State machines for active components only

[nateinaction]

Hey folks, I was attempting to implement an internal state machine into a passive component when I ran across this build error:

error: passive component may not have a state machine instance

I looked into the PR that implemented the error but did not see a rational there or in the linked issues. Why does the component need to have its own thread in order to use the state machine semantics?

[Kronos3]

State machines use the message queues to handle signals. Passive components have no queue. If you don't want a thread but you do want a queue you can use a queued component and drive the queue with a rate group (or another way). active components will have a queue and be handled inside it's thread.

[bocchino]

This is explained in § 11.10 of the FPP User's Guide:

When a state machine instance m is part of a component C, each instance c of C sends m signals to process as it runs. Signals occur in response to commands or port invocations received by c, and they tell m when to change state. c puts the signals on its queue, and m dispatches them. Therefore, if a component C has a state machine instance member m, then its instances c must have queues, i.e., C must be active or queued.

https://nasa.github.io/fpp/fpp-users-guide.html#Defining-Components_State-Machine-Instances

[nateinaction]

Thanks for the responses and the link to the docs section! That answers my question!