Question

Possible Duplicates:
What is the correct way to create a single instance application?
Prevent multiple instances of a given app in .NET?

Do I check whether another process with the same name exists? (What if the user doesn’t have permission to do that?)

Write a file to disk and delete it before exiting? (what about abnormal termination?)

What would be a best practice to do this?

Answer 1

You can use a Mutex.

bool firstInstance = true;
using (Mutex mutex = new Mutex(true, "MyApplicationName", out firstInstance))
{
    if (firstInstance)
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new MainForm());
    }
    else
    {
        // Another instance loaded
    }
}