Currently, one can submit a task to an executor (both ThreadPoolExecutor and ProcessPoolExecutor) during interpreter shutdown. One way to do this is to register function fun with atexit as below. @atexit.register def fun(): pool.submit(print, "apple") The future is accepted and goes into PENDING state. However, this can cause issues if the _python_exit function (located in concurrent/futures/thread.py and/or concurrent/futures/process.py) executes before function fun. Function _python_exit will shutdown the running workers in the pool and hence there will be no workers running by the time fun is executed so the future will be left in PENDING state forever. The solution submitted here is to instead raise a RuntimeException when a task is submitted during interpreter shutdown. This is the same behaviour as when the shutdown method of an executor is called explicitly.
