Fix #3320: we forgot to save/restore the GC register variable
[ghc.git] / rts / sm / GC.c
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 1998-2008
4 *
5 * Generational garbage collector
6 *
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
9 *
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
11 *
12 * ---------------------------------------------------------------------------*/
13
14 #include "PosixSource.h"
15 #include "Rts.h"
16 #include "HsFFI.h"
17
18 #include "Storage.h"
19 #include "RtsUtils.h"
20 #include "Apply.h"
21 #include "Updates.h"
22 #include "Stats.h"
23 #include "Schedule.h"
24 #include "Sanity.h"
25 #include "BlockAlloc.h"
26 #include "ProfHeap.h"
27 #include "Weak.h"
28 #include "Prelude.h"
29 #include "RtsSignals.h"
30 #include "STM.h"
31 #if defined(RTS_GTK_FRONTPANEL)
32 #include "FrontPanel.h"
33 #endif
34 #include "Trace.h"
35 #include "RetainerProfile.h"
36 #include "LdvProfile.h"
37 #include "RaiseAsync.h"
38 #include "Papi.h"
39 #include "Stable.h"
40
41 #include "GC.h"
42 #include "GCThread.h"
43 #include "Compact.h"
44 #include "Evac.h"
45 #include "Scav.h"
46 #include "GCUtils.h"
47 #include "MarkWeak.h"
48 #include "Sparks.h"
49 #include "Sweep.h"
50
51 #include <string.h> // for memset()
52 #include <unistd.h>
53
54 /* -----------------------------------------------------------------------------
55 Global variables
56 -------------------------------------------------------------------------- */
57
58 /* STATIC OBJECT LIST.
59 *
60 * During GC:
61 * We maintain a linked list of static objects that are still live.
62 * The requirements for this list are:
63 *
64 * - we need to scan the list while adding to it, in order to
65 * scavenge all the static objects (in the same way that
66 * breadth-first scavenging works for dynamic objects).
67 *
68 * - we need to be able to tell whether an object is already on
69 * the list, to break loops.
70 *
71 * Each static object has a "static link field", which we use for
72 * linking objects on to the list. We use a stack-type list, consing
73 * objects on the front as they are added (this means that the
74 * scavenge phase is depth-first, not breadth-first, but that
75 * shouldn't matter).
76 *
77 * A separate list is kept for objects that have been scavenged
78 * already - this is so that we can zero all the marks afterwards.
79 *
80 * An object is on the list if its static link field is non-zero; this
81 * means that we have to mark the end of the list with '1', not NULL.
82 *
83 * Extra notes for generational GC:
84 *
85 * Each generation has a static object list associated with it. When
86 * collecting generations up to N, we treat the static object lists
87 * from generations > N as roots.
88 *
89 * We build up a static object list while collecting generations 0..N,
90 * which is then appended to the static object list of generation N+1.
91 */
92
93 /* N is the oldest generation being collected, where the generations
94 * are numbered starting at 0. A major GC (indicated by the major_gc
95 * flag) is when we're collecting all generations. We only attempt to
96 * deal with static objects and GC CAFs when doing a major GC.
97 */
98 nat N;
99 rtsBool major_gc;
100
101 /* Data used for allocation area sizing.
102 */
103 static lnat g0s0_pcnt_kept = 30; // percentage of g0s0 live at last minor GC
104
105 /* Mut-list stats */
106 #ifdef DEBUG
107 nat mutlist_MUTVARS,
108 mutlist_MUTARRS,
109 mutlist_MVARS,
110 mutlist_OTHERS;
111 #endif
112
113 /* Thread-local data for each GC thread
114 */
115 gc_thread **gc_threads = NULL;
116
117 #if !defined(THREADED_RTS)
118 StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(step_workspace)];
119 #endif
120
121 // Number of threads running in *this* GC. Affects how many
122 // step->todos[] lists we have to look in to find work.
123 nat n_gc_threads;
124
125 // For stats:
126 long copied; // *words* copied & scavenged during this GC
127
128 rtsBool work_stealing;
129
130 DECLARE_GCT
131
132 /* -----------------------------------------------------------------------------
133 Static function declarations
134 -------------------------------------------------------------------------- */
135
136 static void mark_root (void *user, StgClosure **root);
137 static void zero_static_object_list (StgClosure* first_static);
138 static nat initialise_N (rtsBool force_major_gc);
139 static void init_collected_gen (nat g, nat threads);
140 static void init_uncollected_gen (nat g, nat threads);
141 static void init_gc_thread (gc_thread *t);
142 static void update_task_list (void);
143 static void resize_generations (void);
144 static void resize_nursery (void);
145 static void start_gc_threads (void);
146 static void scavenge_until_all_done (void);
147 static StgWord inc_running (void);
148 static StgWord dec_running (void);
149 static void wakeup_gc_threads (nat n_threads, nat me);
150 static void shutdown_gc_threads (nat n_threads, nat me);
151
152 #if 0 && defined(DEBUG)
153 static void gcCAFs (void);
154 #endif
155
156 /* -----------------------------------------------------------------------------
157 The mark bitmap & stack.
158 -------------------------------------------------------------------------- */
159
160 #define MARK_STACK_BLOCKS 4
161
162 bdescr *mark_stack_bdescr;
163 StgPtr *mark_stack;
164 StgPtr *mark_sp;
165 StgPtr *mark_splim;
166
167 // Flag and pointers used for falling back to a linear scan when the
168 // mark stack overflows.
169 rtsBool mark_stack_overflowed;
170 bdescr *oldgen_scan_bd;
171 StgPtr oldgen_scan;
172
173 /* -----------------------------------------------------------------------------
174 GarbageCollect: the main entry point to the garbage collector.
175
176 Locks held: all capabilities are held throughout GarbageCollect().
177 -------------------------------------------------------------------------- */
178
179 void
180 GarbageCollect (rtsBool force_major_gc,
181 nat gc_type USED_IF_THREADS,
182 Capability *cap)
183 {
184 bdescr *bd;
185 step *stp;
186 lnat live, allocated, max_copied, avg_copied, slop;
187 gc_thread *saved_gct;
188 nat g, s, t, n;
189
190 // necessary if we stole a callee-saves register for gct:
191 saved_gct = gct;
192
193 #ifdef PROFILING
194 CostCentreStack *prev_CCS;
195 #endif
196
197 ACQUIRE_SM_LOCK;
198
199 #if defined(RTS_USER_SIGNALS)
200 if (RtsFlags.MiscFlags.install_signal_handlers) {
201 // block signals
202 blockUserSignals();
203 }
204 #endif
205
206 ASSERT(sizeof(step_workspace) == 16 * sizeof(StgWord));
207 // otherwise adjust the padding in step_workspace.
208
209 // tell the stats department that we've started a GC
210 stat_startGC();
211
212 // tell the STM to discard any cached closures it's hoping to re-use
213 stmPreGCHook();
214
215 // lock the StablePtr table
216 stablePtrPreGC();
217
218 #ifdef DEBUG
219 mutlist_MUTVARS = 0;
220 mutlist_MUTARRS = 0;
221 mutlist_OTHERS = 0;
222 #endif
223
224 // attribute any costs to CCS_GC
225 #ifdef PROFILING
226 prev_CCS = CCCS;
227 CCCS = CCS_GC;
228 #endif
229
230 /* Approximate how much we allocated.
231 * Todo: only when generating stats?
232 */
233 allocated = calcAllocated();
234
235 /* Figure out which generation to collect
236 */
237 n = initialise_N(force_major_gc);
238
239 #if defined(THREADED_RTS)
240 work_stealing = RtsFlags.ParFlags.parGcLoadBalancing;
241 // It's not always a good idea to do load balancing in parallel
242 // GC. In particular, for a parallel program we don't want to
243 // lose locality by moving cached data into another CPU's cache
244 // (this effect can be quite significant).
245 //
246 // We could have a more complex way to deterimine whether to do
247 // work stealing or not, e.g. it might be a good idea to do it
248 // if the heap is big. For now, we just turn it on or off with
249 // a flag.
250 #endif
251
252 /* Start threads, so they can be spinning up while we finish initialisation.
253 */
254 start_gc_threads();
255
256 #if defined(THREADED_RTS)
257 /* How many threads will be participating in this GC?
258 * We don't try to parallelise minor GCs (unless the user asks for
259 * it with +RTS -gn0), or mark/compact/sweep GC.
260 */
261 if (gc_type == PENDING_GC_PAR) {
262 n_gc_threads = RtsFlags.ParFlags.nNodes;
263 } else {
264 n_gc_threads = 1;
265 }
266 #else
267 n_gc_threads = 1;
268 #endif
269
270 debugTrace(DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
271 N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
272
273 #ifdef RTS_GTK_FRONTPANEL
274 if (RtsFlags.GcFlags.frontpanel) {
275 updateFrontPanelBeforeGC(N);
276 }
277 #endif
278
279 #ifdef DEBUG
280 // check for memory leaks if DEBUG is on
281 memInventory(traceClass(DEBUG_gc));
282 #endif
283
284 // check stack sanity *before* GC
285 IF_DEBUG(sanity, checkFreeListSanity());
286 IF_DEBUG(sanity, checkMutableLists(rtsTrue));
287
288 // Initialise all our gc_thread structures
289 for (t = 0; t < n_gc_threads; t++) {
290 init_gc_thread(gc_threads[t]);
291 }
292
293 // Initialise all the generations/steps that we're collecting.
294 for (g = 0; g <= N; g++) {
295 init_collected_gen(g,n_gc_threads);
296 }
297
298 // Initialise all the generations/steps that we're *not* collecting.
299 for (g = N+1; g < RtsFlags.GcFlags.generations; g++) {
300 init_uncollected_gen(g,n_gc_threads);
301 }
302
303 /* Allocate a mark stack if we're doing a major collection.
304 */
305 if (major_gc && oldest_gen->steps[0].mark) {
306 nat mark_stack_blocks;
307 mark_stack_blocks = stg_max(MARK_STACK_BLOCKS,
308 oldest_gen->steps[0].n_old_blocks / 100);
309 mark_stack_bdescr = allocGroup(mark_stack_blocks);
310 mark_stack = (StgPtr *)mark_stack_bdescr->start;
311 mark_sp = mark_stack;
312 mark_splim = mark_stack + (mark_stack_blocks * BLOCK_SIZE_W);
313 } else {
314 mark_stack_bdescr = NULL;
315 }
316
317 // this is the main thread
318 #ifdef THREADED_RTS
319 if (n_gc_threads == 1) {
320 SET_GCT(gc_threads[0]);
321 } else {
322 SET_GCT(gc_threads[cap->no]);
323 }
324 #else
325 SET_GCT(gc_threads[0]);
326 #endif
327
328 /* -----------------------------------------------------------------------
329 * follow all the roots that we know about:
330 */
331
332 // the main thread is running: this prevents any other threads from
333 // exiting prematurely, so we can start them now.
334 // NB. do this after the mutable lists have been saved above, otherwise
335 // the other GC threads will be writing into the old mutable lists.
336 inc_running();
337 wakeup_gc_threads(n_gc_threads, gct->thread_index);
338
339 // Mutable lists from each generation > N
340 // we want to *scavenge* these roots, not evacuate them: they're not
341 // going to move in this GC.
342 // Also do them in reverse generation order, for the usual reason:
343 // namely to reduce the likelihood of spurious old->new pointers.
344 //
345 for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
346 scavenge_mutable_list(generations[g].saved_mut_list, &generations[g]);
347 freeChain_sync(generations[g].saved_mut_list);
348 generations[g].saved_mut_list = NULL;
349
350 }
351
352 // scavenge the capability-private mutable lists. This isn't part
353 // of markSomeCapabilities() because markSomeCapabilities() can only
354 // call back into the GC via mark_root() (due to the gct register
355 // variable).
356 if (n_gc_threads == 1) {
357 for (n = 0; n < n_capabilities; n++) {
358 scavenge_capability_mut_lists(&capabilities[n]);
359 }
360 } else {
361 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
362 }
363
364 // follow roots from the CAF list (used by GHCi)
365 gct->evac_step = 0;
366 markCAFs(mark_root, gct);
367
368 // follow all the roots that the application knows about.
369 gct->evac_step = 0;
370 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
371 rtsTrue/*prune sparks*/);
372
373 #if defined(RTS_USER_SIGNALS)
374 // mark the signal handlers (signals should be already blocked)
375 markSignalHandlers(mark_root, gct);
376 #endif
377
378 // Mark the weak pointer list, and prepare to detect dead weak pointers.
379 markWeakPtrList();
380 initWeakForGC();
381
382 // Mark the stable pointer table.
383 markStablePtrTable(mark_root, gct);
384
385 /* -------------------------------------------------------------------------
386 * Repeatedly scavenge all the areas we know about until there's no
387 * more scavenging to be done.
388 */
389 for (;;)
390 {
391 scavenge_until_all_done();
392 // The other threads are now stopped. We might recurse back to
393 // here, but from now on this is the only thread.
394
395 // if any blackholes are alive, make the threads that wait on
396 // them alive too.
397 if (traverseBlackholeQueue()) {
398 inc_running();
399 continue;
400 }
401
402 // must be last... invariant is that everything is fully
403 // scavenged at this point.
404 if (traverseWeakPtrList()) { // returns rtsTrue if evaced something
405 inc_running();
406 continue;
407 }
408
409 // If we get to here, there's really nothing left to do.
410 break;
411 }
412
413 shutdown_gc_threads(n_gc_threads, gct->thread_index);
414
415 // Update pointers from the Task list
416 update_task_list();
417
418 // Now see which stable names are still alive.
419 gcStablePtrTable();
420
421 #ifdef PROFILING
422 // We call processHeapClosureForDead() on every closure destroyed during
423 // the current garbage collection, so we invoke LdvCensusForDead().
424 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
425 || RtsFlags.ProfFlags.bioSelector != NULL)
426 LdvCensusForDead(N);
427 #endif
428
429 // NO MORE EVACUATION AFTER THIS POINT!
430
431 // Two-space collector: free the old to-space.
432 // g0s0->old_blocks is the old nursery
433 // g0s0->blocks is to-space from the previous GC
434 if (RtsFlags.GcFlags.generations == 1) {
435 if (g0s0->blocks != NULL) {
436 freeChain(g0s0->blocks);
437 g0s0->blocks = NULL;
438 }
439 }
440
441 // For each workspace, in each thread, move the copied blocks to the step
442 {
443 gc_thread *thr;
444 step_workspace *ws;
445 bdescr *prev, *next;
446
447 for (t = 0; t < n_gc_threads; t++) {
448 thr = gc_threads[t];
449
450 // not step 0
451 if (RtsFlags.GcFlags.generations == 1) {
452 s = 0;
453 } else {
454 s = 1;
455 }
456 for (; s < total_steps; s++) {
457 ws = &thr->steps[s];
458
459 // Push the final block
460 if (ws->todo_bd) {
461 push_scanned_block(ws->todo_bd, ws);
462 }
463
464 ASSERT(gct->scan_bd == NULL);
465 ASSERT(countBlocks(ws->scavd_list) == ws->n_scavd_blocks);
466
467 prev = NULL;
468 for (bd = ws->scavd_list; bd != NULL; bd = bd->link) {
469 ws->step->n_words += bd->free - bd->start;
470 prev = bd;
471 }
472 if (prev != NULL) {
473 prev->link = ws->step->blocks;
474 ws->step->blocks = ws->scavd_list;
475 }
476 ws->step->n_blocks += ws->n_scavd_blocks;
477 }
478 }
479
480 // Add all the partial blocks *after* we've added all the full
481 // blocks. This is so that we can grab the partial blocks back
482 // again and try to fill them up in the next GC.
483 for (t = 0; t < n_gc_threads; t++) {
484 thr = gc_threads[t];
485
486 // not step 0
487 if (RtsFlags.GcFlags.generations == 1) {
488 s = 0;
489 } else {
490 s = 1;
491 }
492 for (; s < total_steps; s++) {
493 ws = &thr->steps[s];
494
495 prev = NULL;
496 for (bd = ws->part_list; bd != NULL; bd = next) {
497 next = bd->link;
498 if (bd->free == bd->start) {
499 if (prev == NULL) {
500 ws->part_list = next;
501 } else {
502 prev->link = next;
503 }
504 freeGroup(bd);
505 ws->n_part_blocks--;
506 } else {
507 ws->step->n_words += bd->free - bd->start;
508 prev = bd;
509 }
510 }
511 if (prev != NULL) {
512 prev->link = ws->step->blocks;
513 ws->step->blocks = ws->part_list;
514 }
515 ws->step->n_blocks += ws->n_part_blocks;
516
517 ASSERT(countBlocks(ws->step->blocks) == ws->step->n_blocks);
518 ASSERT(countOccupied(ws->step->blocks) == ws->step->n_words);
519 }
520 }
521 }
522
523 // Finally: compact or sweep the oldest generation.
524 if (major_gc && oldest_gen->steps[0].mark) {
525 if (oldest_gen->steps[0].compact)
526 compact(gct->scavenged_static_objects);
527 else
528 sweep(&oldest_gen->steps[0]);
529 }
530
531 /* run through all the generations/steps and tidy up
532 */
533 copied = 0;
534 max_copied = 0;
535 avg_copied = 0;
536 {
537 nat i;
538 for (i=0; i < n_gc_threads; i++) {
539 if (n_gc_threads > 1) {
540 debugTrace(DEBUG_gc,"thread %d:", i);
541 debugTrace(DEBUG_gc," copied %ld", gc_threads[i]->copied * sizeof(W_));
542 debugTrace(DEBUG_gc," scanned %ld", gc_threads[i]->scanned * sizeof(W_));
543 debugTrace(DEBUG_gc," any_work %ld", gc_threads[i]->any_work);
544 debugTrace(DEBUG_gc," no_work %ld", gc_threads[i]->no_work);
545 debugTrace(DEBUG_gc," scav_find_work %ld", gc_threads[i]->scav_find_work);
546 }
547 copied += gc_threads[i]->copied;
548 max_copied = stg_max(gc_threads[i]->copied, max_copied);
549 }
550 if (n_gc_threads == 1) {
551 max_copied = 0;
552 avg_copied = 0;
553 } else {
554 avg_copied = copied;
555 }
556 }
557
558 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
559
560 if (g == N) {
561 generations[g].collections++; // for stats
562 if (n_gc_threads > 1) generations[g].par_collections++;
563 }
564
565 // Count the mutable list as bytes "copied" for the purposes of
566 // stats. Every mutable list is copied during every GC.
567 if (g > 0) {
568 nat mut_list_size = 0;
569 for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
570 mut_list_size += bd->free - bd->start;
571 }
572 for (n = 0; n < n_capabilities; n++) {
573 for (bd = capabilities[n].mut_lists[g];
574 bd != NULL; bd = bd->link) {
575 mut_list_size += bd->free - bd->start;
576 }
577 }
578 copied += mut_list_size;
579
580 debugTrace(DEBUG_gc,
581 "mut_list_size: %lu (%d vars, %d arrays, %d MVARs, %d others)",
582 (unsigned long)(mut_list_size * sizeof(W_)),
583 mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS);
584 }
585
586 for (s = 0; s < generations[g].n_steps; s++) {
587 bdescr *next, *prev;
588 stp = &generations[g].steps[s];
589
590 // for generations we collected...
591 if (g <= N) {
592
593 /* free old memory and shift to-space into from-space for all
594 * the collected steps (except the allocation area). These
595 * freed blocks will probaby be quickly recycled.
596 */
597 if (!(g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1)) {
598 if (stp->mark)
599 {
600 // tack the new blocks on the end of the existing blocks
601 if (stp->old_blocks != NULL) {
602
603 prev = NULL;
604 for (bd = stp->old_blocks; bd != NULL; bd = next) {
605
606 next = bd->link;
607
608 if (!(bd->flags & BF_MARKED))
609 {
610 if (prev == NULL) {
611 stp->old_blocks = next;
612 } else {
613 prev->link = next;
614 }
615 freeGroup(bd);
616 stp->n_old_blocks--;
617 }
618 else
619 {
620 stp->n_words += bd->free - bd->start;
621
622 // NB. this step might not be compacted next
623 // time, so reset the BF_MARKED flags.
624 // They are set before GC if we're going to
625 // compact. (search for BF_MARKED above).
626 bd->flags &= ~BF_MARKED;
627
628 // between GCs, all blocks in the heap except
629 // for the nursery have the BF_EVACUATED flag set.
630 bd->flags |= BF_EVACUATED;
631
632 prev = bd;
633 }
634 }
635
636 if (prev != NULL) {
637 prev->link = stp->blocks;
638 stp->blocks = stp->old_blocks;
639 }
640 }
641 // add the new blocks to the block tally
642 stp->n_blocks += stp->n_old_blocks;
643 ASSERT(countBlocks(stp->blocks) == stp->n_blocks);
644 ASSERT(countOccupied(stp->blocks) == stp->n_words);
645 }
646 else // not copacted
647 {
648 freeChain(stp->old_blocks);
649 }
650 stp->old_blocks = NULL;
651 stp->n_old_blocks = 0;
652 }
653
654 /* LARGE OBJECTS. The current live large objects are chained on
655 * scavenged_large, having been moved during garbage
656 * collection from large_objects. Any objects left on
657 * large_objects list are therefore dead, so we free them here.
658 */
659 for (bd = stp->large_objects; bd != NULL; bd = next) {
660 next = bd->link;
661 freeGroup(bd);
662 bd = next;
663 }
664
665 stp->large_objects = stp->scavenged_large_objects;
666 stp->n_large_blocks = stp->n_scavenged_large_blocks;
667
668 }
669 else // for older generations...
670 {
671 /* For older generations, we need to append the
672 * scavenged_large_object list (i.e. large objects that have been
673 * promoted during this GC) to the large_object list for that step.
674 */
675 for (bd = stp->scavenged_large_objects; bd; bd = next) {
676 next = bd->link;
677 dbl_link_onto(bd, &stp->large_objects);
678 }
679
680 // add the new blocks we promoted during this GC
681 stp->n_large_blocks += stp->n_scavenged_large_blocks;
682 }
683 }
684 }
685
686 // update the max size of older generations after a major GC
687 resize_generations();
688
689 // Calculate the amount of live data for stats.
690 live = calcLiveWords();
691
692 // Free the small objects allocated via allocate(), since this will
693 // all have been copied into G0S1 now.
694 if (RtsFlags.GcFlags.generations > 1) {
695 if (g0s0->blocks != NULL) {
696 freeChain(g0s0->blocks);
697 g0s0->blocks = NULL;
698 }
699 g0s0->n_blocks = 0;
700 g0s0->n_words = 0;
701 }
702 alloc_blocks = 0;
703 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
704
705 // Start a new pinned_object_block
706 pinned_object_block = NULL;
707
708 // Free the mark stack.
709 if (mark_stack_bdescr != NULL) {
710 freeGroup(mark_stack_bdescr);
711 }
712
713 // Free any bitmaps.
714 for (g = 0; g <= N; g++) {
715 for (s = 0; s < generations[g].n_steps; s++) {
716 stp = &generations[g].steps[s];
717 if (stp->bitmap != NULL) {
718 freeGroup(stp->bitmap);
719 stp->bitmap = NULL;
720 }
721 }
722 }
723
724 resize_nursery();
725
726 // mark the garbage collected CAFs as dead
727 #if 0 && defined(DEBUG) // doesn't work at the moment
728 if (major_gc) { gcCAFs(); }
729 #endif
730
731 #ifdef PROFILING
732 // resetStaticObjectForRetainerProfiling() must be called before
733 // zeroing below.
734 if (n_gc_threads > 1) {
735 barf("profiling is currently broken with multi-threaded GC");
736 // ToDo: fix the gct->scavenged_static_objects below
737 }
738 resetStaticObjectForRetainerProfiling(gct->scavenged_static_objects);
739 #endif
740
741 // zero the scavenged static object list
742 if (major_gc) {
743 nat i;
744 for (i = 0; i < n_gc_threads; i++) {
745 zero_static_object_list(gc_threads[i]->scavenged_static_objects);
746 }
747 }
748
749 // Reset the nursery
750 resetNurseries();
751
752 // start any pending finalizers
753 RELEASE_SM_LOCK;
754 scheduleFinalizers(cap, old_weak_ptr_list);
755 ACQUIRE_SM_LOCK;
756
757 // send exceptions to any threads which were about to die
758 RELEASE_SM_LOCK;
759 resurrectThreads(resurrected_threads);
760 performPendingThrowTos(exception_threads);
761 ACQUIRE_SM_LOCK;
762
763 // Update the stable pointer hash table.
764 updateStablePtrTable(major_gc);
765
766 // check sanity after GC
767 IF_DEBUG(sanity, checkSanity());
768
769 // extra GC trace info
770 IF_DEBUG(gc, statDescribeGens());
771
772 #ifdef DEBUG
773 // symbol-table based profiling
774 /* heapCensus(to_blocks); */ /* ToDo */
775 #endif
776
777 // restore enclosing cost centre
778 #ifdef PROFILING
779 CCCS = prev_CCS;
780 #endif
781
782 #ifdef DEBUG
783 // check for memory leaks if DEBUG is on
784 memInventory(traceClass(DEBUG_gc));
785 #endif
786
787 #ifdef RTS_GTK_FRONTPANEL
788 if (RtsFlags.GcFlags.frontpanel) {
789 updateFrontPanelAfterGC( N, live );
790 }
791 #endif
792
793 // ok, GC over: tell the stats department what happened.
794 slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
795 stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
796
797 // unlock the StablePtr table
798 stablePtrPostGC();
799
800 // Guess which generation we'll collect *next* time
801 initialise_N(force_major_gc);
802
803 #if defined(RTS_USER_SIGNALS)
804 if (RtsFlags.MiscFlags.install_signal_handlers) {
805 // unblock signals again
806 unblockUserSignals();
807 }
808 #endif
809
810 RELEASE_SM_LOCK;
811
812 SET_GCT(saved_gct);
813 }
814
815 /* -----------------------------------------------------------------------------
816 Figure out which generation to collect, initialise N and major_gc.
817
818 Also returns the total number of blocks in generations that will be
819 collected.
820 -------------------------------------------------------------------------- */
821
822 static nat
823 initialise_N (rtsBool force_major_gc)
824 {
825 int g;
826 nat s, blocks, blocks_total;
827
828 blocks = 0;
829 blocks_total = 0;
830
831 if (force_major_gc) {
832 N = RtsFlags.GcFlags.generations - 1;
833 } else {
834 N = 0;
835 }
836
837 for (g = RtsFlags.GcFlags.generations - 1; g >= 0; g--) {
838 blocks = 0;
839 for (s = 0; s < generations[g].n_steps; s++) {
840 blocks += generations[g].steps[s].n_words / BLOCK_SIZE_W;
841 blocks += generations[g].steps[s].n_large_blocks;
842 }
843 if (blocks >= generations[g].max_blocks) {
844 N = stg_max(N,g);
845 }
846 if ((nat)g <= N) {
847 blocks_total += blocks;
848 }
849 }
850
851 blocks_total += countNurseryBlocks();
852
853 major_gc = (N == RtsFlags.GcFlags.generations-1);
854 return blocks_total;
855 }
856
857 /* -----------------------------------------------------------------------------
858 Initialise the gc_thread structures.
859 -------------------------------------------------------------------------- */
860
861 #define GC_THREAD_INACTIVE 0
862 #define GC_THREAD_STANDING_BY 1
863 #define GC_THREAD_RUNNING 2
864 #define GC_THREAD_WAITING_TO_CONTINUE 3
865
866 static void
867 new_gc_thread (nat n, gc_thread *t)
868 {
869 nat s;
870 step_workspace *ws;
871
872 #ifdef THREADED_RTS
873 t->id = 0;
874 initSpinLock(&t->gc_spin);
875 initSpinLock(&t->mut_spin);
876 ACQUIRE_SPIN_LOCK(&t->gc_spin);
877 t->wakeup = GC_THREAD_INACTIVE; // starts true, so we can wait for the
878 // thread to start up, see wakeup_gc_threads
879 #endif
880
881 t->thread_index = n;
882 t->free_blocks = NULL;
883 t->gc_count = 0;
884
885 init_gc_thread(t);
886
887 #ifdef USE_PAPI
888 t->papi_events = -1;
889 #endif
890
891 for (s = 0; s < total_steps; s++)
892 {
893 ws = &t->steps[s];
894 ws->step = &all_steps[s];
895 ASSERT(s == ws->step->abs_no);
896 ws->my_gct = t;
897
898 ws->todo_bd = NULL;
899 ws->todo_q = newWSDeque(128);
900 ws->todo_overflow = NULL;
901 ws->n_todo_overflow = 0;
902
903 ws->part_list = NULL;
904 ws->n_part_blocks = 0;
905
906 ws->scavd_list = NULL;
907 ws->n_scavd_blocks = 0;
908 }
909 }
910
911
912 void
913 initGcThreads (void)
914 {
915 if (gc_threads == NULL) {
916 #if defined(THREADED_RTS)
917 nat i;
918 gc_threads = stgMallocBytes (RtsFlags.ParFlags.nNodes *
919 sizeof(gc_thread*),
920 "alloc_gc_threads");
921
922 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
923 gc_threads[i] =
924 stgMallocBytes(sizeof(gc_thread) + total_steps * sizeof(step_workspace),
925 "alloc_gc_threads");
926
927 new_gc_thread(i, gc_threads[i]);
928 }
929 #else
930 gc_threads = stgMallocBytes (sizeof(gc_thread*),"alloc_gc_threads");
931 gc_threads[0] = gct;
932 new_gc_thread(0,gc_threads[0]);
933 #endif
934 }
935 }
936
937 void
938 freeGcThreads (void)
939 {
940 if (gc_threads != NULL) {
941 #if defined(THREADED_RTS)
942 nat i;
943 for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
944 stgFree (gc_threads[i]);
945 }
946 stgFree (gc_threads);
947 #else
948 stgFree (gc_threads);
949 #endif
950 gc_threads = NULL;
951 }
952 }
953
954 /* ----------------------------------------------------------------------------
955 Start GC threads
956 ------------------------------------------------------------------------- */
957
958 static volatile StgWord gc_running_threads;
959
960 static StgWord
961 inc_running (void)
962 {
963 StgWord new;
964 new = atomic_inc(&gc_running_threads);
965 ASSERT(new <= n_gc_threads);
966 return new;
967 }
968
969 static StgWord
970 dec_running (void)
971 {
972 ASSERT(gc_running_threads != 0);
973 return atomic_dec(&gc_running_threads);
974 }
975
976 static rtsBool
977 any_work (void)
978 {
979 int s;
980 step_workspace *ws;
981
982 gct->any_work++;
983
984 write_barrier();
985
986 // scavenge objects in compacted generation
987 if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
988 (mark_stack_bdescr != NULL && !mark_stack_empty())) {
989 return rtsTrue;
990 }
991
992 // Check for global work in any step. We don't need to check for
993 // local work, because we have already exited scavenge_loop(),
994 // which means there is no local work for this thread.
995 for (s = total_steps-1; s >= 0; s--) {
996 if (s == 0 && RtsFlags.GcFlags.generations > 1) {
997 continue;
998 }
999 ws = &gct->steps[s];
1000 if (ws->todo_large_objects) return rtsTrue;
1001 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
1002 if (ws->todo_overflow) return rtsTrue;
1003 }
1004
1005 #if defined(THREADED_RTS)
1006 if (work_stealing) {
1007 nat n;
1008 // look for work to steal
1009 for (n = 0; n < n_gc_threads; n++) {
1010 if (n == gct->thread_index) continue;
1011 for (s = total_steps-1; s >= 0; s--) {
1012 ws = &gc_threads[n]->steps[s];
1013 if (!looksEmptyWSDeque(ws->todo_q)) return rtsTrue;
1014 }
1015 }
1016 }
1017 #endif
1018
1019 gct->no_work++;
1020
1021 return rtsFalse;
1022 }
1023
1024 static void
1025 scavenge_until_all_done (void)
1026 {
1027 nat r;
1028
1029 debugTrace(DEBUG_gc, "GC thread %d working", gct->thread_index);
1030
1031 loop:
1032 #if defined(THREADED_RTS)
1033 if (n_gc_threads > 1) {
1034 scavenge_loop();
1035 } else {
1036 scavenge_loop1();
1037 }
1038 #else
1039 scavenge_loop();
1040 #endif
1041
1042 // scavenge_loop() only exits when there's no work to do
1043 r = dec_running();
1044
1045 debugTrace(DEBUG_gc, "GC thread %d idle (%d still running)",
1046 gct->thread_index, r);
1047
1048 while (gc_running_threads != 0) {
1049 // usleep(1);
1050 if (any_work()) {
1051 inc_running();
1052 goto loop;
1053 }
1054 // any_work() does not remove the work from the queue, it
1055 // just checks for the presence of work. If we find any,
1056 // then we increment gc_running_threads and go back to
1057 // scavenge_loop() to perform any pending work.
1058 }
1059
1060 // All threads are now stopped
1061 debugTrace(DEBUG_gc, "GC thread %d finished.", gct->thread_index);
1062 }
1063
1064 #if defined(THREADED_RTS)
1065
1066 void
1067 gcWorkerThread (Capability *cap)
1068 {
1069 gc_thread *saved_gct;
1070
1071 // necessary if we stole a callee-saves register for gct:
1072 saved_gct = gct;
1073
1074 cap->in_gc = rtsTrue;
1075
1076 gct = gc_threads[cap->no];
1077 gct->id = osThreadId();
1078
1079 // Wait until we're told to wake up
1080 RELEASE_SPIN_LOCK(&gct->mut_spin);
1081 gct->wakeup = GC_THREAD_STANDING_BY;
1082 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1083 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1084
1085 #ifdef USE_PAPI
1086 // start performance counters in this thread...
1087 if (gct->papi_events == -1) {
1088 papi_init_eventset(&gct->papi_events);
1089 }
1090 papi_thread_start_gc1_count(gct->papi_events);
1091 #endif
1092
1093 // Every thread evacuates some roots.
1094 gct->evac_step = 0;
1095 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1096 rtsTrue/*prune sparks*/);
1097 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1098
1099 scavenge_until_all_done();
1100
1101 #ifdef USE_PAPI
1102 // count events in this thread towards the GC totals
1103 papi_thread_stop_gc1_count(gct->papi_events);
1104 #endif
1105
1106 // Wait until we're told to continue
1107 RELEASE_SPIN_LOCK(&gct->gc_spin);
1108 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1109 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1110 gct->thread_index);
1111 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1112 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1113
1114 SET_GCT(saved_gct);
1115 }
1116
1117 #endif
1118
1119 #if defined(THREADED_RTS)
1120
1121 void
1122 waitForGcThreads (Capability *cap USED_IF_THREADS)
1123 {
1124 nat n_threads = RtsFlags.ParFlags.nNodes;
1125 nat me = cap->no;
1126 nat i, j;
1127 rtsBool retry = rtsTrue;
1128
1129 while(retry) {
1130 for (i=0; i < n_threads; i++) {
1131 if (i == me) continue;
1132 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1133 prodCapability(&capabilities[i], cap->running_task);
1134 }
1135 }
1136 for (j=0; j < 10000000; j++) {
1137 retry = rtsFalse;
1138 for (i=0; i < n_threads; i++) {
1139 if (i == me) continue;
1140 write_barrier();
1141 setContextSwitches();
1142 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1143 retry = rtsTrue;
1144 }
1145 }
1146 if (!retry) break;
1147 }
1148 }
1149 }
1150
1151 #endif // THREADED_RTS
1152
1153 static void
1154 start_gc_threads (void)
1155 {
1156 #if defined(THREADED_RTS)
1157 gc_running_threads = 0;
1158 #endif
1159 }
1160
1161 static void
1162 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1163 {
1164 #if defined(THREADED_RTS)
1165 nat i;
1166 for (i=0; i < n_threads; i++) {
1167 if (i == me) continue;
1168 inc_running();
1169 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1170 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1171
1172 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1173 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1174 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1175 }
1176 #endif
1177 }
1178
1179 // After GC is complete, we must wait for all GC threads to enter the
1180 // standby state, otherwise they may still be executing inside
1181 // any_work(), and may even remain awake until the next GC starts.
1182 static void
1183 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1184 {
1185 #if defined(THREADED_RTS)
1186 nat i;
1187 for (i=0; i < n_threads; i++) {
1188 if (i == me) continue;
1189 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1190 }
1191 #endif
1192 }
1193
1194 #if defined(THREADED_RTS)
1195 void
1196 releaseGCThreads (Capability *cap USED_IF_THREADS)
1197 {
1198 nat n_threads = RtsFlags.ParFlags.nNodes;
1199 nat me = cap->no;
1200 nat i;
1201 for (i=0; i < n_threads; i++) {
1202 if (i == me) continue;
1203 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1204 barf("releaseGCThreads");
1205
1206 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1207 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1208 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1209 }
1210 }
1211 #endif
1212
1213 /* ----------------------------------------------------------------------------
1214 Initialise a generation that is to be collected
1215 ------------------------------------------------------------------------- */
1216
1217 static void
1218 init_collected_gen (nat g, nat n_threads)
1219 {
1220 nat s, t, i;
1221 step_workspace *ws;
1222 step *stp;
1223 bdescr *bd;
1224
1225 // Throw away the current mutable list. Invariant: the mutable
1226 // list always has at least one block; this means we can avoid a
1227 // check for NULL in recordMutable().
1228 if (g != 0) {
1229 freeChain(generations[g].mut_list);
1230 generations[g].mut_list = allocBlock();
1231 for (i = 0; i < n_capabilities; i++) {
1232 freeChain(capabilities[i].mut_lists[g]);
1233 capabilities[i].mut_lists[g] = allocBlock();
1234 }
1235 }
1236
1237 for (s = 0; s < generations[g].n_steps; s++) {
1238
1239 stp = &generations[g].steps[s];
1240 ASSERT(stp->gen_no == g);
1241
1242 // we'll construct a new list of threads in this step
1243 // during GC, throw away the current list.
1244 stp->old_threads = stp->threads;
1245 stp->threads = END_TSO_QUEUE;
1246
1247 // generation 0, step 0 doesn't need to-space
1248 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1249 continue;
1250 }
1251
1252 // deprecate the existing blocks
1253 stp->old_blocks = stp->blocks;
1254 stp->n_old_blocks = stp->n_blocks;
1255 stp->blocks = NULL;
1256 stp->n_blocks = 0;
1257 stp->n_words = 0;
1258 stp->live_estimate = 0;
1259
1260 // initialise the large object queues.
1261 stp->scavenged_large_objects = NULL;
1262 stp->n_scavenged_large_blocks = 0;
1263
1264 // mark the small objects as from-space
1265 for (bd = stp->old_blocks; bd; bd = bd->link) {
1266 bd->flags &= ~BF_EVACUATED;
1267 }
1268
1269 // mark the large objects as from-space
1270 for (bd = stp->large_objects; bd; bd = bd->link) {
1271 bd->flags &= ~BF_EVACUATED;
1272 }
1273
1274 // for a compacted step, we need to allocate the bitmap
1275 if (stp->mark) {
1276 nat bitmap_size; // in bytes
1277 bdescr *bitmap_bdescr;
1278 StgWord *bitmap;
1279
1280 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1281
1282 if (bitmap_size > 0) {
1283 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1284 / BLOCK_SIZE);
1285 stp->bitmap = bitmap_bdescr;
1286 bitmap = bitmap_bdescr->start;
1287
1288 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1289 bitmap_size, bitmap);
1290
1291 // don't forget to fill it with zeros!
1292 memset(bitmap, 0, bitmap_size);
1293
1294 // For each block in this step, point to its bitmap from the
1295 // block descriptor.
1296 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1297 bd->u.bitmap = bitmap;
1298 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1299
1300 // Also at this point we set the BF_MARKED flag
1301 // for this block. The invariant is that
1302 // BF_MARKED is always unset, except during GC
1303 // when it is set on those blocks which will be
1304 // compacted.
1305 if (!(bd->flags & BF_FRAGMENTED)) {
1306 bd->flags |= BF_MARKED;
1307 }
1308 }
1309 }
1310 }
1311 }
1312
1313 // For each GC thread, for each step, allocate a "todo" block to
1314 // store evacuated objects to be scavenged, and a block to store
1315 // evacuated objects that do not need to be scavenged.
1316 for (t = 0; t < n_threads; t++) {
1317 for (s = 0; s < generations[g].n_steps; s++) {
1318
1319 // we don't copy objects into g0s0, unless -G0
1320 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1321
1322 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1323
1324 ws->todo_large_objects = NULL;
1325
1326 ws->part_list = NULL;
1327 ws->n_part_blocks = 0;
1328
1329 // allocate the first to-space block; extra blocks will be
1330 // chained on as necessary.
1331 ws->todo_bd = NULL;
1332 ASSERT(looksEmptyWSDeque(ws->todo_q));
1333 alloc_todo_block(ws,0);
1334
1335 ws->todo_overflow = NULL;
1336 ws->n_todo_overflow = 0;
1337
1338 ws->scavd_list = NULL;
1339 ws->n_scavd_blocks = 0;
1340 }
1341 }
1342 }
1343
1344
1345 /* ----------------------------------------------------------------------------
1346 Initialise a generation that is *not* to be collected
1347 ------------------------------------------------------------------------- */
1348
1349 static void
1350 init_uncollected_gen (nat g, nat threads)
1351 {
1352 nat s, t, n;
1353 step_workspace *ws;
1354 step *stp;
1355 bdescr *bd;
1356
1357 // save the current mutable lists for this generation, and
1358 // allocate a fresh block for each one. We'll traverse these
1359 // mutable lists as roots early on in the GC.
1360 generations[g].saved_mut_list = generations[g].mut_list;
1361 generations[g].mut_list = allocBlock();
1362 for (n = 0; n < n_capabilities; n++) {
1363 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1364 capabilities[n].mut_lists[g] = allocBlock();
1365 }
1366
1367 for (s = 0; s < generations[g].n_steps; s++) {
1368 stp = &generations[g].steps[s];
1369 stp->scavenged_large_objects = NULL;
1370 stp->n_scavenged_large_blocks = 0;
1371 }
1372
1373 for (s = 0; s < generations[g].n_steps; s++) {
1374
1375 stp = &generations[g].steps[s];
1376
1377 for (t = 0; t < threads; t++) {
1378 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1379
1380 ASSERT(looksEmptyWSDeque(ws->todo_q));
1381 ws->todo_large_objects = NULL;
1382
1383 ws->part_list = NULL;
1384 ws->n_part_blocks = 0;
1385
1386 ws->scavd_list = NULL;
1387 ws->n_scavd_blocks = 0;
1388
1389 // If the block at the head of the list in this generation
1390 // is less than 3/4 full, then use it as a todo block.
1391 if (stp->blocks && isPartiallyFull(stp->blocks))
1392 {
1393 ws->todo_bd = stp->blocks;
1394 ws->todo_free = ws->todo_bd->free;
1395 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1396 stp->blocks = stp->blocks->link;
1397 stp->n_blocks -= 1;
1398 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1399 ws->todo_bd->link = NULL;
1400 // we must scan from the current end point.
1401 ws->todo_bd->u.scan = ws->todo_bd->free;
1402 }
1403 else
1404 {
1405 ws->todo_bd = NULL;
1406 alloc_todo_block(ws,0);
1407 }
1408 }
1409
1410 // deal out any more partial blocks to the threads' part_lists
1411 t = 0;
1412 while (stp->blocks && isPartiallyFull(stp->blocks))
1413 {
1414 bd = stp->blocks;
1415 stp->blocks = bd->link;
1416 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1417 bd->link = ws->part_list;
1418 ws->part_list = bd;
1419 ws->n_part_blocks += 1;
1420 bd->u.scan = bd->free;
1421 stp->n_blocks -= 1;
1422 stp->n_words -= bd->free - bd->start;
1423 t++;
1424 if (t == n_gc_threads) t = 0;
1425 }
1426 }
1427 }
1428
1429 /* -----------------------------------------------------------------------------
1430 Initialise a gc_thread before GC
1431 -------------------------------------------------------------------------- */
1432
1433 static void
1434 init_gc_thread (gc_thread *t)
1435 {
1436 t->static_objects = END_OF_STATIC_LIST;
1437 t->scavenged_static_objects = END_OF_STATIC_LIST;
1438 t->scan_bd = NULL;
1439 t->mut_lists = capabilities[t->thread_index].mut_lists;
1440 t->evac_step = 0;
1441 t->failed_to_evac = rtsFalse;
1442 t->eager_promotion = rtsTrue;
1443 t->thunk_selector_depth = 0;
1444 t->copied = 0;
1445 t->scanned = 0;
1446 t->any_work = 0;
1447 t->no_work = 0;
1448 t->scav_find_work = 0;
1449 }
1450
1451 /* -----------------------------------------------------------------------------
1452 Function we pass to evacuate roots.
1453 -------------------------------------------------------------------------- */
1454
1455 static void
1456 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1457 {
1458 // we stole a register for gct, but this function is called from
1459 // *outside* the GC where the register variable is not in effect,
1460 // so we need to save and restore it here. NB. only call
1461 // mark_root() from the main GC thread, otherwise gct will be
1462 // incorrect.
1463 gc_thread *saved_gct;
1464 saved_gct = gct;
1465 SET_GCT(user);
1466
1467 evacuate(root);
1468
1469 SET_GCT(saved_gct);
1470 }
1471
1472 /* -----------------------------------------------------------------------------
1473 Initialising the static object & mutable lists
1474 -------------------------------------------------------------------------- */
1475
1476 static void
1477 zero_static_object_list(StgClosure* first_static)
1478 {
1479 StgClosure* p;
1480 StgClosure* link;
1481 const StgInfoTable *info;
1482
1483 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1484 info = get_itbl(p);
1485 link = *STATIC_LINK(info, p);
1486 *STATIC_LINK(info,p) = NULL;
1487 }
1488 }
1489
1490 /* ----------------------------------------------------------------------------
1491 Update the pointers from the task list
1492
1493 These are treated as weak pointers because we want to allow a main
1494 thread to get a BlockedOnDeadMVar exception in the same way as any
1495 other thread. Note that the threads should all have been retained
1496 by GC by virtue of being on the all_threads list, we're just
1497 updating pointers here.
1498 ------------------------------------------------------------------------- */
1499
1500 static void
1501 update_task_list (void)
1502 {
1503 Task *task;
1504 StgTSO *tso;
1505 for (task = all_tasks; task != NULL; task = task->all_link) {
1506 if (!task->stopped && task->tso) {
1507 ASSERT(task->tso->bound == task);
1508 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1509 if (tso == NULL) {
1510 barf("task %p: main thread %d has been GC'd",
1511 #ifdef THREADED_RTS
1512 (void *)task->id,
1513 #else
1514 (void *)task,
1515 #endif
1516 task->tso->id);
1517 }
1518 task->tso = tso;
1519 }
1520 }
1521 }
1522
1523 /* ----------------------------------------------------------------------------
1524 Reset the sizes of the older generations when we do a major
1525 collection.
1526
1527 CURRENT STRATEGY: make all generations except zero the same size.
1528 We have to stay within the maximum heap size, and leave a certain
1529 percentage of the maximum heap size available to allocate into.
1530 ------------------------------------------------------------------------- */
1531
1532 static void
1533 resize_generations (void)
1534 {
1535 nat g;
1536
1537 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1538 nat live, size, min_alloc, words;
1539 nat max = RtsFlags.GcFlags.maxHeapSize;
1540 nat gens = RtsFlags.GcFlags.generations;
1541
1542 // live in the oldest generations
1543 if (oldest_gen->steps[0].live_estimate != 0) {
1544 words = oldest_gen->steps[0].live_estimate;
1545 } else {
1546 words = oldest_gen->steps[0].n_words;
1547 }
1548 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1549 oldest_gen->steps[0].n_large_blocks;
1550
1551 // default max size for all generations except zero
1552 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1553 RtsFlags.GcFlags.minOldGenSize);
1554
1555 // minimum size for generation zero
1556 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1557 RtsFlags.GcFlags.minAllocAreaSize);
1558
1559 // Auto-enable compaction when the residency reaches a
1560 // certain percentage of the maximum heap size (default: 30%).
1561 if (RtsFlags.GcFlags.generations > 1 &&
1562 (RtsFlags.GcFlags.compact ||
1563 (max > 0 &&
1564 oldest_gen->steps[0].n_blocks >
1565 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1566 oldest_gen->steps[0].mark = 1;
1567 oldest_gen->steps[0].compact = 1;
1568 // debugBelch("compaction: on\n", live);
1569 } else {
1570 oldest_gen->steps[0].mark = 0;
1571 oldest_gen->steps[0].compact = 0;
1572 // debugBelch("compaction: off\n", live);
1573 }
1574
1575 if (RtsFlags.GcFlags.sweep) {
1576 oldest_gen->steps[0].mark = 1;
1577 }
1578
1579 // if we're going to go over the maximum heap size, reduce the
1580 // size of the generations accordingly. The calculation is
1581 // different if compaction is turned on, because we don't need
1582 // to double the space required to collect the old generation.
1583 if (max != 0) {
1584
1585 // this test is necessary to ensure that the calculations
1586 // below don't have any negative results - we're working
1587 // with unsigned values here.
1588 if (max < min_alloc) {
1589 heapOverflow();
1590 }
1591
1592 if (oldest_gen->steps[0].compact) {
1593 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1594 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1595 }
1596 } else {
1597 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1598 size = (max - min_alloc) / ((gens - 1) * 2);
1599 }
1600 }
1601
1602 if (size < live) {
1603 heapOverflow();
1604 }
1605 }
1606
1607 #if 0
1608 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1609 min_alloc, size, max);
1610 #endif
1611
1612 for (g = 0; g < gens; g++) {
1613 generations[g].max_blocks = size;
1614 }
1615 }
1616 }
1617
1618 /* -----------------------------------------------------------------------------
1619 Calculate the new size of the nursery, and resize it.
1620 -------------------------------------------------------------------------- */
1621
1622 static void
1623 resize_nursery (void)
1624 {
1625 if (RtsFlags.GcFlags.generations == 1)
1626 { // Two-space collector:
1627 nat blocks;
1628
1629 /* set up a new nursery. Allocate a nursery size based on a
1630 * function of the amount of live data (by default a factor of 2)
1631 * Use the blocks from the old nursery if possible, freeing up any
1632 * left over blocks.
1633 *
1634 * If we get near the maximum heap size, then adjust our nursery
1635 * size accordingly. If the nursery is the same size as the live
1636 * data (L), then we need 3L bytes. We can reduce the size of the
1637 * nursery to bring the required memory down near 2L bytes.
1638 *
1639 * A normal 2-space collector would need 4L bytes to give the same
1640 * performance we get from 3L bytes, reducing to the same
1641 * performance at 2L bytes.
1642 */
1643 blocks = g0s0->n_blocks;
1644
1645 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1646 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1647 RtsFlags.GcFlags.maxHeapSize )
1648 {
1649 long adjusted_blocks; // signed on purpose
1650 int pc_free;
1651
1652 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1653
1654 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1655 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1656
1657 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1658 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1659 {
1660 heapOverflow();
1661 }
1662 blocks = adjusted_blocks;
1663 }
1664 else
1665 {
1666 blocks *= RtsFlags.GcFlags.oldGenFactor;
1667 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1668 {
1669 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1670 }
1671 }
1672 resizeNurseries(blocks);
1673 }
1674 else // Generational collector
1675 {
1676 /*
1677 * If the user has given us a suggested heap size, adjust our
1678 * allocation area to make best use of the memory available.
1679 */
1680 if (RtsFlags.GcFlags.heapSizeSuggestion)
1681 {
1682 long blocks;
1683 nat needed = calcNeeded(); // approx blocks needed at next GC
1684
1685 /* Guess how much will be live in generation 0 step 0 next time.
1686 * A good approximation is obtained by finding the
1687 * percentage of g0s0 that was live at the last minor GC.
1688 *
1689 * We have an accurate figure for the amount of copied data in
1690 * 'copied', but we must convert this to a number of blocks, with
1691 * a small adjustment for estimated slop at the end of a block
1692 * (- 10 words).
1693 */
1694 if (N == 0)
1695 {
1696 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1697 / countNurseryBlocks();
1698 }
1699
1700 /* Estimate a size for the allocation area based on the
1701 * information available. We might end up going slightly under
1702 * or over the suggested heap size, but we should be pretty
1703 * close on average.
1704 *
1705 * Formula: suggested - needed
1706 * ----------------------------
1707 * 1 + g0s0_pcnt_kept/100
1708 *
1709 * where 'needed' is the amount of memory needed at the next
1710 * collection for collecting all steps except g0s0.
1711 */
1712 blocks =
1713 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1714 (100 + (long)g0s0_pcnt_kept);
1715
1716 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1717 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1718 }
1719
1720 resizeNurseries((nat)blocks);
1721 }
1722 else
1723 {
1724 // we might have added extra large blocks to the nursery, so
1725 // resize back to minAllocAreaSize again.
1726 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1727 }
1728 }
1729 }
1730
1731 /* -----------------------------------------------------------------------------
1732 Sanity code for CAF garbage collection.
1733
1734 With DEBUG turned on, we manage a CAF list in addition to the SRT
1735 mechanism. After GC, we run down the CAF list and blackhole any
1736 CAFs which have been garbage collected. This means we get an error
1737 whenever the program tries to enter a garbage collected CAF.
1738
1739 Any garbage collected CAFs are taken off the CAF list at the same
1740 time.
1741 -------------------------------------------------------------------------- */
1742
1743 #if 0 && defined(DEBUG)
1744
1745 static void
1746 gcCAFs(void)
1747 {
1748 StgClosure* p;
1749 StgClosure** pp;
1750 const StgInfoTable *info;
1751 nat i;
1752
1753 i = 0;
1754 p = caf_list;
1755 pp = &caf_list;
1756
1757 while (p != NULL) {
1758
1759 info = get_itbl(p);
1760
1761 ASSERT(info->type == IND_STATIC);
1762
1763 if (STATIC_LINK(info,p) == NULL) {
1764 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1765 // black hole it
1766 SET_INFO(p,&stg_BLACKHOLE_info);
1767 p = STATIC_LINK2(info,p);
1768 *pp = p;
1769 }
1770 else {
1771 pp = &STATIC_LINK2(info,p);
1772 p = *pp;
1773 i++;
1774 }
1775
1776 }
1777
1778 debugTrace(DEBUG_gccafs, "%d CAFs live", i);
1779 }
1780 #endif