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Date:	Tue, 15 Oct 2013 16:15:09 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Perl and File Locking
Message-ID:	<20131015141509.GF19383@calimero.vinschen.de>
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On Sep 25 08:25, Warren Young wrote:
> On 9/25/2013 02:24, wynfield AT gmail DOT com wrote:
> >
> >"Your vendor has not defined Fcntl macro O_EXLOCK,"
>=20
> O_EXLOCK is a BSD feature, and Cygwin tries to emulate Linux, not BSD.
>=20
> Minimal testing tells me you can use Cygwin's nonstandard
> F_LCK_MANDATORY feature from Perl.  This script, foo.pl, doesn't
> die:
>=20
>     #!/usr/bin/perl
>     sysopen my $fh, "foo.pl", 0600, O_RDONLY or die "sysopen: $!\n";
>     fcntl $fh, 0x99, 1 or die "fcntl: $!\n";
>=20
> Whether it actually does what you expect is a different question.

Uh, no, don't do that.  O_EXLOCK in the BSD world does *not* mean that
you want mandatory locking.  It only means that the application wants an
exclusive lock on the entire file right at open time, thus allowing an
atomic open/lock under BSD flock semantics.

What you want to do is to call

  sysopen my $fh, "foo.pl", 0600, O_RDONLY ...
  [insert perl equivalent of the flock system call here]

That's not atomic, but this isn't provided (yet) utside the BSD world.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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