CFT: fix OfflineIMAP lockup in single-threaded mode

[Eygene Ryabinkin]

Sun, Jan 27, 2013 at 08:39:13PM +0100, Nicolas Sebrecht wrote:
> Can't say whether the patch really fixes the issue

It should and in my testing -- is, but I am still waiting for Cyril's
review.

> but it's very pleasant to see work like that and activity on the
> repository in general (like Dmitrijs did recently). 

Thanks!

> > One thing that worries me currently is the way that options.singlethreading
> > is propagated from the main code: adding new pseudo-item to the 'general'
> > configuration section isn't that good.  Something like the singleton that
> > will provide read-only access to the options is a better way, in my view.
> 
> Well, as long as contributors and users are aware of what's going on and
> as long as whatever is released as stable is not experimental stuff,
> everything should be ok.

Yes.  I had implemented read-only depot for options, the modified patch
is at
  http://codelabs.ru/patches/offlineimap/2013-fix-deadlock-singlethreaded-IMAP-sync.diff

It additionally teaches folder/IMAP.py not to suggest multithreading while
OfflineIMAP works in single-threaded mode: it is simple, because now we
have global-like object that has all options.

> So, about this subtle and critical topic I'd say it's fine to go step by
> step. This would prevent from non-required headaches and could later
> help to distinguish newly introduced issues coming from the "core" fix
> and the "polishing" commit.

Well, I had missed this paragraph while I was polishing my commit.  Will
split it into two tomorrow.
-- 
rea