Threading

Try this example:

using System;
using System.Threading;

class Program
{
   static void Main()
   {
      // create Mutex with a 'unique' name
      Mutex m = new Mutex(false, "Raps Gao Single Instance App");
      // give any existing instance a chance to shutdown
      if (!m.WaitOne(TimeSpan.FromSeconds(2), false))
      {
         Console.WriteLine("There is already an existing instance running");
      }
      else
      {
         Run();
      }
      m.Dispose();
   }  

   static void Run()
   {
      Console.WriteLine("Program is running - please any key to close down");
      Console.ReadKey(true);
   }
}