MemoryIsANewDisk.java

package org.openjdk.jmh.samples;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.util.Random;

@State(Scope.Benchmark)
public class SortedTest {
    private static final int NO_OF_ITEMS = 5_000_000;

    private int[] values = new int[NO_OF_ITEMS];

    private int[] unsortedOrder = new int[NO_OF_ITEMS];
    private int[] sortedOrder = new int[NO_OF_ITEMS];

    private Random r;


    @Setup
    public void setUp() {
        r = new Random();
        for (int i = 0; i < NO_OF_ITEMS; i++) {
            unsortedOrder[i] = i;
            sortedOrder[i] = i;
            values[i] = r.nextInt();
        }
        shuffleArray(unsortedOrder);

    }

    @Benchmark
    public void testSorted(Blackhole bh) {
        for (int i : sortedOrder) {
            bh.consume(values[i]);
        }
    }

    @Benchmark
    public void testUnsorted(Blackhole bh) {
        for (int i : unsortedOrder) {
            bh.consume(values[i]);
        }
    }

    public static void main(String[] args) throws Throwable {
        Options opt = new OptionsBuilder()
                .include(SortedTest.class.getSimpleName())
                .warmupIterations(5)
                .measurementIterations(20)
                .threads(1)
                .forks(3)
                .syncIterations(true) // try to switch to "false"
                .build();

        new Runner(opt).run();
    }

    static void shuffleArray(int[] ar)
    {
        Random rnd = new Random();
        for (int i = ar.length - 1; i > 0; i--)
        {
            int index = rnd.nextInt(i + 1);
            // Simple swap
            int a = ar[index];
            ar[index] = ar[i];
            ar[i] = a;
        }
    }
}

Benchmark                           Mode  Samples   Score  Score error  Units
o.o.j.s.SortedTest.testSorted      thrpt       60  202.639        5.692  ops/s
o.o.j.s.SortedTest.testUnsorted    thrpt       60   20.917        0.059  ops/s