Function tracker_commit_lock 

pub fn tracker_commit_lock(dir: &Path) -> CommitLock

Hold the tracker checkout that holds dir for one write to its index: a status read, a file write, an add and a commit, a rebase, or a push. A background push keeps the same file locked until git push exits, hook included, so the next ljos call waits here instead of meeting that hook on index.lock. Every ljos writer on the host takes it. Taking it twice in one thread waits forever.