“Unifying the two? — concurrent programs are easily parallelized: should we use the same primitives?Java, C# and others do but it’s a bad idea. At scale, death by context-switching.

Fibers for concurrency (cheap! — have millions) and Domains for parallelism (expensive! — have ~#core ones)”

C# uses fibers called “Tasks” for both concurrency and parallelism. There is no death by context switching. Tasks are cheap: you can have millions of tasks. Tasks are balanced (Cilk-style work stealing task deques). Tasks are executed by a thread pool with ~#core threads.