Re: Darcs-git: a few notes for Git hackers

From: Petr Baudis <pasky@ucw.cz>
Date: May 9, 2005, 21:28 UTC
Message-ID: <20050509212842.GC15712@pasky.ji.cz>
In-Reply-To: <7ihdhc5le2.fsf@lanthane.pps.jussieu.fr>

Dear diary, on Mon, May 09, 2005 at 08:01:25PM CEST, I got a letter where Juliusz Chroboczek <Juliusz.Chroboczek@pps.jussieu.fr> told me that...

Show 10 quoted lines

> 1. Darcs-git uses the fact that Git updates are atomic when reading
> from a Git repository.  Darcs-git almost writes to Git repositories
> atomically, with one exception: it performs a non-atomic
> read/update/write cycle on .git/HEAD.
> 
> For that reason, I'm taking a high-level lock on .git repositories
> whenever I write them.  The lockfile is ``.git/lock''.  I haven't
> thought about whether Darcs can be easily coerced into accessing Git
> repos atomically; have people writing Git wrappers found the need for
> a global lock?

FWIW, Cogito does not lock at all yet - this is one of the things which should be fixed soon.

>  - there's no way to have multiple simultaneous caches, short of
>    hacking at the values of Git's global variables by hand.

See the Brad Robert's patches of Apr 21. I've decided not to apply them since it appears a lot has changed since then and it would be some pain; but they may be a worthy starting point for a more up-to-date patch.

-- 
				Petr "Pasky" Baudis
Stuff: http://pasky.or.cz/
C++: an octopus made by nailing extra legs onto a dog. -- Steve Taylor