HttpClient.SendAsync是否显然崩溃或阻止？

Question

I have a real puzzler here, but first some background.

I am developing (while learning C# and .Net) a WPF application that

• uses HttpClient to connect to a piece of network equipment
• downloads a log file as a .csv (after logging in)
• massages the log entries and present them in a GridView

The way I've been learning is to write each component (login, get_log, process_log, etc) individually as Console apps, then bringing them all together within a WPF framework.

As you can imagine, I was able to get all the individual functions working independently; but when I put all the pieces together it seems the application can't get past the initial connection - essentially a GET of http://10.0.0.1/login.html?/main.html . I stepped through the WPF version and found it went into the client.SendAsync() call but never came back out. (The HttpClient instance's timeout is set for the default 100 seconds and I waited MUCH longer than that.)

While the program is "hung" the app's main window is completely unresponsive: none of the minimize, maximize or close controls work. I can't even drag the window around though I am able to click on other windows, and click on it again to regain focus.

When I watch the network traffic with Wireshark I see my app sending the GET request and the remote device responding with a 200 OK and the appropriate HTML content, but nothing else after that.

I have double- and triple-checked the code between the WPF version and the Console version (for this particular section) and they are identical.

So, my questions are:

1. Has anyone seen anything like this before?
2. Any suggestions for how I might go about figuring out what's going on?

Answer 1

Has anyone seen anything like this before?

Yes

Any suggestions for how I might go about figuring out what's going on?

Never use .Wait() or .Result on async method. Use await instead. On console application this 'might' not be a problem since it doesnt have a synchronization context. However on WPF application you will almost guarantee to run into deadlock if this is run on the UI thread.

If you are interested in more details Stephen Cleary got a great explanation on his blog

Answer 2

Async/await solve blocking issue

    private async void Button_Click(object sender, RoutedEventArgs e)
    {
        using (var httpClient = new HttpClient())
        {
            httpClient.BaseAddress = new Uri("http://localhost");
            HttpRequestMessage httpRequest = new HttpRequestMessage(HttpMethod.Post, "users");
            httpRequest.Content = new StringContent("{name:'admin'}");
            var httpResponse = await httpClient.SendAsync(httpRequest);
            //process http response
        }
    }