From: Erik Faye-Lund Date: Thu, 27 May 2010 14:06:44 GMT Subject: Re: [PATCH] compat: Add another rudimentary poll() emulation Message-ID: In-Reply-To: On Thu, May 27, 2010 at 3:58 PM, Marko Kreen wrote: > On 5/27/10, Erik Faye-Lund wrote: >> On Thu, May 27, 2010 at 3:29 PM, Marko Kreen wrote: >>  > On 5/27/10, Erik Faye-Lund wrote: >>  >> On Thu, May 27, 2010 at 1:00 PM, Erik Faye-Lund >>  >>   wrote: >>  >>  > On Thu, May 27, 2010 at 12:10 PM, Jonathan Nieder wrote: >>  >>  >> Implement the subset of poll() semantics needed by git in terms of >>  >>  >> select(), for use by the Interix port.  Inspired by commit 6ed807f >>  >>  >> (Windows: A rudimentary poll() emulation, 2007-12-01). >>  >>  >> >>  >>  > >>  >>  > A possible problem with this approach is that the maximum number of >>  >>  > file descriptors poll can handle limited by RLIMIT_NOFILE, whereas the >>  >>  > maximum number of file descriptors select can handle is limited by >>  >>  > FD_SETSIZE. >>  >>  > >>  >>  > I don't think this is a big problem in reality, though - both values >>  >>  > seem to be pretty high in most implementations. And IIRC git-daemon is >>  >>  > the only one who needs more than 2, and it doesn't even check >>  >>  > RLIMIT_NOFILE. >>  >>  > >>  >> >>  >> >>  >> To be clear: I think this strategy is the best option (at least for >>  >>  non-Windows, where select() might be our only option). >>  >> >>  >>  But perhaps you should include a check along the lines of this: >>  >> >>  >>  if (nfds > FD_SETSIZE) >>  >>         return errno = EINVAL, error("poll: nfds must be below %d", FD_SETSIZE); >>  >> >>  >>  Just so we can know when the code fails :) >>  > >>  > Well, per your own FD_SET example, the FD_SETSIZE on windows >>  > means different thing than FD_SETSIZE on old-style bitmap-based >>  > select() implementation. >>  > >>  > On Unix, it's max fd number + 1, on windows it's max count. >>  > >> >> >> Are you sure this applies for all Unix, not just some given Unix-y system? > > Not sure.  Just pointing out that the above check is not > universal enough. > Isn't it? How could one possibly pass more than max fd number + 1 file descriptors, since they start at 0? I guess one could specify a given fd more than once, but that'd be kind of redundant... and also very unlikely in our case ;) -- Erik "kusma" Faye-Lund