分类:  .Net技术    ◆ 标签:  #异步编程   #基础   #.Net   ◆ 发布于: 2023-06-04 19:48:39

我们上一章学习了如何手动的取消任何，本章学习使用方法CancellationTokenSource.CancelAfter定时取消任务，本章的源代码可以在这里找到：https://github.com/hylinux/azure-demo/tree/main/dotnet/basic/asyncdemo/CancelTaskByTime

闲话少说，直接上代码。

创建应用

以如下的命令行创建代码：

mkdir CancelTaskByTime
cd CancelTaskByTime
dotnet new console

替换using语句

以编辑器打开文件Program.cs, 替换using语句如下：

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

添加字段

和前面的例子一致:

    static readonly CancellationTokenSource s_cts = new CancellationTokenSource();

    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"
    };

更改Main方法

Main方法改成如下的形式：

    static async Task Main()
    {
        Console.WriteLine("Application started.");

        try
        {
            s_cts.CancelAfter(3500);

            await SumPageSizesAsync();
        }
        catch (TaskCanceledException)
        {
            Console.WriteLine("\nTasks cancelled: timed out.\n");
        }
        finally
        {
            s_cts.Dispose();
        }

        Console.WriteLine("Application ending.");
    }

注意这里定时发送取消的Token, s_cts.CancelAfter(3500), 即可定时取消。

定义其他两个异步方法：

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

        int total = 0;
        foreach (string url in s_urlList)
        {
            int contentLength = await ProcessUrlAsync(url, s_client, s_cts.Token);
            total += contentLength;
        }

        stopwatch.Stop();

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

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

        return content.Length;
    }

即可以运行看结果了，这里主要是需要理解方法CancelAfter。