Field maxSize of event jdk.YoungGenerationConfiguration can be set to Long.MIN_VALUE

[Frederic Thevenet]

Thanks for the clarification, Erik.


On 14/06/2023 09:44, Erik Gahlin wrote:
> Hi Frederic,
>
> I didn't see your post until now, I was on vacation last week..
>
> Yes, Long.MIN_VALUE has special meaning, It means the value is missing 
> or not applicable.
>
> Erik
> ------------------------------------------------------------------------
> *From:* hotspot-jfr-dev <hotspot-jfr-dev-retn at openjdk.org> on behalf 
> of Frederic Thevenet <fthevene at redhat.com>
> *Sent:* Tuesday, June 6, 2023 9:56 PM
> *To:* hotspot-jfr-dev at openjdk.org <hotspot-jfr-dev at openjdk.org>
> *Subject:* Field maxSize of event jdk.YoungGenerationConfiguration can 
> be set to Long.MIN_VALUE
> Hi,
>
> I recently reported on an issue where invoking the command "jfr print"
> on a recording that contain events where one of the field in is an
> amount in bytes whose value is Long.MIN_VALUE (or invoking "toString()"
> on such an event), you'd the following error:
> jfr print: unexpected internal error, Index -1 out of bounds for length 6
>
> Now, I believe the root cause and fix to the issue to be pretty trivial
> and I submitted a PR for that, but I am trying to understand if the
> event that revealed the bug is really supposed to report such a value,
> or if there's another problem at play here.
>
> The event type in question is "jdk.YoungGenerationConfiguration" whose
> "maxSize" field is always equal to Long.MIN_VALUE when the GC in use is
> ShenandoahGC or ZGC.
> Now, I'm guessing that Shenandoah and ZGC not being generational, this
> particular configuration item is probably mostly ignored/useless, in
> which case, I feel it isn't fully unexpected that if present
> nonetheless, such events would be populated with default values which,
> from a cursory glance at gcConfiguration.hpp[2] looks like maxSize is
> set to the maximum value of uintx (which when cast as a java long would
> be Long.MIN_VALUE if I'm not mistaking):
>
> class GCYoungGenerationConfiguration {
>   public:
>    bool has_max_size_default_value() const;
>    uintx max_size() const;
>    uintx min_size() const;
>    intx new_ratio() const;
> };
>
> I'm not 100% sure that my understanding of the whole thing is correct
> here, so please do not hesitate to correct me if it isn't.
>
> Furthermore, I'm unsure whether or not the fact that maxSize is
> effectively set to Long.MIN_VALUE is necessarily an issue here (as long
> as the code that handles the formatting is fixed, of course): maybe the
> value carries a specific meaning I'm unaware of.
>
> I would really appreciate it if someone here is a position to shed some
> light on the matter for me.
>
> Thanks!
> Frederic
>
> [1] https://bugs.openjdk.org/browse/JDK-8309550
> [2]
> https://github.com/openjdk/jdk/blob/4a75fd462c002a209201d8bfc8d6c9eb286a7444/src/hotspot/share/gc/shared/gcConfiguration.hpp#L71
>
> -- 
> Frederic Thevenet
> Senior Software Engineer - OpenJDK
> Red Hat France <https://www.redhat.com>
> BAF5 C2D2 0BE0 1715 5EE1 0815 2065 AD47 B326 EB92
>

-- 
Frederic Thevenet
Senior Software Engineer - OpenJDK
Red Hat France<https://www.redhat.com>
BAF5 C2D2 0BE0 1715 5EE1 0815 2065 AD47 B326 EB92
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