[asyncio] orphan future close loop and cause "RuntimeError: Event loop stopped before Future completed."

[jimmylai]

BPO	30423
Nosy	@asvetlov, @ambv, @1st1, @jimmylai
PRs	[asyncio] bpo-30423 bug: orphan future close loop and cause "RuntimeError: Event loop stopped before Future completed." #1688 [3.6] bpo-30423: call remove_done_callback in finally section (GH-1688) #1755 [3.5] bpo-30423: call remove_done_callback in finally section (GH-1688) #1758 [asyncio] bpo-30423: add regression test for orphan future causes "RuntimeError: Event loop stopped before Future completed." #3295

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

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GitHub fields:

assignee = None
closed_at = <Date 2017-05-23.07:37:31.504>
created_at = <Date 2017-05-21.13:44:28.150>
labels = ['3.7', 'expert-asyncio']
title = '[asyncio] orphan future close loop and cause "RuntimeError: Event loop stopped before Future completed."'
updated_at = <Date 2017-11-01.13:54:48.076>
user = 'https://github.com/jimmylai'

bugs.python.org fields:

activity = <Date 2017-11-01.13:54:48.076>
actor = 'asvetlov'
assignee = 'none'
closed = True
closed_date = <Date 2017-05-23.07:37:31.504>
closer = 'lukasz.langa'
components = ['asyncio']
creation = <Date 2017-05-21.13:44:28.150>
creator = 'jimmylai'
dependencies = []
files = []
hgrepos = []
issue_num = 30423
keywords = []
message_count = 2.0
messages = ['294102', '305382']
nosy_count = 4.0
nosy_names = ['asvetlov', 'lukasz.langa', 'yselivanov', 'jimmylai']
pr_nums = ['1688', '1755', '1758', '3295']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue30423'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[jimmylai]

Problem:
"RuntimeError: Event loop stopped before Future completed." throws when calling run_until_complete().

We investigate and find out some orphan futures stay in the event loop before we run another run_until_complete(another_async_func()).
The orphan future has pending state and is attached with _run_until_complete_cb from previous run_until_complete.
It happens because the orphan future thrown Exception and then raise, thus remove_done_callback(_run_until_complete_cb) didn't called.
Move it to finally section can fix it.
With this patch, we stop seeing the Runtime Error.

[asvetlov]

New changeset d1e3403 by Andrew Svetlov (jimmylai) in branch 'master':
[asyncio] bpo-30423: add regression test for orphan future causes "RuntimeError: Event loop stopped before Future completed." (bpo-3295)
d1e3403