EPOLLPRI when does this case happen?
epoll
Solution
`EPOLLPRI` in `epoll(7)` as well as `POLLPRI` in `poll(2)` is used to receive these urgent data.
Sometimes it's necessary to send high-priority (urgent) data over a connection that may have unread low-priority data at the other end. For example, a user interface process may be interpreting commands and sending them on to another process through a stream connection. The user interface may have filled the stream with as yet unprocessed requests when the user types a command to cancel all outstanding requests. Rather than have the high-priority data wait to be processed after the low-priority data, you can have it sent as out-of-band (OOB) data or urgent data.
A Socket-based IPC Tutorial
To send OOB specify `MSG_OOB` flag in `send(2)`.
Problem
When I set my epoll option, I can see EPOLLPRI. It expalins there is urgent "read" required. When does this actually occur? Is there any way to send in that PRI Mode?