Question

I’m having trouble with the async CTP, trying to figure out what the correct way to handle exceptions is. The code below crashes my program, when as far as I can tell, the await should be catching and rethrowing the exception in the context it is called from, so the Not caught! block should catch the exception.

try {
  await TaskEx.Run(() => {
    throw new Exception();
  });
} catch {
  // Not caught!
}

Thanks for any help or suggestions.

Answer 1

Works fine for me using the beta (rather than the CTP, hence the TaskEx becoming Task):

using System;
using System.Threading.Tasks;

class Test
{
    static void Main()
    {
        Task t = Foo();
        t.Wait();
    }

    static async Task Foo()
    {
        try
        {
            await Task.Run(() => { throw new Exception(); });
        }
        catch (Exception e)
        {
            Console.WriteLine("Bang! " + e);
        }
    }

Output:

Bang! System.Exception: Exception of type 'System.Exception' was thrown.
   at Test.<Foo>b__0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter
            .HandleNonSuccessAndDebuggerNotification(Task task)
   at Test.<Foo>d__2.MoveNext()

What does the same code do on your machine?