Started to climb the Akka mountain

-- Prerequisites

This tutorial assumes that you have Java 1.6 or later installed on you machine and java on your PATH.

You need to make sure that $JAVA_HOME environment variable is set to the root of the Java distribution. You also need to make sure that the $JAVA_HOME/bin is on your PATH:

$ export JAVA_HOME=/usr/lib/jvm/java-6-openjdk
$ export PATH=$PATH:$JAVA_HOME/bin

You can test your installation by invoking java:

$ java -version
java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.9) (6b20-1.9.9-0ubuntu1~10.04.2)
OpenJDK Server VM (build 19.0-b09, mixed mode)

-- Downloading and installing Scala

ou also need to make sure that the scala-2.9.0/bin (if that is the directory where you installed Scala) is on your PATH:

$ export PATH=$PATH:scala-2.9.0/bin

You can test your installation by invoking scala:

$ scala -version
Scala code runner version 2.9.0.final -- Copyright 2002-2011, LAMP/EPFL

-- Downloading and installing Akka

step1: Akka Microkernel (all modules): akka-microkernel-1.1.3.zip (http://akka.io/downloads/akka-microkernel-1.1.3.zip)

step2: Once you have downloaded the distribution unzip it in the folder you would like to have Akka installed in. In my 
case I choose to install it in /home/shawny/software/akka-microkernel-1.1.3, simply by unzipping it to this directory.

step3: set the AKKA_HOME environment variable to the root of the distribution.

$ cd /home/shawny/software/akka-microkernel-1.1.3
$ export AKKA_HOME=`pwd`
$ echo $AKKA_HOME
/home/shawny/software/akka-microkernel-1.1.3

The distribution looks like this:

$ ls -1
config
doc
lib
src

In the config directory we have the Akka conf files.
In the doc directory we have the documentation, API, doc JARs, and also the source files for the tutorials.
In the lib directory we have the Scala and Akka JARs.
In the src directory we have the source JARs for Akka.

-- Downloading and installing SBT

SBT, short for ‘Simple Build Tool’ is an excellent build system written in Scala.

Ref: https://github.com/harrah/xsbt

-- Creating an Akka SBT project

You do that by stepping into the directory you want to create your project in and invoking the sbt command answering the questions for setting up your project (just pressing ENTER will choose the default in square brackets):

Directory e.g: /home/shawny/workspace/scala/test

$ sbt
Project does not exist, create new project? (y/N/s) y
Name: Tutorial 1
Organization: Hakkers Inc
Version [1.0]:
Scala version [2.9.0-1]:
sbt version [0.7.6.RC0]:

-- Copy jar files from home/shawny/software/akka-microkernel-1.1.3/lib to current project lib

shawny@ubuntu:~/workspace/scala/test/lib$ cp /home/shawny/software/akka-microkernel-1.1.3/lib/*.jar .
shawny@ubuntu:~/workspace/scala/test/lib$ cp /home/shawny/software/akka-microkernel-1.1.3/lib/akka/*.jar .

-- Create scala file "Pi.scala" in /home/shawny/workspace/scala/test/src/main/scala

package akka.tutorial.first.scala


import akka.actor.{Actor, PoisonPill}
import Actor._
import akka.routing.{Routing, CyclicIterator}
import Routing._


import java.util.concurrent.CountDownLatch


object Pi extends App {


  calculate(nrOfWorkers = 4, nrOfElements = 10000, nrOfMessages = 10000)


  // ====================
  // ===== Messages =====
  // ====================
  sealed trait PiMessage
  case object Calculate extends PiMessage
  case class Work(start: Int, nrOfElements: Int) extends PiMessage
  case class Result(value: Double) extends PiMessage


  // ==================
  // ===== Worker =====
  // ==================
  class Worker extends Actor {


    // define the work
    def calculatePiFor(start: Int, nrOfElements: Int): Double = {
      var acc = 0.0
      for (i <- start until (start + nrOfElements))
        acc += 4.0 * (1 - (i % 2) * 2) / (2 * i + 1)
      acc
    }


    def receive = {
      case Work(start, nrOfElements) =>
        self reply Result(calculatePiFor(start, nrOfElements)) // perform the work
    }
  }


  // ==================
  // ===== Master =====
  // ==================
  class Master(
    nrOfWorkers: Int, nrOfMessages: Int, nrOfElements: Int, latch: CountDownLatch)
    extends Actor {


    var pi: Double = _
    var nrOfResults: Int = _
    var start: Long = _


    // create the workers
    val workers = Vector.fill(nrOfWorkers)(actorOf[Worker].start())


    // wrap them with a load-balancing router
    val router = Routing.loadBalancerActor(CyclicIterator(workers)).start()


    // message handler
    def receive = {
      case Calculate =>
        // schedule work
        //for (start <- 0 until nrOfMessages) router ! Work(start, nrOfElements)
        for (i <- 0 until nrOfMessages) router ! Work(i * nrOfElements, nrOfElements)


        // send a PoisonPill to all workers telling them to shut down themselves
        router ! Broadcast(PoisonPill)


        // send a PoisonPill to the router, telling him to shut himself down
        router ! PoisonPill


      case Result(value) =>
        // handle result from the worker
        pi += value
        nrOfResults += 1
        if (nrOfResults == nrOfMessages) self.stop()
    }


    override def preStart() {
      start = System.currentTimeMillis
    }


    override def postStop() {
      // tell the world that the calculation is complete
      println(
        "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis"
        .format(pi, (System.currentTimeMillis - start)))
      latch.countDown()
    }
  }


  // ==================
  // ===== Run it =====
  // ==================
  def calculate(nrOfWorkers: Int, nrOfElements: Int, nrOfMessages: Int) {


    // this latch is only plumbing to know when the calculation is completed
    val latch = new CountDownLatch(1)


    // create the master
    val master = actorOf(
      new Master(nrOfWorkers, nrOfMessages, nrOfElements, latch)).start()


    // start the calculation
    master ! Calculate


    // wait for master to shut down
    latch.await()
  }
}

-- Run it inside SBT

shawny@ubuntu:~/workspace/scala/test$ sbt
[info] Building project scala object using sbt 1.0 against Scala 2.9.0
[info]    using sbt.DefaultProject with sbt 0.7.7 and Scala 2.7.7
> update
[info] 
[info] == update ==
[warn] No dependency configuration found, using defaults.
[info] :: retrieving :: taobao#scala-object-using-sbt_2.9.0 [sync]
[info] 	confs: [default]
[info] 	0 artifacts copied, 0 already retrieved (0kB/49ms)
[info] == update ==
[success] Successful.
[info] 
[info] Total time: 1 s, completed Oct 11, 2011 10:31:15 PM
> compile
[info] 
[info] == compile ==
[info]   Source analysis: 1 new/modified, 0 indirectly invalidated, 0 removed.
[info] Compiling main sources...
[info] Compilation successful.
[info]   Post-analysis: 18 classes.
[info] == compile ==
[success] Successful.
[info] 
[info] Total time: 9 s, completed Oct 11, 2011 10:31:27 PM
> run
[info] 
[info] == copy-resources ==
[info] == copy-resources ==
[info] 
[info] == compile ==
[info]   Source analysis: 0 new/modified, 0 indirectly invalidated, 0 removed.
[info] Compiling main sources...
[info] Nothing to compile.
[info]   Post-analysis: 18 classes.
[info] == compile ==
[info] 
[info] == run ==
[info] Running Pi 
AKKA_HOME is defined as [/home/shawny/software/akka-microkernel-1.1.3], loading config from [/home/shawny/software/akka-microkernel-1.1.3/config/akka.conf].


	Pi estimate: 		3.1415926435897883
	Calculation time: 	859 millis
[info] == run ==
[success] Successful.
[info] 
[info] Total time: 2 s, completed Oct 11, 2011 10:31:32 PM

Ref: http://akka.io/docs/akka/1.1.1/intro/getting-started-first-scala.html
        https://github.com/jboner/akka
        http://akka.io/