#11521: Memleak when resolving the action of Integers on an Elliptic Curve
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Reporter: jpflori | Owner: robertwb
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.8
Component: coercion | Keywords: sd35
Work_issues: | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #11900 #715
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Comment(by jpflori):
Replying to [comment:95 SimonKing]:
> Yes, and note that we have two locations for storing the actions: * in
the coercion model * in the attribute `_action_hash` of parents. I found
that having weak references in the coercion model is enough for fixing the
leak - even if one has strong references in `_action_hash`. That is
something I don't fully understand.
As I posted above in ZZ._action_hash equality is tested with "==" (rather
than identity with "is") so in the code of the ticket description where
only "one" curve is used, only one curve gets stored in _action_hash.
If you try the code posted some comments above where (really) different
curves are used, you'll see that the leak is not fixed if you dont use a
similar approach for _action_hash as for the coercion model.
>In the example of the ticket description, we have an action of `ZZ`. `ZZ`
is not subject to garbage collection, hence, having a strong reference in
`ZZ._action_hash` should keep the action alive, and thus the elliptic
curve (namely the different copies of E that are created in the loop).
Anyway, even in that case we would see the drastic slow-down.
> Indeed that would be the consequence. I think that would not be
acceptable: If the user keeps an action, then s/he can rightfully expect
that domain and codomain are automatically kept alive.
The weakref domain and codomain in functors problem could be tackled by
adding an optional parameter for the use of weakref.
By default, the behavior of functors would be as before with strong refs
(and the option to false).
For the coercion models we would set the option to True and use weakref
whenever possible.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11521#comment:96>
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