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 STM to discard any cached closures it's hoping to re-use
213 // tell the stats department that we've started a GC
217 // check for memory leaks if DEBUG is on
227 // attribute any costs to CCS_GC
233 /* Approximate how much we allocated.
234 * Todo: only when generating stats?
236 allocated = calcAllocated();
238 /* Figure out which generation to collect
240 initialise_N(force_major_gc);
242 /* Allocate + initialise the gc_thread structures.
246 /* Start threads, so they can be spinning up while we finish initialisation.
250 /* How many threads will be participating in this GC?
251 * We don't try to parallelise minor GC.
253 #if defined(THREADED_RTS)
257 n_gc_threads = RtsFlags.ParFlags.gcThreads;
263 #ifdef RTS_GTK_FRONTPANEL
264 if (RtsFlags.GcFlags.frontpanel) {
265 updateFrontPanelBeforeGC(N);
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;
278 initSpinLock(&static_objects_sync);
279 initSpinLock(&recordMutableGen_sync);
280 initSpinLock(&gc_alloc_block_sync);
283 // Initialise all the generations/steps that we're collecting.
284 for (g = 0; g <= N; g++) {
285 init_collected_gen(g,n_gc_threads);
288 // Initialise all the generations/steps that we're *not* collecting.
289 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
290 init_uncollected_gen(g,n_gc_threads);
293 /* Allocate a mark stack if we're doing a major collection.
296 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
297 mark_stack = (StgPtr *)mark_stack_bdescr->start;
298 mark_sp = mark_stack;
299 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
301 mark_stack_bdescr = NULL;
304 // Initialise all our gc_thread structures
305 for (t = 0; t < n_gc_threads; t++) {
306 init_gc_thread(&gc_threads[t]);
309 // the main thread is running: this prevents any other threads from
310 // exiting prematurely, so we can start them now.
312 wakeup_gc_threads(n_gc_threads);
317 // this is the main thread
318 gct = &gc_threads[0];
320 /* -----------------------------------------------------------------------
321 * follow all the roots that we know about:
322 * - mutable lists from each generation > N
323 * we want to *scavenge* these roots, not evacuate them: they're not
324 * going to move in this GC.
325 * Also do them in reverse generation order, for the usual reason:
326 * namely to reduce the likelihood of spurious old->new pointers.
329 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
330 generations[g].saved_mut_list = generations[g].mut_list;
331 generations[g].mut_list = allocBlock();
332 // mut_list always has at least one block.
334 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
335 scavenge_mutable_list(&generations[g]);
339 // follow roots from the CAF list (used by GHCi)
343 // follow all the roots that the application knows about.
347 #if defined(RTS_USER_SIGNALS)
348 // mark the signal handlers (signals should be already blocked)
349 markSignalHandlers(mark_root);
352 // Mark the weak pointer list, and prepare to detect dead weak pointers.
356 // Mark the stable pointer table.
357 markStablePtrTable(mark_root);
359 /* -------------------------------------------------------------------------
360 * Repeatedly scavenge all the areas we know about until there's no
361 * more scavenging to be done.
366 // The other threads are now stopped. We might recurse back to
367 // here, but from now on this is the only thread.
369 // if any blackholes are alive, make the threads that wait on
371 if (traverseBlackholeQueue()) {
376 // must be last... invariant is that everything is fully
377 // scavenged at this point.
378 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
383 // If we get to here, there's really nothing left to do.
387 // Update pointers from the Task list
390 // Now see which stable names are still alive.
394 // We call processHeapClosureForDead() on every closure destroyed during
395 // the current garbage collection, so we invoke LdvCensusForDead().
396 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
397 || RtsFlags.ProfFlags.bioSelector != NULL)
401 // NO MORE EVACUATION AFTER THIS POINT!
402 // Finally: compaction of the oldest generation.
403 if (major_gc && oldest_gen->steps[0].is_compacted) {
404 // save number of blocks for stats
405 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
409 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
411 // Two-space collector: free the old to-space.
412 // g0s0->old_blocks is the old nursery
413 // g0s0->blocks is to-space from the previous GC
414 if (RtsFlags.GcFlags.generations == 1) {
415 if (g0s0->blocks != NULL) {
416 freeChain(g0s0->blocks);
421 // For each workspace, in each thread:
422 // * clear the BF_EVACUATED flag from each copied block
423 // * move the copied blocks to the step
429 for (t = 0; t < n_gc_threads; t++) {
430 thr = &gc_threads[t];
432 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
433 for (s = 0; s < generations[g].n_steps; s++) {
434 ws = &thr->steps[g][s];
435 if (g==0 && s==0) continue;
438 // ASSERT( ws->scan_bd == ws->todo_bd );
439 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
441 // Push the final block
442 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
444 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
446 prev = ws->scavd_list;
447 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
448 bd->flags &= ~BF_EVACUATED; // now from-space
451 prev->link = ws->stp->blocks;
452 ws->stp->blocks = ws->scavd_list;
453 ws->stp->n_blocks += ws->n_scavd_blocks;
454 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
460 // Two-space collector: swap the semi-spaces around.
461 // Currently: g0s0->old_blocks is the old nursery
462 // g0s0->blocks is to-space from this GC
463 // We want these the other way around.
464 if (RtsFlags.GcFlags.generations == 1) {
465 bdescr *nursery_blocks = g0s0->old_blocks;
466 nat n_nursery_blocks = g0s0->n_old_blocks;
467 g0s0->old_blocks = g0s0->blocks;
468 g0s0->n_old_blocks = g0s0->n_blocks;
469 g0s0->blocks = nursery_blocks;
470 g0s0->n_blocks = n_nursery_blocks;
473 /* run through all the generations/steps and tidy up
475 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
478 generations[g].collections++; // for stats
481 // Count the mutable list as bytes "copied" for the purposes of
482 // stats. Every mutable list is copied during every GC.
484 nat mut_list_size = 0;
485 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
486 mut_list_size += bd->free - bd->start;
488 copied += mut_list_size;
491 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
492 (unsigned long)(mut_list_size * sizeof(W_)),
493 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
496 for (s = 0; s < generations[g].n_steps; s++) {
498 stp = &generations[g].steps[s];
500 // for generations we collected...
503 /* free old memory and shift to-space into from-space for all
504 * the collected steps (except the allocation area). These
505 * freed blocks will probaby be quickly recycled.
507 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
508 if (stp->is_compacted)
510 // for a compacted step, just shift the new to-space
511 // onto the front of the now-compacted existing blocks.
512 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
513 bd->flags &= ~BF_EVACUATED; // now from-space
515 // tack the new blocks on the end of the existing blocks
516 if (stp->old_blocks != NULL) {
517 for (bd = stp->old_blocks; bd != NULL; bd = next) {
518 // NB. this step might not be compacted next
519 // time, so reset the BF_COMPACTED flags.
520 // They are set before GC if we're going to
521 // compact. (search for BF_COMPACTED above).
522 bd->flags &= ~BF_COMPACTED;
525 bd->link = stp->blocks;
528 stp->blocks = stp->old_blocks;
530 // add the new blocks to the block tally
531 stp->n_blocks += stp->n_old_blocks;
532 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
536 freeChain(stp->old_blocks);
538 stp->old_blocks = NULL;
539 stp->n_old_blocks = 0;
542 /* LARGE OBJECTS. The current live large objects are chained on
543 * scavenged_large, having been moved during garbage
544 * collection from large_objects. Any objects left on
545 * large_objects list are therefore dead, so we free them here.
547 for (bd = stp->large_objects; bd != NULL; bd = next) {
553 // update the count of blocks used by large objects
554 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
555 bd->flags &= ~BF_EVACUATED;
557 stp->large_objects = stp->scavenged_large_objects;
558 stp->n_large_blocks = stp->n_scavenged_large_blocks;
561 else // for older generations...
563 /* For older generations, we need to append the
564 * scavenged_large_object list (i.e. large objects that have been
565 * promoted during this GC) to the large_object list for that step.
567 for (bd = stp->scavenged_large_objects; bd; bd = next) {
569 bd->flags &= ~BF_EVACUATED;
570 dbl_link_onto(bd, &stp->large_objects);
573 // add the new blocks we promoted during this GC
574 stp->n_large_blocks += stp->n_scavenged_large_blocks;
579 // update the max size of older generations after a major GC
580 resize_generations();
582 // Guess the amount of live data for stats.
583 live = calcLiveBlocks() * BLOCK_SIZE_W;
584 debugTrace(DEBUG_gc, "Slop: %ldKB",
585 (live - calcLiveWords()) / (1024/sizeof(W_)));
587 // Free the small objects allocated via allocate(), since this will
588 // all have been copied into G0S1 now.
589 if (RtsFlags.GcFlags.generations > 1) {
590 if (g0s0->blocks != NULL) {
591 freeChain(g0s0->blocks);
597 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
599 // Start a new pinned_object_block
600 pinned_object_block = NULL;
602 // Free the mark stack.
603 if (mark_stack_bdescr != NULL) {
604 freeGroup(mark_stack_bdescr);
608 for (g = 0; g <= N; g++) {
609 for (s = 0; s < generations[g].n_steps; s++) {
610 stp = &generations[g].steps[s];
611 if (stp->bitmap != NULL) {
612 freeGroup(stp->bitmap);
620 // mark the garbage collected CAFs as dead
621 #if 0 && defined(DEBUG) // doesn't work at the moment
622 if (major_gc) { gcCAFs(); }
626 // resetStaticObjectForRetainerProfiling() must be called before
628 resetStaticObjectForRetainerProfiling();
631 // zero the scavenged static object list
633 zero_static_object_list(scavenged_static_objects);
639 // start any pending finalizers
641 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
644 // send exceptions to any threads which were about to die
646 resurrectThreads(resurrected_threads);
649 // Update the stable pointer hash table.
650 updateStablePtrTable(major_gc);
652 // check sanity after GC
653 IF_DEBUG(sanity, checkSanity());
655 // extra GC trace info
656 IF_DEBUG(gc, statDescribeGens());
659 // symbol-table based profiling
660 /* heapCensus(to_blocks); */ /* ToDo */
663 // restore enclosing cost centre
669 // check for memory leaks if DEBUG is on
673 #ifdef RTS_GTK_FRONTPANEL
674 if (RtsFlags.GcFlags.frontpanel) {
675 updateFrontPanelAfterGC( N, live );
679 // ok, GC over: tell the stats department what happened.
680 stat_endGC(allocated, live, copied, N);
682 #if defined(RTS_USER_SIGNALS)
683 if (RtsFlags.MiscFlags.install_signal_handlers) {
684 // unblock signals again
685 unblockUserSignals();
694 /* ---------------------------------------------------------------------------
695 Where are the roots that we know about?
697 - all the threads on the runnable queue
698 - all the threads on the blocked queue
699 - all the threads on the sleeping queue
700 - all the thread currently executing a _ccall_GC
701 - all the "main threads"
703 ------------------------------------------------------------------------ */
706 GetRoots( evac_fn evac )
712 // Each GC thread is responsible for following roots from the
713 // Capability of the same number. There will usually be the same
714 // or fewer Capabilities as GC threads, but just in case there
715 // are more, we mark every Capability whose number is the GC
716 // thread's index plus a multiple of the number of GC threads.
717 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
718 cap = &capabilities[i];
719 evac((StgClosure **)(void *)&cap->run_queue_hd);
720 evac((StgClosure **)(void *)&cap->run_queue_tl);
721 #if defined(THREADED_RTS)
722 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
723 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
725 for (task = cap->suspended_ccalling_tasks; task != NULL;
727 debugTrace(DEBUG_sched,
728 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
729 evac((StgClosure **)(void *)&task->suspended_tso);
732 #if defined(THREADED_RTS)
733 markSparkQueue(evac,cap);
737 #if !defined(THREADED_RTS)
738 evac((StgClosure **)(void *)&blocked_queue_hd);
739 evac((StgClosure **)(void *)&blocked_queue_tl);
740 evac((StgClosure **)(void *)&sleeping_queue);
744 /* -----------------------------------------------------------------------------
745 isAlive determines whether the given closure is still alive (after
746 a garbage collection) or not. It returns the new address of the
747 closure if it is alive, or NULL otherwise.
749 NOTE: Use it before compaction only!
750 It untags and (if needed) retags pointers to closures.
751 -------------------------------------------------------------------------- */
755 isAlive(StgClosure *p)
757 const StgInfoTable *info;
763 /* The tag and the pointer are split, to be merged later when needed. */
764 tag = GET_CLOSURE_TAG(p);
765 q = UNTAG_CLOSURE(p);
767 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
770 // ignore static closures
772 // ToDo: for static closures, check the static link field.
773 // Problem here is that we sometimes don't set the link field, eg.
774 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
776 if (!HEAP_ALLOCED(q)) {
780 // ignore closures in generations that we're not collecting.
782 if (bd->gen_no > N) {
786 // if it's a pointer into to-space, then we're done
787 if (bd->flags & BF_EVACUATED) {
791 // large objects use the evacuated flag
792 if (bd->flags & BF_LARGE) {
796 // check the mark bit for compacted steps
797 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
801 switch (info->type) {
806 case IND_OLDGEN: // rely on compatible layout with StgInd
807 case IND_OLDGEN_PERM:
808 // follow indirections
809 p = ((StgInd *)q)->indirectee;
814 return ((StgEvacuated *)q)->evacuee;
817 if (((StgTSO *)q)->what_next == ThreadRelocated) {
818 p = (StgClosure *)((StgTSO *)q)->link;
830 /* -----------------------------------------------------------------------------
831 Figure out which generation to collect, initialise N and major_gc.
832 -------------------------------------------------------------------------- */
835 initialise_N (rtsBool force_major_gc)
839 if (force_major_gc) {
840 N = RtsFlags.GcFlags.generations - 1;
844 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
845 if (generations[g].steps[0].n_blocks +
846 generations[g].steps[0].n_large_blocks
847 >= generations[g].max_blocks) {
851 major_gc = (N == RtsFlags.GcFlags.generations-1);
855 /* -----------------------------------------------------------------------------
856 Initialise the gc_thread structures.
857 -------------------------------------------------------------------------- */
860 alloc_gc_thread (gc_thread *t, int n)
867 initCondition(&t->wake_cond);
868 initMutex(&t->wake_mutex);
869 t->wakeup = rtsFalse;
874 t->free_blocks = NULL;
883 t->steps = stgMallocBytes(RtsFlags.GcFlags.generations *
884 sizeof(step_workspace *),
885 "initialise_gc_thread");
887 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
889 t->steps[g] = stgMallocBytes(generations[g].n_steps *
890 sizeof(step_workspace),
891 "initialise_gc_thread/2");
893 for (s = 0; s < generations[g].n_steps; s++)
895 ws = &t->steps[g][s];
896 ws->stp = &generations[g].steps[s];
903 ws->buffer_todo_bd = NULL;
905 ws->scavd_list = NULL;
906 ws->n_scavd_blocks = 0;
913 alloc_gc_threads (void)
915 if (gc_threads == NULL) {
916 #if defined(THREADED_RTS)
918 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
922 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
923 alloc_gc_thread(&gc_threads[i], i);
926 gc_threads = stgMallocBytes (sizeof(gc_thread),
929 alloc_gc_thread(gc_threads, 0);
934 /* ----------------------------------------------------------------------------
936 ------------------------------------------------------------------------- */
938 static nat gc_running_threads;
940 #if defined(THREADED_RTS)
941 static Mutex gc_running_mutex;
948 ACQUIRE_LOCK(&gc_running_mutex);
949 n_running = ++gc_running_threads;
950 RELEASE_LOCK(&gc_running_mutex);
958 ACQUIRE_LOCK(&gc_running_mutex);
959 n_running = --gc_running_threads;
960 RELEASE_LOCK(&gc_running_mutex);
965 // gc_thread_work(): Scavenge until there's no work left to do and all
966 // the running threads are idle.
969 gc_thread_work (void)
973 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
975 // gc_running_threads has already been incremented for us; either
976 // this is the main thread and we incremented it inside
977 // GarbageCollect(), or this is a worker thread and the main
978 // thread bumped gc_running_threads before waking us up.
980 // Every thread evacuates some roots.
986 // scavenge_loop() only exits when there's no work to do
989 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
990 gct->thread_index, r);
992 while (gc_running_threads != 0) {
997 // any_work() does not remove the work from the queue, it
998 // just checks for the presence of work. If we find any,
999 // then we increment gc_running_threads and go back to
1000 // scavenge_loop() to perform any pending work.
1003 // All threads are now stopped
1004 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1008 #if defined(THREADED_RTS)
1010 gc_thread_mainloop (void)
1012 while (!gct->exit) {
1014 // Wait until we're told to wake up
1015 ACQUIRE_LOCK(&gct->wake_mutex);
1016 while (!gct->wakeup) {
1017 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1019 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1021 RELEASE_LOCK(&gct->wake_mutex);
1022 gct->wakeup = rtsFalse;
1023 if (gct->exit) break;
1026 // start performance counters in this thread...
1027 if (gct->papi_events == -1) {
1028 papi_init_eventset(&gct->papi_events);
1030 papi_thread_start_gc1_count(gct->papi_events);
1036 // count events in this thread towards the GC totals
1037 papi_thread_stop_gc1_count(gct->papi_events);
1043 #if defined(THREADED_RTS)
1045 gc_thread_entry (gc_thread *my_gct)
1048 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1049 gct->id = osThreadId();
1050 gc_thread_mainloop();
1055 start_gc_threads (void)
1057 #if defined(THREADED_RTS)
1060 static rtsBool done = rtsFalse;
1062 gc_running_threads = 0;
1063 initMutex(&gc_running_mutex);
1066 // Start from 1: the main thread is 0
1067 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1068 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1077 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1079 #if defined(THREADED_RTS)
1081 for (i=1; i < n_threads; i++) {
1083 ACQUIRE_LOCK(&gc_threads[i].wake_mutex);
1084 gc_threads[i].wakeup = rtsTrue;
1085 signalCondition(&gc_threads[i].wake_cond);
1086 RELEASE_LOCK(&gc_threads[i].wake_mutex);
1091 /* ----------------------------------------------------------------------------
1092 Initialise a generation that is to be collected
1093 ------------------------------------------------------------------------- */
1096 init_collected_gen (nat g, nat n_threads)
1103 // Throw away the current mutable list. Invariant: the mutable
1104 // list always has at least one block; this means we can avoid a
1105 // check for NULL in recordMutable().
1107 freeChain(generations[g].mut_list);
1108 generations[g].mut_list = allocBlock();
1109 for (i = 0; i < n_capabilities; i++) {
1110 freeChain(capabilities[i].mut_lists[g]);
1111 capabilities[i].mut_lists[g] = allocBlock();
1115 for (s = 0; s < generations[g].n_steps; s++) {
1117 // generation 0, step 0 doesn't need to-space
1118 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1122 stp = &generations[g].steps[s];
1123 ASSERT(stp->gen_no == g);
1125 // deprecate the existing blocks
1126 stp->old_blocks = stp->blocks;
1127 stp->n_old_blocks = stp->n_blocks;
1131 // we don't have any to-be-scavenged blocks yet
1135 // initialise the large object queues.
1136 stp->scavenged_large_objects = NULL;
1137 stp->n_scavenged_large_blocks = 0;
1139 // mark the large objects as not evacuated yet
1140 for (bd = stp->large_objects; bd; bd = bd->link) {
1141 bd->flags &= ~BF_EVACUATED;
1144 // for a compacted step, we need to allocate the bitmap
1145 if (stp->is_compacted) {
1146 nat bitmap_size; // in bytes
1147 bdescr *bitmap_bdescr;
1150 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1152 if (bitmap_size > 0) {
1153 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1155 stp->bitmap = bitmap_bdescr;
1156 bitmap = bitmap_bdescr->start;
1158 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1159 bitmap_size, bitmap);
1161 // don't forget to fill it with zeros!
1162 memset(bitmap, 0, bitmap_size);
1164 // For each block in this step, point to its bitmap from the
1165 // block descriptor.
1166 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1167 bd->u.bitmap = bitmap;
1168 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1170 // Also at this point we set the BF_COMPACTED flag
1171 // for this block. The invariant is that
1172 // BF_COMPACTED is always unset, except during GC
1173 // when it is set on those blocks which will be
1175 bd->flags |= BF_COMPACTED;
1181 // For each GC thread, for each step, allocate a "todo" block to
1182 // store evacuated objects to be scavenged, and a block to store
1183 // evacuated objects that do not need to be scavenged.
1184 for (t = 0; t < n_threads; t++) {
1185 for (s = 0; s < generations[g].n_steps; s++) {
1187 // we don't copy objects into g0s0, unless -G0
1188 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1190 ws = &gc_threads[t].steps[g][s];
1195 ws->todo_large_objects = NULL;
1197 // allocate the first to-space block; extra blocks will be
1198 // chained on as necessary.
1200 ws->buffer_todo_bd = NULL;
1201 gc_alloc_todo_block(ws);
1203 ws->scavd_list = NULL;
1204 ws->n_scavd_blocks = 0;
1210 /* ----------------------------------------------------------------------------
1211 Initialise a generation that is *not* to be collected
1212 ------------------------------------------------------------------------- */
1215 init_uncollected_gen (nat g, nat threads)
1222 for (s = 0; s < generations[g].n_steps; s++) {
1223 stp = &generations[g].steps[s];
1224 stp->scavenged_large_objects = NULL;
1225 stp->n_scavenged_large_blocks = 0;
1228 for (t = 0; t < threads; t++) {
1229 for (s = 0; s < generations[g].n_steps; s++) {
1231 ws = &gc_threads[t].steps[g][s];
1234 ws->buffer_todo_bd = NULL;
1235 ws->todo_large_objects = NULL;
1237 ws->scavd_list = NULL;
1238 ws->n_scavd_blocks = 0;
1240 // If the block at the head of the list in this generation
1241 // is less than 3/4 full, then use it as a todo block.
1242 if (stp->blocks && isPartiallyFull(stp->blocks))
1244 ws->todo_bd = stp->blocks;
1245 ws->todo_free = ws->todo_bd->free;
1246 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1247 stp->blocks = stp->blocks->link;
1249 ws->todo_bd->link = NULL;
1251 // this block is also the scan block; we must scan
1252 // from the current end point.
1253 ws->scan_bd = ws->todo_bd;
1254 ws->scan = ws->scan_bd->free;
1256 // subtract the contents of this block from the stats,
1257 // because we'll count the whole block later.
1258 copied -= ws->scan_bd->free - ws->scan_bd->start;
1265 gc_alloc_todo_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);