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, );

            int count = ;

            if ((int)handle != -)

            {

                PROCESSENTRY32 pe32 = new PROCESSENTRY32();

                pe32.dwSize = (uint)Marshal.SizeOf(typeof(PROCESSENTRY32));

                int bMore = Process32First(handle, ref pe32);

                while (bMore == )

                {

                    if (pe32.szExeFile == "自己的程序名")

                        count++;

                    bMore = Process32Next(handle, ref pe32);

                }

            }

            if (count > )

            {

                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 = )]//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);

        }

    }

}