Apache Pekko
1.1.0-M1
API
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Apache Pekko/org.apache.pekko.persistence/org.apache.pekko.persistence.fsm/PersistentFSMBase

PersistentFSMBase

org.apache.pekko.persistence.fsm.PersistentFSMBase
trait PersistentFSMBase[S, D, E] 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, _) => ... // convenience 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 -> _ => 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:

 startTimerWithFixedDelay("tock", TockMsg, 1 second) // repeating
 startSingleTimer("lifetime", TerminateMsg, 1 hour) // single-shot
 cancelTimer("tock")
 isTimerActive("tock")

Attributes

Deprecated
true
Source
PersistentFSMBase.scala
Graph
Supertypes
trait ActorLogging
trait Listeners
trait Actor
class Object
trait Matchable
class Any
Show all
Known subtypes
class AbstractPersistentFSMBase[S, D, E]
class AbstractPersistentFSM[S, D, E]
trait LoggingPersistentFSM[S, D, E]
trait PersistentFSM[S, D, E]

Members list

Type members

Classlikes

final class TransformHelper(func: StateFunction)

Attributes

Source
PersistentFSMBase.scala
Supertypes
class Object
trait Matchable
class Any

Types

type Event = Event[D]

Attributes

Source
PersistentFSMBase.scala
type State = State[S, D, E]

Attributes

Source
PersistentFSMBase.scala
type StopEvent = StopEvent[S, D]

Attributes

Source
PersistentFSMBase.scala

Inherited types

type Receive = Receive

Attributes

Inherited from:
Actor
Source
Actor.scala

Value members

Concrete methods

final def cancelTimer(name: String): Unit

Cancel named timer, ensuring that the message is not subsequently delivered (no race).

Cancel named timer, ensuring that the message is not subsequently delivered (no race).

Value parameters

name

of the timer to cancel

Attributes

Source
PersistentFSMBase.scala
final def goto(nextStateName: S): State

Produce transition to other state. Return this from a state function in order to effect the transition.

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.

Value parameters

nextStateName

state designator for the next state

Attributes

Returns

state transition descriptor

Source
PersistentFSMBase.scala
final def isTimerActive(name: String): Boolean

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.

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.

Attributes

Source
PersistentFSMBase.scala
protected def logTermination(reason: Reason): Unit

By default PersistentFSM.Failure is logged at error level and other reason types are not logged. It is possible to override this behavior.

By default PersistentFSM.Failure is logged at error level and other reason types are not logged. It is possible to override this behavior.

Attributes

Source
PersistentFSMBase.scala
final def nextStateData: D

Return next state data (available in onTransition handlers)

Return next state data (available in onTransition handlers)

Attributes

Source
PersistentFSMBase.scala
final def onTermination(terminationHandler: PartialFunction[StopEvent, Unit]): Unit

Set handler which is called upon termination of this FSM actor. Calling this method again will overwrite the previous contents.

Set handler which is called upon termination of this FSM actor. Calling this method again will overwrite the previous contents.

Attributes

Source
PersistentFSMBase.scala
final def onTransition(transitionHandler: TransitionHandler): Unit

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:

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:

onTransition {
 case Old -> New => doSomething
}

It is also possible to supply a 2-ary function object:

onTransition(handler _)

private def handler(from: S, to: S) { ... }

The underscore is unfortunately necessary to enable the nicer syntax shown above (it uses the implicit conversion total2pf under the hood).

Multiple handlers may be installed, and every one of them will be called, not only the first one matching.

Attributes

Source
PersistentFSMBase.scala
override def postStop(): Unit

Call onTermination hook; if you want to retain this behavior when overriding make sure to call 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.

Attributes

Definition Classes
Source
PersistentFSMBase.scala
override def receive: Receive

Scala API: This defines the initial actor behavior, it must return a partial function with the actor logic.

Scala API: This defines the initial actor behavior, it must return a partial function with the actor logic.

Attributes

Definition Classes
Source
PersistentFSMBase.scala
final def setStateTimeout(state: S, timeout: Timeout): Unit

Set state timeout explicitly. This method can safely be used from within a state handler.

Set state timeout explicitly. This method can safely be used from within a state handler.

Attributes

Source
PersistentFSMBase.scala
def startSingleTimer(name: String, msg: Any, delay: FiniteDuration): Unit

Start a timer that will send msg once to the self actor after the given delay.

Start a timer that will send msg once to the self actor after the given delay.

Each timer has a name and if a new timer with same name is started the previous is cancelled. It is guaranteed that a message from the previous timer is not received, even if it was already enqueued in the mailbox when the new timer was started.

Attributes

Source
PersistentFSMBase.scala
def startTimerAtFixedRate(name: String, msg: Any, interval: FiniteDuration): Unit

Schedules a message to be sent repeatedly to the self actor with a given frequency.

Schedules a message to be sent repeatedly to the self actor with a given frequency.

It will compensate the delay for a subsequent message if the sending of previous message was delayed more than specified. In such cases, the actual message interval will differ from the interval passed to the method.

If the execution is delayed longer than the interval, the subsequent message will be sent immediately after the prior one. This also has the consequence that after long garbage collection pauses or other reasons when the JVM was suspended all "missed" messages will be sent when the process wakes up again.

In the long run, the frequency of messages will be exactly the reciprocal of the specified interval.

Warning: startTimerAtFixedRate can result in bursts of scheduled messages after long garbage collection pauses, which may in worst case cause undesired load on the system. Therefore startTimerWithFixedDelay is often preferred.

Each timer has a name and if a new timer with same name is started the previous is cancelled. It is guaranteed that a message from the previous timer is not received, even if it was already enqueued in the mailbox when the new timer was started.

Attributes

Source
PersistentFSMBase.scala
def startTimerWithFixedDelay(name: String, msg: Any, delay: FiniteDuration): Unit

Schedules a message to be sent repeatedly to the self actor with a fixed delay between messages.

Schedules a message to be sent repeatedly to the self actor with a fixed delay between messages.

It will not compensate the delay between messages if scheduling is delayed longer than specified for some reason. The delay between sending of subsequent messages will always be (at least) the given delay.

In the long run, the frequency of messages will generally be slightly lower than the reciprocal of the specified delay.

Each timer has a name and if a new timer with same name is started the previous is cancelled. It is guaranteed that a message from the previous timer is not received, even if it was already enqueued in the mailbox when the new timer was started.

Attributes

Source
PersistentFSMBase.scala
final def startWith(stateName: S, stateData: D, timeout: Timeout): Unit

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.

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.

Value parameters

stateData

initial state data

stateName

initial state designator

timeout

state timeout for the initial state, overriding the default timeout for that state

Attributes

Source
PersistentFSMBase.scala
final def stateData: D

Return current state data (i.e. object of type D)

Return current state data (i.e. object of type D)

Attributes

Source
PersistentFSMBase.scala
final def stateName: S

Return current state name (i.e. object of type S)

Return current state name (i.e. object of type S)

Attributes

Source
PersistentFSMBase.scala
final def stay(): State

Produce "empty" transition descriptor. Return this from a state function when no state change is to be effected.

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 -> S for onTransition to handle use goto instead.

Attributes

Returns

descriptor for staying in current state

Source
PersistentFSMBase.scala
final def stop(): State

Produce change descriptor to stop this FSM actor with reason "Normal".

Produce change descriptor to stop this FSM actor with reason "Normal".

Attributes

Source
PersistentFSMBase.scala
final def stop(reason: Reason): State

Produce change descriptor to stop this FSM actor including specified reason.

Produce change descriptor to stop this FSM actor including specified reason.

Attributes

Source
PersistentFSMBase.scala
final def stop(reason: Reason, stateData: D): State

Produce change descriptor to stop this FSM actor including specified reason.

Produce change descriptor to stop this FSM actor including specified reason.

Attributes

Source
PersistentFSMBase.scala
final def transform(func: StateFunction): TransformHelper

Attributes

Source
PersistentFSMBase.scala
final def when(stateName: S, stateTimeout: FiniteDuration)(stateFunction: StateFunction): Unit

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.

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.

Value parameters

stateFunction

partial function describing response to input

stateName

designator for the state

stateTimeout

default state timeout for this state

Attributes

Source
PersistentFSMBase.scala
final def whenUnhandled(stateFunction: StateFunction): Unit

Set handler which is called upon reception of unhandled messages. Calling this method again will overwrite the previous contents.

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.

Attributes

Source
PersistentFSMBase.scala

Deprecated methods

final def setTimer(name: String, msg: Any, timeout: FiniteDuration, repeat: Boolean): Unit

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.

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.

Value parameters

msg

message to be delivered

name

identifier to be used with cancelTimer()

repeat

send once if false, scheduleAtFixedRate if true

timeout

delay of first message delivery and between subsequent messages

Attributes

Deprecated
[Since version Akka 2.6.0]
Source
PersistentFSMBase.scala

Inherited methods

protected def gossip(msg: Any)(implicit sender: ActorRef): Unit

Sends the supplied message to all current listeners using the provided sender() as sender.

Sends the supplied message to all current listeners using the provided sender() as sender.

Attributes

Inherited from:
Listeners
Source
Listeners.scala
protected def listenerManagement: Receive

Chain this into the receive function.

Chain this into the receive function.

 def receive = listenerManagement orElse …

Attributes

Inherited from:
Listeners
Source
Listeners.scala
def log: LoggingAdapter

Attributes

Inherited from:
ActorLogging
Source
Actor.scala
def postRestart(reason: Throwable): Unit

User overridable callback: By default it calls preStart().

User overridable callback: By default it calls preStart().

Value parameters

reason

the Throwable that caused the restart to happen Is called right AFTER restart on the newly created Actor to allow reinitialization after an Actor crash.

Attributes

Inherited from:
Actor
Source
Actor.scala
def preRestart(reason: Throwable, message: Option[Any]): Unit

Scala API: User overridable callback: '''By default it disposes of all children and then calls postStop().'''

Scala API: User overridable callback: '''By default it disposes of all children and then calls postStop().'''

Value parameters

message

optionally the current message the actor processed when failing, if applicable Is called on a crashed Actor right BEFORE it is restarted to allow clean up of resources before Actor is terminated.

reason

the Throwable that caused the restart to happen

Attributes

Inherited from:
Actor
Source
Actor.scala
def preStart(): Unit

User overridable callback.

User overridable callback.

Is called when an Actor is started. Actors are automatically started asynchronously when created. Empty default implementation.

Attributes

Inherited from:
Actor
Source
Actor.scala
final def sender(): ActorRef

The reference sender Actor of the last received message. Is defined if the message was sent from another Actor, else deadLetters in pekko.actor.ActorSystem.

The reference sender Actor of the last received message. Is defined if the message was sent from another Actor, else deadLetters in pekko.actor.ActorSystem.

WARNING: Only valid within the Actor itself, so do not close over it and publish it to other threads!

Attributes

Inherited from:
Actor
Source
Actor.scala
def supervisorStrategy: SupervisorStrategy

User overridable definition the strategy to use for supervising child actors.

User overridable definition the strategy to use for supervising child actors.

Attributes

Inherited from:
Actor
Source
Actor.scala
def unhandled(message: Any): Unit

User overridable callback.

User overridable callback.

Is called when a message isn't handled by the current behavior of the actor by default it fails with either a pekko.actor.DeathPactException (in case of an unhandled pekko.actor.Terminated message) or publishes an pekko.actor.UnhandledMessage to the actor's system's pekko.event.EventStream

Attributes

Inherited from:
Actor
Source
Actor.scala

Concrete fields

val ->: ->.type

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

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

Attributes

Source
PersistentFSMBase.scala
val Event: Event.type

Attributes

Source
PersistentFSMBase.scala
val StateTimeout: StateTimeout.type

This case object is received in case of a state timeout.

This case object is received in case of a state timeout.

Attributes

Source
PersistentFSMBase.scala
val StopEvent: StopEvent.type

Attributes

Source
PersistentFSMBase.scala

Inherited fields

protected val listeners: Set[ActorRef]

Attributes

Inherited from:
Listeners
Source
Listeners.scala

Implicits

Implicits

final implicit def total2pf(transitionHandler: (S, S) => Unit): TransitionHandler

Convenience wrapper for using a total function instead of a partial function literal. To be used with onTransition.

Convenience wrapper for using a total function instead of a partial function literal. To be used with onTransition.

Attributes

Source
PersistentFSMBase.scala

Inherited implicits

implicit val context: ActorContext

Scala API: Stores the context for this actor, including self, and sender. It is implicit to support operations such as forward.

Scala API: Stores the context for this actor, including self, and sender. It is implicit to support operations such as forward.

WARNING: Only valid within the Actor itself, so do not close over it and publish it to other threads!

pekko.actor.ActorContext is the Scala API. getContext returns a pekko.actor.AbstractActor.ActorContext, which is the Java API of the actor context.

Attributes

Inherited from:
Actor
Source
Actor.scala
final implicit val self: ActorRef

The 'self' field holds the ActorRef for this actor.

The 'self' field holds the ActorRef for this actor.

Can be used to send messages to itself:

self ! message

Attributes

Inherited from:
Actor
Source
Actor.scala
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