//方法一：只禁止多个进程运行
using System;
using System.Collections.Generic;
using System.Windows.Forms;
namespace DuoYeMianIE
{
    static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            bool ret;
            System.Threading.Mutex mutex = new System.Threading.Mutex(true, Application.ProductName, out ret);
            if (ret)
            {
                System.Windows.Forms.Application.EnableVisualStyles();   //这两行实现   XP   可视风格   
                System.Windows.Forms.Application.DoEvents();             //这两行实现   XP   可视风格   
                System.Windows.Forms.Application.Run(new LamBrowser());
                //   Main   为你程序的主窗体，如果是控制台程序不用这句   
                mutex.ReleaseMutex();
            }
            else
            {
                MessageBox.Show(null, "有一个和本程序相同的应用程序已经在运行，请不要同时运行多个本程序。\n\n这个程序即将退出。", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Warning);
                //   提示信息，可以删除。   
                Application.Exit();//退出程序   
            }
        }
    }
}

//方法二：禁止多个进程运行,并当重复运行时激活以前的进程
using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Reflection;
namespace DuoYeMianIE
{
    static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            //Get   the   running   instance.   
            Process instance = RunningInstance();
            if (instance == null)
            {
                System.Windows.Forms.Application.EnableVisualStyles();   //这两行实现   XP   可视风格   
                System.Windows.Forms.Application.DoEvents();
                //There   isn't   another   instance,   show   our   form.   
                System.Windows.Forms.Application.Run(new LamBrowser());
            }    
            else
            {
                //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;
    }
}