异步编程C#5.0

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#异步编程 #C#5.0

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本文介绍C#5.0中异步编程的关键特性，并通过具体示例演示如何使用async和await关键字实现高效的并发操作。示例中包括了网络请求与本地计算任务的并行处理。

C#的演化

这里写图片描述
在这里主要讲的是C#5.0的焦点特性异步

异步的例子

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

namespace 异步编程
{
    class Program
    {
        static void Main(string[] args)
        {
            MyDownloadString ds = new MyDownloadString();
            ds.DoRun();
        }
    }

    class MyDownloadString
    {
        Stopwatch sw = new Stopwatch();

        public void DoRun()
        {
            const int LargeNumber = 600000;
            sw.Start();
            Task<int> t1 = CountCharactersAsync(1, "http://www.microsoft.com");
            Task<int> t2 = CountCharactersAsync(2, "http://www.illustratedcsharp.com");

            CountToALargeNumber(1, LargeNumber);
            CountToALargeNumber(2, LargeNumber);
            CountToALargeNumber(3, LargeNumber);
            CountToALargeNumber(4, LargeNumber);

            Console.WriteLine("Chars in http://www.microsoft.com :{0}", t1.Result);
            Console.WriteLine("Chars in http://www.illustratedcsharp.com :{0}", t2.Result);
        }

        private async Task<int> CountCharactersAsync(int id, string site)
        {
            WebClient wc = new WebClient();
            Console.WriteLine("Starting call {0}: {1, 4 NO} ms", id, sw.Elapsed.TotalMilliseconds);
            string result = await wc.DownloadStringTaskAsync(new Uri(site));
            Console.WriteLine("  Call{0} completed : {1, 4:NO} ms", id, sw.Elapsed.TotalMilliseconds);
            return result.Length;
        }

        private void CountToALargeNumber(int id, int value)
        {
            for (long i = 0; i < value; i++) ;
            Console.WriteLine(" End counting {0}:{1, 4:NO} ms", id, sw.Elapsed.TotalMilliseconds);
        }

    }
}