atomics & fences

Acquire
    cannot move anything up beyond an acquire

Release
    cannot move anything down beyond a release

Note
    acquire/release cannot be reordered with respect to each other
 
What does this mean?

instructions can be reordered from before an acquire to after an acquire
instructions can be reordered from after a release to before a release
acquire cannot be reordered before or after a release
release cannot be reordered before or after an acquire

std::atomic
    read = load_acquire --> read the value == acquire the value
    write = store_release --> write the value == release the value

Sequential Consistency
Transitivity / Causality
Total Store Order