C# 怎样得到本机CPU的核心数？

void WINAPI GetSystemInfo(
__out LPSYSTEM_INFO lpSystemInfo
);
LPSYSTEM_INFO 这个结构里有dwNumberOfProcessors，

typedef struct _SYSTEM_INFO {
union {
DWORD dwOemId;
struct {
WORD wProcessorArchitecture;
WORD wReserved;
} ;
} ;
DWORD dwPageSize;
LPVOID lpMinimumApplicationAddress;
LPVOID lpMaximumApplicationAddress;
DWORD_PTR dwActiveProcessorMask;
DWORD dwNumberOfProcessors;
DWORD dwProcessorType;
DWORD dwAllocationGranularity;
WORD wProcessorLevel;
WORD wProcessorRevision;
} SYSTEM_INFO;