Atomic Variables

1. Overview

A small toolkit of classes that support lock-free thread-safe programming on single variables. In essence, the classes in this package extend the notion of volatile values, fields, and array elements to those that also provide an atomic conditional update operation of the form

2. Example

public class demo {
    public static void main(String[] args) throws InterruptedException {
        InventoryCounter inventoryCounter = new InventoryCounter();
        DecrementingThread decrementingThread = new DecrementingThread(inventoryCounter);
        IncrementingThread incrementingThread = new IncrementingThread(inventoryCounter);

        decrementingThread.start();
        incrementingThread.start();

        decrementingThread.join();
        incrementingThread.join();
        System.out.println(inventoryCounter.getItems());
    }

    public static class DecrementingThread extends Thread {
        private InventoryCounter inventoryCounter;
        public DecrementingThread(InventoryCounter inventoryCounter) {
            this.inventoryCounter = inventoryCounter;
        }

        @Override
        public void run() {
            for (int i = 0; i < 10000; i++) {
                inventoryCounter.decrement();
            }
        }
    }

    public static class IncrementingThread extends Thread {
        private InventoryCounter inventoryCounter;
        public IncrementingThread(InventoryCounter inventoryCounter) {
            this.inventoryCounter = inventoryCounter;
        }

        @Override
        public void run() {
            for (int i = 0; i < 10000; i++) {
                inventoryCounter.increment();
            }
        }
    }

    //Thread unsafe approach
//    public static class InventoryCounter {
//        private int items = 0;
//        public void increment() { items++; }
//        public void decrement() { items--; }
//        public int getItems() { return items; }
//    }

    // Thread safe approach using atomic variable
    public static class InventoryCounter {
        private AtomicInteger item = new AtomicInteger(0);
        public void increment() { item.incrementAndGet(); }
        public void decrement() { item.decrementAndGet(); }
        public int getItems() { return item.get(); }
    }
}

4. Reference

https://docs.oracle.com/javase/tutorial/essential/concurrency/atomicvars.html

https://www.baeldung.com/java-atomic-variables

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html

https://dzone.com/articles/java-concurrency-atomic-variables