Akka 消息传递保证

Question

我正在尝试找出 Akka 支持的消息传递保证。我得出以下结论：

At-most-once : Supported by default

At-least-once : Supported with Akka Persistence

Exactly-once : ?

Akka支持exactly-once吗？如果没有，我将如何实现？

Answer 1

正如您所发现的，Akka 开箱即用地提供最多一次交付。 At-Least-Once 在某些库中可用，例如 Akka Persistence，您可以通过在 actor 中创建 ACK-RETRY 协议来相当轻松地自己创建它。发送方持续定期发送消息，直到接收方确认收到消息。

简而言之，对于 至少一次，责任由发件人承担。例如在 Scala 中：

class Sender(receiver: ActorRef) extends Actor {

  var acknowledged = false

  override def preStart() {
    receiver ! "Do Work"
    system.scheduler.scheduleOnce(50 milliseconds, self, "Retry")
  }

  def receive = {
    case "Retry" => 
      if(!acknowledged) {
        receiver ! "Do Work"
        system.scheduler.scheduleOnce(50 milliseconds, self, "Retry")
      }

    case "Ack" => acknowledged = true
  }
}

class Receiver extends Actor {

  def receive = {
    case "Do Work" => 
      doWork()
      sender ! "Ack"
  }

  def doWork() = {...}
}

但是对于 At-Most-Once 处理，接收方必须确保同一消息的重复实例只会导致工作完成一次。这可以通过让接收器完成的工作是幂等的，以便它可以重复应用，或者让接收器记录它已经处理的内容来实现。对于 At-Most-Once，责任由接收者承担：

class AtMostOnceReceiver extends Actor {

  var workDone = false

  def receive = {

    case "Do Work" =>
      if(!workDone) {
        doWork()
        workDone = true
      }
      sender ! Ack
  }

}

Akka 消息传递保证

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