Unexpected exceptions during benchmark

[Henri Tremblay]

Hi,

I don't get it.
You are putting items in a non-concurrent hashmap from multiple threads.
I have no doubt it will eventually fail.

Reading quickly, the second error seems to be thrown (and could be more
explanatory) when you want more threads then the number of warmup threads.
So you want more threads than the warmup could prime and you get this error.

Anything I'm missing?

Regards,
Henri


On Fri, 22 Sept 2023 at 22:05, John Auden <lovedthefaioli at gmail.com> wrote:

> Hi,
>
> I was trying to create a concurrency benchmark, but noticed that it fails
> in a very basic logic block.
> *I know that it is a bad idea to run benchmarks inside a VM, but I do it
> rather for quick check and because I have debug JDK releases + hsdis there.
> This email is not to submit a bug, but rather just for your information.*
> Host: 16 cores Azure VM (Intel(R) Xeon(R) CPU E5-2673 v4 @ 2.30GHz)
> $ lscpu
> Architecture:          x86_64
> CPU op-mode(s):        32-bit, 64-bit
> Byte Order:            Little Endian
> CPU(s):                16
> On-line CPU(s) list:   0-15
>
> OS: CentOS Linux release 7.9.2009
> JDK: 17.0.5
>
> @Threads(Threads.MAX)
> public class HMBenchmark {
>   private final static Map<Long, Long> map = new HashMap<>(Runtime.getRuntime().availableProcessors());
>
>   @Benchmark
>   public void testHM() {
>     Long id = Thread.currentThread().getId();
>     map.put(id, 0L);
>     for (long i = 0; i < 100_000; i++) {
>       map.put(id, map.get(id) + i);
>     }
>   }
> }
>
> If the number of threads is set above 12 (up to Threads.MAX) this
> benchmark starts to fail. WIth 13, 14, 15 it fails with NPE (even though
> program order should theoretically protect code against NPE):
>
>
>
> *java.lang.NullPointerException: Cannot invoke
> "java.lang.Long.longValue()" because the return value of
> "java.util.Map.get(Object)" is null at
> org.ad.HMBenchmark.testHM(HMBenchmark.java:33) at
> org.ad.jmh_generated.HMBenchmark_testHM_jmhTest.testHM_Throughput(HMBenchmark_testHM_jmhTest.java:78)*
>
> WIth MAX threads (or 16) there is also this interesting exception:
>
>
>
>
> *java.lang.IllegalStateException: More threads than expected at
> org.openjdk.jmh.runner.InfraControlL2.announceWarmupReady(InfraControl.java:222)
> at
> org.openjdk.jmh.runner.InfraControl.announceWarmupReady(InfraControl.java:40)
> at
> org.ad.jmh_generated.HMBenchmark_testHM_jmhTest.testHM_Throughput(HMBenchmark_testHM_jmhTest.java:76)*
>
> Regards,
> Alex Dubrouski
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/jmh-dev/attachments/20230922/149846ee/attachment.htm>