I'm having some architectural doubts about a project (Mac OS X app) I'm working on. It basically consists of two elements: a daemon that runs in the background gathering some data and a viewer used to represent the gathered data.

The daemon should be visible in the status bar (no dock icon) and includes a small menu accessible via the status bar. It saves data in a core data store. One of the menu items is a link which opens the viewer. When this viewer is opened, a normal GUI application should start including a dock icon and menubar. The viewer is also opened when opening the application itself (by double-clicking on the icon).

After some experimenting, I figured out the best way to achieve this functionality is by creating two applications, the main application representing the viewer and a helper utility representing the daemon. One of the reasons I did it this way is that it isn't possible to switch between LSUIElement values instantly to force the daemon/viewer state.

Now I have some questions about this architecture:

  • Both the daemon and viewer application uses the same core data store to save and retrieve data. When having a multi-threaded application I know multiple NSManagedObjectContext objects are needed to correctly synchronize data. What about having multiple applications using the same core data store simultaneously? Is this even possible without having the risk of conflicts, locks, etc.? How do I guarantee consistency?

  • The daemon should always start when the viewer starts. I achieved this by simply looping through all open processes and checking if the bundle identifier of the daemon is listed. If not, the daemon is started using NSWorkspace's launchApplication. This works fine. Now when the user quits the daemon, the viewer should also stop. What is the bes

macos core-data notifications daemon helper
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