[concurrency-interest] Joint Talk for JavaOne?

Nathan Reynolds nathan.reynolds at oracle.com
Mon Apr 9 12:43:45 EDT 2012


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
>     >>>>
>     >>>>
>     >>>>
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