From: Erik Faye-Lund Date: Thu, 27 May 2010 12:00:02 GMT Subject: Re: [PATCH] compat: Add another rudimentary poll() emulation Message-ID: In-Reply-To: On Thu, May 27, 2010 at 1:39 PM, Marko Kreen wrote: > On 5/27/10, 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. >> >>  If we decide to go this route, perhaps it'd make sense to change to >>  this code for Windows also? Our Windows-implementation of poll() has >>  some annoying limitations... > > Example of poll() compat without FD_SETSIZE limit: > >  http://github.com/markokr/plproxy-dev/blob/master/src/poll_compat.c > How does this code convince FD_SET() that the buffer has increased? It looks to me like it depends on a specific FD_SET() implementation... For instance, Windows' FD_SET() implementation is like this: #define FD_SET(fd, set) do { \ if (((fd_set FAR *)(set))->fd_count < FD_SETSIZE) \ ((fd_set FAR *)(set))->fd_array[((fd_set FAR *)(set))->fd_count++]=(fd);\ } while(0) ...so unless another set is passed in, it won't add any more fds once fd_count reaches FD_SETSIZE. Also, FD_SETSIZE is 64 on Windows. IIRC it's 1024 on Linux, so it is much more likely that we encounter this issue on Windows than on Linux, at least ;) -- Erik "kusma" Faye-Lund