What is the difference between the properties of atomicity and volatility of data in the context of multithreading?

In the context of multithreading in Java, the properties of atomicity and volatility have different meanings:

• Atomicity means that an operation is executed entirely or not at all, without intermediate states visible to other threads. For example, incrementing a variable is not an atomic operation because it involves reading, modifying, and writing. To ensure atomicity, classes from the java.util.concurrent.atomic package are used.

• Volatility (volatile) guarantees that reading and writing a variable will happen directly from main memory, not from the processor cache, ensuring visibility of changes between threads. However, volatile does not guarantee the atomicity of complex operations (e.g., incrementing).

Example:

volatile int counter = 0;

// writing to a volatile variable is immediately visible to other threads

AtomicInteger atomicCounter = new AtomicInteger(0);

// atomicCounter.incrementAndGet() is an atomic operation, safe for multithreading

Thus, volatility ensures visibility of changes, while atomicity guarantees the correct execution of operations without interruptions.