Re: git gc --auto aquires *.lock files that make a subsequent git-fetch error out

[Jeff King <peff@peff.net>]

On Wed, Jul 12, 2017 at 10:30:25PM +0200, Ævar Arnfjörð Bjarmason wrote:

> > Is it really "in a row" that's a problem? The second fetch should not
> > begin until the first one is done, including until its auto-gc exits.
> > And even with background gc, we do the ref-locking operations first, due
> > to 62aad1849 (gc --auto: do not lock refs in the background,
> > 2014-05-25).
> >
> >> I happen to run into this on a git.git which has a lot of remotes (most
> >> people on-list whose remotes I know about) and fetch them in parallel:
> >>
> >>     $ git config alias.pfetch
> >>     !parallel 'git fetch {}' ::: $(git remote)
> >
> > Ah, so it's not in a row. It's parallel. Then yes, you may run into
> > problems with the gc locks conflicting with real operations. This isn't
> > really unique to fetch. Any simultaneous operation can run into problems
> > (e.g., on a busy server repo you may see conflicts between pack-refs and
> > regular pushes).
> 
> This is what I thought at first, and I've only encountered the issue in
> this parallel mode (mainly because it's tedious to reproduce). But I
> think the traces below show that it would happen with "git fetch --all"
> & "git remote update" as well, so the parallel invocations didn't
> matter.
> 
> I.e. I'd just update my first remote, then git-gc would start in the
> background and lock refs for my other remotes, which I'd then fail to
> update.

No, it should be OK because of the commit I mentioned at the top of the
quoted section. Each one runs sequentially.

-Peff