#715: Parents probably not reclaimed due to too much caching
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Reporter: robertwb | Owner: somebody
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.8
Component: coercion | Keywords: weak cache coercion
Work_issues: avoid regression | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #9138, #11900
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Comment(by jpflori):
Replying to [comment:74 SimonKing]:
> Replying to [comment:73 jpflori]:
> > Good point about #11521, I'd say because that what I was firstly
interested in. Without it applied, the flaky behavior seem to disappear.
> Good!
> > I'll post timings with all patches, with all patches except for
#11521, and with no patches in a few hours.
> OK, but I guess the timings I provided should be enough to show that the
patch can not remain as it is now.
> > Anyway I guess Volker is right and even with just #715 applied we
should check that actions do not get garbage collected continuously as
your timings suggest.
> Yep. Two potential solutions: 1. Find out why apparently not all actions
are registered in the parent (because then we would have a strong
reference as long as at least the domain is alive). 2. Play with the idea
to have a strong reference on the action but a weak reference from a
functor to its domain and codomain. I'm trying the latter now.
Just to summarize, here is the current problem, please correct me if some
of the following is wrong: we want to let a codomain (resp. domain) get
garbage collected when its only weak reffed outside of the coercion model.
Before the current patch the situation is as follows for actions:
- when an action is resolved, it is cached in a triple dict in the
coercion model with the domain and codomains as keys
- the action is also cached in the dictionnaries in the domain and the
codomain much in the same way
- there is also a similar cache for homsets
The current patch let weakrefs be used for the keys to the above
dictionaries and a weak ref to the corresponding value (which is the
action).
The problem is that as the action is only weak reffed everywhere now, it
gets garbage collected all the time (to be confirmed).
If it is not, then the codomain (resp. domain) will in turn not get
garbage collected, because it will be strongly reffed in the action
strongly reffed in the domain (resp. codomain) (to be confirmed).
The problem for the homset patch is slightly different and is being
discussed in #11521.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/715#comment:75>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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