What does it do in Python 3.11 (e.g. 3.11rc2, now available from python.org)?

I tried, and it seems to give a similar traceback.

~/3.11$ ./python.exe intr.py 
coro start
thread start
coro stop
^Cinterrupted!
thread stop
exception calling callback for <Future at 0x10d283450 state=finished returned NoneType>
Traceback (most recent call last):
  File "/Users/guido/3.11/Lib/concurrent/futures/_base.py", line 340, in _invoke_callbacks
    callback(self)
  File "/Users/guido/3.11/Lib/asyncio/futures.py", line 407, in _call_set_state
    dest_loop.call_soon_threadsafe(_set_state, destination, source)
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
Exception in thread Thread-1 (_do_shutdown):
Traceback (most recent call last):
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 580, in _do_shutdown
    self.call_soon_threadsafe(future.set_result, None)
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/guido/3.11/Lib/threading.py", line 1038, in _bootstrap_inner
    self.run()
  File "/Users/guido/3.11/Lib/threading.py", line 975, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 582, in _do_shutdown
    self.call_soon_threadsafe(future.set_exception, ex)
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "/Users/guido/3.11/Lib/asyncio/base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
~/3.11$ 

Ouch, this is tricky.

I think I understand the last part of the traceback. When a loop is closed, it tries to shut down its default executor. This is done by creating a helper thread (in shutdown_default_executor())) that runs _do_shutdown(). The helper thread blocks until the executor is actually shut down, and then uses call_soon_threadsafe() to report back to the event loop that it's done. Because the thread sleeps for 3 seconds, the by the time this happens the loop's _closed flag has already been set, and call_soon_threadsafe() raises an exception because of this.

Interestingly, the traceback has the form

<traceback 1>
<traceback 2> 

During handling of the above exception, another exception occurred:

<traceback 3>

Now both traceback 2 and traceback 3 are reporting an error in _do_shutdown(). The line numbers suggest that the first call_soon_tnreadsafe() call fails, its exception is caught, and then the second call fails in a similar manner.

So what about traceback 1? This is happening in _call_set_state(), an inner function of _chain_future() which is used to chain the executor's Future (which is not an asyncio.Future but a concurrent.futures.Future) to the future that wraps the run_in_executor() call.

Still with me? It looks like _call_set_state() could simply check whether the destination loop isn't closed, which it does a few lines earlier when it finds the destination future is cancelled.

I'll try to come up with a repro that doesn't require one to hit ^C, and take it from there.

That sounds right, you might be able to create reproducer with _thread.interrupt_main.

I have a fix, but not yet a test.

I spent 30-60 minutes trying to come up with a test case, but I'm pretty unhappy with it. The key thing is that we need to aim the keyboard interrupt to happen once shutdown_default_executor() has entered the await future line. I tried various ways to do this but wasn't very successful. The best thing I can think of is to have a loop in the executor thread that sleeps 1 msec at a time and then checks if the loop._executor_shutdown_called flag is set yet. Once that is set, sleep a little longer (another msec?) and then call _thread.interrupt_main(), in the hope that the extra bit of sleeping is enough to make us reach the await future.

However, when I try this, it doesn't always trigger the bug with Python 3.11rc2 or Python 3.10.

</details>

I'm still seeing this issue on Python 3.11.0 on Windows. That is, if I run the test program in the original comment here and hit Ctrl-C after "coro stop" is printed, I get the same exception traceback:

❯ py .\bug.py
coro start
thread start
coro stop
interrupted!
thread stop
exception calling callback for <Future at 0x250844fd1d0 state=finished returned NoneType>
Traceback (most recent call last):
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\concurrent\futures\_base.py", line 340, in _invoke_callbacks
    callback(self)
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\futures.py", line 401, in _call_set_state
    dest_loop.call_soon_threadsafe(_set_state, destination, source)
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
Exception in thread Thread-1 (_do_shutdown):
Traceback (most recent call last):
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 580, in _do_shutdown
    self.call_soon_threadsafe(future.set_result, None)
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\threading.py", line 1038, in _bootstrap_inner
    self.run()
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\threading.py", line 975, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 582, in _do_shutdown
    self.call_soon_threadsafe(future.set_exception, ex)
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 803, in call_soon_threadsafe
    self._check_closed()
  File "C:\Users\Gustav\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 519, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

Did the fix make it into the 3.11.0 release?

(I found this issue when trying to debug the same error in a program running a subprocess - I assume that create_subprocess_exec uses the threadpool in the background).

I guess we'll have to reopen this. It definitely made it into 3.11 (based on the date it was committed). I am out of bandwidth to personally research this -- do you have time to look into it more? Maybe we only fixed it for Selector event loops and not for the Proactor event loop?

I'm happy to help, but I don't understand enough about asyncio in general, or the proactor/process implementation in particular, to diagnose what the issue might be.