threading._DummyThread.__repr__ raises AssertionError

[TomMyers]

BPO	29376
Nosy	@tim-one, @pitrou, @zhangyangyu
PRs	bpo-29376: Fix assertion error in threading._DummyThread.is_alive() #236 bpo-29376: Fix assertion error in threading._DummyThread.is_alive() #329 bpo-29376: Fix assertion error in threading._DummyThread.is_alive() #330 [Do Not Merge] Sample of CPython life with blurb. #703 [Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	issue29376.patch

^{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 2017-02-27.03:47:40.676>
created_at = <Date 2017-01-25.23:10:08.930>
labels = ['3.7', 'type-bug', 'library']
title = 'threading._DummyThread.__repr__ raises AssertionError'
updated_at = <Date 2017-03-31.16:36:31.580>
user = 'https://bugs.python.org/TomMyers'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:31.580>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2017-02-27.03:47:40.676>
closer = 'xiang.zhang'
components = ['Library (Lib)']
creation = <Date 2017-01-25.23:10:08.930>
creator = 'Tom Myers'
dependencies = []
files = ['46502']
hgrepos = []
issue_num = 29376
keywords = ['patch']
message_count = 5.0
messages = ['286285', '286873', '290370', '290371', '290372']
nosy_count = 4.0
nosy_names = ['tim.peters', 'pitrou', 'xiang.zhang', 'Tom Myers']
pr_nums = ['236', '329', '330', '703', '552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29376'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[TomMyers]

_DummyThread objects have _is_stopped = False, but _tstate_lock = None. This causes an AssertionError in is_alive and __repr__ .

File ".../cp34/lib/python3.4/threading.py", line 814, in __repr__
self.is_alive() # easy way to get ._is_stopped set when appropriate
File ".../cp34/lib/python3.4/threading.py", line 1110, in is_alive
self._wait_for_tstate_lock(False)
File ".../cp34/lib/python3.4/threading.py", line 1066, in _wait_for_tstate_lock
assert self._is_stopped
AssertionError

[zhangyangyu]

This seems an regression from bpo-18808, so nosy Tim and Antoine. Since _DummyThread is always alive and daemonic, I think the solution could be overriding is_alive in _DummyThread and always returning True.

[zhangyangyu]

New changeset 4b6c417 by Xiang Zhang in branch '3.6':
bpo-29376: Fix assertion error in threading._DummyThread.is_alive() (GH-330)
4b6c417

[zhangyangyu]

New changeset 8400ae2 by Xiang Zhang in branch '3.5':
bpo-29376: Fix assertion error in threading._DummyThread.is_alive() (GH-329)
8400ae2

[zhangyangyu]

New changeset f3a9fab by Xiang Zhang in branch 'master':
bpo-29376: Fix assertion error in threading._DummyThread.is_alive() (GH-236)
f3a9fab