On Wed, 4 Jan 2023 04:54:27 GMT, David Holmes <[email protected]> wrote:
>> Serguei Spitsyn has updated the pull request incrementally with one
>> additional commit since the last revision:
>>
>> fix race between VTMS_transition_disable_for_one and start_VTMS_transition
>
> src/hotspot/share/prims/jvmtiThreadState.cpp line 482:
>
>> 480: _VTMS_transition_disable_for_all_count > 0) {
>> 481: MonitorLocker ml(JvmtiVTMSTransition_lock,
>> Mutex::_no_safepoint_check_flag);
>> 482: ml.notify_all();
>
> Checking the counts outside the lock seems really racy. Maybe it is safe in
> the original code but now we have two counters it is very hard to ascertain
> this is correct. Overall I find it very hard to see exactly how these
> counters get used.
This notification code is just an optimization. All related waiting fragments
are with timeouts.
I agree this sync protocol is kind of complicated and also does not scale well.
I'm still thinking on how to improve it.
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PR: https://git.openjdk.org/jdk/pull/11690
