[issue46799] ShareableList memory bloat and performance improvement

[Ting-Che Lin]

Ting-Che Lin <lintingche2012 at gmail.com> added the comment:

So I wrote a patch for this issue and published submitted a MR. When I was working on the patch, I realized that there is another issue related to how string and byte array size alignment is calculated. As seen here: https://github.com/python/cpython/blob/3.10/Lib/multiprocessing/shared_memory.py#L303. 

>>> from multiprocessing.shared_memory import ShareableList
>>> s_list = ShareableList(["12345678"])
>>> s_list.format
'16s'

I changed the calculation of 
self._alignment * (len(item) // self._alignment + 1),
to
self._alignment * max(1, (len(item) - 1) // self._alignment + 1)

With the patch, this will give
>>> from multiprocessing.shared_memory import ShareableList
>>> s_list = ShareableList(["12345678"])
>>> s_list.format
'8s'

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46799>
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