Using Fibers without yield

[Richard (Rikki) Andrew Cattermole]

Here is the source code: 
https://github.com/dlang/dmd/blob/master/druntime/src/core/thread/fiber/base.d

When you call the second fiber, the first is still executing as far as 
the call stack is concerned. It was never yielded.

D's Fiber is a primitive, it has no scheduler or dependency management.

It cannot do anything differently.