[zeromq-dev] EAGAIN on ZMQ_STREAM

[Jens Auer]

Hi Doron,

 

I don’t think it is disconnect. I am testing it on the local network, so there is not much internet infrastructure in between. I am using a pseudo client which logs socket errors, connects and disconnects and I don’t see anything. On the server side, I have a socket monitor which logs socket events but this does not show anything. Finally, if the TCP connection disconnects the ZMQ_STREAM socket shall create the empty disconnect message which I do not receive, neither before or after the EAGAIN. 

 

Best wishes,

  Jens 

 

Von: zeromq-dev [mailto:zeromq-dev-bounces at lists.zeromq.org] Im Auftrag von Doron Somech
Gesendet: Freitag, 17. Juni 2016 22:14
An: ZeroMQ development list
Betreff: Re: [zeromq-dev] EAGAIN on ZMQ_STREAM

 

Why you can exclude the first case? TCP connection can get disconnect quite often.

Anyway from what you are describing it seems the connection got disconnected.

 

On Fri, Jun 17, 2016 at 8:05 PM, Jens Auer <jens.auer at betaversion.net> wrote:

Hi,

I am witnessing something in my system that I didn't expect. I am processing
data at a data rate of 100Mbps, with occasional peaks of 5s of data (=5 *
100Mbps) delivered as fast as possible because an internal buffer is
flushed. I use ZeroMQ internally, but I have to deliver the data on a TCP
plain socket at the endpoint of my system. Here, I use a ZMQ_STREAM socket
where clients connect. Basically, I keep track of connected clients and send
the data to all clients as a copy of the message. The main loop here looks
like
for(auto const& c: clientIdMessages) {
   bool eagain = !socket.send(c.copy(), ZMQ_DONTWAIT | ZMQ_SNDMORE);
   if (!eagain) {
      eagain = !socket.send(msg.copy(), ZMQ_DONTWAIT | ZMQ_SNDMORE);
   }
}

This usually works fine, but from time to time a message is skipped because
send returns with EAGAIN. If I understand the docs correctly, this happens
if the peer is unknown (ZMQ_STREAM behavior) or when the message cannot be
queued. I can exclude the first case, so I must a high HWM for sending
messages. However, I tried to increase the HWM to a huge value of 50 times
the expected message rate and it did not solve the problem. I also tried to
disable the HWM by setting it to 0, which means "no limit". Still, I am
getting an EAGAIN which I don't expect.

I can exclude any previous loss because I have counters showing me that the
full data stream is delivered to the ZMQ_STREAM socket code above. I also
added an assertion on !eagain after sending, and this fires. Are there any
other conditions when I can get EAGAIN from a ZMQ_STREAM socket?

Best wishes,
  Jens


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