Question

The full specializations of std::atomic for integral types provide arithmetic compound assignment operators such as +=, -=, but no *= or /=. The standard states this but as far as I can see there is no reason given. Could someone familiar with the reasoning behind the Atomic Operations Library section shed some light on this?

Answer 1

I think this is related to hardware. Many platforms have atomics to handle += but I don’t know of any that offers *=. Implementing this through locking would be simple, but the interface of std::atomic would be mixing at the same level operations that are somehow cheap with very expensive operations.