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Re: [jwt-dev] Beginning of a monitoring plug-in

About the event mechanism :

This is also done in the context of integration between business applications and workflow engine(s) at runtime.

The idea revolves around defining (Java, WSDL, SCA) a generic WorkflowEventListenerService
  * that a runtime process engine should call on state change
* basically task lifecycle changes : ready, before / after start, before / after stop . These could be the operations of said service, taking as parameter the part of the workflow state (typically a Process's Activity, as defined in the existing WorkflowService) that has changed
     * NB. I think property changes would be too heavy
* and that might be implemented by business applications so they can be notified

So, an eclipse-based UI could use this event mechanism to help the developer monitor runtime processes in a "push" manner (rather than polling), thanks to notifications of the changes to the workflow state.

Open questions are
* where should be the listeners configured ? these possibilities are not mutually exclusive : * the application may use a WorkflowEventSubscribeService implemented engine-side. Should it be fine-grained (ex. listen to a given state of a given activity) or not ?
     * engine side, configured in the process model
* also configured on application side : we could provide a sample Java implementation of the service that merely dispatches to other configured services * should we allow open events, i.e. an additional onCustomEvent(name) method ? * what about using JWT -> executable process format transformations in order to add dispatchingListeners everywhere, for instance to ease activation of monitoring ?

Regards
Marc

Mickael Istria a écrit :
Hello,

I added on the wiki page the model that we use for a workflow state. This model is part of the workflow service API that must use any extension. Of course it can be corrected/improved according to other specific features (it currently fits with Bonita, but we didn't try with other workflow engines). I also added the code of WorkflowService interface, that we use to get the state of the workflow.
It might be interesting for you.

In the Bonita remote implementation of this interface, we only use the "listUserActivities(true, true, login)" method to get all informations about the state of the workflow. Indeed, calling this method with this attributes gives us the whole workflow state, since this workflow state is fully serializable. Thus, you're right, it is a poll mechanism, with all the limits that it involves. (especially the need to refresh to check for modifications)

We are still thinking about an event mechanism, but I'll let Marc tell you more about this, since he has more knowledge on this subject.


Regards,
Mickael




Bryan Hunt a écrit :
This is interesting. I've been doing some more work on my EMF workflow model/engine and I'm about to look at modeling state information and the ability to monitor that state. It sounds like this is using a polling mechanism to monitor the state. Is that correct? I'm considering using an event model for state transitions. I would be concerned about using a polling mechanism especially when running the workflow remotely - performance is critical in my intended application.

Bryan

On Apr 21, 2008, at 10:56 AM, Mickael Istria wrote:

Hello,

I've written a little plug-in framework that can be used to monitor a workflow state from a workflow engine. This is not at all a mature plug-in for the moment, but I hope it is an interesting base for the future.

Monitoring a workflow engine can be done in a few steps:
1. Implement an interface (WorkflowService) with your favorite workflow engine. (We use the "Adapter" design-pattern) 2. Make this service accessible to the user who wants to monitor it in Eclipse (you can use webservices, rmi, or anything you are able to write a client programmaticaly) 3. Implement an extension plug-in which defines the way to acces the service (so called a service provider) from inside Eclipse.

We are currently able to monitor Bonita via a CXF/Aegis WebService (see the wiki for screenshots).

You can find more detailed information and basis for discussion on the JWT wiki at http://wiki.eclipse.org/JWT_Monitoring


Hope you will find it interesting!

Regards,
Mickael




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