examples/mapping.lisp

   1 ;;;; -*- Mode: lisp; indent-tabs-mode: nil -*-
   2 ;;;
   3 ;;; mapping.lisp --- An example for mapping Lisp objects to ints.
   4 ;;;
   5 ;;; Copyright (C) 2007, Luis Oliveira  <loliveira@common-lisp.net>
   6 ;;;
   7 ;;; Permission is hereby granted, free of charge, to any person
   8 ;;; obtaining a copy of this software and associated documentation
   9 ;;; files (the "Software"), to deal in the Software without
  10 ;;; restriction, including without limitation the rights to use, copy,
  11 ;;; modify, merge, publish, distribute, sublicense, and/or sell copies
  12 ;;; of the Software, and to permit persons to whom the Software is
  13 ;;; furnished to do so, subject to the following conditions:
  14 ;;;
  15 ;;; The above copyright notice and this permission notice shall be
  16 ;;; included in all copies or substantial portions of the Software.
  17 ;;;
  18 ;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  19 ;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  20 ;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  21 ;;; NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  22 ;;; HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  23 ;;; WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24 ;;; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  25 ;;; DEALINGS IN THE SOFTWARE.
  26 ;;;
  27
  28 ;;; This is an example on how to tackle the problem of passing Lisp
  29 ;;; object identifiers to foreign code.  It is not a great example,
  30 ;;; but might be useful nevertheless.
  31 ;;;
  32 ;;; Requires trivial-garbage: <http://cliki.net/trivial-garbage>
  33
  34 (defpackage #:cffi-mapping-test
  35   (:use #:common-lisp #:cffi #:trivial-garbage)
  36   (:export #:run))
  37
  38 (in-package #:cffi-mapping-test)
  39
  40 (define-foreign-type lisp-object-type ()
  41   ((weakp :initarg :weakp))
  42   (:actual-type :unsigned-int))
  43
  44 (define-parse-method lisp-object (&key weak-mapping)
  45   (make-instance 'lisp-object-type :weakp weak-mapping))
  46
  47 (defvar *regular-hashtable* (make-hash-table))
  48 (defvar *weak-hashtable* (make-weak-hash-table :weakness :value))
  49 (defvar *regular-counter* 0)
  50 (defvar *weak-counter* 0)
  51
  52 (defun increment-counter (value)
  53   (mod (1+ value) (expt 2 (* 8 (foreign-type-size :unsigned-int)))))
  54
  55 (define-modify-macro incf-counter () increment-counter)
  56
  57 (defmethod translate-to-foreign (value (type lisp-object-type))
  58   (with-slots (weakp) type
  59     (let ((id (if weakp
  60                   (incf-counter *weak-counter*)
  61                   (incf-counter *regular-counter*)))
  62           (ht (if weakp *weak-hashtable* *regular-hashtable*)))
  63       (setf (gethash id ht) value)
  64       id)))
  65
  66 (defmethod translate-from-foreign (int (type lisp-object-type))
  67   (with-slots (weakp) type
  68     (gethash int (if weakp *weak-hashtable* *regular-hashtable*))))
  69
  70 ;;;; Silly example.
  71
  72 (defctype weak-mapping (lisp-object :weak-mapping t))
  73
  74 ;;; (run) => #<FUNCTION (LAMBDA (X)) {11AB46F5}>
  75 (defun run ()
  76   (foreign-funcall "abs" weak-mapping (lambda (x) x) weak-mapping))