[Python-Dev] Python Language Summit EuroPython 2010

[Jesse Noller]

On Wed, Jul 21, 2010 at 11:11 AM, Tim Golden <mail at timgolden.me.uk> wrote:
[...snip...]
> A messy discussion turned on the question of garbage collection of module
> objects, and the order in which finalisers are called if at all, especially
> when reference cycles exist. Marc Andre was proposing a __cleanup__ magic
> function
> for Python modules, which would enable the implementer to define the order
> in which resources are released / closed down. This is quite a subtle area
> and raised the issue of unfinalised objects in a reference cycle whose
> memory has been freed out from under them but which still exist. Martin
> described
> the Java approach where finalisers are called once and then flagged so
> they are not called again even if their object is resurrected. This sounded
> like a useful approach for Python but would break code which expected to
> be able to resurrect an object during its __del__ method... which is not
> expected to account for much code.
>
> Guido pointed out that no-one can be expected to hold enough of the
> complexities
> of this area of Python's implementation in their head, and that an
> implementation
> of some sort would need to be written so that the corner-cases could emerge.

FWIW; I'm currently dealing with a bug in this area w.r.t
multiprocessing and threads and modules we have imported vanishing due
to this issue. I'm interested in hearing more.

The problem affects 2.7 final, as well.

jesse