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GetLogicalProcessorInformation function

Retrieves information about logical processors and related hardware.

To retrieve information about logical processors and related hardware, including processor groups, use the GetLogicalProcessorInformationEx function.

Syntax


BOOL WINAPI GetLogicalProcessorInformation(
  _Out_    PSYSTEM_LOGICAL_PROCESSOR_INFORMATION Buffer,
  _Inout_  PDWORD ReturnLength
);

Parameters

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.

Return value

If the function succeeds, the return value is TRUE and at least one SYSTEM_LOGICAL_PROCESSOR_INFORMATION structure is written to the output buffer.

If the function fails, the return value is FALSE. To get extended error information, call GetLastError.

Remarks

GetLogicalProcessorInformation can be used to get information about the relationship between logical processors in the system, including:

  • The logical processors that are part of a NUMA node.
  • The logical processors that share resources. An example of this type of resource sharing would be hyperthreading scenarios.

Your application can use this information when affinitizing your threads and processes to take best advantage of the hardware properties of the platform, or to determine the number of logical and physical processors for licensing purposes.

Each of the SYSTEM_LOGICAL_PROCESSOR_INFORMATION structures returned in the buffer contains the following:

  • A logical processor affinity mask, which indicates the logical processors that the information in the structure applies to.
  • A logical processor mask of type LOGICAL_PROCESSOR_RELATIONSHIP, which indicates the relationship between the logical processors in the mask. Applications calling this function must be prepared to handle additional indicator values in the future.

Note that the order in which the structures are returned in the buffer may change between calls to this function.

The size of the SYSTEM_LOGICAL_PROCESSOR_INFORMATION structure varies between processor architectures and versions of Windows. For this reason, applications should first call this function to obtain the required buffer size, then dynamically allocate memory for the buffer.

On systems with more than 64 logical processors, the GetLogicalProcessorInformation function retrieves logical processor information about processors in the processor group to which the calling thread is currently assigned. Use the GetLogicalProcessorInformationEx function to retrieve information about processors in all processor groups on the system.

Examples

The following C++ example uses the GetLogicalProcessorInformation function to display information about processors on the current system. Because GetLogicalProcessorInformation is not present on all systems, this example uses the GetProcAddress function instead of calling GetLogicalProcessorInformation directly.

This example reports the number of active processor cores. This example also reports the number of NUMA nodes, physical packages, and caches on systems that support this information. For more information, see the description of the Relationship member of the SYSTEM_LOGICAL_PROCESSOR_INFORMATION structure.

Windows Server 2003, Windows XP Professional x64 Edition, and Windows XP with SP3:  This example reports the number of physical processors rather than the number of active processor cores.



#include <windows.h>
#include <malloc.h>    
#include <stdio.h>
#include <tchar.h>

typedef BOOL (WINAPI *LPFN_GLPI)(
    PSYSTEM_LOGICAL_PROCESSOR_INFORMATION, 
    PDWORD);


// Helper function to count set bits in the processor mask.
DWORD CountSetBits(ULONG_PTR bitMask)
{
    DWORD LSHIFT = sizeof(ULONG_PTR)*8 - 1;
    DWORD bitSetCount = 0;
    ULONG_PTR bitTest = (ULONG_PTR)1 << LSHIFT;    
    DWORD i;
    
    for (i = 0; i <= LSHIFT; ++i)
    {
        bitSetCount += ((bitMask & bitTest)?1:0);
        bitTest/=2;
    }

    return bitSetCount;
}

int _cdecl _tmain ()
{
    LPFN_GLPI glpi;
    BOOL done = FALSE;
    PSYSTEM_LOGICAL_PROCESSOR_INFORMATION buffer = NULL;
    PSYSTEM_LOGICAL_PROCESSOR_INFORMATION ptr = NULL;
    DWORD returnLength = 0;
    DWORD logicalProcessorCount = 0;
    DWORD numaNodeCount = 0;
    DWORD processorCoreCount = 0;
    DWORD processorL1CacheCount = 0;
    DWORD processorL2CacheCount = 0;
    DWORD processorL3CacheCount = 0;
    DWORD processorPackageCount = 0;
    DWORD byteOffset = 0;
    PCACHE_DESCRIPTOR Cache;

    glpi = (LPFN_GLPI) GetProcAddress(
                            GetModuleHandle(TEXT("kernel32")),
                            "GetLogicalProcessorInformation");
    if (NULL == glpi) 
    {
        _tprintf(TEXT("\nGetLogicalProcessorInformation is not supported.\n"));
        return (1);
    }

    while (!done)
    {
        DWORD rc = glpi(buffer, &returnLength);

        if (FALSE == rc) 
        {
            if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) 
            {
                if (buffer) 
                    free(buffer);

                buffer = (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION)malloc(
                        returnLength);

                if (NULL == buffer) 
                {
                    _tprintf(TEXT("\nError: Allocation failure\n"));
                    return (2);
                }
            } 
            else 
            {
                _tprintf(TEXT("\nError %d\n"), GetLastError());
                return (3);
            }
        } 
        else
        {
            done = TRUE;
        }
    }

    ptr = buffer;

    while (byteOffset + sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION) <= returnLength) 
    {
        switch (ptr->Relationship) 
        {
        case RelationNumaNode:
            // Non-NUMA systems report a single record of this type.
            numaNodeCount++;
            break;

        case RelationProcessorCore:
            processorCoreCount++;

            // A hyperthreaded core supplies more than one logical processor.
            logicalProcessorCount += CountSetBits(ptr->ProcessorMask);
            break;

        case RelationCache:
            // Cache data is in ptr->Cache, one CACHE_DESCRIPTOR structure for each cache. 
            Cache = &ptr->Cache;
            if (Cache->Level == 1)
            {
                processorL1CacheCount++;
            }
            else if (Cache->Level == 2)
            {
                processorL2CacheCount++;
            }
            else if (Cache->Level == 3)
            {
                processorL3CacheCount++;
            }
            break;

        case RelationProcessorPackage:
            // Logical processors share a physical package.
            processorPackageCount++;
            break;

        default:
            _tprintf(TEXT("\nError: Unsupported LOGICAL_PROCESSOR_RELATIONSHIP value.\n"));
            break;
        }
        byteOffset += sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION);
        ptr++;
    }

    _tprintf(TEXT("\nGetLogicalProcessorInformation results:\n"));
    _tprintf(TEXT("Number of NUMA nodes: %d\n"), 
             numaNodeCount);
    _tprintf(TEXT("Number of physical processor packages: %d\n"), 
             processorPackageCount);
    _tprintf(TEXT("Number of processor cores: %d\n"), 
             processorCoreCount);
    _tprintf(TEXT("Number of logical processors: %d\n"), 
             logicalProcessorCount);
    _tprintf(TEXT("Number of processor L1/L2/L3 caches: %d/%d/%d\n"), 
             processorL1CacheCount,
             processorL2CacheCount,
             processorL3CacheCount);
    
    free(buffer);

    return 0;
}



Requirements

Minimum supported client

Windows Vista, Windows XP Professional x64 Edition, Windows XP with SP3 [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

WinBase.h on Windows XP, Windows Server 2003, Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2 (include Windows.h);
Sysinfoapi.h on Windows 8 and Windows Server 2012

Library

Kernel32.lib

DLL

Kernel32.dll

See also

GetLogicalProcessorInformationEx
LOGICAL_PROCESSOR_RELATIONSHIP
Process and Thread Functions
SYSTEM_LOGICAL_PROCESSOR_INFORMATION

 

 

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