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;
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 alloc_gc_threads (void);
142 static void init_collected_gen (nat g, nat threads);
143 static void init_uncollected_gen (nat g, nat threads);
144 static void init_gc_thread (gc_thread *t);
145 static void update_task_list (void);
146 static void resize_generations (void);
147 static void resize_nursery (void);
148 static void start_gc_threads (void);
149 static void scavenge_until_all_done (void);
150 static nat inc_running (void);
151 static nat dec_running (void);
152 static void wakeup_gc_threads (nat n_threads);
153 static void shutdown_gc_threads (nat n_threads);
155 #if 0 && defined(DEBUG)
156 static void gcCAFs (void);
159 /* -----------------------------------------------------------------------------
160 The mark bitmap & stack.
161 -------------------------------------------------------------------------- */
163 #define MARK_STACK_BLOCKS 4
165 bdescr *mark_stack_bdescr;
170 // Flag and pointers used for falling back to a linear scan when the
171 // mark stack overflows.
172 rtsBool mark_stack_overflowed;
173 bdescr *oldgen_scan_bd;
176 /* -----------------------------------------------------------------------------
177 GarbageCollect: the main entry point to the garbage collector.
179 Locks held: all capabilities are held throughout GarbageCollect().
180 -------------------------------------------------------------------------- */
183 GarbageCollect ( rtsBool force_major_gc )
187 lnat live, allocated, max_copied, avg_copied, slop;
188 gc_thread *saved_gct;
191 // necessary if we stole a callee-saves register for gct:
195 CostCentreStack *prev_CCS;
200 #if defined(RTS_USER_SIGNALS)
201 if (RtsFlags.MiscFlags.install_signal_handlers) {
207 ASSERT(sizeof(step_workspace) == 16 * sizeof(StgWord));
208 // otherwise adjust the padding in step_workspace.
210 // tell the stats department that we've started a GC
213 // tell the STM to discard any cached closures it's hoping to re-use
222 // attribute any costs to CCS_GC
228 /* Approximate how much we allocated.
229 * Todo: only when generating stats?
231 allocated = calcAllocated();
233 /* Figure out which generation to collect
235 n = initialise_N(force_major_gc);
237 /* Allocate + initialise the gc_thread structures.
241 /* Start threads, so they can be spinning up while we finish initialisation.
245 /* How many threads will be participating in this GC?
246 * We don't try to parallelise minor GC, or mark/compact/sweep GC.
248 #if defined(THREADED_RTS)
249 if (n < (4*1024*1024 / BLOCK_SIZE) || oldest_gen->steps[0].mark) {
252 n_gc_threads = RtsFlags.ParFlags.gcThreads;
257 trace(TRACE_gc|DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
258 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
260 #ifdef RTS_GTK_FRONTPANEL
261 if (RtsFlags.GcFlags.frontpanel) {
262 updateFrontPanelBeforeGC(N);
267 // check for memory leaks if DEBUG is on
268 memInventory(traceClass(DEBUG_gc));
271 // check stack sanity *before* GC (ToDo: check all threads)
272 IF_DEBUG(sanity, checkFreeListSanity());
274 // Initialise all our gc_thread structures
275 for (t = 0; t < n_gc_threads; t++) {
276 init_gc_thread(gc_threads[t]);
279 // Initialise all the generations/steps that we're collecting.
280 for (g = 0; g <= N; g++) {
281 init_collected_gen(g,n_gc_threads);
284 // Initialise all the generations/steps that we're *not* collecting.
285 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
286 init_uncollected_gen(g,n_gc_threads);
289 /* Allocate a mark stack if we're doing a major collection.
292 nat mark_stack_blocks;
293 mark_stack_blocks = stg_max(MARK_STACK_BLOCKS,
294 oldest_gen->steps[0].n_old_blocks / 100);
295 mark_stack_bdescr = allocGroup(mark_stack_blocks);
296 mark_stack = (StgPtr *)mark_stack_bdescr->start;
297 mark_sp = mark_stack;
298 mark_splim = mark_stack + (mark_stack_blocks * BLOCK_SIZE_W);
300 mark_stack_bdescr = NULL;
303 // this is the main thread
306 /* -----------------------------------------------------------------------
307 * follow all the roots that we know about:
308 * - mutable lists from each generation > N
309 * we want to *scavenge* these roots, not evacuate them: they're not
310 * going to move in this GC.
311 * Also do them in reverse generation order, for the usual reason:
312 * namely to reduce the likelihood of spurious old->new pointers.
314 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
315 generations[g].saved_mut_list = generations[g].mut_list;
316 generations[g].mut_list = allocBlock();
317 // mut_list always has at least one block.
320 // the main thread is running: this prevents any other threads from
321 // exiting prematurely, so we can start them now.
322 // NB. do this after the mutable lists have been saved above, otherwise
323 // the other GC threads will be writing into the old mutable lists.
325 wakeup_gc_threads(n_gc_threads);
327 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
328 scavenge_mutable_list(&generations[g]);
331 // follow roots from the CAF list (used by GHCi)
333 markCAFs(mark_root, gct);
335 // follow all the roots that the application knows about.
337 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
339 #if defined(RTS_USER_SIGNALS)
340 // mark the signal handlers (signals should be already blocked)
341 markSignalHandlers(mark_root, gct);
344 // Mark the weak pointer list, and prepare to detect dead weak pointers.
348 // Mark the stable pointer table.
349 markStablePtrTable(mark_root, gct);
351 /* -------------------------------------------------------------------------
352 * Repeatedly scavenge all the areas we know about until there's no
353 * more scavenging to be done.
357 scavenge_until_all_done();
358 // The other threads are now stopped. We might recurse back to
359 // here, but from now on this is the only thread.
361 // if any blackholes are alive, make the threads that wait on
363 if (traverseBlackholeQueue()) {
368 // must be last... invariant is that everything is fully
369 // scavenged at this point.
370 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
375 // If we get to here, there's really nothing left to do.
379 shutdown_gc_threads(n_gc_threads);
381 // Update pointers from the Task list
384 // Now see which stable names are still alive.
388 // We call processHeapClosureForDead() on every closure destroyed during
389 // the current garbage collection, so we invoke LdvCensusForDead().
390 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
391 || RtsFlags.ProfFlags.bioSelector != NULL)
395 // NO MORE EVACUATION AFTER THIS POINT!
397 // Two-space collector: free the old to-space.
398 // g0s0->old_blocks is the old nursery
399 // g0s0->blocks is to-space from the previous GC
400 if (RtsFlags.GcFlags.generations == 1) {
401 if (g0s0->blocks != NULL) {
402 freeChain(g0s0->blocks);
407 // For each workspace, in each thread, move the copied blocks to the step
413 for (t = 0; t < n_gc_threads; t++) {
417 if (RtsFlags.GcFlags.generations == 1) {
422 for (; s < total_steps; s++) {
425 // Push the final block
427 push_scanned_block(ws->todo_bd, ws);
430 ASSERT(gct->scan_bd == NULL);
431 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
434 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
435 ws->step->n_words += bd->free - bd->start;
439 prev->link = ws->step->blocks;
440 ws->step->blocks = ws->scavd_list;
442 ws->step->n_blocks += ws->n_scavd_blocks;
446 // Add all the partial blocks *after* we've added all the full
447 // blocks. This is so that we can grab the partial blocks back
448 // again and try to fill them up in the next GC.
449 for (t = 0; t < n_gc_threads; t++) {
453 if (RtsFlags.GcFlags.generations == 1) {
458 for (; s < total_steps; s++) {
462 for (bd = ws->part_list; bd != NULL; bd = next) {
464 if (bd->free == bd->start) {
466 ws->part_list = next;
473 ws->step->n_words += bd->free - bd->start;
478 prev->link = ws->step->blocks;
479 ws->step->blocks = ws->part_list;
481 ws->step->n_blocks += ws->n_part_blocks;
483 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
484 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
489 // Finally: compact or sweep the oldest generation.
490 if (major_gc && oldest_gen->steps[0].mark) {
491 if (oldest_gen->steps[0].compact)
492 compact(gct->scavenged_static_objects);
494 sweep(&oldest_gen->steps[0]);
497 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
499 /* run through all the generations/steps and tidy up
506 for (i=0; i < n_gc_threads; i++) {
507 if (n_gc_threads > 1) {
508 trace(TRACE_gc,"thread %d:", i);
509 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
510 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
511 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
512 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
513 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
515 copied += gc_threads[i]->copied;
516 max_copied = stg_max(gc_threads[i]->copied, max_copied);
518 if (n_gc_threads == 1) {
526 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
529 generations[g].collections++; // for stats
530 if (n_gc_threads > 1) generations[g].par_collections++;
533 // Count the mutable list as bytes "copied" for the purposes of
534 // stats. Every mutable list is copied during every GC.
536 nat mut_list_size = 0;
537 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
538 mut_list_size += bd->free - bd->start;
540 copied += mut_list_size;
543 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
544 (unsigned long)(mut_list_size * sizeof(W_)),
545 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
548 for (s = 0; s < generations[g].n_steps; s++) {
550 stp = &generations[g].steps[s];
552 // for generations we collected...
555 /* free old memory and shift to-space into from-space for all
556 * the collected steps (except the allocation area). These
557 * freed blocks will probaby be quickly recycled.
559 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
562 // tack the new blocks on the end of the existing blocks
563 if (stp->old_blocks != NULL) {
566 for (bd = stp->old_blocks; bd != NULL; bd = next) {
570 if (!(bd->flags & BF_MARKED))
573 stp->old_blocks = next;
582 stp->n_words += bd->free - bd->start;
584 // NB. this step might not be compacted next
585 // time, so reset the BF_MARKED flags.
586 // They are set before GC if we're going to
587 // compact. (search for BF_MARKED above).
588 bd->flags &= ~BF_MARKED;
590 // between GCs, all blocks in the heap except
591 // for the nursery have the BF_EVACUATED flag set.
592 bd->flags |= BF_EVACUATED;
599 prev->link = stp->blocks;
600 stp->blocks = stp->old_blocks;
603 // add the new blocks to the block tally
604 stp->n_blocks += stp->n_old_blocks;
605 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
606 ASSERT(countOccupied(stp->blocks) == stp->n_words);
610 freeChain(stp->old_blocks);
612 stp->old_blocks = NULL;
613 stp->n_old_blocks = 0;
616 /* LARGE OBJECTS. The current live large objects are chained on
617 * scavenged_large, having been moved during garbage
618 * collection from large_objects. Any objects left on
619 * large_objects list are therefore dead, so we free them here.
621 for (bd = stp->large_objects; bd != NULL; bd = next) {
627 stp->large_objects = stp->scavenged_large_objects;
628 stp->n_large_blocks = stp->n_scavenged_large_blocks;
631 else // for older generations...
633 /* For older generations, we need to append the
634 * scavenged_large_object list (i.e. large objects that have been
635 * promoted during this GC) to the large_object list for that step.
637 for (bd = stp->scavenged_large_objects; bd; bd = next) {
639 dbl_link_onto(bd, &stp->large_objects);
642 // add the new blocks we promoted during this GC
643 stp->n_large_blocks += stp->n_scavenged_large_blocks;
648 // update the max size of older generations after a major GC
649 resize_generations();
651 // Calculate the amount of live data for stats.
652 live = calcLiveWords();
654 // Free the small objects allocated via allocate(), since this will
655 // all have been copied into G0S1 now.
656 if (RtsFlags.GcFlags.generations > 1) {
657 if (g0s0->blocks != NULL) {
658 freeChain(g0s0->blocks);
665 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
667 // Start a new pinned_object_block
668 pinned_object_block = NULL;
670 // Free the mark stack.
671 if (mark_stack_bdescr != NULL) {
672 freeGroup(mark_stack_bdescr);
676 for (g = 0; g <= N; g++) {
677 for (s = 0; s < generations[g].n_steps; s++) {
678 stp = &generations[g].steps[s];
679 if (stp->bitmap != NULL) {
680 freeGroup(stp->bitmap);
688 // mark the garbage collected CAFs as dead
689 #if 0 && defined(DEBUG) // doesn't work at the moment
690 if (major_gc) { gcCAFs(); }
694 // resetStaticObjectForRetainerProfiling() must be called before
696 if (n_gc_threads > 1) {
697 barf("profiling is currently broken with multi-threaded GC");
698 // ToDo: fix the gct->scavenged_static_objects below
700 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
703 // zero the scavenged static object list
706 for (i = 0; i < n_gc_threads; i++) {
707 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
714 // start any pending finalizers
716 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
719 // send exceptions to any threads which were about to die
721 resurrectThreads(resurrected_threads);
722 performPendingThrowTos(exception_threads);
725 // Update the stable pointer hash table.
726 updateStablePtrTable(major_gc);
728 // check sanity after GC
729 IF_DEBUG(sanity, checkSanity());
731 // extra GC trace info
732 if (traceClass(TRACE_gc|DEBUG_gc)) statDescribeGens();
735 // symbol-table based profiling
736 /* heapCensus(to_blocks); */ /* ToDo */
739 // restore enclosing cost centre
745 // check for memory leaks if DEBUG is on
746 memInventory(traceClass(DEBUG_gc));
749 #ifdef RTS_GTK_FRONTPANEL
750 if (RtsFlags.GcFlags.frontpanel) {
751 updateFrontPanelAfterGC( N, live );
755 // ok, GC over: tell the stats department what happened.
756 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
757 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
759 #if defined(RTS_USER_SIGNALS)
760 if (RtsFlags.MiscFlags.install_signal_handlers) {
761 // unblock signals again
762 unblockUserSignals();
771 /* -----------------------------------------------------------------------------
772 Figure out which generation to collect, initialise N and major_gc.
774 Also returns the total number of blocks in generations that will be
776 -------------------------------------------------------------------------- */
779 initialise_N (rtsBool force_major_gc)
782 nat s, blocks, blocks_total;
787 if (force_major_gc) {
788 N = RtsFlags.GcFlags.generations - 1;
793 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
795 for (s = 0; s < generations[g].n_steps; s++) {
796 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
797 blocks += generations[g].steps[s].n_large_blocks;
799 if (blocks >= generations[g].max_blocks) {
803 blocks_total += blocks;
807 blocks_total += countNurseryBlocks();
809 major_gc = (N == RtsFlags.GcFlags.generations-1);
813 /* -----------------------------------------------------------------------------
814 Initialise the gc_thread structures.
815 -------------------------------------------------------------------------- */
818 alloc_gc_thread (int n)
824 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
829 initCondition(&t->wake_cond);
830 initMutex(&t->wake_mutex);
831 t->wakeup = rtsTrue; // starts true, so we can wait for the
832 // thread to start up, see wakeup_gc_threads
837 t->free_blocks = NULL;
846 for (s = 0; s < total_steps; s++)
849 ws->step = &all_steps[s];
850 ASSERT(s == ws->step->abs_no);
854 ws->buffer_todo_bd = NULL;
856 ws->part_list = NULL;
857 ws->n_part_blocks = 0;
859 ws->scavd_list = NULL;
860 ws->n_scavd_blocks = 0;
868 alloc_gc_threads (void)
870 if (gc_threads == NULL) {
871 #if defined(THREADED_RTS)
873 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
877 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
878 gc_threads[i] = alloc_gc_thread(i);
881 gc_threads = stgMallocBytes (sizeof(gc_thread*),
884 gc_threads[0] = alloc_gc_thread(0);
889 /* ----------------------------------------------------------------------------
891 ------------------------------------------------------------------------- */
893 static nat gc_running_threads;
895 #if defined(THREADED_RTS)
896 static Mutex gc_running_mutex;
903 ACQUIRE_LOCK(&gc_running_mutex);
904 n_running = ++gc_running_threads;
905 RELEASE_LOCK(&gc_running_mutex);
906 ASSERT(n_running <= n_gc_threads);
914 ACQUIRE_LOCK(&gc_running_mutex);
915 ASSERT(n_gc_threads != 0);
916 n_running = --gc_running_threads;
917 RELEASE_LOCK(&gc_running_mutex);
931 // scavenge objects in compacted generation
932 if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
933 (mark_stack_bdescr != NULL && !mark_stack_empty())) {
937 // Check for global work in any step. We don't need to check for
938 // local work, because we have already exited scavenge_loop(),
939 // which means there is no local work for this thread.
940 for (s = total_steps-1; s >= 0; s--) {
941 if (s == 0 && RtsFlags.GcFlags.generations > 1) {
945 if (ws->todo_large_objects) return rtsTrue;
946 if (ws->step->todos) return rtsTrue;
955 scavenge_until_all_done (void)
959 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
962 #if defined(THREADED_RTS)
963 if (n_gc_threads > 1) {
972 // scavenge_loop() only exits when there's no work to do
975 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
976 gct->thread_index, r);
978 while (gc_running_threads != 0) {
984 // any_work() does not remove the work from the queue, it
985 // just checks for the presence of work. If we find any,
986 // then we increment gc_running_threads and go back to
987 // scavenge_loop() to perform any pending work.
990 // All threads are now stopped
991 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
994 #if defined(THREADED_RTS)
996 // gc_thread_work(): Scavenge until there's no work left to do and all
997 // the running threads are idle.
1000 gc_thread_work (void)
1002 // gc_running_threads has already been incremented for us; this is
1003 // a worker thread and the main thread bumped gc_running_threads
1004 // before waking us up.
1006 // Every thread evacuates some roots.
1008 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
1010 scavenge_until_all_done();
1015 gc_thread_mainloop (void)
1017 while (!gct->exit) {
1019 // Wait until we're told to wake up
1020 ACQUIRE_LOCK(&gct->wake_mutex);
1021 gct->wakeup = rtsFalse;
1022 while (!gct->wakeup) {
1023 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1025 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1027 RELEASE_LOCK(&gct->wake_mutex);
1028 if (gct->exit) break;
1031 // start performance counters in this thread...
1032 if (gct->papi_events == -1) {
1033 papi_init_eventset(&gct->papi_events);
1035 papi_thread_start_gc1_count(gct->papi_events);
1041 // count events in this thread towards the GC totals
1042 papi_thread_stop_gc1_count(gct->papi_events);
1048 #if defined(THREADED_RTS)
1050 gc_thread_entry (gc_thread *my_gct)
1053 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1054 gct->id = osThreadId();
1055 gc_thread_mainloop();
1060 start_gc_threads (void)
1062 #if defined(THREADED_RTS)
1065 static rtsBool done = rtsFalse;
1067 gc_running_threads = 0;
1068 initMutex(&gc_running_mutex);
1071 // Start from 1: the main thread is 0
1072 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1073 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1082 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1084 #if defined(THREADED_RTS)
1086 for (i=1; i < n_threads; i++) {
1088 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1090 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1091 if (gc_threads[i]->wakeup) {
1092 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1098 gc_threads[i]->wakeup = rtsTrue;
1099 signalCondition(&gc_threads[i]->wake_cond);
1100 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1105 // After GC is complete, we must wait for all GC threads to enter the
1106 // standby state, otherwise they may still be executing inside
1107 // any_work(), and may even remain awake until the next GC starts.
1109 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1111 #if defined(THREADED_RTS)
1114 for (i=1; i < n_threads; i++) {
1116 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1117 wakeup = gc_threads[i]->wakeup;
1118 // wakeup is false while the thread is waiting
1119 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1125 /* ----------------------------------------------------------------------------
1126 Initialise a generation that is to be collected
1127 ------------------------------------------------------------------------- */
1130 init_collected_gen (nat g, nat n_threads)
1137 // Throw away the current mutable list. Invariant: the mutable
1138 // list always has at least one block; this means we can avoid a
1139 // check for NULL in recordMutable().
1141 freeChain(generations[g].mut_list);
1142 generations[g].mut_list = allocBlock();
1143 for (i = 0; i < n_capabilities; i++) {
1144 freeChain(capabilities[i].mut_lists[g]);
1145 capabilities[i].mut_lists[g] = allocBlock();
1149 for (s = 0; s < generations[g].n_steps; s++) {
1151 stp = &generations[g].steps[s];
1152 ASSERT(stp->gen_no == g);
1154 // we'll construct a new list of threads in this step
1155 // during GC, throw away the current list.
1156 stp->old_threads = stp->threads;
1157 stp->threads = END_TSO_QUEUE;
1159 // generation 0, step 0 doesn't need to-space
1160 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1164 // deprecate the existing blocks
1165 stp->old_blocks = stp->blocks;
1166 stp->n_old_blocks = stp->n_blocks;
1170 stp->live_estimate = 0;
1172 // we don't have any to-be-scavenged blocks yet
1174 stp->todos_last = NULL;
1177 // initialise the large object queues.
1178 stp->scavenged_large_objects = NULL;
1179 stp->n_scavenged_large_blocks = 0;
1181 // mark the small objects as from-space
1182 for (bd = stp->old_blocks; bd; bd = bd->link) {
1183 bd->flags &= ~BF_EVACUATED;
1186 // mark the large objects as from-space
1187 for (bd = stp->large_objects; bd; bd = bd->link) {
1188 bd->flags &= ~BF_EVACUATED;
1191 // for a compacted step, we need to allocate the bitmap
1193 nat bitmap_size; // in bytes
1194 bdescr *bitmap_bdescr;
1197 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1199 if (bitmap_size > 0) {
1200 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1202 stp->bitmap = bitmap_bdescr;
1203 bitmap = bitmap_bdescr->start;
1205 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1206 bitmap_size, bitmap);
1208 // don't forget to fill it with zeros!
1209 memset(bitmap, 0, bitmap_size);
1211 // For each block in this step, point to its bitmap from the
1212 // block descriptor.
1213 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1214 bd->u.bitmap = bitmap;
1215 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1217 // Also at this point we set the BF_MARKED flag
1218 // for this block. The invariant is that
1219 // BF_MARKED is always unset, except during GC
1220 // when it is set on those blocks which will be
1222 if (!(bd->flags & BF_FRAGMENTED)) {
1223 bd->flags |= BF_MARKED;
1230 // For each GC thread, for each step, allocate a "todo" block to
1231 // store evacuated objects to be scavenged, and a block to store
1232 // evacuated objects that do not need to be scavenged.
1233 for (t = 0; t < n_threads; t++) {
1234 for (s = 0; s < generations[g].n_steps; s++) {
1236 // we don't copy objects into g0s0, unless -G0
1237 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1239 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1241 ws->todo_large_objects = NULL;
1243 ws->part_list = NULL;
1244 ws->n_part_blocks = 0;
1246 // allocate the first to-space block; extra blocks will be
1247 // chained on as necessary.
1249 ws->buffer_todo_bd = NULL;
1250 alloc_todo_block(ws,0);
1252 ws->scavd_list = NULL;
1253 ws->n_scavd_blocks = 0;
1259 /* ----------------------------------------------------------------------------
1260 Initialise a generation that is *not* to be collected
1261 ------------------------------------------------------------------------- */
1264 init_uncollected_gen (nat g, nat threads)
1271 for (s = 0; s < generations[g].n_steps; s++) {
1272 stp = &generations[g].steps[s];
1273 stp->scavenged_large_objects = NULL;
1274 stp->n_scavenged_large_blocks = 0;
1277 for (s = 0; s < generations[g].n_steps; s++) {
1279 stp = &generations[g].steps[s];
1281 for (t = 0; t < threads; t++) {
1282 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1284 ws->buffer_todo_bd = NULL;
1285 ws->todo_large_objects = NULL;
1287 ws->part_list = NULL;
1288 ws->n_part_blocks = 0;
1290 ws->scavd_list = NULL;
1291 ws->n_scavd_blocks = 0;
1293 // If the block at the head of the list in this generation
1294 // is less than 3/4 full, then use it as a todo block.
1295 if (stp->blocks && isPartiallyFull(stp->blocks))
1297 ws->todo_bd = stp->blocks;
1298 ws->todo_free = ws->todo_bd->free;
1299 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1300 stp->blocks = stp->blocks->link;
1302 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1303 ws->todo_bd->link = NULL;
1304 // we must scan from the current end point.
1305 ws->todo_bd->u.scan = ws->todo_bd->free;
1310 alloc_todo_block(ws,0);
1314 // deal out any more partial blocks to the threads' part_lists
1316 while (stp->blocks && isPartiallyFull(stp->blocks))
1319 stp->blocks = bd->link;
1320 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1321 bd->link = ws->part_list;
1323 ws->n_part_blocks += 1;
1324 bd->u.scan = bd->free;
1326 stp->n_words -= bd->free - bd->start;
1328 if (t == n_gc_threads) t = 0;
1333 // Move the private mutable lists from each capability onto the
1334 // main mutable list for the generation.
1335 for (i = 0; i < n_capabilities; i++) {
1336 for (bd = capabilities[i].mut_lists[g];
1337 bd->link != NULL; bd = bd->link) {
1340 bd->link = generations[g].mut_list;
1341 generations[g].mut_list = capabilities[i].mut_lists[g];
1342 capabilities[i].mut_lists[g] = allocBlock();
1346 /* -----------------------------------------------------------------------------
1347 Initialise a gc_thread before GC
1348 -------------------------------------------------------------------------- */
1351 init_gc_thread (gc_thread *t)
1353 t->static_objects = END_OF_STATIC_LIST;
1354 t->scavenged_static_objects = END_OF_STATIC_LIST;
1357 t->failed_to_evac = rtsFalse;
1358 t->eager_promotion = rtsTrue;
1359 t->thunk_selector_depth = 0;
1364 t->scav_find_work = 0;
1367 /* -----------------------------------------------------------------------------
1368 Function we pass to evacuate roots.
1369 -------------------------------------------------------------------------- */
1372 mark_root(void *user, StgClosure **root)
1374 // we stole a register for gct, but this function is called from
1375 // *outside* the GC where the register variable is not in effect,
1376 // so we need to save and restore it here. NB. only call
1377 // mark_root() from the main GC thread, otherwise gct will be
1379 gc_thread *saved_gct;
1388 /* -----------------------------------------------------------------------------
1389 Initialising the static object & mutable lists
1390 -------------------------------------------------------------------------- */
1393 zero_static_object_list(StgClosure* first_static)
1397 const StgInfoTable *info;
1399 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1401 link = *STATIC_LINK(info, p);
1402 *STATIC_LINK(info,p) = NULL;
1406 /* ----------------------------------------------------------------------------
1407 Update the pointers from the task list
1409 These are treated as weak pointers because we want to allow a main
1410 thread to get a BlockedOnDeadMVar exception in the same way as any
1411 other thread. Note that the threads should all have been retained
1412 by GC by virtue of being on the all_threads list, we're just
1413 updating pointers here.
1414 ------------------------------------------------------------------------- */
1417 update_task_list (void)
1421 for (task = all_tasks; task != NULL; task = task->all_link) {
1422 if (!task->stopped && task->tso) {
1423 ASSERT(task->tso->bound == task);
1424 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1426 barf("task %p: main thread %d has been GC'd",
1439 /* ----------------------------------------------------------------------------
1440 Reset the sizes of the older generations when we do a major
1443 CURRENT STRATEGY: make all generations except zero the same size.
1444 We have to stay within the maximum heap size, and leave a certain
1445 percentage of the maximum heap size available to allocate into.
1446 ------------------------------------------------------------------------- */
1449 resize_generations (void)
1453 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1454 nat live, size, min_alloc, words;
1455 nat max = RtsFlags.GcFlags.maxHeapSize;
1456 nat gens = RtsFlags.GcFlags.generations;
1458 // live in the oldest generations
1459 if (oldest_gen->steps[0].live_estimate != 0) {
1460 words = oldest_gen->steps[0].live_estimate;
1462 words = oldest_gen->steps[0].n_words;
1464 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1465 oldest_gen->steps[0].n_large_blocks;
1467 // default max size for all generations except zero
1468 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1469 RtsFlags.GcFlags.minOldGenSize);
1471 // minimum size for generation zero
1472 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1473 RtsFlags.GcFlags.minAllocAreaSize);
1475 // Auto-enable compaction when the residency reaches a
1476 // certain percentage of the maximum heap size (default: 30%).
1477 if (RtsFlags.GcFlags.generations > 1 &&
1478 (RtsFlags.GcFlags.compact ||
1480 oldest_gen->steps[0].n_blocks >
1481 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1482 oldest_gen->steps[0].mark = 1;
1483 oldest_gen->steps[0].compact = 1;
1484 // debugBelch("compaction: on\n", live);
1486 oldest_gen->steps[0].mark = 0;
1487 oldest_gen->steps[0].compact = 0;
1488 // debugBelch("compaction: off\n", live);
1491 if (RtsFlags.GcFlags.sweep) {
1492 oldest_gen->steps[0].mark = 1;
1495 // if we're going to go over the maximum heap size, reduce the
1496 // size of the generations accordingly. The calculation is
1497 // different if compaction is turned on, because we don't need
1498 // to double the space required to collect the old generation.
1501 // this test is necessary to ensure that the calculations
1502 // below don't have any negative results - we're working
1503 // with unsigned values here.
1504 if (max < min_alloc) {
1508 if (oldest_gen->steps[0].compact) {
1509 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1510 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1513 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1514 size = (max - min_alloc) / ((gens - 1) * 2);
1524 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1525 min_alloc, size, max);
1528 for (g = 0; g < gens; g++) {
1529 generations[g].max_blocks = size;
1534 /* -----------------------------------------------------------------------------
1535 Calculate the new size of the nursery, and resize it.
1536 -------------------------------------------------------------------------- */
1539 resize_nursery (void)
1541 if (RtsFlags.GcFlags.generations == 1)
1542 { // Two-space collector:
1545 /* set up a new nursery. Allocate a nursery size based on a
1546 * function of the amount of live data (by default a factor of 2)
1547 * Use the blocks from the old nursery if possible, freeing up any
1550 * If we get near the maximum heap size, then adjust our nursery
1551 * size accordingly. If the nursery is the same size as the live
1552 * data (L), then we need 3L bytes. We can reduce the size of the
1553 * nursery to bring the required memory down near 2L bytes.
1555 * A normal 2-space collector would need 4L bytes to give the same
1556 * performance we get from 3L bytes, reducing to the same
1557 * performance at 2L bytes.
1559 blocks = g0s0->n_blocks;
1561 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1562 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1563 RtsFlags.GcFlags.maxHeapSize )
1565 long adjusted_blocks; // signed on purpose
1568 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1570 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1571 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1573 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1574 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1578 blocks = adjusted_blocks;
1582 blocks *= RtsFlags.GcFlags.oldGenFactor;
1583 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1585 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1588 resizeNurseries(blocks);
1590 else // Generational collector
1593 * If the user has given us a suggested heap size, adjust our
1594 * allocation area to make best use of the memory available.
1596 if (RtsFlags.GcFlags.heapSizeSuggestion)
1599 nat needed = calcNeeded(); // approx blocks needed at next GC
1601 /* Guess how much will be live in generation 0 step 0 next time.
1602 * A good approximation is obtained by finding the
1603 * percentage of g0s0 that was live at the last minor GC.
1605 * We have an accurate figure for the amount of copied data in
1606 * 'copied', but we must convert this to a number of blocks, with
1607 * a small adjustment for estimated slop at the end of a block
1612 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1613 / countNurseryBlocks();
1616 /* Estimate a size for the allocation area based on the
1617 * information available. We might end up going slightly under
1618 * or over the suggested heap size, but we should be pretty
1621 * Formula: suggested - needed
1622 * ----------------------------
1623 * 1 + g0s0_pcnt_kept/100
1625 * where 'needed' is the amount of memory needed at the next
1626 * collection for collecting all steps except g0s0.
1629 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1630 (100 + (long)g0s0_pcnt_kept);
1632 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1633 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1636 resizeNurseries((nat)blocks);
1640 // we might have added extra large blocks to the nursery, so
1641 // resize back to minAllocAreaSize again.
1642 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1647 /* -----------------------------------------------------------------------------
1648 Sanity code for CAF garbage collection.
1650 With DEBUG turned on, we manage a CAF list in addition to the SRT
1651 mechanism. After GC, we run down the CAF list and blackhole any
1652 CAFs which have been garbage collected. This means we get an error
1653 whenever the program tries to enter a garbage collected CAF.
1655 Any garbage collected CAFs are taken off the CAF list at the same
1657 -------------------------------------------------------------------------- */
1659 #if 0 && defined(DEBUG)
1666 const StgInfoTable *info;
1677 ASSERT(info->type == IND_STATIC);
1679 if (STATIC_LINK(info,p) == NULL) {
1680 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1682 SET_INFO(p,&stg_BLACKHOLE_info);
1683 p = STATIC_LINK2(info,p);
1687 pp = &STATIC_LINK2(info,p);
1694 debugTrace(DEBUG_gccafs, "%d CAFs live", i);