sub _bsd_size_check {
    # kB = kilobytes, kBt = kilobytes * ticks (of CPU):
    my( $userSecs, $sysSecs, $res_kB, $shared_kBt, $data_kBt, $stack_kBt )=
        BSD::Resource::getrusage();
    my @next;
    do {
        # keep refetching until one clock tick passes
        @next= BSD::Resource::getrusage();
    } while(  $data_kBt == $next[4]  );
    # Compute the differences between the two results:
    for( $userSecs, $sysSecs, $res_kB, $shared_kBt, $data_kBt, $stack_kBt ) {
        $_= shift(@next) - $_;
    }
    my $ticks= ( $userSecs + $sysSecs ) * 128;
    my $shared_kB= $shared_kBt / $ticks;
    my $unshared_kB= ( $data_kBt + $stack_kBt ) / $ticks;

    return( $unshared_kB + $shared_kB, $shared_kB );
}