Re: [PATCH 1/4] git-init-db should error out with a message

Alex Riesen <fork0@users.sourceforge.net> writes:

Actually, the users should not have to care how HEAD reference is implemented. It might make sense to use regular file symref regardless of platforms (i.e. never define USE_SYMLINK_HEAD on any platform).

We support reading from either kind of symref, so if we did that, the only case that *could* matter form compatibility point of view is that repositories touched by the updated git is unusable for an ancient git that does not understand regular file symref. From performance and simplicity point of view, however, using symlink when possible is better, and that is what Johannes' patch does.

HOWEVER, I think "falling back" (both in Johannes' patch which is in the "master" branch, and your version) has a funny failure mode. What happens when two processes try redirecting .git/HEAD simultaneously, possibly to different branch heads? Both of them unlink(), one successfully does symlink(), and the other gets EEXIST and falls back to create regular file symref.

Which is probably not so wrong; if this race matters, then you have bigger problem -- the user is doing 'git checkout' of different branches at the same time, or something silly like that. But it does not feel quite right, either.