#yyds干货盘点#.Net Core学习02

异步编程

using System;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace awaitasynv1
{
    internal class Program
    {
        static async Task Main(string[] args)
        {
            //string filename = @"1.txt";

            //StringBuilder sb = new StringBuilder();

            //System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
            //stopwatch.Start();

            //for (int i = 0; i < 10000; i++)
            //{
            //    sb.AppendLine("hello");
            //}

            //File.WriteAllText(filename, sb.ToString());
            //string s = File.ReadAllText(filename);

            //Console.WriteLine(s);
            //stopwatch.Stop();
            //Console.WriteLine(stopwatch.Elapsed.Milliseconds);

            string filename = @"1.txt";
            System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
            stopwatch.Start();
            StringBuilder sb = new StringBuilder();

            for (int i = 0; i < 10000; i++)
            {
                sb.AppendLine("hello");
            }

            await File.WriteAllTextAsync(filename, sb.ToString());

            //Task<string> t = File.ReadAllTextAsync(filename);
            //string b = await t;
            //自动把返回值从 Task取出来
            string s = await File.ReadAllTextAsync(filename);
            Console.WriteLine(s);
            stopwatch.Stop();
            Console.WriteLine(stopwatch.Elapsed.Milliseconds);
        }
    }
}

在线程里进行异步调用

using System;
using System.IO;
using System.Threading;

namespace async03
{
    internal class Program
    {
        static void Main(string[] args)
        {
            ThreadPool.QueueUserWorkItem(async (obj) =>
            {
               while(true)
                {
                    //Console.WriteLine("xxxxxxxxxx");
                    await File.WriteAllTextAsync("1.txt", "111111");
                }
            });
            Console.Read();
        }
    }
}

await,async是语法糖，最终编译成状态机调用

async标记的方法中没有await会被当做同步方法处理

延时

await Task.Delay();

CancellationToken

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    internal class Program
    {
        static async Task Main(string[] args)
        {
            CancellationTokenSource cts = new CancellationTokenSource();
            
            //定时两秒取消
            //cts.CancelAfter(2000);
            CancellationToken cToken = cts.Token;
           DownloadAsync3("https://www.baidu.com", 1111,cToken);

            while(Console.ReadLine() != "q")
            {

            }
            cts.Cancel();
            Console.ReadLine();
        }

        static async Task Main1(string[] args)
        {
            CancellationTokenSource cts = new CancellationTokenSource();

            //cts.CancelAfter(2000);
            CancellationToken cToken = cts.Token;
            await DownloadAsync3("https://www.baidu.com", 1111, cToken);

            while (Console.ReadLine() != "q")
            {

            }
            cts.Cancel();
            Console.ReadLine();
        }

        static async Task DownloadAsync(string url,int n)
        {
            using (HttpClient client = new HttpClient())
            {
                for (int i = 0; i < n; i++)
                {
                    string html = await client.GetStringAsync(url);
                    Console.WriteLine($"{DateTime.Now}:{html}");
                }
            }   
        }

        static async Task DownloadAsync2(string url, int n,CancellationToken cancellationToken )
        {
            using (HttpClient client = new HttpClient())
            {
                for (int i = 0; i < n; i++)
                {
                    string html = await client.GetStringAsync(url);
                    Console.WriteLine($"{DateTime.Now}:{html}");
                   

                    #region 请求被取消情况
                    //if(cancellationToken.IsCancellationRequested)
                    //{
                    //    Console.WriteLine("please cancel");
                    //    break;
                    //}

                    cancellationToken.ThrowIfCancellationRequested();
                    #endregion

                }
            }
        }

        /// <summary>
        /// 手动输入q取消
        /// </summary>
        /// <param name="url"></param>
        /// <param name="n"></param>
        /// <param name="cancellationToken"></param>
        /// <returns></returns>
        static async Task DownloadAsync3(string url, int n, CancellationToken cancellationToken)
        {
            using (HttpClient client = new HttpClient())
            {
                for (int i = 0; i < n; i++)
                {
                   var resp =  await client.GetAsync(url);
                    string html = await resp.Content.ReadAsStringAsync();
                    Console.WriteLine($"{DateTime.Now}:{html}");
                    if(cancellationToken.IsCancellationRequested)
                    {
                        Console.WriteLine("please cancel");
                        break;
                    }

                }
            }
        }
    }
}