1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 1998-2006
5 * Generational garbage collector
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
12 * ---------------------------------------------------------------------------*/
14 #include "PosixSource.h"
19 #include "OSThreads.h"
20 #include "LdvProfile.h"
25 #include "BlockAlloc.h"
31 #include "ParTicky.h" // ToDo: move into Rts.h
32 #include "RtsSignals.h"
36 #if defined(RTS_GTK_FRONTPANEL)
37 #include "FrontPanel.h"
40 #include "RetainerProfile.h"
41 #include "RaiseAsync.h"
53 #include <string.h> // for memset()
55 /* -----------------------------------------------------------------------------
57 -------------------------------------------------------------------------- */
59 /* STATIC OBJECT LIST.
62 * We maintain a linked list of static objects that are still live.
63 * The requirements for this list are:
65 * - we need to scan the list while adding to it, in order to
66 * scavenge all the static objects (in the same way that
67 * breadth-first scavenging works for dynamic objects).
69 * - we need to be able to tell whether an object is already on
70 * the list, to break loops.
72 * Each static object has a "static link field", which we use for
73 * linking objects on to the list. We use a stack-type list, consing
74 * objects on the front as they are added (this means that the
75 * scavenge phase is depth-first, not breadth-first, but that
78 * A separate list is kept for objects that have been scavenged
79 * already - this is so that we can zero all the marks afterwards.
81 * An object is on the list if its static link field is non-zero; this
82 * means that we have to mark the end of the list with '1', not NULL.
84 * Extra notes for generational GC:
86 * Each generation has a static object list associated with it. When
87 * collecting generations up to N, we treat the static object lists
88 * from generations > N as roots.
90 * We build up a static object list while collecting generations 0..N,
91 * which is then appended to the static object list of generation N+1.
93 StgClosure* static_objects; // live static objects
94 StgClosure* scavenged_static_objects; // static objects scavenged so far
96 SpinLock static_objects_sync;
99 /* N is the oldest generation being collected, where the generations
100 * are numbered starting at 0. A major GC (indicated by the major_gc
101 * flag) is when we're collecting all generations. We only attempt to
102 * deal with static objects and GC CAFs when doing a major GC.
107 /* Data used for allocation area sizing.
109 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
119 /* Thread-local data for each GC thread
121 gc_thread **gc_threads = NULL;
122 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
124 // Number of threads running in *this* GC. Affects how many
125 // step->todos[] lists we have to look in to find work.
129 long copied; // *words* copied & scavenged during this GC
132 SpinLock recordMutableGen_sync;
135 /* -----------------------------------------------------------------------------
136 Static function declarations
137 -------------------------------------------------------------------------- */
139 static void mark_root (StgClosure **root);
140 static void zero_static_object_list (StgClosure* first_static);
141 static void initialise_N (rtsBool force_major_gc);
142 static void alloc_gc_threads (void);
143 static void init_collected_gen (nat g, nat threads);
144 static void init_uncollected_gen (nat g, nat threads);
145 static void init_gc_thread (gc_thread *t);
146 static void update_task_list (void);
147 static void resize_generations (void);
148 static void resize_nursery (void);
149 static void start_gc_threads (void);
150 static void gc_thread_work (void);
151 static nat inc_running (void);
152 static nat dec_running (void);
153 static void wakeup_gc_threads (nat n_threads);
155 #if 0 && defined(DEBUG)
156 static void gcCAFs (void);
159 /* -----------------------------------------------------------------------------
160 The mark bitmap & stack.
161 -------------------------------------------------------------------------- */
163 #define MARK_STACK_BLOCKS 4
165 bdescr *mark_stack_bdescr;
170 // Flag and pointers used for falling back to a linear scan when the
171 // mark stack overflows.
172 rtsBool mark_stack_overflowed;
173 bdescr *oldgen_scan_bd;
176 /* -----------------------------------------------------------------------------
177 GarbageCollect: the main entry point to the garbage collector.
179 Locks held: all capabilities are held throughout GarbageCollect().
180 -------------------------------------------------------------------------- */
183 GarbageCollect ( rtsBool force_major_gc )
187 lnat live, allocated;
188 lnat oldgen_saved_blocks = 0;
189 gc_thread *saved_gct;
192 // necessary if we stole a callee-saves register for gct:
196 CostCentreStack *prev_CCS;
201 debugTrace(DEBUG_gc, "starting GC");
203 #if defined(RTS_USER_SIGNALS)
204 if (RtsFlags.MiscFlags.install_signal_handlers) {
210 // tell the stats department that we've started a GC
213 // tell the STM to discard any cached closures it's hoping to re-use
222 // attribute any costs to CCS_GC
228 /* Approximate how much we allocated.
229 * Todo: only when generating stats?
231 allocated = calcAllocated();
233 /* Figure out which generation to collect
235 initialise_N(force_major_gc);
237 /* Allocate + initialise the gc_thread structures.
241 /* Start threads, so they can be spinning up while we finish initialisation.
245 /* How many threads will be participating in this GC?
246 * We don't try to parallelise minor GC.
248 #if defined(THREADED_RTS)
252 n_gc_threads = RtsFlags.ParFlags.gcThreads;
258 #ifdef RTS_GTK_FRONTPANEL
259 if (RtsFlags.GcFlags.frontpanel) {
260 updateFrontPanelBeforeGC(N);
265 // check for memory leaks if DEBUG is on
266 memInventory(traceClass(DEBUG_gc));
269 // check stack sanity *before* GC (ToDo: check all threads)
270 IF_DEBUG(sanity, checkFreeListSanity());
272 /* Initialise the static object lists
274 static_objects = END_OF_STATIC_LIST;
275 scavenged_static_objects = END_OF_STATIC_LIST;
277 // Initialise all the generations/steps that we're collecting.
278 for (g = 0; g <= N; g++) {
279 init_collected_gen(g,n_gc_threads);
282 // Initialise all the generations/steps that we're *not* collecting.
283 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
284 init_uncollected_gen(g,n_gc_threads);
287 /* Allocate a mark stack if we're doing a major collection.
290 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
291 mark_stack = (StgPtr *)mark_stack_bdescr->start;
292 mark_sp = mark_stack;
293 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
295 mark_stack_bdescr = NULL;
298 // Initialise all our gc_thread structures
299 for (t = 0; t < n_gc_threads; t++) {
300 init_gc_thread(gc_threads[t]);
303 // the main thread is running: this prevents any other threads from
304 // exiting prematurely, so we can start them now.
306 wakeup_gc_threads(n_gc_threads);
308 // this is the main thread
311 /* -----------------------------------------------------------------------
312 * follow all the roots that we know about:
313 * - mutable lists from each generation > N
314 * we want to *scavenge* these roots, not evacuate them: they're not
315 * going to move in this GC.
316 * Also do them in reverse generation order, for the usual reason:
317 * namely to reduce the likelihood of spurious old->new pointers.
320 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
321 generations[g].saved_mut_list = generations[g].mut_list;
322 generations[g].mut_list = allocBlock();
323 // mut_list always has at least one block.
325 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
326 scavenge_mutable_list(&generations[g]);
330 // follow roots from the CAF list (used by GHCi)
334 // follow all the roots that the application knows about.
338 #if defined(RTS_USER_SIGNALS)
339 // mark the signal handlers (signals should be already blocked)
340 markSignalHandlers(mark_root);
343 // Mark the weak pointer list, and prepare to detect dead weak pointers.
347 // Mark the stable pointer table.
348 markStablePtrTable(mark_root);
350 /* -------------------------------------------------------------------------
351 * Repeatedly scavenge all the areas we know about until there's no
352 * more scavenging to be done.
357 // The other threads are now stopped. We might recurse back to
358 // here, but from now on this is the only thread.
360 // if any blackholes are alive, make the threads that wait on
362 if (traverseBlackholeQueue()) {
367 // must be last... invariant is that everything is fully
368 // scavenged at this point.
369 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
374 // If we get to here, there's really nothing left to do.
378 // Update pointers from the Task list
381 // Now see which stable names are still alive.
385 // We call processHeapClosureForDead() on every closure destroyed during
386 // the current garbage collection, so we invoke LdvCensusForDead().
387 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
388 || RtsFlags.ProfFlags.bioSelector != NULL)
392 // NO MORE EVACUATION AFTER THIS POINT!
393 // Finally: compaction of the oldest generation.
394 if (major_gc && oldest_gen->steps[0].is_compacted) {
395 // save number of blocks for stats
396 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
400 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
402 // Two-space collector: free the old to-space.
403 // g0s0->old_blocks is the old nursery
404 // g0s0->blocks is to-space from the previous GC
405 if (RtsFlags.GcFlags.generations == 1) {
406 if (g0s0->blocks != NULL) {
407 freeChain(g0s0->blocks);
412 // For each workspace, in each thread:
413 // * clear the BF_EVACUATED flag from each copied block
414 // * move the copied blocks to the step
420 for (t = 0; t < n_gc_threads; t++) {
424 for (s = 1; s < total_steps; s++) {
427 // ASSERT( ws->scan_bd == ws->todo_bd );
428 ASSERT( ws->scan_bd ? ws->scan == ws->scan_bd->free : 1 );
430 // Push the final block
431 if (ws->scan_bd) { push_scan_block(ws->scan_bd, ws); }
433 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
435 prev = ws->scavd_list;
436 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
437 bd->flags &= ~BF_EVACUATED; // now from-space
440 prev->link = ws->stp->blocks;
441 ws->stp->blocks = ws->scavd_list;
442 ws->stp->n_blocks += ws->n_scavd_blocks;
443 ASSERT(countBlocks(ws->stp->blocks) == ws->stp->n_blocks);
448 // Two-space collector: swap the semi-spaces around.
449 // Currently: g0s0->old_blocks is the old nursery
450 // g0s0->blocks is to-space from this GC
451 // We want these the other way around.
452 if (RtsFlags.GcFlags.generations == 1) {
453 bdescr *nursery_blocks = g0s0->old_blocks;
454 nat n_nursery_blocks = g0s0->n_old_blocks;
455 g0s0->old_blocks = g0s0->blocks;
456 g0s0->n_old_blocks = g0s0->n_blocks;
457 g0s0->blocks = nursery_blocks;
458 g0s0->n_blocks = n_nursery_blocks;
461 /* run through all the generations/steps and tidy up
466 for (i=0; i < n_gc_threads; i++) {
468 trace(TRACE_gc,"thread %d:", i);
469 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
470 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
471 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
472 trace(TRACE_gc," scav_global_work %ld", gc_threads[i]->scav_global_work);
473 trace(TRACE_gc," scav_local_work %ld", gc_threads[i]->scav_local_work);
475 copied += gc_threads[i]->copied;
479 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
482 generations[g].collections++; // for stats
485 // Count the mutable list as bytes "copied" for the purposes of
486 // stats. Every mutable list is copied during every GC.
488 nat mut_list_size = 0;
489 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
490 mut_list_size += bd->free - bd->start;
492 copied += mut_list_size;
495 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
496 (unsigned long)(mut_list_size * sizeof(W_)),
497 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
500 for (s = 0; s < generations[g].n_steps; s++) {
502 stp = &generations[g].steps[s];
504 // for generations we collected...
507 /* free old memory and shift to-space into from-space for all
508 * the collected steps (except the allocation area). These
509 * freed blocks will probaby be quickly recycled.
511 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
512 if (stp->is_compacted)
514 // for a compacted step, just shift the new to-space
515 // onto the front of the now-compacted existing blocks.
516 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
517 bd->flags &= ~BF_EVACUATED; // now from-space
519 // tack the new blocks on the end of the existing blocks
520 if (stp->old_blocks != NULL) {
521 for (bd = stp->old_blocks; bd != NULL; bd = next) {
522 // NB. this step might not be compacted next
523 // time, so reset the BF_COMPACTED flags.
524 // They are set before GC if we're going to
525 // compact. (search for BF_COMPACTED above).
526 bd->flags &= ~BF_COMPACTED;
529 bd->link = stp->blocks;
532 stp->blocks = stp->old_blocks;
534 // add the new blocks to the block tally
535 stp->n_blocks += stp->n_old_blocks;
536 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
540 freeChain(stp->old_blocks);
542 stp->old_blocks = NULL;
543 stp->n_old_blocks = 0;
546 /* LARGE OBJECTS. The current live large objects are chained on
547 * scavenged_large, having been moved during garbage
548 * collection from large_objects. Any objects left on
549 * large_objects list are therefore dead, so we free them here.
551 for (bd = stp->large_objects; bd != NULL; bd = next) {
557 // update the count of blocks used by large objects
558 for (bd = stp->scavenged_large_objects; bd != NULL; bd = bd->link) {
559 bd->flags &= ~BF_EVACUATED;
561 stp->large_objects = stp->scavenged_large_objects;
562 stp->n_large_blocks = stp->n_scavenged_large_blocks;
565 else // for older generations...
567 /* For older generations, we need to append the
568 * scavenged_large_object list (i.e. large objects that have been
569 * promoted during this GC) to the large_object list for that step.
571 for (bd = stp->scavenged_large_objects; bd; bd = next) {
573 bd->flags &= ~BF_EVACUATED;
574 dbl_link_onto(bd, &stp->large_objects);
577 // add the new blocks we promoted during this GC
578 stp->n_large_blocks += stp->n_scavenged_large_blocks;
583 // update the max size of older generations after a major GC
584 resize_generations();
586 // Guess the amount of live data for stats.
587 live = calcLiveBlocks() * BLOCK_SIZE_W;
588 debugTrace(DEBUG_gc, "Slop: %ldKB",
589 (live - calcLiveWords()) / (1024/sizeof(W_)));
591 // Free the small objects allocated via allocate(), since this will
592 // all have been copied into G0S1 now.
593 if (RtsFlags.GcFlags.generations > 1) {
594 if (g0s0->blocks != NULL) {
595 freeChain(g0s0->blocks);
601 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
603 // Start a new pinned_object_block
604 pinned_object_block = NULL;
606 // Free the mark stack.
607 if (mark_stack_bdescr != NULL) {
608 freeGroup(mark_stack_bdescr);
612 for (g = 0; g <= N; g++) {
613 for (s = 0; s < generations[g].n_steps; s++) {
614 stp = &generations[g].steps[s];
615 if (stp->bitmap != NULL) {
616 freeGroup(stp->bitmap);
624 // mark the garbage collected CAFs as dead
625 #if 0 && defined(DEBUG) // doesn't work at the moment
626 if (major_gc) { gcCAFs(); }
630 // resetStaticObjectForRetainerProfiling() must be called before
632 resetStaticObjectForRetainerProfiling();
635 // zero the scavenged static object list
637 zero_static_object_list(scavenged_static_objects);
643 // start any pending finalizers
645 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
648 // send exceptions to any threads which were about to die
650 resurrectThreads(resurrected_threads);
653 // Update the stable pointer hash table.
654 updateStablePtrTable(major_gc);
656 // check sanity after GC
657 IF_DEBUG(sanity, checkSanity());
659 // extra GC trace info
660 if (traceClass(TRACE_gc)) statDescribeGens();
663 // symbol-table based profiling
664 /* heapCensus(to_blocks); */ /* ToDo */
667 // restore enclosing cost centre
673 // check for memory leaks if DEBUG is on
674 memInventory(traceClass(DEBUG_gc));
677 #ifdef RTS_GTK_FRONTPANEL
678 if (RtsFlags.GcFlags.frontpanel) {
679 updateFrontPanelAfterGC( N, live );
683 // ok, GC over: tell the stats department what happened.
684 stat_endGC(allocated, live, copied, N);
686 #if defined(RTS_USER_SIGNALS)
687 if (RtsFlags.MiscFlags.install_signal_handlers) {
688 // unblock signals again
689 unblockUserSignals();
698 /* -----------------------------------------------------------------------------
699 * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
700 * implicit slide i.e. after marking all sparks are at the beginning of the
701 * spark pool and the spark pool only contains sparkable closures
702 * -------------------------------------------------------------------------- */
706 markSparkQueue (evac_fn evac, Capability *cap)
708 StgClosure **sparkp, **to_sparkp;
709 nat n, pruned_sparks; // stats only
712 PAR_TICKY_MARK_SPARK_QUEUE_START();
717 pool = &(cap->r.rSparks);
719 ASSERT_SPARK_POOL_INVARIANTS(pool);
721 #if defined(PARALLEL_HASKELL)
728 to_sparkp = pool->hd;
729 while (sparkp != pool->tl) {
730 ASSERT(*sparkp!=NULL);
731 ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
732 // ToDo?: statistics gathering here (also for GUM!)
733 if (closure_SHOULD_SPARK(*sparkp)) {
735 *to_sparkp++ = *sparkp;
736 if (to_sparkp == pool->lim) {
737 to_sparkp = pool->base;
744 if (sparkp == pool->lim) {
748 pool->tl = to_sparkp;
750 PAR_TICKY_MARK_SPARK_QUEUE_END(n);
752 #if defined(PARALLEL_HASKELL)
753 debugTrace(DEBUG_sched,
754 "marked %d sparks and pruned %d sparks on [%x]",
755 n, pruned_sparks, mytid);
757 debugTrace(DEBUG_sched,
758 "marked %d sparks and pruned %d sparks",
762 debugTrace(DEBUG_sched,
763 "new spark queue len=%d; (hd=%p; tl=%p)\n",
764 sparkPoolSize(pool), pool->hd, pool->tl);
768 /* ---------------------------------------------------------------------------
769 Where are the roots that we know about?
771 - all the threads on the runnable queue
772 - all the threads on the blocked queue
773 - all the threads on the sleeping queue
774 - all the thread currently executing a _ccall_GC
775 - all the "main threads"
777 ------------------------------------------------------------------------ */
780 GetRoots( evac_fn evac )
786 // Each GC thread is responsible for following roots from the
787 // Capability of the same number. There will usually be the same
788 // or fewer Capabilities as GC threads, but just in case there
789 // are more, we mark every Capability whose number is the GC
790 // thread's index plus a multiple of the number of GC threads.
791 for (i = gct->thread_index; i < n_capabilities; i += n_gc_threads) {
792 cap = &capabilities[i];
793 evac((StgClosure **)(void *)&cap->run_queue_hd);
794 evac((StgClosure **)(void *)&cap->run_queue_tl);
795 #if defined(THREADED_RTS)
796 evac((StgClosure **)(void *)&cap->wakeup_queue_hd);
797 evac((StgClosure **)(void *)&cap->wakeup_queue_tl);
799 for (task = cap->suspended_ccalling_tasks; task != NULL;
801 debugTrace(DEBUG_sched,
802 "evac'ing suspended TSO %lu", (unsigned long)task->suspended_tso->id);
803 evac((StgClosure **)(void *)&task->suspended_tso);
806 #if defined(THREADED_RTS)
807 markSparkQueue(evac,cap);
811 #if !defined(THREADED_RTS)
812 evac((StgClosure **)(void *)&blocked_queue_hd);
813 evac((StgClosure **)(void *)&blocked_queue_tl);
814 evac((StgClosure **)(void *)&sleeping_queue);
818 /* -----------------------------------------------------------------------------
819 isAlive determines whether the given closure is still alive (after
820 a garbage collection) or not. It returns the new address of the
821 closure if it is alive, or NULL otherwise.
823 NOTE: Use it before compaction only!
824 It untags and (if needed) retags pointers to closures.
825 -------------------------------------------------------------------------- */
829 isAlive(StgClosure *p)
831 const StgInfoTable *info;
837 /* The tag and the pointer are split, to be merged later when needed. */
838 tag = GET_CLOSURE_TAG(p);
839 q = UNTAG_CLOSURE(p);
841 ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
844 // ignore static closures
846 // ToDo: for static closures, check the static link field.
847 // Problem here is that we sometimes don't set the link field, eg.
848 // for static closures with an empty SRT or CONSTR_STATIC_NOCAFs.
850 if (!HEAP_ALLOCED(q)) {
854 // ignore closures in generations that we're not collecting.
856 if (bd->gen_no > N) {
860 // if it's a pointer into to-space, then we're done
861 if (bd->flags & BF_EVACUATED) {
865 // large objects use the evacuated flag
866 if (bd->flags & BF_LARGE) {
870 // check the mark bit for compacted steps
871 if ((bd->flags & BF_COMPACTED) && is_marked((P_)q,bd)) {
875 switch (info->type) {
880 case IND_OLDGEN: // rely on compatible layout with StgInd
881 case IND_OLDGEN_PERM:
882 // follow indirections
883 p = ((StgInd *)q)->indirectee;
888 return ((StgEvacuated *)q)->evacuee;
891 if (((StgTSO *)q)->what_next == ThreadRelocated) {
892 p = (StgClosure *)((StgTSO *)q)->link;
904 /* -----------------------------------------------------------------------------
905 Figure out which generation to collect, initialise N and major_gc.
906 -------------------------------------------------------------------------- */
909 initialise_N (rtsBool force_major_gc)
913 if (force_major_gc) {
914 N = RtsFlags.GcFlags.generations - 1;
918 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
919 if (generations[g].steps[0].n_blocks +
920 generations[g].steps[0].n_large_blocks
921 >= generations[g].max_blocks) {
925 major_gc = (N == RtsFlags.GcFlags.generations-1);
929 /* -----------------------------------------------------------------------------
930 Initialise the gc_thread structures.
931 -------------------------------------------------------------------------- */
934 alloc_gc_thread (int n)
940 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
945 initCondition(&t->wake_cond);
946 initMutex(&t->wake_mutex);
947 t->wakeup = rtsFalse;
952 t->free_blocks = NULL;
961 for (s = 0; s < total_steps; s++)
964 ws->stp = &all_steps[s];
965 ASSERT(s == ws->stp->abs_no);
972 ws->buffer_todo_bd = NULL;
974 ws->scavd_list = NULL;
975 ws->n_scavd_blocks = 0;
983 alloc_gc_threads (void)
985 if (gc_threads == NULL) {
986 #if defined(THREADED_RTS)
988 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
992 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
993 gc_threads[i] = alloc_gc_thread(i);
996 gc_threads = stgMallocBytes (sizeof(gc_thread*),
999 gc_threads[0] = alloc_gc_thread(0);
1004 /* ----------------------------------------------------------------------------
1006 ------------------------------------------------------------------------- */
1008 static nat gc_running_threads;
1010 #if defined(THREADED_RTS)
1011 static Mutex gc_running_mutex;
1018 ACQUIRE_LOCK(&gc_running_mutex);
1019 n_running = ++gc_running_threads;
1020 RELEASE_LOCK(&gc_running_mutex);
1028 ACQUIRE_LOCK(&gc_running_mutex);
1029 n_running = --gc_running_threads;
1030 RELEASE_LOCK(&gc_running_mutex);
1035 // gc_thread_work(): Scavenge until there's no work left to do and all
1036 // the running threads are idle.
1039 gc_thread_work (void)
1043 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1045 // gc_running_threads has already been incremented for us; either
1046 // this is the main thread and we incremented it inside
1047 // GarbageCollect(), or this is a worker thread and the main
1048 // thread bumped gc_running_threads before waking us up.
1050 // Every thread evacuates some roots.
1052 GetRoots(mark_root);
1056 // scavenge_loop() only exits when there's no work to do
1059 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1060 gct->thread_index, r);
1062 while (gc_running_threads != 0) {
1067 // any_work() does not remove the work from the queue, it
1068 // just checks for the presence of work. If we find any,
1069 // then we increment gc_running_threads and go back to
1070 // scavenge_loop() to perform any pending work.
1073 // All threads are now stopped
1074 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1078 #if defined(THREADED_RTS)
1080 gc_thread_mainloop (void)
1082 while (!gct->exit) {
1084 // Wait until we're told to wake up
1085 ACQUIRE_LOCK(&gct->wake_mutex);
1086 while (!gct->wakeup) {
1087 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1089 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1091 RELEASE_LOCK(&gct->wake_mutex);
1092 gct->wakeup = rtsFalse;
1093 if (gct->exit) break;
1096 // start performance counters in this thread...
1097 if (gct->papi_events == -1) {
1098 papi_init_eventset(&gct->papi_events);
1100 papi_thread_start_gc1_count(gct->papi_events);
1106 // count events in this thread towards the GC totals
1107 papi_thread_stop_gc1_count(gct->papi_events);
1113 #if defined(THREADED_RTS)
1115 gc_thread_entry (gc_thread *my_gct)
1118 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1119 gct->id = osThreadId();
1120 gc_thread_mainloop();
1125 start_gc_threads (void)
1127 #if defined(THREADED_RTS)
1130 static rtsBool done = rtsFalse;
1132 gc_running_threads = 0;
1133 initMutex(&gc_running_mutex);
1136 // Start from 1: the main thread is 0
1137 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1138 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1147 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1149 #if defined(THREADED_RTS)
1151 for (i=1; i < n_threads; i++) {
1153 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1154 gc_threads[i]->wakeup = rtsTrue;
1155 signalCondition(&gc_threads[i]->wake_cond);
1156 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1161 /* ----------------------------------------------------------------------------
1162 Initialise a generation that is to be collected
1163 ------------------------------------------------------------------------- */
1166 init_collected_gen (nat g, nat n_threads)
1173 // Throw away the current mutable list. Invariant: the mutable
1174 // list always has at least one block; this means we can avoid a
1175 // check for NULL in recordMutable().
1177 freeChain(generations[g].mut_list);
1178 generations[g].mut_list = allocBlock();
1179 for (i = 0; i < n_capabilities; i++) {
1180 freeChain(capabilities[i].mut_lists[g]);
1181 capabilities[i].mut_lists[g] = allocBlock();
1185 for (s = 0; s < generations[g].n_steps; s++) {
1187 // generation 0, step 0 doesn't need to-space
1188 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1192 stp = &generations[g].steps[s];
1193 ASSERT(stp->gen_no == g);
1195 // deprecate the existing blocks
1196 stp->old_blocks = stp->blocks;
1197 stp->n_old_blocks = stp->n_blocks;
1201 // we don't have any to-be-scavenged blocks yet
1205 // initialise the large object queues.
1206 stp->scavenged_large_objects = NULL;
1207 stp->n_scavenged_large_blocks = 0;
1209 // mark the large objects as not evacuated yet
1210 for (bd = stp->large_objects; bd; bd = bd->link) {
1211 bd->flags &= ~BF_EVACUATED;
1214 // for a compacted step, we need to allocate the bitmap
1215 if (stp->is_compacted) {
1216 nat bitmap_size; // in bytes
1217 bdescr *bitmap_bdescr;
1220 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1222 if (bitmap_size > 0) {
1223 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1225 stp->bitmap = bitmap_bdescr;
1226 bitmap = bitmap_bdescr->start;
1228 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1229 bitmap_size, bitmap);
1231 // don't forget to fill it with zeros!
1232 memset(bitmap, 0, bitmap_size);
1234 // For each block in this step, point to its bitmap from the
1235 // block descriptor.
1236 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1237 bd->u.bitmap = bitmap;
1238 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1240 // Also at this point we set the BF_COMPACTED flag
1241 // for this block. The invariant is that
1242 // BF_COMPACTED is always unset, except during GC
1243 // when it is set on those blocks which will be
1245 bd->flags |= BF_COMPACTED;
1251 // For each GC thread, for each step, allocate a "todo" block to
1252 // store evacuated objects to be scavenged, and a block to store
1253 // evacuated objects that do not need to be scavenged.
1254 for (t = 0; t < n_threads; t++) {
1255 for (s = 0; s < generations[g].n_steps; s++) {
1257 // we don't copy objects into g0s0, unless -G0
1258 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1260 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1265 ws->todo_large_objects = NULL;
1267 // allocate the first to-space block; extra blocks will be
1268 // chained on as necessary.
1270 ws->buffer_todo_bd = NULL;
1271 gc_alloc_todo_block(ws);
1273 ws->scavd_list = NULL;
1274 ws->n_scavd_blocks = 0;
1280 /* ----------------------------------------------------------------------------
1281 Initialise a generation that is *not* to be collected
1282 ------------------------------------------------------------------------- */
1285 init_uncollected_gen (nat g, nat threads)
1292 for (s = 0; s < generations[g].n_steps; s++) {
1293 stp = &generations[g].steps[s];
1294 stp->scavenged_large_objects = NULL;
1295 stp->n_scavenged_large_blocks = 0;
1298 for (t = 0; t < threads; t++) {
1299 for (s = 0; s < generations[g].n_steps; s++) {
1301 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1304 ws->buffer_todo_bd = NULL;
1305 ws->todo_large_objects = NULL;
1307 ws->scavd_list = NULL;
1308 ws->n_scavd_blocks = 0;
1310 // If the block at the head of the list in this generation
1311 // is less than 3/4 full, then use it as a todo block.
1312 if (stp->blocks && isPartiallyFull(stp->blocks))
1314 ws->todo_bd = stp->blocks;
1315 ws->todo_free = ws->todo_bd->free;
1316 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1317 stp->blocks = stp->blocks->link;
1319 ws->todo_bd->link = NULL;
1321 // this block is also the scan block; we must scan
1322 // from the current end point.
1323 ws->scan_bd = ws->todo_bd;
1324 ws->scan = ws->scan_bd->free;
1326 // subtract the contents of this block from the stats,
1327 // because we'll count the whole block later.
1328 copied -= ws->scan_bd->free - ws->scan_bd->start;
1335 gc_alloc_todo_block(ws);
1340 // Move the private mutable lists from each capability onto the
1341 // main mutable list for the generation.
1342 for (i = 0; i < n_capabilities; i++) {
1343 for (bd = capabilities[i].mut_lists[g];
1344 bd->link != NULL; bd = bd->link) {
1347 bd->link = generations[g].mut_list;
1348 generations[g].mut_list = capabilities[i].mut_lists[g];
1349 capabilities[i].mut_lists[g] = allocBlock();
1353 /* -----------------------------------------------------------------------------
1354 Initialise a gc_thread before GC
1355 -------------------------------------------------------------------------- */
1358 init_gc_thread (gc_thread *t)
1361 t->failed_to_evac = rtsFalse;
1362 t->eager_promotion = rtsTrue;
1363 t->thunk_selector_depth = 0;
1367 t->scav_global_work = 0;
1368 t->scav_local_work = 0;
1371 /* -----------------------------------------------------------------------------
1372 Function we pass to GetRoots to evacuate roots.
1373 -------------------------------------------------------------------------- */
1376 mark_root(StgClosure **root)
1381 /* -----------------------------------------------------------------------------
1382 Initialising the static object & mutable lists
1383 -------------------------------------------------------------------------- */
1386 zero_static_object_list(StgClosure* first_static)
1390 const StgInfoTable *info;
1392 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1394 link = *STATIC_LINK(info, p);
1395 *STATIC_LINK(info,p) = NULL;
1399 /* -----------------------------------------------------------------------------
1401 -------------------------------------------------------------------------- */
1408 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1409 c = (StgIndStatic *)c->static_link)
1411 SET_INFO(c, c->saved_info);
1412 c->saved_info = NULL;
1413 // could, but not necessary: c->static_link = NULL;
1415 revertible_caf_list = NULL;
1419 markCAFs( evac_fn evac )
1423 for (c = (StgIndStatic *)caf_list; c != NULL;
1424 c = (StgIndStatic *)c->static_link)
1426 evac(&c->indirectee);
1428 for (c = (StgIndStatic *)revertible_caf_list; c != NULL;
1429 c = (StgIndStatic *)c->static_link)
1431 evac(&c->indirectee);
1435 /* ----------------------------------------------------------------------------
1436 Update the pointers from the task list
1438 These are treated as weak pointers because we want to allow a main
1439 thread to get a BlockedOnDeadMVar exception in the same way as any
1440 other thread. Note that the threads should all have been retained
1441 by GC by virtue of being on the all_threads list, we're just
1442 updating pointers here.
1443 ------------------------------------------------------------------------- */
1446 update_task_list (void)
1450 for (task = all_tasks; task != NULL; task = task->all_link) {
1451 if (!task->stopped && task->tso) {
1452 ASSERT(task->tso->bound == task);
1453 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1455 barf("task %p: main thread %d has been GC'd",
1468 /* ----------------------------------------------------------------------------
1469 Reset the sizes of the older generations when we do a major
1472 CURRENT STRATEGY: make all generations except zero the same size.
1473 We have to stay within the maximum heap size, and leave a certain
1474 percentage of the maximum heap size available to allocate into.
1475 ------------------------------------------------------------------------- */
1478 resize_generations (void)
1482 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1483 nat live, size, min_alloc;
1484 nat max = RtsFlags.GcFlags.maxHeapSize;
1485 nat gens = RtsFlags.GcFlags.generations;
1487 // live in the oldest generations
1488 live = oldest_gen->steps[0].n_blocks +
1489 oldest_gen->steps[0].n_large_blocks;
1491 // default max size for all generations except zero
1492 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1493 RtsFlags.GcFlags.minOldGenSize);
1495 // minimum size for generation zero
1496 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1497 RtsFlags.GcFlags.minAllocAreaSize);
1499 // Auto-enable compaction when the residency reaches a
1500 // certain percentage of the maximum heap size (default: 30%).
1501 if (RtsFlags.GcFlags.generations > 1 &&
1502 (RtsFlags.GcFlags.compact ||
1504 oldest_gen->steps[0].n_blocks >
1505 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1506 oldest_gen->steps[0].is_compacted = 1;
1507 // debugBelch("compaction: on\n", live);
1509 oldest_gen->steps[0].is_compacted = 0;
1510 // debugBelch("compaction: off\n", live);
1513 // if we're going to go over the maximum heap size, reduce the
1514 // size of the generations accordingly. The calculation is
1515 // different if compaction is turned on, because we don't need
1516 // to double the space required to collect the old generation.
1519 // this test is necessary to ensure that the calculations
1520 // below don't have any negative results - we're working
1521 // with unsigned values here.
1522 if (max < min_alloc) {
1526 if (oldest_gen->steps[0].is_compacted) {
1527 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1528 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1531 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1532 size = (max - min_alloc) / ((gens - 1) * 2);
1542 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1543 min_alloc, size, max);
1546 for (g = 0; g < gens; g++) {
1547 generations[g].max_blocks = size;
1552 /* -----------------------------------------------------------------------------
1553 Calculate the new size of the nursery, and resize it.
1554 -------------------------------------------------------------------------- */
1557 resize_nursery (void)
1559 if (RtsFlags.GcFlags.generations == 1)
1560 { // Two-space collector:
1563 /* set up a new nursery. Allocate a nursery size based on a
1564 * function of the amount of live data (by default a factor of 2)
1565 * Use the blocks from the old nursery if possible, freeing up any
1568 * If we get near the maximum heap size, then adjust our nursery
1569 * size accordingly. If the nursery is the same size as the live
1570 * data (L), then we need 3L bytes. We can reduce the size of the
1571 * nursery to bring the required memory down near 2L bytes.
1573 * A normal 2-space collector would need 4L bytes to give the same
1574 * performance we get from 3L bytes, reducing to the same
1575 * performance at 2L bytes.
1577 blocks = g0s0->n_old_blocks;
1579 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1580 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1581 RtsFlags.GcFlags.maxHeapSize )
1583 long adjusted_blocks; // signed on purpose
1586 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1588 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1589 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1591 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1592 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1596 blocks = adjusted_blocks;
1600 blocks *= RtsFlags.GcFlags.oldGenFactor;
1601 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1603 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1606 resizeNurseries(blocks);
1608 else // Generational collector
1611 * If the user has given us a suggested heap size, adjust our
1612 * allocation area to make best use of the memory available.
1614 if (RtsFlags.GcFlags.heapSizeSuggestion)
1617 nat needed = calcNeeded(); // approx blocks needed at next GC
1619 /* Guess how much will be live in generation 0 step 0 next time.
1620 * A good approximation is obtained by finding the
1621 * percentage of g0s0 that was live at the last minor GC.
1623 * We have an accurate figure for the amount of copied data in
1624 * 'copied', but we must convert this to a number of blocks, with
1625 * a small adjustment for estimated slop at the end of a block
1630 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1631 / countNurseryBlocks();
1634 /* Estimate a size for the allocation area based on the
1635 * information available. We might end up going slightly under
1636 * or over the suggested heap size, but we should be pretty
1639 * Formula: suggested - needed
1640 * ----------------------------
1641 * 1 + g0s0_pcnt_kept/100
1643 * where 'needed' is the amount of memory needed at the next
1644 * collection for collecting all steps except g0s0.
1647 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1648 (100 + (long)g0s0_pcnt_kept);
1650 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1651 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1654 resizeNurseries((nat)blocks);
1658 // we might have added extra large blocks to the nursery, so
1659 // resize back to minAllocAreaSize again.
1660 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1665 /* -----------------------------------------------------------------------------
1666 Sanity code for CAF garbage collection.
1668 With DEBUG turned on, we manage a CAF list in addition to the SRT
1669 mechanism. After GC, we run down the CAF list and blackhole any
1670 CAFs which have been garbage collected. This means we get an error
1671 whenever the program tries to enter a garbage collected CAF.
1673 Any garbage collected CAFs are taken off the CAF list at the same
1675 -------------------------------------------------------------------------- */
1677 #if 0 && defined(DEBUG)
1684 const StgInfoTable *info;
1695 ASSERT(info->type == IND_STATIC);
1697 if (STATIC_LINK(info,p) == NULL) {
1698 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1700 SET_INFO(p,&stg_BLACKHOLE_info);
1701 p = STATIC_LINK2(info,p);
1705 pp = &STATIC_LINK2(info,p);
1712 debugTrace(DEBUG_gccafs, "%d CAFs live", i);