package Log::Dispatch::File::Locked;

use strict;
use warnings;

use base qw( Log::Dispatch::File );

our $VERSION = '2.51';

use Fcntl qw(:DEFAULT :flock);

sub _open_file {
    my $self = shift;

    $self->SUPER::_open_file();

    my $fh = $self->{fh};

    flock( $fh, LOCK_EX )
        or die "Cannot lock '$self->{filename}' for writing: $!";

    # just in case there was an append while we waited for the lock
    seek( $fh, 0, 2 )
        or die "Cannot seek to end of '$self->{filename}': $!";
}

1;

# ABSTRACT: Subclass of Log::Dispatch::File to facilitate locking

__END__

=pod

=head1 NAME

Log::Dispatch::File::Locked - Subclass of Log::Dispatch::File to facilitate locking

=head1 VERSION

version 2.51

=head1 SYNOPSIS

  use Log::Dispatch;

  my $log = Log::Dispatch->new(
      outputs => [
          [
              'File::Locked',
              min_level => 'info',
              filename  => 'Somefile.log',
              mode      => '>>',
              newline   => 1
          ]
      ],
  );

  $log->emerg("I've fallen and I can't get up");

=head1 DESCRIPTION

This module acts exactly like L<Log::Dispatch::File> except that it
obtains an exclusive lock on the file while opening it.

=head1 CAVEATS

B<DANGER!> Use very carefully in multi-process environments. Because the lock
is obtained at file open time, not at write time, you may experience deadlocks
in your system.

You can partially work around this by using the C<close_after_write> option,
which causes the file to be re-opened every time a log message is written.

Alternatively, the C<syswrite> option does atomic writes, which may mean that
you don't need locking at all.

See  L<Log::Dispatch::File>) for details on these options.

=head1 SEE ALSO

L<perlfunc/flock>

=head1 AUTHOR

Dave Rolsky <autarch@urth.org>

=head1 COPYRIGHT AND LICENSE

This software is Copyright (c) 2015 by Dave Rolsky.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)

=cut
