akka.pattern

Class Backoff$

java.lang.Object

akka.pattern.Backoff$

public class Backoff$
extends java.lang.Object

Builds back-off options for creating a back-off supervisor. You can pass BackoffOptions to akka.pattern.BackoffSupervisor.props. An example of creating back-off options:

 Backoff.onFailure(childProps, childName, minBackoff, maxBackoff, randomFactor)
               .withManualReset
               .withSupervisorStrategy(
                 OneforOneStrategy(){
                    case e: GivingUpException => Stop
                    case e: RetryableException => Restart
                 }
               )

 

Field Summary

Fields

Modifier and Type	Field and Description
static Backoff$	MODULE$ Static reference to the singleton instance of this Scala object.

Constructor Summary

Constructors

Constructor and Description
Backoff$()

Method Summary

Modifier and Type	Method and Description
BackoffOptions	onFailure(Props childProps, java.lang.String childName, scala.concurrent.duration.FiniteDuration minBackoff, scala.concurrent.duration.FiniteDuration maxBackoff, double randomFactor) Back-off options for creating a back-off supervisor actor that expects a child actor to restart on failure.
BackoffOptions	onStop(Props childProps, java.lang.String childName, scala.concurrent.duration.FiniteDuration minBackoff, scala.concurrent.duration.FiniteDuration maxBackoff, double randomFactor) Back-off options for creating a back-off supervisor actor that expects a child actor to stop on failure.

Methods inherited from class java.lang.Object

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

Field Detail

MODULE$

public static final Backoff$ MODULE$

Static reference to the singleton instance of this Scala object.

Constructor Detail

Backoff$

public Backoff$()

Method Detail

onFailure

public BackoffOptions onFailure(Props childProps,
                                java.lang.String childName,
                                scala.concurrent.duration.FiniteDuration minBackoff,
                                scala.concurrent.duration.FiniteDuration maxBackoff,
                                double randomFactor)

Back-off options for creating a back-off supervisor actor that expects a child actor to restart on failure.

This explicit supervisor behaves similarly to the normal implicit supervision where if an actor throws an exception, the decider on the supervisor will decide when to Stop, Restart, Escalate, Resume the child actor.

When the Restart directive is specified, the supervisor will delay the restart using an exponential back off strategy (bounded by minBackoff and maxBackoff).

This supervisor is intended to be transparent to both the child actor and external actors. Where external actors can send messages to the supervisor as if it was the child and the messages will be forwarded. And when the child is Terminated, the supervisor is also Terminated. Transparent to the child means that the child does not have to be aware that it is being supervised specifically by this actor. Just like it does not need to know when it is being supervised by the usual implicit supervisors. The only caveat is that the ActorRef of the child is not stable, so any user storing the sender() ActorRef from the child response may eventually not be able to communicate with the stored ActorRef. In general all messages to the child should be directed through this actor.

An example of where this supervisor might be used is when you may have an actor that is responsible for continuously polling on a server for some resource that sometimes may be down. Instead of hammering the server continuously when the resource is unavailable, the actor will be restarted with an exponentially increasing back off until the resource is available again.

'''*** This supervisor should not be used with Akka Persistence child actors. Akka Persistence actors shutdown unconditionally on persistFailure()s rather than throw an exception on a failure like normal actors. onStop(akka.actor.Props, java.lang.String, scala.concurrent.duration.FiniteDuration, scala.concurrent.duration.FiniteDuration, double) should be used instead for cases where the child actor terminates itself as a failure signal instead of the normal behavior of throwing an exception. ***''' You can define another supervision strategy by using akka.pattern.BackoffOptions.withSupervisorStrategy on BackoffOptions.

Parameters:

childProps - the Props of the child actor that will be started and supervised

childName - name of the child actor

minBackoff - minimum (initial) duration until the child actor will started again, if it is terminated

maxBackoff - the exponential back-off is capped to this duration

randomFactor - after calculation of the exponential back-off an additional random delay based on this factor is added, e.g. 0.2 adds up to 20% delay. In order to skip this additional delay pass in 0.

Returns:

(undocumented)

onStop

public BackoffOptions onStop(Props childProps,
                             java.lang.String childName,
                             scala.concurrent.duration.FiniteDuration minBackoff,
                             scala.concurrent.duration.FiniteDuration maxBackoff,
                             double randomFactor)

Back-off options for creating a back-off supervisor actor that expects a child actor to stop on failure.

This actor can be used to supervise a child actor and start it again after a back-off duration if the child actor is stopped.

This is useful in situations where the re-start of the child actor should be delayed e.g. in order to give an external resource time to recover before the child actor tries contacting it again (after being restarted).

Specifically this pattern is useful for persistent actors, which are stopped in case of persistence failures. Just restarting them immediately would probably fail again (since the data store is probably unavailable). It is better to try again after a delay.

It supports exponential back-off between the given minBackoff and maxBackoff durations. For example, if minBackoff is 3 seconds and maxBackoff 30 seconds the start attempts will be delayed with 3, 6, 12, 24, 30, 30 seconds. The exponential back-off counter is reset if the actor is not terminated within the minBackoff duration.

In addition to the calculated exponential back-off an additional random delay based the given randomFactor is added, e.g. 0.2 adds up to 20% delay. The reason for adding a random delay is to avoid that all failing actors hit the backend resource at the same time.

You can retrieve the current child ActorRef by sending BackoffSupervisor.GetCurrentChild message to this actor and it will reply with BackoffSupervisor.CurrentChild containing the ActorRef of the current child, if any.

The BackoffSupervisordelegates all messages from the child to the parent of the BackoffSupervisor, with the supervisor as sender.

The BackoffSupervisor forwards all other messages to the child, if it is currently running.

The child can stop itself and send a PoisonPill to the parent supervisor if it wants to do an intentional stop.

Exceptions in the child are handled with the default supervisionStrategy, which can be changed by using BackoffOptions.withSupervisorStrategy(akka.actor.OneForOneStrategy) or BackoffOptions.withDefaultStoppingStrategy(). A Restart will perform a normal immediate restart of the child. A Stop will stop the child, but it will be started again after the back-off duration.

Parameters:

childProps - the Props of the child actor that will be started and supervised

childName - name of the child actor

minBackoff - minimum (initial) duration until the child actor will started again, if it is terminated

maxBackoff - the exponential back-off is capped to this duration

randomFactor - after calculation of the exponential back-off an additional random delay based on this factor is added, e.g. 0.2 adds up to 20% delay. In order to skip this additional delay pass in 0.

Returns:

(undocumented)