Re: Replacement for unlocked refs?

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

Diego Fernandes Nehab wrote:

> Last try... I think we missunderstood each other. :-)


[...]


> My suggestion  is that you use  the userdatum directly to  reference the
> object from Lua.  You can create an associated table  and place a strong
> ref  to it  as a  field in  the  C++ object.  You set  the gettable  and
> settable methods for  the userdatum to access the  associated table. You
> set the garbage collection method  to unref the associated table. (there
> is no self field in the associated table, there is no cycle)

There are still some synchronization problems with this approach, though 
they too could be worked around. Say I have a component, which has both 
Lua and C++ parts. The C++ part is being reference counted.

Lua could hold a reference to the object while the C++ refcount goes to 
zero. At this point I could let it sit around until it's GCed.

Lua could try to GC an object whose refcount > 0. I can't release the 
Lua table because the object could be passed back into Lua later, and I 
don't want to lose any information that's been stored there.

So say I have a C++/Lua object. The userdata gets GCed, but I ignore it 
because the C++ refcount > 0. Now I make a call into Lua and pass my 
object in as a parameter. The call returns, and the C++ refcount gets 
decremented to zero. Can I delete the objects? C++ no longer needs it, 
and Lua tried to GC it earlier. But Lua could have kept a reference to 
the table when I made the Lua call. Or maybe it didn't.

I do understand you're approach and it does work, but it assumes that 
Lua "owns" the object, which is not the case in this instance. I really 
need the ability to store both weak and strong references, which I can 
get with a pair of tables in my scripting interface (although...well, I 
think I made my case earlier).

Thanks for knocking this around with me, I hadn't considered your 
approach before and it did get me thinking.

Jason