use threads;
use warnings;
#use Math::Pari;
use Math::BigInt;

$th1 = threads->new(\&start_thread1, '123' x 11);

$ret1 = $th1->join();

print $ret1, "\n";


sub start_thread1 {
    my $mbi = Math::BigInt->new($_[0]);
    return $mbi;
}
__END__
Outputs:
123123123123123123123123123123123