windows saved in variables, and `save-selected-window'

[Eric Abrahamsen]

I'm writing a minor mode that does a little bit of window management,
including opening two windows on the current buffer, and keeping track
of the two windows in two variables (the variables should be
buffer-local, but I'm seeing the below behavior with regular defvar).

One of the goals is to have a command that conditionally updates what is
displayed in the "other window". The minimum broken version of the code
is below.

During the set up, the two variables *usually* end up pointing to live
windows (ie, #<window 607 on sdfsdgsgdgsg>). Sometimes one of the
variables ends up pointing at a "dead" window: #<window 607>. Either
way, after the use of `save-selected-window' below, one of the windows
is always dead.

Obviously I'm just doing this wrong altogether -- can anyone tell me the
correct approach?

TIA,
Eric

(defvar window-one nil)
(defvar window-two nil)

(define-minor-mode not-a-mode
  "" nil " windows" nil
  (if (null not-a-mode)
      (setq window-one nil
            window-two nil)
    (split-window-sensibly)
    (setq window-one (selected-window))
    (other-window 1)
    (setq window-two (selected-window))))

(defun update-other-window ()
  (interactive)
  (save-selected-window
    (select-window window-one)
    (goto-char (/ (point-max) 2))
    (recenter)))