Question about possible git races

I'd like to write a multithreaded application using git, so I'd like to see if there are any races:

- push vs pull
One thread pushes to the repository while another is pulling from it at the 
same time. I should get the older commit.

- push vs push
Both threads push at the same time. What happens?
Any good way to merge those pushes?
(I have full access to both repos)

Possibly those two aren't fast-forward of each other. I think one of the pushes should abort in this case unless I force it.

- fetch vs fetch
I mean that two threads try to fetch from different repositories to a single 
one. Possibly those two aren't fast-forward of each other.
Any good way to merge those fetches?
(I have full access to both repos)

I'm meaning really bare git there, w/o bash+perl scripts.