The only guide you’ll need on concurrency & multithreading for senior engineers. Pressure test your skills with real-world practice problems from top companies.

Concurrency in Java is one of the most complex and advanced topics brought up during senior engineering interviews. Knowledge of concurrency and multithreading can put interviewees at a considerable advantage. This course lays the foundations of advanced concurrency and multithreading and explains concepts such as Monitors and Deferred Callbacks in depth. It also builds simple and complete solutions to popular concurrency problems that can be asked about in interviews like the Reader-Writer Problem and the Dining Philosopher Problem. While prior knowledge of concurrency is not required to follow through with this course, familiarity with the very basics of concurrency would be helpful.

Java Multithreading for Senior Engineering Interviews

# Explanation
`CyclicBarrier` is a synchronization mechanism introduced in JDK 5 in the `java.util.concurrent` package. It allows multiple threads to wait for each other at a common point (barrier) before continuing execution. The threads wait for each other by calling the `await()` method on the `CyclicBarrier`. All threads that wait for each other to reach barrier are called parties. *You can read-up on designing and implementing a barrier for an interview question [here](href="https://bit.ly/3BJE3wo).


`CyclicBarrier` is initialized with an integer that denotes the number of threads that need to call the `await()` method on the barrier. Second argument in `CyclicBarrier`’s constructor is a `Runnable` instance that includes the action to be executed once the last thread arrives.
The most useful property of `CyclicBarrier` is that it can be reset to its initial state by calling the `reset()` method. It can be reused after all the threads have been released.
Lets take an example where `CyclicBarrier` is initialized with 3 worker threads that will have to cross the  barrier. All the threads need to call the `await()` method. Once all the threads have reached the barrier, it gets broken and each thread starts its execution from that point onwards.

```java
/**
 * Runnable task for each thread.
 */
class Task implements Runnable {
    
    private CyclicBarrier barrier;
    
    public Task(CyclicBarrier barrier) { 
        this.barrier = barrier;
    }
    
    //Await is invoked to wait for other threads
    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + " is waiting on barrier");
            barrier.await();
            //printing after crossing the barrier
            System.out.println(Thread.currentThread().getName() + " has crossed the barrier");
        } catch (InterruptedException ex) {
            Logger.getLogger(Task.class.getName()).log(Level.SEVERE, null, ex);
        } catch (BrokenBarrierException ex) {
            Logger.getLogger(Task.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

}




/**
 * Main thread that demonstrates how to use CyclicBarrier.
 */
public class Main {
    public static void main (String args[]) {

        //Creating CyclicBarrier with 3 parties i.e. 3 Threads needs to call await()
        final CyclicBarrier cb = new CyclicBarrier(3, new Runnable(){

            //Action that executes after the last thread arrives
            @Override
            public void run(){
                System.out.println("All parties have arrived at the barrier, lets continue execution.");
            }
        });

        //starting each thread
        Thread t1 = new Thread(new Task(cb), "Thread 1");
        Thread t2 = new Thread(new Task(cb), "Thread 2");
        Thread t3 = new Thread(new Task(cb), "Thread 3");

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


```

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

CyclicBarrier

Explanation