On Thu, May 27, 2010 at 2:36 PM, Marko Kreen <markokr@xxxxxxxxx> wrote: > On 5/27/10, Erik Faye-Lund <kusmabite@xxxxxxxxxxxxxx> wrote: >> On Thu, May 27, 2010 at 1:39 PM, Marko Kreen <markokr@xxxxxxxxx> wrote: >> > On 5/27/10, Erik Faye-Lund <kusmabite@xxxxxxxxxxxxxx> wrote: >> >> On Thu, May 27, 2010 at 12:10 PM, Jonathan Nieder <jrnieder@xxxxxxxxx> 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 ;) > > Hm, good catch. Seems such compat poll() cannot be done without > OS-specific hacks. > Perhaps getrlimit() could overridden to return FD_SETSIZE for both the soft and hard limit when asking about RLIMIT_NOFILE? In such cases, anyone who passes nfds above FD_SETSIZE hasn't consulted RLIMIT_NOFILE, and should be outside the standard. But your point might have been about a limitless poll()-implementation, like the code you linked tried to achieve. In that context, no. I doubt it's possible to do in a robust fashion. For git, I don't think this is necessary, though. As said, I think git-daemon is the only call-site for poll where nfds can be above 2. And git-daemon's default max-connection is 32, which shouldn't cause much problems. There's the theoretical problem of someone setting --max-connections above their platform's limit, but I don't think we need to touch that ;) > Do you know perhaps what other OS-es have non-bitmap fd_set? No, I don't have much low-level file-descriptor knowledge about other OS'es than Windows, really. -- Erik "kusma" Faye-Lund -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html