#5970: Weak references in Polynomial Ring cache
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Reporter: SimonKing | Owner: malb
Type: defect | Status: needs_work
Priority: critical | Milestone: sage-4.8
Component: commutative algebra | Keywords: polynomial ring
cache weak reference
Work_issues: regression for test_ec_leak? | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by SimonKing):
Aha!
The combination of a finite field with a polynomial ring seems to reveal
the leak:
{{{
sage: K = GF(next_prime(1000))
sage: p = K.order()
sage: predicate = lambda x: is_FiniteField(x) and x.order() == p
sage: del K
sage: gc.collect()
23
sage: [bla for bla in gc.get_objects() if predicate(bla)]
[]
sage: K = GF(next_prime(1000))
sage: P = K['x','y','z']
sage: del P
sage: del K
sage: gc.collect()
39
sage: [bla for bla in gc.get_objects() if predicate(bla)]
[Finite Field of size 1009]
sage: predicate = lambda x: is_MPolynomialRing(x) and
x.variable_names()==['x','y','z']
sage: [bla for bla in gc.get_objects() if predicate(bla)]
[]
}}}
So, the polynomial ring is gone, but the base ring remains. And I think
this is indeed because of the thing tracked at #12215:
* The polynomial ring belongs to the category of algebras over the base
ring (at least by #9138, which I have applied),
* The category is strongly cached (see #12215)
* The category has a reference to its base ring.
So, indeed we absolutely need to have `UniqueRepresentation` use weak
references.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5970#comment:26>
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