[OpenIndiana-discuss] shell script mutex locking or process signaling

[Gary Mills]

On Sat, Jun 01, 2013 at 02:20:09PM +0000, Edward Ned Harvey (openindiana) wrote:
> > From: Gary Mills [mailto:gary_mills at fastmail.fm]
> > 
> > If your method script starts a server process in the background and
> > then immediately exits, it is broken.
> 
> Fortunately for me, I don't have that problem.  The start & stop
> scripts do indeed stay running until the service has reached a
> running or stopped state.  The issue is with regard to concurrency -
> if a service takes a long time to start or stop, or if there's a
> problem with the start or stop, then the ability to launch "stop"
> and have it kill a "start" that's already in progress.

That's where the timeout, set in the manifest, comes into play.
Generally that's sufficient.  I suppose, though, that when you have
a service that's slow to start up or shut down, with a necessarily
long timeout, you may become impatient and want a way to do something
manually.  A method script could catch a signal.  I see a few in
/lib/svc/method that do this:

    $ grep trap *
    coherence:	trap "" SIGHUP
    identity-node:		trap 'intr=1' 2 3
    identity-node:		trap 2 3 ;;
    x11-server:trap Xserver_ready USR1
    x11-server:(trap '' USR1 ; exec /usr/bin/Xserver $CLASSES :$DISPLAY $* &)

You'd only need another command that sent the signal to the method
script.  I've never needed such a thing, but I suspect it would work.

> I swear,
> I've seen multiple instances of the script running concurrently
> before, but now I can't reproduce that.  At least, it can be run
> multiple times in parallel - manually.  If the admin issues "stop"
> while the "start" is still in progress (now that I've added this
> locking etc) then the start script dies gracefully, and the stop
> script does its thing.

-- 
-Gary Mills-		-refurb-		-Winnipeg, Manitoba, Canada-