[ZODB-Dev] transaction "Attempts" class

[Chris McDonough]

On Thu, 2012-03-29 at 07:18 -0400, Jim Fulton wrote:
> On Wed, Mar 28, 2012 at 6:37 PM, Chris McDonough <chrism at plope.com> wrote:
> > On Wed, 2012-03-28 at 17:06 -0400, Jim Fulton wrote:
> >> On Wed, Mar 28, 2012 at 4:37 PM, Chris McDonough <chrism at plope.com> wrote:
> >> > On Wed, 2012-03-28 at 14:21 -0400, Jim Fulton wrote:
> >> ...
> >> > A decorator for running some code in the context of a txn and retrying
> >> > retryable exceptions would be nice higher level behavior. Â I'd be
> >> > willing to do this work over this weekend.
> >>
> >> Cool.  Don't forget the transaction note part. :)
> >> Too many transactions in our apps don't have
> >> notes, especially transactions that happen
> >> outside of web requests.
> >>
> >> > In the meantime, I think the existing attempts context manager still
> >> > needs the small fix I proposed in my original message. Â Can you confirm
> >> > that my understanding of the its intent seems roughly correct?
> >>
> >> I didn't see a statement of intent.  I think your fix us good,
> >> but the code (that I wrote and your fix) makes my head hurt. :)
> >>
> >> I'd say, make some test cases for the bug and make it pass.
> >
> > OK.  Once I fix this "Attempts" bug, I think the decorator code is just
> > a higher level interface that uses it:
> >
> > class job(object):
> >    def __init__(self, attempts=1, note=None, manager=None):
> >        self.attempts = attempts
> >        self.note = note
> >        if manager is None:
> >            manager = transaction.manager
> >        self.manager = manager
> >
> >    def __call__(self, wrapped):
> >        note = self.note
> >        if note is None:
> >            note = getattr(wrapped, '__name__', None)
> >        def inner(*arg, **kw):
> >            for attempt in self.manager.attempts(self.attempts):
> >                with attempt as t:
> >                    t.note(note)
> >                    return wrapped(*arg, **kw)
> >
> > .. or something like that...
> 
> It could be written that way, although I would
> use a much simpler implementation.
> 
> The attempt design was a reach to overcome
> the limitations of the with statement.  I'm not at all happy
> with it, although I couldn't think of anything better at the
> time.  I hate to build on it.

It's brainbusting, yes, but it works.  Do you have any other specific
pattern in mind?

- C