使用AutoResetEvent,ManualResetEvent和ManualResetEventSlim类进行线程间通信

 AutoResetEvent和ManualResetEvent允许线程通过发信号进行通信。

 两者都有两个信号量：True和False。都通过Set()和ReSet()来设置。并且使用WaitOne()的方法阻止当前的线程。

 不同的是AutoResetEvent在调用Set()把信号量释放后(信号量设置为True),然后自动返回到终止状态(信号量为False). 

 线程通过调用 AutoResetEvent 上的 WaitOne 来等待信号。 如果 AutoResetEvent 为非终止状态，则线程会被阻止，并等待当前控制资源的线程通过调用 Set 来通知资源可用。
 调用 Set 向 AutoResetEvent 发信号以释放等待线程。 AutoResetEvent 将保持终止状态，直到一个正在等待的线程被释放，然后自动返回非终止状态。 如果没有任何线程在等待，则状态将无限期地保持为终止状态。
如果当 AutoResetEvent 为终止状态时线程调用 WaitOne，则线程不会被阻止。 AutoResetEvent 将立即释放线程并返回到未触发状态。

 ManualResetEvent在调用Set()后，需要手动调用ReSet()恢复到终止状态。

 ManualResetEventSlim是ManualResetEvent的简化版本，是4.0新增的类。使用Wait()方法来阻止线程。

 MSDN上的代码很好的解释了如何使用：

 Code:

使用AutoResetEvent 

   class Example
    {
        private static AutoResetEvent event_1 = new AutoResetEvent(true); 
        private static AutoResetEvent event_2 = new AutoResetEvent(false);

        static void Main()
        {
            Console.WriteLine("Press Enter to create three threads and start them.\r\n" +
                              "The threads wait on AutoResetEvent #1, which was created\r\n" +
                              "in the signaled state, so the first thread is released.\r\n" +
                              "This puts AutoResetEvent #1 into the unsignaled state.");
            Console.ReadLine();

            for (int i = 1; i < 4; i++)
            {
                Thread t = new Thread(ThreadProc);
                t.Name = "Thread_" + i;
                t.Start();
            }
            Thread.Sleep(1000);

            for (int i = 0; i < 2; i++)
            {
                Console.WriteLine("Press Enter to release another thread.");
                Console.ReadLine();
                event_1.Set();
                Thread.Sleep(250);
            }

            Console.WriteLine("\r\nAll threads are now waiting on AutoResetEvent #2.");
            for (int i = 0; i < 3; i++)
            {
                Console.WriteLine("Press Enter to release a thread.");
                Console.ReadLine();
                event_2.Set();
                Thread.Sleep(250);
            }

            // Visual Studio: Uncomment the following line.
            //Console.Readline();
        }

        static void ThreadProc()
        {
            string name = Thread.CurrentThread.Name;

            Console.WriteLine("{0} waits on AutoResetEvent #1.", name);
            event_1.WaitOne();
            Console.WriteLine("{0} is released from AutoResetEvent #1.", name);

            Console.WriteLine("{0} waits on AutoResetEvent #2.", name);
            event_2.WaitOne();
            Console.WriteLine("{0} is released from AutoResetEvent #2.", name);

            Console.WriteLine("{0} ends.", name);
        }
    }

使用ManualResetEvent

   public class Example
    {
        private static ManualResetEvent mre = new ManualResetEvent(false);

        static void Main()
        {
            Console.WriteLine("\nStart 3 named threads that block on a ManualResetEvent:\n");

            for (int i = 0; i <= 2; i++)
            {
                Thread t = new Thread(ThreadProc);
                t.Name = "Thread_" + i;
                t.Start();
            }

            Thread.Sleep(500);
            Console.WriteLine("\nWhen all three threads have started, press Enter to call Set()" +
                              "\nto release all the threads.\n");
            Console.ReadLine();

            mre.Set();

            Thread.Sleep(500);
            Console.WriteLine("\nWhen a ManualResetEvent is signaled, threads that call WaitOne()" +
                              "\ndo not block. Press Enter to show this.\n");
            Console.ReadLine();

            for (int i = 3; i <= 4; i++)
            {
                Thread t = new Thread(ThreadProc);
                t.Name = "Thread_" + i;
                t.Start();
            }

            Thread.Sleep(500);
            Console.WriteLine("\nPress Enter to call Reset(), so that threads once again block" +
                              "\nwhen they call WaitOne().\n");
            Console.ReadLine();

            mre.Reset();

            // Start a thread that waits on the ManualResetEvent.
            Thread t5 = new Thread(ThreadProc);
            t5.Name = "Thread_5";
            t5.Start();

            Thread.Sleep(500);
            Console.WriteLine("\nPress Enter to call Set() and conclude the demo.");
            Console.ReadLine();

            mre.Set();

            // If you run this example in Visual Studio, uncomment the following line:
            //Console.ReadLine();
        }

        private static void ThreadProc()
        {
            string name = Thread.CurrentThread.Name;

            Console.WriteLine(name + " starts and calls mre.WaitOne()");

            mre.WaitOne();

            Console.WriteLine(name + " ends.");
        }
    }

使用ManualResetEventSlim

   class MRESDemo
    {
        static void Main()
        {
            MRES_SetWaitReset();
            MRES_SpinCountWaitHandle();
            Console.ReadKey();
        }
        static void MRES_SetWaitReset()
        {
            ManualResetEventSlim mres1 = new ManualResetEventSlim(false); // initialize as unsignaled
            ManualResetEventSlim mres2 = new ManualResetEventSlim(false); // initialize as unsignaled
            ManualResetEventSlim mres3 = new ManualResetEventSlim(true);  // initialize as signaled

            var observer = Task.Factory.StartNew(() =>
            {
                mres1.Wait();
                Console.WriteLine("observer sees signaled mres1!");
                Console.WriteLine("observer resetting mres3...");
                mres3.Reset(); 
                Console.WriteLine("observer signalling mres2");
                mres2.Set();
            });
            Console.WriteLine("main thread: mres3.IsSet = {0} (should be true)", mres3.IsSet);
            Console.WriteLine("main thread signalling mres1");
            mres1.Set();
            mres2.Wait();

            Console.WriteLine("main thread sees signaled mres2!");
            Console.WriteLine("main thread: mres3.IsSet = {0} (should be false)", mres3.IsSet);

            observer.Wait(); // make sure that this has fully completed
            mres1.Dispose();
            mres2.Dispose();
            mres3.Dispose();
        }

        static void MRES_SpinCountWaitHandle()
        {
            // Construct a ManualResetEventSlim with a SpinCount of 1000
            // Higher spincount => longer time the MRES will spin-wait before taking lock
            ManualResetEventSlim mres1 = new ManualResetEventSlim(false, 1000);
            ManualResetEventSlim mres2 = new ManualResetEventSlim(false, 1000);

            Task bgTask = Task.Factory.StartNew(() =>
            {
                Thread.Sleep(100);
                Console.WriteLine("Task signalling both MRESes");
                mres1.Set();
                mres2.Set();
            });

            WaitHandle.WaitAll(new WaitHandle[] { mres1.WaitHandle, mres2.WaitHandle });
            Console.WriteLine("WaitHandle.WaitAll(mres1.WaitHandle, mres2.WaitHandle) completed.");

            bgTask.Wait();
            mres1.Dispose();
            mres2.Dispose();
        }
    }