Re: lua_newstate crashes on "setnilvalue(L, registry(L)); ", lua_State L initialized with garbage?

[Joshua Jensen <josh.jjensen@...>]

Roberto Ierusalimschy wrote on 3/16/2017 7:55 AM:
> > Once a few dozens of launching my app I notice crash on start, lua
> > initialization.
> > Keeping in mind that this could be our-code issue, anyway I looked on
> > lua_newstate() implementation.
> > Here it is with my comments:
> >
> > [...]
> >
> > setnilvalue macro gives something like this:
> >
> > [...]
> > 	if (i_o >= L->base && i_o < L->top && !stuckref(i_o))
> > 	{
> > 		i_o->value.gc->gch.refCount--;			// crashed
> What version of Lua are you talking about? Lua does not use reference
> count and nowhere in its code you would find a 'refCount' field.
As far as I am aware, I had the only reference counted implementation of 
Lua 5.1 out there. It was a huge win for the games I worked on, making 
garbage collection blips a non-issue.

However, that implementation used a variable called 'ref' to do the 
calculations:

#define CommonHeader    GCObject *next; GCObject* prev; lu_byte tt; 
lu_byte marked; unsigned short ref

There is obviously another version out there. Still, the following may 
help the OP. If additional consulting is needed for a reference counted 
version of Lua 5.1, feel free to contact me directly.

It did this in lua_newstate():

#if LUA_REFCOUNT
  setnilvalue2n(L, registry(L));
#else
  setnilvalue(registry(L));
#endif

where setnilvalue2n() was defined as:

#define setnilvalue2n(L,obj) ((obj)->tt=LUA_TNIL)

but setnilvalue() was defined as:

#define luarc_release(L,o) { TValue* i_o2 = (o); if(iscollectable(i_o2) 
&& ((--gcvalue(i_o2)->gch.ref)<=0))    \
        {    \
            luarc_releaseobject(L,gcvalue(i_o2));    \
        }    }
#define setnilvalue(obj) { TValue *i_o=(obj); luarc_release(L, i_o); 
i_o->tt=LUA_TNIL; }

I have no idea what stuckref() would do.

-Josh