importer is not idempotent on import tags

[Robie Basak]

For reasons I have yet to debug, when I run the importer it sometimes hangs after finishing the first push (Executing: git push pkg "refs/heads/importer/*:refs/heads/*"). I see a zombie git process, but Python is stuck. I would like a backtrace for this, but that's currently suppressed by default and I haven't got round to changing it to debug.

What I usually do in this case is re-run the git push in a different terminal window. When it says its done, I kill the importer.

This currently means that tags currently do not get pushed in this scenario.

AFAICT, if I were to then throw away my importer directory, the import tags would never get re-created, and they'd forever be missing.

I noticed and recovered this time by pushing the import tag manually.

Incidentally, running the importer again (and it completing fully this time) didn't seem to recover the situation. I expected that it would because the import tag was still local (under importer/import/...). The verbose log did say "git push pkg "refs/tags/importer/*:refs/tags/*"" but this didn't seem to actually do anything. When I ran this manually, only then did it push the tag. I wonder if this is related to my problem of the subprocess hanging Python.

To fix this bug, I think we need to use "git push --atomic" and push both the heads and the tags in the same command (with two refspecs).