FINITE STATE MACHINES(FSM)

WITH AKKA ACTORSWRITING AND UNIT TESTING 'EM

"LIGHTNING TALK" BY PRASANNA KUMAR

WHAT IS FSM?when a program is in a state S and anevent E occurs then do an action A and

change to another state S1

If the above sounds too theoritical to understand ....

IMAGINE A TRAFFIC SIGNALhope you could understand !!!

WHY DO WE NEED FSM?AT LEAST FOR US ...

Model and Execute Rules (we are using it !!!)SimulationsAutomata based programming

WHY THIS PRESENTATIONI want to learn FSM

"FSM" FROM AKKA PERSPECTIVEStateDataMessages to the actor is analogous to EventsActor abstraction itself

sealed trait FSMSignal case class SignalColorData class SignalChangeFSMActor extends Actor with FSM[FSMSignal, SignalColorData] { ..... }

LET'S MODEL FSM

// state - sealed trait FSMSignal case object RedSignal extends FSMSignal case object YellowSignal extends FSMSignal case object GreenSignal extends FSMSignal

// data case class SignalColorData

// event case object ChangeSignal case object RetainSignal

ACTOR CODEclass SignalChangeFSMActor extends Actor with FSM[FSMSignal, SignalColorData] {

// initial state of FSM startWith(RedSignal, SignalColorData())

when(RedSignal) { case Event(ChangeSignal, _) => goto(YellowSignal) case Event(RetainSignal, _) => stay }

when(YellowSignal) { case Event(ChangeSignal, _) => goto(GreenSignal) case Event(RetainSignal, _) => stay }

CONTD ... when(GreenSignal) { case Event(ChangeSignal, _) => goto(RedSignal) case Event(RetainSignal, _) => stay }

onTransition { case RedSignal -> YellowSignal => println("Changing from red to yellow signal - get ready to go") case YellowSignal -> GreenSignal => println("Changing from yellow to green signal - wroooom") case GreenSignal -> RedSignal => println("Changing from green to red signal - stop !!! :(") }

initialize}

UNIT TESTING FSM ACTORS WITHclass FSMActorTest(as: ActorSystem) extends TestKit(as) with ImplicitSender with WordSpecLike with Matchers with BeforeAndAfterAll { // all our test cases}

val fsmRef = TestFSMRef(new SignalChangeFSMActor)

def this() = this(ActorSystem("FSMActorSystem"))

"Our signal emulating FSMActor" must { "be red at initial stage " in { assert(fsmRef.stateName == RedSignal) assert(fsmRef.stateData == SignalColorData()) } "change to yellow after AlternateColour event occured " in { fsmRef ! ChangeSignal // send an event to FSM assert(fsmRef.stateName == YellowSignal) assert(fsmRef.stateData == SignalColorData()) } "change to green after AlternateColour event occured" in { fsmRef ! ChangeSignal assert(fsmRef.stateName == GreenSignal) assert(fsmRef.stateData == SignalColorData()) } "retain should not change the fsm state" in { fsmRef ! RetainSignal assert(fsmRef.stateName == GreenSignal) assert(fsmRef.stateData == SignalColorData()) } } override def afterAll = { println("traffic is clear now - obey traffic rules") }

SESSION TAKEAWAYCode :- https://github.com/prassee/FSMExperiment

HOW I MADE THIS PRESENTATION ?HTML 5CSS 3Presentation :- reveal.jsImages courtesy :- google image search :)

This presentation is CCL licensed - feel free to modify

THANKS :)