RFC: Netx - implement -Xclearcache command line option

[Deepak Bhole]

* Omair Majid <omajid at redhat.com> [2010-09-30 16:50]:
> On 09/30/2010 04:32 PM, Deepak Bhole wrote:
> >* Omair Majid<omajid at redhat.com>  [2010-09-30 16:10]:
> >>Hi,
> >>
> >>I posted this patch way back in 2009, but it looks like it got lost/ignored.
> >>
> 
> Ok, turns out it was my fault: just noticed http://mail.openjdk.java.net/pipermail/distro-pkg-dev/2009-August/006666.html.
> Somehow it slipped off my radar.
> 

Doh. Glad it was re-visited. I doubt the issue will be encountered, but
we might as well fix it instead of waiting for a bug report.

> >>On 07/30/2009 05:18 PM, Omair Majid wrote:
> >>>The attached patch adds the option -Xclearcache to Netx.
> >>>
> >>
> >>Which (and I neglected to explain this last time) makes javaws clean
> >>out its cache by deleting the contents of ~/.netx/cache/
> >>
> >
> >Hmm, what happens if I have another netx app running and javaws is called
> >with -Xclearcache? AFAIK the code has no provisioning to detect if a
> >cache file has been deleted, and to re-download it... does it?
> >
> 
> As far as I can tell, very bad things (not eating babies kind of
> bad, but still...). Depending on the exact timing either the VM will
> crash or a java Exception might be thrown. If the JVM has opened the
> (missing) jar earlier and and wants to open it again to load
> additional classes the VM will most probably crash. Otherwise javaws
> simply wont be able to find the needed jar and will fail to start.
> 
> I suppose I could make some sort of global application lock to stop
> any other javaws instances from starting while -Xclearcache is
> running and to make sure -Xclearcache does not start if any other
> javaws applications are running.
>

It would be hard to set up a locking system that can handle odd cases
like crashed application, multiple instances of same app., etc.

Easiest way I think is to execute jps -l and see if there is more than
one instance of net.sourceforge.jnlp.runtime.Boot. If there is, refuse
to run with -Xclearcache. I am not as worried about the 'don't start
while -Xclearcache is running' case, as there is a far smaller window
where things can go wrong. Plus if they do, it will be right away (as
opposed to an already started app that has modified data, crashing).

Cheers,
Deepak

> Thanks,
> Omair