#12313: Fix yet another memory leak caused by caching of coercion data
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Reporter: SimonKing | Owner:
Type: defect | Status: needs_work
Priority: major | Milestone: sage-pending
Component: memleak | Resolution:
Keywords: coercion weak dictionary | Work issues:
Report Upstream: N/A | Reviewers: Simon King,
Jean-Pierre Flori, John Perry, Nils Bruin
Authors: Simon King, Jean-Pierre Flori | Merged in:
Dependencies: #715, #11521, #12215, #13746 | Stopgaps:
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Comment (by nbruin):
Replying to [comment:268 SimonKing]:
> * Can we be sure that `self.D` is not None when the `TripleDictEraser`
is called?
I think so. Setting `self.D=None` must be part of a dealloc on the
`TripleDictEraser` itself. I don't see how Python could consider it not a
bug to call a `__call__` method that is in the process of being dealloc-ed
(see my [comment:267 remark])
> ... and gc decided to delete it first. Hence, when calling the eraser,
the `TripleDict` itself and not just its buckets is already gone.
That's why the Python GC does take some efforts to avoid calling avoidable
weakref callbacks.
> * Shouldn't the same be done with the `MonoDictEraser`?
I figured this was probably triggered by an interaction of a non-
weakreffable key component holding a reference to a weakreffable key
component, which doesn't happen in `MonoDict`. On the other hand, objects
in `MonoDict` could have a `TripleDict` on an attribute somewhere and I
don't immediately see a proof that such a construct could still lead to
this kind of nasty cycle (especially because I don't quite understand the
nature of the loop here that makes python execute this unnecessary
callback. Apparently Python doesn't purge ''all'' garbage callbacks before
doing ''any'' deletions on cyclic trash)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313#comment:269>
Sage <http://www.sagemath.org>
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