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[Charles Remes]

Take a look at the Clone pattern in the zguide.

http://zguide.zeromq.org/page:all#Reliable-Pub-Sub-Clone-Pattern

This might be what you need.

cr

On May 29, 2014, at 11:20 AM, Jeremy Richemont <jrichemont at gmail.com> wrote:

> 
> Hi. I am struggling to work out how to use zmq to implement the architecture I need. I have a classic publish/subscribe situation except that once client x has subscribed to a topic I need the topic data to be sent to it to be cached if the client dies and resent on reconnect. The data order is important and I can't miss messages should the client be offline for a while.
> 
> The PUB/SUB pattern doesn't seem to know about individual clients and will just stop sending to client x if it dies. Plus I can't find out this has happened and cache the messages, or know when it reconnects.
> 
> To try to get around this I used the REQ/REP pattern so the clients can announce themselves and have some persistence but this is not ideal for a couple of reasons:
> 
> 1) The clients must constantly ask "got any data for me?" which offends my sensibilities
> 
> 2) What happens if there's no data to send to client x but there is to client y? Without zmq I'd have had a thread per client and simply block the one with no data but I can't block client x without also blocking client y in a single thread. 
> 
> Am I trying to shove a round peg in a square hole, here? Is there some way I can get feedback from PUB saying 'failed to send to client x'? so I can cache the messages instead? Or is there some other pattern I should be using?
> 
> Otherwise it's back to low level tcp for me...
> 
> Many thanks;
> 
> Jeremy
> 
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