Description

assignee = None
closed_at = <Date 2014-12-12.13:13:57.454>
created_at = <Date 2014-12-12.12:36:11.806>
labels = ['type-bug', 'library', 'OS-windows']
title = 'cpu_count() unreliable on Windows'
updated_at = <Date 2014-12-12.13:13:57.452>
user = 'https://github.com/mark-summerfield'

activity = <Date 2014-12-12.13:13:57.452>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2014-12-12.13:13:57.454>
closer = 'vstinner'
components = ['Library (Lib)', 'Windows']
creation = <Date 2014-12-12.12:36:11.806>
creator = 'mark'
dependencies = []
files = []
hgrepos = []
issue_num = 23037
keywords = []
message_count = 2.0
messages = ['232540', '232544']
nosy_count = 5.0
nosy_names = ['vstinner', 'tim.golden', 'mark', 'zach.ware', 'steve.dower']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23037'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4']

Activity

1. mark-summerfield commented on Dec 12, 2014

   

   mark-summerfieldmannequin

   on Dec 12, 2014

   MannequinAuthor

   More actions

   In message
   http://bugs.python.org/issue17914#msg188626
   Victor Stenner says

   "On Windows, GetSystemInfo() is called instead of reading an environment variable. I suppose that this function is more reliable."

   From my reading, and based on feedback from one of my customers, I believe he is correct and that GetSystemInfo() ought to be used on Windows. (It is available in pywin32 win32api.)
2. mark-summerfield

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   OS-windows

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Dec 12, 2014
3. vstinner commented on Dec 12, 2014

   

   vstinner

   on Dec 12, 2014

   Member

   More actions

   The code getting the number of processors on Windows is different between the multiprocessing (Python 3.3) and os (Python 3.5) modules.

   multiprocessing (old code):

       try:
           num = int(os.environ['NUMBER_OF_PROCESSORS'])
       except (ValueError, KeyError):
           num = 0
   

   os (new code):

   SYSTEM_INFO sysinfo;
   GetSystemInfo(&sysinfo);
   ncpu = sysinfo.dwNumberOfProcessors;
   

   os.cpu_count() is already implemented with GetSystemInfo() in Python 3.5, so this issue can be closed. Thanks for the reminder Mark, it was useful to double check.

   If you want to take a look at the source code:
   https://hg.python.org/cpython/file/35b7dde7fd53/Modules/posixmodule.c#l16064
4. vstinner

   closed this as completedon Dec 12, 2014
5. ezio-melotti

   transferred this issue fromon Apr 10, 2022

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