open my $tailfh, "tail -F $logfile |" or die "blunze: $!\n";

##</code><code>##

my @lines;
while (<$tailfh>) {
    push @lines, $_;
    unless (-f $lockfile) {
        open my $chunkfh, '>>', $chunkfile or die "more blunze: $!\n";
        $| = 1; # or use IO::File and autoflush
        print $chunkfh @lines;
        close $chunkfh;
        @lines = ();
    }
}