Threadpools, difference between DMD and LDC

[Philippe Sigaud via Digitalmars-d-learn]

> This is correct – the LLVM optimizer indeed gets rid of the loop completely.

OK,that's clever. But I get this even when put a writeln("some msg")
inside the task. I thought a write couldn't be optimized away that way
and that it's a slow operation?

Anyway, I discovered Thread.wait() in core in the meantime, I'll use
that. I just wanted to have tasks taking a different amount of time
each time.

I have another question: it seems I can spawn hundreds of threads
(Heck, even 10_000 is accepted), even when I have 4-8 cores. Is there:
is there a limit to the number of threads? I tried a threadpool
because in my application I feared having to spawn ~100-200 threads
but if that's not the case, I can drastically simplify my code.
Is spawning a thread a slow operation in general?