Task.Wait doesn't propagate exception

[NN---]

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp14
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                var cts = new CancellationTokenSource();
                var task = Task.Run(
                    async () =>
                    {

                            await Task.Delay(TimeSpan.FromSeconds(10), cts.Token);

                    },
                    cts.Token);
                cts.CancelAfter(TimeSpan.FromSeconds(1));
                task.Wait();

                // .NET 2.0 - 3.5 reach this line
                Console.WriteLine("Must not get there");
            }
            catch (AggregateException)
            {
                Console.WriteLine("Expected");
            }
        }
    }
}

I guess related to #120

[theraot]

This happens: The Task gets marked cancelled, but the CancellationToken on the Task says that no cancellation was requested. Why? Because the task has a CancellationToken from the default source. Why? Because Task.Run uses Unwrap and Unwrap does not copy the CancellationToken. I'll fix that.

[NN---]

I tried to find out the reason but didn’t succeed.

[theraot]

Simple test shows that a Task should throw even without a CancellationToken with cancellation requested (Tried in LinqPad):

TaskCompletionSource<int> tcs1 = new TaskCompletionSource<int>();
Task<int> t1 = tcs1.Task;
tcs1.TrySetCanceled();
t1.Wait();

So, I think I'll make it throw when canceled even if the CancellationToken.CancellationToken does not throw.

I'll see if Unwrap should or should not copy the CancellationToken. This could be two bugs instead of one.

[theraot]

Trying the code above in .NET 2.0 throws an AggregateException with TaskCanceledException with a CancellationToken with IsCancellationRequested = true. While the same code in LinqPad has IsCancellationRequested = false.

I can also confirm that Unwrap should copy the CancellationToken.

Edit: that is a total of 3 things to fix:

• TrySetCanceled should not set a CancellationToken
• Task should throw even without CancellationToken.IsCancellationRequested
• Unwrap should copy the CancellationToken

[theraot]

Ok, this is the problem…

If TrySetCanceled does not set a CancellationToken, this line hangs: https://github.com/theraot/Theraot/blob/master/Framework.Core/System/Threading/Tasks/Task.cs#L738

And then #120 comes back.

I haven't found any nice workaround.

--

Edit: To be clear, the changes that I will fix the original issue. The line Console.WriteLine("Must not get there"); won't be reached. It is just that TrySetCanceled will always result in a TaskCanceledException with a cancelled token, while that is not true in .NET framework.

[NN---]

Is there an updated NuGet ?

[theraot]

Just submitted. NuGet 3.2.0.

[NN---]

Thanks a lot !

[NN---]

Works well.