Ah never mind. @Genarito, the ThreadPoolExecutor is supposed to be used as a context manager. In your current code, the script ends and Python starts tearing itself down while `execute_error` is still running in a subprocess.

If you simply use the ThreadPoolExecutor to a context manager, the error goes away::

```python
from multiprocessing import Process
from concurrent.futures import ThreadPoolExecutor


def some_task():
    pass


def execute_error():
    p = Process(target=some_task)
    p.start()
    p.join()
    print(p.exitcode)  # This is always 1 on a ThreadPoolExecutor!!!


# THIS IS THE IMPORTANT CHANGE
with ThreadPoolExecutor(max_workers=4) as executor:
    executor.submit(execute_error)
```