Channels are a good abstraction for message passing and high-level requests in general, which happen a lot in web services for example. But there are other doma

Channels are a good abstraction for message passing and high-level requests in general, which happen a lot in web services for example. But there are other domains (like kernels) and there is not one way to do concurrency. If you need low-latency and small-scope data structure access, you can't afford to synchronize with another worker and have the request processed in a different context. Fine-grained locking (or potentially lock-free concurrency) is much faster here.