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From Rahul Akolkar <rahul.akol...@gmail.com>
Subject Re: [SCXML] Concurrent users
Date Tue, 13 Dec 2005 19:38:32 GMT
On 12/12/05, Mike Sparr - www.goomzee.com <mike@goomzee.com> wrote:
> Rahul,
>
> Your code worked (from your personal snapshot) fine - thanks.
<snip/>

OK, thanks for the update :-)


> One issue
> we're now facing is handling concurrent users from multiple clients.  My
> goal is to use one scxml doc to manage app flow for all users.
<snap/>

Indeed, there will usually be only one SCXML document for a particular
application task (or flow, or dialog) -- which could be of arbitrary
granularity -- yet the per user (or per session) "instances" of the
state machine must be able to execute independently.


> It looks
> like there is one context and it's shared, so if we trigger an event, it
> will affect any user.
<snip/>

Each user should have a separate Commons SCXML engine (or more
precisely, an instance of the org.apache.commons.scxml.SCXMLExecutor
class) assigned, and the events must be channeled to the appropriate
engine for the same user/session.


>  We have created a HashMap (in memory) to store
> key/handle to client for sending response, but are having troubles
> dealing with concurrent users and their state.
>
> For example:
>
> Web request (state 1, event 3)
> IM request (state 2, event 1)
>
> Can the engine handle that or do you know how best to implement?  My
> thought was to store state and last event per user, then navigate to
> that somehow for their requests.  I assume there must be a better way?
>
<snap/>

We have a couple of published Commons SCXML usecases here:

http://jakarta.apache.org/commons/sandbox/scxml/usecases.html

Both the usecases are examples within a servlet container environment
(so similar to what you're attempting), and the SCXMLExecutor instance
gets created when needed, then cached and retrieved from the user's
session.

To summarize:

 * A SCXML document describes the state machine for a task/flow/dialog
in an application.

 * The org.apache.commons.scxml.model.SCXML class is the
representation of the document using the Commons SCXML Java object
model.

 * An appropriately configured SCXMLExecutor instance creates a "live"
state machine (or engine) upon which external events may be fired.

 * SCXMLExecutor instances must be created per user/session and cached
throughout the life of the task/flow/dialog.

-Rahul


> Thanks,
>
>
> Mike
>

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