[diek]

async/await in the general sense doesn't have anything to do with the preemption policy of a particular language implementation. For instance, C# implement async/await as keywords on top of its existing concurrency model.

That's really what it comes down to: cooperative multi-tasking vs preemptive multi-tasking.

Windows 3.1 had cooperative multi-tasking. Everything went great until one program didn't yield control, and then the whole system ground to a halt. That should sound familiar to any Node.js developers with their event loop.

Cooperative multi-tasking also extremely complicates code that actually uses the CPU. If you look inside libuv, it even has to jump through hoops with its encryption functions by effectively calling yield() in between rounds of calculation.

[csharptwdec19]

>If you look inside libuv, it even has to jump through hoops with its encryption functions by effectively calling yield() in between rounds of calculation.

I would have assumed the Yield was there to help with protect against timing pokes...

[unscaled]

Since stackless coroutine schedulers can often be customized, you could (and are encouraged to) launch coroutine code doing heavy performance on a thread based scheduler.