What is CAS (Compare-And-Swap) in multithreaded programming? What is it used for?

CAS (Compare-And-Swap) is an atomic operation in multithreaded programming that compares the value in memory with an expected value and, if they match, replaces it with a new value.

It is used to implement lock-free algorithms and data structures, allowing to avoid race conditions without using heavy locks.

Working principle:

• Compare the current value at an address with the expected value.
• If they match, write the new value.
• If they do not match, the operation does not change the value and reports this.

In Java, CAS is used in classes from the java.util.concurrent.atomic package, such as AtomicInteger. This allows implementing efficient lock-free counters, queues, and other structures.

Example of usage in Java:

import java.util.concurrent.atomic.AtomicInteger;

AtomicInteger atomicInt = new AtomicInteger(0);

boolean updated = atomicInt.compareAndSet(0, 1); // if current value is 0, set to 1

Thus, CAS is a key mechanism for building concurrent algorithms without locks.