add answers to exercise 1-4 chapter 5

Author: ryblovAV

src/main/scala/org/learningconcurrency/exercises/ch5/Ex2.scala

@@ -1,5 +1,72 @@
-package org.learningconcurrency.exercises.ch5
+package org.learningconcurrency
+package exercises
+package ch5
 
-object Ex2 {
+import scala.util.Random
 
+/**
+ * Count the occurrences of the whitespace character in a randomly generated string,
+ * where the probability of a whitespace at each position is determined by a p parameter.
+ *
+ * Use the parallel foreach method.
+ *
+ * Plot a graph that correlates the running time of this operation with the p parameter.
+ */
+object Ex2 extends App {
+
+  import org.learningconcurrency.ch5._
+
+  var r = new Random
+
+  val chars = ('a' to 'z') ++ ('A' to 'Z')
+
+  def generateSymbol(p: Double): Char =
+    if (r.nextDouble() > p) chars(Random.nextInt(chars.length)) else ' '
+
+  def generateString(p: Double, length: Int = 10000): Seq[Char] = {
+    (0 to length).map((i) => generateSymbol(p))
+  }
+
+  def timedForeach(s: Seq[Char]) = {
+    var count = 0
+    def add = synchronized {
+      count += 1
+    }
+
+    warmedTimed(times = 400) {
+      s.par.foreach((s) => if (s == ' ') add)
+    }
+  }
+
+  def timedCount(s: Seq[Char]) = {
+    warmedTimed(times = 400) {
+      s.par.count(_ == ' ')
+    }
+  }
+
+  //probability
+  val p = (0 until 10).map { i => i / 9.0 }
+
+  log("---- Calculation occurrences with foreach method")
+  val dataForeach = p.map((p) => (p, generateString(p))).map {
+    case (p, s) => log(s"p = $p"); (p, timedForeach(s))
+  }
+
+  log("---- Calculation occurrences with count method")
+  val dataCount = p.map((p) => (p, generateString(p))).map {
+    case (p, s) => log(s"p = $p"); (p, timedCount(s))
+  }
+
+  //plot graph
+  //uses https://github.com/quantifind/wisp
+
+  import com.quantifind.charts.Highcharts._
+
+  hold
+  line(dataForeach)
+  line(dataCount)
+  title("Ch5 Ex2")
+  legend(Seq("foreach method", "count method"))
+  xAxis("probability")
+  yAxis("time (ms)")
 }

src/main/scala/org/learningconcurrency/exercises/ch5/Ex3.scala

@@ -1,5 +1,96 @@
-package org.learningconcurrency.exercises.ch5
+package org.learningconcurrency
+package exercises
+package ch5
 
-object Ex3 {
+import scala.annotation.tailrec
+import scalafx.application.JFXApp
+import scalafx.scene.Scene
+import scalafx.scene.layout.Pane
+import scalafx.scene.paint.Color
+import scalafx.scene.shape.Rectangle
+
+/**
+ * Implement a program that renders the Mandelbrot set in parallel.
+ */
+
+object Ex3 extends JFXApp {
+
+  val width = 400
+  val height = 400
+
+  val minX = -1.75
+  val maxX = 0.8
+
+  val minY = -1.2
+  val maxY = 1.2
+
+  val stepX = (maxX - minX) / width
+  val stepY = (maxY - minY) / height
+
+  val threshold = 300
+
+  case class RGB(red: Int, green: Int, blue: Int)
+
+  case class Pixel(x: Int, y: Int, gray: Double)
+
+  def buildPixel(x: Int, y: Int) = {
+    val xc = minX + stepX * x
+    val yc = minY + stepY * y
+
+    val count = calcIterations(x = 0, y = 0, xc = xc, yc = yc, i = 0)
+    
+    Pixel(x = x, y = y, gray = 1.0 - count * 1.0 / threshold)
+  }
+
+  @tailrec
+  def calcIterations(x: Double, y: Double, xc: Double, yc: Double, i: Int): Int = {
+
+    if ((x * x + y * y < 2) && (i < threshold))
+      calcIterations(
+        x = x * x - y * y + xc,
+        y = 2 * x * y + yc,
+        xc = xc,
+        yc = yc,
+        i  = i + 1
+      )
+    else {
+      i
+    }
+  }
+
+  //render set
+  val pixels = (for {
+    x <- 0 until width
+    y <- 0 until height
+  } yield (x,y)).par.map {
+    case (x,y) => buildPixel(x,y)
+  }
+
+  //build javaFX rectangle
+  val rectangles = pixels.map {
+    case p: Pixel => new Rectangle() {
+      x = p.x
+      y = p.y
+      width = 1
+      height = 1
+      fill = Color.gray(p.gray)
+    }
+  }
+
+  val pane = new Pane {
+    content = rectangles.toList
+  }
+
+  //build scene
+  stage = new JFXApp.PrimaryStage {
+    title.value = "Ch5 Ex3"
+    scene = new Scene {
+      fill = Color.gray(1)
+      content = pane
+    }
+  }
+
+  stage.setHeight(width)
+  stage.setWidth(height)
 
 }