Re: [Boost-users] [Statechart] Order of Trigger/Event/Guard at statetransition

Subject: Re: [Boost-users] [Statechart] Order of Trigger/Event/Guard at statetransition
From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2008-12-23 17:37:53

Hi Franz

> I've tried to use the Statechart library for modelling a simple state
> machine. I've created three states and three transitions between them
> and added some debug outputs. When I've looked to the debug outputs I've
> wondered a little bit. I've thought that the processing of events are in
> the order 1) exit actions of source state 2) transition actions and 3)
> entry actions of target state. When I look at my result I see the order
> 1) transition action 2) exit action of source state and 3) entry action
> of target state.

I assume you are referring to the following sequence in the output:

> trigger event 'Event2'
> process event 'Event2'
> process guard 'guard1'
> process action 'action3'
> leave state 'StateB'
> enter state 'StateC'

> Does anybody know what I'm doing wrong here?

Yes, it seems you are confusing the react member function of a state with a 
transition function. I'm referring to the following code fragment:

> sc::result StateB::react(const Event2 & e)
> {
> if (context<FSMSimple>().guard1())
> {
> context<FSMSimple>().action3(e);

This is a direct call to action3 ...

> return transit<StateC>();

... and this is where the transition actually takes place. In order to let 
the transition action execute at the right time, you should replace the 
code:

> context<FSMSimple>().action3(e);
> return transit<StateC>();

with

// untested code
return transit<StateC>(&FSMSimple::action3, e);

Please see: 
<http://www.boost.org/doc/libs/1_37_0/libs/statechart/doc/tutorial.html#TransitionActions>

Please let me know whether that works for you.

Thanks & Regards,

-- 
Andreas Huber
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