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On an edge triggered epoll event I read a socket (or multiple sockets, if required) until there is no more data (EAGAIN or EWOULDBLOCK) then loop back to epoll_wait. What happens if, while processing that read, another socket (one that is not currently being read) becomes ready to read? Would the edge triggered epoll ignore this as it wasn't blocking in an epoll_wait at the time of the trigger/signal or would it return with the socket in the events array immediately on the next call to epoll_wait?
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In edge-triggered mode, a call to epoll_wait will return only when a new event is enqueued with the epoll object, while in level-triggered mode, epoll_wait will return as long as the condition holds.
epoll stands for event poll and is a Linux specific construct. It allows for a process to monitor multiple file descriptors and get notifications when I/O is possible on them. It allows for both edge-triggered as well as level-triggered notifications.
epoll_ctl() is a control function that allows us to add descriptors to a watch set, remove descriptors from a watch set, or reconfigure file descriptors already in the watch set. epoll_wait() waits for I/O events on the watch set, blocking the calling thread until one or more events are detected.
The main difference between epoll and select is that in select() the list of file descriptors to wait on only exists for the duration of a single select() call, and the calling task only stays on the sockets' wait queues for the duration of a single call.
This will indeed work, epoll acts as if all events which happened to the epoll group before you made the epoll_wait call happened the moment you make the call. epoll is designed to be used this way so do not worry about this kind of usage. As long as you handle all of the events which had been triggered at the time epoll_wait returns you need not worry about any which happens between calls to it, they will be caught next time you call it.
Basically: Your usage is fine, keep going :)
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