gettimeofday.lisp

;;;; -*- Mode: lisp; indent-tabs-mode: nil -*-
;;;
;;; gettimeofday.lisp --- Example CFFI binding to gettimeofday(2)
;;;
;;; Copyright (C) 2005-2006, James Bielman <jamesjb@jamesjb.com>
;;;
;;; Permission is hereby granted, free of charge, to any person
;;; obtaining a copy of this software and associated documentation
;;; files (the "Software"), to deal in the Software without
;;; restriction, including without limitation the rights to use, copy,
;;; modify, merge, publish, distribute, sublicense, and/or sell copies
;;; of the Software, and to permit persons to whom the Software is
;;; furnished to do so, subject to the following conditions:
;;;
;;; The above copyright notice and this permission notice shall be
;;; included in all copies or substantial portions of the Software.
;;;
;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
;;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
;;; HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
;;; WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
;;; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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;;;

;;;# CFFI Example: gettimeofday binding
;;;
;;; This example illustrates the use of foreign structures, typedefs,
;;; and using type translators to do checking of input and output
;;; arguments to a foreign function.

;;; Define the TIMEVAL structure used by 'gettimeofday'. This assumes
;;; that 'time_t' is a 'long' --- it would be nice if CFFI could
;;; provide a proper :TIME-T type to help make this portable.
(in-package #:vivace-graph)

(defcstruct timeval
  (tv-sec :long)
  (tv-usec :long))

;;; A NULL-POINTER is a foreign :POINTER that must always be NULL.
;;; Both a NULL pointer and NIL are legal values---any others will
;;; result in a runtime error.
(define-foreign-type null-pointer-type ()
  ()
  (:actual-type :pointer)
  (:simple-parser null-pointer))

;;; This type translator is used to ensure that a NULL-POINTER has a
;;; null value. It also converts NIL to a null pointer.
(defmethod translate-to-foreign (value (type null-pointer-type))
  (cond
    ((null value) (null-pointer))
    ((null-pointer-p value) value)
    (t (error "~A is not a null pointer." value))))

;;; The SYSCALL-RESULT type is an integer type used for the return
;;; value of C functions that return -1 and set errno on errors.
;;; Someday when CFFI has a portable interface for dealing with
;;; 'errno', this error reporting can be more useful.
(define-foreign-type syscall-result-type ()
  ()
  (:actual-type :int)
  (:simple-parser syscall-result))

;;; Type translator to check a SYSCALL-RESULT and signal a Lisp error
;;; if the value is negative.
(defmethod translate-from-foreign (value (type syscall-result-type))
  (if (minusp value)
      (error "System call failed with return value ~D." value)
      value))

;;; Define the Lisp function %GETTIMEOFDAY to call the C function
;;; 'gettimeofday', passing a pointer to the TIMEVAL structure to fill
;;; in. The TZP parameter is deprecated and should be NULL --- we can
;;; enforce this by using our NULL-POINTER type defined above.
(defcfun ("gettimeofday" %gettimeofday) syscall-result
  (tp :pointer)
  (tzp null-pointer))

(defun gettimeofday ()
  (with-foreign-object (tv 'timeval)
    (%gettimeofday tv nil)
    (with-foreign-slots ((tv-sec tv-usec) tv timeval)
      (+ tv-sec (/ tv-usec 1000000)))))