Wait for input

[Ed Symanzik <zik msu edu>]

Let's say I had a app with a button or menu item to connect to a
server.  I can catch that signal and open the connection.

However, if the user has not identified the server, I should
popup a window and get that information.  How do I wait until
they have set that value?

connect_button_pressed()
  if (no_server)
    server_popup();
  connect_to_server(server);