C# 禁止程序多个实例运行

//program.cs
static class Program
{
/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main()
{
bool ret = false;
System.Threading.Mutex running = new System.Threading.Mutex(true, Application.ProductName, out ret);
if (ret)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new FormMain());
running.ReleaseMutex();
}
else
{
MessageBox.Show("程序已经在运行，请不要同时运行多个本程序！", "提示！", MessageBoxButtons.OK, MessageBoxIcon.Information);
Application.Exit();
}
}
}