New submission from Maciej Gol <maciej....@curo.ch>:
Hey guys,
We have a component that archives and unarchives multiple files in separate
threads that started to
misbehave recently.
We have noticed a bunch of `AttributeError: module 'lzma' has no attribute
'LZMAFile'` errors, which are
unexpected because our python is not compiled with LZMA support.
What is unfortunate, is that given the traceback:
Traceback (most recent call last):
File "test.py", line 18, in <module>
list(pool.map(test_lzma, range(100)))
File "/opt/lang/python37/lib/python3.7/concurrent/futures/_base.py", line
598, in result_iterator
yield fs.pop().result()
File "/opt/lang/python37/lib/python3.7/concurrent/futures/_base.py", line
428, in result
return self.__get_result()
File "/opt/lang/python37/lib/python3.7/concurrent/futures/_base.py", line
384, in __get_result
raise self._exception
File "/opt/lang/python37/lib/python3.7/concurrent/futures/thread.py",
line 57, in run
result = self.fn(*self.args, **self.kwargs)
File "test.py", line 14, in test_lzma
tarfile.open(fileobj=buf, mode="r")
File "/opt/lang/python37/lib/python3.7/tarfile.py", line 1573, in open
return func(name, "r", fileobj, **kwargs)
File "/opt/lang/python37/lib/python3.7/tarfile.py", line 1699, in xzopen
fileobj = lzma.LZMAFile(fileobj or name, mode, preset=preset)
AttributeError: module 'lzma' has no attribute 'LZMAFile'
the last line of the traceback is right AFTER this block (tarfile.py:1694):
try:
import lzma
except ImportError:
raise CompressionError("lzma module is not available")
Importing lzma in ipython fails properly:
In [2]: import lzma
---------------------------------------------------------------------------
ModuleNotFoundError Traceback (most recent call last)
<ipython-input-2-c0255b54beb9> in <module>
----> 1 import lzma
/opt/lang/python37/lib/python3.7/lzma.py in <module>
25 import io
26 import os
---> 27 from _lzma import *
28 from _lzma import _encode_filter_properties,
_decode_filter_properties
29 import _compression
ModuleNotFoundError: No module named '_lzma'
When trying to debug the problem, we have noticed it's not deterministic. In
order to reproduce it,
we have created a test python that repeatedly writes an archive to BytesIO and
then reads from it.
Using it with 5 threads and 100 calls, gives very good chances of reproducing
the issue. For us it
was almost every time.
Race condition occurs both on Python 3.7.3 and 3.7.6.
Test script used to reproduce it attached.
I know that the test script writes uncompressed archives and during opening
tries to guess the compression.
But I guess this is a legitimate scenario and should not matter in this case.
----------
files: test.py
messages: 360551
nosy: Maciej Gol
priority: normal
severity: normal
status: open
title: tarfile.open(mode="r") race condition when importing lzma
type: crash
versions: Python 3.7
Added file: https://bugs.python.org/file48860/test.py
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39430>
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