How do I implement compare-and-swap in code?

How do I implement compare-and-swap in code?

Compare-and-swap (CAS) is an atomic operation used in concurrent programming. It compares the current value of a variable to an expected value and, if they match, updates the variable to a new value. Would you like a code example?

Yes, please provide a code example in C++.

Here's a simple implementation in C++:

#include <atomic>

bool compare_and_swap(std::atomic<int>& target, int expected, int desired) {
    return target.compare_exchange_strong(expected, desired);
}

This function uses the compare_exchange_strong method from the <atomic> library.

What are the use cases for compare-and-swap?

CAS is commonly used in lock-free data structures, implementing counters, and managing shared resources in multithreaded applications.

Are there any drawbacks to using compare-and-swap?

Yes, CAS can lead to issues like the ABA problem, where a value changes from A to B and back to A, causing incorrect assumptions. It can also lead to high contention in heavily accessed variables.