#12313: Fix yet another memory leak caused by caching of coercion data
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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:
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Comment (by nbruin):
> After finishing the tests, there is a `RuntimeError` "Unable to start
gap", and the stack is
> {{{
> (<frame object at 0x1408240>,
'/mnt/local/king/SAGE/prereleases/sage-5.3.beta2/local/lib/python2.7/weakref.py',
51, 'remove', [' del self.data[wr.key]\n'], 0)
> }}}
>
This is in the removal callback of a `WeakValueDictionary`. So, what I
*think* is
happening is that an object that is dependent on Gap for its equality test
is
used in a cache somewhere.
Probably during shutting down, the value gets deleted and the dictionary
gets
its callback to remove the value. However, this is during shutdown! Things
are
in funny states. Probably, the deletion from the dictionary doesn't really
matter anyway, because that's probably next in line to be destroyed.
However, the callback doesn't know that!
This is a nasty complication of these weakreffed dictionaries: the
callback code
can run under funny conditions and an equality test can involve a lot in
some
sage objects.
If we could tell our `WeakValueDictionaries` something about their
codomain
their callback could check if that still exists. If not then none of the
entries
matter, so you don't have to bother to locate the appropriate key. Just
delete
them all.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313#comment:199>
Sage <http://www.sagemath.org>
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