Bug Hunter wrote:
> > > we opened a pipe without error. we then did this:
> > > FD_ZERO(&InputFD); // initialize read descriptors
> > >
> > > FD_SET(s,&InputFD); // Add socket to descriptors to
> > > FD_SET(FromDH,&InputFD); // wait on Modem data as well
> > >
> > > FD_ZERO(&wErrorFD);
> > > FD_SET(s,&wErrorFD);
> > > FD_SET(FromDH, &wErrorFD);
> > >
> > > signal(SIGALRM,SignalHandler);
> > >
> > > while(1){
> > > wInputFD = InputFD;
> > > // don't wait more than 500msec before reporting
> > > timeout.tv_sec = 0;
> > > timeout.tv_usec = 500000;
> > > short result =
>select(FD_SETSIZE,&wInputFD,NULL,&wErrorFD,&timeout);
> > > ...
> > >
> > >
> > > We get a 2 from select, then the pipe (FromDH) indicates
> > > an error. errno is zero. There is no error that we can
> > > see. any clues?
> >
> > What do you mean that the pipe `indicates an error'?
> >
> > Note that the third fd_set (fourth argument to select) indicates
> > `exceptional conditions', not necessarily errors.
> >
> > Also, errno is only set if some library function indicates an error
> > (usually by returning -1, NULL, etc). If select() returns 2, then it
> > won't have set errno.
>
> Im sorry, I phrased that badly. wErrorFD indicates an exception for the pipe:
>
> if (FD_ISSET(FromDH,&wErrorFD) )
> {
> /* error */
> }
>
> This always takes the error for the pipe. I don't get this for the
> other handles. Is there something special about pipes that indicate
> an exception??
>
> When we opened the pipe, there were no problems. We opened the pipe like this:
>
> FromDH=open(FROMDH_PIPE,O_RDONLY | O_NONBLOCK);
> if(FromDH<0){
> printf("Error in %s at %d =>",__FILE__,__LINE__);
> perror("Can't open FromDH");
> exit(errno);
> }
> and no error was caught. errno stayed 0.
I don't think that you should use select() on descriptors which are
non-blocking. You would normally either use select() or non-blocking
I/O, but not both.
This *may* be what's causing select() to indicate an exceptional
condition on FromDH.
--
Glynn Clements <[EMAIL PROTECTED]>
