#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 SimonKing):
An action of G on S stores direct references to G and to S.
The action is a functor, and as a functor, it additionally stores a
reference to `Groupoid(G)`, which stores another reference to G, and to
the category of S.
In some cases, the category of S will store references to the base ring of
S (for example, if S is an algebra), which might have a pointer back to S
(for example if the action of `S.base_ring()` on S was registered during
initialisation). In this case, we are lost, since categories are unique
parents and thus strongly cached (unless we apply #12215, which poses some
problems).
For the same reason, creating the groupoid of G will result in an eternal
reference on G (`Groupoid(G)` is strongly cached and it points to G). So,
the best that we can hope for is that we can free S at some point, but we
will never be able to free G.
It starts to be complicated. Time to call it a day...
Perhaps the idea to register actions in the parents (in addition to a weak
cache in the coercion model) is better?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/715#comment:82>
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