1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 1998-2006
5 * Generational garbage collector
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
12 * ---------------------------------------------------------------------------*/
14 #include "PosixSource.h"
19 #include "OSThreads.h"
20 #include "LdvProfile.h"
25 #include "BlockAlloc.h"
31 #include "ParTicky.h" // ToDo: move into Rts.h
32 #include "RtsSignals.h"
36 #if defined(RTS_GTK_FRONTPANEL)
37 #include "FrontPanel.h"
40 #include "RetainerProfile.h"
41 #include "RaiseAsync.h"
53 #include <string.h> // for memset()
55 /* -----------------------------------------------------------------------------
57 -------------------------------------------------------------------------- */
59 /* STATIC OBJECT LIST.
62 * We maintain a linked list of static objects that are still live.
63 * The requirements for this list are:
65 * - we need to scan the list while adding to it, in order to
66 * scavenge all the static objects (in the same way that
67 * breadth-first scavenging works for dynamic objects).
69 * - we need to be able to tell whether an object is already on
70 * the list, to break loops.
72 * Each static object has a "static link field", which we use for
73 * linking objects on to the list. We use a stack-type list, consing
74 * objects on the front as they are added (this means that the
75 * scavenge phase is depth-first, not breadth-first, but that
78 * A separate list is kept for objects that have been scavenged
79 * already - this is so that we can zero all the marks afterwards.
81 * An object is on the list if its static link field is non-zero; this
82 * means that we have to mark the end of the list with '1', not NULL.
84 * Extra notes for generational GC:
86 * Each generation has a static object list associated with it. When
87 * collecting generations up to N, we treat the static object lists
88 * from generations > N as roots.
90 * We build up a static object list while collecting generations 0..N,
91 * which is then appended to the static object list of generation N+1.
93 StgClosure* static_objects; // live static objects
94 StgClosure* scavenged_static_objects; // static objects scavenged so far
96 SpinLock static_objects_sync;
99 /* N is the oldest generation being collected, where the generations
100 * are numbered starting at 0. A major GC (indicated by the major_gc
101 * flag) is when we're collecting all generations. We only attempt to
102 * deal with static objects and GC CAFs when doing a major GC.
107 /* Data used for allocation area sizing.
109 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
119 /* Thread-local data for each GC thread
121 gc_thread **gc_threads = NULL;
122 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
124 // Number of threads running in *this* GC. Affects how many
125 // step->todos[] lists we have to look in to find work.
129 long copied; // *words* copied & scavenged during this GC
132 SpinLock recordMutableGen_sync;
135 /* -----------------------------------------------------------------------------
136 Static function declarations
137 -------------------------------------------------------------------------- */
139 static void mark_root (StgClosure **root);
140 static void zero_static_object_list (StgClosure* first_static);
141 static void initialise_N (rtsBool force_major_gc);
142 static void alloc_gc_threads (void);
143 static void init_collected_gen (nat g, nat threads);
144 static void init_uncollected_gen (nat g, nat threads);
145 static void init_gc_thread (gc_thread *t);
146 static void update_task_list (void);
147 static void resize_generations (void);
148 static void resize_nursery (void);
149 static void start_gc_threads (void);
150 static void gc_thread_work (void);
151 static nat inc_running (void);
152 static nat dec_running (void);
153 static void wakeup_gc_threads (nat n_threads);
155 #if 0 && defined(DEBUG)
156 static void gcCAFs (void);
159 /* -----------------------------------------------------------------------------
160 The mark bitmap & stack.
161 -------------------------------------------------------------------------- */
163 #define MARK_STACK_BLOCKS 4
165 bdescr *mark_stack_bdescr;
170 // Flag and pointers used for falling back to a linear scan when the
171 // mark stack overflows.
172 rtsBool mark_stack_overflowed;
173 bdescr *oldgen_scan_bd;
176 /* -----------------------------------------------------------------------------
177 GarbageCollect: the main entry point to the garbage collector.
179 Locks held: all capabilities are held throughout GarbageCollect().
180 -------------------------------------------------------------------------- */
183 GarbageCollect ( rtsBool force_major_gc )
187 lnat live, allocated;
188 lnat oldgen_saved_blocks = 0;
189 gc_thread *saved_gct;
192 // necessary if we stole a callee-saves register for gct:
196 CostCentreStack *prev_CCS;
201 debugTrace(DEBUG_gc, "starting GC");
203 #if defined(RTS_USER_SIGNALS)
204 if (RtsFlags.MiscFlags.install_signal_handlers) {
210 // tell the stats department that we've started a GC
213 // tell the STM to discard any cached closures it's hoping to re-use
222 // attribute any costs to CCS_GC
228 /* Approximate how much we allocated.
229 * Todo: only when generating stats?
231 allocated = calcAllocated();
233 /* Figure out which generation to collect
235 initialise_N(force_major_gc);
237 /* Allocate + initialise the gc_thread structures.
241 /* Start threads, so they can be spinning up while we finish initialisation.
245 /* How many threads will be participating in this GC?
246 * We don't try to parallelise minor GC.
248 #if defined(THREADED_RTS)
252 n_gc_threads = RtsFlags.ParFlags.gcThreads;
258 #ifdef RTS_GTK_FRONTPANEL
259 if (RtsFlags.GcFlags.frontpanel) {
260 updateFrontPanelBeforeGC(N);
265 // check for memory leaks if DEBUG is on
266 memInventory(traceClass(DEBUG_gc));
269 // check stack sanity *before* GC (ToDo: check all threads)
270 IF_DEBUG(sanity, checkFreeListSanity());
272 /* Initialise the static object lists
274 static_objects = END_OF_STATIC_LIST;
275 scavenged_static_objects = END_OF_STATIC_LIST;
277 // Initialise all the generations/steps that we're collecting.
278 for (g = 0; g <= N; g++) {
279 init_collected_gen(g,n_gc_threads);
282 // Initialise all the generations/steps that we're *not* collecting.
283 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
284 init_uncollected_gen(g,n_gc_threads);
287 /* Allocate a mark stack if we're doing a major collection.
290 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
291 mark_stack = (StgPtr *)mark_stack_bdescr->start;
292 mark_sp = mark_stack;
293 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
295 mark_stack_bdescr = NULL;
298 // Initialise all our gc_thread structures
299 for (t = 0; t < n_gc_threads; t++) {
300 init_gc_thread(gc_threads[t]);
303 // the main thread is running: this prevents any other threads from
304 // exiting prematurely, so we can start them now.
306 wakeup_gc_threads(n_gc_threads);
308 // this is the main thread
311 /* -----------------------------------------------------------------------
312 * follow all the roots that we know about:
313 * - mutable lists from each generation > N
314 * we want to *scavenge* these roots, not evacuate them: they're not
315 * going to move in this GC.
316 * Also do them in reverse generation order, for the usual reason:
317 * namely to reduce the likelihood of spurious old->new pointers.
320 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
321 generations[g].saved_mut_list = generations[g].mut_list;
322 generations[g].mut_list = allocBlock();
323 // mut_list always has at least one block.
325 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
326 scavenge_mutable_list(&generations[g]);
330 // follow roots from the CAF list (used by GHCi)
334 // follow all the roots that the application knows about.
338 #if defined(RTS_USER_SIGNALS)
339 // mark the signal handlers (signals should be already blocked)
340 markSignalHandlers(mark_root);
343 // Mark the weak pointer list, and prepare to detect dead weak pointers.
347 // Mark the stable pointer table.
348 markStablePtrTable(mark_root);
350 /* -------------------------------------------------------------------------
351 * Repeatedly scavenge all the areas we know about until there's no
352 * more scavenging to be done.
357 // The other threads are now stopped. We might recurse back to
358 // here, but from now on this is the only thread.
360 // if any blackholes are alive, make the threads that wait on
362 if (traverseBlackholeQueue()) {
367 // must be last... invariant is that everything is fully
368 // scavenged at this point.
369 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
374 // If we get to here, there's really nothing left to do.
378 // Update pointers from the Task list
381 // Now see which stable names are still alive.
385 // We call processHeapClosureForDead() on every closure destroyed during
386 // the current garbage collection, so we invoke LdvCensusForDead().
387 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
388 || RtsFlags.ProfFlags.bioSelector != NULL)
392 // NO MORE EVACUATION AFTER THIS POINT!
393 // Finally: compaction of the oldest generation.
394 if (major_gc && oldest_gen->steps[0].is_compacted) {
395 // save number of blocks for stats
396 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
400 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
402 // Two-space collector: free the old to-space.
403 // g0s0->old_blocks is the old nursery
404 // g0s0->blocks is to-space from the previous GC
405 if (RtsFlags.GcFlags.generations == 1) {
406 if (g0s0->blocks != NULL) {
407 freeChain(g0s0->blocks);
412 // For each workspace, in each thread:
413 // * clear the BF_EVACUATED flag from each copied block
414 // * move the copied blocks to the step
420 for (t = 0; t < n_gc_threads; t++) {
424 for (s = 1; s < total_steps; s++) {
427 // ASSERT( ws->scan_bd == ws->todo_bd );
428 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
430 // Push the final block
431 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
433 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
435 prev = ws->scavd_list;
436 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
437 bd->flags &= ~BF_EVACUATED; // now from-space
440 prev->link = ws->stp->blocks;
441 ws->stp->blocks = ws->scavd_list;
442 ws->stp->n_blocks += ws->n_scavd_blocks;
443 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
448 // Two-space collector: swap the semi-spaces around.
449 // Currently: g0s0->old_blocks is the old nursery
450 // g0s0->blocks is to-space from this GC
451 // We want these the other way around.
452 if (RtsFlags.GcFlags.generations == 1) {
453 bdescr *nursery_blocks = g0s0->old_blocks;
454 nat n_nursery_blocks = g0s0->n_old_blocks;
455 g0s0->old_blocks = g0s0->blocks;
456 g0s0->n_old_blocks = g0s0->n_blocks;
457 g0s0->blocks = nursery_blocks;
458 g0s0->n_blocks = n_nursery_blocks;
461 /* run through all the generations/steps and tidy up
466 for (i=0; i < n_gc_threads; i++) {
468 trace(TRACE_gc,"thread %d:", i);
469 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
470 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
471 trace(TRACE_gc," scav_global_work %ld", gc_threads[i]->scav_global_work);
472 trace(TRACE_gc," scav_local_work %ld", gc_threads[i]->scav_local_work);
474 copied += gc_threads[i]->copied;
478 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
481 generations[g].collections++; // for stats
484 // Count the mutable list as bytes "copied" for the purposes of
485 // stats. Every mutable list is copied during every GC.
487 nat mut_list_size = 0;
488 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
489 mut_list_size += bd->free - bd->start;
491 copied += mut_list_size;
494 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
495 (unsigned long)(mut_list_size * sizeof(W_)),
496 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
499 for (s = 0; s < generations[g].n_steps; s++) {
501 stp = &generations[g].steps[s];
503 // for generations we collected...
506 /* free old memory and shift to-space into from-space for all
507 * the collected steps (except the allocation area). These
508 * freed blocks will probaby be quickly recycled.
510 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
511 if (stp->is_compacted)
513 // for a compacted step, just shift the new to-space
514 // onto the front of the now-compacted existing blocks.
515 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
516 bd->flags &= ~BF_EVACUATED; // now from-space
518 // tack the new blocks on the end of the existing blocks
519 if (stp->old_blocks != NULL) {
520 for (bd = stp->old_blocks; bd != NULL; bd = next) {
521 // NB. this step might not be compacted next
522 // time, so reset the BF_COMPACTED flags.
523 // They are set before GC if we're going to
524 // compact. (search for BF_COMPACTED above).
525 bd->flags &= ~BF_COMPACTED;
528 bd->link = stp->blocks;
531 stp->blocks = stp->old_blocks;
533 // add the new blocks to the block tally
534 stp->n_blocks += stp->n_old_blocks;
535 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
539 freeChain(stp->old_blocks);
541 stp->old_blocks = NULL;
542 stp->n_old_blocks = 0;
545 /* LARGE OBJECTS. The current live large objects are chained on
546 * scavenged_large, having been moved during garbage
547 * collection from large_objects. Any objects left on
548 * large_objects list are therefore dead, so we free them here.
550 for (bd = stp->large_objects; bd != NULL; bd = next) {
556 // update the count of blocks used by large objects
557 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
558 bd->flags &= ~BF_EVACUATED;
560 stp->large_objects = stp->scavenged_large_objects;
561 stp->n_large_blocks = stp->n_scavenged_large_blocks;
564 else // for older generations...
566 /* For older generations, we need to append the
567 * scavenged_large_object list (i.e. large objects that have been
568 * promoted during this GC) to the large_object list for that step.
570 for (bd = stp->scavenged_large_objects; bd; bd = next) {
572 bd->flags &= ~BF_EVACUATED;
573 dbl_link_onto(bd, &stp->large_objects);
576 // add the new blocks we promoted during this GC
577 stp->n_large_blocks += stp->n_scavenged_large_blocks;
582 // update the max size of older generations after a major GC
583 resize_generations();
585 // Guess the amount of live data for stats.
586 live = calcLiveBlocks() * BLOCK_SIZE_W;
587 debugTrace(DEBUG_gc, "Slop: %ldKB",
588 (live - calcLiveWords()) / (1024/sizeof(W_)));
590 // Free the small objects allocated via allocate(), since this will
591 // all have been copied into G0S1 now.
592 if (RtsFlags.GcFlags.generations > 1) {
593 if (g0s0->blocks != NULL) {
594 freeChain(g0s0->blocks);
600 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
602 // Start a new pinned_object_block
603 pinned_object_block = NULL;
605 // Free the mark stack.
606 if (mark_stack_bdescr != NULL) {
607 freeGroup(mark_stack_bdescr);
611 for (g = 0; g <= N; g++) {
612 for (s = 0; s < generations[g].n_steps; s++) {
613 stp = &generations[g].steps[s];
614 if (stp->bitmap != NULL) {
615 freeGroup(stp->bitmap);
623 // mark the garbage collected CAFs as dead
624 #if 0 && defined(DEBUG) // doesn't work at the moment
625 if (major_gc) { gcCAFs(); }
629 // resetStaticObjectForRetainerProfiling() must be called before
631 resetStaticObjectForRetainerProfiling();
634 // zero the scavenged static object list
636 zero_static_object_list(scavenged_static_objects);
642 // start any pending finalizers
644 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
647 // send exceptions to any threads which were about to die
649 resurrectThreads(resurrected_threads);
652 // Update the stable pointer hash table.
653 updateStablePtrTable(major_gc);
655 // check sanity after GC
656 IF_DEBUG(sanity, checkSanity());
658 // extra GC trace info
659 if (traceClass(TRACE_gc)) statDescribeGens();
662 // symbol-table based profiling
663 /* heapCensus(to_blocks); */ /* ToDo */
666 // restore enclosing cost centre
672 // check for memory leaks if DEBUG is on
673 memInventory(traceClass(DEBUG_gc));
676 #ifdef RTS_GTK_FRONTPANEL
677 if (RtsFlags.GcFlags.frontpanel) {
678 updateFrontPanelAfterGC( N, live );
682 // ok, GC over: tell the stats department what happened.
683 stat_endGC(allocated, live, copied, N);
685 #if defined(RTS_USER_SIGNALS)
686 if (RtsFlags.MiscFlags.install_signal_handlers) {
687 // unblock signals again
688 unblockUserSignals();
697 /* -----------------------------------------------------------------------------
698 * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
699 * implicit slide i.e. after marking all sparks are at the beginning of the
700 * spark pool and the spark pool only contains sparkable closures
701 * -------------------------------------------------------------------------- */
705 markSparkQueue (evac_fn evac, Capability *cap)
707 StgClosure **sparkp, **to_sparkp;
708 nat n, pruned_sparks; // stats only
711 PAR_TICKY_MARK_SPARK_QUEUE_START();
716 pool = &(cap->r.rSparks);
718 ASSERT_SPARK_POOL_INVARIANTS(pool);
720 #if defined(PARALLEL_HASKELL)
727 to_sparkp = pool->hd;
728 while (sparkp != pool->tl) {
729 ASSERT(*sparkp!=NULL);
730 ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
731 // ToDo?: statistics gathering here (also for GUM!)
732 if (closure_SHOULD_SPARK(*sparkp)) {
734 *to_sparkp++ = *sparkp;
735 if (to_sparkp == pool->lim) {
736 to_sparkp = pool->base;
743 if (sparkp == pool->lim) {
747 pool->tl = to_sparkp;
749 PAR_TICKY_MARK_SPARK_QUEUE_END(n);
751 #if defined(PARALLEL_HASKELL)
752 debugTrace(DEBUG_sched,
753 "marked %d sparks and pruned %d sparks on [%x]",
754 n, pruned_sparks, mytid);
756 debugTrace(DEBUG_sched,
757 "marked %d sparks and pruned %d sparks",
761 debugTrace(DEBUG_sched,
762 "new spark queue len=%d; (hd=%p; tl=%p)\n",
763 sparkPoolSize(pool), pool->hd, pool->tl);
767 /* ---------------------------------------------------------------------------
768 Where are the roots that we know about?
770 - all the threads on the runnable queue
771 - all the threads on the blocked queue
772 - all the threads on the sleeping queue
773 - all the thread currently executing a _ccall_GC
774 - all the "main threads"
776 ------------------------------------------------------------------------ */
779 GetRoots( evac_fn evac )
785 // Each GC thread is responsible for following roots from the
786 // Capability of the same number. There will usually be the same
787 // or fewer Capabilities as GC threads, but just in case there
788 // are more, we mark every Capability whose number is the GC
789 // thread's index plus a multiple of the number of GC threads.
790 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
791 cap = &capabilities[i];
792 evac((StgClosure **)(void *)&cap->run_queue_hd);
793 evac((StgClosure **)(void *)&cap->run_queue_tl);
794 #if defined(THREADED_RTS)
795 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
796 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
798 for (task = cap->suspended_ccalling_tasks; task != NULL;
800 debugTrace(DEBUG_sched,
801 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
802 evac((StgClosure **)(void *)&task->suspended_tso);
805 #if defined(THREADED_RTS)
806 markSparkQueue(evac,cap);
810 #if !defined(THREADED_RTS)
811 evac((StgClosure **)(void *)&blocked_queue_hd);
812 evac((StgClosure **)(void *)&blocked_queue_tl);
813 evac((StgClosure **)(void *)&sleeping_queue);
817 /* -----------------------------------------------------------------------------
818 isAlive determines whether the given closure is still alive (after
819 a garbage collection) or not. It returns the new address of the
820 closure if it is alive, or NULL otherwise.
822 NOTE: Use it before compaction only!
823 It untags and (if needed) retags pointers to closures.
824 -------------------------------------------------------------------------- */
828 isAlive(StgClosure *p)
830 const StgInfoTable *info;
836 /* The tag and the pointer are split, to be merged later when needed. */
837 tag = GET_CLOSURE_TAG(p);
838 q = UNTAG_CLOSURE(p);
840 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
843 // ignore static closures
845 // ToDo: for static closures, check the static link field.
846 // Problem here is that we sometimes don't set the link field, eg.
847 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
849 if (!HEAP_ALLOCED(q)) {
853 // ignore closures in generations that we're not collecting.
855 if (bd->gen_no > N) {
859 // if it's a pointer into to-space, then we're done
860 if (bd->flags & BF_EVACUATED) {
864 // large objects use the evacuated flag
865 if (bd->flags & BF_LARGE) {
869 // check the mark bit for compacted steps
870 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
874 switch (info->type) {
879 case IND_OLDGEN: // rely on compatible layout with StgInd
880 case IND_OLDGEN_PERM:
881 // follow indirections
882 p = ((StgInd *)q)->indirectee;
887 return ((StgEvacuated *)q)->evacuee;
890 if (((StgTSO *)q)->what_next == ThreadRelocated) {
891 p = (StgClosure *)((StgTSO *)q)->link;
903 /* -----------------------------------------------------------------------------
904 Figure out which generation to collect, initialise N and major_gc.
905 -------------------------------------------------------------------------- */
908 initialise_N (rtsBool force_major_gc)
912 if (force_major_gc) {
913 N = RtsFlags.GcFlags.generations - 1;
917 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
918 if (generations[g].steps[0].n_blocks +
919 generations[g].steps[0].n_large_blocks
920 >= generations[g].max_blocks) {
924 major_gc = (N == RtsFlags.GcFlags.generations-1);
928 /* -----------------------------------------------------------------------------
929 Initialise the gc_thread structures.
930 -------------------------------------------------------------------------- */
933 alloc_gc_thread (int n)
939 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
944 initCondition(&t->wake_cond);
945 initMutex(&t->wake_mutex);
946 t->wakeup = rtsFalse;
951 t->free_blocks = NULL;
960 for (s = 0; s < total_steps; s++)
963 ws->stp = &all_steps[s];
964 ASSERT(s == ws->stp->abs_no);
971 ws->buffer_todo_bd = NULL;
973 ws->scavd_list = NULL;
974 ws->n_scavd_blocks = 0;
982 alloc_gc_threads (void)
984 if (gc_threads == NULL) {
985 #if defined(THREADED_RTS)
987 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
991 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
992 gc_threads[i] = alloc_gc_thread(i);
995 gc_threads = stgMallocBytes (sizeof(gc_thread*),
998 gc_threads[0] = alloc_gc_thread(0);
1003 /* ----------------------------------------------------------------------------
1005 ------------------------------------------------------------------------- */
1007 static nat gc_running_threads;
1009 #if defined(THREADED_RTS)
1010 static Mutex gc_running_mutex;
1017 ACQUIRE_LOCK(&gc_running_mutex);
1018 n_running = ++gc_running_threads;
1019 RELEASE_LOCK(&gc_running_mutex);
1027 ACQUIRE_LOCK(&gc_running_mutex);
1028 n_running = --gc_running_threads;
1029 RELEASE_LOCK(&gc_running_mutex);
1034 // gc_thread_work(): Scavenge until there's no work left to do and all
1035 // the running threads are idle.
1038 gc_thread_work (void)
1042 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1044 // gc_running_threads has already been incremented for us; either
1045 // this is the main thread and we incremented it inside
1046 // GarbageCollect(), or this is a worker thread and the main
1047 // thread bumped gc_running_threads before waking us up.
1049 // Every thread evacuates some roots.
1051 GetRoots(mark_root);
1055 // scavenge_loop() only exits when there's no work to do
1058 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1059 gct->thread_index, r);
1061 while (gc_running_threads != 0) {
1066 // any_work() does not remove the work from the queue, it
1067 // just checks for the presence of work. If we find any,
1068 // then we increment gc_running_threads and go back to
1069 // scavenge_loop() to perform any pending work.
1072 // All threads are now stopped
1073 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1077 #if defined(THREADED_RTS)
1079 gc_thread_mainloop (void)
1081 while (!gct->exit) {
1083 // Wait until we're told to wake up
1084 ACQUIRE_LOCK(&gct->wake_mutex);
1085 while (!gct->wakeup) {
1086 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1088 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1090 RELEASE_LOCK(&gct->wake_mutex);
1091 gct->wakeup = rtsFalse;
1092 if (gct->exit) break;
1095 // start performance counters in this thread...
1096 if (gct->papi_events == -1) {
1097 papi_init_eventset(&gct->papi_events);
1099 papi_thread_start_gc1_count(gct->papi_events);
1105 // count events in this thread towards the GC totals
1106 papi_thread_stop_gc1_count(gct->papi_events);
1112 #if defined(THREADED_RTS)
1114 gc_thread_entry (gc_thread *my_gct)
1117 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1118 gct->id = osThreadId();
1119 gc_thread_mainloop();
1124 start_gc_threads (void)
1126 #if defined(THREADED_RTS)
1129 static rtsBool done = rtsFalse;
1131 gc_running_threads = 0;
1132 initMutex(&gc_running_mutex);
1135 // Start from 1: the main thread is 0
1136 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1137 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1146 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1148 #if defined(THREADED_RTS)
1150 for (i=1; i < n_threads; i++) {
1152 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1153 gc_threads[i]->wakeup = rtsTrue;
1154 signalCondition(&gc_threads[i]->wake_cond);
1155 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1160 /* ----------------------------------------------------------------------------
1161 Initialise a generation that is to be collected
1162 ------------------------------------------------------------------------- */
1165 init_collected_gen (nat g, nat n_threads)
1172 // Throw away the current mutable list. Invariant: the mutable
1173 // list always has at least one block; this means we can avoid a
1174 // check for NULL in recordMutable().
1176 freeChain(generations[g].mut_list);
1177 generations[g].mut_list = allocBlock();
1178 for (i = 0; i < n_capabilities; i++) {
1179 freeChain(capabilities[i].mut_lists[g]);
1180 capabilities[i].mut_lists[g] = allocBlock();
1184 for (s = 0; s < generations[g].n_steps; s++) {
1186 // generation 0, step 0 doesn't need to-space
1187 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1191 stp = &generations[g].steps[s];
1192 ASSERT(stp->gen_no == g);
1194 // deprecate the existing blocks
1195 stp->old_blocks = stp->blocks;
1196 stp->n_old_blocks = stp->n_blocks;
1200 // we don't have any to-be-scavenged blocks yet
1204 // initialise the large object queues.
1205 stp->scavenged_large_objects = NULL;
1206 stp->n_scavenged_large_blocks = 0;
1208 // mark the large objects as not evacuated yet
1209 for (bd = stp->large_objects; bd; bd = bd->link) {
1210 bd->flags &= ~BF_EVACUATED;
1213 // for a compacted step, we need to allocate the bitmap
1214 if (stp->is_compacted) {
1215 nat bitmap_size; // in bytes
1216 bdescr *bitmap_bdescr;
1219 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1221 if (bitmap_size > 0) {
1222 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1224 stp->bitmap = bitmap_bdescr;
1225 bitmap = bitmap_bdescr->start;
1227 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1228 bitmap_size, bitmap);
1230 // don't forget to fill it with zeros!
1231 memset(bitmap, 0, bitmap_size);
1233 // For each block in this step, point to its bitmap from the
1234 // block descriptor.
1235 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1236 bd->u.bitmap = bitmap;
1237 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1239 // Also at this point we set the BF_COMPACTED flag
1240 // for this block. The invariant is that
1241 // BF_COMPACTED is always unset, except during GC
1242 // when it is set on those blocks which will be
1244 bd->flags |= BF_COMPACTED;
1250 // For each GC thread, for each step, allocate a "todo" block to
1251 // store evacuated objects to be scavenged, and a block to store
1252 // evacuated objects that do not need to be scavenged.
1253 for (t = 0; t < n_threads; t++) {
1254 for (s = 0; s < generations[g].n_steps; s++) {
1256 // we don't copy objects into g0s0, unless -G0
1257 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1259 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1264 ws->todo_large_objects = NULL;
1266 // allocate the first to-space block; extra blocks will be
1267 // chained on as necessary.
1269 ws->buffer_todo_bd = NULL;
1270 gc_alloc_todo_block(ws);
1272 ws->scavd_list = NULL;
1273 ws->n_scavd_blocks = 0;
1279 /* ----------------------------------------------------------------------------
1280 Initialise a generation that is *not* to be collected
1281 ------------------------------------------------------------------------- */
1284 init_uncollected_gen (nat g, nat threads)
1291 for (s = 0; s < generations[g].n_steps; s++) {
1292 stp = &generations[g].steps[s];
1293 stp->scavenged_large_objects = NULL;
1294 stp->n_scavenged_large_blocks = 0;
1297 for (t = 0; t < threads; t++) {
1298 for (s = 0; s < generations[g].n_steps; s++) {
1300 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1303 ws->buffer_todo_bd = NULL;
1304 ws->todo_large_objects = NULL;
1306 ws->scavd_list = NULL;
1307 ws->n_scavd_blocks = 0;
1309 // If the block at the head of the list in this generation
1310 // is less than 3/4 full, then use it as a todo block.
1311 if (stp->blocks && isPartiallyFull(stp->blocks))
1313 ws->todo_bd = stp->blocks;
1314 ws->todo_free = ws->todo_bd->free;
1315 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1316 stp->blocks = stp->blocks->link;
1318 ws->todo_bd->link = NULL;
1320 // this block is also the scan block; we must scan
1321 // from the current end point.
1322 ws->scan_bd = ws->todo_bd;
1323 ws->scan = ws->scan_bd->free;
1325 // subtract the contents of this block from the stats,
1326 // because we'll count the whole block later.
1327 copied -= ws->scan_bd->free - ws->scan_bd->start;
1334 gc_alloc_todo_block(ws);
1339 // Move the private mutable lists from each capability onto the
1340 // main mutable list for the generation.
1341 for (i = 0; i < n_capabilities; i++) {
1342 for (bd = capabilities[i].mut_lists[g];
1343 bd->link != NULL; bd = bd->link) {
1346 bd->link = generations[g].mut_list;
1347 generations[g].mut_list = capabilities[i].mut_lists[g];
1348 capabilities[i].mut_lists[g] = allocBlock();
1352 /* -----------------------------------------------------------------------------
1353 Initialise a gc_thread before GC
1354 -------------------------------------------------------------------------- */
1357 init_gc_thread (gc_thread *t)
1360 t->failed_to_evac = rtsFalse;
1361 t->eager_promotion = rtsTrue;
1362 t->thunk_selector_depth = 0;
1365 t->scav_global_work = 0;
1366 t->scav_local_work = 0;
1369 /* -----------------------------------------------------------------------------
1370 Function we pass to GetRoots to evacuate roots.
1371 -------------------------------------------------------------------------- */
1374 mark_root(StgClosure **root)
1379 /* -----------------------------------------------------------------------------
1380 Initialising the static object & mutable lists
1381 -------------------------------------------------------------------------- */
1384 zero_static_object_list(StgClosure* first_static)
1388 const StgInfoTable *info;
1390 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1392 link = *STATIC_LINK(info, p);
1393 *STATIC_LINK(info,p) = NULL;
1397 /* -----------------------------------------------------------------------------
1399 -------------------------------------------------------------------------- */
1406 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1407 c = (StgIndStatic *)c->static_link)
1409 SET_INFO(c, c->saved_info);
1410 c->saved_info = NULL;
1411 // could, but not necessary: c->static_link = NULL;
1413 revertible_caf_list = NULL;
1417 markCAFs( evac_fn evac )
1421 for (c = (StgIndStatic *)caf_list; c != NULL;
1422 c = (StgIndStatic *)c->static_link)
1424 evac(&c->indirectee);
1426 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1427 c = (StgIndStatic *)c->static_link)
1429 evac(&c->indirectee);
1433 /* ----------------------------------------------------------------------------
1434 Update the pointers from the task list
1436 These are treated as weak pointers because we want to allow a main
1437 thread to get a BlockedOnDeadMVar exception in the same way as any
1438 other thread. Note that the threads should all have been retained
1439 by GC by virtue of being on the all_threads list, we're just
1440 updating pointers here.
1441 ------------------------------------------------------------------------- */
1444 update_task_list (void)
1448 for (task = all_tasks; task != NULL; task = task->all_link) {
1449 if (!task->stopped && task->tso) {
1450 ASSERT(task->tso->bound == task);
1451 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1453 barf("task %p: main thread %d has been GC'd",
1466 /* ----------------------------------------------------------------------------
1467 Reset the sizes of the older generations when we do a major
1470 CURRENT STRATEGY: make all generations except zero the same size.
1471 We have to stay within the maximum heap size, and leave a certain
1472 percentage of the maximum heap size available to allocate into.
1473 ------------------------------------------------------------------------- */
1476 resize_generations (void)
1480 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1481 nat live, size, min_alloc;
1482 nat max = RtsFlags.GcFlags.maxHeapSize;
1483 nat gens = RtsFlags.GcFlags.generations;
1485 // live in the oldest generations
1486 live = oldest_gen->steps[0].n_blocks +
1487 oldest_gen->steps[0].n_large_blocks;
1489 // default max size for all generations except zero
1490 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1491 RtsFlags.GcFlags.minOldGenSize);
1493 // minimum size for generation zero
1494 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1495 RtsFlags.GcFlags.minAllocAreaSize);
1497 // Auto-enable compaction when the residency reaches a
1498 // certain percentage of the maximum heap size (default: 30%).
1499 if (RtsFlags.GcFlags.generations > 1 &&
1500 (RtsFlags.GcFlags.compact ||
1502 oldest_gen->steps[0].n_blocks >
1503 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1504 oldest_gen->steps[0].is_compacted = 1;
1505 // debugBelch("compaction: on\n", live);
1507 oldest_gen->steps[0].is_compacted = 0;
1508 // debugBelch("compaction: off\n", live);
1511 // if we're going to go over the maximum heap size, reduce the
1512 // size of the generations accordingly. The calculation is
1513 // different if compaction is turned on, because we don't need
1514 // to double the space required to collect the old generation.
1517 // this test is necessary to ensure that the calculations
1518 // below don't have any negative results - we're working
1519 // with unsigned values here.
1520 if (max < min_alloc) {
1524 if (oldest_gen->steps[0].is_compacted) {
1525 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1526 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1529 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1530 size = (max - min_alloc) / ((gens - 1) * 2);
1540 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1541 min_alloc, size, max);
1544 for (g = 0; g < gens; g++) {
1545 generations[g].max_blocks = size;
1550 /* -----------------------------------------------------------------------------
1551 Calculate the new size of the nursery, and resize it.
1552 -------------------------------------------------------------------------- */
1555 resize_nursery (void)
1557 if (RtsFlags.GcFlags.generations == 1)
1558 { // Two-space collector:
1561 /* set up a new nursery. Allocate a nursery size based on a
1562 * function of the amount of live data (by default a factor of 2)
1563 * Use the blocks from the old nursery if possible, freeing up any
1566 * If we get near the maximum heap size, then adjust our nursery
1567 * size accordingly. If the nursery is the same size as the live
1568 * data (L), then we need 3L bytes. We can reduce the size of the
1569 * nursery to bring the required memory down near 2L bytes.
1571 * A normal 2-space collector would need 4L bytes to give the same
1572 * performance we get from 3L bytes, reducing to the same
1573 * performance at 2L bytes.
1575 blocks = g0s0->n_old_blocks;
1577 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1578 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1579 RtsFlags.GcFlags.maxHeapSize )
1581 long adjusted_blocks; // signed on purpose
1584 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1586 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1587 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1589 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1590 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1594 blocks = adjusted_blocks;
1598 blocks *= RtsFlags.GcFlags.oldGenFactor;
1599 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1601 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1604 resizeNurseries(blocks);
1606 else // Generational collector
1609 * If the user has given us a suggested heap size, adjust our
1610 * allocation area to make best use of the memory available.
1612 if (RtsFlags.GcFlags.heapSizeSuggestion)
1615 nat needed = calcNeeded(); // approx blocks needed at next GC
1617 /* Guess how much will be live in generation 0 step 0 next time.
1618 * A good approximation is obtained by finding the
1619 * percentage of g0s0 that was live at the last minor GC.
1621 * We have an accurate figure for the amount of copied data in
1622 * 'copied', but we must convert this to a number of blocks, with
1623 * a small adjustment for estimated slop at the end of a block
1628 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1629 / countNurseryBlocks();
1632 /* Estimate a size for the allocation area based on the
1633 * information available. We might end up going slightly under
1634 * or over the suggested heap size, but we should be pretty
1637 * Formula: suggested - needed
1638 * ----------------------------
1639 * 1 + g0s0_pcnt_kept/100
1641 * where 'needed' is the amount of memory needed at the next
1642 * collection for collecting all steps except g0s0.
1645 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1646 (100 + (long)g0s0_pcnt_kept);
1648 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1649 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1652 resizeNurseries((nat)blocks);
1656 // we might have added extra large blocks to the nursery, so
1657 // resize back to minAllocAreaSize again.
1658 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1663 /* -----------------------------------------------------------------------------
1664 Sanity code for CAF garbage collection.
1666 With DEBUG turned on, we manage a CAF list in addition to the SRT
1667 mechanism. After GC, we run down the CAF list and blackhole any
1668 CAFs which have been garbage collected. This means we get an error
1669 whenever the program tries to enter a garbage collected CAF.
1671 Any garbage collected CAFs are taken off the CAF list at the same
1673 -------------------------------------------------------------------------- */
1675 #if 0 && defined(DEBUG)
1682 const StgInfoTable *info;
1693 ASSERT(info->type == IND_STATIC);
1695 if (STATIC_LINK(info,p) == NULL) {
1696 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1698 SET_INFO(p,&stg_BLACKHOLE_info);
1699 p = STATIC_LINK2(info,p);
1703 pp = &STATIC_LINK2(info,p);
1710 debugTrace(DEBUG_gccafs, "%d CAFs live", i);