Subject: Re: Question on streams and buffering for acl5/linux
From: Erik Naggum <>
Date: 1998/12/16
Newsgroups: comp.lang.lisp
Message-ID: <>

* Steve Gonedes <>
| Anyone know if it's possible to turn off the buffering on an output
| character stream in acl5 for linux?  I took a quick look at things, but
| they seem a bit too hairy to poke at.

(defclass unbuffered-stream () ())

(defmethod stream-write-char :after ((stream unbuffered-stream) char)
  (declare (ignore char))
  (force-output stream))

(defmethod stream-write-string :after ((stream unbuffered-stream) string
				       &optional start end)
  (declare (ignore string start end))
  (force-output stream))

  now all you need to do is to create a subclass of unbuffered-stream and a
  "real" stream.  you can either do this a priori by figuring out which
  stream type you will open and use the :CLASS argument to OPEN, or you can
  do it a posteriori by creating the class at run-time.

(defun make-stream-unbuffered (stream)
  "Modify stream so that it does not buffer its data on output."
  (let* ((class-list (list 'unbuffered-stream (type-of stream)))
	 (name (with-standard-io-syntax (format nil "~{~A~^+~}" class-list)))
	 (symbol (intern name #.*package*))
	 (class (or (find-class symbol nil)
		    (clos:ensure-class symbol :direct-superclasses class-list))))
    (change-class stream class))

  the following test code will show what's going on.

(let ((old-class (class-of *standard-output*)))
  (dotimes (i 10) (write-char #\.) (sleep 1))
  (make-stream-unbuffered *standard-output*)
  (dotimes (i 10) (write-char #\.) (sleep 1))
  (change-class *standard-output* old-class))

  there may be other ways, but I've fallen love with this solution, which I
  use for a lot of _very_ different purposes, and which doesn't involve
  low-level hackery with stream internals.

  man who cooks while hacking eats food that has died twice.