libuv notes

Some notes from reading libuv:

• UDP sends seem to be dispatched immediately without any backpressure to the app

• IPV6_V6ONLY uniformly disabled

• In general, uses SetFileCompletionNotificationModes to try and avoid bouncing through the IOCP when possible; they say this is a major performance win. I'm skeptical about this transferring over, though, given our yield point semantics – I think the win they're talking about is basically the greedy write/read optimization.

• Handling of SetFileCompletionNotificationModes for UDP has some significant complications to work around bugs

• On Windows, sets both SO_REUSEADDR and SO_EXCLUSIVEADDR to false, to allow rebinding of TIME_WAIT sockets. But then there's https://github.com/joyent/libuv/issues/150

• On windows, optionally issues multiple AcceptEx calls simultaneously (for efficiency under high accept load I guess)

• There are some complications around cancellation and LSPs... if a "non-IF SLSP" is installed, then libuv uses WSAIoctl to get the base handle before trying to cancel things

  • http://www.komodia.com/KomodiaLSPTypes.pdf
  • http://www.lenholgate.com/blog/2017/01/setfilecompletionnotificationmodes-can-cause-iocp-to-fail-if-a-non-ifs-lsp-is-installed.html