Akka Actor life cycle

Akka provides life cycle methods for Actor. There are following methods to which you can override and provide specific implementation accordingly.

Akka Actor life cycle methods

preStart()
postStop()
preRestart(reason: Throwable, message: Option[Any])
postRestart(reason: Throwable)

Akka Actor Life Cycle

1) preStart()

This is overridable method, so you can override preStart() method to provide specific implementation for an Actor. It is invoked right after the starting of Actor and when an Actor is first created. In case of restart, it is called by postRestart() method.

Akka Actor preStart() Method Example

 import akka.actor._ import akka.actor.TypedActor.PreStart  class LifeCyleMethodsExample extends Actor{   def receive = {     case msg:String => println(msg+” “+self.path.name);  // Getting name of Actor   }   override def preStart(){    // overriding preStart method     println(“preStart method is called”);   } }  object ActorMain{   def main(args:Array[String]){     val actorSystem = ActorSystem(“ActorSystem”);     val actor = actorSystem.actorOf(Props[LifeCyleMethodsExample],”RootActor”);     actor ! “Hello”   } } 

Output:

preStart method is called Hello RootActor

2) postStop()

You can override this method also. After stopping an actor, postStop() method is called. It is an asynchronous method. This method is used to release resources after stopping the Actor. It may be used for deregistering this Actor. Messages sent to a stopped actor will be redirected to the deadLetters of the ActorSystem.

Akka Actor PostStop() Method Example

 import akka.actor._ import akka.actor.TypedActor.PreStart  class LifeCyleMethodsExample extends Actor{   def receive = {     case msg:String => println(msg+” “+self.path.name);  // Getting name of Actor   }   override def postStop(){    // Overriding postStop method     println(“postStop method is called”);   } }  object ActorMain{   def main(args:Array[String]){     val actorSystem = ActorSystem(“ActorSystem”);     val actor = actorSystem.actorOf(Props[LifeCyleMethodsExample],”RootActor”);     actor ! “Hello”          println(“stopping Actor”);     actorSystem.stop(actor);      // Stopping Actor by passing actor reference.    } } 

Output:

Hello RootActor stopping Actor postStop method is called

3) preRestart()

Actor may be restarted in case an exception is thrown. When an actor is restarted, preRestart() method is invoked. The preRestart() method is called with the exception that caused the restart. By default it disposes of all children Actors and then calls postStop() method.

Akka Actor preRestart() Method Example

 println(msg+” “+self.path.name);  // Getting name of Actor     var a:Int =  10/0;      // ArithmethicException occurred   }   override def preRestart(reason:Throwable, message: Option[Any]){    // Overriding preRestart method     println(“preRestart method is called”);     println(“Reason: “+reason)   } }  object ActorMain{   def main(args:Array[String]){     val actorSystem = ActorSystem(“ActorSystem”);     val actor = actorSystem.actorOf(Props[LifeCyleMethodsExample],”RootActor”);     actor ! “Hello”   } } 

Output:

Hello RootActor preRestart method is called Reason: java.lang.ArithmeticException: / by zero

4) postRestart()

This method is invoked right after restarting of newly created Actor. It is used to allow reinitialization after an Actor crash due to exception.

Akka Actor postRestart() Method Example

 import akka.actor._  class LifeCyleMethodsExample extends Actor{   def receive = {     case msg:String => println(msg+” “+self.path.name);  // Getting name of Actor     var a:Int =  10/0;      // ArithmethicException occurred   }   override def postRestart(reason:Throwable){    // Overriding preRestart method     println(“postRestart method is called”);     println(“Reason: “+reason)   } }  object ActorMain{   def main(args:Array[String]){     val actorSystem = ActorSystem(“ActorSystem”);     val actor = actorSystem.actorOf(Props[LifeCyleMethodsExample],”RootActor”);     actor ! “Hello”   } } 

Output

Hello RootActor postRestart method is called Reason: java.lang.ArithmeticException: / by zero

Akka Complete LifeCyle Example

 import akka.actor.{Actor,ActorSystem, Props}  class RootActor extends Actor{   def receive = {     case msg => println(“Message received: “+msg);     10/0;   }   override def preStart(){     super.preStart();     println(“preStart method is called”);   }   override def postStop(){     super.postStop();     println(“postStop method is called”);   }   override def preRestart(reason:Throwable, message: Option[Any]){     super.preRestart(reason, message);     println(“preRestart method is called”);     println(“Reason: “+reason);   }   override def postRestart(reason:Throwable){     super.postRestart(reason);     println(“postRestart is called”);     println(“Reason: “+reason);   } } 

Output:

preStart method is called Message received: Hello Stoping actor postStop method is called preRestart method is called Reason: java.lang.ArithmeticException: / by zero preStart method is called postRestart is called Reason: java.lang.ArithmeticException: / by zero [ERROR] [01/12/2017 15:22:18.475] [ActorSystem-akka.actor.default-dispatcher-5]  [akka://ActorSystem/user/RootActor] / by zero java.lang.ArithmeticException: / by zero at RootActor$$anonfun$receive$1.applyOrElse(ActorLifeCyle.scala:6) at akka.actor.Actor$class.aroundReceive(Actor.scala:496) at RootActor.aroundReceive(ActorLifeCyle.scala:3) at akka.actor.ActorCell.receiveMessage(ActorCell.scala:526) at akka.actor.ActorCell.invoke(ActorCell.scala:495) 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 scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) postStop method is called

Next TopicAkka Actor Send Messages

Akka Actor Life Cycle

Akka Actor life cycle

Akka Actor life cycle methods

1) preStart()

Akka Actor preStart() Method Example

2) postStop()

Akka Actor PostStop() Method Example

3) preRestart()

Akka Actor preRestart() Method Example

4) postRestart()

Akka Actor postRestart() Method Example

Akka Complete LifeCyle Example

Verbal Reasoning | Syllogism 4

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