Reference counting again

[Matt Campbell <mattcampbell@...>]

Hello:

I am once again interested in using reference counting either instead of 
or in addition to Lua's garbage collector.  But my reason has nothing to 
do with speed or responsiveness.

My Lua code often obtains references to COM objects which it doesn't 
own; that is, it doesn't create these objects, and it shouldn't hold the 
last reference to them, thus keeping them from being destroyed.  Some of 
these objects correspond to user interface elements, such as windows and 
controls; these objects implement the IAccessible interface, part of 
Microsoft Active Accessibility.  If such an object has a buggy 
implementation, then holding a reference to that object after the 
corresponding UI element has gone away could lead to a crash when the 
appropriate __gc metamethod finally releases that reference.  So 
reference counting in Lua would ensure that as soon as my code is done 
with a COM object, its reference to the userdatum wrapping that object 
is destroyed; at that time, that userdatum's __gc metamethod would be 
called, releasing the reference to the COM object itself.  So reference 
counting in Lua would lead to greater determinism and easier debugging.

So has anyone implemented a reference counting patch for Lua 5.1?  I 
suppose I could work on it myself, but I haven't studied the Lua core 
enough to make such a deep change with any confidence.

Thanks,
Matt