If you haven't encountered concurrent programming topics before, the last few sections probably got progressively more and more challenging. Mutexes are pretty simple to understand because they model a familiar idea from daily life: getting exclusive access to some resource by putting a lock on it. Read-write locks (shared_mutex) aren't much harder to understand. However, we then took a significant jump upward in esotericism with condition variables--which are hard to grasp partly because they seem to model not a noun (like "padlock") but a sort of prepositional verb phrase: "sleep until, but also, wake." Their opaque name doesn't help much either.
Now we continue our journey into concurrent programming with a topic ...
