Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
package my.akka
import akka.actor.{Actor, ActorRef, ActorSystem, PoisonPill, Props}
import akka.pattern.{Backoff, BackoffSupervisor, ask}
import scala.concurrent.Await
import scala.concurrent.duration._
class Child extends Actor {
println(s"[Child]: created. (path = ${this.self.path}, instance = ${this})")
override def preStart(): Unit = {
println(s"[Child]: preStart called. (path = ${this.self.path}, instance = ${this})")
super.preStart()
}
override def postStop(): Unit = {
println(s"[Child]: postStop called. (path = ${this.self.path}, instance = ${this})")
super.postStop()
}
override def preRestart(reason: Throwable, message: Option[Any]): Unit = {
println(s"[Child]: preRestart called with ($reason, $message). (path = ${this.self.path}, instance = ${this})")
super.preRestart(reason, message)
}
override def postRestart(reason: Throwable): Unit = {
println(s"[Child]: postRestart called with ($reason). (path = ${this.self.path}, instance = ${this})")
super.postRestart(reason)
}
def receive = {
case "boom" =>
throw new Exception("kaboom")
case "get ref" =>
sender() ! self
case a: Any =>
println(s"[Child]: received ${a}")
}
}
object Child {
def props: Props
= Props(new Child)
def backOffOnFailureProps: Props
= BackoffSupervisor.props(
Backoff.onFailure(
Child.props,
childName = "myEcho",
minBackoff = 1.seconds,
maxBackoff = 30.seconds,
randomFactor = 0.2 // adds 20% "noise" to vary the intervals slightly
))
def backOffOnStopProps: Props
= BackoffSupervisor.props(
Backoff.onStop(
Child.props,
childName = "myEcho",
minBackoff = 1.seconds,
maxBackoff = 10.seconds,
randomFactor = 0.2 // adds 20% "noise" to vary the intervals slightly
))
}
object BackoffSuperVisorApp {
def defaultSuperVisorCase(): Unit = {
println(
"""
|default ---------------------------
""".stripMargin)
val system = ActorSystem("app")
try{
/**
* Let's see if "hello" message is received by the child
*/
val child = system.actorOf(Child.props, "child")
Thread.sleep(100)
child ! "hello"
//[Child]: received hello
/**
* Now restart the child with an exception within its receive method
* and see if the `child` ActorRef is still valid (i.e. ActorRef incarnation remains same)
*/
child ! "boom"
Thread.sleep(200)
child ! "hello after normal exception"
//[Child]: received hello after normal exception
/**
* PoisonPill causes the child actor to `Stop`, different from restart.
* The ActorRef incarnation gets updated.
*/
child ! PoisonPill
Thread.sleep(200)
/**
* This causes delivery to deadLetter, since the "incarnation" of ActorRef `child` became obsolete
* after child is "Stopped"
*
* An incarnation is tied to an ActorRef (NOT to its internal actor instance)
* and the same incarnation means "you can keep using the same ActorRef"
*/
child ! "hello after PoisonPill"
// [akka://app/user/parent/child-1] Message [java.lang.String] without sender to Actor[akka://app/user/child#-767539042]
// was not delivered. [1] dead letters encountered.
Thread.sleep(200)
}
finally{
system.terminate()
Thread.sleep(500)
}
}
def backOffOnStopCase(): Unit ={
println(
"""
|backoff onStop ---------------------------
""".stripMargin)
val system = ActorSystem("app")
try{
/**
* Let's see if "hello" message is forwarded to the child
* by the backoff supervisor onStop
*/
implicit val futureTimeout: akka.util.Timeout = 1.second
val backoffSupervisorActor = system.actorOf(Child.backOffOnStopProps, "child")
Thread.sleep(100)
backoffSupervisorActor ! "hello to backoff supervisor" //forwarded to child
//[Child]: received hello to backoff supervisor
/**
* Now "Restart" the child with an exception from its receive method.
* As with the default supervisory strategy, the `child` ActorRef remains valid. (i.e. incarnation kept same)
*/
val child = Await.result(backoffSupervisorActor ? "get ref", 1.second).asInstanceOf[ActorRef]
child ! "boom"
Thread.sleep(2000)
child ! "hello to child after normal exception"
//[Child]: received hello to child after normal exception
/**
* Backoff Supervisor can still forward the message
*/
backoffSupervisorActor ! "hello to backoffSupervisorActor after normal exception"
//[Child]: received hello to backoffSupervisorActor after normal exception
Thread.sleep(200)
/**
* PoisonPill causes the child actor to `Stop`, different from restart.
* The `child` ActorRef incarnation gets updated.
*/
child ! PoisonPill
Thread.sleep(2000)
child ! "hello to child ref after PoisonPill"
//delivered to deadLetters
/**
* Backoff Supervisor can forward the message to its child with the new incarnation
*/
backoffSupervisorActor ! "hello to backoffSupervisorActor after PoisonPill"
//[Child]: received hello to backoffSupervisorActor after PoisonPill
Thread.sleep(200)
}
finally{
system.terminate()
Thread.sleep(500)
}
}
def backOffOnFailureCase(): Unit ={
println(
"""
|backoff onFailure ---------------------------
""".stripMargin)
val system = ActorSystem("app")
try{
/**
* Let's see if "hello" message is forwarded to the child
* by the backoff supervisor onFailure
*/
implicit val futureTimeout: akka.util.Timeout = 1.second
val backoffSupervisorActor = system.actorOf(Child.backOffOnFailureProps, "child")
Thread.sleep(100)
backoffSupervisorActor ! "hello to backoff supervisor" //forwarded to child
//[Child]: received hello to backoff supervisor
/**
* Now "Stop" the child with an exception from its receive method.
* You'll see the difference between "Restart" and "Stop" from here:
*/
val child = Await.result(backoffSupervisorActor ? "get ref", 1.second).asInstanceOf[ActorRef]
child ! "boom"
Thread.sleep(2000)
/**
* Note that this is after normal exception, not after PoisonPill,
* but child is completely "Stopped" and its ActorRef "incarnation" became obsolete
*
* So, the message to the `child` ActorRef is delivered to deadLetters
*/
child ! "hello to child after normal exception"
//causes delivery to deadLetter
/**
* Backoff Supervisor can still forward the message to the new child ActorRef incarnation
*/
backoffSupervisorActor ! "hello to backoffSupervisorActor after normal exception"
//[Child]: received hello to backoffSupervisorActor after normal exception
/**
* You can get a new ActorRef which represents the new incarnation
*/
val newChildRef = Await.result(backoffSupervisorActor ? "get ref", 1.second).asInstanceOf[ActorRef]
newChildRef ! "hello to new child ref after normal exception"
//[Child]: received hello to new child ref after normal exception
Thread.sleep(200)
/**
* No matter whether the supervisory strategy is default or backoff,
* PoisonPill causes the actor to "Stop", not "Restart"
*/
newChildRef ! PoisonPill
Thread.sleep(3000)
newChildRef ! "hello to new child ref after PoisonPill"
//delivered to deadLetters
Thread.sleep(200)
}
finally{
system.terminate()
Thread.sleep(500)
}
}
def main(args: Array[String]): Unit ={
defaultSuperVisorCase()
backOffOnStopCase()
backOffOnFailureCase()
}
}
default ---------------------------

[Child]: created.         (path = akka://app/user/child, instance = my.akka.Child@1456efca)
[Child]: preStart called. (path = akka://app/user/child, instance = my.akka.Child@1456efca)
[Child]: received hello
[Child]: preRestart called with (java.lang.Exception: kaboom, Some(boom)). (path = akka://app/user/child, instance = my.akka.Child@1456efca)
[Child]: postStop called. (path = akka://app/user/child, instance = my.akka.Child@1456efca)
[ERROR] [09/18/2017 02:17:30.555] [app-akka.actor.default-dispatcher-2] [akka://app/user/child] kaboom
java.lang.Exception: kaboom
        at my.akka.Child$$anonfun$receive$1.applyOrElse(BackoffSuperVisorApp.scala:35)
        at akka.actor.Actor.aroundReceive(Actor.scala:514)
        at akka.actor.Actor.aroundReceive$(Actor.scala:512)
        at my.akka.Child.aroundReceive(BackoffSuperVisorApp.scala:10)
        at akka.actor.ActorCell.receiveMessage(ActorCell.scala:527)
        at akka.actor.ActorCell.invoke(ActorCell.scala:496)
        at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)
        at akka.dispatch.Mailbox.run(Mailbox.scala:224)
        at akka.dispatch.Mailbox.exec(Mailbox.scala:234)
        at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
        at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
        at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
        at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

[Child]: created.         (path = akka://app/user/child, instance = my.akka.Child@5ec2b9c5)
[Child]: postRestart called with (java.lang.Exception: kaboom). (path = akka://app/user/child, instance = my.akka.Child@5ec2b9c5)
[Child]: preStart called. (path = akka://app/user/child, instance = my.akka.Child@5ec2b9c5)
[Child]: received hello after normal exception
[Child]: postStop called. (path = akka://app/user/child, instance = my.akka.Child@5ec2b9c5)
[INFO] [09/18/2017 02:17:30.955] [app-akka.actor.default-dispatcher-3] [akka://app/user/child] Message [java.lang.String] without sender to Actor[akka://app/user/child#-1104979952] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

You can see that preRestart and postRestart ARE called with Backoff.onStop.

backoff onStop ---------------------------

[Child]: created.         (path = akka://app/user/child/myEcho, instance = my.akka.Child@6bfb3e83)
[Child]: preStart called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@6bfb3e83)
[Child]: received hello to backoff supervisor
[Child]: preRestart called with (java.lang.Exception: kaboom, Some(boom)). (path = akka://app/user/child/myEcho, instance = my.akka.Child@6bfb3e83)
[ERROR] [09/18/2017 02:17:31.855] [app-akka.actor.default-dispatcher-6] [akka://app/user/child/myEcho] kaboom
java.lang.Exception: kaboom
        at my.akka.Child$$anonfun$receive$1.applyOrElse(BackoffSuperVisorApp.scala:35)
        at akka.actor.Actor.aroundReceive(Actor.scala:514)
        at akka.actor.Actor.aroundReceive$(Actor.scala:512)
        at my.akka.Child.aroundReceive(BackoffSuperVisorApp.scala:10)
        at akka.actor.ActorCell.receiveMessage(ActorCell.scala:527)
        at akka.actor.ActorCell.invoke(ActorCell.scala:496)
        at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)
        at akka.dispatch.Mailbox.run(Mailbox.scala:224)
        at akka.dispatch.Mailbox.exec(Mailbox.scala:234)
        at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
        at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
        at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
        at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

[Child]: postStop called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@6bfb3e83)
[Child]: created.         (path = akka://app/user/child/myEcho, instance = my.akka.Child@4d80e601)
[Child]: postRestart called with (java.lang.Exception: kaboom). (path = akka://app/user/child/myEcho, instance = my.akka.Child@4d80e601)
[Child]: preStart called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@4d80e601)
[Child]: received hello to child after normal exception
[Child]: received hello to backoffSupervisorActor after normal exception
[Child]: postStop called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@4d80e601)
[Child]: created.         (path = akka://app/user/child/myEcho, instance = my.akka.Child@6d3cd821)
[Child]: preStart called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@6d3cd821)
[Child]: received hello to backoffSupervisorActor after PoisonPill
[INFO] [09/18/2017 02:17:36.070] [app-akka.actor.default-dispatcher-7] [akka://app/user/child/myEcho] Message [java.lang.String] without sender to Actor[akka://app/user/child/myEcho#-1620028058] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
[Child]: postStop called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@6d3cd821)

You can see that preRestart and postRestart are NOT called with Backoff.onFailure.

backoff onFailure ---------------------------

[Child]: created.         (path = akka://app/user/child/myEcho, instance = my.akka.Child@496dd7f5)
[Child]: preStart called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@496dd7f5)
[Child]: received hello to backoff supervisor
[Child]: postStop called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@496dd7f5)
[ERROR] [09/18/2017 02:17:36.938] [app-akka.actor.default-dispatcher-5] [akka://app/user/child/myEcho] kaboom
java.lang.Exception: kaboom
        at my.akka.Child$$anonfun$receive$1.applyOrElse(BackoffSuperVisorApp.scala:35)
        at akka.actor.Actor.aroundReceive(Actor.scala:514)
        at akka.actor.Actor.aroundReceive$(Actor.scala:512)
        at my.akka.Child.aroundReceive(BackoffSuperVisorApp.scala:10)
        at akka.actor.ActorCell.receiveMessage(ActorCell.scala:527)
        at akka.actor.ActorCell.invoke(ActorCell.scala:496)
        at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)
        at akka.dispatch.Mailbox.run(Mailbox.scala:224)
        at akka.dispatch.Mailbox.exec(Mailbox.scala:234)
        at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
        at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
        at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
        at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

[Child]: created.         (path = akka://app/user/child/myEcho, instance = my.akka.Child@2f964777)
[Child]: preStart called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@2f964777)
[Child]: received hello to backoffSupervisorActor after normal exception
[INFO] [09/18/2017 02:17:38.952] [app-akka.actor.default-dispatcher-5] [akka://app/user/child/myEcho] Message [java.lang.String] without sender to Actor[akka://app/user/child/myEcho#-893737626] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
[Child]: received hello to new child ref after normal exception
[Child]: postStop called. (path = akka://app/user/child/myEcho, instance = my.akka.Child@2f964777)
[INFO] [09/18/2017 02:17:42.182] [app-akka.actor.default-dispatcher-3] [akka://app/user/child/myEcho] Message [java.lang.String] without sender to Actor[akka://app/user/child/myEcho#2043667113] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment