Writing an Event Provider
An event provider is a COM object that supplies WMI with notifications of intrinsic and extrinsic events. An intrinsic event reports an internal data change to WMI, while an extrinsic event reports a user-defined event not described by an intrinsic event. For example, an event in response to changes, creation, or deletion of the Win32_LogicalDisk class would classify as an intrinsic event. An event that is generated on the basis of something other than the modification, creation, or deletion of an existing WMI object is an extrinsic event. Regardless of the supported class, you can implement all event providers in the same manner.
The following procedure describes how to implement an event provider.
To implement an event provider
- Design and register your class provider with WMI.
- Implement the IWbemProviderInit interface for your provider.
- Implement the
IWbemEventProvider as the primary interface for your provider.
The IWbemEventProvider interface uses the ProviderEvents method to supply events to WMI. For more information, see Implementing the Primary Interface for an Event Provider.
Note Event providers must use the multithreading model "Both".
- Optionally, you may also implement the
IWbemEventProviderQuerySink interface to increase the performance of your event provider.
The IWbemEventProviderQuerySink interface allows the provider to optimize queries before sending a response to WMI, and is most useful for a provider that supplies events of multiple types and that needs to perform as many internal optimizations as possible. For more information, see Optimizing an Event Provider.
- Implement the IWbemEventProviderSecurity interface to limit consumers to certain security identifiers (SIDs) or implement IWbemEventSink::SetSinkSecurity to secure the sink itself. The provider can also set the SECURITY_DESCRIPTOR property in the event class to secure individual events in the MOF code. For more information, see Securing WMI Events.
- Add any additional code necessary for your provider.
When designing your provider, you most likely need to call WMI interfaces. For more information, see Calling a Method.
When retrieving information for a client, you may need to access the security levels for that client. For more information, see Impersonating a Client.
- Replace the preexisting provider with your new code.
You do not need to perform this step if you do not have a preexisting provider to copy over. For more information, see Updating a Provider.
A client application can request an event by registering itself with WMI as an event consumer. For more information, see Receiving a WMI Event.