[zeromq-dev] Greetings & questions about inproc PUB/SUB inside Twisted.

[Matthew Kaufman]

Ugh Zed Shaw is annoying lol.

Hi Zed


On Sat, Jan 26, 2013 at 2:56 PM, David J W <zeromq-dev-subscribe at ominian.net
> wrote:

> Hello,
>    My name is David W, I am a professional code monkey that was first
> introduced to 0MQ via Zed Shaw's talk at PyCon ( believe it was 2010 )
> but only now have gotten the chance to sit down and start learning the
> library.  I am on a sabbatical until ideal after PyCon since I got
> laid off and taking the time out to hit a bucket list ( including
> learning 0MQ ).
>
>   On that note, a few years back as a re-invent the wheel project to
> learn Twisted and COMET I started writing a web MUD engine and
> centered the architecture around two message pipelines:  User action's
> were locked stepped ( User A moved left, tell server, wait for it to
> say yes/no), broadcast to other User's that User A moved left,
> broadcast to all of User A's group they moved left.  NPC's were just
> headless User's driven by a behavior time/tick subprocess that hooked
> upto the same pipelines.    I set that project aside because I
> realized I needed a message queue of some sort and really didn't want
> to setup Rabbit or anything super industrial.
>
>   Now along arrives 0MQ and since this is a personal project the
> priority is more about understanding how 0MQ works then accomplishing
> the actual project.   In the above example I can imagine using 0mq's
> inproc socket's where client's are SUB types ( subscribe to
> map/domain, subscribe to group chat ) and their is a master process
> that has a router socket for incoming work and a pub socket for
> products [ User A in map 1 moved left] ).
>
> So here's my questions:
>    For PUB/SUB the impression is that the actual queue sit's on the
> client socket.  PUB pushes a message to all client's [ regardless of
> setsockopt(zmq.SUBSCRIBE ) ] and the act of reading the socket
> filter's/clears the queue down to what the client is subscribed to.
> Is this correct or is the subscription more intelligent ( PUB keep's a
> subscription roster, see's no one is subscribed, drop's the message OR
> client receives a message, isn't subscribed so it drops the message ).
>
>   Has anyone had any experience running multiple SUB based client's
> inside of one process and are their any severe consequences.  I
> imagine a SUB socket is going to instantiate the needed structures to
> hold a queue, the actual socket, and other house keeping structures
> but so far small tests (1-10 sockets) hasn't show much memory use.
>
>    Additionally, if I do get past digging through 0MQ's mechanics, I
> was thinking it would be best to spin off the PUB side to it's only
> process.  Which leads me to wonder if 0MQ inproc PUB/SUB actually
> relies on some clever memory mapping.  eg Push a message on an inproc
> PUB socket which goes to a shared/mutex locked list and client's just
> read from this one list.
>
>    Apologies if some of these questions seem naive, I haven't gotten
> the chance to read 0mq's C source code yet.
>
> Thanks,
>    Dave
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