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, size, and offset)
256** and link it to 'allgc' list.
257*/
258GCObject *luaC_newobjdt (lua_State *L, int tt, size_t sz, size_t offset) {
259 global_State *g = G(L);
260 char *p = cast_charp(luaM_newobject(L, novariant(tt), sz));
261 GCObject *o = cast(GCObject *, p + offset);
262 o->marked = luaC_white(g);
263 o->tt = tt;
264 o->next = g->allgc;
265 g->allgc = o;
266 return o;
267}
268
269
270GCObject *luaC_newobj (lua_State *L, int tt, size_t sz) {
271 return luaC_newobjdt(L, tt, sz, 0);
272}
273
274/* }====================================================== */
275
276
277
278/*
279** {======================================================
280** Mark functions
281** =======================================================
282*/
283
284
285/*
286** Mark an object. Userdata with no user values, strings, and closed
287** upvalues are visited and turned black here. Open upvalues are
288** already indirectly linked through their respective threads in the
289** 'twups' list, so they don't go to the gray list; nevertheless, they
290** are kept gray to avoid barriers, as their values will be revisited
291** by the thread or by 'remarkupvals'. Other objects are added to the
292** gray list to be visited (and turned black) later. Both userdata and
293** upvalues can call this function recursively, but this recursion goes
294** for at most two levels: An upvalue cannot refer to another upvalue
295** (only closures can), and a userdata's metatable must be a table.
296*/
297static void reallymarkobject (global_State *g, GCObject *o) {
298 switch (o->tt) {
299 case LUA_VSHRSTR:
300 case LUA_VLNGSTR: {
301 set2black(o); /* nothing to visit */
302 break;
303 }
304 case LUA_VUPVAL: {
305 UpVal *uv = gco2upv(o);
306 if (upisopen(uv))
307 set2gray(uv); /* open upvalues are kept gray */
308 else
309 set2black(uv); /* closed upvalues are visited here */
310 markvalue(g, uv->v.p); /* mark its content */
311 break;
312 }
313 case LUA_VUSERDATA: {
314 Udata *u = gco2u(o);
315 if (u->nuvalue == 0) { /* no user values? */
316 markobjectN(g, u->metatable); /* mark its metatable */
317 set2black(u); /* nothing else to mark */
318 break;
319 }
320 /* else... */
321 } /* FALLTHROUGH */
322 case LUA_VLCL: case LUA_VCCL: case LUA_VTABLE:
323 case LUA_VTHREAD: case LUA_VPROTO: {
324 linkobjgclist(o, g->gray); /* to be visited later */
325 break;
326 }
327 default: lua_assert(0); break;
328 }
329}
330
331
332/*
333** mark metamethods for basic types
334*/
335static void markmt (global_State *g) {
336 int i;
337 for (i=0; i < LUA_NUMTAGS; i++)
338 markobjectN(g, g->mt[i]);
339}
340
341
342/*
343** mark all objects in list of being-finalized
344*/
345static lu_mem markbeingfnz (global_State *g) {
346 GCObject *o;
347 lu_mem count = 0;
348 for (o = g->tobefnz; o != NULL; o = o->next) {
349 count++;
350 markobject(g, o);
351 }
352 return count;
353}
354
355
356/*
357** For each non-marked thread, simulates a barrier between each open
358** upvalue and its value. (If the thread is collected, the value will be
359** assigned to the upvalue, but then it can be too late for the barrier
360** to act. The "barrier" does not need to check colors: A non-marked
361** thread must be young; upvalues cannot be older than their threads; so
362** any visited upvalue must be young too.) Also removes the thread from
363** the list, as it was already visited. Removes also threads with no
364** upvalues, as they have nothing to be checked. (If the thread gets an
365** upvalue later, it will be linked in the list again.)
366*/
367static int remarkupvals (global_State *g) {
368 lua_State *thread;
369 lua_State **p = &g->twups;
370 int work = 0; /* estimate of how much work was done here */
371 while ((thread = *p) != NULL) {
372 work++;
373 if (!iswhite(thread) && thread->openupval != NULL)
374 p = &thread->twups; /* keep marked thread with upvalues in the list */
375 else { /* thread is not marked or without upvalues */
376 UpVal *uv;
377 lua_assert(!isold(thread) || thread->openupval == NULL);
378 *p = thread->twups; /* remove thread from the list */
379 thread->twups = thread; /* mark that it is out of list */
380 for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
381 lua_assert(getage(uv) <= getage(thread));
382 work++;
383 if (!iswhite(uv)) { /* upvalue already visited? */
384 lua_assert(upisopen(uv) && isgray(uv));
385 markvalue(g, uv->v.p); /* mark its value */
386 }
387 }
388 }
389 }
390 return work;
391}
392
393
394static void cleargraylists (global_State *g) {
395 g->gray = g->grayagain = NULL;
396 g->weak = g->allweak = g->ephemeron = NULL;
397}
398
399
400/*
401** mark root set and reset all gray lists, to start a new collection
402*/
403static void restartcollection (global_State *g) {
404 cleargraylists(g);
405 markobject(g, g->mainthread);
406 markvalue(g, &g->l_registry);
407 markmt(g);
408 markbeingfnz(g); /* mark any finalizing object left from previous cycle */
409}
410
411/* }====================================================== */
412
413
414/*
415** {======================================================
416** Traverse functions
417** =======================================================
418*/
419
420
421/*
422** Check whether object 'o' should be kept in the 'grayagain' list for
423** post-processing by 'correctgraylist'. (It could put all old objects
424** in the list and leave all the work to 'correctgraylist', but it is
425** more efficient to avoid adding elements that will be removed.) Only
426** TOUCHED1 objects need to be in the list. TOUCHED2 doesn't need to go
427** back to a gray list, but then it must become OLD. (That is what
428** 'correctgraylist' does when it finds a TOUCHED2 object.)
429*/
430static void genlink (global_State *g, GCObject *o) {
431 lua_assert(isblack(o));
432 if (getage(o) == G_TOUCHED1) { /* touched in this cycle? */
433 linkobjgclist(o, g->grayagain); /* link it back in 'grayagain' */
434 } /* everything else do not need to be linked back */
435 else if (getage(o) == G_TOUCHED2)
436 changeage(o, G_TOUCHED2, G_OLD); /* advance age */
437}
438
439
440/*
441** Traverse a table with weak values and link it to proper list. During
442** propagate phase, keep it in 'grayagain' list, to be revisited in the
443** atomic phase. In the atomic phase, if table has any white value,
444** put it in 'weak' list, to be cleared.
445*/
446static void traverseweakvalue (global_State *g, Table *h) {
447 Node *n, *limit = gnodelast(h);
448 /* if there is array part, assume it may have white values (it is not
449 worth traversing it now just to check) */
450 int hasclears = (h->alimit > 0);
451 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
452 if (isempty(gval(n))) /* entry is empty? */
453 clearkey(n); /* clear its key */
454 else {
455 lua_assert(!keyisnil(n));
456 markkey(g, n);
457 if (!hasclears && iscleared(g, gcvalueN(gval(n)))) /* a white value? */
458 hasclears = 1; /* table will have to be cleared */
459 }
460 }
461 if (g->gcstate == GCSatomic && hasclears)
462 linkgclist(h, g->weak); /* has to be cleared later */
463 else
464 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
465}
466
467
468/*
469** Traverse an ephemeron table and link it to proper list. Returns true
470** iff any object was marked during this traversal (which implies that
471** convergence has to continue). During propagation phase, keep table
472** in 'grayagain' list, to be visited again in the atomic phase. In
473** the atomic phase, if table has any white->white entry, it has to
474** be revisited during ephemeron convergence (as that key may turn
475** black). Otherwise, if it has any white key, table has to be cleared
476** (in the atomic phase). In generational mode, some tables
477** must be kept in some gray list for post-processing; this is done
478** by 'genlink'.
479*/
480static int traverseephemeron (global_State *g, Table *h, int inv) {
481 int marked = 0; /* true if an object is marked in this traversal */
482 int hasclears = 0; /* true if table has white keys */
483 int hasww = 0; /* true if table has entry "white-key -> white-value" */
484 unsigned int i;
485 unsigned int asize = luaH_realasize(h);
486 unsigned int nsize = sizenode(h);
487 /* traverse array part */
488 for (i = 0; i < asize; i++) {
489 if (valiswhite(&h->array[i])) {
490 marked = 1;
491 reallymarkobject(g, gcvalue(&h->array[i]));
492 }
493 }
494 /* traverse hash part; if 'inv', traverse descending
495 (see 'convergeephemerons') */
496 for (i = 0; i < nsize; i++) {
497 Node *n = inv ? gnode(h, nsize - 1 - i) : gnode(h, i);
498 if (isempty(gval(n))) /* entry is empty? */
499 clearkey(n); /* clear its key */
500 else if (iscleared(g, gckeyN(n))) { /* key is not marked (yet)? */
501 hasclears = 1; /* table must be cleared */
502 if (valiswhite(gval(n))) /* value not marked yet? */
503 hasww = 1; /* white-white entry */
504 }
505 else if (valiswhite(gval(n))) { /* value not marked yet? */
506 marked = 1;
507 reallymarkobject(g, gcvalue(gval(n))); /* mark it now */
508 }
509 }
510 /* link table into proper list */
511 if (g->gcstate == GCSpropagate)
512 linkgclist(h, g->grayagain); /* must retraverse it in atomic phase */
513 else if (hasww) /* table has white->white entries? */
514 linkgclist(h, g->ephemeron); /* have to propagate again */
515 else if (hasclears) /* table has white keys? */
516 linkgclist(h, g->allweak); /* may have to clean white keys */
517 else
518 genlink(g, obj2gco(h)); /* check whether collector still needs to see it */
519 return marked;
520}
521
522
523static void traversestrongtable (global_State *g, Table *h) {
524 Node *n, *limit = gnodelast(h);
525 unsigned int i;
526 unsigned int asize = luaH_realasize(h);
527 for (i = 0; i < asize; i++) /* traverse array part */
528 markvalue(g, &h->array[i]);
529 for (n = gnode(h, 0); n < limit; n++) { /* traverse hash part */
530 if (isempty(gval(n))) /* entry is empty? */
531 clearkey(n); /* clear its key */
532 else {
533 lua_assert(!keyisnil(n));
534 markkey(g, n);
535 markvalue(g, gval(n));
536 }
537 }
538 genlink(g, obj2gco(h));
539}
540
541
542static lu_mem traversetable (global_State *g, Table *h) {
543 const char *weakkey, *weakvalue;
544 const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
545 TString *smode;
546 markobjectN(g, h->metatable);
547 if (mode && ttisshrstring(mode) && /* is there a weak mode? */
548 (cast_void(smode = tsvalue(mode)),
549 cast_void(weakkey = strchr(getshrstr(smode), 'k')),
550 cast_void(weakvalue = strchr(getshrstr(smode), 'v')),
551 (weakkey || weakvalue))) { /* is really weak? */
552 if (!weakkey) /* strong keys? */
553 traverseweakvalue(g, h);
554 else if (!weakvalue) /* strong values? */
555 traverseephemeron(g, h, 0);
556 else /* all weak */
557 linkgclist(h, g->allweak); /* nothing to traverse now */
558 }
559 else /* not weak */
560 traversestrongtable(g, h);
561 return 1 + h->alimit + 2 * allocsizenode(h);
562}
563
564
565static int traverseudata (global_State *g, Udata *u) {
566 int i;
567 markobjectN(g, u->metatable); /* mark its metatable */
568 for (i = 0; i < u->nuvalue; i++)
569 markvalue(g, &u->uv[i].uv);
570 genlink(g, obj2gco(u));
571 return 1 + u->nuvalue;
572}
573
574
575/*
576** Traverse a prototype. (While a prototype is being build, its
577** arrays can be larger than needed; the extra slots are filled with
578** NULL, so the use of 'markobjectN')
579*/
580static int traverseproto (global_State *g, Proto *f) {
581 int i;
582 markobjectN(g, f->source);
583 for (i = 0; i < f->sizek; i++) /* mark literals */
584 markvalue(g, &f->k[i]);
585 for (i = 0; i < f->sizeupvalues; i++) /* mark upvalue names */
586 markobjectN(g, f->upvalues[i].name);
587 for (i = 0; i < f->sizep; i++) /* mark nested protos */
588 markobjectN(g, f->p[i]);
589 for (i = 0; i < f->sizelocvars; i++) /* mark local-variable names */
590 markobjectN(g, f->locvars[i].varname);
591 return 1 + f->sizek + f->sizeupvalues + f->sizep + f->sizelocvars;
592}
593
594
595static int traverseCclosure (global_State *g, CClosure *cl) {
596 int i;
597 for (i = 0; i < cl->nupvalues; i++) /* mark its upvalues */
598 markvalue(g, &cl->upvalue[i]);
599 return 1 + cl->nupvalues;
600}
601
602/*
603** Traverse a Lua closure, marking its prototype and its upvalues.
604** (Both can be NULL while closure is being created.)
605*/
606static int traverseLclosure (global_State *g, LClosure *cl) {
607 int i;
608 markobjectN(g, cl->p); /* mark its prototype */
609 for (i = 0; i < cl->nupvalues; i++) { /* visit its upvalues */
610 UpVal *uv = cl->upvals[i];
611 markobjectN(g, uv); /* mark upvalue */
612 }
613 return 1 + cl->nupvalues;
614}
615
616
617/*
618** Traverse a thread, marking the elements in the stack up to its top
619** and cleaning the rest of the stack in the final traversal. That
620** ensures that the entire stack have valid (non-dead) objects.
621** Threads have no barriers. In gen. mode, old threads must be visited
622** at every cycle, because they might point to young objects. In inc.
623** mode, the thread can still be modified before the end of the cycle,
624** and therefore it must be visited again in the atomic phase. To ensure
625** these visits, threads must return to a gray list if they are not new
626** (which can only happen in generational mode) or if the traverse is in
627** the propagate phase (which can only happen in incremental mode).
628*/
629static int traversethread (global_State *g, lua_State *th) {
630 UpVal *uv;
631 StkId o = th->stack.p;
632 if (isold(th) || g->gcstate == GCSpropagate)
633 linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
634 if (o == NULL)
635 return 1; /* stack not completely built yet */
636 lua_assert(g->gcstate == GCSatomic ||
637 th->openupval == NULL || isintwups(th));
638 for (; o < th->top.p; o++) /* mark live elements in the stack */
639 markvalue(g, s2v(o));
640 for (uv = th->openupval; uv != NULL; uv = uv->u.open.next)
641 markobject(g, uv); /* open upvalues cannot be collected */
642 if (g->gcstate == GCSatomic) { /* final traversal? */
643 if (!g->gcemergency)
644 luaD_shrinkstack(th); /* do not change stack in emergency cycle */
645 for (o = th->top.p; o < th->stack_last.p + EXTRA_STACK; o++)
646 setnilvalue(s2v(o)); /* clear dead stack slice */
647 /* 'remarkupvals' may have removed thread from 'twups' list */
648 if (!isintwups(th) && th->openupval != NULL) {
649 th->twups = g->twups; /* link it back to the list */
650 g->twups = th;
651 }
652 }
653 return 1 + stacksize(th);
654}
655
656
657/*
658** traverse one gray object, turning it to black.
659*/
660static lu_mem propagatemark (global_State *g) {
661 GCObject *o = g->gray;
662 nw2black(o);
663 g->gray = *getgclist(o); /* remove from 'gray' list */
664 switch (o->tt) {
665 case LUA_VTABLE: return traversetable(g, gco2t(o));
666 case LUA_VUSERDATA: return traverseudata(g, gco2u(o));
667 case LUA_VLCL: return traverseLclosure(g, gco2lcl(o));
668 case LUA_VCCL: return traverseCclosure(g, gco2ccl(o));
669 case LUA_VPROTO: return traverseproto(g, gco2p(o));
670 case LUA_VTHREAD: return traversethread(g, gco2th(o));
671 default: lua_assert(0); return 0;
672 }
673}
674
675
676static lu_mem propagateall (global_State *g) {
677 lu_mem tot = 0;
678 while (g->gray)
679 tot += propagatemark(g);
680 return tot;
681}
682
683
684/*
685** Traverse all ephemeron tables propagating marks from keys to values.
686** Repeat until it converges, that is, nothing new is marked. 'dir'
687** inverts the direction of the traversals, trying to speed up
688** convergence on chains in the same table.
689**
690*/
691static void convergeephemerons (global_State *g) {
692 int changed;
693 int dir = 0;
694 do {
695 GCObject *w;
696 GCObject *next = g->ephemeron; /* get ephemeron list */
697 g->ephemeron = NULL; /* tables may return to this list when traversed */
698 changed = 0;
699 while ((w = next) != NULL) { /* for each ephemeron table */
700 Table *h = gco2t(w);
701 next = h->gclist; /* list is rebuilt during loop */
702 nw2black(h); /* out of the list (for now) */
703 if (traverseephemeron(g, h, dir)) { /* marked some value? */
704 propagateall(g); /* propagate changes */
705 changed = 1; /* will have to revisit all ephemeron tables */
706 }
707 }
708 dir = !dir; /* invert direction next time */
709 } while (changed); /* repeat until no more changes */
710}
711
712/* }====================================================== */
713
714
715/*
716** {======================================================
717** Sweep Functions
718** =======================================================
719*/
720
721
722/*
723** clear entries with unmarked keys from all weaktables in list 'l'
724*/
725static void clearbykeys (global_State *g, GCObject *l) {
726 for (; l; l = gco2t(l)->gclist) {
727 Table *h = gco2t(l);
728 Node *limit = gnodelast(h);
729 Node *n;
730 for (n = gnode(h, 0); n < limit; n++) {
731 if (iscleared(g, gckeyN(n))) /* unmarked key? */
732 setempty(gval(n)); /* remove entry */
733 if (isempty(gval(n))) /* is entry empty? */
734 clearkey(n); /* clear its key */
735 }
736 }
737}
738
739
740/*
741** clear entries with unmarked values from all weaktables in list 'l' up
742** to element 'f'
743*/
744static void clearbyvalues (global_State *g, GCObject *l, GCObject *f) {
745 for (; l != f; l = gco2t(l)->gclist) {
746 Table *h = gco2t(l);
747 Node *n, *limit = gnodelast(h);
748 unsigned int i;
749 unsigned int asize = luaH_realasize(h);
750 for (i = 0; i < asize; i++) {
751 TValue *o = &h->array[i];
752 if (iscleared(g, gcvalueN(o))) /* value was collected? */
753 setempty(o); /* remove entry */
754 }
755 for (n = gnode(h, 0); n < limit; n++) {
756 if (iscleared(g, gcvalueN(gval(n)))) /* unmarked value? */
757 setempty(gval(n)); /* remove entry */
758 if (isempty(gval(n))) /* is entry empty? */
759 clearkey(n); /* clear its key */
760 }
761 }
762}
763
764
765static void freeupval (lua_State *L, UpVal *uv) {
766 if (upisopen(uv))
767 luaF_unlinkupval(uv);
768 luaM_free(L, uv);
769}
770
771
772static void freeobj (lua_State *L, GCObject *o) {
773 switch (o->tt) {
774 case LUA_VPROTO:
775 luaF_freeproto(L, gco2p(o));
776 break;
777 case LUA_VUPVAL:
778 freeupval(L, gco2upv(o));
779 break;
780 case LUA_VLCL: {
781 LClosure *cl = gco2lcl(o);
782 luaM_freemem(L, cl, sizeLclosure(cl->nupvalues));
783 break;
784 }
785 case LUA_VCCL: {
786 CClosure *cl = gco2ccl(o);
787 luaM_freemem(L, cl, sizeCclosure(cl->nupvalues));
788 break;
789 }
790 case LUA_VTABLE:
791 luaH_free(L, gco2t(o));
792 break;
793 case LUA_VTHREAD:
794 luaE_freethread(L, gco2th(o));
795 break;
796 case LUA_VUSERDATA: {
797 Udata *u = gco2u(o);
798 luaM_freemem(L, o, sizeudata(u->nuvalue, u->len));
799 break;
800 }
801 case LUA_VSHRSTR: {
802 TString *ts = gco2ts(o);
803 luaS_remove(L, ts); /* remove it from hash table */
804 luaM_freemem(L, ts, sizelstring(ts->shrlen));
805 break;
806 }
807 case LUA_VLNGSTR: {
808 TString *ts = gco2ts(o);
809 luaM_freemem(L, ts, sizelstring(ts->u.lnglen));
810 break;
811 }
812 default: lua_assert(0);
813 }
814}
815
816
817/*
818** sweep at most 'countin' elements from a list of GCObjects erasing dead
819** objects, where a dead object is one marked with the old (non current)
820** white; change all non-dead objects back to white, preparing for next
821** collection cycle. Return where to continue the traversal or NULL if
822** list is finished. ('*countout' gets the number of elements traversed.)
823*/
824static GCObject **sweeplist (lua_State *L, GCObject **p, int countin,
825 int *countout) {
826 global_State *g = G(L);
827 int ow = otherwhite(g);
828 int i;
829 int white = luaC_white(g); /* current white */
830 for (i = 0; *p != NULL && i < countin; i++) {
831 GCObject *curr = *p;
832 int marked = curr->marked;
833 if (isdeadm(ow, marked)) { /* is 'curr' dead? */
834 *p = curr->next; /* remove 'curr' from list */
835 freeobj(L, curr); /* erase 'curr' */
836 }
837 else { /* change mark to 'white' */
838 curr->marked = cast_byte((marked & ~maskgcbits) | white);
839 p = &curr->next; /* go to next element */
840 }
841 }
842 if (countout)
843 *countout = i; /* number of elements traversed */
844 return (*p == NULL) ? NULL : p;
845}
846
847
848/*
849** sweep a list until a live object (or end of list)
850*/
851static GCObject **sweeptolive (lua_State *L, GCObject **p) {
852 GCObject **old = p;
853 do {
854 p = sweeplist(L, p, 1, NULL);
855 } while (p == old);
856 return p;
857}
858
859/* }====================================================== */
860
861
862/*
863** {======================================================
864** Finalization
865** =======================================================
866*/
867
868/*
869** If possible, shrink string table.
870*/
871static void checkSizes (lua_State *L, global_State *g) {
872 if (!g->gcemergency) {
873 if (g->strt.nuse < g->strt.size / 4) { /* string table too big? */
874 l_mem olddebt = g->GCdebt;
875 luaS_resize(L, g->strt.size / 2);
876 g->GCestimate += g->GCdebt - olddebt; /* correct estimate */
877 }
878 }
879}
880
881
882/*
883** Get the next udata to be finalized from the 'tobefnz' list, and
884** link it back into the 'allgc' list.
885*/
886static GCObject *udata2finalize (global_State *g) {
887 GCObject *o = g->tobefnz; /* get first element */
888 lua_assert(tofinalize(o));
889 g->tobefnz = o->next; /* remove it from 'tobefnz' list */
890 o->next = g->allgc; /* return it to 'allgc' list */
891 g->allgc = o;
892 resetbit(o->marked, FINALIZEDBIT); /* object is "normal" again */
893 if (issweepphase(g))
894 makewhite(g, o); /* "sweep" object */
895 else if (getage(o) == G_OLD1)
896 g->firstold1 = o; /* it is the first OLD1 object in the list */
897 return o;
898}
899
900
901static void dothecall (lua_State *L, void *ud) {
902 UNUSED(ud);
903 luaD_callnoyield(L, L->top.p - 2, 0);
904}
905
906
907static void GCTM (lua_State *L) {
908 global_State *g = G(L);
909 const TValue *tm;
910 TValue v;
911 lua_assert(!g->gcemergency);
912 setgcovalue(L, &v, udata2finalize(g));
913 tm = luaT_gettmbyobj(L, &v, TM_GC);
914 if (!notm(tm)) { /* is there a finalizer? */
915 int status;
916 lu_byte oldah = L->allowhook;
917 int oldgcstp = g->gcstp;
918 g->gcstp |= GCSTPGC; /* avoid GC steps */
919 L->allowhook = 0; /* stop debug hooks during GC metamethod */
920 setobj2s(L, L->top.p++, tm); /* push finalizer... */
921 setobj2s(L, L->top.p++, &v); /* ... and its argument */
922 L->ci->callstatus |= CIST_FIN; /* will run a finalizer */
923 status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top.p - 2), 0);
924 L->ci->callstatus &= ~CIST_FIN; /* not running a finalizer anymore */
925 L->allowhook = oldah; /* restore hooks */
926 g->gcstp = oldgcstp; /* restore state */
927 if (l_unlikely(status != LUA_OK)) { /* error while running __gc? */
928 luaE_warnerror(L, "__gc");
929 L->top.p--; /* pops error object */
930 }
931 }
932}
933
934
935/*
936** Call a few finalizers
937*/
938static int runafewfinalizers (lua_State *L, int n) {
939 global_State *g = G(L);
940 int i;
941 for (i = 0; i < n && g->tobefnz; i++)
942 GCTM(L); /* call one finalizer */
943 return i;
944}
945
946
947/*
948** call all pending finalizers
949*/
950static void callallpendingfinalizers (lua_State *L) {
951 global_State *g = G(L);
952 while (g->tobefnz)
953 GCTM(L);
954}
955
956
957/*
958** find last 'next' field in list 'p' list (to add elements in its end)
959*/
960static GCObject **findlast (GCObject **p) {
961 while (*p != NULL)
962 p = &(*p)->next;
963 return p;
964}
965
966
967/*
968** Move all unreachable objects (or 'all' objects) that need
969** finalization from list 'finobj' to list 'tobefnz' (to be finalized).
970** (Note that objects after 'finobjold1' cannot be white, so they
971** don't need to be traversed. In incremental mode, 'finobjold1' is NULL,
972** so the whole list is traversed.)
973*/
974static void separatetobefnz (global_State *g, int all) {
975 GCObject *curr;
976 GCObject **p = &g->finobj;
977 GCObject **lastnext = findlast(&g->tobefnz);
978 while ((curr = *p) != g->finobjold1) { /* traverse all finalizable objects */
979 lua_assert(tofinalize(curr));
980 if (!(iswhite(curr) || all)) /* not being collected? */
981 p = &curr->next; /* don't bother with it */
982 else {
983 if (curr == g->finobjsur) /* removing 'finobjsur'? */
984 g->finobjsur = curr->next; /* correct it */
985 *p = curr->next; /* remove 'curr' from 'finobj' list */
986 curr->next = *lastnext; /* link at the end of 'tobefnz' list */
987 *lastnext = curr;
988 lastnext = &curr->next;
989 }
990 }
991}
992
993
994/*
995** If pointer 'p' points to 'o', move it to the next element.
996*/
997static void checkpointer (GCObject **p, GCObject *o) {
998 if (o == *p)
999 *p = o->next;
1000}
1001
1002
1003/*
1004** Correct pointers to objects inside 'allgc' list when
1005** object 'o' is being removed from the list.
1006*/
1007static void correctpointers (global_State *g, GCObject *o) {
1008 checkpointer(&g->survival, o);
1009 checkpointer(&g->old1, o);
1010 checkpointer(&g->reallyold, o);
1011 checkpointer(&g->firstold1, o);
1012}
1013
1014
1015/*
1016** if object 'o' has a finalizer, remove it from 'allgc' list (must
1017** search the list to find it) and link it in 'finobj' list.
1018*/
1019void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
1020 global_State *g = G(L);
1021 if (tofinalize(o) || /* obj. is already marked... */
1022 gfasttm(g, mt, TM_GC) == NULL || /* or has no finalizer... */
1023 (g->gcstp & GCSTPCLS)) /* or closing state? */
1024 return; /* nothing to be done */
1025 else { /* move 'o' to 'finobj' list */
1026 GCObject **p;
1027 if (issweepphase(g)) {
1028 makewhite(g, o); /* "sweep" object 'o' */
1029 if (g->sweepgc == &o->next) /* should not remove 'sweepgc' object */
1030 g->sweepgc = sweeptolive(L, g->sweepgc); /* change 'sweepgc' */
1031 }
1032 else
1033 correctpointers(g, o);
1034 /* search for pointer pointing to 'o' */
1035 for (p = &g->allgc; *p != o; p = &(*p)->next) { /* empty */ }
1036 *p = o->next; /* remove 'o' from 'allgc' list */
1037 o->next = g->finobj; /* link it in 'finobj' list */
1038 g->finobj = o;
1039 l_setbit(o->marked, FINALIZEDBIT); /* mark it as such */
1040 }
1041}
1042
1043/* }====================================================== */
1044
1045
1046/*
1047** {======================================================
1048** Generational Collector
1049** =======================================================
1050*/
1051
1052
1053/*
1054** Set the "time" to wait before starting a new GC cycle; cycle will
1055** start when memory use hits the threshold of ('estimate' * pause /
1056** PAUSEADJ). (Division by 'estimate' should be OK: it cannot be zero,
1057** because Lua cannot even start with less than PAUSEADJ bytes).
1058*/
1059static void setpause (global_State *g) {
1060 l_mem threshold, debt;
1061 int pause = getgcparam(g->gcpause);
1062 l_mem estimate = g->GCestimate / PAUSEADJ; /* adjust 'estimate' */
1063 lua_assert(estimate > 0);
1064 threshold = (pause < MAX_LMEM / estimate) /* overflow? */
1065 ? estimate * pause /* no overflow */
1066 : MAX_LMEM; /* overflow; truncate to maximum */
1067 debt = gettotalbytes(g) - threshold;
1068 if (debt > 0) debt = 0;
1069 luaE_setdebt(g, debt);
1070}
1071
1072
1073/*
1074** Sweep a list of objects to enter generational mode. Deletes dead
1075** objects and turns the non dead to old. All non-dead threads---which
1076** are now old---must be in a gray list. Everything else is not in a
1077** gray list. Open upvalues are also kept gray.
1078*/
1079static void sweep2old (lua_State *L, GCObject **p) {
1080 GCObject *curr;
1081 global_State *g = G(L);
1082 while ((curr = *p) != NULL) {
1083 if (iswhite(curr)) { /* is 'curr' dead? */
1084 lua_assert(isdead(g, curr));
1085 *p = curr->next; /* remove 'curr' from list */
1086 freeobj(L, curr); /* erase 'curr' */
1087 }
1088 else { /* all surviving objects become old */
1089 setage(curr, G_OLD);
1090 if (curr->tt == LUA_VTHREAD) { /* threads must be watched */
1091 lua_State *th = gco2th(curr);
1092 linkgclist(th, g->grayagain); /* insert into 'grayagain' list */
1093 }
1094 else if (curr->tt == LUA_VUPVAL && upisopen(gco2upv(curr)))
1095 set2gray(curr); /* open upvalues are always gray */
1096 else /* everything else is black */
1097 nw2black(curr);
1098 p = &curr->next; /* go to next element */
1099 }
1100 }
1101}
1102
1103
1104/*
1105** Sweep for generational mode. Delete dead objects. (Because the
1106** collection is not incremental, there are no "new white" objects
1107** during the sweep. So, any white object must be dead.) For
1108** non-dead objects, advance their ages and clear the color of
1109** new objects. (Old objects keep their colors.)
1110** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced
1111** here, because these old-generation objects are usually not swept
1112** here. They will all be advanced in 'correctgraylist'. That function
1113** will also remove objects turned white here from any gray list.
1114*/
1115static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
1116 GCObject *limit, GCObject **pfirstold1) {
1117 static const lu_byte nextage[] = {
1118 G_SURVIVAL, /* from G_NEW */
1119 G_OLD1, /* from G_SURVIVAL */
1120 G_OLD1, /* from G_OLD0 */
1121 G_OLD, /* from G_OLD1 */
1122 G_OLD, /* from G_OLD (do not change) */
1123 G_TOUCHED1, /* from G_TOUCHED1 (do not change) */
1124 G_TOUCHED2 /* from G_TOUCHED2 (do not change) */
1125 };
1126 int white = luaC_white(g);
1127 GCObject *curr;
1128 while ((curr = *p) != limit) {
1129 if (iswhite(curr)) { /* is 'curr' dead? */
1130 lua_assert(!isold(curr) && isdead(g, curr));
1131 *p = curr->next; /* remove 'curr' from list */
1132 freeobj(L, curr); /* erase 'curr' */
1133 }
1134 else { /* correct mark and age */
1135 if (getage(curr) == G_NEW) { /* new objects go back to white */
1136 int marked = curr->marked & ~maskgcbits; /* erase GC bits */
1137 curr->marked = cast_byte(marked | G_SURVIVAL | white);
1138 }
1139 else { /* all other objects will be old, and so keep their color */
1140 setage(curr, nextage[getage(curr)]);
1141 if (getage(curr) == G_OLD1 && *pfirstold1 == NULL)
1142 *pfirstold1 = curr; /* first OLD1 object in the list */
1143 }
1144 p = &curr->next; /* go to next element */
1145 }
1146 }
1147 return p;
1148}
1149
1150
1151/*
1152** Traverse a list making all its elements white and clearing their
1153** age. In incremental mode, all objects are 'new' all the time,
1154** except for fixed strings (which are always old).
1155*/
1156static void whitelist (global_State *g, GCObject *p) {
1157 int white = luaC_white(g);
1158 for (; p != NULL; p = p->next)
1159 p->marked = cast_byte((p->marked & ~maskgcbits) | white);
1160}
1161
1162
1163/*
1164** Correct a list of gray objects. Return pointer to where rest of the
1165** list should be linked.
1166** Because this correction is done after sweeping, young objects might
1167** be turned white and still be in the list. They are only removed.
1168** 'TOUCHED1' objects are advanced to 'TOUCHED2' and remain on the list;
1169** Non-white threads also remain on the list; 'TOUCHED2' objects become
1170** regular old; they and anything else are removed from the list.
1171*/
1172static GCObject **correctgraylist (GCObject **p) {
1173 GCObject *curr;
1174 while ((curr = *p) != NULL) {
1175 GCObject **next = getgclist(curr);
1176 if (iswhite(curr))
1177 goto remove; /* remove all white objects */
1178 else if (getage(curr) == G_TOUCHED1) { /* touched in this cycle? */
1179 lua_assert(isgray(curr));
1180 nw2black(curr); /* make it black, for next barrier */
1181 changeage(curr, G_TOUCHED1, G_TOUCHED2);
1182 goto remain; /* keep it in the list and go to next element */
1183 }
1184 else if (curr->tt == LUA_VTHREAD) {
1185 lua_assert(isgray(curr));
1186 goto remain; /* keep non-white threads on the list */
1187 }
1188 else { /* everything else is removed */
1189 lua_assert(isold(curr)); /* young objects should be white here */
1190 if (getage(curr) == G_TOUCHED2) /* advance from TOUCHED2... */
1191 changeage(curr, G_TOUCHED2, G_OLD); /* ... to OLD */
1192 nw2black(curr); /* make object black (to be removed) */
1193 goto remove;
1194 }
1195 remove: *p = *next; continue;
1196 remain: p = next; continue;
1197 }
1198 return p;
1199}
1200
1201
1202/*
1203** Correct all gray lists, coalescing them into 'grayagain'.
1204*/
1205static void correctgraylists (global_State *g) {
1206 GCObject **list = correctgraylist(&g->grayagain);
1207 *list = g->weak; g->weak = NULL;
1208 list = correctgraylist(list);
1209 *list = g->allweak; g->allweak = NULL;
1210 list = correctgraylist(list);
1211 *list = g->ephemeron; g->ephemeron = NULL;
1212 correctgraylist(list);
1213}
1214
1215
1216/*
1217** Mark black 'OLD1' objects when starting a new young collection.
1218** Gray objects are already in some gray list, and so will be visited
1219** in the atomic step.
1220*/
1221static void markold (global_State *g, GCObject *from, GCObject *to) {
1222 GCObject *p;
1223 for (p = from; p != to; p = p->next) {
1224 if (getage(p) == G_OLD1) {
1225 lua_assert(!iswhite(p));
1226 changeage(p, G_OLD1, G_OLD); /* now they are old */
1227 if (isblack(p))
1228 reallymarkobject(g, p);
1229 }
1230 }
1231}
1232
1233
1234/*
1235** Finish a young-generation collection.
1236*/
1237static void finishgencycle (lua_State *L, global_State *g) {
1238 correctgraylists(g);
1239 checkSizes(L, g);
1240 g->gcstate = GCSpropagate; /* skip restart */
1241 if (!g->gcemergency)
1242 callallpendingfinalizers(L);
1243}
1244
1245
1246/*
1247** Does a young collection. First, mark 'OLD1' objects. Then does the
1248** atomic step. Then, sweep all lists and advance pointers. Finally,
1249** finish the collection.
1250*/
1251static void youngcollection (lua_State *L, global_State *g) {
1252 GCObject **psurvival; /* to point to first non-dead survival object */
1253 GCObject *dummy; /* dummy out parameter to 'sweepgen' */
1254 lua_assert(g->gcstate == GCSpropagate);
1255 if (g->firstold1) { /* are there regular OLD1 objects? */
1256 markold(g, g->firstold1, g->reallyold); /* mark them */
1257 g->firstold1 = NULL; /* no more OLD1 objects (for now) */
1258 }
1259 markold(g, g->finobj, g->finobjrold);
1260 markold(g, g->tobefnz, NULL);
1261 atomic(L);
1262
1263 /* sweep nursery and get a pointer to its last live element */
1264 g->gcstate = GCSswpallgc;
1265 psurvival = sweepgen(L, g, &g->allgc, g->survival, &g->firstold1);
1266 /* sweep 'survival' */
1267 sweepgen(L, g, psurvival, g->old1, &g->firstold1);
1268 g->reallyold = g->old1;
1269 g->old1 = *psurvival; /* 'survival' survivals are old now */
1270 g->survival = g->allgc; /* all news are survivals */
1271
1272 /* repeat for 'finobj' lists */
1273 dummy = NULL; /* no 'firstold1' optimization for 'finobj' lists */
1274 psurvival = sweepgen(L, g, &g->finobj, g->finobjsur, &dummy);
1275 /* sweep 'survival' */
1276 sweepgen(L, g, psurvival, g->finobjold1, &dummy);
1277 g->finobjrold = g->finobjold1;
1278 g->finobjold1 = *psurvival; /* 'survival' survivals are old now */
1279 g->finobjsur = g->finobj; /* all news are survivals */
1280
1281 sweepgen(L, g, &g->tobefnz, NULL, &dummy);
1282 finishgencycle(L, g);
1283}
1284
1285
1286/*
1287** Clears all gray lists, sweeps objects, and prepare sublists to enter
1288** generational mode. The sweeps remove dead objects and turn all
1289** surviving objects to old. Threads go back to 'grayagain'; everything
1290** else is turned black (not in any gray list).
1291*/
1292static void atomic2gen (lua_State *L, global_State *g) {
1293 cleargraylists(g);
1294 /* sweep all elements making them old */
1295 g->gcstate = GCSswpallgc;
1296 sweep2old(L, &g->allgc);
1297 /* everything alive now is old */
1298 g->reallyold = g->old1 = g->survival = g->allgc;
1299 g->firstold1 = NULL; /* there are no OLD1 objects anywhere */
1300
1301 /* repeat for 'finobj' lists */
1302 sweep2old(L, &g->finobj);
1303 g->finobjrold = g->finobjold1 = g->finobjsur = g->finobj;
1304
1305 sweep2old(L, &g->tobefnz);
1306
1307 g->gckind = KGC_GEN;
1308 g->lastatomic = 0;
1309 g->GCestimate = gettotalbytes(g); /* base for memory control */
1310 finishgencycle(L, g);
1311}
1312
1313
1314/*
1315** Set debt for the next minor collection, which will happen when
1316** memory grows 'genminormul'%.
1317*/
1318static void setminordebt (global_State *g) {
1319 luaE_setdebt(g, -(cast(l_mem, (gettotalbytes(g) / 100)) * g->genminormul));
1320}
1321
1322
1323/*
1324** Enter generational mode. Must go until the end of an atomic cycle
1325** to ensure that all objects are correctly marked and weak tables
1326** are cleared. Then, turn all objects into old and finishes the
1327** collection.
1328*/
1329static lu_mem entergen (lua_State *L, global_State *g) {
1330 lu_mem numobjs;
1331 luaC_runtilstate(L, bitmask(GCSpause)); /* prepare to start a new cycle */
1332 luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
1333 numobjs = atomic(L); /* propagates all and then do the atomic stuff */
1334 atomic2gen(L, g);
1335 setminordebt(g); /* set debt assuming next cycle will be minor */
1336 return numobjs;
1337}
1338
1339
1340/*
1341** Enter incremental mode. Turn all objects white, make all
1342** intermediate lists point to NULL (to avoid invalid pointers),
1343** and go to the pause state.
1344*/
1345static void enterinc (global_State *g) {
1346 whitelist(g, g->allgc);
1347 g->reallyold = g->old1 = g->survival = NULL;
1348 whitelist(g, g->finobj);
1349 whitelist(g, g->tobefnz);
1350 g->finobjrold = g->finobjold1 = g->finobjsur = NULL;
1351 g->gcstate = GCSpause;
1352 g->gckind = KGC_INC;
1353 g->lastatomic = 0;
1354}
1355
1356
1357/*
1358** Change collector mode to 'newmode'.
1359*/
1360void luaC_changemode (lua_State *L, int newmode) {
1361 global_State *g = G(L);
1362 if (newmode != g->gckind) {
1363 if (newmode == KGC_GEN) /* entering generational mode? */
1364 entergen(L, g);
1365 else
1366 enterinc(g); /* entering incremental mode */
1367 }
1368 g->lastatomic = 0;
1369}
1370
1371
1372/*
1373** Does a full collection in generational mode.
1374*/
1375static lu_mem fullgen (lua_State *L, global_State *g) {
1376 enterinc(g);
1377 return entergen(L, g);
1378}
1379
1380
1381/*
1382** Does a major collection after last collection was a "bad collection".
1383**
1384** When the program is building a big structure, it allocates lots of
1385** memory but generates very little garbage. In those scenarios,
1386** the generational mode just wastes time doing small collections, and
1387** major collections are frequently what we call a "bad collection", a
1388** collection that frees too few objects. To avoid the cost of switching
1389** between generational mode and the incremental mode needed for full
1390** (major) collections, the collector tries to stay in incremental mode
1391** after a bad collection, and to switch back to generational mode only
1392** after a "good" collection (one that traverses less than 9/8 objects
1393** of the previous one).
1394** The collector must choose whether to stay in incremental mode or to
1395** switch back to generational mode before sweeping. At this point, it
1396** does not know the real memory in use, so it cannot use memory to
1397** decide whether to return to generational mode. Instead, it uses the
1398** number of objects traversed (returned by 'atomic') as a proxy. The
1399** field 'g->lastatomic' keeps this count from the last collection.
1400** ('g->lastatomic != 0' also means that the last collection was bad.)
1401*/
1402static void stepgenfull (lua_State *L, global_State *g) {
1403 lu_mem newatomic; /* count of traversed objects */
1404 lu_mem lastatomic = g->lastatomic; /* count from last collection */
1405 if (g->gckind == KGC_GEN) /* still in generational mode? */
1406 enterinc(g); /* enter incremental mode */
1407 luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
1408 newatomic = atomic(L); /* mark everybody */
1409 if (newatomic < lastatomic + (lastatomic >> 3)) { /* good collection? */
1410 atomic2gen(L, g); /* return to generational mode */
1411 setminordebt(g);
1412 }
1413 else { /* another bad collection; stay in incremental mode */
1414 g->GCestimate = gettotalbytes(g); /* first estimate */
1415 entersweep(L);
1416 luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
1417 setpause(g);
1418 g->lastatomic = newatomic;
1419 }
1420}
1421
1422
1423/*
1424** Does a generational "step".
1425** Usually, this means doing a minor collection and setting the debt to
1426** make another collection when memory grows 'genminormul'% larger.
1427**
1428** However, there are exceptions. If memory grows 'genmajormul'%
1429** larger than it was at the end of the last major collection (kept
1430** in 'g->GCestimate'), the function does a major collection. At the
1431** end, it checks whether the major collection was able to free a
1432** decent amount of memory (at least half the growth in memory since
1433** previous major collection). If so, the collector keeps its state,
1434** and the next collection will probably be minor again. Otherwise,
1435** we have what we call a "bad collection". In that case, set the field
1436** 'g->lastatomic' to signal that fact, so that the next collection will
1437** go to 'stepgenfull'.
1438**
1439** 'GCdebt <= 0' means an explicit call to GC step with "size" zero;
1440** in that case, do a minor collection.
1441*/
1442static void genstep (lua_State *L, global_State *g) {
1443 if (g->lastatomic != 0) /* last collection was a bad one? */
1444 stepgenfull(L, g); /* do a full step */
1445 else {
1446 lu_mem majorbase = g->GCestimate; /* memory after last major collection */
1447 lu_mem majorinc = (majorbase / 100) * getgcparam(g->genmajormul);
1448 if (g->GCdebt > 0 && gettotalbytes(g) > majorbase + majorinc) {
1449 lu_mem numobjs = fullgen(L, g); /* do a major collection */
1450 if (gettotalbytes(g) < majorbase + (majorinc / 2)) {
1451 /* collected at least half of memory growth since last major
1452 collection; keep doing minor collections. */
1453 lua_assert(g->lastatomic == 0);
1454 }
1455 else { /* bad collection */
1456 g->lastatomic = numobjs; /* signal that last collection was bad */
1457 setpause(g); /* do a long wait for next (major) collection */
1458 }
1459 }
1460 else { /* regular case; do a minor collection */
1461 youngcollection(L, g);
1462 setminordebt(g);
1463 g->GCestimate = majorbase; /* preserve base value */
1464 }
1465 }
1466 lua_assert(isdecGCmodegen(g));
1467}
1468
1469/* }====================================================== */
1470
1471
1472/*
1473** {======================================================
1474** GC control
1475** =======================================================
1476*/
1477
1478
1479/*
1480** Enter first sweep phase.
1481** The call to 'sweeptolive' makes the pointer point to an object
1482** inside the list (instead of to the header), so that the real sweep do
1483** not need to skip objects created between "now" and the start of the
1484** real sweep.
1485*/
1486static void entersweep (lua_State *L) {
1487 global_State *g = G(L);
1488 g->gcstate = GCSswpallgc;
1489 lua_assert(g->sweepgc == NULL);
1490 g->sweepgc = sweeptolive(L, &g->allgc);
1491}
1492
1493
1494/*
1495** Delete all objects in list 'p' until (but not including) object
1496** 'limit'.
1497*/
1498static void deletelist (lua_State *L, GCObject *p, GCObject *limit) {
1499 while (p != limit) {
1500 GCObject *next = p->next;
1501 freeobj(L, p);
1502 p = next;
1503 }
1504}
1505
1506
1507/*
1508** Call all finalizers of the objects in the given Lua state, and
1509** then free all objects, except for the main thread.
1510*/
1511void luaC_freeallobjects (lua_State *L) {
1512 global_State *g = G(L);
1513 g->gcstp = GCSTPCLS; /* no extra finalizers after here */
1514 luaC_changemode(L, KGC_INC);
1515 separatetobefnz(g, 1); /* separate all objects with finalizers */
1516 lua_assert(g->finobj == NULL);
1517 callallpendingfinalizers(L);
1518 deletelist(L, g->allgc, obj2gco(g->mainthread));
1519 lua_assert(g->finobj == NULL); /* no new finalizers */
1520 deletelist(L, g->fixedgc, NULL); /* collect fixed objects */
1521 lua_assert(g->strt.nuse == 0);
1522}
1523
1524
1525static lu_mem atomic (lua_State *L) {
1526 global_State *g = G(L);
1527 lu_mem work = 0;
1528 GCObject *origweak, *origall;
1529 GCObject *grayagain = g->grayagain; /* save original list */
1530 g->grayagain = NULL;
1531 lua_assert(g->ephemeron == NULL && g->weak == NULL);
1532 lua_assert(!iswhite(g->mainthread));
1533 g->gcstate = GCSatomic;
1534 markobject(g, L); /* mark running thread */
1535 /* registry and global metatables may be changed by API */
1536 markvalue(g, &g->l_registry);
1537 markmt(g); /* mark global metatables */
1538 work += propagateall(g); /* empties 'gray' list */
1539 /* remark occasional upvalues of (maybe) dead threads */
1540 work += remarkupvals(g);
1541 work += propagateall(g); /* propagate changes */
1542 g->gray = grayagain;
1543 work += propagateall(g); /* traverse 'grayagain' list */
1544 convergeephemerons(g);
1545 /* at this point, all strongly accessible objects are marked. */
1546 /* Clear values from weak tables, before checking finalizers */
1547 clearbyvalues(g, g->weak, NULL);
1548 clearbyvalues(g, g->allweak, NULL);
1549 origweak = g->weak; origall = g->allweak;
1550 separatetobefnz(g, 0); /* separate objects to be finalized */
1551 work += markbeingfnz(g); /* mark objects that will be finalized */
1552 work += propagateall(g); /* remark, to propagate 'resurrection' */
1553 convergeephemerons(g);
1554 /* at this point, all resurrected objects are marked. */
1555 /* remove dead objects from weak tables */
1556 clearbykeys(g, g->ephemeron); /* clear keys from all ephemeron tables */
1557 clearbykeys(g, g->allweak); /* clear keys from all 'allweak' tables */
1558 /* clear values from resurrected weak tables */
1559 clearbyvalues(g, g->weak, origweak);
1560 clearbyvalues(g, g->allweak, origall);
1561 luaS_clearcache(g);
1562 g->currentwhite = cast_byte(otherwhite(g)); /* flip current white */
1563 lua_assert(g->gray == NULL);
1564 return work; /* estimate of slots marked by 'atomic' */
1565}
1566
1567
1568static int sweepstep (lua_State *L, global_State *g,
1569 int nextstate, GCObject **nextlist) {
1570 if (g->sweepgc) {
1571 l_mem olddebt = g->GCdebt;
1572 int count;
1573 g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX, &count);
1574 g->GCestimate += g->GCdebt - olddebt; /* update estimate */
1575 return count;
1576 }
1577 else { /* enter next state */
1578 g->gcstate = nextstate;
1579 g->sweepgc = nextlist;
1580 return 0; /* no work done */
1581 }
1582}
1583
1584
1585static lu_mem singlestep (lua_State *L) {
1586 global_State *g = G(L);
1587 lu_mem work;
1588 lua_assert(!g->gcstopem); /* collector is not reentrant */
1589 g->gcstopem = 1; /* no emergency collections while collecting */
1590 switch (g->gcstate) {
1591 case GCSpause: {
1592 restartcollection(g);
1593 g->gcstate = GCSpropagate;
1594 work = 1;
1595 break;
1596 }
1597 case GCSpropagate: {
1598 if (g->gray == NULL) { /* no more gray objects? */
1599 g->gcstate = GCSenteratomic; /* finish propagate phase */
1600 work = 0;
1601 }
1602 else
1603 work = propagatemark(g); /* traverse one gray object */
1604 break;
1605 }
1606 case GCSenteratomic: {
1607 work = atomic(L); /* work is what was traversed by 'atomic' */
1608 entersweep(L);
1609 g->GCestimate = gettotalbytes(g); /* first estimate */
1610 break;
1611 }
1612 case GCSswpallgc: { /* sweep "regular" objects */
1613 work = sweepstep(L, g, GCSswpfinobj, &g->finobj);
1614 break;
1615 }
1616 case GCSswpfinobj: { /* sweep objects with finalizers */
1617 work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
1618 break;
1619 }
1620 case GCSswptobefnz: { /* sweep objects to be finalized */
1621 work = sweepstep(L, g, GCSswpend, NULL);
1622 break;
1623 }
1624 case GCSswpend: { /* finish sweeps */
1625 checkSizes(L, g);
1626 g->gcstate = GCScallfin;
1627 work = 0;
1628 break;
1629 }
1630 case GCScallfin: { /* call remaining finalizers */
1631 if (g->tobefnz && !g->gcemergency) {
1632 g->gcstopem = 0; /* ok collections during finalizers */
1633 work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST;
1634 }
1635 else { /* emergency mode or no more finalizers */
1636 g->gcstate = GCSpause; /* finish collection */
1637 work = 0;
1638 }
1639 break;
1640 }
1641 default: lua_assert(0); return 0;
1642 }
1643 g->gcstopem = 0;
1644 return work;
1645}
1646
1647
1648/*
1649** advances the garbage collector until it reaches a state allowed
1650** by 'statemask'
1651*/
1652void luaC_runtilstate (lua_State *L, int statesmask) {
1653 global_State *g = G(L);
1654 while (!testbit(statesmask, g->gcstate))
1655 singlestep(L);
1656}
1657
1658
1659
1660/*
1661** Performs a basic incremental step. The debt and step size are
1662** converted from bytes to "units of work"; then the function loops
1663** running single steps until adding that many units of work or
1664** finishing a cycle (pause state). Finally, it sets the debt that
1665** controls when next step will be performed.
1666*/
1667static void incstep (lua_State *L, global_State *g) {
1668 int stepmul = (getgcparam(g->gcstepmul) | 1); /* avoid division by 0 */
1669 l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
1670 l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
1671 ? ((cast(l_mem, 1) << g->gcstepsize) / WORK2MEM) * stepmul
1672 : MAX_LMEM; /* overflow; keep maximum value */
1673 do { /* repeat until pause or enough "credit" (negative debt) */
1674 lu_mem work = singlestep(L); /* perform one single step */
1675 debt -= work;
1676 } while (debt > -stepsize && g->gcstate != GCSpause);
1677 if (g->gcstate == GCSpause)
1678 setpause(g); /* pause until next cycle */
1679 else {
1680 debt = (debt / stepmul) * WORK2MEM; /* convert 'work units' to bytes */
1681 luaE_setdebt(g, debt);
1682 }
1683}
1684
1685/*
1686** Performs a basic GC step if collector is running. (If collector is
1687** not running, set a reasonable debt to avoid it being called at
1688** every single check.)
1689*/
1690void luaC_step (lua_State *L) {
1691 global_State *g = G(L);
1692 if (!gcrunning(g)) /* not running? */
1693 luaE_setdebt(g, -2000);
1694 else {
1695 if(isdecGCmodegen(g))
1696 genstep(L, g);
1697 else
1698 incstep(L, g);
1699 }
1700}
1701
1702
1703/*
1704** Perform a full collection in incremental mode.
1705** Before running the collection, check 'keepinvariant'; if it is true,
1706** there may be some objects marked as black, so the collector has
1707** to sweep all objects to turn them back to white (as white has not
1708** changed, nothing will be collected).
1709*/
1710static void fullinc (lua_State *L, global_State *g) {
1711 if (keepinvariant(g)) /* black objects? */
1712 entersweep(L); /* sweep everything to turn them back to white */
1713 /* finish any pending sweep phase to start a new cycle */
1714 luaC_runtilstate(L, bitmask(GCSpause));
1715 luaC_runtilstate(L, bitmask(GCSpropagate)); /* start new cycle */
1716 g->gcstate = GCSenteratomic; /* go straight to atomic phase */
1717 luaC_runtilstate(L, bitmask(GCScallfin)); /* run up to finalizers */
1718 /* estimate must be correct after a full GC cycle */
1719 lua_assert(g->GCestimate == gettotalbytes(g));
1720 luaC_runtilstate(L, bitmask(GCSpause)); /* finish collection */
1721 setpause(g);
1722}
1723
1724
1725/*
1726** Performs a full GC cycle; if 'isemergency', set a flag to avoid
1727** some operations which could change the interpreter state in some
1728** unexpected ways (running finalizers and shrinking some structures).
1729*/
1730void luaC_fullgc (lua_State *L, int isemergency) {
1731 global_State *g = G(L);
1732 lua_assert(!g->gcemergency);
1733 g->gcemergency = isemergency; /* set flag */
1734 if (g->gckind == KGC_INC)
1735 fullinc(L, g);
1736 else
1737 fullgen(L, g);
1738 g->gcemergency = 0;
1739}
1740
1741/* }====================================================== */
1742
1743