Creating a Performance Extension DLL
Important
Due to significant performance and reliability limitations, the method for providing performance counter data that this topic describes may be altered or unavailable in the future. Instead, Microsoft recommends that you use the method described in Providing Counter Data Using Version 2.0 for creating new performance counters and that you migrate existing performance counters to use that method as well.
A V1 provider uses a performance DLL that provides counter data to consumers. The performance DLL must export the OpenPerformanceData, CollectPerformanceData, and ClosePerformanceData functions. Typically, you use a module definition (.def) file to export the functions from the DLL. The system calls these functions when a consumer queries performance data.
The first time a consumer calls RegQueryValueEx, or if the consumer uses the RegOpenKey or RegConnectRegistry function to open HKEY_PERFORMANCE_DATA, the system calls the OpenPerformanceData function for each provider that is registered on the computer. The exception is if the provider specifies the list of objects that it supports in the [objects] section of the .INI file. In this case, the system calls the provider only if one of the queried objects matches an object from the list.
The OpenPerformanceData function gives each provider an opportunity to initialize its performance data structures. Then, if the OpenPerformanceData function returns successfully, the system calls the provider's CollectPerformanceData function. Subsequent calls to RegQueryValueEx cause the system to call the CollectPerformanceData function.
When the consumer finishes collecting performance data, it specifies HKEY_PERFORMANCE_DATA in a call to the RegCloseKey function. This causes the system to call the ClosePerformanceData function for each provider. The providers are then unloaded.
It is possible for multiple consumers to collect performance data at the same time. The system calls OpenPerformanceData and ClosePerformanceData functions only once each time the DLL is loaded or unloaded.
Note
Be sure to include extern "C" in your C++ code to prevent the compiler from adding decorations to your function names; otherwise, the system may fail to find your functions.
Note
If an error occurs while loading your performance DLL, finding your functions, or calling your functions, the system will disable the provider for subsequent collections within the same process. In addition, if this occurs while running in a privileged process, the system adds a Disable Performance Counters value to your Performance key to prevent the provider from being loaded in the future.
For more information on writing a performance DLL, see the following topics: