HAO are you~

using System;
using System.Threading;

public class Example
{
    // mre is used to block and release threads manually. It is
    // created in the unsignaled state.
    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();  //開始線程
        }

        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();//這行之前的執行緒(0~4)都還是為Set()。之後的Thread_5才會為Reset()，又恢復不會執行WaitOne後面的code

        // 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();  //阻塞線程，直到調用Set方法才能繼續執行

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

執行結果：

MRE有3種控制執行緒狀態的方法：

1.Set()=>關閉WaitOne訊號，(ThreadPool撈出的)執行緒可以繼續執行.WaitOne()之後的程式
 2.Reset()=>開啟WaitOne訊號，(ThreadPool撈出的)執行緒遇到WaitOne()會被中止
 3.WaitOne()=>MRE設定執行緒中止點，中斷執行緒到重新呼叫Set()。執行緒才會繼續往下執行WaitOne()後面的程式     

 

ManualResetEvent(false) 的建構子參數可以設定初始訊號：

true=>有訊號，預設MRE狀態為Set()，WaitOne失效，可以想像成瑪莉歐吃到無敵星星一樣，遇到WaitOne都不會被阻擋，會往下執行，直到重新呼叫ReSet()時WaitOne()才會重新生效。

false=>無訊號，預設MRE狀態為ReSet()，WaitOne生效()。遇到WaitOne()後執行緒會中止，不會往下執行WaitOne()後的程式，直到重新呼叫Set()時訊號才會變成true，繼續往下執行WaitOne後的程式。如果要把訊號再變為無訊號(false)，則要再呼叫Reset()，不然Set()後，Reset()前，WaitOne()會是一直沒用的狀態了。

 

reference：

ManualResetEvent 類別 = >Microsoft api手冊

C# ManualResetEvent用法

C# 執行緒(Thread)的AutoResetEvent及ManualResetEvent探討 =>想了解AutoResetEvent & ManualResetEvent差別可以看這篇

C#使用AutoResetEvent實現同步