Actor Model in JS

Exploring the potential benefits of implementing APIs in the style of the Actor Model, even in single-threaded programming environments such as Javascript.

TODO

Actor system ActorSystem

• createSystem()
• system.actorOf(IActorFactory) -> ActorRef

Actors Actor

• actor.tell() - fire & forget message
• actor.ask() - ask & await async response from an actor
• actor.stop() - send a message instructing an actor to terminate

Actor context ActorContext

• context.stop(IActorRef) - allow an actor to be stopped via a ref
• context.gracefulStop(IActorRef) - allow an actor to be stopped via a ref with confirmation (for sequencing etc)
• context.actorOf(IActorFactory) - allow an actor to create more actors
• context.parent - allow an actor to access it's parent (in order to send it messages)
• context.self - allow an actor to access it's own ref (in order to send it's self messages)
• context.become(newHandler) - designate a new handler for future messages http://doc.akka.io/docs/akka/current/scala/actors.html#Graceful_Stop
• context.actorSelection(lookup: string) - allow actor lookups via paths, such as /system /deadletter etc

Actor receive method

• receive(payload, message, sender)

• sender.reply() for replying directly to a message

• mappedMethods define 1 function per message name

• handle cancellation of pending message should a new one override it

• pass state into mapped methods for encapsulated state management

• sender - allow every message access to an ActorRef that allow communication with the sender

  receive (payload message sender)
    switch payload
      case 'ping' sender.reply 'pong'
      default sender.reply 'missing'
    
  // callsite
  actor.ask 'ping'
    |> resp console.log 'resp:' + resp

Actor Lifecycle

• actorOf(...)

  • path is reserved
  • uuid is assigned
  • actor instance is created
  • preStart is called on instance

• Incarnation (restarting)

  • preRestart called on old instance
  • new instance replaces old
  • postRestart called on new instance

• Stop, context.stop() or PoisonPill

  • postStop is called on instance
  • actor is removed from the internal system register
  • Terminated is sent to watchers
  • path is free to be used again

• graceful stop http://doc.akka.io/docs/akka/current/scala/actors.html#Graceful_Stop

  • become() - designate a new handler for future messages

Actor References, Paths and Addresses

• actorOf() only ever creates a new actor, and it creates it as a direct child of the context on which this method is invoked (which may be any actor or actor system).
• /deadletters all messages sent to stopped or non-existing actors are re-routed here
• /system is the guardian actor for all system-created top-level actors, e.g. logging listeners or actors automatically deployed by configuration at the start of the actor system.