fork with dynamic number of legs

[ayca]

Hi,

I want to make a workflow definition as such:

.....
....
<fork name="fork" >
 <delegation class="org.jbpm.delegation.fork.DynamicNumberedForkHandler" />
 <transition to="nextstate" />
</fork>
<state name="nextstate">
 <transition to="endstate"/>
</state>
<end-state name="endstate"/>

Then, I will put a variable in the workflow which will hold the number of legs I want to fork. I will start the process and when process comes to the fork, my customised fork handler will execute. It will first of all learn the number of legs wanted by getting the varibale I have put, from the executioncontext. And later on, I want to fork that many legs which all point to the same state (this state will be later a subprocess state actually).
I have tried some tricks of code, but nothing worked out. How shall I write my customised fork handler?




PS : The code I have tried was as follows:

public class DynamicNumberedForkHandler implements ForkHandler {

 public void fork(ForkContext forkContext) throws ExecutionException
 {
 int i = Integer.valueOf(forkContext.getVariable("number_of_forks").toString()).intValue();

 NodeImpl node = (NodeImpl)forkContext.getNode();
 Transition transition = (Transition)node.getLeavingTransitions().iterator().next();

 for(int j=1; j<i;j++)
 {
 TransitionImpl newTransition = new TransitionImpl();
 newTransition.setActions(transition.getActions());
 newTransition.setDefinition((DefinitionImpl)transition.getDefinition());
 newTransition.setDescription(transition.getDescription());
 newTransition.setFrom((NodeImpl)transition.getFrom());
 newTransition.setTo((NodeImpl)transition.getTo());
 newTransition.setId(new Long(j));
 node.addLeavingTransition(newTransition);
 }
 i = 1;
 JoinImpl correspondingJoin = (JoinImpl)((Fork)node).getCorrespondingJoin();
 Iterator iter = forkContext.getNode().getLeavingTransitions().iterator();
 while(iter.hasNext())
 {
 Transition transition2 = (Transition) iter.next();
 TokenImpl childToken = (TokenImpl) forkContext.createToken( transition2, getTokenName(i,transition2) );
 childToken.setReactivationJoin( correspondingJoin );
 }
 }

 private String getTokenName(int index, Transition transition)
 {
 String tokenName = null;
 String transitionName = transition.getName();
 if ( transitionName != null )
 {
 tokenName = transitionName;
 }
 else
 {
 tokenName = "forked-child-"+Integer.toString( index+1 );
 }
 return tokenName;
 }

}

[icyjamie]

I guess this is a variant of:

http://www.jboss.com/index.html?module=bb&op=viewtopic&t=69033

[ayca]

I think not. I am trying to kind of duplicate the single leg in my fork in runtime.

[icyjamie]

Roughly said: try to create multiple tokens for one leg and attach them to the first node of your leg. Tokens are the runtime state of your process, you don't duplicate "legs", you create tokens and attach them to a specific node in the process. You create a runtime "token-tree", and the process definition is a way to gather info how and when tokens should be spawned.
jBpm guys, correct me if I'm totally giving/having the wrong idea.

[kukeltje]

Sorry to say icyjamie......you are right, so no corrections :-)

[ayca]

Okey, and another question about fork. Say a workflow definition as such:

...

<fork name="fork">
 <transition to="nextstate1"/>
 <transition to="nextstate2"/>
</fork>
<state name="nextstate1">
 <transition to="endstate"/>
</state>
<state name="nextstate2">
 <transition to="endstate"/>
</state>
<end-state name="endstate"/>

In this case,
when the fork executes, it happens to be 2 children of root token. But when they reach to the end-state, the root token does not reach to an end since they did not meet at a join. But physically, the workflow is finished. How do you offer to handle this problem?

[icyjamie]

There is no starvation/deadlock/endless loop detecting mechanism. But there is if you write enough tests to support your workflow ;-).

[aguizar]

IMO, there is no actual problem here, as you can always design the process definition to join all forked nodes or rely on end nodes to terminate disjoint children.