anchor.diff:              let thread = Thread this.Run
               threadOpt <- Some thread
               thread.Start ()
  -            while not this.Started do Thread.Sleep 0
  +            while not this.Started do Thread.Yield () |> ignore<bool>
   
           member this.EnqueueMessage message =
               lock messagesLock (fun () ->
  
positive.code: 
              // loop until submission exists
              while Option.isNone this.SubmissionOpt && not this.Terminated do
                  Thread.Sleep 0
  
              // receive submission
              let (eyePosition, eyeSize, eyeMargin) =
  
negative.code: 
              // loop until swapping
              while not this.Swapping && not this.Terminated do
                  Thread.Yield () |> ignore<bool>
  
              // swap
              renderer.Swap ()
  