Re: [Boost-users] [statechart] asynchronous machine's post event question.

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2007-07-26 04:58:23

> According to the code
> struct Working:sc::state< Working, Active >
> {
>   Working(my_context ctx):my_base(ctx)
>   {
>      cout<<__FUNCTION__<<endl;
>      outermost_context_type& machine=outermost_context(); // machine is a 
asynchronous machine.
>      A machine.post_event( EvtTerminate() );
>      B machine.my_scheduler().queue_event( machine.my_handle
(),boost::intrusive_ptr<EvtTerminate>(new EvtTerminate() ) );
>   };
>   ~Working(void)
>   {
> Â Â  Â Â cout<<__FUNCTION__<<endl;
>   }
>
>   typedef sc::transition< EvtIdleWork,Idle > reactions;
> };
> Is there any difference between A and B?

Yes, there is. state_machiney<>.post_event is protected and puts events in a 
queue that is private to the state machine. In an asynchronous state machine 
the events in this queue always have absolute priority over events that are 
queued through the scheduler.
fifo_scheduler<>.queue_event is public and puts all events in a queue that is 
shared between all state machines that are serviced by the scheduler. Even if 
fifo_scheduler services only one asynchronous_state_machine then events posted 
with the B option in your example race with events posted from an external 
source, which is useful only in rare circumstances (e.g. when you write your 
own scheduler whose queue_event function accepts a time when the passed event 
should be dispatched).

> Which is the better and recommended or Is there another better way to post 
event?

See above, you usually want option A.

HTH,

--
Andreas Huber
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