RFR: 8332303: Better JMX interoperability with older JDKs, after removing Subject Delegation

[Serguei Spitsyn]

On Wed, 15 May 2024 16:59:59 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

> Running JConsole from a previous JDK, and attaching to jdk-23 (after [JDK-8326666](https://bugs.openjdk.org/browse/JDK-8326666): Remove the Java Management Extension (JMX) Subject Delegation feature), the MBean tab is blank.
> 
> In javax/management/remote/rmi/RMIConnectionImpl.java:
> addNotificationListener rejects a non-null delegationSubjects array, but older JDKs will send such an array. It could accept the array, and only reject/throw if it contains a non-null Subject (i.e. if an attempt to use subject delegation is really happening).
> 
> Manually testing JConsole, the MBean tab is fully populated and usable.

Looks good in general. Posted a couple of questions though.

src/java.management.rmi/share/classes/javax/management/remote/rmi/RMIConnectionImpl.java line 979:

> 977:             for (Subject s: delegationSubjects) {
> 978:                 if (s != null) {
> 979:                     throw new UnsupportedOperationException("Subject Delegation has been removed.");

Q1: Would it make sense to provide any details about the failing `delegationSubject` element?
Q2: Does this fix needs a CSR?

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PR Review: https://git.openjdk.org/jdk/pull/19253#pullrequestreview-2059157190
PR Review Comment: https://git.openjdk.org/jdk/pull/19253#discussion_r1602337036