Running Akka Streams with Actors
Actors can contain streams, initialize them and use Actor Supervision to define a strategy for the Actor and its stream when the stream returns an error.
Akka Streams Supervision can Resume or Restart a stage, unbeknown to the Actor, or Stop the stream causing the Actor to supervise.
Actor/Akka Streams hybrid applications have the benefits of pure Actor applications with less boilerplate.
CallStream is a generic Actor for running streams. It’s created with a RunnableGraph. SourceQueue must be the Source of the RunnableGraph to take messages received by the Actor. An Actor message of the right type is offered to SourceQueue in CallStream’s receive method. An OfferResult Future is piped back to CallStream’s offerResultHandler it logs a warning if the message was dropped or throws an exception if the queue can’t accept it. Accepted messages are processed by the stream. Exceptions are handled by Actor Supervisors.
CallStreamSupervisor is a generic actor supervisor that creates CallStream with a RunnableGraph and handles its errors. If CallStream’s offerResultHandler throws an exception CallStreamSupervisor has a decider that will either Restart CallStream, Stop it, or Escalate the exception. Messages received by CallStreamSupervisor are forwarded to CallStream. Actors sending messages directly to CallStream should put a DeathWatch on it.
CallStream and CallStreamSupervisor are provided for convenience, users can create their own actors to manage and run streams.
Actor Ref used as a stream’s sink
An Actor Supervisor can create both an actor running a stream and another actor used as its Sink.
Sink.actorRef forwards the message pushed from the last flow to another actor. The supervisor creates the sink actor then the stream actor with the sink actorRef. DeathWatch is put on the sink actor, when it dies, the stream actor is restarted with a new actorRef: example.
Sink.actorRefWithAck adds backpressure when the sink Actor acknowledges messages.