Questions about gen_server

[Enrique Marcote Peña]

Hello,

I've been doing my first module using gen_server and after some moments 
of euphoria, I'm just about to question everything I've done.

I decided to implement a receipt dispenser using the gen_server 
behavior.  , Even though my sample is just a very simple module that 
exports 4 functions, I'd like you to think about it as a driver that 
interacts with a real dispenser (using whatever protocol over TCP/IP):

  start_link()    -> {ok, Pid}
  stamp(Request)  -> {ok, Receipt} | {error, Reason}
  price(Request)  -> {ok, float()} | {error, Reason}
  stop()          -> ok

Requests are solved:

dispenser:start_link().

...later on ...

dispenser:stamp(Request).

...done...

dispenser:stop().


Well, once finished with the implementation I'm not sure if it makes 
sense to use gen_server in such a case.   Does it make sense to use this 
behavior if no State is carried on by the server?  I mean, what about 
servers using mnesia to store the "state",  is it correct to conceive 
them as gen_servers? I'm asking so course I realize that, even the 
dispenser above mentioned is  (in concept) a server, it could also be 
implemented as a simple module exporting the functions stamp/1 and 
price/1  (without using the gen_server). To use this module a direct 
call to dispenser:stamp/1 or dispenser:price/1 could be done when 
needed.  What are the advantages of using the gen_server behavior?  When 
should be used?

Is it reasonable to implement a server that expands a worker for every 
 incoming request? Up to a limited number of course (some kind of pool 
of workers).  Would such a pool fit into a gen_server? How? Are these 
workers gen_servers also?  Do I see gen_servers everywhere?

Thanks in advance.

Best regards,

          Quique