Possible File iteration bug

[Ethan Furman]

Billy Mays wrote:
> A sentinel does provide a work around, but it also passes the problem 
> onto the caller rather than the callee

The callee can easily take care of it -- just block until more is ready. 
  If blocking is not an option, then the caller has to deal with it no 
matter how callee is implemented -- an exception, a sentinel, or some 
signal that says "nope, nothing for ya! try back later!"

~Ethan~