Why is the UnobservedTaskException event handler not triggered for a Task which throws an exception?

Question

I have the below test program which sets up the UnobservedTaskException however the OnTaskException method is never executed. Any ideas?

NOTE:

If I remove the "for loop" then everything works as expected.

static void Main()
{
    SetupUnobservedTaskExceptionHandling();

    Task.Factory.StartNew(() =>
    {
        var counter = 5;
        for (; counter > 0; counter--)
        {
            Console.WriteLine(counter);
            Thread.Sleep(1000);
        }
        throw new InvalidCastException("I threw up!");
    });

    GC.Collect();
    GC.WaitForPendingFinalizers();
    Console.ReadLine();
}

private static void SetupUnobservedTaskExceptionHandling()
{
    TaskScheduler.UnobservedTaskException += OnTaskException;
}

private static void OnTaskException(object sender, UnobservedTaskExceptionEventArgs e)
{
    Console.WriteLine("Error!" + e.Exception);
    e.SetObserved();
}

Answer 1

You are not waiting for the task to finish executing. That means that your app will end before the task throws an exception.

If you simply add a Thread.Sleep and let the task throw the exception you will be notified:

private static void Main()
{
    SetupUnobservedTaskExceptionHandling();

    Task.Factory.StartNew(() =>
    {
        var counter = 5;
        for (; counter > 0; counter--)
        {
            Console.WriteLine(counter);
            Thread.Sleep(1000);
        }
        throw new InvalidCastException("I threw up!");
    });

    Thread.Sleep(10000);

    GC.Collect();
    GC.WaitForPendingFinalizers();
    Console.ReadLine();
}