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我正在研究 Akka 流，并做了一个斐波那契发布者 - 订阅者示例，如下所示。但是，我还不太明白需求最初是如何产生的，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？

斐波那契出版社：

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
    }
  }
}

斐波那契订阅者：

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)
  }
}

斐波那契应用程序：

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

src.via(flow).runWith(sink)

样品运行：问题：最初对 4 的需求是从哪里来的？

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.
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1 回答 1

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对源的初始需求由后期阶段的输入缓冲区提供。这反过来又是通过ActorMaterializerSettings您在初始化ActorMaterializer.

如果你没有通过任何特定的设置，akka 将使用提供的配置来初始化一个；在默认配置中，您会发现它akka.stream.materializer.initial-input-buffer-size设置为 4。更改它应该会改变您的初始需求。

于 2015-10-05T10:13:31.200 回答