Program 2번 실행 방지

Main Program에서 아래 굵은 부분을 추가

        static System.Threading.Mutex singleton = new System.Threading.Mutex(true, "ssPLCADS");
        [STAThread]
        static void Main()
        {

            // Prevent launching my app multiple times
            if (!singleton.WaitOne(TimeSpan.Zero, true))
            {
                //there is already another instance running!
                MessageBox.Show("Instance already running");
                Application.Exit();
            }
            else
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                Application.Run(new FormMain());
            }
        }

**  출처 : https://stackoverflow.com/questions/93989/prevent-multiple-instances-of-a-given-app-in-net