socket/select differences between glibc 2.1 and 2.2

7 Feb 2003

      Hi,

Can anyone please explain the following behaviour. Consider the
following:

int main( int argc, char **argv )
{
  int s;
  fd_set              dread;
  fd_set              dwrite;
  struct timeval      to;

  to.tv_sec = 3;
  to.tv_usec = 0;

  s = socket( AF_INET, SOCK_STREAM, 0 );

  FD_ZERO(&dread);
  FD_ZERO(&dwrite);
  FD_SET(s, &dread);

  if (select(s + 1, &dread, &dwrite, (fd_set *) 0, &to) < 0)
  {
    fprintf(stderr, "Error in select(): errno=%d\n", errno);
    return errno;
  }

  return 0;
}

On a (Suse i386 linux) glibc-2.1.3-27 machine this blocks for the
timeout of 3 seconds and the 'dread' fd_set is cleared and the select
returns 0.

On a (Suse i386 linux) glibc-2.2.2-67 machine this returns immediately
and the 'dread' fd_set is left untouched and the select returns a value of 1.

The program above is a toy that reproduces my problem, while calling
select immediately on 's' may not be a meaningful thing to do, I just
want to know what the correct semantics are and why they have changed.

Cheers

Andy

*********************************************************************
*  Andrew Cheadle                    email:  a.cheadle@doc.ic.ac.uk *
*  Department of Computing           http://www.doc.ic.ac.uk/~amc4/ *
*  Imperial College                                                 *
*  University of London                                             *
*********************************************************************