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/*
* Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
*/
package akka.actor
import language.implicitConversions
import scala.concurrent.duration.Duration
import scala.collection.mutable
import scala.concurrent.duration.FiniteDuration
import scala.concurrent.duration._
import akka.routing.{ Deafen, Listen, Listeners }
import akka.annotation.InternalApi
import akka.util.{ JavaDurationConverters, unused }
object FSM {
/**
* A partial function value which does not match anything and can be used to
* “reset” `whenUnhandled` and `onTermination` handlers.
*
* {{{
* onTermination(FSM.NullFunction)
* }}}
*/
object NullFunction extends PartialFunction[Any, Nothing] {
def isDefinedAt(o: Any) = false
def apply(o: Any) = sys.error("undefined")
}
/**
* Message type which is sent directly to the subscribed actor in
* [[akka.actor.FSM.SubscribeTransitionCallBack]] before sending any
* [[akka.actor.FSM.Transition]] messages.
*/
final case class CurrentState[S](fsmRef: ActorRef, state: S)
/**
* Message type which is used to communicate transitions between states to
* all subscribed listeners (use [[akka.actor.FSM.SubscribeTransitionCallBack]]).
*/
final case class Transition[S](fsmRef: ActorRef, from: S, to: S)
/**
* Send this to an [[akka.actor.FSM]] to request first the [[FSM.CurrentState]]
* and then a series of [[FSM.Transition]] updates. Cancel the subscription
* using [[FSM.UnsubscribeTransitionCallBack]].
*/
final case class SubscribeTransitionCallBack(actorRef: ActorRef)
/**
* Unsubscribe from [[akka.actor.FSM.Transition]] notifications which was
* effected by sending the corresponding [[akka.actor.FSM.SubscribeTransitionCallBack]].
*/
final case class UnsubscribeTransitionCallBack(actorRef: ActorRef)
/**
* Reason why this [[akka.actor.FSM]] is shutting down.
*/
sealed trait Reason
/**
* Default reason if calling `stop()`.
*/
case object Normal extends Reason
/**
* Reason given when someone was calling `system.stop(fsm)` from outside;
* also applies to `Stop` supervision directive.
*/
case object Shutdown extends Reason
/**
* Signifies that the [[akka.actor.FSM]] is shutting itself down because of
* an error, e.g. if the state to transition into does not exist. You can use
* this to communicate a more precise cause to the `onTermination` block.
*/
final case class Failure(cause: Any) extends Reason
/**
* This case object is received in case of a state timeout.
*/
case object StateTimeout
/**
* INTERNAL API
*/
private final case class TimeoutMarker(generation: Long)
/**
* INTERNAL API
*/
@InternalApi
private[akka] final case class Timer(name: String, msg: Any, repeat: Boolean, generation: Int,
owner: AnyRef)(context: ActorContext)
extends NoSerializationVerificationNeeded {
private var ref: Option[Cancellable] = _
private val scheduler = context.system.scheduler
private implicit val executionContext = context.dispatcher
def schedule(actor: ActorRef, timeout: FiniteDuration): Unit = {
val timerMsg = msg match {
case m: AutoReceivedMessage m
case _ this
}
ref = Some(
if (repeat) scheduler.schedule(timeout, timeout, actor, timerMsg)
else scheduler.scheduleOnce(timeout, actor, timerMsg))
}
def cancel(): Unit =
if (ref.isDefined) {
ref.get.cancel()
ref = None
}
}
/**
* This extractor is just convenience for matching a (S, S) pair, including a
* reminder what the new state is.
*/
object `->` {
def unapply[S](in: (S, S)) = Some(in)
}
val `→` = `->`
/**
* Log Entry of the [[akka.actor.LoggingFSM]], can be obtained by calling `getLog`.
*/
final case class LogEntry[S, D](stateName: S, stateData: D, event: Any)
/** Used by `forMax` to signal "cancel stateTimeout" */
private final val SomeMaxFiniteDuration = Some(Long.MaxValue.nanos)
/**
* INTERNAL API
* Using a subclass for binary compatibility reasons
*/
private[akka] class SilentState[S, D](_stateName: S, _stateData: D, _timeout: Option[FiniteDuration], _stopReason: Option[Reason], _replies: List[Any])
extends State[S, D](_stateName, _stateData, _timeout, _stopReason, _replies) {
/**
* INTERNAL API
*/
private[akka] override def notifies: Boolean = false
override def copy(stateName: S = stateName, stateData: D = stateData, timeout: Option[FiniteDuration] = timeout, stopReason: Option[Reason] = stopReason, replies: List[Any] = replies): State[S, D] = {
new SilentState(stateName, stateData, timeout, stopReason, replies)
}
}
/**
* This captures all of the managed state of the [[akka.actor.FSM]]: the state
* name, the state data, possibly custom timeout, stop reason and replies
* accumulated while processing the last message.
*/
case class State[S, D](stateName: S, stateData: D, timeout: Option[FiniteDuration] = None, stopReason: Option[Reason] = None, replies: List[Any] = Nil) {
/**
* INTERNAL API
*/
private[akka] def notifies: Boolean = true
// defined here to be able to override it in SilentState
def copy(stateName: S = stateName, stateData: D = stateData, timeout: Option[FiniteDuration] = timeout, stopReason: Option[Reason] = stopReason, replies: List[Any] = replies): State[S, D] = {
new State(stateName, stateData, timeout, stopReason, replies)
}
/**
* Modify state transition descriptor to include a state timeout for the
* next state. This timeout overrides any default timeout set for the next
* state.
*
* Use Duration.Inf to deactivate an existing timeout.
*/
def forMax(timeout: Duration): State[S, D] = timeout match {
case f: FiniteDuration copy(timeout = Some(f))
case Duration.Inf copy(timeout = SomeMaxFiniteDuration) // we map the Infinite duration to a special marker,
case _ copy(timeout = None) // that means "cancel stateTimeout". This marker is needed
} // so we do not have to break source/binary compat.
// TODO: Can be removed once we can break State#timeout signature to `Option[Duration]`
/**
* JAVA API: Modify state transition descriptor to include a state timeout for the
* next state. This timeout overrides any default timeout set for the next
* state.
*
* Use Duration.Inf to deactivate an existing timeout.
*/
def forMax(timeout: java.time.Duration): State[S, D] = {
import JavaDurationConverters._
forMax(timeout.asScala)
}
/**
* Send reply to sender of the current message, if available.
*
* @return this state transition descriptor
*/
def replying(replyValue: Any): State[S, D] = {
copy(replies = replyValue :: replies)
}
/**
* Modify state transition descriptor with new state data. The data will be
* set when transitioning to the new state.
*/
def using(@deprecatedName('nextStateDate) nextStateData: D): State[S, D] = {
copy(stateData = nextStateData)
}
/**
* INTERNAL API.
*/
private[akka] def withStopReason(reason: Reason): State[S, D] = {
copy(stopReason = Some(reason))
}
/**
* INTERNAL API.
*/
private[akka] def withNotification(notifies: Boolean): State[S, D] = {
if (notifies)
State(stateName, stateData, timeout, stopReason, replies)
else
new SilentState(stateName, stateData, timeout, stopReason, replies)
}
}
/**
* All messages sent to the [[akka.actor.FSM]] will be wrapped inside an
* `Event`, which allows pattern matching to extract both state and data.
*/
final case class Event[D](event: Any, stateData: D) extends NoSerializationVerificationNeeded
/**
* Case class representing the state of the [[akka.actor.FSM]] within the
* `onTermination` block.
*/
final case class StopEvent[S, D](reason: Reason, currentState: S, stateData: D) extends NoSerializationVerificationNeeded
}
/**
* Finite State Machine actor trait. Use as follows:
*
* <pre>
* 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()
* }
* </pre>
*
* Within the partial function the following values are returned for effecting
* state transitions:
*
* - <code>stay</code> for staying in the same state
* - <code>stay using Data(...)</code> for staying in the same state, but with
* different data
* - <code>stay forMax 5.millis</code> for staying with a state timeout; can be
* combined with <code>using</code>
* - <code>goto(...)</code> for changing into a different state; also supports
* <code>using</code> and <code>forMax</code>
* - <code>stop</code> for terminating this FSM actor
*
* Each of the above also supports the method <code>replying(AnyRef)</code> for
* sending a reply before changing state.
*
* While changing state, custom handlers may be invoked which are registered
* using <code>onTransition</code>. This is meant to enable concentrating
* different concerns in different places; you may choose to use
* <code>when</code> for describing the properties of a state, including of
* course initiating transitions, but you can describe the transitions using
* <code>onTransition</code> to avoid having to duplicate that code among
* multiple paths which lead to a transition:
*
* <pre>
* onTransition {
* case Active -&gt; _ =&gt; cancelTimer("activeTimer")
* }
* </pre>
*
* 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 <code>SubscribeTransitionCallback</code> message to this actor.
* Stopping a listener without unregistering will not remove the listener from the
* subscription list; use <code>UnsubscribeTransitionCallback</code> 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:
*
* <pre>
* setTimer("tock", TockMsg, 1 second, true) // repeating
* setTimer("lifetime", TerminateMsg, 1 hour, false) // single-shot
* cancelTimer("tock")
* isTimerActive("tock")
* </pre>
*/
trait FSM[S, D] extends Actor with Listeners with ActorLogging {
import FSM._
type State = FSM.State[S, D]
type Event = FSM.Event[D]
type StopEvent = FSM.StopEvent[S, D]
type StateFunction = scala.PartialFunction[Event, State]
type Timeout = Option[FiniteDuration]
type TransitionHandler = PartialFunction[(S, S), Unit]
/*
* “import” so that these are visible without an import
*/
val Event: FSM.Event.type = FSM.Event
val StopEvent: FSM.StopEvent.type = FSM.StopEvent
/**
* This extractor is just convenience for matching a (S, S) pair, including a
* reminder what the new state is.
*/
val `->` = FSM.`->`
/**
* This case object is received in case of a state timeout.
*/
val StateTimeout = FSM.StateTimeout
/**
* ****************************************
* DSL
* ****************************************
*/
/**
* 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.
*
* @param stateName designator for the state
* @param stateTimeout default state timeout for this state
* @param stateFunction partial function describing response to input
*/
final def when(stateName: S, stateTimeout: FiniteDuration = null)(stateFunction: StateFunction): Unit =
register(stateName, stateFunction, Option(stateTimeout))
/**
* 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 [[akka.actor.Actor#preStart]] and [[akka.actor.Actor#postRestart]].
*
* @param stateName initial state designator
* @param stateData initial state data
* @param timeout state timeout for the initial state, overriding the default timeout for that state
*/
final def startWith(stateName: S, stateData: D, timeout: Timeout = None): Unit =
currentState = FSM.State(stateName, stateData, timeout)
/**
* Produce transition to other state.
* Return this from a state function in order to effect the transition.
*
* This method always triggers transition events, even for `A -> A` transitions.
* If you want to stay in the same state without triggering an state transition event use [[#stay]] instead.
*
* @param nextStateName state designator for the next state
* @return state transition descriptor
*/
final def goto(nextStateName: S): State = FSM.State(nextStateName, currentState.stateData)
/**
* 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.
*
* @return descriptor for staying in current state
*/
final def stay(): State = goto(currentState.stateName).withNotification(false) // cannot directly use currentState because of the timeout field
/**
* Produce change descriptor to stop this FSM actor with reason "Normal".
*/
final def stop(): State = stop(Normal)
/**
* Produce change descriptor to stop this FSM actor including specified reason.
*/
final def stop(reason: Reason): State = stop(reason, currentState.stateData)
/**
* Produce change descriptor to stop this FSM actor including specified reason.
*/
final def stop(reason: Reason, stateData: D): State = stay using stateData withStopReason (reason)
final class TransformHelper(func: StateFunction) {
def using(andThen: PartialFunction[State, State]): StateFunction =
func andThen (andThen orElse { case x x })
}
final def transform(func: StateFunction): TransformHelper = new TransformHelper(func)
/**
* Schedule named timer to deliver message after given delay, possibly repeating.
* Any existing timer with the same name will automatically be canceled before
* adding the new timer.
* @param name identifier to be used with cancelTimer()
* @param msg message to be delivered
* @param timeout delay of first message delivery and between subsequent messages
* @param repeat send once if false, scheduleAtFixedRate if true
*/
final def setTimer(name: String, msg: Any, timeout: FiniteDuration, repeat: Boolean = false): Unit = {
if (debugEvent)
log.debug("setting " + (if (repeat) "repeating " else "") + "timer '" + name + "'/" + timeout + ": " + msg)
if (timers contains name) {
timers(name).cancel
}
val timer = Timer(name, msg, repeat, timerGen.next, this)(context)
timer.schedule(self, timeout)
timers(name) = timer
}
/**
* Cancel named timer, ensuring that the message is not subsequently delivered (no race).
* @param name of the timer to cancel
*/
final def cancelTimer(name: String): Unit = {
if (debugEvent)
log.debug("canceling timer '" + name + "'")
if (timers contains name) {
timers(name).cancel
timers -= name
}
}
/**
* Inquire whether the named timer is still active. Returns true unless the
* timer does not exist, has previously been canceled or if it was a
* single-shot timer whose message was already received.
*/
final def isTimerActive(name: String): Boolean = timers contains name
/**
* Set state timeout explicitly. This method can safely be used from within a
* state handler.
*/
final def setStateTimeout(state: S, timeout: Timeout): Unit = stateTimeouts(state) = timeout
/**
* INTERNAL API, used for testing.
*/
private[akka] final def isStateTimerActive = timeoutFuture.isDefined
/**
* Set handler which is called upon each state transition, i.e. not when
* staying in the same state. This may use the pair extractor defined in the
* FSM companion object like so:
*
* <pre>
* onTransition {
* case Old -&gt; New =&gt; doSomething
* }
* </pre>
*
* It is also possible to supply a 2-ary function object:
*
* <pre>
* onTransition(handler _)
*
* private def handler(from: S, to: S) { ... }
* </pre>
*
* The underscore is unfortunately necessary to enable the nicer syntax shown
* above (it uses the implicit conversion total2pf under the hood).
*
* <b>Multiple handlers may be installed, and every one of them will be
* called, not only the first one matching.</b>
*/
final def onTransition(transitionHandler: TransitionHandler): Unit = transitionEvent :+= transitionHandler
/**
* Convenience wrapper for using a total function instead of a partial
* function literal. To be used with onTransition.
*/
implicit final def total2pf(transitionHandler: (S, S) Unit): TransitionHandler =
new TransitionHandler {
def isDefinedAt(in: (S, S)) = true
def apply(in: (S, S)): Unit = { transitionHandler(in._1, in._2) }
}
/**
* Set handler which is called upon termination of this FSM actor. Calling
* this method again will overwrite the previous contents.
*/
final def onTermination(terminationHandler: PartialFunction[StopEvent, Unit]): Unit =
terminateEvent = terminationHandler
/**
* Set handler which is called upon reception of unhandled messages. Calling
* this method again will overwrite the previous contents.
*
* The current state may be queried using ``stateName``.
*/
final def whenUnhandled(stateFunction: StateFunction): Unit =
handleEvent = stateFunction orElse handleEventDefault
/**
* Verify existence of initial state and setup timers. This should be the
* last call within the constructor, or [[akka.actor.Actor#preStart]] and
* [[akka.actor.Actor#postRestart]]
*
* An initial `currentState -> currentState` notification will be triggered by calling this method.
*
* @see [[#startWith]]
*/
final def initialize(): Unit =
if (currentState != null) makeTransition(currentState)
else throw new IllegalStateException("You must call `startWith` before calling `initialize`")
/**
* Return current state name (i.e. object of type S)
*/
final def stateName: S = {
if (currentState != null) currentState.stateName
else throw new IllegalStateException("You must call `startWith` before using `stateName`")
}
/**
* Return current state data (i.e. object of type D)
*/
final def stateData: D =
if (currentState != null) currentState.stateData
else throw new IllegalStateException("You must call `startWith` before using `stateData`")
/**
* Return next state data (available in onTransition handlers)
*/
final def nextStateData = nextState match {
case null throw new IllegalStateException("nextStateData is only available during onTransition")
case x x.stateData
}
/*
* ****************************************************************
* PRIVATE IMPLEMENTATION DETAILS
* ****************************************************************
*/
private[akka] def debugEvent: Boolean = false
/*
* FSM State data and current timeout handling
*/
private var currentState: State = _
private var timeoutFuture: Option[Cancellable] = None
private var nextState: State = _
private var generation: Long = 0L
/*
* Timer handling
*/
private val timers = mutable.Map[String, Timer]()
private val timerGen = Iterator from 0
/*
* State definitions
*/
private val stateFunctions = mutable.Map[S, StateFunction]()
private val stateTimeouts = mutable.Map[S, Timeout]()
private def register(name: S, function: StateFunction, timeout: Timeout): Unit = {
if (stateFunctions contains name) {
stateFunctions(name) = stateFunctions(name) orElse function
stateTimeouts(name) = timeout orElse stateTimeouts(name)
} else {
stateFunctions(name) = function
stateTimeouts(name) = timeout
}
}
/*
* unhandled event handler
*/
private val handleEventDefault: StateFunction = {
case Event(value, _)
log.warning("unhandled event " + value + " in state " + stateName)
stay
}
private var handleEvent: StateFunction = handleEventDefault
/*
* termination handling
*/
private var terminateEvent: PartialFunction[StopEvent, Unit] = NullFunction
/*
* transition handling
*/
private var transitionEvent: List[TransitionHandler] = Nil
private def handleTransition(prev: S, next: S): Unit = {
val tuple = (prev, next)
for (te transitionEvent) { if (te.isDefinedAt(tuple)) te(tuple) }
}
/*
* *******************************************
* Main actor receive() method
* *******************************************
*/
override def receive: Receive = {
case TimeoutMarker(gen)
if (generation == gen) {
processMsg(StateTimeout, "state timeout")
}
case t @ Timer(name, msg, repeat, gen, owner)
if ((owner eq this) && (timers contains name) && (timers(name).generation == gen)) {
if (timeoutFuture.isDefined) {
timeoutFuture.get.cancel()
timeoutFuture = None
}
generation += 1
if (!repeat) {
timers -= name
}
processMsg(msg, t)
}
case SubscribeTransitionCallBack(actorRef)
// TODO Use context.watch(actor) and receive Terminated(actor) to clean up list
listeners.add(actorRef)
// send current state back as reference point
actorRef ! CurrentState(self, currentState.stateName)
case Listen(actorRef)
// TODO Use context.watch(actor) and receive Terminated(actor) to clean up list
listeners.add(actorRef)
// send current state back as reference point
actorRef ! CurrentState(self, currentState.stateName)
case UnsubscribeTransitionCallBack(actorRef)
listeners.remove(actorRef)
case Deafen(actorRef)
listeners.remove(actorRef)
case value {
if (timeoutFuture.isDefined) {
timeoutFuture.get.cancel()
timeoutFuture = None
}
generation += 1
processMsg(value, sender())
}
}
private def processMsg(value: Any, source: AnyRef): Unit = {
val event = Event(value, currentState.stateData)
processEvent(event, source)
}
private[akka] def processEvent(event: Event, @unused source: AnyRef): Unit = {
val stateFunc = stateFunctions(currentState.stateName)
val nextState = if (stateFunc isDefinedAt event) {
stateFunc(event)
} else {
// handleEventDefault ensures that this is always defined
handleEvent(event)
}
applyState(nextState)
}
private[akka] def applyState(nextState: State): Unit = {
nextState.stopReason match {
case None makeTransition(nextState)
case _
nextState.replies.reverse foreach { r sender() ! r }
terminate(nextState)
context.stop(self)
}
}
private[akka] def makeTransition(nextState: State): Unit = {
if (!stateFunctions.contains(nextState.stateName)) {
terminate(stay withStopReason Failure("Next state %s does not exist".format(nextState.stateName)))
} else {
nextState.replies.reverse foreach { r sender() ! r }
if (currentState.stateName != nextState.stateName || nextState.notifies) {
this.nextState = nextState
handleTransition(currentState.stateName, nextState.stateName)
gossip(Transition(self, currentState.stateName, nextState.stateName))
this.nextState = null
}
currentState = nextState
def scheduleTimeout(d: FiniteDuration): Some[Cancellable] = {
import context.dispatcher
Some(context.system.scheduler.scheduleOnce(d, self, TimeoutMarker(generation)))
}
currentState.timeout match {
case SomeMaxFiniteDuration // effectively disable stateTimeout
case Some(d: FiniteDuration) if d.length >= 0 timeoutFuture = scheduleTimeout(d)
case _
val timeout = stateTimeouts(currentState.stateName)
if (timeout.isDefined) timeoutFuture = scheduleTimeout(timeout.get)
}
}
}
/**
* 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.
*/
override def postStop(): Unit = {
/*
* setting this instance’s state to terminated does no harm during restart
* since the new instance will initialize fresh using startWith()
*/
terminate(stay withStopReason Shutdown)
super.postStop()
}
private def terminate(nextState: State): Unit = {
if (currentState.stopReason.isEmpty) {
val reason = nextState.stopReason.get
logTermination(reason)
for (timer timers.values) timer.cancel()
timers.clear()
timeoutFuture.foreach { _.cancel() }
currentState = nextState
val stopEvent = StopEvent(reason, currentState.stateName, currentState.stateData)
if (terminateEvent.isDefinedAt(stopEvent))
terminateEvent(stopEvent)
}
}
/**
* By default [[FSM.Failure]] is logged at error level and other reason
* types are not logged. It is possible to override this behavior.
*/
protected def logTermination(reason: Reason): Unit = reason match {
case Failure(ex: Throwable) log.error(ex, "terminating due to Failure")
case Failure(msg: AnyRef) log.error(msg.toString)
case _
}
}
/**
* Stackable trait for [[akka.actor.FSM]] which adds a rolling event log and
* debug logging capabilities (analogous to [[akka.event.LoggingReceive]]).
*
* @since 1.2
*/
trait LoggingFSM[S, D] extends FSM[S, D] { this: Actor
import FSM._
def logDepth: Int = 0
private[akka] override val debugEvent = context.system.settings.FsmDebugEvent
private val events = new Array[Event](logDepth)
private val states = new Array[AnyRef](logDepth)
private var pos = 0
private var full = false
private def advance(): Unit = {
val n = pos + 1
if (n == logDepth) {
full = true
pos = 0
} else {
pos = n
}
}
private[akka] abstract override def processEvent(event: Event, source: AnyRef): Unit = {
if (debugEvent) {
val srcstr = source match {
case s: String s
case Timer(name, _, _, _, _) "timer " + name
case a: ActorRef a.toString
case _ "unknown"
}
log.debug("processing {} from {} in state {}", event, srcstr, stateName)
}
if (logDepth > 0) {
states(pos) = stateName.asInstanceOf[AnyRef]
events(pos) = event
advance()
}
val oldState = stateName
super.processEvent(event, source)
val newState = stateName
if (debugEvent && oldState != newState)
log.debug("transition " + oldState + " -> " + newState)
}
/**
* Retrieve current rolling log in oldest-first order. The log is filled with
* each incoming event before processing by the user supplied state handler.
* The log entries are lost when this actor is restarted.
*/
protected def getLog: IndexedSeq[LogEntry[S, D]] = {
val log = events zip states filter (_._1 ne null) map (x LogEntry(x._2.asInstanceOf[S], x._1.stateData, x._1.event))
if (full) {
IndexedSeq() ++ log.drop(pos) ++ log.take(pos)
} else {
IndexedSeq() ++ log
}
}
}