Akka并发编程——第三节：Actor模型（二）

2022-01-02 10:00:10

本节主要内容：

Actor API解析

1. Actor API解析

Actor中的主要成员变量和方法定义如下：

package akka.actor
trait Actor extends scala.AnyRef {
  type Receive = akka.actor.Actor.Receive

  //context变量暴露当前Actor的上下文信息及当前消息
  implicit val context : akka.actor.ActorContext = { /* compiled code */ }

  //self作为当前ActorRef的引用
  implicit final val self : akka.actor.ActorRef = { /* compiled code */ }

  //当前Actor接收到最后一条消息对应的消息发送者(Actor）
  final def sender() : akka.actor.ActorRef = { /* compiled code */ }

  //receive方法，抽象方法，定义Actor的行为逻辑
  def receive : akka.actor.Actor.Receive

  //内部使用API 
  protected[akka] def aroundReceive(receive : akka.actor.Actor.Receive, msg : scala.Any) : scala.Unit = { /* compiled code */ }
  protected[akka] def aroundPreStart() : scala.Unit = { /* compiled code */ }
  protected[akka] def aroundPostStop() : scala.Unit = { /* compiled code */ }
  protected[akka] def aroundPreRestart(reason : scala.Throwable, message : scala.Option[scala.Any]) : scala.Unit = { /* compiled code */ }
  protected[akka] def aroundPostRestart(reason : scala.Throwable) : scala.Unit = { /* compiled code */ }


   //监督策略，用于Actor容错处理
  def supervisorStrategy : akka.actor.SupervisorStrategy = { /* compiled code */ }

  //Hook方法，用于Actor生命周期监控 
  @scala.throws[T](classOf[scala.Exception])
  def preStart() : scala.Unit = { /* compiled code */ }
  @scala.throws[T](classOf[scala.Exception])
  def postStop() : scala.Unit = { /* compiled code */ }
  @scala.throws[T](classOf[scala.Exception])
  def preRestart(reason : scala.Throwable, message : scala.Option[scala.Any]) : scala.Unit = { /* compiled code */ }
  @scala.throws[T](classOf[scala.Exception])
  def postRestart(reason : scala.Throwable) : scala.Unit = { /* compiled code */ }


  //发送给Actor的消息，Actor没有定义相应的处理逻辑时，会调用此方法
  def unhandled(message : scala.Any) : scala.Unit = { /* compiled code */ }
}
object Actor extends scala.AnyRef {
  type Receive = scala.PartialFunction[scala.Any, scala.Unit]

  //空的行为逻辑
  @scala.SerialVersionUID(1)
  object emptyBehavior extends scala.AnyRef with akka.actor.Actor.Receive {
    def isDefinedAt(x : scala.Any) : scala.Boolean = { /* compiled code */ }
    def apply(x : scala.Any) : scala.Nothing = { /* compiled code */ }
  }
  //Sender为null
  @scala.SerialVersionUID(1)
  final val noSender : akka.actor.ActorRef = { /* compiled code */ }
}

（1） Hook方法，preStart()、postStop()方法的使用

/*
 *Actor API: Hook方法
 */
  object Example_05 extends App{
    import akka.actor.Actor
    import akka.actor.ActorSystem
    import akka.actor.Props


    class FirstActor extends Actor with ActorLogging{
      //通过context.actorOf方法创建Actor
      var child:ActorRef = _

      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作
      override def preStart(): Unit ={
        log.info("preStart() in FirstActor")
        //通过context上下文创建Actor
        child = context.actorOf(Props[MyActor], name = "myChild")
      }
      def receive = {
        //向MyActor发送消息
        case x => child ! x;log.info("received "+x)
      }

      //Hook方法，postStop()，Actor停止之后调用
      override def postStop(): Unit = {
        log.info("postStop() in FirstActor")
       }
    }


    class MyActor extends Actor with ActorLogging{
      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作
      override def preStart(): Unit ={
        log.info("preStart() in MyActor")
      }
      def receive = {
        case "test" => log.info("received test")
        case _      => log.info("received unknown message")
      }

      //Hook方法，postStop()，Actor停止之后调用
      override def postStop(): Unit = {
        log.info("postStop() in MyActor")
      }
    }

    val system = ActorSystem("MyActorSystem")
    val systemLog=system.log

    //创建FirstActor对象
    val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

    systemLog.info("准备向myactor发送消息")
    //向myactor发送消息
    myactor!"test"
    myactor! 123
    Thread.sleep(5000)
    //关闭ActorSystem，停止程序的运行
    system.shutdown()
  }

代码运行结果：

[INFO] [04/02/2016 17:04:49.607] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received 123
[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] preStart() in MyActor
[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] received test
[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] received unknown message
[INFO] [04/02/2016 17:04:54.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myChild] postStop() in MyActor
[INFO] [04/02/2016 17:04:54.617] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] postStop() in FirstActor

在代码

 class FirstActor extends Actor with ActorLogging{
      //通过context.actorOf方法创建Actor
      var child:ActorRef = _

      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作
      override def preStart(): Unit ={
        log.info("preStart() in FirstActor")
        //通过context上下文创建Actor
        child = context.actorOf(Props[MyActor], name = "myChild")
      }
      def receive = {
        //向MyActor发送消息
        case x => child ! x;log.info("received "+x)
      }

      //Hook方法，postStop()，Actor停止之后调用，用于完成初始化工作
      override def postStop(): Unit = {
        log.info("postStop() in FirstActor")
      }
    }

中分别对postStop、preStart方法进行了重写，在preStart方法中通过代码

 child = context.actorOf(Props[MyActor], name = "myChild")

对成员变量child进行初始化，然后在postStop方法中使用

 //通过context上下文停止MyActor的运行
        context.stop(child)

停止MyActor的运行。在使用代码

//创建FirstActor对象
val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

创建FirstActor时，便会调用preStart方法完成MyActor的创建，因此首先会执行FirstActor中的preStart()方法

dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor

然后在创建MyActor时执行MyActor中定义的preStart方法

[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] preStart() in MyActor

在执行

//关闭ActorSystem，停止程序的运行
    system.shutdown()

FirstActor作为MyActor的Supervisor，会先停止MyActor，再停止自身，因此先调用MyActor的postStop方法，再调用FirstActor的postStop方法。

（2）成员变量self及成员方法sender方法的使用

整体代码如下：

  /*
 *Actor API:成员变量self及sender()方法的使用
 */
  object Example_05 extends App{
    import akka.actor.Actor
    import akka.actor.ActorSystem
    import akka.actor.Props


    class FirstActor extends Actor with ActorLogging{
      //通过context.actorOf方法创建Actor
      var child:ActorRef = _

      override def preStart(): Unit ={
        log.info("preStart() in FirstActor")
        //通过context上下文创建Actor
        child = context.actorOf(Props[MyActor], name = "myActor")
      }
      def receive = {
        //向MyActor发送消息
        case x => child ! x;log.info("received "+x)
      }


    }


    class MyActor extends Actor with ActorLogging{
      self!"message from self reference"
      def receive = {
        case "test" => log.info("received test");sender()!"message from MyActor"
        case "message from self reference"=>log.info("message from self refrence")
        case _      => log.info("received unknown message");
      }

    }

    val system = ActorSystem("MyActorSystem")
    val systemLog=system.log

    //创建FirstActor对象
    val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

    systemLog.info("准备向myactor发送消息")
    //向myactor发送消息
    myactor!"test"
    myactor! 123
    Thread.sleep(5000)
    //关闭ActorSystem，停止程序的运行
    system.shutdown()
  }

运行结果：

[INFO] [04/02/2016 18:40:37.805] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 18:40:37.805] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received 123
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] message from self refrence
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received message from MyActor
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

代码：

class MyActor extends Actor with ActorLogging{
      self!"message from self reference"
      def receive = {
        case "test" => log.info("received test");sender()!"message from MyActor"
        case "message from self reference"=>log.info("message from self refrence")
        case _      => log.info("received unknown message");
      }

    }

中使用

self!"message from self reference"

向自身发送了一条消息，receive方法通过

        case "message from self reference"=>log.info("message from self refrence")

对这条消息进行处理。receive方法在处理

def receive = {
        case "test" => log.info("received test");sender()!"message from MyActor"

“test”消息时，会调用

sender()!"message from MyActor"

向sender（本例中为FirstActor）发送”message from MyActor”消息，FirstActor使用

 def receive = {
        //向MyActor发送消息
        case x => child ! x;log.info("received "+x)
      }

处理消息时又向MyActor回送该消息，因此最终的输出有两个unknown message，分别对应123和”message from MyActor”

[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

（3） unhandled方法的使用

unhandled方法用于处理没有被receive方法处理的消息，下面的代码给出的是当不重写unhandled方法时的代码

/*
*Actor API:unhandled方法
*/
object Example_06 extends App{
  import akka.actor.Actor
  import akka.actor.ActorSystem
  import akka.actor.Props
  class FirstActor extends Actor with ActorLogging{
    def receive = {
      //向MyActor发送消息
      case "test" => log.info("received test")
    }


  }
  val system = ActorSystem("MyActorSystem")
  val systemLog=system.log

  //创建FirstActor对象
  val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

  systemLog.info("准备向myactor发送消息")
  //向myactor发送消息
  myactor!"test"
  myactor! 123
  Thread.sleep(5000)
  //关闭ActorSystem，停止程序的运行
  system.shutdown()
}

代码输出：

[INFO] [04/02/2016 19:14:11.992] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 19:14:11.992] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test

不难看出，对于

 myactor! 123

发送的这条消息没有被处理，没有任何的处理逻辑。在实际开发过程中，可能会对不能被处理的消息增加一些应对逻辑，此时可以重写unhandled方法，代码如下：

/*
*Actor API:unhandled方法的使用
*/
object Example_06 extends App{
  import akka.actor.Actor
  import akka.actor.ActorSystem
  import akka.actor.Props


  class FirstActor extends Actor with ActorLogging{
    def receive = {
      //向MyActor发送消息
      case "test" => log.info("received test")
    }

    //重写unhandled方法
    override def unhandled(message: Any): Unit = {
      log.info("unhandled message is {}",message)
    }
  }



  val system = ActorSystem("MyActorSystem")
  val systemLog=system.log

  //创建FirstActor对象
  val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

  systemLog.info("准备向myactor发送消息")
  //向myactor发送消息
  myactor!"test"
  myactor! 123
  Thread.sleep(5000)
  //关闭ActorSystem，停止程序的运行
  system.shutdown()
}

代码输出结果：

[INFO] [04/02/2016 19:17:18.458] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 19:17:18.458] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 19:17:18.458] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] unhandled message is 123

其它如preRestart等方法的使用将在Akka容错部分进行讲解。

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码农公寓

1. Actor API解析

（1） Hook方法，preStart()、postStop()方法的使用

（2） 成员变量self及成员方法sender方法的使用

（3） unhandled方法的使用

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（2）成员变量self及成员方法sender方法的使用