Re: __gc visible to lua code...

[Graham Wakefield <lists@...>]

On Mar 30, 2007, at 9:35 AM, Michael Broughton wrote:

> One way you can prevent the __gc metamethod from being called is to  
> create an __index metamethod that filters out private indices. Of  
> course, that would not prevent any C code from calling your  
> finalizer. Overall, I think this solution is too complicated and it  
> will slow down your whole module.

I agree.

> I think it is best to just keep track of the state of your userdata  
> and any associated resources. For example: if your userdata is a  
> struct, add a field to mark when it is finalized. If your userdata  
> is a boxed pointer, make sure you nullify the pointer when you are  
> done with it.

Yes, I've done this now... but still I think __gc should be private  
by default.

> You could also use each userdata's environment table to do  
> something similar.

?  You mean, in __gc set the userdata environment to nil, and then in  
the type-check test if the environment is nil, for example?  Or  
likewise for a field in the environment?  Probably null-checking the  
userdata value is easier.

Another question: is the userdata's environment garbage collected  
when __gc is called, or when the userdata itself is garbage collected?