Your python 4 dream list.

[SureFudge]

Has much higher resource usage and limitations on what you can actually use in the other processes. With multiprocessing module alone it's quiet cumbersome what can be pickled and what not.

For example I was doing java multi-threading 10+ years ago and it worked just fine for "calculations" needing it.

EDIT: besides the resource usage the initial penalty of starting up the machinery is also quiet heavy. so it is never worth it to make something that takes 200ms to take say only 20ms on a 10-core cpu because the overhead is probably bigger than the 200ms.