[Freeciv-Dev] Re: (PR#4111) Client-side AI

["rwetmore@xxxxxxxxxxxx" <rwetmore@xxxxxxxxxxxx>]

Raimar Falke wrote:
[...]
> Yes it is possible that server summarizes data before it sends
> it. However it is possible that than a certain AI want another
> information. Example: the server sends you infos like "player 1 has 20
> archers total". Now the AI however can't do anything with this because
> it rather want to estimate how many archers are in the region around
> its city London. If the server summarizes data the summarization can
> have the wrong point of view.

I think you have a confused notion of how a request/response API or in
simpler terms a function call works, or that code executed in the client
somehow magically is different than the same code executed in the server.
The results returned by a client library function or server RPC call
should not be any different. It shouldn't matter where you handle such
things except from a data availability/security or performance standpoint.

So a server would not "send you infos" unless you requested them any more
than a client called function would return values unless it was called.
And if you called the wrong function or didn't understand its return
result, then that is just a programming error.

[...]
>>Afterall, what is a CMA but a crutch for a human who can't do the
>>complex computations nearly as quickly. CMA in the server or CMA in
>>the client makes no practical difference to its computed result or
>>way in which it is used.
> 
> Here you forgot one fundamental advantage: flexibility. If you change
> the CMA you don't have to update the servers. If for example the
> support for unhappy cities is added you don't have to update all
> servers at pubserver. You only have to update the clients. If CMA was
> a server thing you would have to update both server (obviously) and
> client (add another button or scale to the GUI).

Have you forgotten reality? There are many, many more clients in the world
to update than servers, so updating the servers is always less effort. If
the server implementation is upgraded with bugfixes or better algorithms
then *no* client need to be changed for everyone to have the benefit.

Only if you update the shared API, as in adding a new client CMA action
where you need new data requests or packet operations, do you need to
update both.

 >      Raimar

There is no absolute advantage in doing client or server code, only
different tradeoffs. Thin client systems gain by having a lot of shared
and easily maintained centralized code and data with minimal network
latency and bandwidth problems. Thick clients gain by allowing for
parallel processing that offloads the server CPU bottleneck by shipping
data to a client for processing and in some cases more flexibility (aks
code duplication) for localized customization in processing higher layers.

It may help to think of the overall program as a layered stack from
top of the client application down through the lowest level of the
server code. At any point in the stack you can turn function calls
into RPCs with no real change to the basic operation of the program.
One only observes performance and security issues across the RPC
boundary.

Obviously one wants to localize code on either side of this boundary
so they make as few calls across it with as little raw data transmission
as possible for optimal performance. But apart from that, there are
many ways to do this that are only different in minor tradeoffs.

For a Freeciv AI, the server advantages are far more important in
simulating a challenging opponent. Only when AI research develops to
the point where you can easily build a sophisticated Freeciv memory
and intuition engine will the advantages in parallel processing make
a client AI even remotely competitive.

But for human helper functions like CMA that are just brute force
computations and summaries, there isn't much to choose between client
or server side APIs, so either location for the code is fine.

Cheers,
RossW
=====