The author states: >"A mutex on the fast path of a program severely limits scalability. Instead, Masscan uses "rings" to synchronize things, such as when the u

The author states: >"A mutex on the fast path of a program severely limits scalability. Instead, Masscan uses "rings" to synchronize things, such as when the user-mode TCP stack in the receive thread needs to transmit a packet without interfering with the transmit thread." Is "rings" here referring to PF_RING mentioned in the preceding paragraph or is it referring to a specific synchronization primitive?