Added first tutorial based on Scala and SBT

akka-tutorials/akka-tutorial-pi-sbt/project/build.properties

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+project.organization=se.scalablesolutions.akka
+project.name=Akka Tutorial 1 SBT
+project.version=1.0
+build.scala.versions=2.9.0.RC1
+sbt.version=0.7.5.RC1

akka-tutorials/akka-tutorial-pi-sbt/project/plugins/Plugins.scala

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+import sbt._
+
+class Plugins(info: ProjectInfo) extends PluginDefinition(info) {
+  val akkaRepo   = "Akka Repo" at "http://akka.io/repository"
+  val akkaPlugin = "se.scalablesolutions.akka" % "akka-sbt-plugin" % "1.1-SNAPSHOT"
+}

akka-tutorials/akka-tutorial-pi-sbt/project/plugins/project/build.properties

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+#Project properties
+#Fri Apr 01 12:52:25 CEST 2011
+plugin.uptodate=true

akka-tutorials/akka-tutorial-pi-sbt/src/main/scala/Pi.scala

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+/**
+ * Copyright (C) 2009-2011 Scalable Solutions AB <http://scalablesolutions.se>
+ */
+
+package akka.tutorial.sbt.pi
+
+import akka.actor.{Actor, ActorRef}
+import Actor._
+import akka.routing.{Routing, CyclicIterator}
+import akka.event.EventHandler
+import akka.dispatch.Dispatchers
+
+import System.{currentTimeMillis => now}
+import java.util.concurrent.CountDownLatch
+
+object Main extends App {
+  Pi.calculate
+}
+
+/*
+  Pi estimate:    3.1415926435897883
+
+  === 8 workers (with custom dispatcher 4/4)
+  Calculation time:   5163 millis
+
+  === 8 workers (with default dispatcher)
+  Calculation time:   6789 millis
+
+  === 4 workers
+  Calculation time:   5438 millis
+
+  === 2 workers
+  Calculation time:   6002 millis
+
+  === 1 workers
+  Calculation time:   8173 millis
+*/
+object Pi  {
+  val nrOfWorkers              = 4
+  val nrOfMessages             = 10000
+  val lengthOfCalculationRange = 10000
+
+  // ===== Messages =====
+  sealed trait PiMessage
+  case class Work(arg: Int, fun: (Int) => Double) extends PiMessage
+  case class Result(value: Double) extends PiMessage
+
+  // ===== Worker =====
+  class Worker extends Actor {
+    def receive = {
+      case Work(arg, fun) => self.reply(Result(fun(arg)))
+    }
+  }
+
+  // ===== Master =====
+  class Master(nrOfMessages: Int, latch: CountDownLatch) extends Actor {
+    var pi: Double = _
+    var count: Int = _
+    var start: Long = _
+
+    def receive = {
+      case Result(value) =>
+        pi += value
+        count += 1
+        if (count == nrOfMessages) self.stop
+    }
+
+    override def preStart = start = now
+
+    override def postStop = {
+      EventHandler.info(this, "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis".format(pi, (now - start)))
+      Actor.registry.shutdownAll // shut down all workers
+      latch.countDown
+    }
+  }
+
+  def calculate = {
+    val latch = new CountDownLatch(1)
+
+    // create the master
+    val master = actorOf(new Master(nrOfMessages, latch)).start
+
+    // the master ref is also the 'implicit sender' that the workers should reply to
+    implicit val replyTo = Option(master)
+
+    // create the workers
+    val workers = new Array[ActorRef](nrOfWorkers)
+    for (i <- 0 until nrOfWorkers) workers(i) = actorOf[Worker].start
+
+    // wrap them with a load-balancing router
+    val router = Routing.loadBalancerActor(CyclicIterator(workers)).start
+
+    val fun = (x: Int) => (for (k <- (x * lengthOfCalculationRange) to ((x + 1) * lengthOfCalculationRange - 1)) yield (4 * math.pow(-1, k) / (2 * k + 1))).sum
+
+    // schedule work
+    for (arg <- 0 until nrOfMessages) router ! Work(arg, fun)
+
+    latch.await
+  }
+}
+