Notification

Introduction

File Notification is a form of interprocess communication. An application can ask either a file system (like the RAM disk handler RAM:, df0:, df1:...) or DOS to inform it whenever changes are made to a specific file or directory, making it easy for the application to react to such changes.

The preferences control program, IPrefs, sets up notification on most of the preferences files in ENV:Sys. If the user alters any of these files (which he/she normally does with a preferences editor), the system will notify IPrefs about the change. IPrefs will react to this notification by attempting to alter the user's environment to reflect the preference change. For example, if the user opens the ScreenMode preferences editor and alters the Workbench environment so that the Workbench screen should be a Hires NTSC screen, ScreenMode writes a file called Screenmode.prefs to the ENV:Sys directory which happens to be in RAM:. Because IPrefs has set up notification on this file, the RAM disk file system or DOS will notify IPrefs of the change, IPrefs will read in the Screenmode.prefs file and will try to reset the Workbench screen so it is in Hires NTSC mode.