What a terrible way to achieve network concurrency. You can't possibly think that each upload is using a "core" (as described in the article). That would imply that a two core web server could only serve two files at the same time. Sending a block of data from one file descriptor to another is not a CPU intensive task.
Just use twisted or similar and run as many as you want concurrently with a single thread.
Just use twisted or similar and run as many as you want concurrently with a single thread.