On Thu, Jul 22, 2010 at 9:51 AM, Brett Cannon <br...@python.org> wrote: > > > On Wed, Jul 21, 2010 at 16:58, Antoine Pitrou <solip...@pitrou.net> wrote: >> >> On Wed, 21 Jul 2010 11:42:00 -0400 >> Jesse Noller <jnol...@gmail.com> wrote: >> > On Wed, Jul 21, 2010 at 11:11 AM, Tim Golden <m...@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. >> >> One common resolution is to not use a __del__ method, but instead a >> weakref callback which will do the necessary cleanup of a certain set >> of resources. This is of course not applicable in all situations. > > That's an option. I just remember Tim bringing up something about that > approach that didn't quite work as a complete replacement for __del__. > Basically the whole setting a module's globals to None was done before gc > came into the language. Now that it's there it seems that it might work to > simply let gc clean up the module itself. But this brings in the question of > how to order calling finalizers. It seemed the room had no specific answer > other than it might just have to be near random as figuring out a reasonable > order is hard.
If you have a cycle, there is no other way than breaking it at random, right? Cheers, fijal _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
