[concurrency-interest] Potential threads getting stuck on WAITING(parking) in ReentrantLock

David Holmes davidcholmes at aapt.net.au
Mon Jun 2 22:35:42 EDT 2014

Hi Rafael,

Can you try Oracle JDK 7? This might be:


which was fixed in 8.

  -----Original Message-----
  From: concurrency-interest-bounces at cs.oswego.edu [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of Rafael Brandão
  Sent: Tuesday, 3 June 2014 11:44 AM
  To: Dr Heinz M. Kabutz
  Cc: concurrency-interest at cs.oswego.edu; dholmes at ieee.org
  Subject: Re: [concurrency-interest] Potential threads getting stuck on WAITING(parking) in ReentrantLock


  David, I have now tested it with java version "1.8.0_05", Java(TM) SE Runtime Environment (build 1.8.0_05-b13) and Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode). The problem with my nearly unmodified ReentrantLock getting stuck is no longer happening when I run the experiment. Would you also like me to test with any particular version? Thanks for the tip! Now about StackOverflowError, I don't see how it could be possible (I've posted a link to the code if you want to check), since there's no infinite recursion for example and each test run is relatively low in used resources.

  Heinz, I have posted the code on https://github.com/rafaelbrandao/msc - the latest commit message (it only has 3 commits) contains information on how to reproduce this issue. It seems to be fixed when I use Oracle JDK 8 however.

  What could be causing the stuck threads? Is it possible this is a problem with the ReentrantLock algorithm/implementation?

  Best regards,

  On Sun, Jun 1, 2014 at 2:07 AM, Dr Heinz M. Kabutz <heinz at javaspecialists.eu> wrote:

    Please send us a link to your code, both your ReentrantLock and the test code?

    On 01/06/2014, David Holmes <davidcholmes at aapt.net.au> wrote:
    > Hi Rafael,
    > Does this reproduce with Oracle JDK or only the IcedTea distributions?
    > The most likely issue is the StackOverflowError. Have excluded that
    > possibility?
    > David
    >   -----Original Message-----
    >   From: concurrency-interest-bounces at cs.oswego.edu
    > [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of Rafael
    > Brandão
    >   Sent: Sunday, 1 June 2014 8:50 AM
    >   To: concurrency-interest at cs.oswego.edu
    >   Subject: [concurrency-interest] Potential threads getting stuck on
    > WAITING(parking) in ReentrantLock
    >   Hello,
    >   I'm working on a few changes for ReentrantLock to make A/B tests between
    > the original implementation and my modifications, so my first step was to
    > copy the sources of ReentrantLock, AbstractQueuedSynchronizer (shortly AQS)
    > and AbstractOwnableSynchronizer and put them in a different package. After
    > resolving basic compilation issues, I've found the issue with Unsafe usage
    > (insecurity exception) and I've solved it based on the article found in [1].
    > So basically my ReentrantLock has nothing different from the original except
    > for how I get the Unsafe in AQS.
    >   After that, I've exhaustively conducted the following experiment: 200
    > threads try to increment 1000 times each some integer counter protected by
    > explicit locks. There are 10 counters, so each counter has 20 threads
    > concurrently trying to increment it. The main thread spawns all those
    > threads and then wait for them with join method. Once I've ran this
    > experiment many times (about 30000), it consistently get stuck in a join for
    > some thread when I use my almost unmodified ReentrantLock before 2000th
    > attempt.
    >   I've got the thread stacks in [2] and what I understood from it is that
    > the remaining threads are all stuck waiting for the lock to be released.
    > However I've managed to print the owner of that lock and I see it's unlocked
    > and has no owner:
    >     stuck thread state: WAITING
    >     thread waiting lock: safe.ReentrantLock at 68a6a21a[Unlocked]
    >     lock owner: null
    >   I've been trying to reproduce it with the original ReentrantLock but I
    > didn't get stuck so far. So I'm here to ask you if there's a known issue on
    > ReentrantLock that could cause this situation (and also be extremely
    > unlikely to happen) or if there's something obvious that I should know about
    > the Unsafe usage given it's the only thing changed so far.
    >   I suspect I have some disadvantage given that my nearly unmodified class
    > is not already compiled in the JVM (I could try to build the JDK later), but
    > this could only be a sign that the issue already exists in the code but can
    > only become more likely to happen in a slower implementation. I've also
    > searched for related bugs and the closest thing I've found was [3].

    >   I'm using a Intel(R) Core(tm) i7-3632QM notebook running Ubuntu 12.04. Java

    > version is "1.7.0_55" and I'm using OpenJDK Runtime Environment (IcedTea
    > 2.4.7) (7u55-2.4.7-1ubuntu1~ and OpenJDK 64-Bit Server VM (build
    > 24.51-b03, mixed mode). I've experienced this issue after copying sources of
    > jdk7u, jdk8u and jdk9.
    >   Best regards,
    >   Rafael
    >   [1] http://howtodoinjava.com/2013/10/19/usage-of-class-sun-misc-unsafe/
    >   [2] https://gist.github.com/rafaelbrandao/4ec5f2cd272c4b8b183a
    >   [3] https://bugs.openjdk.java.net/browse/JDK-8028686
    >   --
    >   Rafael Brandão @ CIn - Center of Informatics

    Dr Heinz M. Kabutz (PhD CompSci)
    Author of "The Java(tm) Specialists' Newsletter"
    Sun/Oracle Java Champion 2005-2013
    JavaOne Rockstar Speaker 2012
    Tel: +30 69 75 595 262
    Skype: kabutz

  Rafael Brandão @ CIn - Center of Informatics 
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