jmx-dev RFR: 8373464: Test JdkManagementCheckSince.java fails after JDK-8369736

[Ioi Lam]

Please review this small fix and the plan of action for backporting JDK-8369736 to JDK 26.

(JDK-8369736 is under https://openjdk.org/jeps/3#Late-Enhancement-Request-Process)

**Background**

The "actually introduced version" for `HotSpotAOTCacheMXBean` is found using the `ct.sym` file (JdkManagementCheckSince.java  uses test/jdk/tools/sincechecker/SinceChecker.java, which doesn't read `ct.sym` directly, but uses `JavacTool` with `--release N`, which in turn loads `ct.sym`)


$ unzip -l ./images/jdk/lib/ct.sym | grep HotSpotAOTCacheMXBean.sig
      167 2025-12-11 03:16 R/jdk.management/jdk/management/HotSpotAOTCacheMXBean.sig


"R" is JDK 27 ("1" is JDK 1, "A" is JDK 10, "B" is JDK 11, etc ...)

In comparison, `VirtualThreadSchedulerMXBean` was first introduced in "O" = JDK 24, and its API has not changed since)


$ unzip -l ./images/jdk/lib/ct.sym | grep VirtualThreadSchedulerMXBean.sig
      313 2025-12-11 03:16 OPQR/jdk.management/jdk/management/VirtualThreadSchedulerMXBean.sig


Note that if an API has evolved over time, we may have several `.sig` files:


$ unzip -l ./images/jdk/lib/ct.sym | grep util/Vector.sig
     3058 2025-12-11 03:16 8/java.base/java/util/Vector.sig
     3182 2025-12-11 03:16 9A/java.base/java/util/Vector.sig
     3272 2025-12-11 03:16 BCDEFGHIJKLMNOPQR/java.base/java/util/Vector.sig


`ct.sym` is generated from files in [src/jdk.compiler/share/data/symbols](https://github.com/openjdk/jdk/tree/master/src/jdk.compiler/share/data/symbols)


$ cd src/jdk.compiler/share/data/symbols
$ grep VirtualThreadSchedulerMXBean *
jdk.management-O.sym.txt:class name jdk/management/VirtualThreadSchedulerMXBean


Because `HotSpotAOTCacheMXBean` is not listed in any of the `.sym.txt` files, it's added as version "R" in `ct.sym`


$ grep HotSpotAOTCacheMXBean * | wc
      0 0 0


**Proposed plan of action**

1. In the mainline, update HotSpotAOTCacheMXBean.java to use `@since 27` (this PR) to fix the current test failure in the mainline.

2. When backporting HotSpotAOTCacheMXBean.java to JDK 26 (with approval), it should have `@since 26`.

3. After JDK 26 is finalized, update the mainline:
    - Add HotSpotAOTCacheMXBean to `jdk.management-Q.sym.txt`
    - Update HotSpotAOTCacheMXBean.java to use `@since 26`.

-------------

Commit messages:
 - 8373464: Test JdkManagementCheckSince.java fails after JDK-8369736

Changes: https://git.openjdk.org/jdk/pull/28760/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28760&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373464
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28760/head:pull/28760

PR: https://git.openjdk.org/jdk/pull/28760