异步编程，为什么不执行代码 [英] Async programming, why doesn't the code get executed

问题描述

我对异步编程非常陌生，但是我非常需要在我们的应用程序内部使用它.

I'm quite new to async programming, but I need it badly inside on of our applications.

我只是在控制台应用程序中尝试某些操作，但似乎不起作用.我知道控制台应用程序不支持即开即用，因为WinForms应用程序中没有主线程，例如UI线程.

I'm just trying something inside a Console Application but it doesn't seem to work. I'm aware that a Console Application doesn't support async out of the box as there isn't a main thread like a UI thread in a WinForms Application.

无论如何，这是我正在尝试的方法:

Anyway, here's what I'm trying:

我有一个异步方法，其中包含以下逻辑:

I have an async method which contains the following logic:

public static async Task MainAsync()
{
    Console.WriteLine("This method is being executed.");

    await Task.Delay(3000);

    Console.WriteLine("Async method has finished.");
}

现在，我想从我正在这样做的控制台应用程序中执行此代码，以使其正常工作:

Now, I want to execute this code from a Console Application which I'm doing like this, to make it work:

public static void Main(string[] args)
{
    Task t = MainAsync();
    t.Wait();
}

到目前为止，没有问题，它们的应用程序将按预期执行.首先写一个字符串，然后等待3秒钟，然后打印第二行，并以异步方式打印所有内容.

So far no problem, them application is executed as it's supposed to. First write a single string, then wait 3 seconds, then prints a second line, and all that in an async way.

现在，我为代码创建了一个包装，如下所示:

Now, I've created a wrapper around my code which looks like the following:

public static class AsynchronousContext 
{
    public static void Run(Task task)
    {
        task.Wait();
    }
}

所以，现在我的主要方法可以更改为:

So, now my main method can be changed to:

public static void Main(string[] args)
{
    AsynchronousContext.Run(MainAsync());
}

与上面的示例相同.

现在，我尝试在 Run 方法上创建一个重载，在该重载中我传递了一个 Action .

Now, I've tried to create an overload on the Run method in which I passes an Action.

public static void Run(Action action)
{
    new TaskFactory().StartNew(action).Wait();
}

但是，当我将主方法调用更改为:

However, when I change my main method call to:

AsynchronousContext.Run(() => MainAsync());

该代码不再起作用.我得到第一行，然后是一行，它说可以通过单击一个键(即依次单击主键，在等待之前完成主线程)来完成应用程序.

The code isn't working anymore. I get the first line and than a line that says that the application can be finished by clicking a key, in order words, the main thread finished before the await.

我也尝试了以下方法，但唯一想到的是我没有内容的黑色控制台应用程序:

I've tried the following also, but the only think I got was a black console application without contents:

public static void Run(Action action)
    {
        var task = new Task(action);
        task.Wait();
    }

任何人都可以尽可能简单地解释这里发生的事情吗?

Anyone who can explain as simple as possible what's happening here?

推荐答案

MainAsync 返回 Task .您将它作为 Action 传递给 StartNew ，所以没有办法等待它完成.

MainAsync returns a Task. You are passing this to StartNew as an Action, so there is no way for it to wait for it to finish.

此外， StartNew 没有重载，该重载将接受返回 Task 的函数，因此 StartNew 无法等待使其完成.

In addition, there is no overload to StartNew that would accept a function that returns a Task, so StartNew has no way of waiting for it to finish either.

Task.Run 通常更适合于此，假设您想在线程池线程上运行您的工作.您可以在此博客中阅读 StartNew 的陷阱发布.它有一个接受 Func< Task> :

Task.Run is generally better suited to this, presuming you want to run your work on a thread pool thread. You can read the pitfalls of StartNew in this blog post. It has an overload that accepts a Func<Task>:

public static void Run(Func<Task> createTask)
{
    Task.Run(createTask).Wait();
}

我认为这段代码只是为了演示原理，但是-您通常不希望调用 Wait()，因为这会阻塞.

I assume this code is only to demonstrate the principles, however - you wouldn't ordinarily want to call Wait() as this will block.

这篇关于异步编程，为什么不执行代码的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！