Critical sections, exclusive execution, and atomicity

Imagine you're writing software for a multicore system (well, nowadays, it's typical that you will work on multicore systems, even on most embedded projects). As we mentioned in the introduction, running multiple code paths in parallel is not only safe, it's desirable (why spend those dollars otherwise, right?). On the other hand, concurrent (parallel and simultaneous) code paths within which shared writeable data (also known as shared state) is accessed in any manner is where you are required to guarantee that, at any given point in time, only one thread can work on that data at a time! This is really key; why? Think about it: if you allow multiple concurrent code paths to work in parallel on shared writeable data, you're literally asking for trouble: data corruption (a "race") can occur as a result.