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"
52 #include <string.h> // for memset()
54 /* -----------------------------------------------------------------------------
56 -------------------------------------------------------------------------- */
58 /* STATIC OBJECT LIST.
61 * We maintain a linked list of static objects that are still live.
62 * The requirements for this list are:
64 * - we need to scan the list while adding to it, in order to
65 * scavenge all the static objects (in the same way that
66 * breadth-first scavenging works for dynamic objects).
68 * - we need to be able to tell whether an object is already on
69 * the list, to break loops.
71 * Each static object has a "static link field", which we use for
72 * linking objects on to the list. We use a stack-type list, consing
73 * objects on the front as they are added (this means that the
74 * scavenge phase is depth-first, not breadth-first, but that
77 * A separate list is kept for objects that have been scavenged
78 * already - this is so that we can zero all the marks afterwards.
80 * An object is on the list if its static link field is non-zero; this
81 * means that we have to mark the end of the list with '1', not NULL.
83 * Extra notes for generational GC:
85 * Each generation has a static object list associated with it. When
86 * collecting generations up to N, we treat the static object lists
87 * from generations > N as roots.
89 * We build up a static object list while collecting generations 0..N,
90 * which is then appended to the static object list of generation N+1.
92 StgClosure* static_objects; // live static objects
93 StgClosure* scavenged_static_objects; // static objects scavenged so far
95 SpinLock static_objects_sync;
98 /* N is the oldest generation being collected, where the generations
99 * are numbered starting at 0. A major GC (indicated by the major_gc
100 * flag) is when we're collecting all generations. We only attempt to
101 * deal with static objects and GC CAFs when doing a major GC.
106 /* Data used for allocation area sizing.
108 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
118 /* Thread-local data for each GC thread
120 gc_thread *gc_threads = NULL;
121 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
124 long copied; // *words* copied & scavenged during this GC
125 long scavd_copied; // *words* copied only during this GC
128 SpinLock recordMutableGen_sync;
131 /* -----------------------------------------------------------------------------
132 Static function declarations
133 -------------------------------------------------------------------------- */
135 static void mark_root (StgClosure **root);
136 static void zero_static_object_list (StgClosure* first_static);
137 static void initialise_N (rtsBool force_major_gc);
138 static void alloc_gc_threads (void);
139 static void init_collected_gen (nat g, nat threads);
140 static void init_uncollected_gen (nat g, nat threads);
141 static void init_gc_thread (gc_thread *t);
142 static void update_task_list (void);
143 static void resize_generations (void);
144 static void resize_nursery (void);
145 static void start_gc_threads (void);
146 static void gc_thread_work (void);
147 static nat inc_running (void);
148 static nat dec_running (void);
149 static void wakeup_gc_threads (nat n_threads);
151 #if 0 && defined(DEBUG)
152 static void gcCAFs (void);
155 /* -----------------------------------------------------------------------------
156 The mark bitmap & stack.
157 -------------------------------------------------------------------------- */
159 #define MARK_STACK_BLOCKS 4
161 bdescr *mark_stack_bdescr;
166 // Flag and pointers used for falling back to a linear scan when the
167 // mark stack overflows.
168 rtsBool mark_stack_overflowed;
169 bdescr *oldgen_scan_bd;
172 /* -----------------------------------------------------------------------------
173 GarbageCollect: the main entry point to the garbage collector.
175 Locks held: all capabilities are held throughout GarbageCollect().
176 -------------------------------------------------------------------------- */
179 GarbageCollect ( rtsBool force_major_gc )
183 lnat live, allocated;
184 lnat oldgen_saved_blocks = 0;
185 nat n_threads; // number of threads participating in GC
190 CostCentreStack *prev_CCS;
195 debugTrace(DEBUG_gc, "starting GC");
197 #if defined(RTS_USER_SIGNALS)
198 if (RtsFlags.MiscFlags.install_signal_handlers) {
204 // tell the STM to discard any cached closures it's hoping to re-use
207 // tell the stats department that we've started a GC
211 // check for memory leaks if DEBUG is on
221 // attribute any costs to CCS_GC
227 /* Approximate how much we allocated.
228 * Todo: only when generating stats?
230 allocated = calcAllocated();
232 /* Figure out which generation to collect
234 initialise_N(force_major_gc);
236 /* Allocate + initialise the gc_thread structures.
240 /* Start threads, so they can be spinning up while we finish initialisation.
244 /* How many threads will be participating in this GC?
245 * We don't try to parallelise minor GC.
247 #if defined(THREADED_RTS)
251 n_threads = RtsFlags.ParFlags.gcThreads;
257 #ifdef RTS_GTK_FRONTPANEL
258 if (RtsFlags.GcFlags.frontpanel) {
259 updateFrontPanelBeforeGC(N);
263 // check stack sanity *before* GC (ToDo: check all threads)
264 IF_DEBUG(sanity, checkFreeListSanity());
266 /* Initialise the static object lists
268 static_objects = END_OF_STATIC_LIST;
269 scavenged_static_objects = END_OF_STATIC_LIST;
272 initSpinLock(&static_objects_sync);
273 initSpinLock(&recordMutableGen_sync);
274 initSpinLock(&gc_alloc_block_sync);
277 // Initialise all the generations/steps that we're collecting.
278 for (g = 0; g <= N; g++) {
279 init_collected_gen(g,n_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_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_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_threads);
312 // this is the main thread
313 gct = &gc_threads[0];
315 /* -----------------------------------------------------------------------
316 * follow all the roots that we know about:
317 * - mutable lists from each generation > N
318 * we want to *scavenge* these roots, not evacuate them: they're not
319 * going to move in this GC.
320 * Also do them in reverse generation order, for the usual reason:
321 * namely to reduce the likelihood of spurious old->new pointers.
324 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
325 generations[g].saved_mut_list = generations[g].mut_list;
326 generations[g].mut_list = allocBlock();
327 // mut_list always has at least one block.
329 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
330 scavenge_mutable_list(&generations[g]);
334 // follow roots from the CAF list (used by GHCi)
338 // follow all the roots that the application knows about.
342 // Mark the weak pointer list, and prepare to detect dead weak pointers.
346 // Mark the stable pointer table.
347 markStablePtrTable(mark_root);
349 /* -------------------------------------------------------------------------
350 * Repeatedly scavenge all the areas we know about until there's no
351 * more scavenging to be done.
356 // The other threads are now stopped. We might recurse back to
357 // here, but from now on this is the only thread.
359 // if any blackholes are alive, make the threads that wait on
361 if (traverseBlackholeQueue()) {
366 // must be last... invariant is that everything is fully
367 // scavenged at this point.
368 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
373 // If we get to here, there's really nothing left to do.
377 // Update pointers from the Task list
380 // Now see which stable names are still alive.
384 // We call processHeapClosureForDead() on every closure destroyed during
385 // the current garbage collection, so we invoke LdvCensusForDead().
386 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
387 || RtsFlags.ProfFlags.bioSelector != NULL)
391 // NO MORE EVACUATION AFTER THIS POINT!
392 // Finally: compaction of the oldest generation.
393 if (major_gc && oldest_gen->steps[0].is_compacted) {
394 // save number of blocks for stats
395 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
399 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
401 // Two-space collector: free the old to-space.
402 // g0s0->old_blocks is the old nursery
403 // g0s0->blocks is to-space from the previous GC
404 if (RtsFlags.GcFlags.generations == 1) {
405 if (g0s0->blocks != NULL) {
406 freeChain(g0s0->blocks);
411 // For each workspace, in each thread:
412 // * clear the BF_EVACUATED flag from each copied block
413 // * move the copied blocks to the step
419 for (t = 0; t < n_threads; t++) {
420 thr = &gc_threads[t];
422 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
423 for (s = 0; s < generations[g].n_steps; s++) {
424 ws = &thr->steps[g][s];
425 if (g==0 && s==0) continue;
428 // ASSERT( ws->scan_bd == ws->todo_bd );
429 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
431 // Push the final block
432 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
434 // update stats: we haven't counted the block at the
435 // front of the scavd_list yet.
436 scavd_copied += ws->scavd_list->free - ws->scavd_list->start;
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.
579 // Free the small objects allocated via allocate(), since this will
580 // all have been copied into G0S1 now.
581 if (RtsFlags.GcFlags.generations > 1) {
582 if (g0s0->blocks != NULL) {
583 freeChain(g0s0->blocks);
589 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
591 // Start a new pinned_object_block
592 pinned_object_block = NULL;
594 // Free the mark stack.
595 if (mark_stack_bdescr != NULL) {
596 freeGroup(mark_stack_bdescr);
600 for (g = 0; g <= N; g++) {
601 for (s = 0; s < generations[g].n_steps; s++) {
602 stp = &generations[g].steps[s];
603 if (stp->bitmap != NULL) {
604 freeGroup(stp->bitmap);
612 // mark the garbage collected CAFs as dead
613 #if 0 && defined(DEBUG) // doesn't work at the moment
614 if (major_gc) { gcCAFs(); }
618 // resetStaticObjectForRetainerProfiling() must be called before
620 resetStaticObjectForRetainerProfiling();
623 // zero the scavenged static object list
625 zero_static_object_list(scavenged_static_objects);
631 // start any pending finalizers
633 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
636 // send exceptions to any threads which were about to die
638 resurrectThreads(resurrected_threads);
641 // Update the stable pointer hash table.
642 updateStablePtrTable(major_gc);
644 // check sanity after GC
645 IF_DEBUG(sanity, checkSanity());
647 // extra GC trace info
648 IF_DEBUG(gc, statDescribeGens());
651 // symbol-table based profiling
652 /* heapCensus(to_blocks); */ /* ToDo */
655 // restore enclosing cost centre
661 // check for memory leaks if DEBUG is on
665 #ifdef RTS_GTK_FRONTPANEL
666 if (RtsFlags.GcFlags.frontpanel) {
667 updateFrontPanelAfterGC( N, live );
671 // ok, GC over: tell the stats department what happened.
672 stat_endGC(allocated, live, copied, scavd_copied, N);
674 #if defined(RTS_USER_SIGNALS)
675 if (RtsFlags.MiscFlags.install_signal_handlers) {
676 // unblock signals again
677 unblockUserSignals();
684 /* ---------------------------------------------------------------------------
685 Where are the roots that we know about?
687 - all the threads on the runnable queue
688 - all the threads on the blocked queue
689 - all the threads on the sleeping queue
690 - all the thread currently executing a _ccall_GC
691 - all the "main threads"
693 ------------------------------------------------------------------------ */
695 /* This has to be protected either by the scheduler monitor, or by the
696 garbage collection monitor (probably the latter).
701 GetRoots( evac_fn evac )
707 for (i = 0; i < n_capabilities; i++) {
708 cap = &capabilities[i];
709 evac((StgClosure **)(void *)&cap->run_queue_hd);
710 evac((StgClosure **)(void *)&cap->run_queue_tl);
711 #if defined(THREADED_RTS)
712 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
713 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
715 for (task = cap->suspended_ccalling_tasks; task != NULL;
717 debugTrace(DEBUG_sched,
718 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
719 evac((StgClosure **)(void *)&task->suspended_tso);
724 #if !defined(THREADED_RTS)
725 evac((StgClosure **)(void *)&blocked_queue_hd);
726 evac((StgClosure **)(void *)&blocked_queue_tl);
727 evac((StgClosure **)(void *)&sleeping_queue);
730 // evac((StgClosure **)&blackhole_queue);
732 #if defined(THREADED_RTS)
733 markSparkQueue(evac);
736 #if defined(RTS_USER_SIGNALS)
737 // mark the signal handlers (signals should be already blocked)
738 markSignalHandlers(evac);
742 /* -----------------------------------------------------------------------------
743 isAlive determines whether the given closure is still alive (after
744 a garbage collection) or not. It returns the new address of the
745 closure if it is alive, or NULL otherwise.
747 NOTE: Use it before compaction only!
748 It untags and (if needed) retags pointers to closures.
749 -------------------------------------------------------------------------- */
753 isAlive(StgClosure *p)
755 const StgInfoTable *info;
761 /* The tag and the pointer are split, to be merged later when needed. */
762 tag = GET_CLOSURE_TAG(p);
763 q = UNTAG_CLOSURE(p);
765 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
768 // ignore static closures
770 // ToDo: for static closures, check the static link field.
771 // Problem here is that we sometimes don't set the link field, eg.
772 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
774 if (!HEAP_ALLOCED(q)) {
778 // ignore closures in generations that we're not collecting.
780 if (bd->gen_no > N) {
784 // if it's a pointer into to-space, then we're done
785 if (bd->flags & BF_EVACUATED) {
789 // large objects use the evacuated flag
790 if (bd->flags & BF_LARGE) {
794 // check the mark bit for compacted steps
795 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
799 switch (info->type) {
804 case IND_OLDGEN: // rely on compatible layout with StgInd
805 case IND_OLDGEN_PERM:
806 // follow indirections
807 p = ((StgInd *)q)->indirectee;
812 return ((StgEvacuated *)q)->evacuee;
815 if (((StgTSO *)q)->what_next == ThreadRelocated) {
816 p = (StgClosure *)((StgTSO *)q)->link;
828 /* -----------------------------------------------------------------------------
829 Figure out which generation to collect, initialise N and major_gc.
830 -------------------------------------------------------------------------- */
833 initialise_N (rtsBool force_major_gc)
837 if (force_major_gc) {
838 N = RtsFlags.GcFlags.generations - 1;
842 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
843 if (generations[g].steps[0].n_blocks +
844 generations[g].steps[0].n_large_blocks
845 >= generations[g].max_blocks) {
849 major_gc = (N == RtsFlags.GcFlags.generations-1);
853 /* -----------------------------------------------------------------------------
854 Initialise the gc_thread structures.
855 -------------------------------------------------------------------------- */
858 alloc_gc_thread (gc_thread *t, int n)
865 initCondition(&t->wake_cond);
866 initMutex(&t->wake_mutex);
867 t->wakeup = rtsFalse;
872 t->free_blocks = NULL;
877 t->steps = stgMallocBytes(RtsFlags.GcFlags.generations *
878 sizeof(step_workspace *),
879 "initialise_gc_thread");
881 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
883 t->steps[g] = stgMallocBytes(generations[g].n_steps *
884 sizeof(step_workspace),
885 "initialise_gc_thread/2");
887 for (s = 0; s < generations[g].n_steps; s++)
889 ws = &t->steps[g][s];
890 ws->stp = &generations[g].steps[s];
897 ws->buffer_todo_bd = NULL;
899 ws->scavd_list = NULL;
900 ws->n_scavd_blocks = 0;
907 alloc_gc_threads (void)
909 if (gc_threads == NULL) {
910 #if defined(THREADED_RTS)
912 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
916 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
917 alloc_gc_thread(&gc_threads[i], i);
920 gc_threads = stgMallocBytes (sizeof(gc_thread),
923 alloc_gc_thread(gc_threads, 0);
928 /* ----------------------------------------------------------------------------
930 ------------------------------------------------------------------------- */
932 static nat gc_running_threads;
934 #if defined(THREADED_RTS)
935 static Mutex gc_running_mutex;
942 ACQUIRE_LOCK(&gc_running_mutex);
943 n_running = ++gc_running_threads;
944 RELEASE_LOCK(&gc_running_mutex);
952 ACQUIRE_LOCK(&gc_running_mutex);
953 n_running = --gc_running_threads;
954 RELEASE_LOCK(&gc_running_mutex);
959 // gc_thread_work(): Scavenge until there's no work left to do and all
960 // the running threads are idle.
963 gc_thread_work (void)
967 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
969 // gc_running_threads has already been incremented for us; either
970 // this is the main thread and we incremented it inside
971 // GarbageCollect(), or this is a worker thread and the main
972 // thread bumped gc_running_threads before waking us up.
976 // scavenge_loop() only exits when there's no work to do
979 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
980 gct->thread_index, r);
982 while (gc_running_threads != 0) {
987 // any_work() does not remove the work from the queue, it
988 // just checks for the presence of work. If we find any,
989 // then we increment gc_running_threads and go back to
990 // scavenge_loop() to perform any pending work.
993 // All threads are now stopped
994 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
998 #if defined(THREADED_RTS)
1000 gc_thread_mainloop (void)
1002 while (!gct->exit) {
1004 // Wait until we're told to wake up
1005 ACQUIRE_LOCK(&gct->wake_mutex);
1006 while (!gct->wakeup) {
1007 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1009 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1011 RELEASE_LOCK(&gct->wake_mutex);
1012 gct->wakeup = rtsFalse;
1013 if (gct->exit) break;
1020 #if defined(THREADED_RTS)
1022 gc_thread_entry (gc_thread *my_gct)
1025 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1026 gct->id = osThreadId();
1027 gc_thread_mainloop();
1032 start_gc_threads (void)
1034 #if defined(THREADED_RTS)
1037 static rtsBool done = rtsFalse;
1039 gc_running_threads = 0;
1040 initMutex(&gc_running_mutex);
1043 // Start from 1: the main thread is 0
1044 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1045 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1054 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1056 #if defined(THREADED_RTS)
1058 for (i=1; i < n_threads; i++) {
1060 ACQUIRE_LOCK(&gc_threads[i].wake_mutex);
1061 gc_threads[i].wakeup = rtsTrue;
1062 signalCondition(&gc_threads[i].wake_cond);
1063 RELEASE_LOCK(&gc_threads[i].wake_mutex);
1068 /* ----------------------------------------------------------------------------
1069 Initialise a generation that is to be collected
1070 ------------------------------------------------------------------------- */
1073 init_collected_gen (nat g, nat n_threads)
1080 // Throw away the current mutable list. Invariant: the mutable
1081 // list always has at least one block; this means we can avoid a
1082 // check for NULL in recordMutable().
1084 freeChain(generations[g].mut_list);
1085 generations[g].mut_list = allocBlock();
1086 for (i = 0; i < n_capabilities; i++) {
1087 freeChain(capabilities[i].mut_lists[g]);
1088 capabilities[i].mut_lists[g] = allocBlock();
1092 for (s = 0; s < generations[g].n_steps; s++) {
1094 // generation 0, step 0 doesn't need to-space
1095 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1099 stp = &generations[g].steps[s];
1100 ASSERT(stp->gen_no == g);
1102 // deprecate the existing blocks
1103 stp->old_blocks = stp->blocks;
1104 stp->n_old_blocks = stp->n_blocks;
1108 // we don't have any to-be-scavenged blocks yet
1112 // initialise the large object queues.
1113 stp->scavenged_large_objects = NULL;
1114 stp->n_scavenged_large_blocks = 0;
1116 // mark the large objects as not evacuated yet
1117 for (bd = stp->large_objects; bd; bd = bd->link) {
1118 bd->flags &= ~BF_EVACUATED;
1121 // for a compacted step, we need to allocate the bitmap
1122 if (stp->is_compacted) {
1123 nat bitmap_size; // in bytes
1124 bdescr *bitmap_bdescr;
1127 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1129 if (bitmap_size > 0) {
1130 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1132 stp->bitmap = bitmap_bdescr;
1133 bitmap = bitmap_bdescr->start;
1135 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1136 bitmap_size, bitmap);
1138 // don't forget to fill it with zeros!
1139 memset(bitmap, 0, bitmap_size);
1141 // For each block in this step, point to its bitmap from the
1142 // block descriptor.
1143 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1144 bd->u.bitmap = bitmap;
1145 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1147 // Also at this point we set the BF_COMPACTED flag
1148 // for this block. The invariant is that
1149 // BF_COMPACTED is always unset, except during GC
1150 // when it is set on those blocks which will be
1152 bd->flags |= BF_COMPACTED;
1158 // For each GC thread, for each step, allocate a "todo" block to
1159 // store evacuated objects to be scavenged, and a block to store
1160 // evacuated objects that do not need to be scavenged.
1161 for (t = 0; t < n_threads; t++) {
1162 for (s = 0; s < generations[g].n_steps; s++) {
1164 // we don't copy objects into g0s0, unless -G0
1165 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1167 ws = &gc_threads[t].steps[g][s];
1172 ws->todo_large_objects = NULL;
1174 // allocate the first to-space block; extra blocks will be
1175 // chained on as necessary.
1177 ws->buffer_todo_bd = NULL;
1178 gc_alloc_todo_block(ws);
1180 // allocate a block for "already scavenged" objects. This goes
1181 // on the front of the stp->blocks list, so it won't be
1182 // traversed by the scavenging sweep.
1183 ws->scavd_list = NULL;
1184 ws->n_scavd_blocks = 0;
1185 gc_alloc_scavd_block(ws);
1191 /* ----------------------------------------------------------------------------
1192 Initialise a generation that is *not* to be collected
1193 ------------------------------------------------------------------------- */
1196 init_uncollected_gen (nat g, nat threads)
1203 for (s = 0; s < generations[g].n_steps; s++) {
1204 stp = &generations[g].steps[s];
1205 stp->scavenged_large_objects = NULL;
1206 stp->n_scavenged_large_blocks = 0;
1209 for (t = 0; t < threads; t++) {
1210 for (s = 0; s < generations[g].n_steps; s++) {
1212 ws = &gc_threads[t].steps[g][s];
1215 ws->buffer_todo_bd = NULL;
1216 ws->todo_large_objects = NULL;
1218 // If the block at the head of the list in this generation
1219 // is less than 3/4 full, then use it as a todo block.
1220 if (isPartiallyFull(stp->blocks))
1222 ws->todo_bd = stp->blocks;
1223 stp->blocks = stp->blocks->link;
1225 ws->todo_bd->link = NULL;
1227 // this block is also the scan block; we must scan
1228 // from the current end point.
1229 ws->scan_bd = ws->todo_bd;
1230 ws->scan = ws->scan_bd->free;
1232 // subtract the contents of this block from the stats,
1233 // because we'll count the whole block later.
1234 copied -= ws->scan_bd->free - ws->scan_bd->start;
1241 gc_alloc_todo_block(ws);
1244 // Do the same trick for the scavd block
1245 if (isPartiallyFull(stp->blocks))
1247 ws->scavd_list = stp->blocks;
1248 stp->blocks = stp->blocks->link;
1250 ws->scavd_list->link = NULL;
1251 ws->n_scavd_blocks = 1;
1252 // subtract the contents of this block from the stats,
1253 // because we'll count the whole block later.
1254 scavd_copied -= ws->scavd_list->free - ws->scavd_list->start;
1258 ws->scavd_list = NULL;
1259 ws->n_scavd_blocks = 0;
1260 gc_alloc_scavd_block(ws);
1265 // Move the private mutable lists from each capability onto the
1266 // main mutable list for the generation.
1267 for (i = 0; i < n_capabilities; i++) {
1268 for (bd = capabilities[i].mut_lists[g];
1269 bd->link != NULL; bd = bd->link) {
1272 bd->link = generations[g].mut_list;
1273 generations[g].mut_list = capabilities[i].mut_lists[g];
1274 capabilities[i].mut_lists[g] = allocBlock();
1278 /* -----------------------------------------------------------------------------
1279 Initialise a gc_thread before GC
1280 -------------------------------------------------------------------------- */
1283 init_gc_thread (gc_thread *t)
1286 t->failed_to_evac = rtsFalse;
1287 t->eager_promotion = rtsTrue;
1288 t->thunk_selector_depth = 0;
1291 /* -----------------------------------------------------------------------------
1292 Function we pass to GetRoots to evacuate roots.
1293 -------------------------------------------------------------------------- */
1296 mark_root(StgClosure **root)
1298 *root = evacuate(*root);
1301 /* -----------------------------------------------------------------------------
1302 Initialising the static object & mutable lists
1303 -------------------------------------------------------------------------- */
1306 zero_static_object_list(StgClosure* first_static)
1310 const StgInfoTable *info;
1312 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1314 link = *STATIC_LINK(info, p);
1315 *STATIC_LINK(info,p) = NULL;
1319 /* -----------------------------------------------------------------------------
1321 -------------------------------------------------------------------------- */
1328 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1329 c = (StgIndStatic *)c->static_link)
1331 SET_INFO(c, c->saved_info);
1332 c->saved_info = NULL;
1333 // could, but not necessary: c->static_link = NULL;
1335 revertible_caf_list = NULL;
1339 markCAFs( evac_fn evac )
1343 for (c = (StgIndStatic *)caf_list; c != NULL;
1344 c = (StgIndStatic *)c->static_link)
1346 evac(&c->indirectee);
1348 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1349 c = (StgIndStatic *)c->static_link)
1351 evac(&c->indirectee);
1355 /* ----------------------------------------------------------------------------
1356 Update the pointers from the task list
1358 These are treated as weak pointers because we want to allow a main
1359 thread to get a BlockedOnDeadMVar exception in the same way as any
1360 other thread. Note that the threads should all have been retained
1361 by GC by virtue of being on the all_threads list, we're just
1362 updating pointers here.
1363 ------------------------------------------------------------------------- */
1366 update_task_list (void)
1370 for (task = all_tasks; task != NULL; task = task->all_link) {
1371 if (!task->stopped && task->tso) {
1372 ASSERT(task->tso->bound == task);
1373 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1375 barf("task %p: main thread %d has been GC'd",
1388 /* ----------------------------------------------------------------------------
1389 Reset the sizes of the older generations when we do a major
1392 CURRENT STRATEGY: make all generations except zero the same size.
1393 We have to stay within the maximum heap size, and leave a certain
1394 percentage of the maximum heap size available to allocate into.
1395 ------------------------------------------------------------------------- */
1398 resize_generations (void)
1402 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1403 nat live, size, min_alloc;
1404 nat max = RtsFlags.GcFlags.maxHeapSize;
1405 nat gens = RtsFlags.GcFlags.generations;
1407 // live in the oldest generations
1408 live = oldest_gen->steps[0].n_blocks +
1409 oldest_gen->steps[0].n_large_blocks;
1411 // default max size for all generations except zero
1412 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1413 RtsFlags.GcFlags.minOldGenSize);
1415 // minimum size for generation zero
1416 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1417 RtsFlags.GcFlags.minAllocAreaSize);
1419 // Auto-enable compaction when the residency reaches a
1420 // certain percentage of the maximum heap size (default: 30%).
1421 if (RtsFlags.GcFlags.generations > 1 &&
1422 (RtsFlags.GcFlags.compact ||
1424 oldest_gen->steps[0].n_blocks >
1425 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1426 oldest_gen->steps[0].is_compacted = 1;
1427 // debugBelch("compaction: on\n", live);
1429 oldest_gen->steps[0].is_compacted = 0;
1430 // debugBelch("compaction: off\n", live);
1433 // if we're going to go over the maximum heap size, reduce the
1434 // size of the generations accordingly. The calculation is
1435 // different if compaction is turned on, because we don't need
1436 // to double the space required to collect the old generation.
1439 // this test is necessary to ensure that the calculations
1440 // below don't have any negative results - we're working
1441 // with unsigned values here.
1442 if (max < min_alloc) {
1446 if (oldest_gen->steps[0].is_compacted) {
1447 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1448 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1451 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1452 size = (max - min_alloc) / ((gens - 1) * 2);
1462 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1463 min_alloc, size, max);
1466 for (g = 0; g < gens; g++) {
1467 generations[g].max_blocks = size;
1472 /* -----------------------------------------------------------------------------
1473 Calculate the new size of the nursery, and resize it.
1474 -------------------------------------------------------------------------- */
1477 resize_nursery (void)
1479 if (RtsFlags.GcFlags.generations == 1)
1480 { // Two-space collector:
1483 /* set up a new nursery. Allocate a nursery size based on a
1484 * function of the amount of live data (by default a factor of 2)
1485 * Use the blocks from the old nursery if possible, freeing up any
1488 * If we get near the maximum heap size, then adjust our nursery
1489 * size accordingly. If the nursery is the same size as the live
1490 * data (L), then we need 3L bytes. We can reduce the size of the
1491 * nursery to bring the required memory down near 2L bytes.
1493 * A normal 2-space collector would need 4L bytes to give the same
1494 * performance we get from 3L bytes, reducing to the same
1495 * performance at 2L bytes.
1497 blocks = g0s0->n_old_blocks;
1499 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1500 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1501 RtsFlags.GcFlags.maxHeapSize )
1503 long adjusted_blocks; // signed on purpose
1506 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1508 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1509 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1511 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1512 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1516 blocks = adjusted_blocks;
1520 blocks *= RtsFlags.GcFlags.oldGenFactor;
1521 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1523 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1526 resizeNurseries(blocks);
1528 else // Generational collector
1531 * If the user has given us a suggested heap size, adjust our
1532 * allocation area to make best use of the memory available.
1534 if (RtsFlags.GcFlags.heapSizeSuggestion)
1537 nat needed = calcNeeded(); // approx blocks needed at next GC
1539 /* Guess how much will be live in generation 0 step 0 next time.
1540 * A good approximation is obtained by finding the
1541 * percentage of g0s0 that was live at the last minor GC.
1543 * We have an accurate figure for the amount of copied data in
1544 * 'copied', but we must convert this to a number of blocks, with
1545 * a small adjustment for estimated slop at the end of a block
1550 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1551 / countNurseryBlocks();
1554 /* Estimate a size for the allocation area based on the
1555 * information available. We might end up going slightly under
1556 * or over the suggested heap size, but we should be pretty
1559 * Formula: suggested - needed
1560 * ----------------------------
1561 * 1 + g0s0_pcnt_kept/100
1563 * where 'needed' is the amount of memory needed at the next
1564 * collection for collecting all steps except g0s0.
1567 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1568 (100 + (long)g0s0_pcnt_kept);
1570 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1571 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1574 resizeNurseries((nat)blocks);
1578 // we might have added extra large blocks to the nursery, so
1579 // resize back to minAllocAreaSize again.
1580 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1585 /* -----------------------------------------------------------------------------
1586 Sanity code for CAF garbage collection.
1588 With DEBUG turned on, we manage a CAF list in addition to the SRT
1589 mechanism. After GC, we run down the CAF list and blackhole any
1590 CAFs which have been garbage collected. This means we get an error
1591 whenever the program tries to enter a garbage collected CAF.
1593 Any garbage collected CAFs are taken off the CAF list at the same
1595 -------------------------------------------------------------------------- */
1597 #if 0 && defined(DEBUG)
1604 const StgInfoTable *info;
1615 ASSERT(info->type == IND_STATIC);
1617 if (STATIC_LINK(info,p) == NULL) {
1618 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1620 SET_INFO(p,&stg_BLACKHOLE_info);
1621 p = STATIC_LINK2(info,p);
1625 pp = &STATIC_LINK2(info,p);
1632 debugTrace(DEBUG_gccafs, "%d CAFs live", i);