1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 1998-2008
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"
25 #include "BlockAlloc.h"
29 #include "RtsSignals.h"
31 #if defined(RTS_GTK_FRONTPANEL)
32 #include "FrontPanel.h"
35 #include "RetainerProfile.h"
36 #include "LdvProfile.h"
37 #include "RaiseAsync.h"
47 #include "MarkStack.h"
52 #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.
94 /* N is the oldest generation being collected, where the generations
95 * are numbered starting at 0. A major GC (indicated by the major_gc
96 * flag) is when we're collecting all generations. We only attempt to
97 * deal with static objects and GC CAFs when doing a major GC.
102 /* Data used for allocation area sizing.
104 static lnat g0_pcnt_kept = 30; // percentage of g0 live at last minor GC
114 /* Thread-local data for each GC thread
116 gc_thread **gc_threads = NULL;
118 #if !defined(THREADED_RTS)
119 StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(gen_workspace)];
122 // Number of threads running in *this* GC. Affects how many
123 // step->todos[] lists we have to look in to find work.
127 long copied; // *words* copied & scavenged during this GC
129 rtsBool work_stealing;
133 /* -----------------------------------------------------------------------------
134 Static function declarations
135 -------------------------------------------------------------------------- */
137 static void mark_root (void *user, StgClosure **root);
138 static void zero_static_object_list (StgClosure* first_static);
139 static nat initialise_N (rtsBool force_major_gc);
140 static void init_collected_gen (nat g, nat threads);
141 static void init_uncollected_gen (nat g, nat threads);
142 static void init_gc_thread (gc_thread *t);
143 static void resize_generations (void);
144 static void resize_nursery (void);
145 static void start_gc_threads (void);
146 static void scavenge_until_all_done (void);
147 static StgWord inc_running (void);
148 static StgWord dec_running (void);
149 static void wakeup_gc_threads (nat n_threads, nat me);
150 static void shutdown_gc_threads (nat n_threads, nat me);
152 #if 0 && defined(DEBUG)
153 static void gcCAFs (void);
156 /* -----------------------------------------------------------------------------
158 -------------------------------------------------------------------------- */
160 bdescr *mark_stack_top_bd; // topmost block in the mark stack
161 bdescr *mark_stack_bd; // current block in the mark stack
162 StgPtr mark_sp; // pointer to the next unallocated mark stack entry
164 /* -----------------------------------------------------------------------------
165 GarbageCollect: the main entry point to the garbage collector.
167 Locks held: all capabilities are held throughout GarbageCollect().
168 -------------------------------------------------------------------------- */
171 GarbageCollect (rtsBool force_major_gc,
172 nat gc_type USED_IF_THREADS,
177 lnat live, allocated, max_copied, avg_copied, slop;
178 gc_thread *saved_gct;
181 // necessary if we stole a callee-saves register for gct:
185 CostCentreStack *prev_CCS;
190 #if defined(RTS_USER_SIGNALS)
191 if (RtsFlags.MiscFlags.install_signal_handlers) {
197 ASSERT(sizeof(gen_workspace) == 16 * sizeof(StgWord));
198 // otherwise adjust the padding in gen_workspace.
200 // tell the stats department that we've started a GC
203 // tell the STM to discard any cached closures it's hoping to re-use
206 // lock the StablePtr table
215 // attribute any costs to CCS_GC
221 /* Approximate how much we allocated.
222 * Todo: only when generating stats?
224 allocated = calcAllocated();
226 /* Figure out which generation to collect
228 n = initialise_N(force_major_gc);
230 #if defined(THREADED_RTS)
231 work_stealing = RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
232 N >= RtsFlags.ParFlags.parGcLoadBalancingGen;
233 // It's not always a good idea to do load balancing in parallel
234 // GC. In particular, for a parallel program we don't want to
235 // lose locality by moving cached data into another CPU's cache
236 // (this effect can be quite significant).
238 // We could have a more complex way to deterimine whether to do
239 // work stealing or not, e.g. it might be a good idea to do it
240 // if the heap is big. For now, we just turn it on or off with
244 /* Start threads, so they can be spinning up while we finish initialisation.
248 #if defined(THREADED_RTS)
249 /* How many threads will be participating in this GC?
250 * We don't try to parallelise minor GCs (unless the user asks for
251 * it with +RTS -gn0), or mark/compact/sweep GC.
253 if (gc_type == PENDING_GC_PAR) {
254 n_gc_threads = RtsFlags.ParFlags.nNodes;
262 debugTrace(DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
263 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
265 #ifdef RTS_GTK_FRONTPANEL
266 if (RtsFlags.GcFlags.frontpanel) {
267 updateFrontPanelBeforeGC(N);
272 // check for memory leaks if DEBUG is on
273 memInventory(DEBUG_gc);
276 // check sanity *before* GC
277 IF_DEBUG(sanity, checkSanity(rtsTrue));
279 // Initialise all our gc_thread structures
280 for (t = 0; t < n_gc_threads; t++) {
281 init_gc_thread(gc_threads[t]);
284 // Initialise all the generations/steps that we're collecting.
285 for (g = 0; g <= N; g++) {
286 init_collected_gen(g,n_gc_threads);
289 // Initialise all the generations/steps that we're *not* collecting.
290 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
291 init_uncollected_gen(g,n_gc_threads);
294 /* Allocate a mark stack if we're doing a major collection.
296 if (major_gc && oldest_gen->mark) {
297 mark_stack_bd = allocBlock();
298 mark_stack_top_bd = mark_stack_bd;
299 mark_stack_bd->link = NULL;
300 mark_stack_bd->u.back = NULL;
301 mark_sp = mark_stack_bd->start;
303 mark_stack_bd = NULL;
304 mark_stack_top_bd = NULL;
308 // this is the main thread
310 if (n_gc_threads == 1) {
311 SET_GCT(gc_threads[0]);
313 SET_GCT(gc_threads[cap->no]);
316 SET_GCT(gc_threads[0]);
319 /* -----------------------------------------------------------------------
320 * follow all the roots that we know about:
323 // the main thread is running: this prevents any other threads from
324 // exiting prematurely, so we can start them now.
325 // NB. do this after the mutable lists have been saved above, otherwise
326 // the other GC threads will be writing into the old mutable lists.
328 wakeup_gc_threads(n_gc_threads, gct->thread_index);
330 // Mutable lists from each generation > N
331 // we want to *scavenge* these roots, not evacuate them: they're not
332 // going to move in this GC.
333 // Also do them in reverse generation order, for the usual reason:
334 // namely to reduce the likelihood of spurious old->new pointers.
336 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
337 #if defined(THREADED_RTS)
338 if (n_gc_threads > 1) {
339 scavenge_mutable_list(generations[g].saved_mut_list, &generations[g]);
341 scavenge_mutable_list1(generations[g].saved_mut_list, &generations[g]);
344 scavenge_mutable_list(generations[g].saved_mut_list, &generations[g]);
346 freeChain_sync(generations[g].saved_mut_list);
347 generations[g].saved_mut_list = NULL;
351 // scavenge the capability-private mutable lists. This isn't part
352 // of markSomeCapabilities() because markSomeCapabilities() can only
353 // call back into the GC via mark_root() (due to the gct register
355 if (n_gc_threads == 1) {
356 for (n = 0; n < n_capabilities; n++) {
357 #if defined(THREADED_RTS)
358 scavenge_capability_mut_Lists1(&capabilities[n]);
360 scavenge_capability_mut_lists(&capabilities[n]);
364 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
367 // follow roots from the CAF list (used by GHCi)
369 markCAFs(mark_root, gct);
371 // follow all the roots that the application knows about.
373 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
374 rtsTrue/*prune sparks*/);
376 #if defined(RTS_USER_SIGNALS)
377 // mark the signal handlers (signals should be already blocked)
378 markSignalHandlers(mark_root, gct);
381 // Mark the weak pointer list, and prepare to detect dead weak pointers.
385 // Mark the stable pointer table.
386 markStablePtrTable(mark_root, gct);
388 /* -------------------------------------------------------------------------
389 * Repeatedly scavenge all the areas we know about until there's no
390 * more scavenging to be done.
394 scavenge_until_all_done();
395 // The other threads are now stopped. We might recurse back to
396 // here, but from now on this is the only thread.
398 // if any blackholes are alive, make the threads that wait on
400 if (traverseBlackholeQueue()) {
405 // must be last... invariant is that everything is fully
406 // scavenged at this point.
407 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
412 // If we get to here, there's really nothing left to do.
416 shutdown_gc_threads(n_gc_threads, gct->thread_index);
418 // Now see which stable names are still alive.
422 // We call processHeapClosureForDead() on every closure destroyed during
423 // the current garbage collection, so we invoke LdvCensusForDead().
424 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
425 || RtsFlags.ProfFlags.bioSelector != NULL)
429 // NO MORE EVACUATION AFTER THIS POINT!
431 // Two-space collector: free the old to-space.
432 // g0->old_blocks is the old nursery
433 // g0->blocks is to-space from the previous GC
434 if (RtsFlags.GcFlags.generations == 1) {
435 if (g0->blocks != NULL) {
436 freeChain(g0->blocks);
441 // For each workspace, in each thread, move the copied blocks to the step
447 for (t = 0; t < n_gc_threads; t++) {
450 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
453 // Push the final block
455 push_scanned_block(ws->todo_bd, ws);
458 ASSERT(gct->scan_bd == NULL);
459 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
462 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
463 ws->gen->n_words += bd->free - bd->start;
467 prev->link = ws->gen->blocks;
468 ws->gen->blocks = ws->scavd_list;
470 ws->gen->n_blocks += ws->n_scavd_blocks;
474 // Add all the partial blocks *after* we've added all the full
475 // blocks. This is so that we can grab the partial blocks back
476 // again and try to fill them up in the next GC.
477 for (t = 0; t < n_gc_threads; t++) {
480 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
484 for (bd = ws->part_list; bd != NULL; bd = next) {
486 if (bd->free == bd->start) {
488 ws->part_list = next;
495 ws->gen->n_words += bd->free - bd->start;
500 prev->link = ws->gen->blocks;
501 ws->gen->blocks = ws->part_list;
503 ws->gen->n_blocks += ws->n_part_blocks;
505 ASSERT(countBlocks(ws->gen->blocks) == ws->gen->n_blocks);
506 ASSERT(countOccupied(ws->gen->blocks) == ws->gen->n_words);
511 // Finally: compact or sweep the oldest generation.
512 if (major_gc && oldest_gen->mark) {
513 if (oldest_gen->compact)
514 compact(gct->scavenged_static_objects);
519 /* run through all the generations/steps and tidy up
526 for (i=0; i < n_gc_threads; i++) {
527 if (n_gc_threads > 1) {
528 debugTrace(DEBUG_gc,"thread %d:", i);
529 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
530 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
531 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
532 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
533 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
535 copied += gc_threads[i]->copied;
536 max_copied = stg_max(gc_threads[i]->copied, max_copied);
538 if (n_gc_threads == 1) {
546 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
549 generations[g].collections++; // for stats
550 if (n_gc_threads > 1) generations[g].par_collections++;
553 // Count the mutable list as bytes "copied" for the purposes of
554 // stats. Every mutable list is copied during every GC.
556 nat mut_list_size = 0;
557 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
558 mut_list_size += bd->free - bd->start;
560 for (n = 0; n < n_capabilities; n++) {
561 for (bd = capabilities[n].mut_lists[g];
562 bd != NULL; bd = bd->link) {
563 mut_list_size += bd->free - bd->start;
566 copied += mut_list_size;
569 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
570 (unsigned long)(mut_list_size * sizeof(W_)),
571 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
575 gen = &generations[g];
577 // for generations we collected...
580 /* free old memory and shift to-space into from-space for all
581 * the collected steps (except the allocation area). These
582 * freed blocks will probaby be quickly recycled.
586 // tack the new blocks on the end of the existing blocks
587 if (gen->old_blocks != NULL) {
590 for (bd = gen->old_blocks; bd != NULL; bd = next) {
594 if (!(bd->flags & BF_MARKED))
597 gen->old_blocks = next;
606 gen->n_words += bd->free - bd->start;
608 // NB. this step might not be compacted next
609 // time, so reset the BF_MARKED flags.
610 // They are set before GC if we're going to
611 // compact. (search for BF_MARKED above).
612 bd->flags &= ~BF_MARKED;
614 // between GCs, all blocks in the heap except
615 // for the nursery have the BF_EVACUATED flag set.
616 bd->flags |= BF_EVACUATED;
623 prev->link = gen->blocks;
624 gen->blocks = gen->old_blocks;
627 // add the new blocks to the block tally
628 gen->n_blocks += gen->n_old_blocks;
629 ASSERT(countBlocks(gen->blocks) == gen->n_blocks);
630 ASSERT(countOccupied(gen->blocks) == gen->n_words);
634 freeChain(gen->old_blocks);
637 gen->old_blocks = NULL;
638 gen->n_old_blocks = 0;
640 /* LARGE OBJECTS. The current live large objects are chained on
641 * scavenged_large, having been moved during garbage
642 * collection from large_objects. Any objects left on the
643 * large_objects list are therefore dead, so we free them here.
645 freeChain(gen->large_objects);
646 gen->large_objects = gen->scavenged_large_objects;
647 gen->n_large_blocks = gen->n_scavenged_large_blocks;
648 gen->n_new_large_blocks = 0;
649 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
651 else // for generations > N
653 /* For older generations, we need to append the
654 * scavenged_large_object list (i.e. large objects that have been
655 * promoted during this GC) to the large_object list for that step.
657 for (bd = gen->scavenged_large_objects; bd; bd = next) {
659 dbl_link_onto(bd, &gen->large_objects);
662 // add the new blocks we promoted during this GC
663 gen->n_large_blocks += gen->n_scavenged_large_blocks;
664 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
666 } // for all generations
668 // update the max size of older generations after a major GC
669 resize_generations();
671 // Calculate the amount of live data for stats.
672 live = calcLiveWords();
674 // Free the small objects allocated via allocate(), since this will
675 // all have been copied into G0S1 now.
676 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
678 // Start a new pinned_object_block
679 for (n = 0; n < n_capabilities; n++) {
680 capabilities[n].pinned_object_block = NULL;
683 // Free the mark stack.
684 if (mark_stack_top_bd != NULL) {
685 debugTrace(DEBUG_gc, "mark stack: %d blocks",
686 countBlocks(mark_stack_top_bd));
687 freeChain(mark_stack_top_bd);
691 for (g = 0; g <= N; g++) {
692 gen = &generations[g];
693 if (gen->bitmap != NULL) {
694 freeGroup(gen->bitmap);
701 // mark the garbage collected CAFs as dead
702 #if 0 && defined(DEBUG) // doesn't work at the moment
703 if (major_gc) { gcCAFs(); }
707 // resetStaticObjectForRetainerProfiling() must be called before
709 if (n_gc_threads > 1) {
710 barf("profiling is currently broken with multi-threaded GC");
711 // ToDo: fix the gct->scavenged_static_objects below
713 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
716 // zero the scavenged static object list
719 for (i = 0; i < n_gc_threads; i++) {
720 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
727 // start any pending finalizers
729 scheduleFinalizers(cap, old_weak_ptr_list);
732 // send exceptions to any threads which were about to die
734 resurrectThreads(resurrected_threads);
735 performPendingThrowTos(exception_threads);
738 // Update the stable pointer hash table.
739 updateStablePtrTable(major_gc);
741 // check sanity after GC
742 IF_DEBUG(sanity, checkSanity(rtsTrue));
744 // extra GC trace info
745 IF_DEBUG(gc, statDescribeGens());
748 // symbol-table based profiling
749 /* heapCensus(to_blocks); */ /* ToDo */
752 // restore enclosing cost centre
758 // check for memory leaks if DEBUG is on
759 memInventory(DEBUG_gc);
762 #ifdef RTS_GTK_FRONTPANEL
763 if (RtsFlags.GcFlags.frontpanel) {
764 updateFrontPanelAfterGC( N, live );
768 // ok, GC over: tell the stats department what happened.
769 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
770 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
772 // unlock the StablePtr table
775 // Guess which generation we'll collect *next* time
776 initialise_N(force_major_gc);
778 #if defined(RTS_USER_SIGNALS)
779 if (RtsFlags.MiscFlags.install_signal_handlers) {
780 // unblock signals again
781 unblockUserSignals();
790 /* -----------------------------------------------------------------------------
791 Figure out which generation to collect, initialise N and major_gc.
793 Also returns the total number of blocks in generations that will be
795 -------------------------------------------------------------------------- */
798 initialise_N (rtsBool force_major_gc)
801 nat blocks, blocks_total;
806 if (force_major_gc) {
807 N = RtsFlags.GcFlags.generations - 1;
812 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
814 blocks = generations[g].n_words / BLOCK_SIZE_W
815 + generations[g].n_large_blocks;
817 if (blocks >= generations[g].max_blocks) {
821 blocks_total += blocks;
825 blocks_total += countNurseryBlocks();
827 major_gc = (N == RtsFlags.GcFlags.generations-1);
831 /* -----------------------------------------------------------------------------
832 Initialise the gc_thread structures.
833 -------------------------------------------------------------------------- */
835 #define GC_THREAD_INACTIVE 0
836 #define GC_THREAD_STANDING_BY 1
837 #define GC_THREAD_RUNNING 2
838 #define GC_THREAD_WAITING_TO_CONTINUE 3
841 new_gc_thread (nat n, gc_thread *t)
848 initSpinLock(&t->gc_spin);
849 initSpinLock(&t->mut_spin);
850 ACQUIRE_SPIN_LOCK(&t->gc_spin);
851 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
852 // thread to start up, see wakeup_gc_threads
856 t->free_blocks = NULL;
865 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
868 ws->gen = &generations[g];
869 ASSERT(g == ws->gen->no);
873 ws->todo_q = newWSDeque(128);
874 ws->todo_overflow = NULL;
875 ws->n_todo_overflow = 0;
877 ws->part_list = NULL;
878 ws->n_part_blocks = 0;
880 ws->scavd_list = NULL;
881 ws->n_scavd_blocks = 0;
889 if (gc_threads == NULL) {
890 #if defined(THREADED_RTS)
892 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
896 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
898 stgMallocBytes(sizeof(gc_thread) +
899 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
902 new_gc_thread(i, gc_threads[i]);
905 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
907 new_gc_thread(0,gc_threads[0]);
916 if (gc_threads != NULL) {
917 #if defined(THREADED_RTS)
919 for (i = 0; i < n_capabilities; i++) {
920 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
922 freeWSDeque(gc_threads[i]->gens[g].todo_q);
924 stgFree (gc_threads[i]);
926 stgFree (gc_threads);
928 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
930 freeWSDeque(gc_threads[0]->gens[g].todo_q);
932 stgFree (gc_threads);
938 /* ----------------------------------------------------------------------------
940 ------------------------------------------------------------------------- */
942 static volatile StgWord gc_running_threads;
948 new = atomic_inc(&gc_running_threads);
949 ASSERT(new <= n_gc_threads);
956 ASSERT(gc_running_threads != 0);
957 return atomic_dec(&gc_running_threads);
970 // scavenge objects in compacted generation
971 if (mark_stack_bd != NULL && !mark_stack_empty()) {
975 // Check for global work in any step. We don't need to check for
976 // local work, because we have already exited scavenge_loop(),
977 // which means there is no local work for this thread.
978 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
980 if (ws->todo_large_objects) return rtsTrue;
981 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
982 if (ws->todo_overflow) return rtsTrue;
985 #if defined(THREADED_RTS)
988 // look for work to steal
989 for (n = 0; n < n_gc_threads; n++) {
990 if (n == gct->thread_index) continue;
991 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
992 ws = &gc_threads[n]->gens[g];
993 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
1005 scavenge_until_all_done (void)
1011 traceEventGcWork(&capabilities[gct->thread_index]);
1013 #if defined(THREADED_RTS)
1014 if (n_gc_threads > 1) {
1023 // scavenge_loop() only exits when there's no work to do
1026 traceEventGcIdle(&capabilities[gct->thread_index]);
1028 debugTrace(DEBUG_gc, "%d GC threads still running", r);
1030 while (gc_running_threads != 0) {
1036 // any_work() does not remove the work from the queue, it
1037 // just checks for the presence of work. If we find any,
1038 // then we increment gc_running_threads and go back to
1039 // scavenge_loop() to perform any pending work.
1042 traceEventGcDone(&capabilities[gct->thread_index]);
1045 #if defined(THREADED_RTS)
1048 gcWorkerThread (Capability *cap)
1050 gc_thread *saved_gct;
1052 // necessary if we stole a callee-saves register for gct:
1055 gct = gc_threads[cap->no];
1056 gct->id = osThreadId();
1058 // Wait until we're told to wake up
1059 RELEASE_SPIN_LOCK(&gct->mut_spin);
1060 gct->wakeup = GC_THREAD_STANDING_BY;
1061 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1062 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1065 // start performance counters in this thread...
1066 if (gct->papi_events == -1) {
1067 papi_init_eventset(&gct->papi_events);
1069 papi_thread_start_gc1_count(gct->papi_events);
1072 // Every thread evacuates some roots.
1074 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1075 rtsTrue/*prune sparks*/);
1076 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1078 scavenge_until_all_done();
1081 // count events in this thread towards the GC totals
1082 papi_thread_stop_gc1_count(gct->papi_events);
1085 // Wait until we're told to continue
1086 RELEASE_SPIN_LOCK(&gct->gc_spin);
1087 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1088 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1090 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1091 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1098 #if defined(THREADED_RTS)
1101 waitForGcThreads (Capability *cap USED_IF_THREADS)
1103 nat n_threads = RtsFlags.ParFlags.nNodes;
1106 rtsBool retry = rtsTrue;
1109 for (i=0; i < n_threads; i++) {
1110 if (i == me) continue;
1111 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1112 prodCapability(&capabilities[i], cap->running_task);
1115 for (j=0; j < 10; j++) {
1117 for (i=0; i < n_threads; i++) {
1118 if (i == me) continue;
1120 setContextSwitches();
1121 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1131 #endif // THREADED_RTS
1134 start_gc_threads (void)
1136 #if defined(THREADED_RTS)
1137 gc_running_threads = 0;
1142 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1144 #if defined(THREADED_RTS)
1146 for (i=0; i < n_threads; i++) {
1147 if (i == me) continue;
1149 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1150 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1152 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1153 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1154 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1159 // After GC is complete, we must wait for all GC threads to enter the
1160 // standby state, otherwise they may still be executing inside
1161 // any_work(), and may even remain awake until the next GC starts.
1163 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1165 #if defined(THREADED_RTS)
1167 for (i=0; i < n_threads; i++) {
1168 if (i == me) continue;
1169 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1174 #if defined(THREADED_RTS)
1176 releaseGCThreads (Capability *cap USED_IF_THREADS)
1178 nat n_threads = RtsFlags.ParFlags.nNodes;
1181 for (i=0; i < n_threads; i++) {
1182 if (i == me) continue;
1183 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1184 barf("releaseGCThreads");
1186 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1187 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1188 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1193 /* ----------------------------------------------------------------------------
1194 Initialise a generation that is to be collected
1195 ------------------------------------------------------------------------- */
1198 init_collected_gen (nat g, nat n_threads)
1205 // Throw away the current mutable list. Invariant: the mutable
1206 // list always has at least one block; this means we can avoid a
1207 // check for NULL in recordMutable().
1209 freeChain(generations[g].mut_list);
1210 generations[g].mut_list = allocBlock();
1211 for (i = 0; i < n_capabilities; i++) {
1212 freeChain(capabilities[i].mut_lists[g]);
1213 capabilities[i].mut_lists[g] = allocBlock();
1217 gen = &generations[g];
1218 ASSERT(gen->no == g);
1220 // we'll construct a new list of threads in this step
1221 // during GC, throw away the current list.
1222 gen->old_threads = gen->threads;
1223 gen->threads = END_TSO_QUEUE;
1225 // deprecate the existing blocks
1226 gen->old_blocks = gen->blocks;
1227 gen->n_old_blocks = gen->n_blocks;
1231 gen->live_estimate = 0;
1233 // initialise the large object queues.
1234 gen->scavenged_large_objects = NULL;
1235 gen->n_scavenged_large_blocks = 0;
1237 // mark the small objects as from-space
1238 for (bd = gen->old_blocks; bd; bd = bd->link) {
1239 bd->flags &= ~BF_EVACUATED;
1242 // mark the large objects as from-space
1243 for (bd = gen->large_objects; bd; bd = bd->link) {
1244 bd->flags &= ~BF_EVACUATED;
1247 // for a compacted generation, we need to allocate the bitmap
1249 nat bitmap_size; // in bytes
1250 bdescr *bitmap_bdescr;
1253 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1255 if (bitmap_size > 0) {
1256 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1258 gen->bitmap = bitmap_bdescr;
1259 bitmap = bitmap_bdescr->start;
1261 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1262 bitmap_size, bitmap);
1264 // don't forget to fill it with zeros!
1265 memset(bitmap, 0, bitmap_size);
1267 // For each block in this step, point to its bitmap from the
1268 // block descriptor.
1269 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1270 bd->u.bitmap = bitmap;
1271 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1273 // Also at this point we set the BF_MARKED flag
1274 // for this block. The invariant is that
1275 // BF_MARKED is always unset, except during GC
1276 // when it is set on those blocks which will be
1278 if (!(bd->flags & BF_FRAGMENTED)) {
1279 bd->flags |= BF_MARKED;
1285 // For each GC thread, for each step, allocate a "todo" block to
1286 // store evacuated objects to be scavenged, and a block to store
1287 // evacuated objects that do not need to be scavenged.
1288 for (t = 0; t < n_threads; t++) {
1289 ws = &gc_threads[t]->gens[g];
1291 ws->todo_large_objects = NULL;
1293 ws->part_list = NULL;
1294 ws->n_part_blocks = 0;
1296 // allocate the first to-space block; extra blocks will be
1297 // chained on as necessary.
1299 ASSERT(looksEmptyWSDeque(ws->todo_q));
1300 alloc_todo_block(ws,0);
1302 ws->todo_overflow = NULL;
1303 ws->n_todo_overflow = 0;
1305 ws->scavd_list = NULL;
1306 ws->n_scavd_blocks = 0;
1311 /* ----------------------------------------------------------------------------
1312 Initialise a generation that is *not* to be collected
1313 ------------------------------------------------------------------------- */
1316 init_uncollected_gen (nat g, nat threads)
1323 // save the current mutable lists for this generation, and
1324 // allocate a fresh block for each one. We'll traverse these
1325 // mutable lists as roots early on in the GC.
1326 generations[g].saved_mut_list = generations[g].mut_list;
1327 generations[g].mut_list = allocBlock();
1328 for (n = 0; n < n_capabilities; n++) {
1329 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1330 capabilities[n].mut_lists[g] = allocBlock();
1333 gen = &generations[g];
1335 gen->scavenged_large_objects = NULL;
1336 gen->n_scavenged_large_blocks = 0;
1338 for (t = 0; t < threads; t++) {
1339 ws = &gc_threads[t]->gens[g];
1341 ASSERT(looksEmptyWSDeque(ws->todo_q));
1342 ws->todo_large_objects = NULL;
1344 ws->part_list = NULL;
1345 ws->n_part_blocks = 0;
1347 ws->scavd_list = NULL;
1348 ws->n_scavd_blocks = 0;
1350 // If the block at the head of the list in this generation
1351 // is less than 3/4 full, then use it as a todo block.
1352 if (gen->blocks && isPartiallyFull(gen->blocks))
1354 ws->todo_bd = gen->blocks;
1355 ws->todo_free = ws->todo_bd->free;
1356 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1357 gen->blocks = gen->blocks->link;
1359 gen->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1360 ws->todo_bd->link = NULL;
1361 // we must scan from the current end point.
1362 ws->todo_bd->u.scan = ws->todo_bd->free;
1367 alloc_todo_block(ws,0);
1371 // deal out any more partial blocks to the threads' part_lists
1373 while (gen->blocks && isPartiallyFull(gen->blocks))
1376 gen->blocks = bd->link;
1377 ws = &gc_threads[t]->gens[g];
1378 bd->link = ws->part_list;
1380 ws->n_part_blocks += 1;
1381 bd->u.scan = bd->free;
1383 gen->n_words -= bd->free - bd->start;
1385 if (t == n_gc_threads) t = 0;
1389 /* -----------------------------------------------------------------------------
1390 Initialise a gc_thread before GC
1391 -------------------------------------------------------------------------- */
1394 init_gc_thread (gc_thread *t)
1396 t->static_objects = END_OF_STATIC_LIST;
1397 t->scavenged_static_objects = END_OF_STATIC_LIST;
1399 t->mut_lists = capabilities[t->thread_index].mut_lists;
1401 t->failed_to_evac = rtsFalse;
1402 t->eager_promotion = rtsTrue;
1403 t->thunk_selector_depth = 0;
1408 t->scav_find_work = 0;
1411 /* -----------------------------------------------------------------------------
1412 Function we pass to evacuate roots.
1413 -------------------------------------------------------------------------- */
1416 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1418 // we stole a register for gct, but this function is called from
1419 // *outside* the GC where the register variable is not in effect,
1420 // so we need to save and restore it here. NB. only call
1421 // mark_root() from the main GC thread, otherwise gct will be
1423 gc_thread *saved_gct;
1432 /* -----------------------------------------------------------------------------
1433 Initialising the static object & mutable lists
1434 -------------------------------------------------------------------------- */
1437 zero_static_object_list(StgClosure* first_static)
1441 const StgInfoTable *info;
1443 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1445 link = *STATIC_LINK(info, p);
1446 *STATIC_LINK(info,p) = NULL;
1450 /* ----------------------------------------------------------------------------
1451 Reset the sizes of the older generations when we do a major
1454 CURRENT STRATEGY: make all generations except zero the same size.
1455 We have to stay within the maximum heap size, and leave a certain
1456 percentage of the maximum heap size available to allocate into.
1457 ------------------------------------------------------------------------- */
1460 resize_generations (void)
1464 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1465 nat live, size, min_alloc, words;
1466 nat max = RtsFlags.GcFlags.maxHeapSize;
1467 nat gens = RtsFlags.GcFlags.generations;
1469 // live in the oldest generations
1470 if (oldest_gen->live_estimate != 0) {
1471 words = oldest_gen->live_estimate;
1473 words = oldest_gen->n_words;
1475 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1476 oldest_gen->n_large_blocks;
1478 // default max size for all generations except zero
1479 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1480 RtsFlags.GcFlags.minOldGenSize);
1482 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1483 RtsFlags.GcFlags.heapSizeSuggestion = size;
1486 // minimum size for generation zero
1487 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1488 RtsFlags.GcFlags.minAllocAreaSize);
1490 // Auto-enable compaction when the residency reaches a
1491 // certain percentage of the maximum heap size (default: 30%).
1492 if (RtsFlags.GcFlags.generations > 1 &&
1493 (RtsFlags.GcFlags.compact ||
1495 oldest_gen->n_blocks >
1496 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1497 oldest_gen->mark = 1;
1498 oldest_gen->compact = 1;
1499 // debugBelch("compaction: on\n", live);
1501 oldest_gen->mark = 0;
1502 oldest_gen->compact = 0;
1503 // debugBelch("compaction: off\n", live);
1506 if (RtsFlags.GcFlags.sweep) {
1507 oldest_gen->mark = 1;
1510 // if we're going to go over the maximum heap size, reduce the
1511 // size of the generations accordingly. The calculation is
1512 // different if compaction is turned on, because we don't need
1513 // to double the space required to collect the old generation.
1516 // this test is necessary to ensure that the calculations
1517 // below don't have any negative results - we're working
1518 // with unsigned values here.
1519 if (max < min_alloc) {
1523 if (oldest_gen->compact) {
1524 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1525 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1528 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1529 size = (max - min_alloc) / ((gens - 1) * 2);
1539 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1540 min_alloc, size, max);
1543 for (g = 0; g < gens; g++) {
1544 generations[g].max_blocks = size;
1549 /* -----------------------------------------------------------------------------
1550 Calculate the new size of the nursery, and resize it.
1551 -------------------------------------------------------------------------- */
1554 resize_nursery (void)
1556 lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1558 if (RtsFlags.GcFlags.generations == 1)
1559 { // Two-space collector:
1562 /* set up a new nursery. Allocate a nursery size based on a
1563 * function of the amount of live data (by default a factor of 2)
1564 * Use the blocks from the old nursery if possible, freeing up any
1567 * If we get near the maximum heap size, then adjust our nursery
1568 * size accordingly. If the nursery is the same size as the live
1569 * data (L), then we need 3L bytes. We can reduce the size of the
1570 * nursery to bring the required memory down near 2L bytes.
1572 * A normal 2-space collector would need 4L bytes to give the same
1573 * performance we get from 3L bytes, reducing to the same
1574 * performance at 2L bytes.
1576 blocks = generations[0].n_blocks;
1578 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1579 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1580 RtsFlags.GcFlags.maxHeapSize )
1582 long adjusted_blocks; // signed on purpose
1585 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1587 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1588 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1590 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1591 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1595 blocks = adjusted_blocks;
1599 blocks *= RtsFlags.GcFlags.oldGenFactor;
1600 if (blocks < min_nursery)
1602 blocks = min_nursery;
1605 resizeNurseries(blocks);
1607 else // Generational collector
1610 * If the user has given us a suggested heap size, adjust our
1611 * allocation area to make best use of the memory available.
1613 if (RtsFlags.GcFlags.heapSizeSuggestion)
1616 nat needed = calcNeeded(); // approx blocks needed at next GC
1618 /* Guess how much will be live in generation 0 step 0 next time.
1619 * A good approximation is obtained by finding the
1620 * percentage of g0 that was live at the last minor GC.
1622 * We have an accurate figure for the amount of copied data in
1623 * 'copied', but we must convert this to a number of blocks, with
1624 * a small adjustment for estimated slop at the end of a block
1629 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1630 / countNurseryBlocks();
1633 /* Estimate a size for the allocation area based on the
1634 * information available. We might end up going slightly under
1635 * or over the suggested heap size, but we should be pretty
1638 * Formula: suggested - needed
1639 * ----------------------------
1640 * 1 + g0_pcnt_kept/100
1642 * where 'needed' is the amount of memory needed at the next
1643 * collection for collecting all gens except g0.
1646 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1647 (100 + (long)g0_pcnt_kept);
1649 if (blocks < (long)min_nursery) {
1650 blocks = min_nursery;
1653 resizeNurseries((nat)blocks);
1657 // we might have added extra large blocks to the nursery, so
1658 // resize back to minAllocAreaSize again.
1659 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1664 /* -----------------------------------------------------------------------------
1665 Sanity code for CAF garbage collection.
1667 With DEBUG turned on, we manage a CAF list in addition to the SRT
1668 mechanism. After GC, we run down the CAF list and blackhole any
1669 CAFs which have been garbage collected. This means we get an error
1670 whenever the program tries to enter a garbage collected CAF.
1672 Any garbage collected CAFs are taken off the CAF list at the same
1674 -------------------------------------------------------------------------- */
1676 #if 0 && defined(DEBUG)
1683 const StgInfoTable *info;
1694 ASSERT(info->type == IND_STATIC);
1696 if (STATIC_LINK(info,p) == NULL) {
1697 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1699 SET_INFO(p,&stg_BLACKHOLE_info);
1700 p = STATIC_LINK2(info,p);
1704 pp = &STATIC_LINK2(info,p);
1711 debugTrace(DEBUG_gccafs, "%d CAFs live", i);