Thread Safe Insert/Update

updatevalues.sql

CREATE PROCEDURE updatevalues(@id     int, 
                              @name   varchar(20), 
                              @amount numeric)
AS

IF EXISTS(SELECT * FROM updatetest WHERE id = @id)
  BEGIN
    UPDATE updatetest 
    SET name = @name, 
        amount= @amount
    WHERE id = @id
  END
ELSE
  BEGIN
    INSERT INTO updatetest VALUES (@id, @name, @amount)
  END