xref: /freebsd/sys/contrib/openzfs/module/lua/lgc.c (revision 833a452e9f082a7982a31c21f0da437dbbe0a39d)
1 /* BEGIN CSTYLED */
2 /*
3 ** $Id: lgc.c,v 2.140.1.3 2014/09/01 16:55:08 roberto Exp $
4 ** Garbage Collector
5 ** See Copyright Notice in lua.h
6 */
7 
8 #define lgc_c
9 #define LUA_CORE
10 
11 #include <sys/lua/lua.h>
12 
13 #include "ldebug.h"
14 #include "ldo.h"
15 #include "lfunc.h"
16 #include "lgc.h"
17 #include "lmem.h"
18 #include "lobject.h"
19 #include "lstate.h"
20 #include "lstring.h"
21 #include "ltable.h"
22 #include "ltm.h"
23 
24 
25 
26 /*
27 ** cost of sweeping one element (the size of a small object divided
28 ** by some adjust for the sweep speed)
29 */
30 #define GCSWEEPCOST	((sizeof(TString) + 4) / 4)
31 
32 /* maximum number of elements to sweep in each single step */
33 #define GCSWEEPMAX	(cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))
34 
35 /* maximum number of finalizers to call in each GC step */
36 #define GCFINALIZENUM	4
37 
38 
39 /*
40 ** macro to adjust 'stepmul': 'stepmul' is actually used like
41 ** 'stepmul / STEPMULADJ' (value chosen by tests)
42 */
43 #define STEPMULADJ		200
44 
45 
46 /*
47 ** macro to adjust 'pause': 'pause' is actually used like
48 ** 'pause / PAUSEADJ' (value chosen by tests)
49 */
50 #define PAUSEADJ		100
51 
52 
53 /*
54 ** 'makewhite' erases all color bits plus the old bit and then
55 ** sets only the current white bit
56 */
57 #define maskcolors	(~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
58 #define makewhite(g,x)	\
59  (gch(x)->marked = cast_byte((gch(x)->marked & maskcolors) | luaC_white(g)))
60 
61 #define white2gray(x)	resetbits(gch(x)->marked, WHITEBITS)
62 #define black2gray(x)	resetbit(gch(x)->marked, BLACKBIT)
63 
64 
65 #define isfinalized(x)		testbit(gch(x)->marked, FINALIZEDBIT)
66 
67 #define checkdeadkey(n)	lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))
68 
69 
70 #define checkconsistency(obj)  \
71   lua_longassert(!iscollectable(obj) || righttt(obj))
72 
73 
74 #define markvalue(g,o) { checkconsistency(o); \
75   if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
76 
77 #define markobject(g,t) { if ((t) && iswhite(obj2gco(t))) \
78 		reallymarkobject(g, obj2gco(t)); }
79 
80 static void reallymarkobject (global_State *g, GCObject *o);
81 
82 
83 /*
84 ** {======================================================
85 ** Generic functions
86 ** =======================================================
87 */
88 
89 
90 /*
91 ** one after last element in a hash array
92 */
93 #define gnodelast(h)	gnode(h, cast(size_t, sizenode(h)))
94 
95 
96 /*
97 ** link table 'h' into list pointed by 'p'
98 */
99 #define linktable(h,p)	((h)->gclist = *(p), *(p) = obj2gco(h))
100 
101 
102 /*
103 ** if key is not marked, mark its entry as dead (therefore removing it
104 ** from the table)
105 */
106 static void removeentry (Node *n) {
107   lua_assert(ttisnil(gval(n)));
108   if (valiswhite(gkey(n)))
109     setdeadvalue(gkey(n));  /* unused and unmarked key; remove it */
110 }
111 
112 
113 /*
114 ** tells whether a key or value can be cleared from a weak
115 ** table. Non-collectable objects are never removed from weak
116 ** tables. Strings behave as `values', so are never removed too. for
117 ** other objects: if really collected, cannot keep them; for objects
118 ** being finalized, keep them in keys, but not in values
119 */
120 static int iscleared (global_State *g, const TValue *o) {
121   if (!iscollectable(o)) return 0;
122   else if (ttisstring(o)) {
123     markobject(g, rawtsvalue(o));  /* strings are `values', so are never weak */
124     return 0;
125   }
126   else return iswhite(gcvalue(o));
127 }
128 
129 
130 /*
131 ** barrier that moves collector forward, that is, mark the white object
132 ** being pointed by a black object.
133 */
134 void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
135   global_State *g = G(L);
136   lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
137   lua_assert(g->gcstate != GCSpause);
138   lua_assert(gch(o)->tt != LUA_TTABLE);
139   if (keepinvariantout(g))  /* must keep invariant? */
140     reallymarkobject(g, v);  /* restore invariant */
141   else {  /* sweep phase */
142     lua_assert(issweepphase(g));
143     makewhite(g, o);  /* mark main obj. as white to avoid other barriers */
144   }
145 }
146 
147 
148 /*
149 ** barrier that moves collector backward, that is, mark the black object
150 ** pointing to a white object as gray again. (Current implementation
151 ** only works for tables; access to 'gclist' is not uniform across
152 ** different types.)
153 */
154 void luaC_barrierback_ (lua_State *L, GCObject *o) {
155   global_State *g = G(L);
156   lua_assert(isblack(o) && !isdead(g, o) && gch(o)->tt == LUA_TTABLE);
157   black2gray(o);  /* make object gray (again) */
158   gco2t(o)->gclist = g->grayagain;
159   g->grayagain = o;
160 }
161 
162 
163 /*
164 ** barrier for prototypes. When creating first closure (cache is
165 ** NULL), use a forward barrier; this may be the only closure of the
166 ** prototype (if it is a "regular" function, with a single instance)
167 ** and the prototype may be big, so it is better to avoid traversing
168 ** it again. Otherwise, use a backward barrier, to avoid marking all
169 ** possible instances.
170 */
171 LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c) {
172   global_State *g = G(L);
173   lua_assert(isblack(obj2gco(p)));
174   if (p->cache == NULL) {  /* first time? */
175     luaC_objbarrier(L, p, c);
176   }
177   else {  /* use a backward barrier */
178     black2gray(obj2gco(p));  /* make prototype gray (again) */
179     p->gclist = g->grayagain;
180     g->grayagain = obj2gco(p);
181   }
182 }
183 
184 
185 /*
186 ** check color (and invariants) for an upvalue that was closed,
187 ** i.e., moved into the 'allgc' list
188 */
189 void luaC_checkupvalcolor (global_State *g, UpVal *uv) {
190   GCObject *o = obj2gco(uv);
191   lua_assert(!isblack(o));  /* open upvalues are never black */
192   if (isgray(o)) {
193     if (keepinvariant(g)) {
194       resetoldbit(o);  /* see MOVE OLD rule */
195       gray2black(o);  /* it is being visited now */
196       markvalue(g, uv->v);
197     }
198     else {
199       lua_assert(issweepphase(g));
200       makewhite(g, o);
201     }
202   }
203 }
204 
205 
206 /*
207 ** create a new collectable object (with given type and size) and link
208 ** it to '*list'. 'offset' tells how many bytes to allocate before the
209 ** object itself (used only by states).
210 */
211 GCObject *luaC_newobj (lua_State *L, int tt, size_t sz, GCObject **list,
212                        int offset) {
213   global_State *g = G(L);
214   char *raw = cast(char *, luaM_newobject(L, novariant(tt), sz));
215   GCObject *o = obj2gco(raw + offset);
216   if (list == NULL)
217     list = &g->allgc;  /* standard list for collectable objects */
218   gch(o)->marked = luaC_white(g);
219   gch(o)->tt = tt;
220   gch(o)->next = *list;
221   *list = o;
222   return o;
223 }
224 
225 /* }====================================================== */
226 
227 
228 
229 /*
230 ** {======================================================
231 ** Mark functions
232 ** =======================================================
233 */
234 
235 
236 /*
237 ** mark an object. Userdata, strings, and closed upvalues are visited
238 ** and turned black here. Other objects are marked gray and added
239 ** to appropriate list to be visited (and turned black) later. (Open
240 ** upvalues are already linked in 'headuv' list.)
241 */
242 static void reallymarkobject (global_State *g, GCObject *o) {
243   lu_mem size;
244   white2gray(o);
245   switch (gch(o)->tt) {
246     case LUA_TSHRSTR:
247     case LUA_TLNGSTR: {
248       size = sizestring(gco2ts(o));
249       break;  /* nothing else to mark; make it black */
250     }
251     case LUA_TUSERDATA: {
252       Table *mt = gco2u(o)->metatable;
253       markobject(g, mt);
254       markobject(g, gco2u(o)->env);
255       size = sizeudata(gco2u(o));
256       break;
257     }
258     case LUA_TUPVAL: {
259       UpVal *uv = gco2uv(o);
260       markvalue(g, uv->v);
261       if (uv->v != &uv->u.value)  /* open? */
262         return;  /* open upvalues remain gray */
263       size = sizeof(UpVal);
264       break;
265     }
266     case LUA_TLCL: {
267       gco2lcl(o)->gclist = g->gray;
268       g->gray = o;
269       return;
270     }
271     case LUA_TCCL: {
272       gco2ccl(o)->gclist = g->gray;
273       g->gray = o;
274       return;
275     }
276     case LUA_TTABLE: {
277       linktable(gco2t(o), &g->gray);
278       return;
279     }
280     case LUA_TTHREAD: {
281       gco2th(o)->gclist = g->gray;
282       g->gray = o;
283       return;
284     }
285     case LUA_TPROTO: {
286       gco2p(o)->gclist = g->gray;
287       g->gray = o;
288       return;
289     }
290     default: lua_assert(0); return;
291   }
292   gray2black(o);
293   g->GCmemtrav += size;
294 }
295 
296 
297 /*
298 ** mark metamethods for basic types
299 */
300 static void markmt (global_State *g) {
301   int i;
302   for (i=0; i < LUA_NUMTAGS; i++)
303     markobject(g, g->mt[i]);
304 }
305 
306 
307 /*
308 ** mark all objects in list of being-finalized
309 */
310 static void markbeingfnz (global_State *g) {
311   GCObject *o;
312   for (o = g->tobefnz; o != NULL; o = gch(o)->next) {
313     makewhite(g, o);
314     reallymarkobject(g, o);
315   }
316 }
317 
318 
319 /*
320 ** mark all values stored in marked open upvalues. (See comment in
321 ** 'lstate.h'.)
322 */
323 static void remarkupvals (global_State *g) {
324   UpVal *uv;
325   for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
326     if (isgray(obj2gco(uv)))
327       markvalue(g, uv->v);
328   }
329 }
330 
331 
332 /*
333 ** mark root set and reset all gray lists, to start a new
334 ** incremental (or full) collection
335 */
336 static void restartcollection (global_State *g) {
337   g->gray = g->grayagain = NULL;
338   g->weak = g->allweak = g->ephemeron = NULL;
339   markobject(g, g->mainthread);
340   markvalue(g, &g->l_registry);
341   markmt(g);
342   markbeingfnz(g);  /* mark any finalizing object left from previous cycle */
343 }
344 
345 /* }====================================================== */
346 
347 
348 /*
349 ** {======================================================
350 ** Traverse functions
351 ** =======================================================
352 */
353 
354 static void traverseweakvalue (global_State *g, Table *h) {
355   Node *n, *limit = gnodelast(h);
356   /* if there is array part, assume it may have white values (do not
357      traverse it just to check) */
358   int hasclears = (h->sizearray > 0);
359   for (n = gnode(h, 0); n < limit; n++) {
360     checkdeadkey(n);
361     if (ttisnil(gval(n)))  /* entry is empty? */
362       removeentry(n);  /* remove it */
363     else {
364       lua_assert(!ttisnil(gkey(n)));
365       markvalue(g, gkey(n));  /* mark key */
366       if (!hasclears && iscleared(g, gval(n)))  /* is there a white value? */
367         hasclears = 1;  /* table will have to be cleared */
368     }
369   }
370   if (hasclears)
371     linktable(h, &g->weak);  /* has to be cleared later */
372   else  /* no white values */
373     linktable(h, &g->grayagain);  /* no need to clean */
374 }
375 
376 
377 static int traverseephemeron (global_State *g, Table *h) {
378   int marked = 0;  /* true if an object is marked in this traversal */
379   int hasclears = 0;  /* true if table has white keys */
380   int prop = 0;  /* true if table has entry "white-key -> white-value" */
381   Node *n, *limit = gnodelast(h);
382   int i;
383   /* traverse array part (numeric keys are 'strong') */
384   for (i = 0; i < h->sizearray; i++) {
385     if (valiswhite(&h->array[i])) {
386       marked = 1;
387       reallymarkobject(g, gcvalue(&h->array[i]));
388     }
389   }
390   /* traverse hash part */
391   for (n = gnode(h, 0); n < limit; n++) {
392     checkdeadkey(n);
393     if (ttisnil(gval(n)))  /* entry is empty? */
394       removeentry(n);  /* remove it */
395     else if (iscleared(g, gkey(n))) {  /* key is not marked (yet)? */
396       hasclears = 1;  /* table must be cleared */
397       if (valiswhite(gval(n)))  /* value not marked yet? */
398         prop = 1;  /* must propagate again */
399     }
400     else if (valiswhite(gval(n))) {  /* value not marked yet? */
401       marked = 1;
402       reallymarkobject(g, gcvalue(gval(n)));  /* mark it now */
403     }
404   }
405   if (g->gcstate != GCSatomic || prop)
406     linktable(h, &g->ephemeron);  /* have to propagate again */
407   else if (hasclears)  /* does table have white keys? */
408     linktable(h, &g->allweak);  /* may have to clean white keys */
409   else  /* no white keys */
410     linktable(h, &g->grayagain);  /* no need to clean */
411   return marked;
412 }
413 
414 
415 static void traversestrongtable (global_State *g, Table *h) {
416   Node *n, *limit = gnodelast(h);
417   int i;
418   for (i = 0; i < h->sizearray; i++)  /* traverse array part */
419     markvalue(g, &h->array[i]);
420   for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
421     checkdeadkey(n);
422     if (ttisnil(gval(n)))  /* entry is empty? */
423       removeentry(n);  /* remove it */
424     else {
425       lua_assert(!ttisnil(gkey(n)));
426       markvalue(g, gkey(n));  /* mark key */
427       markvalue(g, gval(n));  /* mark value */
428     }
429   }
430 }
431 
432 
433 static lu_mem traversetable (global_State *g, Table *h) {
434   const char *weakkey, *weakvalue;
435   const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
436   markobject(g, h->metatable);
437   if (mode && ttisstring(mode) &&  /* is there a weak mode? */
438       ((weakkey = strchr(svalue(mode), 'k')),
439        (weakvalue = strchr(svalue(mode), 'v')),
440        (weakkey || weakvalue))) {  /* is really weak? */
441     black2gray(obj2gco(h));  /* keep table gray */
442     if (!weakkey)  /* strong keys? */
443       traverseweakvalue(g, h);
444     else if (!weakvalue)  /* strong values? */
445       traverseephemeron(g, h);
446     else  /* all weak */
447       linktable(h, &g->allweak);  /* nothing to traverse now */
448   }
449   else  /* not weak */
450     traversestrongtable(g, h);
451   return sizeof(Table) + sizeof(TValue) * h->sizearray +
452                          sizeof(Node) * cast(size_t, sizenode(h));
453 }
454 
455 
456 static int traverseproto (global_State *g, Proto *f) {
457   int i;
458   if (f->cache && iswhite(obj2gco(f->cache)))
459     f->cache = NULL;  /* allow cache to be collected */
460   markobject(g, f->source);
461   for (i = 0; i < f->sizek; i++)  /* mark literals */
462     markvalue(g, &f->k[i]);
463   for (i = 0; i < f->sizeupvalues; i++)  /* mark upvalue names */
464     markobject(g, f->upvalues[i].name);
465   for (i = 0; i < f->sizep; i++)  /* mark nested protos */
466     markobject(g, f->p[i]);
467   for (i = 0; i < f->sizelocvars; i++)  /* mark local-variable names */
468     markobject(g, f->locvars[i].varname);
469   return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
470                          sizeof(Proto *) * f->sizep +
471                          sizeof(TValue) * f->sizek +
472                          sizeof(int) * f->sizelineinfo +
473                          sizeof(LocVar) * f->sizelocvars +
474                          sizeof(Upvaldesc) * f->sizeupvalues;
475 }
476 
477 
478 static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
479   int i;
480   for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
481     markvalue(g, &cl->upvalue[i]);
482   return sizeCclosure(cl->nupvalues);
483 }
484 
485 static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
486   int i;
487   markobject(g, cl->p);  /* mark its prototype */
488   for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
489     markobject(g, cl->upvals[i]);
490   return sizeLclosure(cl->nupvalues);
491 }
492 
493 
494 static lu_mem traversestack (global_State *g, lua_State *th) {
495   int n = 0;
496   StkId o = th->stack;
497   if (o == NULL)
498     return 1;  /* stack not completely built yet */
499   for (; o < th->top; o++)  /* mark live elements in the stack */
500     markvalue(g, o);
501   if (g->gcstate == GCSatomic) {  /* final traversal? */
502     StkId lim = th->stack + th->stacksize;  /* real end of stack */
503     for (; o < lim; o++)  /* clear not-marked stack slice */
504       setnilvalue(o);
505   }
506   else {  /* count call infos to compute size */
507     CallInfo *ci;
508     for (ci = &th->base_ci; ci != th->ci; ci = ci->next)
509       n++;
510   }
511   return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
512          sizeof(CallInfo) * n;
513 }
514 
515 
516 /*
517 ** traverse one gray object, turning it to black (except for threads,
518 ** which are always gray).
519 */
520 static void propagatemark (global_State *g) {
521   lu_mem size;
522   GCObject *o = g->gray;
523   lua_assert(isgray(o));
524   gray2black(o);
525   switch (gch(o)->tt) {
526     case LUA_TTABLE: {
527       Table *h = gco2t(o);
528       g->gray = h->gclist;  /* remove from 'gray' list */
529       size = traversetable(g, h);
530       break;
531     }
532     case LUA_TLCL: {
533       LClosure *cl = gco2lcl(o);
534       g->gray = cl->gclist;  /* remove from 'gray' list */
535       size = traverseLclosure(g, cl);
536       break;
537     }
538     case LUA_TCCL: {
539       CClosure *cl = gco2ccl(o);
540       g->gray = cl->gclist;  /* remove from 'gray' list */
541       size = traverseCclosure(g, cl);
542       break;
543     }
544     case LUA_TTHREAD: {
545       lua_State *th = gco2th(o);
546       g->gray = th->gclist;  /* remove from 'gray' list */
547       th->gclist = g->grayagain;
548       g->grayagain = o;  /* insert into 'grayagain' list */
549       black2gray(o);
550       size = traversestack(g, th);
551       break;
552     }
553     case LUA_TPROTO: {
554       Proto *p = gco2p(o);
555       g->gray = p->gclist;  /* remove from 'gray' list */
556       size = traverseproto(g, p);
557       break;
558     }
559     default: lua_assert(0); return;
560   }
561   g->GCmemtrav += size;
562 }
563 
564 
565 static void propagateall (global_State *g) {
566   while (g->gray) propagatemark(g);
567 }
568 
569 
570 static void propagatelist (global_State *g, GCObject *l) {
571   lua_assert(g->gray == NULL);  /* no grays left */
572   g->gray = l;
573   propagateall(g);  /* traverse all elements from 'l' */
574 }
575 
576 /*
577 ** retraverse all gray lists. Because tables may be reinserted in other
578 ** lists when traversed, traverse the original lists to avoid traversing
579 ** twice the same table (which is not wrong, but inefficient)
580 */
581 static void retraversegrays (global_State *g) {
582   GCObject *weak = g->weak;  /* save original lists */
583   GCObject *grayagain = g->grayagain;
584   GCObject *ephemeron = g->ephemeron;
585   g->weak = g->grayagain = g->ephemeron = NULL;
586   propagateall(g);  /* traverse main gray list */
587   propagatelist(g, grayagain);
588   propagatelist(g, weak);
589   propagatelist(g, ephemeron);
590 }
591 
592 
593 static void convergeephemerons (global_State *g) {
594   int changed;
595   do {
596     GCObject *w;
597     GCObject *next = g->ephemeron;  /* get ephemeron list */
598     g->ephemeron = NULL;  /* tables will return to this list when traversed */
599     changed = 0;
600     while ((w = next) != NULL) {
601       next = gco2t(w)->gclist;
602       if (traverseephemeron(g, gco2t(w))) {  /* traverse marked some value? */
603         propagateall(g);  /* propagate changes */
604         changed = 1;  /* will have to revisit all ephemeron tables */
605       }
606     }
607   } while (changed);
608 }
609 
610 /* }====================================================== */
611 
612 
613 /*
614 ** {======================================================
615 ** Sweep Functions
616 ** =======================================================
617 */
618 
619 
620 /*
621 ** clear entries with unmarked keys from all weaktables in list 'l' up
622 ** to element 'f'
623 */
624 static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
625   for (; l != f; l = gco2t(l)->gclist) {
626     Table *h = gco2t(l);
627     Node *n, *limit = gnodelast(h);
628     for (n = gnode(h, 0); n < limit; n++) {
629       if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
630         setnilvalue(gval(n));  /* remove value ... */
631         removeentry(n);  /* and remove entry from table */
632       }
633     }
634   }
635 }
636 
637 
638 /*
639 ** clear entries with unmarked values from all weaktables in list 'l' up
640 ** to element 'f'
641 */
642 static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
643   for (; l != f; l = gco2t(l)->gclist) {
644     Table *h = gco2t(l);
645     Node *n, *limit = gnodelast(h);
646     int i;
647     for (i = 0; i < h->sizearray; i++) {
648       TValue *o = &h->array[i];
649       if (iscleared(g, o))  /* value was collected? */
650         setnilvalue(o);  /* remove value */
651     }
652     for (n = gnode(h, 0); n < limit; n++) {
653       if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
654         setnilvalue(gval(n));  /* remove value ... */
655         removeentry(n);  /* and remove entry from table */
656       }
657     }
658   }
659 }
660 
661 
662 static void freeobj (lua_State *L, GCObject *o) {
663   switch (gch(o)->tt) {
664     case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
665     case LUA_TLCL: {
666       luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
667       break;
668     }
669     case LUA_TCCL: {
670       luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
671       break;
672     }
673     case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
674     case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
675     case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
676     case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
677     case LUA_TSHRSTR:
678       G(L)->strt.nuse--;
679       fallthrough;
680     case LUA_TLNGSTR: {
681       luaM_freemem(L, o, sizestring(gco2ts(o)));
682       break;
683     }
684     default: lua_assert(0);
685   }
686 }
687 
688 
689 #define sweepwholelist(L,p)	sweeplist(L,p,MAX_LUMEM)
690 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);
691 
692 
693 /*
694 ** sweep the (open) upvalues of a thread and resize its stack and
695 ** list of call-info structures.
696 */
697 static void sweepthread (lua_State *L, lua_State *L1) {
698   if (L1->stack == NULL) return;  /* stack not completely built yet */
699   sweepwholelist(L, &L1->openupval);  /* sweep open upvalues */
700   luaE_freeCI(L1);  /* free extra CallInfo slots */
701   /* should not change the stack during an emergency gc cycle */
702   if (G(L)->gckind != KGC_EMERGENCY)
703     luaD_shrinkstack(L1);
704 }
705 
706 
707 /*
708 ** sweep at most 'count' elements from a list of GCObjects erasing dead
709 ** objects, where a dead (not alive) object is one marked with the "old"
710 ** (non current) white and not fixed.
711 ** In non-generational mode, change all non-dead objects back to white,
712 ** preparing for next collection cycle.
713 ** In generational mode, keep black objects black, and also mark them as
714 ** old; stop when hitting an old object, as all objects after that
715 ** one will be old too.
716 ** When object is a thread, sweep its list of open upvalues too.
717 */
718 static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
719   global_State *g = G(L);
720   int ow = otherwhite(g);
721   int toclear, toset;  /* bits to clear and to set in all live objects */
722   int tostop;  /* stop sweep when this is true */
723   if (isgenerational(g)) {  /* generational mode? */
724     toclear = ~0;  /* clear nothing */
725     toset = bitmask(OLDBIT);  /* set the old bit of all surviving objects */
726     tostop = bitmask(OLDBIT);  /* do not sweep old generation */
727   }
728   else {  /* normal mode */
729     toclear = maskcolors;  /* clear all color bits + old bit */
730     toset = luaC_white(g);  /* make object white */
731     tostop = 0;  /* do not stop */
732   }
733   while (*p != NULL && count-- > 0) {
734     GCObject *curr = *p;
735     int marked = gch(curr)->marked;
736     if (isdeadm(ow, marked)) {  /* is 'curr' dead? */
737       *p = gch(curr)->next;  /* remove 'curr' from list */
738       freeobj(L, curr);  /* erase 'curr' */
739     }
740     else {
741       if (testbits(marked, tostop))
742         return NULL;  /* stop sweeping this list */
743       if (gch(curr)->tt == LUA_TTHREAD)
744         sweepthread(L, gco2th(curr));  /* sweep thread's upvalues */
745       /* update marks */
746       gch(curr)->marked = cast_byte((marked & toclear) | toset);
747       p = &gch(curr)->next;  /* go to next element */
748     }
749   }
750   return (*p == NULL) ? NULL : p;
751 }
752 
753 
754 /*
755 ** sweep a list until a live object (or end of list)
756 */
757 static GCObject **sweeptolive (lua_State *L, GCObject **p, int *n) {
758   GCObject ** old = p;
759   int i = 0;
760   do {
761     i++;
762     p = sweeplist(L, p, 1);
763   } while (p == old);
764   if (n) *n += i;
765   return p;
766 }
767 
768 /* }====================================================== */
769 
770 
771 /*
772 ** {======================================================
773 ** Finalization
774 ** =======================================================
775 */
776 
777 static void checkSizes (lua_State *L) {
778   global_State *g = G(L);
779   if (g->gckind != KGC_EMERGENCY) {  /* do not change sizes in emergency */
780     int hs = g->strt.size / 2;  /* half the size of the string table */
781     if (g->strt.nuse < cast(lu_int32, hs))  /* using less than that half? */
782       luaS_resize(L, hs);  /* halve its size */
783     luaZ_freebuffer(L, &g->buff);  /* free concatenation buffer */
784   }
785 }
786 
787 
788 static GCObject *udata2finalize (global_State *g) {
789   GCObject *o = g->tobefnz;  /* get first element */
790   lua_assert(isfinalized(o));
791   g->tobefnz = gch(o)->next;  /* remove it from 'tobefnz' list */
792   gch(o)->next = g->allgc;  /* return it to 'allgc' list */
793   g->allgc = o;
794   resetbit(gch(o)->marked, SEPARATED);  /* mark that it is not in 'tobefnz' */
795   lua_assert(!isold(o));  /* see MOVE OLD rule */
796   if (!keepinvariantout(g))  /* not keeping invariant? */
797     makewhite(g, o);  /* "sweep" object */
798   return o;
799 }
800 
801 
802 static void dothecall (lua_State *L, void *ud) {
803   UNUSED(ud);
804   luaD_call(L, L->top - 2, 0, 0);
805 }
806 
807 
808 static void GCTM (lua_State *L, int propagateerrors) {
809   global_State *g = G(L);
810   const TValue *tm;
811   TValue v;
812   setgcovalue(L, &v, udata2finalize(g));
813   tm = luaT_gettmbyobj(L, &v, TM_GC);
814   if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
815     int status;
816     lu_byte oldah = L->allowhook;
817     int running  = g->gcrunning;
818     L->allowhook = 0;  /* stop debug hooks during GC metamethod */
819     g->gcrunning = 0;  /* avoid GC steps */
820     setobj2s(L, L->top, tm);  /* push finalizer... */
821     setobj2s(L, L->top + 1, &v);  /* ... and its argument */
822     L->top += 2;  /* and (next line) call the finalizer */
823     status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
824     L->allowhook = oldah;  /* restore hooks */
825     g->gcrunning = running;  /* restore state */
826     if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */
827       if (status == LUA_ERRRUN) {  /* is there an error object? */
828         const char *msg = (ttisstring(L->top - 1))
829                             ? svalue(L->top - 1)
830                             : "no message";
831         luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
832         status = LUA_ERRGCMM;  /* error in __gc metamethod */
833       }
834       luaD_throw(L, status);  /* re-throw error */
835     }
836   }
837 }
838 
839 
840 /*
841 ** move all unreachable objects (or 'all' objects) that need
842 ** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
843 */
844 static void separatetobefnz (lua_State *L, int all) {
845   global_State *g = G(L);
846   GCObject **p = &g->finobj;
847   GCObject *curr;
848   GCObject **lastnext = &g->tobefnz;
849   /* find last 'next' field in 'tobefnz' list (to add elements in its end) */
850   while (*lastnext != NULL)
851     lastnext = &gch(*lastnext)->next;
852   while ((curr = *p) != NULL) {  /* traverse all finalizable objects */
853     lua_assert(!isfinalized(curr));
854     lua_assert(testbit(gch(curr)->marked, SEPARATED));
855     if (!(iswhite(curr) || all))  /* not being collected? */
856       p = &gch(curr)->next;  /* don't bother with it */
857     else {
858       l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
859       *p = gch(curr)->next;  /* remove 'curr' from 'finobj' list */
860       gch(curr)->next = *lastnext;  /* link at the end of 'tobefnz' list */
861       *lastnext = curr;
862       lastnext = &gch(curr)->next;
863     }
864   }
865 }
866 
867 
868 /*
869 ** if object 'o' has a finalizer, remove it from 'allgc' list (must
870 ** search the list to find it) and link it in 'finobj' list.
871 */
872 void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
873   global_State *g = G(L);
874   if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
875       isfinalized(o) ||                           /* ... or is finalized... */
876       gfasttm(g, mt, TM_GC) == NULL)                /* or has no finalizer? */
877     return;  /* nothing to be done */
878   else {  /* move 'o' to 'finobj' list */
879     GCObject **p;
880     GCheader *ho = gch(o);
881     if (g->sweepgc == &ho->next) {  /* avoid removing current sweep object */
882       lua_assert(issweepphase(g));
883       g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
884     }
885     /* search for pointer pointing to 'o' */
886     for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
887     *p = ho->next;  /* remove 'o' from root list */
888     ho->next = g->finobj;  /* link it in list 'finobj' */
889     g->finobj = o;
890     l_setbit(ho->marked, SEPARATED);  /* mark it as such */
891     if (!keepinvariantout(g))  /* not keeping invariant? */
892       makewhite(g, o);  /* "sweep" object */
893     else
894       resetoldbit(o);  /* see MOVE OLD rule */
895   }
896 }
897 
898 /* }====================================================== */
899 
900 
901 /*
902 ** {======================================================
903 ** GC control
904 ** =======================================================
905 */
906 
907 
908 /*
909 ** set a reasonable "time" to wait before starting a new GC cycle;
910 ** cycle will start when memory use hits threshold
911 */
912 static void setpause (global_State *g, l_mem estimate) {
913   l_mem debt, threshold;
914   estimate = estimate / PAUSEADJ;  /* adjust 'estimate' */
915   threshold = (g->gcpause < MAX_LMEM / estimate)  /* overflow? */
916             ? estimate * g->gcpause  /* no overflow */
917             : MAX_LMEM;  /* overflow; truncate to maximum */
918   debt = -cast(l_mem, threshold - gettotalbytes(g));
919   luaE_setdebt(g, debt);
920 }
921 
922 
923 #define sweepphases  \
924 	(bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))
925 
926 
927 /*
928 ** enter first sweep phase (strings) and prepare pointers for other
929 ** sweep phases.  The calls to 'sweeptolive' make pointers point to an
930 ** object inside the list (instead of to the header), so that the real
931 ** sweep do not need to skip objects created between "now" and the start
932 ** of the real sweep.
933 ** Returns how many objects it swept.
934 */
935 static int entersweep (lua_State *L) {
936   global_State *g = G(L);
937   int n = 0;
938   g->gcstate = GCSsweepstring;
939   lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
940   /* prepare to sweep strings, finalizable objects, and regular objects */
941   g->sweepstrgc = 0;
942   g->sweepfin = sweeptolive(L, &g->finobj, &n);
943   g->sweepgc = sweeptolive(L, &g->allgc, &n);
944   return n;
945 }
946 
947 
948 /*
949 ** change GC mode
950 */
951 void luaC_changemode (lua_State *L, int mode) {
952   global_State *g = G(L);
953   if (mode == g->gckind) return;  /* nothing to change */
954   if (mode == KGC_GEN) {  /* change to generational mode */
955     /* make sure gray lists are consistent */
956     luaC_runtilstate(L, bitmask(GCSpropagate));
957     g->GCestimate = gettotalbytes(g);
958     g->gckind = KGC_GEN;
959   }
960   else {  /* change to incremental mode */
961     /* sweep all objects to turn them back to white
962        (as white has not changed, nothing extra will be collected) */
963     g->gckind = KGC_NORMAL;
964     entersweep(L);
965     luaC_runtilstate(L, ~sweepphases);
966   }
967 }
968 
969 
970 /*
971 ** call all pending finalizers
972 */
973 static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
974   global_State *g = G(L);
975   while (g->tobefnz) {
976     resetoldbit(g->tobefnz);
977     GCTM(L, propagateerrors);
978   }
979 }
980 
981 
982 void luaC_freeallobjects (lua_State *L) {
983   global_State *g = G(L);
984   int i;
985   separatetobefnz(L, 1);  /* separate all objects with finalizers */
986   lua_assert(g->finobj == NULL);
987   callallpendingfinalizers(L, 0);
988   g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
989   g->gckind = KGC_NORMAL;
990   sweepwholelist(L, &g->finobj);  /* finalizers can create objs. in 'finobj' */
991   sweepwholelist(L, &g->allgc);
992   for (i = 0; i < g->strt.size; i++)  /* free all string lists */
993     sweepwholelist(L, &g->strt.hash[i]);
994   lua_assert(g->strt.nuse == 0);
995 }
996 
997 
998 static l_mem atomic (lua_State *L) {
999   global_State *g = G(L);
1000   l_mem work = -cast(l_mem, g->GCmemtrav);  /* start counting work */
1001   GCObject *origweak, *origall;
1002   lua_assert(!iswhite(obj2gco(g->mainthread)));
1003   markobject(g, L);  /* mark running thread */
1004   /* registry and global metatables may be changed by API */
1005   markvalue(g, &g->l_registry);
1006   markmt(g);  /* mark basic metatables */
1007   /* remark occasional upvalues of (maybe) dead threads */
1008   remarkupvals(g);
1009   propagateall(g);  /* propagate changes */
1010   work += g->GCmemtrav;  /* stop counting (do not (re)count grays) */
1011   /* traverse objects caught by write barrier and by 'remarkupvals' */
1012   retraversegrays(g);
1013   work -= g->GCmemtrav;  /* restart counting */
1014   convergeephemerons(g);
1015   /* at this point, all strongly accessible objects are marked. */
1016   /* clear values from weak tables, before checking finalizers */
1017   clearvalues(g, g->weak, NULL);
1018   clearvalues(g, g->allweak, NULL);
1019   origweak = g->weak; origall = g->allweak;
1020   work += g->GCmemtrav;  /* stop counting (objects being finalized) */
1021   separatetobefnz(L, 0);  /* separate objects to be finalized */
1022   markbeingfnz(g);  /* mark objects that will be finalized */
1023   propagateall(g);  /* remark, to propagate `preserveness' */
1024   work -= g->GCmemtrav;  /* restart counting */
1025   convergeephemerons(g);
1026   /* at this point, all resurrected objects are marked. */
1027   /* remove dead objects from weak tables */
1028   clearkeys(g, g->ephemeron, NULL);  /* clear keys from all ephemeron tables */
1029   clearkeys(g, g->allweak, NULL);  /* clear keys from all allweak tables */
1030   /* clear values from resurrected weak tables */
1031   clearvalues(g, g->weak, origweak);
1032   clearvalues(g, g->allweak, origall);
1033   g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */
1034   work += g->GCmemtrav;  /* complete counting */
1035   return work;  /* estimate of memory marked by 'atomic' */
1036 }
1037 
1038 
1039 static lu_mem singlestep (lua_State *L) {
1040   global_State *g = G(L);
1041   switch (g->gcstate) {
1042     case GCSpause: {
1043       /* start to count memory traversed */
1044       g->GCmemtrav = g->strt.size * sizeof(GCObject*);
1045       lua_assert(!isgenerational(g));
1046       restartcollection(g);
1047       g->gcstate = GCSpropagate;
1048       return g->GCmemtrav;
1049     }
1050     case GCSpropagate: {
1051       if (g->gray) {
1052         lu_mem oldtrav = g->GCmemtrav;
1053         propagatemark(g);
1054         return g->GCmemtrav - oldtrav;  /* memory traversed in this step */
1055       }
1056       else {  /* no more `gray' objects */
1057         lu_mem work;
1058         int sw;
1059         g->gcstate = GCSatomic;  /* finish mark phase */
1060         g->GCestimate = g->GCmemtrav;  /* save what was counted */;
1061         work = atomic(L);  /* add what was traversed by 'atomic' */
1062         g->GCestimate += work;  /* estimate of total memory traversed */
1063         sw = entersweep(L);
1064         return work + sw * GCSWEEPCOST;
1065       }
1066     }
1067     case GCSsweepstring: {
1068       int i;
1069       for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
1070         sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
1071       g->sweepstrgc += i;
1072       if (g->sweepstrgc >= g->strt.size)  /* no more strings to sweep? */
1073         g->gcstate = GCSsweepudata;
1074       return i * GCSWEEPCOST;
1075     }
1076     case GCSsweepudata: {
1077       if (g->sweepfin) {
1078         g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
1079         return GCSWEEPMAX*GCSWEEPCOST;
1080       }
1081       else {
1082         g->gcstate = GCSsweep;
1083         return 0;
1084       }
1085     }
1086     case GCSsweep: {
1087       if (g->sweepgc) {
1088         g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
1089         return GCSWEEPMAX*GCSWEEPCOST;
1090       }
1091       else {
1092         /* sweep main thread */
1093         GCObject *mt = obj2gco(g->mainthread);
1094         sweeplist(L, &mt, 1);
1095         checkSizes(L);
1096         g->gcstate = GCSpause;  /* finish collection */
1097         return GCSWEEPCOST;
1098       }
1099     }
1100     default: lua_assert(0); return 0;
1101   }
1102 }
1103 
1104 
1105 /*
1106 ** advances the garbage collector until it reaches a state allowed
1107 ** by 'statemask'
1108 */
1109 void luaC_runtilstate (lua_State *L, int statesmask) {
1110   global_State *g = G(L);
1111   while (!testbit(statesmask, g->gcstate))
1112     singlestep(L);
1113 }
1114 
1115 
1116 static void generationalcollection (lua_State *L) {
1117   global_State *g = G(L);
1118   lua_assert(g->gcstate == GCSpropagate);
1119   if (g->GCestimate == 0) {  /* signal for another major collection? */
1120     luaC_fullgc(L, 0);  /* perform a full regular collection */
1121     g->GCestimate = gettotalbytes(g);  /* update control */
1122   }
1123   else {
1124     lu_mem estimate = g->GCestimate;
1125     luaC_runtilstate(L, bitmask(GCSpause));  /* run complete (minor) cycle */
1126     g->gcstate = GCSpropagate;  /* skip restart */
1127     if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
1128       g->GCestimate = 0;  /* signal for a major collection */
1129     else
1130       g->GCestimate = estimate;  /* keep estimate from last major coll. */
1131 
1132   }
1133   setpause(g, gettotalbytes(g));
1134   lua_assert(g->gcstate == GCSpropagate);
1135 }
1136 
1137 
1138 static void incstep (lua_State *L) {
1139   global_State *g = G(L);
1140   l_mem debt = g->GCdebt;
1141   int stepmul = g->gcstepmul;
1142   if (stepmul < 40) stepmul = 40;  /* avoid ridiculous low values (and 0) */
1143   /* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
1144   debt = (debt / STEPMULADJ) + 1;
1145   debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
1146   do {  /* always perform at least one single step */
1147     lu_mem work = singlestep(L);  /* do some work */
1148     debt -= work;
1149   } while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
1150   if (g->gcstate == GCSpause)
1151     setpause(g, g->GCestimate);  /* pause until next cycle */
1152   else {
1153     debt = (debt / stepmul) * STEPMULADJ;  /* convert 'work units' to Kb */
1154     luaE_setdebt(g, debt);
1155   }
1156 }
1157 
1158 
1159 /*
1160 ** performs a basic GC step
1161 */
1162 void luaC_forcestep (lua_State *L) {
1163   global_State *g = G(L);
1164   int i;
1165   if (isgenerational(g)) generationalcollection(L);
1166   else incstep(L);
1167   /* run a few finalizers (or all of them at the end of a collect cycle) */
1168   for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
1169     GCTM(L, 1);  /* call one finalizer */
1170 }
1171 
1172 
1173 /*
1174 ** performs a basic GC step only if collector is running
1175 */
1176 void luaC_step (lua_State *L) {
1177   global_State *g = G(L);
1178   if (g->gcrunning) luaC_forcestep(L);
1179   else luaE_setdebt(g, -GCSTEPSIZE);  /* avoid being called too often */
1180 }
1181 
1182 
1183 
1184 /*
1185 ** performs a full GC cycle; if "isemergency", does not call
1186 ** finalizers (which could change stack positions)
1187 */
1188 void luaC_fullgc (lua_State *L, int isemergency) {
1189   global_State *g = G(L);
1190   int origkind = g->gckind;
1191   lua_assert(origkind != KGC_EMERGENCY);
1192   if (isemergency)  /* do not run finalizers during emergency GC */
1193     g->gckind = KGC_EMERGENCY;
1194   else {
1195     g->gckind = KGC_NORMAL;
1196     callallpendingfinalizers(L, 1);
1197   }
1198   if (keepinvariant(g)) {  /* may there be some black objects? */
1199     /* must sweep all objects to turn them back to white
1200        (as white has not changed, nothing will be collected) */
1201     entersweep(L);
1202   }
1203   /* finish any pending sweep phase to start a new cycle */
1204   luaC_runtilstate(L, bitmask(GCSpause));
1205   luaC_runtilstate(L, ~bitmask(GCSpause));  /* start new collection */
1206   luaC_runtilstate(L, bitmask(GCSpause));  /* run entire collection */
1207   if (origkind == KGC_GEN) {  /* generational mode? */
1208     /* generational mode must be kept in propagate phase */
1209     luaC_runtilstate(L, bitmask(GCSpropagate));
1210   }
1211   g->gckind = origkind;
1212   setpause(g, gettotalbytes(g));
1213   if (!isemergency)   /* do not run finalizers during emergency GC */
1214     callallpendingfinalizers(L, 1);
1215 }
1216 
1217 /* }====================================================== */
1218 /* END CSTYLED */
1219