Remote operations synchronization, and hooks

Is there any kind of synchronization with remote operations? That is, can there be any race conditions if multiple clients connect? I'm assuming that such operations are safe, but I couldn't find a place with a concrete description.

More specifically, I'm wondering about writing hooks (specifically, a `post-receive' hook), and it would make things convenient if I knew that it was called synchronously.

And a related question: is there somewhere a summary of how the hooks are called for each operation? The githooks man page specifies some of the relationships but a list with how each operation perform its work would be much more convenient to read through. For example, if a remote update had a list of operations with "grab lock" in the beginning and a "release lock" after running the `post-receive' hook, then I wouldn't have the above question. Also, it's unclear how `post-update' is related to `post-receive' -- there's one comment in the man entry for the former that makes it sound like it is supersedes by the latter, but there's nothing explicit about it.