Re: [PATCH] socket: do not enable POLLOUT for empty out buffer

[Nikolay <nitro@xxxxxxxxxxx>]

Hi Aris,

Sorry, may be I'm wrong with this patch and didn't quite understand the 
purpose of this function.

But I'm currently encountering a problem when working with libssh in 
async non-blocking mode.
I have multiple ssh connections and I do polling in the following way:

while (1) {
  // adding ssh session sockets to eventloop
  // with events taken from ssh_get_poll_flags()
  // also operating with my other sockets here
  ssh_event_dopoll(eventloop, timeout)
  // removing ssh session sockets from eventloop
}

In ssh socket event callback:
if (revents != 0) {
  if (!session_connected_and_authorized) {
    call_ssh_connect_or_auth_again();
  } else {
    ssh_channel_select(session channels for read, write and except);
    // open/exec/close on channels of this session
  }
}

The problem is that when I close the last channel in session, 
ssh_channel_close() sends a packet with ssh_socket_unbuffered_write() 
and enabled POLLOUT on this session socket.
Then my program gets stuck in socket event callback getting POLLOUT over 
and over again.
Because the session have no channels now, ssh_channel_exec() doesn't do 
anything with session socket and it keeps receiving POLLOUT event.
May be you know any hint how to avoid this? Except creating a dummy 
channel :-)
Or may be I'm doing it all wrong?

Thank you in advance!


Best regards, Nikolay Karikh.


> Hi Nikolay,
>
> Thanks for your patch. Is there a particular reason it had to be
> changed? The current behavior of the POLLOUT is to avoid a poll() call
> when sending a new packet. I think the new behavior will force buffering
> + return to the main loop + poll() + send() instead of send() + main
> loop + poll() + main loop again. It can look nasty in debug logs but I
> think it's better for latency.
>
> Aris

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