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Re: autoconf 2.57b: locking fails over NFS

From: Paul Eggert
Subject: Re: autoconf 2.57b: locking fails over NFS
Date: 30 Sep 2003 12:37:38 -0700
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3

>  Paul> If that's the main problem, then we can use a heuristic:
>  Paul> report a lock failure and exit only if MAKEFLAGS contains
>  Paul> -j.  It's a bit of a hack, admittedly.
>  > This sounds like a good solution to me.
> Same here.

OK, I installed this patch.  I can't test it easily, though.
(For one thing, CVS autoconf doesn't build itself on my host,
since it depends on an alpha version of autoconf....)

2003-09-30  Paul Eggert  <address@hidden>

        * lib/Autom4te/XFile.pm: Use Errno.
        (lock): Ignore ENOLCK errors.  Problem reported Andreas Schwab in

Index: XFile.pm
RCS file: /cvsroot/autoconf/autoconf/lib/Autom4te/XFile.pm,v
retrieving revision 1.8
retrieving revision 1.10
diff -p -u -r1.8 -r1.10
--- XFile.pm    13 Sep 2003 22:00:36 -0000      1.8
+++ XFile.pm    30 Sep 2003 19:34:28 -0000      1.10
@@ -87,6 +87,7 @@ require 5.000;
 use strict;
 use Carp;
+use Errno;
 use IO::File;
 use File::Basename;
 use Autom4te::ChannelDefs;
@@ -216,7 +217,15 @@ sub lock
   my ($fh, $mode) = @_;
   # Cannot use @_ here.
-  if (!flock ($fh, $mode))
+  # On some systems (e.g. GNU/Linux with NFSv2), flock(2) does not work over
+  # NFS, but Perl prefers that over fcntl(2) if it exists and if
+  # perl was not built with -Ud_flock.  Normally, this problem is harmless,
+  # so ignore the ENOLCK errors that are reported in that situation,
+  # However, if the invoker is using "make -j", the problem is not harmless,
+  # so report it in that case.  Admittedly this is a bit of a hack.
+  if (!flock ($fh, $mode)
+      && (!$!{ENOLCK} || " $ENV{'MAKEFLAGS'}" =~ / (-j|--jobs)/))
       my $file = $fh->name;
       fatal "cannot lock $file with mode $mode: $!";

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