src/code/weak.lisp

   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   "Allocate and return a weak pointer which points to OBJECT."
  16   (make-weak-pointer object))
  17
  18 #!-sb-fluid (declaim (inline weak-pointer-value))
  19 (defun weak-pointer-value (weak-pointer)
  20   "If WEAK-POINTER is valid, return the value of WEAK-POINTER and T.
  21 If the referent of WEAK-POINTER has been garbage collected,
  22 returns the values NIL and NIL."
  23   (declare (type weak-pointer weak-pointer))
  24   (let ((value (sb!vm::%weak-pointer-value weak-pointer)))
  25     (if (sb!vm::unbound-marker-p value)
  26         (values nil nil)
  27         (values value t))))