Permission denied using mmap on Windows

Bug report

I have a Windows service that creates a memory mapped file using the global scope and a client that reads the global scope. The problem is that the current implementation calls CreateFileMapping() instead of OpenFileMapping(). So when the client tries to connect the global scope, its throws a permission error.

The expected behavior is: Only the server has the permission the create a global memory mapped file and any client can read the created memory mapped file.

Here is a sample code:

server.py

from mmap import mmap
from pickle import load, dump


mm = mmap(-1, 32, tagname=r'Global\test')

last_request_id = None
while True:
    mm.seek(0)
    try:
        request_id = int(load(mm))
        if request_id != last_request_id:
            last_request_id = request_id
            print(request_id)
        
    except Exception:
        pass

client.py

from mmap import mmap
from pickle import dump


with mmap(-1, 32, tagname='Global\test') as mm:
    request_id = 1
    dump(request_id, mm)

Your environment

• CPython versions tested on: 3.11
• Operating system and architecture: Windows 11 - Version 22H2 (OS Build 22621.819)

Comienza en Modules/mmapmodule.c alrededor de la línea 1531 y lee el manejo de mmap en Windows junto con la documentación de CreateFileMapping() y OpenFileMapping(). Reproduce el ejemplo de server.py y client.py en Windows 11. Se considera terminado cuando el servidor puede crear el mapping Global y el cliente puede abrirlo y leerlo sin un error de permisos.