In the US, it's also quite legal to have more than one light, single-engine aircraft operating on the same runway, so long as they are more than 3000' apart. In other words, quite legal for one to be crossing the threshold while another is rolling out 3500' ahead, and a third is turning off 7000' ahead.
And at Oshkosh, they operate closer than that.
(I don't recall ever getting four aircraft on one runway at the same time though, except when operating as a flight.....)