src/code/restart.lisp

   1 ;;;; This software is part of the SBCL system. See the README file for
   2 ;;;; more information.
   3 ;;;;
   4 ;;;; This software is derived from the CMU CL system, which was
   5 ;;;; written at Carnegie Mellon University and released into the
   6 ;;;; public domain. The software is in the public domain and is
   7 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
   8 ;;;; files for more information.
   9
  10 (in-package "SB!KERNEL")
  11
  12 ;;; A comment formerly here about "for DX allocation" was incredibly misleading.
  13 ;;; We (apparently) never want DX allocation of restarts, except in
  14 ;;; INITIAL-THREAD-FUNCTION-TRAMPOLINE where we do, but only "accidentally".
  15 ;;; The accident is that if there is exactly ONE escape point, or there is more
  16 ;;; than one and they all return the same fixed number of values,
  17 ;;; then the generated code is right. If they don't, there's a problem.
  18
  19 ;;; So, following this DEFSTRUCT was a NOTINLINE proclamation, which we need,
  20 ;;; because now that the compiler is smart enough to inline any structure
  21 ;;; constructor anywhere, it can and does. I'm puzzled why, because I thought
  22 ;;; the way this worked was that a local INLINE declaration would always
  23 ;;; "succeed" in finding an inline expansion, but I didn't think that the
  24 ;;; compiler would actually choose of its own free will to do local inlining,
  25 ;;; even though the standard says that's what it *can* do unless told not to.
  26
  27 ;;; Then, if it does inline MAKE-RESTART, a problem occurs in RESTART-BIND
  28 ;;; with a TRULY-DYNAMIC-EXTENT declaration, because restarts go on the stack
  29 ;;; that can't. But I think that itself is a bug. They *should* go on the stack,
  30 ;;; because the chain of cons cells pointing to them is on the stack.
  31 ;;; The restarts are otherwise inaccessible. I'm pretty sure this
  32 ;;; is actually a compiler bug.
  33
  34 ;;; So in a nutshell, there are 2 issues:
  35 ;;; (1) DX seems legitimate, but there may be a compiler bug.
  36 ;;; (2) The logic about when to assume that a structure constructor
  37 ;;;     can automatically be inlined is tricker than its author understands.
  38
  39 (declaim (notinline make-restart))
  40
  41 ;;;; This defstruct should appear before any use of WITH-CONDITION-RESTARTS
  42 ;;;; so that the slot accessors are transformed.
  43
  44 (defstruct (restart (:constructor make-restart
  45                         ;; Having TEST-FUNCTION at the end allows
  46                         ;; to not replicate its default value in RESTART-BIND.
  47                         (name function
  48                          &optional report-function
  49                                    interactive-function
  50                                    test-function))
  51                     (:copier nil) (:predicate nil))
  52   (name (missing-arg) :type symbol :read-only t)
  53   (function (missing-arg) :type function :read-only t)
  54   (report-function nil :type (or null function) :read-only t)
  55   (interactive-function nil :type (or null function) :read-only t)
  56   (test-function (lambda (cond) (declare (ignore cond)) t) :type function :read-only t)
  57   ;; the list of conditions which are currently associated to the
  58   ;; restart. maintained by WITH-CONDITION-RESTARTS in a neither
  59   ;; thread- nor interrupt-safe way. This should not be a problem
  60   ;; however, since safe uses of restarts have to assume dynamic
  61   ;; extent.
  62   (associated-conditions '() :type list))
  63
  64 #!-sb-fluid (declaim (freeze-type restart))