#12215: Memleak in UniqueRepresentation, @cached_method
--------------------------------------------------------------+-------------
Reporter: vbraun | Owner:
Type: defect | Status:
needs_review
Priority: major | Milestone:
sage-5.3
Component: memleak | Resolution:
Keywords: UniqueRepresentation cached_method caching | Work issues:
Rebase wrt #7980
Report Upstream: N/A | Reviewers:
Authors: Simon King | Merged in:
Dependencies: #11115 #11900 #12645 #11599 #12808 #7980 | Stopgaps:
--------------------------------------------------------------+-------------
Changes (by SimonKing):
* status: needs_work => needs_review
Old description:
> The documentation says that UniqueRepresentation uses weak refs, but this
> was switched over to the @cached_method decorator. The latter does
> currently use strong references, so unused unique parents stay in memory
> forever:
> {{{
> import sage.structure.unique_representation
> len(sage.structure.unique_representation.UniqueRepresentation.__classcall__.cache)
>
> for i in range(2,1000):
> ring = ZZ.quotient(ZZ(i))
> vectorspace = ring^2
>
> import gc
> gc.collect()
> len(sage.structure.unique_representation.UniqueRepresentation.__classcall__.cache)
> }}}
> Related tickets:
> * #11521 (needs review, introducing weak references for caching
> homsets), and
> * #715 (needs review, using weak references for caching coerce maps).
> * #5970 (the polynomial rings cache use strong references, which may
> now be a duplicate, as I introduce the weak cache in #715)
>
> Further notes:
> * not everything in Python can be weakref'ed, for example ``None``
> cannot.
> * some results that are expensive to compute should not just be cached
> by a weak reference. Perhaps there is place for a permanent cache, or
> maybe some minimal age before garbage collecting it.
>
> __Apply__
>
> * [attachment:trac12215_weak_cached_function.patch]
> * [attachment:trac12215_segfault_fixes.patch]
New description:
The documentation says that UniqueRepresentation uses weak refs, but this
was switched over to the @cached_method decorator. The latter does
currently use strong references, so unused unique parents stay in memory
forever:
{{{
import sage.structure.unique_representation
len(sage.structure.unique_representation.UniqueRepresentation.__classcall__.cache)
for i in range(2,1000):
ring = ZZ.quotient(ZZ(i))
vectorspace = ring^2
import gc
gc.collect()
len(sage.structure.unique_representation.UniqueRepresentation.__classcall__.cache)
}}}
Related tickets:
* #11521 (needs review, introducing weak references for caching
homsets), and
* #715 (needs review, using weak references for caching coerce maps).
* #5970 (the polynomial rings cache use strong references, which may now
be a duplicate, as I introduce the weak cache in #715)
Further notes:
* not everything in Python can be weakref'ed, for example ``None``
cannot.
* some results that are expensive to compute should not just be cached
by a weak reference. Perhaps there is place for a permanent cache, or
maybe some minimal age before garbage collecting it.
__Apply__
* [attachment:trac12215_weak_cached_function-sk.patch]
* [attachment:trac12215_segfault_fixes.patch]
--
Comment:
The patches are now rebased rel #7980. I have not been able to replace my
first patch, because trac believes that it isn't my patch but Nicolas'...
Apply trac12215_weak_cached_function-sk.patch
trac12215_segfault_fixes.patch
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12215#comment:95>
Sage <http://www.sagemath.org>
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