;; Producer/Consumer-Puffer mit Lock-Conditions

(define-record-type :buffer
  (really-make-buffer data lock available empty)
  buffer?
  (data buffer-data set-buffer-data!)
  (lock buffer-lock)
  (available buffer-available)
  (empty buffer-empty))

(define (make-buffer)
  (let ((lock (make-lock)))
    (really-make-buffer #f
			lock
			(make-lock-condition lock)
			(make-lock-condition lock))))

(define (with-lock lock thunk)
  (obtain-lock lock)
  (let ((value (thunk)))
    (release-lock lock)
    value))

(define (insert buffer value)
  (with-lock (buffer-lock buffer)
    (lambda ()
      (let loop ()
	(cond
	 ((buffer-data buffer)
	  => (lambda (ignore)
	       (wait-lock-condition (buffer-empty buffer))
	       (loop)))
	 (else
	  (set-buffer-data! buffer value)
	  (signal-lock-condition (buffer-available buffer))))))))

(define (remove buffer)
  (with-lock (buffer-lock buffer)
    (lambda ()
      (let loop ()
	(cond
	 ((buffer-data buffer)
	  => (lambda (value)
	       (set-buffer-data! buffer #f)
	       (signal-lock-condition (buffer-empty buffer))
	       value))
	 (else
	  (wait-lock-condition (buffer-available buffer))
	  (loop)))))))