New candidate JEP: 519: Compact Object Headers

[David Alayachew]

Thanks for the response Alex.

Ok, that link was helpful. I can see now that there is definitely a known
limit, and the JEP preceding this one is aware of that limit and designed
around it. All I am missing now is what happens when we go past that limit.
Hopefully Roman can answer that.

Thanks again Alex.

On Tue, May 13, 2025, 7:33 PM Alex Buckley <alex.buckley at oracle.com> wrote:

> On 5/13/2025 4:06 PM, David Alayachew wrote:
> > Silly question -- what happens if you use this feature, but end up with
> > more classes than can fit in the class' object header? I like to think
> > of myself as aware of my project's performance metrics, but the number
> > of classes loaded is not a detail I track.
>
> Not silly -- considered in the prior JEP -- see "Compressed class
> pointers encoding" in https://openjdk.org/jeps/450#Risks-and-Assumptions
>
> The abstract JVM has no limit to the number of loaded classes (see JVMS
> 4.11 for things that do have limits). Maybe Roman can say how much
> stress testing has been performed with the HotSpot implementation to
> discover the practical limit to the number.
>
> Alex
>
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