用Mutex或進程限制使用者在一台電腦上同時開啟兩個程式

     經常我們希望一個程式開啟了以後，不希望開啟另一個執行個體。經過摸索，發現在有兩個方法可以解決，一個是通過進程，另一個是對過互 Mutex 類。
    
      
 1、使用 Mutex ， Mutex 中有個輸出參數可以標誌是否為新開啟的實列，我們通過這個參數來處理。    
using System;
using System.Threading;

public class Test
{
 public static void Main()
 {
  // Set this variable to false if you do not want to request
  // initial ownership of the named mutex.
  bool requestInitialOwnership = true;
  bool mutexWasCreated;

  // Request initial ownership of the named mutex by passing
  // true for the first parameter. Only one system object named
  // "MyMutex" can exist; the local Mutex object represents
  // this system object. If "MyMutex" is created by this call,
  // then mutexWasCreated contains true; otherwise, it contains
  // false.
  Mutex m = new Mutex(requestInitialOwnership, "MyMutex", out mutexWasCreated);
       
  // This thread owns the mutex only if it both requested
  // initial ownership and created the named mutex. Otherwise,
  // it can request the named mutex by calling WaitOne.
  if (!(requestInitialOwnership && mutexWasCreated))
  {
   Console.WriteLine("Waiting for the named mutex.");
   m.WaitOne();
  }

  // Once the process has gained control of the named mutex,
  // hold onto it until the user presses ENTER.
  Console.WriteLine("This process owns the named mutex. " +"Press ENTER to release the mutex and exit.");
  Console.ReadLine();

  // Call ReleaseMutex to allow other threads to gain control
  // of the named mutex. If you keep a reference to the local
  // Mutex, you can call WaitOne to request control of the
  // named mutex.
  m.ReleaseMutex();
 }
}

2 通過進程
  在進程池中尋找當前的進程名的進程。根據是否能找到來處理。下面的例子，先判斷是否已經開啟，如果開啟就把已經開啟的設定最大化，新程式不運行。（下面為WINFORM程式）
  using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace WinTest
{
 /// <summary>
 /// Program 的摘要說明。
 /// </summary>
 public class Program1
 {
  #region 應用程式的主進入點。

  [STAThread]
  static void Main()
  {
   mainForm mainForm = new mainForm();

   Process instance = RunningInstance();
   if (instance == null)
   {
    Application.Run(mainForm);
   }
   else
   {
    HandleRunningInstance(instance);
   }
  }

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

   //遍曆正在有相同名字啟動並執行常式
   foreach (Process process in processes)
   {
    //忽略現有的常式
    if (process.Id != current.Id)
    {
     //確保常式從EXE檔案運行
     if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\\\") ==
      current.MainModule.FileName)
     {
      //返回另一個常式執行個體
      return process;
     }
    }
   }
   //沒有其它的常式，返回Null
   return null;
  }

  private const int WS_SHOWNORMAL = 1; //winuser.h define
  private static void HandleRunningInstance(Process instance)
  {
   //確保視窗沒有被最小化或最大化
   ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);

   //設定真執行個體程為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);

  #endregion
 }
}