Re: accept()ing socket connections with level triggered epoll

[Davide Libenzi]

On Wed, 26 Apr 2006, kyle@xxxxxxx wrote:

> I think I may have found a bug in Linux's implementation of epoll.  My
> program creates a server socket that listens for incoming SOCK_STREAM
> connections.  It uses epoll to wait for notification of a new connection
> (and also to handle the client sockets).  While the client sockets use edge
> triggered epoll, for performance reasons, the server socket uses level
> triggered epoll.
>
> I have found that when I open connections to my program very quickly, it is
> sometimes possible to call accept more than once before reaching the point
> where no more connections are available and EAGAIN is returned.  If I return
> to epoll_wait without accepting all of the available connections, I should
> immediately be notified that a read is still available on the server socket,
> since I am using level triggered epoll for that descriptor (at least that is
> my understanding of how all of this is supposed to work ;).  However, epoll
> does not make this notification.  Even if the program accepts further
> incoming connections, the missed connection is never accepted, and
> eventually times out on the client side.
>
> Kernel version is 2.6.9.  I can provide test code if needed.

Correct, if it's LT you have to get the event because before returning 
from epoll_wait(), the event is automatically re-armed if f_op->poll() 
returns it. Can you post the *minimal* test code for this case?



- Davide


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