alt Hacker NewsI thought it was obvious from context: OS threads are too heavyweight for fine grained concurrency
Go uses userspace threads. It’s also interesting that Go and Java are the only mainstream languages to have gone this route. The reason is that it has a huge penalty when calling FFI of code that doesn’t use green threads whereas this cost isn’t there for async/await.
Also that you have to rewrite the entire standard library, because the kernel knows how to suspend kernel threads on syscalls, but not green threads. (Go and Java already had to do this anyway, of course.)