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I've a piece of code that submits a task to a [ThreadPoolExecutor][1] which starts a [Process][2]. I've realised that in Python 3.8 that Process finished with exit code `0`. But I've updated Python to the 3.9 version and this started to finishing with exit code `1`! Even when the Process executes an empty task.
Here's a minimal example:
```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!!!
executor = ThreadPoolExecutor(max_workers=4)
executor.submit(execute_error)
# execute_error() # IMPORTANT: this works correctly (exit 0)
```
My versions:
```
Ubuntu 21.04
Python 3.9.4
```
**Note** that if `__execute_error` is called outside the ThreadPoolExecutor it works correctly.
Running on Python 3.8.6 exitcode = 0 too.
 [1]: https://docs.python.org/3/library/concurrent.futures.html#threadpoolexecutor
 [2]: https://docs.python.org/3.9/library/multiprocessing.html#multiprocessing.Process