DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C2CF93858D39
Date: Wed, 6 Jul 2022 16:22:47 +0200
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: Typo in <sys/select.h>?
Message-ID: <YsWat3DLV9KEH/UG@calimero.vinschen.de>
Mail-Followup-To: cygwin@cygwin.com
References: <DM8PR09MB70954B30D740E778EB65BA41A5819@DM8PR09MB7095.namprd09.prod.outlook.com>
 <1c3256fd-ed7b-8ee3-adcd-b1d8ef2fff84@cornell.edu>
 <YsU9APd87h5vUJtZ@calimero.vinschen.de>
 <ea3de3f0-ed55-bfcf-f543-a95e38b98599@dronecode.org.uk>
 <YsWZHryhvF3+WcEv@calimero.vinschen.de>
MIME-Version: 1.0
Content-Disposition: inline
In-Reply-To: <YsWZHryhvF3+WcEv@calimero.vinschen.de>
Precedence: list
Reply-To: cygwin@cygwin.com
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: cygwin-bounces+archive-cygwin=delorie.com@cygwin.com
Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie.com@cygwin.com>

On Jul  6 16:15, Corinna Vinschen wrote:
> On Jul  6 15:01, Jon Turney wrote:
> > Remember that 64 is MAXIMUM_WAIT_OBJECTS for WaitForMultipleObjects(), the
> > underlying Win32 API used to implement select(), so using more than 64 hits
> > some complex code to work around that...
> 
> This isn't what FD_SETSIZE is about.  FD_SETSIZE does *NOT* define the
> maximum count of fd's in an fd_set.
> 
> It defines the maximum fd number usable in an fd_set.
> 
> So if FD_SETSIZE is defined low enough:
> 
>   #define FD_SETSIZE 3
>   #include <sys/select.h>
> 
>   /* Only fd's 0, 1, and 2 will be allowed in this fd_set */
>   fd_set set;
> 
>   FD_ZERO (&set);
>   /* This will probaly set fd to 3 */
>   fd = open ("foo", O_RDONLY); 
>   /* So this will (hopefully) fail */
>   FD_SET (fd, &set);

Right, this isn't quite how it works, given fd_set is a bitfield using
unsigned long as basetype under the hood.  This should just outline
the idea behind FD_SETSIZE.


Corinna

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple