Re: [PATCH] compat: Add another rudimentary poll() emulation

On 5/27/10, Erik Faye-Lund [off-list ref] wrote:

On Thu, May 27, 2010 at 1:00 PM, Erik Faye-Lund
 [off-list ref] wrote:
 > On Thu, May 27, 2010 at 12:10 PM, Jonathan Nieder [off-list ref] 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.

Thus on windows the nfds can safely be larger than FD_SETSIZE,
assuming the actual count is smaller.



RLIMIT_NOFILE - I don't see why it is relevant here, as you
get error on open() when you cross the limit.  So how can you
pass more than that meny fds to select()/poll()?

-- 
marko