From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: Typo in <sys/select.h>?
Date: Wed, 6 Jul 2022 16:15:58 +0200 [thread overview]
Message-ID: <YsWZHryhvF3+WcEv@calimero.vinschen.de> (raw)
In-Reply-To: <ea3de3f0-ed55-bfcf-f543-a95e38b98599@dronecode.org.uk>
On Jul 6 15:01, Jon Turney wrote:
> On 06/07/2022 08:42, Corinna Vinschen wrote:
> > On Jul 5 17:51, Ken Brown wrote:
> > > On 7/5/2022 10:13 AM, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via Cygwin wrote:
> >
> > I guess we can change FD_SETSIZE to 1024 as on Linux, albeit this has no
> > real meaning on Cygwin. On Linux, select(2) is really only capable to
> > handle file descriptors numbers up to descriptor number 1023, but Cygwin
> > doesn't have this problem. FD_SETSIZE == 64 was only something to save
> > space. The bigger FD_SETSIZE, the bigger are the default fd_sets,
> > something you don't want on small targets.
> >
> > So, yeah, something like
> >
> > #ifndef FD_SETSIZE
> > # ifdef __CYGWIN__
> > # define FD_SETSIZE 1024
> > # else
> > # define FD_SETSIZE 64
> > # endif
> > #endif
>
> 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);
Corinna
next prev parent reply other threads:[~2022-07-06 14:16 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-05 14:13 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-05 14:55 ` Andrey Repin
2022-07-05 21:51 ` Ken Brown
2022-07-06 7:42 ` Corinna Vinschen
2022-07-06 14:01 ` Jon Turney
2022-07-06 14:15 ` Corinna Vinschen [this message]
2022-07-06 14:22 ` Corinna Vinschen
2022-07-05 15:11 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-06 13:19 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-06 14:17 ` Corinna Vinschen
2022-07-06 14:17 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-06 14:26 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-06 15:07 ` Corinna Vinschen
2022-07-06 15:57 Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-07-06 17:03 ` Ken Brown
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