C# ManualResetEvent 類詳解

定義

ManualResetEvent 類
命名空間：System.Threading
程序集：mscorlib.dll
表示線程同步事件，收到信號時，必須手動重置該事件。 無法繼承此類。

用於對於所有線程的控制：

常見使用方法：
1、初始化；

//true-初始狀態爲發出信號；false-初始狀態爲未發出信號，一般設置爲false，手動來發出信號
 ManualResetEvent mre = new ManualResetEvent(false);

2、阻塞

mre.WaitOne();  //所有線程會被阻塞，直到set後，才執行WaitOne()後的代碼

3、解除阻塞

mre.Set();  //當你想要的狀態達到了，就接觸阻塞，繼續執行線程後面的代碼
//備註： Set()後，如果再調用WaitOne()是無效的，線程不會被阻塞，必須調用Reset()才行

4、重置

mre.Reset();  //重置，只有這樣，當執行WaitOne()的時候纔會再次被阻塞

---

最後上一個官方的案例：

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");
		//中文註釋1：開啓三個線程，每個線程開啓後調用WaitOne()阻塞。
        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();
		//中文註釋2：只有當Set()後纔會執行WaitOne()後的代碼
        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();
		//中文註釋3：繼續再開兩個線程，仍然調用WaitOne(),但是不會阻塞，會繼續執行
        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();
		//中文註釋4：只有Reset()後，下面再開線程就會繼續被阻塞
        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();
		//中文註釋5：再次Set(),就可以了
        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.");
    }
}

/* This example produces output similar to the following:

Start 3 named threads that block on a ManualResetEvent:

Thread_0 starts and calls mre.WaitOne()
Thread_1 starts and calls mre.WaitOne()
Thread_2 starts and calls mre.WaitOne()

When all three threads have started, press Enter to call Set()
to release all the threads.


Thread_2 ends.
Thread_0 ends.
Thread_1 ends.

When a ManualResetEvent is signaled, threads that call WaitOne()
do not block. Press Enter to show this.


Thread_3 starts and calls mre.WaitOne()
Thread_3 ends.
Thread_4 starts and calls mre.WaitOne()
Thread_4 ends.

Press Enter to call Reset(), so that threads once again block
when they call WaitOne().


Thread_5 starts and calls mre.WaitOne()

Press Enter to call Set() and conclude the demo.

Thread_5 ends.
 */

番外：

對比 ManualResetEvent 和 AutoResetEvent
舉例：

AutoResetEvent ：地鐵口刷卡通過，每次刷卡視爲一次Set()，每次只過一個人（一個線程），一般是用來同步訪問資源。

ManualResetEvent :景點大門，每次Set()視爲打開大門，很多人都可以進，無論先來的還是後來的。直到Reset()關閉大門，都不能進了。