Thanks for all the responses and suggestions.

Especially to Hans whose defadvice solution (below)
works very well.

- Dan

 
 > From <ISI.EDU at hans> Tue Oct  7 13:52:06 1997
 > Date: Tue, 7 Oct 1997 11:49:39 -0700
 > From: Hans Chalupsky <ISI.EDU at hans>
 > To: <mickey at dryan> (Daniel Ryan)
 > Cc: <cs.berkeley.edu, at allegro-cl> <n-a-n-o.com at kr>
 > Subject: Re: xemacs lisp listener buffer max size
 > 
 > > Exactly the problem.  We have an application that must run continuously
 > > for *months* while still displaying output to the buffer (thus we 
 > > can't completely turn off output), yet not eventually die because 
 > > a buffer fills up.
 > 
 > > - Dan
 > 
 > Try this (assuming you use the Franz ACL/Emacs interface):
 > 
 > (defvar max-acl-buffer-size 1000000
 >   "Maximal number of output bytes saved in the ACL buffer.")
 > 
 > (defadvice fi::subprocess-filter (before restrict-acl-buffer-size act pre com)
 >   "Restrict the buffer size of the ACL buffer to about `max-acl-buffer-size'."
 >   (let ((buffer (process-buffer (ad-get-arg 0))))
 >     (cond ((and buffer (eq buffer (get-buffer fi:common-lisp-buffer-name)))
 >            (save-excursion
 >              (set-buffer buffer)
 >              (if (> (point-max) max-acl-buffer-size)
 >                  (delete-region 
 >                   1 (- (point-max) 
 >                        (truncate (* 0.9 max-acl-buffer-size))))))))))
 > 
 > Enjoy,
 > 
 > Hans
 > 
 > ------------------------------------------------------------------------------
 > Hans Chalupsky                              USC Information Sciences Institute
 > <isi.edu at hans>                              4676 Admiralty Way
 > (310) 822-1511 Ext.745                      Marina del Rey, CA 90292
 > ------------------------------------------------------------------------------
 >