Re: epoll (was Re: [PATCH] async poll for 2.5)

From: Davide Libenzi (
Date: Wed Oct 16 2002 - 18:51:39 EST

On Wed, 16 Oct 2002, John Gardiner Myers wrote:

> Davide Libenzi wrote:
> >I told you did not understand the API, this code won't work for edge
> >triggered APIs.
> >
> Nonsense. If you wish to make such a claim, you need to provide an
> example of a situation in which it won't work.

Your welcome. This is your code :

for (;;) {
     fd = event_wait(...);
     while (do_io(fd) != EAGAIN);

If the I/O space is not exhausted when you call event_wait(...); you'll
never receive the event because you'll be waiting a 0->1 transaction
without bringing the signal to 0 ( I/O space exhausted ). That one is a
typical use of poll() - select() - /dev/poll and you showed pretty clearly
that you do not seem to understand edge triggered event APIs. If you code
your I/O function like :

int my_io(...) {

        if (event_wait(...))


and you consume only part of the I/O space with the first call to my_io(),
the second call will block _infinitely_.

- Davide

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