Akka 快速入门

Akka的优点太多,高性能、高可靠、高并发、分布式、可容错、可扩展、事件驱动,不一一叙述。不同版本的API差异很大,本文代码运行在 Scala 2.10.3Akka 2.3.2 之上。

<dependency>
<groupId>com.typesafe.akka</groupId>
<artifactId>akka-actor_2.10</artifactId>
<version>2.3.2</version>
</dependency>
<dependency>
<groupId>org.scala-lang</groupId>
<artifactId>scala-library</artifactId>
<version>2.10.3</version>
</dependency>

定义

定义Actor很简单,继承 akka.actor.Actor ,实现receive方法即可。

class Hello extends Actor {
def receive = {
case msg: String => println("hello " + msg)
case _ => println("unexpected message.")
}
}

启动

创建Actor实例需要通过 ActorSystem 。

val system = ActorSystem("HelloSystem")
val hello = system.actorOf(Props[Hello], name = "hello")
val hello1 = system.actorOf(Props[Hello])
val hello2 = system.actorOf(Props(new Hello()))

如果要在 Actor 中继续创建子 Actor,需要使用内置的 ActorContext 对象。

context.actorOf(Props[children], name = "children")

如果要创建远程 Actor,需要通过 actorSelection 方法,原 actorFor 方法不再使用。

context.actorSelection("akka.tcp://HelloRemoteSystem@127.0.0.1:5150/user/RemoteActor")

发消息

巨简单,就是一个!,可以发送任意类型的消息,此消息是异步的。

hello ! "bruce"
hello ! 10086

同步消息的发送需要使用 Future 对象。

implicit val timeout = Timeout(5 seconds)
val future = hello ? "sha"
val result = Await.result(future, timeout.duration).asInstanceOf[String]

停止

有两种方式停止一个Actor。

一种是通过内部 ActorContext.stop() 方法,该方法会将 children actor 逐层杀掉后,再自刎。

def receive = {
case "stop" => context.stop(self)
...
}

另一种是外部喂毒药,通过 ActorRef.tell() 方法实现。后一个参数是向谁reply,这里显然不需要,传空。

hello.tell(PoisonPill.getInstance, ActorRef.noSender);

哼哈示例

哼哈二将本是两位佛寺的门神俗称,是执金刚神的一种。明代小说《封神演义》作者陈仲琳据此附会两员神将,形象威武凶猛。一名郑伦,能鼻哼白气制敌;一名陈奇,能口哈黄气擒将。

object HengHa extends App {
val system = ActorSystem("HengHaSystem")
val ha = system.actorOf(Props[Ha], name = "ha")
val heng = system.actorOf(Props(new Heng(ha)), name = "heng")
heng ! "start"
}
class Heng(ha: ActorRef) extends Actor {
def receive = {
case "start" => ha ! "heng"
case "ha" =>
println("哈")
ha ! "heng"
case _ => println("heng what?")
}
}
class Ha extends Actor {
def receive = {
case "heng" =>
println("哼")
sender ! "ha"
case _ => println("ha what?")
}
}

Run 起来,结果:

...

远程示例

local工程

application.conf

akka {
loglevel = "DEBUG"
actor {
provider = "akka.remote.RemoteActorRefProvider"
}
remote {
enabled-transports = ["akka.remote.netty.tcp"]
netty.tcp {
hostname = "127.0.0.1"
port = 5155
}
}
}

object Local extends App {
val system = ActorSystem("LocalSystem")
val localActor = system.actorOf(Props[LocalActor], name = "LocalActor") // the local actor
localActor ! "START" // start the action
}
class LocalActor extends Actor {
// create the remote actor
val remote = context.actorSelection("akka.tcp://HelloRemoteSystem@127.0.0.1:5150/user/RemoteActor")
var counter = 0
def receive = {
case "START" =>
remote ! "Hello from the LocalActor"
case msg: String =>
println(s"LocalActor received message: '$msg'")
if (counter < 5) {
sender ! "Hello back to you"
counter += 1
}
}
}

remote工程

application.conf

akka {
loglevel = "DEBUG"
actor {
provider = "akka.remote.RemoteActorRefProvider"
}
remote {
enabled-transports = ["akka.remote.netty.tcp"]
netty.tcp {
hostname = "127.0.0.1"
port = 5150
}
}
}

object HelloRemote extends App {
val system = ActorSystem("HelloRemoteSystem")
val remoteActor = system.actorOf(Props[RemoteActor], name = "RemoteActor")
remoteActor ! "The RemoteActor is alive"
}
class RemoteActor extends Actor {
def receive = {
case msg: String =>
println(s"RemoteActor received message '$msg'")
sender ! "Hello from the RemoteActor"
}
}

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