[zeromq-dev] multi-part messages

Martin Sustrik sustrik at 250bpm.com
Sun Jan 22 01:29:16 CET 2012

On 21/01/12 14:38, john skaller wrote:
> Why?
> I can't see what it does. Since there's no transmission until all the parts are collated
> and no reception until all the parts are collated .. what's wrong with the client
> doing that and just sending one big message?

The original reason for introducing multi-part messages was (as Patrick 
correctly explains) to allow for requests messages to gather the list of 
nodes it have travelled through, so that corresponding reply message can 
travel in the opposite direction.

Unfortunately, this functionality, aside of being used by 0MQ itself, 
was exposed to the end users.

That in turn means that application logic is now often mingled with 0MQ 
logic creating a kind of mis-layering problem. Too late to fix that now 

As for zero-copy, as mentioned by Andrew, I guess the standard POSIX 
scatter-gather arrays would be more appropriate.


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