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asyncio.create_subprocess_exec with IO redirection hangs if no global loop set #478

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asyncio.create_subprocess_exec with IO redirection hangs if no global loop set#478
@rutsky

Description

@rutsky
rutsky
opened on Dec 21, 2016

If I set global event loop to None (asyncio.set_event_loop(None)) and explicitly pass everywhere event loop, asyncio.create_subprocess_exec with I/O redirection will hang.

In following example proc.communicate() will never return:

import asyncio.subprocess

async def f(loop):
    proc = await asyncio.create_subprocess_exec(
        'echo',
        stdout=asyncio.subprocess.PIPE,
        loop=loop)

    await proc.communicate()

loop = asyncio.get_event_loop()

asyncio.set_event_loop(None)

date = loop.run_until_complete(f(loop))
loop.close()

With PYTHONASYNCIODEBUG=x:

Traceback (most recent call last):
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 17, in <module>
    date = loop.run_until_complete(f(loop))
  File "/usr/lib/python3.5/asyncio/base_events.py", line 387, in run_until_complete
    return future.result()
  File "/usr/lib/python3.5/asyncio/futures.py", line 274, in result
    raise self._exception
  File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(None)
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 9, in f
    loop=loop)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/subprocess.py", line 212, in create_subprocess_exec
    stderr=stderr, **kwds)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1079, in subprocess_exec
    bufsize, **kwargs)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 187, in _make_subprocess_transport
    self._child_watcher_callback, transp)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 808, in add_child_handler
    self._do_waitpid(pid)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 841, in _do_waitpid
    if self._loop.get_debug():
AttributeError: 'NoneType' object has no attribute 'get_debug'
Task was destroyed but it is pending!
source_traceback: Object created at (most recent call last):
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 17, in <module>
    date = loop.run_until_complete(f(loop))
  File "/usr/lib/python3.5/asyncio/base_events.py", line 375, in run_until_complete
    self.run_forever()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 345, in run_forever
    self._run_once()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1304, in _run_once
    handle._run()
  File "/usr/lib/python3.5/asyncio/events.py", line 125, in _run
    self._callback(*self._args)
  File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(None)
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 9, in f
    loop=loop)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/subprocess.py", line 212, in create_subprocess_exec
    stderr=stderr, **kwds)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1079, in subprocess_exec
    bufsize, **kwargs)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 184, in _make_subprocess_transport
    **kwargs)
  File "/usr/lib/python3.5/asyncio/base_subprocess.py", line 56, in __init__
    self._loop.create_task(self._connect_pipes(waiter))
task: <Task pending coro=<BaseSubprocessTransport._connect_pipes() running at /usr/lib/python3.5/asyncio/base_subprocess.py:171> wait_for=<Future pending cb=[Task._wakeup()] created at /usr/lib/python3.5/asyncio/base_events.py:252> created at /usr/lib/python3.5/asyncio/base_subprocess.py:56>
Future exception was never retrieved
future: <Future finished exception=RuntimeError('Event loop is closed',) created at /usr/lib/python3.5/asyncio/base_events.py:252>
source_traceback: Object created at (most recent call last):
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 17, in <module>
    date = loop.run_until_complete(f(loop))
  File "/usr/lib/python3.5/asyncio/base_events.py", line 375, in run_until_complete
    self.run_forever()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 345, in run_forever
    self._run_once()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1304, in _run_once
    handle._run()
  File "/usr/lib/python3.5/asyncio/events.py", line 125, in _run
    self._callback(*self._args)
  File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(None)
  File "asyncio_subprocess_hangs_wo_global_loop.py", line 9, in f
    loop=loop)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/subprocess.py", line 212, in create_subprocess_exec
    stderr=stderr, **kwds)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 1079, in subprocess_exec
    bufsize, **kwargs)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 105, in __next__
    return self.gen.send(None)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 180, in _make_subprocess_transport
    waiter = self.create_future()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 252, in create_future
    return futures.Future(loop=self)
Traceback (most recent call last):
  File "/usr/lib/python3.5/asyncio/base_events.py", line 989, in connect_read_pipe
    yield from waiter
GeneratorExit

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.5/asyncio/base_subprocess.py", line 171, in _connect_pipes
    proc.stdout)
  File "/usr/lib/python3.5/asyncio/coroutines.py", line 127, in close
    return self.gen.close()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 991, in connect_read_pipe
    transport.close()
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 376, in close
    self._close(None)
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 404, in _close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 497, in call_soon
    handle = self._call_soon(callback, args)
  File "/usr/lib/python3.5/asyncio/base_events.py", line 506, in _call_soon
    self._check_closed()
  File "/usr/lib/python3.5/asyncio/base_events.py", line 334, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

Tested on Ubuntu 16.04, with Python 3.5.2.

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