Wait for System.IO.StreamReader.ReadLineAsync

Question

I want to wait for a line to be read, but only for so long before timing out. This is what I came up with. Is there a better way to do it?

Dim reader As New System.IO.StreamReader(pipe)
Dim nextCommand = Await New Func(Of Task(Of String))(
 Function()
 Dim t = reader.ReadLineAsync()
 If (Not t.Wait(2000)) Then Throw New MyTimeoutExeption()
 Return t
 End Function).Invoke()

Answer 1

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)

• rory.ap: Can you please clarify one thing? Return Await target won't actually continue to await, since it's already completed, right? Is its purpose there only to make sure a Task(Of T) is returned?
• svick: @roryap Yeah. And also to make sure exceptions from target are propagated.
• John Demetriou: What about Timeout?