MapKeySetView.java

package modern.challenge;

import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentHashMap.KeySetView;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Logger;

public final class MapKeySetView {

    private MapKeySetView() {
        throw new AssertionError("Cannot be instantiated");
    }

    private static final Logger logger = Logger.getLogger(KeySetView.class.getName());

    private static final ConcurrentHashMap<Integer, Integer> map = new ConcurrentHashMap<>();
    private static final AtomicInteger count = new AtomicInteger();
    private static final KeySetView<Integer, Integer> keySetView = map.keySet(-1);

    private static final Producer producer = new Producer();
    private static final Consumer consumer = new Consumer();
    private static final ExecutorService producerService
            = Executors.newFixedThreadPool(2);
    private static final ExecutorService consumerService
            = Executors.newFixedThreadPool(2);

    public static final Random rnd = new Random();

    private static class Producer implements Runnable {

        @Override
        public void run() {
            while (true) {

                try {
                    Thread.sleep(rnd.nextInt(3000));
                } catch (InterruptedException ex) {
                    Thread.currentThread().interrupt();
                    logger.severe(() -> "Exception: " + ex);
                }

                int item = (int) (Math.random() * 1000);
                logger.info(() -> "Produced: " + item
                        + " by " + Thread.currentThread().getName());
                map.put(count.incrementAndGet(), item);
            }
        }
    }

    private static class Consumer implements Runnable {

        @Override
        public void run() {
            while (true) {

                try {
                    Thread.sleep(rnd.nextInt(3000));
                } catch (InterruptedException ex) {
                    Thread.currentThread().interrupt();
                    logger.severe(() -> "Exception: " + ex);
                }

                logger.info(()
                        -> "Key set view: " + keySetView
                        + " by " + Thread.currentThread().getName());
                int size = keySetView.size();

                if (size > 1) {
                    int position = 1 + rnd.nextInt(size - 1);
                    if (position <= size / 2) {
                        logger.info(() -> "Adding item -1 to map on position " + (size + 1)
                                + " by " + Thread.currentThread().getName());
                        keySetView.add(size + 1);
                        logger.info(() -> "Map after add -1: " + keySetView.getMap()
                                + " by " + Thread.currentThread().getName());
                    } else {
                        logger.info(() -> "Remove item from position " + position
                                + " by " + Thread.currentThread().getName());
                        keySetView.remove(position);
                        logger.info(() -> "After removing: " + keySetView.getMap()
                                + " by " + Thread.currentThread().getName());
                    }
                }
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {

        System.setProperty("java.util.logging.SimpleFormatter.format",
                "[%1$tT] [%4$-7s] %5$s %n");

        for (int i = 0; i < 2; i++) {
            producerService.execute(producer);
            consumerService.execute(consumer);
        }

        // since the producer and consumer run in a while(true) the application must be stopped manually
    }
}