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 update_task_list (void);
144 static void resize_generations (void);
145 static void resize_nursery (void);
146 static void start_gc_threads (void);
147 static void scavenge_until_all_done (void);
148 static StgWord inc_running (void);
149 static StgWord dec_running (void);
150 static void wakeup_gc_threads (nat n_threads, nat me);
151 static void shutdown_gc_threads (nat n_threads, nat me);
153 #if 0 && defined(DEBUG)
154 static void gcCAFs (void);
157 /* -----------------------------------------------------------------------------
159 -------------------------------------------------------------------------- */
161 bdescr *mark_stack_top_bd; // topmost block in the mark stack
162 bdescr *mark_stack_bd; // current block in the mark stack
163 StgPtr mark_sp; // pointer to the next unallocated mark stack entry
165 /* -----------------------------------------------------------------------------
166 GarbageCollect: the main entry point to the garbage collector.
168 Locks held: all capabilities are held throughout GarbageCollect().
169 -------------------------------------------------------------------------- */
172 GarbageCollect (rtsBool force_major_gc,
173 nat gc_type USED_IF_THREADS,
178 lnat live, allocated, max_copied, avg_copied, slop;
179 gc_thread *saved_gct;
182 // necessary if we stole a callee-saves register for gct:
186 CostCentreStack *prev_CCS;
191 #if defined(RTS_USER_SIGNALS)
192 if (RtsFlags.MiscFlags.install_signal_handlers) {
198 ASSERT(sizeof(gen_workspace) == 16 * sizeof(StgWord));
199 // otherwise adjust the padding in gen_workspace.
201 // tell the stats department that we've started a GC
204 // tell the STM to discard any cached closures it's hoping to re-use
207 // lock the StablePtr table
216 // attribute any costs to CCS_GC
222 /* Approximate how much we allocated.
223 * Todo: only when generating stats?
225 allocated = calcAllocated();
227 /* Figure out which generation to collect
229 n = initialise_N(force_major_gc);
231 #if defined(THREADED_RTS)
232 work_stealing = RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
233 N >= RtsFlags.ParFlags.parGcLoadBalancingGen;
234 // It's not always a good idea to do load balancing in parallel
235 // GC. In particular, for a parallel program we don't want to
236 // lose locality by moving cached data into another CPU's cache
237 // (this effect can be quite significant).
239 // We could have a more complex way to deterimine whether to do
240 // work stealing or not, e.g. it might be a good idea to do it
241 // if the heap is big. For now, we just turn it on or off with
245 /* Start threads, so they can be spinning up while we finish initialisation.
249 #if defined(THREADED_RTS)
250 /* How many threads will be participating in this GC?
251 * We don't try to parallelise minor GCs (unless the user asks for
252 * it with +RTS -gn0), or mark/compact/sweep GC.
254 if (gc_type == PENDING_GC_PAR) {
255 n_gc_threads = RtsFlags.ParFlags.nNodes;
263 debugTrace(DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
264 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
266 #ifdef RTS_GTK_FRONTPANEL
267 if (RtsFlags.GcFlags.frontpanel) {
268 updateFrontPanelBeforeGC(N);
273 // check for memory leaks if DEBUG is on
274 memInventory(DEBUG_gc);
277 // check sanity *before* GC
278 IF_DEBUG(sanity, checkSanity(rtsTrue));
280 // Initialise all our gc_thread structures
281 for (t = 0; t < n_gc_threads; t++) {
282 init_gc_thread(gc_threads[t]);
285 // Initialise all the generations/steps that we're collecting.
286 for (g = 0; g <= N; g++) {
287 init_collected_gen(g,n_gc_threads);
290 // Initialise all the generations/steps that we're *not* collecting.
291 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
292 init_uncollected_gen(g,n_gc_threads);
295 /* Allocate a mark stack if we're doing a major collection.
297 if (major_gc && oldest_gen->mark) {
298 mark_stack_bd = allocBlock();
299 mark_stack_top_bd = mark_stack_bd;
300 mark_stack_bd->link = NULL;
301 mark_stack_bd->u.back = NULL;
302 mark_sp = mark_stack_bd->start;
304 mark_stack_bd = NULL;
305 mark_stack_top_bd = NULL;
309 // this is the main thread
311 if (n_gc_threads == 1) {
312 SET_GCT(gc_threads[0]);
314 SET_GCT(gc_threads[cap->no]);
317 SET_GCT(gc_threads[0]);
320 /* -----------------------------------------------------------------------
321 * follow all the roots that we know about:
324 // the main thread is running: this prevents any other threads from
325 // exiting prematurely, so we can start them now.
326 // NB. do this after the mutable lists have been saved above, otherwise
327 // the other GC threads will be writing into the old mutable lists.
329 wakeup_gc_threads(n_gc_threads, gct->thread_index);
331 // Mutable lists from each generation > N
332 // we want to *scavenge* these roots, not evacuate them: they're not
333 // going to move in this GC.
334 // Also do them in reverse generation order, for the usual reason:
335 // namely to reduce the likelihood of spurious old->new pointers.
337 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
338 #if defined(THREADED_RTS)
339 if (n_gc_threads > 1) {
340 scavenge_mutable_list(generations[g].saved_mut_list, &generations[g]);
342 scavenge_mutable_list1(generations[g].saved_mut_list, &generations[g]);
345 scavenge_mutable_list(generations[g].saved_mut_list, &generations[g]);
347 freeChain_sync(generations[g].saved_mut_list);
348 generations[g].saved_mut_list = NULL;
352 // scavenge the capability-private mutable lists. This isn't part
353 // of markSomeCapabilities() because markSomeCapabilities() can only
354 // call back into the GC via mark_root() (due to the gct register
356 if (n_gc_threads == 1) {
357 for (n = 0; n < n_capabilities; n++) {
358 #if defined(THREADED_RTS)
359 scavenge_capability_mut_Lists1(&capabilities[n]);
361 scavenge_capability_mut_lists(&capabilities[n]);
365 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
368 // follow roots from the CAF list (used by GHCi)
370 markCAFs(mark_root, gct);
372 // follow all the roots that the application knows about.
374 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
375 rtsTrue/*prune sparks*/);
377 #if defined(RTS_USER_SIGNALS)
378 // mark the signal handlers (signals should be already blocked)
379 markSignalHandlers(mark_root, gct);
382 // Mark the weak pointer list, and prepare to detect dead weak pointers.
386 // Mark the stable pointer table.
387 markStablePtrTable(mark_root, gct);
389 /* -------------------------------------------------------------------------
390 * Repeatedly scavenge all the areas we know about until there's no
391 * more scavenging to be done.
395 scavenge_until_all_done();
396 // The other threads are now stopped. We might recurse back to
397 // here, but from now on this is the only thread.
399 // if any blackholes are alive, make the threads that wait on
401 if (traverseBlackholeQueue()) {
406 // must be last... invariant is that everything is fully
407 // scavenged at this point.
408 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
413 // If we get to here, there's really nothing left to do.
417 shutdown_gc_threads(n_gc_threads, gct->thread_index);
419 // Update pointers from the Task list
422 // Now see which stable names are still alive.
426 // We call processHeapClosureForDead() on every closure destroyed during
427 // the current garbage collection, so we invoke LdvCensusForDead().
428 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
429 || RtsFlags.ProfFlags.bioSelector != NULL)
433 // NO MORE EVACUATION AFTER THIS POINT!
435 // Two-space collector: free the old to-space.
436 // g0->old_blocks is the old nursery
437 // g0->blocks is to-space from the previous GC
438 if (RtsFlags.GcFlags.generations == 1) {
439 if (g0->blocks != NULL) {
440 freeChain(g0->blocks);
445 // For each workspace, in each thread, move the copied blocks to the step
451 for (t = 0; t < n_gc_threads; t++) {
454 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
457 // Push the final block
459 push_scanned_block(ws->todo_bd, ws);
462 ASSERT(gct->scan_bd == NULL);
463 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
466 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
467 ws->gen->n_words += bd->free - bd->start;
471 prev->link = ws->gen->blocks;
472 ws->gen->blocks = ws->scavd_list;
474 ws->gen->n_blocks += ws->n_scavd_blocks;
478 // Add all the partial blocks *after* we've added all the full
479 // blocks. This is so that we can grab the partial blocks back
480 // again and try to fill them up in the next GC.
481 for (t = 0; t < n_gc_threads; t++) {
484 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
488 for (bd = ws->part_list; bd != NULL; bd = next) {
490 if (bd->free == bd->start) {
492 ws->part_list = next;
499 ws->gen->n_words += bd->free - bd->start;
504 prev->link = ws->gen->blocks;
505 ws->gen->blocks = ws->part_list;
507 ws->gen->n_blocks += ws->n_part_blocks;
509 ASSERT(countBlocks(ws->gen->blocks) == ws->gen->n_blocks);
510 ASSERT(countOccupied(ws->gen->blocks) == ws->gen->n_words);
515 // Finally: compact or sweep the oldest generation.
516 if (major_gc && oldest_gen->mark) {
517 if (oldest_gen->compact)
518 compact(gct->scavenged_static_objects);
523 /* run through all the generations/steps and tidy up
530 for (i=0; i < n_gc_threads; i++) {
531 if (n_gc_threads > 1) {
532 debugTrace(DEBUG_gc,"thread %d:", i);
533 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
534 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
535 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
536 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
537 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
539 copied += gc_threads[i]->copied;
540 max_copied = stg_max(gc_threads[i]->copied, max_copied);
542 if (n_gc_threads == 1) {
550 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
553 generations[g].collections++; // for stats
554 if (n_gc_threads > 1) generations[g].par_collections++;
557 // Count the mutable list as bytes "copied" for the purposes of
558 // stats. Every mutable list is copied during every GC.
560 nat mut_list_size = 0;
561 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
562 mut_list_size += bd->free - bd->start;
564 for (n = 0; n < n_capabilities; n++) {
565 for (bd = capabilities[n].mut_lists[g];
566 bd != NULL; bd = bd->link) {
567 mut_list_size += bd->free - bd->start;
570 copied += mut_list_size;
573 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
574 (unsigned long)(mut_list_size * sizeof(W_)),
575 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
579 gen = &generations[g];
581 // for generations we collected...
584 /* free old memory and shift to-space into from-space for all
585 * the collected steps (except the allocation area). These
586 * freed blocks will probaby be quickly recycled.
590 // tack the new blocks on the end of the existing blocks
591 if (gen->old_blocks != NULL) {
594 for (bd = gen->old_blocks; bd != NULL; bd = next) {
598 if (!(bd->flags & BF_MARKED))
601 gen->old_blocks = next;
610 gen->n_words += bd->free - bd->start;
612 // NB. this step might not be compacted next
613 // time, so reset the BF_MARKED flags.
614 // They are set before GC if we're going to
615 // compact. (search for BF_MARKED above).
616 bd->flags &= ~BF_MARKED;
618 // between GCs, all blocks in the heap except
619 // for the nursery have the BF_EVACUATED flag set.
620 bd->flags |= BF_EVACUATED;
627 prev->link = gen->blocks;
628 gen->blocks = gen->old_blocks;
631 // add the new blocks to the block tally
632 gen->n_blocks += gen->n_old_blocks;
633 ASSERT(countBlocks(gen->blocks) == gen->n_blocks);
634 ASSERT(countOccupied(gen->blocks) == gen->n_words);
638 freeChain(gen->old_blocks);
641 gen->old_blocks = NULL;
642 gen->n_old_blocks = 0;
644 /* LARGE OBJECTS. The current live large objects are chained on
645 * scavenged_large, having been moved during garbage
646 * collection from large_objects. Any objects left on the
647 * large_objects list are therefore dead, so we free them here.
649 freeChain(gen->large_objects);
650 gen->large_objects = gen->scavenged_large_objects;
651 gen->n_large_blocks = gen->n_scavenged_large_blocks;
652 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
654 else // for generations > N
656 /* For older generations, we need to append the
657 * scavenged_large_object list (i.e. large objects that have been
658 * promoted during this GC) to the large_object list for that step.
660 for (bd = gen->scavenged_large_objects; bd; bd = next) {
662 dbl_link_onto(bd, &gen->large_objects);
665 // add the new blocks we promoted during this GC
666 gen->n_large_blocks += gen->n_scavenged_large_blocks;
667 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
669 } // for all generations
671 // update the max size of older generations after a major GC
672 resize_generations();
674 // Calculate the amount of live data for stats.
675 live = calcLiveWords();
677 // Free the small objects allocated via allocate(), since this will
678 // all have been copied into G0S1 now.
679 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
681 // Start a new pinned_object_block
682 for (n = 0; n < n_capabilities; n++) {
683 capabilities[n].pinned_object_block = NULL;
686 // Free the mark stack.
687 if (mark_stack_top_bd != NULL) {
688 debugTrace(DEBUG_gc, "mark stack: %d blocks",
689 countBlocks(mark_stack_top_bd));
690 freeChain(mark_stack_top_bd);
694 for (g = 0; g <= N; g++) {
695 gen = &generations[g];
696 if (gen->bitmap != NULL) {
697 freeGroup(gen->bitmap);
704 // mark the garbage collected CAFs as dead
705 #if 0 && defined(DEBUG) // doesn't work at the moment
706 if (major_gc) { gcCAFs(); }
710 // resetStaticObjectForRetainerProfiling() must be called before
712 if (n_gc_threads > 1) {
713 barf("profiling is currently broken with multi-threaded GC");
714 // ToDo: fix the gct->scavenged_static_objects below
716 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
719 // zero the scavenged static object list
722 for (i = 0; i < n_gc_threads; i++) {
723 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
730 // start any pending finalizers
732 scheduleFinalizers(cap, old_weak_ptr_list);
735 // send exceptions to any threads which were about to die
737 resurrectThreads(resurrected_threads);
738 performPendingThrowTos(exception_threads);
741 // Update the stable pointer hash table.
742 updateStablePtrTable(major_gc);
744 // check sanity after GC
745 IF_DEBUG(sanity, checkSanity(rtsTrue));
747 // extra GC trace info
748 IF_DEBUG(gc, statDescribeGens());
751 // symbol-table based profiling
752 /* heapCensus(to_blocks); */ /* ToDo */
755 // restore enclosing cost centre
761 // check for memory leaks if DEBUG is on
762 memInventory(DEBUG_gc);
765 #ifdef RTS_GTK_FRONTPANEL
766 if (RtsFlags.GcFlags.frontpanel) {
767 updateFrontPanelAfterGC( N, live );
771 // ok, GC over: tell the stats department what happened.
772 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
773 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
775 // unlock the StablePtr table
778 // Guess which generation we'll collect *next* time
779 initialise_N(force_major_gc);
781 #if defined(RTS_USER_SIGNALS)
782 if (RtsFlags.MiscFlags.install_signal_handlers) {
783 // unblock signals again
784 unblockUserSignals();
793 /* -----------------------------------------------------------------------------
794 Figure out which generation to collect, initialise N and major_gc.
796 Also returns the total number of blocks in generations that will be
798 -------------------------------------------------------------------------- */
801 initialise_N (rtsBool force_major_gc)
804 nat blocks, blocks_total;
809 if (force_major_gc) {
810 N = RtsFlags.GcFlags.generations - 1;
815 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
817 blocks = generations[g].n_words / BLOCK_SIZE_W
818 + generations[g].n_large_blocks;
820 if (blocks >= generations[g].max_blocks) {
824 blocks_total += blocks;
828 blocks_total += countNurseryBlocks();
830 major_gc = (N == RtsFlags.GcFlags.generations-1);
834 /* -----------------------------------------------------------------------------
835 Initialise the gc_thread structures.
836 -------------------------------------------------------------------------- */
838 #define GC_THREAD_INACTIVE 0
839 #define GC_THREAD_STANDING_BY 1
840 #define GC_THREAD_RUNNING 2
841 #define GC_THREAD_WAITING_TO_CONTINUE 3
844 new_gc_thread (nat n, gc_thread *t)
851 initSpinLock(&t->gc_spin);
852 initSpinLock(&t->mut_spin);
853 ACQUIRE_SPIN_LOCK(&t->gc_spin);
854 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
855 // thread to start up, see wakeup_gc_threads
859 t->free_blocks = NULL;
868 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
871 ws->gen = &generations[g];
872 ASSERT(g == ws->gen->no);
876 ws->todo_q = newWSDeque(128);
877 ws->todo_overflow = NULL;
878 ws->n_todo_overflow = 0;
880 ws->part_list = NULL;
881 ws->n_part_blocks = 0;
883 ws->scavd_list = NULL;
884 ws->n_scavd_blocks = 0;
892 if (gc_threads == NULL) {
893 #if defined(THREADED_RTS)
895 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
899 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
901 stgMallocBytes(sizeof(gc_thread) +
902 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
905 new_gc_thread(i, gc_threads[i]);
908 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
910 new_gc_thread(0,gc_threads[0]);
919 if (gc_threads != NULL) {
920 #if defined(THREADED_RTS)
922 for (i = 0; i < n_capabilities; i++) {
923 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
925 freeWSDeque(gc_threads[i]->gens[g].todo_q);
927 stgFree (gc_threads[i]);
929 stgFree (gc_threads);
931 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
933 freeWSDeque(gc_threads[0]->gens[g].todo_q);
935 stgFree (gc_threads);
941 /* ----------------------------------------------------------------------------
943 ------------------------------------------------------------------------- */
945 static volatile StgWord gc_running_threads;
951 new = atomic_inc(&gc_running_threads);
952 ASSERT(new <= n_gc_threads);
959 ASSERT(gc_running_threads != 0);
960 return atomic_dec(&gc_running_threads);
973 // scavenge objects in compacted generation
974 if (mark_stack_bd != NULL && !mark_stack_empty()) {
978 // Check for global work in any step. We don't need to check for
979 // local work, because we have already exited scavenge_loop(),
980 // which means there is no local work for this thread.
981 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
983 if (ws->todo_large_objects) return rtsTrue;
984 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
985 if (ws->todo_overflow) return rtsTrue;
988 #if defined(THREADED_RTS)
991 // look for work to steal
992 for (n = 0; n < n_gc_threads; n++) {
993 if (n == gct->thread_index) continue;
994 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
995 ws = &gc_threads[n]->gens[g];
996 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
1008 scavenge_until_all_done (void)
1014 traceEvent(&capabilities[gct->thread_index], EVENT_GC_WORK);
1016 #if defined(THREADED_RTS)
1017 if (n_gc_threads > 1) {
1026 // scavenge_loop() only exits when there's no work to do
1029 traceEvent(&capabilities[gct->thread_index], EVENT_GC_IDLE);
1031 debugTrace(DEBUG_gc, "%d GC threads still running", r);
1033 while (gc_running_threads != 0) {
1039 // any_work() does not remove the work from the queue, it
1040 // just checks for the presence of work. If we find any,
1041 // then we increment gc_running_threads and go back to
1042 // scavenge_loop() to perform any pending work.
1045 traceEvent(&capabilities[gct->thread_index], EVENT_GC_DONE);
1048 #if defined(THREADED_RTS)
1051 gcWorkerThread (Capability *cap)
1053 gc_thread *saved_gct;
1055 // necessary if we stole a callee-saves register for gct:
1058 gct = gc_threads[cap->no];
1059 gct->id = osThreadId();
1061 // Wait until we're told to wake up
1062 RELEASE_SPIN_LOCK(&gct->mut_spin);
1063 gct->wakeup = GC_THREAD_STANDING_BY;
1064 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1065 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1068 // start performance counters in this thread...
1069 if (gct->papi_events == -1) {
1070 papi_init_eventset(&gct->papi_events);
1072 papi_thread_start_gc1_count(gct->papi_events);
1075 // Every thread evacuates some roots.
1077 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1078 rtsTrue/*prune sparks*/);
1079 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1081 scavenge_until_all_done();
1084 // count events in this thread towards the GC totals
1085 papi_thread_stop_gc1_count(gct->papi_events);
1088 // Wait until we're told to continue
1089 RELEASE_SPIN_LOCK(&gct->gc_spin);
1090 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1091 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1093 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1094 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1101 #if defined(THREADED_RTS)
1104 waitForGcThreads (Capability *cap USED_IF_THREADS)
1106 nat n_threads = RtsFlags.ParFlags.nNodes;
1109 rtsBool retry = rtsTrue;
1112 for (i=0; i < n_threads; i++) {
1113 if (i == me) continue;
1114 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1115 prodCapability(&capabilities[i], cap->running_task);
1118 for (j=0; j < 10; j++) {
1120 for (i=0; i < n_threads; i++) {
1121 if (i == me) continue;
1123 setContextSwitches();
1124 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1134 #endif // THREADED_RTS
1137 start_gc_threads (void)
1139 #if defined(THREADED_RTS)
1140 gc_running_threads = 0;
1145 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1147 #if defined(THREADED_RTS)
1149 for (i=0; i < n_threads; i++) {
1150 if (i == me) continue;
1152 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1153 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1155 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1156 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1157 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1162 // After GC is complete, we must wait for all GC threads to enter the
1163 // standby state, otherwise they may still be executing inside
1164 // any_work(), and may even remain awake until the next GC starts.
1166 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1168 #if defined(THREADED_RTS)
1170 for (i=0; i < n_threads; i++) {
1171 if (i == me) continue;
1172 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1177 #if defined(THREADED_RTS)
1179 releaseGCThreads (Capability *cap USED_IF_THREADS)
1181 nat n_threads = RtsFlags.ParFlags.nNodes;
1184 for (i=0; i < n_threads; i++) {
1185 if (i == me) continue;
1186 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1187 barf("releaseGCThreads");
1189 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1190 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1191 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1196 /* ----------------------------------------------------------------------------
1197 Initialise a generation that is to be collected
1198 ------------------------------------------------------------------------- */
1201 init_collected_gen (nat g, nat n_threads)
1208 // Throw away the current mutable list. Invariant: the mutable
1209 // list always has at least one block; this means we can avoid a
1210 // check for NULL in recordMutable().
1212 freeChain(generations[g].mut_list);
1213 generations[g].mut_list = allocBlock();
1214 for (i = 0; i < n_capabilities; i++) {
1215 freeChain(capabilities[i].mut_lists[g]);
1216 capabilities[i].mut_lists[g] = allocBlock();
1220 gen = &generations[g];
1221 ASSERT(gen->no == g);
1223 // we'll construct a new list of threads in this step
1224 // during GC, throw away the current list.
1225 gen->old_threads = gen->threads;
1226 gen->threads = END_TSO_QUEUE;
1228 // deprecate the existing blocks
1229 gen->old_blocks = gen->blocks;
1230 gen->n_old_blocks = gen->n_blocks;
1234 gen->live_estimate = 0;
1236 // initialise the large object queues.
1237 gen->scavenged_large_objects = NULL;
1238 gen->n_scavenged_large_blocks = 0;
1240 // mark the small objects as from-space
1241 for (bd = gen->old_blocks; bd; bd = bd->link) {
1242 bd->flags &= ~BF_EVACUATED;
1245 // mark the large objects as from-space
1246 for (bd = gen->large_objects; bd; bd = bd->link) {
1247 bd->flags &= ~BF_EVACUATED;
1250 // for a compacted generation, we need to allocate the bitmap
1252 nat bitmap_size; // in bytes
1253 bdescr *bitmap_bdescr;
1256 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1258 if (bitmap_size > 0) {
1259 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1261 gen->bitmap = bitmap_bdescr;
1262 bitmap = bitmap_bdescr->start;
1264 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1265 bitmap_size, bitmap);
1267 // don't forget to fill it with zeros!
1268 memset(bitmap, 0, bitmap_size);
1270 // For each block in this step, point to its bitmap from the
1271 // block descriptor.
1272 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1273 bd->u.bitmap = bitmap;
1274 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1276 // Also at this point we set the BF_MARKED flag
1277 // for this block. The invariant is that
1278 // BF_MARKED is always unset, except during GC
1279 // when it is set on those blocks which will be
1281 if (!(bd->flags & BF_FRAGMENTED)) {
1282 bd->flags |= BF_MARKED;
1288 // For each GC thread, for each step, allocate a "todo" block to
1289 // store evacuated objects to be scavenged, and a block to store
1290 // evacuated objects that do not need to be scavenged.
1291 for (t = 0; t < n_threads; t++) {
1292 ws = &gc_threads[t]->gens[g];
1294 ws->todo_large_objects = NULL;
1296 ws->part_list = NULL;
1297 ws->n_part_blocks = 0;
1299 // allocate the first to-space block; extra blocks will be
1300 // chained on as necessary.
1302 ASSERT(looksEmptyWSDeque(ws->todo_q));
1303 alloc_todo_block(ws,0);
1305 ws->todo_overflow = NULL;
1306 ws->n_todo_overflow = 0;
1308 ws->scavd_list = NULL;
1309 ws->n_scavd_blocks = 0;
1314 /* ----------------------------------------------------------------------------
1315 Initialise a generation that is *not* to be collected
1316 ------------------------------------------------------------------------- */
1319 init_uncollected_gen (nat g, nat threads)
1326 // save the current mutable lists for this generation, and
1327 // allocate a fresh block for each one. We'll traverse these
1328 // mutable lists as roots early on in the GC.
1329 generations[g].saved_mut_list = generations[g].mut_list;
1330 generations[g].mut_list = allocBlock();
1331 for (n = 0; n < n_capabilities; n++) {
1332 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1333 capabilities[n].mut_lists[g] = allocBlock();
1336 gen = &generations[g];
1338 gen->scavenged_large_objects = NULL;
1339 gen->n_scavenged_large_blocks = 0;
1341 for (t = 0; t < threads; t++) {
1342 ws = &gc_threads[t]->gens[g];
1344 ASSERT(looksEmptyWSDeque(ws->todo_q));
1345 ws->todo_large_objects = NULL;
1347 ws->part_list = NULL;
1348 ws->n_part_blocks = 0;
1350 ws->scavd_list = NULL;
1351 ws->n_scavd_blocks = 0;
1353 // If the block at the head of the list in this generation
1354 // is less than 3/4 full, then use it as a todo block.
1355 if (gen->blocks && isPartiallyFull(gen->blocks))
1357 ws->todo_bd = gen->blocks;
1358 ws->todo_free = ws->todo_bd->free;
1359 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1360 gen->blocks = gen->blocks->link;
1362 gen->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1363 ws->todo_bd->link = NULL;
1364 // we must scan from the current end point.
1365 ws->todo_bd->u.scan = ws->todo_bd->free;
1370 alloc_todo_block(ws,0);
1374 // deal out any more partial blocks to the threads' part_lists
1376 while (gen->blocks && isPartiallyFull(gen->blocks))
1379 gen->blocks = bd->link;
1380 ws = &gc_threads[t]->gens[g];
1381 bd->link = ws->part_list;
1383 ws->n_part_blocks += 1;
1384 bd->u.scan = bd->free;
1386 gen->n_words -= bd->free - bd->start;
1388 if (t == n_gc_threads) t = 0;
1392 /* -----------------------------------------------------------------------------
1393 Initialise a gc_thread before GC
1394 -------------------------------------------------------------------------- */
1397 init_gc_thread (gc_thread *t)
1399 t->static_objects = END_OF_STATIC_LIST;
1400 t->scavenged_static_objects = END_OF_STATIC_LIST;
1402 t->mut_lists = capabilities[t->thread_index].mut_lists;
1404 t->failed_to_evac = rtsFalse;
1405 t->eager_promotion = rtsTrue;
1406 t->thunk_selector_depth = 0;
1411 t->scav_find_work = 0;
1414 /* -----------------------------------------------------------------------------
1415 Function we pass to evacuate roots.
1416 -------------------------------------------------------------------------- */
1419 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1421 // we stole a register for gct, but this function is called from
1422 // *outside* the GC where the register variable is not in effect,
1423 // so we need to save and restore it here. NB. only call
1424 // mark_root() from the main GC thread, otherwise gct will be
1426 gc_thread *saved_gct;
1435 /* -----------------------------------------------------------------------------
1436 Initialising the static object & mutable lists
1437 -------------------------------------------------------------------------- */
1440 zero_static_object_list(StgClosure* first_static)
1444 const StgInfoTable *info;
1446 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1448 link = *STATIC_LINK(info, p);
1449 *STATIC_LINK(info,p) = NULL;
1453 /* ----------------------------------------------------------------------------
1454 Update the pointers from the task list
1456 These are treated as weak pointers because we want to allow a main
1457 thread to get a BlockedOnDeadMVar exception in the same way as any
1458 other thread. Note that the threads should all have been retained
1459 by GC by virtue of being on the all_threads list, we're just
1460 updating pointers here.
1461 ------------------------------------------------------------------------- */
1464 update_task_list (void)
1468 for (task = all_tasks; task != NULL; task = task->all_link) {
1469 if (!task->stopped && task->tso) {
1470 ASSERT(task->tso->bound == task);
1471 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1473 barf("task %p: main thread %d has been GC'd",
1486 /* ----------------------------------------------------------------------------
1487 Reset the sizes of the older generations when we do a major
1490 CURRENT STRATEGY: make all generations except zero the same size.
1491 We have to stay within the maximum heap size, and leave a certain
1492 percentage of the maximum heap size available to allocate into.
1493 ------------------------------------------------------------------------- */
1496 resize_generations (void)
1500 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1501 nat live, size, min_alloc, words;
1502 nat max = RtsFlags.GcFlags.maxHeapSize;
1503 nat gens = RtsFlags.GcFlags.generations;
1505 // live in the oldest generations
1506 if (oldest_gen->live_estimate != 0) {
1507 words = oldest_gen->live_estimate;
1509 words = oldest_gen->n_words;
1511 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1512 oldest_gen->n_large_blocks;
1514 // default max size for all generations except zero
1515 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1516 RtsFlags.GcFlags.minOldGenSize);
1518 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1519 RtsFlags.GcFlags.heapSizeSuggestion = size;
1522 // minimum size for generation zero
1523 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1524 RtsFlags.GcFlags.minAllocAreaSize);
1526 // Auto-enable compaction when the residency reaches a
1527 // certain percentage of the maximum heap size (default: 30%).
1528 if (RtsFlags.GcFlags.generations > 1 &&
1529 (RtsFlags.GcFlags.compact ||
1531 oldest_gen->n_blocks >
1532 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1533 oldest_gen->mark = 1;
1534 oldest_gen->compact = 1;
1535 // debugBelch("compaction: on\n", live);
1537 oldest_gen->mark = 0;
1538 oldest_gen->compact = 0;
1539 // debugBelch("compaction: off\n", live);
1542 if (RtsFlags.GcFlags.sweep) {
1543 oldest_gen->mark = 1;
1546 // if we're going to go over the maximum heap size, reduce the
1547 // size of the generations accordingly. The calculation is
1548 // different if compaction is turned on, because we don't need
1549 // to double the space required to collect the old generation.
1552 // this test is necessary to ensure that the calculations
1553 // below don't have any negative results - we're working
1554 // with unsigned values here.
1555 if (max < min_alloc) {
1559 if (oldest_gen->compact) {
1560 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1561 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1564 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1565 size = (max - min_alloc) / ((gens - 1) * 2);
1575 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1576 min_alloc, size, max);
1579 for (g = 0; g < gens; g++) {
1580 generations[g].max_blocks = size;
1585 /* -----------------------------------------------------------------------------
1586 Calculate the new size of the nursery, and resize it.
1587 -------------------------------------------------------------------------- */
1590 resize_nursery (void)
1592 lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1594 if (RtsFlags.GcFlags.generations == 1)
1595 { // Two-space collector:
1598 /* set up a new nursery. Allocate a nursery size based on a
1599 * function of the amount of live data (by default a factor of 2)
1600 * Use the blocks from the old nursery if possible, freeing up any
1603 * If we get near the maximum heap size, then adjust our nursery
1604 * size accordingly. If the nursery is the same size as the live
1605 * data (L), then we need 3L bytes. We can reduce the size of the
1606 * nursery to bring the required memory down near 2L bytes.
1608 * A normal 2-space collector would need 4L bytes to give the same
1609 * performance we get from 3L bytes, reducing to the same
1610 * performance at 2L bytes.
1612 blocks = generations[0].n_blocks;
1614 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1615 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1616 RtsFlags.GcFlags.maxHeapSize )
1618 long adjusted_blocks; // signed on purpose
1621 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1623 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1624 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1626 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1627 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1631 blocks = adjusted_blocks;
1635 blocks *= RtsFlags.GcFlags.oldGenFactor;
1636 if (blocks < min_nursery)
1638 blocks = min_nursery;
1641 resizeNurseries(blocks);
1643 else // Generational collector
1646 * If the user has given us a suggested heap size, adjust our
1647 * allocation area to make best use of the memory available.
1649 if (RtsFlags.GcFlags.heapSizeSuggestion)
1652 nat needed = calcNeeded(); // approx blocks needed at next GC
1654 /* Guess how much will be live in generation 0 step 0 next time.
1655 * A good approximation is obtained by finding the
1656 * percentage of g0 that was live at the last minor GC.
1658 * We have an accurate figure for the amount of copied data in
1659 * 'copied', but we must convert this to a number of blocks, with
1660 * a small adjustment for estimated slop at the end of a block
1665 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1666 / countNurseryBlocks();
1669 /* Estimate a size for the allocation area based on the
1670 * information available. We might end up going slightly under
1671 * or over the suggested heap size, but we should be pretty
1674 * Formula: suggested - needed
1675 * ----------------------------
1676 * 1 + g0_pcnt_kept/100
1678 * where 'needed' is the amount of memory needed at the next
1679 * collection for collecting all gens except g0.
1682 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1683 (100 + (long)g0_pcnt_kept);
1685 if (blocks < (long)min_nursery) {
1686 blocks = min_nursery;
1689 resizeNurseries((nat)blocks);
1693 // we might have added extra large blocks to the nursery, so
1694 // resize back to minAllocAreaSize again.
1695 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1700 /* -----------------------------------------------------------------------------
1701 Sanity code for CAF garbage collection.
1703 With DEBUG turned on, we manage a CAF list in addition to the SRT
1704 mechanism. After GC, we run down the CAF list and blackhole any
1705 CAFs which have been garbage collected. This means we get an error
1706 whenever the program tries to enter a garbage collected CAF.
1708 Any garbage collected CAFs are taken off the CAF list at the same
1710 -------------------------------------------------------------------------- */
1712 #if 0 && defined(DEBUG)
1719 const StgInfoTable *info;
1730 ASSERT(info->type == IND_STATIC);
1732 if (STATIC_LINK(info,p) == NULL) {
1733 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1735 SET_INFO(p,&stg_BLACKHOLE_info);
1736 p = STATIC_LINK2(info,p);
1740 pp = &STATIC_LINK2(info,p);
1747 debugTrace(DEBUG_gccafs, "%d CAFs live", i);