Task.Run differs from Task.Factory.StartNew with TaskCreationOptions.DenyChildAttach & TaskScheduler.Default

main.cs

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

internal static class Program
{
    private static void Main()
    {
        var chan = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 2 });
        Task.Factory.StartNew(async () =>
            {
                for (int i = 1; i <= 4; ++i)
                {
                    while (!chan.Post(i)) await Task.Delay(10);
                    Console.WriteLine($"produced {i}");
                }
                chan.Complete();
                Console.WriteLine("stop producing");
            },
            CancellationToken.None,
            TaskCreationOptions.DenyChildAttach,
            TaskScheduler.Default);

        var task = Task.Factory.StartNew(async () =>
            {
                try
                {
                    while (true)
                    {
                        int i = await chan.ReceiveAsync();
                        Console.WriteLine($"consumed {i}");
                    }
                }
                catch (InvalidOperationException)
                {
                    Console.WriteLine("stop consuming");
                }
            },
            CancellationToken.None,
            TaskCreationOptions.DenyChildAttach,
            TaskScheduler.Default);
        task.Wait();
        Console.WriteLine("stop waiting");
        Thread.Sleep(2020);
    }
}

When run as a console app, this output for instance:

produced 1
produced 2
consumed 1
consumed 2
stop waiting
produced 3
produced 4
stop producing
consumed 3
consumed 4
stop consuming

suggesting that the 2nd task continues after it has ended.

Replace Task.Factory.StartNew with Task.Run and delete the 3 extra arguments, and the output starts making sense.

Adding a .Unwrap() after the StartNew(...) instead gives the same reasonable output.