Re: POLLRDONCE optimisation for epoll users (was: epoll and half

[Davide Libenzi]

On Mon, 14 Jul 2003, Jamie Lokier wrote:

> Jamie Lokier wrote:
> > Anyway, there is a correct answer and I have made the patch so wait
> > for next mail... :)
>
> The patch is included below.  Note, it compiles and has been carefully
> scrutinised by a team of master coders, but never actually run.  Eric,
> you may want to try it out :)
>
> The difference between this and POLLRDHUP is polarity, generality and
> correctness :)
>
> Eric, change the polarity of your test from
>
> 	if (events & POLLRDHUP)
> 		goto read_again;
>
> to
>
> 	if (!(events & POLLRDONCE))
> 		goto read_again;
>
> and it should (fingers crossed) work well.

Ouch, I definitely liked more the POLLHUP thing. It is not linked to epoll
at all. Ok, suppose that our super-fast app choses Edge Triggered epoll
and also, aiming at topp speeds, using the smart read(2) trick :

void my_process_read(my_data *d, unsigned int events) {
	int n, s;

	do {
		s = d->buffer_size - d->in_buffer;
		if ((n = read(d->fd, d->buffer + d->in_buffer, s)) > 0) {
			process_partial_buffer(d, s);
			d->in_buffer += s;
		}
	} while (n == s);
	if (s == -1 && errno != EAGAIN) {
		handle_read_error(d);
		return;
	}
	if (events & EPOLLRDHUP) {
		d->flags |= HANGUP;
		schedule_removal(d);
	}
}

Where this will break by using a POLLRDHUP ?

- Davide