d2217b8786f4ed257aa094e33eee7b04a3490db6
[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 cap->in_gc = rtsTrue;
1070
1071 gct = gc_threads[cap->no];
1072 gct->id = osThreadId();
1073
1074 // Wait until we're told to wake up
1075 RELEASE_SPIN_LOCK(&gct->mut_spin);
1076 gct->wakeup = GC_THREAD_STANDING_BY;
1077 debugTrace(DEBUG_gc, "GC thread %d standing by...", gct->thread_index);
1078 ACQUIRE_SPIN_LOCK(&gct->gc_spin);
1079
1080 #ifdef USE_PAPI
1081 // start performance counters in this thread...
1082 if (gct->papi_events == -1) {
1083 papi_init_eventset(&gct->papi_events);
1084 }
1085 papi_thread_start_gc1_count(gct->papi_events);
1086 #endif
1087
1088 // Every thread evacuates some roots.
1089 gct->evac_step = 0;
1090 markSomeCapabilities(mark_root, gct, gct->thread_index, n_gc_threads,
1091 rtsTrue/*prune sparks*/);
1092 scavenge_capability_mut_lists(&capabilities[gct->thread_index]);
1093
1094 scavenge_until_all_done();
1095
1096 #ifdef USE_PAPI
1097 // count events in this thread towards the GC totals
1098 papi_thread_stop_gc1_count(gct->papi_events);
1099 #endif
1100
1101 // Wait until we're told to continue
1102 RELEASE_SPIN_LOCK(&gct->gc_spin);
1103 gct->wakeup = GC_THREAD_WAITING_TO_CONTINUE;
1104 debugTrace(DEBUG_gc, "GC thread %d waiting to continue...",
1105 gct->thread_index);
1106 ACQUIRE_SPIN_LOCK(&gct->mut_spin);
1107 debugTrace(DEBUG_gc, "GC thread %d on my way...", gct->thread_index);
1108 }
1109
1110 #endif
1111
1112 #if defined(THREADED_RTS)
1113
1114 void
1115 waitForGcThreads (Capability *cap USED_IF_THREADS)
1116 {
1117 nat n_threads = RtsFlags.ParFlags.nNodes;
1118 nat me = cap->no;
1119 nat i, j;
1120 rtsBool retry = rtsTrue;
1121
1122 while(retry) {
1123 for (i=0; i < n_threads; i++) {
1124 if (i == me) continue;
1125 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1126 prodCapability(&capabilities[i], cap->running_task);
1127 }
1128 }
1129 for (j=0; j < 10000000; j++) {
1130 retry = rtsFalse;
1131 for (i=0; i < n_threads; i++) {
1132 if (i == me) continue;
1133 write_barrier();
1134 setContextSwitches();
1135 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) {
1136 retry = rtsTrue;
1137 }
1138 }
1139 if (!retry) break;
1140 }
1141 }
1142 }
1143
1144 #endif // THREADED_RTS
1145
1146 static void
1147 start_gc_threads (void)
1148 {
1149 #if defined(THREADED_RTS)
1150 gc_running_threads = 0;
1151 #endif
1152 }
1153
1154 static void
1155 wakeup_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1156 {
1157 #if defined(THREADED_RTS)
1158 nat i;
1159 for (i=0; i < n_threads; i++) {
1160 if (i == me) continue;
1161 inc_running();
1162 debugTrace(DEBUG_gc, "waking up gc thread %d", i);
1163 if (gc_threads[i]->wakeup != GC_THREAD_STANDING_BY) barf("wakeup_gc_threads");
1164
1165 gc_threads[i]->wakeup = GC_THREAD_RUNNING;
1166 ACQUIRE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1167 RELEASE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1168 }
1169 #endif
1170 }
1171
1172 // After GC is complete, we must wait for all GC threads to enter the
1173 // standby state, otherwise they may still be executing inside
1174 // any_work(), and may even remain awake until the next GC starts.
1175 static void
1176 shutdown_gc_threads (nat n_threads USED_IF_THREADS, nat me USED_IF_THREADS)
1177 {
1178 #if defined(THREADED_RTS)
1179 nat i;
1180 for (i=0; i < n_threads; i++) {
1181 if (i == me) continue;
1182 while (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE) { write_barrier(); }
1183 }
1184 #endif
1185 }
1186
1187 #if defined(THREADED_RTS)
1188 void
1189 releaseGCThreads (Capability *cap USED_IF_THREADS)
1190 {
1191 nat n_threads = RtsFlags.ParFlags.nNodes;
1192 nat me = cap->no;
1193 nat i;
1194 for (i=0; i < n_threads; i++) {
1195 if (i == me) continue;
1196 if (gc_threads[i]->wakeup != GC_THREAD_WAITING_TO_CONTINUE)
1197 barf("releaseGCThreads");
1198
1199 gc_threads[i]->wakeup = GC_THREAD_INACTIVE;
1200 ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
1201 RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
1202 }
1203 }
1204 #endif
1205
1206 /* ----------------------------------------------------------------------------
1207 Initialise a generation that is to be collected
1208 ------------------------------------------------------------------------- */
1209
1210 static void
1211 init_collected_gen (nat g, nat n_threads)
1212 {
1213 nat s, t, i;
1214 step_workspace *ws;
1215 step *stp;
1216 bdescr *bd;
1217
1218 // Throw away the current mutable list. Invariant: the mutable
1219 // list always has at least one block; this means we can avoid a
1220 // check for NULL in recordMutable().
1221 if (g != 0) {
1222 freeChain(generations[g].mut_list);
1223 generations[g].mut_list = allocBlock();
1224 for (i = 0; i < n_capabilities; i++) {
1225 freeChain(capabilities[i].mut_lists[g]);
1226 capabilities[i].mut_lists[g] = allocBlock();
1227 }
1228 }
1229
1230 for (s = 0; s < generations[g].n_steps; s++) {
1231
1232 stp = &generations[g].steps[s];
1233 ASSERT(stp->gen_no == g);
1234
1235 // we'll construct a new list of threads in this step
1236 // during GC, throw away the current list.
1237 stp->old_threads = stp->threads;
1238 stp->threads = END_TSO_QUEUE;
1239
1240 // generation 0, step 0 doesn't need to-space
1241 if (g == 0 && s == 0 && RtsFlags.GcFlags.generations > 1) {
1242 continue;
1243 }
1244
1245 // deprecate the existing blocks
1246 stp->old_blocks = stp->blocks;
1247 stp->n_old_blocks = stp->n_blocks;
1248 stp->blocks = NULL;
1249 stp->n_blocks = 0;
1250 stp->n_words = 0;
1251 stp->live_estimate = 0;
1252
1253 // initialise the large object queues.
1254 stp->scavenged_large_objects = NULL;
1255 stp->n_scavenged_large_blocks = 0;
1256
1257 // mark the small objects as from-space
1258 for (bd = stp->old_blocks; bd; bd = bd->link) {
1259 bd->flags &= ~BF_EVACUATED;
1260 }
1261
1262 // mark the large objects as from-space
1263 for (bd = stp->large_objects; bd; bd = bd->link) {
1264 bd->flags &= ~BF_EVACUATED;
1265 }
1266
1267 // for a compacted step, we need to allocate the bitmap
1268 if (stp->mark) {
1269 nat bitmap_size; // in bytes
1270 bdescr *bitmap_bdescr;
1271 StgWord *bitmap;
1272
1273 bitmap_size = stp->n_old_blocks * BLOCK_SIZE / (sizeof(W_)*BITS_PER_BYTE);
1274
1275 if (bitmap_size > 0) {
1276 bitmap_bdescr = allocGroup((lnat)BLOCK_ROUND_UP(bitmap_size)
1277 / BLOCK_SIZE);
1278 stp->bitmap = bitmap_bdescr;
1279 bitmap = bitmap_bdescr->start;
1280
1281 debugTrace(DEBUG_gc, "bitmap_size: %d, bitmap: %p",
1282 bitmap_size, bitmap);
1283
1284 // don't forget to fill it with zeros!
1285 memset(bitmap, 0, bitmap_size);
1286
1287 // For each block in this step, point to its bitmap from the
1288 // block descriptor.
1289 for (bd=stp->old_blocks; bd != NULL; bd = bd->link) {
1290 bd->u.bitmap = bitmap;
1291 bitmap += BLOCK_SIZE_W / (sizeof(W_)*BITS_PER_BYTE);
1292
1293 // Also at this point we set the BF_MARKED flag
1294 // for this block. The invariant is that
1295 // BF_MARKED is always unset, except during GC
1296 // when it is set on those blocks which will be
1297 // compacted.
1298 if (!(bd->flags & BF_FRAGMENTED)) {
1299 bd->flags |= BF_MARKED;
1300 }
1301 }
1302 }
1303 }
1304 }
1305
1306 // For each GC thread, for each step, allocate a "todo" block to
1307 // store evacuated objects to be scavenged, and a block to store
1308 // evacuated objects that do not need to be scavenged.
1309 for (t = 0; t < n_threads; t++) {
1310 for (s = 0; s < generations[g].n_steps; s++) {
1311
1312 // we don't copy objects into g0s0, unless -G0
1313 if (g==0 && s==0 && RtsFlags.GcFlags.generations > 1) continue;
1314
1315 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1316
1317 ws->todo_large_objects = NULL;
1318
1319 ws->part_list = NULL;
1320 ws->n_part_blocks = 0;
1321
1322 // allocate the first to-space block; extra blocks will be
1323 // chained on as necessary.
1324 ws->todo_bd = NULL;
1325 ASSERT(looksEmptyWSDeque(ws->todo_q));
1326 alloc_todo_block(ws,0);
1327
1328 ws->todo_overflow = NULL;
1329 ws->n_todo_overflow = 0;
1330
1331 ws->scavd_list = NULL;
1332 ws->n_scavd_blocks = 0;
1333 }
1334 }
1335 }
1336
1337
1338 /* ----------------------------------------------------------------------------
1339 Initialise a generation that is *not* to be collected
1340 ------------------------------------------------------------------------- */
1341
1342 static void
1343 init_uncollected_gen (nat g, nat threads)
1344 {
1345 nat s, t, n;
1346 step_workspace *ws;
1347 step *stp;
1348 bdescr *bd;
1349
1350 // save the current mutable lists for this generation, and
1351 // allocate a fresh block for each one. We'll traverse these
1352 // mutable lists as roots early on in the GC.
1353 generations[g].saved_mut_list = generations[g].mut_list;
1354 generations[g].mut_list = allocBlock();
1355 for (n = 0; n < n_capabilities; n++) {
1356 capabilities[n].saved_mut_lists[g] = capabilities[n].mut_lists[g];
1357 capabilities[n].mut_lists[g] = allocBlock();
1358 }
1359
1360 for (s = 0; s < generations[g].n_steps; s++) {
1361 stp = &generations[g].steps[s];
1362 stp->scavenged_large_objects = NULL;
1363 stp->n_scavenged_large_blocks = 0;
1364 }
1365
1366 for (s = 0; s < generations[g].n_steps; s++) {
1367
1368 stp = &generations[g].steps[s];
1369
1370 for (t = 0; t < threads; t++) {
1371 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1372
1373 ASSERT(looksEmptyWSDeque(ws->todo_q));
1374 ws->todo_large_objects = NULL;
1375
1376 ws->part_list = NULL;
1377 ws->n_part_blocks = 0;
1378
1379 ws->scavd_list = NULL;
1380 ws->n_scavd_blocks = 0;
1381
1382 // If the block at the head of the list in this generation
1383 // is less than 3/4 full, then use it as a todo block.
1384 if (stp->blocks && isPartiallyFull(stp->blocks))
1385 {
1386 ws->todo_bd = stp->blocks;
1387 ws->todo_free = ws->todo_bd->free;
1388 ws->todo_lim = ws->todo_bd->start + BLOCK_SIZE_W;
1389 stp->blocks = stp->blocks->link;
1390 stp->n_blocks -= 1;
1391 stp->n_words -= ws->todo_bd->free - ws->todo_bd->start;
1392 ws->todo_bd->link = NULL;
1393 // we must scan from the current end point.
1394 ws->todo_bd->u.scan = ws->todo_bd->free;
1395 }
1396 else
1397 {
1398 ws->todo_bd = NULL;
1399 alloc_todo_block(ws,0);
1400 }
1401 }
1402
1403 // deal out any more partial blocks to the threads' part_lists
1404 t = 0;
1405 while (stp->blocks && isPartiallyFull(stp->blocks))
1406 {
1407 bd = stp->blocks;
1408 stp->blocks = bd->link;
1409 ws = &gc_threads[t]->steps[g * RtsFlags.GcFlags.steps + s];
1410 bd->link = ws->part_list;
1411 ws->part_list = bd;
1412 ws->n_part_blocks += 1;
1413 bd->u.scan = bd->free;
1414 stp->n_blocks -= 1;
1415 stp->n_words -= bd->free - bd->start;
1416 t++;
1417 if (t == n_gc_threads) t = 0;
1418 }
1419 }
1420 }
1421
1422 /* -----------------------------------------------------------------------------
1423 Initialise a gc_thread before GC
1424 -------------------------------------------------------------------------- */
1425
1426 static void
1427 init_gc_thread (gc_thread *t)
1428 {
1429 t->static_objects = END_OF_STATIC_LIST;
1430 t->scavenged_static_objects = END_OF_STATIC_LIST;
1431 t->scan_bd = NULL;
1432 t->mut_lists = capabilities[t->thread_index].mut_lists;
1433 t->evac_step = 0;
1434 t->failed_to_evac = rtsFalse;
1435 t->eager_promotion = rtsTrue;
1436 t->thunk_selector_depth = 0;
1437 t->copied = 0;
1438 t->scanned = 0;
1439 t->any_work = 0;
1440 t->no_work = 0;
1441 t->scav_find_work = 0;
1442 }
1443
1444 /* -----------------------------------------------------------------------------
1445 Function we pass to evacuate roots.
1446 -------------------------------------------------------------------------- */
1447
1448 static void
1449 mark_root(void *user USED_IF_THREADS, StgClosure **root)
1450 {
1451 // we stole a register for gct, but this function is called from
1452 // *outside* the GC where the register variable is not in effect,
1453 // so we need to save and restore it here. NB. only call
1454 // mark_root() from the main GC thread, otherwise gct will be
1455 // incorrect.
1456 gc_thread *saved_gct;
1457 saved_gct = gct;
1458 SET_GCT(user);
1459
1460 evacuate(root);
1461
1462 SET_GCT(saved_gct);
1463 }
1464
1465 /* -----------------------------------------------------------------------------
1466 Initialising the static object & mutable lists
1467 -------------------------------------------------------------------------- */
1468
1469 static void
1470 zero_static_object_list(StgClosure* first_static)
1471 {
1472 StgClosure* p;
1473 StgClosure* link;
1474 const StgInfoTable *info;
1475
1476 for (p = first_static; p != END_OF_STATIC_LIST; p = link) {
1477 info = get_itbl(p);
1478 link = *STATIC_LINK(info, p);
1479 *STATIC_LINK(info,p) = NULL;
1480 }
1481 }
1482
1483 /* ----------------------------------------------------------------------------
1484 Update the pointers from the task list
1485
1486 These are treated as weak pointers because we want to allow a main
1487 thread to get a BlockedOnDeadMVar exception in the same way as any
1488 other thread. Note that the threads should all have been retained
1489 by GC by virtue of being on the all_threads list, we're just
1490 updating pointers here.
1491 ------------------------------------------------------------------------- */
1492
1493 static void
1494 update_task_list (void)
1495 {
1496 Task *task;
1497 StgTSO *tso;
1498 for (task = all_tasks; task != NULL; task = task->all_link) {
1499 if (!task->stopped && task->tso) {
1500 ASSERT(task->tso->bound == task);
1501 tso = (StgTSO *) isAlive((StgClosure *)task->tso);
1502 if (tso == NULL) {
1503 barf("task %p: main thread %d has been GC'd",
1504 #ifdef THREADED_RTS
1505 (void *)task->id,
1506 #else
1507 (void *)task,
1508 #endif
1509 task->tso->id);
1510 }
1511 task->tso = tso;
1512 }
1513 }
1514 }
1515
1516 /* ----------------------------------------------------------------------------
1517 Reset the sizes of the older generations when we do a major
1518 collection.
1519
1520 CURRENT STRATEGY: make all generations except zero the same size.
1521 We have to stay within the maximum heap size, and leave a certain
1522 percentage of the maximum heap size available to allocate into.
1523 ------------------------------------------------------------------------- */
1524
1525 static void
1526 resize_generations (void)
1527 {
1528 nat g;
1529
1530 if (major_gc && RtsFlags.GcFlags.generations > 1) {
1531 nat live, size, min_alloc, words;
1532 nat max = RtsFlags.GcFlags.maxHeapSize;
1533 nat gens = RtsFlags.GcFlags.generations;
1534
1535 // live in the oldest generations
1536 if (oldest_gen->steps[0].live_estimate != 0) {
1537 words = oldest_gen->steps[0].live_estimate;
1538 } else {
1539 words = oldest_gen->steps[0].n_words;
1540 }
1541 live = (words + BLOCK_SIZE_W - 1) / BLOCK_SIZE_W +
1542 oldest_gen->steps[0].n_large_blocks;
1543
1544 // default max size for all generations except zero
1545 size = stg_max(live * RtsFlags.GcFlags.oldGenFactor,
1546 RtsFlags.GcFlags.minOldGenSize);
1547
1548 // minimum size for generation zero
1549 min_alloc = stg_max((RtsFlags.GcFlags.pcFreeHeap * max) / 200,
1550 RtsFlags.GcFlags.minAllocAreaSize);
1551
1552 // Auto-enable compaction when the residency reaches a
1553 // certain percentage of the maximum heap size (default: 30%).
1554 if (RtsFlags.GcFlags.generations > 1 &&
1555 (RtsFlags.GcFlags.compact ||
1556 (max > 0 &&
1557 oldest_gen->steps[0].n_blocks >
1558 (RtsFlags.GcFlags.compactThreshold * max) / 100))) {
1559 oldest_gen->steps[0].mark = 1;
1560 oldest_gen->steps[0].compact = 1;
1561 // debugBelch("compaction: on\n", live);
1562 } else {
1563 oldest_gen->steps[0].mark = 0;
1564 oldest_gen->steps[0].compact = 0;
1565 // debugBelch("compaction: off\n", live);
1566 }
1567
1568 if (RtsFlags.GcFlags.sweep) {
1569 oldest_gen->steps[0].mark = 1;
1570 }
1571
1572 // if we're going to go over the maximum heap size, reduce the
1573 // size of the generations accordingly. The calculation is
1574 // different if compaction is turned on, because we don't need
1575 // to double the space required to collect the old generation.
1576 if (max != 0) {
1577
1578 // this test is necessary to ensure that the calculations
1579 // below don't have any negative results - we're working
1580 // with unsigned values here.
1581 if (max < min_alloc) {
1582 heapOverflow();
1583 }
1584
1585 if (oldest_gen->steps[0].compact) {
1586 if ( (size + (size - 1) * (gens - 2) * 2) + min_alloc > max ) {
1587 size = (max - min_alloc) / ((gens - 1) * 2 - 1);
1588 }
1589 } else {
1590 if ( (size * (gens - 1) * 2) + min_alloc > max ) {
1591 size = (max - min_alloc) / ((gens - 1) * 2);
1592 }
1593 }
1594
1595 if (size < live) {
1596 heapOverflow();
1597 }
1598 }
1599
1600 #if 0
1601 debugBelch("live: %d, min_alloc: %d, size : %d, max = %d\n", live,
1602 min_alloc, size, max);
1603 #endif
1604
1605 for (g = 0; g < gens; g++) {
1606 generations[g].max_blocks = size;
1607 }
1608 }
1609 }
1610
1611 /* -----------------------------------------------------------------------------
1612 Calculate the new size of the nursery, and resize it.
1613 -------------------------------------------------------------------------- */
1614
1615 static void
1616 resize_nursery (void)
1617 {
1618 if (RtsFlags.GcFlags.generations == 1)
1619 { // Two-space collector:
1620 nat blocks;
1621
1622 /* set up a new nursery. Allocate a nursery size based on a
1623 * function of the amount of live data (by default a factor of 2)
1624 * Use the blocks from the old nursery if possible, freeing up any
1625 * left over blocks.
1626 *
1627 * If we get near the maximum heap size, then adjust our nursery
1628 * size accordingly. If the nursery is the same size as the live
1629 * data (L), then we need 3L bytes. We can reduce the size of the
1630 * nursery to bring the required memory down near 2L bytes.
1631 *
1632 * A normal 2-space collector would need 4L bytes to give the same
1633 * performance we get from 3L bytes, reducing to the same
1634 * performance at 2L bytes.
1635 */
1636 blocks = g0s0->n_blocks;
1637
1638 if ( RtsFlags.GcFlags.maxHeapSize != 0 &&
1639 blocks * RtsFlags.GcFlags.oldGenFactor * 2 >
1640 RtsFlags.GcFlags.maxHeapSize )
1641 {
1642 long adjusted_blocks; // signed on purpose
1643 int pc_free;
1644
1645 adjusted_blocks = (RtsFlags.GcFlags.maxHeapSize - 2 * blocks);
1646
1647 debugTrace(DEBUG_gc, "near maximum heap size of 0x%x blocks, blocks = %d, adjusted to %ld",
1648 RtsFlags.GcFlags.maxHeapSize, blocks, adjusted_blocks);
1649
1650 pc_free = adjusted_blocks * 100 / RtsFlags.GcFlags.maxHeapSize;
1651 if (pc_free < RtsFlags.GcFlags.pcFreeHeap) /* might even * be < 0 */
1652 {
1653 heapOverflow();
1654 }
1655 blocks = adjusted_blocks;
1656 }
1657 else
1658 {
1659 blocks *= RtsFlags.GcFlags.oldGenFactor;
1660 if (blocks < RtsFlags.GcFlags.minAllocAreaSize)
1661 {
1662 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1663 }
1664 }
1665 resizeNurseries(blocks);
1666 }
1667 else // Generational collector
1668 {
1669 /*
1670 * If the user has given us a suggested heap size, adjust our
1671 * allocation area to make best use of the memory available.
1672 */
1673 if (RtsFlags.GcFlags.heapSizeSuggestion)
1674 {
1675 long blocks;
1676 nat needed = calcNeeded(); // approx blocks needed at next GC
1677
1678 /* Guess how much will be live in generation 0 step 0 next time.
1679 * A good approximation is obtained by finding the
1680 * percentage of g0s0 that was live at the last minor GC.
1681 *
1682 * We have an accurate figure for the amount of copied data in
1683 * 'copied', but we must convert this to a number of blocks, with
1684 * a small adjustment for estimated slop at the end of a block
1685 * (- 10 words).
1686 */
1687 if (N == 0)
1688 {
1689 g0s0_pcnt_kept = ((copied / (BLOCK_SIZE_W - 10)) * 100)
1690 / countNurseryBlocks();
1691 }
1692
1693 /* Estimate a size for the allocation area based on the
1694 * information available. We might end up going slightly under
1695 * or over the suggested heap size, but we should be pretty
1696 * close on average.
1697 *
1698 * Formula: suggested - needed
1699 * ----------------------------
1700 * 1 + g0s0_pcnt_kept/100
1701 *
1702 * where 'needed' is the amount of memory needed at the next
1703 * collection for collecting all steps except g0s0.
1704 */
1705 blocks =
1706 (((long)RtsFlags.GcFlags.heapSizeSuggestion - (long)needed) * 100) /
1707 (100 + (long)g0s0_pcnt_kept);
1708
1709 if (blocks < (long)RtsFlags.GcFlags.minAllocAreaSize) {
1710 blocks = RtsFlags.GcFlags.minAllocAreaSize;
1711 }
1712
1713 resizeNurseries((nat)blocks);
1714 }
1715 else
1716 {
1717 // we might have added extra large blocks to the nursery, so
1718 // resize back to minAllocAreaSize again.
1719 resizeNurseriesFixed(RtsFlags.GcFlags.minAllocAreaSize);
1720 }
1721 }
1722 }
1723
1724 /* -----------------------------------------------------------------------------
1725 Sanity code for CAF garbage collection.
1726
1727 With DEBUG turned on, we manage a CAF list in addition to the SRT
1728 mechanism. After GC, we run down the CAF list and blackhole any
1729 CAFs which have been garbage collected. This means we get an error
1730 whenever the program tries to enter a garbage collected CAF.
1731
1732 Any garbage collected CAFs are taken off the CAF list at the same
1733 time.
1734 -------------------------------------------------------------------------- */
1735
1736 #if 0 && defined(DEBUG)
1737
1738 static void
1739 gcCAFs(void)
1740 {
1741 StgClosure* p;
1742 StgClosure** pp;
1743 const StgInfoTable *info;
1744 nat i;
1745
1746 i = 0;
1747 p = caf_list;
1748 pp = &caf_list;
1749
1750 while (p != NULL) {
1751
1752 info = get_itbl(p);
1753
1754 ASSERT(info->type == IND_STATIC);
1755
1756 if (STATIC_LINK(info,p) == NULL) {
1757 debugTrace(DEBUG_gccafs, "CAF gc'd at 0x%04lx", (long)p);
1758 // black hole it
1759 SET_INFO(p,&stg_BLACKHOLE_info);
1760 p = STATIC_LINK2(info,p);
1761 *pp = p;
1762 }
1763 else {
1764 pp = &STATIC_LINK2(info,p);
1765 p = *pp;
1766 i++;
1767 }
1768
1769 }
1770
1771 debugTrace(DEBUG_gccafs, "%d CAFs live", i);
1772 }
1773 #endif