Memory order I

What this C++ memory-order interview question tests

This is an easy concurrency question that probes your understanding of memory ordering semantics in C++. It appears frequently in interviews at firms where lock-free programming or thread-safe data structures matter—including trading systems and infrastructure teams.

The question asks you to reason about how atomic operations with different memory-order guarantees interact across threads. Specifically, you'll need to understand the visibility and ordering constraints imposed by each memory order (relaxed, release-acquire, sequential consistency), and how they affect which values can be observed when multiple threads read and write concurrently.

• Acquire-release semantics and synchronization
• Sequential consistency vs. relaxed atomics
• Happens-before relationships between threads
• Compiler and hardware reordering under different memory models