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lua/lgc.c

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/*
** $Id: lgc.c,v 1.158 2002/11/14 11:51:50 roberto Exp roberto $
** Garbage Collector
** See Copyright Notice in lua.h
*/
#include <string.h>
#include "lua.h"
#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"
typedef struct GCState {
GCObject *tmark; /* list of marked objects to be traversed */
GCObject *wk; /* list of traversed key-weak tables (to be cleared) */
GCObject *wv; /* list of traversed value-weak tables */
GCObject *wkv; /* list of traversed key-value weak tables */
global_State *G;
} GCState;
/*
** some userful bit tricks
*/
#define setbit(x,b) ((x) |= (1<<(b)))
#define resetbit(x,b) ((x) &= cast(lu_byte, ~(1<<(b))))
#define testbit(x,b) ((x) & (1<<(b)))
#define unmark(x) resetbit((x)->gch.marked, 0)
#define ismarked(x) ((x)->gch.marked & ((1<<4)|1))
#define strmark(s) setbit((s)->tsv.marked, 0)
#define strunmark(s) resetbit((s)->tsv.marked, 0)
#define isfinalized(u) (!testbit((u)->uv.marked, 1))
#define markfinalized(u) resetbit((u)->uv.marked, 1)
#define KEYWEAKBIT 1
#define VALUEWEAKBIT 2
#define KEYWEAK (1<<KEYWEAKBIT)
#define VALUEWEAK (1<<VALUEWEAKBIT)
#define markobject(st,o) { checkconsistency(o); \
if (iscollectable(o) && !ismarked(gcvalue(o))) reallymarkobject(st,gcvalue(o)); }
#define condmarkobject(st,o,c) { checkconsistency(o); \
if (iscollectable(o) && !ismarked(gcvalue(o)) && (c)) \
reallymarkobject(st,gcvalue(o)); }
#define markvalue(st,t) { if (!ismarked(valtogco(t))) \
reallymarkobject(st, valtogco(t)); }
static void reallymarkobject (GCState *st, GCObject *o) {
lua_assert(!ismarked(o));
setbit(o->gch.marked, 0); /* mark object */
switch (o->gch.tt) {
case LUA_TUSERDATA: {
markvalue(st, gcotou(o)->uv.metatable);
break;
}
case LUA_TFUNCTION: {
gcotocl(o)->c.gclist = st->tmark;
st->tmark = o;
break;
}
case LUA_TTABLE: {
gcotoh(o)->gclist = st->tmark;
st->tmark = o;
break;
}
case LUA_TTHREAD: {
gcototh(o)->gclist = st->tmark;
st->tmark = o;
break;
}
case LUA_TPROTO: {
gcotop(o)->gclist = st->tmark;
st->tmark = o;
break;
}
default: lua_assert(o->gch.tt == LUA_TSTRING);
}
}
static void marktmu (GCState *st) {
GCObject *u;
for (u = st->G->tmudata; u; u = u->gch.next) {
unmark(u); /* may be marked, if left from previous GC */
reallymarkobject(st, u);
}
}
/* move `dead' udata that need finalization to list `tmudata' */
static void separateudata (lua_State *L) {
GCObject **p = &G(L)->rootudata;
GCObject *curr;
GCObject *collected = NULL; /* to collect udata with gc event */
GCObject **lastcollected = &collected;
while ((curr = *p) != NULL) {
lua_assert(curr->gch.tt == LUA_TUSERDATA);
if (ismarked(curr) || isfinalized(gcotou(curr)))
p = &curr->gch.next; /* don't bother with them */
else if (fasttm(L, gcotou(curr)->uv.metatable, TM_GC) == NULL) {
markfinalized(gcotou(curr)); /* don't need finalization */
p = &curr->gch.next;
}
else { /* must call its gc method */
*p = curr->gch.next;
curr->gch.next = NULL; /* link `curr' at the end of `collected' list */
*lastcollected = curr;
lastcollected = &curr->gch.next;
}
}
/* insert collected udata with gc event into `tmudata' list */
*lastcollected = G(L)->tmudata;
G(L)->tmudata = collected;
}
static void removekey (Node *n) {
setnilvalue(val(n)); /* remove corresponding value ... */
if (iscollectable(key(n)))
setttype(key(n), LUA_TNONE); /* dead key; remove it */
}
static void traversetable (GCState *st, Table *h) {
int i;
int weakkey = 0;
int weakvalue = 0;
const TObject *mode;
markvalue(st, h->metatable);
lua_assert(h->lsizenode || h->node == st->G->dummynode);
mode = gfasttm(st->G, h->metatable, TM_MODE);
if (mode && ttisstring(mode)) { /* is there a weak mode? */
weakkey = (strchr(svalue(mode), 'k') != NULL);
weakvalue = (strchr(svalue(mode), 'v') != NULL);
if (weakkey || weakvalue) { /* is really weak? */
GCObject **weaklist;
h->marked &= ~(KEYWEAK | VALUEWEAK); /* clear bits */
h->marked |= (weakkey << KEYWEAKBIT) | (weakvalue << VALUEWEAKBIT);
weaklist = (weakkey && weakvalue) ? &st->wkv :
(weakkey) ? &st->wk :
&st->wv;
h->gclist = *weaklist; /* must be cleared after GC, ... */
*weaklist = valtogco(h); /* ... so put in the appropriate list */
}
}
if (!weakvalue) {
i = sizearray(h);
while (i--)
markobject(st, &h->array[i]);
}
i = sizenode(h);
while (i--) {
Node *n = node(h, i);
if (!ttisnil(val(n))) {
lua_assert(!ttisnil(key(n)));
condmarkobject(st, key(n), !weakkey);
condmarkobject(st, val(n), !weakvalue);
}
}
}
static void traverseproto (GCState *st, Proto *f) {
int i;
strmark(f->source);
for (i=0; i<f->sizek; i++) {
if (ttisstring(f->k+i))
strmark(tsvalue(f->k+i));
}
for (i=0; i<f->sizep; i++)
markvalue(st, f->p[i]);
for (i=0; i<f->sizelocvars; i++) /* mark local-variable names */
strmark(f->locvars[i].varname);
lua_assert(luaG_checkcode(f));
}
static void traverseclosure (GCState *st, Closure *cl) {
if (cl->c.isC) {
int i;
for (i=0; i<cl->c.nupvalues; i++) /* mark its upvalues */
markobject(st, &cl->c.upvalue[i]);
}
else {
int i;
lua_assert(cl->l.nupvalues == cl->l.p->nupvalues);
markvalue(st, hvalue(&cl->l.g));
markvalue(st, cl->l.p);
for (i=0; i<cl->l.nupvalues; i++) { /* mark its upvalues */
UpVal *u = cl->l.upvals[i];
if (!u->marked) {
markobject(st, &u->value);
u->marked = 1;
}
}
}
}
static void checkstacksizes (lua_State *L, StkId max) {
int used = L->ci - L->base_ci; /* number of `ci' in use */
if (4*used < L->size_ci && 2*BASIC_CI_SIZE < L->size_ci)
luaD_reallocCI(L, L->size_ci/2); /* still big enough... */
used = max - L->stack; /* part of stack in use */
if (4*used < L->stacksize && 2*(BASIC_STACK_SIZE+EXTRA_STACK) < L->stacksize)
luaD_reallocstack(L, L->stacksize/2); /* still big enough... */
}
static void traversestack (GCState *st, lua_State *L1) {
StkId o, lim;
CallInfo *ci;
markobject(st, gt(L1));
for (o=L1->stack; o<L1->top; o++)
markobject(st, o);
lim = o;
for (ci = L1->base_ci; ci <= L1->ci; ci++) {
lua_assert(ci->top <= L1->stack_last);
if (lim < ci->top) lim = ci->top;
}
for (; o<=lim; o++) setnilvalue(o);
checkstacksizes(L1, lim);
}
static void propagatemarks (GCState *st) {
while (st->tmark) { /* traverse marked objects */
switch (st->tmark->gch.tt) {
case LUA_TTABLE: {
Table *h = gcotoh(st->tmark);
st->tmark = h->gclist;
traversetable(st, h);
break;
}
case LUA_TFUNCTION: {
Closure *cl = gcotocl(st->tmark);
st->tmark = cl->c.gclist;
traverseclosure(st, cl);
break;
}
case LUA_TTHREAD: {
lua_State *th = gcototh(st->tmark);
st->tmark = th->gclist;
traversestack(st, th);
break;
}
case LUA_TPROTO: {
Proto *p = gcotop(st->tmark);
st->tmark = p->gclist;
traverseproto(st, p);
break;
}
default: lua_assert(0);
}
}
}
static int valismarked (const TObject *o) {
if (ttisstring(o))
strmark(tsvalue(o)); /* strings are `values', so are never weak */
return !iscollectable(o) || testbit(o->value.gc->gch.marked, 0);
}
/*
** clear collected keys from weaktables
*/
static void cleartablekeys (GCObject *l) {
while (l) {
Table *h = gcotoh(l);
int i = sizenode(h);
lua_assert(h->marked & KEYWEAK);
while (i--) {
Node *n = node(h, i);
if (!valismarked(key(n))) /* key was collected? */
removekey(n); /* remove entry from table */
}
l = h->gclist;
}
}
/*
** clear collected values from weaktables
*/
static void cleartablevalues (GCObject *l) {
while (l) {
Table *h = gcotoh(l);
int i = sizearray(h);
lua_assert(h->marked & VALUEWEAK);
while (i--) {
TObject *o = &h->array[i];
if (!valismarked(o)) /* value was collected? */
setnilvalue(o); /* remove value */
}
i = sizenode(h);
while (i--) {
Node *n = node(h, i);
if (!valismarked(val(n))) /* value was collected? */
removekey(n); /* remove entry from table */
}
l = h->gclist;
}
}
static void freeobj (lua_State *L, GCObject *o) {
switch (o->gch.tt) {
case LUA_TPROTO: luaF_freeproto(L, gcotop(o)); break;
case LUA_TFUNCTION: luaF_freeclosure(L, gcotocl(o)); break;
case LUA_TUPVAL: luaM_freelem(L, gcotouv(o)); break;
case LUA_TTABLE: luaH_free(L, gcotoh(o)); break;
case LUA_TTHREAD: {
lua_assert(gcototh(o) != L && gcototh(o) != G(L)->mainthread);
luaE_freethread(L, gcototh(o));
break;
}
case LUA_TSTRING: {
luaM_free(L, o, sizestring(gcotots(o)->tsv.len));
break;
}
case LUA_TUSERDATA: {
luaM_free(L, o, sizeudata(gcotou(o)->uv.len));
break;
}
default: lua_assert(0);
}
}
static int sweeplist (lua_State *L, GCObject **p, int limit) {
GCObject *curr;
int count = 0; /* number of collected items */
while ((curr = *p) != NULL) {
if (curr->gch.marked > limit) {
unmark(curr);
p = &curr->gch.next;
}
else {
count++;
*p = curr->gch.next;
freeobj(L, curr);
}
}
return count;
}
static void sweepstrings (lua_State *L, int all) {
int i;
for (i=0; i<G(L)->strt.size; i++) { /* for each list */
G(L)->strt.nuse -= sweeplist(L, &G(L)->strt.hash[i], all);
}
}
static void checkSizes (lua_State *L) {
/* check size of string hash */
if (G(L)->strt.nuse < cast(ls_nstr, G(L)->strt.size/4) &&
G(L)->strt.size > MINSTRTABSIZE*2)
luaS_resize(L, G(L)->strt.size/2); /* table is too big */
/* check size of buffer */
if (luaZ_sizebuffer(&G(L)->buff) > LUA_MINBUFFER*2) { /* buffer too big? */
size_t newsize = luaZ_sizebuffer(&G(L)->buff) / 2;
luaZ_resizebuffer(L, &G(L)->buff, newsize);
}
G(L)->GCthreshold = 2*G(L)->nblocks; /* new threshold */
}
static void do1gcTM (lua_State *L, Udata *udata) {
const TObject *tm = fasttm(L, udata->uv.metatable, TM_GC);
if (tm != NULL) {
setobj2s(L->top, tm);
setuvalue(L->top+1, udata);
L->top += 2;
luaD_call(L, L->top - 2, 0);
}
}
static void callGCTM (lua_State *L) {
lu_byte oldah = L->allowhook;
L->allowhook = 0; /* stop debug hooks during GC tag methods */
L->top++; /* reserve space to keep udata while runs its gc method */
while (G(L)->tmudata != NULL) {
GCObject *o = G(L)->tmudata;
Udata *udata = gcotou(o);
G(L)->tmudata = udata->uv.next; /* remove udata from `tmudata' */
udata->uv.next = G(L)->rootudata; /* return it to `root' list */
G(L)->rootudata = o;
setuvalue(L->top - 1, udata); /* keep a reference to it */
unmark(o);
markfinalized(udata);
do1gcTM(L, udata);
}
L->top--;
L->allowhook = oldah; /* restore hooks */
}
void luaC_callallgcTM (lua_State *L) {
separateudata(L);
callGCTM(L); /* call their GC tag methods */
}
void luaC_sweep (lua_State *L, int all) {
if (all) all = 256; /* larger than any mark */
sweeplist(L, &G(L)->rootudata, all);
sweepstrings(L, all);
sweeplist(L, &G(L)->rootgc, all);
}
/* mark root set */
static void markroot (GCState *st, lua_State *L) {
global_State *G = st->G;
markobject(st, defaultmeta(L));
markobject(st, registry(L));
traversestack(st, G->mainthread);
if (L != G->mainthread) /* another thread is running? */
markvalue(st, L); /* cannot collect it */
}
static void mark (lua_State *L) {
GCState st;
GCObject *wkv;
st.G = G(L);
st.tmark = NULL;
st.wkv = st.wk = st.wv = NULL;
markroot(&st, L);
propagatemarks(&st); /* mark all reachable objects */
cleartablevalues(st.wkv);
cleartablevalues(st.wv);
wkv = st.wkv; /* keys must be cleared after preserving udata */
st.wkv = NULL;
st.wv = NULL;
separateudata(L); /* separate userdata to be preserved */
marktmu(&st); /* mark `preserved' userdata */
propagatemarks(&st); /* remark, to propagate `preserveness' */
cleartablekeys(wkv);
/* `propagatemarks' may reborne some weak tables; clear them too */
cleartablekeys(st.wk);
cleartablevalues(st.wv);
cleartablekeys(st.wkv);
cleartablevalues(st.wkv);
}
void luaC_collectgarbage (lua_State *L) {
mark(L);
luaC_sweep(L, 0);
checkSizes(L);
callGCTM(L);
}
void luaC_link (lua_State *L, GCObject *o, int tt) {
o->gch.next = G(L)->rootgc;
G(L)->rootgc = o;
o->gch.marked = 0;
o->gch.tt = tt;
}
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