Event loop incorrectly inherited in child processes.

[elprans]

BPO	30972
Nosy	@elprans, @1st1
Files	test.py: Example

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-07-19.22:49:35.008>
labels = ['type-bug', 'expert-asyncio']
title = 'Event loop incorrectly inherited in child processes.'
updated_at = <Date 2017-07-19.22:49:35.008>
user = 'https://github.com/elprans'

bugs.python.org fields:

activity = <Date 2017-07-19.22:49:35.008>
actor = 'Elvis.Pranskevichus'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2017-07-19.22:49:35.008>
creator = 'Elvis.Pranskevichus'
dependencies = []
files = ['47024']
hgrepos = []
issue_num = 30972
keywords = []
message_count = 1.0
messages = ['298693']
nosy_count = 2.0
nosy_names = ['Elvis.Pranskevichus', 'yselivanov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30972'
versions = ['Python 3.6']

[elprans]

The attached example shows that asyncio.get_event_loop still returns parent process' event loop in some cases. It appears that the fix in issue bpo-29703 was incomplete:

PARENT PID: 21947, LOOP: <_UnixSelectorEventLoop running=True closed=False debug=False> at 0x7f0fbe7cfd68
WORKER PID: 21948, LOOP: <_UnixSelectorEventLoop running=True closed=False debug=False> at 0x7f0fbe7cfd68
concurrent.futures.process._RemoteTraceback:
"""
Traceback (most recent call last):
  File "/usr/lib64/python3.6/concurrent/futures/process.py", line 175, in _process_worker
    r = call_item.fn(*call_item.args, **call_item.kwargs)
  File "test.py", line 13, in worker
    return loop.run_until_complete(worker_coro())
  File "/usr/lib64/python3.6/asyncio/base_events.py", line 454, in run_until_complete
    self.run_forever()
  File "/usr/lib64/python3.6/asyncio/base_events.py", line 408, in run_forever
    raise RuntimeError('This event loop is already running')
RuntimeError: This event loop is already running
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "test.py", line 25, in <module>
    loop.run_until_complete(main())
  File "/usr/lib64/python3.6/asyncio/base_events.py", line 466, in run_until_complete
    return future.result()
  File "test.py", line 21, in main
    return await loop.run_in_executor(executor, worker)
RuntimeError: This event loop is already running

[kumaraditya303]

Fixed on main branch:

@kumaraditya303 ➜ /workspaces/cpython (main ✗) $ ./python main.py 
PARENT PID: 11366, LOOP: <_UnixSelectorEventLoop running=True closed=False debug=False> at 0x7fafe6565280
/workspaces/cpython/main.py:11: DeprecationWarning: There is no current event loop
  loop = asyncio.get_event_loop()
WORKER PID: 11367, LOOP: <_UnixSelectorEventLoop running=False closed=False debug=False> at 0x7fafe6e29550
Running coro in process 11367