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From Marc Schier <MSch...@bsquare.com>
Subject RE: SEDA
Date Wed, 04 Sep 2002 15:07:23 GMT
This weekend I had some more concrete ideas about the stage driven process.
I very much like the idea of bringing components together into a staged
driven process using the transparency of the servicemanager. As a default a
component would know nothing about the process it participates in. Currently
the process is synchronous, but we could define a staged driven process as
well.

The idea is that an invocation of a service method on a component is not
straightly executed but with the service manager proxying the service
interface, enqueued as a special type of "request" into the component's
queue. The service manager is responsible for putting together the request
object which contains the method requested to be invoked, the parameters
passed, a reference to the caller (for priority handling) and maybe already
a component reference for the instance on which the method should be invoked
(This allows for load balancing). The request is then enqueued in the
requested service component's event queue, where it sits until dispatched.
When the thread manager has time it dequeues the request and performs the
contained method, pushing any exception into a predefined queue for logging
or handling. Load balancing and multiplexing could be pushed up into the
configuration as well by defining the used stratagies.

This would allow us to use a simple staged driven system without changing
existing component implementations. More advanced stages that implement
interfaces that give more access to the event system could use simple
components in this scenario in an event driven way. These interfaces could
allow the stage e.g. to provide a special queue other than the ones the
manager knows about or allow for processing and filtering the queue, or to
process requests by priority. In this case the component would implement an
event handler interface that takes more than one "request" as an argument.

Unfortunately, we will not be able to use components with methods that have
return values (if we wanted to use the return values). For one that's the
nature of asynchronous method calling, but then again all my components rely
on the return value of the components' service methods. But at least in this
scenario we could achieve a better reuse rate than when using stages as
hardcoded adaptors for existing components.

Let me know what you think...

Cheers, Marc

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