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

[Henrique Moraes]

On Wed, 23 Jul 2025 10:05:16 GMT, Francesco Andreuzzi <duke at openjdk.org> wrote:

> Almost clean backport of JDK-8335619, except for a conflict in the copyright header (year). Adds useful information for users of `java.lang.instrument`.

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.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/2012#issuecomment-3263156989