RFR: 8249004: Reduce ThreadsListHandle overhead in relation to direct handshakes [v13]

[Daniel D.Daugherty]

On Fri, 5 Nov 2021 23:42:07 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> A fix to reduce ThreadsListHandle overhead in relation to handshakes and
>> we add sanity checks for ThreadsListHandles higher in the call stack.
>> 
>> This fix was tested with Mach5 Tier[1-8]; Tier8 is still running.
>
> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
> 
>   coleenp CR - clarify need for ThreadsListHandle in JvmtiEventControllerPrivate::recompute_enabled().

Updated comment has been pushed to this PR.

For some reason, the comments that @coleenp and I are posting in the
"Files changed" view are not showing up here.

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PR: https://git.openjdk.java.net/jdk/pull/4677