Concurrency is hard because we invented a bunch of theoretical machinery (semaphores, mutexes, condition variables,...) and embedded it in languages such that m

Concurrency is hard because we invented a bunch of theoretical machinery (semaphores, mutexes, condition variables,...) and embedded it in languages such that most of the programs one can express are bad: racey or deadlock prone. Compare with modern sequential languages which have near-perfect denotational semantics: anything which compiles means something. If you want practical guidance, my best is to avoid all of the concurrency constructs that are taught in schools. Use log-structured single-writer multiple reader, wait-free, processes and shared memory.