Comment by masklinn

> You get into hairy problems of definition, but you can definitely create an "async" runtime out of "sync" operations: implement an async runtime with calls to C. C doesn't have a concept of "async", and more or less all async runtime end up like this.

While C doesn't have async OS generally provide APIs which are non-blocking, and that is what async runtimes are implemented on top of.

By sync operations I mean implementing an "async" runtime entirely atop blocking operations, without bouncing them through any sort of worker threads or anything.