#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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Changes (by SimonKing):
* work_issues: Find out why some attribute of a parent is deleted before
the parent's elements are deleted =>
Comment:
Replying to [comment:17 vbraun]:
> You are, in fact, leaking memory: `celement_destruct()` is never called
if the `AttributeError` is raised.
Sure. But to my surprise, it isn't noticed in that loop. Surprise,
because...
> I guess it only happens rarely in your test loop, so you don't notice it
in the total memory?
... I thought it would be called in each round of the loop.
> A while ago (when we were both in Kaiserslautern, actually) I fixed
essentially the same error in `multi_polynomial_libsingular.pyx`: To
deallocate a singular ring element you need the singular ring, but the
Python parent can be gone by then. There, I added a new cdef pointer to
the singular ring to the ring elements.
So, you agree with the statement from my previous post that keeping a
reference from the element to the modulus would be the cleanest solution.
Shall I modify sage/rings/polynomial/polynomial_template.pxi accordingly?
But there would be a memory penalty (one additional pointer per
polynomial) and also a time penalty (the pointer needs to be assigned).
> Usually in OOP you are not allowed to throw exceptions from a
destructor.
Sure. The main problem for debugging was that Cython was not able to
provide the location of the error: Note that it just says "Attribute error
in ignored". In fact, it tries to obtain the string representation of the
polynomial, but it fails for the same reason: The parent's modulus is
already gone, and without the modulus, the string representation of the
element can't be determined.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313#comment:18>
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