3 Threads Printing numbers in sequence

Issue

I am trying to write a simple code to print numbers in sequence. Scenario is like

Thread  Number
T1        1
T2        2
T3        3
T1        4
T2        5
T3        6
T1        7
T2        8
T3        9
...and so on.

Here is the

public class ThreadNumberPrinter {

    Object monitor = new Object();
    AtomicInteger number = new AtomicInteger(1);

    public static void main(String[] args) {
        ThreadNumberPrinter tnp = new ThreadNumberPrinter();
        Thread t1 = new Thread(tnp.new Printer(1, 3));
        Thread t2 = new Thread(tnp.new Printer(2, 3));
        Thread t3 = new Thread(tnp.new Printer(3, 3));

        t3.start();
        t1.start();
        t2.start();
    }

    class Printer implements Runnable {

        int threadId;
        int numOfThreads;

        public Printer(int id, int nubOfThreads) {
            threadId = id;
            this.numOfThreads = nubOfThreads;
        }

        public void run() {
            print();
        }

        private void print() {
            try {
                while (true) {
                    Thread.sleep(1000l);
                    synchronized (monitor) {
                        if (number.get() % numOfThreads != threadId) {
                            monitor.wait();
                        } else {
                            System.out.println("ThreadId [" + threadId
                                    + "] printing -->"
                                    + number.getAndIncrement());
                            monitor.notifyAll();
                        }
                    }
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

       }

   }

But just after 2nd thread runs and prints the number 2, all thread get into wait stage and nothing gets printed. I am not sure where I am doing wrong. Any help would be greatly appreciated.

Solution

Well, the problem is that modulo 3 % 3 is 0. Change your threadIds to 0..2 instead of 1..3 and hopefully it should work.

Answered By - sodik