race condition in GC logs

Srinivas Ramakrishna ysr1729 at gmail.com
Tue Aug 25 19:56:15 UTC 2015


-bcc/hotspot-dev
+cc/hotspot-gc-dev

I have a patch for JDK-8133818 (on JDK 8): as suggested here earlier,
besides splitting out Cleaners, it also reports JNI wk refs by counting
them on-the-fly much like for other Reference types.

I'll attach it to the ticket once my testing completes.

thanks.
-- ramki

On Wed, Aug 19, 2015 at 3:20 PM, Kirk Pepperdine <kirk at kodewerk.com> wrote:

> Hi Bengt,
>
> Thanks for filing. I really didn’t consider this a bug but it seems
> reasonable to add clarity in the log.
>
> — Kirk
>
> > On Aug 18, 2015, at 8:39 AM, Bengt Rutisson <bengt.rutisson at oracle.com>
> wrote:
> >
> >
> >
> > On 2015-08-18 12:47, Bengt Rutisson wrote:
> >>
> >> Hi Kirk,
> >>
> >> On 2015-08-18 12:31, Kirk Pepperdine wrote:
> >>> Hi all,
> >>>
> >>> I found this.. in a few logs. Before I started trolling the source
> trying to sort out what the second PhantomReferences count was, I pinged
> Charlie and asked him. He suggested it was a (concurrency??) bug witnessed
> only once by someone else. I’ve now seen it in several logs where the
> numbers reported are different. Sorry for being lazy for not trolling the
> code before asking but is this a bug?
> >>
> >> The second ref count is for cleaner references. They used to be treated
> the same way as phantom references, but a recent improvement was to
> separate the handling of the cleaners to after all phantom references have
> been handled. So, the first count is the "real" phantom references and the
> second count is the cleaner references.
> >>
> >> It's confusing logging, I agree.
> >>
> >> This came in with this fix:
> >> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/2194fdf3fbd9
> >>
> >> since this adds one more call to preclean_discovered_reflist(), which
> is the method that prints the refs count.
> >
> > Thomas was nice and created a bug report for this :)
> >
> > Additional number of processed references printed with
> -XX:+PrintReferenceGC after JDK-8047125
> > https://bugs.openjdk.java.net/browse/JDK-8133818
> >
> > Bengt
> >
> >>
> >> Thanks,
> >> Bengt
> >>
> >>>
> >>> Regards,
> >>> Kirk
> >>>
> >>> Java HotSpot(TM) 64-Bit Server VM (25.51-b03) for linux-amd64 JRE
> (1.8.0_51-b16), built on Jun  8 2015 19:28:07 by "java_re" with gcc 4.3.0
> 20080428 (Red Hat 4.3.0-8)
> >>> Memory: 4k page, physical 9570132k(9340292k free), swap
> 4095996k(4095996k free)
> >>> CommandLine flags: -XX:+AggressiveOpts -XX:G1HeapRegionSize=16777216
> -XX:InitialHeapSize=3221225472 -XX:InitiatingHeapOccupancyPercent=75
> -XX:+ManagementServer -XX:MaxGCPauseMillis=250 -XX:MaxHeapSize=3221225472
> -XX:+ParallelRefProcEnabled -XX:+PerfDisableSharedMem
> -XX:+PrintAdaptiveSizePolicy -XX:+PrintGC
> -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps
> -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintReferenceGC
> -XX:+PrintTenuringDistribution -XX:+UseCompressedClassPointers
> -XX:+UseCompressedOops -XX:+UseG1GC -XX:+UseLargePages
> >>>  0.198: [G1Ergonomics (Heap Sizing) expand the heap, requested
> expansion amount: 3221225472 bytes, attempted expansion amount: 3221225472
> bytes]
> >>> 2015-08-11T08:23:02.219+0200: 7.630: [GC pause (G1 Evacuation Pause)
> (young)
> >>> Desired survivor size 16777216 bytes, new threshold 15 (max 15)
> >>>  7.631: [G1Ergonomics (CSet Construction) start choosing CSet,
> _pending_cards: 0, predicted base time: 10.00 ms, remaining time: 240.00
> ms, target pause time: 250.00 ms]
> >>>  7.631: [G1Ergonomics (CSet Construction) add young regions to CSet,
> eden: 9 regions, survivors: 0 regions, predicted young region time: 3626.58
> ms]
> >>>  7.631: [G1Ergonomics (CSet Construction) finish choosing CSet, eden:
> 9 regions, survivors: 0 regions, old: 0 regions, predicted pause time:
> 3636.58 ms, target pause time: 250.00 ms]
> >>> 7.642: [SoftReference, 0 refs, 0.0006965 secs]7.643: [WeakReference,
> 40 refs, 0.0003039 secs]7.643: [FinalReference, 3477 refs, 0.0036191
> secs]7.647: [PhantomReference, 0 refs, 0 refs, 0.0006649 secs]7.647: [JNI
> Weak Reference, 0.0000119 secs], 0.0173298 secs]
> >>
> >
>
>
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