#12313: Fix yet another memory leak caused by caching of coercion data
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Reporter: SimonKing | Owner: rlm
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: memleak | Keywords: coercion weak dictionary
Work_issues: | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #715
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Comment(by SimonKing):
I have extended my patch by another coercion-related application of
`MonoDict`.
I found that `sage.categories.groupoid.Groupoid` is often resulting in a
memory leak. For example, by #715, polynomial rings are only weakly
cached. But if the groupoid of a polynomial ring is created, then a
''strong'' reference on the polynomial ring is created, preventing it from
being garbage collected. But a groupoid is created as soon as there is an
action of that polynomial ring on another ring. Hence, a memory leak.
The new patch version is overriding the `__classcall__` method of
`sage.categories.groupoid.Groupoid` (that would normally be inherited from
`UniqueRepresentation`) by a method that uses a `MonoDict` for caching. In
addition, there is now only a weak reference to the underlying set of a
groupoid. By consequence, if there is no other strong reference then
`Groupoid(P)` can be garbage collected, but a strong reference to P
prevents `Groupoid(P)` from being garbage collected.
Still needs review.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313#comment:5>
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