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);
737 // Update the stable pointer hash table.
738 updateStablePtrTable(major_gc);
740 // check sanity after GC
741 IF_DEBUG(sanity, checkSanity(rtsTrue));
743 // extra GC trace info
744 IF_DEBUG(gc, statDescribeGens());
747 // symbol-table based profiling
748 /* heapCensus(to_blocks); */ /* ToDo */
751 // restore enclosing cost centre
757 // check for memory leaks if DEBUG is on
758 memInventory(DEBUG_gc);
761 #ifdef RTS_GTK_FRONTPANEL
762 if (RtsFlags.GcFlags.frontpanel) {
763 updateFrontPanelAfterGC( N, live );
767 // ok, GC over: tell the stats department what happened.
768 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
769 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
771 // unlock the StablePtr table
774 // Guess which generation we'll collect *next* time
775 initialise_N(force_major_gc);
777 #if defined(RTS_USER_SIGNALS)
778 if (RtsFlags.MiscFlags.install_signal_handlers) {
779 // unblock signals again
780 unblockUserSignals();
789 /* -----------------------------------------------------------------------------
790 Figure out which generation to collect, initialise N and major_gc.
792 Also returns the total number of blocks in generations that will be
794 -------------------------------------------------------------------------- */
797 initialise_N (rtsBool force_major_gc)
800 nat blocks, blocks_total;
805 if (force_major_gc) {
806 N = RtsFlags.GcFlags.generations - 1;
811 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
813 blocks = generations[g].n_words / BLOCK_SIZE_W
814 + generations[g].n_large_blocks;
816 if (blocks >= generations[g].max_blocks) {
820 blocks_total += blocks;
824 blocks_total += countNurseryBlocks();
826 major_gc = (N == RtsFlags.GcFlags.generations-1);
830 /* -----------------------------------------------------------------------------
831 Initialise the gc_thread structures.
832 -------------------------------------------------------------------------- */
834 #define GC_THREAD_INACTIVE 0
835 #define GC_THREAD_STANDING_BY 1
836 #define GC_THREAD_RUNNING 2
837 #define GC_THREAD_WAITING_TO_CONTINUE 3
840 new_gc_thread (nat n, gc_thread *t)
847 initSpinLock(&t->gc_spin);
848 initSpinLock(&t->mut_spin);
849 ACQUIRE_SPIN_LOCK(&t->gc_spin);
850 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
851 // thread to start up, see wakeup_gc_threads
855 t->free_blocks = NULL;
864 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
867 ws->gen = &generations[g];
868 ASSERT(g == ws->gen->no);
872 ws->todo_q = newWSDeque(128);
873 ws->todo_overflow = NULL;
874 ws->n_todo_overflow = 0;
876 ws->part_list = NULL;
877 ws->n_part_blocks = 0;
879 ws->scavd_list = NULL;
880 ws->n_scavd_blocks = 0;
888 if (gc_threads == NULL) {
889 #if defined(THREADED_RTS)
891 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
895 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
897 stgMallocBytes(sizeof(gc_thread) +
898 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
901 new_gc_thread(i, gc_threads[i]);
904 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
906 new_gc_thread(0,gc_threads[0]);
915 if (gc_threads != NULL) {
916 #if defined(THREADED_RTS)
918 for (i = 0; i < n_capabilities; i++) {
919 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
921 freeWSDeque(gc_threads[i]->gens[g].todo_q);
923 stgFree (gc_threads[i]);
925 stgFree (gc_threads);
927 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
929 freeWSDeque(gc_threads[0]->gens[g].todo_q);
931 stgFree (gc_threads);
937 /* ----------------------------------------------------------------------------
939 ------------------------------------------------------------------------- */
941 static volatile StgWord gc_running_threads;
947 new = atomic_inc(&gc_running_threads);
948 ASSERT(new <= n_gc_threads);
955 ASSERT(gc_running_threads != 0);
956 return atomic_dec(&gc_running_threads);
969 // scavenge objects in compacted generation
970 if (mark_stack_bd != NULL && !mark_stack_empty()) {
974 // Check for global work in any step. We don't need to check for
975 // local work, because we have already exited scavenge_loop(),
976 // which means there is no local work for this thread.
977 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
979 if (ws->todo_large_objects) return rtsTrue;
980 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
981 if (ws->todo_overflow) return rtsTrue;
984 #if defined(THREADED_RTS)
987 // look for work to steal
988 for (n = 0; n < n_gc_threads; n++) {
989 if (n == gct->thread_index) continue;
990 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
991 ws = &gc_threads[n]->gens[g];
992 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
999 #if defined(THREADED_RTS)
1007 scavenge_until_all_done (void)
1013 traceEventGcWork(&capabilities[gct->thread_index]);
1015 #if defined(THREADED_RTS)
1016 if (n_gc_threads > 1) {
1025 // scavenge_loop() only exits when there's no work to do
1028 traceEventGcIdle(&capabilities[gct->thread_index]);
1030 debugTrace(DEBUG_gc, "%d GC threads still running", r);
1032 while (gc_running_threads != 0) {
1038 // any_work() does not remove the work from the queue, it
1039 // just checks for the presence of work. If we find any,
1040 // then we increment gc_running_threads and go back to
1041 // scavenge_loop() to perform any pending work.
1044 traceEventGcDone(&capabilities[gct->thread_index]);
1047 #if defined(THREADED_RTS)
1050 gcWorkerThread (Capability *cap)
1052 gc_thread *saved_gct;
1054 // necessary if we stole a callee-saves register for gct:
1057 gct = gc_threads[cap->no];
1058 gct->id = osThreadId();
1060 // Wait until we're told to wake up
1061 RELEASE_SPIN_LOCK(&gct->mut_spin);
1062 gct->wakeup = GC_THREAD_STANDING_BY;
1063 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1064 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1067 // start performance counters in this thread...
1068 if (gct->papi_events == -1) {
1069 papi_init_eventset(&gct->papi_events);
1071 papi_thread_start_gc1_count(gct->papi_events);
1074 // Every thread evacuates some roots.
1076 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1077 rtsTrue/*prune sparks*/);
1078 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1080 scavenge_until_all_done();
1083 // count events in this thread towards the GC totals
1084 papi_thread_stop_gc1_count(gct->papi_events);
1087 // Wait until we're told to continue
1088 RELEASE_SPIN_LOCK(&gct->gc_spin);
1089 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1090 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1092 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1093 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1100 #if defined(THREADED_RTS)
1103 waitForGcThreads (Capability *cap USED_IF_THREADS)
1105 nat n_threads = RtsFlags.ParFlags.nNodes;
1108 rtsBool retry = rtsTrue;
1111 for (i=0; i < n_threads; i++) {
1112 if (i == me) continue;
1113 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1114 prodCapability(&capabilities[i], cap->running_task);
1117 for (j=0; j < 10; j++) {
1119 for (i=0; i < n_threads; i++) {
1120 if (i == me) continue;
1122 setContextSwitches();
1123 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1133 #endif // THREADED_RTS
1136 start_gc_threads (void)
1138 #if defined(THREADED_RTS)
1139 gc_running_threads = 0;
1144 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1146 #if defined(THREADED_RTS)
1148 for (i=0; i < n_threads; i++) {
1149 if (i == me) continue;
1151 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1152 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1154 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1155 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1156 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1161 // After GC is complete, we must wait for all GC threads to enter the
1162 // standby state, otherwise they may still be executing inside
1163 // any_work(), and may even remain awake until the next GC starts.
1165 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1167 #if defined(THREADED_RTS)
1169 for (i=0; i < n_threads; i++) {
1170 if (i == me) continue;
1171 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1176 #if defined(THREADED_RTS)
1178 releaseGCThreads (Capability *cap USED_IF_THREADS)
1180 nat n_threads = RtsFlags.ParFlags.nNodes;
1183 for (i=0; i < n_threads; i++) {
1184 if (i == me) continue;
1185 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1186 barf("releaseGCThreads");
1188 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1189 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1190 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1195 /* ----------------------------------------------------------------------------
1196 Initialise a generation that is to be collected
1197 ------------------------------------------------------------------------- */
1200 init_collected_gen (nat g, nat n_threads)
1207 // Throw away the current mutable list. Invariant: the mutable
1208 // list always has at least one block; this means we can avoid a
1209 // check for NULL in recordMutable().
1211 freeChain(generations[g].mut_list);
1212 generations[g].mut_list = allocBlock();
1213 for (i = 0; i < n_capabilities; i++) {
1214 freeChain(capabilities[i].mut_lists[g]);
1215 capabilities[i].mut_lists[g] = allocBlock();
1219 gen = &generations[g];
1220 ASSERT(gen->no == g);
1222 // we'll construct a new list of threads in this step
1223 // during GC, throw away the current list.
1224 gen->old_threads = gen->threads;
1225 gen->threads = END_TSO_QUEUE;
1227 // deprecate the existing blocks
1228 gen->old_blocks = gen->blocks;
1229 gen->n_old_blocks = gen->n_blocks;
1233 gen->live_estimate = 0;
1235 // initialise the large object queues.
1236 gen->scavenged_large_objects = NULL;
1237 gen->n_scavenged_large_blocks = 0;
1239 // mark the small objects as from-space
1240 for (bd = gen->old_blocks; bd; bd = bd->link) {
1241 bd->flags &= ~BF_EVACUATED;
1244 // mark the large objects as from-space
1245 for (bd = gen->large_objects; bd; bd = bd->link) {
1246 bd->flags &= ~BF_EVACUATED;
1249 // for a compacted generation, we need to allocate the bitmap
1251 nat bitmap_size; // in bytes
1252 bdescr *bitmap_bdescr;
1255 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1257 if (bitmap_size > 0) {
1258 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1260 gen->bitmap = bitmap_bdescr;
1261 bitmap = bitmap_bdescr->start;
1263 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1264 bitmap_size, bitmap);
1266 // don't forget to fill it with zeros!
1267 memset(bitmap, 0, bitmap_size);
1269 // For each block in this step, point to its bitmap from the
1270 // block descriptor.
1271 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1272 bd->u.bitmap = bitmap;
1273 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1275 // Also at this point we set the BF_MARKED flag
1276 // for this block. The invariant is that
1277 // BF_MARKED is always unset, except during GC
1278 // when it is set on those blocks which will be
1280 if (!(bd->flags & BF_FRAGMENTED)) {
1281 bd->flags |= BF_MARKED;
1287 // For each GC thread, for each step, allocate a "todo" block to
1288 // store evacuated objects to be scavenged, and a block to store
1289 // evacuated objects that do not need to be scavenged.
1290 for (t = 0; t < n_threads; t++) {
1291 ws = &gc_threads[t]->gens[g];
1293 ws->todo_large_objects = NULL;
1295 ws->part_list = NULL;
1296 ws->n_part_blocks = 0;
1298 // allocate the first to-space block; extra blocks will be
1299 // chained on as necessary.
1301 ASSERT(looksEmptyWSDeque(ws->todo_q));
1302 alloc_todo_block(ws,0);
1304 ws->todo_overflow = NULL;
1305 ws->n_todo_overflow = 0;
1307 ws->scavd_list = NULL;
1308 ws->n_scavd_blocks = 0;
1313 /* ----------------------------------------------------------------------------
1314 Initialise a generation that is *not* to be collected
1315 ------------------------------------------------------------------------- */
1318 init_uncollected_gen (nat g, nat threads)
1325 // save the current mutable lists for this generation, and
1326 // allocate a fresh block for each one. We'll traverse these
1327 // mutable lists as roots early on in the GC.
1328 generations[g].saved_mut_list = generations[g].mut_list;
1329 generations[g].mut_list = allocBlock();
1330 for (n = 0; n < n_capabilities; n++) {
1331 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1332 capabilities[n].mut_lists[g] = allocBlock();
1335 gen = &generations[g];
1337 gen->scavenged_large_objects = NULL;
1338 gen->n_scavenged_large_blocks = 0;
1340 for (t = 0; t < threads; t++) {
1341 ws = &gc_threads[t]->gens[g];
1343 ASSERT(looksEmptyWSDeque(ws->todo_q));
1344 ws->todo_large_objects = NULL;
1346 ws->part_list = NULL;
1347 ws->n_part_blocks = 0;
1349 ws->scavd_list = NULL;
1350 ws->n_scavd_blocks = 0;
1352 // If the block at the head of the list in this generation
1353 // is less than 3/4 full, then use it as a todo block.
1354 if (gen->blocks && isPartiallyFull(gen->blocks))
1356 ws->todo_bd = gen->blocks;
1357 ws->todo_free = ws->todo_bd->free;
1358 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1359 gen->blocks = gen->blocks->link;
1361 gen->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1362 ws->todo_bd->link = NULL;
1363 // we must scan from the current end point.
1364 ws->todo_bd->u.scan = ws->todo_bd->free;
1369 alloc_todo_block(ws,0);
1373 // deal out any more partial blocks to the threads' part_lists
1375 while (gen->blocks && isPartiallyFull(gen->blocks))
1378 gen->blocks = bd->link;
1379 ws = &gc_threads[t]->gens[g];
1380 bd->link = ws->part_list;
1382 ws->n_part_blocks += 1;
1383 bd->u.scan = bd->free;
1385 gen->n_words -= bd->free - bd->start;
1387 if (t == n_gc_threads) t = 0;
1391 /* -----------------------------------------------------------------------------
1392 Initialise a gc_thread before GC
1393 -------------------------------------------------------------------------- */
1396 init_gc_thread (gc_thread *t)
1398 t->static_objects = END_OF_STATIC_LIST;
1399 t->scavenged_static_objects = END_OF_STATIC_LIST;
1401 t->mut_lists = capabilities[t->thread_index].mut_lists;
1403 t->failed_to_evac = rtsFalse;
1404 t->eager_promotion = rtsTrue;
1405 t->thunk_selector_depth = 0;
1410 t->scav_find_work = 0;
1413 /* -----------------------------------------------------------------------------
1414 Function we pass to evacuate roots.
1415 -------------------------------------------------------------------------- */
1418 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1420 // we stole a register for gct, but this function is called from
1421 // *outside* the GC where the register variable is not in effect,
1422 // so we need to save and restore it here. NB. only call
1423 // mark_root() from the main GC thread, otherwise gct will be
1425 gc_thread *saved_gct;
1434 /* -----------------------------------------------------------------------------
1435 Initialising the static object & mutable lists
1436 -------------------------------------------------------------------------- */
1439 zero_static_object_list(StgClosure* first_static)
1443 const StgInfoTable *info;
1445 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1447 link = *STATIC_LINK(info, p);
1448 *STATIC_LINK(info,p) = NULL;
1452 /* ----------------------------------------------------------------------------
1453 Reset the sizes of the older generations when we do a major
1456 CURRENT STRATEGY: make all generations except zero the same size.
1457 We have to stay within the maximum heap size, and leave a certain
1458 percentage of the maximum heap size available to allocate into.
1459 ------------------------------------------------------------------------- */
1462 resize_generations (void)
1466 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1467 nat live, size, min_alloc, words;
1468 nat max = RtsFlags.GcFlags.maxHeapSize;
1469 nat gens = RtsFlags.GcFlags.generations;
1471 // live in the oldest generations
1472 if (oldest_gen->live_estimate != 0) {
1473 words = oldest_gen->live_estimate;
1475 words = oldest_gen->n_words;
1477 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1478 oldest_gen->n_large_blocks;
1480 // default max size for all generations except zero
1481 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1482 RtsFlags.GcFlags.minOldGenSize);
1484 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1485 RtsFlags.GcFlags.heapSizeSuggestion = size;
1488 // minimum size for generation zero
1489 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1490 RtsFlags.GcFlags.minAllocAreaSize);
1492 // Auto-enable compaction when the residency reaches a
1493 // certain percentage of the maximum heap size (default: 30%).
1494 if (RtsFlags.GcFlags.generations > 1 &&
1495 (RtsFlags.GcFlags.compact ||
1497 oldest_gen->n_blocks >
1498 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1499 oldest_gen->mark = 1;
1500 oldest_gen->compact = 1;
1501 // debugBelch("compaction: on\n", live);
1503 oldest_gen->mark = 0;
1504 oldest_gen->compact = 0;
1505 // debugBelch("compaction: off\n", live);
1508 if (RtsFlags.GcFlags.sweep) {
1509 oldest_gen->mark = 1;
1512 // if we're going to go over the maximum heap size, reduce the
1513 // size of the generations accordingly. The calculation is
1514 // different if compaction is turned on, because we don't need
1515 // to double the space required to collect the old generation.
1518 // this test is necessary to ensure that the calculations
1519 // below don't have any negative results - we're working
1520 // with unsigned values here.
1521 if (max < min_alloc) {
1525 if (oldest_gen->compact) {
1526 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1527 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1530 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1531 size = (max - min_alloc) / ((gens - 1) * 2);
1541 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1542 min_alloc, size, max);
1545 for (g = 0; g < gens; g++) {
1546 generations[g].max_blocks = size;
1551 /* -----------------------------------------------------------------------------
1552 Calculate the new size of the nursery, and resize it.
1553 -------------------------------------------------------------------------- */
1556 resize_nursery (void)
1558 lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1560 if (RtsFlags.GcFlags.generations == 1)
1561 { // Two-space collector:
1564 /* set up a new nursery. Allocate a nursery size based on a
1565 * function of the amount of live data (by default a factor of 2)
1566 * Use the blocks from the old nursery if possible, freeing up any
1569 * If we get near the maximum heap size, then adjust our nursery
1570 * size accordingly. If the nursery is the same size as the live
1571 * data (L), then we need 3L bytes. We can reduce the size of the
1572 * nursery to bring the required memory down near 2L bytes.
1574 * A normal 2-space collector would need 4L bytes to give the same
1575 * performance we get from 3L bytes, reducing to the same
1576 * performance at 2L bytes.
1578 blocks = generations[0].n_blocks;
1580 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1581 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1582 RtsFlags.GcFlags.maxHeapSize )
1584 long adjusted_blocks; // signed on purpose
1587 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1589 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1590 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1592 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1593 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1597 blocks = adjusted_blocks;
1601 blocks *= RtsFlags.GcFlags.oldGenFactor;
1602 if (blocks < min_nursery)
1604 blocks = min_nursery;
1607 resizeNurseries(blocks);
1609 else // Generational collector
1612 * If the user has given us a suggested heap size, adjust our
1613 * allocation area to make best use of the memory available.
1615 if (RtsFlags.GcFlags.heapSizeSuggestion)
1618 nat needed = calcNeeded(); // approx blocks needed at next GC
1620 /* Guess how much will be live in generation 0 step 0 next time.
1621 * A good approximation is obtained by finding the
1622 * percentage of g0 that was live at the last minor GC.
1624 * We have an accurate figure for the amount of copied data in
1625 * 'copied', but we must convert this to a number of blocks, with
1626 * a small adjustment for estimated slop at the end of a block
1631 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1632 / countNurseryBlocks();
1635 /* Estimate a size for the allocation area based on the
1636 * information available. We might end up going slightly under
1637 * or over the suggested heap size, but we should be pretty
1640 * Formula: suggested - needed
1641 * ----------------------------
1642 * 1 + g0_pcnt_kept/100
1644 * where 'needed' is the amount of memory needed at the next
1645 * collection for collecting all gens except g0.
1648 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1649 (100 + (long)g0_pcnt_kept);
1651 if (blocks < (long)min_nursery) {
1652 blocks = min_nursery;
1655 resizeNurseries((nat)blocks);
1659 // we might have added extra large blocks to the nursery, so
1660 // resize back to minAllocAreaSize again.
1661 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1666 /* -----------------------------------------------------------------------------
1667 Sanity code for CAF garbage collection.
1669 With DEBUG turned on, we manage a CAF list in addition to the SRT
1670 mechanism. After GC, we run down the CAF list and blackhole any
1671 CAFs which have been garbage collected. This means we get an error
1672 whenever the program tries to enter a garbage collected CAF.
1674 Any garbage collected CAFs are taken off the CAF list at the same
1676 -------------------------------------------------------------------------- */
1678 #if 0 && defined(DEBUG)
1685 const StgInfoTable *info;
1696 ASSERT(info->type == IND_STATIC);
1698 if (STATIC_LINK(info,p) == NULL) {
1699 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1701 SET_INFO(p,&stg_BLACKHOLE_info);
1702 p = STATIC_LINK2(info,p);
1706 pp = &STATIC_LINK2(info,p);
1713 debugTrace(DEBUG_gccafs, "%d CAFs live", i);