[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Robin Scheibler]

Robin Scheibler  added the comment:

Thank you very much for your help!

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Guido van Rossum]

Guido van Rossum  added the comment:

No, let's leave 3.7 alone -- it's in security-fixes-only mode.

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resolution:  -> fixed
stage:  -> resolved
status: open -> closed

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Robin Scheibler]

Robin Scheibler  added the comment:

Thanks for the suggestion. I had indeed run into some issues with fork vs spawn 
before.

I have tested with 3.8.5 and 3.9.1 and the bug doesn't occur with these more 
recent versions.

Should I leave the bug open since 3.7 is still supported ?

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Ned Deily]

Ned Deily  added the comment:

Also note that there are known problems with using the "fork" start method of 
multiprocessing on macOS. As of Python 3.8, the default start methord on macOS 
is now "spawn":

https://docs.python.org/3.9/library/multiprocessing.html#contexts-and-start-methods

Try using "spawn" and/or upgrade to a more recent version of Python 3 (3.9.1 is 
current).

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nosy: +ned.deily

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Robin Scheibler]

Robin Scheibler  added the comment:

Thank you very much for the reply! I was indeed hesitating where to post the 
issue. I have now cross-posted in the sounddevice issue tracker.

https://github.com/spatialaudio/python-sounddevice/issues/302

I'll update the issue if things progress on that side.

The sounddevice is essentially a wrapper around the portaudio library, similar 
to pyaudio. I have tried the test code with an import of pyaudio rather than 
sounddevice, but the issue does not happen in that case.

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Guido van Rossum]

Guido van Rossum  added the comment:

I would assume it’s some interaction between threads and fork. Have you asked 
the authors of sound device about this?

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nosy: +gvanrossum

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[issue42850] Process hangs when calling urllib.request in a multiprocessing.Process with import of sounddevice package

[Robin Scheibler]

New submission from Robin Scheibler :

I am having an issue with using urllib in a multiprocessing.Process when the 
package sounddevice (https://github.com/spatialaudio/python-sounddevice) has 
been already imported.

The sub-process hangs upon calling urllib.request.urlopen (and methods from the 
requests package too).

1. If the package sounddevice is not imported, things work as expected.
2. If the package sounddevice is imported, but urllib.request.urlopen is called 
once prior to launching thee sub-process, then things also work as expected.

I have attached a file containing code to reproduce the issue.

I have run this example file in:
- Python 3.7.9 (conda distribution)
- Mac OS X 10.15.7

# Running the code as is reproduces the problem
> python ./test_mp_req.py
Nothing in the queue. Leave.
wait for process to terminate...
finished

# Running the code with either line 8 commented *or* line 32 uncommented
# gives the expected output
> python ./test_mp_req.py
Received https://api.github.com. Send GET request... done.
Received https://www.google.com. Send GET request... done.
https://api.github.com: ok
https://www.google.com: ok
Nothing in the queue. Leave.
wait for process to terminate...
finished

--
components: Interpreter Core, Library (Lib), ctypes
files: test_mp_req.py
messages: 384562
nosy: fakufaku
priority: normal
severity: normal
status: open
title: Process hangs when calling urllib.request in a multiprocessing.Process 
with import of sounddevice package
type: crash
versions: Python 3.7
Added file: https://bugs.python.org/file49724/test_mp_req.py

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