[launchd-dev] can i do this with launchd? (on-demand auto-restart daemons)

[Ian]

thank you for the thorough response. i'll investigate more about the  
python thing. since it is an existing codebase, i'll have to look into  
the last two options.

thanks,

ian

On Aug 29, 2008, at 3:28 AM, Quinn wrote:

> At 1:12 -0700 28/8/08, Ian wrote:
>> can i do this with launchd?
>
> Yes.  This is exactly the sort of thing that launchd excels at.
>
>> 1. it should start when the cocoa GUI is started (either manually or
>> via a startup item)
>
> The best way to handle this is to have the daemon launch when a
> client connects to its TCP socket.  You do this by setting up the
> "Sockets" dictionary in your launchd property list file.  launchd
> will open and listen to the socket on your behalf.  When a connection
> comes in, launchd will run your daemon and pass the listening socket
> to it.  When your daemon quits, launchd will resume listening on the
> socket.
>
> The SampleD sample code shows this basic process.
>
> <http://developer.apple.com/samplecode/SampleD/index.html>
>
>> 2. if the daemon dies for whatever reason, launchd should restart it
>
> Typically you only want launchd to restart the daemon if someone has
> connected to the TCP socket.  That's the default behaviour.  However,
> you can arrange for other behaviour by way of the "KeepAlive"
> property.  See <x-man-page://5/launchd.plist> for details.
>
>> 3. if the GUI is closed, the daemon should be shut off without
>> having it restart.
>
> When the GUI quits the TCP connection to the daemon will close.  When
> the daemon has no open connections, it should quit (after some
> debounce period).
>
> The only real wrinkle in this is Python.  When writing a launchd
> daemon you have to "check in" with launchd to get access to your
> listening socket.  That requires use of the <launch.h> API.  AFAIK
> there's no direct Python binding to that.  It's a simple C API, so if
> you're familiar with glue Python to C it shouldn't present a serious
> obstacle.  Otherwise, you might investigate wrapping your Python code
> within PyObjC so you can do the launchd check in from C and then do
> all the real work from Python.
>
> S+E
> -- 
> Quinn "The Eskimo!"                    <http://www.apple.com/developer/ 
> >
> Apple Developer Relations, Developer Technical Support, Core OS/ 
> Hardware
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