use warnings;
use strict;
use threads;
use Math::MPFR qw(:mpfr);

my ($x, $inex) = Rmpfr_init_set_d_nobless(11.625, MPFR_RNDN);

my $thr1 = threads->create(
             sub {
                 print Rmpfr_get_d($x, MPFR_RNDN), "\n";
                 return 23;
                 } );

my $res = $thr1->join();
Math::MPFR::DESTROY($x);
print $res;

__END__

OUTPUTS:
11.625
23