Just noting that the `multiprocessing` module can be used instead. In the example, add import multiprocessing as mp and change with concurrent.futures.ProcessPoolExecutor() as executor: to with mp.Pool() as executor: That's all it takes. On my 4-core Win10 box (8 logical cores), that continued to work fine even when passing 1024 to mp.Pool() (although it obviously burned time and RAM to create over a thousand processes). Some quick Googling strongly suggests there's no reasonably general way to overcome the Windows-defined MAXIMUM_WAIT_OBJECTS=64 for implementations that call the Windows WaitForMultipleObjects().