From: Mike Hommey <mh@glandium.org>
Date: Thu, 16 Apr 2020 04:24:49 GMT
Subject: Order of operations at the end of fast-import?
Message-ID: <20200416042449.ztgyrdunsrzt7avp@glandium.org>

Hi,

I just noticed that the order of operations at the end of fast-import
are:
- end_packfile
- dump_branches
- dump_tags

The first may create loose objects if the pack is small (per
fastimport.unpackLimit, defaulting to 100). The latter two create refs.

There seems to be a theoretical race condition here, if something else
triggers a gc at the "wrong" time, the loose objects might be cleaned up
and the branches/tags refs become dangling.

I understand that the packfile does need to be finished before creating
the refs, and that the unpacking replaces that when there aren't enough
objects, but wouldn't it be more data-safe to actually finish the pack,
create the refs, and then unpack?

Mike