1/*
2** $Id: lgc.c,v 2.215.1.2 2017/08/31 16:15:27 roberto Exp $
3** Garbage Collector
4** See Copyright Notice in lua.h
5*/
6
7#define lgc_c
8#define LUA_CORE
9
10#include "lprefix.h"
11
12
13#include <string.h>
14
15#include "lua.h"
16
17#include "ldebug.h"
18#include "ldo.h"
19#include "lfunc.h"
20#include "lgc.h"
21#include "lmem.h"
22#include "lobject.h"
23#include "lstate.h"
24#include "lstring.h"
25#include "ltable.h"
26#include "ltm.h"
27
28
29/*
30** internal state for collector while inside the atomic phase. The
31** collector should never be in this state while running regular code.
32*/
33#define GCSinsideatomic (GCSpause + 1)
34
35/*
36** cost of sweeping one element (the size of a small object divided
37** by some adjust for the sweep speed)
38*/
39#define GCSWEEPCOST ((sizeof(TString) + 4) / 4)
40
41/* maximum number of elements to sweep in each single step */
42#define GCSWEEPMAX (cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
43
44/* cost of calling one finalizer */
45#define GCFINALIZECOST GCSWEEPCOST
46
47
48/*
49** macro to adjust 'stepmul': 'stepmul' is actually used like
50** 'stepmul / STEPMULADJ' (value chosen by tests)
51*/
52#define STEPMULADJ 200
53
54
55/*
56** macro to adjust 'pause': 'pause' is actually used like
57** 'pause / PAUSEADJ' (value chosen by tests)
58*/
59#define PAUSEADJ 100
60
61
62/*
63** 'makewhite' erases all color bits then sets only the current white
64** bit
65*/
66#define maskcolors (~(bitmask(BLACKBIT) | WHITEBITS))
67#define makewhite(g,x) \
68 (x->marked = cast_byte((x->marked & maskcolors) | luaC_white(g)))
69
70#define white2gray(x) resetbits(x->marked, WHITEBITS)
71#define black2gray(x) resetbit(x->marked, BLACKBIT)
72
73
74#define valiswhite(x) (iscollectable(x) && iswhite(gcvalue(x)))
75
76#define checkdeadkey(n) lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
77
78
79#define checkconsistency(obj) \
80 lua_longassert(!iscollectable(obj) || righttt(obj))
81
82
83#define markvalue(g,o) { checkconsistency(o); \
84 if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
85
86#define markobject(g,t) { if (iswhite(t)) reallymarkobject(g, obj2gco(t)); }
87
88/*
89** mark an object that can be NULL (either because it is really optional,
90** or it was stripped as debug info, or inside an uncompleted structure)
91*/
92#define markobjectN(g,t) { if (t) markobject(g,t); }
93
94static void reallymarkobject (global_State *g, GCObject *o);
95
96
97/*
98** {======================================================
99** Generic functions
100** =======================================================
101*/
102
103
104/*
105** one after last element in a hash array
106*/
107#define gnodelast(h) gnode(h, cast(size_t, sizenode(h)))
108
109
110/*
111** link collectable object 'o' into list pointed by 'p'
112*/
113#define linkgclist(o,p) ((o)->gclist = (p), (p) = obj2gco(o))
114
115
116/*
117** If key is not marked, mark its entry as dead. This allows key to be
118** collected, but keeps its entry in the table. A dead node is needed
119** when Lua looks up for a key (it may be part of a chain) and when
120** traversing a weak table (key might be removed from the table during
121** traversal). Other places never manipulate dead keys, because its
122** associated nil value is enough to signal that the entry is logically
123** empty.
124*/
125static void removeentry (Node *n) {
126 lua_assert(ttisnil(gval(n)));
127 if (valiswhite(gkey(n)))
128 setdeadvalue(wgkey(n)); /* unused and unmarked key; remove it */
129}
130
131
132/*
133** tells whether a key or value can be cleared from a weak
134** table. Non-collectable objects are never removed from weak
135** tables. Strings behave as 'values', so are never removed too. for
136** other objects: if really collected, cannot keep them; for objects
137** being finalized, keep them in keys, but not in values
138*/
139static int iscleared (global_State *g, const TValue *o) {
140 if (!iscollectable(o)) return 0;
141 else if (ttisstring(o)) {
142 markobject(g, tsvalue(o)); /* strings are 'values', so are never weak */
143 return 0;
144 }
145 else return iswhite(gcvalue(o));
146}
147
148
149/*
150** barrier that moves collector forward, that is, mark the white object
151** being pointed by a black object. (If in sweep phase, clear the black
152** object to white [sweep it] to avoid other barrier calls for this
153** same object.)
154*/
155void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
156 global_State *g = G(L);
157 lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
158 if (keepinvariant(g)) /* must keep invariant? */
159 reallymarkobject(g, v); /* restore invariant */
160 else { /* sweep phase */
161 lua_assert(issweepphase(g));
162 makewhite(g, o); /* mark main obj. as white to avoid other barriers */
163 }
164}
165
166
167/*
168** barrier that moves collector backward, that is, mark the black object
169** pointing to a white object as gray again.
170*/
171void luaC_barrierback_ (lua_State *L, Table *t) {
172 global_State *g = G(L);
173 lua_assert(isblack(t) && !isdead(g, t));
174 black2gray(t); /* make table gray (again) */
175 linkgclist(t, g->grayagain);
176}
177
178
179/*
180** barrier for assignments to closed upvalues. Because upvalues are
181** shared among closures, it is impossible to know the color of all
182** closures pointing to it. So, we assume that the object being assigned
183** must be marked.
184*/
185void luaC_upvalbarrier_ (lua_State *L, UpVal *uv) {
186 global_State *g = G(L);
187 GCObject *o = gcvalue(uv->v);
188 lua_assert(!upisopen(uv)); /* ensured by macro luaC_upvalbarrier */
189 if (keepinvariant(g))
190 markobject(g, o);
191}
192
193
194void luaC_fix (lua_State *L, GCObject *o) {
195 global_State *g = G(L);
196 lua_assert(g->allgc == o); /* object must be 1st in 'allgc' list! */
197 white2gray(o); /* they will be gray forever */
198 g->allgc = o->next; /* remove object from 'allgc' list */
199 o->next = g->fixedgc; /* link it to 'fixedgc' list */
200 g->fixedgc = o;
201}
202
203
204/*
205** create a new collectable object (with given type and size) and link
206** it to 'allgc' list.
207*/
208GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
209 global_State *g = G(L);
210 GCObject *o = cast(GCObject *, luaM_newobject(L, novariant(tt), sz));
211 o->marked = luaC_white(g);
212 o->tt = tt;
213 o->next = g->allgc;
214 g->allgc = o;
215 return o;
216}
217
218/* }====================================================== */
219
220
221
222/*
223** {======================================================
224** Mark functions
225** =======================================================
226*/
227
228
229/*
230** mark an object. Userdata, strings, and closed upvalues are visited
231** and turned black here. Other objects are marked gray and added
232** to appropriate list to be visited (and turned black) later. (Open
233** upvalues are already linked in 'headuv' list.)
234*/
235static void reallymarkobject (global_State *g, GCObject *o) {
236 reentry:
237 white2gray(o);
238 switch (o->tt) {
239 case LUA_TSHRSTR: {
240 gray2black(o);
241 g->GCmemtrav += sizelstring(gco2ts(o)->shrlen);
242 break;
243 }
244 case LUA_TLNGSTR: {
245 gray2black(o);
246 g->GCmemtrav += sizelstring(gco2ts(o)->u.lnglen);
247 break;
248 }
249 case LUA_TUSERDATA: {
250 TValue uvalue;
251 markobjectN(g, gco2u(o)->metatable); /* mark its metatable */
252 gray2black(o);
253 g->GCmemtrav += sizeudata(gco2u(o));
254 getuservalue(g->mainthread, gco2u(o), &uvalue);
255 if (valiswhite(&uvalue)) { /* markvalue(g, &uvalue); */
256 o = gcvalue(&uvalue);
257 goto reentry;
258 }
259 break;
260 }
261 case LUA_TLCL: {
262 linkgclist(gco2lcl(o), g->gray);
263 break;
264 }
265 case LUA_TCCL: {
266 linkgclist(gco2ccl(o), g->gray);
267 break;
268 }
269 case LUA_TTABLE: {
270 linkgclist(gco2t(o), g->gray);
271 break;
272 }
273 case LUA_TTHREAD: {
274 linkgclist(gco2th(o), g->gray);
275 break;
276 }
277 case LUA_TPROTO: {
278 linkgclist(gco2p(o), g->gray);
279 break;
280 }
281 default: lua_assert(0); break;
282 }
283}
284
285
286/*
287** mark metamethods for basic types
288*/
289static void markmt (global_State *g) {
290 int i;
291 for (i=0; i < LUA_NUMTAGS; i++)
292 markobjectN(g, g->mt[i]);
293}
294
295
296/*
297** mark all objects in list of being-finalized
298*/
299static void markbeingfnz (global_State *g) {
300 GCObject *o;
301 for (o = g->tobefnz; o != NULL; o = o->next)
302 markobject(g, o);
303}
304
305
306/*
307** Mark all values stored in marked open upvalues from non-marked threads.
308** (Values from marked threads were already marked when traversing the
309** thread.) Remove from the list threads that no longer have upvalues and
310** not-marked threads.
311*/
312static void remarkupvals (global_State *g) {
313 lua_State *thread;
314 lua_State **p = &g->twups;
315 while ((thread = *p) != NULL) {
316 lua_assert(!isblack(thread)); /* threads are never black */
317 if (isgray(thread) && thread->openupval != NULL)
318 p = &thread->twups; /* keep marked thread with upvalues in the list */
319 else { /* thread is not marked or without upvalues */
320 UpVal *uv;
321 *p = thread->twups; /* remove thread from the list */
322 thread->twups = thread; /* mark that it is out of list */
323 for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
324 if (uv->u.open.touched) {
325 markvalue(g, uv->v); /* remark upvalue's value */
326 uv->u.open.touched = 0;
327 }
328 }
329 }
330 }
331}
332
333
334/*
335** mark root set and reset all gray lists, to start a new collection
336*/
337static 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/*
356** Traverse a table with weak values and link it to proper list. During
357** propagate phase, keep it in 'grayagain' list, to be revisited in the
358** atomic phase. In the atomic phase, if table has any white value,
359** put it in 'weak' list, to be cleared.
360*/
361static void traverseweakvalue (global_State *g, Table *h) {
362 Node *n, *limit = gnodelast(h);
363 /* if there is array part, assume it may have white values (it is not
364 worth traversing it now just to check) */
365 int hasclears = (h->sizearray > 0);
366 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
367 checkdeadkey(n);
368 if (ttisnil(gval(n))) /* entry is empty? */
369 removeentry(n); /* remove it */
370 else {
371 lua_assert(!ttisnil(gkey(n)));
372 markvalue(g, gkey(n)); /* mark key */
373 if (!hasclears && iscleared(g, gval(n))) /* is there a white value? */
374 hasclears = 1; /* table will have to be cleared */
375 }
376 }
377 if (g->gcstate == GCSpropagate)
378 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
379 else if (hasclears)
380 linkgclist(h, g->weak); /* has to be cleared later */
381}
382
383
384/*
385** Traverse an ephemeron table and link it to proper list. Returns true
386** iff any object was marked during this traversal (which implies that
387** convergence has to continue). During propagation phase, keep table
388** in 'grayagain' list, to be visited again in the atomic phase. In
389** the atomic phase, if table has any white->white entry, it has to
390** be revisited during ephemeron convergence (as that key may turn
391** black). Otherwise, if it has any white key, table has to be cleared
392** (in the atomic phase).
393*/
394static int traverseephemeron (global_State *g, Table *h) {
395 int marked = 0; /* true if an object is marked in this traversal */
396 int hasclears = 0; /* true if table has white keys */
397 int hasww = 0; /* true if table has entry "white-key -> white-value" */
398 Node *n, *limit = gnodelast(h);
399 unsigned int i;
400 /* traverse array part */
401 for (i = 0; i < h->sizearray; i++) {
402 if (valiswhite(&h->array[i])) {
403 marked = 1;
404 reallymarkobject(g, gcvalue(&h->array[i]));
405 }
406 }
407 /* traverse hash part */
408 for (n = gnode(h, 0); n < limit; n++) {
409 checkdeadkey(n);
410 if (ttisnil(gval(n))) /* entry is empty? */
411 removeentry(n); /* remove it */
412 else if (iscleared(g, gkey(n))) { /* key is not marked (yet)? */
413 hasclears = 1; /* table must be cleared */
414 if (valiswhite(gval(n))) /* value not marked yet? */
415 hasww = 1; /* white-white entry */
416 }
417 else if (valiswhite(gval(n))) { /* value not marked yet? */
418 marked = 1;
419 reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
420 }
421 }
422 /* link table into proper list */
423 if (g->gcstate == GCSpropagate)
424 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
425 else if (hasww) /* table has white->white entries? */
426 linkgclist(h, g->ephemeron); /* have to propagate again */
427 else if (hasclears) /* table has white keys? */
428 linkgclist(h, g->allweak); /* may have to clean white keys */
429 return marked;
430}
431
432
433static void traversestrongtable (global_State *g, Table *h) {
434 Node *n, *limit = gnodelast(h);
435 unsigned int i;
436 for (i = 0; i < h->sizearray; i++) /* traverse array part */
437 markvalue(g, &h->array[i]);
438 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
439 checkdeadkey(n);
440 if (ttisnil(gval(n))) /* entry is empty? */
441 removeentry(n); /* remove it */
442 else {
443 lua_assert(!ttisnil(gkey(n)));
444 markvalue(g, gkey(n)); /* mark key */
445 markvalue(g, gval(n)); /* mark value */
446 }
447 }
448}
449
450
451static lu_mem traversetable (global_State *g, Table *h) {
452 const char *weakkey, *weakvalue;
453 const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
454 markobjectN(g, h->metatable);
455 if (mode && ttisstring(mode) && /* is there a weak mode? */
456 ((weakkey = strchr(svalue(mode), 'k')),
457 (weakvalue = strchr(svalue(mode), 'v')),
458 (weakkey || weakvalue))) { /* is really weak? */
459 black2gray(h); /* keep table gray */
460 if (!weakkey) /* strong keys? */
461 traverseweakvalue(g, h);
462 else if (!weakvalue) /* strong values? */
463 traverseephemeron(g, h);
464 else /* all weak */
465 linkgclist(h, g->allweak); /* nothing to traverse now */
466 }
467 else /* not weak */
468 traversestrongtable(g, h);
469 return sizeof(Table) + sizeof(TValue) * h->sizearray +
470 sizeof(Node) * cast(size_t, allocsizenode(h));
471}
472
473
474/*
475** Traverse a prototype. (While a prototype is being build, its
476** arrays can be larger than needed; the extra slots are filled with
477** NULL, so the use of 'markobjectN')
478*/
479static int traverseproto (global_State *g, Proto *f) {
480 int i;
481 if (f->cache && iswhite(f->cache))
482 f->cache = NULL; /* allow cache to be collected */
483 markobjectN(g, f->source);
484 for (i = 0; i < f->sizek; i++) /* mark literals */
485 markvalue(g, &f->k[i]);
486 for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
487 markobjectN(g, f->upvalues[i].name);
488 for (i = 0; i < f->sizep; i++) /* mark nested protos */
489 markobjectN(g, f->p[i]);
490 for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
491 markobjectN(g, f->locvars[i].varname);
492 return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
493 sizeof(Proto *) * f->sizep +
494 sizeof(TValue) * f->sizek +
495 sizeof(int) * f->sizelineinfo +
496 sizeof(LocVar) * f->sizelocvars +
497 sizeof(Upvaldesc) * f->sizeupvalues;
498}
499
500
501static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
502 int i;
503 for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
504 markvalue(g, &cl->upvalue[i]);
505 return sizeCclosure(cl->nupvalues);
506}
507
508/*
509** open upvalues point to values in a thread, so those values should
510** be marked when the thread is traversed except in the atomic phase
511** (because then the value cannot be changed by the thread and the
512** thread may not be traversed again)
513*/
514static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
515 int i;
516 markobjectN(g, cl->p); /* mark its prototype */
517 for (i = 0; i < cl->nupvalues; i++) { /* mark its upvalues */
518 UpVal *uv = cl->upvals[i];
519 if (uv != NULL) {
520 if (upisopen(uv) && g->gcstate != GCSinsideatomic)
521 uv->u.open.touched = 1; /* can be marked in 'remarkupvals' */
522 else
523 markvalue(g, uv->v);
524 }
525 }
526 return sizeLclosure(cl->nupvalues);
527}
528
529
530static lu_mem traversethread (global_State *g, lua_State *th) {
531 StkId o = th->stack;
532 if (o == NULL)
533 return 1; /* stack not completely built yet */
534 lua_assert(g->gcstate == GCSinsideatomic ||
535 th->openupval == NULL || isintwups(th));
536 for (; o < th->top; o++) /* mark live elements in the stack */
537 markvalue(g, o);
538 if (g->gcstate == GCSinsideatomic) { /* final traversal? */
539 StkId lim = th->stack + th->stacksize; /* real end of stack */
540 for (; o < lim; o++) /* clear not-marked stack slice */
541 setnilvalue(o);
542 /* 'remarkupvals' may have removed thread from 'twups' list */
543 if (!isintwups(th) && th->openupval != NULL) {
544 th->twups = g->twups; /* link it back to the list */
545 g->twups = th;
546 }
547 }
548 else if (g->gckind != KGC_EMERGENCY)
549 luaD_shrinkstack(th); /* do not change stack in emergency cycle */
550 return (sizeof(lua_State) + sizeof(TValue) * th->stacksize +
551 sizeof(CallInfo) * th->nci);
552}
553
554
555/*
556** traverse one gray object, turning it to black (except for threads,
557** which are always gray).
558*/
559static void propagatemark (global_State *g) {
560 lu_mem size;
561 GCObject *o = g->gray;
562 lua_assert(isgray(o));
563 gray2black(o);
564 switch (o->tt) {
565 case LUA_TTABLE: {
566 Table *h = gco2t(o);
567 g->gray = h->gclist; /* remove from 'gray' list */
568 size = traversetable(g, h);
569 break;
570 }
571 case LUA_TLCL: {
572 LClosure *cl = gco2lcl(o);
573 g->gray = cl->gclist; /* remove from 'gray' list */
574 size = traverseLclosure(g, cl);
575 break;
576 }
577 case LUA_TCCL: {
578 CClosure *cl = gco2ccl(o);
579 g->gray = cl->gclist; /* remove from 'gray' list */
580 size = traverseCclosure(g, cl);
581 break;
582 }
583 case LUA_TTHREAD: {
584 lua_State *th = gco2th(o);
585 g->gray = th->gclist; /* remove from 'gray' list */
586 linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
587 black2gray(o);
588 size = traversethread(g, th);
589 break;
590 }
591 case LUA_TPROTO: {
592 Proto *p = gco2p(o);
593 g->gray = p->gclist; /* remove from 'gray' list */
594 size = traverseproto(g, p);
595 break;
596 }
597 default: lua_assert(0); return;
598 }
599 g->GCmemtrav += size;
600}
601
602
603static void propagateall (global_State *g) {
604 while (g->gray) propagatemark(g);
605}
606
607
608static void convergeephemerons (global_State *g) {
609 int changed;
610 do {
611 GCObject *w;
612 GCObject *next = g->ephemeron; /* get ephemeron list */
613 g->ephemeron = NULL; /* tables may return to this list when traversed */
614 changed = 0;
615 while ((w = next) != NULL) {
616 next = gco2t(w)->gclist;
617 if (traverseephemeron(g, gco2t(w))) { /* traverse marked some value? */
618 propagateall(g); /* propagate changes */
619 changed = 1; /* will have to revisit all ephemeron tables */
620 }
621 }
622 } while (changed);
623}
624
625/* }====================================================== */
626
627
628/*
629** {======================================================
630** Sweep Functions
631** =======================================================
632*/
633
634
635/*
636** clear entries with unmarked keys from all weaktables in list 'l' up
637** to element 'f'
638*/
639static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
640 for (; l != f; l = gco2t(l)->gclist) {
641 Table *h = gco2t(l);
642 Node *n, *limit = gnodelast(h);
643 for (n = gnode(h, 0); n < limit; n++) {
644 if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
645 setnilvalue(gval(n)); /* remove value ... */
646 }
647 if (ttisnil(gval(n))) /* is entry empty? */
648 removeentry(n); /* remove entry from table */
649 }
650 }
651}
652
653
654/*
655** clear entries with unmarked values from all weaktables in list 'l' up
656** to element 'f'
657*/
658static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
659 for (; l != f; l = gco2t(l)->gclist) {
660 Table *h = gco2t(l);
661 Node *n, *limit = gnodelast(h);
662 unsigned int i;
663 for (i = 0; i < h->sizearray; i++) {
664 TValue *o = &h->array[i];
665 if (iscleared(g, o)) /* value was collected? */
666 setnilvalue(o); /* remove value */
667 }
668 for (n = gnode(h, 0); n < limit; n++) {
669 if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
670 setnilvalue(gval(n)); /* remove value ... */
671 removeentry(n); /* and remove entry from table */
672 }
673 }
674 }
675}
676
677
678void luaC_upvdeccount (lua_State *L, UpVal *uv) {
679 lua_assert(uv->refcount > 0);
680 uv->refcount--;
681 if (uv->refcount == 0 && !upisopen(uv))
682 luaM_free(L, uv);
683}
684
685
686static void freeLclosure (lua_State *L, LClosure *cl) {
687 int i;
688 for (i = 0; i < cl->nupvalues; i++) {
689 UpVal *uv = cl->upvals[i];
690 if (uv)
691 luaC_upvdeccount(L, uv);
692 }
693 luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
694}
695
696
697static void freeobj (lua_State *L, GCObject *o) {
698 switch (o->tt) {
699 case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
700 case LUA_TLCL: {
701 freeLclosure(L, gco2lcl(o));
702 break;
703 }
704 case LUA_TCCL: {
705 luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
706 break;
707 }
708 case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
709 case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
710 case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
711 case LUA_TSHRSTR:
712 luaS_remove(L, gco2ts(o)); /* remove it from hash table */
713 luaM_freemem(L, o, sizelstring(gco2ts(o)->shrlen));
714 break;
715 case LUA_TLNGSTR: {
716 luaM_freemem(L, o, sizelstring(gco2ts(o)->u.lnglen));
717 break;
718 }
719 default: lua_assert(0);
720 }
721}
722
723
724#define sweepwholelist(L,p) sweeplist(L,p,MAX_LUMEM)
725static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
726
727
728/*
729** sweep at most 'count' elements from a list of GCObjects erasing dead
730** objects, where a dead object is one marked with the old (non current)
731** white; change all non-dead objects back to white, preparing for next
732** collection cycle. Return where to continue the traversal or NULL if
733** list is finished.
734*/
735static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
736 global_State *g = G(L);
737 int ow = otherwhite(g);
738 int white = luaC_white(g); /* current white */
739 while (*p != NULL && count-- > 0) {
740 GCObject *curr = *p;
741 int marked = curr->marked;
742 if (isdeadm(ow, marked)) { /* is 'curr' dead? */
743 *p = curr->next; /* remove 'curr' from list */
744 freeobj(L, curr); /* erase 'curr' */
745 }
746 else { /* change mark to 'white' */
747 curr->marked = cast_byte((marked & maskcolors) | white);
748 p = &curr->next; /* go to next element */
749 }
750 }
751 return (*p == NULL) ? NULL : p;
752}
753
754
755/*
756** sweep a list until a live object (or end of list)
757*/
758static GCObject **sweeptolive (lua_State *L, GCObject **p) {
759 GCObject **old = p;
760 do {
761 p = sweeplist(L, p, 1);
762 } while (p == old);
763 return p;
764}
765
766/* }====================================================== */
767
768
769/*
770** {======================================================
771** Finalization
772** =======================================================
773*/
774
775/*
776** If possible, shrink string table
777*/
778static void checkSizes (lua_State *L, global_State *g) {
779 if (g->gckind != KGC_EMERGENCY) {
780 l_mem olddebt = g->GCdebt;
781 if (g->strt.nuse < g->strt.size / 4) /* string table too big? */
782 luaS_resize(L, g->strt.size / 2); /* shrink it a little */
783 g->GCestimate += g->GCdebt - olddebt; /* update estimate */
784 }
785}
786
787
788static GCObject *udata2finalize (global_State *g) {
789 GCObject *o = g->tobefnz; /* get first element */
790 lua_assert(tofinalize(o));
791 g->tobefnz = o->next; /* remove it from 'tobefnz' list */
792 o->next = g->allgc; /* return it to 'allgc' list */
793 g->allgc = o;
794 resetbit(o->marked, FINALIZEDBIT); /* object is "normal" again */
795 if (issweepphase(g))
796 makewhite(g, o); /* "sweep" object */
797 return o;
798}
799
800
801static void dothecall (lua_State *L, void *ud) {
802 UNUSED(ud);
803 luaD_callnoyield(L, L->top - 2, 0);
804}
805
806
807static void GCTM (lua_State *L, int propagateerrors) {
808 global_State *g = G(L);
809 const TValue *tm;
810 TValue v;
811 setgcovalue(L, &v, udata2finalize(g));
812 tm = luaT_gettmbyobj(L, &v, TM_GC);
813 if (tm != NULL && ttisfunction(tm)) { /* is there a finalizer? */
814 int status;
815 lu_byte oldah = L->allowhook;
816 int running = g->gcrunning;
817 L->allowhook = 0; /* stop debug hooks during GC metamethod */
818 g->gcrunning = 0; /* avoid GC steps */
819 setobj2s(L, L->top, tm); /* push finalizer... */
820 setobj2s(L, L->top + 1, &v); /* ... and its argument */
821 L->top += 2; /* and (next line) call the finalizer */
822 L->ci->callstatus |= CIST_FIN; /* will run a finalizer */
823 status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
824 L->ci->callstatus &= ~CIST_FIN; /* not running a finalizer anymore */
825 L->allowhook = oldah; /* restore hooks */
826 g->gcrunning = running; /* restore state */
827 if (status != LUA_OK && propagateerrors) { /* error while running __gc? */
828 if (status == LUA_ERRRUN) { /* is there an error object? */
829 const char *msg = (ttisstring(L->top - 1))
830 ? svalue(L->top - 1)
831 : "no message";
832 luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
833 status = LUA_ERRGCMM; /* error in __gc metamethod */
834 }
835 luaD_throw(L, status); /* re-throw error */
836 }
837 }
838}
839
840
841/*
842** call a few (up to 'g->gcfinnum') finalizers
843*/
844static int runafewfinalizers (lua_State *L) {
845 global_State *g = G(L);
846 unsigned int i;
847 lua_assert(!g->tobefnz || g->gcfinnum > 0);
848 for (i = 0; g->tobefnz && i < g->gcfinnum; i++)
849 GCTM(L, 1); /* call one finalizer */
850 g->gcfinnum = (!g->tobefnz) ? 0 /* nothing more to finalize? */
851 : g->gcfinnum * 2; /* else call a few more next time */
852 return i;
853}
854
855
856/*
857** call all pending finalizers
858*/
859static void callallpendingfinalizers (lua_State *L) {
860 global_State *g = G(L);
861 while (g->tobefnz)
862 GCTM(L, 0);
863}
864
865
866/*
867** find last 'next' field in list 'p' list (to add elements in its end)
868*/
869static GCObject **findlast (GCObject **p) {
870 while (*p != NULL)
871 p = &(*p)->next;
872 return p;
873}
874
875
876/*
877** move all unreachable objects (or 'all' objects) that need
878** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
879*/
880static void separatetobefnz (global_State *g, int all) {
881 GCObject *curr;
882 GCObject **p = &g->finobj;
883 GCObject **lastnext = findlast(&g->tobefnz);
884 while ((curr = *p) != NULL) { /* traverse all finalizable objects */
885 lua_assert(tofinalize(curr));
886 if (!(iswhite(curr) || all)) /* not being collected? */
887 p = &curr->next; /* don't bother with it */
888 else {
889 *p = curr->next; /* remove 'curr' from 'finobj' list */
890 curr->next = *lastnext; /* link at the end of 'tobefnz' list */
891 *lastnext = curr;
892 lastnext = &curr->next;
893 }
894 }
895}
896
897
898/*
899** if object 'o' has a finalizer, remove it from 'allgc' list (must
900** search the list to find it) and link it in 'finobj' list.
901*/
902void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
903 global_State *g = G(L);
904 if (tofinalize(o) || /* obj. is already marked... */
905 gfasttm(g, mt, TM_GC) == NULL) /* or has no finalizer? */
906 return; /* nothing to be done */
907 else { /* move 'o' to 'finobj' list */
908 GCObject **p;
909 if (issweepphase(g)) {
910 makewhite(g, o); /* "sweep" object 'o' */
911 if (g->sweepgc == &o->next) /* should not remove 'sweepgc' object */
912 g->sweepgc = sweeptolive(L, g->sweepgc); /* change 'sweepgc' */
913 }
914 /* search for pointer pointing to 'o' */
915 for (p = &g->allgc; *p != o; p = &(*p)->next) { /* empty */ }
916 *p = o->next; /* remove 'o' from 'allgc' list */
917 o->next = g->finobj; /* link it in 'finobj' list */
918 g->finobj = o;
919 l_setbit(o->marked, FINALIZEDBIT); /* mark it as such */
920 }
921}
922
923/* }====================================================== */
924
925
926
927/*
928** {======================================================
929** GC control
930** =======================================================
931*/
932
933
934/*
935** Set a reasonable "time" to wait before starting a new GC cycle; cycle
936** will start when memory use hits threshold. (Division by 'estimate'
937** should be OK: it cannot be zero (because Lua cannot even start with
938** less than PAUSEADJ bytes).
939*/
940static void setpause (global_State *g) {
941 l_mem threshold, debt;
942 l_mem estimate = g->GCestimate / PAUSEADJ; /* adjust 'estimate' */
943 lua_assert(estimate > 0);
944 threshold = (g->gcpause < MAX_LMEM / estimate) /* overflow? */
945 ? estimate * g->gcpause /* no overflow */
946 : MAX_LMEM; /* overflow; truncate to maximum */
947 debt = gettotalbytes(g) - threshold;
948 luaE_setdebt(g, debt);
949}
950
951
952/*
953** Enter first sweep phase.
954** The call to 'sweeplist' tries to make pointer point to an object
955** inside the list (instead of to the header), so that the real sweep do
956** not need to skip objects created between "now" and the start of the
957** real sweep.
958*/
959static void entersweep (lua_State *L) {
960 global_State *g = G(L);
961 g->gcstate = GCSswpallgc;
962 lua_assert(g->sweepgc == NULL);
963 g->sweepgc = sweeplist(L, &g->allgc, 1);
964}
965
966
967void luaC_freeallobjects (lua_State *L) {
968 global_State *g = G(L);
969 separatetobefnz(g, 1); /* separate all objects with finalizers */
970 lua_assert(g->finobj == NULL);
971 callallpendingfinalizers(L);
972 lua_assert(g->tobefnz == NULL);
973 g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
974 g->gckind = KGC_NORMAL;
975 sweepwholelist(L, &g->finobj);
976 sweepwholelist(L, &g->allgc);
977 sweepwholelist(L, &g->fixedgc); /* collect fixed objects */
978 lua_assert(g->strt.nuse == 0);
979}
980
981
982static l_mem atomic (lua_State *L) {
983 global_State *g = G(L);
984 l_mem work;
985 GCObject *origweak, *origall;
986 GCObject *grayagain = g->grayagain; /* save original list */
987 lua_assert(g->ephemeron == NULL && g->weak == NULL);
988 lua_assert(!iswhite(g->mainthread));
989 g->gcstate = GCSinsideatomic;
990 g->GCmemtrav = 0; /* start counting work */
991 markobject(g, L); /* mark running thread */
992 /* registry and global metatables may be changed by API */
993 markvalue(g, &g->l_registry);
994 markmt(g); /* mark global metatables */
995 /* remark occasional upvalues of (maybe) dead threads */
996 remarkupvals(g);
997 propagateall(g); /* propagate changes */
998 work = g->GCmemtrav; /* stop counting (do not recount 'grayagain') */
999 g->gray = grayagain;
1000 propagateall(g); /* traverse 'grayagain' list */
1001 g->GCmemtrav = 0; /* restart counting */
1002 convergeephemerons(g);
1003 /* at this point, all strongly accessible objects are marked. */
1004 /* Clear values from weak tables, before checking finalizers */
1005 clearvalues(g, g->weak, NULL);
1006 clearvalues(g, g->allweak, NULL);
1007 origweak = g->weak; origall = g->allweak;
1008 work += g->GCmemtrav; /* stop counting (objects being finalized) */
1009 separatetobefnz(g, 0); /* separate objects to be finalized */
1010 g->gcfinnum = 1; /* there may be objects to be finalized */
1011 markbeingfnz(g); /* mark objects that will be finalized */
1012 propagateall(g); /* remark, to propagate 'resurrection' */
1013 g->GCmemtrav = 0; /* restart counting */
1014 convergeephemerons(g);
1015 /* at this point, all resurrected objects are marked. */
1016 /* remove dead objects from weak tables */
1017 clearkeys(g, g->ephemeron, NULL); /* clear keys from all ephemeron tables */
1018 clearkeys(g, g->allweak, NULL); /* clear keys from all 'allweak' tables */
1019 /* clear values from resurrected weak tables */
1020 clearvalues(g, g->weak, origweak);
1021 clearvalues(g, g->allweak, origall);
1022 luaS_clearcache(g);
1023 g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
1024 work += g->GCmemtrav; /* complete counting */
1025 return work; /* estimate of memory marked by 'atomic' */
1026}
1027
1028
1029static lu_mem sweepstep (lua_State *L, global_State *g,
1030 int nextstate, GCObject **nextlist) {
1031 if (g->sweepgc) {
1032 l_mem olddebt = g->GCdebt;
1033 g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
1034 g->GCestimate += g->GCdebt - olddebt; /* update estimate */
1035 if (g->sweepgc) /* is there still something to sweep? */
1036 return (GCSWEEPMAX * GCSWEEPCOST);
1037 }
1038 /* else enter next state */
1039 g->gcstate = nextstate;
1040 g->sweepgc = nextlist;
1041 return 0;
1042}
1043
1044
1045static lu_mem singlestep (lua_State *L) {
1046 global_State *g = G(L);
1047 switch (g->gcstate) {
1048 case GCSpause: {
1049 g->GCmemtrav = g->strt.size * sizeof(GCObject*);
1050 restartcollection(g);
1051 g->gcstate = GCSpropagate;
1052 return g->GCmemtrav;
1053 }
1054 case GCSpropagate: {
1055 g->GCmemtrav = 0;
1056 lua_assert(g->gray);
1057 propagatemark(g);
1058 if (g->gray == NULL) /* no more gray objects? */
1059 g->gcstate = GCSatomic; /* finish propagate phase */
1060 return g->GCmemtrav; /* memory traversed in this step */
1061 }
1062 case GCSatomic: {
1063 lu_mem work;
1064 propagateall(g); /* make sure gray list is empty */
1065 work = atomic(L); /* work is what was traversed by 'atomic' */
1066 entersweep(L);
1067 g->GCestimate = gettotalbytes(g); /* first estimate */;
1068 return work;
1069 }
1070 case GCSswpallgc: { /* sweep "regular" objects */
1071 return sweepstep(L, g, GCSswpfinobj, &g->finobj);
1072 }
1073 case GCSswpfinobj: { /* sweep objects with finalizers */
1074 return sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
1075 }
1076 case GCSswptobefnz: { /* sweep objects to be finalized */
1077 return sweepstep(L, g, GCSswpend, NULL);
1078 }
1079 case GCSswpend: { /* finish sweeps */
1080 makewhite(g, g->mainthread); /* sweep main thread */
1081 checkSizes(L, g);
1082 g->gcstate = GCScallfin;
1083 return 0;
1084 }
1085 case GCScallfin: { /* call remaining finalizers */
1086 if (g->tobefnz && g->gckind != KGC_EMERGENCY) {
1087 int n = runafewfinalizers(L);
1088 return (n * GCFINALIZECOST);
1089 }
1090 else { /* emergency mode or no more finalizers */
1091 g->gcstate = GCSpause; /* finish collection */
1092 return 0;
1093 }
1094 }
1095 default: lua_assert(0); return 0;
1096 }
1097}
1098
1099
1100/*
1101** advances the garbage collector until it reaches a state allowed
1102** by 'statemask'
1103*/
1104void luaC_runtilstate (lua_State *L, int statesmask) {
1105 global_State *g = G(L);
1106 while (!testbit(statesmask, g->gcstate))
1107 singlestep(L);
1108}
1109
1110
1111/*
1112** get GC debt and convert it from Kb to 'work units' (avoid zero debt
1113** and overflows)
1114*/
1115static l_mem getdebt (global_State *g) {
1116 l_mem debt = g->GCdebt;
1117 int stepmul = g->gcstepmul;
1118 if (debt <= 0) return 0; /* minimal debt */
1119 else {
1120 debt = (debt / STEPMULADJ) + 1;
1121 debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
1122 return debt;
1123 }
1124}
1125
1126/*
1127** performs a basic GC step when collector is running
1128*/
1129void luaC_step (lua_State *L) {
1130 global_State *g = G(L);
1131 l_mem debt = getdebt(g); /* GC deficit (be paid now) */
1132 if (!g->gcrunning) { /* not running? */
1133 luaE_setdebt(g, -GCSTEPSIZE * 10); /* avoid being called too often */
1134 return;
1135 }
1136 do { /* repeat until pause or enough "credit" (negative debt) */
1137 lu_mem work = singlestep(L); /* perform one single step */
1138 debt -= work;
1139 } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
1140 if (g->gcstate == GCSpause)
1141 setpause(g); /* pause until next cycle */
1142 else {
1143 debt = (debt / g->gcstepmul) * STEPMULADJ; /* convert 'work units' to Kb */
1144 luaE_setdebt(g, debt);
1145 runafewfinalizers(L);
1146 }
1147}
1148
1149
1150/*
1151** Performs a full GC cycle; if 'isemergency', set a flag to avoid
1152** some operations which could change the interpreter state in some
1153** unexpected ways (running finalizers and shrinking some structures).
1154** Before running the collection, check 'keepinvariant'; if it is true,
1155** there may be some objects marked as black, so the collector has
1156** to sweep all objects to turn them back to white (as white has not
1157** changed, nothing will be collected).
1158*/
1159void luaC_fullgc (lua_State *L, int isemergency) {
1160 global_State *g = G(L);
1161 lua_assert(g->gckind == KGC_NORMAL);
1162 if (isemergency) g->gckind = KGC_EMERGENCY; /* set flag */
1163 if (keepinvariant(g)) { /* black objects? */
1164 entersweep(L); /* sweep everything to turn them back to white */
1165 }
1166 /* finish any pending sweep phase to start a new cycle */
1167 luaC_runtilstate(L, bitmask(GCSpause));
1168 luaC_runtilstate(L, ~bitmask(GCSpause)); /* start new collection */
1169 luaC_runtilstate(L, bitmask(GCScallfin)); /* run up to finalizers */
1170 /* estimate must be correct after a full GC cycle */
1171 lua_assert(g->GCestimate == gettotalbytes(g));
1172 luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
1173 g->gckind = KGC_NORMAL;
1174 setpause(g);
1175}
1176
1177/* }====================================================== */
1178
1179
1180