[6.x] problem with AIO, non-blocking sockets on freebSD and IE7 on windows.

Bruce Evans brde at optusnet.com.au
Mon Jun 25 16:52:56 UTC 2007

On Fri, 22 Jun 2007, Julian Elischer wrote:

> If one has an event-driven process that accepts tcp connections, one needs to 
> set eh non-blocking socket option and use kqueue or similar to schedule work.
> This is ok for data transfers, however when it comes to the close() call 
> there is a problem.  The problem in in the following code in so_close()
>               if (so->so_options & SO_LINGER) {
>                       if ((so->so_state & SS_ISDISCONNECTING) &&
>                           (so->so_state & SS_NBIO))
>                               goto drop;
> ...
> drop:
>  [ continues on to destroy socket ]
> because SS_NBIO is set, the socket acts as if SO_LINGER was set, with a 
> timeout of 0.
> the result of this, is the following behaviour:

[ patckets in flight get lost ]

This seems to be the correct behaviour.  The application doesn't care
about its data and/or wants to close the descriptor without blocking,
so it doesn't turn off the blocking flag and/or wait for i/o to complete
(so that it can see if the i/o actually worked) before calling close().

I implemented this behaviour for tty drivers in FreeBSD.  Old BSD tty
drivers didn't check the nonblocking flag and didn't have a timeout,
so close() on tty devices tended to hang forever (normally at long
weekends) even for closes that should have been nonblocking.


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