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Re: Are targetless transitions on an ancestor always preempted?

From: Jim Barnett <1jhbarnett@gmail.com>
Date: Wed, 29 Oct 2014 16:24:16 -0400
Message-ID: <54514CF0.10009@gmail.com>
To: Gavin Kistner <phrogz@me.com>
CC: www-voice@w3.org, Chris Nuernberger <chrisn@nvidia.com>
  Glad the explanation helped.  Would you like to suggest the wording - 
I'm not sure exactly where you want the "and"s and I doubt that adding 
them randomly will improve things much.

-  Jim
On 10/29/2014 4:06 PM, Gavin Kistner wrote:
> Ha, thank you. I feel better. I had previously been concentrating on 
> the exit-set-intersection, which is why I was focused on targetless. 
> So that didn't hurt my head much.
> However, I had not grasped the concept of promoting a non-preempted 
> transition to the active descendant atomic state(s). I see it now in 
> "A transition T is /enabled/ by named event E in atomic state S if a) 
> T's source state is S or an ancestor of S".
> So, thanks! That helped.
> P.S. I think that the definition I quoted above could use an explicit 
> "and" or two in the first sentence to clearly differentiate it from a 
> possibly ambiguous "or" case.
> --
> (-, /\ \/ / /\/
> On Oct 29, 2014, at 09:33 AM, Jim Barnett <1jhbarnett@gmail.com> wrote:
>> Gavin,
>>  Chear up, we have been collectively confused by this subject for years.
>> [Q1]  Yes, "foo" is consumed by the transition in state A, so the 
>> outer transition (the one in state innerwrap) is not selected.  You 
>> are correct that clause c is the relevant item here.  (But note that 
>> the whole definition talks about optimal enablement in a specific 
>> atomic state.  That will be relevant in the answer to your next 
>> question.)
>> [Q2]  The log message will not occur, because foo is consumed by the 
>> transitions in States A1 and A2.  However if there were no transition 
>> in A2 the situation would be different.  In that case, the transition 
>> in outerwrap would be optimally enabled in atomic state A2 because 
>> there's no transition to block it. That is, we pick the optimally 
>> enabled transition in _each_ atomic state _independent_ of the other 
>> states.  (Now go lie down until your head stops spinning because it's 
>> about to get weirder.)  However we must check for potential conflicts 
>> between the transitions chosen in the atomic states.  Two transitions 
>> conflict if their exit sets intersect.  The transition in outerwrap 
>> is a targetless transition, and therefore has no exit set.  Thus it 
>> does not conflict with the transition in A1, so both of them will get 
>> taken. (Now go take a stiff drink.)
>> [Q3] Yes, both states are entered. The two transitions do not 
>> conflict since their exit sets do not intersect.
>> - Jim
>> On 10/29/2014 10:51 AM, Gavin Kistner wrote:
>>> I still, disturbingly, struggle to gain intuition on  section 3.13 
>>> of the spec. Please help me by clarifying:
>>>     <scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0">
>>>       <state id="innerwrap">
>>>         <transition event="foo"><log label="Should I 
>>> run?"/></transition>
>>>         <state id="A"><transition event="foo" target="B" 
>>> type="internal"/></state>
>>>         <state id="B"/>
>>>       </state>
>>>     </scxml>
>>> My intuition tells me that a "foo" event should be ‘consumed’ by the 
>>> inner transition and not ‘bubble’ out. That the outer log message 
>>> should not run.
>>> [Q1] Is this correct?
>>> It is, I think, confirmed by this text: "Definition: A transition T 
>>> is optimally enabled by event E in atomic state S if a) T is enabled 
>>> by E in S and b) no transition that precedes T in document order in 
>>> T's source state is enabled by E in S and c) no transition is 
>>> enabled by E in S in any descendant of T's source state."
>>> Part (c) prevents the targetless transition above from executing. Yes?
>>> Now, what about parallel?
>>>     <scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0">
>>>       <parallel id="outerwrap">
>>>         <transition event="foo"><log label="Should I 
>>> run?"/></transition>
>>>         <state id="inner1">
>>>           <state id="A1"><transition event="foo" target="B1" 
>>> type="internal"/></state>
>>>           <state id="B1"/>
>>>         </state>
>>>         <state id="inner2">
>>>           <state id="A2"><transition event="foo" target="B2" 
>>> type="internal"/></state>
>>>           <state id="B2"/>
>>>         </state>
>>>       </parallel>
>>>     </scxml>
>>> [Q2] If "foo" occurs, should the log message occur?
>>> The same spec above seems to tell me that it should not, as long as 
>>> the transitions in inner1 or inner2 are present. Even if the 
>>> transition in inner2 was not present, the fact that any child of the 
>>> parallel was enabled by it means that the outer targetless 
>>> transition is preempted per (c).
>>> And finally, for good measure:
>>> [Q3] If "foo" occurs, should both B1 and B2 be entered?
>>> My intuition tells me yes, because that's what parallel is all 
>>> about, yo. I think this is supported because part (b) of the above 
>>> quoted definition does not apply. One transition precedes the other 
>>> in document order, but they are not part of the same hierarchy when 
>>> we consider the source state of each transition. Correct?
>>> Thanks for your help. :)
Received on Wednesday, 29 October 2014 20:24:48 UTC

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