Using java.util.concurrent Collections and Classes

Introduction

The java.util.concurrent package in Java provides a range of collections and utilities designed to handle concurrent programming tasks. These classes ensure thread-safe operations, making them ideal for multi-threaded environments. In this blog, we will explore two key components: CyclicBarrier and CopyOnWriteArrayList.

1. CyclicBarrier

The CyclicBarrier is a synchronization aid that allows a group of threads to wait for each other to reach a common barrier point. It is reusable and is often used in scenarios where threads need to perform tasks in phases.

Example:

import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierExample {
    public static void main(String[] args) {
        int parties = 3;
        CyclicBarrier barrier = new CyclicBarrier(parties, () -> 
            System.out.println("All parties have arrived. Proceeding to the next phase."));

        Runnable task = () -> {
            try {
                System.out.println(Thread.currentThread().getName() + " is waiting at the barrier.");
                barrier.await();
                System.out.println(Thread.currentThread().getName() + " has crossed the barrier.");
            } catch (Exception e) {
                e.printStackTrace();
            }
        };

        for (int i = 0; i < parties; i++) {
            new Thread(task).start();
        }
    }
}

In this example, three threads wait at the barrier. Once all have arrived, they proceed to the next phase.

2. CopyOnWriteArrayList

The CopyOnWriteArrayList is a thread-safe variant of ArrayList. It creates a new copy of the underlying array on each write operation, making it ideal for scenarios where reads are more frequent than writes.

Example:

import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteArrayListExample {
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();

        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");

        // Reading from the list
        System.out.println("Initial List: " + list);

        // Modifying the list in a thread-safe way
        list.add("Date");
        System.out.println("Updated List: " + list);

        // Iterating over the list
        for (String fruit : list) {
            System.out.println(fruit);
        }
    }
}

This demonstrates how the CopyOnWriteArrayList allows safe modifications while iterating.

3. Other Notable Classes in java.util.concurrent

Besides CyclicBarrier and CopyOnWriteArrayList, the java.util.concurrent package offers several other useful utilities:

• ConcurrentHashMap: A thread-safe implementation of HashMap.
• BlockingQueue: Supports thread-safe producer-consumer patterns.
• Semaphore: Manages access to a limited resource pool.
• CountDownLatch: Allows threads to wait for a set of operations to complete.

Conclusion

The java.util.concurrent package is a cornerstone for modern Java concurrency. Classes like CyclicBarrier and CopyOnWriteArrayList make it easier to write safe and efficient multi-threaded programs. By understanding and leveraging these tools, developers can build scalable and robust applications.