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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"asyncio subprocess stdout occasionally lost (3.11.0 → 3.11.1 regression)","articleBody":"\u003c!--\r\n  If you're new to Python and you're not sure whether what you're experiencing is a bug, the CPython issue tracker is not\r\n  the right place to seek help. Consider the following options instead:\r\n\r\n  - reading the Python tutorial: https://docs.python.org/3/tutorial/\r\n  - posting in the \"Users\" category on discuss.python.org: https://discuss.python.org/c/users/7\r\n  - emailing the Python-list mailing list: https://mail.python.org/mailman/listinfo/python-list\r\n  - searching our issue tracker (https://github.com/python/cpython/issues) to see if\r\n    your problem has already been reported\r\n--\u003e\r\n\r\n# Bug report\r\n\r\nSo, 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:\r\n\r\n```\r\nimport asyncio\r\n\r\nasync def main():\r\n    attempt = 1\r\n    while True:\r\n        proc = await asyncio.create_subprocess_exec('/bin/echo', 'test', stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE)\r\n\r\n        stdout, stderr = await proc.communicate()\r\n\r\n        text = stdout.decode('utf-8').strip()\r\n\r\n        if text != 'test':\r\n            raise RuntimeError(f'FAIL on attempt {attempt}: output=\"{text}\"')\r\n\r\n        attempt += 1\r\n\r\nasyncio.run(main())\r\n```\r\n\r\nYou 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:\r\n```\r\nRuntimeError: FAIL on attempt 3823: output=\"\"\r\n```\r\n\r\n# Your environment\r\n\r\n\u003c!-- Include as many relevant details as possible about the environment you experienced the bug in --\u003e\r\n\r\n- CPython versions tested on: 3.11.1\r\n- Operating system and architecture: FreeBSD 13.1 amd64\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-100154\n* gh-100398\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/AMDmi3","@type":"Person","name":"AMDmi3"},"datePublished":"2022-12-09T11:48:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/100133/cpython/issues/100133"}