[concurrency-interest] Suspecting a problem in recent jdk-9 builds

Martin Buchholz martinrb at google.com
Wed Dec 28 11:56:33 EST 2016


Experience suggests that such problems are *usually* in the application
code, but of course there are undiscovered bugs in java.util.concurrent.

Since only you can reproduce the problem, only you can narrow down the
possible root causes.  You could build your own openjdk9, bisect to the
exact commit that is causing problems, but it would be a lot of work, and
it might in the end be a change to hotspot gc, with root cause still
unknown...

On Wed, Dec 28, 2016 at 1:30 AM, Antoine Tissier <ati at activeviam.com> wrote:

> Hi,
>
> We have been running benchmarks for our in-memory analytics software
> ActivePivot on a M6.32 machine (Solaris Sparc, 8 TB RAM, 2304 logical cores
> (288 physical cores)).
> Our benchmarks involve high parallelism along with many queries divided in
> a high number of tasks (CountedCompleters) in the ForkJoinPool. With build
> 145 of jdk-9, some tasks are not executed, causing larger completion
> problems. However, with the earlier build 111, the problem does not occur.
>
> On a smaller Linux machine (Linux amd 64, 64 logical cores (32 physical
> cores), 512 GB RAM) but with a similar setup, the problem was not
> reproduced.
>
> The problem seems to arise when a large number of completers (>20 000) are
> involved: forking tasks works well but when submitting tasks to a new pool,
> it seems that their compute method is sometimes not called.
> We indeed log every call to ForkJoinPool.submit, as well as everytime a
> completer enters its compute method, and clearly see that once in a while,
> the task is never computed after having been submitted. We let the system
> run for an additional hour, and there was no more progress even though the
> system was idle. Thread dumps did not show any suspect activity (all worker
> threads were idle).
>
> We tried to reproduce the problem with a similar but more simple test, but
> it was not successful.
>
> Are you aware of any concurrency/task completion problems in the more
> recent builds of jdk-9 ?
> Are there any additional tests that we could run in order to diagnose this
> issue ?
>
> Best regards,
> Antoine
>
>
>
> --
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>
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> <https://www.youtube.com/channel/UCGjYnbjlPamN0RvSm3eGqCw> Antoine Tissier
> *Junior Software Engineer*
>
>
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> [image: Skype]antoine_tissier
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>
>
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