General Change Notification: 2 The Mechanics of GCN

The basic GCN functionality manages lists of objects that are interested in specific changes. For each particular change that needs to be monitored, a separate list is needed. A completely separate "list of lists" containing an inventory of all GCN lists is also created. This will serve as the "search" table, while the particular GCN list will serve as the "messaging" list. When an event is detected, the GCN mechanism will search through the list of lists, seeing if a notification list is interested in a particular change, and send the appropriate messages if the objects do indeed wish notification of the event.

There are several reasons why you would want to use GCN:

Ease of use
The GCN mechanism eliminates the need to monitor and dispatch messages relating to system changes.
Commonality
The GCN mechanism provides a common platform for communication between applications in certain cases.
The system expects you to
Many messages sent by the system expect a GCN mechanism to intercept them. Although you can intercept these messages manually, it is easier to take advantage of GCN's built-in functions.

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