CountDownEvent 不会等到所有信号都被调用

Question

我正在查看此站点以获取 threads。 我一直在使用代码来回答“CountdownEvent 是否停止所有线程？”这个问题。 我得到的答案是否定的。然后我决定使用传递给 CountdownEvent 的数字。这是我的代码

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);
        }
    }
}

我预计调用 SaySomethingELse() 的线程会执行，但其他线程也会执行，即使只调用了四个信号。

为什么要这样做？

谢谢，

dhoehna

Answer 1

在我看来，您的 Signal 和 Wait 方向错误。如果您希望SaySomething 呼叫等待倒计时到达 0，您应该呼叫 Wait。这是一个例子：

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);
        }
    }
}

输出：

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...在我看来，您想等待所有线程完成，然后再继续主线程。如果是这样，您忘记了 SaySomethingElse() 中的 Signal()。这可以防止 CountDown.CurrentCount 达到 0（零），这就是您的主线程“卡住”的原因。您将其设置为 4，它只会下降到 1（一）。修复它，你应该得到想要的？结果：

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();
    }
}

输出：

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