Is there an agreed protocol for git repo locking?

As I understand it, the normal use case for git is one in which a
single user performs a number of git operations in sequence on a
private repo.

As such, locking issues don't normally arise - the user is only doing
one thing at once.

I am working on an idea which will imply the need for concurrently
executing processes to modify the repo, in particular refs.  I
specifically don't want to have a repo for each process precisely
because I don't want to incur the costs of repo creation for every
process and, in any case, I need them to share the refs.

In my use case, I may need locks that span several otherwise atomic
operations - therefore relying on atomic locks that each git tool
might employ for safety is not sufficient.

Is there an agreed upon locking protocol for the git repo? Is there
tool support for this locking?

The case for adding it is that locking protocols only work if everyone
agrees on the same protocol. The easiest way to do this would be to
provide tools that enforce the desired locking protocol.

jon.