If func creates lots objects and appends them to a list, and runs over and over, pool.map(func...) will eventually eat up all memories. Cleaning the list at the end of func does not help.

One can reproduce by running the attached file.

By contrast, after replacing ThreadPool with the theading module (see the commented out lines), memory usage will not grow continuously.

By the way, I used what's in Debian stretch, i.e. python 2.7.11 and 3.5.1.