Akka（9）： 分布式运算：Remoting-远程构建式

   上篇我们讨论了Akka-Remoting。我们说Akka-Remoting是一种点对点的通讯方式，能使两个不同JVM上Akka-ActorSystem上的两个Actor之间可以相互沟通。Akka-Remoting还没有实现完全的Actor位置透明（location transparency），因为一个Actor还必须在获得对方Actor确切地址信息后才能启动与之沟通过程。Akka-Remoting支持“远程查找”和“远程构建”两种沟通方式。由于篇幅所限，我们只介绍了“远程查找”。在这一篇里我们将会讨论“远程构建”方式。

同样，我们先通过项目结构来分析：

lazy val local = (project in file("."))  .settings(commonSettings)  .settings(    name := "remoteCreateDemo"  ).aggregate(calculator,remote).dependsOn(calculator)lazy val calculator = (project in file("calculator"))  .settings(commonSettings)  .settings(    name := "calculator"  )lazy val remote = (project in file("remote"))  .settings(commonSettings)  .settings(    name := "remoteSystem"  ).aggregate(calculator).dependsOn(calculator)

远程构建的过程大致是这样的：由local通知remote启动构建Actor；remote从本地库中查找Actor的类定义（class）并把它载入内存。由于驱动、使用远程Actor是在local进行的，所以local,remote项目还必须共享Calculator，包括Calculator的功能消息。这项要求我们在.sbt中用aggregate(calculator)来协同编译。

我们把Calculator的监管supervisor也包括在这个源码文件里。现在这个calculator是个包括监管、功能、消息的完整项目了。Calculator源代码如下：

package remoteCreation.calculatorimport akka.actor._import scala.concurrent.duration._object Calcultor {  sealed trait MathOps  case class Num(dnum: Double) extends MathOps  case class Add(dnum: Double) extends MathOps  case class Sub(dnum: Double) extends MathOps  case class Mul(dnum: Double) extends MathOps  case class Div(dnum: Double) extends MathOps  sealed trait CalcOps  case object Clear extends CalcOps  case object GetResult extends CalcOps  def props = Props(new Calcultor)  def supervisorProps = Props(new SupervisorActor)}class Calcultor extends Actor with ActorLogging {  import Calcultor._  var result: Double = 0.0   //internal state  override def receive: Receive = {    case Num(d) => result = d    case Add(d) => result += d    case Sub(d) => result -= d    case Mul(d) => result *= d    case Div(d) =>      val _ = result.toInt / d.toInt   //yield ArithmeticException      result /= d    case Clear => result = 0.0    case GetResult =>      sender() ! s"Result of calculation is: $result"  }  override def preRestart(reason: Throwable, message: Option[Any]): Unit = {    log.info(s"Restarting calculator: ${reason.getMessage}")    super.preRestart(reason, message)  }}class SupervisorActor extends Actor {  def decider: PartialFunction[Throwable,SupervisorStrategy.Directive] = {    case _: ArithmeticException => SupervisorStrategy.Resume  }  override def supervisorStrategy: SupervisorStrategy =    OneForOneStrategy(maxNrOfRetries = 5, withinTimeRange = 5 seconds){      decider.orElse(SupervisorStrategy.defaultDecider)    }  val calcActor = context.actorOf(Calcultor.props,"calculator")  override def receive: Receive = {    case msg@ _ => calcActor.forward(msg)  }}

与上一个例子的”远程查找式“相同，remote需要为Remoting公开一个端口。我们可以照搬.conf配置文件内容：remote/src/main/resources/application.conf

akka {  actor {    provider = remote  }  remote {    enabled-transports = ["akka.remote.netty.tcp"]    netty.tcp {      hostname = "127.0.0.1"      port = 2552    }    log-sent-messages = on    log-received-messages = on  }}

由于远程构建和使用是在local上进行的，在remote上我们只需要启动ActorSystem就行了：

import com.typesafe.config.ConfigFactoryimport akka.actor._object CalculatorRunner extends App {  val remoteSystem = ActorSystem("remoteSystem",ConfigFactory.load("application"))  println("Remote system started.")  scala.io.StdIn.readLine()  remoteSystem.terminate()}

Calculator的构建是在localSystem上启动的，我们需要在配置文件中描述远程构建标的（还是未能实现位置透明）：local/src/main/resources/application.conf

akka {  actor {    provider = remote,    deployment {      "/calculator" {        remote = "akka.tcp://remoteSystem@127.0.0.1:2552"      }    }  }  remote {    netty.tcp {      hostname = "127.0.0.1",      port=2554    }  }}

注意：上面这个/calculator设置实际上指的是SupervisorActor。

现在我们可以在local上开始构建calculator，然后使用它来运算了：

import akka.actor._import remoteCreation.calculator.Calcultor._import scala.concurrent.duration._import akka.pattern._object RemotingCreate extends App {  val localSystem = ActorSystem("localSystem")  val calcActor = localSystem.actorOf(props,    name = "calculator")   //created SupervisorActor  import localSystem.dispatcher  calcActor ! Clear  calcActor ! Num(13.0)  calcActor ! Mul(1.5)  implicit val timeout = akka.util.Timeout(1 second)  ((calcActor ? GetResult).mapTo[String]) foreach println  scala.io.StdIn.readLine()  calcActor ! Div(0.0)  calcActor ! Div(1.5)  calcActor ! Add(100.0)  ((calcActor ? GetResult).mapTo[String]) foreach println  scala.io.StdIn.readLine()  localSystem.terminate()}

从代码上看构建calculator（SupervisorActor）过程与普通的Actor构建没分别，所有细节都放在配置文件里了。但是，要注意actorOf的name必须与配置文档中的设置匹配。

试运行结果与上一个例子相同。值得注意的是实际远程构建的是一个SupervisorActor。Calculator的构建是SupervisorActor构建的其中一部分。从运算结果看：这个SupervisorActor也实现了它的功能。

下面是这次示范的源代码：

local/build.sbt

lazy val commonSettings = seq (  name := "RemoteCreateDemo",  version := "1.0",  scalaVersion := "2.11.8",  libraryDependencies := Seq(    "com.typesafe.akka" %% "akka-actor" % "2.5.2",    "com.typesafe.akka" %% "akka-remote" % "2.5.2"  ))lazy val local = (project in file("."))  .settings(commonSettings)  .settings(    name := "remoteCreateDemo"  ).aggregate(calculator).dependsOn(calculator)lazy val calculator = (project in file("calculator"))  .settings(commonSettings)  .settings(    name := "calculator"  )lazy val remote = (project in file("remote"))  .settings(commonSettings)  .settings(    name := "remoteSystem"  ).aggregate(calculator).dependsOn(calculator)

calculator/calculator.scala

package remoteCreation.calculatorimport akka.actor._import scala.concurrent.duration._object Calcultor {  sealed trait MathOps  case class Num(dnum: Double) extends MathOps  case class Add(dnum: Double) extends MathOps  case class Sub(dnum: Double) extends MathOps  case class Mul(dnum: Double) extends MathOps  case class Div(dnum: Double) extends MathOps  sealed trait CalcOps  case object Clear extends CalcOps  case object GetResult extends CalcOps  def props = Props(new Calcultor)  def supervisorProps = Props(new SupervisorActor)}class Calcultor extends Actor with ActorLogging {  import Calcultor._  var result: Double = 0.0   //internal state  override def receive: Receive = {    case Num(d) => result = d    case Add(d) => result += d    case Sub(d) => result -= d    case Mul(d) => result *= d    case Div(d) =>      val _ = result.toInt / d.toInt   //yield ArithmeticException      result /= d    case Clear => result = 0.0    case GetResult =>      sender() ! s"Result of calculation is: $result"  }  override def preRestart(reason: Throwable, message: Option[Any]): Unit = {    log.info(s"Restarting calculator: ${reason.getMessage}")    super.preRestart(reason, message)  }}class SupervisorActor extends Actor {  def decider: PartialFunction[Throwable,SupervisorStrategy.Directive] = {    case _: ArithmeticException => SupervisorStrategy.Resume  }  override def supervisorStrategy: SupervisorStrategy =    OneForOneStrategy(maxNrOfRetries = 5, withinTimeRange = 5 seconds){      decider.orElse(SupervisorStrategy.defaultDecider)    }  val calcActor = context.actorOf(Calcultor.props,"calculator")  override def receive: Receive = {    case msg@ _ => calcActor.forward(msg)  }}

remote/src/main/resources/application.conf

akka {  actor {    provider = remote  }  remote {    enabled-transports = ["akka.remote.netty.tcp"]    netty.tcp {      hostname = "127.0.0.1"      port = 2552    }    log-sent-messages = on    log-received-messages = on  }}

remote/CalculatorRunner.scala

package remoteCreation.remoteimport com.typesafe.config.ConfigFactoryimport akka.actor._object CalculatorRunner extends App {  val remoteSystem = ActorSystem("remoteSystem",ConfigFactory.load("application"))  println("Remote system started.")  scala.io.StdIn.readLine()  remoteSystem.terminate()}

local/src/main/resources/application.conf

akka {  actor {    provider = remote,    deployment {      "/calculator" {        remote = "akka.tcp://remoteSystem@127.0.0.1:2552"      }    }  }  remote {    netty.tcp {      hostname = "127.0.0.1",      port=2554    }  }}

local/RemotingCreation.scala

import akka.actor._import remoteCreation.calculator.Calcultor._import scala.concurrent.duration._import akka.pattern._object RemotingCreate extends App {  val localSystem = ActorSystem("localSystem")  val calcActor = localSystem.actorOf(props,    name = "calculator")  //created SupervisorActor  import localSystem.dispatcher  calcActor ! Clear  calcActor ! Num(13.0)  calcActor ! Mul(1.5)  implicit val timeout = akka.util.Timeout(1 second)  ((calcActor ? GetResult).mapTo[String]) foreach println  scala.io.StdIn.readLine()  calcActor ! Div(0.0)  calcActor ! Div(1.5)  calcActor ! Add(100.0)  ((calcActor ? GetResult).mapTo[String]) foreach println  scala.io.StdIn.readLine()  localSystem.terminate()}