Re: avoid a 1-second sleep in every configure script

[Ralf Wildenhues]

* Jim Meyering wrote on Sat, Aug 29, 2009 at 10:14:19PM CEST:
> Ralf Wildenhues wrote:
> > I think we can fix most instances of this wait portably, without looking
> > at subsecond time stamps: let's just try without sleeping first, and
> > only if that fails, try again after sleeping.  What do you think about
> > the patch below (diff -w shown only, due to large reindentation)?
> >
> > Only missing bit still is a good testsuite addition to ensure that it
> > still catches messed-up time stamps.

> That looks like a fine approach.
> I tested it simply by inserting this line
> 
>      test $am_try = 1 && touch --ref="$srcdir/configure" conftest.file
> 
> right after the echo timestamp... one, and verified (with inserted
> set -x ... set +x) that the sleep 1 was run.
> 
> That's no good for a test-suite addition, I know, but better than nothing.
> I suppose a test could set the time of $srcdir/configure
> to a second in the future, just before running ./configure,
> but even then it'd be a race.

Yeah.  Let's defer the test to later.  (I tested it by touching the
configure script with a time 1 hour in the future.)

I've committed the patch now, to be merged in  branch-1.11 and master,
with the only additional change to avoid a second sleep in the error
path.

Cheers, and thanks again, (and sorry for the multi-second delay ;-)
Ralf

    Avoid sleeping for one second most of the time in sanity check.
    
    * m4/sanity.m4 (AM_SANITY_CHECK): Try sanity check first without
    sleeping for a second, and only if that failed, sleep and try
    again, to avoid the delay in the common case of a configure
    script that is older than a second, or a system with sub-second
    time stamp granularity.
    Report and different patch by Jim Meyering.

diff --git a/m4/sanity.m4 b/m4/sanity.m4
index 3d2f304..db87c8b 100644
--- a/m4/sanity.m4
+++ b/m4/sanity.m4
@@ -1,21 +1,18 @@
 # Check to make sure that the build environment is sane.    -*- Autoconf -*-
 
-# Copyright (C) 1996, 1997, 2000, 2001, 2003, 2005, 2008
+# Copyright (C) 1996, 1997, 2000, 2001, 2003, 2005, 2008, 2009
 # Free Software Foundation, Inc.
 #
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
 # with or without modifications, as long as this notice is preserved.
 
-# serial 5
+# serial 6
 
 # AM_SANITY_CHECK
 # ---------------
 AC_DEFUN([AM_SANITY_CHECK],
 [AC_MSG_CHECKING([whether build environment is sane])
-# Just in case
-sleep 1
-echo timestamp > conftest.file
 # Reject unsafe characters in $srcdir or the absolute working directory
 # name.  Accept space and tab only in the latter.
 am_lf='
@@ -35,23 +32,30 @@ esac
 # (eg FreeBSD returns the mod time of the symlink's containing
 # directory).
 if (
-   set X `ls -Lt "$srcdir/configure" conftest.file 2> /dev/null`
-   if test "$[*]" = "X"; then
-      # -L didn't work.
-      set X `ls -t "$srcdir/configure" conftest.file`
-   fi
-   rm -f conftest.file
-   if test "$[*]" != "X $srcdir/configure conftest.file" \
-      && test "$[*]" != "X conftest.file $srcdir/configure"; then
-
-      # If neither matched, then we have a broken ls.  This can happen
-      # if, for instance, CONFIG_SHELL is bash and it inherits a
-      # broken ls alias from the environment.  This has actually
-      # happened.  Such a system could not be considered "sane".
-      AC_MSG_ERROR([ls -t appears to fail.  Make sure there is not a broken
-alias in your environment])
-   fi
+   for am_try in 1 2; do
+     echo timestamp > conftest.file
+     set X `ls -Lt "$srcdir/configure" conftest.file 2> /dev/null`
+     if test "$[*]" = "X"; then
+       # -L didn't work.
+       set X `ls -t "$srcdir/configure" conftest.file`
+     fi
+     rm -f conftest.file
+     if test "$[*]" != "X $srcdir/configure conftest.file" \
+       && test "$[*]" != "X conftest.file $srcdir/configure"; then
 
+       # If neither matched, then we have a broken ls.  This can happen
+       # if, for instance, CONFIG_SHELL is bash and it inherits a
+       # broken ls alias from the environment.  This has actually
+       # happened.  Such a system could not be considered "sane".
+       AC_MSG_ERROR([ls -t appears to fail.  Make sure there is not a broken
+  alias in your environment])
+     fi
+     if test "$[2]" = conftest.file || test $am_try -eq 2; then
+       break
+     fi
+     # Just in case.
+     sleep 1
+   done
    test "$[2]" = conftest.file
    )
 then