Re: Perl and File Locking

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Sep 25 08:25, Warren Young wrote:
> On 9/25/2013 02:24, wynfield@gmail.com wrote:
> >
> >"Your vendor has not defined Fcntl macro O_EXLOCK,"
> 
> O_EXLOCK is a BSD feature, and Cygwin tries to emulate Linux, not BSD.
> 
> Minimal testing tells me you can use Cygwin's nonstandard
> F_LCK_MANDATORY feature from Perl.  This script, foo.pl, doesn't
> die:
> 
>     #!/usr/bin/perl
>     sysopen my $fh, "foo.pl", 0600, O_RDONLY or die "sysopen: $!\n";
>     fcntl $fh, 0x99, 1 or die "fcntl: $!\n";
> 
> 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

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

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