sub write_logfile ($$) {
    use Time::HiRes 'time';
    my ($file, $message) = @_;
    chomp($message);
    if (defined($file)) {
        open OLDERR, ">&STDERR";
        open STDERR, ">>$file";
        flock STDERR, 8;
        print OLDERR "";
    };
    print STDERR time, " [", $$, "] ", $message, "\n";
    if (defined($file)) {
        close STDERR;
        open STDERR, ">&OLDERR";
    };
};