concurrent fetches to update same mirror

If two or more different users perform a git-fetch on the same mirror 
(--mirror) repo concurrently, could that cause corruption?  I tried a manual 
test using the git protocol over separate machines and they both thought 
they needed to do the full updates and they both appeared to work.  I'm not 
sure if git is serializing this, or if it is possible for concurrent fetches 
to step on each other.

v/r,
Neal