Home > Programming > Series About Java Concurrency – Pt. 5

Series About Java Concurrency – Pt. 5

After quite some time, here is a concurrency related puzzle once again: Take a look at the following program and try to predict its output:

package com.wordpress.mlangc.concurrent;

import java.util.concurrent.atomic.AtomicInteger;

public class ThreadNoMore extends Thread
{
    private static final int N_THREADS = 16;
    private static final AtomicInteger threadsStarted = new AtomicInteger();
    
    private final long ctorThreadId = Thread.currentThread().getId();
    
    @Override
    public synchronized void start()
    {
        if(ctorThreadId != Thread.currentThread().getId())
            threadsStarted.incrementAndGet();
    }
    
    public static void main(String[] args) throws InterruptedException
    {
        Thread[] threads = new Thread[N_THREADS];
        for(int i = 0; i != N_THREADS; ++i)
            threads[i] = new ThreadNoMore();
        
        for(Thread th : threads)
            th.start();
        
        for(Thread th : threads)
            th.join();
        
        System.out.println("threadsStarted: " + threadsStarted);
    }
}

The solution, together with a detailed explanation will be available soon.

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Categories: Programming Tags: , ,
  1. February 13, 2013 at 16:44 | #1

    This code is misleading, as the start() override never calls super.start(). So no thread is ever started really. The condition in start() is always false as the calling thread is always the creating thread. join() also never actually blocks (as no thread was started). The program always prints 0.

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