RFR: 8343840: Rewrite the ObjectMonitor lists [v2]

[Fredrik Bredberg]

On Thu, 27 Feb 2025 14:09:45 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update after review by David and Coleen.
>
> src/hotspot/share/runtime/objectMonitor.cpp line 701:
> 
>> 699: void ObjectMonitor::add_to_entry_list(JavaThread* current, ObjectWaiter* node) {
>> 700:   node->_prev   = nullptr;
>> 701:   node->TState  = ObjectWaiter::TS_ENTER;
> 
> I think you should do this in a future cleanup.  The ObjectWaiter's constructor should initialize these fields to TS_ENTER or TS_WAIT when it's created  and make prev, next null (or 0xBAD?).  And fix the constructor to have an initialization list instead.

Sounds like a plan.

> src/hotspot/share/runtime/synchronizer.cpp line 369:
> 
>> 367:       // We have one or more waiters. Since this is an inflated monitor
>> 368:       // that we own, we can transfer one or more threads from the waitset
>> 369:       // to the entry_list here and now, avoiding the slow-path.
> 
> Not related to this change but I found that this quick_notify isn't quicker.

Let's make quick_notify quicker (in another RFE).

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PR Review Comment: https://git.openjdk.org/jdk/pull/23421#discussion_r1973883699
PR Review Comment: https://git.openjdk.org/jdk/pull/23421#discussion_r1973878764