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
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++) {
427 for (s = 1; s < total_steps; s++) {
430 // ASSERT( ws->scan_bd == ws->todo_bd );
431 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
433 // Push the final block
434 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
436 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
438 prev = ws->scavd_list;
439 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
440 bd->flags &= ~BF_EVACUATED; // now from-space
443 prev->link = ws->stp->blocks;
444 ws->stp->blocks = ws->scavd_list;
445 ws->stp->n_blocks += ws->n_scavd_blocks;
446 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
451 // Two-space collector: swap the semi-spaces around.
452 // Currently: g0s0->old_blocks is the old nursery
453 // g0s0->blocks is to-space from this GC
454 // We want these the other way around.
455 if (RtsFlags.GcFlags.generations == 1) {
456 bdescr *nursery_blocks = g0s0->old_blocks;
457 nat n_nursery_blocks = g0s0->n_old_blocks;
458 g0s0->old_blocks = g0s0->blocks;
459 g0s0->n_old_blocks = g0s0->n_blocks;
460 g0s0->blocks = nursery_blocks;
461 g0s0->n_blocks = n_nursery_blocks;
464 /* run through all the generations/steps and tidy up
466 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
469 generations[g].collections++; // for stats
472 // Count the mutable list as bytes "copied" for the purposes of
473 // stats. Every mutable list is copied during every GC.
475 nat mut_list_size = 0;
476 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
477 mut_list_size += bd->free - bd->start;
479 copied += mut_list_size;
482 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
483 (unsigned long)(mut_list_size * sizeof(W_)),
484 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
487 for (s = 0; s < generations[g].n_steps; s++) {
489 stp = &generations[g].steps[s];
491 // for generations we collected...
494 /* free old memory and shift to-space into from-space for all
495 * the collected steps (except the allocation area). These
496 * freed blocks will probaby be quickly recycled.
498 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
499 if (stp->is_compacted)
501 // for a compacted step, just shift the new to-space
502 // onto the front of the now-compacted existing blocks.
503 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
504 bd->flags &= ~BF_EVACUATED; // now from-space
506 // tack the new blocks on the end of the existing blocks
507 if (stp->old_blocks != NULL) {
508 for (bd = stp->old_blocks; bd != NULL; bd = next) {
509 // NB. this step might not be compacted next
510 // time, so reset the BF_COMPACTED flags.
511 // They are set before GC if we're going to
512 // compact. (search for BF_COMPACTED above).
513 bd->flags &= ~BF_COMPACTED;
516 bd->link = stp->blocks;
519 stp->blocks = stp->old_blocks;
521 // add the new blocks to the block tally
522 stp->n_blocks += stp->n_old_blocks;
523 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
527 freeChain(stp->old_blocks);
529 stp->old_blocks = NULL;
530 stp->n_old_blocks = 0;
533 /* LARGE OBJECTS. The current live large objects are chained on
534 * scavenged_large, having been moved during garbage
535 * collection from large_objects. Any objects left on
536 * large_objects list are therefore dead, so we free them here.
538 for (bd = stp->large_objects; bd != NULL; bd = next) {
544 // update the count of blocks used by large objects
545 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
546 bd->flags &= ~BF_EVACUATED;
548 stp->large_objects = stp->scavenged_large_objects;
549 stp->n_large_blocks = stp->n_scavenged_large_blocks;
552 else // for older generations...
554 /* For older generations, we need to append the
555 * scavenged_large_object list (i.e. large objects that have been
556 * promoted during this GC) to the large_object list for that step.
558 for (bd = stp->scavenged_large_objects; bd; bd = next) {
560 bd->flags &= ~BF_EVACUATED;
561 dbl_link_onto(bd, &stp->large_objects);
564 // add the new blocks we promoted during this GC
565 stp->n_large_blocks += stp->n_scavenged_large_blocks;
570 // update the max size of older generations after a major GC
571 resize_generations();
573 // Guess the amount of live data for stats.
574 live = calcLiveBlocks() * BLOCK_SIZE_W;
575 debugTrace(DEBUG_gc, "Slop: %ldKB",
576 (live - calcLiveWords()) / (1024/sizeof(W_)));
578 // Free the small objects allocated via allocate(), since this will
579 // all have been copied into G0S1 now.
580 if (RtsFlags.GcFlags.generations > 1) {
581 if (g0s0->blocks != NULL) {
582 freeChain(g0s0->blocks);
588 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
590 // Start a new pinned_object_block
591 pinned_object_block = NULL;
593 // Free the mark stack.
594 if (mark_stack_bdescr != NULL) {
595 freeGroup(mark_stack_bdescr);
599 for (g = 0; g <= N; g++) {
600 for (s = 0; s < generations[g].n_steps; s++) {
601 stp = &generations[g].steps[s];
602 if (stp->bitmap != NULL) {
603 freeGroup(stp->bitmap);
611 // mark the garbage collected CAFs as dead
612 #if 0 && defined(DEBUG) // doesn't work at the moment
613 if (major_gc) { gcCAFs(); }
617 // resetStaticObjectForRetainerProfiling() must be called before
619 resetStaticObjectForRetainerProfiling();
622 // zero the scavenged static object list
624 zero_static_object_list(scavenged_static_objects);
630 // start any pending finalizers
632 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
635 // send exceptions to any threads which were about to die
637 resurrectThreads(resurrected_threads);
640 // Update the stable pointer hash table.
641 updateStablePtrTable(major_gc);
643 // check sanity after GC
644 IF_DEBUG(sanity, checkSanity());
646 // extra GC trace info
647 IF_DEBUG(gc, statDescribeGens());
650 // symbol-table based profiling
651 /* heapCensus(to_blocks); */ /* ToDo */
654 // restore enclosing cost centre
660 // check for memory leaks if DEBUG is on
661 memInventory(traceClass(DEBUG_gc));
664 #ifdef RTS_GTK_FRONTPANEL
665 if (RtsFlags.GcFlags.frontpanel) {
666 updateFrontPanelAfterGC( N, live );
670 // ok, GC over: tell the stats department what happened.
671 stat_endGC(allocated, live, copied, N);
673 #if defined(RTS_USER_SIGNALS)
674 if (RtsFlags.MiscFlags.install_signal_handlers) {
675 // unblock signals again
676 unblockUserSignals();
685 /* -----------------------------------------------------------------------------
686 * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
687 * implicit slide i.e. after marking all sparks are at the beginning of the
688 * spark pool and the spark pool only contains sparkable closures
689 * -------------------------------------------------------------------------- */
693 markSparkQueue (evac_fn evac, Capability *cap)
695 StgClosure **sparkp, **to_sparkp;
696 nat n, pruned_sparks; // stats only
699 PAR_TICKY_MARK_SPARK_QUEUE_START();
704 pool = &(cap->r.rSparks);
706 ASSERT_SPARK_POOL_INVARIANTS(pool);
708 #if defined(PARALLEL_HASKELL)
715 to_sparkp = pool->hd;
716 while (sparkp != pool->tl) {
717 ASSERT(*sparkp!=NULL);
718 ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
719 // ToDo?: statistics gathering here (also for GUM!)
720 if (closure_SHOULD_SPARK(*sparkp)) {
722 *to_sparkp++ = *sparkp;
723 if (to_sparkp == pool->lim) {
724 to_sparkp = pool->base;
731 if (sparkp == pool->lim) {
735 pool->tl = to_sparkp;
737 PAR_TICKY_MARK_SPARK_QUEUE_END(n);
739 #if defined(PARALLEL_HASKELL)
740 debugTrace(DEBUG_sched,
741 "marked %d sparks and pruned %d sparks on [%x]",
742 n, pruned_sparks, mytid);
744 debugTrace(DEBUG_sched,
745 "marked %d sparks and pruned %d sparks",
749 debugTrace(DEBUG_sched,
750 "new spark queue len=%d; (hd=%p; tl=%p)\n",
751 sparkPoolSize(pool), pool->hd, pool->tl);
755 /* ---------------------------------------------------------------------------
756 Where are the roots that we know about?
758 - all the threads on the runnable queue
759 - all the threads on the blocked queue
760 - all the threads on the sleeping queue
761 - all the thread currently executing a _ccall_GC
762 - all the "main threads"
764 ------------------------------------------------------------------------ */
767 GetRoots( evac_fn evac )
773 // Each GC thread is responsible for following roots from the
774 // Capability of the same number. There will usually be the same
775 // or fewer Capabilities as GC threads, but just in case there
776 // are more, we mark every Capability whose number is the GC
777 // thread's index plus a multiple of the number of GC threads.
778 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
779 cap = &capabilities[i];
780 evac((StgClosure **)(void *)&cap->run_queue_hd);
781 evac((StgClosure **)(void *)&cap->run_queue_tl);
782 #if defined(THREADED_RTS)
783 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
784 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
786 for (task = cap->suspended_ccalling_tasks; task != NULL;
788 debugTrace(DEBUG_sched,
789 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
790 evac((StgClosure **)(void *)&task->suspended_tso);
793 #if defined(THREADED_RTS)
794 markSparkQueue(evac,cap);
798 #if !defined(THREADED_RTS)
799 evac((StgClosure **)(void *)&blocked_queue_hd);
800 evac((StgClosure **)(void *)&blocked_queue_tl);
801 evac((StgClosure **)(void *)&sleeping_queue);
805 /* -----------------------------------------------------------------------------
806 isAlive determines whether the given closure is still alive (after
807 a garbage collection) or not. It returns the new address of the
808 closure if it is alive, or NULL otherwise.
810 NOTE: Use it before compaction only!
811 It untags and (if needed) retags pointers to closures.
812 -------------------------------------------------------------------------- */
816 isAlive(StgClosure *p)
818 const StgInfoTable *info;
824 /* The tag and the pointer are split, to be merged later when needed. */
825 tag = GET_CLOSURE_TAG(p);
826 q = UNTAG_CLOSURE(p);
828 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
831 // ignore static closures
833 // ToDo: for static closures, check the static link field.
834 // Problem here is that we sometimes don't set the link field, eg.
835 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
837 if (!HEAP_ALLOCED(q)) {
841 // ignore closures in generations that we're not collecting.
843 if (bd->gen_no > N) {
847 // if it's a pointer into to-space, then we're done
848 if (bd->flags & BF_EVACUATED) {
852 // large objects use the evacuated flag
853 if (bd->flags & BF_LARGE) {
857 // check the mark bit for compacted steps
858 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
862 switch (info->type) {
867 case IND_OLDGEN: // rely on compatible layout with StgInd
868 case IND_OLDGEN_PERM:
869 // follow indirections
870 p = ((StgInd *)q)->indirectee;
875 return ((StgEvacuated *)q)->evacuee;
878 if (((StgTSO *)q)->what_next == ThreadRelocated) {
879 p = (StgClosure *)((StgTSO *)q)->link;
891 /* -----------------------------------------------------------------------------
892 Figure out which generation to collect, initialise N and major_gc.
893 -------------------------------------------------------------------------- */
896 initialise_N (rtsBool force_major_gc)
900 if (force_major_gc) {
901 N = RtsFlags.GcFlags.generations - 1;
905 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
906 if (generations[g].steps[0].n_blocks +
907 generations[g].steps[0].n_large_blocks
908 >= generations[g].max_blocks) {
912 major_gc = (N == RtsFlags.GcFlags.generations-1);
916 /* -----------------------------------------------------------------------------
917 Initialise the gc_thread structures.
918 -------------------------------------------------------------------------- */
921 alloc_gc_thread (int n)
927 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
932 initCondition(&t->wake_cond);
933 initMutex(&t->wake_mutex);
934 t->wakeup = rtsFalse;
939 t->free_blocks = NULL;
948 for (s = 0; s < total_steps; s++)
951 ws->stp = &all_steps[s];
952 ASSERT(s == ws->stp->abs_no);
959 ws->buffer_todo_bd = NULL;
961 ws->scavd_list = NULL;
962 ws->n_scavd_blocks = 0;
970 alloc_gc_threads (void)
972 if (gc_threads == NULL) {
973 #if defined(THREADED_RTS)
975 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
979 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
980 gc_threads[i] = alloc_gc_thread(i);
983 gc_threads = stgMallocBytes (sizeof(gc_thread*),
986 gc_threads[0] = alloc_gc_thread(0);
991 /* ----------------------------------------------------------------------------
993 ------------------------------------------------------------------------- */
995 static nat gc_running_threads;
997 #if defined(THREADED_RTS)
998 static Mutex gc_running_mutex;
1005 ACQUIRE_LOCK(&gc_running_mutex);
1006 n_running = ++gc_running_threads;
1007 RELEASE_LOCK(&gc_running_mutex);
1015 ACQUIRE_LOCK(&gc_running_mutex);
1016 n_running = --gc_running_threads;
1017 RELEASE_LOCK(&gc_running_mutex);
1022 // gc_thread_work(): Scavenge until there's no work left to do and all
1023 // the running threads are idle.
1026 gc_thread_work (void)
1030 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1032 // gc_running_threads has already been incremented for us; either
1033 // this is the main thread and we incremented it inside
1034 // GarbageCollect(), or this is a worker thread and the main
1035 // thread bumped gc_running_threads before waking us up.
1037 // Every thread evacuates some roots.
1039 GetRoots(mark_root);
1043 // scavenge_loop() only exits when there's no work to do
1046 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1047 gct->thread_index, r);
1049 while (gc_running_threads != 0) {
1054 // any_work() does not remove the work from the queue, it
1055 // just checks for the presence of work. If we find any,
1056 // then we increment gc_running_threads and go back to
1057 // scavenge_loop() to perform any pending work.
1060 // All threads are now stopped
1061 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1065 #if defined(THREADED_RTS)
1067 gc_thread_mainloop (void)
1069 while (!gct->exit) {
1071 // Wait until we're told to wake up
1072 ACQUIRE_LOCK(&gct->wake_mutex);
1073 while (!gct->wakeup) {
1074 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1076 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1078 RELEASE_LOCK(&gct->wake_mutex);
1079 gct->wakeup = rtsFalse;
1080 if (gct->exit) break;
1083 // start performance counters in this thread...
1084 if (gct->papi_events == -1) {
1085 papi_init_eventset(&gct->papi_events);
1087 papi_thread_start_gc1_count(gct->papi_events);
1093 // count events in this thread towards the GC totals
1094 papi_thread_stop_gc1_count(gct->papi_events);
1100 #if defined(THREADED_RTS)
1102 gc_thread_entry (gc_thread *my_gct)
1105 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1106 gct->id = osThreadId();
1107 gc_thread_mainloop();
1112 start_gc_threads (void)
1114 #if defined(THREADED_RTS)
1117 static rtsBool done = rtsFalse;
1119 gc_running_threads = 0;
1120 initMutex(&gc_running_mutex);
1123 // Start from 1: the main thread is 0
1124 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1125 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1134 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1136 #if defined(THREADED_RTS)
1138 for (i=1; i < n_threads; i++) {
1140 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1141 gc_threads[i]->wakeup = rtsTrue;
1142 signalCondition(&gc_threads[i]->wake_cond);
1143 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1148 /* ----------------------------------------------------------------------------
1149 Initialise a generation that is to be collected
1150 ------------------------------------------------------------------------- */
1153 init_collected_gen (nat g, nat n_threads)
1160 // Throw away the current mutable list. Invariant: the mutable
1161 // list always has at least one block; this means we can avoid a
1162 // check for NULL in recordMutable().
1164 freeChain(generations[g].mut_list);
1165 generations[g].mut_list = allocBlock();
1166 for (i = 0; i < n_capabilities; i++) {
1167 freeChain(capabilities[i].mut_lists[g]);
1168 capabilities[i].mut_lists[g] = allocBlock();
1172 for (s = 0; s < generations[g].n_steps; s++) {
1174 // generation 0, step 0 doesn't need to-space
1175 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1179 stp = &generations[g].steps[s];
1180 ASSERT(stp->gen_no == g);
1182 // deprecate the existing blocks
1183 stp->old_blocks = stp->blocks;
1184 stp->n_old_blocks = stp->n_blocks;
1188 // we don't have any to-be-scavenged blocks yet
1192 // initialise the large object queues.
1193 stp->scavenged_large_objects = NULL;
1194 stp->n_scavenged_large_blocks = 0;
1196 // mark the large objects as not evacuated yet
1197 for (bd = stp->large_objects; bd; bd = bd->link) {
1198 bd->flags &= ~BF_EVACUATED;
1201 // for a compacted step, we need to allocate the bitmap
1202 if (stp->is_compacted) {
1203 nat bitmap_size; // in bytes
1204 bdescr *bitmap_bdescr;
1207 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1209 if (bitmap_size > 0) {
1210 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1212 stp->bitmap = bitmap_bdescr;
1213 bitmap = bitmap_bdescr->start;
1215 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1216 bitmap_size, bitmap);
1218 // don't forget to fill it with zeros!
1219 memset(bitmap, 0, bitmap_size);
1221 // For each block in this step, point to its bitmap from the
1222 // block descriptor.
1223 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1224 bd->u.bitmap = bitmap;
1225 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1227 // Also at this point we set the BF_COMPACTED flag
1228 // for this block. The invariant is that
1229 // BF_COMPACTED is always unset, except during GC
1230 // when it is set on those blocks which will be
1232 bd->flags |= BF_COMPACTED;
1238 // For each GC thread, for each step, allocate a "todo" block to
1239 // store evacuated objects to be scavenged, and a block to store
1240 // evacuated objects that do not need to be scavenged.
1241 for (t = 0; t < n_threads; t++) {
1242 for (s = 0; s < generations[g].n_steps; s++) {
1244 // we don't copy objects into g0s0, unless -G0
1245 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1247 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1252 ws->todo_large_objects = NULL;
1254 // allocate the first to-space block; extra blocks will be
1255 // chained on as necessary.
1257 ws->buffer_todo_bd = NULL;
1258 gc_alloc_todo_block(ws);
1260 ws->scavd_list = NULL;
1261 ws->n_scavd_blocks = 0;
1267 /* ----------------------------------------------------------------------------
1268 Initialise a generation that is *not* to be collected
1269 ------------------------------------------------------------------------- */
1272 init_uncollected_gen (nat g, nat threads)
1279 for (s = 0; s < generations[g].n_steps; s++) {
1280 stp = &generations[g].steps[s];
1281 stp->scavenged_large_objects = NULL;
1282 stp->n_scavenged_large_blocks = 0;
1285 for (t = 0; t < threads; t++) {
1286 for (s = 0; s < generations[g].n_steps; s++) {
1288 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1291 ws->buffer_todo_bd = NULL;
1292 ws->todo_large_objects = NULL;
1294 ws->scavd_list = NULL;
1295 ws->n_scavd_blocks = 0;
1297 // If the block at the head of the list in this generation
1298 // is less than 3/4 full, then use it as a todo block.
1299 if (stp->blocks && isPartiallyFull(stp->blocks))
1301 ws->todo_bd = stp->blocks;
1302 ws->todo_free = ws->todo_bd->free;
1303 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1304 stp->blocks = stp->blocks->link;
1306 ws->todo_bd->link = NULL;
1308 // this block is also the scan block; we must scan
1309 // from the current end point.
1310 ws->scan_bd = ws->todo_bd;
1311 ws->scan = ws->scan_bd->free;
1313 // subtract the contents of this block from the stats,
1314 // because we'll count the whole block later.
1315 copied -= ws->scan_bd->free - ws->scan_bd->start;
1322 gc_alloc_todo_block(ws);
1327 // Move the private mutable lists from each capability onto the
1328 // main mutable list for the generation.
1329 for (i = 0; i < n_capabilities; i++) {
1330 for (bd = capabilities[i].mut_lists[g];
1331 bd->link != NULL; bd = bd->link) {
1334 bd->link = generations[g].mut_list;
1335 generations[g].mut_list = capabilities[i].mut_lists[g];
1336 capabilities[i].mut_lists[g] = allocBlock();
1340 /* -----------------------------------------------------------------------------
1341 Initialise a gc_thread before GC
1342 -------------------------------------------------------------------------- */
1345 init_gc_thread (gc_thread *t)
1348 t->failed_to_evac = rtsFalse;
1349 t->eager_promotion = rtsTrue;
1350 t->thunk_selector_depth = 0;
1353 /* -----------------------------------------------------------------------------
1354 Function we pass to GetRoots to evacuate roots.
1355 -------------------------------------------------------------------------- */
1358 mark_root(StgClosure **root)
1363 /* -----------------------------------------------------------------------------
1364 Initialising the static object & mutable lists
1365 -------------------------------------------------------------------------- */
1368 zero_static_object_list(StgClosure* first_static)
1372 const StgInfoTable *info;
1374 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1376 link = *STATIC_LINK(info, p);
1377 *STATIC_LINK(info,p) = NULL;
1381 /* -----------------------------------------------------------------------------
1383 -------------------------------------------------------------------------- */
1390 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1391 c = (StgIndStatic *)c->static_link)
1393 SET_INFO(c, c->saved_info);
1394 c->saved_info = NULL;
1395 // could, but not necessary: c->static_link = NULL;
1397 revertible_caf_list = NULL;
1401 markCAFs( evac_fn evac )
1405 for (c = (StgIndStatic *)caf_list; c != NULL;
1406 c = (StgIndStatic *)c->static_link)
1408 evac(&c->indirectee);
1410 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1411 c = (StgIndStatic *)c->static_link)
1413 evac(&c->indirectee);
1417 /* ----------------------------------------------------------------------------
1418 Update the pointers from the task list
1420 These are treated as weak pointers because we want to allow a main
1421 thread to get a BlockedOnDeadMVar exception in the same way as any
1422 other thread. Note that the threads should all have been retained
1423 by GC by virtue of being on the all_threads list, we're just
1424 updating pointers here.
1425 ------------------------------------------------------------------------- */
1428 update_task_list (void)
1432 for (task = all_tasks; task != NULL; task = task->all_link) {
1433 if (!task->stopped && task->tso) {
1434 ASSERT(task->tso->bound == task);
1435 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1437 barf("task %p: main thread %d has been GC'd",
1450 /* ----------------------------------------------------------------------------
1451 Reset the sizes of the older generations when we do a major
1454 CURRENT STRATEGY: make all generations except zero the same size.
1455 We have to stay within the maximum heap size, and leave a certain
1456 percentage of the maximum heap size available to allocate into.
1457 ------------------------------------------------------------------------- */
1460 resize_generations (void)
1464 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1465 nat live, size, min_alloc;
1466 nat max = RtsFlags.GcFlags.maxHeapSize;
1467 nat gens = RtsFlags.GcFlags.generations;
1469 // live in the oldest generations
1470 live = oldest_gen->steps[0].n_blocks +
1471 oldest_gen->steps[0].n_large_blocks;
1473 // default max size for all generations except zero
1474 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1475 RtsFlags.GcFlags.minOldGenSize);
1477 // minimum size for generation zero
1478 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1479 RtsFlags.GcFlags.minAllocAreaSize);
1481 // Auto-enable compaction when the residency reaches a
1482 // certain percentage of the maximum heap size (default: 30%).
1483 if (RtsFlags.GcFlags.generations > 1 &&
1484 (RtsFlags.GcFlags.compact ||
1486 oldest_gen->steps[0].n_blocks >
1487 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1488 oldest_gen->steps[0].is_compacted = 1;
1489 // debugBelch("compaction: on\n", live);
1491 oldest_gen->steps[0].is_compacted = 0;
1492 // debugBelch("compaction: off\n", live);
1495 // if we're going to go over the maximum heap size, reduce the
1496 // size of the generations accordingly. The calculation is
1497 // different if compaction is turned on, because we don't need
1498 // to double the space required to collect the old generation.
1501 // this test is necessary to ensure that the calculations
1502 // below don't have any negative results - we're working
1503 // with unsigned values here.
1504 if (max < min_alloc) {
1508 if (oldest_gen->steps[0].is_compacted) {
1509 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1510 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1513 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1514 size = (max - min_alloc) / ((gens - 1) * 2);
1524 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1525 min_alloc, size, max);
1528 for (g = 0; g < gens; g++) {
1529 generations[g].max_blocks = size;
1534 /* -----------------------------------------------------------------------------
1535 Calculate the new size of the nursery, and resize it.
1536 -------------------------------------------------------------------------- */
1539 resize_nursery (void)
1541 if (RtsFlags.GcFlags.generations == 1)
1542 { // Two-space collector:
1545 /* set up a new nursery. Allocate a nursery size based on a
1546 * function of the amount of live data (by default a factor of 2)
1547 * Use the blocks from the old nursery if possible, freeing up any
1550 * If we get near the maximum heap size, then adjust our nursery
1551 * size accordingly. If the nursery is the same size as the live
1552 * data (L), then we need 3L bytes. We can reduce the size of the
1553 * nursery to bring the required memory down near 2L bytes.
1555 * A normal 2-space collector would need 4L bytes to give the same
1556 * performance we get from 3L bytes, reducing to the same
1557 * performance at 2L bytes.
1559 blocks = g0s0->n_old_blocks;
1561 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1562 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1563 RtsFlags.GcFlags.maxHeapSize )
1565 long adjusted_blocks; // signed on purpose
1568 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1570 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1571 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1573 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1574 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1578 blocks = adjusted_blocks;
1582 blocks *= RtsFlags.GcFlags.oldGenFactor;
1583 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1585 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1588 resizeNurseries(blocks);
1590 else // Generational collector
1593 * If the user has given us a suggested heap size, adjust our
1594 * allocation area to make best use of the memory available.
1596 if (RtsFlags.GcFlags.heapSizeSuggestion)
1599 nat needed = calcNeeded(); // approx blocks needed at next GC
1601 /* Guess how much will be live in generation 0 step 0 next time.
1602 * A good approximation is obtained by finding the
1603 * percentage of g0s0 that was live at the last minor GC.
1605 * We have an accurate figure for the amount of copied data in
1606 * 'copied', but we must convert this to a number of blocks, with
1607 * a small adjustment for estimated slop at the end of a block
1612 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1613 / countNurseryBlocks();
1616 /* Estimate a size for the allocation area based on the
1617 * information available. We might end up going slightly under
1618 * or over the suggested heap size, but we should be pretty
1621 * Formula: suggested - needed
1622 * ----------------------------
1623 * 1 + g0s0_pcnt_kept/100
1625 * where 'needed' is the amount of memory needed at the next
1626 * collection for collecting all steps except g0s0.
1629 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1630 (100 + (long)g0s0_pcnt_kept);
1632 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1633 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1636 resizeNurseries((nat)blocks);
1640 // we might have added extra large blocks to the nursery, so
1641 // resize back to minAllocAreaSize again.
1642 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1647 /* -----------------------------------------------------------------------------
1648 Sanity code for CAF garbage collection.
1650 With DEBUG turned on, we manage a CAF list in addition to the SRT
1651 mechanism. After GC, we run down the CAF list and blackhole any
1652 CAFs which have been garbage collected. This means we get an error
1653 whenever the program tries to enter a garbage collected CAF.
1655 Any garbage collected CAFs are taken off the CAF list at the same
1657 -------------------------------------------------------------------------- */
1659 #if 0 && defined(DEBUG)
1666 const StgInfoTable *info;
1677 ASSERT(info->type == IND_STATIC);
1679 if (STATIC_LINK(info,p) == NULL) {
1680 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1682 SET_INFO(p,&stg_BLACKHOLE_info);
1683 p = STATIC_LINK2(info,p);
1687 pp = &STATIC_LINK2(info,p);
1694 debugTrace(DEBUG_gccafs, "%d CAFs live", i);