4. (Upd: 8 visible cores due to hyperthreading )

I don't understand the... surprise? To be clear, that's

# ikegami
lock ${ $mutexes{$k} };
++$hash{$k};
[download]

# browseruk
lock ${ $hash{$k} };
++${ $hash{$k} };
[download]

(with proper initialisation)