I thought about the issue further. The approach with the "state[]"
feature reduces problematic "store" operations a lot in most cases, it
is however not perfect to avoid the original issue about parallel
execution.

For example (though quite artificial), let's suppose if two git commands
start simultaneously where the credential is input automatically by
"expect" command. Two "osxkeychain store" commands will then run
simultaneously.

I hope new descriptions are convincing.

Koji Nakamaru