為什么我的線程池的線程無法同時完成

Question

在main函數中，我編寫以下代碼：

            ThreadPool.SetMaxThreads(200, 200);

        for (int i = 0; i < 100; i++)
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadWhichWillCallSQL_test), i);
            Thread.Sleep(1);
        }

和線程功能如下：

        static public void ThreadWhichWillCallSQL_test(Object o1)
    {
        Thread.Sleep(5000);
        Console.WriteLine(DateTime.Now.ToString()); 
        return;
    }

輸出為：

    5/25/2017 2:00:01 PM
5/25/2017 2:00:01 PM
5/25/2017 2:00:01 PM
5/25/2017 2:00:01 PM
5/25/2017 2:00:02 PM
5/25/2017 2:00:03 PM
5/25/2017 2:00:04 PM
5/25/2017 2:00:05 PM
5/25/2017 2:00:05 PM
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5/25/2017 2:00:06 PM
5/25/2017 2:00:07 PM
5/25/2017 2:00:07 PM
5/25/2017 2:00:08 PM
5/25/2017 2:00:08 PM
5/25/2017 2:00:09 PM
5/25/2017 2:00:09 PM
5/25/2017 2:00:10 PM
5/25/2017 2:00:10 PM
5/25/2017 2:00:10 PM
5/25/2017 2:00:11 PM
5/25/2017 2:00:11 PM
5/25/2017 2:00:11 PM
5/25/2017 2:00:11 PM
5/25/2017 2:00:12 PM
5/25/2017 2:00:12 PM
5/25/2017 2:00:12 PM
5/25/2017 2:00:13 PM
5/25/2017 2:00:13 PM
5/25/2017 2:00:13 PM
5/25/2017 2:00:14 PM
5/25/2017 2:00:14 PM
5/25/2017 2:00:14 PM
5/25/2017 2:00:15 PM
5/25/2017 2:00:15 PM
5/25/2017 2:00:15 PM
5/25/2017 2:00:15 PM
5/25/2017 2:00:16 PM
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5/25/2017 2:00:18 PM
5/25/2017 2:00:18 PM
5/25/2017 2:00:18 PM
5/25/2017 2:00:18 PM
5/25/2017 2:00:19 PM
5/25/2017 2:00:19 PM
5/25/2017 2:00:19 PM
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5/25/2017 2:00:22 PM
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5/25/2017 2:00:22 PM
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5/25/2017 2:00:23 PM
5/25/2017 2:00:23 PM
5/25/2017 2:00:23 PM
5/25/2017 2:00:23 PM
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5/25/2017 2:00:24 PM
5/25/2017 2:00:24 PM
5/25/2017 2:00:24 PM
5/25/2017 2:00:24 PM
5/25/2017 2:00:24 PM
5/25/2017 2:00:25 PM
5/25/2017 2:00:25 PM
5/25/2017 2:00:25 PM
5/25/2017 2:00:25 PM
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5/25/2017 2:00:26 PM
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5/25/2017 2:00:26 PM
5/25/2017 2:00:26 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:27 PM
5/25/2017 2:00:28 PM
5/25/2017 2:00:28 PM
5/25/2017 2:00:28 PM
5/25/2017 2:00:28 PM
5/25/2017 2:00:28 PM

您會注意到所有線程完成的整個過程持續了將近28秒，據我了解，這100個線程也許無法同時完成，但也不能有那么多的時間差異。

我也已經設定

ThreadPool.SetMaxThreads(200, 200);

並且只分配100個線程，所以不應有任何線程等待別人停止，對嗎？

這是完整的代碼

        using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Threading;

    namespace ThreadpoolDelay
    {
        class Program
        {
            static void Main(string[] args)
            {
                try
                {
                    ThreadPool.SetMaxThreads(200, 200);

                    for (int i = 0; i < 30; i++)
                    {
                        ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadWhichWillCallSQL_test), i);
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e.ToString());
                }

                Console.WriteLine("\nPress ENTER to continue...");
                Console.Read();
            }
            public static void ThreadWhichWillCallSQL_test(Object o1)
            {
                Thread.Sleep(5000);
                Console.WriteLine(DateTime.Now.ToString());
                return;
            }

        }
    }

Answer 1

在您的示例中，線程不會同時啟動。 在SetMaxThreads之后添加以下調用

ThreadPool.SetMinThreads(200, 200);

這將使線程同時啟動。 這與ThreadPool線程創建機制有關。 我建議閱讀ThreadPool文檔以獲取詳細信息。

為了更正確地調試它，請更新您的ThreadWhichWillCallSQL_test方法以也添加開始時間：

    static void ThreadWhichWillCallSQL_test(object o1)
    {
        Console.WriteLine("start:"  + DateTime.Now);
        Thread.Sleep(5000);
        Console.WriteLine("finish: " + DateTime.Now);
    }

Answer 2

好問題。

線程拉動中線程的執行取決於許多因素，其中一個因素是cpu core。 它把線程運行在每個內核中，一旦完成，就放另一個線程。

示例：如果有4個核心CPU。 它同時並行放置4個線程，然后在線程完成其任務時放置下一個線程。 機制不完全一樣。 此外，您還設置了5秒的延遲（線程休眠），因此計算就像有4個核心：（30個線程/ 4個核心）* 5那樣，並非完全相同。

您也可以在此處看到更多信息： https : //msdn.microsoft.com/zh-cn/library/3dasc8as(v=vs.80).aspx