Implementing OpenPerformanceData

The OpenPerformanceData function gives the provider an opportunity to initialize its performance data structures. The system calls your open function the first time a consumer calls RegQueryValueEx, or if the consumer uses the RegOpenKey or RegConnectRegistry function to open HKEY_PERFORMANCE_DATA.

The following example shows an implementation of the OpenPerformanceData function. The header file that contains the definition of the counters used in this function follows this example. If you use C++ to implement this function, be sure to use extern "C" when you declare your function. The counter offset constants used in this example are defined the CounterOffsets.h file shown in Adding Counter Names and Description to the Registry.

#include "provider.h"

// Callback that the performance service calls once for each consumer that wants 
// to consume one or more of your counters. You can use this notification to 
// prepare the counter data structures and setup communications with the 
// application that is providing the actual performance data.
extern "C" DWORD APIENTRY OpenPerfData(LPWSTR pContext)
    DWORD FirstCounterIndex = 0;
    DWORD FirstHelpIndex = 0;
    DWORD DataSize = sizeof(DWORD);  // Used in the RegQueryValueEx call
    HKEY hkey;

    // Use g_OpenCount to prevent initializing the data more than once.
    if (g_OpenCount > 1)
        goto cleanup;

    // Retrieve the application specific context data
    // if you define an Export value under the 
    // HKLM\SYSTEM\CurrentControlSet\Services\MyProvider\Linkage key.
    // The context string is a REG_MULTI_SZ string.

    if (pContext)
        for (; *pContext; pContext += (wcslen(pContext)+1))
            // Do something with the string.

    // Retrieve the starting index values for your counters and help strings. You add 
    // your offset values (see Adding Counter Names and Descriptions to the Registry)
    // to these index values to determine your actual object and counter index values.

    if (ERROR_SUCCESS == rc)
        rc = RegQueryValueEx(hkey, L"First Counter", NULL, NULL, (LPBYTE)&FirstCounterIndex, &DataSize);
        if (ERROR_SUCCESS == rc)
            rc = RegQueryValueEx(hkey, L"First Help", NULL, NULL, (LPBYTE)&FirstHelpIndex, &DataSize);        


    // If you could not open the key or retrieve the value, exit.

    if (ERROR_SUCCESS != rc)
        // If you return a non-success code, the service adds a Disable Performance 
        // Counters value to your Performance key to disable your provider.
        // Consider logging an event and returning success instead of failing.

        rc = ERROR_SUCCESS;
        goto cleanup;

    // Initialize the Transfer object. This is a single instance object, so you can
    // initialize each member of the object and its counters.

    ZeroMemory(&g_Transfer, TransferSize);
    g_Transfer.Object.TotalByteLength = TransferSize;
    g_Transfer.Object.DefinitionLength = sizeof(PERF_OBJECT_TYPE) + 
        sizeof(PERF_COUNTER_DEFINITION) * NumberOfTransferCounters;
    g_Transfer.Object.HeaderLength = sizeof(PERF_OBJECT_TYPE);
    g_TransferIndex = FirstCounterIndex;
    g_Transfer.Object.ObjectNameTitleIndex = g_TransferIndex;
    g_Transfer.Object.ObjectHelpTitleIndex = FirstHelpIndex;
    g_Transfer.Object.DetailLevel = PERF_DETAIL_ADVANCED;
    g_Transfer.Object.NumCounters = NumberOfTransferCounters;
    g_Transfer.Object.DefaultCounter = -1;  // No default counter
    g_Transfer.Object.NumInstances = PERF_NO_INSTANCES;

    // Initialize the bytes sent counter.

    g_Transfer.BytesSentCounter.ByteLength = sizeof(PERF_COUNTER_DEFINITION);
    g_Transfer.BytesSentCounter.CounterNameTitleIndex = FirstCounterIndex + BYTES_SENT;
    g_Transfer.BytesSentCounter.CounterHelpTitleIndex = FirstHelpIndex + BYTES_SENT;
    g_Transfer.BytesSentCounter.DetailLevel = PERF_DETAIL_ADVANCED;
    g_Transfer.BytesSentCounter.CounterType = PERF_COUNTER_RAWCOUNT;
    g_Transfer.BytesSentCounter.CounterSize = sizeof(DWORD);
    g_Transfer.BytesSentCounter.CounterOffset = BytesSentOffset;

    // Initialize the available bandwidth counter.

    g_Transfer.AvailableBandwidthCounter.ByteLength = sizeof(PERF_COUNTER_DEFINITION);
    g_Transfer.AvailableBandwidthCounter.CounterNameTitleIndex = FirstCounterIndex + AVAILABLE_BANDWIDTH;
    g_Transfer.AvailableBandwidthCounter.CounterHelpTitleIndex = FirstHelpIndex + AVAILABLE_BANDWIDTH;
    g_Transfer.AvailableBandwidthCounter.DetailLevel = PERF_DETAIL_ADVANCED;
    g_Transfer.AvailableBandwidthCounter.CounterType = PERF_RAW_FRACTION;
    g_Transfer.AvailableBandwidthCounter.CounterSize = sizeof(DWORD);
    g_Transfer.AvailableBandwidthCounter.CounterOffset = AvailableBandwidthOffset;

    // Initialize the total bandwidth counter. This is a base counter for the
    // available bandwidth counter. You do not specify index values for base counters.

    g_Transfer.TotalBandwidthBaseCounter.ByteLength = sizeof(PERF_COUNTER_DEFINITION);
    g_Transfer.TotalBandwidthBaseCounter.CounterType = PERF_RAW_BASE;
    g_Transfer.TotalBandwidthBaseCounter.CounterSize = sizeof(DWORD);
    g_Transfer.TotalBandwidthBaseCounter.CounterOffset = TotalBandwidthBaseOffset;

    // Specify the size of the counter block which contains the raw counter values. 

    g_Transfer.CounterBlock.ByteLength = EndOfTransferData;

    // Initialize the Peer object. This is a multiple instance object. You cannot 
    // initialize all members of the Peer object because you do not know how 
    // many instances there will be until the object data is queried. You set 
    // the TotalByteLength and NumInstances members in the CollectPerfData function.

    ZeroMemory(&g_Peer, sizeof(PEER));
    g_Peer.Object.DefinitionLength = sizeof(PERF_OBJECT_TYPE) + 
        sizeof(PERF_COUNTER_DEFINITION) * NumberOfPeerCounters;
    g_Peer.Object.HeaderLength = sizeof(PERF_OBJECT_TYPE);
    g_PeerIndex = FirstCounterIndex + PEER_OBJECT;
    g_Peer.Object.ObjectNameTitleIndex = g_PeerIndex;
    g_Peer.Object.ObjectHelpTitleIndex = FirstHelpIndex + PEER_OBJECT;
    g_Peer.Object.DetailLevel = PERF_DETAIL_ADVANCED;
    g_Peer.Object.NumCounters = NumberOfPeerCounters;
    g_Peer.Object.DefaultCounter = -1;  // No default counter

    // Initialize the bytes served counter.

    g_Peer.BytesServedCounter.ByteLength = sizeof(PERF_COUNTER_DEFINITION);
    g_Peer.BytesServedCounter.CounterNameTitleIndex = FirstCounterIndex + BYTES_SERVED;
    g_Peer.BytesServedCounter.CounterHelpTitleIndex = FirstHelpIndex + BYTES_SERVED;
    g_Peer.BytesServedCounter.DetailLevel = PERF_DETAIL_ADVANCED;
    g_Peer.BytesServedCounter.CounterType = PERF_COUNTER_RAWCOUNT;
    g_Peer.BytesServedCounter.CounterSize = sizeof(DWORD);
    g_Peer.BytesServedCounter.CounterOffset = BytesServedOffset;

    InterlockedIncrement(&g_OpenCount);  // Decremented in ClosePerfData

    return rc;

The following is the header file used in this example.

#ifndef _PROVIDER_H
#define _PROVIDER_H

#include <windows.h>
#include <strsafe.h>
#include "CounterOffsets.h"

extern "C" DWORD APIENTRY OpenPerfData(LPWSTR pContext);
extern "C" DWORD APIENTRY CollectPerfData(LPWSTR pQuery, PVOID* ppData, LPDWORD pcbData, LPDWORD pObjectsReturned);
extern "C" DWORD APIENTRY ClosePerfData();
BOOL IsQuerySupported(LPWSTR pQuery, DWORD* pQueriedObjects);
DWORD GetQuerySize(DWORD QueriedObjects);

// Define the Transfer counter object. This object is a single 
// instance counter object, so you can define it completely.
typedef struct _transfer 
    PERF_COUNTER_DEFINITION AvailableBandwidthCounter;
    PERF_COUNTER_DEFINITION TotalBandwidthBaseCounter;
    PERF_COUNTER_BLOCK CounterBlock;
    DWORD BytesSentData;
    DWORD AvailableBandwidthData;
    DWORD TotalBandwidthData;

// Define offsets to counter data
#define BytesSentOffset sizeof(PERF_COUNTER_BLOCK)
#define AvailableBandwidthOffset BytesSentOffset + sizeof(DWORD)
#define TotalBandwidthBaseOffset AvailableBandwidthOffset + sizeof(DWORD)
#define EndOfTransferData TotalBandwidthBaseOffset + sizeof(DWORD)
#define TransferSize sizeof(TRANSFER)

#define NumberOfTransferCounters 3


// Define the Peer counter object. This object is a multiple
// instance object, so you must define the object and instances
// separately.
typedef struct _peer {

typedef struct _peerinstance {
  DWORD BytesServedData;

#define BytesServedOffset sizeof(PERF_COUNTER_BLOCK)
#define EndOfPeerData BytesServedOffset + sizeof(DWORD)
#define NumberOfPeerCounters 1

// For this example, the instances are static, so predefine the names.
#define INSTANCE_NAME_1 L"Peer 1"
#define INSTANCE_NAME_2 L"Peer 2"
#define PERFORMANCE_REGISTRY_PATH L"SYSTEM\\CurrentControlSet\\Services\\MyApplication\\Performance"

typedef enum _queriedflags { 

TRANSFER g_Transfer;             // Transfer object
PEER g_Peer;                     // Peer object
DWORD g_TransferIndex = 0;       // Index value for the Transfer object
DWORD g_PeerIndex = 0;           // Index value for the Peer object
DWORD g_QueriedObjects = 0;      // Objects that were queried
UNALIGNED LONG g_OpenCount = 0;  // Reference count for the number of times
                                 // that OpenPerfData is called.

The following example shows the module definition (.def) file used to export the open, collect, and close functions.

LIBRARY    "PerfProvider"

    OpenPerfData    @1
    CollectPerfData    @2
    ClosePerfData    @3

The following example shows an implementation of the ClosePerformanceData function. The system calls your close function when a consumer calls the RegCloseKey to close HKEY_PERFORMANCE_DATA. Providers use this call to release any resources that they have allocated.

// Callback that the performance service calls once for each consumer that has
// finished consuming your performance counters. Cleanup any resources that 
// you allocated for your performance counters.
extern "C" DWORD APIENTRY ClosePerfData(void)
    if (g_OpenCount > 0)

    return ERROR_SUCCESS;