Comment by reinitctxoffset

Not if you define the behavior. Many programming languages have robust memory models ranging from "happens before" style systems like those in Java or Modern C++ to the Software Transactional Memory system in GHC/Haskell.

Correct, shared mutation is an extremely well-understood problem in the sense that there are points in the programming language design space that admit it with present technology.

As always, there are tradeoffs.