[issue17914] add os.cpu_count()

[STINNER Victor]

STINNER Victor added the comment:

In my patch cpu_count.patch, I changed posix_cpu_count():

 * rewrite Mac OS X implementation: code in 5e0c56557390 looks wrong. It gets a MIB but then don't use it when calling _bsd_cpu_count(). But I didn't check my patch nor the commit version on Mac OS X.
 * use "int ncpu;" instead of "long ncpu;" when calling mpctl() and sysctl(). For mpctl(), ncpu is used to store the result, so a wide type is ok. But for sysctl(), we pass a pointer. What happens if sysctl() expects int whereas we pass a pointer to a long? We announce sizeof(int)!?
 * inline _bsd_cpu_count()

Sorry for this late review.

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<http://bugs.python.org/issue17914>
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