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
186 gc_thread *saved_gct;
189 // necessary if we stole a callee-saves register for gct:
193 CostCentreStack *prev_CCS;
198 debugTrace(DEBUG_gc, "starting GC");
200 #if defined(RTS_USER_SIGNALS)
201 if (RtsFlags.MiscFlags.install_signal_handlers) {
207 // tell the STM to discard any cached closures it's hoping to re-use
210 // tell the stats department that we've started a GC
214 // check for memory leaks if DEBUG is on
224 // attribute any costs to CCS_GC
230 /* Approximate how much we allocated.
231 * Todo: only when generating stats?
233 allocated = calcAllocated();
235 /* Figure out which generation to collect
237 initialise_N(force_major_gc);
239 /* Allocate + initialise the gc_thread structures.
243 /* Start threads, so they can be spinning up while we finish initialisation.
247 /* How many threads will be participating in this GC?
248 * We don't try to parallelise minor GC.
250 #if defined(THREADED_RTS)
254 n_threads = RtsFlags.ParFlags.gcThreads;
260 #ifdef RTS_GTK_FRONTPANEL
261 if (RtsFlags.GcFlags.frontpanel) {
262 updateFrontPanelBeforeGC(N);
266 // check stack sanity *before* GC (ToDo: check all threads)
267 IF_DEBUG(sanity, checkFreeListSanity());
269 /* Initialise the static object lists
271 static_objects = END_OF_STATIC_LIST;
272 scavenged_static_objects = END_OF_STATIC_LIST;
275 initSpinLock(&static_objects_sync);
276 initSpinLock(&recordMutableGen_sync);
277 initSpinLock(&gc_alloc_block_sync);
280 // Initialise all the generations/steps that we're collecting.
281 for (g = 0; g <= N; g++) {
282 init_collected_gen(g,n_threads);
285 // Initialise all the generations/steps that we're *not* collecting.
286 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
287 init_uncollected_gen(g,n_threads);
290 /* Allocate a mark stack if we're doing a major collection.
293 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
294 mark_stack = (StgPtr *)mark_stack_bdescr->start;
295 mark_sp = mark_stack;
296 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
298 mark_stack_bdescr = NULL;
301 // Initialise all our gc_thread structures
302 for (t = 0; t < n_threads; t++) {
303 init_gc_thread(&gc_threads[t]);
306 // the main thread is running: this prevents any other threads from
307 // exiting prematurely, so we can start them now.
309 wakeup_gc_threads(n_threads);
315 // this is the main thread
316 gct = &gc_threads[0];
318 /* -----------------------------------------------------------------------
319 * follow all the roots that we know about:
320 * - mutable lists from each generation > N
321 * we want to *scavenge* these roots, not evacuate them: they're not
322 * going to move in this GC.
323 * Also do them in reverse generation order, for the usual reason:
324 * namely to reduce the likelihood of spurious old->new pointers.
327 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
328 generations[g].saved_mut_list = generations[g].mut_list;
329 generations[g].mut_list = allocBlock();
330 // mut_list always has at least one block.
332 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
333 scavenge_mutable_list(&generations[g]);
337 // follow roots from the CAF list (used by GHCi)
341 // follow all the roots that the application knows about.
345 // Mark the weak pointer list, and prepare to detect dead weak pointers.
349 // Mark the stable pointer table.
350 markStablePtrTable(mark_root);
352 /* -------------------------------------------------------------------------
353 * Repeatedly scavenge all the areas we know about until there's no
354 * more scavenging to be done.
359 // The other threads are now stopped. We might recurse back to
360 // here, but from now on this is the only thread.
362 // if any blackholes are alive, make the threads that wait on
364 if (traverseBlackholeQueue()) {
369 // must be last... invariant is that everything is fully
370 // scavenged at this point.
371 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
376 // If we get to here, there's really nothing left to do.
380 // Update pointers from the Task list
383 // Now see which stable names are still alive.
387 // We call processHeapClosureForDead() on every closure destroyed during
388 // the current garbage collection, so we invoke LdvCensusForDead().
389 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
390 || RtsFlags.ProfFlags.bioSelector != NULL)
394 // NO MORE EVACUATION AFTER THIS POINT!
395 // Finally: compaction of the oldest generation.
396 if (major_gc && oldest_gen->steps[0].is_compacted) {
397 // save number of blocks for stats
398 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
402 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
404 // Two-space collector: free the old to-space.
405 // g0s0->old_blocks is the old nursery
406 // g0s0->blocks is to-space from the previous GC
407 if (RtsFlags.GcFlags.generations == 1) {
408 if (g0s0->blocks != NULL) {
409 freeChain(g0s0->blocks);
414 // For each workspace, in each thread:
415 // * clear the BF_EVACUATED flag from each copied block
416 // * move the copied blocks to the step
422 for (t = 0; t < n_threads; t++) {
423 thr = &gc_threads[t];
425 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
426 for (s = 0; s < generations[g].n_steps; s++) {
427 ws = &thr->steps[g][s];
428 if (g==0 && s==0) continue;
431 // ASSERT( ws->scan_bd == ws->todo_bd );
432 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
434 // Push the final block
435 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
437 // update stats: we haven't counted the block at the
438 // front of the scavd_list yet.
439 scavd_copied += ws->scavd_list->free - ws->scavd_list->start;
441 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
443 prev = ws->scavd_list;
444 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
445 bd->flags &= ~BF_EVACUATED; // now from-space
448 prev->link = ws->stp->blocks;
449 ws->stp->blocks = ws->scavd_list;
450 ws->stp->n_blocks += ws->n_scavd_blocks;
451 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
457 // Two-space collector: swap the semi-spaces around.
458 // Currently: g0s0->old_blocks is the old nursery
459 // g0s0->blocks is to-space from this GC
460 // We want these the other way around.
461 if (RtsFlags.GcFlags.generations == 1) {
462 bdescr *nursery_blocks = g0s0->old_blocks;
463 nat n_nursery_blocks = g0s0->n_old_blocks;
464 g0s0->old_blocks = g0s0->blocks;
465 g0s0->n_old_blocks = g0s0->n_blocks;
466 g0s0->blocks = nursery_blocks;
467 g0s0->n_blocks = n_nursery_blocks;
470 /* run through all the generations/steps and tidy up
472 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
475 generations[g].collections++; // for stats
478 // Count the mutable list as bytes "copied" for the purposes of
479 // stats. Every mutable list is copied during every GC.
481 nat mut_list_size = 0;
482 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
483 mut_list_size += bd->free - bd->start;
485 copied += mut_list_size;
488 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
489 (unsigned long)(mut_list_size * sizeof(W_)),
490 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
493 for (s = 0; s < generations[g].n_steps; s++) {
495 stp = &generations[g].steps[s];
497 // for generations we collected...
500 /* free old memory and shift to-space into from-space for all
501 * the collected steps (except the allocation area). These
502 * freed blocks will probaby be quickly recycled.
504 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
505 if (stp->is_compacted)
507 // for a compacted step, just shift the new to-space
508 // onto the front of the now-compacted existing blocks.
509 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
510 bd->flags &= ~BF_EVACUATED; // now from-space
512 // tack the new blocks on the end of the existing blocks
513 if (stp->old_blocks != NULL) {
514 for (bd = stp->old_blocks; bd != NULL; bd = next) {
515 // NB. this step might not be compacted next
516 // time, so reset the BF_COMPACTED flags.
517 // They are set before GC if we're going to
518 // compact. (search for BF_COMPACTED above).
519 bd->flags &= ~BF_COMPACTED;
522 bd->link = stp->blocks;
525 stp->blocks = stp->old_blocks;
527 // add the new blocks to the block tally
528 stp->n_blocks += stp->n_old_blocks;
529 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
533 freeChain(stp->old_blocks);
535 stp->old_blocks = NULL;
536 stp->n_old_blocks = 0;
539 /* LARGE OBJECTS. The current live large objects are chained on
540 * scavenged_large, having been moved during garbage
541 * collection from large_objects. Any objects left on
542 * large_objects list are therefore dead, so we free them here.
544 for (bd = stp->large_objects; bd != NULL; bd = next) {
550 // update the count of blocks used by large objects
551 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
552 bd->flags &= ~BF_EVACUATED;
554 stp->large_objects = stp->scavenged_large_objects;
555 stp->n_large_blocks = stp->n_scavenged_large_blocks;
558 else // for older generations...
560 /* For older generations, we need to append the
561 * scavenged_large_object list (i.e. large objects that have been
562 * promoted during this GC) to the large_object list for that step.
564 for (bd = stp->scavenged_large_objects; bd; bd = next) {
566 bd->flags &= ~BF_EVACUATED;
567 dbl_link_onto(bd, &stp->large_objects);
570 // add the new blocks we promoted during this GC
571 stp->n_large_blocks += stp->n_scavenged_large_blocks;
576 // update the max size of older generations after a major GC
577 resize_generations();
579 // Guess the amount of live data for stats.
582 // Free the small objects allocated via allocate(), since this will
583 // all have been copied into G0S1 now.
584 if (RtsFlags.GcFlags.generations > 1) {
585 if (g0s0->blocks != NULL) {
586 freeChain(g0s0->blocks);
592 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
594 // Start a new pinned_object_block
595 pinned_object_block = NULL;
597 // Free the mark stack.
598 if (mark_stack_bdescr != NULL) {
599 freeGroup(mark_stack_bdescr);
603 for (g = 0; g <= N; g++) {
604 for (s = 0; s < generations[g].n_steps; s++) {
605 stp = &generations[g].steps[s];
606 if (stp->bitmap != NULL) {
607 freeGroup(stp->bitmap);
615 // mark the garbage collected CAFs as dead
616 #if 0 && defined(DEBUG) // doesn't work at the moment
617 if (major_gc) { gcCAFs(); }
621 // resetStaticObjectForRetainerProfiling() must be called before
623 resetStaticObjectForRetainerProfiling();
626 // zero the scavenged static object list
628 zero_static_object_list(scavenged_static_objects);
634 // start any pending finalizers
636 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
639 // send exceptions to any threads which were about to die
641 resurrectThreads(resurrected_threads);
644 // Update the stable pointer hash table.
645 updateStablePtrTable(major_gc);
647 // check sanity after GC
648 IF_DEBUG(sanity, checkSanity());
650 // extra GC trace info
651 IF_DEBUG(gc, statDescribeGens());
654 // symbol-table based profiling
655 /* heapCensus(to_blocks); */ /* ToDo */
658 // restore enclosing cost centre
664 // check for memory leaks if DEBUG is on
668 #ifdef RTS_GTK_FRONTPANEL
669 if (RtsFlags.GcFlags.frontpanel) {
670 updateFrontPanelAfterGC( N, live );
674 // ok, GC over: tell the stats department what happened.
675 stat_endGC(allocated, live, copied, scavd_copied, N);
677 #if defined(RTS_USER_SIGNALS)
678 if (RtsFlags.MiscFlags.install_signal_handlers) {
679 // unblock signals again
680 unblockUserSignals();
689 /* ---------------------------------------------------------------------------
690 Where are the roots that we know about?
692 - all the threads on the runnable queue
693 - all the threads on the blocked queue
694 - all the threads on the sleeping queue
695 - all the thread currently executing a _ccall_GC
696 - all the "main threads"
698 ------------------------------------------------------------------------ */
700 /* This has to be protected either by the scheduler monitor, or by the
701 garbage collection monitor (probably the latter).
706 GetRoots( evac_fn evac )
712 for (i = 0; i < n_capabilities; i++) {
713 cap = &capabilities[i];
714 evac((StgClosure **)(void *)&cap->run_queue_hd);
715 evac((StgClosure **)(void *)&cap->run_queue_tl);
716 #if defined(THREADED_RTS)
717 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
718 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
720 for (task = cap->suspended_ccalling_tasks; task != NULL;
722 debugTrace(DEBUG_sched,
723 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
724 evac((StgClosure **)(void *)&task->suspended_tso);
729 #if !defined(THREADED_RTS)
730 evac((StgClosure **)(void *)&blocked_queue_hd);
731 evac((StgClosure **)(void *)&blocked_queue_tl);
732 evac((StgClosure **)(void *)&sleeping_queue);
735 // evac((StgClosure **)&blackhole_queue);
737 #if defined(THREADED_RTS)
738 markSparkQueue(evac);
741 #if defined(RTS_USER_SIGNALS)
742 // mark the signal handlers (signals should be already blocked)
743 markSignalHandlers(evac);
747 /* -----------------------------------------------------------------------------
748 isAlive determines whether the given closure is still alive (after
749 a garbage collection) or not. It returns the new address of the
750 closure if it is alive, or NULL otherwise.
752 NOTE: Use it before compaction only!
753 It untags and (if needed) retags pointers to closures.
754 -------------------------------------------------------------------------- */
758 isAlive(StgClosure *p)
760 const StgInfoTable *info;
766 /* The tag and the pointer are split, to be merged later when needed. */
767 tag = GET_CLOSURE_TAG(p);
768 q = UNTAG_CLOSURE(p);
770 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
773 // ignore static closures
775 // ToDo: for static closures, check the static link field.
776 // Problem here is that we sometimes don't set the link field, eg.
777 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
779 if (!HEAP_ALLOCED(q)) {
783 // ignore closures in generations that we're not collecting.
785 if (bd->gen_no > N) {
789 // if it's a pointer into to-space, then we're done
790 if (bd->flags & BF_EVACUATED) {
794 // large objects use the evacuated flag
795 if (bd->flags & BF_LARGE) {
799 // check the mark bit for compacted steps
800 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
804 switch (info->type) {
809 case IND_OLDGEN: // rely on compatible layout with StgInd
810 case IND_OLDGEN_PERM:
811 // follow indirections
812 p = ((StgInd *)q)->indirectee;
817 return ((StgEvacuated *)q)->evacuee;
820 if (((StgTSO *)q)->what_next == ThreadRelocated) {
821 p = (StgClosure *)((StgTSO *)q)->link;
833 /* -----------------------------------------------------------------------------
834 Figure out which generation to collect, initialise N and major_gc.
835 -------------------------------------------------------------------------- */
838 initialise_N (rtsBool force_major_gc)
842 if (force_major_gc) {
843 N = RtsFlags.GcFlags.generations - 1;
847 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
848 if (generations[g].steps[0].n_blocks +
849 generations[g].steps[0].n_large_blocks
850 >= generations[g].max_blocks) {
854 major_gc = (N == RtsFlags.GcFlags.generations-1);
858 /* -----------------------------------------------------------------------------
859 Initialise the gc_thread structures.
860 -------------------------------------------------------------------------- */
863 alloc_gc_thread (gc_thread *t, int n)
870 initCondition(&t->wake_cond);
871 initMutex(&t->wake_mutex);
872 t->wakeup = rtsFalse;
877 t->free_blocks = NULL;
882 t->steps = stgMallocBytes(RtsFlags.GcFlags.generations *
883 sizeof(step_workspace *),
884 "initialise_gc_thread");
886 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
888 t->steps[g] = stgMallocBytes(generations[g].n_steps *
889 sizeof(step_workspace),
890 "initialise_gc_thread/2");
892 for (s = 0; s < generations[g].n_steps; s++)
894 ws = &t->steps[g][s];
895 ws->stp = &generations[g].steps[s];
902 ws->buffer_todo_bd = NULL;
904 ws->scavd_list = NULL;
905 ws->n_scavd_blocks = 0;
912 alloc_gc_threads (void)
914 if (gc_threads == NULL) {
915 #if defined(THREADED_RTS)
917 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
921 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
922 alloc_gc_thread(&gc_threads[i], i);
925 gc_threads = stgMallocBytes (sizeof(gc_thread),
928 alloc_gc_thread(gc_threads, 0);
933 /* ----------------------------------------------------------------------------
935 ------------------------------------------------------------------------- */
937 static nat gc_running_threads;
939 #if defined(THREADED_RTS)
940 static Mutex gc_running_mutex;
947 ACQUIRE_LOCK(&gc_running_mutex);
948 n_running = ++gc_running_threads;
949 RELEASE_LOCK(&gc_running_mutex);
957 ACQUIRE_LOCK(&gc_running_mutex);
958 n_running = --gc_running_threads;
959 RELEASE_LOCK(&gc_running_mutex);
964 // gc_thread_work(): Scavenge until there's no work left to do and all
965 // the running threads are idle.
968 gc_thread_work (void)
972 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
974 // gc_running_threads has already been incremented for us; either
975 // this is the main thread and we incremented it inside
976 // GarbageCollect(), or this is a worker thread and the main
977 // thread bumped gc_running_threads before waking us up.
981 // scavenge_loop() only exits when there's no work to do
984 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
985 gct->thread_index, r);
987 while (gc_running_threads != 0) {
992 // any_work() does not remove the work from the queue, it
993 // just checks for the presence of work. If we find any,
994 // then we increment gc_running_threads and go back to
995 // scavenge_loop() to perform any pending work.
998 // All threads are now stopped
999 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1003 #if defined(THREADED_RTS)
1005 gc_thread_mainloop (void)
1007 while (!gct->exit) {
1009 // Wait until we're told to wake up
1010 ACQUIRE_LOCK(&gct->wake_mutex);
1011 while (!gct->wakeup) {
1012 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1014 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1016 RELEASE_LOCK(&gct->wake_mutex);
1017 gct->wakeup = rtsFalse;
1018 if (gct->exit) break;
1025 #if defined(THREADED_RTS)
1027 gc_thread_entry (gc_thread *my_gct)
1030 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1031 gct->id = osThreadId();
1032 gc_thread_mainloop();
1037 start_gc_threads (void)
1039 #if defined(THREADED_RTS)
1042 static rtsBool done = rtsFalse;
1044 gc_running_threads = 0;
1045 initMutex(&gc_running_mutex);
1048 // Start from 1: the main thread is 0
1049 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1050 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1059 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1061 #if defined(THREADED_RTS)
1063 for (i=1; i < n_threads; i++) {
1065 ACQUIRE_LOCK(&gc_threads[i].wake_mutex);
1066 gc_threads[i].wakeup = rtsTrue;
1067 signalCondition(&gc_threads[i].wake_cond);
1068 RELEASE_LOCK(&gc_threads[i].wake_mutex);
1073 /* ----------------------------------------------------------------------------
1074 Initialise a generation that is to be collected
1075 ------------------------------------------------------------------------- */
1078 init_collected_gen (nat g, nat n_threads)
1085 // Throw away the current mutable list. Invariant: the mutable
1086 // list always has at least one block; this means we can avoid a
1087 // check for NULL in recordMutable().
1089 freeChain(generations[g].mut_list);
1090 generations[g].mut_list = allocBlock();
1091 for (i = 0; i < n_capabilities; i++) {
1092 freeChain(capabilities[i].mut_lists[g]);
1093 capabilities[i].mut_lists[g] = allocBlock();
1097 for (s = 0; s < generations[g].n_steps; s++) {
1099 // generation 0, step 0 doesn't need to-space
1100 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1104 stp = &generations[g].steps[s];
1105 ASSERT(stp->gen_no == g);
1107 // deprecate the existing blocks
1108 stp->old_blocks = stp->blocks;
1109 stp->n_old_blocks = stp->n_blocks;
1113 // we don't have any to-be-scavenged blocks yet
1117 // initialise the large object queues.
1118 stp->scavenged_large_objects = NULL;
1119 stp->n_scavenged_large_blocks = 0;
1121 // mark the large objects as not evacuated yet
1122 for (bd = stp->large_objects; bd; bd = bd->link) {
1123 bd->flags &= ~BF_EVACUATED;
1126 // for a compacted step, we need to allocate the bitmap
1127 if (stp->is_compacted) {
1128 nat bitmap_size; // in bytes
1129 bdescr *bitmap_bdescr;
1132 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1134 if (bitmap_size > 0) {
1135 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1137 stp->bitmap = bitmap_bdescr;
1138 bitmap = bitmap_bdescr->start;
1140 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1141 bitmap_size, bitmap);
1143 // don't forget to fill it with zeros!
1144 memset(bitmap, 0, bitmap_size);
1146 // For each block in this step, point to its bitmap from the
1147 // block descriptor.
1148 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1149 bd->u.bitmap = bitmap;
1150 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1152 // Also at this point we set the BF_COMPACTED flag
1153 // for this block. The invariant is that
1154 // BF_COMPACTED is always unset, except during GC
1155 // when it is set on those blocks which will be
1157 bd->flags |= BF_COMPACTED;
1163 // For each GC thread, for each step, allocate a "todo" block to
1164 // store evacuated objects to be scavenged, and a block to store
1165 // evacuated objects that do not need to be scavenged.
1166 for (t = 0; t < n_threads; t++) {
1167 for (s = 0; s < generations[g].n_steps; s++) {
1169 // we don't copy objects into g0s0, unless -G0
1170 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1172 ws = &gc_threads[t].steps[g][s];
1177 ws->todo_large_objects = NULL;
1179 // allocate the first to-space block; extra blocks will be
1180 // chained on as necessary.
1182 ws->buffer_todo_bd = NULL;
1183 gc_alloc_todo_block(ws);
1185 // allocate a block for "already scavenged" objects. This goes
1186 // on the front of the stp->blocks list, so it won't be
1187 // traversed by the scavenging sweep.
1188 ws->scavd_list = NULL;
1189 ws->n_scavd_blocks = 0;
1190 gc_alloc_scavd_block(ws);
1196 /* ----------------------------------------------------------------------------
1197 Initialise a generation that is *not* to be collected
1198 ------------------------------------------------------------------------- */
1201 init_uncollected_gen (nat g, nat threads)
1208 for (s = 0; s < generations[g].n_steps; s++) {
1209 stp = &generations[g].steps[s];
1210 stp->scavenged_large_objects = NULL;
1211 stp->n_scavenged_large_blocks = 0;
1214 for (t = 0; t < threads; t++) {
1215 for (s = 0; s < generations[g].n_steps; s++) {
1217 ws = &gc_threads[t].steps[g][s];
1220 ws->buffer_todo_bd = NULL;
1221 ws->todo_large_objects = NULL;
1223 // If the block at the head of the list in this generation
1224 // is less than 3/4 full, then use it as a todo block.
1225 if (isPartiallyFull(stp->blocks))
1227 ws->todo_bd = stp->blocks;
1228 stp->blocks = stp->blocks->link;
1230 ws->todo_bd->link = NULL;
1232 // this block is also the scan block; we must scan
1233 // from the current end point.
1234 ws->scan_bd = ws->todo_bd;
1235 ws->scan = ws->scan_bd->free;
1237 // subtract the contents of this block from the stats,
1238 // because we'll count the whole block later.
1239 copied -= ws->scan_bd->free - ws->scan_bd->start;
1246 gc_alloc_todo_block(ws);
1249 // Do the same trick for the scavd block
1250 if (isPartiallyFull(stp->blocks))
1252 ws->scavd_list = stp->blocks;
1253 stp->blocks = stp->blocks->link;
1255 ws->scavd_list->link = NULL;
1256 ws->n_scavd_blocks = 1;
1257 // subtract the contents of this block from the stats,
1258 // because we'll count the whole block later.
1259 scavd_copied -= ws->scavd_list->free - ws->scavd_list->start;
1263 ws->scavd_list = NULL;
1264 ws->n_scavd_blocks = 0;
1265 gc_alloc_scavd_block(ws);
1270 // Move the private mutable lists from each capability onto the
1271 // main mutable list for the generation.
1272 for (i = 0; i < n_capabilities; i++) {
1273 for (bd = capabilities[i].mut_lists[g];
1274 bd->link != NULL; bd = bd->link) {
1277 bd->link = generations[g].mut_list;
1278 generations[g].mut_list = capabilities[i].mut_lists[g];
1279 capabilities[i].mut_lists[g] = allocBlock();
1283 /* -----------------------------------------------------------------------------
1284 Initialise a gc_thread before GC
1285 -------------------------------------------------------------------------- */
1288 init_gc_thread (gc_thread *t)
1291 t->failed_to_evac = rtsFalse;
1292 t->eager_promotion = rtsTrue;
1293 t->thunk_selector_depth = 0;
1296 /* -----------------------------------------------------------------------------
1297 Function we pass to GetRoots to evacuate roots.
1298 -------------------------------------------------------------------------- */
1301 mark_root(StgClosure **root)
1306 /* -----------------------------------------------------------------------------
1307 Initialising the static object & mutable lists
1308 -------------------------------------------------------------------------- */
1311 zero_static_object_list(StgClosure* first_static)
1315 const StgInfoTable *info;
1317 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1319 link = *STATIC_LINK(info, p);
1320 *STATIC_LINK(info,p) = NULL;
1324 /* -----------------------------------------------------------------------------
1326 -------------------------------------------------------------------------- */
1333 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1334 c = (StgIndStatic *)c->static_link)
1336 SET_INFO(c, c->saved_info);
1337 c->saved_info = NULL;
1338 // could, but not necessary: c->static_link = NULL;
1340 revertible_caf_list = NULL;
1344 markCAFs( evac_fn evac )
1348 for (c = (StgIndStatic *)caf_list; c != NULL;
1349 c = (StgIndStatic *)c->static_link)
1351 evac(&c->indirectee);
1353 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1354 c = (StgIndStatic *)c->static_link)
1356 evac(&c->indirectee);
1360 /* ----------------------------------------------------------------------------
1361 Update the pointers from the task list
1363 These are treated as weak pointers because we want to allow a main
1364 thread to get a BlockedOnDeadMVar exception in the same way as any
1365 other thread. Note that the threads should all have been retained
1366 by GC by virtue of being on the all_threads list, we're just
1367 updating pointers here.
1368 ------------------------------------------------------------------------- */
1371 update_task_list (void)
1375 for (task = all_tasks; task != NULL; task = task->all_link) {
1376 if (!task->stopped && task->tso) {
1377 ASSERT(task->tso->bound == task);
1378 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1380 barf("task %p: main thread %d has been GC'd",
1393 /* ----------------------------------------------------------------------------
1394 Reset the sizes of the older generations when we do a major
1397 CURRENT STRATEGY: make all generations except zero the same size.
1398 We have to stay within the maximum heap size, and leave a certain
1399 percentage of the maximum heap size available to allocate into.
1400 ------------------------------------------------------------------------- */
1403 resize_generations (void)
1407 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1408 nat live, size, min_alloc;
1409 nat max = RtsFlags.GcFlags.maxHeapSize;
1410 nat gens = RtsFlags.GcFlags.generations;
1412 // live in the oldest generations
1413 live = oldest_gen->steps[0].n_blocks +
1414 oldest_gen->steps[0].n_large_blocks;
1416 // default max size for all generations except zero
1417 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1418 RtsFlags.GcFlags.minOldGenSize);
1420 // minimum size for generation zero
1421 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1422 RtsFlags.GcFlags.minAllocAreaSize);
1424 // Auto-enable compaction when the residency reaches a
1425 // certain percentage of the maximum heap size (default: 30%).
1426 if (RtsFlags.GcFlags.generations > 1 &&
1427 (RtsFlags.GcFlags.compact ||
1429 oldest_gen->steps[0].n_blocks >
1430 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1431 oldest_gen->steps[0].is_compacted = 1;
1432 // debugBelch("compaction: on\n", live);
1434 oldest_gen->steps[0].is_compacted = 0;
1435 // debugBelch("compaction: off\n", live);
1438 // if we're going to go over the maximum heap size, reduce the
1439 // size of the generations accordingly. The calculation is
1440 // different if compaction is turned on, because we don't need
1441 // to double the space required to collect the old generation.
1444 // this test is necessary to ensure that the calculations
1445 // below don't have any negative results - we're working
1446 // with unsigned values here.
1447 if (max < min_alloc) {
1451 if (oldest_gen->steps[0].is_compacted) {
1452 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1453 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1456 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1457 size = (max - min_alloc) / ((gens - 1) * 2);
1467 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1468 min_alloc, size, max);
1471 for (g = 0; g < gens; g++) {
1472 generations[g].max_blocks = size;
1477 /* -----------------------------------------------------------------------------
1478 Calculate the new size of the nursery, and resize it.
1479 -------------------------------------------------------------------------- */
1482 resize_nursery (void)
1484 if (RtsFlags.GcFlags.generations == 1)
1485 { // Two-space collector:
1488 /* set up a new nursery. Allocate a nursery size based on a
1489 * function of the amount of live data (by default a factor of 2)
1490 * Use the blocks from the old nursery if possible, freeing up any
1493 * If we get near the maximum heap size, then adjust our nursery
1494 * size accordingly. If the nursery is the same size as the live
1495 * data (L), then we need 3L bytes. We can reduce the size of the
1496 * nursery to bring the required memory down near 2L bytes.
1498 * A normal 2-space collector would need 4L bytes to give the same
1499 * performance we get from 3L bytes, reducing to the same
1500 * performance at 2L bytes.
1502 blocks = g0s0->n_old_blocks;
1504 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1505 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1506 RtsFlags.GcFlags.maxHeapSize )
1508 long adjusted_blocks; // signed on purpose
1511 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1513 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1514 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1516 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1517 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1521 blocks = adjusted_blocks;
1525 blocks *= RtsFlags.GcFlags.oldGenFactor;
1526 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1528 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1531 resizeNurseries(blocks);
1533 else // Generational collector
1536 * If the user has given us a suggested heap size, adjust our
1537 * allocation area to make best use of the memory available.
1539 if (RtsFlags.GcFlags.heapSizeSuggestion)
1542 nat needed = calcNeeded(); // approx blocks needed at next GC
1544 /* Guess how much will be live in generation 0 step 0 next time.
1545 * A good approximation is obtained by finding the
1546 * percentage of g0s0 that was live at the last minor GC.
1548 * We have an accurate figure for the amount of copied data in
1549 * 'copied', but we must convert this to a number of blocks, with
1550 * a small adjustment for estimated slop at the end of a block
1555 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1556 / countNurseryBlocks();
1559 /* Estimate a size for the allocation area based on the
1560 * information available. We might end up going slightly under
1561 * or over the suggested heap size, but we should be pretty
1564 * Formula: suggested - needed
1565 * ----------------------------
1566 * 1 + g0s0_pcnt_kept/100
1568 * where 'needed' is the amount of memory needed at the next
1569 * collection for collecting all steps except g0s0.
1572 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1573 (100 + (long)g0s0_pcnt_kept);
1575 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1576 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1579 resizeNurseries((nat)blocks);
1583 // we might have added extra large blocks to the nursery, so
1584 // resize back to minAllocAreaSize again.
1585 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1590 /* -----------------------------------------------------------------------------
1591 Sanity code for CAF garbage collection.
1593 With DEBUG turned on, we manage a CAF list in addition to the SRT
1594 mechanism. After GC, we run down the CAF list and blackhole any
1595 CAFs which have been garbage collected. This means we get an error
1596 whenever the program tries to enter a garbage collected CAF.
1598 Any garbage collected CAFs are taken off the CAF list at the same
1600 -------------------------------------------------------------------------- */
1602 #if 0 && defined(DEBUG)
1609 const StgInfoTable *info;
1620 ASSERT(info->type == IND_STATIC);
1622 if (STATIC_LINK(info,p) == NULL) {
1623 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1625 SET_INFO(p,&stg_BLACKHOLE_info);
1626 p = STATIC_LINK2(info,p);
1630 pp = &STATIC_LINK2(info,p);
1637 debugTrace(DEBUG_gccafs, "%d CAFs live", i);