如何让程序只运行一次实例

最近在做一个系统的客户端时，遇到一个问题：客户端运行在服务器上时，如果同一个用户或其他用户运行了这个客户端，可能会导致错误。这就要求该程序的实例只能运行一次。

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Reflection;

namespace EMCNameCardMail
{
    static class Program
    {
        /// 

        /// 应用程序的主入口点。
        /// 
        [STAThread]
        static void Main()
        {
            
            //Get the running instance.
            Process instance = RunningInstance();
            if (instance == null)
            {
                //There isn't another instance, show our form.
              
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                Application.Run(new MailForm());
            }
            else
            {
                MessageBox.Show("你只能运行该程序的一个实例!", "**系统邮件群发客户端", MessageBoxButtons.OK, MessageBoxIcon.Information);
                //There is another instance of this process.
                HandleRunningInstance(instance);
            }

        }
        public static Process RunningInstance()
        {
            Process current = Process.GetCurrentProcess();
            Process[] processes = Process.GetProcessesByName(current.ProcessName);

            //Loop through the running processes in with the same name
            foreach (Process process in processes)
            {
                //Ignore the current process
                if (process.Id != current.Id)
                {
                    //Make sure that the process is running from the exe file.
                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "//") ==
                    current.MainModule.FileName)
                    {
                        //Return the other process instance.
                        return process;
                    }
                }
            }

            //No other instance was found, return null.
            return null;
        }


        public static void HandleRunningInstance(Process instance)
        {
            //Make sure the window is not minimized or maximized
            ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);

            //Set the real intance to foreground window
            SetForegroundWindow(instance.MainWindowHandle);
        }

        [DllImport("User32.dll")]
        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);
        [DllImport("User32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);
        private const int WS_SHOWNORMAL = 1;





    }
}