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    SubjectRe: POLLRDONCE optimisation for epoll users (was: epoll and half closed TCP connections)
    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

    -
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