You might be thinking of something not entirely unlike I/O completion portsL https://en.wikipedia.org/wiki/Input/output_completion_port https://en.wikipedia.org

You might be thinking of something not entirely unlike I/O completion portsL https://en.wikipedia.org/wiki/Input/output_completion_port https://en.wikipedia.org/wiki/Input/output_completion_port There's also kqueue/kevent, which came before epoll and which is arguably superior.