1;;;; weak pointer support
2
3;;;; This software is part of the SBCL system. See the README file for
4;;;; more information.
5;;;;
6;;;; This software is derived from the CMU CL system, which was
7;;;; written at Carnegie Mellon University and released into the
8;;;; public domain. The software is in the public domain and is
9;;;; provided with absolutely no warranty. See the COPYING and CREDITS
10;;;; files for more information.
11
12(in-package "SB!IMPL")
13
14(defun make-weak-pointer (object)
15  #!+sb-doc
16  "Allocate and return a weak pointer which points to OBJECT."
17  (make-weak-pointer object))
18
19#!-sb-fluid (declaim (inline weak-pointer-value))
20(defun weak-pointer-value (weak-pointer)
21  #!+sb-doc
22  "If WEAK-POINTER is valid, return the value of WEAK-POINTER and T.
23If the referent of WEAK-POINTER has been garbage collected,
24returns the values NIL and NIL."
25  (declare (type weak-pointer weak-pointer))
26  ;; We don't need to wrap this with a WITHOUT-GCING, because once we
27  ;; have extracted the value, our reference to it will keep the weak
28  ;; pointer from becoming broken. We just have to make sure the
29  ;; compiler won't reorder these primitives.
30  ;;
31  ;; FIXME: Might it be a good idea to tweak the DEFKNOWNs for
32  ;; %WEAK-POINTER-VALUE and %WEAK-POINTER-BROKEN, so that the
33  ;; compiler will never try to reorder them even in code where we
34  ;; neglect to frame them in a LET?
35  (let ((value (sb!c::%weak-pointer-value weak-pointer))
36        (broken (sb!c::%weak-pointer-broken weak-pointer)))
37    (values value (not broken))))
38