ActorSystem singleton injection - scala

Question

In my project, I have to use actors and schedulers. All my need can be accomplished by using one actor system only. But I need the schedulers and actors in more than one class. So my question, if I should inject the actor system in each class like below, will it create only one actor System or more than one? I don't want to create more than one actor system since it is not a recommended practice.
import akka.actor.ActorSystem
#Singleton
class someClass #Inject()(actorSystem: ActorSystem){....} // abstract class ActorSystem extends ActorRefFactory
#Singleton
class anotherClass #Inject()(actorSystem: ActorSystem){....}
Or I should create another object and declare an actor system within it and use it everywhere like this:
import akka.actor._
object actorSystemObject {
val system: ActorSystem = ActorSystem()
}
Which method will be better and standard?

Answer 1

Assuming you are using guice, try providing a singleton like so
#Provides
#Singleton
def getActorSystem: ActorSystem = ActorSystem()
for example
import akka.actor.ActorSystem
import com.google.inject.{AbstractModule, Guice, Inject, Injector, Provides, Singleton}
import scala.jdk.CollectionConverters._
class MyModule extends AbstractModule {
#Provides
#Singleton
def getActorSystem: ActorSystem = ActorSystem()
}
#Singleton
class SomeClass #Inject()(actorSystem: ActorSystem) {
println(actorSystem.hashCode())
}
#Singleton
class SomeOtherClass #Inject()(actorSystem: ActorSystem) {
println(actorSystem.hashCode())
}
object Hello extends App {
val injector: Injector = Guice.createInjector(List(new MyModule).asJava)
injector.getInstance(classOf[SomeClass])
injector.getInstance(classOf[SomeOtherClass])
}
which outputs something like
1731656333
1731656333
where we see the same ActorSystem is injected as evident by the same hashCode.
Say we remove #Singleton provider like so
#Provides
def getActorSystem: ActorSystem = ActorSystem()
then hashCodes differ, for example,
2050462663
1117871068