Re: [Administrivia] On ruby and contrib/

From: Jeff King <peff@peff.net>
Date: Jun 8, 2013, 17:15 UTC
Message-ID: <20130608171513.GA28029@sigill.intra.peff.net>
In-Reply-To: <CAMP44s192hzh8AWU-Eg1VVVXjZ9qyNqHw99X6y48MXJn3DHw+Q@mail.gmail.com>

On Sat, Jun 08, 2013 at 08:20:28AM -0500, Felipe Contreras wrote:

Show 8 quoted lines

> > There are a lot of static variables in builtin/ (and outside too),
> > which make it non-entrant, or at least not safe.
> 
> So?
> 
> > fork provides a process space isolation, some depend on that.
> 
> Process space isolation from what?

Manipulation of global variables. Here are a few examples off the top of my head:

Try running "git diff" from your Ruby hook, then try running "git diff-files" within the same process. I believe the latter will start respecting porcelain diff config like diff.mnemonicprefix. To clear state you need to reset a list of global variables back to their initial states (some of which are the BSS-default zero, but some of which are not).

Try running "git log" followed by another "git log". The log family of commands does not clear its marks from the commit objects, since it expects to exit after the traversal. The second log will sometimes give wrong answers if its traversal overlaps with the first (e.g., commits marked SEEN or UNINTERESTING that should not be). You can add a call to clear them at the end of the process, but that does not cover any cases where we die().

These are problems that can be solved. But there is a lot of work involved in finding these subtle bugs and coming up with fixes. I think you would be better off working on an implementation of git that was designed from scratch to work in-process, like libgit2. And it even has an actively developed and maintained Ruby binding[1].

libgit2 doesn't have feature parity with regular git yet, but there are many clients based around it that use the library internally for speed, and then exec regular git to fill in the gaps.

-Peff

[1] https://github.com/libgit2/rugged