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 // must be last... invariant is that everything is fully
399 // scavenged at this point.
400 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
405 // If we get to here, there's really nothing left to do.
409 shutdown_gc_threads(n_gc_threads, gct->thread_index);
411 // Now see which stable names are still alive.
415 if (n_gc_threads == 1) {
416 for (n = 0; n < n_capabilities; n++) {
417 pruneSparkQueue(&capabilities[n]);
420 pruneSparkQueue(&capabilities[gct->thread_index]);
425 // We call processHeapClosureForDead() on every closure destroyed during
426 // the current garbage collection, so we invoke LdvCensusForDead().
427 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
428 || RtsFlags.ProfFlags.bioSelector != NULL)
432 // NO MORE EVACUATION AFTER THIS POINT!
434 // Two-space collector: free the old to-space.
435 // g0->old_blocks is the old nursery
436 // g0->blocks is to-space from the previous GC
437 if (RtsFlags.GcFlags.generations == 1) {
438 if (g0->blocks != NULL) {
439 freeChain(g0->blocks);
444 // For each workspace, in each thread, move the copied blocks to the step
450 for (t = 0; t < n_gc_threads; t++) {
453 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
456 // Push the final block
458 push_scanned_block(ws->todo_bd, ws);
461 ASSERT(gct->scan_bd == NULL);
462 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
465 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
466 ws->gen->n_words += bd->free - bd->start;
470 prev->link = ws->gen->blocks;
471 ws->gen->blocks = ws->scavd_list;
473 ws->gen->n_blocks += ws->n_scavd_blocks;
477 // Add all the partial blocks *after* we've added all the full
478 // blocks. This is so that we can grab the partial blocks back
479 // again and try to fill them up in the next GC.
480 for (t = 0; t < n_gc_threads; t++) {
483 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
487 for (bd = ws->part_list; bd != NULL; bd = next) {
489 if (bd->free == bd->start) {
491 ws->part_list = next;
498 ws->gen->n_words += bd->free - bd->start;
503 prev->link = ws->gen->blocks;
504 ws->gen->blocks = ws->part_list;
506 ws->gen->n_blocks += ws->n_part_blocks;
508 ASSERT(countBlocks(ws->gen->blocks) == ws->gen->n_blocks);
509 ASSERT(countOccupied(ws->gen->blocks) == ws->gen->n_words);
514 // Finally: compact or sweep the oldest generation.
515 if (major_gc && oldest_gen->mark) {
516 if (oldest_gen->compact)
517 compact(gct->scavenged_static_objects);
522 /* run through all the generations/steps and tidy up
529 for (i=0; i < n_gc_threads; i++) {
530 if (n_gc_threads > 1) {
531 debugTrace(DEBUG_gc,"thread %d:", i);
532 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
533 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
534 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
535 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
536 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
538 copied += gc_threads[i]->copied;
539 max_copied = stg_max(gc_threads[i]->copied, max_copied);
541 if (n_gc_threads == 1) {
549 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
552 generations[g].collections++; // for stats
553 if (n_gc_threads > 1) generations[g].par_collections++;
556 // Count the mutable list as bytes "copied" for the purposes of
557 // stats. Every mutable list is copied during every GC.
559 nat mut_list_size = 0;
560 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
561 mut_list_size += bd->free - bd->start;
563 for (n = 0; n < n_capabilities; n++) {
564 for (bd = capabilities[n].mut_lists[g];
565 bd != NULL; bd = bd->link) {
566 mut_list_size += bd->free - bd->start;
569 copied += mut_list_size;
572 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
573 (unsigned long)(mut_list_size * sizeof(W_)),
574 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
578 gen = &generations[g];
580 // for generations we collected...
583 /* free old memory and shift to-space into from-space for all
584 * the collected steps (except the allocation area). These
585 * freed blocks will probaby be quickly recycled.
589 // tack the new blocks on the end of the existing blocks
590 if (gen->old_blocks != NULL) {
593 for (bd = gen->old_blocks; bd != NULL; bd = next) {
597 if (!(bd->flags & BF_MARKED))
600 gen->old_blocks = next;
609 gen->n_words += bd->free - bd->start;
611 // NB. this step might not be compacted next
612 // time, so reset the BF_MARKED flags.
613 // They are set before GC if we're going to
614 // compact. (search for BF_MARKED above).
615 bd->flags &= ~BF_MARKED;
617 // between GCs, all blocks in the heap except
618 // for the nursery have the BF_EVACUATED flag set.
619 bd->flags |= BF_EVACUATED;
626 prev->link = gen->blocks;
627 gen->blocks = gen->old_blocks;
630 // add the new blocks to the block tally
631 gen->n_blocks += gen->n_old_blocks;
632 ASSERT(countBlocks(gen->blocks) == gen->n_blocks);
633 ASSERT(countOccupied(gen->blocks) == gen->n_words);
637 freeChain(gen->old_blocks);
640 gen->old_blocks = NULL;
641 gen->n_old_blocks = 0;
643 /* LARGE OBJECTS. The current live large objects are chained on
644 * scavenged_large, having been moved during garbage
645 * collection from large_objects. Any objects left on the
646 * large_objects list are therefore dead, so we free them here.
648 freeChain(gen->large_objects);
649 gen->large_objects = gen->scavenged_large_objects;
650 gen->n_large_blocks = gen->n_scavenged_large_blocks;
651 gen->n_new_large_blocks = 0;
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);
740 // Update the stable pointer hash table.
741 updateStablePtrTable(major_gc);
743 // check sanity after GC
744 IF_DEBUG(sanity, checkSanity(rtsTrue));
746 // extra GC trace info
747 IF_DEBUG(gc, statDescribeGens());
750 // symbol-table based profiling
751 /* heapCensus(to_blocks); */ /* ToDo */
754 // restore enclosing cost centre
760 // check for memory leaks if DEBUG is on
761 memInventory(DEBUG_gc);
764 #ifdef RTS_GTK_FRONTPANEL
765 if (RtsFlags.GcFlags.frontpanel) {
766 updateFrontPanelAfterGC( N, live );
770 // ok, GC over: tell the stats department what happened.
771 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
772 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
774 // unlock the StablePtr table
777 // Guess which generation we'll collect *next* time
778 initialise_N(force_major_gc);
780 #if defined(RTS_USER_SIGNALS)
781 if (RtsFlags.MiscFlags.install_signal_handlers) {
782 // unblock signals again
783 unblockUserSignals();
792 /* -----------------------------------------------------------------------------
793 Figure out which generation to collect, initialise N and major_gc.
795 Also returns the total number of blocks in generations that will be
797 -------------------------------------------------------------------------- */
800 initialise_N (rtsBool force_major_gc)
803 nat blocks, blocks_total;
808 if (force_major_gc) {
809 N = RtsFlags.GcFlags.generations - 1;
814 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
816 blocks = generations[g].n_words / BLOCK_SIZE_W
817 + generations[g].n_large_blocks;
819 if (blocks >= generations[g].max_blocks) {
823 blocks_total += blocks;
827 blocks_total += countNurseryBlocks();
829 major_gc = (N == RtsFlags.GcFlags.generations-1);
833 /* -----------------------------------------------------------------------------
834 Initialise the gc_thread structures.
835 -------------------------------------------------------------------------- */
837 #define GC_THREAD_INACTIVE 0
838 #define GC_THREAD_STANDING_BY 1
839 #define GC_THREAD_RUNNING 2
840 #define GC_THREAD_WAITING_TO_CONTINUE 3
843 new_gc_thread (nat n, gc_thread *t)
850 initSpinLock(&t->gc_spin);
851 initSpinLock(&t->mut_spin);
852 ACQUIRE_SPIN_LOCK(&t->gc_spin);
853 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
854 // thread to start up, see wakeup_gc_threads
858 t->free_blocks = NULL;
867 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
870 ws->gen = &generations[g];
871 ASSERT(g == ws->gen->no);
875 ws->todo_q = newWSDeque(128);
876 ws->todo_overflow = NULL;
877 ws->n_todo_overflow = 0;
879 ws->part_list = NULL;
880 ws->n_part_blocks = 0;
882 ws->scavd_list = NULL;
883 ws->n_scavd_blocks = 0;
891 if (gc_threads == NULL) {
892 #if defined(THREADED_RTS)
894 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
898 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
900 stgMallocBytes(sizeof(gc_thread) +
901 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
904 new_gc_thread(i, gc_threads[i]);
907 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
909 new_gc_thread(0,gc_threads[0]);
918 if (gc_threads != NULL) {
919 #if defined(THREADED_RTS)
921 for (i = 0; i < n_capabilities; i++) {
922 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
924 freeWSDeque(gc_threads[i]->gens[g].todo_q);
926 stgFree (gc_threads[i]);
928 stgFree (gc_threads);
930 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
932 freeWSDeque(gc_threads[0]->gens[g].todo_q);
934 stgFree (gc_threads);
940 /* ----------------------------------------------------------------------------
942 ------------------------------------------------------------------------- */
944 static volatile StgWord gc_running_threads;
950 new = atomic_inc(&gc_running_threads);
951 ASSERT(new <= n_gc_threads);
958 ASSERT(gc_running_threads != 0);
959 return atomic_dec(&gc_running_threads);
972 // scavenge objects in compacted generation
973 if (mark_stack_bd != NULL && !mark_stack_empty()) {
977 // Check for global work in any step. We don't need to check for
978 // local work, because we have already exited scavenge_loop(),
979 // which means there is no local work for this thread.
980 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
982 if (ws->todo_large_objects) return rtsTrue;
983 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
984 if (ws->todo_overflow) return rtsTrue;
987 #if defined(THREADED_RTS)
990 // look for work to steal
991 for (n = 0; n < n_gc_threads; n++) {
992 if (n == gct->thread_index) continue;
993 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
994 ws = &gc_threads[n]->gens[g];
995 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
1002 #if defined(THREADED_RTS)
1010 scavenge_until_all_done (void)
1016 traceEventGcWork(&capabilities[gct->thread_index]);
1018 #if defined(THREADED_RTS)
1019 if (n_gc_threads > 1) {
1028 // scavenge_loop() only exits when there's no work to do
1031 traceEventGcIdle(&capabilities[gct->thread_index]);
1033 debugTrace(DEBUG_gc, "%d GC threads still running", r);
1035 while (gc_running_threads != 0) {
1041 // any_work() does not remove the work from the queue, it
1042 // just checks for the presence of work. If we find any,
1043 // then we increment gc_running_threads and go back to
1044 // scavenge_loop() to perform any pending work.
1047 traceEventGcDone(&capabilities[gct->thread_index]);
1050 #if defined(THREADED_RTS)
1053 gcWorkerThread (Capability *cap)
1055 gc_thread *saved_gct;
1057 // necessary if we stole a callee-saves register for gct:
1060 gct = gc_threads[cap->no];
1061 gct->id = osThreadId();
1063 // Wait until we're told to wake up
1064 RELEASE_SPIN_LOCK(&gct->mut_spin);
1065 gct->wakeup = GC_THREAD_STANDING_BY;
1066 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1067 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1070 // start performance counters in this thread...
1071 if (gct->papi_events == -1) {
1072 papi_init_eventset(&gct->papi_events);
1074 papi_thread_start_gc1_count(gct->papi_events);
1077 // Every thread evacuates some roots.
1079 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1080 rtsTrue/*prune sparks*/);
1081 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1083 scavenge_until_all_done();
1086 // Now that the whole heap is marked, we discard any sparks that
1087 // were found to be unreachable. The main GC thread is currently
1088 // marking heap reachable via weak pointers, so it is
1089 // non-deterministic whether a spark will be retained if it is
1090 // only reachable via weak pointers. To fix this problem would
1091 // require another GC barrier, which is too high a price.
1092 pruneSparkQueue(cap);
1096 // count events in this thread towards the GC totals
1097 papi_thread_stop_gc1_count(gct->papi_events);
1100 // Wait until we're told to continue
1101 RELEASE_SPIN_LOCK(&gct->gc_spin);
1102 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1103 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1105 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1106 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1113 #if defined(THREADED_RTS)
1116 waitForGcThreads (Capability *cap USED_IF_THREADS)
1118 const nat n_threads = RtsFlags.ParFlags.nNodes;
1119 const nat me = cap->no;
1121 rtsBool retry = rtsTrue;
1124 for (i=0; i < n_threads; i++) {
1125 if (i == me) continue;
1126 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1127 prodCapability(&capabilities[i], cap->running_task);
1130 for (j=0; j < 10; j++) {
1132 for (i=0; i < n_threads; i++) {
1133 if (i == me) continue;
1135 setContextSwitches();
1136 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1146 #endif // THREADED_RTS
1149 start_gc_threads (void)
1151 #if defined(THREADED_RTS)
1152 gc_running_threads = 0;
1157 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1159 #if defined(THREADED_RTS)
1161 for (i=0; i < n_threads; i++) {
1162 if (i == me) continue;
1164 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1165 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1167 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1168 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1169 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1174 // After GC is complete, we must wait for all GC threads to enter the
1175 // standby state, otherwise they may still be executing inside
1176 // any_work(), and may even remain awake until the next GC starts.
1178 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1180 #if defined(THREADED_RTS)
1182 for (i=0; i < n_threads; i++) {
1183 if (i == me) continue;
1184 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1189 #if defined(THREADED_RTS)
1191 releaseGCThreads (Capability *cap USED_IF_THREADS)
1193 const nat n_threads = RtsFlags.ParFlags.nNodes;
1194 const nat me = cap->no;
1196 for (i=0; i < n_threads; i++) {
1197 if (i == me) continue;
1198 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1199 barf("releaseGCThreads");
1201 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1202 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1203 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1208 /* ----------------------------------------------------------------------------
1209 Initialise a generation that is to be collected
1210 ------------------------------------------------------------------------- */
1213 init_collected_gen (nat g, nat n_threads)
1220 // Throw away the current mutable list. Invariant: the mutable
1221 // list always has at least one block; this means we can avoid a
1222 // check for NULL in recordMutable().
1224 freeChain(generations[g].mut_list);
1225 generations[g].mut_list = allocBlock();
1226 for (i = 0; i < n_capabilities; i++) {
1227 freeChain(capabilities[i].mut_lists[g]);
1228 capabilities[i].mut_lists[g] = allocBlock();
1232 gen = &generations[g];
1233 ASSERT(gen->no == g);
1235 // we'll construct a new list of threads in this step
1236 // during GC, throw away the current list.
1237 gen->old_threads = gen->threads;
1238 gen->threads = END_TSO_QUEUE;
1240 // deprecate the existing blocks
1241 gen->old_blocks = gen->blocks;
1242 gen->n_old_blocks = gen->n_blocks;
1246 gen->live_estimate = 0;
1248 // initialise the large object queues.
1249 gen->scavenged_large_objects = NULL;
1250 gen->n_scavenged_large_blocks = 0;
1252 // mark the small objects as from-space
1253 for (bd = gen->old_blocks; bd; bd = bd->link) {
1254 bd->flags &= ~BF_EVACUATED;
1257 // mark the large objects as from-space
1258 for (bd = gen->large_objects; bd; bd = bd->link) {
1259 bd->flags &= ~BF_EVACUATED;
1262 // for a compacted generation, we need to allocate the bitmap
1264 nat bitmap_size; // in bytes
1265 bdescr *bitmap_bdescr;
1268 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1270 if (bitmap_size > 0) {
1271 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1273 gen->bitmap = bitmap_bdescr;
1274 bitmap = bitmap_bdescr->start;
1276 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1277 bitmap_size, bitmap);
1279 // don't forget to fill it with zeros!
1280 memset(bitmap, 0, bitmap_size);
1282 // For each block in this step, point to its bitmap from the
1283 // block descriptor.
1284 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1285 bd->u.bitmap = bitmap;
1286 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1288 // Also at this point we set the BF_MARKED flag
1289 // for this block. The invariant is that
1290 // BF_MARKED is always unset, except during GC
1291 // when it is set on those blocks which will be
1293 if (!(bd->flags & BF_FRAGMENTED)) {
1294 bd->flags |= BF_MARKED;
1300 // For each GC thread, for each step, allocate a "todo" block to
1301 // store evacuated objects to be scavenged, and a block to store
1302 // evacuated objects that do not need to be scavenged.
1303 for (t = 0; t < n_threads; t++) {
1304 ws = &gc_threads[t]->gens[g];
1306 ws->todo_large_objects = NULL;
1308 ws->part_list = NULL;
1309 ws->n_part_blocks = 0;
1311 // allocate the first to-space block; extra blocks will be
1312 // chained on as necessary.
1314 ASSERT(looksEmptyWSDeque(ws->todo_q));
1315 alloc_todo_block(ws,0);
1317 ws->todo_overflow = NULL;
1318 ws->n_todo_overflow = 0;
1320 ws->scavd_list = NULL;
1321 ws->n_scavd_blocks = 0;
1326 /* ----------------------------------------------------------------------------
1327 Initialise a generation that is *not* to be collected
1328 ------------------------------------------------------------------------- */
1331 init_uncollected_gen (nat g, nat threads)
1338 // save the current mutable lists for this generation, and
1339 // allocate a fresh block for each one. We'll traverse these
1340 // mutable lists as roots early on in the GC.
1341 generations[g].saved_mut_list = generations[g].mut_list;
1342 generations[g].mut_list = allocBlock();
1343 for (n = 0; n < n_capabilities; n++) {
1344 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1345 capabilities[n].mut_lists[g] = allocBlock();
1348 gen = &generations[g];
1350 gen->scavenged_large_objects = NULL;
1351 gen->n_scavenged_large_blocks = 0;
1353 for (t = 0; t < threads; t++) {
1354 ws = &gc_threads[t]->gens[g];
1356 ASSERT(looksEmptyWSDeque(ws->todo_q));
1357 ws->todo_large_objects = NULL;
1359 ws->part_list = NULL;
1360 ws->n_part_blocks = 0;
1362 ws->scavd_list = NULL;
1363 ws->n_scavd_blocks = 0;
1365 // If the block at the head of the list in this generation
1366 // is less than 3/4 full, then use it as a todo block.
1367 if (gen->blocks && isPartiallyFull(gen->blocks))
1369 ws->todo_bd = gen->blocks;
1370 ws->todo_free = ws->todo_bd->free;
1371 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1372 gen->blocks = gen->blocks->link;
1374 gen->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1375 ws->todo_bd->link = NULL;
1376 // we must scan from the current end point.
1377 ws->todo_bd->u.scan = ws->todo_bd->free;
1382 alloc_todo_block(ws,0);
1386 // deal out any more partial blocks to the threads' part_lists
1388 while (gen->blocks && isPartiallyFull(gen->blocks))
1391 gen->blocks = bd->link;
1392 ws = &gc_threads[t]->gens[g];
1393 bd->link = ws->part_list;
1395 ws->n_part_blocks += 1;
1396 bd->u.scan = bd->free;
1398 gen->n_words -= bd->free - bd->start;
1400 if (t == n_gc_threads) t = 0;
1404 /* -----------------------------------------------------------------------------
1405 Initialise a gc_thread before GC
1406 -------------------------------------------------------------------------- */
1409 init_gc_thread (gc_thread *t)
1411 t->static_objects = END_OF_STATIC_LIST;
1412 t->scavenged_static_objects = END_OF_STATIC_LIST;
1414 t->mut_lists = capabilities[t->thread_index].mut_lists;
1416 t->failed_to_evac = rtsFalse;
1417 t->eager_promotion = rtsTrue;
1418 t->thunk_selector_depth = 0;
1423 t->scav_find_work = 0;
1426 /* -----------------------------------------------------------------------------
1427 Function we pass to evacuate roots.
1428 -------------------------------------------------------------------------- */
1431 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1433 // we stole a register for gct, but this function is called from
1434 // *outside* the GC where the register variable is not in effect,
1435 // so we need to save and restore it here. NB. only call
1436 // mark_root() from the main GC thread, otherwise gct will be
1438 gc_thread *saved_gct;
1447 /* -----------------------------------------------------------------------------
1448 Initialising the static object & mutable lists
1449 -------------------------------------------------------------------------- */
1452 zero_static_object_list(StgClosure* first_static)
1456 const StgInfoTable *info;
1458 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1460 link = *STATIC_LINK(info, p);
1461 *STATIC_LINK(info,p) = NULL;
1465 /* ----------------------------------------------------------------------------
1466 Reset the sizes of the older generations when we do a major
1469 CURRENT STRATEGY: make all generations except zero the same size.
1470 We have to stay within the maximum heap size, and leave a certain
1471 percentage of the maximum heap size available to allocate into.
1472 ------------------------------------------------------------------------- */
1475 resize_generations (void)
1479 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1480 nat live, size, min_alloc, words;
1481 const nat max = RtsFlags.GcFlags.maxHeapSize;
1482 const nat gens = RtsFlags.GcFlags.generations;
1484 // live in the oldest generations
1485 if (oldest_gen->live_estimate != 0) {
1486 words = oldest_gen->live_estimate;
1488 words = oldest_gen->n_words;
1490 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1491 oldest_gen->n_large_blocks;
1493 // default max size for all generations except zero
1494 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1495 RtsFlags.GcFlags.minOldGenSize);
1497 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1498 RtsFlags.GcFlags.heapSizeSuggestion = size;
1501 // minimum size for generation zero
1502 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1503 RtsFlags.GcFlags.minAllocAreaSize);
1505 // Auto-enable compaction when the residency reaches a
1506 // certain percentage of the maximum heap size (default: 30%).
1507 if (RtsFlags.GcFlags.compact ||
1509 oldest_gen->n_blocks >
1510 (RtsFlags.GcFlags.compactThreshold * max) / 100)) {
1511 oldest_gen->mark = 1;
1512 oldest_gen->compact = 1;
1513 // debugBelch("compaction: on\n", live);
1515 oldest_gen->mark = 0;
1516 oldest_gen->compact = 0;
1517 // debugBelch("compaction: off\n", live);
1520 if (RtsFlags.GcFlags.sweep) {
1521 oldest_gen->mark = 1;
1524 // if we're going to go over the maximum heap size, reduce the
1525 // size of the generations accordingly. The calculation is
1526 // different if compaction is turned on, because we don't need
1527 // to double the space required to collect the old generation.
1530 // this test is necessary to ensure that the calculations
1531 // below don't have any negative results - we're working
1532 // with unsigned values here.
1533 if (max < min_alloc) {
1537 if (oldest_gen->compact) {
1538 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1539 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1542 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1543 size = (max - min_alloc) / ((gens - 1) * 2);
1553 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1554 min_alloc, size, max);
1557 for (g = 0; g < gens; g++) {
1558 generations[g].max_blocks = size;
1563 /* -----------------------------------------------------------------------------
1564 Calculate the new size of the nursery, and resize it.
1565 -------------------------------------------------------------------------- */
1568 resize_nursery (void)
1570 const lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1572 if (RtsFlags.GcFlags.generations == 1)
1573 { // Two-space collector:
1576 /* set up a new nursery. Allocate a nursery size based on a
1577 * function of the amount of live data (by default a factor of 2)
1578 * Use the blocks from the old nursery if possible, freeing up any
1581 * If we get near the maximum heap size, then adjust our nursery
1582 * size accordingly. If the nursery is the same size as the live
1583 * data (L), then we need 3L bytes. We can reduce the size of the
1584 * nursery to bring the required memory down near 2L bytes.
1586 * A normal 2-space collector would need 4L bytes to give the same
1587 * performance we get from 3L bytes, reducing to the same
1588 * performance at 2L bytes.
1590 blocks = generations[0].n_blocks;
1592 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1593 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1594 RtsFlags.GcFlags.maxHeapSize )
1596 long adjusted_blocks; // signed on purpose
1599 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1601 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1602 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1604 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1605 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1609 blocks = adjusted_blocks;
1613 blocks *= RtsFlags.GcFlags.oldGenFactor;
1614 if (blocks < min_nursery)
1616 blocks = min_nursery;
1619 resizeNurseries(blocks);
1621 else // Generational collector
1624 * If the user has given us a suggested heap size, adjust our
1625 * allocation area to make best use of the memory available.
1627 if (RtsFlags.GcFlags.heapSizeSuggestion)
1630 const nat needed = calcNeeded(); // approx blocks needed at next GC
1632 /* Guess how much will be live in generation 0 step 0 next time.
1633 * A good approximation is obtained by finding the
1634 * percentage of g0 that was live at the last minor GC.
1636 * We have an accurate figure for the amount of copied data in
1637 * 'copied', but we must convert this to a number of blocks, with
1638 * a small adjustment for estimated slop at the end of a block
1643 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1644 / countNurseryBlocks();
1647 /* Estimate a size for the allocation area based on the
1648 * information available. We might end up going slightly under
1649 * or over the suggested heap size, but we should be pretty
1652 * Formula: suggested - needed
1653 * ----------------------------
1654 * 1 + g0_pcnt_kept/100
1656 * where 'needed' is the amount of memory needed at the next
1657 * collection for collecting all gens except g0.
1660 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1661 (100 + (long)g0_pcnt_kept);
1663 if (blocks < (long)min_nursery) {
1664 blocks = min_nursery;
1667 resizeNurseries((nat)blocks);
1671 // we might have added extra large blocks to the nursery, so
1672 // resize back to minAllocAreaSize again.
1673 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1678 /* -----------------------------------------------------------------------------
1679 Sanity code for CAF garbage collection.
1681 With DEBUG turned on, we manage a CAF list in addition to the SRT
1682 mechanism. After GC, we run down the CAF list and blackhole any
1683 CAFs which have been garbage collected. This means we get an error
1684 whenever the program tries to enter a garbage collected CAF.
1686 Any garbage collected CAFs are taken off the CAF list at the same
1688 -------------------------------------------------------------------------- */
1690 #if 0 && defined(DEBUG)
1697 const StgInfoTable *info;
1708 ASSERT(info->type == IND_STATIC);
1710 if (STATIC_LINK(info,p) == NULL) {
1711 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1713 SET_INFO(p,&stg_BLACKHOLE_info);
1714 p = STATIC_LINK2(info,p);
1718 pp = &STATIC_LINK2(info,p);
1725 debugTrace(DEBUG_gccafs, "%d CAFs live", i);