Accessing Performance Data in C++
The WMI high-performance API is a series of interfaces that obtain data from Performance Counter Classes. These interfaces require use of a refresher object to increase the sampling rate. For more information about using the refresher object in scripting, see Accessing Performance Data in Script and WMI Tasks: Performance Monitoring.
The following sections are discussed in this topic:
Refreshing Performance Data
A refresher object increases data provider and client performance by retrieving data without crossing process boundaries. If both the client and the server are located on the same computer, a refresher loads the high-performance provider in-process to the client, and copies data directly from provider objects into client objects. If the client and the server are located on different computers, the refresher increases performance by caching objects on the remote computer, and transmitting minimal data sets to the client.
A refresher also:
Automatically reconnects a client to a remote WMI service when a network error occurs, or the remote computer is restarted.
By default, a refresher attempts to reconnect your application to the relevant high-performance provider when a remote connection between the two computers fails. To prevent the reconnection, pass the WBEM_FLAG_REFRESH_NO_AUTO_RECONNECT flag in the Refresh method call. Scripting clients must set the SWbemRefresher.AutoReconnect property to FALSE.
Loads multiple objects and enumerators that are provided by the same or different providers.
Allows you to add multiple objects, enumerators, or both to a refresher.
Enumerates objects.
Like other providers, a high-performance provider can enumerate objects.
After you finish writing your high-performance client, you may want to improve your response time. Because the IWbemObjectAccess interface is optimized for speed, the interface is not intrinsically threadsafe. Therefore, during a refresh operation, do not access the refreshable object or enumeration. To protect objects across threads during IWbemObjectAccess method calls, use the IWbemObjectAccess::Lock and Unlock methods. For improved performance, synchronize your threads so that you do not need to lock individual threads. Reducing threads and synchronizing groups of objects for refresh operations provides the best overall performance.
Adding Enumerators to the WMI Refresher
Both the number of instances and data in each instance are refreshed by adding an enumerator to the refresher so that each call to IWbemRefresher::Refresh results in a complete enumeration.
The following C++ code example 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 add an enumerator to a refresher.
To add an enumerator to a refresher
Call the IWbemConfigureRefresher::AddEnum method using the path to the refreshable object and the IWbemServices interface.
The refresher returns a pointer to an IWbemHiPerfEnum interface. You can use the IWbemHiPerfEnum interface to access the objects in the enumeration.
IWbemHiPerfEnum* pEnum = NULL; long lID; IWbemConfigureRefresher* pConfig; IWbemServices* pNameSpace; // Add an enumerator to the refresher. if (FAILED (hr = pConfig->AddEnum( pNameSpace, L"Win32_PerfRawData_PerfProc_Process", 0, NULL, &pEnum, &lID))) { goto CLEANUP; } pConfig->Release(); pConfig = NULL;Create a loop that performs the following actions:
Refreshes the object by using a call to IWbemRefresher::Refresh.
Provides an array of IWbemObjectAccess interface pointers to the IWbemHiPerfEnum::GetObjects method.
Accesses the properties of the enumerator by using the IWbemObjectAccess methods passed into GetObjects.
A property handle can be passed to each IWbemObjectAccess instance to retrieve the refreshed value. The client must call Release to release the IWbemObjectAccess pointers returned by GetObjects.
Example
The following C++ code example enumerates a high-performance class, where the client retrieves a property handle from the first object, and reuses the handle for the remainder of the refresh operation. Each call to the Refresh method updates the number of instances and the instance data.
#define _WIN32_DCOM
#include <iostream>
using namespace std;
#include <Wbemidl.h>
#pragma comment(lib, "wbemuuid.lib")
int __cdecl wmain(int argc, wchar_t* argv[])
{
// To add error checking,
// check returned HRESULT below where collected.
HRESULT hr = S_OK;
IWbemRefresher *pRefresher = NULL;
IWbemConfigureRefresher *pConfig = NULL;
IWbemHiPerfEnum *pEnum = NULL;
IWbemServices *pNameSpace = NULL;
IWbemLocator *pWbemLocator = NULL;
IWbemObjectAccess **apEnumAccess = NULL;
BSTR bstrNameSpace = NULL;
long lID = 0;
long lVirtualBytesHandle = 0;
long lIDProcessHandle = 0;
DWORD dwVirtualBytes = 0;
DWORD dwProcessId = 0;
DWORD dwNumObjects = 0;
DWORD dwNumReturned = 0;
DWORD dwIDProcess = 0;
DWORD i=0;
int x=0;
if (FAILED (hr = CoInitializeEx(NULL,COINIT_MULTITHREADED)))
{
goto CLEANUP;
}
if (FAILED (hr = CoInitializeSecurity(
NULL,
-1,
NULL,
NULL,
RPC_C_AUTHN_LEVEL_NONE,
RPC_C_IMP_LEVEL_IMPERSONATE,
NULL, EOAC_NONE, 0)))
{
goto CLEANUP;
}
if (FAILED (hr = CoCreateInstance(
CLSID_WbemLocator,
NULL,
CLSCTX_INPROC_SERVER,
IID_IWbemLocator,
(void**) &pWbemLocator)))
{
goto CLEANUP;
}
// Connect to the desired namespace.
bstrNameSpace = SysAllocString(L"\\\\.\\root\\cimv2");
if (NULL == bstrNameSpace)
{
hr = E_OUTOFMEMORY;
goto CLEANUP;
}
if (FAILED (hr = pWbemLocator->ConnectServer(
bstrNameSpace,
NULL, // User name
NULL, // Password
NULL, // Locale
0L, // Security flags
NULL, // Authority
NULL, // Wbem context
&pNameSpace)))
{
goto CLEANUP;
}
pWbemLocator->Release();
pWbemLocator=NULL;
SysFreeString(bstrNameSpace);
bstrNameSpace = NULL;
if (FAILED (hr = CoCreateInstance(
CLSID_WbemRefresher,
NULL,
CLSCTX_INPROC_SERVER,
IID_IWbemRefresher,
(void**) &pRefresher)))
{
goto CLEANUP;
}
if (FAILED (hr = pRefresher->QueryInterface(
IID_IWbemConfigureRefresher,
(void **)&pConfig)))
{
goto CLEANUP;
}
// Add an enumerator to the refresher.
if (FAILED (hr = pConfig->AddEnum(
pNameSpace,
L"Win32_PerfRawData_PerfProc_Process",
0,
NULL,
&pEnum,
&lID)))
{
goto CLEANUP;
}
pConfig->Release();
pConfig = NULL;
// Get a property handle for the VirtualBytes property.
// Refresh the object ten times and retrieve the value.
for(x = 0; x < 10; x++)
{
dwNumReturned = 0;
dwIDProcess = 0;
dwNumObjects = 0;
if (FAILED (hr =pRefresher->Refresh(0L)))
{
goto CLEANUP;
}
hr = pEnum->GetObjects(0L,
dwNumObjects,
apEnumAccess,
&dwNumReturned);
// If the buffer was not big enough,
// allocate a bigger buffer and retry.
if (hr == WBEM_E_BUFFER_TOO_SMALL
&& dwNumReturned > dwNumObjects)
{
apEnumAccess = new IWbemObjectAccess*[dwNumReturned];
if (NULL == apEnumAccess)
{
hr = E_OUTOFMEMORY;
goto CLEANUP;
}
SecureZeroMemory(apEnumAccess,
dwNumReturned*sizeof(IWbemObjectAccess*));
dwNumObjects = dwNumReturned;
if (FAILED (hr = pEnum->GetObjects(0L,
dwNumObjects,
apEnumAccess,
&dwNumReturned)))
{
goto CLEANUP;
}
}
else
{
if (hr == WBEM_S_NO_ERROR)
{
hr = WBEM_E_NOT_FOUND;
goto CLEANUP;
}
}
// First time through, get the handles.
if (0 == x)
{
CIMTYPE VirtualBytesType;
CIMTYPE ProcessHandleType;
if (FAILED (hr = apEnumAccess[0]->GetPropertyHandle(
L"VirtualBytes",
&VirtualBytesType,
&lVirtualBytesHandle)))
{
goto CLEANUP;
}
if (FAILED (hr = apEnumAccess[0]->GetPropertyHandle(
L"IDProcess",
&ProcessHandleType,
&lIDProcessHandle)))
{
goto CLEANUP;
}
}
for (i = 0; i < dwNumReturned; i++)
{
if (FAILED (hr = apEnumAccess[i]->ReadDWORD(
lVirtualBytesHandle,
&dwVirtualBytes)))
{
goto CLEANUP;
}
if (FAILED (hr = apEnumAccess[i]->ReadDWORD(
lIDProcessHandle,
&dwIDProcess)))
{
goto CLEANUP;
}
wprintf(L"Process ID %lu is using %lu bytes\n",
dwIDProcess, dwVirtualBytes);
// Done with the object
apEnumAccess[i]->Release();
apEnumAccess[i] = NULL;
}
if (NULL != apEnumAccess)
{
delete [] apEnumAccess;
apEnumAccess = NULL;
}
// Sleep for a second.
Sleep(1000);
}
// exit loop here
CLEANUP:
if (NULL != bstrNameSpace)
{
SysFreeString(bstrNameSpace);
}
if (NULL != apEnumAccess)
{
for (i = 0; i < dwNumReturned; i++)
{
if (apEnumAccess[i] != NULL)
{
apEnumAccess[i]->Release();
apEnumAccess[i] = NULL;
}
}
delete [] apEnumAccess;
}
if (NULL != pWbemLocator)
{
pWbemLocator->Release();
}
if (NULL != pNameSpace)
{
pNameSpace->Release();
}
if (NULL != pEnum)
{
pEnum->Release();
}
if (NULL != pConfig)
{
pConfig->Release();
}
if (NULL != pRefresher)
{
pRefresher->Release();
}
CoUninitialize();
if (FAILED (hr))
{
wprintf (L"Error status=%08x\n",hr);
}
return 1;
}
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