Fibers, what for?

[Patric Dexheimer via Digitalmars-d-learn]

On Monday, 13 June 2016 at 00:57:11 UTC, Alex Parrill wrote:
> Also note that Vibe.d, the largest fiber-based framework D has 
> to offer, is capable of running several coroutines in parallel 
> on multiple threads, meaning you must use the same level of 
> synchronization as if you were using threads.

Vibe.d framework share the same fibers between threads?
Or each thread have his own fibers?
I was trying this(shared fibers) but it didnt work.