[infinispan-dev] lock acquisition - "finally release" it

[Philippe Van Dyck]

On Mon, May 17, 2010 at 11:47 AM, Manik Surtani <manik at jboss.org> wrote:

>
> On 16 May 2010, at 18:35, Philippe Van Dyck wrote:
>
> > Hi all,
> >
> > in a servlet environment, you sometimes have to claim back a thread for
> your thread pool.
> > Jetty has a nice "denial of service attack" filter and a setting
> (maxIdleTime) interrupting servlet threads if nothing comes out (nothing is
> written in the pipe).
> >
> > Well it does not play well with infinispan. Everybody knows that when you
> open a stream, the best way to reclaim scarce resources is to close it in a
> 'finally' statement. What about applying it to infinispan locking mechanism
> ? ;-)
> >
> > Calls to acquireLock should be guarded by a finally {releaseLock} (at
> least to catch an interruptedException)
>
> This is a good point, in the event of a failure (for whatever reason) the
> lock may still be acquired and should be cleaned up.  Care to create a JIRA
> for this?
>

Done - ISPN-444 </browse/ISPN-444>


>
> > It looks very easy to implement, but since releaseLock does not seems to
> be called every time in the code, I need help !
> >
> > The only places where aquireLock is called are
> CacheLoaderInterceptor.loadIfNeeded and
> EntryFactoryImpl.wrapEntryForWriting.
> >
> > And BTW, the locks never expire ... so if you interrupt a thread and the
> lock is not released, you better say bye bye to the cache entry!
>
> Hmm.  While I agree in principle (we could implement a max lock period in
> the config file), how do you see this working in practice?  Maintain
> timestamps of all acquired locks, and have a maintenance thread regularly
> check these for locks that have expired (and then interrupt the locking
> thread)?
>

I think there is a need for this kind of cleanup whatever the reason a lock
is in 'stale' mode.

But IMHO there is a lot of cleanup to do when you interrupt a thread !

What about some timeout callback attached to each lock ?

Now, to test this, you should replay test suites with a 'one millisecond'
timeout and ensure that everything is correctly cleaned up.
Great way to improve the quality of the code, but hell of a job!

Cheers,

phil



>
> Cheers
> Manik
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
>
>
>
>
>
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