...
package main;
use threads;
use Devel::Peek;

my $o = O->new();
print $o;

$o->set( "abcde" );
print $o->get();

print "\nthreaded\n";

async {
    print $o->get( );
    $o->set( 12345 );
    print $o->get( );
}->join;

print $o->get();

__END__
C:\test>xso
N:rv:000000000035E128 o:0000000003FFA818
O=SCALAR(0x3ffa818)
S:rv;000000000035E248 o:0000000003C318F0
G:rv;000000000035E248 o:0000000003C318F0 old:000000000035E128
abcde

threaded

G:rv;0000000004258CA8 o:0000000004229090 old:0000000000000000

S:rv;0000000004258CA8 o:0000000004229090
G:rv;0000000004258CA8 o:0000000004229090 old:0000000004259920
12345
G:rv;000000000035E248 o:0000000003C318F0 old:000000000035E128
abcde