#11521: Memleak when resolving the action of Integers on an Elliptic Curve
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Reporter: jpflori | Owner: robertwb
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.2
Component: coercion | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by jpflori):
I'm having a look at your problem right now. Here are some hints to study
the problem, mostly stolen from
[http://trac.sagemath.org/sage_trac/search/opensearch?q=ticket%3A10548
#10548].
I put it here for the record, and so that i can go faster next time.
First, if I only create the finite fields and do nothing with them, I do
not seem to get a memleak. Some fields are not garbage collected
immediately, but calling gc.collect() does the trick.
{{{
sage: import gc
sage: for p in prime_range(10**5):
....: k = GF(p)
....:
sage: del p, k
sage: gc.collect()
1265
sage: from sage.rings.finite_rings.finite_field_prime_modn import
FiniteField_prime_modn as FF
sage: L = [x for x in gc.get_objects() if isinstance(x, FF)]
sage: len(L)
1
sage: L
[Finite Field of size 2]
}}}
Of course I guess you actually do something with your finite fields.
So here is a small example causing the fields to stay cached.
{{{
sage: import gc
sage: for p in prime_range(10**5):
....: k = GF(p)
....:
sage: del p, k
sage: gc.collect()
0
}}}
The zero here is bad and indeed
{{{
sage: from sage.rings.finite_rings.finite_field_prime_modn import
FiniteField_prime_modn as FF
sage: L = [x for x in gc.get_objects() if isinstance(x, FF)]
sage: len(L)
9592
}}}
If you want to know where it comes from you can use the objgraph python
module (on my debian I just installed the python-objgraph package, updated
sys.path in Sage to include '/usr/lib/python2.6/dist-packages')
{{{
sage: sys.path.append('/usr/lib/python2.6/dist-packages')
sage: import inspect, objgraph
sage:
objgraph.show_backrefs(L[-1],filename='/home/jp/br.png',extra_ignore=[id(L)])
}}}
And look at the png or use
{{{
sage: brc =
objgraph.find_backref_chain(L[-1],inspect.ismodule,max_depth=15,extra_ignore=[id(L)])
sage: map(type,brc)
[<type 'module'>, <type 'dict'>, <type 'dict'>,...
sage: brc[0]
<module 'sage.categories.homset'...
}}}
So the culprit is "_cache" in sage.categories.homset which has a direct
reference to the finite fields in its keys.
The clean solution woul be to used weakref in the keys (let's say
something as WeakKeyDirectory in python).
However, resetting cache should be a (potentially partial) workaround (and
could kill your Sage?).
{{{
sage: sage.categories.homset.cache = {}
sage: gc.collect()
376595
}}}
It also seems to be enough if I do "a = k.random_element(); a = a+a" in
the for loop, but not if I add "a = 47*a+3".
I'm currently investigating that last case.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11521#comment:8>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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