Hazelcast Demo

HashMapRacer.java

import java.util.HashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.stream.IntStream;

public class HashMapRacer {
    //
    private final HashMap<String, Long> raceTrack;
    private final ExecutorService execService;
    private final String SHARED_KEY = "SUM";
    //
    private final int threadPoolSize;
    private final int taskRepetitionCount;
    //
    private AtomicLong totalTaskExecutionCount;

    public HashMapRacer(final int threadCount, final int taskRepetitionCount) {
        this.raceTrack = new HashMap<>();
        this.raceTrack.put(SHARED_KEY, 0L);
        // init racers
        this.threadPoolSize = threadCount;
        this.taskRepetitionCount = taskRepetitionCount;
        execService = Executors.newFixedThreadPool(threadCount);
    }

    public void initRacers() {
        this.totalTaskExecutionCount = new AtomicLong(0L);
        //
        IntStream.range(0, this.threadPoolSize).forEach((int index) -> {
            execService.execute(() -> {
                for (int i = 0; i < taskRepetitionCount; i++) {
                    long sum = raceTrack.get(SHARED_KEY);
                    System.out.println("SUM value updated! [Thread: " + Thread.currentThread().getName() + " ]" + " sum -> " + sum + " sum+1 -> " + (sum + 1));
                    raceTrack.put(SHARED_KEY, (sum + 1));
                    //
                    totalTaskExecutionCount.incrementAndGet();
                }
            });
        });
    }

    public void completeDemo() throws InterruptedException {
        execService.shutdown();
        this.execService.awaitTermination(10, TimeUnit.SECONDS);
        //
        System.out.println("Demo Completed");
        final long sum = raceTrack.get(SHARED_KEY);
        final long expectedSum = (this.threadPoolSize * this.taskRepetitionCount);
        System.out.println( "[ SUM: " + sum + " ]" + " [ Expected Sum: " + expectedSum + " ] " + " [ Total Task Exec Count: " + totalTaskExecutionCount.get() + " ]");
        totalTaskExecutionCount.set(0L);
    }

    public static void main(String[] args) throws Exception {
        //
        final int threadCount = 9;
        final int taskRepetitionCount = 100;
        //
        HashMapRacer demo = new HashMapRacer(threadCount, taskRepetitionCount);
        demo.initRacers();
        demo.completeDemo();
    }
}

SharedObject.java

class SharedObject {
    private static final Object LOCK = new Object();
    private static Object o = null;

    public static Object retrieve() {
        if (o == null) {
            synchronized (LOCK) {
                // double checked locking
                if (o == null) {
                    o = create();
                }
            }
        }
        return o;
    }

    private static Object create() {
        // mock implementation, would actually return a useful object
        return new Object();
    }
}