Re: [PATCH] nproc: use `sysctl' when it is available.

[Bruno Haible]

Hi,

Giuseppe Scrivano wrote:
> On BSDs, where SC_NPROCESSORS_ONLN is not available, the number of
> online processors can be retrieved using `sysctl'.
> 
> From 73c11226e320c1144887daeb15e3f549b0bb2ee5 Mon Sep 17 00:00:00 2001
> From: Giuseppe Scrivano <address@hidden>
> Date: Sun, 18 Oct 2009 01:20:14 +0200
> Subject: [PATCH] nproc: use `sysctl' when it is available.
> 
> * lib/nproc.c (num_processors): If `sysctl' is available, use it to
> get the number of online processors.
> ---
>  lib/nproc.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/lib/nproc.c b/lib/nproc.c
> index 9a6e23a..f45feaf 100644
> --- a/lib/nproc.c
> +++ b/lib/nproc.c
> @@ -34,5 +34,15 @@ num_processors (void)
>      return nprocs;
>  #endif
>  
> +#ifdef HW_NCPU
> +  int ret;
> +  int mib[2] = {CTL_HW, HW_NCPU};
> +  long int nprocs;
> +  size_t len = sizeof (nprocs);
> +  ret = sysctl (mib, 2, &nprocs, &len, NULL, 0);
> +  if (ret == 0)
> +    return nprocs;
> +#endif
> +
>    return 1;
>  }

Thanks for the patch. It has a number of problems:
  - It is a nop, because HW_NCPU is defined in <sys/sysctl.h>, but this
    header file is not included. (Did you try "nm nproc.o"?)
  - The nprocs variable must be an 'int', not 'long int'. That's how it's
    documented in the sys/sysctl.h, and that's also what MacOS X 10.5 in 64-bit
    mode requires.
  - The function is documented to guarantee a positive return value. This is
    not ensured here.
  - On platforms which have both the sysconf approach and HW_NCPU, your patch
    introduces declarations after statements, which is does not work with ANSI C
    compilers.

But these can all be fixed. I'm applying the patch below.


2009-10-18  Giuseppe Scrivano  <address@hidden>
            Bruno Haible  <address@hidden>

        Implement nproc for NetBSD, OpenBSD.
        * lib/nproc.c: Include <sys/types.h>, <sys/param.h>, <sys/sysctl.h>.
        (ARRAY_SIZE): New macro.
        (num_processors): On BSD systems, try sysctl of HW_NCPU.
        * m4/nproc.m4: New file.
        * modules/nproc (Files): Add m4/nproc.m4.
        (configure.ac): Invoke gl_NPROC. Remove AC_LIBOBJ invocation.
        (Makefile.am): Instead, augment lib_SOURCES.

--- lib/nproc.c.orig    2009-10-18 10:08:29.000000000 +0200
+++ lib/nproc.c 2009-10-18 10:07:34.000000000 +0200
@@ -23,15 +23,43 @@
 
 #include <unistd.h>
 
+#include <sys/types.h>
+
+#if HAVE_SYS_PARAM_H
+# include <sys/param.h>
+#endif
+
+#if HAVE_SYS_SYSCTL_H
+# include <sys/sysctl.h>
+#endif
+
+#define ARRAY_SIZE(a) (sizeof (a) / sizeof ((a)[0]))
+
 /* Return the total number of processors.  The result is guaranteed to
    be at least 1.  */
 unsigned long int
 num_processors (void)
 {
-#ifdef _SC_NPROCESSORS_ONLN
-  long int nprocs = sysconf (_SC_NPROCESSORS_ONLN);
-  if (0 < nprocs)
-    return nprocs;
+#if defined _SC_NPROCESSORS_ONLN
+  { /* This works on glibc, MacOS X 10.5, FreeBSD, AIX, OSF/1, Solaris, Cygwin,
+       Haiku.  */
+    long int nprocs = sysconf (_SC_NPROCESSORS_ONLN);
+    if (0 < nprocs)
+      return nprocs;
+  }
+#endif
+
+#if HAVE_SYSCTL && defined HW_NCPU
+  { /* This works on MacOS X, FreeBSD, NetBSD, OpenBSD.  */
+    int nprocs;
+    size_t len = sizeof (nprocs);
+    static int mib[2] = { CTL_HW, HW_NCPU };
+
+    if (sysctl (mib, ARRAY_SIZE (mib), &nprocs, &len, NULL, 0) == 0
+       && len == sizeof (nprocs)
+       && 0 < nprocs)
+      return nprocs;
+  }
 #endif
 
   return 1;
--- modules/nproc.orig  2009-10-18 10:08:29.000000000 +0200
+++ modules/nproc       2009-10-18 09:33:19.000000000 +0200
@@ -4,14 +4,16 @@
 Files:
 lib/nproc.h
 lib/nproc.c
+m4/nproc.m4
 
 Depends-on:
 unistd
 
 configure.ac:
-AC_LIBOBJ([nproc])
+gl_NPROC
 
 Makefile.am:
+lib_SOURCES += nproc.c
 
 Include:
 "nproc.h"
================================= m4/nproc.m4 =================================
# nproc.m4 serial 1
dnl Copyright (C) 2009 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_NPROC],
[
  gl_PREREQ_NPROC
])

# Prerequisites of lib/nproc.c.
AC_DEFUN([gl_PREREQ_NPROC],
[
  AC_CHECK_HEADERS([sys/param.h],,, [AC_INCLUDES_DEFAULT])
  dnl <sys/sysctl.h> requires <sys/param.h> on OpenBSD 4.0.
  AC_CHECK_HEADERS([sys/sysctl.h],,,
    [AC_INCLUDES_DEFAULT
     #if HAVE_SYS_PARAM_H
     # include <sys/param.h>
     #endif
    ])
  AC_CHECK_FUNCS([sysctl])
])