Re: [Boost-users] FW: statechart::asynchronous_state_machineand state-local storage

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2008-08-02 10:17:34

Hi Tim

> I have two instances of the same state machine, which are launched as
> asynchronous_state_machines.
> 
> I also have some state-local storage in these state machines that I would
> like to be able to access from outside the state machines. Actually, to be
> more precise, I want each instance of the state machine to be able to access
> a single member variable of its twin.

Ok.

> The problem is, if I create an asynchronous state machine in the usual way
> (via fifo_scheduler<>::initiate_processor() and fifo_scheduler<>::operator
> (), it seems that the actual instance of the state machine is buried in the
> framework somewhere; I don't have access to a pointer to the state machine
> itself.

That's intentional. If a thread A would be able to directly access a state 
machine that is serviced by a thread B then often race conditions and/or 
deadlocks would result.

> Can anyone tell me how I go about getting a reference to the state machine
> that is instantiated when fifo_scheduler<>::initiate_processor 
> is called?

You can't, see above. Two asynchronous state machine must only exchange data in 
a, well, asynchronous manner. That is, have the requesting state machine post 
an event to the other FSM, which in turn posts the requested data in an event 
back to the requesting FSM. Of course you'll have to be careful to always 
*copy* the data and never let both state machines access the same data through 
e.g. pointers.

HTH,

--
Andreas Huber
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