Threadpools, difference between DMD and LDC

[Philippe Sigaud via Digitalmars-d-learn]

I'm trying to grok message passing. That's my very first foray
into this, so I'm probably making every mistake in the book :-)

I wrote a small threadpool test, it's there:

http://dpaste.dzfl.pl/3d3a65a00425

I'm playing with the number of threads and the number of tasks,
and getting a feel about how message passing works. I must say I
quite like it: it's a bit like suddenly being able to safely
return different types from a function.

What I don't get is the difference between DMD (I'm using 2.065)
and LDC (0.14-alpha1).

For DMD, I compile with -O -inline -noboundscheck
For LDC, I use -03 -inline

LDC gives me smaller executables than DMD (also, 3 to 5 times
smaller than 0.13, good job!) but above all else incredibly,
astoundingly faster. I'm used to LDC producing 20-30% faster
programs, but here it's 1000 times faster!

8 threads, 1000 tasks: DMD:  4000 ms, LDC: 3 ms (!)

So my current hypothesis is a) I'm doing something wrong or b)
the tasks are optimized away or something.

Can someone confirm the results and tell me what I'm doing wrong?