[zeromq-dev] ZMQ_FLAT_PULL feature discussion

[Pieter Hintjens]

It's an interesting use case. The simplest answer is to indeed pull
off messages in user space and only process a message when the client
queues appear empty.

It's a fairly common strategy in older pub-sub systems to drop oldest
data or conflate data (so newer keys replace older ones) but it costs
a lot in CPU and slows things down.

If you want to make an experimental patch on ROUTER, go for it. Try to
find a name that explains what you're really doing, which is to limit
the incoming queue for each client to one request.
(ZMQ_ROUTER_CONFLATE?) Also, if this can work on other socket types,
it probably should.

-Pieter


On Fri, Jun 7, 2013 at 11:53 AM, Daniel Krikun <krikun.daniel at gmail.com> wrote:
> Hi all,
>
> I have a setup, where a server does graphics rendering based on client
> requests, that is, clients send geometric data (position, orientation,
> etc.) and the server runs in cycles: process incoming messages and do
> some rendering.
> Occasionally, the clients might be faster and few messages get
> themselves queued on the server queue. However, only the most recent
> message is of interest as the server does not renders the objects as
> they were a couple of cycles before.
>
> To solve the problem, I have extended the ZMQ_ROUTER socket (via
> subclassing) so that it has a background thread that empties the
> socket message queue and stores the last message. The message is
> stored in a double-buffer (one for each client, this is why I need a
> router socket type). Then, when the server calls recv() on my extended
> socket, it gets one of the stored messages (if there are any).
>
> I ask myself whether some similar functionality should be put inside
> zeromq (say, under ZMQ_FLAT_PULL socket type), left as is in a "user
> space" or maybe I should use UDP instead?
>
>
> Thank you,
>
> --
> Daniel Krikun
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