;;; -*-lisp-*-
;;;
;;; Weak pointers and data structures
;;;
;;; (c) 2008 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This program 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 2 of the License, or
;;; (at your option) any later version.
;;;
;;; This program 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, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(cl:defpackage #:weak
  (:use #:common-lisp)
  #+sbcl
    (:import-from #:sb-ext #:make-weak-pointer #:weak-pointer-value)
  #+(or cmu clisp)
    (:import-from #:ext #:make-weak-pointer #:weak-pointer-value)
  (:export #:make-weak-pointer #:weak-pointer-value))
(cl:in-package #:weak)

#+(or allegro common-lispworks)
(progn
  (defun make-weak-pointer (object)
    (make-array 1 :initial-contents (list object) :weak t))
  (defun weak-pointer-value (weak)
    (aref weak 0)))

#+ecl
(progn
  (ffi:clines
   "static GC_PTR fetch_obj(GC_PTR p) { return *(cl_object *)p; }")
  (defun make-weak-pointer (object)
    (ffi:c-inline (object) (:object) :pointer-void "
      {
	cl_object *weak = GC_malloc_atomic(sizeof(cl_object));
	*weak = #0;
	GC_general_register_disappearing_link(weak, GC_base(#0));
	@(return) = weak;
      }"
      :one-liner nil))
  (defun weak-pointer-value (weak)
    (ffi:c-inline (weak) (:pointer-void) (values :object :object) "
      {
	cl_object obj = GC_call_with_alloc_lock(fetch_obj, #0);
	if (obj) { @(return 0) = obj; @(return 1) = @t; }
	else { @(return 0) = @nil; @(return 1) = @nil; }
      }"
      :one-liner nil)))

#-(or sbcl cmu clisp allegro common-lispworks ecl)
(progn
  (defun make-weak-pointer (object) object)
  (defun weak-pointer-value (weak) (values weak t)))

;;;----- That's all, folks --------------------------------------------------