Parallel programming is not hard if you follow the "just use a mutex and you avoid race conditions" mantra. However, this book dives deep into what mutexes actually do, what the hardware below is doing, and alternatives to a mutex for a speed increase. This can be anything from lockless algorithms to RCU, which the author of this book wrote it in Linux kernel.

There's a comment above about Haskell and how you don't have to really put any thought into making things parallel. That's great for 99% of cases, but other times you need higher performance where it matters how the concurrency is implemented.