[issue41344] SharedMemory crash when size is 0

[Vinay Sharma]

New submission from Vinay Sharma <vinay0410sharma at gmail.com>:

On running this: shm = SharedMemory(create=True, size=0)
I get the following error:



Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/multiprocessing/shared_memory.py", line 111, in __init__
    self._mmap = mmap.mmap(self._fd, size)
ValueError: cannot mmap an empty file
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 63, in apport_excepthook
    from apport.fileutils import likely_packaged, get_recent_crashes
  File "/usr/lib/python3/dist-packages/apport/__init__.py", line 5, in <module>
    from apport.report import Report
  File "/usr/lib/python3/dist-packages/apport/report.py", line 30, in <module>
    import apport.fileutils
  File "/usr/lib/python3/dist-packages/apport/fileutils.py", line 23, in <module>
    from apport.packaging_impl import impl as packaging
  File "/usr/lib/python3/dist-packages/apport/packaging_impl.py", line 24, in <module>
    import apt
  File "/usr/lib/python3/dist-packages/apt/__init__.py", line 23, in <module>
    import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'

Original exception was:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/multiprocessing/shared_memory.py", line 111, in __init__
    self._mmap = mmap.mmap(self._fd, size)
ValueError: cannot mmap an empty file
>>> shm = SharedMemory(create=True, size=0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/multiprocessing/shared_memory.py", line 111, in __init__
    self._mmap = mmap.mmap(self._fd, size)
ValueError: cannot mmap an empty file
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 63, in apport_excepthook
    from apport.fileutils import likely_packaged, get_recent_crashes
  File "/usr/lib/python3/dist-packages/apport/__init__.py", line 5, in <module>
    from apport.report import Report
  File "/usr/lib/python3/dist-packages/apport/report.py", line 30, in <module>
    import apport.fileutils
  File "/usr/lib/python3/dist-packages/apport/fileutils.py", line 23, in <module>
    from apport.packaging_impl import impl as packaging
  File "/usr/lib/python3/dist-packages/apport/packaging_impl.py", line 24, in <module>
    import apt
  File "/usr/lib/python3/dist-packages/apt/__init__.py", line 23, in <module>
    import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'

Original exception was:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/multiprocessing/shared_memory.py", line 111, in __init__
    self._mmap = mmap.mmap(self._fd, size)
ValueError: cannot mmap an empty file


This can be simply resolved by adding a check when size passed is 0, so that a shared memory segment is never created.
Currently, the following is coded:

if not size >= 0:
    raise ValueError("'size' must be a positive integer")

I believe this should be changed to:
if not size > 0:
    raise ValueError("'size' must be a positive integer")

As zero is not a positive and integer and is causing problems.

----------
components: Library (Lib)
messages: 373990
nosy: vinay0410
priority: normal
severity: normal
status: open
title: SharedMemory crash when size is 0
type: crash
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41344>
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