ThreadSafeQueue.java

package modern.challenge;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Logger;

public class ThreadSafeQueue {

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

    // Switch to ArrayDeque to see how the same item is consumed multiple times.
    // Since poll() retrieves and removes the head of this queue this should not happen.  
    // private static final Deque<Integer> queue = new ArrayDeque<>(10000);
    private static final BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10000);

    private static final AtomicInteger itemNr = new AtomicInteger();
    private static final Producer producer = new Producer();
    private static final Consumer consumer = new Consumer();
    private static ExecutorService producerService
            = Executors.newFixedThreadPool(3);
    private static ExecutorService consumerService
            = Executors.newFixedThreadPool(3);

    private static class Producer implements Runnable {

        @Override
        public void run() {
            while (true) {
                int item = itemNr.incrementAndGet();
                queue.add(item);
                logger.info(() -> "Produced: " + item
                        + " by " + Thread.currentThread().getName());
            }
        }
    }

    private static class Consumer implements Runnable {

        @Override
        public void run() {
            while (true) {
                Integer item = queue.poll();
                if (item != null) {
                    logger.info(() -> "Consumed: " + item
                            + " 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 < 3; i++) {
            producerService.execute(producer);
            consumerService.execute(consumer);
        }

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