[concurrency-interest] Joint Talk for JavaOne?

Nathan Reynolds nathan.reynolds at oracle.com
Tue Apr 10 12:25:20 EDT 2012


Consider a ring FIFO buffer with only 1 reader and 1 writer thread.  
This can be implemented using volatiles for the read and write indexes.  
At some point, the reader thread is going to load the write index.  Java 
Path Finder will flag a problem if it can find a thread interleaving 
where the reader thread is loading the write index and the writer thread 
is storing the write index.  The code is thread safe but Java Path 
Finder doesn't like it.  The workaround is to use a AtomicInteger's or 
AtomicIntegerFieldUpdater's get() and set() for Java Path Finder testing.

jpf-racefinder is a sub-project which addresses the problem of Java 
relaxed memory model (i.e. JDK 5).  I played with this about 2 years ago 
and it needed an maintenance update to work with the current version of 
Java Path Finder.  The web pages for it have been updated so it might be 
usable now.  See the example on this page for the problem it solves.  
http://www.cise.ufl.edu/research/JavaRacefinder/Java_RaceFinder/JRF_Home.html  
It seems like that the ring buffer example above would work just fine.

Java Path Finder probably supports all of java.util.concurrent.  The 
difficulty with these classes is state explosion because of all the 
different ways threads can interact within these classes.  
jpf-concurrent is a sub-project which has custom implementations of 
these classes.  These custom implementations use special Java Path 
Finder APIs to reduce or eliminate state explosion.  This is a two-edge 
sword though.  Sometimes you need some state explosion in order for your 
code to be fully tested.  Java Path Finder can be customized for these 
needs.

Nathan Reynolds 
<http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> | 
Consulting Member of Technical Staff | 602.333.9091
Oracle PSR Engineering <http://psr.us.oracle.com/> | Server Technology

On 4/10/2012 4:44 AM, Kearney, Joe wrote:
>
> Does lack of support for volatile fields render this tool useless for 
> testing non-blocking concurrency and concurrent programs that don't 
> only use synchronized blocks?
>
> In particular does it support locking through LockSupport, AQS and 
> friends -- for example does it understand uses of Phaser or CyclicBarrier?
>
> Is there a list somewhere of these limitations? Perhaps these things 
> are spread around the sub-projects.
>
> Thanks,
>
> Joe
>
> *From:*concurrency-interest-bounces at cs.oswego.edu 
> [mailto:concurrency-interest-bounces at cs.oswego.edu] *On Behalf Of 
> *Nathan Reynolds
> *Sent:* 09 April 2012 17:44
> *To:* Mohan Radhakrishnan
> *Cc:* Concurrency-interest at cs.oswego.edu
> *Subject:* Re: [concurrency-interest] Joint Talk for JavaOne?
>
> Java Path Finder is great for finding deadlocks and data races.  
> However, it has its limitations.
>
>  1. The search space is exponential in the number of threads (i.e.
>     O(2^t )).  This program has way too many threads.  One would have
>     to reduce the threads to a bare minimum.
>  2. The Java Memory Model (i.e. volatile fields) isn't supported. 
>     That isn't a problem in this case but something to be aware of.
>
> Otherwise, I rely on Java Path Finder to prove that my code is going 
> to work in concurrent situations.  It has found a ton of concurrency 
> bugs in my code.
>
> Nathan Reynolds 
> <http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> | 
> Consulting Member of Technical Staff | 602.333.9091
> Oracle PSR Engineering <http://psr.us.oracle.com/> | Server Technology
>
>
> On 4/8/2012 8:23 PM, Mohan Radhakrishnan wrote:
>
> I could look at the first deadlock by dumping locks and threads. I was 
> planning to find the next one using Java Path Finder but I think it is 
> not recommended for such a big codebase. I am not sure. Its heuristics 
> might take too much memory.
>
> Mohan
>
> On Mon, Apr 9, 2012 at 3:59 AM, <mabrouk2005 at gmail.com 
> <mailto:mabrouk2005 at gmail.com>> wrote:
>
> Nice exercise Dr Heinz,
>
> As others mentioned there were 2 kind of deadlocks the first one was
> very is easy to find via jconsole so likeI thought that was it and
> went and fixed that but then when ran it again it hang it so I knew
> thee was more. the interesting thing the jconsole did not detect the
> AWT deadlock it showed no deadlock even though the app hang. I had to
> force stack dump and get clues to where is the deadlock. Does anyone
> have experienced something like this with jconsole not detecting AWT
> deadlocks?
>
> Thanks again for the nice exercise and the great java news letter I am
> a big fan.
>
> Cheers,
> Mabrouk
>
>
> On Sat, Apr 7, 2012 at 7:42 AM, Remi Forax <forax at univ-mlv.fr 
> <mailto:forax at univ-mlv.fr>> wrote:
> > No, it's more an AWRY or Java2D bug.
> >
> > Rémi
> >
> > Sent from my Phone
> >
> >
> > ----- Reply message -----
> > From: "Ben Evans" <benjamin.john.evans at gmail.com 
> <mailto:benjamin.john.evans at gmail.com>>
> > To: "Dr Heinz M. Kabutz" <heinz at javaspecialists.eu 
> <mailto:heinz at javaspecialists.eu>>
> > Cc: "Rémi Forax" <forax at univ-mlv.fr <mailto:forax at univ-mlv.fr>>, 
> <concurrency-interest at cs.oswego.edu 
> <mailto:concurrency-interest at cs.oswego.edu>>
> > Subject: [concurrency-interest] Joint Talk for JavaOne?
> > Date: Sat, Apr 7, 2012 10:43
> >
> >
> > Heinz, was this with the new jdk8 + lambda build?
> >
> > If so, we should report this crash back to lambda-dev.
> >
> > Thanks,
> >
> > Ben
> >
> > On Sat, Apr 7, 2012 at 11:17 AM, Dr Heinz M. Kabutz
> > <heinz at javaspecialists.eu <mailto:heinz at javaspecialists.eu>> wrote:
> >> I see JDK8 crashes even with the vanilla Java2Demo from JDK 1.6.  I see
> >> that
> >> the Java2Demo has been removed from the demos folder of JDK 1.7 and 
> 1.8.
> >>  It
> >> thus is a Java 8 issue, rather than the changes I made to the code.
> >>  Thanks
> >> for the warning Rémi.
> >>
> >>
> >> Regards
> >>
> >> Heinz
> >> --
> >> Dr Heinz M. Kabutz (PhD CompSci)
> >> Author of "The Java(tm) Specialists' Newsletter"
> >> Sun Java Champion
> >> IEEE Certified Software Development Professional
> >> http://www.javaspecialists.eu
> >> Tel: +30 69 75 595 262
> >> Skype: kabutz
> >>
> >>
> >> On 4/6/12 1:51 AM, Rémi Forax wrote:
> >>>
> >>> jdk8 crashes if I click on images of the tapped pane.
> >>>
> >>> Rémi
> >>>
> >>> On 04/05/2012 10:35 PM, Dr Heinz M. Kabutz wrote:
> >>>>
> >>>> Yes, you are correct.
> >>>>
> >>>> However, the mistake most programmers make is to #1 scratch around in
> >>>> the
> >>>> source code to try and discover the problem and #2 then fix it 
> without
> >>>> really understanding what they are doing.  I think the lesson is 
> bigger
> >>>> if
> >>>> we give them the source code.  In addition, it is probably more
> >>>> difficult to
> >>>> solve if you have the sources to muse over.
> >>>> Regards
> >>>>
> >>>> Heinz
> >>>> --
> >>>> Dr Heinz M. Kabutz (PhD CompSci)
> >>>> Author of "The Java(tm) Specialists' Newsletter"
> >>>> Sun Java Champion
> >>>> IEEE Certified Software Development Professional
> >>>> http://www.javaspecialists.eu
> >>>> Tel: +30 69 75 595 262
> >>>> Skype: kabutz
> >>>>
> >>>>
> >>>> On 4/5/12 11:30 PM, Nathan Reynolds wrote:
> >>>>>
> >>>>> I guess it is a good idea to not initially include the source 
> code in
> >>>>> the workshop because many times I initially don't have the 
> source code
> >>>>> when
> >>>>> trying to figure out performance or scalability problems.
> >>>>>
> >>>>> Nathan Reynolds
> >>>>> <http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> |
> >>>>> Consulting
> >>>>> Member of Technical Staff | 602.333.9091
> >>>>> Oracle PSR Engineering <http://psr.us.oracle.com/> | Server 
> Technology
> >>>>>
> >>>>> On 4/5/2012 1:22 PM, Dr Heinz M. Kabutz wrote:
> >>>>>>
> >>>>>> Sorry Nathan, here is the zip file including the source code an 
> an Ant
> >>>>>> script to build the code.  Sorry for accidentally excluding 
> that from
> >>>>>> the
> >>>>>> file I sent earlier.  The problem was between the chair and the
> >>>>>> keyboard.
> >>>>>>  However, one should be able to pinpoint the deadlock without 
> seeing a
> >>>>>> line
> >>>>>> of code.  At the workshop I presented in Spain last week, most 
> of the
> >>>>>> programmers immediately started delving into the code before 
> they knew
> >>>>>> where
> >>>>>> to look.
> >>>>>> Regards
> >>>>>>
> >>>>>> Heinz
> >>>>>> --
> >>>>>> Dr Heinz M. Kabutz (PhD CompSci)
> >>>>>> Author of "The Java(tm) Specialists' Newsletter"
> >>>>>> Sun Java Champion
> >>>>>> IEEE Certified Software Development Professional
> >>>>>> http://www.javaspecialists.eu
> >>>>>> Tel: +30 69 75 595 262
> >>>>>> Skype: kabutz
> >>>>>>
> >>>>>> On 4/5/12 10:29 PM, Nathan Reynolds wrote:
> >>>>>>>
> >>>>>>> I took the bait and tried out the demo on HotSpot 7 Update 3.  It
> >>>>>>> didn't deadlock for a minute or two.  Then the application 
> froze.  I
> >>>>>>> then
> >>>>>>> used jstack to dump the call stacks.  At the end of the report, it
> >>>>>>> said
> >>>>>>> "Found one Java-level deadlock".  It then dumped out the locks and
> >>>>>>> threads
> >>>>>>> involved in the deadlock.  I never looked at the source code... in
> >>>>>>> fact it
> >>>>>>> wasn't in the zip file.  This took about 5-7 minutes from starting
> >>>>>>> the
> >>>>>>> application to finding the deadlock in the call stacks.
> >>>>>>>
> >>>>>>> A 100 good Java developers?  Really?  I guess I can 
> understand.  Most
> >>>>>>> engineers don't understand locks.  Most of the time I get answers
> >>>>>>> like one
> >>>>>>> should put a lock around shared variables.  This is accurate 
> but they
> >>>>>>> can't
> >>>>>>> really go any deeper.
> >>>>>>>
> >>>>>>> It sounds like the material of your presentation should be 
> very good.
> >>>>>>>  It covers things that the deadlock detection tool probably can't
> >>>>>>> figure
> >>>>>>> out.
> >>>>>>>
> >>>>>>> So, it seems like you have everything figured out.  Why do you 
> need
> >>>>>>> someone else?
> >>>>>>>
> >>>>>>> Nathan Reynolds
> >>>>>>> <http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> |
> >>>>>>> Consulting
> >>>>>>> Member of Technical Staff | 602.333.9091
> >>>>>>> Oracle PSR Engineering <http://psr.us.oracle.com/> | Server
> >>>>>>> Technology
> >>>>>>>
> >>>>>>> On 4/5/2012 12:03 PM, Dr Heinz M. Kabutz wrote:
> >>>>>>>>
> >>>>>>>> Hi Nathan,
> >>>>>>>>
> >>>>>>>> a stack trace will only show you a certain class of obvious
> >>>>>>>> deadlocks
> >>>>>>>> that are easy to find and solve.  I remember solving deadlocks
> >>>>>>>> /before/ we
> >>>>>>>> had the brilliant deadlock detection tool in the 
> ThreadMXBean.  Yes,
> >>>>>>>> the
> >>>>>>>> deadlock detection tool shows you /some/ deadlocks, but 
> definitely
> >>>>>>>> not all
> >>>>>>>> of them.  I can think of a bunch that it would not find:
> >>>>>>>>
> >>>>>>>> 1. Semaphores running out of permits
> >>>>>>>> 2. ReadWriteLocks trying to upgrade from write lock to read lock
> >>>>>>>> 3. Resource deadlocks
> >>>>>>>>
> >>>>>>>> And some others that I will not describe in detail, such as some
> >>>>>>>> nasty livelocks that we can cause which will hang up the JVM :-)
> >>>>>>>>
> >>>>>>>> I agree with Kirk - it should probably be a 3 hour workshop. 
>  I've
> >>>>>>>> done this three times now - twice in Spain and once via webinar.
> >>>>>>>>  The
> >>>>>>>> workshop would involve some lessons on deadlocks, what causes 
> them
> >>>>>>>> and how
> >>>>>>>> we can prevent them.  Also an explanation as to why we see 
> them so
> >>>>>>>> seldom in
> >>>>>>>> real production.  I've got material prepared for this 
> workshop.  And
> >>>>>>>> then a
> >>>>>>>> practical part to the workshop where they can try to find a 
> deadlock
> >>>>>>>> in a
> >>>>>>>> body of code.
> >>>>>>>>
> >>>>>>>> Attached is an example of the workshop.  You can try find the
> >>>>>>>> deadlock if you like.  I've shown it to almost 100 good Java
> >>>>>>>> developers and
> >>>>>>>> so far, not one has found it by themselves.  I would expect that
> >>>>>>>> they should
> >>>>>>>> find it in 5 minutes.  In our workshop they would obviously be
> >>>>>>>> helped a bit
> >>>>>>>> with hints, so that they can walk away with a good 
> experience.  Use
> >>>>>>>> anything
> >>>>>>>> you like.  Oscilloscope, jstack, jconsole, whatever you like. 
>  Only
> >>>>>>>> rule for
> >>>>>>>> you guys on the "concurrency-interest" list is: you can only 
> look at
> >>>>>>>> the
> >>>>>>>> code once you've found the problem, otherwise it would be too 
> easy
> >>>>>>>> for you
> >>>>>>>> :-)  Once you have found it, you can also fix the code and 
> make sure
> >>>>>>>> that
> >>>>>>>> the code then works correctly.
> >>>>>>>> Regards
> >>>>>>>>
> >>>>>>>> Heinz
> >>>>>>>> --
> >>>>>>>> Dr Heinz M. Kabutz (PhD CompSci)
> >>>>>>>> Author of "The Java(tm) Specialists' Newsletter"
> >>>>>>>> Sun Java Champion
> >>>>>>>> IEEE Certified Software Development Professional
> >>>>>>>> http://www.javaspecialists.eu
> >>>>>>>> Tel: +30 69 75 595 262
> >>>>>>>> Skype: kabutz
> >>>>>>>>
> >>>>>>>> On 4/5/12 8:01 PM, Nathan Reynolds wrote:
> >>>>>>>>>
> >>>>>>>>> I am curious as to the intended content of your presentation.
> >>>>>>>>>  Here's some ideas.  I wondering what you are planing on doing.
> >>>>>>>>>
> >>>>>>>>>  1. Printing the call stacks with lock information using a tool
> >>>>>>>>>    such as jstack
> >>>>>>>>>  2. Press the "Detect Deadlock" button in JConsole
> >>>>>>>>>  3. Dealing with Lock and Condition objects instead of
> >>>>>>>>>    synchronized blocks
> >>>>>>>>>  4. Detecting live lock
> >>>>>>>>>  5. Distributed deadlocks
> >>>>>>>>>
> >>>>>>>>> Nathan Reynolds
> >>>>>>>>> <http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> |
> >>>>>>>>> Consulting
> >>>>>>>>> Member of Technical Staff | 602.333.9091
> >>>>>>>>> Oracle PSR Engineering <http://psr.us.oracle.com/> | Server
> >>>>>>>>> Technology
> >>>>>>>>>
> >>>>>>>>> On 4/5/2012 7:57 AM, Dr Heinz M. Kabutz wrote:
> >>>>>>>>>>
> >>>>>>>>>> Good afternoon,
> >>>>>>>>>>
> >>>>>>>>>> I am thinking of submitting a talk on finding and diagnosing
> >>>>>>>>>> deadlocks for JavaOne.  It might be a workshop, instead of a
> >>>>>>>>>> simple
> >>>>>>>>>> conference talk.  Or we might be able to turn the talk into a
> >>>>>>>>>> workshop where
> >>>>>>>>>> they need to find a deadlock in a body of code.  Could be
> >>>>>>>>>> something
> >>>>>>>>>> different, which might go incredibly well or crash in a 
> blaze of
> >>>>>>>>>> flames.
> >>>>>>>>>>  Would any of you be interested in co-presenting this with 
> me at
> >>>>>>>>>> JavaOne?
> >>>>>>>>>>
> >>>>>>>>>> Regards
> >>>>>>>>>>
> >>>>>>>>>> Heinz
> >>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> Concurrency-interest mailing list
> >>>> Concurrency-interest at cs.oswego.edu 
> <mailto:Concurrency-interest at cs.oswego.edu>
> >>>> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
> >>>
> >>>
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