[issue37607] segfault running code in jupyter on macOS 10.14.5 - crashed on child side of fork pre-exec

[Ned Deily]

Ned Deily  added the comment:

> should I report issue to libcurl

It wouldn't hurt although they probably are aware of the problem.

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[issue37607] segfault running code in jupyter on macOS 10.14.5 - crashed on child side of fork pre-exec

[wesinator]

wesinator <13hu...@gmail.com> added the comment:

Thanks ned - should I report issue to libcurl ?

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[issue37607] segfault running code in jupyter on macOS 10.14.5 - crashed on child side of fork pre-exec

[Ned Deily]

Ned Deily  added the comment:

Looking at the macOS crash report you supplied (thanks!), the crash is 
occurring below libcurl which is called by the third-party pycurl module, so 
not in Python Standard Library code. And the crash appears to another of 
macOS's attempts to catch doing unsafe calls to system frameorks when forking 
withing an exec: note the "crashed on child side of fork pre-exec" message.  
This is a well-know pitfall particularly on macOS which is why we changed the 
default for the multiprocessing module on macOS as Victor noted above.  There 
are various articles out there about the general problem, like 
https://www.evanjones.ca/fork-is-dangerous.html.  If you are still seeing the 
problem, you may need to restructure your application to avoid fork without 
exec.  Good luck!

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resolution:  -> third party
stage:  -> resolved
status: open -> closed

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[issue37607] segfault running code in jupyter on macOS 10.14.5 - crashed on child side of fork pre-exec

[STINNER Victor]

STINNER Victor  added the comment:

See bpo-33725 and multiprocessing documentation:
https://docs.python.org/dev/library/multiprocessing.html#contexts-and-start-methods

"Changed in version 3.8: On macOS, the spawn start method is now the default. 
The fork start method should be considered unsafe as it can lead to crashes of 
the subprocess. See bpo-33725."

Change the start method to spawn.

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nosy: +vstinner

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[issue37607] segfault running code in jupyter on macOS 10.14.5 - crashed on child side of fork pre-exec

[wesinator]

New submission from wesinator <13hu...@gmail.com>:

python 3.7.4 (homebrew) macOS 10.14.5
16 GB DDR4

segfault encountered when running test code in jupyter. 

Application Specific Information:
crashed on child side of fork pre-exec

I'm not in a position to share the code unfortunately, but I can say it was 
running multiple iterations of subprocess.Popen() within a multiprocessing Pool 
using os.cpu_count() / 2 number of processes (in this case 12/2 = 6). 


macOS .crash dump file attached

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components: macOS
files: Python_2019-07-16-123850_MacBook-Pro.crash
messages: 348032
nosy: ned.deily, ronaldoussoren, wesinator
priority: normal
severity: normal
status: open
title: segfault running code in jupyter on macOS 10.14.5 - crashed on child 
side of fork pre-exec
type: crash
versions: Python 3.7
Added file: 
https://bugs.python.org/file48487/Python_2019-07-16-123850_MacBook-Pro.crash

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