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Re: [SCXML] Algorithm mainEventLoop and the internalQueue

From: Roger Hoover <roger.hoover@gmail.com>
Date: Tue, 28 Jul 2009 11:23:42 -0700
Message-ID: <44cb1ba30907281123r3a8a604yeede1aa19579774@mail.gmail.com>
To: Philipp Kolhoff <philipp.kolhoff@googlemail.com>
Cc: www-voice@w3.org
Hi Philipp,

Where did you find the description of the SCXML algorithm?  I'd like to take
a look.

Thanks,

Roger

On Mon, Jul 27, 2009 at 12:55 PM, Philipp Kolhoff <
philipp.kolhoff@googlemail.com> wrote:

> (Sorry for duplicates, I did not use my registered email before)
> Hi there,
> I've been working with Statecharts and esp. SCXML for a longer time now. I
> started implementing an interpreter in C# and C++ first for my
> Diploma-Thesis, which got then published in "Game AI Wisdom 4" and later
> found use in my companies Point&Click-Adventure Engine. Now i started to
> work on an interpreter written in ActionScript to get a library that any
> Flex developer can slap into her RIA/game. So when I came back I found the
> description of the Algorithm for interpreting SCXML's and that was a great
> help to re-implement my interpreter.
> However I stumbled upon a part in the mainEventLoop after implementing it
> and running some Test-SCXML's... maybe I did not get it right, but I think
> there maybe a mistake:
>
> Take a scxml snipplet like this:
>
> <parallel id="InTest">
> <state id="s1">
>    <initial>
>       <transition target="s11"/>
>    </initial>
>    <state id="s11"/>
>    <final id="s12"/>
> </state>
> <state id="s2">
>    <initial>
>       <transition target="s21"/>
>    </initial>
>    <state id="s21"/>
>    <final id="s22"/>
> </state>
> <transition event="InTest.Done" target="f"/>
> </parallel>
>
> .......
>
> // now take any newly enabled null transitions and any transitions
> triggered by internal events
> macroStepComplete = false;
> until(macroStepComplete):
>   enabledTransitions = selectEventlessTransitions()
>   if (enabledTransitions.isEmpty()):        internalEvent =
> internalQueue.dequeue()// this call returns immediately if no event is
> available
>      if (internalEvent):
>         datamodel.assignValue("event", internalEvent)
>         enabledTransitions = selectTransitions(internalEvent)
>          if (enabledTransitions):
>      microstep(enabledTransitions.toList()
>   else:
>      macroStepComplete = true
> ......
>
> Suppose during the execution of an external event more than one internal
> event is queued. This happens often if a parallel-state is "Done" and its
> children are as well. In the case listed above, there would be generated the
> events s1.Done, s2.Done and InTest.Done in that order (if proper transitions
> would exist and the events would be fired). During the next macro step, the
> first internalEvent is dequeued ("s1.Done"), but no transition will be
> enabled. That would mark the macroStep as complete and no other internal
> event is handled until the next external event is dispatched.
> Imho, there should be done something like this more likely:
>
> if (enabledTransitions):
>  microstep(enabledTransitions.toList()
> else:
>  macroStepComplete = internalQueue.isEmpty()
>
> So, if the internalQueue is not empty, the macrostep will dequeue the next
> event in the internal queue.
>
> Any opinions?
>
> Best regards,
> Philipp Kolhoff
>
>
>
>
Received on Tuesday, 28 July 2009 21:44:37 GMT

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