Make parallel use of inferiors when computing channel instance derivations,
and when extracting information about a revision. This should allow for some
horizontal scalability, reducing the impact of additional systems for which
derivations need computing.
This commit also fixes an apparent issue with package replacements, as
previously the wrong id was used, and this hid some issues around
deduplication.
Just have one fiber at the moment, but this will enable using fibers for
parallelism in the future.
Fibers seemed to cause problems with the logging setup, which was a bit odd in
the first place. So move logging to the parent process which is better anyway.
Listing remote branches through libgit2 will list branches that don't exist on
the remote. I think branch-list is more listing branch references, and you can
have references to a remote branch where the remote branch doesn't exist. This
isn't very useful here though, as I'm trying to work out what remote branches
exist.
There's remote-ls which might help, but I can't figure out how to get the
commits for branches from that.
Therefore, just bodge the two things together in to a big mess. I seem to be
able to get commits from branch-list that hopefully match what's on the
remote (although I'm not confident about this), and I think remote-ls does
allow checking what branches exist.
This is mostly a workaround for the occasional problems with the guix-commits
mailing list, as it can break and then the data service doesn't learn about
new revisions until the problem is fixed.
I think it's still a generally good feature though, and allows deploying the
data service without it consuming emails to learn about new revisions, and is
a step towards integrating some kind of way of notifying the data service to
poll.
There's an issue where sometimes for i686-linux and armhf-linux, only a few
package derivations are computed.
This commit tries to simplify the code, and adds some conditional logging for
the guix package, which might help reveal what's going on.
