在一个循环中创建新线程 [英] creating new threads in a loop

问题描述

我试图理解为什么这个代码不工作

I'm trying to understand why this code is not working.

    private static object _lock;

    public static void Main (string[] args)
    {
        Thread thread;
        _lock = new object();

        foreach (int num in Enumerable.Range(0,5)) {
            thread  = new Thread (() => print(num.ToString()));
            thread.Start(); 
        }
    }

    public static void print(string text)
    {
        lock(_lock)
        {
            Console.WriteLine(text);
        }
    }

我最终的输出

I end up with an output of

4
1
4
4
3

4 1 4 4 3

或其他任何随机数的数字。为什么会重复的数字？

or any other random number of digits. Why does it repeat digits?

推荐答案

由于每个线程都指的是循环变量，并在没有得到自己的副本。时间创建线程

Because each thread is refering to the loop variable, and does not get its own copy at the time you create the thread.

注意，编译器警告你：访问修改封的

Notice that the compiler is warning you: "Access to a modified closure".

    foreach (int num in Enumerable.Range(0,5))
    {
        int loopnum = num;

        thread = new Thread(() => print(loopnum.ToString())); 
        thread.Start();  
    }

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