using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Reflection;
//*****************************************************
 static class Program
  {
    /// <summary>
    /// 该函数设置由不同线程产生的窗口的显示状态。
    /// </summary>
    /// <param name="hWnd">窗口句柄</param>
    /// <param name="cmdShow">指定窗口如何显示。查看允许值列表，请查阅ShowWlndow函数的说明部分。</param>
    /// <returns>如果函数原来可见，返回值为非零；如果函数原来被隐藏，返回值为零。</returns>
    [DllImport("User32.dll")]
    private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);
    /// <summary>
    /// 该函数将创建指定窗口的线程设置到前台，并且激活该窗口。键盘输入转向该窗口，并为用户改各种可视的记号。系统给创建前台窗口的线程分配的权限稍高于其他线程。
    /// </summary>
    /// <param name="hWnd">将被激活并被调入前台的窗口句柄。</param>
    /// <returns>如果窗口设入了前台，返回值为非零；如果窗口未被设入前台，返回值为零。</returns>
    [DllImport("User32.dll")]
    private static extern bool SetForegroundWindow(IntPtr hWnd);
    private const int WS_SHOWNORMAL = 1;

    /// <summary>
    /// 应用程序的主入口点。
    /// </summary>
    [STAThread]
    static void Main()
    {
      Application.EnableVisualStyles();
      Application.SetCompatibleTextRenderingDefault(false);
      Process instance = RunningInstance();
      if (instance == null)
      {
        Form1 frm = new Form1();
        Application.Run(new Form1());
      }
      else
      {
        HandleRunningInstance(instance);
      }

    }
    /// <summary>
    /// 获取正在运行的实例，没有运行的实例返回null;
    /// </summary>
    public static Process RunningInstance()
    {
      Process current = Process.GetCurrentProcess();
      Process[] processes = Process.GetProcessesByName(current.ProcessName);
      foreach (Process process in processes)
      {
        if (process.Id != current.Id)
        {
          if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
          {
            return process;
          }
        }
      }
      return null;
    }

    /// <summary>
    /// 显示已运行的程序。
    /// </summary>
    public static void HandleRunningInstance(Process instance)
    {
      ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL); //显示，可以注释掉
      SetForegroundWindow(instance.MainWindowHandle);      //放到前端
    }
  }

//=====创建互斥体法：=====
bool blnIsRunning;
Mutex mutexApp = new Mutex(false, Assembly.GetExecutingAssembly().FullName, out  blnIsRunning);
if (!blnIsRunning)
{
  MessageBox.Show("程序已经运行！", "提示",
  MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  return;
}  



//保证同时只有一个客户端在运行  
System.Threading.Mutex mutexMyapplication = new System.Threading.Mutex(false, "OnePorcess.exe");
if (!mutexMyapplication.WaitOne(100, false))
{
  MessageBox.Show("程序" + Application.ProductName + "已经运行！", Application.ProductName,
  MessageBoxButtons.OK, MessageBoxIcon.Error);
  return;
}


//=====判断进程法：(修改程序名字后依然能执行)=====
Process current = Process.GetCurrentProcess();
Process[] processes = Process.GetProcessesByName(current.ProcessName);
foreach (Process process in processes)
{
  if (process.Id != current.Id)
  {
    if (process.MainModule.FileName
    == current.MainModule.FileName)
    {
      MessageBox.Show("程序已经运行！", Application.ProductName,
      MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
      return;
    }
  }
}

static void Main() 
{ 
  bool createNew; 
  using (System.Threading.Mutex m = new System.Threading.Mutex(true, Application.ProductName, out createNew)) 
  { 
    if (createNew) 
    { 
      Application.EnableVisualStyles(); 
      Application.SetCompatibleTextRenderingDefault(false); 
      Application.Run(new Form1()); 
    } 
    else 
    { 
      MessageBox.Show("Only one instance of this application is allowed!"); 
    } 
  } 
}
Boolean createdNew; //返回是否赋予了使用线程的互斥体初始所属权
System.Threading.Mutex instance = new System.Threading.Mutex(true, "MutexName", out createdNew); //同步基元变量
if (createdNew) //赋予了线程初始所属权，也就是首次使用互斥体
{
Application.Run(new Form1()); /s/这句是系统自动写的
instance.ReleaseMutex();
}
else
{
MessageBox.Show("已经启动了一个程序，请先退出！","系统提示",MessageBoxButtons.OK,MessageBoxIcon.Error);
Application.Exit();
}

Process.Start(Process.GetCurrentProcess().ProcessName + ".exe");
Application.Exit();

Process.Start(Process.GetCurrentProcess().ProcessName + ".exe");
Application.Exit();