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comparison lib/lua/lua-5.2.2/lgc.c @ 1866:41cc4dd3c122

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Lua 5.2.2 added.
author Nomad
date Wed, 16 Oct 2013 13:34:26 +0200
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1848:3b39b70e8e93 1866:41cc4dd3c122
1 /*
2 ** $Id: lgc.c,v 2.140 2013/03/16 21:10:18 roberto Exp $
3 ** Garbage Collector
4 ** See Copyright Notice in lua.h
5 */
6
7 #include <string.h>
8
9 #define lgc_c
10 #define LUA_CORE
11
12 #include "lua.h"
13
14 #include "ldebug.h"
15 #include "ldo.h"
16 #include "lfunc.h"
17 #include "lgc.h"
18 #include "lmem.h"
19 #include "lobject.h"
20 #include "lstate.h"
21 #include "lstring.h"
22 #include "ltable.h"
23 #include "ltm.h"
24
25
26
27 /*
28 ** cost of sweeping one element (the size of a small object divided
29 ** by some adjust for the sweep speed)
30 */
31 #define GCSWEEPCOST ((sizeof(TString) + 4) / 4)
32
33 /* maximum number of elements to sweep in each single step */
34 #define GCSWEEPMAX (cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
35
36 /* maximum number of finalizers to call in each GC step */
37 #define GCFINALIZENUM 4
38
39
40 /*
41 ** macro to adjust 'stepmul': 'stepmul' is actually used like
42 ** 'stepmul / STEPMULADJ' (value chosen by tests)
43 */
44 #define STEPMULADJ 200
45
46
47 /*
48 ** macro to adjust 'pause': 'pause' is actually used like
49 ** 'pause / PAUSEADJ' (value chosen by tests)
50 */
51 #define PAUSEADJ 100
52
53
54 /*
55 ** 'makewhite' erases all color bits plus the old bit and then
56 ** sets only the current white bit
57 */
58 #define maskcolors (~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
59 #define makewhite(g,x) \
60 (gch(x)->marked = cast_byte((gch(x)->marked & maskcolors) | luaC_white(g)))
61
62 #define white2gray(x) resetbits(gch(x)->marked, WHITEBITS)
63 #define black2gray(x) resetbit(gch(x)->marked, BLACKBIT)
64
65
66 #define isfinalized(x) testbit(gch(x)->marked, FINALIZEDBIT)
67
68 #define checkdeadkey(n) lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
69
70
71 #define checkconsistency(obj) \
72 lua_longassert(!iscollectable(obj) || righttt(obj))
73
74
75 #define markvalue(g,o) { checkconsistency(o); \
76 if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
77
78 #define markobject(g,t) { if ((t) && iswhite(obj2gco(t))) \
79 reallymarkobject(g, obj2gco(t)); }
80
81 static void reallymarkobject (global_State *g, GCObject *o);
82
83
84 /*
85 ** {======================================================
86 ** Generic functions
87 ** =======================================================
88 */
89
90
91 /*
92 ** one after last element in a hash array
93 */
94 #define gnodelast(h) gnode(h, cast(size_t, sizenode(h)))
95
96
97 /*
98 ** link table 'h' into list pointed by 'p'
99 */
100 #define linktable(h,p) ((h)->gclist = *(p), *(p) = obj2gco(h))
101
102
103 /*
104 ** if key is not marked, mark its entry as dead (therefore removing it
105 ** from the table)
106 */
107 static void removeentry (Node *n) {
108 lua_assert(ttisnil(gval(n)));
109 if (valiswhite(gkey(n)))
110 setdeadvalue(gkey(n)); /* unused and unmarked key; remove it */
111 }
112
113
114 /*
115 ** tells whether a key or value can be cleared from a weak
116 ** table. Non-collectable objects are never removed from weak
117 ** tables. Strings behave as `values', so are never removed too. for
118 ** other objects: if really collected, cannot keep them; for objects
119 ** being finalized, keep them in keys, but not in values
120 */
121 static int iscleared (global_State *g, const TValue *o) {
122 if (!iscollectable(o)) return 0;
123 else if (ttisstring(o)) {
124 markobject(g, rawtsvalue(o)); /* strings are `values', so are never weak */
125 return 0;
126 }
127 else return iswhite(gcvalue(o));
128 }
129
130
131 /*
132 ** barrier that moves collector forward, that is, mark the white object
133 ** being pointed by a black object.
134 */
135 void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
136 global_State *g = G(L);
137 lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
138 lua_assert(g->gcstate != GCSpause);
139 lua_assert(gch(o)->tt != LUA_TTABLE);
140 if (keepinvariantout(g)) /* must keep invariant? */
141 reallymarkobject(g, v); /* restore invariant */
142 else { /* sweep phase */
143 lua_assert(issweepphase(g));
144 makewhite(g, o); /* mark main obj. as white to avoid other barriers */
145 }
146 }
147
148
149 /*
150 ** barrier that moves collector backward, that is, mark the black object
151 ** pointing to a white object as gray again. (Current implementation
152 ** only works for tables; access to 'gclist' is not uniform across
153 ** different types.)
154 */
155 void luaC_barrierback_ (lua_State *L, GCObject *o) {
156 global_State *g = G(L);
157 lua_assert(isblack(o) && !isdead(g, o) && gch(o)->tt == LUA_TTABLE);
158 black2gray(o); /* make object gray (again) */
159 gco2t(o)->gclist = g->grayagain;
160 g->grayagain = o;
161 }
162
163
164 /*
165 ** barrier for prototypes. When creating first closure (cache is
166 ** NULL), use a forward barrier; this may be the only closure of the
167 ** prototype (if it is a "regular" function, with a single instance)
168 ** and the prototype may be big, so it is better to avoid traversing
169 ** it again. Otherwise, use a backward barrier, to avoid marking all
170 ** possible instances.
171 */
172 LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c) {
173 global_State *g = G(L);
174 lua_assert(isblack(obj2gco(p)));
175 if (p->cache == NULL) { /* first time? */
176 luaC_objbarrier(L, p, c);
177 }
178 else { /* use a backward barrier */
179 black2gray(obj2gco(p)); /* make prototype gray (again) */
180 p->gclist = g->grayagain;
181 g->grayagain = obj2gco(p);
182 }
183 }
184
185
186 /*
187 ** check color (and invariants) for an upvalue that was closed,
188 ** i.e., moved into the 'allgc' list
189 */
190 void luaC_checkupvalcolor (global_State *g, UpVal *uv) {
191 GCObject *o = obj2gco(uv);
192 lua_assert(!isblack(o)); /* open upvalues are never black */
193 if (isgray(o)) {
194 if (keepinvariant(g)) {
195 resetoldbit(o); /* see MOVE OLD rule */
196 gray2black(o); /* it is being visited now */
197 markvalue(g, uv->v);
198 }
199 else {
200 lua_assert(issweepphase(g));
201 makewhite(g, o);
202 }
203 }
204 }
205
206
207 /*
208 ** create a new collectable object (with given type and size) and link
209 ** it to '*list'. 'offset' tells how many bytes to allocate before the
210 ** object itself (used only by states).
211 */
212 GCObject *luaC_newobj (lua_State *L, int tt, size_t sz, GCObject **list,
213 int offset) {
214 global_State *g = G(L);
215 char *raw = cast(char *, luaM_newobject(L, novariant(tt), sz));
216 GCObject *o = obj2gco(raw + offset);
217 if (list == NULL)
218 list = &g->allgc; /* standard list for collectable objects */
219 gch(o)->marked = luaC_white(g);
220 gch(o)->tt = tt;
221 gch(o)->next = *list;
222 *list = o;
223 return o;
224 }
225
226 /* }====================================================== */
227
228
229
230 /*
231 ** {======================================================
232 ** Mark functions
233 ** =======================================================
234 */
235
236
237 /*
238 ** mark an object. Userdata, strings, and closed upvalues are visited
239 ** and turned black here. Other objects are marked gray and added
240 ** to appropriate list to be visited (and turned black) later. (Open
241 ** upvalues are already linked in 'headuv' list.)
242 */
243 static void reallymarkobject (global_State *g, GCObject *o) {
244 lu_mem size;
245 white2gray(o);
246 switch (gch(o)->tt) {
247 case LUA_TSHRSTR:
248 case LUA_TLNGSTR: {
249 size = sizestring(gco2ts(o));
250 break; /* nothing else to mark; make it black */
251 }
252 case LUA_TUSERDATA: {
253 Table *mt = gco2u(o)->metatable;
254 markobject(g, mt);
255 markobject(g, gco2u(o)->env);
256 size = sizeudata(gco2u(o));
257 break;
258 }
259 case LUA_TUPVAL: {
260 UpVal *uv = gco2uv(o);
261 markvalue(g, uv->v);
262 if (uv->v != &uv->u.value) /* open? */
263 return; /* open upvalues remain gray */
264 size = sizeof(UpVal);
265 break;
266 }
267 case LUA_TLCL: {
268 gco2lcl(o)->gclist = g->gray;
269 g->gray = o;
270 return;
271 }
272 case LUA_TCCL: {
273 gco2ccl(o)->gclist = g->gray;
274 g->gray = o;
275 return;
276 }
277 case LUA_TTABLE: {
278 linktable(gco2t(o), &g->gray);
279 return;
280 }
281 case LUA_TTHREAD: {
282 gco2th(o)->gclist = g->gray;
283 g->gray = o;
284 return;
285 }
286 case LUA_TPROTO: {
287 gco2p(o)->gclist = g->gray;
288 g->gray = o;
289 return;
290 }
291 default: lua_assert(0); return;
292 }
293 gray2black(o);
294 g->GCmemtrav += size;
295 }
296
297
298 /*
299 ** mark metamethods for basic types
300 */
301 static void markmt (global_State *g) {
302 int i;
303 for (i=0; i < LUA_NUMTAGS; i++)
304 markobject(g, g->mt[i]);
305 }
306
307
308 /*
309 ** mark all objects in list of being-finalized
310 */
311 static void markbeingfnz (global_State *g) {
312 GCObject *o;
313 for (o = g->tobefnz; o != NULL; o = gch(o)->next) {
314 makewhite(g, o);
315 reallymarkobject(g, o);
316 }
317 }
318
319
320 /*
321 ** mark all values stored in marked open upvalues. (See comment in
322 ** 'lstate.h'.)
323 */
324 static void remarkupvals (global_State *g) {
325 UpVal *uv;
326 for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
327 if (isgray(obj2gco(uv)))
328 markvalue(g, uv->v);
329 }
330 }
331
332
333 /*
334 ** mark root set and reset all gray lists, to start a new
335 ** incremental (or full) collection
336 */
337 static void restartcollection (global_State *g) {
338 g->gray = g->grayagain = NULL;
339 g->weak = g->allweak = g->ephemeron = NULL;
340 markobject(g, g->mainthread);
341 markvalue(g, &g->l_registry);
342 markmt(g);
343 markbeingfnz(g); /* mark any finalizing object left from previous cycle */
344 }
345
346 /* }====================================================== */
347
348
349 /*
350 ** {======================================================
351 ** Traverse functions
352 ** =======================================================
353 */
354
355 static void traverseweakvalue (global_State *g, Table *h) {
356 Node *n, *limit = gnodelast(h);
357 /* if there is array part, assume it may have white values (do not
358 traverse it just to check) */
359 int hasclears = (h->sizearray > 0);
360 for (n = gnode(h, 0); n < limit; n++) {
361 checkdeadkey(n);
362 if (ttisnil(gval(n))) /* entry is empty? */
363 removeentry(n); /* remove it */
364 else {
365 lua_assert(!ttisnil(gkey(n)));
366 markvalue(g, gkey(n)); /* mark key */
367 if (!hasclears && iscleared(g, gval(n))) /* is there a white value? */
368 hasclears = 1; /* table will have to be cleared */
369 }
370 }
371 if (hasclears)
372 linktable(h, &g->weak); /* has to be cleared later */
373 else /* no white values */
374 linktable(h, &g->grayagain); /* no need to clean */
375 }
376
377
378 static int traverseephemeron (global_State *g, Table *h) {
379 int marked = 0; /* true if an object is marked in this traversal */
380 int hasclears = 0; /* true if table has white keys */
381 int prop = 0; /* true if table has entry "white-key -> white-value" */
382 Node *n, *limit = gnodelast(h);
383 int i;
384 /* traverse array part (numeric keys are 'strong') */
385 for (i = 0; i < h->sizearray; i++) {
386 if (valiswhite(&h->array[i])) {
387 marked = 1;
388 reallymarkobject(g, gcvalue(&h->array[i]));
389 }
390 }
391 /* traverse hash part */
392 for (n = gnode(h, 0); n < limit; n++) {
393 checkdeadkey(n);
394 if (ttisnil(gval(n))) /* entry is empty? */
395 removeentry(n); /* remove it */
396 else if (iscleared(g, gkey(n))) { /* key is not marked (yet)? */
397 hasclears = 1; /* table must be cleared */
398 if (valiswhite(gval(n))) /* value not marked yet? */
399 prop = 1; /* must propagate again */
400 }
401 else if (valiswhite(gval(n))) { /* value not marked yet? */
402 marked = 1;
403 reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
404 }
405 }
406 if (prop)
407 linktable(h, &g->ephemeron); /* have to propagate again */
408 else if (hasclears) /* does table have white keys? */
409 linktable(h, &g->allweak); /* may have to clean white keys */
410 else /* no white keys */
411 linktable(h, &g->grayagain); /* no need to clean */
412 return marked;
413 }
414
415
416 static void traversestrongtable (global_State *g, Table *h) {
417 Node *n, *limit = gnodelast(h);
418 int i;
419 for (i = 0; i < h->sizearray; i++) /* traverse array part */
420 markvalue(g, &h->array[i]);
421 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
422 checkdeadkey(n);
423 if (ttisnil(gval(n))) /* entry is empty? */
424 removeentry(n); /* remove it */
425 else {
426 lua_assert(!ttisnil(gkey(n)));
427 markvalue(g, gkey(n)); /* mark key */
428 markvalue(g, gval(n)); /* mark value */
429 }
430 }
431 }
432
433
434 static lu_mem traversetable (global_State *g, Table *h) {
435 const char *weakkey, *weakvalue;
436 const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
437 markobject(g, h->metatable);
438 if (mode && ttisstring(mode) && /* is there a weak mode? */
439 ((weakkey = strchr(svalue(mode), 'k')),
440 (weakvalue = strchr(svalue(mode), 'v')),
441 (weakkey || weakvalue))) { /* is really weak? */
442 black2gray(obj2gco(h)); /* keep table gray */
443 if (!weakkey) /* strong keys? */
444 traverseweakvalue(g, h);
445 else if (!weakvalue) /* strong values? */
446 traverseephemeron(g, h);
447 else /* all weak */
448 linktable(h, &g->allweak); /* nothing to traverse now */
449 }
450 else /* not weak */
451 traversestrongtable(g, h);
452 return sizeof(Table) + sizeof(TValue) * h->sizearray +
453 sizeof(Node) * cast(size_t, sizenode(h));
454 }
455
456
457 static int traverseproto (global_State *g, Proto *f) {
458 int i;
459 if (f->cache && iswhite(obj2gco(f->cache)))
460 f->cache = NULL; /* allow cache to be collected */
461 markobject(g, f->source);
462 for (i = 0; i < f->sizek; i++) /* mark literals */
463 markvalue(g, &f->k[i]);
464 for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
465 markobject(g, f->upvalues[i].name);
466 for (i = 0; i < f->sizep; i++) /* mark nested protos */
467 markobject(g, f->p[i]);
468 for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
469 markobject(g, f->locvars[i].varname);
470 return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
471 sizeof(Proto *) * f->sizep +
472 sizeof(TValue) * f->sizek +
473 sizeof(int) * f->sizelineinfo +
474 sizeof(LocVar) * f->sizelocvars +
475 sizeof(Upvaldesc) * f->sizeupvalues;
476 }
477
478
479 static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
480 int i;
481 for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
482 markvalue(g, &cl->upvalue[i]);
483 return sizeCclosure(cl->nupvalues);
484 }
485
486 static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
487 int i;
488 markobject(g, cl->p); /* mark its prototype */
489 for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
490 markobject(g, cl->upvals[i]);
491 return sizeLclosure(cl->nupvalues);
492 }
493
494
495 static lu_mem traversestack (global_State *g, lua_State *th) {
496 StkId o = th->stack;
497 if (o == NULL)
498 return 1; /* stack not completely built yet */
499 for (; o < th->top; o++)
500 markvalue(g, o);
501 if (g->gcstate == GCSatomic) { /* final traversal? */
502 StkId lim = th->stack + th->stacksize; /* real end of stack */
503 for (; o < lim; o++) /* clear not-marked stack slice */
504 setnilvalue(o);
505 }
506 return sizeof(lua_State) + sizeof(TValue) * th->stacksize;
507 }
508
509
510 /*
511 ** traverse one gray object, turning it to black (except for threads,
512 ** which are always gray).
513 */
514 static void propagatemark (global_State *g) {
515 lu_mem size;
516 GCObject *o = g->gray;
517 lua_assert(isgray(o));
518 gray2black(o);
519 switch (gch(o)->tt) {
520 case LUA_TTABLE: {
521 Table *h = gco2t(o);
522 g->gray = h->gclist; /* remove from 'gray' list */
523 size = traversetable(g, h);
524 break;
525 }
526 case LUA_TLCL: {
527 LClosure *cl = gco2lcl(o);
528 g->gray = cl->gclist; /* remove from 'gray' list */
529 size = traverseLclosure(g, cl);
530 break;
531 }
532 case LUA_TCCL: {
533 CClosure *cl = gco2ccl(o);
534 g->gray = cl->gclist; /* remove from 'gray' list */
535 size = traverseCclosure(g, cl);
536 break;
537 }
538 case LUA_TTHREAD: {
539 lua_State *th = gco2th(o);
540 g->gray = th->gclist; /* remove from 'gray' list */
541 th->gclist = g->grayagain;
542 g->grayagain = o; /* insert into 'grayagain' list */
543 black2gray(o);
544 size = traversestack(g, th);
545 break;
546 }
547 case LUA_TPROTO: {
548 Proto *p = gco2p(o);
549 g->gray = p->gclist; /* remove from 'gray' list */
550 size = traverseproto(g, p);
551 break;
552 }
553 default: lua_assert(0); return;
554 }
555 g->GCmemtrav += size;
556 }
557
558
559 static void propagateall (global_State *g) {
560 while (g->gray) propagatemark(g);
561 }
562
563
564 static void propagatelist (global_State *g, GCObject *l) {
565 lua_assert(g->gray == NULL); /* no grays left */
566 g->gray = l;
567 propagateall(g); /* traverse all elements from 'l' */
568 }
569
570 /*
571 ** retraverse all gray lists. Because tables may be reinserted in other
572 ** lists when traversed, traverse the original lists to avoid traversing
573 ** twice the same table (which is not wrong, but inefficient)
574 */
575 static void retraversegrays (global_State *g) {
576 GCObject *weak = g->weak; /* save original lists */
577 GCObject *grayagain = g->grayagain;
578 GCObject *ephemeron = g->ephemeron;
579 g->weak = g->grayagain = g->ephemeron = NULL;
580 propagateall(g); /* traverse main gray list */
581 propagatelist(g, grayagain);
582 propagatelist(g, weak);
583 propagatelist(g, ephemeron);
584 }
585
586
587 static void convergeephemerons (global_State *g) {
588 int changed;
589 do {
590 GCObject *w;
591 GCObject *next = g->ephemeron; /* get ephemeron list */
592 g->ephemeron = NULL; /* tables will return to this list when traversed */
593 changed = 0;
594 while ((w = next) != NULL) {
595 next = gco2t(w)->gclist;
596 if (traverseephemeron(g, gco2t(w))) { /* traverse marked some value? */
597 propagateall(g); /* propagate changes */
598 changed = 1; /* will have to revisit all ephemeron tables */
599 }
600 }
601 } while (changed);
602 }
603
604 /* }====================================================== */
605
606
607 /*
608 ** {======================================================
609 ** Sweep Functions
610 ** =======================================================
611 */
612
613
614 /*
615 ** clear entries with unmarked keys from all weaktables in list 'l' up
616 ** to element 'f'
617 */
618 static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
619 for (; l != f; l = gco2t(l)->gclist) {
620 Table *h = gco2t(l);
621 Node *n, *limit = gnodelast(h);
622 for (n = gnode(h, 0); n < limit; n++) {
623 if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
624 setnilvalue(gval(n)); /* remove value ... */
625 removeentry(n); /* and remove entry from table */
626 }
627 }
628 }
629 }
630
631
632 /*
633 ** clear entries with unmarked values from all weaktables in list 'l' up
634 ** to element 'f'
635 */
636 static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
637 for (; l != f; l = gco2t(l)->gclist) {
638 Table *h = gco2t(l);
639 Node *n, *limit = gnodelast(h);
640 int i;
641 for (i = 0; i < h->sizearray; i++) {
642 TValue *o = &h->array[i];
643 if (iscleared(g, o)) /* value was collected? */
644 setnilvalue(o); /* remove value */
645 }
646 for (n = gnode(h, 0); n < limit; n++) {
647 if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
648 setnilvalue(gval(n)); /* remove value ... */
649 removeentry(n); /* and remove entry from table */
650 }
651 }
652 }
653 }
654
655
656 static void freeobj (lua_State *L, GCObject *o) {
657 switch (gch(o)->tt) {
658 case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
659 case LUA_TLCL: {
660 luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
661 break;
662 }
663 case LUA_TCCL: {
664 luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
665 break;
666 }
667 case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
668 case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
669 case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
670 case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
671 case LUA_TSHRSTR:
672 G(L)->strt.nuse--;
673 /* go through */
674 case LUA_TLNGSTR: {
675 luaM_freemem(L, o, sizestring(gco2ts(o)));
676 break;
677 }
678 default: lua_assert(0);
679 }
680 }
681
682
683 #define sweepwholelist(L,p) sweeplist(L,p,MAX_LUMEM)
684 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
685
686
687 /*
688 ** sweep the (open) upvalues of a thread and resize its stack and
689 ** list of call-info structures.
690 */
691 static void sweepthread (lua_State *L, lua_State *L1) {
692 if (L1->stack == NULL) return; /* stack not completely built yet */
693 sweepwholelist(L, &L1->openupval); /* sweep open upvalues */
694 luaE_freeCI(L1); /* free extra CallInfo slots */
695 /* should not change the stack during an emergency gc cycle */
696 if (G(L)->gckind != KGC_EMERGENCY)
697 luaD_shrinkstack(L1);
698 }
699
700
701 /*
702 ** sweep at most 'count' elements from a list of GCObjects erasing dead
703 ** objects, where a dead (not alive) object is one marked with the "old"
704 ** (non current) white and not fixed.
705 ** In non-generational mode, change all non-dead objects back to white,
706 ** preparing for next collection cycle.
707 ** In generational mode, keep black objects black, and also mark them as
708 ** old; stop when hitting an old object, as all objects after that
709 ** one will be old too.
710 ** When object is a thread, sweep its list of open upvalues too.
711 */
712 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
713 global_State *g = G(L);
714 int ow = otherwhite(g);
715 int toclear, toset; /* bits to clear and to set in all live objects */
716 int tostop; /* stop sweep when this is true */
717 if (isgenerational(g)) { /* generational mode? */
718 toclear = ~0; /* clear nothing */
719 toset = bitmask(OLDBIT); /* set the old bit of all surviving objects */
720 tostop = bitmask(OLDBIT); /* do not sweep old generation */
721 }
722 else { /* normal mode */
723 toclear = maskcolors; /* clear all color bits + old bit */
724 toset = luaC_white(g); /* make object white */
725 tostop = 0; /* do not stop */
726 }
727 while (*p != NULL && count-- > 0) {
728 GCObject *curr = *p;
729 int marked = gch(curr)->marked;
730 if (isdeadm(ow, marked)) { /* is 'curr' dead? */
731 *p = gch(curr)->next; /* remove 'curr' from list */
732 freeobj(L, curr); /* erase 'curr' */
733 }
734 else {
735 if (testbits(marked, tostop))
736 return NULL; /* stop sweeping this list */
737 if (gch(curr)->tt == LUA_TTHREAD)
738 sweepthread(L, gco2th(curr)); /* sweep thread's upvalues */
739 /* update marks */
740 gch(curr)->marked = cast_byte((marked & toclear) | toset);
741 p = &gch(curr)->next; /* go to next element */
742 }
743 }
744 return (*p == NULL) ? NULL : p;
745 }
746
747
748 /*
749 ** sweep a list until a live object (or end of list)
750 */
751 static GCObject **sweeptolive (lua_State *L, GCObject **p, int *n) {
752 GCObject ** old = p;
753 int i = 0;
754 do {
755 i++;
756 p = sweeplist(L, p, 1);
757 } while (p == old);
758 if (n) *n += i;
759 return p;
760 }
761
762 /* }====================================================== */
763
764
765 /*
766 ** {======================================================
767 ** Finalization
768 ** =======================================================
769 */
770
771 static void checkSizes (lua_State *L) {
772 global_State *g = G(L);
773 if (g->gckind != KGC_EMERGENCY) { /* do not change sizes in emergency */
774 int hs = g->strt.size / 2; /* half the size of the string table */
775 if (g->strt.nuse < cast(lu_int32, hs)) /* using less than that half? */
776 luaS_resize(L, hs); /* halve its size */
777 luaZ_freebuffer(L, &g->buff); /* free concatenation buffer */
778 }
779 }
780
781
782 static GCObject *udata2finalize (global_State *g) {
783 GCObject *o = g->tobefnz; /* get first element */
784 lua_assert(isfinalized(o));
785 g->tobefnz = gch(o)->next; /* remove it from 'tobefnz' list */
786 gch(o)->next = g->allgc; /* return it to 'allgc' list */
787 g->allgc = o;
788 resetbit(gch(o)->marked, SEPARATED); /* mark that it is not in 'tobefnz' */
789 lua_assert(!isold(o)); /* see MOVE OLD rule */
790 if (!keepinvariantout(g)) /* not keeping invariant? */
791 makewhite(g, o); /* "sweep" object */
792 return o;
793 }
794
795
796 static void dothecall (lua_State *L, void *ud) {
797 UNUSED(ud);
798 luaD_call(L, L->top - 2, 0, 0);
799 }
800
801
802 static void GCTM (lua_State *L, int propagateerrors) {
803 global_State *g = G(L);
804 const TValue *tm;
805 TValue v;
806 setgcovalue(L, &v, udata2finalize(g));
807 tm = luaT_gettmbyobj(L, &v, TM_GC);
808 if (tm != NULL && ttisfunction(tm)) { /* is there a finalizer? */
809 int status;
810 lu_byte oldah = L->allowhook;
811 int running = g->gcrunning;
812 L->allowhook = 0; /* stop debug hooks during GC metamethod */
813 g->gcrunning = 0; /* avoid GC steps */
814 setobj2s(L, L->top, tm); /* push finalizer... */
815 setobj2s(L, L->top + 1, &v); /* ... and its argument */
816 L->top += 2; /* and (next line) call the finalizer */
817 status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
818 L->allowhook = oldah; /* restore hooks */
819 g->gcrunning = running; /* restore state */
820 if (status != LUA_OK && propagateerrors) { /* error while running __gc? */
821 if (status == LUA_ERRRUN) { /* is there an error object? */
822 const char *msg = (ttisstring(L->top - 1))
823 ? svalue(L->top - 1)
824 : "no message";
825 luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
826 status = LUA_ERRGCMM; /* error in __gc metamethod */
827 }
828 luaD_throw(L, status); /* re-throw error */
829 }
830 }
831 }
832
833
834 /*
835 ** move all unreachable objects (or 'all' objects) that need
836 ** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
837 */
838 static void separatetobefnz (lua_State *L, int all) {
839 global_State *g = G(L);
840 GCObject **p = &g->finobj;
841 GCObject *curr;
842 GCObject **lastnext = &g->tobefnz;
843 /* find last 'next' field in 'tobefnz' list (to add elements in its end) */
844 while (*lastnext != NULL)
845 lastnext = &gch(*lastnext)->next;
846 while ((curr = *p) != NULL) { /* traverse all finalizable objects */
847 lua_assert(!isfinalized(curr));
848 lua_assert(testbit(gch(curr)->marked, SEPARATED));
849 if (!(iswhite(curr) || all)) /* not being collected? */
850 p = &gch(curr)->next; /* don't bother with it */
851 else {
852 l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
853 *p = gch(curr)->next; /* remove 'curr' from 'finobj' list */
854 gch(curr)->next = *lastnext; /* link at the end of 'tobefnz' list */
855 *lastnext = curr;
856 lastnext = &gch(curr)->next;
857 }
858 }
859 }
860
861
862 /*
863 ** if object 'o' has a finalizer, remove it from 'allgc' list (must
864 ** search the list to find it) and link it in 'finobj' list.
865 */
866 void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
867 global_State *g = G(L);
868 if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
869 isfinalized(o) || /* ... or is finalized... */
870 gfasttm(g, mt, TM_GC) == NULL) /* or has no finalizer? */
871 return; /* nothing to be done */
872 else { /* move 'o' to 'finobj' list */
873 GCObject **p;
874 GCheader *ho = gch(o);
875 if (g->sweepgc == &ho->next) { /* avoid removing current sweep object */
876 lua_assert(issweepphase(g));
877 g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
878 }
879 /* search for pointer pointing to 'o' */
880 for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
881 *p = ho->next; /* remove 'o' from root list */
882 ho->next = g->finobj; /* link it in list 'finobj' */
883 g->finobj = o;
884 l_setbit(ho->marked, SEPARATED); /* mark it as such */
885 if (!keepinvariantout(g)) /* not keeping invariant? */
886 makewhite(g, o); /* "sweep" object */
887 else
888 resetoldbit(o); /* see MOVE OLD rule */
889 }
890 }
891
892 /* }====================================================== */
893
894
895 /*
896 ** {======================================================
897 ** GC control
898 ** =======================================================
899 */
900
901
902 /*
903 ** set a reasonable "time" to wait before starting a new GC cycle;
904 ** cycle will start when memory use hits threshold
905 */
906 static void setpause (global_State *g, l_mem estimate) {
907 l_mem debt, threshold;
908 estimate = estimate / PAUSEADJ; /* adjust 'estimate' */
909 threshold = (g->gcpause < MAX_LMEM / estimate) /* overflow? */
910 ? estimate * g->gcpause /* no overflow */
911 : MAX_LMEM; /* overflow; truncate to maximum */
912 debt = -cast(l_mem, threshold - gettotalbytes(g));
913 luaE_setdebt(g, debt);
914 }
915
916
917 #define sweepphases \
918 (bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))
919
920
921 /*
922 ** enter first sweep phase (strings) and prepare pointers for other
923 ** sweep phases. The calls to 'sweeptolive' make pointers point to an
924 ** object inside the list (instead of to the header), so that the real
925 ** sweep do not need to skip objects created between "now" and the start
926 ** of the real sweep.
927 ** Returns how many objects it swept.
928 */
929 static int entersweep (lua_State *L) {
930 global_State *g = G(L);
931 int n = 0;
932 g->gcstate = GCSsweepstring;
933 lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
934 /* prepare to sweep strings, finalizable objects, and regular objects */
935 g->sweepstrgc = 0;
936 g->sweepfin = sweeptolive(L, &g->finobj, &n);
937 g->sweepgc = sweeptolive(L, &g->allgc, &n);
938 return n;
939 }
940
941
942 /*
943 ** change GC mode
944 */
945 void luaC_changemode (lua_State *L, int mode) {
946 global_State *g = G(L);
947 if (mode == g->gckind) return; /* nothing to change */
948 if (mode == KGC_GEN) { /* change to generational mode */
949 /* make sure gray lists are consistent */
950 luaC_runtilstate(L, bitmask(GCSpropagate));
951 g->GCestimate = gettotalbytes(g);
952 g->gckind = KGC_GEN;
953 }
954 else { /* change to incremental mode */
955 /* sweep all objects to turn them back to white
956 (as white has not changed, nothing extra will be collected) */
957 g->gckind = KGC_NORMAL;
958 entersweep(L);
959 luaC_runtilstate(L, ~sweepphases);
960 }
961 }
962
963
964 /*
965 ** call all pending finalizers
966 */
967 static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
968 global_State *g = G(L);
969 while (g->tobefnz) {
970 resetoldbit(g->tobefnz);
971 GCTM(L, propagateerrors);
972 }
973 }
974
975
976 void luaC_freeallobjects (lua_State *L) {
977 global_State *g = G(L);
978 int i;
979 separatetobefnz(L, 1); /* separate all objects with finalizers */
980 lua_assert(g->finobj == NULL);
981 callallpendingfinalizers(L, 0);
982 g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
983 g->gckind = KGC_NORMAL;
984 sweepwholelist(L, &g->finobj); /* finalizers can create objs. in 'finobj' */
985 sweepwholelist(L, &g->allgc);
986 for (i = 0; i < g->strt.size; i++) /* free all string lists */
987 sweepwholelist(L, &g->strt.hash[i]);
988 lua_assert(g->strt.nuse == 0);
989 }
990
991
992 static l_mem atomic (lua_State *L) {
993 global_State *g = G(L);
994 l_mem work = -cast(l_mem, g->GCmemtrav); /* start counting work */
995 GCObject *origweak, *origall;
996 lua_assert(!iswhite(obj2gco(g->mainthread)));
997 markobject(g, L); /* mark running thread */
998 /* registry and global metatables may be changed by API */
999 markvalue(g, &g->l_registry);
1000 markmt(g); /* mark basic metatables */
1001 /* remark occasional upvalues of (maybe) dead threads */
1002 remarkupvals(g);
1003 propagateall(g); /* propagate changes */
1004 work += g->GCmemtrav; /* stop counting (do not (re)count grays) */
1005 /* traverse objects caught by write barrier and by 'remarkupvals' */
1006 retraversegrays(g);
1007 work -= g->GCmemtrav; /* restart counting */
1008 convergeephemerons(g);
1009 /* at this point, all strongly accessible objects are marked. */
1010 /* clear values from weak tables, before checking finalizers */
1011 clearvalues(g, g->weak, NULL);
1012 clearvalues(g, g->allweak, NULL);
1013 origweak = g->weak; origall = g->allweak;
1014 work += g->GCmemtrav; /* stop counting (objects being finalized) */
1015 separatetobefnz(L, 0); /* separate objects to be finalized */
1016 markbeingfnz(g); /* mark objects that will be finalized */
1017 propagateall(g); /* remark, to propagate `preserveness' */
1018 work -= g->GCmemtrav; /* restart counting */
1019 convergeephemerons(g);
1020 /* at this point, all resurrected objects are marked. */
1021 /* remove dead objects from weak tables */
1022 clearkeys(g, g->ephemeron, NULL); /* clear keys from all ephemeron tables */
1023 clearkeys(g, g->allweak, NULL); /* clear keys from all allweak tables */
1024 /* clear values from resurrected weak tables */
1025 clearvalues(g, g->weak, origweak);
1026 clearvalues(g, g->allweak, origall);
1027 g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
1028 work += g->GCmemtrav; /* complete counting */
1029 return work; /* estimate of memory marked by 'atomic' */
1030 }
1031
1032
1033 static lu_mem singlestep (lua_State *L) {
1034 global_State *g = G(L);
1035 switch (g->gcstate) {
1036 case GCSpause: {
1037 /* start to count memory traversed */
1038 g->GCmemtrav = g->strt.size * sizeof(GCObject*);
1039 lua_assert(!isgenerational(g));
1040 restartcollection(g);
1041 g->gcstate = GCSpropagate;
1042 return g->GCmemtrav;
1043 }
1044 case GCSpropagate: {
1045 if (g->gray) {
1046 lu_mem oldtrav = g->GCmemtrav;
1047 propagatemark(g);
1048 return g->GCmemtrav - oldtrav; /* memory traversed in this step */
1049 }
1050 else { /* no more `gray' objects */
1051 lu_mem work;
1052 int sw;
1053 g->gcstate = GCSatomic; /* finish mark phase */
1054 g->GCestimate = g->GCmemtrav; /* save what was counted */;
1055 work = atomic(L); /* add what was traversed by 'atomic' */
1056 g->GCestimate += work; /* estimate of total memory traversed */
1057 sw = entersweep(L);
1058 return work + sw * GCSWEEPCOST;
1059 }
1060 }
1061 case GCSsweepstring: {
1062 int i;
1063 for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
1064 sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
1065 g->sweepstrgc += i;
1066 if (g->sweepstrgc >= g->strt.size) /* no more strings to sweep? */
1067 g->gcstate = GCSsweepudata;
1068 return i * GCSWEEPCOST;
1069 }
1070 case GCSsweepudata: {
1071 if (g->sweepfin) {
1072 g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
1073 return GCSWEEPMAX*GCSWEEPCOST;
1074 }
1075 else {
1076 g->gcstate = GCSsweep;
1077 return 0;
1078 }
1079 }
1080 case GCSsweep: {
1081 if (g->sweepgc) {
1082 g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
1083 return GCSWEEPMAX*GCSWEEPCOST;
1084 }
1085 else {
1086 /* sweep main thread */
1087 GCObject *mt = obj2gco(g->mainthread);
1088 sweeplist(L, &mt, 1);
1089 checkSizes(L);
1090 g->gcstate = GCSpause; /* finish collection */
1091 return GCSWEEPCOST;
1092 }
1093 }
1094 default: lua_assert(0); return 0;
1095 }
1096 }
1097
1098
1099 /*
1100 ** advances the garbage collector until it reaches a state allowed
1101 ** by 'statemask'
1102 */
1103 void luaC_runtilstate (lua_State *L, int statesmask) {
1104 global_State *g = G(L);
1105 while (!testbit(statesmask, g->gcstate))
1106 singlestep(L);
1107 }
1108
1109
1110 static void generationalcollection (lua_State *L) {
1111 global_State *g = G(L);
1112 lua_assert(g->gcstate == GCSpropagate);
1113 if (g->GCestimate == 0) { /* signal for another major collection? */
1114 luaC_fullgc(L, 0); /* perform a full regular collection */
1115 g->GCestimate = gettotalbytes(g); /* update control */
1116 }
1117 else {
1118 lu_mem estimate = g->GCestimate;
1119 luaC_runtilstate(L, bitmask(GCSpause)); /* run complete (minor) cycle */
1120 g->gcstate = GCSpropagate; /* skip restart */
1121 if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
1122 g->GCestimate = 0; /* signal for a major collection */
1123 else
1124 g->GCestimate = estimate; /* keep estimate from last major coll. */
1125
1126 }
1127 setpause(g, gettotalbytes(g));
1128 lua_assert(g->gcstate == GCSpropagate);
1129 }
1130
1131
1132 static void incstep (lua_State *L) {
1133 global_State *g = G(L);
1134 l_mem debt = g->GCdebt;
1135 int stepmul = g->gcstepmul;
1136 if (stepmul < 40) stepmul = 40; /* avoid ridiculous low values (and 0) */
1137 /* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
1138 debt = (debt / STEPMULADJ) + 1;
1139 debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
1140 do { /* always perform at least one single step */
1141 lu_mem work = singlestep(L); /* do some work */
1142 debt -= work;
1143 } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
1144 if (g->gcstate == GCSpause)
1145 setpause(g, g->GCestimate); /* pause until next cycle */
1146 else {
1147 debt = (debt / stepmul) * STEPMULADJ; /* convert 'work units' to Kb */
1148 luaE_setdebt(g, debt);
1149 }
1150 }
1151
1152
1153 /*
1154 ** performs a basic GC step
1155 */
1156 void luaC_forcestep (lua_State *L) {
1157 global_State *g = G(L);
1158 int i;
1159 if (isgenerational(g)) generationalcollection(L);
1160 else incstep(L);
1161 /* run a few finalizers (or all of them at the end of a collect cycle) */
1162 for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
1163 GCTM(L, 1); /* call one finalizer */
1164 }
1165
1166
1167 /*
1168 ** performs a basic GC step only if collector is running
1169 */
1170 void luaC_step (lua_State *L) {
1171 global_State *g = G(L);
1172 if (g->gcrunning) luaC_forcestep(L);
1173 else luaE_setdebt(g, -GCSTEPSIZE); /* avoid being called too often */
1174 }
1175
1176
1177
1178 /*
1179 ** performs a full GC cycle; if "isemergency", does not call
1180 ** finalizers (which could change stack positions)
1181 */
1182 void luaC_fullgc (lua_State *L, int isemergency) {
1183 global_State *g = G(L);
1184 int origkind = g->gckind;
1185 lua_assert(origkind != KGC_EMERGENCY);
1186 if (isemergency) /* do not run finalizers during emergency GC */
1187 g->gckind = KGC_EMERGENCY;
1188 else {
1189 g->gckind = KGC_NORMAL;
1190 callallpendingfinalizers(L, 1);
1191 }
1192 if (keepinvariant(g)) { /* may there be some black objects? */
1193 /* must sweep all objects to turn them back to white
1194 (as white has not changed, nothing will be collected) */
1195 entersweep(L);
1196 }
1197 /* finish any pending sweep phase to start a new cycle */
1198 luaC_runtilstate(L, bitmask(GCSpause));
1199 luaC_runtilstate(L, ~bitmask(GCSpause)); /* start new collection */
1200 luaC_runtilstate(L, bitmask(GCSpause)); /* run entire collection */
1201 if (origkind == KGC_GEN) { /* generational mode? */
1202 /* generational mode must be kept in propagate phase */
1203 luaC_runtilstate(L, bitmask(GCSpropagate));
1204 }
1205 g->gckind = origkind;
1206 setpause(g, gettotalbytes(g));
1207 if (!isemergency) /* do not run finalizers during emergency GC */
1208 callallpendingfinalizers(L, 1);
1209 }
1210
1211 /* }====================================================== */
1212
1213