Re: CachedClass referential comparison issues (potential bug)

Anyone have thoughts on this? I'm happy to go straight to filing a JIRA
issue, and can probably PR a fix for this bug as I understand it, but I
don't want to plow ahead here if there's a lack of acceptance/belief that
this is a real issue - and certainly not if I don't have buy-in on the fix
I might write.

Thanks,

Chris

On Mon, 2 Feb 2026 at 11:50, Chris Dennis <[email protected]> wrote:

> Hi All,
>
> I've been dealing with sporadic failures of Groovy based tests with
> false overload disambiguation issues when running on OpenJ9 with
> `-Xsoftrefthreshold0` - this essentially turns soft references into weak
> references - they get cleared very quickly. The cause for my failures
> appears to be that Groovy is relying on referential equality (or
> inequality) between CachedClass instances to infer things about the
> associated Java class relationship. My logging though shows that the
> mapping here isn't truly canonical though - at least not under OpenJ9 in
> this configuration. I'm seeing instances where the runtime is comparing two
> different instances of CachedClass derived from the same ClassInfo and
> falsely inferring that the two classes are distinct and therefore
> populating method caches with duplicate method instances and giving me
> false ambiguous overload failures.
>
> I'm attempting to narrow down how exactly this is happening and whether
> the cause is OpenJ9 incorrectly clearing a soft reference to a strongly
> reachable instance, or is due to Groovy missing one or more
> reachabilityFences to prevent early clearing of these references.
>
> Looking forward to peoples insights and/or thoughts on how best to
> approach this. A simple fix would be to only rely on referential
> (in)equality for a fast path check, with fallback to a more robust check.
> Alternatively, the (much harder) but likely cleaner path is to fix the
> underlying Groovy and/or OpenJ9 bug. Note that if this is a Groovy bug
> around reachability then I don't think it's safe to assume that this cannot
> happen on Hotspot either now, or in the future if/when GC behavior there
> changes
>
> Thanks,
>
> Chris
>
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