如何写一个“等待"方法? [英] How to write an "awaitable" method?

问题描述

我终于开始研究 async &await 关键字，我有点像get"，但是我见过的所有示例都调用了 .Net 框架中的异步方法，例如这个，它调用了HttpClient.GetStringAsync().

I'm finally looking into the async & await keywords, which I kind of "get", but all the examples I've seen call async methods in the .Net framework, e.g. this one, which calls HttpClient.GetStringAsync().

我不太清楚的是这种方法中发生了什么，以及我将如何编写自己的awaitable"程序.方法.是否像将要异步运行的代码封装在 Task 中并返回它一样简单?

What I'm not so clear on is what goes on in such a method, and how I would write my own "awaitable" method. Is it as simple as wrapping the code that I want to run asynchronously in a Task and returning that?

推荐答案

就这么简单

Task.Run(() => ExpensiveTask());

使其成为可等待的方法:

To make it an awaitable method:

public Task ExpensiveTaskAsync()
{
    return Task.Run(() => ExpensiveTask());
}

这里重要的是返回一个任务.该方法甚至不必标记为异步.(只需进一步阅读它即可进入图片)

The important thing here is to return a task. The method doesn't even have to be marked async. (Just read a little bit further for it to come into the picture)

现在这可以称为

async public void DoStuff()
{
    PrepareExpensiveTask();
    await ExpensiveTaskAsync();
    UseResultsOfExpensiveTask();
}

请注意，这里的方法签名表示 async，因为该方法可能会将控制权返回给调用者，直到 ExpensiveTaskAsync() 返回.此外，在这种情况下，昂贵意味着耗时，例如 Web 请求或类似请求.要将繁重的计算发送到另一个线程，通常最好使用旧"方法，即用于 GUI 应用程序的 System.ComponentModel.BackgroundWorker 或 System.Threading.Thread.

Note that here the method signature says async, since the method may return control to the caller until ExpensiveTaskAsync() returns. Also, expensive in this case means time-consuming, like a web request or similar. To send off heavy computation to another thread, it is usually better to use the "old" approaches, i.e. System.ComponentModel.BackgroundWorker for GUI applications or System.Threading.Thread.

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