linux-kernel - Re: unexpected extra pollout events from epoll

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Date:	Sun, 26 Oct 2008 20:48:35 -0700 (PDT)
From:	Paul P <ppak_98@...oo.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: unexpected extra pollout events from epoll

> Which version of epoll do you have? The epoll_wait()
> function does not 
> accept an event mask (like you write above,
> EPOLLIN|EPOLLOUT). 

lol, I was a bit tired when I wrote that.  Ok, ignore the stuff related 
to epoll_wait in my previous post.

> As optimization, if the EPOLLOUT bit is already set, you
> don't need to 
> keep calling epoll_ctl(fd,MOD,EPOLLOUT).

This is good to know.

So, I've got a few questions about what happens to data that accumulates 
while I am sending and the fd is set to EPOLLOUT?  If I am send out a 
large buffer and incoming data wants to stream in on a full duplex 
connection, what happens to that data when I am processing the socket 
while it is in epollout mode?  

Is the following accurate?  When data comes in while I am sending, I guess 
the data fills up the receive buffers until they are full and then it 
stops accepting data until it is cleared out?  When I switch back to 
EPOLLIN, I'm guessing that I will get a notification on that fd that there 
is data waiting.

The other question I have is there a way to do full-duplex networking so 
that I can receive network messages while I am sending or vice versa?  It 
seems that the method of switching the socket between EPOLLIN and EPOLLOUT 
means that I can't do both operations simultaneously.  Thanks

Paul

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