Hvordan bruger jeg låsetip, så to parallelle forespørgsler returnerer ikke-krydsende resultater?

Dette burde gøre tricket.

BEGIN TRANSACTION
DECLARE @taskId
SELECT TOP (1) @taskid = TaskId FROM Tasks WITH (UPDLOCK, READPAST) WHERE State = 'ReadyForProcessing' 
UPDATE Tasks SET State = 'Processing' WHERE TaskId = @taskid
COMMIT TRAN