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"
48 #include "MarkStack.h"
53 #include <string.h> // for memset()
56 /* -----------------------------------------------------------------------------
58 -------------------------------------------------------------------------- */
60 /* STATIC OBJECT LIST.
63 * We maintain a linked list of static objects that are still live.
64 * The requirements for this list are:
66 * - we need to scan the list while adding to it, in order to
67 * scavenge all the static objects (in the same way that
68 * breadth-first scavenging works for dynamic objects).
70 * - we need to be able to tell whether an object is already on
71 * the list, to break loops.
73 * Each static object has a "static link field", which we use for
74 * linking objects on to the list. We use a stack-type list, consing
75 * objects on the front as they are added (this means that the
76 * scavenge phase is depth-first, not breadth-first, but that
79 * A separate list is kept for objects that have been scavenged
80 * already - this is so that we can zero all the marks afterwards.
82 * An object is on the list if its static link field is non-zero; this
83 * means that we have to mark the end of the list with '1', not NULL.
85 * Extra notes for generational GC:
87 * Each generation has a static object list associated with it. When
88 * collecting generations up to N, we treat the static object lists
89 * from generations > N as roots.
91 * We build up a static object list while collecting generations 0..N,
92 * which is then appended to the static object list of generation N+1.
95 /* N is the oldest generation being collected, where the generations
96 * are numbered starting at 0. A major GC (indicated by the major_gc
97 * flag) is when we're collecting all generations. We only attempt to
98 * deal with static objects and GC CAFs when doing a major GC.
103 /* Data used for allocation area sizing.
105 static lnat g0_pcnt_kept = 30; // percentage of g0 live at last minor GC
115 /* Thread-local data for each GC thread
117 gc_thread **gc_threads = NULL;
119 #if !defined(THREADED_RTS)
120 StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(gen_workspace)];
123 // Number of threads running in *this* GC. Affects how many
124 // step->todos[] lists we have to look in to find work.
128 long copied; // *words* copied & scavenged during this GC
130 rtsBool work_stealing;
134 /* -----------------------------------------------------------------------------
135 Static function declarations
136 -------------------------------------------------------------------------- */
138 static void mark_root (void *user, StgClosure **root);
139 static void zero_static_object_list (StgClosure* first_static);
140 static nat initialise_N (rtsBool force_major_gc);
141 static void prepare_collected_gen (generation *gen);
142 static void prepare_uncollected_gen (generation *gen);
143 static void init_gc_thread (gc_thread *t);
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 me);
151 static void shutdown_gc_threads (nat me);
152 static void collect_gct_blocks (void);
154 #if 0 && defined(DEBUG)
155 static void gcCAFs (void);
158 /* -----------------------------------------------------------------------------
160 -------------------------------------------------------------------------- */
162 bdescr *mark_stack_top_bd; // topmost block in the mark stack
163 bdescr *mark_stack_bd; // current block in the mark stack
164 StgPtr mark_sp; // pointer to the next unallocated mark stack entry
166 /* -----------------------------------------------------------------------------
167 GarbageCollect: the main entry point to the garbage collector.
169 Locks held: all capabilities are held throughout GarbageCollect().
170 -------------------------------------------------------------------------- */
173 GarbageCollect (rtsBool force_major_gc,
174 nat gc_type USED_IF_THREADS,
179 lnat live_blocks, live_words, allocated, max_copied, avg_copied;
180 gc_thread *saved_gct;
183 // necessary if we stole a callee-saves register for gct:
187 CostCentreStack *prev_CCS;
192 #if defined(RTS_USER_SIGNALS)
193 if (RtsFlags.MiscFlags.install_signal_handlers) {
199 ASSERT(sizeof(gen_workspace) == 16 * sizeof(StgWord));
200 // otherwise adjust the padding in gen_workspace.
202 // this is the main thread
203 SET_GCT(gc_threads[cap->no]);
205 // tell the stats department that we've started a GC
208 // lock the StablePtr table
217 // attribute any costs to CCS_GC
223 /* Approximate how much we allocated.
224 * Todo: only when generating stats?
226 allocated = calcAllocated(rtsFalse/* don't count the nursery yet */);
228 /* Figure out which generation to collect
230 n = initialise_N(force_major_gc);
232 #if defined(THREADED_RTS)
233 work_stealing = RtsFlags.ParFlags.parGcLoadBalancingEnabled &&
234 N >= RtsFlags.ParFlags.parGcLoadBalancingGen;
235 // It's not always a good idea to do load balancing in parallel
236 // GC. In particular, for a parallel program we don't want to
237 // lose locality by moving cached data into another CPU's cache
238 // (this effect can be quite significant).
240 // We could have a more complex way to deterimine whether to do
241 // work stealing or not, e.g. it might be a good idea to do it
242 // if the heap is big. For now, we just turn it on or off with
246 /* Start threads, so they can be spinning up while we finish initialisation.
250 #if defined(THREADED_RTS)
251 /* How many threads will be participating in this GC?
252 * We don't try to parallelise minor GCs (unless the user asks for
253 * it with +RTS -gn0), or mark/compact/sweep GC.
255 if (gc_type == PENDING_GC_PAR) {
256 n_gc_threads = RtsFlags.ParFlags.nNodes;
264 debugTrace(DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
265 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
267 #ifdef RTS_GTK_FRONTPANEL
268 if (RtsFlags.GcFlags.frontpanel) {
269 updateFrontPanelBeforeGC(N);
274 // check for memory leaks if DEBUG is on
275 memInventory(DEBUG_gc);
278 // check sanity *before* GC
279 IF_DEBUG(sanity, checkSanity(rtsFalse /* before GC */, major_gc));
281 // Initialise all the generations/steps that we're collecting.
282 for (g = 0; g <= N; g++) {
283 prepare_collected_gen(&generations[g]);
285 // Initialise all the generations/steps that we're *not* collecting.
286 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
287 prepare_uncollected_gen(&generations[g]);
290 // Prepare this gc_thread
293 /* Allocate a mark stack if we're doing a major collection.
295 if (major_gc && oldest_gen->mark) {
296 mark_stack_bd = allocBlock();
297 mark_stack_top_bd = mark_stack_bd;
298 mark_stack_bd->link = NULL;
299 mark_stack_bd->u.back = NULL;
300 mark_sp = mark_stack_bd->start;
302 mark_stack_bd = NULL;
303 mark_stack_top_bd = NULL;
307 /* -----------------------------------------------------------------------
308 * follow all the roots that we know about:
311 // the main thread is running: this prevents any other threads from
312 // exiting prematurely, so we can start them now.
313 // NB. do this after the mutable lists have been saved above, otherwise
314 // the other GC threads will be writing into the old mutable lists.
316 wakeup_gc_threads(gct->thread_index);
318 traceEventGcWork(gct->cap);
320 // scavenge the capability-private mutable lists. This isn't part
321 // of markSomeCapabilities() because markSomeCapabilities() can only
322 // call back into the GC via mark_root() (due to the gct register
324 if (n_gc_threads == 1) {
325 for (n = 0; n < n_capabilities; n++) {
326 #if defined(THREADED_RTS)
327 scavenge_capability_mut_Lists1(&capabilities[n]);
329 scavenge_capability_mut_lists(&capabilities[n]);
333 scavenge_capability_mut_lists(gct->cap);
336 // follow roots from the CAF list (used by GHCi)
337 gct->evac_gen_no = 0;
338 markCAFs(mark_root, gct);
340 // follow all the roots that the application knows about.
341 gct->evac_gen_no = 0;
342 if (n_gc_threads == 1) {
343 for (n = 0; n < n_capabilities; n++) {
344 markCapability(mark_root, gct, &capabilities[n],
345 rtsTrue/*don't mark sparks*/);
348 markCapability(mark_root, gct, cap, rtsTrue/*don't mark sparks*/);
351 markScheduler(mark_root, gct);
353 #if defined(RTS_USER_SIGNALS)
354 // mark the signal handlers (signals should be already blocked)
355 markSignalHandlers(mark_root, gct);
358 // Mark the weak pointer list, and prepare to detect dead weak pointers.
362 // Mark the stable pointer table.
363 markStablePtrTable(mark_root, gct);
365 /* -------------------------------------------------------------------------
366 * Repeatedly scavenge all the areas we know about until there's no
367 * more scavenging to be done.
371 scavenge_until_all_done();
372 // The other threads are now stopped. We might recurse back to
373 // here, but from now on this is the only thread.
375 // must be last... invariant is that everything is fully
376 // scavenged at this point.
377 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
382 // If we get to here, there's really nothing left to do.
386 shutdown_gc_threads(gct->thread_index);
388 // Now see which stable names are still alive.
392 if (n_gc_threads == 1) {
393 for (n = 0; n < n_capabilities; n++) {
394 pruneSparkQueue(&capabilities[n]);
397 pruneSparkQueue(gct->cap);
402 // We call processHeapClosureForDead() on every closure destroyed during
403 // the current garbage collection, so we invoke LdvCensusForDead().
404 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
405 || RtsFlags.ProfFlags.bioSelector != NULL)
409 // NO MORE EVACUATION AFTER THIS POINT!
411 // Two-space collector: free the old to-space.
412 // g0->old_blocks is the old nursery
413 // g0->blocks is to-space from the previous GC
414 if (RtsFlags.GcFlags.generations == 1) {
415 if (g0->blocks != NULL) {
416 freeChain(g0->blocks);
421 // Finally: compact or sweep the oldest generation.
422 if (major_gc && oldest_gen->mark) {
423 if (oldest_gen->compact)
424 compact(gct->scavenged_static_objects);
434 for (i=0; i < n_gc_threads; i++) {
435 if (n_gc_threads > 1) {
436 debugTrace(DEBUG_gc,"thread %d:", i);
437 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
438 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
439 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
440 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
441 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
443 copied += gc_threads[i]->copied;
444 max_copied = stg_max(gc_threads[i]->copied, max_copied);
446 if (n_gc_threads == 1) {
454 // Run through all the generations/steps and tidy up.
456 // - count the amount of "live" data (live_words, live_blocks)
457 // - count the amount of "copied" data in this GC (copied)
459 // - make to-space the new from-space (set BF_EVACUATED on all blocks)
464 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
467 generations[g].collections++; // for stats
468 if (n_gc_threads > 1) generations[g].par_collections++;
471 // Count the mutable list as bytes "copied" for the purposes of
472 // stats. Every mutable list is copied during every GC.
474 nat mut_list_size = 0;
475 for (n = 0; n < n_capabilities; n++) {
476 mut_list_size += countOccupied(capabilities[n].mut_lists[g]);
478 copied += mut_list_size;
481 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
482 (unsigned long)(mut_list_size * sizeof(W_)),
483 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
487 gen = &generations[g];
489 // for generations we collected...
492 /* free old memory and shift to-space into from-space for all
493 * the collected steps (except the allocation area). These
494 * freed blocks will probaby be quickly recycled.
498 // tack the new blocks on the end of the existing blocks
499 if (gen->old_blocks != NULL) {
502 for (bd = gen->old_blocks; bd != NULL; bd = next) {
506 if (!(bd->flags & BF_MARKED))
509 gen->old_blocks = next;
518 gen->n_words += bd->free - bd->start;
520 // NB. this step might not be compacted next
521 // time, so reset the BF_MARKED flags.
522 // They are set before GC if we're going to
523 // compact. (search for BF_MARKED above).
524 bd->flags &= ~BF_MARKED;
526 // between GCs, all blocks in the heap except
527 // for the nursery have the BF_EVACUATED flag set.
528 bd->flags |= BF_EVACUATED;
535 prev->link = gen->blocks;
536 gen->blocks = gen->old_blocks;
539 // add the new blocks to the block tally
540 gen->n_blocks += gen->n_old_blocks;
541 ASSERT(countBlocks(gen->blocks) == gen->n_blocks);
542 ASSERT(countOccupied(gen->blocks) == gen->n_words);
546 freeChain(gen->old_blocks);
549 gen->old_blocks = NULL;
550 gen->n_old_blocks = 0;
552 /* LARGE OBJECTS. The current live large objects are chained on
553 * scavenged_large, having been moved during garbage
554 * collection from large_objects. Any objects left on the
555 * large_objects list are therefore dead, so we free them here.
557 freeChain(gen->large_objects);
558 gen->large_objects = gen->scavenged_large_objects;
559 gen->n_large_blocks = gen->n_scavenged_large_blocks;
560 gen->n_new_large_words = 0;
562 else // for generations > N
564 /* For older generations, we need to append the
565 * scavenged_large_object list (i.e. large objects that have been
566 * promoted during this GC) to the large_object list for that step.
568 for (bd = gen->scavenged_large_objects; bd; bd = next) {
570 dbl_link_onto(bd, &gen->large_objects);
573 // add the new blocks we promoted during this GC
574 gen->n_large_blocks += gen->n_scavenged_large_blocks;
577 ASSERT(countBlocks(gen->large_objects) == gen->n_large_blocks);
579 gen->scavenged_large_objects = NULL;
580 gen->n_scavenged_large_blocks = 0;
583 live_words += genLiveWords(gen);
584 live_blocks += genLiveBlocks(gen);
586 // add in the partial blocks in the gen_workspaces, but ignore gen 0
587 // if this is a local GC (we can't count another capability's part_list)
590 for (i = 0; i < n_capabilities; i++) {
591 live_words += gcThreadLiveWords(i, gen->no);
592 live_blocks += gcThreadLiveBlocks(i, gen->no);
595 } // for all generations
597 // update the max size of older generations after a major GC
598 resize_generations();
600 // Free the mark stack.
601 if (mark_stack_top_bd != NULL) {
602 debugTrace(DEBUG_gc, "mark stack: %d blocks",
603 countBlocks(mark_stack_top_bd));
604 freeChain(mark_stack_top_bd);
608 for (g = 0; g <= N; g++) {
609 gen = &generations[g];
610 if (gen->bitmap != NULL) {
611 freeGroup(gen->bitmap);
616 // Reset the nursery: make the blocks empty
617 allocated += clearNurseries();
623 // mark the garbage collected CAFs as dead
624 #if 0 && defined(DEBUG) // doesn't work at the moment
625 if (major_gc) { gcCAFs(); }
629 // resetStaticObjectForRetainerProfiling() must be called before
631 if (n_gc_threads > 1) {
632 barf("profiling is currently broken with multi-threaded GC");
633 // ToDo: fix the gct->scavenged_static_objects below
635 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
638 // zero the scavenged static object list
641 if (n_gc_threads == 1) {
642 zero_static_object_list(gct->scavenged_static_objects);
644 for (i = 0; i < n_gc_threads; i++) {
645 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
650 // Update the stable pointer hash table.
651 updateStablePtrTable(major_gc);
653 // unlock the StablePtr table. Must be before scheduleFinalizers(),
654 // because a finalizer may call hs_free_fun_ptr() or
655 // hs_free_stable_ptr(), both of which access the StablePtr table.
658 // Start any pending finalizers. Must be after
659 // updateStablePtrTable() and stablePtrPostGC() (see #4221).
661 scheduleFinalizers(cap, old_weak_ptr_list);
664 // check sanity after GC
665 // before resurrectThreads(), because that might overwrite some
666 // closures, which will cause problems with THREADED where we don't
668 IF_DEBUG(sanity, checkSanity(rtsTrue /* after GC */, major_gc));
670 // send exceptions to any threads which were about to die
672 resurrectThreads(resurrected_threads);
677 need = BLOCKS_TO_MBLOCKS(n_alloc_blocks);
678 got = mblocks_allocated;
679 /* If the amount of data remains constant, next major GC we'll
680 require (F+1)*need. We leave (F+2)*need in order to reduce
681 repeated deallocation and reallocation. */
682 need = (RtsFlags.GcFlags.oldGenFactor + 2) * need;
684 returnMemoryToOS(got - need);
688 // extra GC trace info
689 IF_DEBUG(gc, statDescribeGens());
692 // symbol-table based profiling
693 /* heapCensus(to_blocks); */ /* ToDo */
696 // restore enclosing cost centre
702 // check for memory leaks if DEBUG is on
703 memInventory(DEBUG_gc);
706 #ifdef RTS_GTK_FRONTPANEL
707 if (RtsFlags.GcFlags.frontpanel) {
708 updateFrontPanelAfterGC( N, live );
712 // ok, GC over: tell the stats department what happened.
713 stat_endGC(gct, allocated, live_words,
714 copied, N, max_copied, avg_copied,
715 live_blocks * BLOCK_SIZE_W - live_words /* slop */);
717 // Guess which generation we'll collect *next* time
718 initialise_N(force_major_gc);
720 #if defined(RTS_USER_SIGNALS)
721 if (RtsFlags.MiscFlags.install_signal_handlers) {
722 // unblock signals again
723 unblockUserSignals();
732 /* -----------------------------------------------------------------------------
733 Figure out which generation to collect, initialise N and major_gc.
735 Also returns the total number of blocks in generations that will be
737 -------------------------------------------------------------------------- */
740 initialise_N (rtsBool force_major_gc)
743 nat blocks, blocks_total;
748 if (force_major_gc) {
749 N = RtsFlags.GcFlags.generations - 1;
754 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
756 blocks = generations[g].n_words / BLOCK_SIZE_W
757 + generations[g].n_large_blocks;
759 if (blocks >= generations[g].max_blocks) {
763 blocks_total += blocks;
767 blocks_total += countNurseryBlocks();
769 major_gc = (N == RtsFlags.GcFlags.generations-1);
773 /* -----------------------------------------------------------------------------
774 Initialise the gc_thread structures.
775 -------------------------------------------------------------------------- */
777 #define GC_THREAD_INACTIVE 0
778 #define GC_THREAD_STANDING_BY 1
779 #define GC_THREAD_RUNNING 2
780 #define GC_THREAD_WAITING_TO_CONTINUE 3
783 new_gc_thread (nat n, gc_thread *t)
788 t->cap = &capabilities[n];
792 initSpinLock(&t->gc_spin);
793 initSpinLock(&t->mut_spin);
794 ACQUIRE_SPIN_LOCK(&t->gc_spin);
795 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
796 // thread to start up, see wakeup_gc_threads
800 t->free_blocks = NULL;
809 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
812 ws->gen = &generations[g];
813 ASSERT(g == ws->gen->no);
817 // alloc_todo_block(ws,0);
818 // but can't, because it uses gct which isn't set up at this point.
819 // Hence, allocate a block for todo_bd manually:
821 bdescr *bd = allocBlock(); // no lock, locks aren't initialised yet
822 initBdescr(bd, ws->gen, ws->gen->to);
823 bd->flags = BF_EVACUATED;
824 bd->u.scan = bd->free = bd->start;
827 ws->todo_free = bd->free;
828 ws->todo_lim = bd->start + BLOCK_SIZE_W;
831 ws->todo_q = newWSDeque(128);
832 ws->todo_overflow = NULL;
833 ws->n_todo_overflow = 0;
834 ws->todo_large_objects = NULL;
836 ws->part_list = NULL;
837 ws->n_part_blocks = 0;
839 ws->scavd_list = NULL;
840 ws->n_scavd_blocks = 0;
848 if (gc_threads == NULL) {
849 #if defined(THREADED_RTS)
851 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
855 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
857 stgMallocBytes(sizeof(gc_thread) +
858 RtsFlags.GcFlags.generations * sizeof(gen_workspace),
861 new_gc_thread(i, gc_threads[i]);
864 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
866 new_gc_thread(0,gc_threads[0]);
875 if (gc_threads != NULL) {
876 #if defined(THREADED_RTS)
878 for (i = 0; i < n_capabilities; i++) {
879 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
881 freeWSDeque(gc_threads[i]->gens[g].todo_q);
883 stgFree (gc_threads[i]);
885 stgFree (gc_threads);
887 for (g = 0; g < RtsFlags.GcFlags.generations; g++)
889 freeWSDeque(gc_threads[0]->gens[g].todo_q);
891 stgFree (gc_threads);
897 /* ----------------------------------------------------------------------------
899 ------------------------------------------------------------------------- */
901 static volatile StgWord gc_running_threads;
907 new = atomic_inc(&gc_running_threads);
908 ASSERT(new <= n_gc_threads);
915 ASSERT(gc_running_threads != 0);
916 return atomic_dec(&gc_running_threads);
929 // scavenge objects in compacted generation
930 if (mark_stack_bd != NULL && !mark_stack_empty()) {
934 // Check for global work in any step. We don't need to check for
935 // local work, because we have already exited scavenge_loop(),
936 // which means there is no local work for this thread.
937 for (g = 0; g < (int)RtsFlags.GcFlags.generations; g++) {
939 if (ws->todo_large_objects) return rtsTrue;
940 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
941 if (ws->todo_overflow) return rtsTrue;
944 #if defined(THREADED_RTS)
947 // look for work to steal
948 for (n = 0; n < n_gc_threads; n++) {
949 if (n == gct->thread_index) continue;
950 for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
951 ws = &gc_threads[n]->gens[g];
952 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
959 #if defined(THREADED_RTS)
967 scavenge_until_all_done (void)
973 #if defined(THREADED_RTS)
974 if (n_gc_threads > 1) {
983 collect_gct_blocks();
985 // scavenge_loop() only exits when there's no work to do
988 traceEventGcIdle(gct->cap);
990 debugTrace(DEBUG_gc, "%d GC threads still running", r);
992 while (gc_running_threads != 0) {
996 traceEventGcWork(gct->cap);
999 // any_work() does not remove the work from the queue, it
1000 // just checks for the presence of work. If we find any,
1001 // then we increment gc_running_threads and go back to
1002 // scavenge_loop() to perform any pending work.
1005 traceEventGcDone(gct->cap);
1008 #if defined(THREADED_RTS)
1011 gcWorkerThread (Capability *cap)
1013 gc_thread *saved_gct;
1015 // necessary if we stole a callee-saves register for gct:
1018 gct = gc_threads[cap->no];
1019 gct->id = osThreadId();
1021 stat_gcWorkerThreadStart(gct);
1023 // Wait until we're told to wake up
1024 RELEASE_SPIN_LOCK(&gct->mut_spin);
1025 gct->wakeup = GC_THREAD_STANDING_BY;
1026 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1027 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1030 // start performance counters in this thread...
1031 if (gct->papi_events == -1) {
1032 papi_init_eventset(&gct->papi_events);
1034 papi_thread_start_gc1_count(gct->papi_events);
1037 init_gc_thread(gct);
1039 traceEventGcWork(gct->cap);
1041 // Every thread evacuates some roots.
1042 gct->evac_gen_no = 0;
1043 markCapability(mark_root, gct, cap, rtsTrue/*prune sparks*/);
1044 scavenge_capability_mut_lists(cap);
1046 scavenge_until_all_done();
1049 // Now that the whole heap is marked, we discard any sparks that
1050 // were found to be unreachable. The main GC thread is currently
1051 // marking heap reachable via weak pointers, so it is
1052 // non-deterministic whether a spark will be retained if it is
1053 // only reachable via weak pointers. To fix this problem would
1054 // require another GC barrier, which is too high a price.
1055 pruneSparkQueue(cap);
1059 // count events in this thread towards the GC totals
1060 papi_thread_stop_gc1_count(gct->papi_events);
1063 // Wait until we're told to continue
1064 RELEASE_SPIN_LOCK(&gct->gc_spin);
1065 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1066 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1068 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1069 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1071 // record the time spent doing GC in the Task structure
1072 stat_gcWorkerThreadDone(gct);
1079 #if defined(THREADED_RTS)
1082 waitForGcThreads (Capability *cap USED_IF_THREADS)
1084 const nat n_threads = RtsFlags.ParFlags.nNodes;
1085 const nat me = cap->no;
1087 rtsBool retry = rtsTrue;
1090 for (i=0; i < n_threads; i++) {
1091 if (i == me) continue;
1092 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1093 prodCapability(&capabilities[i], cap->running_task);
1096 for (j=0; j < 10; j++) {
1098 for (i=0; i < n_threads; i++) {
1099 if (i == me) continue;
1101 setContextSwitches();
1102 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1112 #endif // THREADED_RTS
1115 start_gc_threads (void)
1117 #if defined(THREADED_RTS)
1118 gc_running_threads = 0;
1123 wakeup_gc_threads (nat me USED_IF_THREADS)
1125 #if defined(THREADED_RTS)
1128 if (n_gc_threads == 1) return;
1130 for (i=0; i < n_gc_threads; i++) {
1131 if (i == me) continue;
1133 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1134 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1136 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1137 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1138 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1143 // After GC is complete, we must wait for all GC threads to enter the
1144 // standby state, otherwise they may still be executing inside
1145 // any_work(), and may even remain awake until the next GC starts.
1147 shutdown_gc_threads (nat me USED_IF_THREADS)
1149 #if defined(THREADED_RTS)
1152 if (n_gc_threads == 1) return;
1154 for (i=0; i < n_gc_threads; i++) {
1155 if (i == me) continue;
1156 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1161 #if defined(THREADED_RTS)
1163 releaseGCThreads (Capability *cap USED_IF_THREADS)
1165 const nat n_threads = RtsFlags.ParFlags.nNodes;
1166 const nat me = cap->no;
1168 for (i=0; i < n_threads; i++) {
1169 if (i == me) continue;
1170 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1171 barf("releaseGCThreads");
1173 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1174 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1175 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1180 /* ----------------------------------------------------------------------------
1181 Initialise a generation that is to be collected
1182 ------------------------------------------------------------------------- */
1185 prepare_collected_gen (generation *gen)
1191 // Throw away the current mutable list. Invariant: the mutable
1192 // list always has at least one block; this means we can avoid a
1193 // check for NULL in recordMutable().
1196 for (i = 0; i < n_capabilities; i++) {
1197 freeChain(capabilities[i].mut_lists[g]);
1198 capabilities[i].mut_lists[g] = allocBlock();
1202 gen = &generations[g];
1203 ASSERT(gen->no == g);
1205 // we'll construct a new list of threads in this step
1206 // during GC, throw away the current list.
1207 gen->old_threads = gen->threads;
1208 gen->threads = END_TSO_QUEUE;
1210 // deprecate the existing blocks
1211 gen->old_blocks = gen->blocks;
1212 gen->n_old_blocks = gen->n_blocks;
1216 gen->live_estimate = 0;
1218 // initialise the large object queues.
1219 ASSERT(gen->scavenged_large_objects == NULL);
1220 ASSERT(gen->n_scavenged_large_blocks == 0);
1222 // grab all the partial blocks stashed in the gc_thread workspaces and
1223 // move them to the old_blocks list of this gen.
1224 for (n = 0; n < n_capabilities; n++) {
1225 ws = &gc_threads[n]->gens[gen->no];
1227 for (bd = ws->part_list; bd != NULL; bd = next) {
1229 bd->link = gen->old_blocks;
1230 gen->old_blocks = bd;
1231 gen->n_old_blocks += bd->blocks;
1233 ws->part_list = NULL;
1234 ws->n_part_blocks = 0;
1236 ASSERT(ws->scavd_list == NULL);
1237 ASSERT(ws->n_scavd_blocks == 0);
1239 if (ws->todo_free != ws->todo_bd->start) {
1240 ws->todo_bd->free = ws->todo_free;
1241 ws->todo_bd->link = gen->old_blocks;
1242 gen->old_blocks = ws->todo_bd;
1243 gen->n_old_blocks += ws->todo_bd->blocks;
1244 alloc_todo_block(ws,0); // always has one block.
1248 // mark the small objects as from-space
1249 for (bd = gen->old_blocks; bd; bd = bd->link) {
1250 bd->flags &= ~BF_EVACUATED;
1253 // mark the large objects as from-space
1254 for (bd = gen->large_objects; bd; bd = bd->link) {
1255 bd->flags &= ~BF_EVACUATED;
1258 // for a compacted generation, we need to allocate the bitmap
1260 nat bitmap_size; // in bytes
1261 bdescr *bitmap_bdescr;
1264 bitmap_size = gen->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1266 if (bitmap_size > 0) {
1267 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1269 gen->bitmap = bitmap_bdescr;
1270 bitmap = bitmap_bdescr->start;
1272 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1273 bitmap_size, bitmap);
1275 // don't forget to fill it with zeros!
1276 memset(bitmap, 0, bitmap_size);
1278 // For each block in this step, point to its bitmap from the
1279 // block descriptor.
1280 for (bd=gen->old_blocks; bd != NULL; bd = bd->link) {
1281 bd->u.bitmap = bitmap;
1282 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1284 // Also at this point we set the BF_MARKED flag
1285 // for this block. The invariant is that
1286 // BF_MARKED is always unset, except during GC
1287 // when it is set on those blocks which will be
1289 if (!(bd->flags & BF_FRAGMENTED)) {
1290 bd->flags |= BF_MARKED;
1293 // BF_SWEPT should be marked only for blocks that are being
1294 // collected in sweep()
1295 bd->flags &= ~BF_SWEPT;
1302 /* ----------------------------------------------------------------------------
1303 Save the mutable lists in saved_mut_lists
1304 ------------------------------------------------------------------------- */
1307 stash_mut_list (Capability *cap, nat gen_no)
1309 cap->saved_mut_lists[gen_no] = cap->mut_lists[gen_no];
1310 cap->mut_lists[gen_no] = allocBlock_sync();
1313 /* ----------------------------------------------------------------------------
1314 Initialise a generation that is *not* to be collected
1315 ------------------------------------------------------------------------- */
1318 prepare_uncollected_gen (generation *gen)
1323 ASSERT(gen->no > 0);
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 for (i = 0; i < n_capabilities; i++) {
1329 stash_mut_list(&capabilities[i], gen->no);
1332 ASSERT(gen->scavenged_large_objects == NULL);
1333 ASSERT(gen->n_scavenged_large_blocks == 0);
1336 /* -----------------------------------------------------------------------------
1337 Collect the completed blocks from a GC thread and attach them to
1339 -------------------------------------------------------------------------- */
1342 collect_gct_blocks (void)
1348 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
1351 // there may still be a block attached to ws->todo_bd;
1352 // leave it there to use next time.
1354 if (ws->scavd_list != NULL) {
1355 ACQUIRE_SPIN_LOCK(&ws->gen->sync);
1357 ASSERT(gct->scan_bd == NULL);
1358 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
1361 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
1362 ws->gen->n_words += bd->free - bd->start;
1366 prev->link = ws->gen->blocks;
1367 ws->gen->blocks = ws->scavd_list;
1369 ws->gen->n_blocks += ws->n_scavd_blocks;
1371 ws->scavd_list = NULL;
1372 ws->n_scavd_blocks = 0;
1374 RELEASE_SPIN_LOCK(&ws->gen->sync);
1379 /* -----------------------------------------------------------------------------
1380 Initialise a gc_thread before GC
1381 -------------------------------------------------------------------------- */
1384 init_gc_thread (gc_thread *t)
1386 t->static_objects = END_OF_STATIC_LIST;
1387 t->scavenged_static_objects = END_OF_STATIC_LIST;
1389 t->mut_lists = t->cap->mut_lists;
1391 t->failed_to_evac = rtsFalse;
1392 t->eager_promotion = rtsTrue;
1393 t->thunk_selector_depth = 0;
1398 t->scav_find_work = 0;
1401 /* -----------------------------------------------------------------------------
1402 Function we pass to evacuate roots.
1403 -------------------------------------------------------------------------- */
1406 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1408 // we stole a register for gct, but this function is called from
1409 // *outside* the GC where the register variable is not in effect,
1410 // so we need to save and restore it here. NB. only call
1411 // mark_root() from the main GC thread, otherwise gct will be
1413 gc_thread *saved_gct;
1422 /* -----------------------------------------------------------------------------
1423 Initialising the static object & mutable lists
1424 -------------------------------------------------------------------------- */
1427 zero_static_object_list(StgClosure* first_static)
1431 const StgInfoTable *info;
1433 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1435 link = *STATIC_LINK(info, p);
1436 *STATIC_LINK(info,p) = NULL;
1440 /* ----------------------------------------------------------------------------
1441 Reset the sizes of the older generations when we do a major
1444 CURRENT STRATEGY: make all generations except zero the same size.
1445 We have to stay within the maximum heap size, and leave a certain
1446 percentage of the maximum heap size available to allocate into.
1447 ------------------------------------------------------------------------- */
1450 resize_generations (void)
1454 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1455 nat live, size, min_alloc, words;
1456 const nat max = RtsFlags.GcFlags.maxHeapSize;
1457 const nat gens = RtsFlags.GcFlags.generations;
1459 // live in the oldest generations
1460 if (oldest_gen->live_estimate != 0) {
1461 words = oldest_gen->live_estimate;
1463 words = oldest_gen->n_words;
1465 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1466 oldest_gen->n_large_blocks;
1468 // default max size for all generations except zero
1469 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1470 RtsFlags.GcFlags.minOldGenSize);
1472 if (RtsFlags.GcFlags.heapSizeSuggestionAuto) {
1473 RtsFlags.GcFlags.heapSizeSuggestion = size;
1476 // minimum size for generation zero
1477 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1478 RtsFlags.GcFlags.minAllocAreaSize);
1480 // Auto-enable compaction when the residency reaches a
1481 // certain percentage of the maximum heap size (default: 30%).
1482 if (RtsFlags.GcFlags.compact ||
1484 oldest_gen->n_blocks >
1485 (RtsFlags.GcFlags.compactThreshold * max) / 100)) {
1486 oldest_gen->mark = 1;
1487 oldest_gen->compact = 1;
1488 // debugBelch("compaction: on\n", live);
1490 oldest_gen->mark = 0;
1491 oldest_gen->compact = 0;
1492 // debugBelch("compaction: off\n", live);
1495 if (RtsFlags.GcFlags.sweep) {
1496 oldest_gen->mark = 1;
1499 // if we're going to go over the maximum heap size, reduce the
1500 // size of the generations accordingly. The calculation is
1501 // different if compaction is turned on, because we don't need
1502 // to double the space required to collect the old generation.
1505 // this test is necessary to ensure that the calculations
1506 // below don't have any negative results - we're working
1507 // with unsigned values here.
1508 if (max < min_alloc) {
1512 if (oldest_gen->compact) {
1513 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1514 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1517 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1518 size = (max - min_alloc) / ((gens - 1) * 2);
1528 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1529 min_alloc, size, max);
1532 for (g = 0; g < gens; g++) {
1533 generations[g].max_blocks = size;
1538 /* -----------------------------------------------------------------------------
1539 Calculate the new size of the nursery, and resize it.
1540 -------------------------------------------------------------------------- */
1543 resize_nursery (void)
1545 const lnat min_nursery = RtsFlags.GcFlags.minAllocAreaSize * n_capabilities;
1547 if (RtsFlags.GcFlags.generations == 1)
1548 { // Two-space collector:
1551 /* set up a new nursery. Allocate a nursery size based on a
1552 * function of the amount of live data (by default a factor of 2)
1553 * Use the blocks from the old nursery if possible, freeing up any
1556 * If we get near the maximum heap size, then adjust our nursery
1557 * size accordingly. If the nursery is the same size as the live
1558 * data (L), then we need 3L bytes. We can reduce the size of the
1559 * nursery to bring the required memory down near 2L bytes.
1561 * A normal 2-space collector would need 4L bytes to give the same
1562 * performance we get from 3L bytes, reducing to the same
1563 * performance at 2L bytes.
1565 blocks = generations[0].n_blocks;
1567 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1568 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1569 RtsFlags.GcFlags.maxHeapSize )
1571 long adjusted_blocks; // signed on purpose
1574 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1576 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1577 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1579 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1580 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1584 blocks = adjusted_blocks;
1588 blocks *= RtsFlags.GcFlags.oldGenFactor;
1589 if (blocks < min_nursery)
1591 blocks = min_nursery;
1594 resizeNurseries(blocks);
1596 else // Generational collector
1599 * If the user has given us a suggested heap size, adjust our
1600 * allocation area to make best use of the memory available.
1602 if (RtsFlags.GcFlags.heapSizeSuggestion)
1605 const nat needed = calcNeeded(); // approx blocks needed at next GC
1607 /* Guess how much will be live in generation 0 step 0 next time.
1608 * A good approximation is obtained by finding the
1609 * percentage of g0 that was live at the last minor GC.
1611 * We have an accurate figure for the amount of copied data in
1612 * 'copied', but we must convert this to a number of blocks, with
1613 * a small adjustment for estimated slop at the end of a block
1618 g0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1619 / countNurseryBlocks();
1622 /* Estimate a size for the allocation area based on the
1623 * information available. We might end up going slightly under
1624 * or over the suggested heap size, but we should be pretty
1627 * Formula: suggested - needed
1628 * ----------------------------
1629 * 1 + g0_pcnt_kept/100
1631 * where 'needed' is the amount of memory needed at the next
1632 * collection for collecting all gens except g0.
1635 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1636 (100 + (long)g0_pcnt_kept);
1638 if (blocks < (long)min_nursery) {
1639 blocks = min_nursery;
1642 resizeNurseries((nat)blocks);
1646 // we might have added extra large blocks to the nursery, so
1647 // resize back to minAllocAreaSize again.
1648 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1653 /* -----------------------------------------------------------------------------
1654 Sanity code for CAF garbage collection.
1656 With DEBUG turned on, we manage a CAF list in addition to the SRT
1657 mechanism. After GC, we run down the CAF list and blackhole any
1658 CAFs which have been garbage collected. This means we get an error
1659 whenever the program tries to enter a garbage collected CAF.
1661 Any garbage collected CAFs are taken off the CAF list at the same
1663 -------------------------------------------------------------------------- */
1665 #if 0 && defined(DEBUG)
1672 const StgInfoTable *info;
1683 ASSERT(info->type == IND_STATIC);
1685 if (STATIC_LINK(info,p) == NULL) {
1686 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1688 SET_INFO(p,&stg_BLACKHOLE_info);
1689 p = STATIC_LINK2(info,p);
1693 pp = &STATIC_LINK2(info,p);
1700 debugTrace(DEBUG_gccafs, "%d CAFs live", i);