Mutex

一个同步基元，也可用于进程间同步。 

即进程同步 当然也可以线程同步 

所以在线程同步角度来说，Monitor开销小，优于Mutex，

要实现进程同步，Monitor也干不了，Mutex是首选。

MSDN 实例：

This example shows how a Mutex is used to synchronize access
to a protected resource. Unlike Monitor, Mutex can be used with
WaitHandle.WaitAll and WaitAny, and can be passed across
AppDomain boundaries.

using System;
using System.Threading;

class Test
{
    // Create a new Mutex. The creating thread does not own the
    // Mutex.
    private static Mutex mut = new Mutex();
    private const int numIterations = 1;
    private const int numThreads = 3;

    static void Main()
    {
        // Create the threads that will use the protected resource.
        for(int i = 0; i < numThreads; i++)
        {
            Thread myThread = new Thread(new ThreadStart(MyThreadProc));
            myThread.Name = String.Format("Thread{0}", i + 1);
            myThread.Start();
        }

        // The main thread exits, but the application continues to
        // run until all foreground threads have exited.
    }

    private static void MyThreadProc()
    {
        for(int i = 0; i < numIterations; i++)
        {
            UseResource();
        }
    }

    // This method represents a resource that must be synchronized
    // so that only one thread at a time can enter.
    private static void UseResource()
    {
        // Wait until it is safe to enter.
        mut.WaitOne();

        Console.WriteLine("{0} has entered the protected area", 
            Thread.CurrentThread.Name);

        // Place code to access non-reentrant resources here.

        // Simulate some work.
        Thread.Sleep(500);

        Console.WriteLine("{0} is leaving the protected area
", 
            Thread.CurrentThread.Name);

        // Release the Mutex.
        mut.ReleaseMutex();
    }
}

    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 0; i < 20; i++)
            {
                Thread t = new Thread(Run);

                t.Start();
            }

            Console.Read();
        }

        static int count = 0;

        static Mutex mutex = new Mutex();

        static void Run()
        {
            Thread.Sleep(100);

            mutex.WaitOne();

            Console.WriteLine("当前数字：{0}", ++count);

            mutex.ReleaseMutex();
        }
    }

进程同步运行2个exe实例：

    class Program
    {
        static void Main(string[] args)
        {
            Thread t = new Thread(Run);

            t.Start();

            Console.Read();
        }

        static Mutex mutex = new Mutex(false, "tsp");

        static void Run()
        {
            mutex.WaitOne();

            Console.WriteLine("当前时间：{0}我是线程:{1}，我已经进去临界区", DateTime.Now, Thread.CurrentThread.GetHashCode());

            Thread.Sleep(10000);

            Console.WriteLine("
当前时间:{0}我是线程:{1}，我准备退出临界区", DateTime.Now, Thread.CurrentThread.GetHashCode());

            mutex.ReleaseMutex();
        }
    }

延伸 同理 一个运行程序只希望启动一个实例:

查看msdn

    public partial class App : System.Windows.Application
    {
        Mutex mutex;

        public App()
        {
            this.Startup += new StartupEventHandler(App_Startup);
        }

        void App_Startup(object sender, StartupEventArgs e)
        {
            bool ret;
            mutex = new Mutex(false, Process.GetCurrentProcess().ProcessName, out ret);
            if (!ret)
            {
                MessageBox.Show("程序已打开", "", MessageBoxButton.OK, MessageBoxImage.Stop);
                Environment.Exit(0);
            }
        }
    }