.NET核心ASP控制器中的线程化

Question

我已经为.net Core3.0Web应用程序做了一个干净的项目，我正在努力理解ThreadPool是如何在C#中工作的。

namespace TestASPSelf.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;

        public static int countThread = 0;

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }

        public IActionResult Index()
        {

            int workerThreads;
            int portThreads;

            ThreadPool.GetMaxThreads(out workerThreads, out portThreads);
            Console.WriteLine("\nMaximum worker threads: \t{0}" +
                              "\nMaximum completion port threads: {1}",
                workerThreads, portThreads);

            ThreadPool.GetAvailableThreads(out workerThreads,
                out portThreads);
            Console.WriteLine("\nAvailable worker threads: \t{0}" +
                              "\nAvailable completion port threads: {1}\n",
                workerThreads, portThreads);    

                Console.WriteLine("countThread = " + countThread);

            return View();
        }

        class Z
        {
            public static void WaitTest(object o)
            {
                countThread++;
                while (true)
                {
                    Thread.Sleep(1000);
                }
            }
        }

        public IActionResult Privacy()
        {
            for (int i = 0; i < 100; i++)
            {
                Console.WriteLine("starting thread "+i);
                ThreadPool.QueueUserWorkItem(new WaitCallback(Z.WaitTest));
            }

            return View();
        }
}
}

当http://localhost:5000/Home/Privacy打开时，它挂起一段时间(大约40-80秒)，但我知道，它中的for循环逻辑几乎立即完成。当http://localhost:5000/打开之后，它也会挂起40-80秒，结果在控制台countThread = 100中。当线程启动时，app的CPU使用率约为5-10% .

我正在努力理解：

1)第一个原因是为什么ASP控制器每页挂起40-80秒，而CPU使用率为5-10 %时运行100个线程。CPU有很多资源，RAM也是免费的，但是为什么ASP控制器的页面方法是挂起的呢？

2)如何在运行线程数量有限的情况下在ThreadPool中创建C#？如果我正确理解方法public static bool SetMinThreads (int workerThreads, int completionPortThreads);，它会影响应用程序的所有线程。如何在活动线程数量有限的情况下创建ThreadPool对象，比如Java中的ExecutorService？例如，线程池的Java代码可能如下所示

ExecutorService executor = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++) {
            Runnable worker = new WorkerThread("" + i);
            executor.execute(worker);
          }
        executor.shutdown();
        while (!executor.isTerminated()) {
        }

3)如何防止ASP控制器的所有方法挂起，并使“真正的”线程，如Java中的线程？

Answer 1

ThreadPool.QueueUserWorkItem(new WaitCallback(Z.WaitTest));

用这个你做了一件非常错误的事。您将导致线程池中的线程阻塞，因此池无法完成处理请求和处理新请求。

在某个时候，池中的一个线程设法返回并处理您的下一个请求，但是由于重载池，线程再次挂起。

至于你的其他问题，请解释一下你想要达到的目标。你的问题似乎试图解决一个不被理解的问题。

更新：在亚瑟的评论之后。

如果你要下载文件，你应该使用任务和异步等待.IO操作不消耗线程(更多的这里)。

创建N个任务，每个任务下载一个文件，然后等待Task.WhenAll。伪码：

List<Task> tasks = new List<Task>();
for (int i = 0; i < filesToDownloadCount; i++)
{
   var t = new Task ( () => { /* ... code to download your file here ... */});
   tasks.Add (t);
}
await t.WhenAll (tasks);

这种方法将为您提供最佳的吞吐量，瓶颈将是您的带宽，而不是CPU。

Answer 2

ThreadPool类有几个静态方法，包括当线程池工作线程可用时负责调用线程池工作线程的QueueUserWorkItem。如果线程池中没有可用的辅助线程，则等待线程可用。

using System;  
using System.Threading;  

class ThreadPoolSample  
{  
    // Background task   
    static void BackgroundTask(Object stateInfo)  
    {  
        Console.WriteLine("Hello! I'm a worker from ThreadPool");  
        Thread.Sleep(1000);          
    }  

    static void BackgroundTaskWithObject(Object stateInfo)  
    {  
        Person data = (Person)stateInfo;          
        Console.WriteLine($"Hi {data.Name} from ThreadPool.");  
        Thread.Sleep(1000);  
    }  
    static void Main(string[] args)  
    {  
        // Use ThreadPool for a worker thread        
        ThreadPool.QueueUserWorkItem(BackgroundTask);  
        Console.WriteLine("Main thread does some work, then sleeps.");  
        Thread.Sleep(500);  

        // Create an object and pass it to ThreadPool worker thread  
        Person p = new Person("Mahesh Chand", 40, "Male");  
        ThreadPool.QueueUserWorkItem(BackgroundTaskWithObject, p);  

        int workers, ports;  

        // Get maximum number of threads  
        ThreadPool.GetMaxThreads(out workers, out ports);  
        Console.WriteLine($"Maximum worker threads: {workers} ");  
        Console.WriteLine($"Maximum completion port threads: {ports}");  

        // Get available threads  
        ThreadPool.GetAvailableThreads(out workers, out ports);  
        Console.WriteLine($"Availalbe worker threads: {workers} ");  
        Console.WriteLine($"Available completion port threads: {ports}");  

        // Set minimum threads  
        int minWorker, minIOC;  
        ThreadPool.GetMinThreads(out minWorker, out minIOC);  
        ThreadPool.SetMinThreads(4, minIOC);  

        // Get total number of processes availalbe on the machine  
        int processCount = Environment.ProcessorCount;  
        Console.WriteLine($"No. of processes available on the system: {processCount}");  

        // Get minimum number of threads  
        ThreadPool.GetMinThreads(out workers, out ports);  
        Console.WriteLine($"Minimum worker threads: {workers} ");  
        Console.WriteLine($"Minimum completion port threads: {ports}");  

        Console.ReadKey();  
    }  

        // Create a Person class  
        public class Person  
        {  
            public string Name { get; set; }  
            public int Age { get; set; }  
            public string Sex { get; set; }  

            public Person(string name, int age, string sex)  
            {  
                this.Name = name;  
                this.Age = age;  
                this.Sex = sex;  
            }  
        }  
}