分类:  .Net技术    ◆ 标签:  #异步编程   #基础   #.Net   ◆ 发布于: 2023-06-04 19:50:54

本节演示如何使用方法WhenAny()来巧妙的处理多个任务的await, 一定要仔细阅读代码。
本节代码可以从这里找到:https://github.com/hylinux/azure-demo/tree/main/dotnet/basic/asyncdemo/WhenAnyDemo

创建应用

使用如下的命令创建应用

mkdir WhenAnyDemo
cd WhenAnyDemo
dotnet new console

替换using

以编辑器打开文件Program.cs，替换如下的using语句

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

定义字段

我们这里还是使用下载web服务器的内容作为应用场景

        static readonly HttpClient s_client = new HttpClient
        {
            MaxResponseContentBufferSize = 1_000_000
        };

        static readonly IEnumerable<string> s_urlList = new string[]
        {
            "https://docs.microsoft.com",
            "https://docs.microsoft.com/aspnet/core",
            "https://docs.microsoft.com/azure",
            "https://docs.microsoft.com/azure/devops",
            "https://docs.microsoft.com/dotnet",
            "https://docs.microsoft.com/dynamics365",
            "https://docs.microsoft.com/education",
            "https://docs.microsoft.com/enterprise-mobility-security",
            "https://docs.microsoft.com/gaming",
            "https://docs.microsoft.com/graph",
            "https://docs.microsoft.com/microsoft-365",
            "https://docs.microsoft.com/office",
            "https://docs.microsoft.com/powershell",
            "https://docs.microsoft.com/sql",
            "https://docs.microsoft.com/surface",
            "https://docs.microsoft.com/system-center",
            "https://docs.microsoft.com/visualstudio",
            "https://docs.microsoft.com/windows",
            "https://docs.microsoft.com/xamarin"
        };

更新方法Main

更新方法Main

static Task Main() => SumPageSizesAsync();

定义方法SumPageSizesAsync

       static async Task SumPageSizesAsync()
        {
            var stopwatch = Stopwatch.StartNew();

            IEnumerable<Task<int>> downloadTasksQuery =
                from url in s_urlList
                select ProcessUrlAsync(url, s_client);

            List<Task<int>> downloadTasks = downloadTasksQuery.ToList();

            int total = 0;
            while (downloadTasks.Any())
            {
                Task<int> finishedTask = await Task.WhenAny(downloadTasks);
                downloadTasks.Remove(finishedTask);
                total += await finishedTask;
            }

            stopwatch.Stop();

            Console.WriteLine($"\nTotal bytes returned:  {total:#,#}");
            Console.WriteLine($"Elapsed time:          {stopwatch.Elapsed}\n");
        }

定义方法ProcessUrlAsync

定义方法ProcessUrlAsync

        static async Task<int> ProcessUrlAsync(string url, HttpClient client)
        {
            byte[] content = await client.GetByteArrayAsync(url);
            Console.WriteLine($"{url,-60} {content.Length,10:#,#}");

            return content.Length;
        }

运行代码测试实例。