[Python-3000] refleak in test_io?

[Thomas Wouters]

On 8/30/07, "Martin v. Löwis" <martin at v.loewis.de> wrote:
>
> > I tried recreating the leak with more controllable types, but I haven't
> > got very far. It seems to be caused by some weird interaction between
> > io.FileIO, _fileio._FileIO and io.IOBase, specifically io.IOBase.__del_
> > _() calling self.close(), and io.FileIO.close() calling
> > _fileio._FileIO.close() *and* io.RawIOBase.close(). The weird thing is
> > that the contents of RawIOBase.close() doesn't matter. The mere act of
> > calling RawBaseIO.close (self) causes the leak. Remove the call, or
> > change it into an attribute fetch, and the leak is gone. I'm stumped.
>
> I think the problem is that the class remains referenced in
> io.RawIOBase._abc_cache:
>
> py> io.RawIOBase._abc_cache
> set()
> py> class f(io.RawIOBase):pass
> ...
> py> isinstance(f(), io.RawIOBase)
> True
> py> io.RawIOBase._abc_cache
> {<class '__main__.f'>}
> py> del f
> py> io.RawIOBase._abc_cache
> {<class '__main__.f'>}
>
> Each time test_destructor is called, another class will be added to
> _abc_cache.


Ahh, thanks, I missed that cache. After browsing the code a bit it seems to
me the _abc_cache and _abc_negative_cache need to be turned into weak sets.
(Since a class can appear in any number of caches, positive and negative, we
can't just check refcounts on the items in the caches.) Do we have a weak
set implementation anywhere yet? I think I have one lying around I wrote for
someone else a while back, it could be added to the weakref module.

-- 
Thomas Wouters <thomas at python.org>

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