topic Re: Inclusive Gateway Support? in Alfresco Archive

Inclusive Gateway Support?

tidetom — Wed, 20 Jul 2011 08:18:07 GMT

Hello,I was wondering if anyone has an idea of when the Inclusive Gateway will be available for use in Activiti? Currently we can use a Parallel Gateway, however any conditionExpressions placed on outgoing sequenceFlows from the Parallel Gateway are not evaluated. This forces us to put an Exclusiv

Re: Inclusive Gateway Support?

trademak — Thu, 21 Jul 2011 07:30:23 GMT

Hi Tom,

We don't have a timeframe for this feature. I do understand your use case.
Is it something you would be willing to contribute? That would speed things up.

Best regards,

Re: Inclusive Gateway Support?

tidetom — Thu, 21 Jul 2011 17:23:03 GMT

Hi Tijs,

I might be able to help contribute on this feature, but I would need some help getting pointed in the right direction. I have yet to dabble too much into the Activiti source code.

If you or someone else on the team could point me at the various places where the exclusive gateway is added and used inside Activiti, that would help me get started on the inclusive gateway behavior. Also, it would be helpful to know where the logic itself to check the conditional expression on the sequence flow gets evaluated. I'd also be interested in how to get the Inclusive Gateway added as an element in the Activiti Designer plugin for Eclipse.

If you can supply this information, I'll take a look and get an idea of the scope of the effort. Out of curiosity, do you have an idea for the scope of the effort off the top of your head?

Thanks,
Tom

Re: Inclusive Gateway Support?

trademak — Fri, 22 Jul 2011 06:57:26 GMT

Hi Tom,

Great!
Feel free to contact me if you need any help on this.
The BpmnParse class is the one that parses the BPMN 2.0 XML file. So there you should add the inclusive gateway XML portion.
Then in the org.activiti.engine.impl.bpmn.behavior package you can find the various implementation classes, including the ExclusiveGatewayActivityBehavior and the ParallelGatewayActivityBehavior. The Inclusive gateway is a combination of both these gateways so the challenge would be to combine them into the new InclusiveGatewayActivityBehavior class.

Best regards,

Re: Inclusive Gateway Support?

ronald_van_kuij — Fri, 22 Jul 2011 08:00:43 GMT

Then in the org.activiti.engine.impl.bpmn.behavior package you can find the various implementation classes, including the ExclusiveGatewayActivityBehavior and the ParallelGatewayActivityBehavior. The Inclusive gateway is a combination of both these gateways so the challenge would be to combine them into the new InclusiveGatewayActivityBehavior class.

Or see if a GatewayActivityBehaviour base class can be created of which they all inherit common stuff (I hate duplicate code ;-))

Re: Inclusive Gateway Support?

tidetom — Sat, 23 Jul 2011 05:32:15 GMT

Thanks guys, I'll take a look and get back to you. I also requested committer status, however haven't received a response yet … though probably will need some time to take a look at the existing code and make changes before it's needed.

Re: Inclusive Gateway Support?

trademak — Sat, 23 Jul 2011 10:41:19 GMT

Great. If you agree I think it's better to submit a diff patch to the JIRA issue and we'll take a second look at it.
Then we can submit the patch or you can do it yourself if that's your preference.

Thanks,

Re: Inclusive Gateway Support?

tidetom — Tue, 26 Jul 2011 21:55:37 GMT

Sorry for my delayed reply … yes, that'd be fine to submit a patch. I'd prefer to get a code reviewer on this anyways Thanks

Re: Inclusive Gateway Support?

tidetom — Wed, 27 Jul 2011 06:32:48 GMT

I've done some initial investigation into the Inclusive-OR behavior, and was wondering if you could double-check me on this…

It looks to me like the behavior for implementing Inclusive-OR actually already exists. If you take a look at org/activiti/engine/impl/bpmn/behavior/ExclusiveGatewayActivityBehavior.java, it has the following inheritance tree and only overrides the "leave" method of the parent:

+ ExclusiveGatewayActivityBehavior
+ GatewayActivityBehavior (abstract - no implementation)
+ FlowNodeActivityBehavior
- delegates implementation to org/activiti/engine/impl/bpmn/behavior/BpmnActivityBehavior.java

The implementation of FlowNodeActivityBehavior looks like:

/**
   * Default way of leaving a BPMN 2.0 activity: evaluate the conditions on the
   * outgoing sequence flow and take those that evaluate to true.
   */
  protected void leave(ActivityExecution execution) {
    bpmnActivityBehavior.performDefaultOutgoingBehavior(execution);
  }

If you take a look at the implementation of BpmnActivityBehavior#performDefaultOutgoingBehavior, it actually implements the logic that one would expect of an Inclusive-OR … it checks the condition on each outgoing transition. If the condition evaluates to true (or if conditions are disabled) then transition will be added to the list of transitions that will be executed. If there are multiple valid transitions, all transitions will be executed (similar to the Parallel Gateway implementation).

As it looks to me, the implementation of InclusiveGatewayActivityBehavior could simply extend from GatewayActivityBehavior and leave the implementation as-is (with no overrides). The purpose of creating the extension would just be to support future change.

Then, the InclusiveGatewayActivityBehavior would be called from BpmnParse.java (as you mention above … this would need to be added), and everything would seem to be all set (with the exception of the designer piece).

The only further question I would have would be whether it makes sense for InclusiveGatewayActivityBehavior to have an implementation of "leaveIgnoreConditions". I suppose ExclusiveGatewayActivityBehavior does not override this implementation, so InclusiveGatewayActivityBehavior wouldn't need to either, however I'd leave that to the experts to determine.

Any thoughts on this?

Thanks,
Tom

Re: Inclusive Gateway Support?

tidetom — Wed, 27 Jul 2011 07:40:29 GMT

Also, if you could point me at the JIRA item, I have a patch that includes a fix under this assumption. I've also patched the ProcessDiagramCanvas and ProcessDiagramGenerator to programmatically draw the the inclusive gateway per the BPMN spec.

Re: Inclusive Gateway Support?

trademak — Thu, 28 Jul 2011 15:07:32 GMT

Hi,

I think your description of the inclusive gatway is correct.
Did you write unit tests to test this implementation?
You can create the JIRA issue yourself and attach a path if you have one available.

Thanks,

Re: Inclusive Gateway Support?

tidetom — Thu, 28 Jul 2011 15:56:32 GMT

I'll be working on some unit tests in the next couple of days. I was also planning on looking into the designer piece of inclusive gateway.

I've created a JIRA issue to track the effort: http://jira.codehaus.org/browse/ACT-890 and submit patches against.

Re: Inclusive Gateway Support?

tidetom — Sun, 07 Aug 2011 21:27:54 GMT

Hi Tijs,

I've submitted a patch to http://jira.codehaus.org/browse/ACT-890 which contains support for Inclusive Gateway in the Activiti engine. I did not do any code for the designer, however it would seem that someone has already started on an Inclusive Gateway for the designer based upon the designer source code. If you need me to look into that further, let me know.

I did end up adding some specific behavior to the Inclusive Gateway Behavior because the error handling in the default code simply ended execution when a path couldn't be found after logging a FINE level log message. I wanted to be consistent with Exclusive Gateway Behavior, and instead fail the execution with an ActivitiException. You'll see, however, that I've kept existing functionality consistent with the implementation for anyone using the old code.

NOTE: I used the Activiti project's specific Eclipse code formatter, and unfortunately some of the old code had not been formatted with it … so the diff is a little bit unwieldy for some of the files. As long as it's applied soon, it shouldn't cause any problems.

Let me know how the integration goes…

Thanks,
Tom

Re: Inclusive Gateway Support?

trademak — Mon, 08 Aug 2011 07:07:49 GMT

Hi Tom,

I already had a quick look at the patch and it's looking good. We'll be looking at it more thoroughly today and update the JIRA.
How did you see that someone is working on Inclusive gateway support in the Designer?

Best regards,

Re: Inclusive Gateway Support?

tidetom — Tue, 09 Aug 2011 21:28:04 GMT

I must have run my query incorrectly (to find "Inclusive*" code inside the designer project). Re-running the query now I don't see any code in the designer for Inclusive Gateway behavior. Sorry about that — probably had started the query from the wrong location.

I can take a look into the designer piece if you'd like, but likely will not be able to start until next week or the week after due to schedule constraints.

Let me know what you think…

Thanks,
Tom

Re: Inclusive Gateway Support?

trademak — Wed, 10 Aug 2011 20:58:52 GMT

Hi Tom,

Unfortunately we won't be able to include the inclusive gateway in Activiti 5.7 because we already have a code freeze.
But we'll make sure it's included in the next release (5.8). Also, before the end of this month it'll be included in the trunk, so you can already use the source code.

If you'll be able to look into the Designer support that's great.

Best regards,

Re: Inclusive Gateway Support?

tidetom — Mon, 15 Aug 2011 21:19:47 GMT

Hi Tijs,

That's fine on the time frame. I spent a little time and put together some patches for adding Inclusive Gateway behavior to the designer. This is my first experience working with the designer, but I think most things went smoothly. I wasn't able to test the code, though, so would appreciate your help in testing it after applying the patch. The main class needing review/testing is AddInclusiveGatewayFeature in the org.activiti.designer.gui project, I drew the circle in the center of the polygon to the best of my knowledge, but haven't worked with Graphiti before and can't be sure that it worked correctly.

I've put the patches in ACT-890: http://jira.codehaus.org/browse/ACT-890

Let me know how it goes…

Thanks,
Tom

Re: Inclusive Gateway Support?

jbarrez — Fri, 26 Aug 2011 16:07:26 GMT

Tom,

I took a look at your patch for the inclusive gateway as committed by Tijs. It's however hard to see how the implementation matches with what the spec says:

The Inclusive Gateway is activated if
• At least one incoming Sequence Flow has at least one token and
• For every directed path formed by sequence flow that
- starts with a Sequence Flow f of the diagram that has a token,
- ends with an incoming Sequence Flow of the inclusive gateway that has no token, and
- does not visit the Inclusive Gateway,
• There is also a directed path formed by Sequence Flow that - starts with ,
- ends with an incoming Sequence Flow of the inclusive gateway that has a token, and
- does not visit the Inclusive Gateway.
Upon execution, a token is consumed from each incoming Sequence Flow that has a token. A token will be produced on some of the outgoing Sequence Flows.
In order to determine the outgoing Sequence Flows that receive a token, all conditions on the outgoing Sequence Flows are evaluated. The eval- uation does not have to respect a certain order. For every condition which evaluates to true, a token MUST be passed on the respective Sequence Flow.
If and only if none of the conditions evaluates to true, the token is passed on the default Sequence Flow.
In case all conditions evaluate to false and a default flow has not been specified, the Inclusive Gateway throws an exception.

The last part of the spec is satisfied by changing the bpmnactivitybehavior (by throwing an exception).
However, I do not see how the tokens are checked on reachability of the gateway. Can you shed some light on this?

Re: Inclusive Gateway Support?

tidetom — Fri, 26 Aug 2011 17:40:16 GMT

Joram,

Thanks for looking at the code. As mentioned in an earlier post, I'm very new to the Activiti source code (first code check-in) and think a code review is very necessary to make sure I didn't miss anything. (in other words, I claim ignorance )

I used ExclusiveGateway as my template, and based upon the specification description below, I think I handled all of this section of the specification:

Upon execution, a token is consumed from each incoming Sequence Flow that has a token. A token will be produced on some of the outgoing Sequence Flows. In order to determine the outgoing Sequence Flows that receive a token, all conditions on the outgoing Sequence Flows are evaluated. The evaluation does not have to respect a certain order. For every condition which evaluates to true, a token MUST be passed on the respective Sequence Flow.
If and only if none of the conditions evaluates to true, the token is passed on the default Sequence Flow.
In case all conditions evaluate to false and a default flow has not been specified, the Inclusive Gateway throws an exception.

However, I did not look on the "reachability of the gateway", as you mention, probably because it's not handled by ExclusiveGateway (unless I missed it). In the source, it looked like reachability was handled somewhere outside of the "behavior". Regardless, based on the specification, I would expect that the following segment still needs to be verified / fixed before the release of inclusive gateway by someone like yourself that has more experience in the Activiti source code:

The Inclusive Gateway is activated if
1. At least one incoming Sequence Flow has at least one token and
   a. For every directed path formed by sequence flow that starts with a Sequence Flow f
      of the diagram that has a token, ends with an incoming Sequence Flow of the inclusive
      gateway that has no token, and does not visit the Inclusive Gateway,
   b. There is also a directed path formed by Sequence Flow that starts with , ends with
      an incoming Sequence Flow of the inclusive gateway that has a token, and does not
      visit the Inclusive Gateway.

I'd be interested to know where this code goes, and if you can point me in the right direction as to where I can evaluate the incoming sequence flows, I'd be more than willing to look into a solution.

Thanks,
Tom

Re: Inclusive Gateway Support?

tidetom — Fri, 26 Aug 2011 19:46:12 GMT

I see that my implementation was very simplistic and only works for "downstream" inclusive behavior. Activation does not work properly when handling upstream sequence flows after reading more on the inclusive gateway behavior here:

http://www.itu.dk/people/maca/papers/CCH10.pdf

I'll likely need some help with implementing the above behavior, as I simply don't know the Activiti APIs well enough to look upstream for potential token-based activation of sequence flows, and to protect against race-conditions in the activation of the inclusive gateway. Willing to learn though if anyone can point me in the right direction…

Sorry for the confusion.

Tom