[New-bugs-announce] [issue38973] Shared Memory List Returns 0 Length

[Derek Frombach]

New submission from Derek Frombach <neoredstone at gmail.com>:

When accessing Shared Memory Lists, occasionally the shared memory list will have a length of zero for only one line of code.

Even know the length of the list is constant and greater than zero, when accessing this list, like say sml[0], python returns a ValueError complaining that sml is an empty list.

As well, if you print out sml on the very next line in the exception handler, then you get a full length list, with no access issues whatsoever.

This isn't a locking issue, since locks were acquired before writing to the lists, and released after writing.  This is a shared memory list runtime access consistency issue.

An Example of this Issue can be Seen Here:
https://github.com/uofrobotics/RPLidarVidStream

The issue is in the process_data function, only when smd, sma, smq, or sml are read from.

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components: Extension Modules, IO, Interpreter Core, asyncio, ctypes
files: 20191203_194951.jpg
messages: 357817
nosy: Derek Frombach, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: Shared Memory List Returns 0 Length
type: crash
versions: Python 3.8
Added file: https://bugs.python.org/file48757/20191203_194951.jpg

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38973>
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