Scala，基於JVM的併發語言

無意中看到這篇文章，開始還以為是在Java中實現Threadless的併發，結果看下去才發現是基於JVM的一門語言 Scala。它物件導向，函式式，靜態型別，更重要是克隆了Erlang裡面的程式間通訊的概念。

下載後，使用它的編譯器編譯，生成了很多.class，原來不是用Java來解析執行，而是編譯成JVM相容的位元組碼，並且能夠呼叫java類庫。這裡是一個PingPong的例子

package examples.actors

import scala.actors.Actor
import scala.actors.Actor._

abstract class PingMessage
case class MsgStart() extends PingMessage
case class MsgPingInit(count: int, pong: Pong) extends PingMessage
case class MsgSendPing extends PingMessage
case class MsgPong(sender: Pong) extends PingMessage

abstract class PongMessage
case class MsgPing(sender: Ping) extends PongMessage
case class MsgStop() extends PongMessage

object PingPong {
  def main(args : Array[String]): Unit = {
    val ping = new Ping
    ping.start
    val pong = new Pong
    pong.start
    ping ! MsgPingInit(100000, pong)
    ping ! MsgStart
  }
}

class Ping extends Actor {
  def act(): unit = {
    loop(0, null)
  }
  def loop(pingsLeft: int, pong: Pong): unit = {
    react {
      case MsgPingInit(count, pong) => {
        System.out.println("Ping: Initializing with count:"+count+":"+pong)
        loop(count, pong)
      }
      case MsgStart() => {
        System.out.println("Ping: starting.")
        pong ! MsgPing(this)
        loop(pingsLeft-1, pong)
      }
      case MsgSendPing() => {
        pong ! MsgPing(this)
        loop(pingsLeft-1, pong)
      }
      case MsgPong(pidS) => {
        if (pingsLeft % 100 == 0) {
          System.out.println("Ping: pong from: "+pidS)
        }
        if (pingsLeft > 0)
          this ! MsgSendPing()
        else {
          System.out.println("Ping: Stop.")
          pong ! MsgStop()
        }
        loop(pingsLeft, pong)
      }
    }
  }
}

class Pong extends Actor {
  def act(): unit = {
    loop(0)
  }

  def loop(pongCount: int): unit = {
    react {
      case MsgPing(pidPing) => {
        if (pongCount % 100 == 0) {
          System.out.println("Pong: ping:"+pongCount+" from: "+pidPing)
        }
        pidPing ! MsgPong(this)
        loop(pongCount+1)
      }
      case MsgStop() => {
        System.out.println("Pong: Stop.")
        System.exit(0)
      }
    }
  }
}

編譯：
D:\scala-2.3.3\bin>scalac -d classes D:\scala-2.3.3\doc\scala-devel\scala\exampl
es\actors\PingPong.scala

執行：scala -cp classes examples.actors.PingPong

輸出：
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85300 from: examples.actors.Ping@dd87b2
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85400 from: examples.actors.Ping@dd87b2
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85500 from: examples.actors.Ping@dd87b2
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85600 from: examples.actors.Ping@dd87b2
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85700 from: examples.actors.Ping@dd87b2
Ping: pong from: examples.actors.Pong@1a73d3c
Pong: ping:85800 from: examples.actors.Ping@dd87b2

用JAD反編譯了生成的.class，裡面基本上沒有用太多反射，效能應該還是值得信賴的。

這語言是05年開發的，現在最新版本2.3.3。感覺它只是克隆了微程式間訊息通訊，模式匹配這些部分，對於分佈這方面還沒有涉及。關注之。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/13270562/viewspace-277837/，如需轉載，請註明出處，否則將追究法律責任。