>In a very high concurrency environment with OS based threads it is not always the case. We're talking about green threads, remember? >Async or green threads

>In a very high concurrency environment with OS based threads it is not always the case. We're talking about green threads, remember? >Async or green threads have a smaller overhead of switching, but any CPU based concurrency is usually missing The point is that async and green threads are the same thing, just one has a better interface. Of course they both have the same downside.