#lang scheme/base

;; load average through the foreign interface.
;; Probably works only on linux, bsd, and Solaris systems.
;; Inspired by reading
;;   http://blog.viridian-project.de/2008/01/24/getting-started-with-cffi/
(require scheme/foreign
         (only-in (lib "1.ss" "srfi") take)
         (prefix-in c: scheme/contract))
(unsafe!)


(c:provide/contract [getloadavg (c:-> (c:listof number?))])

(define _getloadavg
  (get-ffi-obj "getloadavg" #f (_fun _cvector _int -> _int)))

;; getloadavg: -> (listof number?)
;; Returns the load average over the last 1, 5, and 15 minutes.
(define (getloadavg)
  (let* ([length 3]
         [buffer (make-cvector _double length)]
         [number-of-samples (_getloadavg buffer length)])
    (take (cvector->list buffer) number-of-samples)))