RFR: 8320318: ObjectMonitor Responsible thread

[Fredrik Bredberg]

On Tue, 10 Sep 2024 19:48:50 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Removed the concept of an ObjectMonitor Responsible thread.
>> 
>> The reason to have an ObjectMonitor Responsible thread was to avoid threads getting stranded due to a hole in the successor protocol. This hole was there because adding the necessary memory barrier was considered too expensive some 20 years ago.
>> 
>> The ObjectMonitor Responsible thread code adds complexity, and doing timed parks just to avoid getting stranded is not the way forward. More info about the problems with the ObjectMonitor responsible thread can be found in [JDK-8320318](https://bugs.openjdk.org/browse/JDK-8320318).
>> 
>> After removing the ObjectMonitor Responsible thread we see increased performance on all supported platforms except Windows. [JDK-8339730](https://bugs.openjdk.org/browse/JDK-8339730) has been created to handle this.
>> 
>> Passes tier1-tier7 on supported platforms.
>> x64, AArch64, Riscv64, ppc64le and s390x passes ok on the test/micro/org/openjdk/bench/vm/lang/LockUnlock.java test.
>> Arm32 and Zero doesn't need any changes as far as I can tell.
>
> src/hotspot/share/runtime/objectMonitor.cpp line 353:
> 
>> 351: 
>> 352: void ObjectMonitor::enter_for_with_contention_mark(JavaThread* locking_thread, ObjectMonitorContentionMark& contention_mark) {
>> 353:   DEBUG_ONLY(bool success = ) ObjectMonitor::enterI_with_contention_mark(locking_thread, contention_mark);
> 
> This is kind of noisy with DEBUG_ONLY.  If you remove DEBUG_ONLY, does the windows compiler complain that you're not using the variable success in the product build?

I don't know. I come from a planet where warnings was errors, and just brought along the old habit to my new planet. I'll check with the Windows compiler.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19454#discussion_r1754324872