#12313: Fix yet another memory leak caused by caching of coercion data
--------------------------------------------------+-------------------------
Reporter: SimonKing | Owner:
Type: defect | Status:
needs_review
Priority: major | Milestone: sage-5.3
Component: memleak | Resolution:
Keywords: coercion weak dictionary | Work issues:
Report Upstream: N/A | Reviewers: Simon King,
Jean-Pierre Flori, John Perry
Authors: Simon King, Jean-Pierre Flori | Merged in:
Dependencies: #11521, #11599, #12969, #12215 | Stopgaps:
--------------------------------------------------+-------------------------
Comment (by nbruin):
I think two dictionaries are to blame: `_cache` in
`sage/rings/polynomial/polynomial_ring_constructor.py` and `self._cache`
in `UniqueFactory`. If I change both to `dict()` I don't get an error. If
either is `Weak`, I do get the error.
In the process I saw how precarious `remove` methods are. I wanted to put
a `sys.stderr.write` in the `remove` function in `WeakValueDictionary`. I
ended up with
{{{
def __init__(self, *args, **kw):
MYSTDERR=sys.stderr
def remove(wr, selfref=ref(self)):
self = selfref()
if self is not None:
MYSTDERR.write("REMOVING A KEY\n");
del self.data[wr.key]
self._remove = remove
UserDict.UserDict.__init__(self, *args, **kw)
}}}
(so `remove` is a closure that keeps a reference to `MYSTDERR`) because
anything less would lead to errors. Apparently you cannot assume that the
globals dictionary of your module is still intact when your remove method
runs. That is such a restriction that I think we cannot expect people to
write their equality testers to survive in such a harsh environment. We
either have to track down all caches and tear them down in a more friendly
setting or we have to go with a "safe" WeakValueDictionary, which doesn't
call methods on keys upon removal.
I'm learning much more about Python than I ever wanted to know ...
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313#comment:217>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en.
