RFC: Netx - implement -Xclearcache command line option

Tue Oct 5 16:23:02 PDT 2010

On 15:44 Tue 05 Oct     , Deepak Bhole wrote:
> * Omair Majid <omajid at redhat.com> [2010-10-05 15:42]:
> > On 10/05/2010 03:32 PM, Deepak Bhole wrote:
> > >* Omair Majid<omajid at redhat.com>  [2010-10-05 14:45]:
> > >>On 10/04/2010 03:17 PM, Omair Majid wrote:
> > >>>On 09/30/2010 05:27 PM, Deepak Bhole wrote:
> > >>>>* 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.
> > >>>>
> > >>>
> > >>>Yeah, you are right. I thought about it for a bit, and I dont see a
> > >>>simple way to make it work using locks.
> > >>>
> > >>>>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).
> > >>>>
> > >>>
> > >>>That's a great idea! Unfortunately I dont think we can rely on jps. jps
> > >>>is part of the JDK as opposed to the JRE - we can not be sure that users
> > >>>have it on their machine. I tried looking into the sources for jps to
> > >>>find out how it works. The JVM creates /tmp/hsperfdata_$USER/$PID files
> > >>>which contain the information that jps can parse and display. The files
> > >>>are in a binary format so parsing it is not trivial (and the file format
> > >>>is not guaranteed to be final). I am going to dig around a bit to see if
> > >>>there is any other simple solution to this
> > >>>
> > >>
> > >>I am attaching the updated patch. This one uses an alternate
> > >>implementation based on file locks (exclusive and shared). A normal
> > >>javaws process acquires a shared lock on /tmp/$USER/netx/instance
> > >>during startup (when an instance of Launcher is created), and
> > >>releases the lock when the JVM shutsdown. Multiple javaws processes
> > >>can share the lock and run simultaneously.
> > >>
> > >>The javaws process that is trying to clear the cache checks for the
> > >>file and tries to acquire an exclusive lock. If it succeeds, it goes
> > >>ahead and clears the cache; otherwise it prints out an error to the
> > >>user and exits.
> > >>
> > >>Thoughts?
> > >>
> > >
> > >Just one minor thing... for the plugin, we use
> > >/tmp/icedteaplugin-$user for data storage. For the above, can you please
> > >change it to /tmp/netx-$user for consistency?
> > >
> > 
> > Sure. But netx is already using /tmp/$USER/netx/locks/ for creating
> > single instance locks (most of the paths netx uses are be defined in
> > JNLPRuntime - though there are a few entries missing [like
> > ~/.netx/pcache and ~/.netx/cache]). Do you want me to fix that as
> > well?
> > 
> 
> Ah okay nevermind then. I wasn't aware that the dir was already being
> used for something else. Keep it as it is then I'd say. At some point in
> the future we should consolidate both plugin and netx to use a single
> dir. But that is for another time.
> 

In which case, the plugin should be altered to use netx's system, as NetX
can be built without the plugin but the opposite is not true.

I also think /tmp/$USER/netx is much cleaner.

> Cheers,
> Deepak
> 
> > >Rest looks good! Assuming you have tested this, please go ahead and
> > >apply to HEAD and all active branches.
> > >
> > 
> > Thanks for the review!

Please see my comments in the previous e-mail before pushing.

> > 
> > Cheers,
> > Omair

-- 
Andrew :)

Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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