C#: restrict a program to a single instance

static void Main()
{
Process ThisProcess = Process.GetCurrentProcess();
Process [] AllProcesses = Process.GetProcessesByName(ThisProcess.ProcessName);
if (AllProcesses.Length > 1)
{
MessageBox.Show(ThisProcess.ProcessName + " is already running", ThisProcess.ProcessName, MessageBoxButtons.OK, MessageBoxIcon.Error);
} else {
Application.Run(new MainForm());
}
}