[omniORB] CORBA Design Questions

[Wernke zur Borg]

Hi Olaf,
 
> 
> We are investigating using CORBA / omniORB / omniORBpy for an
> application that controls hardware.  The client will send commands to
> the server / hardware (that part is easy).
> 
> Here are the two parts I like some high level design advice 
> on to get me
> started.
> 
> *** First, how do I implement the server sending unsolicited status
> information back to the client?

There are multiple options; I can suggest a solution that has been
working fine for me. You define a listener (callback) interface in your
IDL. This interface is implemented by the client and used by the server.
With the first server call the client passes the IOR of a listener
object to the server, then the server can asynchronously call back the
client.
 
> *** Secondly (and more importantly), how do I implement the client
> sending an abort type command to the server?  The important 
> part is that
> the abort command needs to be send immediately (even if 
> another command
> or a response to a command potentially sending large amounts 
> of data is
> in progress).

Your server will by default be multithreaded, therefore, a call of a
(possibly oneway) abort() method will be executed by the server while
other operations may be in progress. Interrupting these ongoing
operations will be an implementation task for your application. Also
your client must be ready to call abort() while other operations are
blocking, therefore your client will have to be multithreaded as well.

>
> There will be a single server but there can be multiple clients.
>

Solutions depends on how tightly server and client are coupled. If the
server must get aware of client "disconnections" the concept of a
session oriented protocol will be of benefit. Just in short: A session
can be opened and closed by the client. The server can abort a session
with a callback on the SessionListener interface. Optionally, a
heartbeat protocol ensures to both sides that the other side is still
alive.

I do not know if this concept fits your needs; other people may have
other ideas for you. You can mail me if you are interested in more
details.

Regards, Wernke