Thanks for all the articles! I read the one about io_submit in the meantime. I actually hoped it would be as async as the API suggests, so it seems a bit disappointing for my use-case. Do you know if when I would schedule multiple writes via io_submit, whether it would block until all sockets have written something, or only until at least one has written something?

I guess the fact that one has to guess and try how those APIs behave makes me most nervous and would make me prevent from using those. An async IO system should be very well-behaved, and not block at arbitrary points.