[libvirt] Re: [PATCH 04/12] Domain Events - rpc changes

Daniel P. Berrange berrange at redhat.com
Tue Oct 21 13:51:44 UTC 2008

On Tue, Oct 21, 2008 at 08:57:51AM -0400, Ben Guthro wrote:
> This is very similar to what I had in the original patch,
> where on the server side, we just increment/decrement a callback_registered counter,
> then keep the list of callbacks/opaque data on the client.
> The server would then send one rpc to each connected client, whose job it would be
> to multiplex this out to all registered callbacks.
> There would still be a "one-for-one" for register/deregister, but 
> this scheme has the following advantages for efficency:
> a.) Fewer RPC calls (less data on the wire - one-to-many for events firing)
> b.) Less RPC data passed on register/deregister (no need for cb/user_data)
> c.) Code is simpler - no need to invent yet another data structure, and list for tracking tokens
> Daniel - what are your thoughts on this? 
> This is similar to what I had originally implemented, but I'm not
> sure if you objected to this part of it, or not...

The bit I didn't like about the original was the extra logic on the server
side of the impl. If we can keep the explicit register & unregister RPC
calls, and require the client todo all ref-counting & multiplexing, then
I wouldn't mind this approach.

eg, on the client side, on the first 'register' API call, send
the 'register' RPC call. Then just count subsequent 'register'
API calls, and don't bother with the 'register' RPC call. Once
the 'unregister' has been called the matching number of times
it can send the 'unregister' the RPC call. 

So the 'remote_internal.c' would have to take care of broadcasting
the single incoming event, to all registered listeners of that 
particular client.

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