Re: [boost] [FSM] request for tips on fsm code project.

From: andrea carbone (andrea.carbone_at_[hidden])
Date: 2008-08-27 05:07:32

Dear Andrey,
yes this is what I have in mind.
I will apply for the virtual base solution.

I  will do some test .... but  ..I have a doubt: does it need to be a
singleton instance?
Or a plain pointer to an object instance will do the trick as well?

Thanks for your answer!
And good luck for the review!!

andrea

Andrey Semashev-2 wrote:
> 
> andrea carbone wrote:
>> Hello,
>> 
>> I need to handle the states of a process.
>> The process will be implemented in a class containing all required
>> methods
>> and data.
>> Think for example to sensor management.
>> Init (connect the device).
>> Setup (configuration).
>> Idle (nop).
>> AcquireSingleData,
>> AcquireMultiData ... 
>> etc.
>> 
>> I need a unique instance of the sensor object.
>> 
>> How can I make all the states aware of this unique instance?
>> Avoiding singletons ... if possible.
>> 
>> Is there some way in boost::fsm to automatically realize this design?
> 
> No, the library does not provide any way to control instancing of FSM or
> other objects, if that is what you mean. However, if you already have a
> singleton of your object that represents the sensor, you can pass a
> reference or pointer to it in an initialization event to the FSM.
> 
>   struct Sensor : noncopyable
>   {
>     // Returns the singleton instance
>     static Sensor* get();
> 
>   private:
>     Sensor();
>   };
> 
>   struct InitEvent { Sensor* pSensor; };
> 
>   typedef mpl::vector<
>     Uninitialized,
>     Init,
>     Setup,
>     ...
>   >::type States_t;
> 
>   // The struct contains common data for all states
>   struct Common
>   {
>     Sensor* m_pSensor;
>   };
> 
>   struct Uninitialized :
>     fsm::state< Uninitialized, States_t >,
>     virtual Common
>   {
>     void on_process(InitEvent const& evt)
>     {
>       m_pSensor = evt.pSensor;
>       switch_to< Init >();
>     }
>   };
> 
>   ...
> 
>   fsm::state_machine< States_t > fsm;
>   fsm.process(InitEvent(Sensor::get()));
> 
> Alternatively, you can set the pointer directly in the FSM by using the
> "get" method of the state machine.
> 
>   fsm.get< Common >().m_pSensor = Sensor::get();
> 
> But I would prefer the former way since it expresses the intent more
> clearly.
> 
> Note that the pointer to the sensor is stored in a virtual base class of
> all states, which means that every state uses the single m_pSensor
> pointer.
> 
> I hope that helps.
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