Issue 43884: Cannot cleanly kill a subprocess using high-level asyncio APIs

There doesn't appear to be a way to prematurely kill a subprocess using the high-level asyncio subprocess APIs (https://docs.python.org/3.9/library/asyncio-subprocess.html) without getting a traceback on exit.

On exit, the attached program writes the following to stderr:

$ python3.9 kill_subprocess.py

Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x1065f0dc0>
Traceback (most recent call last):
    ...
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

If I uncomment `# process._transport.close()` or comment `asyncio.sleep(1)`, the walkback disappears. (I get the same behavior in python 3.8. I haven't tried other python versions.)

Reproducing the program here:

    import asyncio
    
    async def test():
        process = await asyncio.create_subprocess_shell(
            "sleep 2 && echo done",
            stdout=asyncio.subprocess.PIPE,
        )
        await asyncio.sleep(1)
        process.kill()
        await process.wait()
        # process._transport.close()
    
    asyncio.run(test())

Can I use the high-level API to kill a subprocess cleanly without having to access the protected member process._transport? Seems like an oversight perhaps?

Running kill_subprocess.py on Windows 10, I get these results:

Python 3.7.2 (tags/v3.7.2:9a3ffc0492)
    - raises NotImplementedError in base_events.py, _make_subprocess_transport
Python 3.8.2 (tags/v3.8.2:7b3ab59)
    - Success
Python 3.9.0 (tags/v3.9.0:9cf6752)
    - Success
Python 3.10.0a6 (tags/v3.10.0a6:cc12888)
    - Success

What is your OS?

I see this on MacOS and Linux, but I suspect any Unix-like system would have the same behavior.

I'm also experiencing this, with virtually identical code, on macOS 10.15.7. The given fix (process._transport.close()) also works for me, so I'm just using that workaround for the time being.

@asvetlov Do you have any insight for this issue?

pull_requests: + pull_request29734
stage: patch review