Indeed, the article is quite misleading by supposing that atomic variables are magic at the hardware level. On some hardware yes, on others no. As an example th

Indeed, the article is quite misleading by supposing that atomic variables are magic at the hardware level. On some hardware yes, on others no. As an example the original AWS Graviton is vanilla armv8-a without atomics, so atomic concepts in languages are simulated with retry loops having unbounded latency. Your thread that wants to increment an atomic may be blocked literally forever if there are enough contenders for that cache line. Library mutex implementations are usually hybrids with limited atomic spinlocks, with pauses or sleeps, then fallbacks to heavyweight synchronization with fairness features such as futex. On certain Intel hardware we also have lightweight userspace notification when a given address has been written. That can be used for adaptive wakeup on atomic values but it is "lightweight" relative to futex, since it still requires a rdtsc and still amounts to an efficient spinloop. On Intel Atom CPUs you can do this with up to 4 threads for free, but 100 threads will still be a mess.