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

Antoine Tissier ati at activeviam.com
Wed Dec 28 04:30:01 EST 2016


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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