Question

我正在Akka溪流上切牙，并按照以下方式做了一个斐波纳契出版商用户示例。但是，我还不太了解最初如何生成需求以及它与订阅者的请求策略有什么关系。有人可以解释一下吗？

FibonacciPublisher：

class FibonacciPublisher extends ActorPublisher[Long] with ActorLogging {
  private val queue = Queue[Long](0, 1)

  def receive = {
    case Request(_) => // _ is the demand
      log.debug("Received request; demand = {}.", totalDemand)
      publish
    case Cancel =>
      log.info("Stopping.")
      context.stop(self)
    case unknown => log.warning("Received unknown event: {}.", unknown)
  }

  final def publish = {
    while (isActive && totalDemand > 0) {
      val next = queue.head
      queue += (queue.dequeue + queue.head)

      log.debug("Producing fibonacci number: {}.", next)

      onNext(next)

      if (next > 5000) self ! Cancel
    }
  }
}

FibonacciSubscriber：

class FibonacciSubscriber extends ActorSubscriber with ActorLogging {
  val requestStrategy = WatermarkRequestStrategy(20)

  def receive = {
    case OnNext(fib: Long) =>
      log.debug("Received Fibonacci number: {}", fib)

      if (fib > 5000) self ! OnComplete
    case OnError(ex: Exception) =>
      log.error(ex, ex.getMessage)
      self ! OnComplete
    case OnComplete =>
      log.info("Fibonacci stream completed.")
      context.stop(self)
    case unknown => log.warning("Received unknown event: {}.", unknown)
  }
}

Fibonacci App：

val src = Source.actorPublisher(Props[FibonacciPublisher])
val flow = Flow[Long].map { _ * 2 }
val sink = Sink.actorSubscriber(Props[FibonacciSubscriber])

src.via(flow).runWith(sink)

示例运行：问题：4的初始需求来自哪里？

2015-10-03 23:10:49.120 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Received request; demand = 4.
2015-10-03 23:10:49.120 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 0.
2015-10-03 23:10:49.121 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 1.
2015-10-03 23:10:49.121 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 1.
2015-10-03 23:10:49.121 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 2.
2015-10-03 23:10:49.122 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciSubscriber - Received Fibonacci number: 0
2015-10-03 23:10:49.122 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciSubscriber - Received Fibonacci number: 2
2015-10-03 23:10:49.123 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Received request; demand = 2.
2015-10-03 23:10:49.123 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciSubscriber - Received Fibonacci number: 2
2015-10-03 23:10:49.124 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciSubscriber - Received Fibonacci number: 4
2015-10-03 23:10:49.124 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 3.
2015-10-03 23:10:49.125 [fibonacci-akka.actor.default-dispatcher-2] [DEBUG] n.a.s.f.FibonacciProducer - Producing fibonacci number: 5.

Answer 1

您的源的初始需求由后期的输入缓冲区提供。反过来，这是通过初始化ActorMaterializerSettings时传递的ActorMaterializer实例进行配置的。

如果您未通过任何特定设置，akka将使用提供的配置初始化一个; in the default configuration您可以发现akka.stream.materializer.initial-input-buffer-size设置为4.更改应更改您的初始需求。

Akka / Scala：你能解释一下这个Akka Streams流程中会发生什么吗？

1 个答案: