1/*
2** $Id: lgc.c $
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#include <stdio.h>
13#include <string.h>
14
15
16#include "lua.h"
17
18#include "ldebug.h"
19#include "ldo.h"
20#include "lfunc.h"
21#include "lgc.h"
22#include "lmem.h"
23#include "lobject.h"
24#include "lstate.h"
25#include "lstring.h"
26#include "ltable.h"
27#include "ltm.h"
28
29
30/*
31** Maximum number of elements to sweep in each single step.
32** (Large enough to dissipate fixed overheads but small enough
33** to allow small steps for the collector.)
34*/
35#define GCSWEEPMAX 100
36
37/*
38** Maximum number of finalizers to call in each single step.
39*/
40#define GCFINMAX 10
41
42
43/*
44** Cost of calling one finalizer.
45*/
46#define GCFINALIZECOST 50
47
48
49/*
50** The equivalent, in bytes, of one unit of "work" (visiting a slot,
51** sweeping an object, etc.)
52*/
53#define WORK2MEM sizeof(TValue)
54
55
56/*
57** macro to adjust 'pause': 'pause' is actually used like
58** 'pause / PAUSEADJ' (value chosen by tests)
59*/
60#define PAUSEADJ 100
61
62
63/* mask with all color bits */
64#define maskcolors (bitmask(BLACKBIT) | WHITEBITS)
65
66/* mask with all GC bits */
67#define maskgcbits (maskcolors | AGEBITS)
68
69
70/* macro to erase all color bits then set only the current white bit */
71#define makewhite(g,x) \
72 (x->marked = cast_byte((x->marked & ~maskcolors) | luaC_white(g)))
73
74/* make an object gray (neither white nor black) */
75#define set2gray(x) resetbits(x->marked, maskcolors)
76
77
78/* make an object black (coming from any color) */
79#define set2black(x) \
80 (x->marked = cast_byte((x->marked & ~WHITEBITS) | bitmask(BLACKBIT)))
81
82
83#define valiswhite(x) (iscollectable(x) && iswhite(gcvalue(x)))
84
85#define keyiswhite(n) (keyiscollectable(n) && iswhite(gckey(n)))
86
87
88/*
89** Protected access to objects in values
90*/
91#define gcvalueN(o) (iscollectable(o) ? gcvalue(o) : NULL)
92
93
94#define markvalue(g,o) { checkliveness(g->mainthread,o); \
95 if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
96
97#define markkey(g, n) { if keyiswhite(n) reallymarkobject(g,gckey(n)); }
98
99#define markobject(g,t) { if (iswhite(t)) reallymarkobject(g, obj2gco(t)); }
100
101/*
102** mark an object that can be NULL (either because it is really optional,
103** or it was stripped as debug info, or inside an uncompleted structure)
104*/
105#define markobjectN(g,t) { if (t) markobject(g,t); }
106
107static void reallymarkobject (global_State *g, GCObject *o);
108static lu_mem atomic (lua_State *L);
109static void entersweep (lua_State *L);
110
111
112/*
113** {======================================================
114** Generic functions
115** =======================================================
116*/
117
118
119/*
120** one after last element in a hash array
121*/
122#define gnodelast(h) gnode(h, cast_sizet(sizenode(h)))
123
124
125static GCObject **getgclist (GCObject *o) {
126 switch (o->tt) {
127 case LUA_VTABLE: return &gco2t(o)->gclist;
128 case LUA_VLCL: return &gco2lcl(o)->gclist;
129 case LUA_VCCL: return &gco2ccl(o)->gclist;
130 case LUA_VTHREAD: return &gco2th(o)->gclist;
131 case LUA_VPROTO: return &gco2p(o)->gclist;
132 case LUA_VUSERDATA: {
133 Udata *u = gco2u(o);
134 lua_assert(u->nuvalue > 0);
135 return &u->gclist;
136 }
137 default: lua_assert(0); return 0;
138 }
139}
140
141
142/*
143** Link a collectable object 'o' with a known type into the list 'p'.
144** (Must be a macro to access the 'gclist' field in different types.)
145*/
146#define linkgclist(o,p) linkgclist_(obj2gco(o), &(o)->gclist, &(p))
147
148static void linkgclist_ (GCObject *o, GCObject **pnext, GCObject **list) {
149 lua_assert(!isgray(o)); /* cannot be in a gray list */
150 *pnext = *list;
151 *list = o;
152 set2gray(o); /* now it is */
153}
154
155
156/*
157** Link a generic collectable object 'o' into the list 'p'.
158*/
159#define linkobjgclist(o,p) linkgclist_(obj2gco(o), getgclist(o), &(p))
160
161
162
163/*
164** Clear keys for empty entries in tables. If entry is empty, mark its
165** entry as dead. This allows the collection of the key, but keeps its
166** entry in the table: its removal could break a chain and could break
167** a table traversal. Other places never manipulate dead keys, because
168** its associated empty value is enough to signal that the entry is
169** logically empty.
170*/
171static void clearkey (Node *n) {
172 lua_assert(isempty(gval(n)));
173 if (keyiscollectable(n))
174 setdeadkey(n); /* unused key; remove it */
175}
176
177
178/*
179** tells whether a key or value can be cleared from a weak
180** table. Non-collectable objects are never removed from weak
181** tables. Strings behave as 'values', so are never removed too. for
182** other objects: if really collected, cannot keep them; for objects
183** being finalized, keep them in keys, but not in values
184*/
185static int iscleared (global_State *g, const GCObject *o) {
186 if (o == NULL) return 0; /* non-collectable value */
187 else if (novariant(o->tt) == LUA_TSTRING) {
188 markobject(g, o); /* strings are 'values', so are never weak */
189 return 0;
190 }
191 else return iswhite(o);
192}
193
194
195/*
196** Barrier that moves collector forward, that is, marks the white object
197** 'v' being pointed by the black object 'o'. In the generational
198** mode, 'v' must also become old, if 'o' is old; however, it cannot
199** be changed directly to OLD, because it may still point to non-old
200** objects. So, it is marked as OLD0. In the next cycle it will become
201** OLD1, and in the next it will finally become OLD (regular old). By
202** then, any object it points to will also be old. If called in the
203** incremental sweep phase, it clears the black object to white (sweep
204** it) to avoid other barrier calls for this same object. (That cannot
205** be done is generational mode, as its sweep does not distinguish
206** whites from deads.)
207*/
208void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
209 global_State *g = G(L);
210 lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
211 if (keepinvariant(g)) { /* must keep invariant? */
212 reallymarkobject(g, v); /* restore invariant */
213 if (isold(o)) {
214 lua_assert(!isold(v)); /* white object could not be old */
215 setage(v, G_OLD0); /* restore generational invariant */
216 }
217 }
218 else { /* sweep phase */
219 lua_assert(issweepphase(g));
220 if (g->gckind == KGC_INC) /* incremental mode? */
221 makewhite(g, o); /* mark 'o' as white to avoid other barriers */
222 }
223}
224
225
226/*
227** barrier that moves collector backward, that is, mark the black object
228** pointing to a white object as gray again.
229*/
230void luaC_barrierback_ (lua_State *L, GCObject *o) {
231 global_State *g = G(L);
232 lua_assert(isblack(o) && !isdead(g, o));
233 lua_assert((g->gckind == KGC_GEN) == (isold(o) && getage(o) != G_TOUCHED1));
234 if (getage(o) == G_TOUCHED2) /* already in gray list? */
235 set2gray(o); /* make it gray to become touched1 */
236 else /* link it in 'grayagain' and paint it gray */
237 linkobjgclist(o, g->grayagain);
238 if (isold(o)) /* generational mode? */
239 setage(o, G_TOUCHED1); /* touched in current cycle */
240}
241
242
243void luaC_fix (lua_State *L, GCObject *o) {
244 global_State *g = G(L);
245 lua_assert(g->allgc == o); /* object must be 1st in 'allgc' list! */
246 set2gray(o); /* they will be gray forever */
247 setage(o, G_OLD); /* and old forever */
248 g->allgc = o->next; /* remove object from 'allgc' list */
249 o->next = g->fixedgc; /* link it to 'fixedgc' list */
250 g->fixedgc = o;
251}
252
253
254/*
255** create a new collectable object (with given type and size) and link
256** it to 'allgc' list.
257*/
258GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
259 global_State *g = G(L);
260 GCObject *o = cast(GCObject *, luaM_newobject(L, novariant(tt), sz));
261 o->marked = luaC_white(g);
262 o->tt = tt;
263 o->next = g->allgc;
264 g->allgc = o;
265 return o;
266}
267
268/* }====================================================== */
269
270
271
272/*
273** {======================================================
274** Mark functions
275** =======================================================
276*/
277
278
279/*
280** Mark an object. Userdata with no user values, strings, and closed
281** upvalues are visited and turned black here. Open upvalues are
282** already indirectly linked through their respective threads in the
283** 'twups' list, so they don't go to the gray list; nevertheless, they
284** are kept gray to avoid barriers, as their values will be revisited
285** by the thread or by 'remarkupvals'. Other objects are added to the
286** gray list to be visited (and turned black) later. Both userdata and
287** upvalues can call this function recursively, but this recursion goes
288** for at most two levels: An upvalue cannot refer to another upvalue
289** (only closures can), and a userdata's metatable must be a table.
290*/
291static void reallymarkobject (global_State *g, GCObject *o) {
292 switch (o->tt) {
293 case LUA_VSHRSTR:
294 case LUA_VLNGSTR: {
295 set2black(o); /* nothing to visit */
296 break;
297 }
298 case LUA_VUPVAL: {
299 UpVal *uv = gco2upv(o);
300 if (upisopen(uv))
301 set2gray(uv); /* open upvalues are kept gray */
302 else
303 set2black(uv); /* closed upvalues are visited here */
304 markvalue(g, uv->v); /* mark its content */
305 break;
306 }
307 case LUA_VUSERDATA: {
308 Udata *u = gco2u(o);
309 if (u->nuvalue == 0) { /* no user values? */
310 markobjectN(g, u->metatable); /* mark its metatable */
311 set2black(u); /* nothing else to mark */
312 break;
313 }
314 /* else... */
315 } /* FALLTHROUGH */
316 case LUA_VLCL: case LUA_VCCL: case LUA_VTABLE:
317 case LUA_VTHREAD: case LUA_VPROTO: {
318 linkobjgclist(o, g->gray); /* to be visited later */
319 break;
320 }
321 default: lua_assert(0); break;
322 }
323}
324
325
326/*
327** mark metamethods for basic types
328*/
329static void markmt (global_State *g) {
330 int i;
331 for (i=0; i < LUA_NUMTAGS; i++)
332 markobjectN(g, g->mt[i]);
333}
334
335
336/*
337** mark all objects in list of being-finalized
338*/
339static lu_mem markbeingfnz (global_State *g) {
340 GCObject *o;
341 lu_mem count = 0;
342 for (o = g->tobefnz; o != NULL; o = o->next) {
343 count++;
344 markobject(g, o);
345 }
346 return count;
347}
348
349
350/*
351** For each non-marked thread, simulates a barrier between each open
352** upvalue and its value. (If the thread is collected, the value will be
353** assigned to the upvalue, but then it can be too late for the barrier
354** to act. The "barrier" does not need to check colors: A non-marked
355** thread must be young; upvalues cannot be older than their threads; so
356** any visited upvalue must be young too.) Also removes the thread from
357** the list, as it was already visited. Removes also threads with no
358** upvalues, as they have nothing to be checked. (If the thread gets an
359** upvalue later, it will be linked in the list again.)
360*/
361static int remarkupvals (global_State *g) {
362 lua_State *thread;
363 lua_State **p = &g->twups;
364 int work = 0; /* estimate of how much work was done here */
365 while ((thread = *p) != NULL) {
366 work++;
367 if (!iswhite(thread) && thread->openupval != NULL)
368 p = &thread->twups; /* keep marked thread with upvalues in the list */
369 else { /* thread is not marked or without upvalues */
370 UpVal *uv;
371 lua_assert(!isold(thread) || thread->openupval == NULL);
372 *p = thread->twups; /* remove thread from the list */
373 thread->twups = thread; /* mark that it is out of list */
374 for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
375 lua_assert(getage(uv) <= getage(thread));
376 work++;
377 if (!iswhite(uv)) { /* upvalue already visited? */
378 lua_assert(upisopen(uv) && isgray(uv));
379 markvalue(g, uv->v); /* mark its value */
380 }
381 }
382 }
383 }
384 return work;
385}
386
387
388static void cleargraylists (global_State *g) {
389 g->gray = g->grayagain = NULL;
390 g->weak = g->allweak = g->ephemeron = NULL;
391}
392
393
394/*
395** mark root set and reset all gray lists, to start a new collection
396*/
397static void restartcollection (global_State *g) {
398 cleargraylists(g);
399 markobject(g, g->mainthread);
400 markvalue(g, &g->l_registry);
401 markmt(g);
402 markbeingfnz(g); /* mark any finalizing object left from previous cycle */
403}
404
405/* }====================================================== */
406
407
408/*
409** {======================================================
410** Traverse functions
411** =======================================================
412*/
413
414
415/*
416** Check whether object 'o' should be kept in the 'grayagain' list for
417** post-processing by 'correctgraylist'. (It could put all old objects
418** in the list and leave all the work to 'correctgraylist', but it is
419** more efficient to avoid adding elements that will be removed.) Only
420** TOUCHED1 objects need to be in the list. TOUCHED2 doesn't need to go
421** back to a gray list, but then it must become OLD. (That is what
422** 'correctgraylist' does when it finds a TOUCHED2 object.)
423*/
424static void genlink (global_State *g, GCObject *o) {
425 lua_assert(isblack(o));
426 if (getage(o) == G_TOUCHED1) { /* touched in this cycle? */
427 linkobjgclist(o, g->grayagain); /* link it back in 'grayagain' */
428 } /* everything else do not need to be linked back */
429 else if (getage(o) == G_TOUCHED2)
430 changeage(o, G_TOUCHED2, G_OLD); /* advance age */
431}
432
433
434/*
435** Traverse a table with weak values and link it to proper list. During
436** propagate phase, keep it in 'grayagain' list, to be revisited in the
437** atomic phase. In the atomic phase, if table has any white value,
438** put it in 'weak' list, to be cleared.
439*/
440static void traverseweakvalue (global_State *g, Table *h) {
441 Node *n, *limit = gnodelast(h);
442 /* if there is array part, assume it may have white values (it is not
443 worth traversing it now just to check) */
444 int hasclears = (h->alimit > 0);
445 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
446 if (isempty(gval(n))) /* entry is empty? */
447 clearkey(n); /* clear its key */
448 else {
449 lua_assert(!keyisnil(n));
450 markkey(g, n);
451 if (!hasclears && iscleared(g, gcvalueN(gval(n)))) /* a white value? */
452 hasclears = 1; /* table will have to be cleared */
453 }
454 }
455 if (g->gcstate == GCSatomic && hasclears)
456 linkgclist(h, g->weak); /* has to be cleared later */
457 else
458 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
459}
460
461
462/*
463** Traverse an ephemeron table and link it to proper list. Returns true
464** iff any object was marked during this traversal (which implies that
465** convergence has to continue). During propagation phase, keep table
466** in 'grayagain' list, to be visited again in the atomic phase. In
467** the atomic phase, if table has any white->white entry, it has to
468** be revisited during ephemeron convergence (as that key may turn
469** black). Otherwise, if it has any white key, table has to be cleared
470** (in the atomic phase). In generational mode, some tables
471** must be kept in some gray list for post-processing; this is done
472** by 'genlink'.
473*/
474static int traverseephemeron (global_State *g, Table *h, int inv) {
475 int marked = 0; /* true if an object is marked in this traversal */
476 int hasclears = 0; /* true if table has white keys */
477 int hasww = 0; /* true if table has entry "white-key -> white-value" */
478 unsigned int i;
479 unsigned int asize = luaH_realasize(h);
480 unsigned int nsize = sizenode(h);
481 /* traverse array part */
482 for (i = 0; i < asize; i++) {
483 if (valiswhite(&h->array[i])) {
484 marked = 1;
485 reallymarkobject(g, gcvalue(&h->array[i]));
486 }
487 }
488 /* traverse hash part; if 'inv', traverse descending
489 (see 'convergeephemerons') */
490 for (i = 0; i < nsize; i++) {
491 Node *n = inv ? gnode(h, nsize - 1 - i) : gnode(h, i);
492 if (isempty(gval(n))) /* entry is empty? */
493 clearkey(n); /* clear its key */
494 else if (iscleared(g, gckeyN(n))) { /* key is not marked (yet)? */
495 hasclears = 1; /* table must be cleared */
496 if (valiswhite(gval(n))) /* value not marked yet? */
497 hasww = 1; /* white-white entry */
498 }
499 else if (valiswhite(gval(n))) { /* value not marked yet? */
500 marked = 1;
501 reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
502 }
503 }
504 /* link table into proper list */
505 if (g->gcstate == GCSpropagate)
506 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
507 else if (hasww) /* table has white->white entries? */
508 linkgclist(h, g->ephemeron); /* have to propagate again */
509 else if (hasclears) /* table has white keys? */
510 linkgclist(h, g->allweak); /* may have to clean white keys */
511 else
512 genlink(g, obj2gco(h)); /* check whether collector still needs to see it */
513 return marked;
514}
515
516
517static void traversestrongtable (global_State *g, Table *h) {
518 Node *n, *limit = gnodelast(h);
519 unsigned int i;
520 unsigned int asize = luaH_realasize(h);
521 for (i = 0; i < asize; i++) /* traverse array part */
522 markvalue(g, &h->array[i]);
523 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
524 if (isempty(gval(n))) /* entry is empty? */
525 clearkey(n); /* clear its key */
526 else {
527 lua_assert(!keyisnil(n));
528 markkey(g, n);
529 markvalue(g, gval(n));
530 }
531 }
532 genlink(g, obj2gco(h));
533}
534
535
536static lu_mem traversetable (global_State *g, Table *h) {
537 const char *weakkey, *weakvalue;
538 const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
539 markobjectN(g, h->metatable);
540 if (mode && ttisstring(mode) && /* is there a weak mode? */
541 (cast_void(weakkey = strchr(svalue(mode), 'k')),
542 cast_void(weakvalue = strchr(svalue(mode), 'v')),
543 (weakkey || weakvalue))) { /* is really weak? */
544 if (!weakkey) /* strong keys? */
545 traverseweakvalue(g, h);
546 else if (!weakvalue) /* strong values? */
547 traverseephemeron(g, h, 0);
548 else /* all weak */
549 linkgclist(h, g->allweak); /* nothing to traverse now */
550 }
551 else /* not weak */
552 traversestrongtable(g, h);
553 return 1 + h->alimit + 2 * allocsizenode(h);
554}
555
556
557static int traverseudata (global_State *g, Udata *u) {
558 int i;
559 markobjectN(g, u->metatable); /* mark its metatable */
560 for (i = 0; i < u->nuvalue; i++)
561 markvalue(g, &u->uv[i].uv);
562 genlink(g, obj2gco(u));
563 return 1 + u->nuvalue;
564}
565
566
567/*
568** Traverse a prototype. (While a prototype is being build, its
569** arrays can be larger than needed; the extra slots are filled with
570** NULL, so the use of 'markobjectN')
571*/
572static int traverseproto (global_State *g, Proto *f) {
573 int i;
574 markobjectN(g, f->source);
575 for (i = 0; i < f->sizek; i++) /* mark literals */
576 markvalue(g, &f->k[i]);
577 for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
578 markobjectN(g, f->upvalues[i].name);
579 for (i = 0; i < f->sizep; i++) /* mark nested protos */
580 markobjectN(g, f->p[i]);
581 for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
582 markobjectN(g, f->locvars[i].varname);
583 return 1 + f->sizek + f->sizeupvalues + f->sizep + f->sizelocvars;
584}
585
586
587static int traverseCclosure (global_State *g, CClosure *cl) {
588 int i;
589 for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
590 markvalue(g, &cl->upvalue[i]);
591 return 1 + cl->nupvalues;
592}
593
594/*
595** Traverse a Lua closure, marking its prototype and its upvalues.
596** (Both can be NULL while closure is being created.)
597*/
598static int traverseLclosure (global_State *g, LClosure *cl) {
599 int i;
600 markobjectN(g, cl->p); /* mark its prototype */
601 for (i = 0; i < cl->nupvalues; i++) { /* visit its upvalues */
602 UpVal *uv = cl->upvals[i];
603 markobjectN(g, uv); /* mark upvalue */
604 }
605 return 1 + cl->nupvalues;
606}
607
608
609/*
610** Traverse a thread, marking the elements in the stack up to its top
611** and cleaning the rest of the stack in the final traversal. That
612** ensures that the entire stack have valid (non-dead) objects.
613** Threads have no barriers. In gen. mode, old threads must be visited
614** at every cycle, because they might point to young objects. In inc.
615** mode, the thread can still be modified before the end of the cycle,
616** and therefore it must be visited again in the atomic phase. To ensure
617** these visits, threads must return to a gray list if they are not new
618** (which can only happen in generational mode) or if the traverse is in
619** the propagate phase (which can only happen in incremental mode).
620*/
621static int traversethread (global_State *g, lua_State *th) {
622 UpVal *uv;
623 StkId o = th->stack;
624 if (isold(th) || g->gcstate == GCSpropagate)
625 linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
626 if (o == NULL)
627 return 1; /* stack not completely built yet */
628 lua_assert(g->gcstate == GCSatomic ||
629 th->openupval == NULL || isintwups(th));
630 for (; o < th->top; o++) /* mark live elements in the stack */
631 markvalue(g, s2v(o));
632 for (uv = th->openupval; uv != NULL; uv = uv->u.open.next)
633 markobject(g, uv); /* open upvalues cannot be collected */
634 if (g->gcstate == GCSatomic) { /* final traversal? */
635 for (; o < th->stack_last + EXTRA_STACK; o++)
636 setnilvalue(s2v(o)); /* clear dead stack slice */
637 /* 'remarkupvals' may have removed thread from 'twups' list */
638 if (!isintwups(th) && th->openupval != NULL) {
639 th->twups = g->twups; /* link it back to the list */
640 g->twups = th;
641 }
642 }
643 else if (!g->gcemergency)
644 luaD_shrinkstack(th); /* do not change stack in emergency cycle */
645 return 1 + stacksize(th);
646}
647
648
649/*
650** traverse one gray object, turning it to black.
651*/
652static lu_mem propagatemark (global_State *g) {
653 GCObject *o = g->gray;
654 nw2black(o);
655 g->gray = *getgclist(o); /* remove from 'gray' list */
656 switch (o->tt) {
657 case LUA_VTABLE: return traversetable(g, gco2t(o));
658 case LUA_VUSERDATA: return traverseudata(g, gco2u(o));
659 case LUA_VLCL: return traverseLclosure(g, gco2lcl(o));
660 case LUA_VCCL: return traverseCclosure(g, gco2ccl(o));
661 case LUA_VPROTO: return traverseproto(g, gco2p(o));
662 case LUA_VTHREAD: return traversethread(g, gco2th(o));
663 default: lua_assert(0); return 0;
664 }
665}
666
667
668static lu_mem propagateall (global_State *g) {
669 lu_mem tot = 0;
670 while (g->gray)
671 tot += propagatemark(g);
672 return tot;
673}
674
675
676/*
677** Traverse all ephemeron tables propagating marks from keys to values.
678** Repeat until it converges, that is, nothing new is marked. 'dir'
679** inverts the direction of the traversals, trying to speed up
680** convergence on chains in the same table.
681**
682*/
683static void convergeephemerons (global_State *g) {
684 int changed;
685 int dir = 0;
686 do {
687 GCObject *w;
688 GCObject *next = g->ephemeron; /* get ephemeron list */
689 g->ephemeron = NULL; /* tables may return to this list when traversed */
690 changed = 0;
691 while ((w = next) != NULL) { /* for each ephemeron table */
692 Table *h = gco2t(w);
693 next = h->gclist; /* list is rebuilt during loop */
694 nw2black(h); /* out of the list (for now) */
695 if (traverseephemeron(g, h, dir)) { /* marked some value? */
696 propagateall(g); /* propagate changes */
697 changed = 1; /* will have to revisit all ephemeron tables */
698 }
699 }
700 dir = !dir; /* invert direction next time */
701 } while (changed); /* repeat until no more changes */
702}
703
704/* }====================================================== */
705
706
707/*
708** {======================================================
709** Sweep Functions
710** =======================================================
711*/
712
713
714/*
715** clear entries with unmarked keys from all weaktables in list 'l'
716*/
717static void clearbykeys (global_State *g, GCObject *l) {
718 for (; l; l = gco2t(l)->gclist) {
719 Table *h = gco2t(l);
720 Node *limit = gnodelast(h);
721 Node *n;
722 for (n = gnode(h, 0); n < limit; n++) {
723 if (iscleared(g, gckeyN(n))) /* unmarked key? */
724 setempty(gval(n)); /* remove entry */
725 if (isempty(gval(n))) /* is entry empty? */
726 clearkey(n); /* clear its key */
727 }
728 }
729}
730
731
732/*
733** clear entries with unmarked values from all weaktables in list 'l' up
734** to element 'f'
735*/
736static void clearbyvalues (global_State *g, GCObject *l, GCObject *f) {
737 for (; l != f; l = gco2t(l)->gclist) {
738 Table *h = gco2t(l);
739 Node *n, *limit = gnodelast(h);
740 unsigned int i;
741 unsigned int asize = luaH_realasize(h);
742 for (i = 0; i < asize; i++) {
743 TValue *o = &h->array[i];
744 if (iscleared(g, gcvalueN(o))) /* value was collected? */
745 setempty(o); /* remove entry */
746 }
747 for (n = gnode(h, 0); n < limit; n++) {
748 if (iscleared(g, gcvalueN(gval(n)))) /* unmarked value? */
749 setempty(gval(n)); /* remove entry */
750 if (isempty(gval(n))) /* is entry empty? */
751 clearkey(n); /* clear its key */
752 }
753 }
754}
755
756
757static void freeupval (lua_State *L, UpVal *uv) {
758 if (upisopen(uv))
759 luaF_unlinkupval(uv);
760 luaM_free(L, uv);
761}
762
763
764static void freeobj (lua_State *L, GCObject *o) {
765 switch (o->tt) {
766 case LUA_VPROTO:
767 luaF_freeproto(L, gco2p(o));
768 break;
769 case LUA_VUPVAL:
770 freeupval(L, gco2upv(o));
771 break;
772 case LUA_VLCL: {
773 LClosure *cl = gco2lcl(o);
774 luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
775 break;
776 }
777 case LUA_VCCL: {
778 CClosure *cl = gco2ccl(o);
779 luaM_freemem(L, cl, sizeCclosure(cl->nupvalues));
780 break;
781 }
782 case LUA_VTABLE:
783 luaH_free(L, gco2t(o));
784 break;
785 case LUA_VTHREAD:
786 luaE_freethread(L, gco2th(o));
787 break;
788 case LUA_VUSERDATA: {
789 Udata *u = gco2u(o);
790 luaM_freemem(L, o, sizeudata(u->nuvalue, u->len));
791 break;
792 }
793 case LUA_VSHRSTR: {
794 TString *ts = gco2ts(o);
795 luaS_remove(L, ts); /* remove it from hash table */
796 luaM_freemem(L, ts, sizelstring(ts->shrlen));
797 break;
798 }
799 case LUA_VLNGSTR: {
800 TString *ts = gco2ts(o);
801 luaM_freemem(L, ts, sizelstring(ts->u.lnglen));
802 break;
803 }
804 default: lua_assert(0);
805 }
806}
807
808
809/*
810** sweep at most 'countin' elements from a list of GCObjects erasing dead
811** objects, where a dead object is one marked with the old (non current)
812** white; change all non-dead objects back to white, preparing for next
813** collection cycle. Return where to continue the traversal or NULL if
814** list is finished. ('*countout' gets the number of elements traversed.)
815*/
816static GCObject **sweeplist (lua_State *L, GCObject **p, int countin,
817 int *countout) {
818 global_State *g = G(L);
819 int ow = otherwhite(g);
820 int i;
821 int white = luaC_white(g); /* current white */
822 for (i = 0; *p != NULL && i < countin; i++) {
823 GCObject *curr = *p;
824 int marked = curr->marked;
825 if (isdeadm(ow, marked)) { /* is 'curr' dead? */
826 *p = curr->next; /* remove 'curr' from list */
827 freeobj(L, curr); /* erase 'curr' */
828 }
829 else { /* change mark to 'white' */
830 curr->marked = cast_byte((marked & ~maskgcbits) | white);
831 p = &curr->next; /* go to next element */
832 }
833 }
834 if (countout)
835 *countout = i; /* number of elements traversed */
836 return (*p == NULL) ? NULL : p;
837}
838
839
840/*
841** sweep a list until a live object (or end of list)
842*/
843static GCObject **sweeptolive (lua_State *L, GCObject **p) {
844 GCObject **old = p;
845 do {
846 p = sweeplist(L, p, 1, NULL);
847 } while (p == old);
848 return p;
849}
850
851/* }====================================================== */
852
853
854/*
855** {======================================================
856** Finalization
857** =======================================================
858*/
859
860/*
861** If possible, shrink string table.
862*/
863static void checkSizes (lua_State *L, global_State *g) {
864 if (!g->gcemergency) {
865 if (g->strt.nuse < g->strt.size / 4) { /* string table too big? */
866 l_mem olddebt = g->GCdebt;
867 luaS_resize(L, g->strt.size / 2);
868 g->GCestimate += g->GCdebt - olddebt; /* correct estimate */
869 }
870 }
871}
872
873
874/*
875** Get the next udata to be finalized from the 'tobefnz' list, and
876** link it back into the 'allgc' list.
877*/
878static GCObject *udata2finalize (global_State *g) {
879 GCObject *o = g->tobefnz; /* get first element */
880 lua_assert(tofinalize(o));
881 g->tobefnz = o->next; /* remove it from 'tobefnz' list */
882 o->next = g->allgc; /* return it to 'allgc' list */
883 g->allgc = o;
884 resetbit(o->marked, FINALIZEDBIT); /* object is "normal" again */
885 if (issweepphase(g))
886 makewhite(g, o); /* "sweep" object */
887 else if (getage(o) == G_OLD1)
888 g->firstold1 = o; /* it is the first OLD1 object in the list */
889 return o;
890}
891
892
893static void dothecall (lua_State *L, void *ud) {
894 UNUSED(ud);
895 luaD_callnoyield(L, L->top - 2, 0);
896}
897
898
899static void GCTM (lua_State *L) {
900 global_State *g = G(L);
901 const TValue *tm;
902 TValue v;
903 lua_assert(!g->gcemergency);
904 setgcovalue(L, &v, udata2finalize(g));
905 tm = luaT_gettmbyobj(L, &v, TM_GC);
906 if (!notm(tm)) { /* is there a finalizer? */
907 int status;
908 lu_byte oldah = L->allowhook;
909 int running = g->gcrunning;
910 L->allowhook = 0; /* stop debug hooks during GC metamethod */
911 g->gcrunning = 0; /* avoid GC steps */
912 setobj2s(L, L->top++, tm); /* push finalizer... */
913 setobj2s(L, L->top++, &v); /* ... and its argument */
914 L->ci->callstatus |= CIST_FIN; /* will run a finalizer */
915 status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
916 L->ci->callstatus &= ~CIST_FIN; /* not running a finalizer anymore */
917 L->allowhook = oldah; /* restore hooks */
918 g->gcrunning = running; /* restore state */
919 if (l_unlikely(status != LUA_OK)) { /* error while running __gc? */
920 luaE_warnerror(L, "__gc metamethod");
921 L->top--; /* pops error object */
922 }
923 }
924}
925
926
927/*
928** Call a few finalizers
929*/
930static int runafewfinalizers (lua_State *L, int n) {
931 global_State *g = G(L);
932 int i;
933 for (i = 0; i < n && g->tobefnz; i++)
934 GCTM(L); /* call one finalizer */
935 return i;
936}
937
938
939/*
940** call all pending finalizers
941*/
942static void callallpendingfinalizers (lua_State *L) {
943 global_State *g = G(L);
944 while (g->tobefnz)
945 GCTM(L);
946}
947
948
949/*
950** find last 'next' field in list 'p' list (to add elements in its end)
951*/
952static GCObject **findlast (GCObject **p) {
953 while (*p != NULL)
954 p = &(*p)->next;
955 return p;
956}
957
958
959/*
960** Move all unreachable objects (or 'all' objects) that need
961** finalization from list 'finobj' to list 'tobefnz' (to be finalized).
962** (Note that objects after 'finobjold1' cannot be white, so they
963** don't need to be traversed. In incremental mode, 'finobjold1' is NULL,
964** so the whole list is traversed.)
965*/
966static void separatetobefnz (global_State *g, int all) {
967 GCObject *curr;
968 GCObject **p = &g->finobj;
969 GCObject **lastnext = findlast(&g->tobefnz);
970 while ((curr = *p) != g->finobjold1) { /* traverse all finalizable objects */
971 lua_assert(tofinalize(curr));
972 if (!(iswhite(curr) || all)) /* not being collected? */
973 p = &curr->next; /* don't bother with it */
974 else {
975 if (curr == g->finobjsur) /* removing 'finobjsur'? */
976 g->finobjsur = curr->next; /* correct it */
977 *p = curr->next; /* remove 'curr' from 'finobj' list */
978 curr->next = *lastnext; /* link at the end of 'tobefnz' list */
979 *lastnext = curr;
980 lastnext = &curr->next;
981 }
982 }
983}
984
985
986/*
987** If pointer 'p' points to 'o', move it to the next element.
988*/
989static void checkpointer (GCObject **p, GCObject *o) {
990 if (o == *p)
991 *p = o->next;
992}
993
994
995/*
996** Correct pointers to objects inside 'allgc' list when
997** object 'o' is being removed from the list.
998*/
999static void correctpointers (global_State *g, GCObject *o) {
1000 checkpointer(&g->survival, o);
1001 checkpointer(&g->old1, o);
1002 checkpointer(&g->reallyold, o);
1003 checkpointer(&g->firstold1, o);
1004}
1005
1006
1007/*
1008** if object 'o' has a finalizer, remove it from 'allgc' list (must
1009** search the list to find it) and link it in 'finobj' list.
1010*/
1011void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
1012 global_State *g = G(L);
1013 if (tofinalize(o) || /* obj. is already marked... */
1014 gfasttm(g, mt, TM_GC) == NULL) /* or has no finalizer? */
1015 return; /* nothing to be done */
1016 else { /* move 'o' to 'finobj' list */
1017 GCObject **p;
1018 if (issweepphase(g)) {
1019 makewhite(g, o); /* "sweep" object 'o' */
1020 if (g->sweepgc == &o->next) /* should not remove 'sweepgc' object */
1021 g->sweepgc = sweeptolive(L, g->sweepgc); /* change 'sweepgc' */
1022 }
1023 else
1024 correctpointers(g, o);
1025 /* search for pointer pointing to 'o' */
1026 for (p = &g->allgc; *p != o; p = &(*p)->next) { /* empty */ }
1027 *p = o->next; /* remove 'o' from 'allgc' list */
1028 o->next = g->finobj; /* link it in 'finobj' list */
1029 g->finobj = o;
1030 l_setbit(o->marked, FINALIZEDBIT); /* mark it as such */
1031 }
1032}
1033
1034/* }====================================================== */
1035
1036
1037/*
1038** {======================================================
1039** Generational Collector
1040** =======================================================
1041*/
1042
1043static void setpause (global_State *g);
1044
1045
1046/*
1047** Sweep a list of objects to enter generational mode. Deletes dead
1048** objects and turns the non dead to old. All non-dead threads---which
1049** are now old---must be in a gray list. Everything else is not in a
1050** gray list. Open upvalues are also kept gray.
1051*/
1052static void sweep2old (lua_State *L, GCObject **p) {
1053 GCObject *curr;
1054 global_State *g = G(L);
1055 while ((curr = *p) != NULL) {
1056 if (iswhite(curr)) { /* is 'curr' dead? */
1057 lua_assert(isdead(g, curr));
1058 *p = curr->next; /* remove 'curr' from list */
1059 freeobj(L, curr); /* erase 'curr' */
1060 }
1061 else { /* all surviving objects become old */
1062 setage(curr, G_OLD);
1063 if (curr->tt == LUA_VTHREAD) { /* threads must be watched */
1064 lua_State *th = gco2th(curr);
1065 linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
1066 }
1067 else if (curr->tt == LUA_VUPVAL && upisopen(gco2upv(curr)))
1068 set2gray(curr); /* open upvalues are always gray */
1069 else /* everything else is black */
1070 nw2black(curr);
1071 p = &curr->next; /* go to next element */
1072 }
1073 }
1074}
1075
1076
1077/*
1078** Sweep for generational mode. Delete dead objects. (Because the
1079** collection is not incremental, there are no "new white" objects
1080** during the sweep. So, any white object must be dead.) For
1081** non-dead objects, advance their ages and clear the color of
1082** new objects. (Old objects keep their colors.)
1083** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced
1084** here, because these old-generation objects are usually not swept
1085** here. They will all be advanced in 'correctgraylist'. That function
1086** will also remove objects turned white here from any gray list.
1087*/
1088static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
1089 GCObject *limit, GCObject **pfirstold1) {
1090 static const lu_byte nextage[] = {
1091 G_SURVIVAL, /* from G_NEW */
1092 G_OLD1, /* from G_SURVIVAL */
1093 G_OLD1, /* from G_OLD0 */
1094 G_OLD, /* from G_OLD1 */
1095 G_OLD, /* from G_OLD (do not change) */
1096 G_TOUCHED1, /* from G_TOUCHED1 (do not change) */
1097 G_TOUCHED2 /* from G_TOUCHED2 (do not change) */
1098 };
1099 int white = luaC_white(g);
1100 GCObject *curr;
1101 while ((curr = *p) != limit) {
1102 if (iswhite(curr)) { /* is 'curr' dead? */
1103 lua_assert(!isold(curr) && isdead(g, curr));
1104 *p = curr->next; /* remove 'curr' from list */
1105 freeobj(L, curr); /* erase 'curr' */
1106 }
1107 else { /* correct mark and age */
1108 if (getage(curr) == G_NEW) { /* new objects go back to white */
1109 int marked = curr->marked & ~maskgcbits; /* erase GC bits */
1110 curr->marked = cast_byte(marked | G_SURVIVAL | white);
1111 }
1112 else { /* all other objects will be old, and so keep their color */
1113 setage(curr, nextage[getage(curr)]);
1114 if (getage(curr) == G_OLD1 && *pfirstold1 == NULL)
1115 *pfirstold1 = curr; /* first OLD1 object in the list */
1116 }
1117 p = &curr->next; /* go to next element */
1118 }
1119 }
1120 return p;
1121}
1122
1123
1124/*
1125** Traverse a list making all its elements white and clearing their
1126** age. In incremental mode, all objects are 'new' all the time,
1127** except for fixed strings (which are always old).
1128*/
1129static void whitelist (global_State *g, GCObject *p) {
1130 int white = luaC_white(g);
1131 for (; p != NULL; p = p->next)
1132 p->marked = cast_byte((p->marked & ~maskgcbits) | white);
1133}
1134
1135
1136/*
1137** Correct a list of gray objects. Return pointer to where rest of the
1138** list should be linked.
1139** Because this correction is done after sweeping, young objects might
1140** be turned white and still be in the list. They are only removed.
1141** 'TOUCHED1' objects are advanced to 'TOUCHED2' and remain on the list;
1142** Non-white threads also remain on the list; 'TOUCHED2' objects become
1143** regular old; they and anything else are removed from the list.
1144*/
1145static GCObject **correctgraylist (GCObject **p) {
1146 GCObject *curr;
1147 while ((curr = *p) != NULL) {
1148 GCObject **next = getgclist(curr);
1149 if (iswhite(curr))
1150 goto remove; /* remove all white objects */
1151 else if (getage(curr) == G_TOUCHED1) { /* touched in this cycle? */
1152 lua_assert(isgray(curr));
1153 nw2black(curr); /* make it black, for next barrier */
1154 changeage(curr, G_TOUCHED1, G_TOUCHED2);
1155 goto remain; /* keep it in the list and go to next element */
1156 }
1157 else if (curr->tt == LUA_VTHREAD) {
1158 lua_assert(isgray(curr));
1159 goto remain; /* keep non-white threads on the list */
1160 }
1161 else { /* everything else is removed */
1162 lua_assert(isold(curr)); /* young objects should be white here */
1163 if (getage(curr) == G_TOUCHED2) /* advance from TOUCHED2... */
1164 changeage(curr, G_TOUCHED2, G_OLD); /* ... to OLD */
1165 nw2black(curr); /* make object black (to be removed) */
1166 goto remove;
1167 }
1168 remove: *p = *next; continue;
1169 remain: p = next; continue;
1170 }
1171 return p;
1172}
1173
1174
1175/*
1176** Correct all gray lists, coalescing them into 'grayagain'.
1177*/
1178static void correctgraylists (global_State *g) {
1179 GCObject **list = correctgraylist(&g->grayagain);
1180 *list = g->weak; g->weak = NULL;
1181 list = correctgraylist(list);
1182 *list = g->allweak; g->allweak = NULL;
1183 list = correctgraylist(list);
1184 *list = g->ephemeron; g->ephemeron = NULL;
1185 correctgraylist(list);
1186}
1187
1188
1189/*
1190** Mark black 'OLD1' objects when starting a new young collection.
1191** Gray objects are already in some gray list, and so will be visited
1192** in the atomic step.
1193*/
1194static void markold (global_State *g, GCObject *from, GCObject *to) {
1195 GCObject *p;
1196 for (p = from; p != to; p = p->next) {
1197 if (getage(p) == G_OLD1) {
1198 lua_assert(!iswhite(p));
1199 changeage(p, G_OLD1, G_OLD); /* now they are old */
1200 if (isblack(p))
1201 reallymarkobject(g, p);
1202 }
1203 }
1204}
1205
1206
1207/*
1208** Finish a young-generation collection.
1209*/
1210static void finishgencycle (lua_State *L, global_State *g) {
1211 correctgraylists(g);
1212 checkSizes(L, g);
1213 g->gcstate = GCSpropagate; /* skip restart */
1214 if (!g->gcemergency)
1215 callallpendingfinalizers(L);
1216}
1217
1218
1219/*
1220** Does a young collection. First, mark 'OLD1' objects. Then does the
1221** atomic step. Then, sweep all lists and advance pointers. Finally,
1222** finish the collection.
1223*/
1224static void youngcollection (lua_State *L, global_State *g) {
1225 GCObject **psurvival; /* to point to first non-dead survival object */
1226 GCObject *dummy; /* dummy out parameter to 'sweepgen' */
1227 lua_assert(g->gcstate == GCSpropagate);
1228 if (g->firstold1) { /* are there regular OLD1 objects? */
1229 markold(g, g->firstold1, g->reallyold); /* mark them */
1230 g->firstold1 = NULL; /* no more OLD1 objects (for now) */
1231 }
1232 markold(g, g->finobj, g->finobjrold);
1233 markold(g, g->tobefnz, NULL);
1234 atomic(L);
1235
1236 /* sweep nursery and get a pointer to its last live element */
1237 g->gcstate = GCSswpallgc;
1238 psurvival = sweepgen(L, g, &g->allgc, g->survival, &g->firstold1);
1239 /* sweep 'survival' */
1240 sweepgen(L, g, psurvival, g->old1, &g->firstold1);
1241 g->reallyold = g->old1;
1242 g->old1 = *psurvival; /* 'survival' survivals are old now */
1243 g->survival = g->allgc; /* all news are survivals */
1244
1245 /* repeat for 'finobj' lists */
1246 dummy = NULL; /* no 'firstold1' optimization for 'finobj' lists */
1247 psurvival = sweepgen(L, g, &g->finobj, g->finobjsur, &dummy);
1248 /* sweep 'survival' */
1249 sweepgen(L, g, psurvival, g->finobjold1, &dummy);
1250 g->finobjrold = g->finobjold1;
1251 g->finobjold1 = *psurvival; /* 'survival' survivals are old now */
1252 g->finobjsur = g->finobj; /* all news are survivals */
1253
1254 sweepgen(L, g, &g->tobefnz, NULL, &dummy);
1255 finishgencycle(L, g);
1256}
1257
1258
1259/*
1260** Clears all gray lists, sweeps objects, and prepare sublists to enter
1261** generational mode. The sweeps remove dead objects and turn all
1262** surviving objects to old. Threads go back to 'grayagain'; everything
1263** else is turned black (not in any gray list).
1264*/
1265static void atomic2gen (lua_State *L, global_State *g) {
1266 cleargraylists(g);
1267 /* sweep all elements making them old */
1268 g->gcstate = GCSswpallgc;
1269 sweep2old(L, &g->allgc);
1270 /* everything alive now is old */
1271 g->reallyold = g->old1 = g->survival = g->allgc;
1272 g->firstold1 = NULL; /* there are no OLD1 objects anywhere */
1273
1274 /* repeat for 'finobj' lists */
1275 sweep2old(L, &g->finobj);
1276 g->finobjrold = g->finobjold1 = g->finobjsur = g->finobj;
1277
1278 sweep2old(L, &g->tobefnz);
1279
1280 g->gckind = KGC_GEN;
1281 g->lastatomic = 0;
1282 g->GCestimate = gettotalbytes(g); /* base for memory control */
1283 finishgencycle(L, g);
1284}
1285
1286
1287/*
1288** Enter generational mode. Must go until the end of an atomic cycle
1289** to ensure that all objects are correctly marked and weak tables
1290** are cleared. Then, turn all objects into old and finishes the
1291** collection.
1292*/
1293static lu_mem entergen (lua_State *L, global_State *g) {
1294 lu_mem numobjs;
1295 luaC_runtilstate(L, bitmask(GCSpause)); /* prepare to start a new cycle */
1296 luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
1297 numobjs = atomic(L); /* propagates all and then do the atomic stuff */
1298 atomic2gen(L, g);
1299 return numobjs;
1300}
1301
1302
1303/*
1304** Enter incremental mode. Turn all objects white, make all
1305** intermediate lists point to NULL (to avoid invalid pointers),
1306** and go to the pause state.
1307*/
1308static void enterinc (global_State *g) {
1309 whitelist(g, g->allgc);
1310 g->reallyold = g->old1 = g->survival = NULL;
1311 whitelist(g, g->finobj);
1312 whitelist(g, g->tobefnz);
1313 g->finobjrold = g->finobjold1 = g->finobjsur = NULL;
1314 g->gcstate = GCSpause;
1315 g->gckind = KGC_INC;
1316 g->lastatomic = 0;
1317}
1318
1319
1320/*
1321** Change collector mode to 'newmode'.
1322*/
1323void luaC_changemode (lua_State *L, int newmode) {
1324 global_State *g = G(L);
1325 if (newmode != g->gckind) {
1326 if (newmode == KGC_GEN) /* entering generational mode? */
1327 entergen(L, g);
1328 else
1329 enterinc(g); /* entering incremental mode */
1330 }
1331 g->lastatomic = 0;
1332}
1333
1334
1335/*
1336** Does a full collection in generational mode.
1337*/
1338static lu_mem fullgen (lua_State *L, global_State *g) {
1339 enterinc(g);
1340 return entergen(L, g);
1341}
1342
1343
1344/*
1345** Set debt for the next minor collection, which will happen when
1346** memory grows 'genminormul'%.
1347*/
1348static void setminordebt (global_State *g) {
1349 luaE_setdebt(g, -(cast(l_mem, (gettotalbytes(g) / 100)) * g->genminormul));
1350}
1351
1352
1353/*
1354** Does a major collection after last collection was a "bad collection".
1355**
1356** When the program is building a big structure, it allocates lots of
1357** memory but generates very little garbage. In those scenarios,
1358** the generational mode just wastes time doing small collections, and
1359** major collections are frequently what we call a "bad collection", a
1360** collection that frees too few objects. To avoid the cost of switching
1361** between generational mode and the incremental mode needed for full
1362** (major) collections, the collector tries to stay in incremental mode
1363** after a bad collection, and to switch back to generational mode only
1364** after a "good" collection (one that traverses less than 9/8 objects
1365** of the previous one).
1366** The collector must choose whether to stay in incremental mode or to
1367** switch back to generational mode before sweeping. At this point, it
1368** does not know the real memory in use, so it cannot use memory to
1369** decide whether to return to generational mode. Instead, it uses the
1370** number of objects traversed (returned by 'atomic') as a proxy. The
1371** field 'g->lastatomic' keeps this count from the last collection.
1372** ('g->lastatomic != 0' also means that the last collection was bad.)
1373*/
1374static void stepgenfull (lua_State *L, global_State *g) {
1375 lu_mem newatomic; /* count of traversed objects */
1376 lu_mem lastatomic = g->lastatomic; /* count from last collection */
1377 if (g->gckind == KGC_GEN) /* still in generational mode? */
1378 enterinc(g); /* enter incremental mode */
1379 luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
1380 newatomic = atomic(L); /* mark everybody */
1381 if (newatomic < lastatomic + (lastatomic >> 3)) { /* good collection? */
1382 atomic2gen(L, g); /* return to generational mode */
1383 setminordebt(g);
1384 }
1385 else { /* another bad collection; stay in incremental mode */
1386 g->GCestimate = gettotalbytes(g); /* first estimate */;
1387 entersweep(L);
1388 luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
1389 setpause(g);
1390 g->lastatomic = newatomic;
1391 }
1392}
1393
1394
1395/*
1396** Does a generational "step".
1397** Usually, this means doing a minor collection and setting the debt to
1398** make another collection when memory grows 'genminormul'% larger.
1399**
1400** However, there are exceptions. If memory grows 'genmajormul'%
1401** larger than it was at the end of the last major collection (kept
1402** in 'g->GCestimate'), the function does a major collection. At the
1403** end, it checks whether the major collection was able to free a
1404** decent amount of memory (at least half the growth in memory since
1405** previous major collection). If so, the collector keeps its state,
1406** and the next collection will probably be minor again. Otherwise,
1407** we have what we call a "bad collection". In that case, set the field
1408** 'g->lastatomic' to signal that fact, so that the next collection will
1409** go to 'stepgenfull'.
1410**
1411** 'GCdebt <= 0' means an explicit call to GC step with "size" zero;
1412** in that case, do a minor collection.
1413*/
1414static void genstep (lua_State *L, global_State *g) {
1415 if (g->lastatomic != 0) /* last collection was a bad one? */
1416 stepgenfull(L, g); /* do a full step */
1417 else {
1418 lu_mem majorbase = g->GCestimate; /* memory after last major collection */
1419 lu_mem majorinc = (majorbase / 100) * getgcparam(g->genmajormul);
1420 if (g->GCdebt > 0 && gettotalbytes(g) > majorbase + majorinc) {
1421 lu_mem numobjs = fullgen(L, g); /* do a major collection */
1422 if (gettotalbytes(g) < majorbase + (majorinc / 2)) {
1423 /* collected at least half of memory growth since last major
1424 collection; keep doing minor collections */
1425 setminordebt(g);
1426 }
1427 else { /* bad collection */
1428 g->lastatomic = numobjs; /* signal that last collection was bad */
1429 setpause(g); /* do a long wait for next (major) collection */
1430 }
1431 }
1432 else { /* regular case; do a minor collection */
1433 youngcollection(L, g);
1434 setminordebt(g);
1435 g->GCestimate = majorbase; /* preserve base value */
1436 }
1437 }
1438 lua_assert(isdecGCmodegen(g));
1439}
1440
1441/* }====================================================== */
1442
1443
1444/*
1445** {======================================================
1446** GC control
1447** =======================================================
1448*/
1449
1450
1451/*
1452** Set the "time" to wait before starting a new GC cycle; cycle will
1453** start when memory use hits the threshold of ('estimate' * pause /
1454** PAUSEADJ). (Division by 'estimate' should be OK: it cannot be zero,
1455** because Lua cannot even start with less than PAUSEADJ bytes).
1456*/
1457static void setpause (global_State *g) {
1458 l_mem threshold, debt;
1459 int pause = getgcparam(g->gcpause);
1460 l_mem estimate = g->GCestimate / PAUSEADJ; /* adjust 'estimate' */
1461 lua_assert(estimate > 0);
1462 threshold = (pause < MAX_LMEM / estimate) /* overflow? */
1463 ? estimate * pause /* no overflow */
1464 : MAX_LMEM; /* overflow; truncate to maximum */
1465 debt = gettotalbytes(g) - threshold;
1466 if (debt > 0) debt = 0;
1467 luaE_setdebt(g, debt);
1468}
1469
1470
1471/*
1472** Enter first sweep phase.
1473** The call to 'sweeptolive' makes the pointer point to an object
1474** inside the list (instead of to the header), so that the real sweep do
1475** not need to skip objects created between "now" and the start of the
1476** real sweep.
1477*/
1478static void entersweep (lua_State *L) {
1479 global_State *g = G(L);
1480 g->gcstate = GCSswpallgc;
1481 lua_assert(g->sweepgc == NULL);
1482 g->sweepgc = sweeptolive(L, &g->allgc);
1483}
1484
1485
1486/*
1487** Delete all objects in list 'p' until (but not including) object
1488** 'limit'.
1489*/
1490static void deletelist (lua_State *L, GCObject *p, GCObject *limit) {
1491 while (p != limit) {
1492 GCObject *next = p->next;
1493 freeobj(L, p);
1494 p = next;
1495 }
1496}
1497
1498
1499/*
1500** Call all finalizers of the objects in the given Lua state, and
1501** then free all objects, except for the main thread.
1502*/
1503void luaC_freeallobjects (lua_State *L) {
1504 global_State *g = G(L);
1505 luaC_changemode(L, KGC_INC);
1506 separatetobefnz(g, 1); /* separate all objects with finalizers */
1507 lua_assert(g->finobj == NULL);
1508 callallpendingfinalizers(L);
1509 deletelist(L, g->allgc, obj2gco(g->mainthread));
1510 deletelist(L, g->finobj, NULL);
1511 deletelist(L, g->fixedgc, NULL); /* collect fixed objects */
1512 lua_assert(g->strt.nuse == 0);
1513}
1514
1515
1516static lu_mem atomic (lua_State *L) {
1517 global_State *g = G(L);
1518 lu_mem work = 0;
1519 GCObject *origweak, *origall;
1520 GCObject *grayagain = g->grayagain; /* save original list */
1521 g->grayagain = NULL;
1522 lua_assert(g->ephemeron == NULL && g->weak == NULL);
1523 lua_assert(!iswhite(g->mainthread));
1524 g->gcstate = GCSatomic;
1525 markobject(g, L); /* mark running thread */
1526 /* registry and global metatables may be changed by API */
1527 markvalue(g, &g->l_registry);
1528 markmt(g); /* mark global metatables */
1529 work += propagateall(g); /* empties 'gray' list */
1530 /* remark occasional upvalues of (maybe) dead threads */
1531 work += remarkupvals(g);
1532 work += propagateall(g); /* propagate changes */
1533 g->gray = grayagain;
1534 work += propagateall(g); /* traverse 'grayagain' list */
1535 convergeephemerons(g);
1536 /* at this point, all strongly accessible objects are marked. */
1537 /* Clear values from weak tables, before checking finalizers */
1538 clearbyvalues(g, g->weak, NULL);
1539 clearbyvalues(g, g->allweak, NULL);
1540 origweak = g->weak; origall = g->allweak;
1541 separatetobefnz(g, 0); /* separate objects to be finalized */
1542 work += markbeingfnz(g); /* mark objects that will be finalized */
1543 work += propagateall(g); /* remark, to propagate 'resurrection' */
1544 convergeephemerons(g);
1545 /* at this point, all resurrected objects are marked. */
1546 /* remove dead objects from weak tables */
1547 clearbykeys(g, g->ephemeron); /* clear keys from all ephemeron tables */
1548 clearbykeys(g, g->allweak); /* clear keys from all 'allweak' tables */
1549 /* clear values from resurrected weak tables */
1550 clearbyvalues(g, g->weak, origweak);
1551 clearbyvalues(g, g->allweak, origall);
1552 luaS_clearcache(g);
1553 g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
1554 lua_assert(g->gray == NULL);
1555 return work; /* estimate of slots marked by 'atomic' */
1556}
1557
1558
1559static int sweepstep (lua_State *L, global_State *g,
1560 int nextstate, GCObject **nextlist) {
1561 if (g->sweepgc) {
1562 l_mem olddebt = g->GCdebt;
1563 int count;
1564 g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX, &count);
1565 g->GCestimate += g->GCdebt - olddebt; /* update estimate */
1566 return count;
1567 }
1568 else { /* enter next state */
1569 g->gcstate = nextstate;
1570 g->sweepgc = nextlist;
1571 return 0; /* no work done */
1572 }
1573}
1574
1575
1576static lu_mem singlestep (lua_State *L) {
1577 global_State *g = G(L);
1578 lu_mem work;
1579 lua_assert(!g->gcstopem); /* collector is not reentrant */
1580 g->gcstopem = 1; /* no emergency collections while collecting */
1581 switch (g->gcstate) {
1582 case GCSpause: {
1583 restartcollection(g);
1584 g->gcstate = GCSpropagate;
1585 work = 1;
1586 break;
1587 }
1588 case GCSpropagate: {
1589 if (g->gray == NULL) { /* no more gray objects? */
1590 g->gcstate = GCSenteratomic; /* finish propagate phase */
1591 work = 0;
1592 }
1593 else
1594 work = propagatemark(g); /* traverse one gray object */
1595 break;
1596 }
1597 case GCSenteratomic: {
1598 work = atomic(L); /* work is what was traversed by 'atomic' */
1599 entersweep(L);
1600 g->GCestimate = gettotalbytes(g); /* first estimate */;
1601 break;
1602 }
1603 case GCSswpallgc: { /* sweep "regular" objects */
1604 work = sweepstep(L, g, GCSswpfinobj, &g->finobj);
1605 break;
1606 }
1607 case GCSswpfinobj: { /* sweep objects with finalizers */
1608 work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
1609 break;
1610 }
1611 case GCSswptobefnz: { /* sweep objects to be finalized */
1612 work = sweepstep(L, g, GCSswpend, NULL);
1613 break;
1614 }
1615 case GCSswpend: { /* finish sweeps */
1616 checkSizes(L, g);
1617 g->gcstate = GCScallfin;
1618 work = 0;
1619 break;
1620 }
1621 case GCScallfin: { /* call remaining finalizers */
1622 if (g->tobefnz && !g->gcemergency) {
1623 g->gcstopem = 0; /* ok collections during finalizers */
1624 work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST;
1625 }
1626 else { /* emergency mode or no more finalizers */
1627 g->gcstate = GCSpause; /* finish collection */
1628 work = 0;
1629 }
1630 break;
1631 }
1632 default: lua_assert(0); return 0;
1633 }
1634 g->gcstopem = 0;
1635 return work;
1636}
1637
1638
1639/*
1640** advances the garbage collector until it reaches a state allowed
1641** by 'statemask'
1642*/
1643void luaC_runtilstate (lua_State *L, int statesmask) {
1644 global_State *g = G(L);
1645 while (!testbit(statesmask, g->gcstate))
1646 singlestep(L);
1647}
1648
1649
1650/*
1651** Performs a basic incremental step. The debt and step size are
1652** converted from bytes to "units of work"; then the function loops
1653** running single steps until adding that many units of work or
1654** finishing a cycle (pause state). Finally, it sets the debt that
1655** controls when next step will be performed.
1656*/
1657static void incstep (lua_State *L, global_State *g) {
1658 int stepmul = (getgcparam(g->gcstepmul) | 1); /* avoid division by 0 */
1659 l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
1660 l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
1661 ? ((cast(l_mem, 1) << g->gcstepsize) / WORK2MEM) * stepmul
1662 : MAX_LMEM; /* overflow; keep maximum value */
1663 do { /* repeat until pause or enough "credit" (negative debt) */
1664 lu_mem work = singlestep(L); /* perform one single step */
1665 debt -= work;
1666 } while (debt > -stepsize && g->gcstate != GCSpause);
1667 if (g->gcstate == GCSpause)
1668 setpause(g); /* pause until next cycle */
1669 else {
1670 debt = (debt / stepmul) * WORK2MEM; /* convert 'work units' to bytes */
1671 luaE_setdebt(g, debt);
1672 }
1673}
1674
1675/*
1676** performs a basic GC step if collector is running
1677*/
1678void luaC_step (lua_State *L) {
1679 global_State *g = G(L);
1680 lua_assert(!g->gcemergency);
1681 if (g->gcrunning) { /* running? */
1682 if(isdecGCmodegen(g))
1683 genstep(L, g);
1684 else
1685 incstep(L, g);
1686 }
1687}
1688
1689
1690/*
1691** Perform a full collection in incremental mode.
1692** Before running the collection, check 'keepinvariant'; if it is true,
1693** there may be some objects marked as black, so the collector has
1694** to sweep all objects to turn them back to white (as white has not
1695** changed, nothing will be collected).
1696*/
1697static void fullinc (lua_State *L, global_State *g) {
1698 if (keepinvariant(g)) /* black objects? */
1699 entersweep(L); /* sweep everything to turn them back to white */
1700 /* finish any pending sweep phase to start a new cycle */
1701 luaC_runtilstate(L, bitmask(GCSpause));
1702 luaC_runtilstate(L, bitmask(GCScallfin)); /* run up to finalizers */
1703 /* estimate must be correct after a full GC cycle */
1704 lua_assert(g->GCestimate == gettotalbytes(g));
1705 luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
1706 setpause(g);
1707}
1708
1709
1710/*
1711** Performs a full GC cycle; if 'isemergency', set a flag to avoid
1712** some operations which could change the interpreter state in some
1713** unexpected ways (running finalizers and shrinking some structures).
1714*/
1715void luaC_fullgc (lua_State *L, int isemergency) {
1716 global_State *g = G(L);
1717 lua_assert(!g->gcemergency);
1718 g->gcemergency = isemergency; /* set flag */
1719 if (g->gckind == KGC_INC)
1720 fullinc(L, g);
1721 else
1722 fullgen(L, g);
1723 g->gcemergency = 0;
1724}
1725
1726/* }====================================================== */
1727
1728
1729