Publisher-Subscriber Thread Implementation

PublisherSubscriberTest.java

package edu.pk.java.test;

import java.util.Random;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

import static edu.pk.java.test.PublisherSubscriberTest.*;

public class PublisherSubscriberTest {
    private static final int QUEUE_MAX_SIZE = 100;
    public static final long THREAD_WAIT_TIME_IN_MS = 20;

    public static void main(String[] args) {
        BlockingQueue<Integer> buffer = new ArrayBlockingQueue<>(QUEUE_MAX_SIZE);
        Writer writer = new Writer(buffer);
        Reader reader1 = new Reader(buffer);
        Reader reader2 = new Reader(buffer);
        Reader reader3 = new Reader(buffer);
        new Thread(writer).start();
        new Thread(reader1).start();
        new Thread(reader2).start();
        new Thread(reader3).start();

        try {
            Thread.sleep(200L); // This is for testing purpose. Wait and Send shutdown signal after this.
        } catch (InterruptedException e) {
        }
        Writer.setShutDown(true);
        Reader.setShutDown(true, false);
    }
}

class Writer implements Runnable {
    private BlockingQueue<Integer> queue;
    private static volatile boolean isShutDown;

    public Writer(BlockingQueue<Integer> queue) {
        this.queue = queue;
    }

    @Override
    public void run() {
        Random random = new Random();
        while (!isShutDown) {
            int nextInt = random.nextInt(Integer.MAX_VALUE);
            try {
                // wait for 200ms, then retry
                while (!queue.offer(nextInt, THREAD_WAIT_TIME_IN_MS, TimeUnit.MILLISECONDS)) {
                    System.out.println("Retrying........");
                }
                System.out.printf("\n%s:%s -> %d", "Writing by", Thread.currentThread().getName(), nextInt);
            } catch (InterruptedException e) {
            }
        }
    }

    public static void setShutDown(boolean shutDown) {
        isShutDown = shutDown;
    }
}

class Reader implements Runnable {
    private BlockingQueue<Integer> queue;
    private static volatile boolean isShutDown; // this will trigger shutdown signal but it will read the remaining items from the buffer if isForced = FALSE
    private static volatile boolean isForced; // this is to stop immediately

    public Reader(BlockingQueue<Integer> queue) {
        this.queue = queue;
    }

    @Override
    public void run() {
        while (true) {
            // check for shutdown signal
            boolean shutdown = false;
            if (isShutDown && isForced)
                shutdown = true;
            else if (isShutDown && !isForced && queue.size() < 1) // if isForced = FALSE, read remaining items from buffer
                shutdown = true;

            if (shutdown) {
                break; // Stop Reading
            }
            try {
                // Wait for 200ms if no item to retrieve from buffer
                Integer poll = queue.poll(THREAD_WAIT_TIME_IN_MS, TimeUnit.MILLISECONDS);
                if (poll != null)
                    System.out.printf("\n%30s:%s -> %d", "Reading by", Thread.currentThread().getName(), poll);
            } catch (InterruptedException e) {
            }
        }
        System.out.println("Remaining items:" + queue);
    }

    public static void setShutDown(boolean shutDown, boolean forced) {
        isShutDown = shutDown;
        isForced = forced;
    }
}