`asyncio.create_subprocess_exec`: cannot read `/dev/stdin`

test.py の reproducer から始め、Docker 上の Linux で vanilla asyncio と動作を比較します。uvloop/loop.pyx、uvloop/handles/stream.pyx、uvloop/handles/handle.pyx を通して subprocess の stdin 処理を追跡します。uvloop で /dev/stdin サブプロセスが closed-transport error なしに b'test' を出力すれば完了です。

• uvloop version: uvloop==0.17.0
• Python version: Python 3.10.10
• Platform: Linux 0af9a1603f81 5.10.76-linuxkit #1 SMP Mon Nov 8 10:21:19 UTC 2021 x86_64 GNU/Linux (in a Docker container)
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: yes
• Does uvloop behave differently from vanilla asyncio? How?: yes. Vanilla asyncio had a similar issue patched: https://github.com/python/cpython/issues/90522

Processes run with asyncio.create_subprocess_exec fail to read from /dev/stdin with uvloop but not with asyncio

asyncio had a similar issue fixed recently (in January 2022): https://github.com/python/cpython/issues/90522
This was backported to 3.10 and 3.11

I can reproduce this on Linux in a Docker container, with either Mac OS or Linux as hosts
I cannot reproduce this on Mac OS (seems to work fine)

Logs:

# PYTHONASYNCIODEBUG=1 python test.py
cat: /dev/stdin: No such device or address
Traceback (most recent call last):
  File "//test.py", line 16, in <module>
    asyncio.run(f())
  File "/usr/local/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete
  File "//test.py", line 13, in f
    stdout, _ = await proc.communicate("test".encode("utf-8"))
  File "/usr/local/lib/python3.10/asyncio/subprocess.py", line 195, in communicate
    stdin, stdout, stderr = await tasks.gather(stdin, stdout, stderr)
  File "/usr/local/lib/python3.10/asyncio/subprocess.py", line 147, in _feed_stdin
    self.stdin.write(input)
  File "/usr/local/lib/python3.10/asyncio/streams.py", line 325, in write
    self._transport.write(data)
  File "uvloop/handles/stream.pyx", line 674, in uvloop.loop.UVStream.write
  File "uvloop/handles/handle.pyx", line 159, in uvloop.loop.UVHandle._ensure_alive
RuntimeError: unable to perform operation on <WriteUnixTransport closed=True reading=False 0x7f64e3186dc0>; the handler is closed

Expected (using asyncio):

# PYTHONASYNCIODEBUG=1 python test.py
b'test'

Code to reproduce:

import asyncio

# Commenting out `uvloop` below fixes the issue
import uvloop
uvloop.install()

async def f():
    proc = await asyncio.create_subprocess_exec(
        "cat",
        "/dev/stdin",
        stdin=asyncio.subprocess.PIPE,
        stdout=asyncio.subprocess.PIPE,
    )
    stdout, _ = await proc.communicate("test".encode("utf-8"))
    print(stdout)

asyncio.run(f())