Packages

c

akka.contrib.throttle

TimerBasedThrottler

class TimerBasedThrottler extends Actor with FSM[State, Data]

A throttler that uses a timer to control the message delivery rate.

Throttling

A throttler is an actor that is defined through a target actor and a rate (of type akka.contrib.throttle.Throttler.Rate). You set or change the target and rate at any time through the akka.contrib.throttle.Throttler.SetTarget and akka.contrib.throttle.Throttler.SetRate messages, respectively. When you send the throttler any other message msg, it will put the message msg into an internal queue and eventually send all queued messages to the target, at a speed that respects the given rate. If no target is currently defined then the messages will be queued and will be delivered as soon as a target gets set.

A throttler understands actor messages of type akka.contrib.throttle.Throttler.SetTarget, akka.contrib.throttle.Throttler.SetRate, in addition to any other messages, which the throttler will consider as messages to be sent to the target.

Transparency

Notice that the throttler forwards messages, i.e., the target will see the original message sender (and not the throttler) as the sender of the message.

Persistence

Throttlers usually use an internal queue to keep the messages that need to be sent to the target. You therefore cannot rely on the throttler's inbox size in order to learn how much messages are outstanding.

It is left to the implementation whether the internal queue is persisted over application restarts or actor failure.

Processing messages

The target should process messages as fast as possible. If the target requires substantial time to process messages, it should distribute its work to other actors (using for example something like a BalancingDispatcher), otherwise the resulting system will always work below the threshold rate.

Example: Suppose the throttler has a rate of 3msg/s and the target requires 1s to process a message. This system will only process messages at a rate of 1msg/s: the target will receive messages at at most 3msg/s but as it handles them synchronously and each of them takes 1s, its inbox will grow and grow. In such a situation, the target should distribute its messages to a set of worker actors so that individual messages can be handled in parallel.

Example

For example, if you set a rate like "3 messages in 1 second", the throttler will send the first three messages immediately to the target actor but will need to impose a delay before sending out further messages:

// A simple actor that prints whatever it receives
class Printer extends Actor {
  def receive = {
    case x => println(x)
  }
}

val printer = system.actorOf(Props[Printer], "printer")

// The throttler for this example, setting the rate
val throttler = system.actorOf(Props(classOf[TimerBasedThrottler], 3 msgsPer 1.second))

// Set the target
throttler ! SetTarget(Some(printer))
// These three messages will be sent to the printer immediately
throttler ! "1"
throttler ! "2"
throttler ! "3"
// These two will wait at least until 1 second has passed
throttler ! "4"
throttler ! "5"

Implementation notes

This throttler implementation internally installs a timer that repeats every rate.durationInMillis and enables rate.numberOfCalls additional calls to take place. A TimerBasedThrottler uses very few system resources, provided the rate's duration is not too fine-grained (which would cause a lot of timer invocations); for example, it does not store the calling history as other throttlers may need to do.

However, a TimerBasedThrottler only provides weak guarantees on the rate (see also this blog post):

  • Only delivery times are taken into account: if, for example, the throttler is used to throttle requests to an external web service then only the start times of the web requests are considered. If a web request takes very long on the server then more than rate.numberOfCalls-many requests may be observed on the server in an interval of duration rate.durationInMillis().
  • There may be intervals of duration rate.durationInMillis() that contain more than rate.numberOfCalls message deliveries: a TimerBasedThrottler only makes guarantees for the intervals of its own timer, namely that no more than rate.numberOfCalls-many messages are delivered within such intervals. Other intervals on the timeline may contain more calls.

For some applications, these guarantees may not be sufficient.

Known issues

  • If you change the rate using SetRate(rate), the actual rate may in fact be higher for the overlapping period (i.e., durationInMillis()) of the new and old rate. Therefore, changing the rate frequently is not recommended with the current implementation.
  • The queue of messages to be delivered is not persisted in any way; actor or system failure will cause the queued messages to be lost.
Source
TimerBasedThrottler.scala
See also

akka.contrib.throttle.Throttler

Linear Supertypes
FSM[TimerBasedThrottler.State, Data], ActorLogging, Listeners, Actor, AnyRef, Any
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  1. TimerBasedThrottler
  2. FSM
  3. ActorLogging
  4. Listeners
  5. Actor
  6. AnyRef
  7. Any
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  1. by any2stringadd
  2. by StringFormat
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Instance Constructors

  1. new TimerBasedThrottler(rate: Rate)

Type Members

  1. final class TransformHelper extends AnyRef
    Definition Classes
    FSM
  2. type Event = actor.FSM.Event[Data]
    Definition Classes
    FSM
  3. type Receive = PartialFunction[Any, Unit]
    Definition Classes
    Actor
  4. type State = actor.FSM.State[TimerBasedThrottler.State, Data]
    Definition Classes
    FSM
  5. type StateFunction = PartialFunction[Event, State]
    Definition Classes
    FSM
  6. type StopEvent = actor.FSM.StopEvent[TimerBasedThrottler.State, Data]
    Definition Classes
    FSM
  7. type Timeout = Option[FiniteDuration]
    Definition Classes
    FSM
  8. type TransitionHandler = PartialFunction[(TimerBasedThrottler.State, TimerBasedThrottler.State), Unit]
    Definition Classes
    FSM

Value Members

  1. val ->: actor.FSM.->.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.

    Definition Classes
    FSM
  2. val Event: actor.FSM.Event.type
    Definition Classes
    FSM
  3. val StateTimeout: actor.FSM.StateTimeout.type

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

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

    Definition Classes
    FSM
  4. val StopEvent: actor.FSM.StopEvent.type
    Definition Classes
    FSM
  5. 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

    Definition Classes
    FSM
  6. implicit val context: ActorContext

    Stores the context for this actor, including self, and sender.

    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!

    akka.actor.ActorContext is the Scala API. getContext returns a akka.actor.UntypedActorContext, which is the Java API of the actor context.

    Definition Classes
    Actor
  7. final def goto(nextStateName: TimerBasedThrottler.State): 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

    Definition Classes
    FSM
  8. 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 akka.actor.Actor#preStart and akka.actor.Actor#postRestart

    An initial currentState -> currentState notification will be triggered by calling this method.

    Definition Classes
    FSM
    See also

    #startWith

  9. 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.

    Definition Classes
    FSM
  10. def log: LoggingAdapter
    Definition Classes
    ActorLogging
  11. final def nextStateData: Data

    Return next state data (available in onTransition handlers)

    Return next state data (available in onTransition handlers)

    Definition Classes
    FSM
  12. 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.

    Definition Classes
    FSM
  13. 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.

    Definition Classes
    FSM
  14. 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] )
  15. 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
  16. def preRestart(reason: Throwable, message: Option[Any]): Unit

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

    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] )
  17. 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] )
  18. var rate: Rate
  19. def receive: Receive

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

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

    Definition Classes
    FSM → Actor
  20. 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
  21. 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 akka.actor.ActorSystem.

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

    Definition Classes
    Actor
  22. final def setStateTimeout(state: TimerBasedThrottler.State, timeout: Timeout): Unit

    Set state timeout explicitly.

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

    Definition Classes
    FSM
  23. 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

    Definition Classes
    FSM
  24. final def startWith(stateName: TimerBasedThrottler.State, stateData: Data, 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 akka.actor.Actor#preStart and akka.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

    Definition Classes
    FSM
  25. final def stateData: Data

    Return current state data (i.e.

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

    Definition Classes
    FSM
  26. final def stateName: TimerBasedThrottler.State

    Return current state name (i.e.

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

    Definition Classes
    FSM
  27. 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

    Definition Classes
    FSM
  28. final def stop(reason: Reason, stateData: Data): State

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

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

    Definition Classes
    FSM
  29. 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.

    Definition Classes
    FSM
  30. 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".

    Definition Classes
    FSM
  31. 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
  32. implicit final def total2pf(transitionHandler: (TimerBasedThrottler.State, TimerBasedThrottler.State) ⇒ 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.

    Definition Classes
    FSM
  33. final def transform(func: StateFunction): TransformHelper
    Definition Classes
    FSM
  34. 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 akka.actor.DeathPactException (in case of an unhandled akka.actor.Terminated message) or publishes an akka.actor.UnhandledMessage to the actor's system's akka.event.EventStream

    Definition Classes
    Actor
  35. final def when(stateName: TimerBasedThrottler.State, 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

    Definition Classes
    FSM
  36. 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.

    Definition Classes
    FSM