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

[Markus Grönlund]

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

How do you match up the timestamps? Because without the oop, the connection between the two events is lost.

Are we measuring how long time it takes to deflate a monitor? How useful is that information?

Deflations can also happen asynchronously. If so, the thread information cannot be used to pair them up either.

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PR Comment: https://git.openjdk.org/jdk/pull/24121#issuecomment-2747859838