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From Rahul Akolkar <rahul.akol...@gmail.com>
Subject Re: [scxml] events triggered in onentry
Date Wed, 18 May 2011 00:55:50 GMT
On Tue, May 17, 2011 at 8:37 PM, Ryan <rnideffer@gmail.com> wrote:
> Looks like I signed up for this mailing list about 5 hours too late. Reading
> today's reply from Rahul, he notes:
>
> "You should inject events from within a custom action by adding to the set
> of derived events (param of execute method) which will be processed in a
> subsequent microstep, rather than triggering another event on the executor
> (if thats what you're doing)."
>
> Once I added the TriggerEvent to the Collection of derived events, the
> transition condition evaluated to 'true' as expected.
>
> Is this explained in the documentation and I just missed it? I'm curious as
> to when it would be desirable to trigger an event on the SCXMLExecutor
> instance itself versus adding it to the derived events collection.
>
<snip/>

Synchronous cases like custom actions (pretty much the only case)
should produce derived events (rather than attempting re-entrant
triggers).

Asynchronous cases like invoke or delayed sends should trigger events
on the executor.

If expected frequency of external triggers on a state machine is high
(many per sec), its a good idea to maintain a separate synchronized
event queue.

Finally, there is always room for better docs, FAQ etc. -- happy to
look at any suggested patches [1] for improvement. Site source is here
[2].

-Rahul

[1] http://commons.apache.org/scxml/issue-tracking.html
[2] http://svn.apache.org/repos/asf/commons/proper/scxml/trunk/src/site/


> Ryan
>
> On Tue, May 17, 2011 at 5:22 PM, Ryan <rnideffer@gmail.com> wrote:
>
>> I have the following simple SCXML document:
>>
>> <scxml xmlns="http://www.w3.org/2005/07/scxml"
>>             xmlns:my="http://www.my.com"
>>             version="1.0"
>>             initialstate="welcome">
>>
>>     <state id="welcome">
>>         <onentry>
>>             <my:play filename="welcome"/>
>>         </onentry>
>>         <transition cond="${_eventdata eq 'blah'}" target="end"/>
>>     </state>
>>     <state id="end" final="true">
>>         <onentry/>
>>     </state>
>> </scxml>
>>
>> My approach is to generate events from custom actions, then act on those
>> events in my transitions. To test this approach, I hardcoded the generation
>> of an event in my Play.class action:
>>
>>         TriggerEvent evt = new TriggerEvent("agi.keypress",
>> TriggerEvent.SIGNAL_EVENT, "blah");
>>         scInstance.getExecutor().triggerEvent(evt);
>>
>> However, I can't seem to get the <transition/> to recognize this event.
>> Here is log output as the state machine runs:
>>
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdata = blah
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdatamap = {agi.keypress=blah}
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdata = null
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdatamap = null
>> [org.apache.commons.scxml.SCXMLExecutor] (Asterisk-Java
>> DaemonPool-1-thread-1) Current States: []
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdata = null
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdatamap = {welcome.entry=null}
>> [org.apache.commons.scxml.Evaluator] (Asterisk-Java DaemonPool-1-thread-1)
>> ${_eventdata eq 'blah'} = false
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _ALL_NAMESPACES = null
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdata = null
>> [org.apache.commons.scxml.Context] (Asterisk-Java DaemonPool-1-thread-1)
>> _eventdatamap = {welcome.entry=null}
>> [org.apache.commons.scxml.SCXMLExecutor] (Asterisk-Java
>> DaemonPool-1-thread-1) Current States: [welcome]
>>
>> Why is the _eventdata/_eventdatamap pair being printed twice to start? The
>> first time it has the event I've triggered, the second time its empty. Then
>> after this, you see that the welcome.entry event triggered, then the JSP EL
>> condition evaluates to false.
>>
>> My initial guess is that I've misunderstood the state machine algorithm,
>> and my attempt to trigger an event from the <onentry/> is flawed.
>>
>> How should I go about this?
>>
>> Thanks,
>> Ryan
>>
>>
>>
>

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