Module: Concurrent::Actor::Behaviour

Actors have modular architecture, which is achieved by combining a light core with chain of behaviours. Each message or internal event propagates through the chain allowing the behaviours react based on their responsibility.

• Linking:

  > Links the actor to other actors and sends actor’s events to them, like: :terminated, :paused, :resumed, errors, etc. Linked actor needs to handle those messages.

  listener = AdHoc.spawn name: :listener do
    lambda do |message|
      case message
      when Reference
        if message.ask!(:linked?)
          message << :unlink
        else
          message << :link
        end
      else
        puts "got event #{message.inspect} from #{envelope.sender}"
      end
    end
  end
  
  an_actor = AdHoc.spawn name: :an_actor, supervise: true, behaviour_definition: Behaviour.restarting_behaviour_definition do
    lambda { |message| raise 'failed'}
  end
  
  # link the actor
  listener.ask(an_actor).wait
  an_actor.ask(:fail).wait
  # unlink the actor
  listener.ask(an_actor).wait
  an_actor.ask(:fail).wait
  an_actor << :terminate!

  produces only two events, other events happened after unlinking

  got event #<RuntimeError: failed> from #<Concurrent::Actor::Reference /an_actor (Concurrent::Actor::Utils::AdHoc)>
  got event :reset from #<Concurrent::Actor::Reference /an_actor (Concurrent::Actor::Utils::AdHoc)>

• Awaits:

  > Accepts :await messages. Which allows to wait on Actor to process all previously send messages.

  actor << :a << :b
  actor.ask(:await).wait # blocks until :a and :b are processed

• Pausing:

  > Allows to pause actors on errors. When paused all arriving messages are collected and processed after the actor is resumed or reset. Resume will simply continue with next message. Reset also reinitialized context.

• Supervising:

  > Handles supervised actors. Handle configures what to do with failed child: :terminate!, :resume!, :reset!, or :restart!. Strategy sets :one_for_one (restarts just failed actor) or :one_for_all (restarts all child actors).

• Supervising:

  > Handles supervised actors. Handle configures what to do with failed child: :terminate!, :resume!, :reset!, or :restart!. Strategy sets :one_for_one (restarts just failed actor) or :one_for_all (restarts all child actors).

• ExecutesContext:

  > Delegates messages and events to AbstractContext instance.

• ErrorsOnUnknownMessage:

  > Simply fails when message arrives here. It’s usually the last behaviour.

• Termination:

  > Handles actor termination. Waits until all its children are terminated, can be configured on behaviour initialization.

• RemovesChild:

  > Removes terminated children.

If needed new behaviours can be added, or old one removed to get required behaviour.

• Context uses Array of behaviours and their construction parameters.

  [[Behaviour::SetResults, :terminate!],
   [Behaviour::RemovesChild],
   [Behaviour::Termination],
   [Behaviour::Linking],
   [Behaviour::Awaits],
   [Behaviour::ExecutesContext],
   [Behaviour::ErrorsOnUnknownMessage]]

• RestartingContext uses Array of behaviours and their construction parameters.

  [[Behaviour::SetResults, :pause!],
   [Behaviour::RemovesChild],
   [Behaviour::Termination],
   [Behaviour::Linking],
   [Behaviour::Pausing],
   [Behaviour::Supervising, :reset!, :one_for_one],
   [Behaviour::Awaits],
   [Behaviour::ExecutesContext],
   [Behaviour::ErrorsOnUnknownMessage]]