Why doesn’t await on Task.WhenAll throw an AggregateException?

by

I know this is a question that’s already answered but the chosen answer doesn’t really solve the OP’s problem, so I thought I would post this.

This solution gives you the aggregate exception (i.e. all the exceptions that were thrown by the various tasks) and doesn’t block (workflow is still asynchronous).

async Task Main()
{
    var task = Task.WhenAll(A(), B());

    try
    {
        var results = await task;
        Console.WriteLine(results);
    }
    catch (Exception)
    {
        if (task.Exception != null)
        {
            throw task.Exception;
        }
    }
}

public async Task<int> A()
{
    await Task.Delay(100);
    throw new Exception("A");
}

public async Task<int> B()
{
    await Task.Delay(100);
    throw new Exception("B");
}

The key is to save a reference to the aggregate task before you await it, then you can access its Exception property which holds your AggregateException (even if only one task threw an exception).

Hope this is still useful. I know I had this problem today.

More Related Contents:

  1. Deciphering the .NET clr20r3 exception parameters P1..P10
  2. Should we switch to use async I/O by default?
  3. What is the correct way to make a custom .NET Exception serializable?
  4. What is a “first chance exception”?
  5. Single-threaded apartment – cannot instantiate ActiveX control
  6. ArgumentNullException or NullReferenceException from extension method?
  7. Conditions when finally does not execute in a .NET try-finally block
  8. Should I derive custom exceptions from Exception or ApplicationException in .NET?
  9. Why should I always make my Exceptions [serializable]? (.NET)
  10. How to repair COMException error 80040154?
  11. How to overcome StackOverflowException bypassing unhandled exception handling in .NET
  12. How to deserialize a JObject to .NET object
  13. How to cancel a long-running Database operation?
  14. What causing this “Invalid length for a Base-64 char array”
  15. Why does NotImplementedException exist?
  16. Is it possible to catch an access violation exception in .NET?
  17. Are nested Try/Catch blocks a bad idea?
  18. Service has zero application (non-infrastructure) endpoints
  19. How do I test an async method with NUnit (or possibly with another framework)?
  20. Detecting what the target object is when NullReferenceException is thrown
  21. Close and Dispose – which to call?
  22. Databinding an enum property to a ComboBox in WPF
  23. Is there a memory limit for a single .NET process
  24. Controlling Application’s Volume: By Process-ID
  25. Using “GO” within a transaction
  26. Could not find any resources appropriate for the specified culture or the neutral culture
  27. Unit testing a multithreaded application?
  28. RestSharp serialization to JSON, object is not using SerializeAs attribute as expected
  29. Exception.Message vs Exception.ToString()
  30. Determine whether .NET assemblies were built from the same source

Leave a Comment