RFR: 8352414: JFR: JavaMonitorDeflateEvent crashes when deflated monitor object is dead [v2]

[David Holmes]

On Thu, 20 Mar 2025 07:06:25 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Little regression crept in with [JDK-8351142](https://bugs.openjdk.org/browse/JDK-8351142): on the deflation path, object associated with monitor can be already dead. 
>> 
>> A new stress test fails within seconds without a fix. It also covers other monitor events, so we have extra coverage there as well.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, new stress test now passes
>>  - [x] Linux x86_64 server fastdebug, `jdk_jfr`
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Emit the event anyway

src/hotspot/share/runtime/objectMonitor.cpp line 744:

> 742:     // Emit the event anyway, but without details.
> 743:     event->set_monitorClass(nullptr);
> 744:     event->set_address(0);

Shouldn't this be the default state of the event?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24121#discussion_r2006925295