Re: Confused by Lua garbage collection tear down order when there are references between objects

[Philipp Janda <siffiejoe@...>]

Am 22.05.2014 08:05 schröbte Eric Wing:
> > I don't think that anyone has mentioned this yet, but I guess you mean
> > something like this:
> > *   put B in A's uservalue table to keep it alive as long as A is alive
> > *   put a weak back reference to A in B's uservalue table
> > *   in A's finalizer free A if it hasn't been freed before by someone else
> > *   in B's finalizer first free A if the weak back reference still
> > exists and A hasn't been freed before, and then free B itself if it
> > hasn't been freed before
>
> One thing I noticed is that the uservalue table of my objectA being
> finalized in the _gc callback still has a reference to objectB, even
> if objectB's _gc callback was invoked before this one. (I suppose this
> is for if you need resurrection?)

Unless I mixed up A and B, A's uservalue table is supposed to hold 
strong references to B, and strong references are never cleared from a 
table. B should have a weak uservalue table with references to A, but 
you can't say exactly when the references are cleared (Lua 5.2 at least 
says whether it will happen before or after A's finalizer).


Philipp