bpo-30581: Windows: os.cpu_count() returns wrong number of processors (#2934)
* Fixes #30581 by adding a path to use newer GetMaximumProcessorCount API on Windows calls to os.cpu_count()
* Add NEWS.d entry for bpo-30581, os.cpu_count on Windows.
* Tweak NEWS entry
diff --git a/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
new file mode 100644
index 0000000..6591fa0
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2017-08-04-10-05-19.bpo-30581.OQhR7l.rst
@@ -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.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index f057787..e8138d5 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -11174,9 +11174,22 @@
{
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");
+
+ static DWORD(CALLBACK *_GetMaximumProcessorCount)(WORD) = NULL;
+ *(FARPROC*)&_GetMaximumProcessorCount = GetProcAddress(hKernel32,
+ "GetMaximumProcessorCount");
+ if (_GetMaximumProcessorCount != NULL) {
+ ncpu = _GetMaximumProcessorCount(ALL_PROCESSOR_GROUPS);
+ }
+ 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)