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Title: __import__ is not thread-safe on Python 3
Type: Stage:
Components: Versions: Python 3.9, Python 3.8, Python 3.7
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Martin Laus, Valentyn Tymofieiev, brett.cannon, eric.snow, gjb1002, gregory.p.smith, ncoghlan, repalviglator, ryan.petrello
Priority: normal Keywords:

Created on 2019-11-21 19:11 by Valentyn Tymofieiev, last changed 2022-04-11 14:59 by admin.

File name Uploaded Description Edit Valentyn Tymofieiev, 2019-11-21 19:11 Valentyn Tymofieiev, 2019-11-21 19:13 Valentyn Tymofieiev, 2019-11-21 22:30
Messages (14)
msg357198 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 19:11
Attached consistently fails for me on Python 3.7.5 and earlier Python 3 versions that I have tried with 

  File "/usr/lib/python3.7/", line 926, in _bootstrap_inner
  File "/usr/lib/python3.7/", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "", line 8, in t2
    return __import__("tensorflow.estimator", level=0)
ModuleNotFoundError: No module named 'tensorflow.estimator

Threads in this example finish successfully if executed sequentially.

I have not tried higher versions of Python, but I cannot reproduce this on Python 2.7. 

Is this an expected behavior?

Thank you.
msg357199 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 19:13
Attached fails with   

File "<frozen importlib._bootstrap>", line 980, in _find_and_load
  File "<frozen importlib._bootstrap>", line 149, in __enter__
  File "<frozen importlib._bootstrap>", line 94, in acquire
_frozen_importlib._DeadlockError: deadlock detected by _ModuleLock('tensorflow_transform.tf_metadata.metadata_io')

under the same conditions.
msg357202 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 19:31
Possibly related:
msg357214 - (view) Author: Brett Cannon (brett.cannon) * (Python committer) Date: 2019-11-21 20:20
Can you test this with a package that isn't tensorflow (e.g. something else in the stdlib or something created manually; basically a smaller reproducer)? It's hard to diagnose if this is really Python or not without a smaller reproducer as tensorflow might be doing some things behind the scenes that would break this due to it being an extension module.
msg357227 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 22:30
Attaching a minimal repro with simple project hierarchy.
msg357228 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 22:31
Repro: unpack

(fails on Python 3.7, but not on 2.7).
msg357230 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 22:33 in has a left-over comment:
# Requires pip install tensorflow==2.0.0 tensorflow-transform==0.15.0 
Please ignore that.
msg357234 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-21 23:01
The behavior changes between Python 3.2 (no deadlock) and Python 3.3 (deadlock). Deadlock also reproducible on Python 3.8.
msg357464 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2019-11-25 22:49
@brett.cannon, looks like I inadvertently dropped you from nosy list, so in case you missed the updates - please take a look at Thank you.
msg360068 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2020-01-15 17:28
Just checking - is an acceptable repro for this issue?
msg360069 - (view) Author: Brett Cannon (brett.cannon) * (Python committer) Date: 2020-01-15 18:44
@valentyn just assume it's good enough unless some asks otherwise. People are probably too busy right now to be looking at this and so you might be waiting a while for a more definitive answer.
msg362746 - (view) Author: Ryan Petrello (ryan.petrello) Date: 2020-02-26 22:09
I believe I'm also encountering some version of this bug while importing code from the kombu library within a multi-threaded context.

For what it's worth, I'm able to reproduce the reported deadlock ( using python3.8 on RHEL8 and CentOS 8 builds.

More details about what I'm encountering here:

My intended workaround for now is to just not use a thread (we'll see if it helps):
msg375958 - (view) Author: Kyle Mulka (repalviglator) Date: 2020-08-26 20:27
Was able to reproduce with Python 3.9.0rc1 using macOS 10.15.5
msg408052 - (view) Author: Valentyn Tymofieiev (Valentyn Tymofieiev) Date: 2021-12-08 22:53
Given that the behavior changes between Python 3.2 (no deadlock) and Python 3.3 (deadlock), this should be easily bisectable if someone has the right setup to build and run Python versions from sources in that range.
Date User Action Args
2022-04-11 14:59:23adminsetgithub: 83065
2021-12-08 22:53:27Valentyn Tymofieievsetmessages: + msg408052
2021-12-08 22:31:14gregory.p.smithsetnosy: + gregory.p.smith
2020-08-26 20:27:52repalviglatorsetmessages: + msg375958
2020-08-26 20:22:18repalviglatorsetnosy: + repalviglator

versions: + Python 3.9
2020-04-17 14:48:34Martin Laussetnosy: + Martin Laus
2020-03-31 11:12:19gjb1002setnosy: + gjb1002
2020-02-26 22:09:39ryan.petrellosetnosy: + ryan.petrello
messages: + msg362746
2020-01-15 18:44:24brett.cannonsetmessages: + msg360069
2020-01-15 17:28:51Valentyn Tymofieievsetmessages: + msg360068
2019-11-25 22:49:12Valentyn Tymofieievsetmessages: + msg357464
2019-11-25 22:43:41Valentyn Tymofieievsetnosy: + brett.cannon, ncoghlan, eric.snow
2019-11-25 22:42:20Valentyn Tymofieievsetnosy: + Valentyn Tymofieiev, - brett.cannon
2019-11-25 22:42:00Valentyn Tymofieievsetnosy: + brett.cannon, - Valentyn Tymofieiev
2019-11-22 03:08:51Valentyn Tymofieievsetversions: + Python 3.8
2019-11-21 23:01:41Valentyn Tymofieievsetmessages: + msg357234
2019-11-21 22:33:02Valentyn Tymofieievsetmessages: + msg357230
2019-11-21 22:31:34Valentyn Tymofieievsetmessages: + msg357228
2019-11-21 22:30:19Valentyn Tymofieievsetfiles: +
nosy: - brett.cannon, ncoghlan, eric.snow
messages: + msg357227

2019-11-21 20:20:18brett.cannonsetmessages: + msg357214
2019-11-21 20:11:53brett.cannonsetnosy: + brett.cannon, ncoghlan, eric.snow
2019-11-21 19:31:56Valentyn Tymofieievsetmessages: + msg357202
2019-11-21 19:13:24Valentyn Tymofieievsetfiles: +

messages: + msg357199
2019-11-21 19:11:54Valentyn Tymofieievcreate