Userspace IO is a thing though. Even with traditional kernel side IO, you might not want to attempt a syscall if the socket is known not to be ready. Also whe

Userspace IO is a thing though. Even with traditional kernel side IO, you might not want to attempt a syscall if the socket is known not to be ready. Also when implementing purely userspace synchronization primitives, being able to swap to a different context purely in userspace is nice.