UnobservedTaskException is not killing the process

Question

I am trying to understand the UnobservedTaskException issue in .NET 4.0 so I wrote the folloging code

TaskScheduler.UnobservedTaskException += (sender, eventArgs) => Console.WriteLine("unobserved");

Task.Factory.StartNew(() => { throw new Exception(); }, TaskCreationOptions.LongRunning);
using (var autoResetEvent = new AutoResetEvent(false))
{
    autoResetEvent.WaitOne(TimeSpan.FromSeconds(10));
}
Console.WriteLine("Collecting");
GC.Collect();
GC.WaitForPendingFinalizers();

Console.WriteLine("Still working ");
Console.ReadKey();
Console.WriteLine("Still working ");
Console.WriteLine("Still working ");
Console.ReadKey();

UnobservedTaskException is fired and then my app just keeps working. However according to MSDN the process should be killed. Can anyone tell me why ?

How do you make sure this runs on .Net 4.0? – i3arnon Aug 08 '15 at 21:01 — i3arnon, Aug 08 '15 at 21:01

score 4 · Accepted Answer · answered Aug 08 '15 at 21:05

If you run this code on a machine that only has .Net 4.0 installed it will indeed crash.

Since all the .Net versions since 4.0 were in-place updates even if you target your application for .Net 4.0 it will run on a later version on a machine that has one.

To get the same behavior of .Net 4.0 while running on a later version you can add this to your app.config file (as described in TaskScheduler.UnobservedTaskException Event):

<runtime> 
    <ThrowUnobservedTaskExceptions enabled="true"/> 
</runtime>

UnobservedTaskException is not killing the process

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