Stay running?

Hi,

How can we instruct an Rust program to run24/7 in background without consuming many resources.
For instance i want the app to ‘watch’ one folder and if change happens move the new file to another folder.

Having a loop will kill the cpu and i’m wondering what is the logic around this.

The program must not terminate if it encounters an error.

I’m not looking for code solution but the explanation of have this works?

Thanks