use Fcntl 'LOCK_EX';

=head2 C<sem_lock>

Pass C<sem_lock> a file name and will will add a .sem extension, open the
semaphore (creating if necessary), and get an exclusive lock on the file.  The
function returns a file handle that should be passed to sem_unlock() to unlock
the file.  If the program terminates, the file will be unlocked automatically.

=cut

sub sem_lock
{
	my $sem_file = shift || die "No file specified";
	$sem_file .= '.sem';
	open my $fh, ">", $sem_file or die "Cannot open semaphore $sem_file: $!";
	flock $fh, LOCK_EX          or die "Cannot get exclusive lock on $sem_file: $!";
	return $fh;
}

=head2 C<sem_unlock>

Pass C<sem_unlock> a file handle and it will close it.  It returns true or false
depending on success or failure.  It doesn't I<unlock> the file as this happens
automatically when a file is closed.  This function is primarily just to
complement C<sem_lock>.

=cut

sub sem_unlock
{
	my $fh = shift;
	close $fh or return 0;
	return 1;
}