[politician]

IOCP is the top item on my (short) list of things Windows simply does better. The performance boost you see from designing a server for IOCP from the ground up is jaw-dropping. However, it's hard to grok because it's a very different model, most servers are proprietary code, and the MSDN documentation is barely sufficient (at least, back when I was writing IOCP-based servers in '09).

[trentnelson]

Yeah, I had to figure out how to leverage all the new threadpool stuff with async sockets from scratch for PyParallel, none of the MSDN docs detailed how AcceptEx() and ConnectEx() and DisconnectEx() and all that jazz were meant to be used with CreateThreadpoolIo(), StartThreadpoolIo() etc.

Even bought a couple of Microsoft books and they only covered it at the file I/O level, too. And the last Winsock book is reaaaaaally getting old.

Also, registered I/O is a similar jump in jaw-dropping performance. Disable completion notifications, pre-register all of your buffers on large pages, and use timers to schedule bulk de-queuing of all available completion events.

You definitely need a feedback loop in there to fine-tune the timings, but holy hell does it fly. You basically get a guaranteed-max-latency state machine (given bandwidth, computational cost of request processing, and number of clients connected).