There are quite a few airports in mainland Europe where arriving and departing passengers are not separated. Amsterdam being a prime example, it's split into Schengen and non-Schengen areas, but within those areas passengers arriving and departing can mingle. Security is done at the gate or at the entrance to the Schengen area (where there is also immigration). Passengers connecting between Schengen flights don't have a security re-check as they have been screened to EU/EEA standards. Otherwise security is done at the gate for non-Schengen flights.