Re: BUG: Race condition due to reflog expiry in "gc"

> I'm still working on fixing a race condition I encountered in "gc"
> recently, but am not 100% sure of the fix. So I thought I'd send a
> braindump of what I have so far in case it jolts any memories.
>
> The problem is that when we "gc" we run "reflog expire --all". This
> iterates over the reflogs, and takes a *.lock for each reference.
>
> It'll fail intermittendly in two ways:
>
>  1. If something is concurrently committing to the repo it'll fail
>     because we for a tiny amount of time hold a HEAD.lock file, so HEAD
>     can't be updated.
>
>  2. On a repository that's just being "git fetch"'d by some concurrent
>     process the "gc" will fail, because the ref's SHA1 has changed,
>     which we inspect as we aquire the lock.