Answer by jcoder for Are volatile reads and writes atomic on Windows+VisualC?

Yes they are atomic on windows/vc++ (Assuming you meet alignment requirements etc or course)

However for a lock you would need an atomic test and set, or compare and exchange instuction or similar, not just an atomic update or read.

Otherwise there is no way to test the lock and claim it in one indivisable operation.

EDIT: As commented below, all aligned memory accesses on x86 of 32bit or below are atomic anyway. The key point is that volatile makes the memory accesses ordered. (Thanks for pointing this out in the comments)