classification
Title: ctypes.from_buffer counterpart to actively remove the mapping
Type: behavior Stage:
Components: ctypes Versions: Python 3.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: frispete
Priority: normal Keywords:

Created on 2016-12-14 11:36 by frispete, last changed 2016-12-14 11:36 by frispete.

Messages (1)
msg283188 - (view) Author: Hans-Peter Jansen (frispete) * Date: 2016-12-14 11:36
In an attempt of using ctypes.from_buffer() to map a structure to a memory mapped file, it is important to destroy the mapping after use, because the mmap won't be resizable or freeable correctly until then.

The best approach, I was able to came up with is using a context manager, but calling the dtor of the mapping in __exit__ is not enough, which results to code like this:

with StructMap(ctypes_struct, mm, offest) as smap:
    smap.xxx = 'blabla'
del smap # necessary, but ugly

Without the del, the "with" variable still exist in the local context, hence the mapping still exist, until it is explicitly destroyed.

I hope, that ctypes is able to (or can be made to) actively remove the mapping in the __exit__ part of the context manager.

I've put some code on stackoverflow to play with this:

http://stackoverflow.com/questions/41077696/python-ctypes-from-buffer-mapping-with-context-manager-into-memory-mapped-file

The problem seems to exist with the linux mmap implementation only.
History
Date User Action Args
2016-12-14 11:36:48frispetecreate