[jfkebwjsbx]

That does not follow. Long-running CPU-only tasks are a thing and they may not be aware of each other.

With cooperative multitasking, launching something like a parallel compilation would make your machine unusable.

[jcranmer]

It is true that it's possible to screw your machine your over in that manner. I was pointing out that the large number of threads wasn't evidence in support of that fact, but rather the contrary; the threads have to already be using existing facilities that provide cooperative sleeping points.