异步方法在控制台应用程序中效果不佳

Question

我正在使用下面的代码，想测试并行编程，但是有一些问题。

using System;
using System.Threading.Tasks;

namespace DemoParallelApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("*** Main Method Start ***");
            Operation();
            Console.WriteLine("*** Main Method End ***");
        }
        static void Operation()
        {
            Console.WriteLine("*** Operation Method Start ***");
            var task1 = Delay(5000);
            Console.WriteLine("*** Operation Method End ***");
        }

        static async Task<int> Delay(int ms)
        {
            Console.WriteLine($"Start {ms}(ms) Delay");
            await Task.Delay(ms);
            Console.WriteLine($"End {ms}(ms) Delay");
            return ms;
        }
    }
}

结果是这样的：

*** Main Method Start ***
*** Operation Method Start
*** Start 5000(ms) Delay
*** Operation Method End ***
*** Main Method End ***

不过我觉得应该是这样的：

*** Main Method Start ***
*** Operation Method Start ***
Start 5000(ms) Delay
*** Operation Method End ***
*** Main Method End ***
End 5000(ms) Delay

有什么问题吗？

Answer 1

您需要等待延迟：

static async Task Operation()
{
    Console.WriteLine("*** Operation Method Start ***");
    var task1 = await Delay(5000);
    Console.WriteLine("*** Operation Method End ***");
}

并使用 await 调用 Operation，在您的情况下 main 方法不是 asyncable 您可以这样做：

Task.Run(() => Operation()).GetAwaiter().GetResult();

Answer 2

您的程序在 Wait 之前完成并终止（包括“等待”方法）。您需要在某处等待 Delay 返回的任务。要获得所需的输出，您可以这样做，例如（使用 C# 7.1 async Main feature）：

class Program
{
    static async Task Main(string[] args)
    {
        Console.WriteLine("*** Main Method Start ***");
        var t = Operation();
        Console.WriteLine("*** Main Method End ***");
        await t;
    }
    static Task Operation()
    {
        Console.WriteLine("*** Operation Method Start ***");
         var task1 = Delay(5000);
        Console.WriteLine("*** Operation Method End ***");
         return task1 ;
    }

    static async Task<int> Delay(int ms)
    {
        Console.WriteLine($"Start {ms}(ms) Delay");
        await Task.Delay(ms);
        Console.WriteLine($"End {ms}(ms) Delay");
        return ms;
    }
}

异步方法在控制台应用程序中效果不佳

Asynchronous method does not work well in Console application

c#

asynchronous

.net-core

parallel-processing

console-application