Parallelism in 2021 should not be tightly coupled across threads if performance matters, the limitations of that model are well-understood. There is no way to make that comparatively efficient; the CPU cache waste alone ensures that. Nothing you can do with thread support in a programming language will be competitive with e.g. a purpose-built scheduler + native coroutines.

… The state-of-the-art architectures are all, effectively, single-threaded with latency-hiding. This model has a lot of mechanical sympathy with real silicon which is why it is used. It is also pleasantly simple in practice. - HN

see Green Thread