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.

Thanks for spotting this.  I will take a look soon, unless someone beats me to it.

New changeset c4b695f85e141f57d22d8edf7bc2c756da136918 by Antoine Pitrou (Mark Nemec) in branch 'master':
bpo-33097: Fix submit accepting callable after executor shutdown by interpreter exit (GH-6144)
https://github.com/python/cpython/commit/c4b695f85e141f57d22d8edf7bc2c756da136918

New changeset b26265900a18a184997c3c3a1fa6a5bf29703ec9 by Antoine Pitrou (Miss Islington (bot)) in branch '3.7':
bpo-33097: Fix submit accepting callable after executor shutdown by interpreter exit (GH-6144) (GH-6445)
https://github.com/python/cpython/commit/b26265900a18a184997c3c3a1fa6a5bf29703ec9

Thanks your contribution Mark!

Happy to contribute! Thanks for the review :)