How can I restrict the number of instances of my C program?

Question

Title says it all, I need to only allow one instance of my C program to be run. How can I accomplish this?

Answer 1

You can use shared memory for this purpose. Shared memory is an OS-level mechanism.

1. Start instance #1 of your app
   • The app checks the shared memory if there is a value stored
   • If not, the app stores some value into the shared memory.
2. Start instance #2 of your app
   • The app checks the shared memory if there is a value stored
   • The app sees there's already a shared memory value with a value and kills itself

You can use the shared memory to store the specific number of instances your app is allowed to run.