Wait for System.IO.StreamReader.ReadLineAsync
For operations that don't support cancellation themselves, You can combine Task.WhenAny() with Task.Delay():

Async Function TryAwait(Of T)(target As Task(Of T), delay as Integer) As Task(Of T)
    Dim completed = Await Task.WhenAny(target, Task.Delay(delay))
    If completed Is target Then
        Return Await target
    End If

    Throw New TimeoutException()
End Function


Usage:

Dim nextCommand = Await TryAwait(reader.ReadLineAsync(), 2000)