Accessing WMI Preinstalled Performance Classes

The WMI repository contains preinstalled performance classes for all the performance library objects. For example, instances of the raw data performance class Win32_PerfRawData_PerfProc_Process represent processes. This performance object is visible in System Monitor as the Process object.

The PageFaultsPerSec property of Win32_PerfRawData_PerfProc_Process represents the Page Faults per second performance counter for the process. The Win32_PerfFormattedData classes contain the calculated data values displayed in System Monitor (Perfmon.exe). The value of the PageFaultsPerSec property of Win32_PerfFormattedData_PerfProc_Process is the same as when it appears in System Monitor.

Use either the COM API for WMI or the Scripting API for WMI to access performance data through the Performance Counter Classes. In both cases a refresher object is required to obtain each data sample. For more information and script code examples for using refreshers and accessing performance classes, see WMI Tasks: Performance Monitoring. For more information, see Accessing Performance Data in Script.

Accessing Performance Data from C++

The following C++ code example uses the Performance Counter provider Wbemperf.dll to access predefined high-performance classes. It creates a refresher object and adds an object to the refresher. The object is a Win32_PerfRawData_PerfProc_Process instance that monitors the performance of a specific process. The code only reads one counter property in the process object, the VirtualBytes property. The code requires the following references and #include statements to compile correctly.


#define _WIN32_DCOM
#include <iostream>
using namespace std;
#include <wbemidl.h>
# pragma comment(lib, "wbemuuid.lib")

The following procedure shows how to access data from a high-performance provider in C++.

Aa384740.wedge(en-us,VS.85).gifTo access data from a high-performance provider in C++

  1. Establish a connection to the WMI namespace, and set WMI security by using a call to IWbemLocator::ConnectServer and CoSetProxyBlanket.

    This step is a standard step for creating any WMI client application. For more information, see Creating a WMI Application Using C++.

  2. Create a refresher object by using CoCreateInstance with CLSID_WbemRefresher. Request an IWbemConfigureRefresher interface through the QueryInterface method. Request an IWbemRefresher interface through the QueryInterface method.

    The IWbemRefresher interface is the main interface for the WMI Refresher object.

    The following C++ code example shows how to retrieve IWbemConfigureRefresher.

    
    
    IWbemRefresher* pRefresher = NULL;
    
    HRESULT hr = CoCreateInstance(
        CLSID_WbemRefresher,
        NULL,
        CLSCTX_INPROC_SERVER,
        IID_IWbemRefresher,
        (void**) &pRefresher);
    
    IWbemConfigureRefresher* pConfig = NULL;
    
    pRefresher->QueryInterface( 
        IID_IWbemConfigureRefresher,
        (void**) &pConfig
      );
    
    
    
  3. Add an object to the refresher through a call to the IWbemConfigureRefresher::AddObjectByPath method.

    When you add an object to the refresher, WMI refreshes the object whenever you call the IWbemRefresher::Refresh method. The object you add designates the provider in its class qualifiers.

    The following C++ code example shows how to call AddObjectByPath.

    
    IWbemClassObject* pObj = NULL;
    IWbemServices* pNameSpace = NULL;
    
    // Add the instance to be refreshed.
    hr = pConfig->AddObjectByPath(
         pNameSpace,
         L"Win32_PerfRawData_PerfProc_Process.Name=\"WINWORD\"",
         0L,
         NULL,
         &pObj,
         NULL
    );
    if (FAILED(hr))
    {
       cout << "Could not add object. Error code: 0x"
            << hex << hr << endl;
       pNameSpace->Release();
       return hr;
    }
    
    
  4. To set up faster access to the object, connect to the IWbemObjectAccess interface through QueryInterface on the IWbemClassObject interface.

    The following C++ code example shows how to retrieve a pointer to the object using IWbemObjectAccess instead of IWbemClassObject.

    
        // For quick property retrieval, use IWbemObjectAccess.    
        IWbemObjectAccess* pAcc = NULL;
        pObj->QueryInterface( IID_IWbemObjectAccess, (void**) &pAcc );
        // This is not required.
        pObj->Release();
    
    

    The IWbemObjectAccess interface increases performance because you can get handles to specific counter properties, and it requires that you lock and unlock the object in your code, which is an operation that IWbemClassObject performs for each property access.

  5. Obtain the handles of the properties to examine by using calls to the IWbemObjectAccess::GetPropertyHandle method.

    Property handles are the same for all instances of a class, which means that use the property handle you retrieve from a specific instance for all instances of a specific class. You can also obtain a handle from a class object to retrieve property values from an instance object.

    The following C++ code example shows how to retrieve a property handle.

    
        // Get a property handle for the VirtualBytes property
        long lVirtualBytesHandle = 0;
        DWORD dwVirtualBytes = 0;
        CIMTYPE variant;
    
        hr = pAcc->GetPropertyHandle(L"VirtualBytes",
             &variant,
             &lVirtualBytesHandle 
        );
        if (FAILED(hr))
        {
           cout << "Could not get property handle. Error code: 0x"
                << hex << hr << endl;
           return hr;
        }
    
    
  6. Create a programming loop that performs the following actions:

    • Refresh the object with a call to IWbemRefresher::Refresh by using the pointer created in the previous call to CoCreateInstance.

      In this call, the WMI Refresher refreshes the client object by using data that the provider supplies.

    • Perform any action as necessary on the object, such as retrieving a property name, data type, or value.

      You can access the property through the property handle obtained earlier. Due to the Refresh call, WMI refreshes the property each time through the loop.

The following C++ example shows how to use the WMI high-performance API.


// Get the local locator object
IWbemServices* pNameSpace = NULL;
IWbemLocator* pWbemLocator = NULL;
CIMTYPE variant;
VARIANT VT;

CoCreateInstance( CLSID_WbemLocator, NULL,
    CLSCTX_INPROC_SERVER, IID_IWbemLocator, (void**) &pWbemLocator
);

// Connect to the desired namespace
BSTR bstrNameSpace = SysAllocString( L"\\\\.\\root\\cimv2" );

HRESULT hr = WBEM_S_NO_ERROR;

hr = pWbemLocator->ConnectServer(
     bstrNameSpace,      // Namespace name
     NULL,               // User name
     NULL,               // Password
     NULL,               // Locale
     0L,                 // Security flags
     NULL,               // Authority
     NULL,               // Wbem context
     &pNameSpace         // Namespace
);

if ( SUCCEEDED( hr ) )
{
    // Set namespace security.
    IUnknown* pUnk = NULL;
    pNameSpace->QueryInterface( IID_IUnknown, (void**) &pUnk );

    hr = CoSetProxyBlanket(
         pNameSpace, 
         RPC_C_AUTHN_WINNT, 
         RPC_C_AUTHZ_NONE, 
         NULL, 
         RPC_C_AUTHN_LEVEL_DEFAULT, 
         RPC_C_IMP_LEVEL_IMPERSONATE,
         NULL, 
         EOAC_NONE 
    );
    if (FAILED(hr))
    {
       cout << "Cannot set proxy blanket. Error code: 0x"
            << hex << hr << endl;
       pNameSpace->Release();
       return hr;
    }

    hr = CoSetProxyBlanket(pUnk, 
         RPC_C_AUTHN_WINNT, 
         RPC_C_AUTHZ_NONE, 
         NULL, 
         RPC_C_AUTHN_LEVEL_DEFAULT, 
         RPC_C_IMP_LEVEL_IMPERSONATE,
         NULL, 
         EOAC_NONE 
    );
    if (FAILED(hr))
    {
       cout << "Cannot set proxy blanket. Error code: 0x"
            << hex << hr << endl;
       pUnk->Release();
       return hr;
    }

    // Clean up the IUnknown.
    pUnk->Release();

    IWbemRefresher* pRefresher = NULL;
    IWbemConfigureRefresher* pConfig = NULL;

    // Create a WMI Refresher and get a pointer to the
    // IWbemConfigureRefresher interface.
    CoCreateInstance(CLSID_WbemRefresher, 
                     NULL,
                     CLSCTX_INPROC_SERVER, 
                     IID_IWbemRefresher, 
                     (void**) &pRefresher 
    );
    
    pRefresher->QueryInterface(IID_IWbemConfigureRefresher,
                               (void**) &pConfig );

    IWbemClassObject* pObj = NULL;

    // Add the instance to be refreshed.
    pConfig->AddObjectByPath(
       pNameSpace,
       L"Win32_PerfRawData_PerfProc_Process.Name=\"WINWORD\"",
       0L,
       NULL,
       &pObj,
       NULL 
    );
    if (FAILED(hr))
    {
       cout << "Cannot add object. Error code: 0x"
            << hex << hr << endl;
       pNameSpace->Release();
       
       return hr;
    }

    // For quick property retrieval, use IWbemObjectAccess.    
    IWbemObjectAccess* pAcc = NULL;
    pObj->QueryInterface(IID_IWbemObjectAccess, 
                         (void**) &pAcc );

    // This is not required.
    pObj->Release();

    // Get a property handle for the VirtualBytes property.
    long lVirtualBytesHandle = 0;
    DWORD dwVirtualBytes = 0;

    pAcc->GetPropertyHandle(L"VirtualBytes", 
                            &variant, 
                            &lVirtualBytesHandle );

    // Refresh the object ten times and retrieve the value.
    for( int x = 0; x < 10; x++ )
    {
        pRefresher->Refresh( 0L );
        pAcc->ReadDWORD( lVirtualBytesHandle, &dwVirtualBytes );
        printf( "Process is using %lu bytes\n", dwVirtualBytes );
        // Sleep for a second.
        Sleep( 1000 );
    }
    // Clean up all the objects.
    pAcc->Release();
    // Done with these too.
    pConfig->Release();
    pRefresher->Release();
    pNameSpace->Release();
}
SysFreeString( bstrNameSpace );
pWbemLocator->Release();


Related topics

Performance Counter Classes
WMI Tasks: Performance Monitoring

 

 

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