Bug report

So, I've updated python from 3.11.0 to 3.11.1 and one of my utilities which runs a lot of external processes with asyncio.create_subprocess_exec started failing in different places in weird ways. It turned out that with some probability asyncio.subprocess.Process.communicate() would now return an empty stdout. Here's a repro:

import asyncio

async def main():
    attempt = 1
    while True:
        proc = await asyncio.create_subprocess_exec('/bin/echo', 'test', stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE)

        stdout, stderr = await proc.communicate()

        text = stdout.decode('utf-8').strip()

        if text != 'test':
            raise RuntimeError(f'FAIL on attempt {attempt}: output="{text}"')

        attempt += 1

asyncio.run(main())

You may have to wait somewhat for the problem to reproduce, but for me it fails in under 15 seconds more or less reliably. Possible output:

RuntimeError: FAIL on attempt 3823: output=""

Your environment

• CPython versions tested on: 3.11.1
• Operating system and architecture: FreeBSD 13.1 amd64

Linked PRs

• GH-100133: fix asyncio subprocess losing stderr and stdout output #100154
• [3.11] GH-100133: fix asyncio subprocess losing stderr and stdout output (GH-100154) #100398