[Python-Dev] Cycle collection enhancement idea

[eyal.lotem+pyutils@gmail.com]

On Jun 29, 5:12 pm, "eyal.lotem+pyut... at gmail.com"
<eyal.lo... at gmail.com> wrote:
> On Jun 29, 3:36 pm, Antoine Pitrou <solip... at pitrou.net> wrote:
>
> > eyal.lotem+pyutils <at> gmail.com <eyal.lotem <at> gmail.com> writes:
>
> > > That would be no worse than what happens now - but its still not
> > > perfect (__del__ ordering issues). Also, you would need to temporarily
> > > revive the cycles as mentioned above (to avoid accessibility of
> > > partially destructed objects).
>
> > The idea is to call all __del__'s *before* any object in the cycle is
> > deallocated (that is, call them manually rather than as part of deallocating
> > them). That way you shouldn't have the issues mentioned above.
>
> Firstly, as I said above: you will still have __del__ ordering issues.
> Secondly, the destructor itself currently calls __del__, so if you
> call __del__ before any deallocation, it will get called again as part
> of the deallocation.  Might be a technicality but it will still
> probably require some code restructuring to work around (or making
> that code even more hairy).

Additionally, there is another problem: If the cycle is not
temporarily revived, and you call __del__ manually, it may break the
cycle by removing the references.
Thus, objects in the cycle will go down to refcount=0 during your
attempt to call __del__'s on the objects in the cycle.
The only sane thing is to temporarily revive the entire cycle so you
can safely call __del__'s on it.  Then, you might want to disable the
normal __del__ calling that occurs as part of the later destruction of
the cycle.

>
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