Test sequential and parallel mandelbrot in Java 8 with JMH. (http://openjdk.java.net/projects/code-tools/jmh/)

Mandelbrot.java

package benchmark;

import java.util.stream.*;
import org.openjdk.jmh.annotations.*;
import java.util.concurrent.TimeUnit;
import java.util.*;
 
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@BenchmarkMode(Mode.AverageTime)
public class MyBenchmark {
 
    // example ported from https://msmvps.com/blogs/jon_skeet/archive/2007/10/03/linq-to-silliness-generating-a-mandelbrot-with-parallel-potential.aspx
    static int MaxIterations = 1000;
    static double SampleWidth = 3.2;
    static double SampleHeight = 2.5;
    static double OffsetX = -2.1;
    static double OffsetY = -1.25;
    static int ImageWidth = 900;
    static int ImageHeight = (int) (SampleHeight * ImageWidth / SampleWidth);
    static double[] rowPoints, columnPoints;
 
    static {
	rowPoints = IntStream.range(0, ImageHeight).mapToDouble(i -> i).toArray();
	columnPoints = IntStream.range(0, ImageWidth).mapToDouble(i -> i).toArray();
    }
 
    static int ComputeMandelbrotIndex(double row, double col) {
	double x = (col * SampleWidth) / ImageWidth + OffsetX;
	double y = (row * SampleHeight) / ImageHeight + OffsetY;
 
	double y0 = y;
	double x0 = x;
 
	for (int i = 0; i < MaxIterations; i++) {
	    if (x * x + y * y >= 4) {
		return (byte) ((i % 255) + 1);
	    }
	    double xtemp = x * x - y * y + x0;
	    y = 2 * x * y + y0;
	    x = xtemp;
	}
	return 0;
    }
 
    @GenerateMicroBenchmark
    public double[] mandelbrotSeq() {
	double[] data
	    = DoubleStream.of(rowPoints)
	    .flatMap(rowPoint -> DoubleStream.of(columnPoints)
		     .map(columnPoint -> ComputeMandelbrotIndex(rowPoint, columnPoint)))
	    .toArray();
	return data;
    }
 
    @GenerateMicroBenchmark
    public double[] mandelbrotPar() {
	double[] data
	    = DoubleStream.of(rowPoints)
	    .parallel()
	    .flatMap(rowPoint -> DoubleStream.of(columnPoints)
		     .map(columnPoint -> ComputeMandelbrotIndex(rowPoint, columnPoint)))
	    .toArray();
	return data;
    }
}