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Producer-consumer problem - both end up waiting

new to multithreading. I wrote this program which should be a solution to the producer-consumer problem. The problem is that both a producer and a consumer end up in the waiting state. What seems to be wrong? (And everything else what is wrong ^_^) Thanks in advance.
Main class:
package producer.consumer2;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Buffer<Integer> bf = new Buffer<>(10);
Producer prod = new Producer(bf);
Consumer cons = new Consumer(bf);
prod.setConsumer(cons);
cons.setProducer(prod);
new Thread(prod).start();
new Thread(cons).start();
if(quitInput()) {
prod.terminate();
cons.terminate();
}
}
private static boolean quitInput() {
Scanner sc = new Scanner(System.in);
String line = sc.nextLine();
do {
if(line.toLowerCase().equals("q") || line.toLowerCase().equals("quit")) {
sc.close();
return true;
}
line = sc.nextLine();
} while(true);
}
}
Buffer class:
package producer.consumer2;
import java.util.ArrayList;
public class Buffer<E> {
private final int MAX_LENGTH;
private ArrayList<E> values;
public Buffer(int length){
MAX_LENGTH = length;
values = new ArrayList<E>(length);
}
public synchronized void add(E e) {
if(values.size() < MAX_LENGTH) {
values.add(e);
System.out.println(values);
} else {
throw new RuntimeException("Buffer is full at the moment.");
}
}
public synchronized boolean isEmpty() {
return values.size() == 0;
}
public synchronized boolean isFull() {
return values.size() >= MAX_LENGTH ? true : false;
}
public synchronized E remove(int index) {
E val = values.remove(index);
System.out.println(values);
return val;
}
}
Consumer class:
package producer.consumer2;
public class Consumer implements Runnable {
private final Buffer<Integer> bf;
private volatile boolean running = true;
private Producer prod;
public Consumer(Buffer<Integer> bf) {
this.bf = bf;
}
public void setProducer(Producer prod) {
this.prod = prod;
}
#Override
public void run() {
int sum = 0;
int counter = 0;
while (running) {
if (bf.isEmpty()) {
if (prod != null) {
synchronized (prod) {
prod.notify();
}
}
myWait(0);
} else {
sum += bf.remove(0);
counter++;
}
}
System.out.println("for first " + counter + " nums an avg = " + ((double) sum / counter));
}
private void myWait(long millisecs) {
System.out.println("consumer is waiting.");
try {
synchronized (this) {
this.wait(millisecs);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("consumer is NOT waiting.");
}
public void terminate() {
this.running = false;
}
}
Producer class:
package producer.consumer2;
public class Producer implements Runnable {
private final Buffer<Integer> bf;
private volatile boolean running = true;
private Consumer cons;
public Producer(Buffer<Integer> bf) {
this.bf = bf;
}
public void setConsumer(Consumer cons) {
this.cons = cons;
}
#Override
public void run() {
int counter = 1;
while (running) {
if (bf.isFull()) {
if (cons != null) {
synchronized (cons) {
cons.notify();
}
}
myWait(0);
} else {
bf.add(counter);
counter++;
}
}
}
private void myWait(long millisecs) {
System.out.println("producer is waiting.");
try {
synchronized (this) {
this.wait(millisecs);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("producer is NOT waiting.");
}
public void terminate() {
this.running = false;
}
}

Looks like a regular case of 'missed signal'. Since both consumer and producer just wait without checking a condition, yu have no way to ensure the notify actually happens during the waiting.
e.g. in Consumer :
if (prod != null) {
synchronized (prod) {
prod.notify();
}
}
myWait(0);
Note that if, after prod.notify() the Production thread does all of its work, and notifies the consumer, before it even starts waiting, the consumer will start waiting for a signal that's already been given, and missed.
Always take into account that waiting may not be needed anymore. So always check a condition before even starting to wait. In your case here, the consumer should not even begin waiting if the buffer is full. And likewise the producer should not start waiting if the buffer is empty.
It's also possible to get spurious wake ups. So you'll have to re-check the condition when returning from waiting. The typical idiom is this :
synchronized(monitor) {
while (!stateBasedCondition) {
monitor.wait();
}
}

Producer Consumer using Multithreading

My producer-consumer problem runs perfectly for 1 producer and 1 consumer. It fails to run for 2 producer and 2 consumer. It is reaching some unknown deadlock state. I'm not able to debug. Can anyone please help me with it?
Constraint: One Producer has to produce upto 64 items. And consumer runs until it clears all produced items.
import java.util.Random;
import java.util.Scanner;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
class Producer implements Runnable {
private static int count = 1;
private Random rg = new Random();
private BlockingQueue<Object> queue = null;
private static int pc = 0;
static int maxPc = 0;
public Producer(BlockingQueue<Object> queue) {
this.queue = queue;
}
#Override
public void run() {
synchronized (queue) {
while(pc <= maxPc) {
try {
produce(pc++);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public void produce(int pc) throws InterruptedException {
synchronized(queue) {
while(queue.size() == 8) {
System.out.println(Thread.currentThread().getName() + " : Buffer full: waiting for consumer");
queue.wait();
}
}
synchronized(queue) {
System.out.println("Producer: " + Thread.currentThread().getName() + " adding item "+ pc + " to the queue");
queue.add(pc);
//Thread.sleep(1);
queue.notifyAll();
}
}
}
class Consumer implements Runnable {
private static int consumeCount = 0;
private BlockingQueue<Object> queue = null;
private Random rg = new Random();
public Consumer(BlockingQueue<Object> queue) {
this.queue = queue;
}
#Override
public void run() {
while(true) {
try {
consume();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void consume() throws InterruptedException {
synchronized(queue) {
while(queue.isEmpty()) {
System.out.println(Thread.currentThread().getName() + ": Buffer empty: waiting for producer");
queue.wait();
}
}
synchronized(queue) {
//Thread.sleep(1);
System.out.println("Consumer: "+ Thread.currentThread().getName()+" removing item " + queue.take() + " from the queue");
consumeCount++;
queue.notifyAll();
if(consumeCount == ParallelProcess.maxCC + 1)
System.exit(0);
}
}
}
public class ParallelProcess {
static int maxCC = 0;
int numProducer;
int numConsumer;
private Thread[] cThreads;
private Thread[] pThreads;
private BlockingQueue<Object> queue = null;
public ParallelProcess(int numProducer, int numConsumer, int queueSize) {
this.numProducer = numProducer;
this.numConsumer = numConsumer;
this.queue = new ArrayBlockingQueue<Object>(queueSize);
// create consumer thread objects
cThreads = new Thread[numConsumer];
for (int i = 0; i < numConsumer; i++) {
cThreads[i] = new Thread(new Consumer(queue));
}
// create producer thread objects
pThreads = new Thread[numProducer];
for (int i = 0; i < numProducer; i++) {
pThreads[i] = new Thread(new Producer(queue));
}
}
public void execute() {
// start consumer threads
for (Thread t : cThreads) {
t.start();
}
// start producer threads
for (Thread t : pThreads) {
//System.out.println("tc");
t.start();
}
}
public static void main(String[] args) {
// provide number of producers, number of consumers and the
// max-queue-length
Scanner sc = new Scanner(System.in);
System.out.println("Enter no. of producer and conumer");
int n = sc.nextInt();
ParallelProcess process = new ParallelProcess(n, n, 8);
maxCC = n*64;
Producer.maxPc = maxCC;
process.execute();
// (new Thread()).start();
System.out.println("Thread: " + Thread.currentThread().getName() + " `enter code here`FINISHED");
}
}

First, you should merge synchronized block of the wait and queue.add(pc) to make it automatic, otherwise it might cause some inconstency.
Secondly, you should call queue.notify before wait, otherwise both producer and consumer might be blocked in wait state.
produce method:
public void produce(int pc) throws InterruptedException {
synchronized(queue) {
while(queue.size() == 8) {
System.out.println(Thread.currentThread().getName() + " : Buffer full: waiting for consumer");
queue.notifyAll();
queue.wait();
}
System.out.println("Producer: " + Thread.currentThread().getName() + " adding item "+ pc + " to the queue");
queue.add(pc);
//Thread.sleep(1);
queue.notifyAll();
}
}
consume method:
public void consume() throws InterruptedException {
synchronized(queue) {
while(queue.isEmpty()) {
System.out.println(Thread.currentThread().getName() + ": Buffer empty: waiting for producer");
queue.notifyAll();
queue.wait();
}
System.out.println("Consumer: "+ Thread.currentThread().getName()+" removing item " + queue.take() + " from the queue");
consumeCount++;
if(consumeCount == ParallelProcess.maxCC + 1)
System.exit(0);
}
}

Java - Improving Consumer Producer with MultiThreading using ConcurrentHashMap

i am trying to solve consumer-producer problem with multi-Threading by using ConcurrentHashMap and newFixedThreadPool.
my goal is to make diffrerent threads to put and remove from hashmap simultaneously and Ensure that map size will not be bigger than MAXQUEUE,
unique key to each element.
the program below isn't behave as i descirbed, it's fill the map until the size is 20 and then it removes 20 and so on.
I need some help to make it bahave as the description,
also i will be glad to get suggestion to improve the code.
this is my Producer Class:
public class Producer extends Thread
{
static final int MAXQUEUE = 20;
private ConcurrentHashMap<Long, String> myMap = new ConcurrentHashMap<Long, String>();
private AtomicLong m_Key = new AtomicLong(0);
public void run()
{
try
{
while (true)
{
putMessage();
}
} catch (InterruptedException e)
{
}
}
private void putMessage() throws InterruptedException
{
synchronized(this)
{
while (myMap.size() == MAXQUEUE)
{
wait();
}
myMap.put(this.m_Key.incrementAndGet(), "Hello");
System.out.println(Thread.currentThread().getName() + " put message; key " + this.m_Key);
notify();
//Later, when the necessary event happens, the thread that is running it calls notify() from a block synchronized on the same object.
}
}
// Called by Consumer
public void removeElementFromMap() throws InterruptedException
{
synchronized(this)
{
notify();
while (myMap.size() == 0)
{
wait();
}
for (Iterator<Entry<Long, String>> iter = this.myMap.entrySet().iterator() ; iter.hasNext() ; )
{
Map.Entry<Long, String> entry = iter.next();
System.out.println("Removed element with key " + entry.getKey() );
iter.remove();
}
}
}
}
Consumer Class:
public class Consumer extends Thread
{
Producer producer;
public void Consumer(Producer p)
{
producer = p;
}
public void run()
{
try
{
while (true)
{
producer.removeElementFromMap();
}
} catch (InterruptedException e)
{
e.printStackTrace();
}
}
Main Class:
public class Main
{
public static void main(String[] args)
{
Producer producer = new Producer();
ExecutorService producersExecutors = Executors.newFixedThreadPool(5);
Consumer consumer = new Consumer(producer);
ExecutorService consumersExecutors = Executors.newFixedThreadPool(5);
for(int i=0;i<5;i++)
{
producersExecutors.execute(producer);
consumersExecutors.execute(consumer);
}
}
}

You can use blocking queues available in Java e.g. ArrayBlockingQueue.
But if you still want to use map and your own way of handling this then may be you can do it like below -
public class MapTest {
public static void main(String[] args) {
DataStore dataStore = new DataStore(100);
ExecutorService executorService = Executors.newFixedThreadPool(10);
for (int i = 0; i < 5; i++) {
executorService.execute(new Producer(dataStore));
executorService.execute(new Consumer(dataStore));
}
}
}
class DataStore {
private final int maxQueueSize;
private Lock lock = new ReentrantLock();
private AtomicInteger queueSize = new AtomicInteger(0);
private AtomicLong keyGenerator = new AtomicLong(0);
private Map<Long, String> map = new HashMap<Long, String>();
public DataStore(int maxQueueSize) {
this.maxQueueSize = maxQueueSize;
}
public void putMessage() throws InterruptedException {
while (queueSize.get() == maxQueueSize) {
Thread.sleep(10);
}
lock.lock();
try {
if (queueSize.get() < maxQueueSize) {
map.put(keyGenerator.incrementAndGet(), "Hello");
queueSize.incrementAndGet();
System.out.println(Thread.currentThread().getName() + " put message; key " + keyGenerator.get() + ", queue size: " + queueSize.get());
}
} finally {
lock.unlock();
}
}
public void removeMessage() throws InterruptedException {
while (queueSize.get() == 0) {
Thread.sleep(10);
}
lock.lock();
try {
if (queueSize.get() > 0) {
Iterator<Long> keyIterator = map.keySet().iterator();
if (keyIterator.hasNext()) {
Long key = keyIterator.next();
map.remove(key);
queueSize.decrementAndGet();
System.out.println(Thread.currentThread().getName() + " removed message; key: " + key + ", queue size: " + queueSize.get());
}
}
} finally {
lock.unlock();
}
}
}
class Producer implements Runnable {
private DataStore dataStore;
public Producer(DataStore dataStore) {
this.dataStore = dataStore;
}
public void run() {
try {
while (true) {
dataStore.putMessage();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class Consumer implements Runnable {
private DataStore dataStore;
public Consumer(DataStore dataStore) {
this.dataStore = dataStore;
}
public void run() {
try {
while (true) {
dataStore.removeMessage();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

How to make sure two threads printing even odd numbers maintain even first then odd order for this implementation?

I have created two runnable jobs: PrintEvenNumbersJob and PrintOddNumbersJob and spawned two threads to execute these jobs. This seems to work perfectly fine! But I smell something suspicious about this implementation. Can I have some comments and advice on this implementation?
The problem that I see with this implementation is that the program terminates only when thread1 gains the lock to the object lock first otherwise it print the odd first even second order and doesn't terminate unless I supply yet another statement "lock.notify" after for statement in PrintEvenNumbersJob (as in this implementation). My question here is how to make sure that thread1 is executed first.
public class PrintEvenNumbersJob implements Runnable {
private Object lock;
public PrintEvenNumbersJob(Object lock) {
this.lock = lock;
}
#Override
public void run() {
synchronized (lock) {
for (int i = 0; i <= 10; i += 2) {
lock.notify();
System.out.println(i);
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
lock.notify(); // not required if thread1 gains lock first
}
}
}
public class PrintOddNumbersJob implements Runnable {
private Object lock;
public PrintOddNumbersJob(Object lock) {
this.lock = lock;
}
#Override
public void run() {
synchronized (lock) {
for (int i = 1; i < 10; i += 2) {
lock.notify();
System.out.println(i);
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
lock.notify();
}
}
}
public class EvenOddManager {
public static void main(String[] args) {
Object lock = new Object();
PrintEvenNumbersJob printEvenNumbersJob = new PrintEvenNumbersJob(lock);
PrintOddNumbersJob printOddNumbersJob = new PrintOddNumbersJob(lock);
Thread thread1 = new Thread(printEvenNumbersJob);
Thread thread2 = new Thread(printOddNumbersJob);
thread2.start();
thread1.start();
}
}

Have you try using Semaphores? It's easier because you don't need to worry about the order that wait and notify are called (if you call notify before the wait, it's "lost")
Sample code:
import java.util.concurrent.*;
public class Test {
private final Semaphore oddJobPermits = new Semaphore(0);
private final Semaphore evenJobPermits = new Semaphore(1);
private class EvenJob implements Runnable {
public void run() {
for (int i = 0; i < 10; i++) {
try {
evenJobPermits.acquire();
System.out.println(i * 2);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
oddJobPermits.release();
}
}
}
}
private class OddJob implements Runnable {
public void run() {
for (int i = 0; i < 10; i++) {
try {
oddJobPermits.acquire();
System.out.println(i * 2 + 1);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
evenJobPermits.release();
}
}
}
}
public void run() {
new Thread(new EvenJob()).start();
new Thread(new OddJob()).start();
}
public static void main(String[] args) {
new Test().run();
}
}

I believe you will need a referee:
public class Referee {
private boolean evensTurn = true;
public void waitMyTurn(boolean even) {
synchronized(this) {
while (even != evensTurn) {
try {
wait();
} finally {
}
}
}
}
public void done() {
synchronized(this) {
evensTurn = !evensTurn;
notify();
}
}
}
public class PrintEvenNumbersJob implements Runnable {
private Referee referee;
public PrintEvenNumbersJob(Referee referee) {
this.referee = referee;
}
#Override
public void run() {
for (int i = 0; i <= 10; i += 2) {
referee.waitMyTurn(true);
System.out.println(i);
referee.done();
}
}
}
public class PrintOddNumbersJob implements Runnable {
private Referee referee;
public PrintOddNumbersJob(Referee referee) {
this.referee = referee;
}
#Override
public void run() {
for (int i = 0; i <= 10; i += 2) {
referee.waitMyTurn(false);
System.out.println(i);
referee.done();
}
}
}

I tried and tested this code. It works using Semaphore
public class TestSemaphore
{
public static void main(String[] args)
throws Exception
{
AtomicInteger count = new AtomicInteger();
Semaphore s = new Semaphore(1, true);
Semaphore t = new Semaphore(1, true);
OddNumberThread oThread = new OddNumberThread(count, s, t);
EvenNumberThread eThread = new EvenNumberThread(count, s, t);
eThread.start();
oThread.start();
}
static class EvenNumberThread
extends Thread
{
private AtomicInteger count;
private Semaphore s, t;
public EvenNumberThread(AtomicInteger pCount, Semaphore pS, Semaphore pT)
{
super("Even");
count = pCount;
s = pS;
t = pT;
}
#Override
public void run()
{
// Make this thread wait until even thread starts, Order will be incorrect if removed these lines.
s.acquireUninterruptibly();
while (count.intValue() <= 10)
{
try
{
// Double checking to make it work
s.acquireUninterruptibly();
System.out.println(getName() + " " + count.getAndIncrement());
}
finally
{
t.release();
}
}
}
}
static class OddNumberThread
extends Thread
{
private AtomicInteger count;
private Semaphore s, t;
public OddNumberThread(AtomicInteger pCount, Semaphore pS, Semaphore pT)
{
super("Odd");
count = pCount;
s = pS;
t = pT;
}
#Override
public void run()
{
// Start this thread first and start printing, Order will be incorrect if removed these lines.
t.acquireUninterruptibly();
s.release();
while (count.intValue() <= 10)
{
try
{
t.acquireUninterruptibly();
System.out.println(getName() + " " + count.getAndIncrement());
}
finally
{
s.release();
}
}
}
}
}

Producer Consumer using threads

I’m writing a program that implements the Producer Consumer problem in Java using multithreading concepts. Below are few details how I’m supposed to do it:
1) The main thread should create a buffer with capacity specified as a command line argument. The number of producer and consumer threads are also specified as command line arguments. I’m supposed to assign a unique number to each producer and consumer thread. How do I assign a unique number to producer and consumer threads?
2) The producer thread operates in an infinite loop. It produces a data item (a string) with the following format: <producer number>_<data item number>. For example the 1st data item from thread number 1 will be 1_1 and second data item from thread number 3 will be 3_2. How do create data items in such a format?
3) Then the Producer thread writes an entry into the producer log file (< producer number > “Generated” <data item>). Upon writing the log entry, it attempts to insert into the buffer. If insertion is successful, it creates an entry into the log file (<producer number> <data item> “Insertion successful”). How do I write such a code?
Below is the Java code I wrote.
import java.util.*;
import java.util.logging.*;
public class PC2
{
public static void main(String args[])
{
ArrayList<Integer> queue = new ArrayList<Integer>();
int size = Integer.parseInt(args[2]);
Thread[] prod = new Thread[Integer.parseInt(args[0])];
Thread[] cons = new Thread[Integer.parseInt(args[1])];
for(int i=0; i<prod.length; i++)
{
prod[i] = new Thread(new Producer(queue, size));
prod[i].start();
}
for(int i=0; i<cons.length; i++)
{
cons[i] = new Thread(new Consumer(queue, size));
cons[i].start();
}
}
}
class Producer extends Thread
{
private final ArrayList<Integer> queue;
private final int size;
public Producer(ArrayList<Integer> queue, int size)
{
this.queue = queue;
this.size = size;
}
public void run()
{
while(true){
for(int i=0; i<size; i++)
{
System.out.println("Produced: "+i+" by id " +Thread.currentThread().getId());
try
{
produce(i);
Thread.sleep(3000);
}
catch(Exception e)
{
Logger.getLogger(Producer.class.getName()).log(Level.SEVERE, null, e);
}
}}
}
public void produce(int i) throws InterruptedException
{
while(queue.size() == size)
{
synchronized(queue)
{
System.out.println("Queue is full "+Thread.currentThread().getName() +" is waiting, size: "+queue.size());
queue.wait();
}
}
synchronized(queue)
{
queue.add(i);
queue.notifyAll();
}
}
}
class Consumer extends Thread
{
private final ArrayList<Integer> queue;
private final int size;
public Consumer(ArrayList<Integer> queue, int size)
{
this.queue = queue;
this.size = size;
}
public void run()
{
while(true)
{
try
{ System.out.println("Consumed: "+consume());
Thread.sleep(1000);
}
catch(Exception e)
{
Logger.getLogger(Consumer.class.getName()).log(Level.SEVERE, null, e);
}
}
}
public int consume() throws InterruptedException
{
while(queue.isEmpty())
{
synchronized(queue)
{
System.out.println("Queue is empty "+Thread.currentThread().getName()+" is waiting, size: "+queue.size());
queue.wait();
}
}
synchronized (queue)
{
queue.notifyAll();
System.out.println("Consumed by id "+Thread.currentThread().getId());
return (Integer) queue.remove(0);
}
}
}
How can I carry out the above steps?

I’m supposed to assign a unique number to each producer and consumer
thread. How do I assign a unique number to producer and consumer
threads?
Add an instance (non-static) variable to the Producer/Consumer classes. When you initialize the new Producer/Consumer Objects, pass in the unique number. You can keep track of what number you're on with an int counter in your main class.
2) The producer thread operates in an infinite loop. It produces a
data item (a string) with the following format: < producer number >_<
data item number > . For example the 1st data item from thread number
1 will be 1_1 and second data item from thread number 3 will be 3_2.
How do create data items in such a format?
Use synchronized methods and/or atomic variables. Look into Java Concurrency.
3) Then the Producer thread writes an entry into the producer log file
(< producer number > “Generated” < data item >). Upon writing the log
entry, it attempts to insert into the buffer. If insertion is
successful, it creates an entry into the log file (< producer number >
< data item > “Insertion successful”). How do I write such a code?
My answer is the same as the previous question: read about Java concurrency. Spend an hour reading about synchronization, locks, and atomic variables and I guarantee you will easily write your program.

For producer consumer problem best solution is BlockingQueue. I was testing a few things so designed same kind of program now modified it as per your need.
See if it helps.
import java.util.concurrent.*;
public class ThreadingExample {
public static void main(String args[]){
BlockingQueue<Message> blockingQueue = new ArrayBlockingQueue<Message>(100);
ExecutorService exec = Executors.newCachedThreadPool();
exec.execute(new Producer(blockingQueue));
exec.execute(new Consumer(blockingQueue));
}
}
class Message{
private static int count=0;
int messageId;
Message(){
this.messageId=count++;
System.out.print("message Id"+messageId+" Created ");
}
}
class Producer implements Runnable{
private BlockingQueue<Message> blockingQueue;
Producer(BlockingQueue<Message> blockingQueue){
this.blockingQueue=blockingQueue;
}
#Override
public void run(){
while(!Thread.interrupted()){
System.out.print("Producer Started");
try {
blockingQueue.put(new Message());
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Producer Done");
}
}
}
class Consumer implements Runnable{
private BlockingQueue<Message> blockingQueue;
Consumer(BlockingQueue<Message> blockingQueue){
this.blockingQueue=blockingQueue;
}
#Override
public void run(){
while(!Thread.interrupted()){
System.out.print("Concumer Started");
try{
Message message = blockingQueue.take();
System.out.print("message Id"+message.messageId+" Consumed ");
}
catch(InterruptedException e){
e.printStackTrace();
}
System.out.println("Concumer Done");
}
}
}

I tried the following which might work for you, except for the buffer condition on 3, which you can add the part of the code by yourself.
Hope this helps.
public class Message {
private String msg;
public Message(String msg) {
super();
this.msg = msg;
}
public String getMsg(){
return msg;
}
}
import java.util.concurrent.BlockingQueue;
public class Producer implements Runnable {
private BlockingQueue<Message> queue;
private boolean run = true;
public Producer(BlockingQueue<Message> queue) {
super();
this.queue = queue;
}
public void setRun(boolean val) {
this.run = val;
}
#Override
public void run() {
int i = 0;
while (run) {
Message msg = new Message(Thread.currentThread().getName() + "_"+ i);
try {
Thread.sleep(i * 100);
queue.put(msg);
System.out.println("Producer: "+Thread.currentThread().getName()+" produced and added to the queue: "+msg.getMsg());
} catch (InterruptedException e) {
e.printStackTrace();
}
i++;
if(i==10){
setRun(false);
System.out.println(Thread.currentThread().getName()+" stopped");
}
}
}
}
import java.util.concurrent.BlockingQueue;
public class Consumer implements Runnable{
private BlockingQueue<Message> queue;
private boolean run = true;
public Consumer(BlockingQueue<Message> queue) {
super();
this.queue = queue;
}
public void setRun(boolean val){
this.run = val;
}
#Override
public void run() {
while(run){
try {
Thread.sleep(100);
Message msg = queue.take();
System.out.println("Consumer: "+Thread.currentThread().getName()+" generated/consumed "+msg.getMsg());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
import java.util.Scanner;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
public class ProducerConsumerMain {
public static void main(String[] args) {
System.out
.println("please enter the number of producer:consumer:size of the queue in order");
Scanner scan = new Scanner(System.in);
Thread[] prodThreads = new Thread[scan.nextInt()];
Thread[] consThreads = new Thread[scan.nextInt()];
BlockingQueue<Message> queue = new ArrayBlockingQueue<Message>(scan.nextInt());
for (int i = 0; i < prodThreads.length; i++) {
prodThreads[i] = new Thread(new Producer(queue), "" + i);
prodThreads[i].start();
}
for (int i = 0; i < consThreads.length; i++) {
consThreads[i] = new Thread(new Consumer(queue), "" + i);
consThreads[i].start();
}
}
}

Please refer the below code. You can change the constant values based on the command line arguments. I have tested the code, its working as per your requirement.
import java.util.LinkedList;
import java.util.Queue;
public class ProducerConsumerProblem {
public static int CAPACITY = 10; // At a time maximum of 10 tasks can be
// produced.
public static int PRODUCERS = 2;
public static int CONSUMERS = 4;
public static void main(String args[]) {
Queue<String> mTasks = new LinkedList<String>();
for (int i = 1; i <= PRODUCERS; i++) {
Thread producer = new Thread(new Producer(mTasks));
producer.setName("Producer " + i);
producer.start();
}
for (int i = 1; i <= CONSUMERS; i++) {
Thread consumer = new Thread(new Consumer(mTasks));
consumer.setName("Consumer " + i);
consumer.start();
}
}
}
class Producer implements Runnable {
Queue<String> mSharedTasks;
int taskCount = 1;
public Producer(Queue<String> mSharedTasks) {
super();
this.mSharedTasks = mSharedTasks;
}
#Override
public void run() {
while (true) {
synchronized (mSharedTasks) {
try {
if (mSharedTasks.size() == ProducerConsumerProblem.CAPACITY) {
System.out.println("Producer Waiting!!");
mSharedTasks.wait();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
while (mSharedTasks.size() != ProducerConsumerProblem.CAPACITY) {
try {
Thread.sleep(50);
} catch (InterruptedException e) {
}
String produceHere = Thread.currentThread().getName()
+ "_Item number_" + taskCount++;
synchronized (mSharedTasks) {
mSharedTasks.add(produceHere);
System.out.println(produceHere);
if (mSharedTasks.size() == 1) {
mSharedTasks.notifyAll(); // Informs consumer that there
// is something to consume.
}
}
}
}
}
}
class Consumer implements Runnable {
Queue<String> mSharedTasks;
public Consumer(Queue<String> mSharedTasks) {
super();
this.mSharedTasks = mSharedTasks;
}
#Override
public void run() {
while (true) {
synchronized (mSharedTasks) {
if (mSharedTasks.isEmpty()) { // Checks whether there is no task
// to consume.
try {
mSharedTasks.wait(); // Waits for producer to produce!
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
while (!mSharedTasks.isEmpty()) { // Consumes till task list is
// empty
try {
// Consumer consumes late hence producer has to wait...!
Thread.sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
synchronized (mSharedTasks) {
System.out.println(Thread.currentThread().getName()
+ " consumed " + mSharedTasks.poll());
if (mSharedTasks.size() == ProducerConsumerProblem.CAPACITY - 1)
mSharedTasks.notifyAll();
}
}
}
}
}

public class ProducerConsumerTest {
public static void main(String[] args) {
CubbyHole c = new CubbyHole();
Producer p1 = new Producer(c, 1);
Consumer c1 = new Consumer(c, 1);
p1.start();
c1.start();
}
}
class CubbyHole {
private int contents;
private boolean available = false;
public synchronized int get() {
while (available == false) {
try {
wait();
} catch (InterruptedException e) {
}
}
available = false;
notifyAll();
return contents;
}
public synchronized void put(int value) {
while (available == true) {
try {
wait();
} catch (InterruptedException e) {
}
}
contents = value;
available = true;
notifyAll();
}
}
class Consumer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Consumer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
int value = 0;
for (int i = 0; i < 10; i++) {
value = cubbyhole.get();
System.out.println("Consumer #"
+ this.number
+ " got: " + value);
}
}
}
class Producer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Producer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
for (int i = 0; i < 10; i++) {
cubbyhole.put(i);
System.out.println("Producer #" + this.number
+ " put: " + i);
try {
sleep((int) (Math.random() * 100));
} catch (InterruptedException e) {
}
}
}
}