lkml.org 
[lkml]   [2011]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: Does Linux select() violate POSIX?
From
On Sun, Jun 19, 2011 at 3:32 PM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>
> It's worth noting that the POSIX semantics are actually unimplementable
> for some network protocols anyway particularly on send. TCP is a fine
> example. A remote TCP isn't *supposed* to shrink its window but they can
> do, and that that point the space select() saw for a send is closed down
> again by the remote host.

Which makes me wonder what *BSD does for such a situation. Although
not enough to check the source. :-)

> All sorts of similar issues appear all over the place. There are also
> interesting API corner cases such as the behaviour of
>
>        listen()
>        select
>                        connection made
>        select returns
>                        remote closes connection
>        accept
>                        behaviour is not determinate

Hm, I thought this was what ECONNABORTED was for?

That is, accept() might return ECONNABORTED, or it might return a
descriptor and then a later operation on that descriptor would fail
with ECONNRESET... But either way, select() followed by accept() need
not block.

> (and in general POSIX doens't address sockets well)

Well, no argument there.

> So for portable code always mix select and poll with non blocking I/O. It
> doesn't matter what the specs say, the real world says drive defensively
> 8)

No argument here, either. This was mostly for a barroom bet (well,
StackOverflow... same thing), but also because I was curious. There
are not a lot of ways in which Linux chooses to violate POSIX. Which
might make a fun list to put together, come to think of it.

Thanks again, Alan.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-06-20 00:49    [from the cache]
©2003-2011 Jasper Spaans