软件设计 2017-06-21
Akka是一种消息驱动运算模式,它实现跨JVM程序运算的方式是通过能跨JVM的消息系统来调动分布在不同JVM上ActorSystem中的Actor进行运算,前题是Akka的地址系统可以支持跨JVM定位。Akka的消息系统最高境界可以实现所谓的Actor位置透明化,这样在Akka编程中就无须关注Actor具体在哪个JVM上运行,分布式Actor编程从方式上跟普通Actor编程就不会有什么区别了。Akka的Remoting是一种点对点的跨JVM消息通道,让一个JVM上ActorSystem中的某个Actor可以连接另一个JVM上ActorSystem中的另一个Actor。两个JVM上的ActorSystem之间只需具备TCP网络连接功能就可以实现Akka Remoting了。Akka-Remoting还没有实现完全的位置透明化,因为用户还必须在代码里或者配置文件里指明目标Actor的具体地址。
Akka-Remoting提供了两种Actor之间的沟通方法:
1、远程查找:通过路径Path查找在远程机上已经创建存在的Actor,获取ActorRef后进行沟通
2、远程创建:在远程机上直接创建Actor作为沟通对象
Akka-Remoting的主要应用应该是把一些任务部署到远程机上去运算。发起方(Local JVM)在这里面的主要作用是任务分配,有点像Akka-Router。我们可以用下面的例子来示范:模拟一个计算器,可以进行连续的加减乘除,保留累计结果。我们会把这个计算器部署到远程机上,然后从本机与之沟通分配运算任务及获取运算结果。这个计算器就是个简单的Actor:
import akka.actor._ object Calculator { 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 } class Calcultor extends Actor { import Calculator._ 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) => result = result / d case Clear => result = 0.0 case GetResult => sender() ! s"Result of calculation is: $result" } }
就是一个简单的Actor实现,跟Remoting没什么关系。
下面我们会在一个远程机上部署这个Calculator Actor。 先看看这个示范的项目结构:remoteLookup/build.sbt
lazy val commonSettings = seq ( name := "RemoteLookupDemo", 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 := "localSystem" ).aggregate(messages,remote).dependsOn(messages) lazy val messages = (project in file("messages")) .settings(commonSettings) .settings( name := "commands" ) lazy val remote = (project in file("remote")) .settings(commonSettings) .settings( name := "remoteSystem" ).aggregate(messages).dependsOn(messages)
在这里我们分了三个项目:local是主项目,messages和remote是分项目(subprojects)。messages里只有OpsMessages.scala一个源文件:
package remoteLookup.messages object Messages { 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 }
我们看到:这个文件是把上面的Calculator支持的消息拆了出来。这是因为Calculator Actor会在另一个JVM remote上部署,而我们会从local JVM里向Calculator发送操作消息,所以Messages必须是local和remote共享的。这个要求我们通过dependOn(messages)实现了。现在Calculator是在remote项目里定义的:remote/Calculator.scala
package remoteLookup.remote import akka.actor._ import remoteLookup.messages.Messages._ object CalcProps { def props = Props(new Calcultor) } class Calcultor extends Actor with ActorLogging { 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) } }
由于ArithmeticException默认的处理策略SupervisorStrategy是Restart,一旦输入Div(0.0)时会重启将result清零。我们可以在remote上加一个Supervisor来把异常处理策略改为Resume。
下面我们先在remote项目本地对Calculator的功能进行测试:remote/CalculatorRunner.scala
package remoteLookup.remote import akka.actor._ import akka.pattern._ import remoteLookup.messages.Messages._ import scala.concurrent.duration._ 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(CalcProps.props,"calculator") override def receive: Receive = { case msg@ _ => calcActor.forward(msg) } } object CalculatorRunner extends App { val remoteSystem = ActorSystem("remoteSystem") val calcActor = remoteSystem.actorOf(Props[SupervisorActor],"supervisorActor") import remoteSystem.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() remoteSystem.terminate() }
测试运算得出以下结果:
Result of calculation is: 19.5 Result of calculation is: 113.0 [WARN] [06/20/2017 19:28:10.720] [remoteSystem-akka.actor.default-dispatcher-4] [akka://remoteSystem/user/parentActor/calculator] / by zero
supervisorActor实现了它应有的功能。
下面进行远程查找示范:首先,remote需要把Calculator向外发布。这可以通过配置文件设置实现: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 } }
上面这段的意思是:所有向外公开Actor的地址前缀为:akka.tcp://[email protected]:2552/user/???
那么Calculator的完整地址path应该就是:akka.tcp://[email protected]:2552/user/supervisorActor/calculator
Akka-Remoting提供了两种远程查找方式:actorSelection.resolveOne方法和Identify消息确认。无论如何,local都需要进行Remoting配置: local/src/main/resources/application.conf
akka { actor { provider = remote } remote { enabled-transports = ["akka.remote.netty.tcp"] netty.tcp { hostname = "127.0.0.1" port = 0 } } }
port=0的意思是由系统自动选择任何可用的端口。现在我们完成了Remoting设置,也得到了在远程机上Calculator的具体地址,应该足够进行远程Actor沟通了。我们先用actorSelection.resolveOne示范。resolveOne源代码如下:
/** * Resolve the [[ActorRef]] matching this selection. * The result is returned as a Future that is completed with the [[ActorRef]] * if such an actor exists. It is completed with failure [[ActorNotFound]] if * no such actor exists or the identification didn't complete within the * supplied `timeout`. * * Under the hood it talks to the actor to verify its existence and acquire its * [[ActorRef]]. */ def resolveOne()(implicit timeout: Timeout): Future[ActorRef] = { implicit val ec = ExecutionContexts.sameThreadExecutionContext val p = Promise[ActorRef]() this.ask(Identify(None)) onComplete { case Success(ActorIdentity(_, Some(ref))) ⇒ p.success(ref) case _ ⇒ p.failure(ActorNotFound(this)) } p.future }
resolveOne返回Future[ActorRef],我们可以用Future的函数组件(combinator)来操作:localAccessDemo.scala
import akka.actor._ import akka.util.Timeout import scala.concurrent.duration._ import akka.pattern._ import remoteLookup.messages.Messages._ object LocalSelectionDemo extends App { val localSystem = ActorSystem("localSystem") import localSystem.dispatcher val path = "akka.tcp://[email protected]:2552/user/supervisorActor/calculator" implicit val timeout = Timeout(5 seconds) for (calcActor : ActorRef <- localSystem.actorSelection(path).resolveOne()) { calcActor ! Clear calcActor ! Num(13.0) calcActor ! Mul(1.5) ((calcActor ? GetResult).mapTo[String]) foreach println calcActor ! Div(0.0) calcActor ! Div(1.5) calcActor ! Add(100.0) ((calcActor ? GetResult).mapTo[String]) foreach println } scala.io.StdIn.readLine() localSystem.terminate() }
因为resolveOne返回的是个Future[x],我们可以用for来对嵌在Future内的x进行操作。现在remoteSystem只需要构建Calculator待用就行了:remote/CalculatorRunner.scala
package remoteLookup.remote import akka.actor._ import akka.pattern._ import remoteLookup.messages.Messages._ import scala.concurrent.duration._ 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(CalcProps.props,"calculator") override def receive: Receive = { case msg@ _ => calcActor.forward(msg) } } object CalculatorRunner extends App { val remoteSystem = ActorSystem("remoteSystem") val calcActor = remoteSystem.actorOf(Props[SupervisorActor],"supervisorActor") /* import remoteSystem.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() remoteSystem.terminate() }
注意:注销的操作转移到了localSelectionDemo里。
先运行remote项目:
INFO] [06/20/2017 21:24:37.955] [main] [akka.remote.Remoting] Starting remoting [INFO] [06/20/2017 21:24:38.091] [main] [akka.remote.Remoting] Remoting started; listening on addresses :[akka.tcp://[email protected]:2552] [INFO] [06/20/2017 21:24:38.092] [main] [akka.remote.Remoting] Remoting now listens on addresses: [akka.tcp://[email protected]:2552]
remoteSystem开始监视配置的公开地址。
用sbt run 运行local:
Result of calculation is: 19.5 Result of calculation is: 113.0
结果正确。supervisorActor的SupervisorStrategy起到了应有的作用。
remote项目输出显示也能证明:
[INFO] [06/20/2017 21:24:37.955] [main] [akka.remote.Remoting] Starting remoting [INFO] [06/20/2017 21:24:38.091] [main] [akka.remote.Remoting] Remoting started; listening on addresses :[akka.tcp://[email protected]:2552] [INFO] [06/20/2017 21:24:38.092] [main] [akka.remote.Remoting] Remoting now listens on addresses: [akka.tcp://[email protected]:2552] [WARN] [06/20/2017 21:27:06.330] [remoteSystem-akka.actor.default-dispatcher-4] [akka://remoteSystem/user/supervisorActor/calculator] / by zero [ERROR] [06/20/2017 21:27:34.176] [remoteSystem-akka.remote.default-remote-dispatcher-5] [akka.tcp://[email protected]:2552/system/endpointManager/reliableEndpointWriter-akka.tcp%3A%2F%2FlocalSystem%40127.0.0.1%3A60601-0/endpointWriter] AssociationError [akka.tcp://[email protected]:2552] <- [akka.tcp://[email protected]:60601]: Error [Shut down address: akka.tcp://[email protected]:60601] [ akka.remote.ShutDownAssociation: Shut down address: akka.tcp://[email protected]:60601 Caused by: akka.remote.transport.Transport$InvalidAssociationException: The remote system terminated the association because it is shutting down. ]
下面我们试着用Identify消息确认方式来复演上述例子。Akka是如下这样定义有关Identify消息确认的:
/** * A message all Actors will understand, that when processed will reply with * [[akka.actor.ActorIdentity]] containing the `ActorRef`. The `messageId` * is returned in the `ActorIdentity` message as `correlationId`. */ @SerialVersionUID(1L) final case class Identify(messageId: Any) extends AutoReceivedMessage with NotInfluenceReceiveTimeout /** * Reply to [[akka.actor.Identify]]. Contains * `Some(ref)` with the `ActorRef` of the actor replying to the request or * `None` if no actor matched the request. * The `correlationId` is taken from the `messageId` in * the `Identify` message. */ @SerialVersionUID(1L) final case class ActorIdentity(correlationId: Any, ref: Option[ActorRef]) { if (ref.isDefined && ref.get == null) { throw new IllegalArgumentException("ActorIdentity created with ref = Some(null) is not allowed, " + "this could happen when serializing with Scala 2.12 and deserializing with Scala 2.11 which is not supported.") } /** * Java API: `ActorRef` of the actor replying to the request or * null if no actor matched the request. */ @deprecated("Use getActorRef instead", "2.5.0") def getRef: ActorRef = ref.orNull /** * Java API: `ActorRef` of the actor replying to the request or * not defined if no actor matched the request. */ def getActorRef: Optional[ActorRef] = { import scala.compat.java8.OptionConverters._ ref.asJava } }
如果拿上面的例子,我们就会向远程机上的Calculator地址发送Identify(path),而Calculator返回ActorIdentity消息,参数包括correlationId = path, ref = Calculator的ActorRef。 下面是使用示范代码:
object LocalIdentifyDemo extends App { class RemoteCalc extends Actor with ActorLogging { val path = "akka.tcp://[email protected]:2552/user/supervisorActor/calculator" context.actorSelection(path) ! Identify(path) //send req for ActorRef import context.dispatcher implicit val timeout = Timeout(5 seconds) override def receive: Receive = { case ActorIdentity(p,someRef) if p.equals(path) => someRef foreach { calcActor => calcActor ! Clear calcActor ! Num(13.0) calcActor ! Mul(1.5) ((calcActor ? GetResult).mapTo[String]) foreach println calcActor ! Div(0.0) calcActor ! Div(1.5) calcActor ! Add(100.0) ((calcActor ? GetResult).mapTo[String]) foreach println } } } val localSystem = ActorSystem("localSystem") val localActor = localSystem.actorOf(Props[RemoteCalc],"localActor") scala.io.StdIn.readLine() localSystem.terminate() }
Identify消息确认机制是一种Actor沟通模式,所以我们需要构建一个RemoteCalc Actor,把程序包嵌在这个Actor里面。当receive收到确认消息ActorIdentity后获取ActorRef运算程序。
查看运算结果,正确。
下面是这次示范的完整源代码:
build.sbt
lazy val commonSettings = seq ( name := "RemoteLookupDemo", 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 := "remoteLookupDemo" ).aggregate(messages,remote).dependsOn(messages) lazy val messages = (project in file("messages")) .settings(commonSettings) .settings( name := "commands" ) lazy val remote = (project in file("remote")) .settings(commonSettings) .settings( name := "remoteSystem" ).aggregate(messages).dependsOn(messages)
messages/OpsMessages.scala
package remoteLookup.messages object Messages { 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 }
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/Calculator.scala
package remoteLookup.remote import akka.actor._ import remoteLookup.messages.Messages._ object CalcProps { def props = Props(new Calcultor) } class Calcultor extends Actor with ActorLogging { 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) } }
remote/CalculatorRunner.scala
package remoteLookup.remote import akka.actor._ import akka.pattern._ import remoteLookup.messages.Messages._ import scala.concurrent.duration._ 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(CalcProps.props,"calculator") override def receive: Receive = { case msg@ _ => calcActor.forward(msg) } } object CalculatorRunner extends App { val remoteSystem = ActorSystem("remoteSystem") val calcActor = remoteSystem.actorOf(Props[SupervisorActor],"supervisorActor") /* import remoteSystem.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() remoteSystem.terminate() }
local/src/main/resources/application.conf
akka { actor { provider = remote } remote { enabled-transports = ["akka.remote.netty.tcp"] netty.tcp { hostname = "127.0.0.1" port = 0 } } }
local/localAccessDemo.scala
import akka.actor._ import akka.util.Timeout import scala.concurrent.duration._ import akka.pattern._ import remoteLookup.messages.Messages._ object LocalSelectionDemo extends App { val localSystem = ActorSystem("localSystem") import localSystem.dispatcher val path = "akka.tcp://[email protected]:2552/user/supervisorActor/calculator" implicit val timeout = Timeout(5 seconds) for (calcActor : ActorRef <- localSystem.actorSelection(path).resolveOne()) { calcActor ! Clear calcActor ! Num(13.0) calcActor ! Mul(1.5) ((calcActor ? GetResult).mapTo[String]) foreach println calcActor ! Div(0.0) calcActor ! Div(1.5) calcActor ! Add(100.0) ((calcActor ? GetResult).mapTo[String]) foreach println } scala.io.StdIn.readLine() localSystem.terminate() } object LocalIdentifyDemo extends App { class RemoteCalc extends Actor with ActorLogging { val path = "akka.tcp://[email protected]:2552/user/supervisorActor/calculator" context.actorSelection(path) ! Identify(path) //semd req for ActorRef import context.dispatcher implicit val timeout = Timeout(5 seconds) override def receive: Receive = { case ActorIdentity(p,someRef) if p.equals(path) => someRef foreach { calcActor => calcActor ! Clear calcActor ! Num(13.0) calcActor ! Mul(1.5) ((calcActor ? GetResult).mapTo[String]) foreach println calcActor ! Div(0.0) calcActor ! Div(1.5) calcActor ! Add(100.0) ((calcActor ? GetResult).mapTo[String]) foreach println } } } val localSystem = ActorSystem("localSystem") val localActor = localSystem.actorOf(Props[RemoteCalc],"localActor") scala.io.StdIn.readLine() localSystem.terminate() }