CountDownEvent不會等到所有信號都被調用

Question

我正在查看本網站的threads。 我一直在玩代碼來回答問題「CountdownEvent是否停止所有線程？」 我得到的答案是否定的。然後我決定玩傳入CountdownEvent的數字。這裏是我的代碼

namespace ThreadPractice 
{ 
    class Program 
    { 
     static CountdownEvent CountDown = new CountdownEvent(4); 
     static void Main() 
     { 
      new Thread(() => SaySomething("I am Thread one.")).Start(); 
      new Thread(() => SaySomething("I am thread two.")).Start(); 
      new Thread(() => SaySomethingElse("Hello From a different Thread")).Start(); 
      new Thread(() => SaySomething("I am Thread Three.")).Start(); 
      CountDown.Wait(); 
      Console.Read(); 
     } 

     static void SaySomething(string Something) 
     { 
      Thread.Sleep(1000); 
      Console.WriteLine(Something); 
      CountDown.Signal(); 
     } 

     static void SaySomethingElse(string SomethingElse) 
     { 
      Thread.Sleep(1000); 
      Console.WriteLine(SomethingElse); 
     } 
    } 
} 

我期待的是調用SaySomethingELse線程（）來執行，但其他線程執行，同時即使只有四個信號已被調用。

它爲什麼這樣做？

感謝，

dhoehna

Answer 1

它看起來像你對我已經有了Signal和Wait以錯誤的方式。如果您希望SaySomething調用等待倒數到達0，則應該調用Wait。這裏有一個例子：

using System; 
using System.Threading; 

namespace ThreadPractice 
{ 
    class Program 
    { 
     static CountdownEvent CountDown = new CountdownEvent(4); 
     static void Main() 
     { 
      new Thread(() => SaySomething("I am Thread one.")).Start(); 
      new Thread(() => SaySomething("I am thread two.")).Start(); 
      new Thread(() => SaySomethingElse("Hello From a different Thread")).Start(); 
      new Thread(() => SaySomething("I am Thread Three.")).Start(); 
      for (int i = 0; i < 4; i++) 
      { 
       Console.WriteLine("Calling Signal (time #{0})", i); 
       CountDown.Signal(); 
       Thread.Sleep(1000); 
      } 
      Console.WriteLine("Done"); 
     } 

     static void SaySomething(string Something) 
     { 
      CountDown.Wait(); 
      Console.WriteLine(Something); 
     } 

     static void SaySomethingElse(string SomethingElse) 
     { 
      Thread.Sleep(1000); 
      Console.WriteLine(SomethingElse); 
     } 
    } 
} 

輸出：

Calling Signal (time #0) 
Hello From a different Thread 
Calling Signal (time #1) 
Calling Signal (time #2) 
Calling Signal (time #3) 
I am Thread one. 
I am Thread Three. 
I am thread two. 
Done 

Answer 2

嗯...它像要等待所有的線程在主線程繼續之前完成在我看來。如果是這樣，你忘記了SaySomethingElse（）中的Signal（）。這可以防止CountDown.CurrentCount達到0（零），這就是爲什麼你的主線程「卡住」你將它設置爲4，它只能下降到1（一）。修復它，你應該得到所需的？結果：

class Program 
{ 
    static CountdownEvent CountDown = new CountdownEvent(4); 
    static void Main() 
    { 
     new Thread(() => SaySomething("I am Thread one.")).Start(); 
     new Thread(() => SaySomething("I am thread two.")).Start(); 
     new Thread(() => SaySomethingElse("Hello From a different Thread")).Start(); 
     new Thread(() => SaySomething("I am Thread Three.")).Start(); 

     CountDown.Wait(); 

     Console.WriteLine("Done!"); 
     Console.Read(); 
    } 

    static void SaySomething(string Something) 
    { 
     Thread.Sleep(1000); 
     Console.WriteLine(Something); 
     CountDown.Signal(); 
    } 

    static void SaySomethingElse(string SomethingElse) 
    { 
     Thread.Sleep(1000); 
     Console.WriteLine(SomethingElse); 
     CountDown.Signal(); 
    } 
} 

輸出：

I am Thread one. 
I am thread two. 
Hello From a different Thread 
I am Thread Three. 
Done!