Fibers should be appreciated in context. They are great at Google because in general the function running on a fiber has no need to ever enter the potentially blocking region. In fibers one has to manually annotate the fact that one is, for example, calling read on a pipe. This works within google because nobody makes system calls from application code and the relevant libraries that need to (mutex) handle it. As a xoogler what I’d like to see opened up is not fibers, which I’d need a new kernel for, but EventManager. EM would be immediately useful to many people.