C++: What is std::atomic?

std::atomic — thread-safe atomic operations.

1std::atomic<int> counter{0};
2
3void increment() {
4    counter.fetch_add(1, std::memory_order_relaxed);
5}
6
7// Wait until value is set
8counter.wait(0); // blocks until counter != 0

Memory orders:

• relaxed: no ordering guarantees
• acquire: subsequent reads see writes
• release: prior writes visible to others
• seq_cst: total order (default)

Lock-free guarantee:

1if (counter.is_lock_free()) {
2    // guaranteed lock-free on this platform
3}

When to use:

• Simple counters/flags
• Producer-consumer signaling
• Avoid mutexes for simple cases