Re: Possible closure bug in 4.1 snapshot
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- Subject: Re: Possible closure bug in 4.1 snapshot
- From: Edgar Toernig <froese@...>
- Date: 2001年11月28日 21:12:29 +0100
Roberto Ierusalimschy wrote:
>
> > First idea: create struct UpVal during OP_CLOSURE, these are linked
> > into lua_State, struct UpVal performs an additional indirection.
>
> Another solution is to "decompose" the upval address into a base and an
> index.
Should work too. But I think it's more complicated without being faster.
This would be the relevant routines for my proposal (structures from my
previous posting; assuming GC'ed struct UpVal; untested, may not even
compile!):
lvm.c:
case OP_GETUPVAL: {
int b = GETARG_B(i);
setobj(ra, cl->upvals[b]->valp);
break;
}
case OP_SETUPVAL: {
int b = GETARG_B(i);
setobj(cl->upvals[b]->valp, ra);
break;
}
case OP_CLOSURE: {
...
for (j=0; j<nup; j++, pc++) {
if (GET_OPCODE(*pc) == OP_GETUPVAL)
ncl->l.upvals[j] = cl->upvals[GETARG_B(*pc)];
else
ncl->l.upvals[j] = luaF_localUpVal(L, base + GETARG_B(*pc));
}
setclvalue(ra, ncl);
break;
}
lfunc.c:
void luaF_localUpVal (lua_State *L, StkId loc)
{
UpVal **pp, *p;
for (pp = &L->openupval; (p = *pp) != NULL; pp = &p->u.next)
{
if (p->valp == loc)
return p;
if (p->valp < loc)
break;
}
p = luaM_new(L, UpVal);
p->marked = 0;
p->next = G(L)->rootupval;
G(L)->rootupval = p;
p->valp = loc;
p->u.next = *pp;
*pp = p;
return p;
}
void luaF_close (lua_State *L, StkId downto)
{
UpVal p;
while ((p = L->openupval) != NULL && p->valp >= downto)
{
L->openupval = p->u.next;
p->u.value = *p->valp;
p->valp = &p->u.value;
}
}
See? Much simpler. Uses less memory. And, as said, I don't think
it's slower.
Ciao, ET.
PS: You can save an additional word per upvalue if you make them
reference counted instead of GC'ed.