sub Main {
    my( $msglimit ) = @_;
    use threads::Q;
    my $qout = threads::Q->new( 50 );
    threads->create( \&message_sender, $qout )->detach();    ## can't join me :)
    my $hear = threads->create( \&message_receiver, $qout, $msglimit );
    my( @ret ) = $hear->join; ## blocking
    print "Bye join @ret\n";
}