gnupg/tests/gpgscm/ffi.scm

;; FFI interface for TinySCHEME.
;;
;; Copyright (C) 2016 g10 Code GmbH
;;
;; This file is part of GnuPG.
;;
;; GnuPG is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3 of the License, or
;; (at your option) any later version.
;;
;; GnuPG is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, see <http://www.gnu.org/licenses/>.

;; Foreign function wrapper.  Expects F to return a list with the
;; first element being the `error_t' value returned by the foreign
;; function.  The error is thrown, or the cdr of the result is
;; returned.
(define (ffi-apply name f args)
  (let ((result (apply f args)))
    (cond
     ((string? result)
      (ffi-fail name args result))
     ((not (= (car result) 0))
      (ffi-fail name args (strerror (car result))))
     ((and (= (car result) 0) (pair? (cdr result))) (cadr result))
     ((= (car result) 0) '())
     (else
      (throw (list "Result violates FFI calling convention: " result))))))

(define (ffi-fail name args message)
  (let ((args' (open-output-string)))
    (write (cons (string->symbol name) args) args')
    (throw (string-append
	    (get-output-string args') ": " message))))

;; Pseudo-definitions for foreign functions.  Evaluates to no code,
;; but serves as documentation.
(macro (ffi-define form))

;; Runtime support.

;; Low-level mechanism to terminate the process.
(ffi-define (_exit status))

;; High-level mechanism to terminate the process is to throw an error
;; of the form (*interpreter-exit* status).  This gives automatic
;; resource management a chance to clean up.
(define *interpreter-exit* (gensym))
(define (throw . x)
  (cond
   ((more-handlers?)
    (apply (pop-handler) x))
   ((and (= 2 (length x)) (equal? *interpreter-exit* (car x)))
    (*run-atexit-handlers*)
    (_exit (cadr x)))
   (else
    (apply error x))))
(set! *error-hook* throw)

;; Terminate the process returning STATUS to the parent.
(define (exit status)
  (throw *interpreter-exit* status))

;; A list of functions run at interpreter shutdown.
(define *atexit-handlers* (list))

;; Execute all these functions.
(define (*run-atexit-handlers*)
  (unless (null? *atexit-handlers*)
	  (let ((proc (car *atexit-handlers*)))
	    ;; Drop proc from the list so that it will not get
	    ;; executed again even if it raises an exception.
	    (set! *atexit-handlers* (cdr *atexit-handlers*))
	    (proc)
	    (*run-atexit-handlers*))))

;; Register a function to be run at interpreter shutdown.
(define (atexit proc)
  (set! *atexit-handlers* (cons proc *atexit-handlers*)))