System Pool Behavior
The following discussion highlights the actions taken by the system pool when event notices are sent and when no biometric operations are pending.
When a biometric unit generates an event notice, the system pool uses a cascading filter to dispatch the notice and assign it one of the following priority levels:
- High priority is assigned to explicit matching and enrollment requests generated by clients.
- Medium priority is assigned to unexpected or unclaimed matching or enrollment events.
- Low priority is assigned to navigation events.
Capture events are delivered in the following sequence:
- If the current focus window is waiting for a matching or an enrollment operation, the sample is processed and sent to the client that owns the current focus window.
- If the capture event is unclaimed by the current focus window and an unclaimed event handler has been registered with the Windows Biometric service, the capture event is sent to this handler.
- If the event remains unclaimed, it is discarded.
If the event is a navigation event and a navigation event handler has been registered with the Windows Biometric service, the capture event is sent to this handler. If there is no event handler, the event is discarded.
When there are no clients waiting for explicit matching or enrollment requests to complete, the system pool determines whether to automatically generate repeated capture requests and send the resulting event notice to the unclaimed event handler or wait for navigation events and send them to the navigation event handler.
If an unclaimed event handler has been registered with the Windows Biometric service, the system pool performs the following actions:
- The navigation mode for the sensor is disabled.
- Unclaimed operations are sent to the event handler regardless of window focus.
- If there are no outstanding requests for a biometric operation, an automatic capture is performed.
If a navigation handler has been registered with the Windows Biometric service, the system pool does the following:
- The biometric units in the system pool are placed into a navigation state if no biometric operations are pending.
- Navigation events are disabled if a match or enrollment event notice is sent by a client.
- If an unclaimed events handler has been registered, navigation events are disabled.