[Python-Dev] gcmodule issue w/adding __del__ to generator objects

[Phillip J. Eby]

One more note; I tried changing generators to set their gi_frame to None 
whenever the generator finishes normally or with an error; this eliminated 
most of the reference cycles, and I was able to make test_generators work 
correctly with only 3 explicit close() calls, for the "fun" tests that use 
objects which hold references to generators that in turn reference the object.

So, I think I've got this sorted out, assuming that I'm not doing something 
hideously insane by having 'has_finalizer()' always check tp_del even for 
non-heap types, and defining a tp_del slot for generators to call close() in.

I ended up having to copy a bunch of stuff from typeobject.c in order to 
make this work, as there doesn't appear to be any way to share stuff like 
subtype_del and subtype_dealloc in a meaningful way with the generator code.


At 06:00 PM 6/18/2005 -0400, Phillip J. Eby wrote:
>Argh!  My email client's shortcut for Send is Ctrl-E, which is the same as
>end-of-line in the editor I've been using all day.  Anyway, the problem is
>that it seems to me as though actually checking for tp_del is too
>aggressive (conservative?) for generators, because sometimes a generator
>object is finished or un-started, and therefore can't resurrect objects
>during close().  However, I don't really know how to implement another
>strategy; gcmodule isn't exactly my forte.  :)  Any input from the GC gurus
>would be appreciated.  Thanks!
>
>At 05:56 PM 6/18/2005 -0400, Phillip J. Eby wrote:
> >At 05:50 PM 6/18/2005 -0400, Phillip J. Eby wrote:
> > >Working on the PEP 342/343 generator enhancements, I've got working
> > >send/throw/close() methods, but am not sure how to deal with getting
> > >__del__ to invoke close().  Naturally, I can add a "__del__" entry to its
> > >methods list easily enough, but the 'has_finalizer()' function in
> > >gcmodule.c only checks for a __del__ attribute on instance objects, 
> and for
> > >tp_del on heap types.
> > >
> > >It looks to me like the correct fix would be to check for tp_del always,
> > >not just on heap types.  However, when I tried this, I started getting
> > >warnings from the tests, saying that 22 uncollectable objects were being
> > >created (all generators, in test_generators).
> > >
> > >It seems that the tests create cycles via globals(), since they define a
> > >bunch of generator functions and then call them, saving the generator
> > >iterators (or objects that reference them) in global variables
> > >
> > >after investigating this a bit, it seems to me that either has_finalizer()
> > >needs to
> >
> >Whoops.  I hit send by accident.  Anyway, the issue seems to mostly be that
> >the tests create generator-iterators in global variables.  With a bit of
> >effort, I've been able to stomp most of the cycles.
>
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