Basics

Actors are higher level concurrency models which receive messages, process them and update their internal state. Within processing actor can spawn finite number of children actors and send finite number of messages to other actors.

This can be visualized as a simple diagram:

Usage

The basic actors usage requires defining a Stateful for describing actor's behavior. Then actor's creation is done with passing supervision manner, initial state and mentioned Stateful.

Imports required for example:

import java.io.File

import zio.actors.Actor.Stateful
import zio.actors._
import zio.{UIO, ZIO}

Our domain that will be used:

sealed trait Command[+_]
case class DoubleCommand(value: Int) extends Command[Int]

Our actor's assigment will be to double received values. Here's the Stateful implementation:

val stateful = new Stateful[Any, Unit, Command] {
  override def receive[A](state: Unit, msg: Command[A], context: Context): UIO[(Unit, A)] =
    msg match {
      case DoubleCommand(value) => ZIO.succeed(((), value * 2))
    }
}

Then we are ready to instantiate the actor and fire off messages:

for {
  system  <- ActorSystem("mySystem")
  actor   <- system.make("actor1", Supervisor.none, (), stateful)
  doubled <- actor ! DoubleCommand(42)
} yield doubled

This is fire-and-forget interaction pattern where caller is blocked until recipients confirms enqueueing message in mailbox queue. There's also ask interaction pattern where for caller sending a message is completed after receiving response message from recipient. It's performed via ? method.

From recipient's point of view these two interaction patterns are indistinguishable.

Configuration

For each ActorSystem created there should be a config entry in configuration file. By default configuration file is expected to be at ./src/main/resources/application.conf. Exemplary configuration entry for an ActorSystem named Test1:

Test1.zio.actors.remoting {
  hostname = "127.0.0.1"
  port = 1234
}

Custom configuration file can be provided when instantiating ActorSystem:

ActorSystem("mySystem", Some(new File("./my/custom/path/app.conf")))