How to prevent multiple executables from application

I am curious what would be the proper way to prevent a user from opening multiple executables of the same application. The reason I desire this type of functionality is because files are being manipulated by the executable and if another executable fires up and starts manipulating the files it could cause some issues. What is the best way to make sure that, if the executable is already running, the program either focuses on the current executable or denies the 2nd one from being launched?

Thanks for any help!