[concurrency-interest] LinkedBlockingDeque deadlock?

Ariel Weisberg ariel at weisberg.ws
Wed Jul 15 15:24:12 EDT 2009


Hi,

I have found that there are two different failure modes without
involving -XX:+UseMembar. There is the LBD deadlock and then
there is the dead socket in between two nodes. Either failure can
occur with the same code and settings. It appears that the dead
socket problem is more common. The LBD failure is also not
correlated with any specific LBD (originally saw it with only the
LBD for an Initiator's mailbox).

With -XX:+UseMembar the system is noticeably more reliable and
tends to run much longer without failing (although it can still
fail immediately). When it does fail it has been due to a dead
connection. I have not reproduced a deadlock on an LBD with
-XX:+UseMembar.

I also found that the dead socket issue was reproducible twice on
Dell Poweredge 2970s (two socket AMD). It takes an hour or so to
reproduce the dead socket problem on the 2970. I have not
recreated the LBD issue on them although given how difficult the
socket issue is to reproduce it may be that I have not run them
long enough. On the AMD machines I did not use -XX:+UseMembar.

Ariel

On Mon, 13 Jul 2009 18:59 -0400, "Ariel Weisberg"
<ariel at weisberg.ws> wrote:

Hi all.

Sorry Martin I missed reading your last email. I am not confident
that I will get a small reproducible test case in a reasonable
time frame. Reproducing it with the application is easy and I
will see what I can do about getting the source available.

One interesting thing I can tell you is that if I remove the
LinkedBlockingDeque from the mailbox of the Initiator the system
still deadlocks. The cluster has a TCP mesh topology so any node
can deliver messages to any other node. One of the connections
goes dead and neither side detects that there is a problem. I add
some assertions to the network selection thread to check that all
the connections in the cluster are still healthy and assert that
they have the correct interests set.

Here are the things it checks for  to make sure each connection
is working:
>                             for (ForeignHost.Port port :
foreignHostPorts) {
>
assert(port.m_selectionKey.isValid());
>
assert(port.m_selectionKey.selector() == m_selector);
>                             assert(port.m_channel.isOpen());
>
assert(((SocketChannel)port.m_channel).isConnected());
>
assert(((SocketChannel)port.m_channel).socket().isInputShutdown()
== false);
>
assert(((SocketChannel)port.m_channel).socket().isOutputShutdown(
) == false);
>
assert(((SocketChannel)port.m_channel).isOpen());
>
assert(((SocketChannel)port.m_channel).isRegistered());
>
assert(((SocketChannel)port.m_channel).keyFor(m_selector) !=
null);
>
assert(((SocketChannel)port.m_channel).keyFor(m_selector) ==
port.m_selectionKey);
>                             if
(m_selector.selectedKeys().contains(port.m_selectionKey)) {
>
assert((port.m_selectionKey.interestOps() & SelectionKey.OP_READ)
!= 0);
>
assert((port.m_selectionKey.interestOps() &
SelectionKey.OP_WRITE) != 0);
>                             } else {
>                                 if (port.isRunning()) {
>
assert(port.m_selectionKey.interestOps() == 0);
>                                 } else {
>
port.m_selectionKey.interestOps(SelectionKey.OP_READ |
SelectionKey.OP_WRITE);
>                                     assert((port.interestOps()
& SelectionKey.OP_READ) != 0);
>                                     assert((port.interestOps()
& SelectionKey.OP_WRITE) != 0);
>                                 }
>                             }
>                             assert(m_selector.isOpen());
>
assert(m_selector.keys().contains(port.m_selectionKey));
OP_READ | OP_WRITE is set as the interest ops every time through,
and there is no other code that changes the interest ops during
execution. The application will run for a while and then one of
the connections will stop being selected on both sides. If I step
in with the debugger on either side everything looks correct. The
keys have the correct interest ops and the selectors have the
keys in their key set.

What I suspect is happening is that a bug on one node stops the
socket from being selected (for both read and write), and
eventually the socket fills up and can't be written to by the
other side.

If I can get my VPN access together tomorrow I will run with
-XX:+UseMembar and also try running on some 8-core AMD machines.
Otherwise I will have to get to it Wednesday.

Thanks,

Ariel Weisberg


On Tue, 14 Jul 2009 05:00 +1000, "David Holmes"
<davidcholmes at aapt.net.au> wrote:

Martin,



I don't think this is due to LBQ/D. This is looking similar to a
couple of other ReentrantLock/AQS "lost wakeup" hangs that I've
got on the radar. We have a reprodeucible test case for one issue
but it only fails on one kind of system - x4450. I'm on vacation
most of this week but will try and get back to this next week.



Ariel: one thing to try please see if -XX:+UseMembar fixes the
problem.



Thanks,

David Holmes

-----Original Message-----
From: Martin Buchholz [mailto:martinrb at google.com]
Sent: Tuesday, 14 July 2009 8:38 AM
To: Ariel Weisberg
Cc: davidcholmes at aapt.net.au; core-libs-dev;
concurrency-interest at cs.oswego.edu
Subject: Re: [concurrency-interest] LinkedBlockingDeque deadlock?

  I did some stack trace eyeballing and did a mini-audit of the
  LinkedBlockingDeque code, with a view to finding possible
  bugs,
  and came up empty.  Maybe it's a deep bug in hotspot?
  Ariel, it would be good if you could get a reproducible test
  case soonish,
  while someone on the planet has the motivation and familiarity
  to fix it.
  In another month I may disavow all knowledge of
  j.u.c.*Blocking*
  Martin

On Wed, Jul 8, 2009 at 15:57, Ariel Weisberg
<[1]ariel at weisberg.ws> wrote:

  Hi,

> The poll()ing thread is blocked waiting for the internal lock,
but
> there's
> no indication of any thread owning that lock. You're using an
OpenJDK 6
> build ... can you try JDK7 ?


  I got a chance to do that today. I downloaded JDK 7 from
  [2]http://www.java.net/download/jdk7/binaries/jdk-7-ea-bin-b63
  -linux-x64-02_jul_2009.bin
  and was able to reproduce the problem. I have attached the
  stack trace
  from running the 1.7 version. It is the same situation as
  before except
  there are 9 execution sites running on each host. There are no
  threads
  that are missing or that have been restarted. Foo Network
  thread
  (selector thread) and Network Thread - 0 are waiting on
  0x00002aaab43d3b28. I also ran with JDK 7 and 6 and
  LinkedBlockingQueue
  and was not able to recreate the problem using that structure.

> I don't recall anything similar to this, but I don't know what
version
> that
> OpenJDK6 build relates to.


  The cluster is running on CentOS 5.3.
  >[aweisberg at 3f ~]$ rpm -qi
  java-1.6.0-openjdk-1.6.0.0-0.30.b09.el5
  >Name        : java-1.6.0-openjdk           Relocations: (not
  relocatable)
  >Version     : 1.6.0.0                           Vendor:
  CentOS
  >Release     : 0.30.b09.el5                  Build Date: Tue
  07 Apr 2009 07:24:52 PM EDT
  >Install Date: Thu 11 Jun 2009 03:27:46 PM EDT      Build
  Host: [3]builder10.centos.org
  >Group       : Development/Languages         Source RPM:
  java-1.6.0-openjdk-1.6.0.0-0.30.b09.el5.src.rpm
  >Size        : 76336266                         License: GPLv2
  with exceptions
  >Signature   : DSA/SHA1, Wed 08 Apr 2009 07:55:13 AM EDT, Key
  ID a8a447dce8562897
  >URL         : [4]http://icedtea.classpath.org/
  >Summary     : OpenJDK Runtime Environment
  >Description :
  >The OpenJDK runtime environment.

> Make sure you haven't missed any exceptions occurring in other
threads.

  There are no threads missing in the application (terminated
  threads are
  not replaced) and there is a try catch pair (prints error and
  rethrows)
  around the run loop of each thread. It is possible that an
  exception may
  have been swallowed up somewhere.

>A small reproducible test case from you would be useful.

  I am working on that. I wrote a test case that mimics the
  application's
  use of the LBD, but I have not succeeded in reproducing the
  problem in
  the test case. The app has a single thread (network selector)
  that polls
  the LBD and several threads (ExecutionSites, and network
  threads that
  return results from remote ExecutionSites) that offer results
  into the
  queue. About 120k items will go into/out of the deque each
  second. In
  the actual app the problem is reproducible but inconsistent.
  If I run on
  my dual core laptop I can't reproduce it, and it is less
  likely to occur
  with a small cluster, but with 6 nodes (~560k
  transactions/sec) the
  problem will usually appear. Sometimes the cluster will run
  for several
  minutes without issue and other times it will deadlock
  immediately.
  Thanks,
  Ariel

On Wed, 08 Jul 2009 05:14 +1000, "Martin Buchholz"
<[5]martinrb at google.com> wrote:
>[+core-libs-dev]
>
>Doug Lea and I are (slowly) working on a new version of
LinkedBlockingDeque.
>I was not aware of a deadlock but can vaguely imagine how it
might happen.
>A small reproducible test case from you would be useful.
>
>Unfinished work in progress can be found here:
>[6]http://cr.openjdk.java.net/~martin/webrevs/openjdk7/BlockingQ
ueue/
>
>Martin


  On Wed, 08 Jul 2009 05:14 +1000, "David Holmes"

<[7]davidcholmes at aapt.net.au> wrote:
>


> Ariel,
>
> The poll()ing thread is blocked waiting for the internal lock,
but
> there's
> no indication of any thread owning that lock. You're using an
OpenJDK 6
> build ... can you try JDK7 ?
>
> I don't recall anything similar to this, but I don't know what
version
> that
> OpenJDK6 build relates to.
>
> Make sure you haven't missed any exceptions occurring in other
threads.
>
> David Holmes
>
> > -----Original Message-----
> > From: [8]concurrency-interest-bounces at cs.oswego.edu
> > [mailto:[9]concurrency-interest-bounces at cs.oswego.edu]On
Behalf Of Ariel
> > Weisberg
> > Sent: Wednesday, 8 July 2009 8:31 AM
> > To: [10]concurrency-interest at cs.oswego.edu
> > Subject: [concurrency-interest] LinkedBlockingDeque deadlock?
> >
> >
> > Hi all,
> >
> > I did a search on LinkedBlockingDeque and didn't find
anything similar
> > to what I am seeing. Attached is the stack trace from an
application
> > that is deadlocked with three threads waiting for
0x00002aaab3e91080
> > (threads "ExecutionSite: 26", "ExecutionSite:27", and
"Network
> > Selector"). The execution sites are attempting to offer
results to the
> > deque and the network thread is trying to poll for them using
the
> > non-blocking version of poll. I am seeing the network thread
never
> > return from poll (straight poll()). Do my eyes deceive me?
> >
> > Thanks,
> >
> > Ariel Weisberg
> >
>

References

1. mailto:ariel at weisberg.ws
2. http://www.java.net/download/jdk7/binaries/jdk-7-ea-bin-b63-linux-x64-02_jul_2009.bin
3. http://builder10.centos.org/
4. http://icedtea.classpath.org/
5. mailto:martinrb at google.com
6. http://cr.openjdk.java.net/%7Emartin/webrevs/openjdk7/BlockingQueue/
7. mailto:davidcholmes at aapt.net.au
8. mailto:concurrency-interest-bounces at cs.oswego.edu
9. mailto:concurrency-interest-bounces at cs.oswego.edu
  10. mailto:concurrency-interest at cs.oswego.edu
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