Can Quasar fibers be efficiently used with other (popular) Java libraries that build on top of the standard libraries? If not, I don't consider that to be good

Can Quasar fibers be efficiently used with other (popular) Java libraries that build on top of the standard libraries? If not, I don't consider that to be good developer experience. That is more of a mistake that cannot be rectified. Async IO is also fine. The question is, what is your current ecosystem built on top of. AFAIK the answer with Java is definitely not async IO or fibers. Yes, structural interfaces in Go are implemented poorly. But the standard library uses them very tastefully, putting most standard libraries to shame :) Go also has Closer, and its a separate interface - interfaces are minimal which makes them much easier to implement and more generally applicable.