Re: reduce forks during autoconf

[Bruno Haible]

Hi Eric,

> I noticed the following, as part of investigating why autoconf on m4's tree 
> was 
> so slow on cygwin:
> 
> $ cd m4
> $ autoconf --trace m4_syscmd --trace m4_esyscmd | wc
>      72     570    4742
> 
> It turns out that my additions last September are the culprit [1, 2].  OK to 
> apply this patch, which cuts down the number of syscmd forks from 72 to 2?  
> Here's how the autoconf run looks when catching the error:
> 
> $ mv lib/error.c{,.bak}
> $ autoconf -f
> missing lib/error.c
> configure.ac:68: error: problem checking LIBSOURCES
> m4/gnulib-comp.m4:42: M4_INIT is expanded from...
> configure.ac:68: the top level
> autom4te: /usr/local/bin/m4 failed with exit status: 1

Very good observation! When autoconf is slow, I usually blame 'm4', not
the number of forks :-)

I committed your patch with three small modifications:

  - Add comments. It wasn't clear to me in the beginning why the two variables
    were defined as m4 macros and not as shell variables (naive expectation).

  - Change the error message to be a little more explicit:

    $ autoconf -f
    missing file gllib/error.c
    configure.ac:114: error: expected source file, required through 
AC_LIBSOURCES, not found
    configure.ac:28: gl_INIT is expanded from...
    configure.ac:114: the top level
    autom4te: /packages/gnu/bin/m4 failed with exit status: 1

  - Change the prefix of the two variables. The prefix "AC_" is not appropriate
    since it's gnulib which defines them, not autoconf. Furthermore, when I see
    how, in func_import, two blocks of
    func_emit_initmacro_start/func_emit_initmacro_end are used to produce a
    single gl_INIT macro, it is safer to prefix the variables with
    "gl_" in one case and "gltests_" in the other case. Your version was not
    wrong, since the variables are exploited in func_emit_initmacro_end,
    not in func_emit_initmacro_done, but it's a walk on very thin ice.

Many thanks! It's tricky code.

Bruno


2008-05-13  Eric Blake  <address@hidden>
            Bruno Haible  <address@hidden>

        Reduce number of forks required during autoconf.
        * gnulib-tool (func_emit_initmacro_start): Prepare gl_LIBSOURCES_LIST
        and gl_LIBSOURCES_DIR.
        (func_emit_initmacro_end): Use them here in a single m4_syscmd...
        (func_emit_initmacro_done) <gl_LIBSOURCES>: ...rather than in one
        m4_syscmd per file.
        <m4_foreach_w>: Move...
        * m4/gnulib-common.m4 (m4_foreach_w): ...here.

*** gnulib-tool.orig    2008-05-14 02:04:47.000000000 +0200
--- gnulib-tool 2008-05-14 01:59:13.000000000 +0200
***************
*** 2046,2051 ****
--- 2046,2059 ----
    # We let automake know about the files to be distributed through the
    # EXTRA_lib_SOURCES variable.
    echo "  m4_pushdef([AC_LIBSOURCES], 
m4_defn([${macro_prefix_arg}_LIBSOURCES]))"
+   # Create data variables for checking the presence of files that are 
mentioned
+   # as AC_LIBSOURCES arguments. These are m4 variables, not shell variables,
+   # because we want the check to happen when the configure file is created,
+   # not when it is run. ${macro_prefix_arg}_LIBSOURCES_LIST is the list of
+   # files to check for. ${macro_prefix_arg}_LIBSOURCES_DIR is the subdirectory
+   # in which to expect them.
+   echo "  m4_pushdef([${macro_prefix_arg}_LIBSOURCES_LIST], [])"
+   echo "  m4_pushdef([${macro_prefix_arg}_LIBSOURCES_DIR], [])"
    echo "  gl_COMMON"
  }
  
***************
*** 2055,2060 ****
--- 2063,2085 ----
  func_emit_initmacro_end ()
  {
    macro_prefix_arg="$1"
+   # Check the presence of files that are mentioned as AC_LIBSOURCES arguments.
+   # The check is performed only when autoconf is run from the directory where
+   # the configure.ac resides; if it is run from a different directory, the
+   # check is skipped.
+   echo "  m4_ifval([${macro_prefix_arg}_LIBSOURCES_LIST], ["
+   echo "    m4_syscmd([test ! -d ]${macro_prefix_arg}_LIBSOURCES_DIR[ ||"
+   echo "      for gl_file in ]${macro_prefix_arg}_LIBSOURCES_LIST[ ; do"
+   echo "        if test ! -r ]${macro_prefix_arg}_LIBSOURCES_DIR[/\$gl_file ; 
then"
+   echo "          echo \"missing file 
]${macro_prefix_arg}_LIBSOURCES_DIR[/\$gl_file\" >&2"
+   echo "          exit 1"
+   echo "        fi"
+   echo "      done])dnl"
+   echo "      m4_if(m4_sysval, [0], [],"
+   echo "        [AC_FATAL([expected source file, required through 
AC_LIBSOURCES, not found])])"
+   echo "  ])"
+   echo "  m4_popdef([${macro_prefix_arg}_LIBSOURCES_DIR])"
+   echo "  m4_popdef([${macro_prefix_arg}_LIBSOURCES_LIST])"
    echo "  m4_popdef([AC_LIBSOURCES])"
    echo "  m4_popdef([AC_REPLACE_FUNCS])"
    echo "  m4_popdef([AC_LIBOBJ])"
***************
*** 2090,2102 ****
    echo "  ${macro_prefix_arg}_LIBOBJS=\"\$${macro_prefix_arg}_LIBOBJS 
\$1.\$ac_objext\""
    echo "])"
    echo
-   echo "# m4_foreach_w is provided by autoconf-2.59c and later."
-   echo "# This definition is to accommodate developers using versions"
-   echo "# of autoconf older than that."
-   echo "m4_ifndef([m4_foreach_w],"
-   echo "  [m4_define([m4_foreach_w],"
-   echo "    [m4_foreach([\$1], m4_split(m4_normalize([\$2]), [ ]), [\$3])])])"
-   echo
    echo "# Like AC_REPLACE_FUNCS, except that the module name goes"
    echo "# into ${macro_prefix_arg}_LIBOBJS instead of into LIBOBJS."
    echo "AC_DEFUN([${macro_prefix_arg}_REPLACE_FUNCS], ["
--- 2115,2120 ----
***************
*** 2111,2119 ****
    echo "AC_DEFUN([${macro_prefix_arg}_LIBSOURCES], ["
    echo "  m4_foreach([_gl_NAME], [\$1], ["
    echo "    m4_if(_gl_NAME, [alloca.c], [], ["
!   echo "      m4_syscmd([test -r $sourcebase_arg/]_gl_NAME[ || test ! -d 
$sourcebase_arg])dnl"
!   echo "      m4_if(m4_sysval, [0], [],"
!   echo "        [AC_FATAL([missing $sourcebase_arg/]_gl_NAME)])"
    echo "    ])"
    echo "  ])"
    echo "])"
--- 2129,2136 ----
    echo "AC_DEFUN([${macro_prefix_arg}_LIBSOURCES], ["
    echo "  m4_foreach([_gl_NAME], [\$1], ["
    echo "    m4_if(_gl_NAME, [alloca.c], [], ["
!   echo "      m4_define([${macro_prefix_arg}_LIBSOURCES_DIR], 
[$sourcebase_arg])"
!   echo "      m4_append_uniq([${macro_prefix_arg}_LIBSOURCES_LIST], _gl_NAME, 
[ ])"
    echo "    ])"
    echo "  ])"
    echo "])"
*** m4/gnulib-common.m4.orig    2008-05-14 02:04:47.000000000 +0200
--- m4/gnulib-common.m4 2008-05-14 01:32:09.000000000 +0200
***************
*** 1,4 ****
! # gnulib-common.m4 serial 4
  dnl Copyright (C) 2007-2008 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
--- 1,4 ----
! # gnulib-common.m4 serial 5
  dnl Copyright (C) 2007-2008 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
***************
*** 31,36 ****
--- 31,43 ----
      [Define to 1 when using the gnulib module ]$1[.])
  ])
  
+ # m4_foreach_w
+ # is a backport of autoconf-2.59c's m4_foreach_w.
+ # Remove this macro when we can assume autoconf >= 2.60.
+ m4_ifndef([m4_foreach_w],
+   [m4_define([m4_foreach_w],
+     [m4_foreach([$1], m4_split(m4_normalize([$2]), [ ]), [$3])])])
+ 
  # AC_PROG_MKDIR_P
  # is a backport of autoconf-2.60's AC_PROG_MKDIR_P.
  # Remove this macro when we can assume autoconf >= 2.60.