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Date:	Fri, 17 Apr 2009 12:01:48 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: [1.7] flock change breaks autotools 'make -j2'
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On Apr 16 20:39, Eric Blake wrote:
> This change in cygwin 1.7:
> 
> - File locking is now advisory, not mandatory anymore.  The fcntl(2) and
>   the new lockf(2) APIs create and maintain locks with POSIX semantics,
>   the flock(2) API creates and maintains locks with BSD semantics.
>   POSIX and BSD locks are independent of each other.
> 
> is causing parallel make bugs in autotooled projects:
> 
> http://lists.gnu.org/archive/html/bug-automake/2009-04/msg00048.html
> 
> The problem is that perl's flock is no longer locking files the way it
> used to, so parallel instances of autom4te (the engine behind both
> autoconf and automake) end up stomping on each others' output.  I
> don't know if it something that needs to be fixed in perl, in
> automake's XFile::lock wrapper around perl's flock, or even in cygwin
> itself.  But it seems like if two instances of the same perl program
> are using the same advisory locking mechanism, that they should keep
> each other out of the file properly (advisory means that processes not
> using flock can still stomp on the file, but not other processes using
> the same locking mechanism).

Default question:  Do you have a simple testcase to reproduce this
problem?  I'm going to play with the lock.pl perl script from
http://lists.gnu.org/archive/html/bug-automake/2009-04/msg00053.html but
I don't know if I can get it working.  Perl isn't exactly my domain.
I'd prefer a testcase in C.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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