Pipe and select : sample code not working - macos

Question

Am I missing something ?
I want to come out of select by calling write in another thread... It never comes out of select.
Code is tested on OSX snow.
fd_set rio, wio;
int pfd[2];
void test(int sleep_time)
{
sleep(sleep_time);
char buf[] = "1";
write(pfd[1], buf, 1);
}
int main(int argc, char* argv[])
{
char buff[80];
int ended = 0;
pipe(pfd);
FD_ZERO(&rio);
FD_ZERO(&wio);
FD_SET(pfd[1], &wio);
FD_SET(pfd[0], &rio);
pthread_t tid; /* the thread identifier */
pthread_attr_t attr; /* set of thread attributes */
pthread_attr_init(&attr);
pthread_create(tid, NULL, test, 3);
while (!ended)
{
// Check my numbers ... they do not go over 1 ... so 2
if (select(2, &rio, &wio, NULL, 0) < 0)
perror("select");
else
{
if (FD_ISSET(pfd[1], &wio))
{
if ((read(pfd[0], &buff, 80))<0)
perror("read");
ended = 1;
}
}
}

Answer 1

I believe you have 2 errors:
1 - your select call is limiting the check to a max of fd 2, where the pipe will probably have larger FDs since 0, 1, and 2 are already opened for stdin, stdout, stderr. The pipe FDs will presumably have fds 3 and 4 so you actually need to determine the larger of the 2 pipe FDs and use that for the limit in the select instead of 2.
int maxfd = pfd[1];
if( pfd[0] > maxfd ) {
maxfd = pfd[0];
}
...
2 - After select returns, you are looking at the wio and pipe write FD when you need to instead look to see if there is anything available to READ:
if (FD_ISSET(pfd[0], &rio)) {