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);
311 // this is the main thread
312 gct = &gc_threads[0];
314 /* -----------------------------------------------------------------------
315 * follow all the roots that we know about:
316 * - mutable lists from each generation > N
317 * we want to *scavenge* these roots, not evacuate them: they're not
318 * going to move in this GC.
319 * Also do them in reverse generation order, for the usual reason:
320 * namely to reduce the likelihood of spurious old->new pointers.
323 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
324 generations[g].saved_mut_list = generations[g].mut_list;
325 generations[g].mut_list = allocBlock();
326 // mut_list always has at least one block.
328 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
329 scavenge_mutable_list(&generations[g]);
333 // follow roots from the CAF list (used by GHCi)
337 // follow all the roots that the application knows about.
341 #if defined(RTS_USER_SIGNALS)
342 // mark the signal handlers (signals should be already blocked)
343 markSignalHandlers(mark_root);
346 // Mark the weak pointer list, and prepare to detect dead weak pointers.
350 // Mark the stable pointer table.
351 markStablePtrTable(mark_root);
353 /* -------------------------------------------------------------------------
354 * Repeatedly scavenge all the areas we know about until there's no
355 * more scavenging to be done.
360 // The other threads are now stopped. We might recurse back to
361 // here, but from now on this is the only thread.
363 // if any blackholes are alive, make the threads that wait on
365 if (traverseBlackholeQueue()) {
370 // must be last... invariant is that everything is fully
371 // scavenged at this point.
372 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
377 // If we get to here, there's really nothing left to do.
381 // Update pointers from the Task list
384 // Now see which stable names are still alive.
388 // We call processHeapClosureForDead() on every closure destroyed during
389 // the current garbage collection, so we invoke LdvCensusForDead().
390 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
391 || RtsFlags.ProfFlags.bioSelector != NULL)
395 // NO MORE EVACUATION AFTER THIS POINT!
396 // Finally: compaction of the oldest generation.
397 if (major_gc && oldest_gen->steps[0].is_compacted) {
398 // save number of blocks for stats
399 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
403 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
405 // Two-space collector: free the old to-space.
406 // g0s0->old_blocks is the old nursery
407 // g0s0->blocks is to-space from the previous GC
408 if (RtsFlags.GcFlags.generations == 1) {
409 if (g0s0->blocks != NULL) {
410 freeChain(g0s0->blocks);
415 // For each workspace, in each thread:
416 // * clear the BF_EVACUATED flag from each copied block
417 // * move the copied blocks to the step
423 for (t = 0; t < n_gc_threads; t++) {
424 thr = &gc_threads[t];
426 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
427 for (s = 0; s < generations[g].n_steps; s++) {
428 ws = &thr->steps[g][s];
429 if (g==0 && s==0) continue;
432 // ASSERT( ws->scan_bd == ws->todo_bd );
433 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
435 // Push the final block
436 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
438 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
440 prev = ws->scavd_list;
441 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
442 bd->flags &= ~BF_EVACUATED; // now from-space
445 prev->link = ws->stp->blocks;
446 ws->stp->blocks = ws->scavd_list;
447 ws->stp->n_blocks += ws->n_scavd_blocks;
448 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
454 // Two-space collector: swap the semi-spaces around.
455 // Currently: g0s0->old_blocks is the old nursery
456 // g0s0->blocks is to-space from this GC
457 // We want these the other way around.
458 if (RtsFlags.GcFlags.generations == 1) {
459 bdescr *nursery_blocks = g0s0->old_blocks;
460 nat n_nursery_blocks = g0s0->n_old_blocks;
461 g0s0->old_blocks = g0s0->blocks;
462 g0s0->n_old_blocks = g0s0->n_blocks;
463 g0s0->blocks = nursery_blocks;
464 g0s0->n_blocks = n_nursery_blocks;
467 /* run through all the generations/steps and tidy up
469 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
472 generations[g].collections++; // for stats
475 // Count the mutable list as bytes "copied" for the purposes of
476 // stats. Every mutable list is copied during every GC.
478 nat mut_list_size = 0;
479 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
480 mut_list_size += bd->free - bd->start;
482 copied += mut_list_size;
485 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
486 (unsigned long)(mut_list_size * sizeof(W_)),
487 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
490 for (s = 0; s < generations[g].n_steps; s++) {
492 stp = &generations[g].steps[s];
494 // for generations we collected...
497 /* free old memory and shift to-space into from-space for all
498 * the collected steps (except the allocation area). These
499 * freed blocks will probaby be quickly recycled.
501 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
502 if (stp->is_compacted)
504 // for a compacted step, just shift the new to-space
505 // onto the front of the now-compacted existing blocks.
506 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
507 bd->flags &= ~BF_EVACUATED; // now from-space
509 // tack the new blocks on the end of the existing blocks
510 if (stp->old_blocks != NULL) {
511 for (bd = stp->old_blocks; bd != NULL; bd = next) {
512 // NB. this step might not be compacted next
513 // time, so reset the BF_COMPACTED flags.
514 // They are set before GC if we're going to
515 // compact. (search for BF_COMPACTED above).
516 bd->flags &= ~BF_COMPACTED;
519 bd->link = stp->blocks;
522 stp->blocks = stp->old_blocks;
524 // add the new blocks to the block tally
525 stp->n_blocks += stp->n_old_blocks;
526 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
530 freeChain(stp->old_blocks);
532 stp->old_blocks = NULL;
533 stp->n_old_blocks = 0;
536 /* LARGE OBJECTS. The current live large objects are chained on
537 * scavenged_large, having been moved during garbage
538 * collection from large_objects. Any objects left on
539 * large_objects list are therefore dead, so we free them here.
541 for (bd = stp->large_objects; bd != NULL; bd = next) {
547 // update the count of blocks used by large objects
548 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
549 bd->flags &= ~BF_EVACUATED;
551 stp->large_objects = stp->scavenged_large_objects;
552 stp->n_large_blocks = stp->n_scavenged_large_blocks;
555 else // for older generations...
557 /* For older generations, we need to append the
558 * scavenged_large_object list (i.e. large objects that have been
559 * promoted during this GC) to the large_object list for that step.
561 for (bd = stp->scavenged_large_objects; bd; bd = next) {
563 bd->flags &= ~BF_EVACUATED;
564 dbl_link_onto(bd, &stp->large_objects);
567 // add the new blocks we promoted during this GC
568 stp->n_large_blocks += stp->n_scavenged_large_blocks;
573 // update the max size of older generations after a major GC
574 resize_generations();
576 // Guess the amount of live data for stats.
577 live = calcLiveBlocks() * BLOCK_SIZE_W;
578 debugTrace(DEBUG_gc, "Slop: %ldKB",
579 (live - calcLiveWords()) / (1024/sizeof(W_)));
581 // Free the small objects allocated via allocate(), since this will
582 // all have been copied into G0S1 now.
583 if (RtsFlags.GcFlags.generations > 1) {
584 if (g0s0->blocks != NULL) {
585 freeChain(g0s0->blocks);
591 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
593 // Start a new pinned_object_block
594 pinned_object_block = NULL;
596 // Free the mark stack.
597 if (mark_stack_bdescr != NULL) {
598 freeGroup(mark_stack_bdescr);
602 for (g = 0; g <= N; g++) {
603 for (s = 0; s < generations[g].n_steps; s++) {
604 stp = &generations[g].steps[s];
605 if (stp->bitmap != NULL) {
606 freeGroup(stp->bitmap);
614 // mark the garbage collected CAFs as dead
615 #if 0 && defined(DEBUG) // doesn't work at the moment
616 if (major_gc) { gcCAFs(); }
620 // resetStaticObjectForRetainerProfiling() must be called before
622 resetStaticObjectForRetainerProfiling();
625 // zero the scavenged static object list
627 zero_static_object_list(scavenged_static_objects);
633 // start any pending finalizers
635 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
638 // send exceptions to any threads which were about to die
640 resurrectThreads(resurrected_threads);
643 // Update the stable pointer hash table.
644 updateStablePtrTable(major_gc);
646 // check sanity after GC
647 IF_DEBUG(sanity, checkSanity());
649 // extra GC trace info
650 IF_DEBUG(gc, statDescribeGens());
653 // symbol-table based profiling
654 /* heapCensus(to_blocks); */ /* ToDo */
657 // restore enclosing cost centre
663 // check for memory leaks if DEBUG is on
664 memInventory(traceClass(DEBUG_gc));
667 #ifdef RTS_GTK_FRONTPANEL
668 if (RtsFlags.GcFlags.frontpanel) {
669 updateFrontPanelAfterGC( N, live );
673 // ok, GC over: tell the stats department what happened.
674 stat_endGC(allocated, live, copied, N);
676 #if defined(RTS_USER_SIGNALS)
677 if (RtsFlags.MiscFlags.install_signal_handlers) {
678 // unblock signals again
679 unblockUserSignals();
688 /* -----------------------------------------------------------------------------
689 * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
690 * implicit slide i.e. after marking all sparks are at the beginning of the
691 * spark pool and the spark pool only contains sparkable closures
692 * -------------------------------------------------------------------------- */
696 markSparkQueue (evac_fn evac, Capability *cap)
698 StgClosure **sparkp, **to_sparkp;
699 nat n, pruned_sparks; // stats only
702 PAR_TICKY_MARK_SPARK_QUEUE_START();
707 pool = &(cap->r.rSparks);
709 ASSERT_SPARK_POOL_INVARIANTS(pool);
711 #if defined(PARALLEL_HASKELL)
718 to_sparkp = pool->hd;
719 while (sparkp != pool->tl) {
720 ASSERT(*sparkp!=NULL);
721 ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
722 // ToDo?: statistics gathering here (also for GUM!)
723 if (closure_SHOULD_SPARK(*sparkp)) {
725 *to_sparkp++ = *sparkp;
726 if (to_sparkp == pool->lim) {
727 to_sparkp = pool->base;
734 if (sparkp == pool->lim) {
738 pool->tl = to_sparkp;
740 PAR_TICKY_MARK_SPARK_QUEUE_END(n);
742 #if defined(PARALLEL_HASKELL)
743 debugTrace(DEBUG_sched,
744 "marked %d sparks and pruned %d sparks on [%x]",
745 n, pruned_sparks, mytid);
747 debugTrace(DEBUG_sched,
748 "marked %d sparks and pruned %d sparks",
752 debugTrace(DEBUG_sched,
753 "new spark queue len=%d; (hd=%p; tl=%p)\n",
754 sparkPoolSize(pool), pool->hd, pool->tl);
758 /* ---------------------------------------------------------------------------
759 Where are the roots that we know about?
761 - all the threads on the runnable queue
762 - all the threads on the blocked queue
763 - all the threads on the sleeping queue
764 - all the thread currently executing a _ccall_GC
765 - all the "main threads"
767 ------------------------------------------------------------------------ */
770 GetRoots( evac_fn evac )
776 // Each GC thread is responsible for following roots from the
777 // Capability of the same number. There will usually be the same
778 // or fewer Capabilities as GC threads, but just in case there
779 // are more, we mark every Capability whose number is the GC
780 // thread's index plus a multiple of the number of GC threads.
781 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
782 cap = &capabilities[i];
783 evac((StgClosure **)(void *)&cap->run_queue_hd);
784 evac((StgClosure **)(void *)&cap->run_queue_tl);
785 #if defined(THREADED_RTS)
786 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
787 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
789 for (task = cap->suspended_ccalling_tasks; task != NULL;
791 debugTrace(DEBUG_sched,
792 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
793 evac((StgClosure **)(void *)&task->suspended_tso);
796 #if defined(THREADED_RTS)
797 markSparkQueue(evac,cap);
801 #if !defined(THREADED_RTS)
802 evac((StgClosure **)(void *)&blocked_queue_hd);
803 evac((StgClosure **)(void *)&blocked_queue_tl);
804 evac((StgClosure **)(void *)&sleeping_queue);
808 /* -----------------------------------------------------------------------------
809 isAlive determines whether the given closure is still alive (after
810 a garbage collection) or not. It returns the new address of the
811 closure if it is alive, or NULL otherwise.
813 NOTE: Use it before compaction only!
814 It untags and (if needed) retags pointers to closures.
815 -------------------------------------------------------------------------- */
819 isAlive(StgClosure *p)
821 const StgInfoTable *info;
827 /* The tag and the pointer are split, to be merged later when needed. */
828 tag = GET_CLOSURE_TAG(p);
829 q = UNTAG_CLOSURE(p);
831 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
834 // ignore static closures
836 // ToDo: for static closures, check the static link field.
837 // Problem here is that we sometimes don't set the link field, eg.
838 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
840 if (!HEAP_ALLOCED(q)) {
844 // ignore closures in generations that we're not collecting.
846 if (bd->gen_no > N) {
850 // if it's a pointer into to-space, then we're done
851 if (bd->flags & BF_EVACUATED) {
855 // large objects use the evacuated flag
856 if (bd->flags & BF_LARGE) {
860 // check the mark bit for compacted steps
861 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
865 switch (info->type) {
870 case IND_OLDGEN: // rely on compatible layout with StgInd
871 case IND_OLDGEN_PERM:
872 // follow indirections
873 p = ((StgInd *)q)->indirectee;
878 return ((StgEvacuated *)q)->evacuee;
881 if (((StgTSO *)q)->what_next == ThreadRelocated) {
882 p = (StgClosure *)((StgTSO *)q)->link;
894 /* -----------------------------------------------------------------------------
895 Figure out which generation to collect, initialise N and major_gc.
896 -------------------------------------------------------------------------- */
899 initialise_N (rtsBool force_major_gc)
903 if (force_major_gc) {
904 N = RtsFlags.GcFlags.generations - 1;
908 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
909 if (generations[g].steps[0].n_blocks +
910 generations[g].steps[0].n_large_blocks
911 >= generations[g].max_blocks) {
915 major_gc = (N == RtsFlags.GcFlags.generations-1);
919 /* -----------------------------------------------------------------------------
920 Initialise the gc_thread structures.
921 -------------------------------------------------------------------------- */
924 alloc_gc_thread (gc_thread *t, int n)
931 initCondition(&t->wake_cond);
932 initMutex(&t->wake_mutex);
933 t->wakeup = rtsFalse;
938 t->free_blocks = NULL;
947 t->steps = stgMallocBytes(RtsFlags.GcFlags.generations *
948 sizeof(step_workspace *),
949 "initialise_gc_thread");
951 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
953 t->steps[g] = stgMallocBytes(generations[g].n_steps *
954 sizeof(step_workspace),
955 "initialise_gc_thread/2");
957 for (s = 0; s < generations[g].n_steps; s++)
959 ws = &t->steps[g][s];
960 ws->stp = &generations[g].steps[s];
967 ws->buffer_todo_bd = NULL;
969 ws->scavd_list = NULL;
970 ws->n_scavd_blocks = 0;
977 alloc_gc_threads (void)
979 if (gc_threads == NULL) {
980 #if defined(THREADED_RTS)
982 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
986 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
987 alloc_gc_thread(&gc_threads[i], i);
990 gc_threads = stgMallocBytes (sizeof(gc_thread),
993 alloc_gc_thread(gc_threads, 0);
998 /* ----------------------------------------------------------------------------
1000 ------------------------------------------------------------------------- */
1002 static nat gc_running_threads;
1004 #if defined(THREADED_RTS)
1005 static Mutex gc_running_mutex;
1012 ACQUIRE_LOCK(&gc_running_mutex);
1013 n_running = ++gc_running_threads;
1014 RELEASE_LOCK(&gc_running_mutex);
1022 ACQUIRE_LOCK(&gc_running_mutex);
1023 n_running = --gc_running_threads;
1024 RELEASE_LOCK(&gc_running_mutex);
1029 // gc_thread_work(): Scavenge until there's no work left to do and all
1030 // the running threads are idle.
1033 gc_thread_work (void)
1037 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1039 // gc_running_threads has already been incremented for us; either
1040 // this is the main thread and we incremented it inside
1041 // GarbageCollect(), or this is a worker thread and the main
1042 // thread bumped gc_running_threads before waking us up.
1044 // Every thread evacuates some roots.
1046 GetRoots(mark_root);
1050 // scavenge_loop() only exits when there's no work to do
1053 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1054 gct->thread_index, r);
1056 while (gc_running_threads != 0) {
1061 // any_work() does not remove the work from the queue, it
1062 // just checks for the presence of work. If we find any,
1063 // then we increment gc_running_threads and go back to
1064 // scavenge_loop() to perform any pending work.
1067 // All threads are now stopped
1068 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1072 #if defined(THREADED_RTS)
1074 gc_thread_mainloop (void)
1076 while (!gct->exit) {
1078 // Wait until we're told to wake up
1079 ACQUIRE_LOCK(&gct->wake_mutex);
1080 while (!gct->wakeup) {
1081 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1083 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1085 RELEASE_LOCK(&gct->wake_mutex);
1086 gct->wakeup = rtsFalse;
1087 if (gct->exit) break;
1090 // start performance counters in this thread...
1091 if (gct->papi_events == -1) {
1092 papi_init_eventset(&gct->papi_events);
1094 papi_thread_start_gc1_count(gct->papi_events);
1100 // count events in this thread towards the GC totals
1101 papi_thread_stop_gc1_count(gct->papi_events);
1107 #if defined(THREADED_RTS)
1109 gc_thread_entry (gc_thread *my_gct)
1112 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1113 gct->id = osThreadId();
1114 gc_thread_mainloop();
1119 start_gc_threads (void)
1121 #if defined(THREADED_RTS)
1124 static rtsBool done = rtsFalse;
1126 gc_running_threads = 0;
1127 initMutex(&gc_running_mutex);
1130 // Start from 1: the main thread is 0
1131 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1132 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1141 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1143 #if defined(THREADED_RTS)
1145 for (i=1; i < n_threads; i++) {
1147 ACQUIRE_LOCK(&gc_threads[i].wake_mutex);
1148 gc_threads[i].wakeup = rtsTrue;
1149 signalCondition(&gc_threads[i].wake_cond);
1150 RELEASE_LOCK(&gc_threads[i].wake_mutex);
1155 /* ----------------------------------------------------------------------------
1156 Initialise a generation that is to be collected
1157 ------------------------------------------------------------------------- */
1160 init_collected_gen (nat g, nat n_threads)
1167 // Throw away the current mutable list. Invariant: the mutable
1168 // list always has at least one block; this means we can avoid a
1169 // check for NULL in recordMutable().
1171 freeChain(generations[g].mut_list);
1172 generations[g].mut_list = allocBlock();
1173 for (i = 0; i < n_capabilities; i++) {
1174 freeChain(capabilities[i].mut_lists[g]);
1175 capabilities[i].mut_lists[g] = allocBlock();
1179 for (s = 0; s < generations[g].n_steps; s++) {
1181 // generation 0, step 0 doesn't need to-space
1182 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1186 stp = &generations[g].steps[s];
1187 ASSERT(stp->gen_no == g);
1189 // deprecate the existing blocks
1190 stp->old_blocks = stp->blocks;
1191 stp->n_old_blocks = stp->n_blocks;
1195 // we don't have any to-be-scavenged blocks yet
1199 // initialise the large object queues.
1200 stp->scavenged_large_objects = NULL;
1201 stp->n_scavenged_large_blocks = 0;
1203 // mark the large objects as not evacuated yet
1204 for (bd = stp->large_objects; bd; bd = bd->link) {
1205 bd->flags &= ~BF_EVACUATED;
1208 // for a compacted step, we need to allocate the bitmap
1209 if (stp->is_compacted) {
1210 nat bitmap_size; // in bytes
1211 bdescr *bitmap_bdescr;
1214 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1216 if (bitmap_size > 0) {
1217 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1219 stp->bitmap = bitmap_bdescr;
1220 bitmap = bitmap_bdescr->start;
1222 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1223 bitmap_size, bitmap);
1225 // don't forget to fill it with zeros!
1226 memset(bitmap, 0, bitmap_size);
1228 // For each block in this step, point to its bitmap from the
1229 // block descriptor.
1230 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1231 bd->u.bitmap = bitmap;
1232 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1234 // Also at this point we set the BF_COMPACTED flag
1235 // for this block. The invariant is that
1236 // BF_COMPACTED is always unset, except during GC
1237 // when it is set on those blocks which will be
1239 bd->flags |= BF_COMPACTED;
1245 // For each GC thread, for each step, allocate a "todo" block to
1246 // store evacuated objects to be scavenged, and a block to store
1247 // evacuated objects that do not need to be scavenged.
1248 for (t = 0; t < n_threads; t++) {
1249 for (s = 0; s < generations[g].n_steps; s++) {
1251 // we don't copy objects into g0s0, unless -G0
1252 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1254 ws = &gc_threads[t].steps[g][s];
1259 ws->todo_large_objects = NULL;
1261 // allocate the first to-space block; extra blocks will be
1262 // chained on as necessary.
1264 ws->buffer_todo_bd = NULL;
1265 gc_alloc_todo_block(ws);
1267 ws->scavd_list = NULL;
1268 ws->n_scavd_blocks = 0;
1274 /* ----------------------------------------------------------------------------
1275 Initialise a generation that is *not* to be collected
1276 ------------------------------------------------------------------------- */
1279 init_uncollected_gen (nat g, nat threads)
1286 for (s = 0; s < generations[g].n_steps; s++) {
1287 stp = &generations[g].steps[s];
1288 stp->scavenged_large_objects = NULL;
1289 stp->n_scavenged_large_blocks = 0;
1292 for (t = 0; t < threads; t++) {
1293 for (s = 0; s < generations[g].n_steps; s++) {
1295 ws = &gc_threads[t].steps[g][s];
1298 ws->buffer_todo_bd = NULL;
1299 ws->todo_large_objects = NULL;
1301 ws->scavd_list = NULL;
1302 ws->n_scavd_blocks = 0;
1304 // If the block at the head of the list in this generation
1305 // is less than 3/4 full, then use it as a todo block.
1306 if (stp->blocks && isPartiallyFull(stp->blocks))
1308 ws->todo_bd = stp->blocks;
1309 ws->todo_free = ws->todo_bd->free;
1310 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1311 stp->blocks = stp->blocks->link;
1313 ws->todo_bd->link = NULL;
1315 // this block is also the scan block; we must scan
1316 // from the current end point.
1317 ws->scan_bd = ws->todo_bd;
1318 ws->scan = ws->scan_bd->free;
1320 // subtract the contents of this block from the stats,
1321 // because we'll count the whole block later.
1322 copied -= ws->scan_bd->free - ws->scan_bd->start;
1329 gc_alloc_todo_block(ws);
1334 // Move the private mutable lists from each capability onto the
1335 // main mutable list for the generation.
1336 for (i = 0; i < n_capabilities; i++) {
1337 for (bd = capabilities[i].mut_lists[g];
1338 bd->link != NULL; bd = bd->link) {
1341 bd->link = generations[g].mut_list;
1342 generations[g].mut_list = capabilities[i].mut_lists[g];
1343 capabilities[i].mut_lists[g] = allocBlock();
1347 /* -----------------------------------------------------------------------------
1348 Initialise a gc_thread before GC
1349 -------------------------------------------------------------------------- */
1352 init_gc_thread (gc_thread *t)
1355 t->failed_to_evac = rtsFalse;
1356 t->eager_promotion = rtsTrue;
1357 t->thunk_selector_depth = 0;
1360 /* -----------------------------------------------------------------------------
1361 Function we pass to GetRoots to evacuate roots.
1362 -------------------------------------------------------------------------- */
1365 mark_root(StgClosure **root)
1370 /* -----------------------------------------------------------------------------
1371 Initialising the static object & mutable lists
1372 -------------------------------------------------------------------------- */
1375 zero_static_object_list(StgClosure* first_static)
1379 const StgInfoTable *info;
1381 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1383 link = *STATIC_LINK(info, p);
1384 *STATIC_LINK(info,p) = NULL;
1388 /* -----------------------------------------------------------------------------
1390 -------------------------------------------------------------------------- */
1397 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1398 c = (StgIndStatic *)c->static_link)
1400 SET_INFO(c, c->saved_info);
1401 c->saved_info = NULL;
1402 // could, but not necessary: c->static_link = NULL;
1404 revertible_caf_list = NULL;
1408 markCAFs( evac_fn evac )
1412 for (c = (StgIndStatic *)caf_list; c != NULL;
1413 c = (StgIndStatic *)c->static_link)
1415 evac(&c->indirectee);
1417 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1418 c = (StgIndStatic *)c->static_link)
1420 evac(&c->indirectee);
1424 /* ----------------------------------------------------------------------------
1425 Update the pointers from the task list
1427 These are treated as weak pointers because we want to allow a main
1428 thread to get a BlockedOnDeadMVar exception in the same way as any
1429 other thread. Note that the threads should all have been retained
1430 by GC by virtue of being on the all_threads list, we're just
1431 updating pointers here.
1432 ------------------------------------------------------------------------- */
1435 update_task_list (void)
1439 for (task = all_tasks; task != NULL; task = task->all_link) {
1440 if (!task->stopped && task->tso) {
1441 ASSERT(task->tso->bound == task);
1442 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1444 barf("task %p: main thread %d has been GC'd",
1457 /* ----------------------------------------------------------------------------
1458 Reset the sizes of the older generations when we do a major
1461 CURRENT STRATEGY: make all generations except zero the same size.
1462 We have to stay within the maximum heap size, and leave a certain
1463 percentage of the maximum heap size available to allocate into.
1464 ------------------------------------------------------------------------- */
1467 resize_generations (void)
1471 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1472 nat live, size, min_alloc;
1473 nat max = RtsFlags.GcFlags.maxHeapSize;
1474 nat gens = RtsFlags.GcFlags.generations;
1476 // live in the oldest generations
1477 live = oldest_gen->steps[0].n_blocks +
1478 oldest_gen->steps[0].n_large_blocks;
1480 // default max size for all generations except zero
1481 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1482 RtsFlags.GcFlags.minOldGenSize);
1484 // minimum size for generation zero
1485 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1486 RtsFlags.GcFlags.minAllocAreaSize);
1488 // Auto-enable compaction when the residency reaches a
1489 // certain percentage of the maximum heap size (default: 30%).
1490 if (RtsFlags.GcFlags.generations > 1 &&
1491 (RtsFlags.GcFlags.compact ||
1493 oldest_gen->steps[0].n_blocks >
1494 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1495 oldest_gen->steps[0].is_compacted = 1;
1496 // debugBelch("compaction: on\n", live);
1498 oldest_gen->steps[0].is_compacted = 0;
1499 // debugBelch("compaction: off\n", live);
1502 // if we're going to go over the maximum heap size, reduce the
1503 // size of the generations accordingly. The calculation is
1504 // different if compaction is turned on, because we don't need
1505 // to double the space required to collect the old generation.
1508 // this test is necessary to ensure that the calculations
1509 // below don't have any negative results - we're working
1510 // with unsigned values here.
1511 if (max < min_alloc) {
1515 if (oldest_gen->steps[0].is_compacted) {
1516 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1517 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1520 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1521 size = (max - min_alloc) / ((gens - 1) * 2);
1531 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1532 min_alloc, size, max);
1535 for (g = 0; g < gens; g++) {
1536 generations[g].max_blocks = size;
1541 /* -----------------------------------------------------------------------------
1542 Calculate the new size of the nursery, and resize it.
1543 -------------------------------------------------------------------------- */
1546 resize_nursery (void)
1548 if (RtsFlags.GcFlags.generations == 1)
1549 { // Two-space collector:
1552 /* set up a new nursery. Allocate a nursery size based on a
1553 * function of the amount of live data (by default a factor of 2)
1554 * Use the blocks from the old nursery if possible, freeing up any
1557 * If we get near the maximum heap size, then adjust our nursery
1558 * size accordingly. If the nursery is the same size as the live
1559 * data (L), then we need 3L bytes. We can reduce the size of the
1560 * nursery to bring the required memory down near 2L bytes.
1562 * A normal 2-space collector would need 4L bytes to give the same
1563 * performance we get from 3L bytes, reducing to the same
1564 * performance at 2L bytes.
1566 blocks = g0s0->n_old_blocks;
1568 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1569 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1570 RtsFlags.GcFlags.maxHeapSize )
1572 long adjusted_blocks; // signed on purpose
1575 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1577 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1578 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1580 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1581 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1585 blocks = adjusted_blocks;
1589 blocks *= RtsFlags.GcFlags.oldGenFactor;
1590 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1592 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1595 resizeNurseries(blocks);
1597 else // Generational collector
1600 * If the user has given us a suggested heap size, adjust our
1601 * allocation area to make best use of the memory available.
1603 if (RtsFlags.GcFlags.heapSizeSuggestion)
1606 nat needed = calcNeeded(); // approx blocks needed at next GC
1608 /* Guess how much will be live in generation 0 step 0 next time.
1609 * A good approximation is obtained by finding the
1610 * percentage of g0s0 that was live at the last minor GC.
1612 * We have an accurate figure for the amount of copied data in
1613 * 'copied', but we must convert this to a number of blocks, with
1614 * a small adjustment for estimated slop at the end of a block
1619 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1620 / countNurseryBlocks();
1623 /* Estimate a size for the allocation area based on the
1624 * information available. We might end up going slightly under
1625 * or over the suggested heap size, but we should be pretty
1628 * Formula: suggested - needed
1629 * ----------------------------
1630 * 1 + g0s0_pcnt_kept/100
1632 * where 'needed' is the amount of memory needed at the next
1633 * collection for collecting all steps except g0s0.
1636 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1637 (100 + (long)g0s0_pcnt_kept);
1639 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1640 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1643 resizeNurseries((nat)blocks);
1647 // we might have added extra large blocks to the nursery, so
1648 // resize back to minAllocAreaSize again.
1649 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1654 /* -----------------------------------------------------------------------------
1655 Sanity code for CAF garbage collection.
1657 With DEBUG turned on, we manage a CAF list in addition to the SRT
1658 mechanism. After GC, we run down the CAF list and blackhole any
1659 CAFs which have been garbage collected. This means we get an error
1660 whenever the program tries to enter a garbage collected CAF.
1662 Any garbage collected CAFs are taken off the CAF list at the same
1664 -------------------------------------------------------------------------- */
1666 #if 0 && defined(DEBUG)
1673 const StgInfoTable *info;
1684 ASSERT(info->type == IND_STATIC);
1686 if (STATIC_LINK(info,p) == NULL) {
1687 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1689 SET_INFO(p,&stg_BLACKHOLE_info);
1690 p = STATIC_LINK2(info,p);
1694 pp = &STATIC_LINK2(info,p);
1701 debugTrace(DEBUG_gccafs, "%d CAFs live", i);