Taming Concurrency: Understanding Atomic Variables in Java

3 min readJul 5, 2023

Introduction

Welcome to today’s topic, where we’ll explore the fascinating world of Java concurrency and explore the idea of atomic variables. As they enable us to carry out some operations atomically, or as a single, indivisible operation, atomic variables are essential for managing concurrent programming.

A key feature of Java is concurrency, which enables several threads to operate simultaneously, boosting the efficiency and speed of our systems. However, it has inherent drawbacks, including race conditions — commonly known as data inconsistencies and thread interference — and thread interference. Atomic variables can help in this situation.

What are Atomic Variables?

In Java, atomic variables reside under the java.util.concurrent.atomic package. They offer thread-safe, lock-free programming, which enhances efficiency and prevents deadlock situations that could arise from traditional synchronization techniques.

An atomic operation is indivisible. This means that once an operation starts executing, it runs to completion without being interrupted by another thread. This atomicity is vital for concurrent programming because it helps prevent race conditions.

For instance, consider the following increment operation:

count++;

It seems simple enough. However, when we dive deeper, this operation consists of three discrete steps:

Read the current value of count.
Increment the value by one.
Write the updated value back to count.

In a multi-threaded environment, it’s entirely possible for a thread to be preempted after the read operation, and before the write operation. Another thread could then read the same (old) value of count, increment it, and write it back. When the first thread resumes execution and writes its value back to count, it overwrites the value from the second thread. As a result, even though count++ has been invoked twice, count has only incremented once.

Atomic variables help to solve this problem by ensuring that the entire operation is atomic and therefore cannot be interrupted.

Java’s Atomic Classes

Java provides several atomic classes, such as:

AtomicInteger
AtomicLong
AtomicBoolean
AtomicReference

And more…

Let’s take a look at an example using AtomicInteger:

AtomicInteger count = new AtomicInteger(0);
count.incrementAndGet();

In this example, incrementAndGet() is an atomic operation. It increments the value of count by one and returns the updated value. No matter how many threads are concurrently invoking this method, it will always correctly increment count.

Advantages of Using Atomic Variables

Atomic variables come with several benefits:

1. Performance: Atomic variables are more efficient than synchronized blocks or methods. This is because they rely on hardware-level support for atomicity (e.g., compare-and-swap (CAS) instructions) rather than expensive lock-based techniques.

2. Deadlock Safety: Since atomic variables don’t use locks, they are immune to deadlocks — a significant problem in multi-threaded programming.

3. Visibility: Atomic variables have built-in visibility features. When a variable is shared between multiple threads, changes made by one thread are immediately visible to other threads.

Wrapping Up

Atomic variables are a powerful tool for handling concurrency in Java. They offer a more efficient, safer alternative to traditional synchronization techniques, providing a robust solution to the many challenges posed by multi-threaded programming.

Understanding and using atomic variables effectively is critical for writing high-performance, concurrent Java applications. By mastering this concept, you’re adding a valuable skill to your Java programming repertoire.

In the next post, we’ll be exploring another essential aspect of concurrent programming — Java’s Concurrent Collections. Stay tuned, and happy coding!