Package org.apache.pekko.actor

Interface FSM<S,D>

All Superinterfaces:
Actor, ActorLogging, Listeners
All Known Subinterfaces:
LoggingFSM<S,D>
All Known Implementing Classes:
AbstractFSM, AbstractFSMWithStash, AbstractLoggingFSM, ClusterSingletonManager
public interface FSM<S,D> extends Actor, Listeners, ActorLogging
Finite State Machine actor trait. Use as follows: 

   object A {
     trait State
     case class One extends State
     case class Two extends State

     case class Data(i : Int)
   }

   class A extends Actor with FSM[A.State, A.Data] {
     import A._

     startWith(One, Data(42))
     when(One) {
         case Event(SomeMsg, Data(x)) => ...
         case Event(SomeOtherMsg, _) => ... // when data not needed
     }
     when(Two, stateTimeout = 5 seconds) { ... }
     initialize()
   }

Within the partial function the following values are returned for effecting state transitions:

- stay for staying in the same state - stay using Data(...) for staying in the same state, but with different data - stay forMax 5.millis for staying with a state timeout; can be combined with using - goto(...) for changing into a different state; also supports using and forMax - stop for terminating this FSM actor

Each of the above also supports the method replying(AnyRef) for sending a reply before changing state.

While changing state, custom handlers may be invoked which are registered using onTransition. This is meant to enable concentrating different concerns in different places; you may choose to use when for describing the properties of a state, including of course initiating transitions, but you can describe the transitions using onTransition to avoid having to duplicate that code among multiple paths which lead to a transition: 

 onTransition {
   case Active -&gt; _ =&gt; cancelTimer("activeTimer")
 }

Multiple such blocks are supported and all of them will be called, not only the first matching one.

Another feature is that other actors may subscribe for transition events by sending a SubscribeTransitionCallback message to this actor. Stopping a listener without unregistering will not remove the listener from the subscription list; use UnsubscribeTransitionCallback before stopping the listener.

State timeouts set an upper bound to the time which may pass before another message is received in the current state. If no external message is available, then upon expiry of the timeout a StateTimeout message is sent. Note that this message will only be received in the state for which the timeout was set and that any message received will cancel the timeout (possibly to be started again by the next transition).

Another feature is the ability to install and cancel single-shot as well as repeated timers which arrange for the sending of a user-specified message: 

   setTimer("tock", TockMsg, 1 second, true) // repeating
   setTimer("lifetime", TerminateMsg, 1 hour, false) // single-shot
   cancelTimer("tock")
   isTimerActive("tock")

  • Method Details

    • org$apache$pekko$actor$FSM$_setter_$Event_$eq

      void org$apache$pekko$actor$FSM$_setter_$Event_$eq(FSM.Event$ x$1)

    • org$apache$pekko$actor$FSM$_setter_$StopEvent_$eq

      void org$apache$pekko$actor$FSM$_setter_$StopEvent_$eq(FSM.StopEvent$ x$1)

    • org$apache$pekko$actor$FSM$_setter_$StateTimeout_$eq

      void org$apache$pekko$actor$FSM$_setter_$StateTimeout_$eq(FSM.StateTimeout$ x$1)
      This case object is received in case of a state timeout.

    • super$postStop

      void super$postStop()
      Call onTermination hook; if you want to retain this behavior when overriding make sure to call super.postStop().

      Please note that this method is called by default from preRestart(), so override that one if onTermination shall not be called during restart.

    • Event

      FSM.Event$ Event()

    • StopEvent

      FSM.StopEvent$ StopEvent()

    • $minus$greater

      FSM.$minus$greater$ $minus$greater()
      This extractor is just convenience for matching a (S, S) pair, including a reminder what the new state is.

    • StateTimeout

      FSM.StateTimeout$ StateTimeout()
      This case object is received in case of a state timeout.

    • when

      void when(S stateName, scala.concurrent.duration.FiniteDuration stateTimeout, scala.PartialFunction<FSM.Event<D>,FSM.State<S,D>> stateFunction)
      Insert a new StateFunction at the end of the processing chain for the given state. If the stateTimeout parameter is set, entering this state without a differing explicit timeout setting will trigger a StateTimeout event; the same is true when using #stay.

      Parameters:
      stateName - designator for the state
      stateTimeout - default state timeout for this state
      stateFunction - partial function describing response to input

    • when$default$2

      scala.concurrent.duration.FiniteDuration when$default$2()

    • startWith

      void startWith(S stateName, D stateData, scala.Option<scala.concurrent.duration.FiniteDuration> timeout)
      Set initial state. Call this method from the constructor before the initialize() method. If different state is needed after a restart this method, followed by initialize(), can be used in the actor life cycle hooks pekko.actor.Actor#preStart and pekko.actor.Actor#postRestart.

      Parameters:
      stateName - initial state designator
      stateData - initial state data
      timeout - state timeout for the initial state, overriding the default timeout for that state

    • startWith$default$3

      scala.Option<scala.concurrent.duration.FiniteDuration> startWith$default$3()

    • stay

      FSM.State<S,D> stay()
      Produce "empty" transition descriptor. Return this from a state function when no state change is to be effected.

      No transition event will be triggered by stay(). If you want to trigger an event like S -&gt; S for onTransition to handle use goto instead.

      Returns:
      descriptor for staying in current state

    • stop

      FSM.State<S,D> stop()
      Produce change descriptor to stop this FSM actor with reason "Normal".

    • stop

      FSM.State<S,D> stop(FSM.Reason reason)
      Produce change descriptor to stop this FSM actor including specified reason.

    • stop

      FSM.State<S,D> stop(FSM.Reason reason, D stateData)
      Produce change descriptor to stop this FSM actor including specified reason.

    • transform

      FSM<S,D>.TransformHelper transform(scala.PartialFunction<FSM.Event<D>,FSM.State<S,D>> func)

    • startTimerWithFixedDelay

      void startTimerWithFixedDelay(String name, Object msg, scala.concurrent.duration.FiniteDuration delay)

    • startTimerAtFixedRate

      void startTimerAtFixedRate(String name, Object msg, scala.concurrent.duration.FiniteDuration interval)

    • startSingleTimer

      void startSingleTimer(String name, Object msg, scala.concurrent.duration.FiniteDuration delay)

    • startTimer

      void startTimer(String name, Object msg, scala.concurrent.duration.FiniteDuration timeout, FSM.TimerMode mode)

    • cancelTimer

      void cancelTimer(String name)

    • isTimerActive

      boolean isTimerActive(String name)

    • setStateTimeout

      void setStateTimeout(S state, scala.Option<scala.concurrent.duration.FiniteDuration> timeout)

    • isStateTimerActive

      boolean isStateTimerActive()

    • onTransition

      void onTransition(scala.PartialFunction<scala.Tuple2<S,S>,scala.runtime.BoxedUnit> transitionHandler)

    • total2pf

      scala.PartialFunction<scala.Tuple2<S,S>,scala.runtime.BoxedUnit> total2pf(scala.Function2<S,S,scala.runtime.BoxedUnit> transitionHandler)

    • onTermination

      void onTermination(scala.PartialFunction<FSM.StopEvent<S,D>,scala.runtime.BoxedUnit> terminationHandler)

    • whenUnhandled

      void whenUnhandled(scala.PartialFunction<FSM.Event<D>,FSM.State<S,D>> stateFunction)

    • initialize

      void initialize()

    • stateName

      S stateName()

    • stateData

      D stateData()

    • nextStateData

      D nextStateData()

    • debugEvent

      boolean debugEvent()

    • currentState_$eq

      void currentState_$eq(FSM.State<S,D> x$1)

    • timeoutFuture_$eq

      void timeoutFuture_$eq(scala.Option<Cancellable> x$1)

    • nextState_$eq

      void nextState_$eq(FSM.State<S,D> x$1)

    • generation_$eq

      void generation_$eq(long x$1)

    • register

      void register(S name, scala.PartialFunction<FSM.Event<D>,FSM.State<S,D>> function, scala.Option<scala.concurrent.duration.FiniteDuration> timeout)

    • handleEvent_$eq

      void handleEvent_$eq(scala.PartialFunction<FSM.Event<D>,FSM.State<S,D>> x$1)

    • terminateEvent_$eq

      void terminateEvent_$eq(scala.PartialFunction<FSM.StopEvent<S,D>,scala.runtime.BoxedUnit> x$1)

    • transitionEvent_$eq

      void transitionEvent_$eq(scala.collection.immutable.List<scala.PartialFunction<scala.Tuple2<S,S>,scala.runtime.BoxedUnit>> x$1)

    • handleTransition

      void handleTransition(S prev, S next)

    • receive

      scala.PartialFunction<Object,scala.runtime.BoxedUnit> receive()
      Description copied from interface: Actor
      Scala API: This defines the initial actor behavior, it must return a partial function with the actor logic.
      Specified by:
      receive in interface Actor

    • processMsg

      void processMsg(Object value, Object source)

    • processEvent

      void processEvent(FSM.Event<D> event, Object source)

    • applyState

      void applyState(FSM.State<S,D> nextState)

    • makeTransition

      void makeTransition(FSM.State<S,D> nextState)

    • postStop

      void postStop()
      Description copied from interface: Actor
      User overridable callback.

      Is called asynchronously after 'actor.stop()' is invoked. Empty default implementation.
      Specified by:
      postStop in interface Actor

    • terminate

      void terminate(FSM.State<S,D> nextState)

    • logTermination

      void logTermination(FSM.Reason reason)
      By default pekko.actor.FSM.Failure is logged at error level and other reason types are not logged. It is possible to override this behavior.