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Posted to user@commons.apache.org by Madhwaraj Rao <ma...@yahoo.com> on 2006/09/27 10:56:57 UTC
[SCXML] error reporting on invalid events
Hello,
I tried sending an invalid event to the state machine
and didn't see any error being reported. By invalid I
mean this event was not expected in the current state.
Does the SCXMLSemanticsImpl report an error (via the
the ErrorReporter) when such an event is silently
discarded?
Thanks
--
Raj
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Re: [SCXML] error reporting on invalid events
Posted by Rahul Akolkar <ra...@gmail.com>.
On 9/29/06, Rahul Akolkar <ra...@gmail.com> wrote:
> On 9/29/06, Madhwaraj Rao <ma...@yahoo.com> wrote:
<snip/>
>
> > Ideally, I would have liked a onEvent() callback in
> > the EntryListener.
> >
> <snip/>
>
> Not sure I understand.
>
<snap/>
Umm, did you mean onError() callback on ErrorReporter? (that makes
sense to me ;-)
-Rahul
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Re: [SCXML] error reporting on invalid events
Posted by Madhwaraj Rao <ma...@yahoo.com>.
Hi Rahul,
Thanks for your suggested work arounds. I think the
count check on the SCXMLListener tracer would work for
e for now. But I am eagerly waiting for 0.6 with your
enhancement :-)
To clarify, if there had been an onEvent() callback, I
could have easily checked if the event made it. I was
considering events that do not effect to a state
transition (due to a condition, for example). Now,
with the work around, I will ensure that all events do
effect a state transition for now.
Also, thanks for your sugegstions on implementing role
based events. That was very helpful.
Regards
--
Raj
--- Rahul Akolkar <ra...@gmail.com> wrote:
> On 9/29/06, Madhwaraj Rao <ma...@yahoo.com>
> wrote:
> > Hi Rahul,
> >
> > I found it difficult to implement your suggestion.
> > Events are asynchronous in my system, and having
> this
> > approach of first triggering an event, and
> verifying
> > that it resulted in a state transition (in an
> > EntryListener.onTransition()) is error prone. What
> if
> > an event didn't result in a state transition?
> >
> <snip/>
>
> Then you know its "invalid" (I keep quoting it since
> there is no such
> thing, I'm just using the term in the context of
> your application).
>
>
> > Can you please sned me a code snippet with your
> > approach so I can really verify that it could be
> > applicable for me?
> >
> <snap/>
>
> Sure. Here are examples of the workarounds I was
> talking about:
>
> <example-1>
>
> Set before =
> executor.getCurrentStatus().getStates();
>
> // fire the event(s) ... executor.triggerEvent(...)
> etc.
>
> Set after = executor.getCurrentStatus().getStates();
>
> // compare before and after (ofcourse, won't work if
> there are self transitions)
>
> </example-1>
>
> -- OR --
>
> <example-2>
>
> // say tracer tracks the count of the number of
> transitions followed
> SCXMLListener tracer = new TransitionTracer();
> executor.addListener(scxml, tracer); // scxml is the
> oacsm.SCXML instance
>
> int before = tracer.count();
>
> // fire the event(s) ... executor.triggerEvent(...)
> etc.
>
> int after = tracer.count();
>
> // if after == before, invalid
>
> </example-2>
>
> etc. ...
>
>
> > Ideally, I would have liked a onEvent() callback
> in
> > the EntryListener.
> >
> <snip/>
>
> Not sure I understand.
>
>
> > My other requirement is to prevent some events to
> > effect a state transition if the user role doesn't
> > have the right privileges.
> >
> <snap/>
>
> Yes, this is a common requirement. You can implement
> it:
>
> * As a layer around Commons SCXML, using whatever
> means you choose to
> verify the user access rights as a function of the
> current user and
> current status of the state machine
>
> * As conditionals inside the SCXML document itself,
> guarding
> transitions and datamodel access appropriately
> (possibly using custom
> functions within the expression language chosen)
>
> -Rahul
>
>
> > Thanks
> > --
> > Raj
> >
> > --- Rahul Akolkar <ra...@gmail.com> wrote:
> >
> > > On 9/27/06, Madhwaraj Rao
> <ma...@yahoo.com>
> > > wrote:
> > > > Hello,
> > > >
> > > > I tried sending an invalid event to the state
> > > machine
> > > > and didn't see any error being reported. By
> > > invalid I
> > > > mean this event was not expected in the
> current
> > > state.
> > > >
> > > > Does the SCXMLSemanticsImpl report an error
> (via
> > > the
> > > > the ErrorReporter) when such an event is
> silently
> > > > discarded?
> > > >
> > > <snip/>
> > >
> > > No, because the semantics treat it as simply an
> > > inconsequential
> > > trigger (causing no change to the state
> machine),
> > > rather than an
> > > error.
> > >
> > > One of the ways you could track this is to
> register
> > > a SCXMLListener on
> > > the executor and track onTransition() callbacks
> (if
> > > you get none, the
> > > trigger is "invalid" -- per your definition
> above).
> > >
> > > -Rahul
> > >
> > >
> > > > Thanks
> > > > --
> > > > Raj
> > > >
> > >
> > >
>
>
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Re: [SCXML] error reporting on invalid events
Posted by Rahul Akolkar <ra...@gmail.com>.
On 9/29/06, Madhwaraj Rao <ma...@yahoo.com> wrote:
> Hi Rahul,
>
> I found it difficult to implement your suggestion.
> Events are asynchronous in my system, and having this
> approach of first triggering an event, and verifying
> that it resulted in a state transition (in an
> EntryListener.onTransition()) is error prone. What if
> an event didn't result in a state transition?
>
<snip/>
Then you know its "invalid" (I keep quoting it since there is no such
thing, I'm just using the term in the context of your application).
> Can you please sned me a code snippet with your
> approach so I can really verify that it could be
> applicable for me?
>
<snap/>
Sure. Here are examples of the workarounds I was talking about:
<example-1>
Set before = executor.getCurrentStatus().getStates();
// fire the event(s) ... executor.triggerEvent(...) etc.
Set after = executor.getCurrentStatus().getStates();
// compare before and after (ofcourse, won't work if there are self transitions)
</example-1>
-- OR --
<example-2>
// say tracer tracks the count of the number of transitions followed
SCXMLListener tracer = new TransitionTracer();
executor.addListener(scxml, tracer); // scxml is the oacsm.SCXML instance
int before = tracer.count();
// fire the event(s) ... executor.triggerEvent(...) etc.
int after = tracer.count();
// if after == before, invalid
</example-2>
etc. ...
> Ideally, I would have liked a onEvent() callback in
> the EntryListener.
>
<snip/>
Not sure I understand.
> My other requirement is to prevent some events to
> effect a state transition if the user role doesn't
> have the right privileges.
>
<snap/>
Yes, this is a common requirement. You can implement it:
* As a layer around Commons SCXML, using whatever means you choose to
verify the user access rights as a function of the current user and
current status of the state machine
* As conditionals inside the SCXML document itself, guarding
transitions and datamodel access appropriately (possibly using custom
functions within the expression language chosen)
-Rahul
> Thanks
> --
> Raj
>
> --- Rahul Akolkar <ra...@gmail.com> wrote:
>
> > On 9/27/06, Madhwaraj Rao <ma...@yahoo.com>
> > wrote:
> > > Hello,
> > >
> > > I tried sending an invalid event to the state
> > machine
> > > and didn't see any error being reported. By
> > invalid I
> > > mean this event was not expected in the current
> > state.
> > >
> > > Does the SCXMLSemanticsImpl report an error (via
> > the
> > > the ErrorReporter) when such an event is silently
> > > discarded?
> > >
> > <snip/>
> >
> > No, because the semantics treat it as simply an
> > inconsequential
> > trigger (causing no change to the state machine),
> > rather than an
> > error.
> >
> > One of the ways you could track this is to register
> > a SCXMLListener on
> > the executor and track onTransition() callbacks (if
> > you get none, the
> > trigger is "invalid" -- per your definition above).
> >
> > -Rahul
> >
> >
> > > Thanks
> > > --
> > > Raj
> > >
> >
> >
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Re: [SCXML] error reporting on invalid events
Posted by Madhwaraj Rao <ma...@yahoo.com>.
Hi Rahul,
I found it difficult to implement your suggestion.
Events are asynchronous in my system, and having this
approach of first triggering an event, and verifying
that it resulted in a state transition (in an
EntryListener.onTransition()) is error prone. What if
an event didn't result in a state transition?
Can you please sned me a code snippet with your
approach so I can really verify that it could be
applicable for me?
Ideally, I would have liked a onEvent() callback in
the EntryListener.
My other requirement is to prevent some events to
effect a state transition if the user role doesn't
have the right privileges.
Thanks
--
Raj
--- Rahul Akolkar <ra...@gmail.com> wrote:
> On 9/27/06, Madhwaraj Rao <ma...@yahoo.com>
> wrote:
> > Hello,
> >
> > I tried sending an invalid event to the state
> machine
> > and didn't see any error being reported. By
> invalid I
> > mean this event was not expected in the current
> state.
> >
> > Does the SCXMLSemanticsImpl report an error (via
> the
> > the ErrorReporter) when such an event is silently
> > discarded?
> >
> <snip/>
>
> No, because the semantics treat it as simply an
> inconsequential
> trigger (causing no change to the state machine),
> rather than an
> error.
>
> One of the ways you could track this is to register
> a SCXMLListener on
> the executor and track onTransition() callbacks (if
> you get none, the
> trigger is "invalid" -- per your definition above).
>
> -Rahul
>
>
> > Thanks
> > --
> > Raj
> >
>
>
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> To unsubscribe, e-mail:
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> For additional commands, e-mail:
> commons-user-help@jakarta.apache.org
>
>
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Re: [SCXML] error reporting on invalid events
Posted by Rahul Akolkar <ra...@gmail.com>.
On 9/27/06, Madhwaraj Rao <ma...@yahoo.com> wrote:
> Hello,
>
> I tried sending an invalid event to the state machine
> and didn't see any error being reported. By invalid I
> mean this event was not expected in the current state.
>
> Does the SCXMLSemanticsImpl report an error (via the
> the ErrorReporter) when such an event is silently
> discarded?
>
<snip/>
No, because the semantics treat it as simply an inconsequential
trigger (causing no change to the state machine), rather than an
error.
One of the ways you could track this is to register a SCXMLListener on
the executor and track onTransition() callbacks (if you get none, the
trigger is "invalid" -- per your definition above).
-Rahul
> Thanks
> --
> Raj
>
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