RFR: 8298853: JvmtiVTMSTransitionDisabler should support disabling one virtual thread transitions [v2]

[David Holmes]

On Mon, 19 Dec 2022 12:27:08 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> @dholmes-ora
>> Thank you for looking at this fix and for the comments.
>> I will on replying and resolving them.
>
> This update just follows the common pattern which was introduced about two years ago. At the moment I do not remember the exact reason. This code needs to wait for the counter to become zero and to use `ThreadBlockInVM` which can reach a safepoint in the destructor. Can we lock with a safepoint check in this case? Or we should get rid of the `ThreadBlockInVM` then?
> I'll check if this can be fixed.

This can be a separate RFE if the reason for it being a nosafepoint lock no longer holds. It would be cleaner to use a normal safepoint checking lock than to artificially make the thread safepoint-safe before using it.

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PR: https://git.openjdk.org/jdk/pull/11690