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sbcl/.quicklisp/dists/quicklisp/software/cffi_0.20.1/examples/mapping.lisp

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+;;;; -*- Mode: lisp; indent-tabs-mode: nil -*-
+;;;
+;;; mapping.lisp --- An example for mapping Lisp objects to ints.
+;;;
+;;; Copyright (C) 2007, Luis Oliveira  <loliveira@common-lisp.net>
+;;;
+;;; 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
+;;; DEALINGS IN THE SOFTWARE.
+;;;
+
+;;; This is an example on how to tackle the problem of passing Lisp
+;;; object identifiers to foreign code.  It is not a great example,
+;;; but might be useful nevertheless.
+;;;
+;;; Requires trivial-garbage: <http://cliki.net/trivial-garbage>
+
+(defpackage #:cffi-mapping-test
+  (:use #:common-lisp #:cffi #:trivial-garbage)
+  (:export #:run))
+
+(in-package #:cffi-mapping-test)
+
+(define-foreign-type lisp-object-type ()
+  ((weakp :initarg :weakp))
+  (:actual-type :unsigned-int))
+
+(define-parse-method lisp-object (&key weak-mapping)
+  (make-instance 'lisp-object-type :weakp weak-mapping))
+
+(defvar *regular-hashtable* (make-hash-table))
+(defvar *weak-hashtable* (make-weak-hash-table :weakness :value))
+(defvar *regular-counter* 0)
+(defvar *weak-counter* 0)
+
+(defun increment-counter (value)
+  (mod (1+ value) (expt 2 (* 8 (foreign-type-size :unsigned-int)))))
+
+(define-modify-macro incf-counter () increment-counter)
+
+(defmethod translate-to-foreign (value (type lisp-object-type))
+  (with-slots (weakp) type
+    (let ((id (if weakp
+                  (incf-counter *weak-counter*)
+                  (incf-counter *regular-counter*)))
+          (ht (if weakp *weak-hashtable* *regular-hashtable*)))
+      (setf (gethash id ht) value)
+      id)))
+
+(defmethod translate-from-foreign (int (type lisp-object-type))
+  (with-slots (weakp) type
+    (gethash int (if weakp *weak-hashtable* *regular-hashtable*))))
+
+;;;; Silly example.
+
+(defctype weak-mapping (lisp-object :weak-mapping t))
+
+;;; (run) => #<FUNCTION (LAMBDA (X)) {11AB46F5}>
+(defun run ()
+  (foreign-funcall "abs" weak-mapping (lambda (x) x) weak-mapping))