Behavior : State Machine Diagrams - State Machine Processing - Run-To-Completion

5 important questions on Behavior : State Machine Diagrams - State Machine Processing - Run-To-Completion

What is a Run-to-completion (RTC) paradigm?

A UML state machine completes processing of each event before it can start processing the next event.

What is the Run-to-Completion process?

In this approach, the system processes events in discrete, atomic RTC steps.

New events cannot interrupt the processing of the current event and must be stored (in an EVENT POOL) until the state
machine becomes idle again.

What this means is that each state machine continues processing until it reaches a WAIT POINT, when it is eligible to accept new events.

What happens at a Wait Point?

At a wait point, all processing in the state machine has been completed, except perhaps for do/behaviors.

Once a wait point is reached, the events in the EVENT POOL are evaluated to see if the state machine is currently waiting on them for some transition. (The pool is usually thought of as an EVENT QUEUE).

What is a State Machine Step?

If an enabled event is there, the state machine accepts the event and processes the transition.

It then stops at the next wait point, where the cycle continues again.

The sequence of behaviors between wait points is called a State Machine STEP.

What happens with events that are not processed?

Events that are not processed off the pool are generally dropped.

They will need to be resent to the state machines for them to be considered.

The order the events are examined from the pool is not specified, though the pool is usually considered an EVENT QUEUE.

However, because completion events have priority, they will be dispatched ahead of any other events in the pool.

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