RFR: 8351484: Race condition in max stats in MonitorList::add [v2]

[Zhengyu Gu]

On Mon, 10 Mar 2025 19:34:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See bug for the description of the race. New gtest test case reliably catches fire on my 5950X desktop without this fix.
>> 
>> I needed to add the proper constructor for `MonitorList` to make it testable. In our regular code, it is statically allocated, so its fields are implicitly initialized.
>> 
>> I also made counter updates `_relaxed` for completeness.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, new test now passes
>>  - [x] GHA
>
> Aleksey Shipilev has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Can check <=
>  - Object handle

src/hotspot/share/runtime/synchronizer.cpp line 83:

> 81:   do {
> 82:     old_max = Atomic::load(&_max);
> 83:     if (count < old_max) {

Can breakout when `count == old_max`

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/23961#discussion_r1987903286