Epoll

epoll Edge-Triggered Readiness Requires Draining

An edge-triggered epoll consumer can block while unread data is still buffered. The failure appears when an event is consumed, only part of the available input is read, and the event loop returns to epoll_wait() expecting another notification for the bytes that remain. This behavior follows directly from EPOLLET. Edge-triggered notification reports changes in readiness rather than continuously reporting a ready condition. Once a readiness transition has produced an event, leaving the file descriptor ready does not itself create a new transition.