I have a actor like this:
class MyActor[T] extends Actor {
def receive = {
case Option1(t: T) =>
doWork(t) onComplete .....
case Option2 =>
}
def doWork(T): Future[T]{
}
}
Then I have an actor that inherits from the above:
class OtherActor extends MyActor {
val m = mutable.Map.empty[Int, User]
override def doWork(..) = {
//
}
}
Now in my OtherActor actor I want to add some methods to the receive method, how can I do this?
You can define the additional behavior in a Receive block inside OuterActor and chain that behavior to its parent's behavior with orElse:
class OtherActor extends MyActor {
val m = mutable.Map.empty[Int, User]
override def doWork(...) = ???
val otherBehavior: Receive = {
case ...
}
override def receive = otherBehavior.orElse(super.receive)
}
This is possible because Receive is just a type alias for PartialFunction[Any, Unit]. More information on composing actor behaviors is found here.
As a side note, you should prefer var m = immutable.Map.empty[Int, User] instead of val m = mutable.Map.empty[Int, User] in order to help avoid exposing the actor's state, as described in this answer.
Related
From Akka Cookbook, example from chapter Persistent Actors. In SamplePersistentActor.scala there is line of code that I don't quite understand. Here's the full code of 2 files.
SamplePersistentActor.scala:
class SamplePersistenceActor extends PersistentActor {
override val persistenceId = "unique-id-1"
var state = ActiveUsers()
def updateState(event:Event) = state = state.update(event)
val receiveRecover: Receive = {
case evt: Event => updateState(evt)
case SnapshotOffer(_, snapshot: ActiveUsers) => state = snapshot
}
override val receiveCommand: Receive = {
case UserUpdate(userId, Add) =>
persist(AddUserEvent(userId))(updateState)
case UserUpdate(userId, Remove) =>
persist(RemoveUserEvent(userId))(updateState)
case "snap" => saveSnapshot(state)
case "print" => println(state)
}
}
SamplePersistentModel.scala:
sealed trait UserAction
case object Add extends UserAction
case object Remove extends UserAction
case class UserUpdate(userId: String, action: UserAction)
sealed trait Event
case class AddUserEvent(userId: String) extends Event
case class RemoveUserEvent(userId: String) extends Event
case class ActiveUsers(users: Set[String] = Set.empty[String])
{
def update(evt: Event)= evt match {
case AddUserEvent(userId) => copy(users + userId)
case RemoveUserEvent(userId) => copy(users.filterNot(_ == userId))
}
override def toString = s"$users"
}
My question
What is the purpose of = state (or = this.state if I'm correct) in line def updateState(event:Event) = state = state.update(event). Why can't we just use def updateState(event:Event) = state.update(event)?
Found similar in documentation example.
In your sample code:
def updateState(event: Event) = state = state.update(event)
is equivalent to:
def updateState(event: Event) = { state = state.update(event) }
So, updateState is a function of Event => Unit, which is exactly what method persist expects as its second parameter:
persist(AddUserEvent(userId))(updateState)
Below is the signature of method persist in Akka PersistentActor:
trait PersistentActor extends Eventsourced with PersistenceIdentity {
// ...
def persist[A](event: A)(handler: A => Unit): Unit = {
internalPersist(event)(handler)
}
// ...
}
It expects a EventType => Unit handler code block as its second parameter to handle specific persistence business logic that generally involves updating internal states of the actor.
Why can't we just use def updateState(event:Event) = state.update(event)?
The reason for the reassignment to the state variable is that update creates a new object. In other words, calling state.update doesn't mutate state; it makes a copy of state with the updated information.
This is the case with the example that you referenced:
var state = ExampleState()
def updateState(event: Evt): Unit =
state = state.updated(event)
Looking at the code for ExampleState, we see that the updated method actually creates a new ExampleState object:
def updated(evt: Evt): ExampleState = copy(evt.data :: events)
Say I have the below:
type Receive = PartialFunction[Any, Unit]
trait Functionality {
/**
* A set containing all Receive functions
*/
var allReceives: Set[Receive] = Set[Receive]()
}
Now other trait's can extend Functionality and do awesome stuff. Example:
trait LoadBalancer extends Functionality{
def body:Receive = {
case ...
}
allReceives += body
}
And ultimately my class:
class Main with LoadBalancer with SecurityFunctionality
with OtherFunctionality with Functionality{
def receive = {
case x if allReceives.foldLeft(false) { (z, f) => if (f isDefinedAt x) { f(x); true } else z } == true => ()
}
def body: Receive = {
}
allReceives += body
}
Question: What I wish to do is, in Main I need to call body function of all the traits that I have inherited. This way my code can be loosely coupled and I can add/remove functionality at a go.
The above works, but I do not like it as the compiler cannot guarantee that any trait that extends Functionality should add its body to allReceives.
I cannot declare def body:Receive in Functionality as then my implementation in Main will override body implementations of other traits. I am sure there should be a smarter way!
On second thought, composition really might be a better option here. This is a simpler solution, without any funny "abstract override"s:
object Main {
type Receive = PartialFunction[Any, Unit]
trait Receiver {
def receive: Receive
}
class LoadBalancer extends Receiver {
override def receive: Receive = {
case "one" => println("LoadBalancer received one")
}
}
class OtherFunctionality extends Receiver {
override def receive: Receive = {
case "two" => println("OtherFunctionality received two")
}
}
class MainFunctionality extends Receiver {
override def receive: Receive = {
case "three" => println("MainFunctionality received three")
}
}
class CompositeReceiver(receivers: List[Receiver]) extends Receiver {
override def receive: Receive = {
case msg =>
receivers.find(_.receive.isDefinedAt(msg)) map (_.receive(msg))
}
}
def main(args: Array[String]) {
val main = new CompositeReceiver(List(new OtherFunctionality, new LoadBalancer, new MainFunctionality))
main.receive("one")
main.receive("two")
main.receive("three")
}
}
This does not really answer your question, but here is a solution using the stackable traits pattern. Alas you still need to call super.receive as the last case in each trait, but I could not find a way around that yet.
object Main {
type Receive = PartialFunction[Any, Unit]
trait Receiver {
def receive: Receive
}
trait LoadBalancer extends Receiver {
abstract override def receive: Receive = {
case "one" => println("LoadBalancer received one")
case msg => super.receive(msg)
}
}
trait OtherFunctionality extends Receiver {
abstract override def receive: Receive = {
case "two" => println("OtherFunctionality received two")
case msg => super.receive(msg)
}
}
class Main extends Receiver {
override def receive: Receive = {
case "three" => println("Main received three")
}
}
def main(args: Array[String]) {
val main = new Main with OtherFunctionality with LoadBalancer
main.receive("one")
main.receive("two")
main.receive("three")
}
}
I have to actor classes which looks similar to this form:
class ActorSupervisorOne(prop: Prop) extends Actor {
val dbSuper = context.actorOf(prop)
val subActor = context.actorOf(Props(new SubActorClass(dbSuper) with **SomeHandlersOne**))
def receive = {
case msg =>
subActor forward msg
}
}
class ActorSupervisorTwo(prop: Prop) extends Actor {
val dbSuper = context.actorOf(prop)
val subActor = context.actorOf(Props(new SubActorClass(dbSuper) with **SomeHandlersTwo**))
def receive = {
case msg =>
subActor forward msg
}
}
The only difference between them in mixing trait. Abstract it with type parameter or abstract type member won't work. I've tried the following solution, but it looks ugly and still have code duplication:
abstract class Super extends Actor {
_: {
val handler: Props
} =>
lazy val actor = context.actorOf(handler)
def receive = {
case msg =>
actor forward msg
}
}
class ActorSupervisorOne(val dbSuper: ActorRef) extends Super {
val handler = Props(new SubActorClass(dbSuper) with SomeHandlersOne)
actor
}
class ActorSupervisorTwo(val dbSuper: ActorRef) extends Super {
val handler = Props(new SubActorClass(dbSuper) with SomeHandlersTwo)
actor
}
But in this case i have to call actor to initialize it correctly or it won't work. Are there any other solution how this can be reduced?
You could probably use reflection to choose the SomeHandlersXYZ at runtime, but if you don't want to resort to reflection then I don't think that there is a way of achieving what you want without at least duplicating the subactor instantiation code (see this answer of mine for an explanation). You could do it the following way (sketched), where you basically pass in a factory function:
class ActorSupervisor(prop: Prop, getSubActor: Actor => SubActorClass) extends Actor {
val dbSuper = context.actorOf(prop)
val subActor = context.actorOf(Props(getSubActor(dbSuper)))
def receive = {
case msg =>
subActor forward msg
}
}
val asOne = new ActorSupervisor(..., a => new SubActorClass(a) with SomeHandlersOne)
val asTwo = new ActorSupervisor(..., a => new SubActorClass(a) with SomeHandlersTwo)
What about this solution:
class ActorSupervisor(subActor: => Actor) extends Actor {
val actor = context.actorOf(Props(statsProps))
def receive = {
case msg =>
actor forward msg
}
}
and then, like in Malte Schwerhoff you can create new actor like this:
val first = new ActorSupervisor(new SubActorClass(...) with SomeHandlersOne)
I think that more elegant colution can be achived with macros, but i'm not good at them
You can pass the puck on onReceive.
class ClassMixed(params: Options*)
extends BaseClass(params: _*)
with Mixin {
override def receive =
mixinReceive orElse receive
}
where Mixin has a method called mixinReceive and BaseClass overrides receive
trait A extends Actor {
private val s = Set[Int]()
override def act() {
loop {
react {
// case code that modifies s
}
}
}
}
trait B extends Actor {
private val t = Set[String]()
override def act() {
loop {
react {
// case code that modifies t
}
}
}
}
val c = new C with A with B //...?
What I really want is some sort of auto-combining of B.act() and C.act(), but with trait mix-ins, only B.act() will be called. Is there an easy way to accomplish this?
EDIT: Here is a half-solution I've found. I say 'half' because the original traits no longer extend Actor, and C with A with B needs to be defined as a class as opposed to dynamic mixing-in. Maybe I should call it a 'quarter-solution'?
Maybe you could make a trait that forwards the message on to a list of other Actors, so that you don't have to modify A or B:
trait C extends Actor {
private val acts: Seq[Actor] = Seq(new A{}, new B{})
override def act() {
acts foreach (_.start)
loop {
react { case x => acts foreach { _ ! x } }
}
}
}
You could of course leave acts abstract or override it with a different set when you instantiate this.
Extending the Actor class:
import actors.Actor
class MixableActor extends Actor {
protected var acts = List[PartialFunction[Any, Unit]]()
final override def act() {
loop {
react {
acts.reduce((a, b) => a orElse b)
}
}
}
final def receive(act: PartialFunction[Any, Unit]) {
acts = act :: acts
}
}
Sample Code:
abstract class Node extends MixableActor {
...
}
trait User extends MixableActor {
val files = scala.collection.mutable.Set[Data]()
}
trait Provider extends User {
receive({
case ("provide", file: Data) =>
provide(file)
}: PartialFunction[Any, Unit])
}
trait Consumer extends User {
receive({
case ("consume", file: Data) =>
consume(file)
}: PartialFunction[Any, Unit])
}
Sample Usage:
val provider = new Node with Provider
val consumer = new Node with Consumer
val provider_and_consumer = new Node with Provider with Consumer
Consider these two traits:
trait Poked extends Actor {
override def receive = {
case Poke(port, x) => ReceivePoke(port, x)
}
def ReceivePoke(port: String, x: Any)
}
trait Peeked extends Actor {
override def receive = {
case Peek(port) => ReceivePeek(port)
}
def ReceivePeek(port: String)
}
Now consider I can create a new Actor that implements both traits:
val peekedpoked = actorRef(new Actor extends Poked with Peeked)
How do I compose the receive handlers? i.e., the receiver should be something like the following code, though "automatically generated" (i.e., all traits should compose):
def receive = (Poked.receive: Receive) orElse (Peeked.receive: Receive) orElse ...
You can use super[T] to reference members of particular super classes/traits.
For example:
trait IntActor extends Actor {
def receive = {
case i: Int => println("Int!")
}
}
trait StringActor extends Actor {
def receive = {
case s: String => println("String!")
}
}
class IntOrString extends Actor with IntActor with StringActor {
override def receive = super[IntActor].receive orElse super[StringActor].receive
}
val a = actorOf[IntOrString].start
a ! 5 //prints Int!
a ! "Hello" //prints String!
Edit:
In response to Hugo's comment, here's a solution that allows you to compose the mixins without having to manually wire their receives together. Essentially it involves a base trait with a mutable List[Receive], and each mixed-in trait calls a method to add its own receive to the list.
trait ComposableActor extends Actor {
private var receives: List[Receive] = List()
protected def registerReceive(receive: Receive) {
receives = receive :: receives
}
def receive = receives reduce {_ orElse _}
}
trait IntActor extends ComposableActor {
registerReceive {
case i: Int => println("Int!")
}
}
trait StringActor extends ComposableActor {
registerReceive {
case s: String => println("String!")
}
}
val a = actorOf(new ComposableActor with IntActor with StringActor).start
a ! 5 //prints Int!
a ! "test" //prints String!
The only thing to keep in mind is that the order of the receives should not be important, since you won't be able to easily predict which one is first in the chain, though you could solve that by using a mutable hashmap instead of a list.
You can use empty Receive in base actor class and chain receives in their definitions.
Sample for Akka 2.0-M2:
import akka.actor.Actor
import akka.actor.Props
import akka.event.Logging
import akka.actor.ActorSystem
class Logger extends Actor {
val log = Logging(context.system, this)
override def receive = new Receive {
def apply(any: Any) = {}
def isDefinedAt(any: Any) = false
}
}
trait Errors extends Logger {
override def receive = super.receive orElse {
case "error" => log.info("received error")
}
}
trait Warns extends Logger {
override def receive = super.receive orElse {
case "warn" => log.info("received warn")
}
}
object Main extends App {
val system = ActorSystem("mysystem")
val actor = system.actorOf(Props(new Logger with Errors with Warns), name = "logger")
actor ! "error"
actor ! "warn"
}