RFR: 8296492: Remove ObjectLocker in JVMTI get_subgroups call

[David Holmes]

On Tue, 8 Nov 2022 00:58:44 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> The JVM code took a ThreadGroup lock before poking into ThreadGroup fields.  Call a method in the ThreadGroup to call the synchronized method instead.
> Tested with tier 1-4.

This is a nice simplification of the VM side of the code! I do have to wonder why this was implemented the way it was rather than doing the simple upcall as you now do, but I suspect it was just performance, which should not be an issue today.

One query/concern about exception handling.

Thanks.

src/hotspot/share/prims/jvmtiEnvBase.cpp line 810:

> 808:   if (HAS_PENDING_EXCEPTION) {
> 809:     CLEAR_PENDING_EXCEPTION;
> 810:     return JVMTI_ERROR_OUT_OF_MEMORY;

Do we need to handle unexpected exceptions better, rather than just claiming they are OOME?

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PR: https://git.openjdk.org/jdk/pull/11033