;;;; weak pointer support

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!EXT")

(defun make-weak-pointer (object)
  #!+sb-doc
  "Allocates and returns a weak pointer which points to OBJECT."
  (declare (values weak-pointer))
  (make-weak-pointer object))

#!-sb-fluid (declaim (inline weak-pointer-value))
(defun weak-pointer-value (weak-pointer)
  #!+sb-doc
  "If WEAK-POINTER is valid, returns the value of WEAK-POINTER and T.
   If the referent of WEAK-POINTER has been garbage collected, returns
   the values NIL and NIL."
  (declare (type weak-pointer weak-pointer)
	   (values t (member t nil)))
  ;; We don't need to wrap this with a without-gcing, because once we have
  ;; extracted the value, our reference to it will keep the weak pointer
  ;; from becoming broken. We just have to make sure the compiler won't
  ;; reorder these primitives.
  (let ((value (sb!c::%weak-pointer-value weak-pointer))
	(broken (sb!c::%weak-pointer-broken weak-pointer)))
    (values value (not broken))))