This is similar to the pusher thread, but a separate thread because git
pushes can be done in parallel with exports, and updating a big export
should not prevent other git pushes going out in the meantime.
The exportThread only runs at most every 30 seconds, since updating an
export is more expensive than pushing. This may need to be tuned.
Added a separate channel for export commits; the committer records a
commit in that channel.
Also, reconnectRemotes records a dummy commit, to make the exporter
thread wake up and make sure all exports are up-to-date. So,
connecting a drive with a directory special remote export will
immediately update it, and getting online will automatically
update S3 and WebDAV exports.
The transfer queue is not involved in exports. Instead, failed
exports are retried much like failed pushes.
This commit was sponsored by Ewen McNeill.
I now have this topology working:
assistant ---> {bare repo, special remote} <--- assistant
And, I think, also this one:
+----------- bare repo --------+
v v
assistant ---> special remote <--- assistant
While before with assistant <---> assistant connections, both sides got
location info updated after a transfer, in this topology, the bare repo
*might* get its location info updated, but the other assistant has no way to
know that it did. And a special remote doesn't record location info,
so transfers to it won't propigate out location log changes at all.
So, for these to work, after a transfer succeeds, the git-annex branch
needs to be pushed. This is done by recording a synthetic commit has
occurred, which lets the pusher handle pushing out the change (which will
include actually committing any still journalled changes to the git-annex
branch).
Of course, this means rather a lot more syncing action than happened
before. At least the pusher bundles together very close together pushes,
somewhat. Currently it just waits 2 seconds between each push.
