On Concurrency

[Bienlein via Digitalmars-d-learn]

> One key difference is that coroutines won't make your programs 
> run faster. It is a modelling mechanism that can simplify your 
> programs where you otherwise would have to implement a state 
> machine.

This is also my impression when I look at this code (see 
http://www.99-bottles-of-beer.net/language-d-2547.html) that 
implements 99 bottles of beer in D with fibers. What seems to be 
happening is some alternating handover of the CPU.

But when I run the code all 4 cores of my machine are under load 
and it looks like the runtime were able to make things run in 
parallel somehow. Now I'm really confused ...