Re: concurrent fetches to update same mirror

Jeff King [off-list ref] writes:

Interestingly, in the case of ref _creation_, not update, like this:

  mkdir repo && cd repo && git init
  git remote add origin some-remote-repo-that-takes-a-few-seconds
  xterm -e 'git fetch -v; read' & xterm -e 'git fetch -v; read'

then both will happily update, the second one overwriting the results of
the first. It seems in the case of locking a ref which previously didn't
exist, we don't enforce that it still doesn't exist.

We probably should, especially when there is no --force or +prefix is
involved.