[jdk21u-dev] RFR: 8335619: Add an @apiNote to j.l.i.ClassFileTransformer to warn about recursive class loading and ClassCircularityErrors

[Volker Simonis]

On Sat, 6 Sep 2025 19:45:10 GMT, Henrique Moraes <duke at openjdk.org> wrote:

> Although this issue manifests primarily when using Project Loom (Virtual Threads), that makes it even more critical. Loom is the flagship feature of JDK 21 and the main reason many enterprises are adopting this LTS release.
> 
> With this bug, major instrumentation tools (AppDynamics, DataDog, New Relic, etc.) cannot function correctly on JDK 21 with Loom, effectively blocking safe adoption of one of the most important features in modern Java.
> 
> I strongly urge the maintainers to **prioritize the integration of this backport into 21u**, as it is a blocker for enterprise production environments that depend on monitoring and observability.

@Cirocc, I don't understand your comment. While I agree that this change should be downported, I don't understand how it can "unblock" monitoring/instrumentation tools because this PR only adds an API note to the documentation.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/2012#issuecomment-3266239816