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"
53 #include <string.h> // for memset()
56 /* -----------------------------------------------------------------------------
58 -------------------------------------------------------------------------- */
60 /* STATIC OBJECT LIST.
63 * We maintain a linked list of static objects that are still live.
64 * The requirements for this list are:
66 * - we need to scan the list while adding to it, in order to
67 * scavenge all the static objects (in the same way that
68 * breadth-first scavenging works for dynamic objects).
70 * - we need to be able to tell whether an object is already on
71 * the list, to break loops.
73 * Each static object has a "static link field", which we use for
74 * linking objects on to the list. We use a stack-type list, consing
75 * objects on the front as they are added (this means that the
76 * scavenge phase is depth-first, not breadth-first, but that
79 * A separate list is kept for objects that have been scavenged
80 * already - this is so that we can zero all the marks afterwards.
82 * An object is on the list if its static link field is non-zero; this
83 * means that we have to mark the end of the list with '1', not NULL.
85 * Extra notes for generational GC:
87 * Each generation has a static object list associated with it. When
88 * collecting generations up to N, we treat the static object lists
89 * from generations > N as roots.
91 * We build up a static object list while collecting generations 0..N,
92 * which is then appended to the static object list of generation N+1.
95 /* N is the oldest generation being collected, where the generations
96 * are numbered starting at 0. A major GC (indicated by the major_gc
97 * flag) is when we're collecting all generations. We only attempt to
98 * deal with static objects and GC CAFs when doing a major GC.
103 /* Data used for allocation area sizing.
105 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
115 /* Thread-local data for each GC thread
117 gc_thread **gc_threads = NULL;
118 // gc_thread *gct = NULL; // this thread's gct TODO: make thread-local
120 // Number of threads running in *this* GC. Affects how many
121 // step->todos[] lists we have to look in to find work.
125 long copied; // *words* copied & scavenged during this GC
128 SpinLock recordMutableGen_sync;
133 /* -----------------------------------------------------------------------------
134 Static function declarations
135 -------------------------------------------------------------------------- */
137 static void mark_root (void *user, StgClosure **root);
138 static void zero_static_object_list (StgClosure* first_static);
139 static nat initialise_N (rtsBool force_major_gc);
140 static void alloc_gc_threads (void);
141 static void init_collected_gen (nat g, nat threads);
142 static void init_uncollected_gen (nat g, nat threads);
143 static void init_gc_thread (gc_thread *t);
144 static void update_task_list (void);
145 static void resize_generations (void);
146 static void resize_nursery (void);
147 static void start_gc_threads (void);
148 static void scavenge_until_all_done (void);
149 static nat inc_running (void);
150 static nat dec_running (void);
151 static void wakeup_gc_threads (nat n_threads);
152 static void shutdown_gc_threads (nat n_threads);
154 #if 0 && defined(DEBUG)
155 static void gcCAFs (void);
158 /* -----------------------------------------------------------------------------
159 The mark bitmap & stack.
160 -------------------------------------------------------------------------- */
162 #define MARK_STACK_BLOCKS 4
164 bdescr *mark_stack_bdescr;
169 // Flag and pointers used for falling back to a linear scan when the
170 // mark stack overflows.
171 rtsBool mark_stack_overflowed;
172 bdescr *oldgen_scan_bd;
175 /* -----------------------------------------------------------------------------
176 GarbageCollect: the main entry point to the garbage collector.
178 Locks held: all capabilities are held throughout GarbageCollect().
179 -------------------------------------------------------------------------- */
182 GarbageCollect ( rtsBool force_major_gc )
186 lnat live, allocated, max_copied, avg_copied, slop;
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 // Update pointers from capabilities (probably just the spark queues)
381 updateCapabilitiesPostGC();
383 // Now see which stable names are still alive.
387 // We call processHeapClosureForDead() on every closure destroyed during
388 // the current garbage collection, so we invoke LdvCensusForDead().
389 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
390 || RtsFlags.ProfFlags.bioSelector != NULL)
394 // NO MORE EVACUATION AFTER THIS POINT!
396 // Two-space collector: free the old to-space.
397 // g0s0->old_blocks is the old nursery
398 // g0s0->blocks is to-space from the previous GC
399 if (RtsFlags.GcFlags.generations == 1) {
400 if (g0s0->blocks != NULL) {
401 freeChain(g0s0->blocks);
406 // For each workspace, in each thread, move the copied blocks to the step
412 for (t = 0; t < n_gc_threads; t++) {
416 if (RtsFlags.GcFlags.generations == 1) {
421 for (; s < total_steps; s++) {
424 // Push the final block
426 push_scanned_block(ws->todo_bd, ws);
429 ASSERT(gct->scan_bd == NULL);
430 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
433 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
434 ws->step->n_words += bd->free - bd->start;
438 prev->link = ws->step->blocks;
439 ws->step->blocks = ws->scavd_list;
441 ws->step->n_blocks += ws->n_scavd_blocks;
445 // Add all the partial blocks *after* we've added all the full
446 // blocks. This is so that we can grab the partial blocks back
447 // again and try to fill them up in the next GC.
448 for (t = 0; t < n_gc_threads; t++) {
452 if (RtsFlags.GcFlags.generations == 1) {
457 for (; s < total_steps; s++) {
461 for (bd = ws->part_list; bd != NULL; bd = next) {
463 if (bd->free == bd->start) {
465 ws->part_list = next;
472 ws->step->n_words += bd->free - bd->start;
477 prev->link = ws->step->blocks;
478 ws->step->blocks = ws->part_list;
480 ws->step->n_blocks += ws->n_part_blocks;
482 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
483 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
488 // Finally: compaction of the oldest generation.
489 if (major_gc && oldest_gen->steps[0].is_compacted) {
490 compact(gct->scavenged_static_objects);
493 IF_DEBUG(sanity, checkGlobalTSOList(rtsFalse));
495 /* run through all the generations/steps and tidy up
502 for (i=0; i < n_gc_threads; i++) {
503 if (n_gc_threads > 1) {
504 trace(TRACE_gc,"thread %d:", i);
505 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
506 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
507 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
508 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
509 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
511 copied += gc_threads[i]->copied;
512 max_copied = stg_max(gc_threads[i]->copied, max_copied);
514 if (n_gc_threads == 1) {
522 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
525 generations[g].collections++; // for stats
526 if (n_gc_threads > 1) generations[g].par_collections++;
529 // Count the mutable list as bytes "copied" for the purposes of
530 // stats. Every mutable list is copied during every GC.
532 nat mut_list_size = 0;
533 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
534 mut_list_size += bd->free - bd->start;
536 copied += mut_list_size;
539 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
540 (unsigned long)(mut_list_size * sizeof(W_)),
541 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
544 for (s = 0; s < generations[g].n_steps; s++) {
546 stp = &generations[g].steps[s];
548 // for generations we collected...
551 /* free old memory and shift to-space into from-space for all
552 * the collected steps (except the allocation area). These
553 * freed blocks will probaby be quickly recycled.
555 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
556 if (stp->is_compacted)
558 // tack the new blocks on the end of the existing blocks
559 if (stp->old_blocks != NULL) {
560 for (bd = stp->old_blocks; bd != NULL; bd = next) {
561 stp->n_words += bd->free - bd->start;
563 // NB. this step might not be compacted next
564 // time, so reset the BF_COMPACTED flags.
565 // They are set before GC if we're going to
566 // compact. (search for BF_COMPACTED above).
567 bd->flags &= ~BF_COMPACTED;
569 // between GCs, all blocks in the heap except
570 // for the nursery have the BF_EVACUATED flag set.
571 bd->flags |= BF_EVACUATED;
575 bd->link = stp->blocks;
578 stp->blocks = stp->old_blocks;
580 // add the new blocks to the block tally
581 stp->n_blocks += stp->n_old_blocks;
582 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
583 ASSERT(countOccupied(stp->blocks) == stp->n_words);
587 freeChain(stp->old_blocks);
589 stp->old_blocks = NULL;
590 stp->n_old_blocks = 0;
593 /* LARGE OBJECTS. The current live large objects are chained on
594 * scavenged_large, having been moved during garbage
595 * collection from large_objects. Any objects left on
596 * large_objects list are therefore dead, so we free them here.
598 for (bd = stp->large_objects; bd != NULL; bd = next) {
604 stp->large_objects = stp->scavenged_large_objects;
605 stp->n_large_blocks = stp->n_scavenged_large_blocks;
608 else // for older generations...
610 /* For older generations, we need to append the
611 * scavenged_large_object list (i.e. large objects that have been
612 * promoted during this GC) to the large_object list for that step.
614 for (bd = stp->scavenged_large_objects; bd; bd = next) {
616 dbl_link_onto(bd, &stp->large_objects);
619 // add the new blocks we promoted during this GC
620 stp->n_large_blocks += stp->n_scavenged_large_blocks;
625 // update the max size of older generations after a major GC
626 resize_generations();
628 // Calculate the amount of live data for stats.
629 live = calcLiveWords();
631 // Free the small objects allocated via allocate(), since this will
632 // all have been copied into G0S1 now.
633 if (RtsFlags.GcFlags.generations > 1) {
634 if (g0s0->blocks != NULL) {
635 freeChain(g0s0->blocks);
642 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
644 // Start a new pinned_object_block
645 pinned_object_block = NULL;
647 // Free the mark stack.
648 if (mark_stack_bdescr != NULL) {
649 freeGroup(mark_stack_bdescr);
653 for (g = 0; g <= N; g++) {
654 for (s = 0; s < generations[g].n_steps; s++) {
655 stp = &generations[g].steps[s];
656 if (stp->bitmap != NULL) {
657 freeGroup(stp->bitmap);
665 // mark the garbage collected CAFs as dead
666 #if 0 && defined(DEBUG) // doesn't work at the moment
667 if (major_gc) { gcCAFs(); }
671 // resetStaticObjectForRetainerProfiling() must be called before
673 if (n_gc_threads > 1) {
674 barf("profiling is currently broken with multi-threaded GC");
675 // ToDo: fix the gct->scavenged_static_objects below
677 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
680 // zero the scavenged static object list
683 for (i = 0; i < n_gc_threads; i++) {
684 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
691 // start any pending finalizers
693 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
696 // send exceptions to any threads which were about to die
698 resurrectThreads(resurrected_threads);
699 performPendingThrowTos(exception_threads);
702 // Update the stable pointer hash table.
703 updateStablePtrTable(major_gc);
705 // check sanity after GC
706 IF_DEBUG(sanity, checkSanity());
708 // extra GC trace info
709 if (traceClass(TRACE_gc|DEBUG_gc)) statDescribeGens();
712 // symbol-table based profiling
713 /* heapCensus(to_blocks); */ /* ToDo */
716 // restore enclosing cost centre
722 // check for memory leaks if DEBUG is on
723 memInventory(traceClass(DEBUG_gc));
726 #ifdef RTS_GTK_FRONTPANEL
727 if (RtsFlags.GcFlags.frontpanel) {
728 updateFrontPanelAfterGC( N, live );
732 // ok, GC over: tell the stats department what happened.
733 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
734 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
736 #if defined(RTS_USER_SIGNALS)
737 if (RtsFlags.MiscFlags.install_signal_handlers) {
738 // unblock signals again
739 unblockUserSignals();
748 /* -----------------------------------------------------------------------------
749 Figure out which generation to collect, initialise N and major_gc.
751 Also returns the total number of blocks in generations that will be
753 -------------------------------------------------------------------------- */
756 initialise_N (rtsBool force_major_gc)
759 nat s, blocks, blocks_total;
764 if (force_major_gc) {
765 N = RtsFlags.GcFlags.generations - 1;
770 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
772 for (s = 0; s < generations[g].n_steps; s++) {
773 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
774 blocks += generations[g].steps[s].n_large_blocks;
776 if (blocks >= generations[g].max_blocks) {
780 blocks_total += blocks;
784 blocks_total += countNurseryBlocks();
786 major_gc = (N == RtsFlags.GcFlags.generations-1);
790 /* -----------------------------------------------------------------------------
791 Initialise the gc_thread structures.
792 -------------------------------------------------------------------------- */
795 alloc_gc_thread (int n)
801 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
806 initCondition(&t->wake_cond);
807 initMutex(&t->wake_mutex);
808 t->wakeup = rtsTrue; // starts true, so we can wait for the
809 // thread to start up, see wakeup_gc_threads
814 t->free_blocks = NULL;
823 for (s = 0; s < total_steps; s++)
826 ws->step = &all_steps[s];
827 ASSERT(s == ws->step->abs_no);
831 ws->buffer_todo_bd = NULL;
833 ws->part_list = NULL;
834 ws->n_part_blocks = 0;
836 ws->scavd_list = NULL;
837 ws->n_scavd_blocks = 0;
845 alloc_gc_threads (void)
847 if (gc_threads == NULL) {
848 #if defined(THREADED_RTS)
850 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
854 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
855 gc_threads[i] = alloc_gc_thread(i);
858 gc_threads = stgMallocBytes (sizeof(gc_thread*),
861 gc_threads[0] = alloc_gc_thread(0);
866 /* ----------------------------------------------------------------------------
868 ------------------------------------------------------------------------- */
870 static nat gc_running_threads;
872 #if defined(THREADED_RTS)
873 static Mutex gc_running_mutex;
880 ACQUIRE_LOCK(&gc_running_mutex);
881 n_running = ++gc_running_threads;
882 RELEASE_LOCK(&gc_running_mutex);
883 ASSERT(n_running <= n_gc_threads);
891 ACQUIRE_LOCK(&gc_running_mutex);
892 ASSERT(n_gc_threads != 0);
893 n_running = --gc_running_threads;
894 RELEASE_LOCK(&gc_running_mutex);
899 scavenge_until_all_done (void)
903 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
907 // scavenge_loop() only exits when there's no work to do
910 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
911 gct->thread_index, r);
913 while (gc_running_threads != 0) {
919 // any_work() does not remove the work from the queue, it
920 // just checks for the presence of work. If we find any,
921 // then we increment gc_running_threads and go back to
922 // scavenge_loop() to perform any pending work.
925 // All threads are now stopped
926 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
929 #if defined(THREADED_RTS)
931 // gc_thread_work(): Scavenge until there's no work left to do and all
932 // the running threads are idle.
935 gc_thread_work (void)
937 // gc_running_threads has already been incremented for us; this is
938 // a worker thread and the main thread bumped gc_running_threads
939 // before waking us up.
941 // Every thread evacuates some roots.
943 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
945 scavenge_until_all_done();
950 gc_thread_mainloop (void)
954 // Wait until we're told to wake up
955 ACQUIRE_LOCK(&gct->wake_mutex);
956 gct->wakeup = rtsFalse;
957 while (!gct->wakeup) {
958 debugTrace(DEBUG_gc, "GC thread %d standing by...",
960 waitCondition(&gct->wake_cond, &gct->wake_mutex);
962 RELEASE_LOCK(&gct->wake_mutex);
963 if (gct->exit) break;
966 // start performance counters in this thread...
967 if (gct->papi_events == -1) {
968 papi_init_eventset(&gct->papi_events);
970 papi_thread_start_gc1_count(gct->papi_events);
976 // count events in this thread towards the GC totals
977 papi_thread_stop_gc1_count(gct->papi_events);
983 #if defined(THREADED_RTS)
985 gc_thread_entry (gc_thread *my_gct)
988 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
989 gct->id = osThreadId();
990 gc_thread_mainloop();
995 start_gc_threads (void)
997 #if defined(THREADED_RTS)
1000 static rtsBool done = rtsFalse;
1002 gc_running_threads = 0;
1003 initMutex(&gc_running_mutex);
1006 // Start from 1: the main thread is 0
1007 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1008 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1017 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1019 #if defined(THREADED_RTS)
1021 for (i=1; i < n_threads; i++) {
1023 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1025 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1026 if (gc_threads[i]->wakeup) {
1027 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1033 gc_threads[i]->wakeup = rtsTrue;
1034 signalCondition(&gc_threads[i]->wake_cond);
1035 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1040 // After GC is complete, we must wait for all GC threads to enter the
1041 // standby state, otherwise they may still be executing inside
1042 // any_work(), and may even remain awake until the next GC starts.
1044 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1046 #if defined(THREADED_RTS)
1049 for (i=1; i < n_threads; i++) {
1051 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1052 wakeup = gc_threads[i]->wakeup;
1053 // wakeup is false while the thread is waiting
1054 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1060 /* ----------------------------------------------------------------------------
1061 Initialise a generation that is to be collected
1062 ------------------------------------------------------------------------- */
1065 init_collected_gen (nat g, nat n_threads)
1072 // Throw away the current mutable list. Invariant: the mutable
1073 // list always has at least one block; this means we can avoid a
1074 // check for NULL in recordMutable().
1076 freeChain(generations[g].mut_list);
1077 generations[g].mut_list = allocBlock();
1078 for (i = 0; i < n_capabilities; i++) {
1079 freeChain(capabilities[i].mut_lists[g]);
1080 capabilities[i].mut_lists[g] = allocBlock();
1084 for (s = 0; s < generations[g].n_steps; s++) {
1086 stp = &generations[g].steps[s];
1087 ASSERT(stp->gen_no == g);
1089 // we'll construct a new list of threads in this step
1090 // during GC, throw away the current list.
1091 stp->old_threads = stp->threads;
1092 stp->threads = END_TSO_QUEUE;
1094 // generation 0, step 0 doesn't need to-space
1095 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1099 // deprecate the existing blocks
1100 stp->old_blocks = stp->blocks;
1101 stp->n_old_blocks = stp->n_blocks;
1106 // we don't have any to-be-scavenged blocks yet
1108 stp->todos_last = NULL;
1111 // initialise the large object queues.
1112 stp->scavenged_large_objects = NULL;
1113 stp->n_scavenged_large_blocks = 0;
1115 // mark the small objects as from-space
1116 for (bd = stp->old_blocks; bd; bd = bd->link) {
1117 bd->flags &= ~BF_EVACUATED;
1120 // mark the large objects as from-space
1121 for (bd = stp->large_objects; bd; bd = bd->link) {
1122 bd->flags &= ~BF_EVACUATED;
1125 // for a compacted step, we need to allocate the bitmap
1126 if (stp->is_compacted) {
1127 nat bitmap_size; // in bytes
1128 bdescr *bitmap_bdescr;
1131 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1133 if (bitmap_size > 0) {
1134 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1136 stp->bitmap = bitmap_bdescr;
1137 bitmap = bitmap_bdescr->start;
1139 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1140 bitmap_size, bitmap);
1142 // don't forget to fill it with zeros!
1143 memset(bitmap, 0, bitmap_size);
1145 // For each block in this step, point to its bitmap from the
1146 // block descriptor.
1147 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1148 bd->u.bitmap = bitmap;
1149 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1151 // Also at this point we set the BF_COMPACTED flag
1152 // for this block. The invariant is that
1153 // BF_COMPACTED is always unset, except during GC
1154 // when it is set on those blocks which will be
1156 bd->flags |= BF_COMPACTED;
1162 // For each GC thread, for each step, allocate a "todo" block to
1163 // store evacuated objects to be scavenged, and a block to store
1164 // evacuated objects that do not need to be scavenged.
1165 for (t = 0; t < n_threads; t++) {
1166 for (s = 0; s < generations[g].n_steps; s++) {
1168 // we don't copy objects into g0s0, unless -G0
1169 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1171 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1173 ws->todo_large_objects = NULL;
1175 ws->part_list = NULL;
1176 ws->n_part_blocks = 0;
1178 // allocate the first to-space block; extra blocks will be
1179 // chained on as necessary.
1181 ws->buffer_todo_bd = NULL;
1182 alloc_todo_block(ws,0);
1184 ws->scavd_list = NULL;
1185 ws->n_scavd_blocks = 0;
1191 /* ----------------------------------------------------------------------------
1192 Initialise a generation that is *not* to be collected
1193 ------------------------------------------------------------------------- */
1196 init_uncollected_gen (nat g, nat threads)
1203 for (s = 0; s < generations[g].n_steps; s++) {
1204 stp = &generations[g].steps[s];
1205 stp->scavenged_large_objects = NULL;
1206 stp->n_scavenged_large_blocks = 0;
1209 for (s = 0; s < generations[g].n_steps; s++) {
1211 stp = &generations[g].steps[s];
1213 for (t = 0; t < threads; t++) {
1214 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1216 ws->buffer_todo_bd = NULL;
1217 ws->todo_large_objects = NULL;
1219 ws->part_list = NULL;
1220 ws->n_part_blocks = 0;
1222 ws->scavd_list = NULL;
1223 ws->n_scavd_blocks = 0;
1225 // If the block at the head of the list in this generation
1226 // is less than 3/4 full, then use it as a todo block.
1227 if (stp->blocks && isPartiallyFull(stp->blocks))
1229 ws->todo_bd = stp->blocks;
1230 ws->todo_free = ws->todo_bd->free;
1231 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1232 stp->blocks = stp->blocks->link;
1234 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1235 ws->todo_bd->link = NULL;
1236 // we must scan from the current end point.
1237 ws->todo_bd->u.scan = ws->todo_bd->free;
1242 alloc_todo_block(ws,0);
1246 // deal out any more partial blocks to the threads' part_lists
1248 while (stp->blocks && isPartiallyFull(stp->blocks))
1251 stp->blocks = bd->link;
1252 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1253 bd->link = ws->part_list;
1255 ws->n_part_blocks += 1;
1256 bd->u.scan = bd->free;
1258 stp->n_words -= bd->free - bd->start;
1260 if (t == n_gc_threads) t = 0;
1265 // Move the private mutable lists from each capability onto the
1266 // main mutable list for the generation.
1267 for (i = 0; i < n_capabilities; i++) {
1268 for (bd = capabilities[i].mut_lists[g];
1269 bd->link != NULL; bd = bd->link) {
1272 bd->link = generations[g].mut_list;
1273 generations[g].mut_list = capabilities[i].mut_lists[g];
1274 capabilities[i].mut_lists[g] = allocBlock();
1278 /* -----------------------------------------------------------------------------
1279 Initialise a gc_thread before GC
1280 -------------------------------------------------------------------------- */
1283 init_gc_thread (gc_thread *t)
1285 t->static_objects = END_OF_STATIC_LIST;
1286 t->scavenged_static_objects = END_OF_STATIC_LIST;
1289 t->failed_to_evac = rtsFalse;
1290 t->eager_promotion = rtsTrue;
1291 t->thunk_selector_depth = 0;
1296 t->scav_find_work = 0;
1299 /* -----------------------------------------------------------------------------
1300 Function we pass to evacuate roots.
1301 -------------------------------------------------------------------------- */
1304 mark_root(void *user, StgClosure **root)
1306 // we stole a register for gct, but this function is called from
1307 // *outside* the GC where the register variable is not in effect,
1308 // so we need to save and restore it here. NB. only call
1309 // mark_root() from the main GC thread, otherwise gct will be
1311 gc_thread *saved_gct;
1320 /* -----------------------------------------------------------------------------
1321 Initialising the static object & mutable lists
1322 -------------------------------------------------------------------------- */
1325 zero_static_object_list(StgClosure* first_static)
1329 const StgInfoTable *info;
1331 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1333 link = *STATIC_LINK(info, p);
1334 *STATIC_LINK(info,p) = NULL;
1338 /* ----------------------------------------------------------------------------
1339 Update the pointers from the task list
1341 These are treated as weak pointers because we want to allow a main
1342 thread to get a BlockedOnDeadMVar exception in the same way as any
1343 other thread. Note that the threads should all have been retained
1344 by GC by virtue of being on the all_threads list, we're just
1345 updating pointers here.
1346 ------------------------------------------------------------------------- */
1349 update_task_list (void)
1353 for (task = all_tasks; task != NULL; task = task->all_link) {
1354 if (!task->stopped && task->tso) {
1355 ASSERT(task->tso->bound == task);
1356 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1358 barf("task %p: main thread %d has been GC'd",
1371 /* ----------------------------------------------------------------------------
1372 Reset the sizes of the older generations when we do a major
1375 CURRENT STRATEGY: make all generations except zero the same size.
1376 We have to stay within the maximum heap size, and leave a certain
1377 percentage of the maximum heap size available to allocate into.
1378 ------------------------------------------------------------------------- */
1381 resize_generations (void)
1385 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1386 nat live, size, min_alloc;
1387 nat max = RtsFlags.GcFlags.maxHeapSize;
1388 nat gens = RtsFlags.GcFlags.generations;
1390 // live in the oldest generations
1391 live = (oldest_gen->steps[0].n_words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W+
1392 oldest_gen->steps[0].n_large_blocks;
1394 // default max size for all generations except zero
1395 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1396 RtsFlags.GcFlags.minOldGenSize);
1398 // minimum size for generation zero
1399 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1400 RtsFlags.GcFlags.minAllocAreaSize);
1402 // Auto-enable compaction when the residency reaches a
1403 // certain percentage of the maximum heap size (default: 30%).
1404 if (RtsFlags.GcFlags.generations > 1 &&
1405 (RtsFlags.GcFlags.compact ||
1407 oldest_gen->steps[0].n_blocks >
1408 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1409 oldest_gen->steps[0].is_compacted = 1;
1410 // debugBelch("compaction: on\n", live);
1412 oldest_gen->steps[0].is_compacted = 0;
1413 // debugBelch("compaction: off\n", live);
1416 // if we're going to go over the maximum heap size, reduce the
1417 // size of the generations accordingly. The calculation is
1418 // different if compaction is turned on, because we don't need
1419 // to double the space required to collect the old generation.
1422 // this test is necessary to ensure that the calculations
1423 // below don't have any negative results - we're working
1424 // with unsigned values here.
1425 if (max < min_alloc) {
1429 if (oldest_gen->steps[0].is_compacted) {
1430 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1431 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1434 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1435 size = (max - min_alloc) / ((gens - 1) * 2);
1445 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1446 min_alloc, size, max);
1449 for (g = 0; g < gens; g++) {
1450 generations[g].max_blocks = size;
1455 /* -----------------------------------------------------------------------------
1456 Calculate the new size of the nursery, and resize it.
1457 -------------------------------------------------------------------------- */
1460 resize_nursery (void)
1462 if (RtsFlags.GcFlags.generations == 1)
1463 { // Two-space collector:
1466 /* set up a new nursery. Allocate a nursery size based on a
1467 * function of the amount of live data (by default a factor of 2)
1468 * Use the blocks from the old nursery if possible, freeing up any
1471 * If we get near the maximum heap size, then adjust our nursery
1472 * size accordingly. If the nursery is the same size as the live
1473 * data (L), then we need 3L bytes. We can reduce the size of the
1474 * nursery to bring the required memory down near 2L bytes.
1476 * A normal 2-space collector would need 4L bytes to give the same
1477 * performance we get from 3L bytes, reducing to the same
1478 * performance at 2L bytes.
1480 blocks = g0s0->n_blocks;
1482 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1483 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1484 RtsFlags.GcFlags.maxHeapSize )
1486 long adjusted_blocks; // signed on purpose
1489 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1491 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1492 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1494 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1495 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1499 blocks = adjusted_blocks;
1503 blocks *= RtsFlags.GcFlags.oldGenFactor;
1504 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1506 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1509 resizeNurseries(blocks);
1511 else // Generational collector
1514 * If the user has given us a suggested heap size, adjust our
1515 * allocation area to make best use of the memory available.
1517 if (RtsFlags.GcFlags.heapSizeSuggestion)
1520 nat needed = calcNeeded(); // approx blocks needed at next GC
1522 /* Guess how much will be live in generation 0 step 0 next time.
1523 * A good approximation is obtained by finding the
1524 * percentage of g0s0 that was live at the last minor GC.
1526 * We have an accurate figure for the amount of copied data in
1527 * 'copied', but we must convert this to a number of blocks, with
1528 * a small adjustment for estimated slop at the end of a block
1533 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1534 / countNurseryBlocks();
1537 /* Estimate a size for the allocation area based on the
1538 * information available. We might end up going slightly under
1539 * or over the suggested heap size, but we should be pretty
1542 * Formula: suggested - needed
1543 * ----------------------------
1544 * 1 + g0s0_pcnt_kept/100
1546 * where 'needed' is the amount of memory needed at the next
1547 * collection for collecting all steps except g0s0.
1550 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1551 (100 + (long)g0s0_pcnt_kept);
1553 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1554 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1557 resizeNurseries((nat)blocks);
1561 // we might have added extra large blocks to the nursery, so
1562 // resize back to minAllocAreaSize again.
1563 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1568 /* -----------------------------------------------------------------------------
1569 Sanity code for CAF garbage collection.
1571 With DEBUG turned on, we manage a CAF list in addition to the SRT
1572 mechanism. After GC, we run down the CAF list and blackhole any
1573 CAFs which have been garbage collected. This means we get an error
1574 whenever the program tries to enter a garbage collected CAF.
1576 Any garbage collected CAFs are taken off the CAF list at the same
1578 -------------------------------------------------------------------------- */
1580 #if 0 && defined(DEBUG)
1587 const StgInfoTable *info;
1598 ASSERT(info->type == IND_STATIC);
1600 if (STATIC_LINK(info,p) == NULL) {
1601 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1603 SET_INFO(p,&stg_BLACKHOLE_info);
1604 p = STATIC_LINK2(info,p);
1608 pp = &STATIC_LINK2(info,p);
1615 debugTrace(DEBUG_gccafs, "%d CAFs live", i);