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
--
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
