How can I prevent synchronous continuations on a Task?

Question

I have some library (socket networking) code that provides a Task-based API for pending responses to requests, based on TaskCompletionSource

Answer 1

New in .NET 4.6:

.NET 4.6 contains a new TaskCreationOptions: RunContinuationsAsynchronously.

---

Since you're willing to use Reflection to access private fields...

You can mark the TCS's Task with the TASK_STATE_THREAD_WAS_ABORTED flag, which would cause all continuations not to be inlined.

const int TASK_STATE_THREAD_WAS_ABORTED = 134217728;

var stateField = typeof(Task).GetField("m_stateFlags", BindingFlags.NonPublic | BindingFlags.Instance);
stateField.SetValue(task, (int) stateField.GetValue(task) | TASK_STATE_THREAD_WAS_ABORTED);

Edit:

Instead of using Reflection emit, I suggest you use expressions. This is much more readable and has the advantage of being PCL-compatible:

var taskParameter = Expression.Parameter(typeof (Task));
const string stateFlagsFieldName = "m_stateFlags";
var setter =
    Expression.Lambda>(
        Expression.Assign(Expression.Field(taskParameter, stateFlagsFieldName),
            Expression.Or(Expression.Field(taskParameter, stateFlagsFieldName),
                Expression.Constant(TASK_STATE_THREAD_WAS_ABORTED))), taskParameter).Compile();

Without using Reflection:

If anyone's interested, I've figured out a way to do this without Reflection, but it is a bit "dirty" as well, and of course carries a non-negligible perf penalty:

try
{
    Thread.CurrentThread.Abort();
}
catch (ThreadAbortException)
{
    source.TrySetResult(123);
    Thread.ResetAbort();
}