Re: Select with device and stdin not working

[Ketil Froyn]

On 25 Jul 2001, M. Tavasti wrote:

> Here program where I get problems:
>
> int fd;
> fd_set rfds;
>
> fd = open("/dev/random", O_RDWR );
>
> while(1) {
>         FD_ZERO(&rfds);
>         FD_SET(fd,&rfds);
>         FD_SET(fileno(stdin),&rfds);
>         if( select(fd+1, &rfds, NULL, NULL, NULL  ) > 0) {
>                 fprintf(stderr,"Select\n");
>                 fflush(stderr);
>                 if(FD_ISSET(fd,&rfds)) {
>                  .......
>                 } else if(FD_ISSET(fileno(stdin),&rfds) ) {
>                  ......
>                 }
>         }
> }

It looks like you are sending the original fd_set to select. Remember that
it is modified in place. What is probably happening is that select returns
at once when it gets something from /dev/random, and rfds is now modified
to only contain this. The next time select runs, it will only be checking
for input from /dev/random. You have to make a copy of rfds that is set
every time, and send that instead.

Ketil