FSM

Companion object FSM

trait FSM[S, D] extends Actor with Listeners with 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 -> _ => 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")

Source: FSM.scala

Linear Supertypes

ActorLogging, Listeners, Actor, AnyRef, Any

Known Subclasses

AbstractFSM, AbstractFSMWithStash, AbstractLoggingFSM, LoggingFSM, ClusterSingletonManager

Type Hierarchy

Ordering

Alphabetic
By Inheritance

Inherited

FSM
ActorLogging
Listeners
Actor
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Visibility

Public
Protected

Type Members

type Event = FSM.Event[D]
type Receive = PartialFunction[Any, Unit]
Definition Classes
Actor
type State = FSM.State[S, D]
type StateFunction = PartialFunction[Event, State]
type StopEvent = FSM.StopEvent[S, D]
type Timeout = Option[FiniteDuration]
final class TransformHelper extends AnyRef
type TransitionHandler = PartialFunction[(S, S), Unit]

Value Members

final def !=(arg0: Any): Boolean
Definition Classes
AnyRef → Any
final def ##: Int
Definition Classes
AnyRef → Any
def +(other: String): String
Implicit
This member is added by an implicit conversion from FSM[S, D] toany2stringadd[FSM[S, D]] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd
val ->: FSM.->.type
This extractor is just convenience for matching a (S, S) pair, including a reminder what the new state is.
final def ==(arg0: Any): Boolean
Definition Classes
AnyRef → Any
val Event: FSM.Event.type
val StateTimeout: FSM.StateTimeout.type
This case object is received in case of a state timeout.
val StopEvent: FSM.StopEvent.type
def aroundPostRestart(reason: Throwable): Unit
INTERNAL API.
INTERNAL API.
Can be overridden to intercept calls to postRestart. Calls postRestart by default.
Attributes
protected[pekko]
Definition Classes
Actor
Annotations
@InternalApi()
def aroundPostStop(): Unit
INTERNAL API.
INTERNAL API.
Can be overridden to intercept calls to postStop. Calls postStop by default.
Attributes
protected[pekko]
Definition Classes
Actor
Annotations
@InternalApi()
def aroundPreRestart(reason: Throwable, message: Option[Any]): Unit
INTERNAL API.
INTERNAL API.
Can be overridden to intercept calls to preRestart. Calls preRestart by default.
Attributes
protected[pekko]
Definition Classes
Actor
Annotations
@InternalApi()
def aroundPreStart(): Unit
INTERNAL API.
INTERNAL API.
Can be overridden to intercept calls to preStart. Calls preStart by default.
Attributes
protected[pekko]
Definition Classes
Actor
Annotations
@InternalApi()
def aroundReceive(receive: Actor.Receive, msg: Any): Unit
INTERNAL API.
INTERNAL API.
Can be overridden to intercept calls to this actor's current behavior.
receive
current behavior.
msg
current message.
Attributes
protected[pekko]
Definition Classes
Actor
Annotations
@InternalApi()
final def asInstanceOf[T0]: T0
Definition Classes
Any
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).
name
of the timer to cancel
def clone(): AnyRef
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @HotSpotIntrinsicCandidate() @native()
implicit val context: ActorContext
Scala API: Stores the context for this actor, including self, and sender.
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.
Definition Classes
Actor
def ensuring(cond: (FSM[S, D]) => Boolean, msg: => Any): FSM[S, D]
Implicit
This member is added by an implicit conversion from FSM[S, D] toEnsuring[FSM[S, D]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (FSM[S, D]) => Boolean): FSM[S, D]
Implicit
This member is added by an implicit conversion from FSM[S, D] toEnsuring[FSM[S, D]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: => Any): FSM[S, D]
Implicit
This member is added by an implicit conversion from FSM[S, D] toEnsuring[FSM[S, D]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): FSM[S, D]
Implicit
This member is added by an implicit conversion from FSM[S, D] toEnsuring[FSM[S, D]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
final def eq(arg0: AnyRef): Boolean
Definition Classes
AnyRef
def equals(arg0: AnyRef): Boolean
Definition Classes
AnyRef → Any
final def getClass(): Class[_ <: AnyRef]
Definition Classes
AnyRef → Any
Annotations
@HotSpotIntrinsicCandidate() @native()
def gossip(msg: Any)(implicit sender: ActorRef = Actor.noSender): 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
protected
Definition Classes
Listeners
final def goto(nextStateName: S): State
Produce transition to other state.
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.
nextStateName
state designator for the next state
returns
state transition descriptor
def hashCode(): Int
Definition Classes
AnyRef → Any
Annotations
@HotSpotIntrinsicCandidate() @native()
final def initialize(): Unit
Verify existence of initial state and setup timers.
Verify existence of initial state and setup timers. This should be the last call within the constructor, or pekko.actor.Actor#preStart and pekko.actor.Actor#postRestart
An initial currentState -> currentState notification will be triggered by calling this method.
See also
#startWith
final def isInstanceOf[T0]: Boolean
Definition Classes
Any
final def isTimerActive(name: String): Boolean
Inquire whether the named timer is still active.
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.
def listenerManagement: Actor.Receive
Chain this into the receive function.
Chain this into the receive function.
```
def receive = listenerManagement orElse …
```
Attributes
protected
Definition Classes
Listeners
val listeners: Set[ActorRef]
Attributes
protected
Definition Classes
Listeners
def log: LoggingAdapter
Definition Classes
ActorLogging
def logTermination(reason: Reason): Unit
By default pekko.actor.FSM.Failure is logged at error level and other reason types are not logged.
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.
Attributes
protected
final def ne(arg0: AnyRef): Boolean
Definition Classes
AnyRef
final def nextStateData: D
Return next state data (available in onTransition handlers)
final def notify(): Unit
Definition Classes
AnyRef
Annotations
@HotSpotIntrinsicCandidate() @native()
final def notifyAll(): Unit
Definition Classes
AnyRef
Annotations
@HotSpotIntrinsicCandidate() @native()
final def onTermination(terminationHandler: PartialFunction[StopEvent, Unit]): Unit
Set handler which is called upon termination of this FSM actor.
Set handler which is called upon termination of this FSM actor. Calling this method again will overwrite the previous contents.
final def onTransition(transitionHandler: TransitionHandler): Unit
Set handler which is called upon each state transition, i.e.
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.
def postRestart(reason: Throwable): Unit
User overridable callback: By default it calls preStart().
User overridable callback: By default it calls preStart().
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.
Definition Classes
Actor
Annotations
@throws(classOf[Exception])
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.
Definition Classes
FSM → Actor
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().
reason
the Throwable that caused the restart to happen
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.
Definition Classes
Actor
Annotations
@throws(classOf[Exception])
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.
Definition Classes
Actor
Annotations
@throws(classOf[Exception])
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.
Definition Classes
FSM → Actor
implicit final 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
```
Definition Classes
Actor
final def sender(): ActorRef
The reference sender Actor of the last received message.
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!
Definition Classes
Actor
final def setStateTimeout(state: S, timeout: Timeout): Unit
Set state timeout explicitly.
Set state timeout explicitly. This method can safely be used from within a state handler.
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.
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.
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.
final def startWith(stateName: S, stateData: D, timeout: Timeout = None): Unit
Set initial state.
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.
stateName
initial state designator
stateData
initial state data
timeout
state timeout for the initial state, overriding the default timeout for that state
final def stateData: D
Return current state data (i.e.
Return current state data (i.e. object of type D)
final def stateName: S
Return current state name (i.e.
Return current state name (i.e. object of type S)
final def stay(): State
Produce "empty" transition descriptor.
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.
returns
descriptor for staying in current state
final def stop(reason: Reason, stateData: D): State
Produce change descriptor to stop this FSM actor including specified reason.
final def stop(reason: Reason): State
Produce change descriptor to stop this FSM actor including specified reason.
final def stop(): State
Produce change descriptor to stop this FSM actor with reason "Normal".
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.
Definition Classes
Actor
final def synchronized[T0](arg0: => T0): T0
Definition Classes
AnyRef
def toString(): String
Definition Classes
AnyRef → Any
implicit final def total2pf(transitionHandler: (S, S) => Unit): TransitionHandler
Convenience wrapper for using a total function instead of a partial function literal.
Convenience wrapper for using a total function instead of a partial function literal. To be used with onTransition.
final def transform(func: StateFunction): TransformHelper
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
Definition Classes
Actor
final def wait(arg0: Long, arg1: Int): Unit
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long): Unit
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()
final def wait(): Unit
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
final def when(stateName: S, stateTimeout: FiniteDuration = null)(stateFunction: StateFunction): Unit
Insert a new StateFunction at the end of the processing chain for the given state.
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.
stateName
designator for the state
stateTimeout
default state timeout for this state
stateFunction
partial function describing response to input
final def whenUnhandled(stateFunction: StateFunction): Unit
Set handler which is called upon reception of unhandled messages.
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.

Shadowed Implicit Value Members

def ->[B](y: B): (FSM[S, D], B)
Implicit
This member is added by an implicit conversion from FSM[S, D] toArrowAssoc[FSM[S, D]] performed by method ArrowAssoc in scala.Predef.
Shadowing
This implicitly inherited member is shadowed by one or more members in this class.
To access this member you can use a type ascription:
(fSM: ArrowAssoc[FSM[S, D]]).->(y)
Definition Classes
ArrowAssoc
Annotations
@inline()

Deprecated Value Members

def finalize(): Unit
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable]) @Deprecated
Deprecated
(Since version 9)
def formatted(fmtstr: String): String
Implicit
This member is added by an implicit conversion from FSM[S, D] toStringFormat[FSM[S, D]] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@deprecated @inline()
Deprecated
(Since version 2.12.16) Use formatString.format(value) instead of value.formatted(formatString), or use the f"" string interpolator. In Java 15 and later, formatted resolves to the new method in String which has reversed parameters.
final def setTimer(name: String, msg: Any, timeout: FiniteDuration, repeat: Boolean = false): Unit
Schedule named timer to deliver message after given delay, possibly repeating.
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.
name
identifier to be used with cancelTimer()
msg
message to be delivered
timeout
delay of first message delivery and between subsequent messages
repeat
send once if false, scheduleAtFixedRate if true
Annotations
@deprecated
Deprecated
(Since version Akka 2.6.0) Use startSingleTimer, startTimerWithFixedDelay or startTimerAtFixedRate instead. This has the same semantics as startTimerAtFixedRate, but startTimerWithFixedDelay is often preferred.
def →[B](y: B): (FSM[S, D], B)
Implicit
This member is added by an implicit conversion from FSM[S, D] toArrowAssoc[FSM[S, D]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@deprecated
Deprecated
(Since version 2.13.0) Use -> instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

Packages

FSM

Companion object FSM

trait FSM[S, D] extends Actor with Listeners with ActorLogging

Type Members

Value Members

Shadowed Implicit Value Members

Deprecated Value Members

Inherited from ActorLogging

Inherited from Listeners

Inherited from Actor

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromFSM[S, D] to any2stringadd[FSM[S, D]]

Inherited by implicit conversion StringFormat fromFSM[S, D] to StringFormat[FSM[S, D]]

Inherited by implicit conversion Ensuring fromFSM[S, D] to Ensuring[FSM[S, D]]

Inherited by implicit conversion ArrowAssoc fromFSM[S, D] to ArrowAssoc[FSM[S, D]]

Ungrouped

Packages

FSM

Companion object FSM

trait FSM[S, D] extends Actor with Listeners with ActorLogging

Type Members

Value Members

Shadowed Implicit Value Members

Deprecated Value Members

Inherited from ActorLogging

Inherited from Listeners

Inherited from Actor

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromFSM[S, D] to any2stringadd[FSM[S, D]]

Inherited by implicit conversion StringFormat fromFSM[S, D] to StringFormat[FSM[S, D]]

Inherited by implicit conversion Ensuring fromFSM[S, D] to Ensuring[FSM[S, D]]

Inherited by implicit conversion ArrowAssoc fromFSM[S, D] to ArrowAssoc[FSM[S, D]]

Ungrouped

FSM