#11521: Use weak references to cache homsets
--------------------------------------------------+-------------------------
Reporter: jpflori | Owner: robertwb
Type: defect | Status:
positive_review
Priority: major | Milestone: sage-5.5
Component: coercion | Resolution:
Keywords: sd35 | Work issues:
Report Upstream: N/A | Reviewers: Jean-Pierre
Flori, Nils Bruin
Authors: Simon King | Merged in:
Dependencies: #12969; to be merged with #715 | Stopgaps:
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Changes (by nbruin):
* status: needs_work => positive_review
Old description:
> Originally, this ticket was about the following memory leak when
> computing with elliptic curves:
>
> {{{
> sage: K = GF(1<<55,'t')
> sage: a = K.random_element()
> sage: while 1:
> ....: E = EllipticCurve(j=a); P = E.random_point(); 2*P;
> }}}
> This example is in fact solved by #715. However, while working on that
> ticket, another leak has been found, namely
>
> {{{
> sage: for p in prime_range(10^5):
> ....: K = GF(p)
> ....: a = K(0)
> ....:
> sage: import gc
> sage: gc.collect()
> 0
> }}}
> So, I suggest to start with #715 and solve the second memory leak on top
> of it. It seems that a strong cache for homsets is to blame. I suggest to
> use the weak `TripleDict` instead, which were introduced in #715.
>
> '''To be merged with #715 and #13447'''. Apply
>
> * the patches from #715
> * [attachment:trac_11521_homset_weakcache_combined.patch]
> * [attachment:trac_11521_callback.patch]
New description:
Originally, this ticket was about the following memory leak when computing
with elliptic curves:
{{{
sage: K = GF(1<<55,'t')
sage: a = K.random_element()
sage: while 1:
....: E = EllipticCurve(j=a); P = E.random_point(); 2*P;
}}}
This example is in fact solved by #715. However, while working on that
ticket, another leak has been found, namely
{{{
sage: for p in prime_range(10^5):
....: K = GF(p)
....: a = K(0)
....:
sage: import gc
sage: gc.collect()
0
}}}
So, I suggest to start with #715 and solve the second memory leak on top
of it. It seems that a strong cache for homsets is to blame. I suggest to
use the weak `TripleDict` instead, which were introduced in #715.
'''To be merged with #715 and #13447'''. Apply
* the patches from #715
* [attachment:trac_11521_homset_weakcache_combined.patch]
* [attachment:trac_11521_callback.patch]
* [attachment:trac_11521_doctestfix.patch]
--
Comment:
OK, I've adapted two doctests to reflect that polynomial rings still are
not garbage collected. Furthermore, I backported two changes from #13447:
- A change to a doctest for modular forms spaces, which depended on
previously cached computation. Since these things do get collected now,
the caching was lost. The rewrite forces recomputation, so the dependence
on things not getting deleted is removed
- The ignored `AttributeError` (which doesn't cause a doctest failure, by
the way. The warning is only visible because it happened near a doctest
that failed for another reason). Since we found where this ignore was
happening anyway
[http://trac.sagemath.org/sage_trac/ticket/13447#comment:30] we might as
well fix it now. It's a side-effect of things getting collected, but the
change itself doesn't depend on the proper refcounting details that #13447
itself is hanging on.
All doctests pass for me with this, so back to positive review.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11521#comment:182>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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