namespace MyNameSpace
{
    static class Program
    {
        [DllImport("Toolhelp.dll")]
        public static extern IntPtr CreateToolhelp32Snapshot(uint flags, uint processid);
        [DllImport("Toolhelp.dll")]
        public static extern int Process32First(IntPtr handle, ref PROCESSENTRY32 pe);
        [DllImport("Toolhelp.dll")]
        public static extern int Process32Next(IntPtr handle, ref PROCESSENTRY32 pe);
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [MTAThread]
        static void Main()
        {
            IntPtr handle = CreateToolhelp32Snapshot((uint)SnapShotFlags.TH32CS_SNAPPROCESS, 0);
            int count = 0;
            if ((int)handle != -1)
            {
                PROCESSENTRY32 pe32 = new PROCESSENTRY32();
                pe32.dwSize = (uint)Marshal.SizeOf(typeof(PROCESSENTRY32));
                int bMore = Process32First(handle, ref pe32);
                while (bMore == 1)
                {
                    if (pe32.szExeFile == "自己的程序名")
                        count++;
                    bMore = Process32Next(handle, ref pe32);
                }
            }
            if (count > 1)
            {
                MessageBox.Show("程序已经运行!");
                return;
            }
            else
            Application.Run(new FrmLogin());

        }
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct PROCESSENTRY32
    {
        public uint dwSize;
        public uint cntUsage;
        public uint th32ProcessID;
        public IntPtr th32DefaultHeapID;
        public uint th32ModuleID;
        public uint cntThreads;
        public uint th32ParentProcessID;
        public int pcPriClassBase;
        public uint dwFlags;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]//注意，此处为宽字符
        public string szExeFile;
        public uint th32MemoryBase;
        public uint th32AccessKey;
    }

    public enum SnapShotFlags : uint
    {
        TH32CS_SNAPHEAPLIST = 0x00000001,
        TH32CS_SNAPPROCESS = 0x00000002,
        TH32CS_SNAPTHREAD = 0x00000004,
        TH32CS_SNAPMODULE = 0x00000008,
        TH32CS_SNAPALL = (TH32CS_SNAPHEAPLIST | TH32CS_SNAPPROCESS | TH32CS_SNAPTHREAD | TH32CS_SNAPMODULE),
        TH32CS_GETALLMODS = 0x80000000
    }

}

using OpenNETCF.Threading;

namespace MyNameSpace
{
    static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [MTAThread]
        static void Main()
        {
            bool firstInstance;
            OpenNETCF.Threading.NamedMutex mutex = new OpenNETCF.Threading.NamedMutex(false, "自己起个名字", out firstInstance);
            if (!firstInstance)
            {
                MessageBox.Show("程序已启动");
                return;
            }

            Application.Run(new FrmLogin());
            GC.KeepAlive(mutex);

        }
    }


}