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 // Update pointers from capabilities (probably just the spark queues)
385 updateCapabilitiesPostGC();
387 // Now see which stable names are still alive.
391 // We call processHeapClosureForDead() on every closure destroyed during
392 // the current garbage collection, so we invoke LdvCensusForDead().
393 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
394 || RtsFlags.ProfFlags.bioSelector != NULL)
398 // NO MORE EVACUATION AFTER THIS POINT!
400 // Two-space collector: free the old to-space.
401 // g0s0->old_blocks is the old nursery
402 // g0s0->blocks is to-space from the previous GC
403 if (RtsFlags.GcFlags.generations == 1) {
404 if (g0s0->blocks != NULL) {
405 freeChain(g0s0->blocks);
410 // For each workspace, in each thread, move the copied blocks to the step
416 for (t = 0; t < n_gc_threads; t++) {
420 if (RtsFlags.GcFlags.generations == 1) {
425 for (; s < total_steps; s++) {
428 // Push the final block
430 push_scanned_block(ws->todo_bd, ws);
433 ASSERT(gct->scan_bd == NULL);
434 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
437 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
438 ws->step->n_words += bd->free - bd->start;
442 prev->link = ws->step->blocks;
443 ws->step->blocks = ws->scavd_list;
445 ws->step->n_blocks += ws->n_scavd_blocks;
449 // Add all the partial blocks *after* we've added all the full
450 // blocks. This is so that we can grab the partial blocks back
451 // again and try to fill them up in the next GC.
452 for (t = 0; t < n_gc_threads; t++) {
456 if (RtsFlags.GcFlags.generations == 1) {
461 for (; s < total_steps; s++) {
465 for (bd = ws->part_list; bd != NULL; bd = next) {
467 if (bd->free == bd->start) {
469 ws->part_list = next;
476 ws->step->n_words += bd->free - bd->start;
481 prev->link = ws->step->blocks;
482 ws->step->blocks = ws->part_list;
484 ws->step->n_blocks += ws->n_part_blocks;
486 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
487 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
492 // Finally: compact or sweep the oldest generation.
493 if (major_gc && oldest_gen->steps[0].mark) {
494 if (oldest_gen->steps[0].compact)
495 compact(gct->scavenged_static_objects);
497 sweep(&oldest_gen->steps[0]);
500 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
502 /* run through all the generations/steps and tidy up
509 for (i=0; i < n_gc_threads; i++) {
510 if (n_gc_threads > 1) {
511 trace(TRACE_gc,"thread %d:", i);
512 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
513 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
514 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
515 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
516 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
518 copied += gc_threads[i]->copied;
519 max_copied = stg_max(gc_threads[i]->copied, max_copied);
521 if (n_gc_threads == 1) {
529 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
532 generations[g].collections++; // for stats
533 if (n_gc_threads > 1) generations[g].par_collections++;
536 // Count the mutable list as bytes "copied" for the purposes of
537 // stats. Every mutable list is copied during every GC.
539 nat mut_list_size = 0;
540 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
541 mut_list_size += bd->free - bd->start;
543 copied += mut_list_size;
546 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
547 (unsigned long)(mut_list_size * sizeof(W_)),
548 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
551 for (s = 0; s < generations[g].n_steps; s++) {
553 stp = &generations[g].steps[s];
555 // for generations we collected...
558 /* free old memory and shift to-space into from-space for all
559 * the collected steps (except the allocation area). These
560 * freed blocks will probaby be quickly recycled.
562 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
565 // tack the new blocks on the end of the existing blocks
566 if (stp->old_blocks != NULL) {
569 for (bd = stp->old_blocks; bd != NULL; bd = next) {
573 if (!(bd->flags & BF_MARKED))
576 stp->old_blocks = next;
585 stp->n_words += bd->free - bd->start;
587 // NB. this step might not be compacted next
588 // time, so reset the BF_MARKED flags.
589 // They are set before GC if we're going to
590 // compact. (search for BF_MARKED above).
591 bd->flags &= ~BF_MARKED;
593 // between GCs, all blocks in the heap except
594 // for the nursery have the BF_EVACUATED flag set.
595 bd->flags |= BF_EVACUATED;
602 prev->link = stp->blocks;
603 stp->blocks = stp->old_blocks;
606 // add the new blocks to the block tally
607 stp->n_blocks += stp->n_old_blocks;
608 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
609 ASSERT(countOccupied(stp->blocks) == stp->n_words);
613 freeChain(stp->old_blocks);
615 stp->old_blocks = NULL;
616 stp->n_old_blocks = 0;
619 /* LARGE OBJECTS. The current live large objects are chained on
620 * scavenged_large, having been moved during garbage
621 * collection from large_objects. Any objects left on
622 * large_objects list are therefore dead, so we free them here.
624 for (bd = stp->large_objects; bd != NULL; bd = next) {
630 stp->large_objects = stp->scavenged_large_objects;
631 stp->n_large_blocks = stp->n_scavenged_large_blocks;
634 else // for older generations...
636 /* For older generations, we need to append the
637 * scavenged_large_object list (i.e. large objects that have been
638 * promoted during this GC) to the large_object list for that step.
640 for (bd = stp->scavenged_large_objects; bd; bd = next) {
642 dbl_link_onto(bd, &stp->large_objects);
645 // add the new blocks we promoted during this GC
646 stp->n_large_blocks += stp->n_scavenged_large_blocks;
651 // update the max size of older generations after a major GC
652 resize_generations();
654 // Calculate the amount of live data for stats.
655 live = calcLiveWords();
657 // Free the small objects allocated via allocate(), since this will
658 // all have been copied into G0S1 now.
659 if (RtsFlags.GcFlags.generations > 1) {
660 if (g0s0->blocks != NULL) {
661 freeChain(g0s0->blocks);
668 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
670 // Start a new pinned_object_block
671 pinned_object_block = NULL;
673 // Free the mark stack.
674 if (mark_stack_bdescr != NULL) {
675 freeGroup(mark_stack_bdescr);
679 for (g = 0; g <= N; g++) {
680 for (s = 0; s < generations[g].n_steps; s++) {
681 stp = &generations[g].steps[s];
682 if (stp->bitmap != NULL) {
683 freeGroup(stp->bitmap);
691 // mark the garbage collected CAFs as dead
692 #if 0 && defined(DEBUG) // doesn't work at the moment
693 if (major_gc) { gcCAFs(); }
697 // resetStaticObjectForRetainerProfiling() must be called before
699 if (n_gc_threads > 1) {
700 barf("profiling is currently broken with multi-threaded GC");
701 // ToDo: fix the gct->scavenged_static_objects below
703 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
706 // zero the scavenged static object list
709 for (i = 0; i < n_gc_threads; i++) {
710 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
717 // start any pending finalizers
719 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
722 // send exceptions to any threads which were about to die
724 resurrectThreads(resurrected_threads);
725 performPendingThrowTos(exception_threads);
728 // Update the stable pointer hash table.
729 updateStablePtrTable(major_gc);
731 // check sanity after GC
732 IF_DEBUG(sanity, checkSanity());
734 // extra GC trace info
735 if (traceClass(TRACE_gc|DEBUG_gc)) statDescribeGens();
738 // symbol-table based profiling
739 /* heapCensus(to_blocks); */ /* ToDo */
742 // restore enclosing cost centre
748 // check for memory leaks if DEBUG is on
749 memInventory(traceClass(DEBUG_gc));
752 #ifdef RTS_GTK_FRONTPANEL
753 if (RtsFlags.GcFlags.frontpanel) {
754 updateFrontPanelAfterGC( N, live );
758 // ok, GC over: tell the stats department what happened.
759 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
760 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
762 #if defined(RTS_USER_SIGNALS)
763 if (RtsFlags.MiscFlags.install_signal_handlers) {
764 // unblock signals again
765 unblockUserSignals();
774 /* -----------------------------------------------------------------------------
775 Figure out which generation to collect, initialise N and major_gc.
777 Also returns the total number of blocks in generations that will be
779 -------------------------------------------------------------------------- */
782 initialise_N (rtsBool force_major_gc)
785 nat s, blocks, blocks_total;
790 if (force_major_gc) {
791 N = RtsFlags.GcFlags.generations - 1;
796 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
798 for (s = 0; s < generations[g].n_steps; s++) {
799 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
800 blocks += generations[g].steps[s].n_large_blocks;
802 if (blocks >= generations[g].max_blocks) {
806 blocks_total += blocks;
810 blocks_total += countNurseryBlocks();
812 major_gc = (N == RtsFlags.GcFlags.generations-1);
816 /* -----------------------------------------------------------------------------
817 Initialise the gc_thread structures.
818 -------------------------------------------------------------------------- */
821 alloc_gc_thread (int n)
827 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
832 initCondition(&t->wake_cond);
833 initMutex(&t->wake_mutex);
834 t->wakeup = rtsTrue; // starts true, so we can wait for the
835 // thread to start up, see wakeup_gc_threads
840 t->free_blocks = NULL;
849 for (s = 0; s < total_steps; s++)
852 ws->step = &all_steps[s];
853 ASSERT(s == ws->step->abs_no);
857 ws->buffer_todo_bd = NULL;
859 ws->part_list = NULL;
860 ws->n_part_blocks = 0;
862 ws->scavd_list = NULL;
863 ws->n_scavd_blocks = 0;
871 alloc_gc_threads (void)
873 if (gc_threads == NULL) {
874 #if defined(THREADED_RTS)
876 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
880 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
881 gc_threads[i] = alloc_gc_thread(i);
884 gc_threads = stgMallocBytes (sizeof(gc_thread*),
887 gc_threads[0] = alloc_gc_thread(0);
892 /* ----------------------------------------------------------------------------
894 ------------------------------------------------------------------------- */
896 static nat gc_running_threads;
898 #if defined(THREADED_RTS)
899 static Mutex gc_running_mutex;
906 ACQUIRE_LOCK(&gc_running_mutex);
907 n_running = ++gc_running_threads;
908 RELEASE_LOCK(&gc_running_mutex);
909 ASSERT(n_running <= n_gc_threads);
917 ACQUIRE_LOCK(&gc_running_mutex);
918 ASSERT(n_gc_threads != 0);
919 n_running = --gc_running_threads;
920 RELEASE_LOCK(&gc_running_mutex);
934 // scavenge objects in compacted generation
935 if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
936 (mark_stack_bdescr != NULL && !mark_stack_empty())) {
940 // Check for global work in any step. We don't need to check for
941 // local work, because we have already exited scavenge_loop(),
942 // which means there is no local work for this thread.
943 for (s = total_steps-1; s >= 0; s--) {
944 if (s == 0 && RtsFlags.GcFlags.generations > 1) {
948 if (ws->todo_large_objects) return rtsTrue;
949 if (ws->step->todos) return rtsTrue;
958 scavenge_until_all_done (void)
962 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
965 #if defined(THREADED_RTS)
966 if (n_gc_threads > 1) {
975 // scavenge_loop() only exits when there's no work to do
978 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
979 gct->thread_index, r);
981 while (gc_running_threads != 0) {
987 // any_work() does not remove the work from the queue, it
988 // just checks for the presence of work. If we find any,
989 // then we increment gc_running_threads and go back to
990 // scavenge_loop() to perform any pending work.
993 // All threads are now stopped
994 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
997 #if defined(THREADED_RTS)
999 // gc_thread_work(): Scavenge until there's no work left to do and all
1000 // the running threads are idle.
1003 gc_thread_work (void)
1005 // gc_running_threads has already been incremented for us; this is
1006 // a worker thread and the main thread bumped gc_running_threads
1007 // before waking us up.
1009 // Every thread evacuates some roots.
1011 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
1013 scavenge_until_all_done();
1018 gc_thread_mainloop (void)
1020 while (!gct->exit) {
1022 // Wait until we're told to wake up
1023 ACQUIRE_LOCK(&gct->wake_mutex);
1024 gct->wakeup = rtsFalse;
1025 while (!gct->wakeup) {
1026 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1028 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1030 RELEASE_LOCK(&gct->wake_mutex);
1031 if (gct->exit) break;
1034 // start performance counters in this thread...
1035 if (gct->papi_events == -1) {
1036 papi_init_eventset(&gct->papi_events);
1038 papi_thread_start_gc1_count(gct->papi_events);
1044 // count events in this thread towards the GC totals
1045 papi_thread_stop_gc1_count(gct->papi_events);
1051 #if defined(THREADED_RTS)
1053 gc_thread_entry (gc_thread *my_gct)
1056 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1057 gct->id = osThreadId();
1058 gc_thread_mainloop();
1063 start_gc_threads (void)
1065 #if defined(THREADED_RTS)
1068 static rtsBool done = rtsFalse;
1070 gc_running_threads = 0;
1071 initMutex(&gc_running_mutex);
1074 // Start from 1: the main thread is 0
1075 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1076 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1085 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1087 #if defined(THREADED_RTS)
1089 for (i=1; i < n_threads; i++) {
1091 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1093 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1094 if (gc_threads[i]->wakeup) {
1095 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1101 gc_threads[i]->wakeup = rtsTrue;
1102 signalCondition(&gc_threads[i]->wake_cond);
1103 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1108 // After GC is complete, we must wait for all GC threads to enter the
1109 // standby state, otherwise they may still be executing inside
1110 // any_work(), and may even remain awake until the next GC starts.
1112 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1114 #if defined(THREADED_RTS)
1117 for (i=1; i < n_threads; i++) {
1119 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1120 wakeup = gc_threads[i]->wakeup;
1121 // wakeup is false while the thread is waiting
1122 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1128 /* ----------------------------------------------------------------------------
1129 Initialise a generation that is to be collected
1130 ------------------------------------------------------------------------- */
1133 init_collected_gen (nat g, nat n_threads)
1140 // Throw away the current mutable list. Invariant: the mutable
1141 // list always has at least one block; this means we can avoid a
1142 // check for NULL in recordMutable().
1144 freeChain(generations[g].mut_list);
1145 generations[g].mut_list = allocBlock();
1146 for (i = 0; i < n_capabilities; i++) {
1147 freeChain(capabilities[i].mut_lists[g]);
1148 capabilities[i].mut_lists[g] = allocBlock();
1152 for (s = 0; s < generations[g].n_steps; s++) {
1154 stp = &generations[g].steps[s];
1155 ASSERT(stp->gen_no == g);
1157 // we'll construct a new list of threads in this step
1158 // during GC, throw away the current list.
1159 stp->old_threads = stp->threads;
1160 stp->threads = END_TSO_QUEUE;
1162 // generation 0, step 0 doesn't need to-space
1163 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1167 // deprecate the existing blocks
1168 stp->old_blocks = stp->blocks;
1169 stp->n_old_blocks = stp->n_blocks;
1173 stp->live_estimate = 0;
1175 // we don't have any to-be-scavenged blocks yet
1177 stp->todos_last = NULL;
1180 // initialise the large object queues.
1181 stp->scavenged_large_objects = NULL;
1182 stp->n_scavenged_large_blocks = 0;
1184 // mark the small objects as from-space
1185 for (bd = stp->old_blocks; bd; bd = bd->link) {
1186 bd->flags &= ~BF_EVACUATED;
1189 // mark the large objects as from-space
1190 for (bd = stp->large_objects; bd; bd = bd->link) {
1191 bd->flags &= ~BF_EVACUATED;
1194 // for a compacted step, we need to allocate the bitmap
1196 nat bitmap_size; // in bytes
1197 bdescr *bitmap_bdescr;
1200 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1202 if (bitmap_size > 0) {
1203 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1205 stp->bitmap = bitmap_bdescr;
1206 bitmap = bitmap_bdescr->start;
1208 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1209 bitmap_size, bitmap);
1211 // don't forget to fill it with zeros!
1212 memset(bitmap, 0, bitmap_size);
1214 // For each block in this step, point to its bitmap from the
1215 // block descriptor.
1216 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1217 bd->u.bitmap = bitmap;
1218 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1220 // Also at this point we set the BF_MARKED flag
1221 // for this block. The invariant is that
1222 // BF_MARKED is always unset, except during GC
1223 // when it is set on those blocks which will be
1225 if (!(bd->flags & BF_FRAGMENTED)) {
1226 bd->flags |= BF_MARKED;
1233 // For each GC thread, for each step, allocate a "todo" block to
1234 // store evacuated objects to be scavenged, and a block to store
1235 // evacuated objects that do not need to be scavenged.
1236 for (t = 0; t < n_threads; t++) {
1237 for (s = 0; s < generations[g].n_steps; s++) {
1239 // we don't copy objects into g0s0, unless -G0
1240 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1242 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1244 ws->todo_large_objects = NULL;
1246 ws->part_list = NULL;
1247 ws->n_part_blocks = 0;
1249 // allocate the first to-space block; extra blocks will be
1250 // chained on as necessary.
1252 ws->buffer_todo_bd = NULL;
1253 alloc_todo_block(ws,0);
1255 ws->scavd_list = NULL;
1256 ws->n_scavd_blocks = 0;
1262 /* ----------------------------------------------------------------------------
1263 Initialise a generation that is *not* to be collected
1264 ------------------------------------------------------------------------- */
1267 init_uncollected_gen (nat g, nat threads)
1274 for (s = 0; s < generations[g].n_steps; s++) {
1275 stp = &generations[g].steps[s];
1276 stp->scavenged_large_objects = NULL;
1277 stp->n_scavenged_large_blocks = 0;
1280 for (s = 0; s < generations[g].n_steps; s++) {
1282 stp = &generations[g].steps[s];
1284 for (t = 0; t < threads; t++) {
1285 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1287 ws->buffer_todo_bd = NULL;
1288 ws->todo_large_objects = NULL;
1290 ws->part_list = NULL;
1291 ws->n_part_blocks = 0;
1293 ws->scavd_list = NULL;
1294 ws->n_scavd_blocks = 0;
1296 // If the block at the head of the list in this generation
1297 // is less than 3/4 full, then use it as a todo block.
1298 if (stp->blocks && isPartiallyFull(stp->blocks))
1300 ws->todo_bd = stp->blocks;
1301 ws->todo_free = ws->todo_bd->free;
1302 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1303 stp->blocks = stp->blocks->link;
1305 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1306 ws->todo_bd->link = NULL;
1307 // we must scan from the current end point.
1308 ws->todo_bd->u.scan = ws->todo_bd->free;
1313 alloc_todo_block(ws,0);
1317 // deal out any more partial blocks to the threads' part_lists
1319 while (stp->blocks && isPartiallyFull(stp->blocks))
1322 stp->blocks = bd->link;
1323 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1324 bd->link = ws->part_list;
1326 ws->n_part_blocks += 1;
1327 bd->u.scan = bd->free;
1329 stp->n_words -= bd->free - bd->start;
1331 if (t == n_gc_threads) t = 0;
1336 // Move the private mutable lists from each capability onto the
1337 // main mutable list for the generation.
1338 for (i = 0; i < n_capabilities; i++) {
1339 for (bd = capabilities[i].mut_lists[g];
1340 bd->link != NULL; bd = bd->link) {
1343 bd->link = generations[g].mut_list;
1344 generations[g].mut_list = capabilities[i].mut_lists[g];
1345 capabilities[i].mut_lists[g] = allocBlock();
1349 /* -----------------------------------------------------------------------------
1350 Initialise a gc_thread before GC
1351 -------------------------------------------------------------------------- */
1354 init_gc_thread (gc_thread *t)
1356 t->static_objects = END_OF_STATIC_LIST;
1357 t->scavenged_static_objects = END_OF_STATIC_LIST;
1360 t->failed_to_evac = rtsFalse;
1361 t->eager_promotion = rtsTrue;
1362 t->thunk_selector_depth = 0;
1367 t->scav_find_work = 0;
1370 /* -----------------------------------------------------------------------------
1371 Function we pass to evacuate roots.
1372 -------------------------------------------------------------------------- */
1375 mark_root(void *user, StgClosure **root)
1377 // we stole a register for gct, but this function is called from
1378 // *outside* the GC where the register variable is not in effect,
1379 // so we need to save and restore it here. NB. only call
1380 // mark_root() from the main GC thread, otherwise gct will be
1382 gc_thread *saved_gct;
1391 /* -----------------------------------------------------------------------------
1392 Initialising the static object & mutable lists
1393 -------------------------------------------------------------------------- */
1396 zero_static_object_list(StgClosure* first_static)
1400 const StgInfoTable *info;
1402 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1404 link = *STATIC_LINK(info, p);
1405 *STATIC_LINK(info,p) = NULL;
1409 /* ----------------------------------------------------------------------------
1410 Update the pointers from the task list
1412 These are treated as weak pointers because we want to allow a main
1413 thread to get a BlockedOnDeadMVar exception in the same way as any
1414 other thread. Note that the threads should all have been retained
1415 by GC by virtue of being on the all_threads list, we're just
1416 updating pointers here.
1417 ------------------------------------------------------------------------- */
1420 update_task_list (void)
1424 for (task = all_tasks; task != NULL; task = task->all_link) {
1425 if (!task->stopped && task->tso) {
1426 ASSERT(task->tso->bound == task);
1427 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1429 barf("task %p: main thread %d has been GC'd",
1442 /* ----------------------------------------------------------------------------
1443 Reset the sizes of the older generations when we do a major
1446 CURRENT STRATEGY: make all generations except zero the same size.
1447 We have to stay within the maximum heap size, and leave a certain
1448 percentage of the maximum heap size available to allocate into.
1449 ------------------------------------------------------------------------- */
1452 resize_generations (void)
1456 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1457 nat live, size, min_alloc, words;
1458 nat max = RtsFlags.GcFlags.maxHeapSize;
1459 nat gens = RtsFlags.GcFlags.generations;
1461 // live in the oldest generations
1462 if (oldest_gen->steps[0].live_estimate != 0) {
1463 words = oldest_gen->steps[0].live_estimate;
1465 words = oldest_gen->steps[0].n_words;
1467 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1468 oldest_gen->steps[0].n_large_blocks;
1470 // default max size for all generations except zero
1471 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1472 RtsFlags.GcFlags.minOldGenSize);
1474 // minimum size for generation zero
1475 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1476 RtsFlags.GcFlags.minAllocAreaSize);
1478 // Auto-enable compaction when the residency reaches a
1479 // certain percentage of the maximum heap size (default: 30%).
1480 if (RtsFlags.GcFlags.generations > 1 &&
1481 (RtsFlags.GcFlags.compact ||
1483 oldest_gen->steps[0].n_blocks >
1484 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1485 oldest_gen->steps[0].mark = 1;
1486 oldest_gen->steps[0].compact = 1;
1487 // debugBelch("compaction: on\n", live);
1489 oldest_gen->steps[0].mark = 0;
1490 oldest_gen->steps[0].compact = 0;
1491 // debugBelch("compaction: off\n", live);
1494 if (RtsFlags.GcFlags.sweep) {
1495 oldest_gen->steps[0].mark = 1;
1498 // if we're going to go over the maximum heap size, reduce the
1499 // size of the generations accordingly. The calculation is
1500 // different if compaction is turned on, because we don't need
1501 // to double the space required to collect the old generation.
1504 // this test is necessary to ensure that the calculations
1505 // below don't have any negative results - we're working
1506 // with unsigned values here.
1507 if (max < min_alloc) {
1511 if (oldest_gen->steps[0].compact) {
1512 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1513 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1516 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1517 size = (max - min_alloc) / ((gens - 1) * 2);
1527 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1528 min_alloc, size, max);
1531 for (g = 0; g < gens; g++) {
1532 generations[g].max_blocks = size;
1537 /* -----------------------------------------------------------------------------
1538 Calculate the new size of the nursery, and resize it.
1539 -------------------------------------------------------------------------- */
1542 resize_nursery (void)
1544 if (RtsFlags.GcFlags.generations == 1)
1545 { // Two-space collector:
1548 /* set up a new nursery. Allocate a nursery size based on a
1549 * function of the amount of live data (by default a factor of 2)
1550 * Use the blocks from the old nursery if possible, freeing up any
1553 * If we get near the maximum heap size, then adjust our nursery
1554 * size accordingly. If the nursery is the same size as the live
1555 * data (L), then we need 3L bytes. We can reduce the size of the
1556 * nursery to bring the required memory down near 2L bytes.
1558 * A normal 2-space collector would need 4L bytes to give the same
1559 * performance we get from 3L bytes, reducing to the same
1560 * performance at 2L bytes.
1562 blocks = g0s0->n_blocks;
1564 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1565 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1566 RtsFlags.GcFlags.maxHeapSize )
1568 long adjusted_blocks; // signed on purpose
1571 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1573 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1574 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1576 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1577 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1581 blocks = adjusted_blocks;
1585 blocks *= RtsFlags.GcFlags.oldGenFactor;
1586 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1588 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1591 resizeNurseries(blocks);
1593 else // Generational collector
1596 * If the user has given us a suggested heap size, adjust our
1597 * allocation area to make best use of the memory available.
1599 if (RtsFlags.GcFlags.heapSizeSuggestion)
1602 nat needed = calcNeeded(); // approx blocks needed at next GC
1604 /* Guess how much will be live in generation 0 step 0 next time.
1605 * A good approximation is obtained by finding the
1606 * percentage of g0s0 that was live at the last minor GC.
1608 * We have an accurate figure for the amount of copied data in
1609 * 'copied', but we must convert this to a number of blocks, with
1610 * a small adjustment for estimated slop at the end of a block
1615 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1616 / countNurseryBlocks();
1619 /* Estimate a size for the allocation area based on the
1620 * information available. We might end up going slightly under
1621 * or over the suggested heap size, but we should be pretty
1624 * Formula: suggested - needed
1625 * ----------------------------
1626 * 1 + g0s0_pcnt_kept/100
1628 * where 'needed' is the amount of memory needed at the next
1629 * collection for collecting all steps except g0s0.
1632 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1633 (100 + (long)g0s0_pcnt_kept);
1635 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1636 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1639 resizeNurseries((nat)blocks);
1643 // we might have added extra large blocks to the nursery, so
1644 // resize back to minAllocAreaSize again.
1645 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1650 /* -----------------------------------------------------------------------------
1651 Sanity code for CAF garbage collection.
1653 With DEBUG turned on, we manage a CAF list in addition to the SRT
1654 mechanism. After GC, we run down the CAF list and blackhole any
1655 CAFs which have been garbage collected. This means we get an error
1656 whenever the program tries to enter a garbage collected CAF.
1658 Any garbage collected CAFs are taken off the CAF list at the same
1660 -------------------------------------------------------------------------- */
1662 #if 0 && defined(DEBUG)
1669 const StgInfoTable *info;
1680 ASSERT(info->type == IND_STATIC);
1682 if (STATIC_LINK(info,p) == NULL) {
1683 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1685 SET_INFO(p,&stg_BLACKHOLE_info);
1686 p = STATIC_LINK2(info,p);
1690 pp = &STATIC_LINK2(info,p);
1697 debugTrace(DEBUG_gccafs, "%d CAFs live", i);