OSError: [Errno 6] No such device or address: '/proc/self/fd/1' when using asyncio.create_subprocess_*

• uvloop==0.16.0 and uvloop==0.17.0:
• python3.8.10 and python3.10.5:
• Platform: Ubuntu20.04:
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env? -> Yes, but there is not more output:
• Does uvloop behave differently from vanilla asyncio? How? It uses socket instead of pipe for the file descriptors of the subprocess. This gives me an OSError6:

Uvloop does not handle subprocess pipes properly. It doesn not matter if I use asyncio.subprocess.PIPE or subprocess.PIPE. How can I access stdout/stderr of a asyncio subprocess? Is this behavior intended?

Running the proof of concept:

import asyncio, subprocess
async def poc():
    proc = await asyncio.create_subprocess_shell(
        "ls -lsh /proc/self/fd",
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE,
    )
    stdout, stderr = await proc.communicate()
    print(stdout, stderr)
    proc = await asyncio.create_subprocess_shell(
        "python3 -c \"f=open('/proc/self/fd/1', 'w'); f.write('test')\"", stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE
    )
    stdout, stderr = await proc.communicate()
    print(stdout, stderr)

async def poc1():
    proc = await asyncio.create_subprocess_shell(
        "ls -lsh /proc/self/fd",
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE,
    )
    stdout, stderr = await proc.communicate()
    print(stdout, stderr)
    proc = await asyncio.create_subprocess_shell(
        "python3 -c \"f=open('/proc/self/fd/1', 'w'); f.write('test')\"", stdout=subprocess.PIPE, stderr=subprocess.PIPE
    )
    stdout, stderr = await proc.communicate()
    print(stdout, stderr)

print("Default loop")
asyncio.run(poc())
asyncio.run(poc1())

import uvloop
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

print("uvloop")
print("asyncio pipe")
asyncio.run(poc())
print("subprocess pipe")
asyncio.run(poc1())

Yields the following output:

Default loop
b'total 0\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 0 -> /dev/pts/10\n0 l-wx------ 1 peter peter 64 Sep 22 12:19 1 -> pipe:[8435934]\n0 l-wx------ 1 peter peter 64 Sep 22 12:19 2 -> pipe:[8435935]\n0 lr-x------ 1 peter peter 64 Sep 22 12:19 3 -> /proc/625365/fd\n' b''
b'test' b''
b'total 0\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 0 -> /dev/pts/10\n0 l-wx------ 1 peter peter 64 Sep 22 12:19 1 -> pipe:[8435942]\n0 l-wx------ 1 peter peter 64 Sep 22 12:19 2 -> pipe:[8435943]\n0 lr-x------ 1 peter peter 64 Sep 22 12:19 3 -> /proc/625371/fd\n' b''
b'test' b''
uvloop
asyncio pipe
b'total 0\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 0 -> /dev/pts/10\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 1 -> socket:[8435953]\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 2 -> socket:[8435955]\n0 lr-x------ 1 peter peter 64 Sep 22 12:19 3 -> /proc/625376/fd\n' b''
b'' b'Traceback (most recent call last):\n  File "<string>", line 1, in <module>\nOSError: [Errno 6] No such device or address: \'/proc/self/fd/1\'\n'
subprocess pipe
b'total 0\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 0 -> /dev/pts/10\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 1 -> socket:[8396454]\n0 lrwx------ 1 peter peter 64 Sep 22 12:19 2 -> socket:[8396456]\n0 lr-x------ 1 peter peter 64 Sep 22 12:19 3 -> /proc/625380/fd\n' b''
b'' b'Traceback (most recent call last):\n  File "<string>", line 1, in <module>\nOSError: [Errno 6] No such device or address: \'/proc/self/fd/1\'\n'

As we can see, once uvloop is running the calls that worked earlier are crashing. The observable difference is that uvloop maps sockets to stdout/stderr whereas default asyncio uses pipes

Start by running the supplied proof of concept with vanilla asyncio and uvloop, focusing on asyncio.create_subprocess_shell, PIPE handling, and uvloop.EventLoopPolicy. Compare the stdout and stderr file descriptors and error output; done means the reported subprocess pipe behavior is understood and the reproduction no longer produces the OSError.