step if
937 if (step->hp + size >= step->hpLim) {
941 for(to = step->hp, from = (P_)src; size>0; --size) {
947 upd_evacuee(src,(StgClosure *)dest);
948 return (StgClosure *)dest;
951 /* Special version of copy() for when we only want to copy the info
952 * pointer of an object, but reserve some padding after it. This is
953 * used to optimise evacuation of BLACKHOLEs.
956 static __inline__ StgClosure *
957 copyPart(StgClosure *src, nat size_to_reserve, nat size_to_copy, step *step)
961 TICK_GC_WORDS_COPIED(size_to_copy);
962 if (step->gen->no < evac_gen) {
963 #ifdef NO_EAGER_PROMOTION
964 failed_to_evac = rtsTrue;
966 step = &generations[evac_gen].steps[0];
970 if (step->hp + size_to_reserve >= step->hpLim) {
974 for(to = step->hp, from = (P_)src; size_to_copy>0; --size_to_copy) {
979 step->hp += size_to_reserve;
980 upd_evacuee(src,(StgClosure *)dest);
981 return (StgClosure *)dest;
984 /* -----------------------------------------------------------------------------
985 Evacuate a large object
987 This just consists of removing the object from the (doubly-linked)
988 large_alloc_list, and linking it on to the (singly-linked)
989 new_large_objects list, from where it will be scavenged later.
991 Convention: bd->evacuated is /= 0 for a large object that has been
992 evacuated, or 0 otherwise.
993 -------------------------------------------------------------------------- */
996 evacuate_large(StgPtr p, rtsBool mutable)
998 bdescr *bd = Bdescr(p);
1001 /* should point to the beginning of the block */
1002 ASSERT(((W_)p & BLOCK_MASK) == 0);
1004 /* already evacuated? */
1005 if (bd->evacuated) {
1006 /* Don't forget to set the failed_to_evac flag if we didn't get
1007 * the desired destination (see comments in evacuate()).
1009 if (bd->gen->no < evac_gen) {
1010 failed_to_evac = rtsTrue;
1011 TICK_GC_FAILED_PROMOTION();
1017 /* remove from large_object list */
1019 bd->back->link = bd->link;
1020 } else { /* first object in the list */
1021 step->large_objects = bd->link;
1024 bd->link->back = bd->back;
1027 /* link it on to the evacuated large object list of the destination step
1029 step = bd->step->to;
1030 if (step->gen->no < evac_gen) {
1031 #ifdef NO_EAGER_PROMOTION
1032 failed_to_evac = rtsTrue;
1034 step = &generations[evac_gen].steps[0];
1039 bd->gen = step->gen;
1040 bd->link = step->new_large_objects;
1041 step->new_large_objects = bd;
1045 recordMutable((StgMutClosure *)p);
1049 /* -----------------------------------------------------------------------------
1050 Adding a MUT_CONS to an older generation.
1052 This is necessary from time to time when we end up with an
1053 old-to-new generation pointer in a non-mutable object. We defer
1054 the promotion until the next GC.
1055 -------------------------------------------------------------------------- */
1058 mkMutCons(StgClosure *ptr, generation *gen)
1063 step = &gen->steps[0];
1065 /* chain a new block onto the to-space for the destination step if
1068 if (step->hp + sizeofW(StgIndOldGen) >= step->hpLim) {
1072 q = (StgMutVar *)step->hp;
1073 step->hp += sizeofW(StgMutVar);
1075 SET_HDR(q,&MUT_CONS_info,CCS_GC);
1077 recordOldToNewPtrs((StgMutClosure *)q);
1079 return (StgClosure *)q;
1082 /* -----------------------------------------------------------------------------
1085 This is called (eventually) for every live object in the system.
1087 The caller to evacuate specifies a desired generation in the
1088 evac_gen global variable. The following conditions apply to
1089 evacuating an object which resides in generation M when we're
1090 collecting up to generation N
1094 else evac to step->to
1096 if M < evac_gen evac to evac_gen, step 0
1098 if the object is already evacuated, then we check which generation
1101 if M >= evac_gen do nothing
1102 if M < evac_gen set failed_to_evac flag to indicate that we
1103 didn't manage to evacuate this object into evac_gen.
1105 -------------------------------------------------------------------------- */
1109 evacuate(StgClosure *q)
1114 const StgInfoTable *info;
1117 if (HEAP_ALLOCED(q)) {
1119 if (bd->gen->no > N) {
1120 /* Can't evacuate this object, because it's in a generation
1121 * older than the ones we're collecting. Let's hope that it's
1122 * in evac_gen or older, or we will have to make an IND_OLDGEN object.
1124 if (bd->gen->no < evac_gen) {
1126 failed_to_evac = rtsTrue;
1127 TICK_GC_FAILED_PROMOTION();
1131 step = bd->step->to;
1134 /* make sure the info pointer is into text space */
1135 ASSERT(q && (LOOKS_LIKE_GHC_INFO(GET_INFO(q))
1136 || IS_HUGS_CONSTR_INFO(GET_INFO(q))));
1139 switch (info -> type) {
1142 return copy(q,bco_sizeW(stgCast(StgBCO*,q)),step);
1145 ASSERT(q->header.info != &MUT_CONS_info);
1147 to = copy(q,sizeW_fromITBL(info),step);
1148 recordMutable((StgMutClosure *)to);
1155 return copy(q,sizeofW(StgHeader)+1,step);
1157 case THUNK_1_0: /* here because of MIN_UPD_SIZE */
1162 #ifdef NO_PROMOTE_THUNKS
1163 if (bd->gen->no == 0 &&
1164 bd->step->no != 0 &&
1165 bd->step->no == bd->gen->n_steps-1) {
1169 return copy(q,sizeofW(StgHeader)+2,step);
1177 return copy(q,sizeofW(StgHeader)+2,step);
1183 case IND_OLDGEN_PERM:
1189 return copy(q,sizeW_fromITBL(info),step);
1193 return copyPart(q,BLACKHOLE_sizeW(),sizeofW(StgHeader),step);
1196 to = copy(q,BLACKHOLE_sizeW(),step);
1197 recordMutable((StgMutClosure *)to);
1200 case THUNK_SELECTOR:
1202 const StgInfoTable* selectee_info;
1203 StgClosure* selectee = ((StgSelector*)q)->selectee;
1206 selectee_info = get_itbl(selectee);
1207 switch (selectee_info->type) {
1216 StgWord32 offset = info->layout.selector_offset;
1218 /* check that the size is in range */
1220 (StgWord32)(selectee_info->layout.payload.ptrs +
1221 selectee_info->layout.payload.nptrs));
1223 /* perform the selection! */
1224 q = selectee->payload[offset];
1226 /* if we're already in to-space, there's no need to continue
1227 * with the evacuation, just update the source address with
1228 * a pointer to the (evacuated) constructor field.
1230 if (HEAP_ALLOCED(q)) {
1231 bdescr *bd = Bdescr((P_)q);
1232 if (bd->evacuated) {
1233 if (bd->gen->no < evac_gen) {
1234 failed_to_evac = rtsTrue;
1235 TICK_GC_FAILED_PROMOTION();
1241 /* otherwise, carry on and evacuate this constructor field,
1242 * (but not the constructor itself)
1251 case IND_OLDGEN_PERM:
1252 selectee = stgCast(StgInd *,selectee)->indirectee;
1256 selectee = stgCast(StgCAF *,selectee)->value;
1260 selectee = stgCast(StgEvacuated*,selectee)->evacuee;
1270 case THUNK_SELECTOR:
1271 /* aargh - do recursively???? */
1276 /* not evaluated yet */
1280 barf("evacuate: THUNK_SELECTOR: strange selectee");
1283 return copy(q,THUNK_SELECTOR_sizeW(),step);
1287 /* follow chains of indirections, don't evacuate them */
1288 q = ((StgInd*)q)->indirectee;
1292 if (info->srt_len > 0 && major_gc &&
1293 THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
1294 THUNK_STATIC_LINK((StgClosure *)q) = static_objects;
1295 static_objects = (StgClosure *)q;
1300 if (info->srt_len > 0 && major_gc &&
1301 FUN_STATIC_LINK((StgClosure *)q) == NULL) {
1302 FUN_STATIC_LINK((StgClosure *)q) = static_objects;
1303 static_objects = (StgClosure *)q;
1308 if (major_gc && IND_STATIC_LINK((StgClosure *)q) == NULL) {
1309 IND_STATIC_LINK((StgClosure *)q) = static_objects;
1310 static_objects = (StgClosure *)q;
1315 if (major_gc && STATIC_LINK(info,(StgClosure *)q) == NULL) {
1316 STATIC_LINK(info,(StgClosure *)q) = static_objects;
1317 static_objects = (StgClosure *)q;
1321 case CONSTR_INTLIKE:
1322 case CONSTR_CHARLIKE:
1323 case CONSTR_NOCAF_STATIC:
1324 /* no need to put these on the static linked list, they don't need
1339 /* shouldn't see these */
1340 barf("evacuate: stack frame\n");
1344 /* these are special - the payload is a copy of a chunk of stack,
1346 return copy(q,pap_sizeW(stgCast(StgPAP*,q)),step);
1349 /* Already evacuated, just return the forwarding address.
1350 * HOWEVER: if the requested destination generation (evac_gen) is
1351 * older than the actual generation (because the object was
1352 * already evacuated to a younger generation) then we have to
1353 * set the failed_to_evac flag to indicate that we couldn't
1354 * manage to promote the object to the desired generation.
1356 if (evac_gen > 0) { /* optimisation */
1357 StgClosure *p = ((StgEvacuated*)q)->evacuee;
1358 if (Bdescr((P_)p)->gen->no < evac_gen) {
1359 /* fprintf(stderr,"evac failed!\n");*/
1360 failed_to_evac = rtsTrue;
1361 TICK_GC_FAILED_PROMOTION();
1364 return ((StgEvacuated*)q)->evacuee;
1368 nat size = arr_words_sizeW(stgCast(StgArrWords*,q));
1370 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1371 evacuate_large((P_)q, rtsFalse);
1374 /* just copy the block */
1375 return copy(q,size,step);
1380 case MUT_ARR_PTRS_FROZEN:
1382 nat size = mut_arr_ptrs_sizeW(stgCast(StgMutArrPtrs*,q));
1384 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1385 evacuate_large((P_)q, info->type == MUT_ARR_PTRS);
1388 /* just copy the block */
1389 to = copy(q,size,step);
1390 if (info->type == MUT_ARR_PTRS) {
1391 recordMutable((StgMutClosure *)to);
1399 StgTSO *tso = stgCast(StgTSO *,q);
1400 nat size = tso_sizeW(tso);
1403 /* Large TSOs don't get moved, so no relocation is required.
1405 if (size >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
1406 evacuate_large((P_)q, rtsTrue);
1409 /* To evacuate a small TSO, we need to relocate the update frame
1413 StgTSO *new_tso = (StgTSO *)copy((StgClosure *)tso,tso_sizeW(tso),step);
1415 diff = (StgPtr)new_tso - (StgPtr)tso; /* In *words* */
1417 /* relocate the stack pointers... */
1418 new_tso->su = (StgUpdateFrame *) ((StgPtr)new_tso->su + diff);
1419 new_tso->sp = (StgPtr)new_tso->sp + diff;
1420 new_tso->splim = (StgPtr)new_tso->splim + diff;
1422 relocate_TSO(tso, new_tso);
1424 recordMutable((StgMutClosure *)new_tso);
1425 return (StgClosure *)new_tso;
1431 fprintf(stderr,"evacuate: unimplemented/strange closure type\n");
1435 barf("evacuate: strange closure type");
1441 /* -----------------------------------------------------------------------------
1442 relocate_TSO is called just after a TSO has been copied from src to
1443 dest. It adjusts the update frame list for the new location.
1444 -------------------------------------------------------------------------- */
1447 relocate_TSO(StgTSO *src, StgTSO *dest)
1454 diff = (StgPtr)dest->sp - (StgPtr)src->sp; /* In *words* */
1458 while ((P_)su < dest->stack + dest->stack_size) {
1459 switch (get_itbl(su)->type) {
1461 /* GCC actually manages to common up these three cases! */
1464 su->link = (StgUpdateFrame *) ((StgPtr)su->link + diff);
1469 cf = (StgCatchFrame *)su;
1470 cf->link = (StgUpdateFrame *) ((StgPtr)cf->link + diff);
1475 sf = (StgSeqFrame *)su;
1476 sf->link = (StgUpdateFrame *) ((StgPtr)sf->link + diff);
1485 barf("relocate_TSO");
1494 scavenge_srt(const StgInfoTable *info)
1496 StgClosure **srt, **srt_end;
1498 /* evacuate the SRT. If srt_len is zero, then there isn't an
1499 * srt field in the info table. That's ok, because we'll
1500 * never dereference it.
1502 srt = stgCast(StgClosure **,info->srt);
1503 srt_end = srt + info->srt_len;
1504 for (; srt < srt_end; srt++) {
1505 /* Special-case to handle references to closures hiding out in DLLs, since
1506 double indirections required to get at those. The code generator knows
1507 which is which when generating the SRT, so it stores the (indirect)
1508 reference to the DLL closure in the table by first adding one to it.
1509 We check for this here, and undo the addition before evacuating it.
1511 If the SRT entry hasn't got bit 0 set, the SRT entry points to a
1512 closure that's fixed at link-time, and no extra magic is required.
1514 #ifdef ENABLE_WIN32_DLL_SUPPORT
1515 if ( stgCast(unsigned long,*srt) & 0x1 ) {
1516 evacuate(*stgCast(StgClosure**,(stgCast(unsigned long, *srt) & ~0x1)));
1526 /* -----------------------------------------------------------------------------
1527 Scavenge a given step until there are no more objects in this step
1530 evac_gen is set by the caller to be either zero (for a step in a
1531 generation < N) or G where G is the generation of the step being
1534 We sometimes temporarily change evac_gen back to zero if we're
1535 scavenging a mutable object where early promotion isn't such a good
1537 -------------------------------------------------------------------------- */
1541 scavenge(step *step)
1544 const StgInfoTable *info;
1546 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
1551 failed_to_evac = rtsFalse;
1553 /* scavenge phase - standard breadth-first scavenging of the
1557 while (bd != step->hp_bd || p < step->hp) {
1559 /* If we're at the end of this block, move on to the next block */
1560 if (bd != step->hp_bd && p == bd->free) {
1566 q = p; /* save ptr to object */
1568 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO((StgClosure *)p))
1569 || IS_HUGS_CONSTR_INFO(GET_INFO((StgClosure *)p))));
1571 info = get_itbl((StgClosure *)p);
1572 switch (info -> type) {
1576 StgBCO* bco = stgCast(StgBCO*,p);
1578 for (i = 0; i < bco->n_ptrs; i++) {
1579 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
1581 p += bco_sizeW(bco);
1586 /* treat MVars specially, because we don't want to evacuate the
1587 * mut_link field in the middle of the closure.
1590 StgMVar *mvar = ((StgMVar *)p);
1592 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
1593 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
1594 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
1595 p += sizeofW(StgMVar);
1596 evac_gen = saved_evac_gen;
1604 ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
1605 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1606 p += sizeofW(StgHeader) + 2;
1611 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1612 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1618 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1619 p += sizeofW(StgHeader) + 1;
1624 p += sizeofW(StgHeader) + 2; /* MIN_UPD_SIZE */
1630 p += sizeofW(StgHeader) + 1;
1637 p += sizeofW(StgHeader) + 2;
1644 ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
1645 p += sizeofW(StgHeader) + 2;
1660 end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
1661 for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
1662 (StgClosure *)*p = evacuate((StgClosure *)*p);
1664 p += info->layout.payload.nptrs;
1669 if (step->gen->no != 0) {
1670 SET_INFO(((StgClosure *)p), &IND_OLDGEN_PERM_info);
1673 case IND_OLDGEN_PERM:
1674 ((StgIndOldGen *)p)->indirectee =
1675 evacuate(((StgIndOldGen *)p)->indirectee);
1676 if (failed_to_evac) {
1677 failed_to_evac = rtsFalse;
1678 recordOldToNewPtrs((StgMutClosure *)p);
1680 p += sizeofW(StgIndOldGen);
1685 StgCAF *caf = (StgCAF *)p;
1687 caf->body = evacuate(caf->body);
1688 if (failed_to_evac) {
1689 failed_to_evac = rtsFalse;
1690 recordOldToNewPtrs((StgMutClosure *)p);
1692 caf->mut_link = NULL;
1694 p += sizeofW(StgCAF);
1700 StgCAF *caf = (StgCAF *)p;
1702 caf->body = evacuate(caf->body);
1703 caf->value = evacuate(caf->value);
1704 if (failed_to_evac) {
1705 failed_to_evac = rtsFalse;
1706 recordOldToNewPtrs((StgMutClosure *)p);
1708 caf->mut_link = NULL;
1710 p += sizeofW(StgCAF);
1715 /* ignore MUT_CONSs */
1716 if (((StgMutVar *)p)->header.info != &MUT_CONS_info) {
1718 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
1719 evac_gen = saved_evac_gen;
1721 p += sizeofW(StgMutVar);
1726 p += BLACKHOLE_sizeW();
1731 StgBlockingQueue *bh = (StgBlockingQueue *)p;
1732 (StgClosure *)bh->blocking_queue =
1733 evacuate((StgClosure *)bh->blocking_queue);
1734 if (failed_to_evac) {
1735 failed_to_evac = rtsFalse;
1736 recordMutable((StgMutClosure *)bh);
1738 p += BLACKHOLE_sizeW();
1742 case THUNK_SELECTOR:
1744 StgSelector *s = (StgSelector *)p;
1745 s->selectee = evacuate(s->selectee);
1746 p += THUNK_SELECTOR_sizeW();
1752 barf("scavenge:IND???\n");
1754 case CONSTR_INTLIKE:
1755 case CONSTR_CHARLIKE:
1757 case CONSTR_NOCAF_STATIC:
1761 /* Shouldn't see a static object here. */
1762 barf("scavenge: STATIC object\n");
1774 /* Shouldn't see stack frames here. */
1775 barf("scavenge: stack frame\n");
1777 case AP_UPD: /* same as PAPs */
1779 /* Treat a PAP just like a section of stack, not forgetting to
1780 * evacuate the function pointer too...
1783 StgPAP* pap = stgCast(StgPAP*,p);
1785 pap->fun = evacuate(pap->fun);
1786 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1787 p += pap_sizeW(pap);
1792 /* nothing to follow */
1793 p += arr_words_sizeW(stgCast(StgArrWords*,p));
1797 /* follow everything */
1801 evac_gen = 0; /* repeatedly mutable */
1802 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1803 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1804 (StgClosure *)*p = evacuate((StgClosure *)*p);
1806 evac_gen = saved_evac_gen;
1810 case MUT_ARR_PTRS_FROZEN:
1811 /* follow everything */
1813 StgPtr start = p, next;
1815 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
1816 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
1817 (StgClosure *)*p = evacuate((StgClosure *)*p);
1819 if (failed_to_evac) {
1820 /* we can do this easier... */
1821 recordMutable((StgMutClosure *)start);
1822 failed_to_evac = rtsFalse;
1833 /* chase the link field for any TSOs on the same queue */
1834 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
1835 if (tso->blocked_on) {
1836 tso->blocked_on = evacuate(tso->blocked_on);
1838 /* scavenge this thread's stack */
1839 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
1840 evac_gen = saved_evac_gen;
1841 p += tso_sizeW(tso);
1848 barf("scavenge: unimplemented/strange closure type\n");
1854 /* If we didn't manage to promote all the objects pointed to by
1855 * the current object, then we have to designate this object as
1856 * mutable (because it contains old-to-new generation pointers).
1858 if (failed_to_evac) {
1859 mkMutCons((StgClosure *)q, &generations[evac_gen]);
1860 failed_to_evac = rtsFalse;
1868 /* -----------------------------------------------------------------------------
1869 Scavenge one object.
1871 This is used for objects that are temporarily marked as mutable
1872 because they contain old-to-new generation pointers. Only certain
1873 objects can have this property.
1874 -------------------------------------------------------------------------- */
1876 scavenge_one(StgClosure *p)
1881 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1882 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1886 switch (info -> type) {
1889 case FUN_1_0: /* hardly worth specialising these guys */
1909 case IND_OLDGEN_PERM:
1914 end = (P_)p->payload + info->layout.payload.ptrs;
1915 for (q = (P_)p->payload; q < end; q++) {
1916 (StgClosure *)*q = evacuate((StgClosure *)*q);
1925 case THUNK_SELECTOR:
1927 StgSelector *s = (StgSelector *)p;
1928 s->selectee = evacuate(s->selectee);
1932 case AP_UPD: /* same as PAPs */
1934 /* Treat a PAP just like a section of stack, not forgetting to
1935 * evacuate the function pointer too...
1938 StgPAP* pap = (StgPAP *)p;
1940 pap->fun = evacuate(pap->fun);
1941 scavenge_stack((P_)pap->payload, (P_)pap->payload + pap->n_args);
1946 /* This might happen if for instance a MUT_CONS was pointing to a
1947 * THUNK which has since been updated. The IND_OLDGEN will
1948 * be on the mutable list anyway, so we don't need to do anything
1954 barf("scavenge_one: strange object");
1957 no_luck = failed_to_evac;
1958 failed_to_evac = rtsFalse;
1963 /* -----------------------------------------------------------------------------
1964 Scavenging mutable lists.
1966 We treat the mutable list of each generation > N (i.e. all the
1967 generations older than the one being collected) as roots. We also
1968 remove non-mutable objects from the mutable list at this point.
1969 -------------------------------------------------------------------------- */
1972 scavenge_mut_once_list(generation *gen)
1975 StgMutClosure *p, *next, *new_list;
1977 p = gen->mut_once_list;
1978 new_list = END_MUT_LIST;
1982 failed_to_evac = rtsFalse;
1984 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
1986 /* make sure the info pointer is into text space */
1987 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
1988 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
1991 switch(info->type) {
1994 case IND_OLDGEN_PERM:
1996 /* Try to pull the indirectee into this generation, so we can
1997 * remove the indirection from the mutable list.
1999 ((StgIndOldGen *)p)->indirectee =
2000 evacuate(((StgIndOldGen *)p)->indirectee);
2003 /* Debugging code to print out the size of the thing we just
2007 StgPtr start = gen->steps[0].scan;
2008 bdescr *start_bd = gen->steps[0].scan_bd;
2010 scavenge(&gen->steps[0]);
2011 if (start_bd != gen->steps[0].scan_bd) {
2012 size += (P_)BLOCK_ROUND_UP(start) - start;
2013 start_bd = start_bd->link;
2014 while (start_bd != gen->steps[0].scan_bd) {
2015 size += BLOCK_SIZE_W;
2016 start_bd = start_bd->link;
2018 size += gen->steps[0].scan -
2019 (P_)BLOCK_ROUND_DOWN(gen->steps[0].scan);
2021 size = gen->steps[0].scan - start;
2023 fprintf(stderr,"evac IND_OLDGEN: %d bytes\n", size * sizeof(W_));
2027 /* failed_to_evac might happen if we've got more than two
2028 * generations, we're collecting only generation 0, the
2029 * indirection resides in generation 2 and the indirectee is
2032 if (failed_to_evac) {
2033 failed_to_evac = rtsFalse;
2034 p->mut_link = new_list;
2037 /* the mut_link field of an IND_STATIC is overloaded as the
2038 * static link field too (it just so happens that we don't need
2039 * both at the same time), so we need to NULL it out when
2040 * removing this object from the mutable list because the static
2041 * link fields are all assumed to be NULL before doing a major
2049 /* MUT_CONS is a kind of MUT_VAR, except it that we try to remove
2050 * it from the mutable list if possible by promoting whatever it
2053 ASSERT(p->header.info == &MUT_CONS_info);
2054 if (scavenge_one(((StgMutVar *)p)->var) == rtsTrue) {
2055 /* didn't manage to promote everything, so put the
2056 * MUT_CONS back on the list.
2058 p->mut_link = new_list;
2065 StgCAF *caf = (StgCAF *)p;
2066 caf->body = evacuate(caf->body);
2067 caf->value = evacuate(caf->value);
2068 if (failed_to_evac) {
2069 failed_to_evac = rtsFalse;
2070 p->mut_link = new_list;
2080 StgCAF *caf = (StgCAF *)p;
2081 caf->body = evacuate(caf->body);
2082 if (failed_to_evac) {
2083 failed_to_evac = rtsFalse;
2084 p->mut_link = new_list;
2093 /* shouldn't have anything else on the mutables list */
2094 barf("scavenge_mut_once_list: strange object?");
2098 gen->mut_once_list = new_list;
2103 scavenge_mutable_list(generation *gen)
2106 StgMutClosure *p, *next;
2108 p = gen->saved_mut_list;
2112 failed_to_evac = rtsFalse;
2114 for (; p != END_MUT_LIST; p = next, next = p->mut_link) {
2116 /* make sure the info pointer is into text space */
2117 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
2118 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
2121 switch(info->type) {
2123 case MUT_ARR_PTRS_FROZEN:
2124 /* remove this guy from the mutable list, but follow the ptrs
2125 * anyway (and make sure they get promoted to this gen).
2130 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2132 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
2133 (StgClosure *)*q = evacuate((StgClosure *)*q);
2137 if (failed_to_evac) {
2138 failed_to_evac = rtsFalse;
2139 p->mut_link = gen->mut_list;
2146 /* follow everything */
2147 p->mut_link = gen->mut_list;
2152 end = (P_)p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2153 for (q = (P_)((StgMutArrPtrs *)p)->payload; q < end; q++) {
2154 (StgClosure *)*q = evacuate((StgClosure *)*q);
2160 /* MUT_CONS is a kind of MUT_VAR, except that we try to remove
2161 * it from the mutable list if possible by promoting whatever it
2164 ASSERT(p->header.info != &MUT_CONS_info);
2165 ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
2166 p->mut_link = gen->mut_list;
2172 StgMVar *mvar = (StgMVar *)p;
2173 (StgClosure *)mvar->head = evacuate((StgClosure *)mvar->head);
2174 (StgClosure *)mvar->tail = evacuate((StgClosure *)mvar->tail);
2175 (StgClosure *)mvar->value = evacuate((StgClosure *)mvar->value);
2176 p->mut_link = gen->mut_list;
2183 StgTSO *tso = (StgTSO *)p;
2185 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
2186 if (tso->blocked_on) {
2187 tso->blocked_on = evacuate(tso->blocked_on);
2189 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2191 /* Don't take this TSO off the mutable list - it might still
2192 * point to some younger objects (because we set evac_gen to 0
2195 tso->mut_link = gen->mut_list;
2196 gen->mut_list = (StgMutClosure *)tso;
2202 StgBlockingQueue *bh = (StgBlockingQueue *)p;
2203 (StgClosure *)bh->blocking_queue =
2204 evacuate((StgClosure *)bh->blocking_queue);
2205 p->mut_link = gen->mut_list;
2211 /* shouldn't have anything else on the mutables list */
2212 barf("scavenge_mut_list: strange object?");
2218 scavenge_static(void)
2220 StgClosure* p = static_objects;
2221 const StgInfoTable *info;
2223 /* Always evacuate straight to the oldest generation for static
2225 evac_gen = oldest_gen->no;
2227 /* keep going until we've scavenged all the objects on the linked
2229 while (p != END_OF_STATIC_LIST) {
2233 /* make sure the info pointer is into text space */
2234 ASSERT(p && (LOOKS_LIKE_GHC_INFO(GET_INFO(p))
2235 || IS_HUGS_CONSTR_INFO(GET_INFO(p))));
2237 /* Take this object *off* the static_objects list,
2238 * and put it on the scavenged_static_objects list.
2240 static_objects = STATIC_LINK(info,p);
2241 STATIC_LINK(info,p) = scavenged_static_objects;
2242 scavenged_static_objects = p;
2244 switch (info -> type) {
2248 StgInd *ind = (StgInd *)p;
2249 ind->indirectee = evacuate(ind->indirectee);
2251 /* might fail to evacuate it, in which case we have to pop it
2252 * back on the mutable list (and take it off the
2253 * scavenged_static list because the static link and mut link
2254 * pointers are one and the same).
2256 if (failed_to_evac) {
2257 failed_to_evac = rtsFalse;
2258 scavenged_static_objects = STATIC_LINK(info,p);
2259 ((StgMutClosure *)ind)->mut_link = oldest_gen->mut_once_list;
2260 oldest_gen->mut_once_list = (StgMutClosure *)ind;
2274 next = (P_)p->payload + info->layout.payload.ptrs;
2275 /* evacuate the pointers */
2276 for (q = (P_)p->payload; q < next; q++) {
2277 (StgClosure *)*q = evacuate((StgClosure *)*q);
2283 barf("scavenge_static");
2286 ASSERT(failed_to_evac == rtsFalse);
2288 /* get the next static object from the list. Remeber, there might
2289 * be more stuff on this list now that we've done some evacuating!
2290 * (static_objects is a global)
2296 /* -----------------------------------------------------------------------------
2297 scavenge_stack walks over a section of stack and evacuates all the
2298 objects pointed to by it. We can use the same code for walking
2299 PAPs, since these are just sections of copied stack.
2300 -------------------------------------------------------------------------- */
2303 scavenge_stack(StgPtr p, StgPtr stack_end)
2306 const StgInfoTable* info;
2310 * Each time around this loop, we are looking at a chunk of stack
2311 * that starts with either a pending argument section or an
2312 * activation record.
2315 while (p < stack_end) {
2318 /* If we've got a tag, skip over that many words on the stack */
2319 if (IS_ARG_TAG((W_)q)) {
2324 /* Is q a pointer to a closure?
2326 if (! LOOKS_LIKE_GHC_INFO(q) ) {
2328 if ( 0 && LOOKS_LIKE_STATIC_CLOSURE(q) ) { /* Is it a static closure? */
2329 ASSERT(closure_STATIC(stgCast(StgClosure*,q)));
2331 /* otherwise, must be a pointer into the allocation space. */
2334 (StgClosure *)*p = evacuate((StgClosure *)q);
2340 * Otherwise, q must be the info pointer of an activation
2341 * record. All activation records have 'bitmap' style layout
2344 info = get_itbl((StgClosure *)p);
2346 switch (info->type) {
2348 /* Dynamic bitmap: the mask is stored on the stack */
2350 bitmap = ((StgRetDyn *)p)->liveness;
2351 p = (P_)&((StgRetDyn *)p)->payload[0];
2354 /* probably a slow-entry point return address: */
2360 /* Specialised code for update frames, since they're so common.
2361 * We *know* the updatee points to a BLACKHOLE, CAF_BLACKHOLE,
2362 * or BLACKHOLE_BQ, so just inline the code to evacuate it here.
2366 StgUpdateFrame *frame = (StgUpdateFrame *)p;
2368 nat type = get_itbl(frame->updatee)->type;
2370 p += sizeofW(StgUpdateFrame);
2371 if (type == EVACUATED) {
2372 frame->updatee = evacuate(frame->updatee);
2375 bdescr *bd = Bdescr((P_)frame->updatee);
2377 if (bd->gen->no > N) {
2378 if (bd->gen->no < evac_gen) {
2379 failed_to_evac = rtsTrue;
2384 /* Don't promote blackholes */
2386 if (!(step->gen->no == 0 &&
2388 step->no == step->gen->n_steps-1)) {
2395 to = copyPart(frame->updatee, BLACKHOLE_sizeW(),
2396 sizeofW(StgHeader), step);
2397 frame->updatee = to;
2400 to = copy(frame->updatee, BLACKHOLE_sizeW(), step);
2401 frame->updatee = to;
2402 recordMutable((StgMutClosure *)to);
2405 barf("scavenge_stack: UPDATE_FRAME updatee");
2410 /* small bitmap (< 32 entries, or 64 on a 64-bit machine) */
2417 bitmap = info->layout.bitmap;
2420 while (bitmap != 0) {
2421 if ((bitmap & 1) == 0) {
2422 (StgClosure *)*p = evacuate((StgClosure *)*p);
2425 bitmap = bitmap >> 1;
2432 /* large bitmap (> 32 entries) */
2437 StgLargeBitmap *large_bitmap;
2440 large_bitmap = info->layout.large_bitmap;
2443 for (i=0; i<large_bitmap->size; i++) {
2444 bitmap = large_bitmap->bitmap[i];
2445 q = p + sizeof(W_) * 8;
2446 while (bitmap != 0) {
2447 if ((bitmap & 1) == 0) {
2448 (StgClosure *)*p = evacuate((StgClosure *)*p);
2451 bitmap = bitmap >> 1;
2453 if (i+1 < large_bitmap->size) {
2455 (StgClosure *)*p = evacuate((StgClosure *)*p);
2461 /* and don't forget to follow the SRT */
2466 barf("scavenge_stack: weird activation record found on stack.\n");
2471 /*-----------------------------------------------------------------------------
2472 scavenge the large object list.
2474 evac_gen set by caller; similar games played with evac_gen as with
2475 scavenge() - see comment at the top of scavenge(). Most large
2476 objects are (repeatedly) mutable, so most of the time evac_gen will
2478 --------------------------------------------------------------------------- */
2481 scavenge_large(step *step)
2485 const StgInfoTable* info;
2486 nat saved_evac_gen = evac_gen; /* used for temporarily changing evac_gen */
2488 evac_gen = 0; /* most objects are mutable */
2489 bd = step->new_large_objects;
2491 for (; bd != NULL; bd = step->new_large_objects) {
2493 /* take this object *off* the large objects list and put it on
2494 * the scavenged large objects list. This is so that we can
2495 * treat new_large_objects as a stack and push new objects on
2496 * the front when evacuating.
2498 step->new_large_objects = bd->link;
2499 dbl_link_onto(bd, &step->scavenged_large_objects);
2502 info = get_itbl(stgCast(StgClosure*,p));
2504 switch (info->type) {
2506 /* only certain objects can be "large"... */
2509 /* nothing to follow */
2513 /* follow everything */
2517 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2518 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2519 (StgClosure *)*p = evacuate((StgClosure *)*p);
2524 case MUT_ARR_PTRS_FROZEN:
2525 /* follow everything */
2527 StgPtr start = p, next;
2529 evac_gen = saved_evac_gen; /* not really mutable */
2530 next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
2531 for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
2532 (StgClosure *)*p = evacuate((StgClosure *)*p);
2535 if (failed_to_evac) {
2536 recordMutable((StgMutClosure *)start);
2543 StgBCO* bco = stgCast(StgBCO*,p);
2545 evac_gen = saved_evac_gen;
2546 for (i = 0; i < bco->n_ptrs; i++) {
2547 bcoConstCPtr(bco,i) = evacuate(bcoConstCPtr(bco,i));
2558 /* chase the link field for any TSOs on the same queue */
2559 (StgClosure *)tso->link = evacuate((StgClosure *)tso->link);
2560 if (tso->blocked_on) {
2561 tso->blocked_on = evacuate(tso->blocked_on);
2563 /* scavenge this thread's stack */
2564 scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
2569 barf("scavenge_large: unknown/strange object");
2575 zero_static_object_list(StgClosure* first_static)
2579 const StgInfoTable *info;
2581 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
2583 link = STATIC_LINK(info, p);
2584 STATIC_LINK(info,p) = NULL;
2588 /* This function is only needed because we share the mutable link
2589 * field with the static link field in an IND_STATIC, so we have to
2590 * zero the mut_link field before doing a major GC, which needs the
2591 * static link field.
2593 * It doesn't do any harm to zero all the mutable link fields on the
2597 zero_mutable_list( StgMutClosure *first )
2599 StgMutClosure *next, *c;
2601 for (c = first; c != END_MUT_LIST; c = next) {
2607 /* -----------------------------------------------------------------------------
2609 -------------------------------------------------------------------------- */
2611 void RevertCAFs(void)
2613 while (enteredCAFs != END_CAF_LIST) {
2614 StgCAF* caf = enteredCAFs;
2616 enteredCAFs = caf->link;
2617 ASSERT(get_itbl(caf)->type == CAF_ENTERED);
2618 SET_INFO(caf,&CAF_UNENTERED_info);
2619 caf->value = stgCast(StgClosure*,0xdeadbeef);
2620 caf->link = stgCast(StgCAF*,0xdeadbeef);
2622 enteredCAFs = END_CAF_LIST;
2625 void revert_dead_CAFs(void)
2627 StgCAF* caf = enteredCAFs;
2628 enteredCAFs = END_CAF_LIST;
2629 while (caf != END_CAF_LIST) {
2632 new = (StgCAF*)isAlive((StgClosure*)caf);
2634 new->link = enteredCAFs;
2638 SET_INFO(caf,&CAF_UNENTERED_info);
2639 caf->value = (StgClosure*)0xdeadbeef;
2640 caf->link = (StgCAF*)0xdeadbeef;
2646 /* -----------------------------------------------------------------------------
2647 Sanity code for CAF garbage collection.
2649 With DEBUG turned on, we manage a CAF list in addition to the SRT
2650 mechanism. After GC, we run down the CAF list and blackhole any
2651 CAFs which have been garbage collected. This means we get an error
2652 whenever the program tries to enter a garbage collected CAF.
2654 Any garbage collected CAFs are taken off the CAF list at the same
2656 -------------------------------------------------------------------------- */
2664 const StgInfoTable *info;
2675 ASSERT(info->type == IND_STATIC);
2677 if (STATIC_LINK(info,p) == NULL) {
2678 IF_DEBUG(gccafs, fprintf(stderr, "CAF gc'd at 0x%04x\n", (int)p));
2680 SET_INFO(p,&BLACKHOLE_info);
2681 p = STATIC_LINK2(info,p);
2685 pp = &STATIC_LINK2(info,p);
2692 /* fprintf(stderr, "%d CAFs live\n", i); */
2696 /* -----------------------------------------------------------------------------
2699 Whenever a thread returns to the scheduler after possibly doing
2700 some work, we have to run down the stack and black-hole all the
2701 closures referred to by update frames.
2702 -------------------------------------------------------------------------- */
2705 threadLazyBlackHole(StgTSO *tso)
2707 StgUpdateFrame *update_frame;
2708 StgBlockingQueue *bh;
2711 stack_end = &tso->stack[tso->stack_size];
2712 update_frame = tso->su;
2715 switch (get_itbl(update_frame)->type) {
2718 update_frame = stgCast(StgCatchFrame*,update_frame)->link;
2722 bh = (StgBlockingQueue *)update_frame->updatee;
2724 /* if the thunk is already blackholed, it means we've also
2725 * already blackholed the rest of the thunks on this stack,
2726 * so we can stop early.
2728 * The blackhole made for a CAF is a CAF_BLACKHOLE, so they
2729 * don't interfere with this optimisation.
2731 if (bh->header.info == &BLACKHOLE_info) {
2735 if (bh->header.info != &BLACKHOLE_BQ_info &&
2736 bh->header.info != &CAF_BLACKHOLE_info) {
2737 SET_INFO(bh,&BLACKHOLE_info);
2740 update_frame = update_frame->link;
2744 update_frame = stgCast(StgSeqFrame*,update_frame)->link;
2750 barf("threadPaused");
2755 /* -----------------------------------------------------------------------------
2758 * Code largely pinched from old RTS, then hacked to bits. We also do
2759 * lazy black holing here.
2761 * -------------------------------------------------------------------------- */
2764 threadSqueezeStack(StgTSO *tso)
2766 lnat displacement = 0;
2767 StgUpdateFrame *frame;
2768 StgUpdateFrame *next_frame; /* Temporally next */
2769 StgUpdateFrame *prev_frame; /* Temporally previous */
2771 rtsBool prev_was_update_frame;
2773 bottom = &(tso->stack[tso->stack_size]);
2776 /* There must be at least one frame, namely the STOP_FRAME.
2778 ASSERT((P_)frame < bottom);
2780 /* Walk down the stack, reversing the links between frames so that
2781 * we can walk back up as we squeeze from the bottom. Note that
2782 * next_frame and prev_frame refer to next and previous as they were
2783 * added to the stack, rather than the way we see them in this
2784 * walk. (It makes the next loop less confusing.)
2786 * Stop if we find an update frame pointing to a black hole
2787 * (see comment in threadLazyBlackHole()).
2791 /* bottom - sizeof(StgStopFrame) is the STOP_FRAME */
2792 while ((P_)frame < bottom - sizeofW(StgStopFrame)) {
2793 prev_frame = frame->link;
2794 frame->link = next_frame;
2797 if (get_itbl(frame)->type == UPDATE_FRAME
2798 && frame->updatee->header.info == &BLACKHOLE_info) {
2803 /* Now, we're at the bottom. Frame points to the lowest update
2804 * frame on the stack, and its link actually points to the frame
2805 * above. We have to walk back up the stack, squeezing out empty
2806 * update frames and turning the pointers back around on the way
2809 * The bottom-most frame (the STOP_FRAME) has not been altered, and
2810 * we never want to eliminate it anyway. Just walk one step up
2811 * before starting to squeeze. When you get to the topmost frame,
2812 * remember that there are still some words above it that might have
2819 prev_was_update_frame = (get_itbl(prev_frame)->type == UPDATE_FRAME);
2822 * Loop through all of the frames (everything except the very
2823 * bottom). Things are complicated by the fact that we have
2824 * CATCH_FRAMEs and SEQ_FRAMEs interspersed with the update frames.
2825 * We can only squeeze when there are two consecutive UPDATE_FRAMEs.
2827 while (frame != NULL) {
2829 StgPtr frame_bottom = (P_)frame + sizeofW(StgUpdateFrame);
2830 rtsBool is_update_frame;
2832 next_frame = frame->link;
2833 is_update_frame = (get_itbl(frame)->type == UPDATE_FRAME);
2836 * 1. both the previous and current frame are update frames
2837 * 2. the current frame is empty
2839 if (prev_was_update_frame && is_update_frame &&
2840 (P_)prev_frame == frame_bottom + displacement) {
2842 /* Now squeeze out the current frame */
2843 StgClosure *updatee_keep = prev_frame->updatee;
2844 StgClosure *updatee_bypass = frame->updatee;
2847 fprintf(stderr, "squeezing frame at %p\n", frame);
2850 /* Deal with blocking queues. If both updatees have blocked
2851 * threads, then we should merge the queues into the update
2852 * frame that we're keeping.
2854 * Alternatively, we could just wake them up: they'll just go
2855 * straight to sleep on the proper blackhole! This is less code
2856 * and probably less bug prone, although it's probably much
2859 #if 0 /* do it properly... */
2860 if (GET_INFO(updatee_bypass) == BLACKHOLE_BQ_info) {
2861 /* Sigh. It has one. Don't lose those threads! */
2862 if (GET_INFO(updatee_keep) == BLACKHOLE_BQ_info) {
2863 /* Urgh. Two queues. Merge them. */
2864 P_ keep_tso = ((StgBlockingQueue *)updatee_keep)->blocking_queue;
2866 while (keep_tso->link != END_TSO_QUEUE) {
2867 keep_tso = keep_tso->link;
2869 keep_tso->link = ((StgBlockingQueue *)updatee_bypass)->blocking_queue;
2872 /* For simplicity, just swap the BQ for the BH */
2873 P_ temp = updatee_keep;
2875 updatee_keep = updatee_bypass;
2876 updatee_bypass = temp;
2878 /* Record the swap in the kept frame (below) */
2879 prev_frame->updatee = updatee_keep;
2884 TICK_UPD_SQUEEZED();
2885 UPD_IND(updatee_bypass, updatee_keep); /* this wakes the threads up */
2887 sp = (P_)frame - 1; /* sp = stuff to slide */
2888 displacement += sizeofW(StgUpdateFrame);
2891 /* No squeeze for this frame */
2892 sp = frame_bottom - 1; /* Keep the current frame */
2894 /* Do lazy black-holing.
2896 if (is_update_frame) {
2897 StgBlockingQueue *bh = (StgBlockingQueue *)frame->updatee;
2898 if (bh->header.info != &BLACKHOLE_BQ_info &&
2899 bh->header.info != &CAF_BLACKHOLE_info) {
2900 SET_INFO(bh,&BLACKHOLE_info);
2904 /* Fix the link in the current frame (should point to the frame below) */
2905 frame->link = prev_frame;
2906 prev_was_update_frame = is_update_frame;
2909 /* Now slide all words from sp up to the next frame */
2911 if (displacement > 0) {
2912 P_ next_frame_bottom;
2914 if (next_frame != NULL)
2915 next_frame_bottom = (P_)next_frame + sizeofW(StgUpdateFrame);
2917 next_frame_bottom = tso->sp - 1;
2920 fprintf(stderr, "sliding [%p, %p] by %ld\n", sp, next_frame_bottom,
2924 while (sp >= next_frame_bottom) {
2925 sp[displacement] = *sp;
2929 (P_)prev_frame = (P_)frame + displacement;
2933 tso->sp += displacement;
2934 tso->su = prev_frame;
2937 /* -----------------------------------------------------------------------------
2940 * We have to prepare for GC - this means doing lazy black holing
2941 * here. We also take the opportunity to do stack squeezing if it's
2943 * -------------------------------------------------------------------------- */
2946 threadPaused(StgTSO *tso)
2948 if ( RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue )
2949 threadSqueezeStack(tso); /* does black holing too */
2951 threadLazyBlackHole(tso);