Using httpclient in MVC application [duplicate]

Question

When I invoke below function in a console app, it just works. But when I add the same to a MVC controller, execution never reaches JsonConvert line. Any idea, what I am missing.

Calling code

GetVersion(url).Result.FileVersion

Method

public static async Task<Version> GetVersion(string url, string hostHeader)
{
    var client = new HttpClient();
    if (!string.IsNullOrEmpty(hostHeader))
    {
        client.DefaultRequestHeaders.Host = hostHeader;
    }
    var version = await client.GetStringAsync(url);
    var output = JsonConvert.DeserializeObject<Version>(version);
    client.Dispose();
    return output;
}

Which MVC Version are you using?

ckv
– ckv

2013-12-17 05:26:11 +00:00
Commented Dec 17, 2013 at 5:26 — ckv
– ckv, Commented Dec 17, 2013 at 5:26
MVC4, .net4.5, vs2012

ragche
– ragche

2013-12-17 05:26:45 +00:00
Commented Dec 17, 2013 at 5:26 — ragche
– ragche, Commented Dec 17, 2013 at 5:26

Stephen Cleary · Accepted Answer · 2013-12-17 05:28:20Z

9

You are causing a deadlock, as I explain on my blog. By default, await captures a "context" (in this case, the ASP.NET request context) and uses that to resume the async method. The ASP.NET request context only allows one thread in at a time, and you're blocking that thread by calling Result, thus preventing the async method from completing.

Your console app doesn't deadlock because it doesn't have a "context", so the async methods resume on the thread pool.

The solution is to change the calling code to use:

(await GetVersion(url)).FileVersion

answered Dec 17, 2013 at 5:28

Stephen Cleary

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1 Comment

ragche Over a year ago

Thank you, this works. I will read your blog in detail to understand more

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