akka.contrib.throttle
Class TimerBasedThrottler

java.lang.Object
  akka.contrib.throttle.TimerBasedThrottler

All Implemented Interfaces:

Actor, ActorLogging, FSM<TimerBasedThrottler.State,TimerBasedThrottler.Data>, Listeners

public class TimerBasedThrottler
extends java.lang.Object
implements Actor, FSM<TimerBasedThrottler.State,TimerBasedThrottler.Data>

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

==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.

See Also:

Throttler

Nested Class Summary

static class	TimerBasedThrottler.Active$
static class	TimerBasedThrottler.Data
static class	TimerBasedThrottler.Data$
static class	TimerBasedThrottler.Idle$
static class	TimerBasedThrottler.Message
static class	TimerBasedThrottler.Message$
static interface	TimerBasedThrottler.State
static class	TimerBasedThrottler.Tick$

Nested classes/interfaces inherited from interface akka.actor.FSM

FSM.$minus$greater$, FSM.CurrentState<S>, FSM.CurrentState$, FSM.Event, FSM.Event$, FSM.Failure, FSM.Failure$, FSM.LogEntry<S,D>, FSM.LogEntry$, FSM.Normal$, FSM.NullFunction$, FSM.Reason, FSM.Shutdown$, FSM.State$, FSM.StateTimeout$, FSM.StopEvent, FSM.StopEvent$, FSM.SubscribeTransitionCallBack, FSM.SubscribeTransitionCallBack$, FSM.TransformHelper, FSM.Transition<S>, FSM.Transition$, FSM.UnsubscribeTransitionCallBack, FSM.UnsubscribeTransitionCallBack$

Nested classes/interfaces inherited from interface akka.actor.Actor

Actor.emptyBehavior$

Constructor Summary

TimerBasedThrottler(Throttler.Rate rate)

Method Summary

Throttler.Rate

rate()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface akka.actor.FSM

applyState, cancelTimer, currentState, debugEvent, generation, handleEvent, handleEventDefault, handleTransition, initialize, isStateTimerActive, isTimerActive, logTermination, makeTransition, nextState, nextStateData, onTermination, onTransition, postStop, processEvent, processMsg, receive, register, setStateTimeout, setTimer, startWith, stateData, stateFunctions, stateName, StateTimeout, stateTimeouts, stay, stop, stop, stop, terminate, terminateEvent, timeoutFuture, timerGen, timers, total2pf, transform, transitionEvent, when, whenUnhandled

Methods inherited from interface akka.actor.Actor

context, noSender, postRestart, preRestart, preStart, self, sender, supervisorStrategy, unhandled

Methods inherited from interface akka.routing.Listeners

gossip, listenerManagement, listeners

Methods inherited from interface akka.actor.ActorLogging

log

Constructor Detail

TimerBasedThrottler

public TimerBasedThrottler(Throttler.Rate rate)

Method Detail

rate

public Throttler.Rate rate()