Question

I am completely puzzled. I was so sure that .NET shuts the whole application domain if there is uncaught exception in a thread that I never tested this.

However I just tried the following code and it doesn’t fail… Could anyone please explain why?

(Tried in .NET 4 and 3.5)

static void Main(string[] args)
{
    Console.WriteLine("Main thread {0}", Thread.CurrentThread.ManagedThreadId);

    Action a = new Action(() =>
    {
        Console.WriteLine("Background thread {0}", Thread.CurrentThread.ManagedThreadId);

        throw new ApplicationException("test exception");
    });

    a.BeginInvoke(null, null);

    Console.ReadLine();
}

Answer 1

This is happening because the BeginInvoke uses ThreadPool internally and when ThreadPool any unhadled exceptions will be silence fail. However if you use a.EndInvoke then the unhadled exception will be throw at the EndInvoke method.

Note: as João Angelo stated that using ThreadPool methods directly “like ThreadPool.QueueUserWorkItems and UnsafeQueueUserWorkItem” will throw exceptions at 2.0 and above.