By default, File.read does block, yes. As it crosses into libc, it releases Ruby's interpreter lock, allowing another Ruby thread to execute while it blocks. R

By default, File.read does block, yes. As it crosses into libc, it releases Ruby's interpreter lock, allowing another Ruby thread to execute while it blocks. Ruby 1.9 added Fibers. These are coroutines with their own call stack that yield and resume explicitly. They're like Goroutines but without Go's scheduler. Fibers are commonly used to build Enumerators, internal iterators support external iteration. File.read in a Fiber still blocks by default. Ruby 3.0 added support for truly asynchronous File.read. The batteries are not included. A fiber scheduler is required to enable this optional feature: https://docs.ruby-lang.org/en/3.3/Fiber.html#class-Fiber-label-Non-blocking+Fibers https://docs.ruby-lang.org/en/3.3/Fiber.html#class-Fiber-lab... https://brunosutic.com/blog/ruby-fiber-scheduler https://brunosutic.com/blog/ruby-fiber-scheduler