Bug 18560 - TaskScheduler.UnobservedTaskException raised for trapped exceptions from Task.Factory.FromAsync
Summary: TaskScheduler.UnobservedTaskException raised for trapped exceptions from Task...
Status: RESOLVED FIXED
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: 3.2.x
Hardware: PC Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2014-03-24 17:52 UTC by Dave Dunkin
Modified: 2014-03-31 13:16 UTC (History)
3 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED FIXED

Description Dave Dunkin 2014-03-24 17:52:48 UTC
If an exception is thrown from async code adapted with Task.Factory.FromAsync and later caught, UnobservedTaskException is still raised. This is related to bug 17015.

Reproduced with Xamarin.iOS 7.2.0.2.



using System;
using System.Threading.Tasks;
using MonoTouch.UIKit;
using MonoTouch.Foundation;

namespace UnhandledExceptionRepro
{
	[Register("UnhandledExceptionReproViewController")]
	public partial class UnhandledExceptionReproViewController :
		UIViewController
	{
		public UnhandledExceptionReproViewController(IntPtr handle)
			: base(handle)
		{
		}

		public override async void ViewDidLoad()
		{
			base.ViewDidLoad();

			TaskScheduler.UnobservedTaskException += (sender, e) =>
			{
				if (e.Exception != null)
				{
					InvokeOnMainThread(() =>
						new UIAlertView("unobserved task exception",
							e.Exception.Message, null, "Ok", null).Show());
				}
			};

			try
			{
				await getResult();
			}
			catch (Exception ex)
			{
				new UIAlertView("trapped exception", ex.Message, null, "Ok",
					null).Show();
			}
		}

		private async Task getResult()
		{
			await Task.Delay(10);

			await Task.Factory.FromAsync(BeginFoo(), EndFoo);
		}

		IAsyncResult BeginFoo()
		{
			Action foo = () => {};
			AsyncCallback cb = _ => {};
			return foo.BeginInvoke(cb, null);
		}

		void EndFoo(IAsyncResult result)
		{
			throw new Exception("boom");
		}
	}
}
Comment 1 Marek Safar 2014-03-31 13:16:16 UTC
This issue is already fixed in Xamarin.iOS 7.2.1 or newer