Multiple FSM

# Finite States Machine Module - Multiple

1. Overview

The pyRa-Ya FSM module allows to create independent FSM objects, and they can be executed and used in different parts of the code without problem

This document presents the methodology to use execute FSMs inside FSMs, so you can easily create modular applications and behaviors. We’re modify the example in Finite States Machine Module - Simple, to make it modular.

This document will use the pyRa-Ya example called fsm_multiple to explain the working of the module (example available here).

2. FSM to implement

Consider the FSM below:

The first three states keep the same, just localize and then navigate to home, after that it gets the IDLE state. We’re going to call this FSM the main_task, and not it’s very simple and easy to read, it just “manages” other tasks.

All the “sub-behaviors” are embedded in unique states: TEMPERATURE, KITCHEN, BEDROOM, and LAUNDRY. Our new implementation will execute an entirely new FSM in each of those states:

3. Implementation

Now, our application will include 5 folders inside the FSMs folder:

• main_task
• temperature
• kitchen
• bedroom
• laundry

Each of them includes the files to describe each FSM, you can check them in the example.

Here we’re going to focus on how to include and execute the sub-FSMs from the main FSM. First, we create them in the main_task Helpers class, so we can easily access them from any transition or action:

# src/FSMs/main_task/helpers.py

...

def __init__(self, app: RayaApplication):        
        self.app = app
        # Vabiables
        self.last_ui_result = None
        self.fsm_temperature = FSM(app=self.app, name='temperature')
        self.fsm_kitchen = FSM(app=self.app, name='kitchen')
        self.fsm_bedroom = FSM(app=self.app, name='bedroom')
        self.fsm_laundry = FSM(app=self.app, name='laundry')

...

Then, we just need to start the sub-FSM in background when the main FSM gets the corresponding state, for example:

# src/FSMs/main_task/actions.py

class Actions(BaseActions):

...

    async def enter_KITCHEN(self):
        await self.helpers.fsm_kitchen.run_in_background()

...

And we leave the state when that FSM finishes its execution (capturing the error in case the sub-FSM failed):

# src/FSMs/main_task/transitions.py

class Transitions(BaseTransitions):

...

	  async def KITCHEN(self):
        if self.helpers.fsm_kitchen.has_finished():
            if self.helpers.fsm_kitchen.was_successful():
                self.set_state('IDLE')
            else:
                self.abort(*self.fsm_main_task.get_error())

...