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From Rahul Akolkar <rahul.akol...@gmail.com>
Subject Re: [Commons SCXML] - Parallel states and external invocation. Best practice.
Date Mon, 19 Apr 2010 21:25:36 GMT
On Mon, Apr 19, 2010 at 7:33 AM, Andrew Mansfield <AMansfie@globeop.com> wrote:
> Hi,
>
> I am attempting to build a state machine that essentially models my
> applications workflow.
>
> To do this I have built a simple custom component invoker that can be
> executed from the <invoke/> tag to execute Java code. The
> 'id.invoke.done' event simply transitions to the next state in the
> workflow. The flexibility is required as components will be plugged in
> for different configurations to change default behaviour often.
>
> e.g.
>
>   <state id="s1">
>        <invoke targettype="component_invoker" srcexpr="componentId1"/>
>        <transition event="s1.invoke.done" cond="cond1 != null"
> target="s2" />
>        <transition event="s1.invoke.done" target="s3" />
>    </state>
>
>    <state id="s2">
>        <invoke targettype="component_invoker" srcexpr="componentId2"/>
>        <transition event="s2.invoke.done" target="s3" />
>    </state>
>
>    <state id="s3" final="true">
>
>    </state>
>
> What I want to do is allow for parallel execution of states which
> themselves have the abilty to invoke external code. I.e.
>
>    <state id="s1">
>        <invoke targettype="component_invoker" srcexpr="componentId1"/>
>        <transition event="s1.invoke.done" cond="cond1 != null"
> target="s2" />
>        <transition event="s1.invoke.done" target="s3" />
>    </state>
>
>    <state id="s2">
>        <invoke targettype="component_invoker" srcexpr="componentId2"/>
>        <transition event="s2.invoke.done" target="p1" />
>    </state>
>
>        <parallel id="p1">
>
>                <state id="sub1">
>                <invoke targettype="component_invoker" src="comp1"/>
>                <transition event="sub1.invoke.done" target="s3" />
>                </state>
>
>            <state id="sub2">
>                <invoke targettype="component_invoker" src="comp2"/>
>                <transition event="sub2.invoke.done" target="s3" />
>            </state>
>
>            <transition event="p1.done" target="s3" />
>
>        </parallel>
>
>    <state id="s3" final="true">
>
>    </state>
>
> What I can;t seem to work out is how to exit my component invocations
> from the substates correctly. Is it event possible to achieve what I am
> trying to do or is there a better way to do this ?
>
<snip/>

Sure, it is possible.

When the orthogonal regions have no substructure, any of the
transitions such as those gating on events "sub1.invoke.done" or
"sub2.invoke.done" cause the entire parallel to be exited. If you want
join-like behavior where the parallel waits for both invokes (or more,
if more than two regions) to be finished before transitioning out,
then its best to model it as such using final children of regions and
waiting for all regions to transition to their respective finals.

So, reworking the example above, along these lines:

  <state id="s1">
    <invoke targettype="component_invoker" srcexpr="componentId1"/>
    <transition event="s1.invoke.done" cond="cond1 != null" target="s2" />
    <transition event="s1.invoke.done" target="s3" />
  </state>

  <state id="s2">
    <invoke targettype="component_invoker" srcexpr="componentId2"/>
    <transition event="s2.invoke.done" target="p1" />
  </state>

  <parallel id="p1">

    <state id="region1">

      <state id="sub1">
        <invoke targettype="component_invoker" src="comp1"/>
        <transition event="sub1.invoke.done" target="final1" />
      </state>

      <final id="final1"/>

    </state>

    <state id="region2">

      <state id="sub2">
        <invoke targettype="component_invoker" src="comp2"/>
        <transition event="sub2.invoke.done" target="final2" />
      </state>

      <final id="final2"/>

    </state>

    <transition event="p1.done" target="s3" />

  </parallel>

  <state id="s3" final="true">
     ...

-Rahul


> Any help would be much appreciated.
>
> Regards,
> Andy
>

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