Re: Replacement for unlocked refs?

["J. Perkins" <jason@...>]

Peter Loveday wrote:

> I do something identical to this in a project; the userdata pointer in Lua
> is exactly the same as any C++ reference to the object in the way it is
> reference counted.  As you say, the gc just decrements the count.  This
> also works well with multiple Lua references to the same object via
> different userdata objects (in 4.1), as each different one just holds a
> ref on the object.


How do you pass your userdata object into Lua calls?  That is, say I 
have C++ code that wants to call a function like:

int doSomething(MyObject* obj);

...where obj exists in both C++ and Lua. If doSomething were a 
wrapper to a Lua function, you would have to push the name of the 
function, and then the argument. If you can't keep a weak reference 
to the userdata object in Lua, how would you push obj onto the Lua 
stack?

Hmm, now that I think about it...I guess I could just call 
newuserdatabox(), as there's no reason why I need to use the exact 
same Lua object for the call. Then I can increment my refcount, and 
GC will be called once for every Lua instance of the userdata. That 
*could* create a whole mess of duplicate userdata's that need 
collecting but it would work. I'll have to get a rough estimate of 
how many extra objects I'd be creating with this approach.

Thanks for the insight, much appreciated.

Jason



> I don't have the requirement of C++ having a Lua table, as in this example,
> but I can't see why that wouldn't work more or less the same way; Lua maintains
> the refcount, C++ can effectively hold a ref as long as it likes, and release
> it when it wants.
>
> Love, Light and Peace,
> - Peter Loveday
> eyeon Software