C#多线程---I/O线程实现异步请求

一、场景

利用I/O线程来模拟浏览器对服务器请求的异步操作。

二、例子

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

namespace IOThread
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ForegroundColor = ConsoleColor.DarkGreen;
            PrintThreadInfo("Print info in Main");
            Console.ResetColor();
            Console.WriteLine();

            // 发出一个异步Web请求
            WebRequest webrequest = WebRequest.Create("http://www.cnblogs.com/");
            webrequest.BeginGetResponse(ProcessWebResponse, webrequest);
            Console.WriteLine("");

            Console.Read();
        }
        // 回调方法
        private static void ProcessWebResponse(IAsyncResult result)
        {
            Thread.Sleep(500);
            PrintThreadInfo("ProcessWebResponse Method start");

            WebRequest webrequest = (WebRequest)result.AsyncState;
            using (WebResponse webresponse = webrequest.EndGetResponse(result))
            {
                Console.WriteLine("Content Length is : " + webresponse.ContentLength);
            }
        }
        private static void PrintThreadInfo(string info)
        {
            Console.WriteLine(info);
            Console.WriteLine($"ThreadId:{Thread.CurrentThread.ManagedThreadId}
IsBackgroundThread:{Thread.CurrentThread.IsBackground}
IsThreadPoolThread:{Thread.CurrentThread.IsThreadPoolThread}");
            int workerThread = 0;
            int ioThread = 0;
            ThreadPool.GetMaxThreads(out workerThread, out ioThread);
            Console.WriteLine($"MaxWorkerThread:{workerThread}
MaxIoThread:{ioThread}");
            int workerThreadAvailable = 0;
            int ioThreadAvailable = 0;
            ThreadPool.GetAvailableThreads(out workerThreadAvailable, out ioThreadAvailable);
            Console.WriteLine($"AvailableWorkerThread:{workerThreadAvailable}
AvailableIoThread:{ioThreadAvailable}");
        }
    }
}

运行结果如下：

 分析：

webrequest.BeginGetResponse(ProcessWebResponse, webrequest)的返回类型是IAsyncResult。在返回之前，会把IAsyncResult这个类型的变量中的AsyncState这个属性

用webrequest来填充，然后将IAsyncResult这个类型的变量传递给ProcessWebResponse回调，这个回调函数是运行在线程池的IO线程上的。