[zeromq-dev] Question about multiple Pub/Sub sockets

gonzalo diethelm gdiethelm at dcv.cl
Sun Mar 7 04:05:24 CET 2010


I apologize in advance for the soup letter. Please bear with me for just
three short paragraphs.

Say I have one process A, from which I wish to notify about certain
events by using Pub/Sub sockets, so that I can decouple the notifier
from the receivers of those notifications. A would generate events E, F
and G.

On the receiver side, say I have processes P and Q; P is interested in
events E and F, Q is interested in events F and G. I could have process
A open three Pub sockets, for events E, F and G; then from P I would
open Sub sockets E and F, and from Q I would open Sub sockets F and G.
Presto! A can just go ahead and send out notifications, without worrying
if there are 1, 2 or 10 processes listening to them.

Now, let's say I want to add a new process B, which generates events F,
G and H. So for the case of event F, I now have two processes (A and B)
generating the same event, and two processes (P and Q) interested in
that event. How would I do this? Although P and Q can open the same Sub
socket for event F, I don't think it would be possible for both A and B
to open the same Pub socket for that event. Or am I wrong?

The only way I can think of implementing this pattern would be to have
one intermediate process N which acts as the central notifier. A and B
send all events to N (using Downstream sockets), which is now the ONLY
process opening Pub sockets and sending out notifications. This would
work, and it may even be "right"; the only concern would be that I now
centralize all notifications in a single point of failure.

I would appreciate your thoughts on this pattern, even to be told I am
totally wrong about it. Thanks in advance.

-- 
Gonzalo Diethelm 



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