Apple Network Setup - Manual (Page 20)

C H A P T E R 1
About Network Setup
20 Network Setup Database Fundamentals
reading, it reads the area directly. Network Setup simply notes that the area is
open for synchronization purposes (see the section “Preference Coherency”
(page 21)). For writing, the process is somewhat different.
When an application opens an area for writing, Network Setup creates a
temporary area that is an exact duplicate of the default area. It then returns the
temporary area ID to the application. The application can now change the
temporary area without affecting running network services. When the
application is done making changes, it commits the changes to the database.
Committing changes is an atomic process that overwrites the default area with
the contents of the temporary area and causes the protocol stacks to reconfigure
themselves for the new configuration.
Alternatively, the writing application can choose to abort the modifications, in
response to which Network Setup discards the temporary area and the system
continues to use the configuration in the default area.
Figure 1-6 shows this process diagrammatically.
Figure 1-6 Reading and writing the default area
Multiple applications can open the Network Setup database for reading, but
only one application at a time can open the database for writing.When an
application commits changes to the default area, Network Setup notifies each
application that has opened the database for reading that a change has
occurred, as explained in the next section, “Preference Coherency.”
Reading
Open for reading
Close for reading
Default area
Default area
being read
Default area
Open for write
Commit
Writing
Default area
Temporary area
being written
Updated default area
abort