Adding Bert's personal email address in CC. I hope he can add some insights here...
Thanks, Geert On Monday, August 4, 2014 6:31:06 PM UTC+2, Geert Jansen wrote: > > Hi, > > ever since I first got interested in async IO I have been operating on > this assumption: > > 1. select() on Windows is bad, IOCP is good. > > Since IOCP is completion based, but for polling you need a ready-based > API, I deduced from the above: > > 2. fd/HANDLE/SOCKET polling on Windows is inefficient. > > However, after looking at src/win/poll.c it seems that my assumption #2 is > false because there is a method to get efficient, IOCP based polling to > work on Windows. It appears to be using a super low-level IO control that > isn't even defined in the Windows header files. Libuv calls this > "IOCTL_AFD_POLL" which is "9 | METHOD_BUFFERED". The implementation seems > to come from Bert Belder's "epoll_windows" package. > > First off it is really cool that such an API exists and that Bert found it > (out of curiosity I wonder how). I can't find any reference on this > anywhere. The only reference I found on MSDN is a CVE for a privilege > escalation in AfdPoll which I assume is the same thing. And I found a > second reference in ReactOS which appears to implement this as well. > > Looking through poll.c it seems that the IOCP based poll is called > "fast_poll" and the select based one "slow_poll". Which one is selected > depends on whether getsockopt(SO_PROTOCOL_INFOW) returns a provider that > matches a certain set of GUIDs. > > It would be useful to know when I can expect fast_poll to work and when > not. I'm assuming it depends on the Windows version and other factors too. > The answer is actually pretty important I think because if efficient > polling is readily available on Windows then it becomes waaaay easier to > integrate 3rd party libraries into a libuv based application. Many > libraries support being plugged into an event loop but they want to pass > you an FD, and they want to be called back when it is ready. Without a fast > poll, I cannot use this interface and expect it works efficiently on both > Unix and Windows. The library would need to be able to accept data that is > already read via a memory buffer. The only library I know that supports > both FD based IO and memory buffer based IO is OpenSSL. There might be a > few more but I doubt there are many. All other library that I've seen only > supports async IO via FD polling. > > Can anybody give a clarification on when I can expect fast_poll to work? > > Regards, > Geert > -- You received this message because you are subscribed to the Google Groups "libuv" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/libuv. For more options, visit https://groups.google.com/d/optout.
