#11521: Use weak references to cache homsets
--------------------------------------------------+-------------------------
Reporter: jpflori | Owner: robertwb
Type: defect | Status:
needs_review
Priority: major | Milestone: sage-5.3
Component: coercion | Resolution:
Keywords: sd35 | Work issues:
Report Upstream: N/A | Reviewers: Jean-Pierre
Flori
Authors: Simon King | Merged in:
Dependencies: #12969; to be merged with #715 | Stopgaps:
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Comment (by nbruin):
'''sage/categories/homset.py''':
{{{
_cache = TripleDict(53)
}}}
I guess this 53 is a tuned parameter. Can you comment on the choice?
line 214
{{{
try:
H = _cache[key]()
except KeyError:
H = None
if H:
}}}
Could it happen that bool(H) is false if H is not None? Perhaps safer to
test
`H is not None`? I'm not saying that you should. Just comment please.
line 247 (same thing)
line 263
{{{
_cache[key] = weakref.ref(H)
}}}
Can you clarify the following: The way I read this is that H will not be
protected against GC (good!), but that `_cache` will be be storing a
strong(?)
reference to `key`, meaning that the entry in `_cache` under `key` will
linger
with a dead weakref afterwards. Shouldn't there be a callback registered
here
with the weakref that contacts `_cache` to remove the `key` entry when `H`
gets
collected? It may be that your #715 changes already make `_cache` into
essentially a
`WeakKeyDict`, but it seems to me that `_cache` should still have a
callback
registered on the `weakref` to `H` as well, to remove the entry if `H`
gets GCd.
I haven't done extensive testing myself, but you have and the bot happy,
so I don't think me running tests would change much.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11521#comment:145>
Sage <http://www.sagemath.org>
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