Re: [Emacs-diffs] master d02c2f7 4/4: Speed up maybe_gc when GC is inhibited

[Paul Eggert <eggert@cs.ucla.edu>]

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Pip Cet wrote:

> This looks unsafe to me.

Right you are, of course; thanks for checking that. I installed the attached.

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From 5d4dd552c29279b8a9e6ed269a2dc3afc36f73b9 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sun, 21 Jul 2019 12:31:51 -0700
Subject: [PATCH] Fix lifetime error in previous patch

Problem reported by Pip Cet in:
https://lists.gnu.org/r/emacs-devel/2019-07/msg00520.html
* src/alloc.c (inhibit_garbage_collection): Use new function.
(allow_garbage_collection): Accept intmax_t, not pointer.
* src/eval.c (default_toplevel_binding, do_one_unbind)
(backtrace_eval_unrewind, Fbacktrace__locals, mark_specpdl):
Support SPECPDL_UNWIND_INTMAX.
(record_unwind_protect_excursion): New function.
* src/lisp.h (enum specbind_tag): New constant SPECPDL_UNWIND_INTMAX.
(union specbinding): New member unwind_intmax.
---
 src/alloc.c |  8 +++-----
 src/eval.c  | 16 ++++++++++++++++
 src/lisp.h  |  7 +++++++
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/src/alloc.c b/src/alloc.c
index 50015808e5..aa9200f2eb 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -5505,10 +5505,9 @@ staticpro (Lisp_Object const *varaddress)
    consing_until_gc to speed up maybe_gc when GC is inhibited.  */
 
 static void
-allow_garbage_collection (void *ptr)
+allow_garbage_collection (intmax_t consing)
 {
-  object_ct *p = ptr;
-  consing_until_gc = *p;
+  consing_until_gc = consing;
   garbage_collection_inhibited--;
 }
 
@@ -5516,8 +5515,7 @@ ptrdiff_t
 inhibit_garbage_collection (void)
 {
   ptrdiff_t count = SPECPDL_INDEX ();
-  object_ct consing = consing_until_gc;
-  record_unwind_protect_ptr (allow_garbage_collection, &consing);
+  record_unwind_protect_intmax (allow_garbage_collection, consing_until_gc);
   garbage_collection_inhibited++;
   consing_until_gc = OBJECT_CT_MAX;
   return count;
diff --git a/src/eval.c b/src/eval.c
index 02a6c3555a..b890aa6f7f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -674,6 +674,7 @@ default_toplevel_binding (Lisp_Object symbol)
 	case SPECPDL_UNWIND_ARRAY:
 	case SPECPDL_UNWIND_PTR:
 	case SPECPDL_UNWIND_INT:
+	case SPECPDL_UNWIND_INTMAX:
 	case SPECPDL_UNWIND_EXCURSION:
 	case SPECPDL_UNWIND_VOID:
 	case SPECPDL_BACKTRACE:
@@ -3394,6 +3395,15 @@ record_unwind_protect_int (void (*function) (int), int arg)
   grow_specpdl ();
 }
 
+void
+record_unwind_protect_intmax (void (*function) (intmax_t), intmax_t arg)
+{
+  specpdl_ptr->unwind_intmax.kind = SPECPDL_UNWIND_INTMAX;
+  specpdl_ptr->unwind_intmax.func = function;
+  specpdl_ptr->unwind_intmax.arg = arg;
+  grow_specpdl ();
+}
+
 void
 record_unwind_protect_excursion (void)
 {
@@ -3448,6 +3458,9 @@ do_one_unbind (union specbinding *this_binding, bool unwinding,
     case SPECPDL_UNWIND_INT:
       this_binding->unwind_int.func (this_binding->unwind_int.arg);
       break;
+    case SPECPDL_UNWIND_INTMAX:
+      this_binding->unwind_intmax.func (this_binding->unwind_intmax.arg);
+      break;
     case SPECPDL_UNWIND_VOID:
       this_binding->unwind_void.func ();
       break;
@@ -3784,6 +3797,7 @@ backtrace_eval_unrewind (int distance)
 	case SPECPDL_UNWIND_ARRAY:
 	case SPECPDL_UNWIND_PTR:
 	case SPECPDL_UNWIND_INT:
+	case SPECPDL_UNWIND_INTMAX:
 	case SPECPDL_UNWIND_VOID:
 	case SPECPDL_BACKTRACE:
 	  break;
@@ -3917,6 +3931,7 @@ NFRAMES and BASE specify the activation frame to use, as in `backtrace-frame'.
 	  case SPECPDL_UNWIND_ARRAY:
 	  case SPECPDL_UNWIND_PTR:
 	  case SPECPDL_UNWIND_INT:
+	  case SPECPDL_UNWIND_INTMAX:
 	  case SPECPDL_UNWIND_EXCURSION:
 	  case SPECPDL_UNWIND_VOID:
 	  case SPECPDL_BACKTRACE:
@@ -3979,6 +3994,7 @@ mark_specpdl (union specbinding *first, union specbinding *ptr)
 
 	case SPECPDL_UNWIND_PTR:
 	case SPECPDL_UNWIND_INT:
+	case SPECPDL_UNWIND_INTMAX:
         case SPECPDL_UNWIND_VOID:
 	  break;
 
diff --git a/src/lisp.h b/src/lisp.h
index 6d101fed90..9d37629bc4 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3156,6 +3156,7 @@ enum specbind_tag {
 				   Its elements are potential Lisp_Objects.  */
   SPECPDL_UNWIND_PTR,		/* Likewise, on void *.  */
   SPECPDL_UNWIND_INT,		/* Likewise, on int.  */
+  SPECPDL_UNWIND_INTMAX,	/* Likewise, on intmax_t.  */
   SPECPDL_UNWIND_EXCURSION,	/* Likewise, on an execursion.  */
   SPECPDL_UNWIND_VOID,		/* Likewise, with no arg.  */
   SPECPDL_BACKTRACE,		/* An element of the backtrace.  */
@@ -3191,6 +3192,11 @@ union specbinding
       void (*func) (int);
       int arg;
     } unwind_int;
+    struct {
+      ENUM_BF (specbind_tag) kind : CHAR_BIT;
+      void (*func) (intmax_t);
+      intmax_t arg;
+    } unwind_intmax;
     struct {
       ENUM_BF (specbind_tag) kind : CHAR_BIT;
       Lisp_Object marker, window;
@@ -4118,6 +4124,7 @@ extern void record_unwind_protect (void (*) (Lisp_Object), Lisp_Object);
 extern void record_unwind_protect_array (Lisp_Object *, ptrdiff_t);
 extern void record_unwind_protect_ptr (void (*) (void *), void *);
 extern void record_unwind_protect_int (void (*) (int), int);
+extern void record_unwind_protect_intmax (void (*) (intmax_t), intmax_t);
 extern void record_unwind_protect_void (void (*) (void));
 extern void record_unwind_protect_excursion (void);
 extern void record_unwind_protect_nothing (void);
-- 
2.17.1