QueueUserWorkItem怪异行为

Question

我正在使用ThreadPool.QueueUserWorkItem()启动一些后台任务。

ThreadPool并发行为很奇怪。我的CPU有4个逻辑核。我希望只有4个正在运行的线程。但是，示例代码显示了不同的行为。

• 在时间的1/2/3中，为什么会触发mores线程？

下面是示例代码：

class Program
{
    static DateTime s_startTime = new DateTime();
    public static void Main()
    {
        // Queue the task.
        s_startTime = DateTime.Now;
        for (int i = 0; i < 1000; i++)
        {
            ThreadPool.QueueUserWorkItem(ThreadProc, i);
        }
        Console.WriteLine("Main thread does some work, then sleeps.");
        Thread.Sleep(100 * 1000);

        Console.WriteLine("Main thread exits.");
    }

    // This thread procedure performs the task.
    static void ThreadProc(Object i)
    {
        DateTime thread_starttime = DateTime.Now;
        int a = Convert.ToInt32(i);
        double ss = (thread_starttime - s_startTime).TotalSeconds;
        Console.WriteLine("time:" + ss + ", start " + a);
        Thread.Sleep(10 * 1000);
        DateTime e = DateTime.Now;
        double ee = (e - s_startTime).TotalSeconds;
        Console.WriteLine("time:" + ee + ", end " + a);
    }
}

输出

Main thread does some work, then sleeps.
time:0.0040027, start 0
time:0.0360007, start 3
time:0.0360007, start 1
time:0.0360007, start 2
time:1.0178537, start 4
time:2.0191713, start 5
time:3.019311, start 6
time:4.0194503, start 7
time:5.0195775, start 8
time:6.0195875, start 9
time:7.0219127, start 10
time:8.0214611, start 11
time:9.0181507, start 12
time:10.020686, end 0
time:10.020686, start 13
time:10.020686, start 14
time:10.038517, end 1
time:10.038517, start 15
time:10.038517, end 3
time:10.0403473, start 16
time:10.038517, end 2
time:10.0413736, start 17
time:11.0233302, end 4
time:11.0243333, start 18
time:11.0243333, start 19

Answer 1

更多的线程将被触发，因为你没有让你的核心忙碌。

Thread.Sleep允许线程生成。由于您的工作人员主要是睡眠而不是CPU绑定，所以调度程序可以自由安排更多线程。