#13394: Write a WeakValueDictionary with safer key removal
-------------------------------------+-------------------------------------
Reporter: nbruin | Owner: rlm
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.13
Component: memleak | Resolution:
Keywords: | Merged in:
Authors: Simon King, Nils | Reviewers: Simon King
Bruin | Work issues:
Report Upstream: None of the above | Commit:
- read trac for reasoning. | 851cc9522dde332561101f1c84182a0a84b8eed4
Branch: | Stopgaps:
u/SimonKing/ticket/13394 |
Dependencies: |
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Comment (by SimonKing):
Bad news. When trying to turn your stress test into an indirect test,
things didn't work for me:
{{{
sage: B=3
sage: L = [None]*B
sage: D1 = WeakValueDictionary()
sage: D2 = WeakValueDictionary()
sage: import gc
sage: for i in range(100):
....: ki = floor(random()*B)
....: vi = C(floor(random()*B))
....: print "assign",ki,id(vi),"to D1"
....: D1[ki] = vi
....: print "assign",ki,id(vi),"to D2"
....: D2[ki] = vi
....: print "assign",ki,id(vi),"to L"
....: L[ki] = vi
....: ko = floor(random()*B)
....: if ko in D1:
....: print "delete",ko,id(L[ko]),"from D1"
....: del D1[ko]
....: print "delete",ko,id(L[ko]),"from L"
....: L[ko] = None
....: _ = gc.collect()
....: assert D1 == D2
assign 2 220846028 to D1
assign 2 220846028 to D2
assign 2 220846028 to L
assign 0 220845964 to D1
assign 0 220845964 to D2
assign 0 220845964 to L
assign 1 220845932 to D1
assign 1 220845932 to D2
assign 1 220845932 to L
delete 0 220845964 from D1
delete 0 220845964 from L
bye-bye 220845964
assign 2 221294892 to D1
assign 2 221294892 to D2
assign 2 221294892 to L
bye-bye 220846028
delete 1 220845932 from D1
delete 1 220845932 from L
bye-bye 220845932
assign 0 221294764 to D1
assign 0 221294764 to D2
assign 0 221294764 to L
delete 2 221294892 from D1
delete 2 221294892 from L
bye-bye 221294892
assign 1 221294700 to D1
assign 1 221294700 to D2
assign 1 221294700 to L
delete 1 221294700 from D1
delete 1 221294700 from L
Traceback (most recent call last):
...
AssertionError:
}}}
Do you think this is from a design flaw (race condition) in my test? Or do
you think it is a genuine problem of our code?
To my understanding, deletion of a value (and thus execution of the
callback) should happen immediately after replacing the value on the list
`L`: Cyclic garbage collection is not involved, and hence there should be
no delay. However, just to be on the safe side, I explicitly added a
garbage collection.
Or did I misunderstand how deallocation of Python objects without
reference cycles is working? Can there be a delay?
--
Ticket URL: <http://trac.sagemath.org/ticket/13394#comment:73>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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