Where, in any action against two or more defendants, the process is served on part of them, the plaintiff may proceed to judgment as to any so served, and either discontinue it as to the others or from time to time, as the process is served as to such others, proceed to judgment as to them until judgment be obtained against all. Such discontinuance of the action as to any defendant not served with process shall not operate as a bar of any subsequent action which may be brought against him for the same cause.