Hi,
I have been playing around with the boost MSM libraries, to know more about them. I am creating a vending machine simulation with a sub-machine for accepting payment from the user. The vending machine has 3 states: waiting (where the machine just waits for the user to start processing), selection (where user selects a product. The machine makes a transition to this state from "waiting" state if the event "key_press" occurs and if the key pressed is the start button (checked by a guard condition).). After a product is selected the machine goes in payment state, which is a submachine that accepts payment in quarters. After the payment is received (it is fixed $1 for all products, just to make it simple) the machine again goes in the waiting state dispensing the product (action: dispatch_item).
The submachine Payment has 4 states: Payment_init which just displays a message and then makes an immediate automatic transition to the next state "Paying". In this state the machine just waits for the "coin_insert" event to occur (which represents inserting a quarter). Once the "coin_insert" event occurs it makes a transition to "check_payment" state which checks if sufficient amount was paid. If not it again makes an automatic transition to "Paying" state, else it moves to the "Payment_done" state which is the last state in the submachine. This state generates an event "last_state" which is an indicator that the payment has been made and should cause a transition from the submachine "Payment" to waiting state (which I am not observing). The transition tables for both the machines are: (btw I am using the functors as the front end.)
<snip>
The code for payment_done state is: struct payment_done: public msm::front::state { template
void on_entry(Event const &, FSM &fsm) { cout << "---------------" << endl; cout << "Payment_done" << endl; fsm.process_event(last_state()); } };
The FSM template argument, for a given state, is the state machine immediately containing the state, in your case, Payment, which cannot process this event. Later, I plan to provide you with more (although I have mixed feelings to this feature), at best the list of all state machines in the path to your state. There are several ways to solve this, but the UML "standard" way is to make payment_done an exit pseudo state (msm::front::exit_pseudo_state).
As you can see the event "last_state" is occurring in the payment_done state but the transition is not taking place. I can post the entire code is someone is interested but I am just playing around with the libraries so the code (and some logic too) is not sophisticated at all. Still I can post it if someone wants to take a look at it.
Including a minimum working code is always helpful and would help me try your example out, so in general, yes, it is a good idea. Regards, Christophe