sub child
{
    my $url = shift;
    my $glue = 'data';
    my %options = (
        create    => 'no',
        destroy   => 'no',
        );
    my %mxs;
    my $knot = tie %mxs, 'IPC::Shareable', $glue, { %options } or
        die "client: tie failed\n";
    $knot->shlock;
    push( @{$mxs{$url}}, map { $_->exchange } mx($url));
    $knot->shunlock;
    exit;
}