使用 HttpWebRequest.GetResponseAsync 进行异步和等待

Async and Await with HttpWebRequest.GetResponseAsync(使用 HttpWebRequest.GetResponseAsync 进行异步和等待)

问题描述

我在发出 Web 请求时尝试使用 Async 和 Await，但我发现它永远不会超过 await 行.我是通过 Metro 应用程序执行此操作的，但我也在 winforms 应用程序中验证了问题.

I am trying to use Async and Await when making a web request and am finding that it never gets past the await line. I am doing this from a Metro app, but I also verified the problem in a winforms app.

public async Task<string> DoSomething()
{
    string url = "http://imgur.com/gallery/VcBfl.json";
    HttpWebRequest request = HttpWebRequest.CreateHttp(url);

    var ws = await request.GetResponseAsync();

    return ws.ResponseUri.ToString(); ;
}

如果我不使用 await 而是执行同步等待，它可以工作，但我需要它异步运行.

If I don't use await and instead perform a synchronous wait, it works, but I need this to run asynchronously.

我在这段代码中遗漏了什么导致等待永远不会返回?

What am I missing in this code that is causing the await to never return?

推荐答案

我怀疑你的调用堆栈更进一步，你要么在调用 Wait 要么 Result返回任务.这将导致死锁，正如我在我的博客中描述的那样.

I suspect that further up your call stack, you're either calling Wait or Result on the returned Task. This will cause a deadlock, as I describe on my blog.

遵循这些最佳做法以避免死锁:

Follow these best practices to avoid the deadlock:

1. 不要阻塞 async 代码；一直使用 async.
2. 在您的库"方法中，使用 ConfigureAwait(false).

1. Don't block on async code; use async all the way down.
2. In your "library" methods, use ConfigureAwait(false).

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