Re: Cocoa daemon

FROM : Jens Alfke
DATE : Fri Aug 01 21:28:18 2008

On 1 Aug '08, at 5:17 AM, Ivan C Myrvold wrote:

> I try to implement the menu in the NSStatusBar systemStatusBar.


That class is in the AppKit framework. Daemons must not link against 
AppKit, or any other framework, like HLTB, that would connect to the 
window server. (I believe the big Daemons-and-Agents technote has a 
list of what frameworks are OK.)

The reason is that a daemon runs at a lower level of the system than 
the window server or a user login session. Daemons should not 
generally perform per-user functions because they don't run as a real 
user (typically they're either root, or a special-purpose pseudo-user 
like 'www'.)

If you want to run a background process on behalf of a particular 
login session, use an agent. This is much like writing a daemon except 
that you put the launchd plist in ~/Library/LaunchAgents or /Library/
LaunchAgents.

Agents should also ideally not link against AppKit or connect to the 
WindowServer; this helps limit the system resources they use. If you 
really need to have a UI, such as an NSStatusItem, you should package 
your daemon in a .app bundle, using the LSUIElement Info.plist key so 
that it won't show up in the Dock.

Again, the technote describes all of this. It's definitely required 
reading if you're writing any kind of daemon/agent/background process.

—Jens_______________________________________________

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