> Async Ruby is similar to Go's goroutine model. Goroutines are just (lightweight) threads - they can run in parallel. You need locks whenever you access share

> Async Ruby is similar to Go's goroutine model. Goroutines are just (lightweight) threads - they can run in parallel. You need locks whenever you access shared data. AFAIK Ruby’s fibers are cooperatively scheduled and can only yield at function calls. Code that doesn’t make a function call (e.g. incrementing an integer) is safe to run on multiple fibers without locks. For comparison, Python’s stackless coroutines can safely do anything except `await` without requiring locks.