RFR: 8356251: Need minor cleanup for interp_only_mode [v3]

[Leonid Mesnik]

On Thu, 8 May 2025 22:07:40 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> This is a minor cleanup for the JVMTI `interp_only_mode` implementation which includes the following changes:
>>  - The `interp_only_mode` in `JavaThread` is represented with a counter which is incremented and decremented. This is confusing because this value should only take values `0` or `1`. Asserts are placed to make sure it is never going out of bounds. The `interp_only_mode` in a `JavaThread` is checked by the interpreter chunks which expect it to be an `integer`. This cleanup has no intention to make it a boolean.
>>  - The function `JvmtiThreadState::process_pending_interp_only()` does a sync on the `JvmtiThreadState_lock` which is not really needed and is being removed. It is called in a `VTMS` transition and so, can not clash with the `SetEventNotificationMode` because it sets a `JvmtiVTMSTransitionDisabler`.
>>  
>>  Testing:
>>   - TBD: Mach5 tiers 1-6
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review: added comment with clarification

Marked as reviewed by lmesnik (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25060#pullrequestreview-2826655094