RFR: 8296492: Remove ObjectLocker in JVMTI get_subgroups call [v5]

[Alan Bateman]

On Wed, 9 Nov 2022 09:32:42 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Forgot a null check.
>
> src/hotspot/share/prims/jvmtiEnvBase.cpp line 557:
> 
>> 555: JvmtiEnvBase::new_jthreadGroupArray(int length, objArrayHandle groups) {
>> 556:   if (length == 0) {
>> 557:     return NULL;
> 
> I do not think returning NULL is allowed for JVMTI `GetThreadGroupChildren()`.
> Please, see: [GetThreadGroupChildren](https://docs.oracle.com/en/java/javase/19/docs/specs/jvmti.html#GetThreadGroupChildren)

I don't think this has changed. Right now, if there are no child subgroups then *group_count_ptr will be 0 and *groups_ptr will be NULL as there is no memory to deallocate. JVMTI Deallocate is specified to do nothing when called with NULL.

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