ASDF as it exists now is not capable of running anything in parallel.
Faré has an experimental project to do this, called POIU, but I
can't speak for its status. Until very recently, SBCL was incapable of
compiling files in parallel, and still today, lots of code does
not-thread-safe stuff at load-time, so I'm not convinced it's
practically possible to make ASDF parallel via shared-memory threaded
concurrency. I believe POIU compiles each component in a separate
process, then loads them sequentially.
I see, that's good to know. At least it's an implementation limitation and not a design limitation I guess.
POIU compiles files in a fork, on supported implementations that it knows how to fork on (SBCL, CCL with a patch, CLISP, ACL). It used to work well, but it wasn't updated to take into account the new planning infrastructure of ASDF 3.3, and requires some love. It looks like it's still working, but it's probably not doing all the right things across build phases. Good luck untangling it.
-#f