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:
412 // * clear the BF_EVACUATED flag from each copied block
413 // * move the copied blocks to the step
419 for (t = 0; t < n_gc_threads; t++) {
423 if (RtsFlags.GcFlags.generations == 1) {
428 for (; s < total_steps; s++) {
431 // Push the final block
433 push_scanned_block(ws->todo_bd, ws);
436 ASSERT(gct->scan_bd == NULL);
437 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
440 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
441 ws->step->n_words += bd->free - bd->start;
445 prev->link = ws->step->blocks;
446 ws->step->blocks = ws->scavd_list;
448 ws->step->n_blocks += ws->n_scavd_blocks;
451 for (bd = ws->part_list; bd != NULL; bd = next) {
453 if (bd->free == bd->start) {
455 ws->part_list = next;
462 ws->step->n_words += bd->free - bd->start;
467 prev->link = ws->step->blocks;
468 ws->step->blocks = ws->part_list;
470 ws->step->n_blocks += ws->n_part_blocks;
472 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
473 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
478 /* run through all the generations/steps and tidy up
485 for (i=0; i < n_gc_threads; i++) {
486 if (n_gc_threads > 1) {
487 trace(TRACE_gc,"thread %d:", i);
488 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
489 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
490 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
491 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
492 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
494 copied += gc_threads[i]->copied;
495 max_copied = stg_max(gc_threads[i]->copied, max_copied);
497 if (n_gc_threads == 1) {
505 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
508 generations[g].collections++; // for stats
509 if (n_gc_threads > 1) generations[g].par_collections++;
512 // Count the mutable list as bytes "copied" for the purposes of
513 // stats. Every mutable list is copied during every GC.
515 nat mut_list_size = 0;
516 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
517 mut_list_size += bd->free - bd->start;
519 copied += mut_list_size;
522 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
523 (unsigned long)(mut_list_size * sizeof(W_)),
524 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
527 for (s = 0; s < generations[g].n_steps; s++) {
529 stp = &generations[g].steps[s];
531 // for generations we collected...
534 /* free old memory and shift to-space into from-space for all
535 * the collected steps (except the allocation area). These
536 * freed blocks will probaby be quickly recycled.
538 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
539 if (stp->is_compacted)
541 // for a compacted step, just shift the new to-space
542 // onto the front of the now-compacted existing blocks.
543 for (bd = stp->blocks; bd != NULL; bd = bd->link) {
544 stp->n_words += bd->free - bd->start;
546 // tack the new blocks on the end of the existing blocks
547 if (stp->old_blocks != NULL) {
548 for (bd = stp->old_blocks; bd != NULL; bd = next) {
549 // NB. this step might not be compacted next
550 // time, so reset the BF_COMPACTED flags.
551 // They are set before GC if we're going to
552 // compact. (search for BF_COMPACTED above).
553 bd->flags &= ~BF_COMPACTED;
556 bd->link = stp->blocks;
559 stp->blocks = stp->old_blocks;
561 // add the new blocks to the block tally
562 stp->n_blocks += stp->n_old_blocks;
563 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
564 ASSERT(countOccupied(stp->blocks) == stp->n_words);
568 freeChain(stp->old_blocks);
570 stp->old_blocks = NULL;
571 stp->n_old_blocks = 0;
574 /* LARGE OBJECTS. The current live large objects are chained on
575 * scavenged_large, having been moved during garbage
576 * collection from large_objects. Any objects left on
577 * large_objects list are therefore dead, so we free them here.
579 for (bd = stp->large_objects; bd != NULL; bd = next) {
585 stp->large_objects = stp->scavenged_large_objects;
586 stp->n_large_blocks = stp->n_scavenged_large_blocks;
589 else // for older generations...
591 /* For older generations, we need to append the
592 * scavenged_large_object list (i.e. large objects that have been
593 * promoted during this GC) to the large_object list for that step.
595 for (bd = stp->scavenged_large_objects; bd; bd = next) {
597 dbl_link_onto(bd, &stp->large_objects);
600 // add the new blocks we promoted during this GC
601 stp->n_large_blocks += stp->n_scavenged_large_blocks;
606 // update the max size of older generations after a major GC
607 resize_generations();
609 // Calculate the amount of live data for stats.
610 live = calcLiveWords();
612 // Free the small objects allocated via allocate(), since this will
613 // all have been copied into G0S1 now.
614 if (RtsFlags.GcFlags.generations > 1) {
615 if (g0s0->blocks != NULL) {
616 freeChain(g0s0->blocks);
623 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
625 // Start a new pinned_object_block
626 pinned_object_block = NULL;
628 // Free the mark stack.
629 if (mark_stack_bdescr != NULL) {
630 freeGroup(mark_stack_bdescr);
634 for (g = 0; g <= N; g++) {
635 for (s = 0; s < generations[g].n_steps; s++) {
636 stp = &generations[g].steps[s];
637 if (stp->bitmap != NULL) {
638 freeGroup(stp->bitmap);
646 // mark the garbage collected CAFs as dead
647 #if 0 && defined(DEBUG) // doesn't work at the moment
648 if (major_gc) { gcCAFs(); }
652 // resetStaticObjectForRetainerProfiling() must be called before
654 if (n_gc_threads > 1) {
655 barf("profiling is currently broken with multi-threaded GC");
656 // ToDo: fix the gct->scavenged_static_objects below
658 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
661 // zero the scavenged static object list
664 for (i = 0; i < n_gc_threads; i++) {
665 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
672 // start any pending finalizers
674 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
677 // send exceptions to any threads which were about to die
679 resurrectThreads(resurrected_threads);
682 // Update the stable pointer hash table.
683 updateStablePtrTable(major_gc);
685 // check sanity after GC
686 IF_DEBUG(sanity, checkSanity());
688 // extra GC trace info
689 if (traceClass(TRACE_gc|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(traceClass(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 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
714 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
716 #if defined(RTS_USER_SIGNALS)
717 if (RtsFlags.MiscFlags.install_signal_handlers) {
718 // unblock signals again
719 unblockUserSignals();
728 /* -----------------------------------------------------------------------------
729 Figure out which generation to collect, initialise N and major_gc.
731 Also returns the total number of blocks in generations that will be
733 -------------------------------------------------------------------------- */
736 initialise_N (rtsBool force_major_gc)
739 nat s, blocks, blocks_total;
744 if (force_major_gc) {
745 N = RtsFlags.GcFlags.generations - 1;
750 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
752 for (s = 0; s < generations[g].n_steps; s++) {
753 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
754 blocks += generations[g].steps[s].n_large_blocks;
756 if (blocks >= generations[g].max_blocks) {
760 blocks_total += blocks;
764 blocks_total += countNurseryBlocks();
766 major_gc = (N == RtsFlags.GcFlags.generations-1);
770 /* -----------------------------------------------------------------------------
771 Initialise the gc_thread structures.
772 -------------------------------------------------------------------------- */
775 alloc_gc_thread (int n)
781 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
786 initCondition(&t->wake_cond);
787 initMutex(&t->wake_mutex);
788 t->wakeup = rtsTrue; // starts true, so we can wait for the
789 // thread to start up, see wakeup_gc_threads
794 t->free_blocks = NULL;
803 for (s = 0; s < total_steps; s++)
806 ws->step = &all_steps[s];
807 ASSERT(s == ws->step->abs_no);
811 ws->buffer_todo_bd = NULL;
813 ws->part_list = NULL;
814 ws->n_part_blocks = 0;
816 ws->scavd_list = NULL;
817 ws->n_scavd_blocks = 0;
825 alloc_gc_threads (void)
827 if (gc_threads == NULL) {
828 #if defined(THREADED_RTS)
830 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
834 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
835 gc_threads[i] = alloc_gc_thread(i);
838 gc_threads = stgMallocBytes (sizeof(gc_thread*),
841 gc_threads[0] = alloc_gc_thread(0);
846 /* ----------------------------------------------------------------------------
848 ------------------------------------------------------------------------- */
850 static nat gc_running_threads;
852 #if defined(THREADED_RTS)
853 static Mutex gc_running_mutex;
860 ACQUIRE_LOCK(&gc_running_mutex);
861 n_running = ++gc_running_threads;
862 RELEASE_LOCK(&gc_running_mutex);
863 ASSERT(n_running <= n_gc_threads);
871 ACQUIRE_LOCK(&gc_running_mutex);
872 ASSERT(n_gc_threads != 0);
873 n_running = --gc_running_threads;
874 RELEASE_LOCK(&gc_running_mutex);
879 scavenge_until_all_done (void)
883 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
887 // scavenge_loop() only exits when there's no work to do
890 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
891 gct->thread_index, r);
893 while (gc_running_threads != 0) {
899 // any_work() does not remove the work from the queue, it
900 // just checks for the presence of work. If we find any,
901 // then we increment gc_running_threads and go back to
902 // scavenge_loop() to perform any pending work.
905 // All threads are now stopped
906 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
909 #if defined(THREADED_RTS)
911 // gc_thread_work(): Scavenge until there's no work left to do and all
912 // the running threads are idle.
915 gc_thread_work (void)
917 // gc_running_threads has already been incremented for us; this is
918 // a worker thread and the main thread bumped gc_running_threads
919 // before waking us up.
921 // Every thread evacuates some roots.
923 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
925 scavenge_until_all_done();
930 gc_thread_mainloop (void)
934 // Wait until we're told to wake up
935 ACQUIRE_LOCK(&gct->wake_mutex);
936 gct->wakeup = rtsFalse;
937 while (!gct->wakeup) {
938 debugTrace(DEBUG_gc, "GC thread %d standing by...",
940 waitCondition(&gct->wake_cond, &gct->wake_mutex);
942 RELEASE_LOCK(&gct->wake_mutex);
943 if (gct->exit) break;
946 // start performance counters in this thread...
947 if (gct->papi_events == -1) {
948 papi_init_eventset(&gct->papi_events);
950 papi_thread_start_gc1_count(gct->papi_events);
956 // count events in this thread towards the GC totals
957 papi_thread_stop_gc1_count(gct->papi_events);
963 #if defined(THREADED_RTS)
965 gc_thread_entry (gc_thread *my_gct)
968 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
969 gct->id = osThreadId();
970 gc_thread_mainloop();
975 start_gc_threads (void)
977 #if defined(THREADED_RTS)
980 static rtsBool done = rtsFalse;
982 gc_running_threads = 0;
983 initMutex(&gc_running_mutex);
986 // Start from 1: the main thread is 0
987 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
988 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
997 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
999 #if defined(THREADED_RTS)
1001 for (i=1; i < n_threads; i++) {
1003 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1005 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1006 if (gc_threads[i]->wakeup) {
1007 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1013 gc_threads[i]->wakeup = rtsTrue;
1014 signalCondition(&gc_threads[i]->wake_cond);
1015 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1020 // After GC is complete, we must wait for all GC threads to enter the
1021 // standby state, otherwise they may still be executing inside
1022 // any_work(), and may even remain awake until the next GC starts.
1024 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1026 #if defined(THREADED_RTS)
1029 for (i=1; i < n_threads; i++) {
1031 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1032 wakeup = gc_threads[i]->wakeup;
1033 // wakeup is false while the thread is waiting
1034 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1040 /* ----------------------------------------------------------------------------
1041 Initialise a generation that is to be collected
1042 ------------------------------------------------------------------------- */
1045 init_collected_gen (nat g, nat n_threads)
1052 // Throw away the current mutable list. Invariant: the mutable
1053 // list always has at least one block; this means we can avoid a
1054 // check for NULL in recordMutable().
1056 freeChain(generations[g].mut_list);
1057 generations[g].mut_list = allocBlock();
1058 for (i = 0; i < n_capabilities; i++) {
1059 freeChain(capabilities[i].mut_lists[g]);
1060 capabilities[i].mut_lists[g] = allocBlock();
1064 for (s = 0; s < generations[g].n_steps; s++) {
1066 // generation 0, step 0 doesn't need to-space
1067 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1071 stp = &generations[g].steps[s];
1072 ASSERT(stp->gen_no == g);
1074 // deprecate the existing blocks
1075 stp->old_blocks = stp->blocks;
1076 stp->n_old_blocks = stp->n_blocks;
1081 // we don't have any to-be-scavenged blocks yet
1083 stp->todos_last = NULL;
1086 // initialise the large object queues.
1087 stp->scavenged_large_objects = NULL;
1088 stp->n_scavenged_large_blocks = 0;
1090 // mark the small objects as from-space
1091 for (bd = stp->old_blocks; bd; bd = bd->link) {
1092 bd->flags &= ~BF_EVACUATED;
1095 // mark the large objects as from-space
1096 for (bd = stp->large_objects; bd; bd = bd->link) {
1097 bd->flags &= ~BF_EVACUATED;
1100 // for a compacted step, we need to allocate the bitmap
1101 if (stp->is_compacted) {
1102 nat bitmap_size; // in bytes
1103 bdescr *bitmap_bdescr;
1106 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1108 if (bitmap_size > 0) {
1109 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1111 stp->bitmap = bitmap_bdescr;
1112 bitmap = bitmap_bdescr->start;
1114 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1115 bitmap_size, bitmap);
1117 // don't forget to fill it with zeros!
1118 memset(bitmap, 0, bitmap_size);
1120 // For each block in this step, point to its bitmap from the
1121 // block descriptor.
1122 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1123 bd->u.bitmap = bitmap;
1124 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1126 // Also at this point we set the BF_COMPACTED flag
1127 // for this block. The invariant is that
1128 // BF_COMPACTED is always unset, except during GC
1129 // when it is set on those blocks which will be
1131 bd->flags |= BF_COMPACTED;
1137 // For each GC thread, for each step, allocate a "todo" block to
1138 // store evacuated objects to be scavenged, and a block to store
1139 // evacuated objects that do not need to be scavenged.
1140 for (t = 0; t < n_threads; t++) {
1141 for (s = 0; s < generations[g].n_steps; s++) {
1143 // we don't copy objects into g0s0, unless -G0
1144 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1146 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1148 ws->todo_large_objects = NULL;
1150 ws->part_list = NULL;
1151 ws->n_part_blocks = 0;
1153 // allocate the first to-space block; extra blocks will be
1154 // chained on as necessary.
1156 ws->buffer_todo_bd = NULL;
1157 alloc_todo_block(ws,0);
1159 ws->scavd_list = NULL;
1160 ws->n_scavd_blocks = 0;
1166 /* ----------------------------------------------------------------------------
1167 Initialise a generation that is *not* to be collected
1168 ------------------------------------------------------------------------- */
1171 init_uncollected_gen (nat g, nat threads)
1178 for (s = 0; s < generations[g].n_steps; s++) {
1179 stp = &generations[g].steps[s];
1180 stp->scavenged_large_objects = NULL;
1181 stp->n_scavenged_large_blocks = 0;
1184 for (t = 0; t < threads; t++) {
1185 for (s = 0; s < generations[g].n_steps; s++) {
1187 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1190 ws->buffer_todo_bd = NULL;
1191 ws->todo_large_objects = NULL;
1193 ws->part_list = NULL;
1194 ws->n_part_blocks = 0;
1196 ws->scavd_list = NULL;
1197 ws->n_scavd_blocks = 0;
1199 // If the block at the head of the list in this generation
1200 // is less than 3/4 full, then use it as a todo block.
1201 if (stp->blocks && isPartiallyFull(stp->blocks))
1203 ws->todo_bd = stp->blocks;
1204 ws->todo_free = ws->todo_bd->free;
1205 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1206 stp->blocks = stp->blocks->link;
1208 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1209 ws->todo_bd->link = NULL;
1210 // we must scan from the current end point.
1211 ws->todo_bd->u.scan = ws->todo_bd->free;
1216 alloc_todo_block(ws,0);
1221 // Move the private mutable lists from each capability onto the
1222 // main mutable list for the generation.
1223 for (i = 0; i < n_capabilities; i++) {
1224 for (bd = capabilities[i].mut_lists[g];
1225 bd->link != NULL; bd = bd->link) {
1228 bd->link = generations[g].mut_list;
1229 generations[g].mut_list = capabilities[i].mut_lists[g];
1230 capabilities[i].mut_lists[g] = allocBlock();
1234 /* -----------------------------------------------------------------------------
1235 Initialise a gc_thread before GC
1236 -------------------------------------------------------------------------- */
1239 init_gc_thread (gc_thread *t)
1241 t->static_objects = END_OF_STATIC_LIST;
1242 t->scavenged_static_objects = END_OF_STATIC_LIST;
1245 t->failed_to_evac = rtsFalse;
1246 t->eager_promotion = rtsTrue;
1247 t->thunk_selector_depth = 0;
1252 t->scav_find_work = 0;
1255 /* -----------------------------------------------------------------------------
1256 Function we pass to evacuate roots.
1257 -------------------------------------------------------------------------- */
1260 mark_root(void *user, StgClosure **root)
1262 // we stole a register for gct, but this function is called from
1263 // *outside* the GC where the register variable is not in effect,
1264 // so we need to save and restore it here. NB. only call
1265 // mark_root() from the main GC thread, otherwise gct will be
1267 gc_thread *saved_gct;
1276 /* -----------------------------------------------------------------------------
1277 Initialising the static object & mutable lists
1278 -------------------------------------------------------------------------- */
1281 zero_static_object_list(StgClosure* first_static)
1285 const StgInfoTable *info;
1287 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1289 link = *STATIC_LINK(info, p);
1290 *STATIC_LINK(info,p) = NULL;
1294 /* ----------------------------------------------------------------------------
1295 Update the pointers from the task list
1297 These are treated as weak pointers because we want to allow a main
1298 thread to get a BlockedOnDeadMVar exception in the same way as any
1299 other thread. Note that the threads should all have been retained
1300 by GC by virtue of being on the all_threads list, we're just
1301 updating pointers here.
1302 ------------------------------------------------------------------------- */
1305 update_task_list (void)
1309 for (task = all_tasks; task != NULL; task = task->all_link) {
1310 if (!task->stopped && task->tso) {
1311 ASSERT(task->tso->bound == task);
1312 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1314 barf("task %p: main thread %d has been GC'd",
1327 /* ----------------------------------------------------------------------------
1328 Reset the sizes of the older generations when we do a major
1331 CURRENT STRATEGY: make all generations except zero the same size.
1332 We have to stay within the maximum heap size, and leave a certain
1333 percentage of the maximum heap size available to allocate into.
1334 ------------------------------------------------------------------------- */
1337 resize_generations (void)
1341 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1342 nat live, size, min_alloc;
1343 nat max = RtsFlags.GcFlags.maxHeapSize;
1344 nat gens = RtsFlags.GcFlags.generations;
1346 // live in the oldest generations
1347 live = (oldest_gen->steps[0].n_words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W+
1348 oldest_gen->steps[0].n_large_blocks;
1350 // default max size for all generations except zero
1351 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1352 RtsFlags.GcFlags.minOldGenSize);
1354 // minimum size for generation zero
1355 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1356 RtsFlags.GcFlags.minAllocAreaSize);
1358 // Auto-enable compaction when the residency reaches a
1359 // certain percentage of the maximum heap size (default: 30%).
1360 if (RtsFlags.GcFlags.generations > 1 &&
1361 (RtsFlags.GcFlags.compact ||
1363 oldest_gen->steps[0].n_blocks >
1364 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1365 oldest_gen->steps[0].is_compacted = 1;
1366 // debugBelch("compaction: on\n", live);
1368 oldest_gen->steps[0].is_compacted = 0;
1369 // debugBelch("compaction: off\n", live);
1372 // if we're going to go over the maximum heap size, reduce the
1373 // size of the generations accordingly. The calculation is
1374 // different if compaction is turned on, because we don't need
1375 // to double the space required to collect the old generation.
1378 // this test is necessary to ensure that the calculations
1379 // below don't have any negative results - we're working
1380 // with unsigned values here.
1381 if (max < min_alloc) {
1385 if (oldest_gen->steps[0].is_compacted) {
1386 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1387 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1390 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1391 size = (max - min_alloc) / ((gens - 1) * 2);
1401 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1402 min_alloc, size, max);
1405 for (g = 0; g < gens; g++) {
1406 generations[g].max_blocks = size;
1411 /* -----------------------------------------------------------------------------
1412 Calculate the new size of the nursery, and resize it.
1413 -------------------------------------------------------------------------- */
1416 resize_nursery (void)
1418 if (RtsFlags.GcFlags.generations == 1)
1419 { // Two-space collector:
1422 /* set up a new nursery. Allocate a nursery size based on a
1423 * function of the amount of live data (by default a factor of 2)
1424 * Use the blocks from the old nursery if possible, freeing up any
1427 * If we get near the maximum heap size, then adjust our nursery
1428 * size accordingly. If the nursery is the same size as the live
1429 * data (L), then we need 3L bytes. We can reduce the size of the
1430 * nursery to bring the required memory down near 2L bytes.
1432 * A normal 2-space collector would need 4L bytes to give the same
1433 * performance we get from 3L bytes, reducing to the same
1434 * performance at 2L bytes.
1436 blocks = g0s0->n_blocks;
1438 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1439 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1440 RtsFlags.GcFlags.maxHeapSize )
1442 long adjusted_blocks; // signed on purpose
1445 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1447 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1448 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1450 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1451 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1455 blocks = adjusted_blocks;
1459 blocks *= RtsFlags.GcFlags.oldGenFactor;
1460 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1462 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1465 resizeNurseries(blocks);
1467 else // Generational collector
1470 * If the user has given us a suggested heap size, adjust our
1471 * allocation area to make best use of the memory available.
1473 if (RtsFlags.GcFlags.heapSizeSuggestion)
1476 nat needed = calcNeeded(); // approx blocks needed at next GC
1478 /* Guess how much will be live in generation 0 step 0 next time.
1479 * A good approximation is obtained by finding the
1480 * percentage of g0s0 that was live at the last minor GC.
1482 * We have an accurate figure for the amount of copied data in
1483 * 'copied', but we must convert this to a number of blocks, with
1484 * a small adjustment for estimated slop at the end of a block
1489 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1490 / countNurseryBlocks();
1493 /* Estimate a size for the allocation area based on the
1494 * information available. We might end up going slightly under
1495 * or over the suggested heap size, but we should be pretty
1498 * Formula: suggested - needed
1499 * ----------------------------
1500 * 1 + g0s0_pcnt_kept/100
1502 * where 'needed' is the amount of memory needed at the next
1503 * collection for collecting all steps except g0s0.
1506 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1507 (100 + (long)g0s0_pcnt_kept);
1509 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1510 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1513 resizeNurseries((nat)blocks);
1517 // we might have added extra large blocks to the nursery, so
1518 // resize back to minAllocAreaSize again.
1519 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1524 /* -----------------------------------------------------------------------------
1525 Sanity code for CAF garbage collection.
1527 With DEBUG turned on, we manage a CAF list in addition to the SRT
1528 mechanism. After GC, we run down the CAF list and blackhole any
1529 CAFs which have been garbage collected. This means we get an error
1530 whenever the program tries to enter a garbage collected CAF.
1532 Any garbage collected CAFs are taken off the CAF list at the same
1534 -------------------------------------------------------------------------- */
1536 #if 0 && defined(DEBUG)
1543 const StgInfoTable *info;
1554 ASSERT(info->type == IND_STATIC);
1556 if (STATIC_LINK(info,p) == NULL) {
1557 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1559 SET_INFO(p,&stg_BLACKHOLE_info);
1560 p = STATIC_LINK2(info,p);
1564 pp = &STATIC_LINK2(info,p);
1571 debugTrace(DEBUG_gccafs, "%d CAFs live", i);