[PATCH 2 of 2] keyword: eliminate potential reference cycles from kwrepo

[Martin Geisler]

Christian Ebert <blacktrash at gmx.net> writes:

Hi Christian

> [...
>
> ATM there is a mixture of self.repomemberfunc and repo.repomemberfunc,
> and when I tried to clean this up Matt chimed in like so:
>
> http://marc.info/?l=mercurial-devel&m=124654567201924&w=2

Ah, I had forgotten about that mail...

>>>         def kwcommitctx(self, ctx, error=False):
>>>             wlock = lock = None
>>>             try:
>>> -                wlock = self.wlock()
>>> -                lock = self.lock()
>>> +                wlock = super(kwrepo, self).wlock()
>>> +                lock = super(kwrepo, self).lock()
>
> Third working alternative:
>                  wlock = repo.wlock()
>                  lock = repo.wlock()
>
> Basically I thought it would be good to use 1 of the 3 alternatives
> throughout.
>
>> Why is this necessary? The kwrepo class does not override the wlock
>> and lock methods, so I don't see why you would explicitly call the
>> superclass' methods?
>
> I'm not sure if this is necessary either. My layman's understanding
> is: it doesn't break, it works, fine ;-) However, this attitude is
> difficult to reconcile with my desire for consistency. And after
> Matt's reply I /believe/ calling the superclass method explicitly is
> safer.

I think he was talking about a different situation. He talked about
doing

  self.foo = self.bar

which apparently creates a reference cycle between self and itself(!)...
I don't know the finer details of Python reference counting, but it
surpricing that such an assignment should be dangerous.

However, you're simply calling a superclass' method and assigning the
result to a local variable. When the variable goes out of scope the
refcount of the superclass should go down as expected.

In any case, I think I'll let Matt or someone else decide on these
patches :-)

-- 
Martin Geisler

VIFF (Virtual Ideal Functionality Framework) brings easy and efficient
SMPC (Secure Multiparty Computation) to Python. See: http://viff.dk/.
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