RFR: 8356251: Need minor cleanup for interp_only_mode

[Serguei Spitsyn]

On Tue, 6 May 2025 18:29:22 GMT, Leonid Mesnik <lmesnik 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
>
> src/hotspot/share/runtime/javaThread.hpp line 1177:
> 
>> 1175:   bool is_interp_only_mode()                { return (_interp_only_mode != 0); }
>> 1176:   int get_interp_only_mode()                { return _interp_only_mode; }
>> 1177:   int set_interp_only_mode(int val)         { return _interp_only_mode = val; }
> 
> Ther get_interp_only_mode() /set_interp_only_mode(int val)  also might be eliminated and replaced by set/clear instead.

Good suggestion, thanks. Updated, it is being tested now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25060#discussion_r2076576748