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 
94 static 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 */
removeentry(Node * n)125 static 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 */
iscleared(global_State * g,const TValue * o)139 static 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 */
luaC_barrier_(lua_State * L,GCObject * o,GCObject * v)155 void 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 */
luaC_barrierback_(lua_State * L,Table * t)171 void 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 */
luaC_upvalbarrier_(lua_State * L,UpVal * uv)185 void 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 
luaC_fix(lua_State * L,GCObject * o)194 void 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 */
luaC_newobj(lua_State * L,int tt,size_t sz)208 GCObject *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 */
reallymarkobject(global_State * g,GCObject * o)235 static 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 */
markmt(global_State * g)289 static 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 */
markbeingfnz(global_State * g)299 static 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 */
remarkupvals(global_State * g)312 static 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 */
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 
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 */
traverseweakvalue(global_State * g,Table * h)361 static 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 */
traverseephemeron(global_State * g,Table * h)394 static 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 
traversestrongtable(global_State * g,Table * h)433 static 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 
traversetable(global_State * g,Table * h)451 static 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 */
traverseproto(global_State * g,Proto * f)479 static 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 
traverseCclosure(global_State * g,CClosure * cl)501 static 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 */
traverseLclosure(global_State * g,LClosure * cl)514 static 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 
traversethread(global_State * g,lua_State * th)530 static 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 */
propagatemark(global_State * g)559 static 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 
propagateall(global_State * g)603 static void propagateall (global_State *g) {
604   while (g->gray) propagatemark(g);
605 }
606 
607 
convergeephemerons(global_State * g)608 static 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 */
clearkeys(global_State * g,GCObject * l,GCObject * f)639 static 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 */
clearvalues(global_State * g,GCObject * l,GCObject * f)658 static 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 
luaC_upvdeccount(lua_State * L,UpVal * uv)678 void 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 
freeLclosure(lua_State * L,LClosure * cl)686 static 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 
freeobj(lua_State * L,GCObject * o)697 static 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)
725 static 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 */
sweeplist(lua_State * L,GCObject ** p,lu_mem count)735 static 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 */
sweeptolive(lua_State * L,GCObject ** p)758 static 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 */
checkSizes(lua_State * L,global_State * g)778 static 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 
udata2finalize(global_State * g)788 static 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 
dothecall(lua_State * L,void * ud)801 static void dothecall (lua_State *L, void *ud) {
802   UNUSED(ud);
803   luaD_callnoyield(L, L->top - 2, 0);
804 }
805 
806 
GCTM(lua_State * L,int propagateerrors)807 static 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 */
runafewfinalizers(lua_State * L)844 static 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 */
callallpendingfinalizers(lua_State * L)859 static 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 */
findlast(GCObject ** p)869 static 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 */
separatetobefnz(global_State * g,int all)880 static 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 */
luaC_checkfinalizer(lua_State * L,GCObject * o,Table * mt)902 void 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 */
setpause(global_State * g)940 static 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 */
entersweep(lua_State * L)959 static 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 
luaC_freeallobjects(lua_State * L)967 void 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 
atomic(lua_State * L)982 static 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 
sweepstep(lua_State * L,global_State * g,int nextstate,GCObject ** nextlist)1029 static 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 
singlestep(lua_State * L)1045 static 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 */
luaC_runtilstate(lua_State * L,int statesmask)1104 void 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 */
getdebt(global_State * g)1115 static 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 */
luaC_step(lua_State * L)1129 void 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 */
luaC_fullgc(lua_State * L,int isemergency)1159 void 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