Cisco Cisco Configuration Engine 3.5.3 开发者指南

Any application that subscribes to mapped subjects must resolve again upon receiving the change 
notification because their listeners would otherwise become outdated. The application shall then create 
listeners on the newly returned subjects after deleting the old listeners. 

Applications that cache or save the results of the resolve method should also call resolve again if a 
change occurs in the data store.

There is a potential timing mismatch with the interaction discussed above. Suppose that a data change 
notification is sent out because of a grouping information change. It takes a finite amount of time for a 
subscribing client application to process the notification and update its listeners. While this is going on, 
if a publishing application calls the Namespace Mapper to resolve a given subject, it will be returned the 
set of new mappings. If the new subjects are published on the Integration Bus before the subscriber 
updates the listeners, the published events will be lost. 

Hence there is a window during which the subscriber could lose events. The duration of the window 
could vary depending on the number of listeners to be updated by the subscriber. It is suggested that 
group and namespace administrations be done within a system maintenance window and sufficient 
waiting time be given, after the changes, before resuming the regular operations. 

There are three applications in Cisco Configuration Engine using the Namespace mapper:

Event Gateway

Intelligent Modular Gateway (IMGW)

Configuration Server

The Event Gateway acts as a proxy for agent-enabled devices and calls the NSM client API to resolve 
the subjects passed by devices connected to it. Since it subscribes to the mapped subjects, the Event 
Gateway should act on the change notification and update its listeners.

The IMGW process acts in the same way as the Event Gateway except that it acts on behalf of devices 
that do not have agents running. It also subscribes to mapped subjects and hence should handle the 
change notification and update its listeners and caches.

The Configuration calls the NSM client API to resolve subjects and publishes on them. It also listens to 
event ID change events and status events from the device. So it must also call the Data Change 
Notification Interface and update its listeners.