#14159: Don't install callbacks on values of TripleDict, MonoDict
-----------------------------+----------------------------------------------
Reporter: nbruin | Owner: tbd
Type: PLEASE CHANGE | Status: new
Priority: major | Milestone: sage-5.8
Component: PLEASE CHANGE | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
-----------------------------+----------------------------------------------
In #11521
[http://trac.sagemath.org/sage_trac/attachment/ticket/11521/trac_11521_callback.patch
trac_11521_callback.patch] a callback was installed on a weakref *value*
of a !TripleDict:
{{{
_cache[key] = KeyedRef(H, _cache.eraser, (id(X),id(Y),id(category)))
}}}
That's not safe: If the value under that key gets changed while the value
remains in memory, the callback will be executed and remove an entry that
now has an unrelated value!
So: Either prove that the value under this key will not change for the
lifetime of H (keep in mind that cyclic references can extend the lifetime
of an otherwise unreachable object essentially indefinitely, so the proof
needs to include that all key components survive H, otherwise those ids
could get reused) or provide a more selective callback (for instance,
ensure that the value is still as expected before deleting).
Another point is that the API of `_cache.eraser` isn't really published,
so this behaviour is probably better encapsulated in a method on the dict
itself.
See [http://trac.sagemath.org/sage_trac/ticket/12313#comment:317 #12313
comment 317] for a situation that likely implicates these callbacks
(someone has to hold strong references to these keys in order to set the
dict, so the absence of the keys suggests a spurious execution of this
kind of callback)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14159>
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 unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac?hl=en.
For more options, visit https://groups.google.com/groups/opt_out.
