App Doesn't Crash While Debugging, but Does When Running Normally

Question

System Information

• Windows 10 Technical Preview (build 9926)
• Visual Studio Community 2013
  
  Attempting to debug on:
• [AT&T] Lumia 635 (Windows 10 Technical Preview for phones build 9941 w/ Lumia Cyan)
• [AT&T] Lumia 1520 (Windows Phone 8.1 with Lumia Denim and PfD)
• [Unlocked] BLU Win Jr (Windows Phone 8.1 with PfD)
• [Verizon] Lumia Icon (Windows Phone 8.1 with Lumia Denim and PfD)

---

I trying to get location services working in my app. Previously, I had Visual Studio throw the error. It was an ArgumentException with the message "Use of undefined keyword value 1 for event TaskScheduled in async". Googling didn't turn up any solutions.

Here is the code:

Geolocator Locator = new Geolocator();
Geoposition Position = await Locator.GetGeopositionAsync();
Geocoordinate Coordinate = Position.Coordinate;

When I could get the error to be thrown, the exception was thrown on the 2nd or 3rd line in the sample above. I simplified the original code to try and fix it, but this is the original:

Geolocator Locator = new Geolocator();
Geocoordinate Coordinate = (await Locator.GetGeopositionAsync()).Position.Coordinate;

The entire app works when debugging, but crashes almost instantaneously otherwise.

This is a Windows 8.1 Universal project, focusing on the phone project.

Thanks in advance

---

EDIT: As requested, here is the full method:

private static bool CheckConnection()
{
    ConnectionProfile connections = NetworkInformation.GetInternetConnectionProfile();
    bool internet = connections != null && connections.GetNetworkConnectivityLevel() == NetworkConnectivityLevel.InternetAccess;
    return internet;
}
public static async Task<double> GetTemperature(bool Force)
{
    if (CheckConnection() || Force)
    {
        Geolocator Locator = new Geolocator();
        await Task.Yield(); //Error occurs here
        Geoposition Position = await Locator.GetGeopositionAsync();
        Geocoordinate Coordinate = Position.Coordinate;
        HttpClient Client = new HttpClient();
        double Temperature;
        Uri u = new Uri(string.Format("http://api.worldweatheronline.com/free/v1/weather.ashx?q={0},{1}&format=xml&num_of_days=1&date=today&cc=yes&key={2}",
                                      Coordinate.Point.Position.Latitude,
                                      Coordinate.Point.Position.Longitude,
                                      "API KEY"),
                                      UriKind.Absolute);
        string Raw = await Client.GetStringAsync(u);
        XElement main = XElement.Parse(Raw), current_condition, temp_c;
        current_condition = main.Element("current_condition");
        temp_c = current_condition.Element("temp_C");
        Temperature = Convert.ToDouble(temp_c.Value);
        switch (Memory.TempUnit)
        {
            case 0:
                Temperature = Convertions.Temperature.CelsiusToFahrenheit(Temperature);
                break;
            case 2:
                Temperature = Convertions.Temperature.CelsiusToKelvin(Temperature);
                break;
        }
        return Temperature;
    }
    else
    {
        throw new InvalidOperationException("Cannot connect to the weather server.");
    }
}

---

EDIT 2: I've asked for help on Twitter, and received a reply asking for a repro project. I recreated the major portion of the original app, but I could not get the error. However, errors may occur for you so here's the project.

---

EDIT 3: If it helps at all, here are the exception details:

System.ArgumentException occurred
  _HResult=-2147024809
  _message=Use of undefined keyword value 1 for event TaskScheduled.
  HResult=-2147024809
  IsTransient=false
  Message=Use of undefined keyword value 1 for event TaskScheduled.
  Source=mscorlib
  StackTrace:
       at System.Diagnostics.Tracing.ManifestBuilder.GetKeywords(UInt64 keywords, String eventName)
  InnerException: 

Answer 1

Having checked this and this, I believe this is a bug in .NET async/await infrastructure for WinRT. I couldn't repro it, but I encourage you to try the following workaround, see if it works for you.

• Factor out all asynchronous awaitable calls from OnNavigatedTo into a separate async Task method, e.g. ContinueAsync:

  async Task ContinueAsync()
  {
      Geolocator Locator = new Geolocator();
      Geoposition Position = await Locator.GetGeopositionAsync();
      Geocoordinate Coordinate = Position.Coordinate; 
  
      // ...
  
      var messageDialog = new Windows.UI.Popups.MessageDialog("Hello");
      await messageDialog.ShowAsync();
  
      // ...
  }
  

• Remove async modifier from OnNavigatedTo and call ContinueAsync from OnNavigatedTo like this:

  var scheduler = TaskScheduler.FromCurrentSynchronizationContext();
  Task.Factory.StartNew(
      () => ContinueAsync(), 
      CancellationToken.None, TaskCreationOptions.None, scheduler).
      Unwrap().
      ContinueWith(t => 
      {
          try
          {
              t.GetAwaiter().GetResult();
          }
          catch (Exception ex)
          {
              Debug.WriteLine(ex);
              throw; // re-throw or handle somehow
          }
      }, 
      CancellationToken.None,            
      TaskContinuationOptions.NotOnRanToCompletion, 
      scheduler);
  

Let us know if it helps :)

---

Updated, apparently, the bug is somewhere in the TPL logging provider, TplEtwProvider. You can see it's getting created if you add the below code. So far, I couldn't find a way to disable this event source (either directly or via Reflection):

internal class MyEventListener : EventListener
{
    protected override void OnEventSourceCreated(EventSource eventSource)
    {
        base.OnEventSourceCreated(eventSource);
        if (eventSource.Name == "System.Threading.Tasks.TplEventSource")
        {
            var enabled = eventSource.IsEnabled();

            // trying to disable - unsupported command :(
            System.Diagnostics.Tracing.EventSource.SendCommand(
                eventSource, EventCommand.Disable, new System.Collections.Generic.Dictionary<string, string>());
        }
    }
}

// ...
public sealed partial class App : Application
{
    static MyEventListener listener = new MyEventListener();
}