Async requests with .NET core

Question

I need a little help to find out my problem. I've used ASP.NET core and i'm fairly familiar with that, although .NET core C# seems to be "crashing" and exiting when trying to make my async request.

I have a method that returns the external IP of the system

private async Task<string> getExternalIP()
    {
        using (System.Net.Http.HttpClient HC = new System.Net.Http.HttpClient())
        {
            return await HC.GetStringAsync("https://api.ipify.org/");
        }

    }

This should work, but it exits when it reaches the HC.GetStringAsync. I've also tried putting a breakpoint on it but it doesn't actually run.

I'm trying to call the method by using

string Address = await getExternalIP();

Any help is thankful, hopefully i'm not just overlooking something.

Thanks!

@SLaks I've re-enabled all exception notices. No exception is being thrown. — Sasha, Oct 27 '16 at 19:26
@ProNinjaCat [Exception handling with async void](http://stackoverflow.com/questions/6284267/async-exception-handling-with-void) — Matias Cicero, Oct 27 '16 at 19:30
It appears that Async support may have been removed for .NET core applications. http://stackoverflow.com/questions/38114553/are-async-console-applications-supported-in-net-core — Sasha, Oct 27 '16 at 19:31
Are you certain your HttpClient is successfully instantiated? — David W, Oct 27 '16 at 19:44
Yep most certain, about to test on a normal console app and see if it works — Sasha, Oct 27 '16 at 19:53
I think you are dealing with a problem associated with the SynchronizationContext present at the time you call the async method. Can you post some of your calling code? You may be getting zapped by deadlock detection. — David W, Oct 27 '16 at 20:01
Managed to get it fixed, see the answer I posted :) Thanks for helping — Sasha, Oct 27 '16 at 20:02

Matias Cicero · Accepted Answer · 2016-10-27T20:33:30.360

12

Your proposed solution is not good at all.

It is synchronous
It can cause a deadlock

As an alternative, try this approach:

private async Task<string> GetExternalIP()
{
    using (HttpClient client = new HttpClient())
        return await client.GetStringAsync("https://api.ipify.org/");
}

Your calling method should be asynchronous too:

public async Task CallingMethod()
{
     // ...
     string address = await GetExternalIP();
     // ...
}

The reason it was not working for you before was caused by the use of async void instead of async Task (guessed this by the comments).

async void is an asynchronous method that cannot be awaited. That means, you just call it and forget about it. You won't catch any exception, you won't get any return value.

async Task is an awaitable asynchronous method that does not return anything. It is the asynchronous counterpart for a void synchronous method. Furthermore, since it is awaitable, you'll also be able to catch any exception that may rise on the asynchronous code.

edited Oct 27 '16 at 20:33

answered Oct 27 '16 at 20:24

Matias Cicero

25,439
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I originally had something similar to this, but the problem is the "CallingMethod" ends up not returning and the application exits. No exception, no message. – Sasha Oct 27 '16 at 20:29
@ProNinjaCat Because you were using `async void` and not `async Task`. You'll also need to `await CallingMethod()` from whoever calls it. – Matias Cicero Oct 27 '16 at 20:30
I have the async Task running await getExternalIP() and the getExternalIP() method the exact same, but it still doesn't execute. – Sasha Oct 27 '16 at 20:31
@ProNinjaCat Are you awaiting `CallingMethod()` too? – Matias Cicero Oct 27 '16 at 20:32
That's inside my Main(), which doesn't allow Async in it's signature – Sasha Oct 27 '16 at 20:34
1

@ProNinjaCat Then that's why it never ran. You never awaited it. If you want an async console app, see [this question](http://stackoverflow.com/questions/17630506/async-at-console-app-in-c). – mason Oct 27 '16 at 20:35
@mason This was the problem, thanks for figuring this out otherwise I would of probably kept my solution! – Sasha Oct 27 '16 at 20:38
@ProNinjaCat Glad we came to an understanding. If you consider this answer helpful to you (and to others), please mark it as accepted. – Matias Cicero Oct 27 '16 at 22:40

Async requests with .NET core

1 Answers1