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bpo-30581: Windows: os.cpu_count() returns wrong number of processors #2934

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Merged
merged 3 commits into from
Aug 30, 2017
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bpo-30581: Windows: os.cpu_count() returns wrong number of processors #2934

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73adde2
Fixes #30581 by adding a path to use newer GetMaximumProcessorCount A…
crwilcox Jul 28, 2017
ef1b704
Add NEWS.d entry for bpo-30581, os.cpu_count on Windows.
crwilcox Aug 4, 2017
780ea3c
Tweak NEWS entry
pitrou Aug 30, 2017
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
os.cpu_count() now returns the correct number of processors on Windows
when the number of logical processors is greater than 64.
19 changes: 16 additions & 3 deletions Modules/posixmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11128,9 +11128,22 @@ os_cpu_count_impl(PyObject *module)
{
int ncpu = 0;
#ifdef MS_WINDOWS
SYSTEM_INFO sysinfo;
GetSystemInfo(&sysinfo);
ncpu = sysinfo.dwNumberOfProcessors;
/* Vista is supported and the GetMaximumProcessorCount API is Win7+
Need to fallback to Vista behavior if this call isn't present */
HINSTANCE hKernel32;
hKernel32 = GetModuleHandleW(L"KERNEL32");
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Does the handle need to be closed after using it?

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Other places in posixmodule use this but on closer inspection they are all in methods.

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No, GetModuleHandle does not increase the refcount on the module (it also only works on already-loaded modules, but kernel32 is guaranteed to be there).


static DWORD(CALLBACK *_GetMaximumProcessorCount)(WORD) = NULL;
*(FARPROC*)&_GetMaximumProcessorCount = GetProcAddress(hKernel32,
"GetMaximumProcessorCount");
if (_GetMaximumProcessorCount != NULL) {
ncpu = _GetMaximumProcessorCount(ALL_PROCESSOR_GROUPS);
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Is ALL_PROCESSOR_GROUPS always defined at compile-time, even before Windows 7?

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I think this may be just windows 7 forward. I know the result needs to run on Pre-Windows 7, does it also need to compile?

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In the Windows 10 SDK (which is required) the symbol is always defined. We filter APIs to those available on Vista, but that symbol is not excluded when you do that.

}
else {
SYSTEM_INFO sysinfo;
GetSystemInfo(&sysinfo);
ncpu = sysinfo.dwNumberOfProcessors;
}
#elif defined(__hpux)
ncpu = mpctl(MPC_GETNUMSPUS, NULL, NULL);
#elif defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
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