Re: userdata and the gc

[Adrian Sietsma <adrian_groups@...>]

Answering myself:
> Will a userdata's address change when the gc runs ?
>
> ie:
>
> lua_pushstring(L,"foo");
> p = lua_newuserdata(L,sizeof(foo));
> lua_rawset(L,LUA_REGISTRYINDEX);
-- note the userdata is no longer on the stack here
> ... do something to force a gc
>
> lua_pushstring(L,"foo");
> lua_rawget(L,LUA_REGISTRYINDEX);
> p1 = lua_touserdata(L,-1);
> assert (p==p1); <----------------
>
> Adrian

I would guess that the answer is that a (full) usedata would be safe as long 
as it is on the stack, but that the gc may move the ud (and thus invalidate 
the pointer), once it is off the c stack.

This would imply that having full userdata on the stack may cause the 
garbage collector to be unable to run to completion.

Adrian