[oakenshield]

My 2 cents: many file systems do not have a file locking feature that can enforce file locking. In unix-like systems, file locks (e.g., lockf(3)) are "advisory" rather than mandatory, meaning it's up to the higher-layer apps to check whether another program has locked a file and voluntarily stop.

Any apps that do implement this feature likely do so by making the original file read-only and having the first app that opens the file work on a copy. However, I think Windows may have a mandatory file locking mechanism.