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"
19 #include "OSThreads.h"
20 #include "LdvProfile.h"
25 #include "BlockAlloc.h"
31 #include "ParTicky.h" // ToDo: move into Rts.h
32 #include "RtsSignals.h"
36 #if defined(RTS_GTK_FRONTPANEL)
37 #include "FrontPanel.h"
40 #include "RetainerProfile.h"
41 #include "RaiseAsync.h"
54 #include <string.h> // for memset()
57 /* -----------------------------------------------------------------------------
59 -------------------------------------------------------------------------- */
61 /* STATIC OBJECT LIST.
64 * We maintain a linked list of static objects that are still live.
65 * The requirements for this list are:
67 * - we need to scan the list while adding to it, in order to
68 * scavenge all the static objects (in the same way that
69 * breadth-first scavenging works for dynamic objects).
71 * - we need to be able to tell whether an object is already on
72 * the list, to break loops.
74 * Each static object has a "static link field", which we use for
75 * linking objects on to the list. We use a stack-type list, consing
76 * objects on the front as they are added (this means that the
77 * scavenge phase is depth-first, not breadth-first, but that
80 * A separate list is kept for objects that have been scavenged
81 * already - this is so that we can zero all the marks afterwards.
83 * An object is on the list if its static link field is non-zero; this
84 * means that we have to mark the end of the list with '1', not NULL.
86 * Extra notes for generational GC:
88 * Each generation has a static object list associated with it. When
89 * collecting generations up to N, we treat the static object lists
90 * from generations > N as roots.
92 * We build up a static object list while collecting generations 0..N,
93 * which is then appended to the static object list of generation N+1.
96 /* N is the oldest generation being collected, where the generations
97 * are numbered starting at 0. A major GC (indicated by the major_gc
98 * flag) is when we're collecting all generations. We only attempt to
99 * deal with static objects and GC CAFs when doing a major GC.
104 /* Data used for allocation area sizing.
106 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
116 /* Thread-local data for each GC thread
118 gc_thread **gc_threads = NULL;
119 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
121 // Number of threads running in *this* GC. Affects how many
122 // step->todos[] lists we have to look in to find work.
126 long copied; // *words* copied & scavenged during this GC
129 SpinLock recordMutableGen_sync;
132 /* -----------------------------------------------------------------------------
133 Static function declarations
134 -------------------------------------------------------------------------- */
136 static void mark_root (void *user, StgClosure **root);
137 static void zero_static_object_list (StgClosure* first_static);
138 static nat initialise_N (rtsBool force_major_gc);
139 static void alloc_gc_threads (void);
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 nat inc_running (void);
149 static nat dec_running (void);
150 static void wakeup_gc_threads (nat n_threads);
151 static void shutdown_gc_threads (nat n_threads);
153 #if 0 && defined(DEBUG)
154 static void gcCAFs (void);
157 /* -----------------------------------------------------------------------------
158 The mark bitmap & stack.
159 -------------------------------------------------------------------------- */
161 #define MARK_STACK_BLOCKS 4
163 bdescr *mark_stack_bdescr;
168 // Flag and pointers used for falling back to a linear scan when the
169 // mark stack overflows.
170 rtsBool mark_stack_overflowed;
171 bdescr *oldgen_scan_bd;
174 /* -----------------------------------------------------------------------------
175 GarbageCollect: the main entry point to the garbage collector.
177 Locks held: all capabilities are held throughout GarbageCollect().
178 -------------------------------------------------------------------------- */
181 GarbageCollect ( rtsBool force_major_gc )
185 lnat live, allocated, max_copied, avg_copied, slop;
186 lnat oldgen_saved_blocks = 0;
187 gc_thread *saved_gct;
190 // necessary if we stole a callee-saves register for gct:
194 CostCentreStack *prev_CCS;
199 #if defined(RTS_USER_SIGNALS)
200 if (RtsFlags.MiscFlags.install_signal_handlers) {
206 ASSERT(sizeof(step_workspace) == 16 * sizeof(StgWord));
207 // otherwise adjust the padding in step_workspace.
209 // tell the stats department that we've started a GC
212 // tell the STM to discard any cached closures it's hoping to re-use
221 // attribute any costs to CCS_GC
227 /* Approximate how much we allocated.
228 * Todo: only when generating stats?
230 allocated = calcAllocated();
232 /* Figure out which generation to collect
234 n = initialise_N(force_major_gc);
236 /* Allocate + initialise the gc_thread structures.
240 /* Start threads, so they can be spinning up while we finish initialisation.
244 /* How many threads will be participating in this GC?
245 * We don't try to parallelise minor GC.
247 #if defined(THREADED_RTS)
248 if (n < (4*1024*1024 / BLOCK_SIZE)) {
251 n_gc_threads = RtsFlags.ParFlags.gcThreads;
256 trace(TRACE_gc|DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
257 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
259 #ifdef RTS_GTK_FRONTPANEL
260 if (RtsFlags.GcFlags.frontpanel) {
261 updateFrontPanelBeforeGC(N);
266 // check for memory leaks if DEBUG is on
267 memInventory(traceClass(DEBUG_gc));
270 // check stack sanity *before* GC (ToDo: check all threads)
271 IF_DEBUG(sanity, checkFreeListSanity());
273 // Initialise all our gc_thread structures
274 for (t = 0; t < n_gc_threads; t++) {
275 init_gc_thread(gc_threads[t]);
278 // Initialise all the generations/steps that we're collecting.
279 for (g = 0; g <= N; g++) {
280 init_collected_gen(g,n_gc_threads);
283 // Initialise all the generations/steps that we're *not* collecting.
284 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
285 init_uncollected_gen(g,n_gc_threads);
288 /* Allocate a mark stack if we're doing a major collection.
291 mark_stack_bdescr = allocGroup(MARK_STACK_BLOCKS);
292 mark_stack = (StgPtr *)mark_stack_bdescr->start;
293 mark_sp = mark_stack;
294 mark_splim = mark_stack + (MARK_STACK_BLOCKS * BLOCK_SIZE_W);
296 mark_stack_bdescr = NULL;
299 // this is the main thread
302 /* -----------------------------------------------------------------------
303 * follow all the roots that we know about:
304 * - mutable lists from each generation > N
305 * we want to *scavenge* these roots, not evacuate them: they're not
306 * going to move in this GC.
307 * Also do them in reverse generation order, for the usual reason:
308 * namely to reduce the likelihood of spurious old->new pointers.
310 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
311 generations[g].saved_mut_list = generations[g].mut_list;
312 generations[g].mut_list = allocBlock();
313 // mut_list always has at least one block.
316 // the main thread is running: this prevents any other threads from
317 // exiting prematurely, so we can start them now.
318 // NB. do this after the mutable lists have been saved above, otherwise
319 // the other GC threads will be writing into the old mutable lists.
321 wakeup_gc_threads(n_gc_threads);
323 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
324 scavenge_mutable_list(&generations[g]);
327 // follow roots from the CAF list (used by GHCi)
329 markCAFs(mark_root, gct);
331 // follow all the roots that the application knows about.
333 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
335 #if defined(RTS_USER_SIGNALS)
336 // mark the signal handlers (signals should be already blocked)
337 markSignalHandlers(mark_root, gct);
340 // Mark the weak pointer list, and prepare to detect dead weak pointers.
344 // Mark the stable pointer table.
345 markStablePtrTable(mark_root, gct);
347 /* -------------------------------------------------------------------------
348 * Repeatedly scavenge all the areas we know about until there's no
349 * more scavenging to be done.
353 scavenge_until_all_done();
354 // The other threads are now stopped. We might recurse back to
355 // here, but from now on this is the only thread.
357 // if any blackholes are alive, make the threads that wait on
359 if (traverseBlackholeQueue()) {
364 // must be last... invariant is that everything is fully
365 // scavenged at this point.
366 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
371 // If we get to here, there's really nothing left to do.
375 shutdown_gc_threads(n_gc_threads);
377 // Update pointers from the Task list
380 // Now see which stable names are still alive.
384 // We call processHeapClosureForDead() on every closure destroyed during
385 // the current garbage collection, so we invoke LdvCensusForDead().
386 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
387 || RtsFlags.ProfFlags.bioSelector != NULL)
391 // NO MORE EVACUATION AFTER THIS POINT!
392 // Finally: compaction of the oldest generation.
393 if (major_gc && oldest_gen->steps[0].is_compacted) {
394 // save number of blocks for stats
395 oldgen_saved_blocks = oldest_gen->steps[0].n_old_blocks;
396 compact(gct->scavenged_static_objects);
399 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
401 // Two-space collector: free the old to-space.
402 // g0s0->old_blocks is the old nursery
403 // g0s0->blocks is to-space from the previous GC
404 if (RtsFlags.GcFlags.generations == 1) {
405 if (g0s0->blocks != NULL) {
406 freeChain(g0s0->blocks);
411 // For each workspace, in each thread, move the copied blocks to the step
417 for (t = 0; t < n_gc_threads; t++) {
421 if (RtsFlags.GcFlags.generations == 1) {
426 for (; s < total_steps; s++) {
429 // Push the final block
431 push_scanned_block(ws->todo_bd, ws);
434 ASSERT(gct->scan_bd == NULL);
435 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
438 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
439 ws->step->n_words += bd->free - bd->start;
443 prev->link = ws->step->blocks;
444 ws->step->blocks = ws->scavd_list;
446 ws->step->n_blocks += ws->n_scavd_blocks;
450 // Add all the partial blocks *after* we've added all the full
451 // blocks. This is so that we can grab the partial blocks back
452 // again and try to fill them up in the next GC.
453 for (t = 0; t < n_gc_threads; t++) {
457 if (RtsFlags.GcFlags.generations == 1) {
462 for (; s < total_steps; s++) {
466 for (bd = ws->part_list; bd != NULL; bd = next) {
468 if (bd->free == bd->start) {
470 ws->part_list = next;
477 ws->step->n_words += bd->free - bd->start;
482 prev->link = ws->step->blocks;
483 ws->step->blocks = ws->part_list;
485 ws->step->n_blocks += ws->n_part_blocks;
487 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
488 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
493 /* run through all the generations/steps and tidy up
500 for (i=0; i < n_gc_threads; i++) {
501 if (n_gc_threads > 1) {
502 trace(TRACE_gc,"thread %d:", i);
503 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
504 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
505 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
506 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
507 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
509 copied += gc_threads[i]->copied;
510 max_copied = stg_max(gc_threads[i]->copied, max_copied);
512 if (n_gc_threads == 1) {
520 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
523 generations[g].collections++; // for stats
524 if (n_gc_threads > 1) generations[g].par_collections++;
527 // Count the mutable list as bytes "copied" for the purposes of
528 // stats. Every mutable list is copied during every GC.
530 nat mut_list_size = 0;
531 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
532 mut_list_size += bd->free - bd->start;
534 copied += mut_list_size;
537 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
538 (unsigned long)(mut_list_size * sizeof(W_)),
539 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
542 for (s = 0; s < generations[g].n_steps; s++) {
544 stp = &generations[g].steps[s];
546 // for generations we collected...
549 /* free old memory and shift to-space into from-space for all
550 * the collected steps (except the allocation area). These
551 * freed blocks will probaby be quickly recycled.
553 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
554 if (stp->is_compacted)
556 // for a compacted step, just shift the new to-space
557 // onto the front of the now-compacted existing blocks.
558 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
559 stp->n_words += bd->free - bd->start;
561 // tack the new blocks on the end of the existing blocks
562 if (stp->old_blocks != NULL) {
563 for (bd = stp->old_blocks; bd != NULL; bd = next) {
564 // NB. this step might not be compacted next
565 // time, so reset the BF_COMPACTED flags.
566 // They are set before GC if we're going to
567 // compact. (search for BF_COMPACTED above).
568 bd->flags &= ~BF_COMPACTED;
571 bd->link = stp->blocks;
574 stp->blocks = stp->old_blocks;
576 // add the new blocks to the block tally
577 stp->n_blocks += stp->n_old_blocks;
578 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
579 ASSERT(countOccupied(stp->blocks) == stp->n_words);
583 freeChain(stp->old_blocks);
585 stp->old_blocks = NULL;
586 stp->n_old_blocks = 0;
589 /* LARGE OBJECTS. The current live large objects are chained on
590 * scavenged_large, having been moved during garbage
591 * collection from large_objects. Any objects left on
592 * large_objects list are therefore dead, so we free them here.
594 for (bd = stp->large_objects; bd != NULL; bd = next) {
600 stp->large_objects = stp->scavenged_large_objects;
601 stp->n_large_blocks = stp->n_scavenged_large_blocks;
604 else // for older generations...
606 /* For older generations, we need to append the
607 * scavenged_large_object list (i.e. large objects that have been
608 * promoted during this GC) to the large_object list for that step.
610 for (bd = stp->scavenged_large_objects; bd; bd = next) {
612 dbl_link_onto(bd, &stp->large_objects);
615 // add the new blocks we promoted during this GC
616 stp->n_large_blocks += stp->n_scavenged_large_blocks;
621 // update the max size of older generations after a major GC
622 resize_generations();
624 // Calculate the amount of live data for stats.
625 live = calcLiveWords();
627 // Free the small objects allocated via allocate(), since this will
628 // all have been copied into G0S1 now.
629 if (RtsFlags.GcFlags.generations > 1) {
630 if (g0s0->blocks != NULL) {
631 freeChain(g0s0->blocks);
638 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
640 // Start a new pinned_object_block
641 pinned_object_block = NULL;
643 // Free the mark stack.
644 if (mark_stack_bdescr != NULL) {
645 freeGroup(mark_stack_bdescr);
649 for (g = 0; g <= N; g++) {
650 for (s = 0; s < generations[g].n_steps; s++) {
651 stp = &generations[g].steps[s];
652 if (stp->bitmap != NULL) {
653 freeGroup(stp->bitmap);
661 // mark the garbage collected CAFs as dead
662 #if 0 && defined(DEBUG) // doesn't work at the moment
663 if (major_gc) { gcCAFs(); }
667 // resetStaticObjectForRetainerProfiling() must be called before
669 if (n_gc_threads > 1) {
670 barf("profiling is currently broken with multi-threaded GC");
671 // ToDo: fix the gct->scavenged_static_objects below
673 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
676 // zero the scavenged static object list
679 for (i = 0; i < n_gc_threads; i++) {
680 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
687 // start any pending finalizers
689 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
692 // send exceptions to any threads which were about to die
694 resurrectThreads(resurrected_threads);
697 // Update the stable pointer hash table.
698 updateStablePtrTable(major_gc);
700 // check sanity after GC
701 IF_DEBUG(sanity, checkSanity());
703 // extra GC trace info
704 if (traceClass(TRACE_gc|DEBUG_gc)) statDescribeGens();
707 // symbol-table based profiling
708 /* heapCensus(to_blocks); */ /* ToDo */
711 // restore enclosing cost centre
717 // check for memory leaks if DEBUG is on
718 memInventory(traceClass(DEBUG_gc));
721 #ifdef RTS_GTK_FRONTPANEL
722 if (RtsFlags.GcFlags.frontpanel) {
723 updateFrontPanelAfterGC( N, live );
727 // ok, GC over: tell the stats department what happened.
728 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
729 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
731 #if defined(RTS_USER_SIGNALS)
732 if (RtsFlags.MiscFlags.install_signal_handlers) {
733 // unblock signals again
734 unblockUserSignals();
743 /* -----------------------------------------------------------------------------
744 Figure out which generation to collect, initialise N and major_gc.
746 Also returns the total number of blocks in generations that will be
748 -------------------------------------------------------------------------- */
751 initialise_N (rtsBool force_major_gc)
754 nat s, blocks, blocks_total;
759 if (force_major_gc) {
760 N = RtsFlags.GcFlags.generations - 1;
765 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
767 for (s = 0; s < generations[g].n_steps; s++) {
768 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
769 blocks += generations[g].steps[s].n_large_blocks;
771 if (blocks >= generations[g].max_blocks) {
775 blocks_total += blocks;
779 blocks_total += countNurseryBlocks();
781 major_gc = (N == RtsFlags.GcFlags.generations-1);
785 /* -----------------------------------------------------------------------------
786 Initialise the gc_thread structures.
787 -------------------------------------------------------------------------- */
790 alloc_gc_thread (int n)
796 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
801 initCondition(&t->wake_cond);
802 initMutex(&t->wake_mutex);
803 t->wakeup = rtsTrue; // starts true, so we can wait for the
804 // thread to start up, see wakeup_gc_threads
809 t->free_blocks = NULL;
818 for (s = 0; s < total_steps; s++)
821 ws->step = &all_steps[s];
822 ASSERT(s == ws->step->abs_no);
826 ws->buffer_todo_bd = NULL;
828 ws->part_list = NULL;
829 ws->n_part_blocks = 0;
831 ws->scavd_list = NULL;
832 ws->n_scavd_blocks = 0;
840 alloc_gc_threads (void)
842 if (gc_threads == NULL) {
843 #if defined(THREADED_RTS)
845 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
849 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
850 gc_threads[i] = alloc_gc_thread(i);
853 gc_threads = stgMallocBytes (sizeof(gc_thread*),
856 gc_threads[0] = alloc_gc_thread(0);
861 /* ----------------------------------------------------------------------------
863 ------------------------------------------------------------------------- */
865 static nat gc_running_threads;
867 #if defined(THREADED_RTS)
868 static Mutex gc_running_mutex;
875 ACQUIRE_LOCK(&gc_running_mutex);
876 n_running = ++gc_running_threads;
877 RELEASE_LOCK(&gc_running_mutex);
878 ASSERT(n_running <= n_gc_threads);
886 ACQUIRE_LOCK(&gc_running_mutex);
887 ASSERT(n_gc_threads != 0);
888 n_running = --gc_running_threads;
889 RELEASE_LOCK(&gc_running_mutex);
894 scavenge_until_all_done (void)
898 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
902 // scavenge_loop() only exits when there's no work to do
905 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
906 gct->thread_index, r);
908 while (gc_running_threads != 0) {
914 // any_work() does not remove the work from the queue, it
915 // just checks for the presence of work. If we find any,
916 // then we increment gc_running_threads and go back to
917 // scavenge_loop() to perform any pending work.
920 // All threads are now stopped
921 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
924 #if defined(THREADED_RTS)
926 // gc_thread_work(): Scavenge until there's no work left to do and all
927 // the running threads are idle.
930 gc_thread_work (void)
932 // gc_running_threads has already been incremented for us; this is
933 // a worker thread and the main thread bumped gc_running_threads
934 // before waking us up.
936 // Every thread evacuates some roots.
938 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
940 scavenge_until_all_done();
945 gc_thread_mainloop (void)
949 // Wait until we're told to wake up
950 ACQUIRE_LOCK(&gct->wake_mutex);
951 gct->wakeup = rtsFalse;
952 while (!gct->wakeup) {
953 debugTrace(DEBUG_gc, "GC thread %d standing by...",
955 waitCondition(&gct->wake_cond, &gct->wake_mutex);
957 RELEASE_LOCK(&gct->wake_mutex);
958 if (gct->exit) break;
961 // start performance counters in this thread...
962 if (gct->papi_events == -1) {
963 papi_init_eventset(&gct->papi_events);
965 papi_thread_start_gc1_count(gct->papi_events);
971 // count events in this thread towards the GC totals
972 papi_thread_stop_gc1_count(gct->papi_events);
978 #if defined(THREADED_RTS)
980 gc_thread_entry (gc_thread *my_gct)
983 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
984 gct->id = osThreadId();
985 gc_thread_mainloop();
990 start_gc_threads (void)
992 #if defined(THREADED_RTS)
995 static rtsBool done = rtsFalse;
997 gc_running_threads = 0;
998 initMutex(&gc_running_mutex);
1001 // Start from 1: the main thread is 0
1002 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1003 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1012 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1014 #if defined(THREADED_RTS)
1016 for (i=1; i < n_threads; i++) {
1018 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1020 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1021 if (gc_threads[i]->wakeup) {
1022 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1028 gc_threads[i]->wakeup = rtsTrue;
1029 signalCondition(&gc_threads[i]->wake_cond);
1030 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1035 // After GC is complete, we must wait for all GC threads to enter the
1036 // standby state, otherwise they may still be executing inside
1037 // any_work(), and may even remain awake until the next GC starts.
1039 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1041 #if defined(THREADED_RTS)
1044 for (i=1; i < n_threads; i++) {
1046 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1047 wakeup = gc_threads[i]->wakeup;
1048 // wakeup is false while the thread is waiting
1049 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1055 /* ----------------------------------------------------------------------------
1056 Initialise a generation that is to be collected
1057 ------------------------------------------------------------------------- */
1060 init_collected_gen (nat g, nat n_threads)
1067 // Throw away the current mutable list. Invariant: the mutable
1068 // list always has at least one block; this means we can avoid a
1069 // check for NULL in recordMutable().
1071 freeChain(generations[g].mut_list);
1072 generations[g].mut_list = allocBlock();
1073 for (i = 0; i < n_capabilities; i++) {
1074 freeChain(capabilities[i].mut_lists[g]);
1075 capabilities[i].mut_lists[g] = allocBlock();
1079 for (s = 0; s < generations[g].n_steps; s++) {
1081 // generation 0, step 0 doesn't need to-space
1082 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1086 stp = &generations[g].steps[s];
1087 ASSERT(stp->gen_no == g);
1089 // deprecate the existing blocks
1090 stp->old_blocks = stp->blocks;
1091 stp->n_old_blocks = stp->n_blocks;
1096 // we don't have any to-be-scavenged blocks yet
1098 stp->todos_last = NULL;
1101 // initialise the large object queues.
1102 stp->scavenged_large_objects = NULL;
1103 stp->n_scavenged_large_blocks = 0;
1105 // mark the small objects as from-space
1106 for (bd = stp->old_blocks; bd; bd = bd->link) {
1107 bd->flags &= ~BF_EVACUATED;
1110 // mark the large objects as from-space
1111 for (bd = stp->large_objects; bd; bd = bd->link) {
1112 bd->flags &= ~BF_EVACUATED;
1115 // for a compacted step, we need to allocate the bitmap
1116 if (stp->is_compacted) {
1117 nat bitmap_size; // in bytes
1118 bdescr *bitmap_bdescr;
1121 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1123 if (bitmap_size > 0) {
1124 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1126 stp->bitmap = bitmap_bdescr;
1127 bitmap = bitmap_bdescr->start;
1129 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1130 bitmap_size, bitmap);
1132 // don't forget to fill it with zeros!
1133 memset(bitmap, 0, bitmap_size);
1135 // For each block in this step, point to its bitmap from the
1136 // block descriptor.
1137 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1138 bd->u.bitmap = bitmap;
1139 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1141 // Also at this point we set the BF_COMPACTED flag
1142 // for this block. The invariant is that
1143 // BF_COMPACTED is always unset, except during GC
1144 // when it is set on those blocks which will be
1146 bd->flags |= BF_COMPACTED;
1152 // For each GC thread, for each step, allocate a "todo" block to
1153 // store evacuated objects to be scavenged, and a block to store
1154 // evacuated objects that do not need to be scavenged.
1155 for (t = 0; t < n_threads; t++) {
1156 for (s = 0; s < generations[g].n_steps; s++) {
1158 // we don't copy objects into g0s0, unless -G0
1159 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1161 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1163 ws->todo_large_objects = NULL;
1165 ws->part_list = NULL;
1166 ws->n_part_blocks = 0;
1168 // allocate the first to-space block; extra blocks will be
1169 // chained on as necessary.
1171 ws->buffer_todo_bd = NULL;
1172 alloc_todo_block(ws,0);
1174 ws->scavd_list = NULL;
1175 ws->n_scavd_blocks = 0;
1181 /* ----------------------------------------------------------------------------
1182 Initialise a generation that is *not* to be collected
1183 ------------------------------------------------------------------------- */
1186 init_uncollected_gen (nat g, nat threads)
1193 for (s = 0; s < generations[g].n_steps; s++) {
1194 stp = &generations[g].steps[s];
1195 stp->scavenged_large_objects = NULL;
1196 stp->n_scavenged_large_blocks = 0;
1199 for (s = 0; s < generations[g].n_steps; s++) {
1201 stp = &generations[g].steps[s];
1203 for (t = 0; t < threads; t++) {
1204 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1206 ws->buffer_todo_bd = NULL;
1207 ws->todo_large_objects = NULL;
1209 ws->part_list = NULL;
1210 ws->n_part_blocks = 0;
1212 ws->scavd_list = NULL;
1213 ws->n_scavd_blocks = 0;
1215 // If the block at the head of the list in this generation
1216 // is less than 3/4 full, then use it as a todo block.
1217 if (stp->blocks && isPartiallyFull(stp->blocks))
1219 ws->todo_bd = stp->blocks;
1220 ws->todo_free = ws->todo_bd->free;
1221 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1222 stp->blocks = stp->blocks->link;
1224 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1225 ws->todo_bd->link = NULL;
1226 // we must scan from the current end point.
1227 ws->todo_bd->u.scan = ws->todo_bd->free;
1232 alloc_todo_block(ws,0);
1236 // deal out any more partial blocks to the threads' part_lists
1238 while (stp->blocks && isPartiallyFull(stp->blocks))
1241 stp->blocks = bd->link;
1242 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1243 bd->link = ws->part_list;
1245 ws->n_part_blocks += 1;
1246 bd->u.scan = bd->free;
1248 stp->n_words -= bd->free - bd->start;
1250 if (t == n_gc_threads) t = 0;
1255 // Move the private mutable lists from each capability onto the
1256 // main mutable list for the generation.
1257 for (i = 0; i < n_capabilities; i++) {
1258 for (bd = capabilities[i].mut_lists[g];
1259 bd->link != NULL; bd = bd->link) {
1262 bd->link = generations[g].mut_list;
1263 generations[g].mut_list = capabilities[i].mut_lists[g];
1264 capabilities[i].mut_lists[g] = allocBlock();
1268 /* -----------------------------------------------------------------------------
1269 Initialise a gc_thread before GC
1270 -------------------------------------------------------------------------- */
1273 init_gc_thread (gc_thread *t)
1275 t->static_objects = END_OF_STATIC_LIST;
1276 t->scavenged_static_objects = END_OF_STATIC_LIST;
1279 t->failed_to_evac = rtsFalse;
1280 t->eager_promotion = rtsTrue;
1281 t->thunk_selector_depth = 0;
1286 t->scav_find_work = 0;
1289 /* -----------------------------------------------------------------------------
1290 Function we pass to evacuate roots.
1291 -------------------------------------------------------------------------- */
1294 mark_root(void *user, StgClosure **root)
1296 // we stole a register for gct, but this function is called from
1297 // *outside* the GC where the register variable is not in effect,
1298 // so we need to save and restore it here. NB. only call
1299 // mark_root() from the main GC thread, otherwise gct will be
1301 gc_thread *saved_gct;
1310 /* -----------------------------------------------------------------------------
1311 Initialising the static object & mutable lists
1312 -------------------------------------------------------------------------- */
1315 zero_static_object_list(StgClosure* first_static)
1319 const StgInfoTable *info;
1321 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1323 link = *STATIC_LINK(info, p);
1324 *STATIC_LINK(info,p) = NULL;
1328 /* ----------------------------------------------------------------------------
1329 Update the pointers from the task list
1331 These are treated as weak pointers because we want to allow a main
1332 thread to get a BlockedOnDeadMVar exception in the same way as any
1333 other thread. Note that the threads should all have been retained
1334 by GC by virtue of being on the all_threads list, we're just
1335 updating pointers here.
1336 ------------------------------------------------------------------------- */
1339 update_task_list (void)
1343 for (task = all_tasks; task != NULL; task = task->all_link) {
1344 if (!task->stopped && task->tso) {
1345 ASSERT(task->tso->bound == task);
1346 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1348 barf("task %p: main thread %d has been GC'd",
1361 /* ----------------------------------------------------------------------------
1362 Reset the sizes of the older generations when we do a major
1365 CURRENT STRATEGY: make all generations except zero the same size.
1366 We have to stay within the maximum heap size, and leave a certain
1367 percentage of the maximum heap size available to allocate into.
1368 ------------------------------------------------------------------------- */
1371 resize_generations (void)
1375 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1376 nat live, size, min_alloc;
1377 nat max = RtsFlags.GcFlags.maxHeapSize;
1378 nat gens = RtsFlags.GcFlags.generations;
1380 // live in the oldest generations
1381 live = (oldest_gen->steps[0].n_words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W+
1382 oldest_gen->steps[0].n_large_blocks;
1384 // default max size for all generations except zero
1385 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1386 RtsFlags.GcFlags.minOldGenSize);
1388 // minimum size for generation zero
1389 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1390 RtsFlags.GcFlags.minAllocAreaSize);
1392 // Auto-enable compaction when the residency reaches a
1393 // certain percentage of the maximum heap size (default: 30%).
1394 if (RtsFlags.GcFlags.generations > 1 &&
1395 (RtsFlags.GcFlags.compact ||
1397 oldest_gen->steps[0].n_blocks >
1398 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1399 oldest_gen->steps[0].is_compacted = 1;
1400 // debugBelch("compaction: on\n", live);
1402 oldest_gen->steps[0].is_compacted = 0;
1403 // debugBelch("compaction: off\n", live);
1406 // if we're going to go over the maximum heap size, reduce the
1407 // size of the generations accordingly. The calculation is
1408 // different if compaction is turned on, because we don't need
1409 // to double the space required to collect the old generation.
1412 // this test is necessary to ensure that the calculations
1413 // below don't have any negative results - we're working
1414 // with unsigned values here.
1415 if (max < min_alloc) {
1419 if (oldest_gen->steps[0].is_compacted) {
1420 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1421 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1424 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1425 size = (max - min_alloc) / ((gens - 1) * 2);
1435 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1436 min_alloc, size, max);
1439 for (g = 0; g < gens; g++) {
1440 generations[g].max_blocks = size;
1445 /* -----------------------------------------------------------------------------
1446 Calculate the new size of the nursery, and resize it.
1447 -------------------------------------------------------------------------- */
1450 resize_nursery (void)
1452 if (RtsFlags.GcFlags.generations == 1)
1453 { // Two-space collector:
1456 /* set up a new nursery. Allocate a nursery size based on a
1457 * function of the amount of live data (by default a factor of 2)
1458 * Use the blocks from the old nursery if possible, freeing up any
1461 * If we get near the maximum heap size, then adjust our nursery
1462 * size accordingly. If the nursery is the same size as the live
1463 * data (L), then we need 3L bytes. We can reduce the size of the
1464 * nursery to bring the required memory down near 2L bytes.
1466 * A normal 2-space collector would need 4L bytes to give the same
1467 * performance we get from 3L bytes, reducing to the same
1468 * performance at 2L bytes.
1470 blocks = g0s0->n_blocks;
1472 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1473 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1474 RtsFlags.GcFlags.maxHeapSize )
1476 long adjusted_blocks; // signed on purpose
1479 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1481 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1482 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1484 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1485 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1489 blocks = adjusted_blocks;
1493 blocks *= RtsFlags.GcFlags.oldGenFactor;
1494 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1496 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1499 resizeNurseries(blocks);
1501 else // Generational collector
1504 * If the user has given us a suggested heap size, adjust our
1505 * allocation area to make best use of the memory available.
1507 if (RtsFlags.GcFlags.heapSizeSuggestion)
1510 nat needed = calcNeeded(); // approx blocks needed at next GC
1512 /* Guess how much will be live in generation 0 step 0 next time.
1513 * A good approximation is obtained by finding the
1514 * percentage of g0s0 that was live at the last minor GC.
1516 * We have an accurate figure for the amount of copied data in
1517 * 'copied', but we must convert this to a number of blocks, with
1518 * a small adjustment for estimated slop at the end of a block
1523 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1524 / countNurseryBlocks();
1527 /* Estimate a size for the allocation area based on the
1528 * information available. We might end up going slightly under
1529 * or over the suggested heap size, but we should be pretty
1532 * Formula: suggested - needed
1533 * ----------------------------
1534 * 1 + g0s0_pcnt_kept/100
1536 * where 'needed' is the amount of memory needed at the next
1537 * collection for collecting all steps except g0s0.
1540 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1541 (100 + (long)g0s0_pcnt_kept);
1543 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1544 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1547 resizeNurseries((nat)blocks);
1551 // we might have added extra large blocks to the nursery, so
1552 // resize back to minAllocAreaSize again.
1553 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1558 /* -----------------------------------------------------------------------------
1559 Sanity code for CAF garbage collection.
1561 With DEBUG turned on, we manage a CAF list in addition to the SRT
1562 mechanism. After GC, we run down the CAF list and blackhole any
1563 CAFs which have been garbage collected. This means we get an error
1564 whenever the program tries to enter a garbage collected CAF.
1566 Any garbage collected CAFs are taken off the CAF list at the same
1568 -------------------------------------------------------------------------- */
1570 #if 0 && defined(DEBUG)
1577 const StgInfoTable *info;
1588 ASSERT(info->type == IND_STATIC);
1590 if (STATIC_LINK(info,p) == NULL) {
1591 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1593 SET_INFO(p,&stg_BLACKHOLE_info);
1594 p = STATIC_LINK2(info,p);
1598 pp = &STATIC_LINK2(info,p);
1605 debugTrace(DEBUG_gccafs, "%d CAFs live", i);