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 /* run through all the generations/steps and tidy up
504 for (i=0; i < n_gc_threads; i++) {
505 if (n_gc_threads > 1) {
506 trace(TRACE_gc,"thread %d:", i);
507 trace(TRACE_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
508 trace(TRACE_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
509 trace(TRACE_gc," any_work %ld", gc_threads[i]->any_work);
510 trace(TRACE_gc," no_work %ld", gc_threads[i]->no_work);
511 trace(TRACE_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
513 copied += gc_threads[i]->copied;
514 max_copied = stg_max(gc_threads[i]->copied, max_copied);
516 if (n_gc_threads == 1) {
524 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
527 generations[g].collections++; // for stats
528 if (n_gc_threads > 1) generations[g].par_collections++;
531 // Count the mutable list as bytes "copied" for the purposes of
532 // stats. Every mutable list is copied during every GC.
534 nat mut_list_size = 0;
535 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
536 mut_list_size += bd->free - bd->start;
538 copied += mut_list_size;
541 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
542 (unsigned long)(mut_list_size * sizeof(W_)),
543 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
546 for (s = 0; s < generations[g].n_steps; s++) {
548 stp = &generations[g].steps[s];
550 // for generations we collected...
553 /* free old memory and shift to-space into from-space for all
554 * the collected steps (except the allocation area). These
555 * freed blocks will probaby be quickly recycled.
557 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
560 // tack the new blocks on the end of the existing blocks
561 if (stp->old_blocks != NULL) {
564 for (bd = stp->old_blocks; bd != NULL; bd = next) {
568 if (!(bd->flags & BF_MARKED))
571 stp->old_blocks = next;
580 stp->n_words += bd->free - bd->start;
582 // NB. this step might not be compacted next
583 // time, so reset the BF_MARKED flags.
584 // They are set before GC if we're going to
585 // compact. (search for BF_MARKED above).
586 bd->flags &= ~BF_MARKED;
588 // between GCs, all blocks in the heap except
589 // for the nursery have the BF_EVACUATED flag set.
590 bd->flags |= BF_EVACUATED;
597 prev->link = stp->blocks;
598 stp->blocks = stp->old_blocks;
601 // add the new blocks to the block tally
602 stp->n_blocks += stp->n_old_blocks;
603 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
604 ASSERT(countOccupied(stp->blocks) == stp->n_words);
608 freeChain(stp->old_blocks);
610 stp->old_blocks = NULL;
611 stp->n_old_blocks = 0;
614 /* LARGE OBJECTS. The current live large objects are chained on
615 * scavenged_large, having been moved during garbage
616 * collection from large_objects. Any objects left on
617 * large_objects list are therefore dead, so we free them here.
619 for (bd = stp->large_objects; bd != NULL; bd = next) {
625 stp->large_objects = stp->scavenged_large_objects;
626 stp->n_large_blocks = stp->n_scavenged_large_blocks;
629 else // for older generations...
631 /* For older generations, we need to append the
632 * scavenged_large_object list (i.e. large objects that have been
633 * promoted during this GC) to the large_object list for that step.
635 for (bd = stp->scavenged_large_objects; bd; bd = next) {
637 dbl_link_onto(bd, &stp->large_objects);
640 // add the new blocks we promoted during this GC
641 stp->n_large_blocks += stp->n_scavenged_large_blocks;
646 // update the max size of older generations after a major GC
647 resize_generations();
649 // Calculate the amount of live data for stats.
650 live = calcLiveWords();
652 // Free the small objects allocated via allocate(), since this will
653 // all have been copied into G0S1 now.
654 if (RtsFlags.GcFlags.generations > 1) {
655 if (g0s0->blocks != NULL) {
656 freeChain(g0s0->blocks);
663 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
665 // Start a new pinned_object_block
666 pinned_object_block = NULL;
668 // Free the mark stack.
669 if (mark_stack_bdescr != NULL) {
670 freeGroup(mark_stack_bdescr);
674 for (g = 0; g <= N; g++) {
675 for (s = 0; s < generations[g].n_steps; s++) {
676 stp = &generations[g].steps[s];
677 if (stp->bitmap != NULL) {
678 freeGroup(stp->bitmap);
686 // mark the garbage collected CAFs as dead
687 #if 0 && defined(DEBUG) // doesn't work at the moment
688 if (major_gc) { gcCAFs(); }
692 // resetStaticObjectForRetainerProfiling() must be called before
694 if (n_gc_threads > 1) {
695 barf("profiling is currently broken with multi-threaded GC");
696 // ToDo: fix the gct->scavenged_static_objects below
698 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
701 // zero the scavenged static object list
704 for (i = 0; i < n_gc_threads; i++) {
705 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
712 // start any pending finalizers
714 scheduleFinalizers(last_free_capability, old_weak_ptr_list);
717 // send exceptions to any threads which were about to die
719 resurrectThreads(resurrected_threads);
720 performPendingThrowTos(exception_threads);
723 // Update the stable pointer hash table.
724 updateStablePtrTable(major_gc);
726 // check sanity after GC
727 IF_DEBUG(sanity, checkSanity());
729 // extra GC trace info
730 if (traceClass(TRACE_gc|DEBUG_gc)) statDescribeGens();
733 // symbol-table based profiling
734 /* heapCensus(to_blocks); */ /* ToDo */
737 // restore enclosing cost centre
743 // check for memory leaks if DEBUG is on
744 memInventory(traceClass(DEBUG_gc));
747 #ifdef RTS_GTK_FRONTPANEL
748 if (RtsFlags.GcFlags.frontpanel) {
749 updateFrontPanelAfterGC( N, live );
753 // ok, GC over: tell the stats department what happened.
754 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
755 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
757 #if defined(RTS_USER_SIGNALS)
758 if (RtsFlags.MiscFlags.install_signal_handlers) {
759 // unblock signals again
760 unblockUserSignals();
769 /* -----------------------------------------------------------------------------
770 Figure out which generation to collect, initialise N and major_gc.
772 Also returns the total number of blocks in generations that will be
774 -------------------------------------------------------------------------- */
777 initialise_N (rtsBool force_major_gc)
780 nat s, blocks, blocks_total;
785 if (force_major_gc) {
786 N = RtsFlags.GcFlags.generations - 1;
791 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
793 for (s = 0; s < generations[g].n_steps; s++) {
794 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
795 blocks += generations[g].steps[s].n_large_blocks;
797 if (blocks >= generations[g].max_blocks) {
801 blocks_total += blocks;
805 blocks_total += countNurseryBlocks();
807 major_gc = (N == RtsFlags.GcFlags.generations-1);
811 /* -----------------------------------------------------------------------------
812 Initialise the gc_thread structures.
813 -------------------------------------------------------------------------- */
816 alloc_gc_thread (int n)
822 t = stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
827 initCondition(&t->wake_cond);
828 initMutex(&t->wake_mutex);
829 t->wakeup = rtsTrue; // starts true, so we can wait for the
830 // thread to start up, see wakeup_gc_threads
835 t->free_blocks = NULL;
844 for (s = 0; s < total_steps; s++)
847 ws->step = &all_steps[s];
848 ASSERT(s == ws->step->abs_no);
852 ws->buffer_todo_bd = NULL;
854 ws->part_list = NULL;
855 ws->n_part_blocks = 0;
857 ws->scavd_list = NULL;
858 ws->n_scavd_blocks = 0;
866 alloc_gc_threads (void)
868 if (gc_threads == NULL) {
869 #if defined(THREADED_RTS)
871 gc_threads = stgMallocBytes (RtsFlags.ParFlags.gcThreads *
875 for (i = 0; i < RtsFlags.ParFlags.gcThreads; i++) {
876 gc_threads[i] = alloc_gc_thread(i);
879 gc_threads = stgMallocBytes (sizeof(gc_thread*),
882 gc_threads[0] = alloc_gc_thread(0);
887 /* ----------------------------------------------------------------------------
889 ------------------------------------------------------------------------- */
891 static nat gc_running_threads;
893 #if defined(THREADED_RTS)
894 static Mutex gc_running_mutex;
901 ACQUIRE_LOCK(&gc_running_mutex);
902 n_running = ++gc_running_threads;
903 RELEASE_LOCK(&gc_running_mutex);
904 ASSERT(n_running <= n_gc_threads);
912 ACQUIRE_LOCK(&gc_running_mutex);
913 ASSERT(n_gc_threads != 0);
914 n_running = --gc_running_threads;
915 RELEASE_LOCK(&gc_running_mutex);
929 // scavenge objects in compacted generation
930 if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
931 (mark_stack_bdescr != NULL && !mark_stack_empty())) {
935 // Check for global work in any step. We don't need to check for
936 // local work, because we have already exited scavenge_loop(),
937 // which means there is no local work for this thread.
938 for (s = total_steps-1; s >= 0; s--) {
939 if (s == 0 && RtsFlags.GcFlags.generations > 1) {
943 if (ws->todo_large_objects) return rtsTrue;
944 if (ws->step->todos) return rtsTrue;
953 scavenge_until_all_done (void)
957 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
960 #if defined(THREADED_RTS)
961 if (n_gc_threads > 1) {
970 // scavenge_loop() only exits when there's no work to do
973 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
974 gct->thread_index, r);
976 while (gc_running_threads != 0) {
982 // any_work() does not remove the work from the queue, it
983 // just checks for the presence of work. If we find any,
984 // then we increment gc_running_threads and go back to
985 // scavenge_loop() to perform any pending work.
988 // All threads are now stopped
989 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
992 #if defined(THREADED_RTS)
994 // gc_thread_work(): Scavenge until there's no work left to do and all
995 // the running threads are idle.
998 gc_thread_work (void)
1000 // gc_running_threads has already been incremented for us; this is
1001 // a worker thread and the main thread bumped gc_running_threads
1002 // before waking us up.
1004 // Every thread evacuates some roots.
1006 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads);
1008 scavenge_until_all_done();
1013 gc_thread_mainloop (void)
1015 while (!gct->exit) {
1017 // Wait until we're told to wake up
1018 ACQUIRE_LOCK(&gct->wake_mutex);
1019 gct->wakeup = rtsFalse;
1020 while (!gct->wakeup) {
1021 debugTrace(DEBUG_gc, "GC thread %d standing by...",
1023 waitCondition(&gct->wake_cond, &gct->wake_mutex);
1025 RELEASE_LOCK(&gct->wake_mutex);
1026 if (gct->exit) break;
1029 // start performance counters in this thread...
1030 if (gct->papi_events == -1) {
1031 papi_init_eventset(&gct->papi_events);
1033 papi_thread_start_gc1_count(gct->papi_events);
1039 // count events in this thread towards the GC totals
1040 papi_thread_stop_gc1_count(gct->papi_events);
1046 #if defined(THREADED_RTS)
1048 gc_thread_entry (gc_thread *my_gct)
1051 debugTrace(DEBUG_gc, "GC thread %d starting...", gct->thread_index);
1052 gct->id = osThreadId();
1053 gc_thread_mainloop();
1058 start_gc_threads (void)
1060 #if defined(THREADED_RTS)
1063 static rtsBool done = rtsFalse;
1065 gc_running_threads = 0;
1066 initMutex(&gc_running_mutex);
1069 // Start from 1: the main thread is 0
1070 for (i = 1; i < RtsFlags.ParFlags.gcThreads; i++) {
1071 createOSThread(&id, (OSThreadProc*)&gc_thread_entry,
1080 wakeup_gc_threads (nat n_threads USED_IF_THREADS)
1082 #if defined(THREADED_RTS)
1084 for (i=1; i < n_threads; i++) {
1086 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1088 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1089 if (gc_threads[i]->wakeup) {
1090 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1096 gc_threads[i]->wakeup = rtsTrue;
1097 signalCondition(&gc_threads[i]->wake_cond);
1098 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1103 // After GC is complete, we must wait for all GC threads to enter the
1104 // standby state, otherwise they may still be executing inside
1105 // any_work(), and may even remain awake until the next GC starts.
1107 shutdown_gc_threads (nat n_threads USED_IF_THREADS)
1109 #if defined(THREADED_RTS)
1112 for (i=1; i < n_threads; i++) {
1114 ACQUIRE_LOCK(&gc_threads[i]->wake_mutex);
1115 wakeup = gc_threads[i]->wakeup;
1116 // wakeup is false while the thread is waiting
1117 RELEASE_LOCK(&gc_threads[i]->wake_mutex);
1123 /* ----------------------------------------------------------------------------
1124 Initialise a generation that is to be collected
1125 ------------------------------------------------------------------------- */
1128 init_collected_gen (nat g, nat n_threads)
1135 // Throw away the current mutable list. Invariant: the mutable
1136 // list always has at least one block; this means we can avoid a
1137 // check for NULL in recordMutable().
1139 freeChain(generations[g].mut_list);
1140 generations[g].mut_list = allocBlock();
1141 for (i = 0; i < n_capabilities; i++) {
1142 freeChain(capabilities[i].mut_lists[g]);
1143 capabilities[i].mut_lists[g] = allocBlock();
1147 for (s = 0; s < generations[g].n_steps; s++) {
1149 stp = &generations[g].steps[s];
1150 ASSERT(stp->gen_no == g);
1152 // we'll construct a new list of threads in this step
1153 // during GC, throw away the current list.
1154 stp->old_threads = stp->threads;
1155 stp->threads = END_TSO_QUEUE;
1157 // generation 0, step 0 doesn't need to-space
1158 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1162 // deprecate the existing blocks
1163 stp->old_blocks = stp->blocks;
1164 stp->n_old_blocks = stp->n_blocks;
1168 stp->live_estimate = 0;
1170 // we don't have any to-be-scavenged blocks yet
1172 stp->todos_last = NULL;
1175 // initialise the large object queues.
1176 stp->scavenged_large_objects = NULL;
1177 stp->n_scavenged_large_blocks = 0;
1179 // mark the small objects as from-space
1180 for (bd = stp->old_blocks; bd; bd = bd->link) {
1181 bd->flags &= ~BF_EVACUATED;
1184 // mark the large objects as from-space
1185 for (bd = stp->large_objects; bd; bd = bd->link) {
1186 bd->flags &= ~BF_EVACUATED;
1189 // for a compacted step, we need to allocate the bitmap
1191 nat bitmap_size; // in bytes
1192 bdescr *bitmap_bdescr;
1195 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1197 if (bitmap_size > 0) {
1198 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1200 stp->bitmap = bitmap_bdescr;
1201 bitmap = bitmap_bdescr->start;
1203 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1204 bitmap_size, bitmap);
1206 // don't forget to fill it with zeros!
1207 memset(bitmap, 0, bitmap_size);
1209 // For each block in this step, point to its bitmap from the
1210 // block descriptor.
1211 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1212 bd->u.bitmap = bitmap;
1213 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1215 // Also at this point we set the BF_MARKED flag
1216 // for this block. The invariant is that
1217 // BF_MARKED is always unset, except during GC
1218 // when it is set on those blocks which will be
1220 if (!(bd->flags & BF_FRAGMENTED)) {
1221 bd->flags |= BF_MARKED;
1228 // For each GC thread, for each step, allocate a "todo" block to
1229 // store evacuated objects to be scavenged, and a block to store
1230 // evacuated objects that do not need to be scavenged.
1231 for (t = 0; t < n_threads; t++) {
1232 for (s = 0; s < generations[g].n_steps; s++) {
1234 // we don't copy objects into g0s0, unless -G0
1235 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1237 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1239 ws->todo_large_objects = NULL;
1241 ws->part_list = NULL;
1242 ws->n_part_blocks = 0;
1244 // allocate the first to-space block; extra blocks will be
1245 // chained on as necessary.
1247 ws->buffer_todo_bd = NULL;
1248 alloc_todo_block(ws,0);
1250 ws->scavd_list = NULL;
1251 ws->n_scavd_blocks = 0;
1257 /* ----------------------------------------------------------------------------
1258 Initialise a generation that is *not* to be collected
1259 ------------------------------------------------------------------------- */
1262 init_uncollected_gen (nat g, nat threads)
1269 for (s = 0; s < generations[g].n_steps; s++) {
1270 stp = &generations[g].steps[s];
1271 stp->scavenged_large_objects = NULL;
1272 stp->n_scavenged_large_blocks = 0;
1275 for (s = 0; s < generations[g].n_steps; s++) {
1277 stp = &generations[g].steps[s];
1279 for (t = 0; t < threads; t++) {
1280 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1282 ws->buffer_todo_bd = NULL;
1283 ws->todo_large_objects = NULL;
1285 ws->part_list = NULL;
1286 ws->n_part_blocks = 0;
1288 ws->scavd_list = NULL;
1289 ws->n_scavd_blocks = 0;
1291 // If the block at the head of the list in this generation
1292 // is less than 3/4 full, then use it as a todo block.
1293 if (stp->blocks && isPartiallyFull(stp->blocks))
1295 ws->todo_bd = stp->blocks;
1296 ws->todo_free = ws->todo_bd->free;
1297 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1298 stp->blocks = stp->blocks->link;
1300 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1301 ws->todo_bd->link = NULL;
1302 // we must scan from the current end point.
1303 ws->todo_bd->u.scan = ws->todo_bd->free;
1308 alloc_todo_block(ws,0);
1312 // deal out any more partial blocks to the threads' part_lists
1314 while (stp->blocks && isPartiallyFull(stp->blocks))
1317 stp->blocks = bd->link;
1318 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1319 bd->link = ws->part_list;
1321 ws->n_part_blocks += 1;
1322 bd->u.scan = bd->free;
1324 stp->n_words -= bd->free - bd->start;
1326 if (t == n_gc_threads) t = 0;
1331 // Move the private mutable lists from each capability onto the
1332 // main mutable list for the generation.
1333 for (i = 0; i < n_capabilities; i++) {
1334 for (bd = capabilities[i].mut_lists[g];
1335 bd->link != NULL; bd = bd->link) {
1338 bd->link = generations[g].mut_list;
1339 generations[g].mut_list = capabilities[i].mut_lists[g];
1340 capabilities[i].mut_lists[g] = allocBlock();
1344 /* -----------------------------------------------------------------------------
1345 Initialise a gc_thread before GC
1346 -------------------------------------------------------------------------- */
1349 init_gc_thread (gc_thread *t)
1351 t->static_objects = END_OF_STATIC_LIST;
1352 t->scavenged_static_objects = END_OF_STATIC_LIST;
1355 t->failed_to_evac = rtsFalse;
1356 t->eager_promotion = rtsTrue;
1357 t->thunk_selector_depth = 0;
1362 t->scav_find_work = 0;
1365 /* -----------------------------------------------------------------------------
1366 Function we pass to evacuate roots.
1367 -------------------------------------------------------------------------- */
1370 mark_root(void *user, StgClosure **root)
1372 // we stole a register for gct, but this function is called from
1373 // *outside* the GC where the register variable is not in effect,
1374 // so we need to save and restore it here. NB. only call
1375 // mark_root() from the main GC thread, otherwise gct will be
1377 gc_thread *saved_gct;
1386 /* -----------------------------------------------------------------------------
1387 Initialising the static object & mutable lists
1388 -------------------------------------------------------------------------- */
1391 zero_static_object_list(StgClosure* first_static)
1395 const StgInfoTable *info;
1397 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1399 link = *STATIC_LINK(info, p);
1400 *STATIC_LINK(info,p) = NULL;
1404 /* ----------------------------------------------------------------------------
1405 Update the pointers from the task list
1407 These are treated as weak pointers because we want to allow a main
1408 thread to get a BlockedOnDeadMVar exception in the same way as any
1409 other thread. Note that the threads should all have been retained
1410 by GC by virtue of being on the all_threads list, we're just
1411 updating pointers here.
1412 ------------------------------------------------------------------------- */
1415 update_task_list (void)
1419 for (task = all_tasks; task != NULL; task = task->all_link) {
1420 if (!task->stopped && task->tso) {
1421 ASSERT(task->tso->bound == task);
1422 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1424 barf("task %p: main thread %d has been GC'd",
1437 /* ----------------------------------------------------------------------------
1438 Reset the sizes of the older generations when we do a major
1441 CURRENT STRATEGY: make all generations except zero the same size.
1442 We have to stay within the maximum heap size, and leave a certain
1443 percentage of the maximum heap size available to allocate into.
1444 ------------------------------------------------------------------------- */
1447 resize_generations (void)
1451 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1452 nat live, size, min_alloc, words;
1453 nat max = RtsFlags.GcFlags.maxHeapSize;
1454 nat gens = RtsFlags.GcFlags.generations;
1456 // live in the oldest generations
1457 if (oldest_gen->steps[0].live_estimate != 0) {
1458 words = oldest_gen->steps[0].live_estimate;
1460 words = oldest_gen->steps[0].n_words;
1462 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1463 oldest_gen->steps[0].n_large_blocks;
1465 // default max size for all generations except zero
1466 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1467 RtsFlags.GcFlags.minOldGenSize);
1469 // minimum size for generation zero
1470 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1471 RtsFlags.GcFlags.minAllocAreaSize);
1473 // Auto-enable compaction when the residency reaches a
1474 // certain percentage of the maximum heap size (default: 30%).
1475 if (RtsFlags.GcFlags.generations > 1 &&
1476 (RtsFlags.GcFlags.compact ||
1478 oldest_gen->steps[0].n_blocks >
1479 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1480 oldest_gen->steps[0].mark = 1;
1481 oldest_gen->steps[0].compact = 1;
1482 // debugBelch("compaction: on\n", live);
1484 oldest_gen->steps[0].mark = 0;
1485 oldest_gen->steps[0].compact = 0;
1486 // debugBelch("compaction: off\n", live);
1489 if (RtsFlags.GcFlags.sweep) {
1490 oldest_gen->steps[0].mark = 1;
1493 // if we're going to go over the maximum heap size, reduce the
1494 // size of the generations accordingly. The calculation is
1495 // different if compaction is turned on, because we don't need
1496 // to double the space required to collect the old generation.
1499 // this test is necessary to ensure that the calculations
1500 // below don't have any negative results - we're working
1501 // with unsigned values here.
1502 if (max < min_alloc) {
1506 if (oldest_gen->steps[0].compact) {
1507 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1508 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1511 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1512 size = (max - min_alloc) / ((gens - 1) * 2);
1522 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1523 min_alloc, size, max);
1526 for (g = 0; g < gens; g++) {
1527 generations[g].max_blocks = size;
1532 /* -----------------------------------------------------------------------------
1533 Calculate the new size of the nursery, and resize it.
1534 -------------------------------------------------------------------------- */
1537 resize_nursery (void)
1539 if (RtsFlags.GcFlags.generations == 1)
1540 { // Two-space collector:
1543 /* set up a new nursery. Allocate a nursery size based on a
1544 * function of the amount of live data (by default a factor of 2)
1545 * Use the blocks from the old nursery if possible, freeing up any
1548 * If we get near the maximum heap size, then adjust our nursery
1549 * size accordingly. If the nursery is the same size as the live
1550 * data (L), then we need 3L bytes. We can reduce the size of the
1551 * nursery to bring the required memory down near 2L bytes.
1553 * A normal 2-space collector would need 4L bytes to give the same
1554 * performance we get from 3L bytes, reducing to the same
1555 * performance at 2L bytes.
1557 blocks = g0s0->n_blocks;
1559 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1560 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1561 RtsFlags.GcFlags.maxHeapSize )
1563 long adjusted_blocks; // signed on purpose
1566 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1568 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1569 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1571 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1572 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1576 blocks = adjusted_blocks;
1580 blocks *= RtsFlags.GcFlags.oldGenFactor;
1581 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1583 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1586 resizeNurseries(blocks);
1588 else // Generational collector
1591 * If the user has given us a suggested heap size, adjust our
1592 * allocation area to make best use of the memory available.
1594 if (RtsFlags.GcFlags.heapSizeSuggestion)
1597 nat needed = calcNeeded(); // approx blocks needed at next GC
1599 /* Guess how much will be live in generation 0 step 0 next time.
1600 * A good approximation is obtained by finding the
1601 * percentage of g0s0 that was live at the last minor GC.
1603 * We have an accurate figure for the amount of copied data in
1604 * 'copied', but we must convert this to a number of blocks, with
1605 * a small adjustment for estimated slop at the end of a block
1610 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1611 / countNurseryBlocks();
1614 /* Estimate a size for the allocation area based on the
1615 * information available. We might end up going slightly under
1616 * or over the suggested heap size, but we should be pretty
1619 * Formula: suggested - needed
1620 * ----------------------------
1621 * 1 + g0s0_pcnt_kept/100
1623 * where 'needed' is the amount of memory needed at the next
1624 * collection for collecting all steps except g0s0.
1627 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1628 (100 + (long)g0s0_pcnt_kept);
1630 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1631 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1634 resizeNurseries((nat)blocks);
1638 // we might have added extra large blocks to the nursery, so
1639 // resize back to minAllocAreaSize again.
1640 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1645 /* -----------------------------------------------------------------------------
1646 Sanity code for CAF garbage collection.
1648 With DEBUG turned on, we manage a CAF list in addition to the SRT
1649 mechanism. After GC, we run down the CAF list and blackhole any
1650 CAFs which have been garbage collected. This means we get an error
1651 whenever the program tries to enter a garbage collected CAF.
1653 Any garbage collected CAFs are taken off the CAF list at the same
1655 -------------------------------------------------------------------------- */
1657 #if 0 && defined(DEBUG)
1664 const StgInfoTable *info;
1675 ASSERT(info->type == IND_STATIC);
1677 if (STATIC_LINK(info,p) == NULL) {
1678 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1680 SET_INFO(p,&stg_BLACKHOLE_info);
1681 p = STATIC_LINK2(info,p);
1685 pp = &STATIC_LINK2(info,p);
1692 debugTrace(DEBUG_gccafs, "%d CAFs live", i);