RFR: 8359437: Make users and test suite not able to set LockingMode flag

[David Holmes]

On Mon, 23 Jun 2025 10:39:59 GMT, Anton Artemov <duke at openjdk.org> wrote:

>> test/hotspot/jtreg/runtime/Monitor/StressWrapper_TestRecursiveLocking_36M.java line 36:
>> 
>>> 34:  *     -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
>>> 35:  *     -Xint
>>> 36:  *     -XX:LockingMode=0
>> 
>> I was wondering why these LockingMode=0 test cases were not setting `VerifyHeavyMonitors` instead, but I'm assuming the intent now is that we will only test that mode when it is set externally by the user (or in our case a particular test task definition)?
>> 
>> I also realized we can only test heavy monitors in tests where we explicitly control the monitor creation places and hence can call the WB method to force inflation. That obviously reduces the test coverage for that mode quite significantly - but perhaps that will be handled if in the future we implicitly reenable forced inflation and do away with the WB usage.
>
> My understanding is that VerifyHeavyMonitors requires LockingMode = 0, see line 1852 of arguments.cpp. So one has to set both at the same time, not one instead of another. Now locking mode is hardcoded to lightweight, and there is no way to use the incompatible `VerifyHeavyMonitors` option.

My understanding was that `VerifyHeavyMonitors` was to be used as a replacement for `LockingMode=0` aka `UseHeavyMonitors`. But as Coleen has requested all `VerifyHeavyMonitors` testing be removed this is now a moot point.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25847#discussion_r2162866307