#11521: Memleak when resolving the action of Integers on an Elliptic Curve
------------------------+---------------------------------------------------
Reporter: jpflori | Owner: robertwb
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: coercion | Keywords: sd35
Work_issues: | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #11900 #715
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Comment(by SimonKing):
It turns out that the failing test had in fact a wrong design. It was:
{{{
sage: import gc
sage: from sage.rings.polynomial.multi_polynomial_libsingular
import MPolynomialRing_libsingular
sage: from sage.libs.singular.ring import ring_refcount_dict
sage: n = len(ring_refcount_dict)
sage: R = MPolynomialRing_libsingular(GF(547), 2, ('x', 'y'),
TermOrder('degrevlex', 2))
sage: len(ring_refcount_dict) == n + 1
True
sage: Q = copy(R) # indirect doctest
sage: p = R.gen(0) ^2+R.gen(1)^2
sage: q = copy(p)
sage: del R
sage: del Q
sage: del p
sage: del q
sage: gc.collect() # random output
sage: len(ring_refcount_dict) == n
True
}}}
Hence, before n is defined, no garbage collection takes place. This is, of
course, not correct: The ring_refcount_dict may contain references to a
ring created in another doctest, that is only garbage collected in the
line before `len(ring_refcount_dict)==n`.
In other words: The test did not fail ''because'' there was a memory leak.
When I insert a garbage collection right before the definition of n, the
test works, and in addition the warning about `AttributeError` being
ignored vanishes.
The patch fixes the memory leak caused by a strong homset cache (which was
not addressed by #715):
{{{
sage: for p in prime_range(10^3):
....: K = GF(p)
....: a = K(0)
....:
sage: import gc
sage: gc.collect()
3128
sage: LE = [x for x in gc.get_objects() if isinstance(x,type(K))]
sage: LE
[Finite Field of size 2, Finite Field of size 997]
}}}
The patch adds a new doctest demonstrating that it is fixed.
Needs review!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11521#comment:117>
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