1 /*
2 ** $Id: lgc.c,v 2.140.1.2 2013/04/26 18:22:05 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 */
removeentry(Node * n)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 */
iscleared(global_State * g,const TValue * o)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 */
luaC_barrier_(lua_State * L,GCObject * o,GCObject * v)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 */
luaC_barrierback_(lua_State * L,GCObject * o)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 */
luaC_barrierproto_(lua_State * L,Proto * p,Closure * c)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 */
luaC_checkupvalcolor(global_State * g,UpVal * uv)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 */
luaC_newobj(lua_State * L,int tt,size_t sz,GCObject ** list,int offset)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 = (lu_byte)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 */
reallymarkobject(global_State * g,GCObject * o)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 */
markmt(global_State * g)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 */
markbeingfnz(global_State * g)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 */
remarkupvals(global_State * g)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 */
restartcollection(global_State * g)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 
traverseweakvalue(global_State * g,Table * h)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 
traverseephemeron(global_State * g,Table * h)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 
traversestrongtable(global_State * g,Table * h)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 
traversetable(global_State * g,Table * h)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 
traverseproto(global_State * g,Proto * f)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 
traverseCclosure(global_State * g,CClosure * cl)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 
traverseLclosure(global_State * g,LClosure * cl)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 
traversestack(global_State * g,lua_State * th)495 static lu_mem traversestack (global_State *g, lua_State *th) {
496   int n = 0;
497   StkId o = th->stack;
498   if (o == NULL)
499     return 1;  /* stack not completely built yet */
500   for (; o < th->top; o++)  /* mark live elements in the stack */
501     markvalue(g, o);
502   if (g->gcstate == GCSatomic) {  /* final traversal? */
503     StkId lim = th->stack + th->stacksize;  /* real end of stack */
504     for (; o < lim; o++)  /* clear not-marked stack slice */
505       setnilvalue(o);
506   }
507   else {  /* count call infos to compute size */
508     CallInfo *ci;
509     for (ci = &th->base_ci; ci != th->ci; ci = ci->next)
510       n++;
511   }
512   return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
513          sizeof(CallInfo) * n;
514 }
515 
516 
517 /*
518 ** traverse one gray object, turning it to black (except for threads,
519 ** which are always gray).
520 */
propagatemark(global_State * g)521 static void propagatemark (global_State *g) {
522   lu_mem size;
523   GCObject *o = g->gray;
524   lua_assert(isgray(o));
525   gray2black(o);
526   switch (gch(o)->tt) {
527     case LUA_TTABLE: {
528       Table *h = gco2t(o);
529       g->gray = h->gclist;  /* remove from 'gray' list */
530       size = traversetable(g, h);
531       break;
532     }
533     case LUA_TLCL: {
534       LClosure *cl = gco2lcl(o);
535       g->gray = cl->gclist;  /* remove from 'gray' list */
536       size = traverseLclosure(g, cl);
537       break;
538     }
539     case LUA_TCCL: {
540       CClosure *cl = gco2ccl(o);
541       g->gray = cl->gclist;  /* remove from 'gray' list */
542       size = traverseCclosure(g, cl);
543       break;
544     }
545     case LUA_TTHREAD: {
546       lua_State *th = gco2th(o);
547       g->gray = th->gclist;  /* remove from 'gray' list */
548       th->gclist = g->grayagain;
549       g->grayagain = o;  /* insert into 'grayagain' list */
550       black2gray(o);
551       size = traversestack(g, th);
552       break;
553     }
554     case LUA_TPROTO: {
555       Proto *p = gco2p(o);
556       g->gray = p->gclist;  /* remove from 'gray' list */
557       size = traverseproto(g, p);
558       break;
559     }
560     default: lua_assert(0); return;
561   }
562   g->GCmemtrav += size;
563 }
564 
565 
propagateall(global_State * g)566 static void propagateall (global_State *g) {
567   while (g->gray) propagatemark(g);
568 }
569 
570 
propagatelist(global_State * g,GCObject * l)571 static void propagatelist (global_State *g, GCObject *l) {
572   lua_assert(g->gray == NULL);  /* no grays left */
573   g->gray = l;
574   propagateall(g);  /* traverse all elements from 'l' */
575 }
576 
577 /*
578 ** retraverse all gray lists. Because tables may be reinserted in other
579 ** lists when traversed, traverse the original lists to avoid traversing
580 ** twice the same table (which is not wrong, but inefficient)
581 */
retraversegrays(global_State * g)582 static void retraversegrays (global_State *g) {
583   GCObject *weak = g->weak;  /* save original lists */
584   GCObject *grayagain = g->grayagain;
585   GCObject *ephemeron = g->ephemeron;
586   g->weak = g->grayagain = g->ephemeron = NULL;
587   propagateall(g);  /* traverse main gray list */
588   propagatelist(g, grayagain);
589   propagatelist(g, weak);
590   propagatelist(g, ephemeron);
591 }
592 
593 
convergeephemerons(global_State * g)594 static void convergeephemerons (global_State *g) {
595   int changed;
596   do {
597     GCObject *w;
598     GCObject *next = g->ephemeron;  /* get ephemeron list */
599     g->ephemeron = NULL;  /* tables will return to this list when traversed */
600     changed = 0;
601     while ((w = next) != NULL) {
602       next = gco2t(w)->gclist;
603       if (traverseephemeron(g, gco2t(w))) {  /* traverse marked some value? */
604         propagateall(g);  /* propagate changes */
605         changed = 1;  /* will have to revisit all ephemeron tables */
606       }
607     }
608   } while (changed);
609 }
610 
611 /* }====================================================== */
612 
613 
614 /*
615 ** {======================================================
616 ** Sweep Functions
617 ** =======================================================
618 */
619 
620 
621 /*
622 ** clear entries with unmarked keys from all weaktables in list 'l' up
623 ** to element 'f'
624 */
clearkeys(global_State * g,GCObject * l,GCObject * f)625 static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
626   for (; l != f; l = gco2t(l)->gclist) {
627     Table *h = gco2t(l);
628     Node *n, *limit = gnodelast(h);
629     for (n = gnode(h, 0); n < limit; n++) {
630       if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
631         setnilvalue(gval(n));  /* remove value ... */
632         removeentry(n);  /* and remove entry from table */
633       }
634     }
635   }
636 }
637 
638 
639 /*
640 ** clear entries with unmarked values from all weaktables in list 'l' up
641 ** to element 'f'
642 */
clearvalues(global_State * g,GCObject * l,GCObject * f)643 static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
644   for (; l != f; l = gco2t(l)->gclist) {
645     Table *h = gco2t(l);
646     Node *n, *limit = gnodelast(h);
647     int i;
648     for (i = 0; i < h->sizearray; i++) {
649       TValue *o = &h->array[i];
650       if (iscleared(g, o))  /* value was collected? */
651         setnilvalue(o);  /* remove value */
652     }
653     for (n = gnode(h, 0); n < limit; n++) {
654       if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
655         setnilvalue(gval(n));  /* remove value ... */
656         removeentry(n);  /* and remove entry from table */
657       }
658     }
659   }
660 }
661 
662 
freeobj(lua_State * L,GCObject * o)663 static void freeobj (lua_State *L, GCObject *o) {
664   switch (gch(o)->tt) {
665     case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
666     case LUA_TLCL: {
667       luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
668       break;
669     }
670     case LUA_TCCL: {
671       luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
672       break;
673     }
674     case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
675     case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
676     case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
677     case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
678     case LUA_TSHRSTR:
679       G(L)->strt.nuse--;
680       /* go through */
681     case LUA_TLNGSTR: {
682       luaM_freemem(L, o, sizestring(gco2ts(o)));
683       break;
684     }
685     default: lua_assert(0);
686   }
687 }
688 
689 
690 #define sweepwholelist(L,p) sweeplist(L,p,MAX_LUMEM)
691 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
692 
693 
694 /*
695 ** sweep the (open) upvalues of a thread and resize its stack and
696 ** list of call-info structures.
697 */
sweepthread(lua_State * L,lua_State * L1)698 static void sweepthread (lua_State *L, lua_State *L1) {
699   if (L1->stack == NULL) return;  /* stack not completely built yet */
700   sweepwholelist(L, &L1->openupval);  /* sweep open upvalues */
701   luaE_freeCI(L1);  /* free extra CallInfo slots */
702   /* should not change the stack during an emergency gc cycle */
703   if (G(L)->gckind != KGC_EMERGENCY)
704     luaD_shrinkstack(L1);
705 }
706 
707 
708 /*
709 ** sweep at most 'count' elements from a list of GCObjects erasing dead
710 ** objects, where a dead (not alive) object is one marked with the "old"
711 ** (non current) white and not fixed.
712 ** In non-generational mode, change all non-dead objects back to white,
713 ** preparing for next collection cycle.
714 ** In generational mode, keep black objects black, and also mark them as
715 ** old; stop when hitting an old object, as all objects after that
716 ** one will be old too.
717 ** When object is a thread, sweep its list of open upvalues too.
718 */
sweeplist(lua_State * L,GCObject ** p,lu_mem count)719 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
720   global_State *g = G(L);
721   int ow = otherwhite(g);
722   int toclear, toset;  /* bits to clear and to set in all live objects */
723   int tostop;  /* stop sweep when this is true */
724   if (isgenerational(g)) {  /* generational mode? */
725     toclear = ~0;  /* clear nothing */
726     toset = bitmask(OLDBIT);  /* set the old bit of all surviving objects */
727     tostop = bitmask(OLDBIT);  /* do not sweep old generation */
728   }
729   else {  /* normal mode */
730     toclear = maskcolors;  /* clear all color bits + old bit */
731     toset = luaC_white(g);  /* make object white */
732     tostop = 0;  /* do not stop */
733   }
734   while (*p != NULL && count-- > 0) {
735     GCObject *curr = *p;
736     int marked = gch(curr)->marked;
737     if (isdeadm(ow, marked)) {  /* is 'curr' dead? */
738       *p = gch(curr)->next;  /* remove 'curr' from list */
739       freeobj(L, curr);  /* erase 'curr' */
740     }
741     else {
742       if (testbits(marked, tostop))
743         return NULL;  /* stop sweeping this list */
744       if (gch(curr)->tt == LUA_TTHREAD)
745         sweepthread(L, gco2th(curr));  /* sweep thread's upvalues */
746       /* update marks */
747       gch(curr)->marked = cast_byte((marked & toclear) | toset);
748       p = &gch(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 */
sweeptolive(lua_State * L,GCObject ** p,int * n)758 static GCObject **sweeptolive (lua_State *L, GCObject **p, int *n) {
759   GCObject ** old = p;
760   int i = 0;
761   do {
762     i++;
763     p = sweeplist(L, p, 1);
764   } while (p == old);
765   if (n) *n += i;
766   return p;
767 }
768 
769 /* }====================================================== */
770 
771 
772 /*
773 ** {======================================================
774 ** Finalization
775 ** =======================================================
776 */
777 
checkSizes(lua_State * L)778 static void checkSizes (lua_State *L) {
779   global_State *g = G(L);
780   if (g->gckind != KGC_EMERGENCY) {  /* do not change sizes in emergency */
781     int hs = g->strt.size / 2;  /* half the size of the string table */
782     if (g->strt.nuse < cast(lu_int32, hs))  /* using less than that half? */
783       luaS_resize(L, hs);  /* halve its size */
784     luaZ_freebuffer(L, &g->buff);  /* free concatenation buffer */
785   }
786 }
787 
788 
udata2finalize(global_State * g)789 static GCObject *udata2finalize (global_State *g) {
790   GCObject *o = g->tobefnz;  /* get first element */
791   lua_assert(isfinalized(o));
792   g->tobefnz = gch(o)->next;  /* remove it from 'tobefnz' list */
793   gch(o)->next = g->allgc;  /* return it to 'allgc' list */
794   g->allgc = o;
795   resetbit(gch(o)->marked, SEPARATED);  /* mark that it is not in 'tobefnz' */
796   lua_assert(!isold(o));  /* see MOVE OLD rule */
797   if (!keepinvariantout(g))  /* not keeping invariant? */
798     makewhite(g, o);  /* "sweep" object */
799   return o;
800 }
801 
802 
dothecall(lua_State * L,void * ud)803 static void dothecall (lua_State *L, void *ud) {
804   UNUSED(ud);
805   luaD_call(L, L->top - 2, 0, 0);
806 }
807 
808 
GCTM(lua_State * L,int propagateerrors)809 static void GCTM (lua_State *L, int propagateerrors) {
810   global_State *g = G(L);
811   const TValue *tm;
812   TValue v;
813   setgcovalue(L, &v, udata2finalize(g));
814   tm = luaT_gettmbyobj(L, &v, TM_GC);
815   if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
816     int status;
817     lu_byte oldah = L->allowhook;
818     int running  = g->gcrunning;
819     L->allowhook = 0;  /* stop debug hooks during GC metamethod */
820     g->gcrunning = 0;  /* avoid GC steps */
821     setobj2s(L, L->top, tm);  /* push finalizer... */
822     setobj2s(L, L->top + 1, &v);  /* ... and its argument */
823     L->top += 2;  /* and (next line) call the finalizer */
824     status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
825     L->allowhook = oldah;  /* restore hooks */
826     g->gcrunning = (lu_byte)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 ** move all unreachable objects (or 'all' objects) that need
843 ** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
844 */
separatetobefnz(lua_State * L,int all)845 static void separatetobefnz (lua_State *L, int all) {
846   global_State *g = G(L);
847   GCObject **p = &g->finobj;
848   GCObject *curr;
849   GCObject **lastnext = &g->tobefnz;
850   /* find last 'next' field in 'tobefnz' list (to add elements in its end) */
851   while (*lastnext != NULL)
852     lastnext = &gch(*lastnext)->next;
853   while ((curr = *p) != NULL) {  /* traverse all finalizable objects */
854     lua_assert(!isfinalized(curr));
855     lua_assert(testbit(gch(curr)->marked, SEPARATED));
856     if (!(iswhite(curr) || all))  /* not being collected? */
857       p = &gch(curr)->next;  /* don't bother with it */
858     else {
859       l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
860       *p = gch(curr)->next;  /* remove 'curr' from 'finobj' list */
861       gch(curr)->next = *lastnext;  /* link at the end of 'tobefnz' list */
862       *lastnext = curr;
863       lastnext = &gch(curr)->next;
864     }
865   }
866 }
867 
868 
869 /*
870 ** if object 'o' has a finalizer, remove it from 'allgc' list (must
871 ** search the list to find it) and link it in 'finobj' list.
872 */
luaC_checkfinalizer(lua_State * L,GCObject * o,Table * mt)873 void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
874   global_State *g = G(L);
875   if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
876       isfinalized(o) ||                           /* ... or is finalized... */
877       gfasttm(g, mt, TM_GC) == NULL)                /* or has no finalizer? */
878     return;  /* nothing to be done */
879   else {  /* move 'o' to 'finobj' list */
880     GCObject **p;
881     GCheader *ho = gch(o);
882     if (g->sweepgc == &ho->next) {  /* avoid removing current sweep object */
883       lua_assert(issweepphase(g));
884       g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
885     }
886     /* search for pointer pointing to 'o' */
887     for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
888     *p = ho->next;  /* remove 'o' from root list */
889     ho->next = g->finobj;  /* link it in list 'finobj' */
890     g->finobj = o;
891     l_setbit(ho->marked, SEPARATED);  /* mark it as such */
892     if (!keepinvariantout(g))  /* not keeping invariant? */
893       makewhite(g, o);  /* "sweep" object */
894     else
895       resetoldbit(o);  /* see MOVE OLD rule */
896   }
897 }
898 
899 /* }====================================================== */
900 
901 
902 /*
903 ** {======================================================
904 ** GC control
905 ** =======================================================
906 */
907 
908 
909 /*
910 ** set a reasonable "time" to wait before starting a new GC cycle;
911 ** cycle will start when memory use hits threshold
912 */
setpause(global_State * g,l_mem estimate)913 static void setpause (global_State *g, l_mem estimate) {
914   l_mem debt, threshold;
915   estimate = estimate / PAUSEADJ;  /* adjust 'estimate' */
916   threshold = (g->gcpause < MAX_LMEM / estimate)  /* overflow? */
917             ? estimate * g->gcpause  /* no overflow */
918             : MAX_LMEM;  /* overflow; truncate to maximum */
919   debt = -cast(l_mem, threshold - gettotalbytes(g));
920   luaE_setdebt(g, debt);
921 }
922 
923 
924 #define sweepphases  \
925     (bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))
926 
927 
928 /*
929 ** enter first sweep phase (strings) and prepare pointers for other
930 ** sweep phases.  The calls to 'sweeptolive' make pointers point to an
931 ** object inside the list (instead of to the header), so that the real
932 ** sweep do not need to skip objects created between "now" and the start
933 ** of the real sweep.
934 ** Returns how many objects it swept.
935 */
entersweep(lua_State * L)936 static int entersweep (lua_State *L) {
937   global_State *g = G(L);
938   int n = 0;
939   g->gcstate = GCSsweepstring;
940   lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
941   /* prepare to sweep strings, finalizable objects, and regular objects */
942   g->sweepstrgc = 0;
943   g->sweepfin = sweeptolive(L, &g->finobj, &n);
944   g->sweepgc = sweeptolive(L, &g->allgc, &n);
945   return n;
946 }
947 
948 
949 /*
950 ** change GC mode
951 */
luaC_changemode(lua_State * L,int mode)952 void luaC_changemode (lua_State *L, int mode) {
953   global_State *g = G(L);
954   if (mode == g->gckind) return;  /* nothing to change */
955   if (mode == KGC_GEN) {  /* change to generational mode */
956     /* make sure gray lists are consistent */
957     luaC_runtilstate(L, bitmask(GCSpropagate));
958     g->GCestimate = gettotalbytes(g);
959     g->gckind = KGC_GEN;
960   }
961   else {  /* change to incremental mode */
962     /* sweep all objects to turn them back to white
963        (as white has not changed, nothing extra will be collected) */
964     g->gckind = KGC_NORMAL;
965     entersweep(L);
966     luaC_runtilstate(L, ~sweepphases);
967   }
968 }
969 
970 
971 /*
972 ** call all pending finalizers
973 */
callallpendingfinalizers(lua_State * L,int propagateerrors)974 static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
975   global_State *g = G(L);
976   while (g->tobefnz) {
977     resetoldbit(g->tobefnz);
978     GCTM(L, propagateerrors);
979   }
980 }
981 
982 
luaC_freeallobjects(lua_State * L)983 void luaC_freeallobjects (lua_State *L) {
984   global_State *g = G(L);
985   int i;
986   separatetobefnz(L, 1);  /* separate all objects with finalizers */
987   lua_assert(g->finobj == NULL);
988   callallpendingfinalizers(L, 0);
989   g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
990   g->gckind = KGC_NORMAL;
991   sweepwholelist(L, &g->finobj);  /* finalizers can create objs. in 'finobj' */
992   sweepwholelist(L, &g->allgc);
993   for (i = 0; i < g->strt.size; i++)  /* free all string lists */
994     sweepwholelist(L, &g->strt.hash[i]);
995   lua_assert(g->strt.nuse == 0);
996 }
997 
998 
atomic(lua_State * L)999 static l_mem atomic (lua_State *L) {
1000   global_State *g = G(L);
1001   l_mem work = -cast(l_mem, g->GCmemtrav);  /* start counting work */
1002   GCObject *origweak, *origall;
1003   lua_assert(!iswhite(obj2gco(g->mainthread)));
1004   markobject(g, L);  /* mark running thread */
1005   /* registry and global metatables may be changed by API */
1006   markvalue(g, &g->l_registry);
1007   markmt(g);  /* mark basic metatables */
1008   /* remark occasional upvalues of (maybe) dead threads */
1009   remarkupvals(g);
1010   propagateall(g);  /* propagate changes */
1011   work += g->GCmemtrav;  /* stop counting (do not (re)count grays) */
1012   /* traverse objects caught by write barrier and by 'remarkupvals' */
1013   retraversegrays(g);
1014   work -= g->GCmemtrav;  /* restart counting */
1015   convergeephemerons(g);
1016   /* at this point, all strongly accessible objects are marked. */
1017   /* clear values from weak tables, before checking finalizers */
1018   clearvalues(g, g->weak, NULL);
1019   clearvalues(g, g->allweak, NULL);
1020   origweak = g->weak; origall = g->allweak;
1021   work += g->GCmemtrav;  /* stop counting (objects being finalized) */
1022   separatetobefnz(L, 0);  /* separate objects to be finalized */
1023   markbeingfnz(g);  /* mark objects that will be finalized */
1024   propagateall(g);  /* remark, to propagate `preserveness' */
1025   work -= g->GCmemtrav;  /* restart counting */
1026   convergeephemerons(g);
1027   /* at this point, all resurrected objects are marked. */
1028   /* remove dead objects from weak tables */
1029   clearkeys(g, g->ephemeron, NULL);  /* clear keys from all ephemeron tables */
1030   clearkeys(g, g->allweak, NULL);  /* clear keys from all allweak tables */
1031   /* clear values from resurrected weak tables */
1032   clearvalues(g, g->weak, origweak);
1033   clearvalues(g, g->allweak, origall);
1034   g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */
1035   work += g->GCmemtrav;  /* complete counting */
1036   return work;  /* estimate of memory marked by 'atomic' */
1037 }
1038 
1039 
singlestep(lua_State * L)1040 static lu_mem singlestep (lua_State *L) {
1041   global_State *g = G(L);
1042   switch (g->gcstate) {
1043     case GCSpause: {
1044       /* start to count memory traversed */
1045       g->GCmemtrav = g->strt.size * sizeof(GCObject*);
1046       lua_assert(!isgenerational(g));
1047       restartcollection(g);
1048       g->gcstate = GCSpropagate;
1049       return g->GCmemtrav;
1050     }
1051     case GCSpropagate: {
1052       if (g->gray) {
1053         lu_mem oldtrav = g->GCmemtrav;
1054         propagatemark(g);
1055         return g->GCmemtrav - oldtrav;  /* memory traversed in this step */
1056       }
1057       else {  /* no more `gray' objects */
1058         lu_mem work;
1059         int sw;
1060         g->gcstate = GCSatomic;  /* finish mark phase */
1061         g->GCestimate = g->GCmemtrav;  /* save what was counted */;
1062         work = atomic(L);  /* add what was traversed by 'atomic' */
1063         g->GCestimate += work;  /* estimate of total memory traversed */
1064         sw = entersweep(L);
1065         return work + sw * GCSWEEPCOST;
1066       }
1067     }
1068     case GCSsweepstring: {
1069       int i;
1070       for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
1071         sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
1072       g->sweepstrgc += i;
1073       if (g->sweepstrgc >= g->strt.size)  /* no more strings to sweep? */
1074         g->gcstate = GCSsweepudata;
1075       return i * GCSWEEPCOST;
1076     }
1077     case GCSsweepudata: {
1078       if (g->sweepfin) {
1079         g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
1080         return GCSWEEPMAX*GCSWEEPCOST;
1081       }
1082       else {
1083         g->gcstate = GCSsweep;
1084         return 0;
1085       }
1086     }
1087     case GCSsweep: {
1088       if (g->sweepgc) {
1089         g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
1090         return GCSWEEPMAX*GCSWEEPCOST;
1091       }
1092       else {
1093         /* sweep main thread */
1094         GCObject *mt = obj2gco(g->mainthread);
1095         sweeplist(L, &mt, 1);
1096         checkSizes(L);
1097         g->gcstate = GCSpause;  /* finish collection */
1098         return GCSWEEPCOST;
1099       }
1100     }
1101     default: lua_assert(0); return 0;
1102   }
1103 }
1104 
1105 
1106 /*
1107 ** advances the garbage collector until it reaches a state allowed
1108 ** by 'statemask'
1109 */
luaC_runtilstate(lua_State * L,int statesmask)1110 void luaC_runtilstate (lua_State *L, int statesmask) {
1111   global_State *g = G(L);
1112   while (!testbit(statesmask, g->gcstate))
1113     singlestep(L);
1114 }
1115 
1116 
generationalcollection(lua_State * L)1117 static void generationalcollection (lua_State *L) {
1118   global_State *g = G(L);
1119   lua_assert(g->gcstate == GCSpropagate);
1120   if (g->GCestimate == 0) {  /* signal for another major collection? */
1121     luaC_fullgc(L, 0);  /* perform a full regular collection */
1122     g->GCestimate = gettotalbytes(g);  /* update control */
1123   }
1124   else {
1125     lu_mem estimate = g->GCestimate;
1126     luaC_runtilstate(L, bitmask(GCSpause));  /* run complete (minor) cycle */
1127     g->gcstate = GCSpropagate;  /* skip restart */
1128     if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
1129       g->GCestimate = 0;  /* signal for a major collection */
1130     else
1131       g->GCestimate = estimate;  /* keep estimate from last major coll. */
1132 
1133   }
1134   setpause(g, gettotalbytes(g));
1135   lua_assert(g->gcstate == GCSpropagate);
1136 }
1137 
1138 
incstep(lua_State * L)1139 static void incstep (lua_State *L) {
1140   global_State *g = G(L);
1141   l_mem debt = g->GCdebt;
1142   int stepmul = g->gcstepmul;
1143   if (stepmul < 40) stepmul = 40;  /* avoid ridiculous low values (and 0) */
1144   /* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
1145   debt = (debt / STEPMULADJ) + 1;
1146   debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
1147   do {  /* always perform at least one single step */
1148     lu_mem work = singlestep(L);  /* do some work */
1149     debt -= work;
1150   } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
1151   if (g->gcstate == GCSpause)
1152     setpause(g, g->GCestimate);  /* pause until next cycle */
1153   else {
1154     debt = (debt / stepmul) * STEPMULADJ;  /* convert 'work units' to Kb */
1155     luaE_setdebt(g, debt);
1156   }
1157 }
1158 
1159 
1160 /*
1161 ** performs a basic GC step
1162 */
luaC_forcestep(lua_State * L)1163 void luaC_forcestep (lua_State *L) {
1164   global_State *g = G(L);
1165   int i;
1166   if (isgenerational(g)) generationalcollection(L);
1167   else incstep(L);
1168   /* run a few finalizers (or all of them at the end of a collect cycle) */
1169   for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
1170     GCTM(L, 1);  /* call one finalizer */
1171 }
1172 
1173 
1174 /*
1175 ** performs a basic GC step only if collector is running
1176 */
luaC_step(lua_State * L)1177 void luaC_step (lua_State *L) {
1178   global_State *g = G(L);
1179   if (g->gcrunning) luaC_forcestep(L);
1180   else luaE_setdebt(g, -GCSTEPSIZE);  /* avoid being called too often */
1181 }
1182 
1183 
1184 
1185 /*
1186 ** performs a full GC cycle; if "isemergency", does not call
1187 ** finalizers (which could change stack positions)
1188 */
luaC_fullgc(lua_State * L,int isemergency)1189 void luaC_fullgc (lua_State *L, int isemergency) {
1190   global_State *g = G(L);
1191   int origkind = g->gckind;
1192   lua_assert(origkind != KGC_EMERGENCY);
1193   if (isemergency)  /* do not run finalizers during emergency GC */
1194     g->gckind = KGC_EMERGENCY;
1195   else {
1196     g->gckind = KGC_NORMAL;
1197     callallpendingfinalizers(L, 1);
1198   }
1199   if (keepinvariant(g)) {  /* may there be some black objects? */
1200     /* must sweep all objects to turn them back to white
1201        (as white has not changed, nothing will be collected) */
1202     entersweep(L);
1203   }
1204   /* finish any pending sweep phase to start a new cycle */
1205   luaC_runtilstate(L, bitmask(GCSpause));
1206   luaC_runtilstate(L, ~bitmask(GCSpause));  /* start new collection */
1207   luaC_runtilstate(L, bitmask(GCSpause));  /* run entire collection */
1208   if (origkind == KGC_GEN) {  /* generational mode? */
1209     /* generational mode must be kept in propagate phase */
1210     luaC_runtilstate(L, bitmask(GCSpropagate));
1211   }
1212   g->gckind = (lu_byte)origkind;
1213   setpause(g, gettotalbytes(g));
1214   if (!isemergency)   /* do not run finalizers during emergency GC */
1215     callallpendingfinalizers(L, 1);
1216 }
1217 
1218 /* }====================================================== */
1219 
1220 
1221