GetLogicalProcessorInformation

最近在看《windows核心編程》，看到如何得到處理器信息，不是太明白，下面是得到處理器核心數的代碼，我本身加了一些註釋。

//得到處理器核心數
 void ShowProcessors()
 {
PSYSTEM_LOGICAL_PROCESSOR_INFORMATION pBuffer = NULL;
DWORD dwSize = 0;
DWORD procCoreCount;

//得到有dwSize的大小
BOOL bResult = GetLogicalProcessorInformation(pBuffer, &dwSize);
if(GetLastError() != ERROR_INSUFFICIENT_BUFFER){
	_tprintf(TEXT("Impossible to get processor information\n"));
	return;
}

//得到SYSTEM_LOGICAL_PROCESSOR_INFORMATION數組，數組中包含了全部邏輯處理器信息
pBuffer = (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION)malloc(dwSize);
bResult = GetLogicalProcessorInformation(pBuffer, &dwSize);
if(!bResult){
	free(pBuffer);
	_tprintf(TEXT("Impossible to get processor information\n"));
	return;
}

procCoreCount = 0;
//邏輯處理器數量
DWORD lpiCount = dwSize / sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION);
for(DWORD current = 0; current < lpiCount; current++){
	//邏輯處理器的Relationship爲RelationProcessorCore，表示該邏輯處理器是處理器核心
	if(pBuffer[current].Relationship == RelationProcessorCore){
		//該標誌表示處理器的用途
		if(pBuffer[current].ProcessorCore.Flags == 1){
			_tprintf(TEXT(" + one CPU core (HyperThreading)\n"));
		} else {
			_tprintf(TEXT("+ one CPU socket\n"));
		}
		procCoreCount++;

	}
}
_tprintf(TEXT("-> %d active CPU(s) \n"), procCoreCount);

free(pBuffer);
 }

一開始不懂爲何要調用兩次GetLogicalProcessorInformation函數，後來查了一下msdn，得知第一次是得到系統有多少個邏輯處理器數，也就是須要傳遞多大的SYSTEM_LOGICAL_PROCESSOR_INFORMATION數組給GetLogicalProcessorInformation函數，第二次調用的時候，函數會給pBuffer數組賦值。下面是MSDN上給出的關於函數的註解：

函數原型： BOOL WINAPI GetLogicalProcessorInformation( Out PSYSTEM_LOGICAL_PROCESSOR_INFORMATION Buffer, Inout PDWORD ReturnLength );

Buffer [out] A pointer to a buffer that receives an array of SYSTEM_LOGICAL_PROCESSOR_INFORMATION structures. If the function fails, the contents of this buffer are undefined.

ReturnLength [in, out] On input, specifies the length of the buffer pointed to by Buffer, in bytes. If the buffer is large enough to contain all of the data, this function succeeds and ReturnLength is set to the number of bytes returned. If the buffer is not large enough to contain all of the data, the function fails, GetLastError returns ERROR_INSUFFICIENT_BUFFER, and ReturnLength is set to the buffer length required to contain all of the data. If the function fails with an error other than ERROR_INSUFFICIENT_BUFFER, the value of ReturnLength is undefined.

參考： http://blog.csdn.net/zyl910/article/details/7547264