RFR: 8296492: Remove ObjectLocker in JVMTI get_subgroups call

[Alan Bateman]

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.

src/java.base/share/classes/java/lang/ThreadGroup.java line 802:

> 800:         int length = groups.size();
> 801:         return groups.toArray(new ThreadGroup[length]);
> 802:     }

Would you mind changing the comment to "Returns a snapshot of the subgroups as an array, used by JVMTI.", only to be consistent with the other methods that return subgroups as they all document it as a "snapshot". Also I think I would rename this to subgroupsAsArray as there isn't a "subgroups array".

If you want, `return groups.toArray(new ThreadGroup[0]);` will do the sizing for you.

Minor nit, you've additional blank lines after this method, I assume you only meant to add one.

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