> Normally, this should not happen if the script is properly installed as
> a rc start and stop script. When the machine is shut down, webkit should
> be stopped properly and the PID_FILE deleted.
>
You are right. I have verified ThreadedAppServer does respond to
SIGTERM during host shutdown and deletes the PID file. I had to
hard-reset my OS X box a few months ago and I think I've had a PID file
with a low process ID causing problems since then. (I didn't have time
to look into the problem immediately and just invoked AppServer manually
the few times I've needed it. This is a testing system.)
> So instead of simply testing whether a process exists, we could check
> the process command as well and require it to be something like
> "python Launch.py ThreadedAppserver"
>
> But this would still fail if you run several Webware instances. We need
> to check whether the process really belongs to the PID_FILE.
>
For the reason you give, I too think this is a bad idea.
> > Perhaps webkit should use fcntl.flock?
>
> Just so I understand properly: You suggest that the PID_FILE is created
> with a lock (you can also use os.open for that), and then the start
> script checks with "fuser" whether the process in the PID_FILE is the
> same as the one that has PID_FILE locked? That should work, but it
> would waste a file descriptor, and I'm not sure whether fuser is
> available everywhere.
>
I'm not familiar with fuser, but I think you are right that os.open is
more portable than fnctl.flock. Therefore I'm suggesting that
ThreadedAppServer could lock PID_FILE. The OS will automatically
release this lock when ThreadedAppServer exits. Then the webkit script
can attempt to lock PID_FILE before starting ThreadedAppServer. If it
fails then ThreadedAppServer must still be running.
I had not considered the loss of a file descriptor, although I don't
think this is too high a price.
> Maybe the following would be better. It does not need any locking.
>
> PID=`cat $PID_FILE`
> if [ tr \\000 \\040 < /proc/$PID/cmdline | grep -q " -i $PID_FILE " ]
> then conclude that Webware is still running...
>
Unfortunately OS X does not include /proc and therefore FreeBSD probably
doesn't either. My impression is that /proc is a relatively recent
innovation.
Oliver
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