Async methods doesn't seem to work on Windows Phone

Question

I have the following piece of code (WPF, Windows Phone 8.1):

HttpClient client = new HttpClient();
var httpResult = client.GetAsync(feed.Url, ct);
string feedData = await httpResult.Result.Content.ReadAsStringAsync();

var sf = new SyndicationFeed();
sf.Load(feedData);

I'm trying to debug this code. However, after the line:

string feedData = await httpResult.Result.Content.ReadAsStringAsync();

debugger seems to let application run on its own and never reaches the next line. Why is that? Am I doing something wrong?

It's asynchronous, it will reach it when the information is there. — Christo S. Christov, Jan 09 '15 at 19:49
@CodingChief I can't imagine downloading short XML file via Wifi taking more than 1 minute. — Spook, Jan 10 '15 at 10:12
as John said you were probably in a deadlock that's why it was taking so much time. — Christo S. Christov, Jan 10 '15 at 13:47
Please note that Windows Phone is not the same as WPF; please consider removing the tag and the content. — Peter Torr - MSFT, Jan 12 '15 at 16:43

John Koerner · Accepted Answer · 2015-01-09T20:18:03.823

2

Depending on if you are calling result or wait on the task somewhere upstream, this can result in a deadlock as noted in Stephen Cleary's blog post.

Mitigate this by awaiting the client.GetAsync() and use ConfigureAwait where possible to minimize chances of deadlocks:

HttpClient client = new HttpClient();
var httpResult = await client.GetAsync(feed.Url, ct).ConfigureAwait(false);
string feedData = await httpResult.Content.ReadAsStringAsync().ConfigureAwait(false);

var sf = new SyndicationFeed();
sf.Load(feedData)

edited Jan 09 '15 at 20:18

answered Jan 09 '15 at 20:11

John Koerner

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Also, change any upstream `Wait` or `Result` calls to use `await` instead. – Stephen Cleary Jan 10 '15 at 00:49
@StephenCleary Actually this was the core problem - I waited for the method I posted above via Wait. But this bothers me a little - is there a (working) way to force do some async task synchronously? – Spook Jan 10 '15 at 10:15
1

The work is being done asynchronously. The `ConfigureAwait(false)` indicates that when the work is done you don't care what thread is used to resume the rest of the work. – John Koerner Jan 10 '15 at 13:28
@Spook: [No](http://stackoverflow.com/questions/27869403/calling-a-3rd-party-async-task-method-synchronously/27871579#27871579). – Stephen Cleary Jan 11 '15 at 04:03
@StephenCleary Ok, I expressed myself wrong. By "forcing to run synchronously" I meant waiting for a Task to complete before succeeding further. This should be done by Wait, but it causes deadlocks. So is there another, proper way to do that? – Spook Jan 11 '15 at 09:01
@Spook: Yes, just use `await task;` instead of `task.Wait();`. – Stephen Cleary Jan 11 '15 at 13:26
@StephenCleary And if I don't want the calling method to be *async*? – Spook Jan 13 '15 at 17:34
@Spook: It's doing asynchronous work, so it should be `async`. `async` does "grow" through the code base naturally, and this should be embraced. – Stephen Cleary Jan 13 '15 at 19:57

Async methods doesn't seem to work on Windows Phone

1 Answers1