You've used the requisite search terms -- file and lock.

So why didn't you search for a howto?

And, not just BTW, most of your "simplicity sake" (sic) discussion simply adds verbosity and concepts that are irrelevant to "jsut (sic) what steps" are required to accomplish file locking during a specific set of operations.

OTOH, you don't tell us what OS (which is relevant, as JavaFan points out) nor do you show us any code or pseudocode illustrating what you've tried and where you're stuck.