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Detecting X11.app with launchd, was Re: The meaning(s) of $DISPLAY

Subject: Detecting X11.app with launchd, was Re: The meaning(s) of $DISPLAY
From: Ben Byer <email@hidden>
Date: Mon, 19 Nov 2007 01:06:46 -0800
Delivered-to: email@hidden
Delivered-to: email@hidden

On Nov 18, 2007, at 10:14 PM, Nathaniel Gray wrote:

On Nov 18, 2007 4:20 PM, Ben Byer <email@hidden> wrote:
On Nov 18, 2007, at 2:31 PM, Nathaniel Gray wrote:
I'm pretty happy with the new way, but I *would* like a bulletproof
way of knowing if $DISPLAY is connected to a running X server.
Why? :D
Is it really so hard to imagine a situation where you don't want to
launch an X server if it's not already running?  Even if we ignore the
X11.app icon bouncing up in the dock it's not like ~/.xinitrc is
guaranteed to be free of side-effects.
I've got some code (mostly working around the lack of accessibility info in X) that tries to connect to DISPLAY as a way of checking for a running X server, since that seemed like the best way of detecting that.
In all seriousness, what end goal are you trying to accomplish? Why do you need to know if an X server is running, unless you then want to use it (by connecting to $DISPLAY)?
Because my program is not primarily an X11 client, it's a multi-mode
program that has an X11 module.  The current approach is that when
it's triggered it tries to connect to DISPLAY, and if that doesn't
work the X11 module does nothing.  There's still lots of other
interesting work to be done, just not in X.
If you want to know the whole story, check out the website:
http://www.n8gray.org/code/forget-me-not

See, this is why I wanted more info about what you would like to accomplish. Launchd can answer this question for you, and it can do so in a way that is robust (i.e. it won't get confused if you have multiple users logged in to the same machine.)

If you want to test this out on the command line, the command "launchctl list org.x.X11" will spit out a plist data structure that describes that LaunchAgent. If it is currently running for the current user, it will list the pid of the process along with the other attributes of the launchd plist. So, you just need to use this functionality in your program; you can even use the programmatic interface to launchd to get this info. (As far as I know, this should degrade gracefully back to at least Tiger, if not Panther -- a Tiger user won't have anything that matches org.x.X11, so the launchd check will have no effect).

My ObjC is horrendous and I wasn't able to figure out how to properly test this, but I hope the attached patch will point you in the right direction.

Attachment: FMN-X11-launchd.patch
Description: Binary data

Since that's no longer appropriate I need a replacement, and I really hope you aren't going to say "ps -a -U $USER | grep X11" or some such. ;^)
How about this?
# If no display has been specified, deduce local display number from X11 process. if [ "$DISPLAY" = "" ]; then export DISPLAY = `ps auxww | grep $USER | egrep '(Xauthority|/Applications/Utilities/X11.app/Contents/MacOS/X11 .*: [0-9]+$)' | grep -v grep | sed 's/^.*$:[0-9][0-9]*$$/\1/'` fi
I just started to write an indignant reply but then I realized you're
probably kidding.  You must be kidding, right?  :-)

Oh, please. I'm not unreasonable! Martin correctly guessed the owner of that code; unfortunately, it fails on Leopard because we moved X11.app. :/ -- Ben Byer CoreOS / BSD Technology Group, XDarwin maintainer

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Follow-Ups:
- Re: Detecting X11.app with launchd, was Re: The meaning(s) of $DISPLAY
  - From: "Nathaniel Gray" <email@hidden>

References:
	>Re: Explanation of X implementations (From: John Bassett <email@hidden>)
	>Re: Explanation of X implementations (From: Ben Byer <email@hidden>)
	>Re: Explanation of X implementations (From: "Ambrose Li" <email@hidden>)
	>The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: Eric Gouriou <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: "Ambrose Li" <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: "Andrew J. Hesford" <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: "Ambrose Li" <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: Ben Byer <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: "Nathaniel Gray" <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: Ben Byer <email@hidden>)
	>Re: The meaning(s) of $DISPLAY (was Re: Explanation of X implementations) (From: "Nathaniel Gray" <email@hidden>)

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