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

A event about a deflated monitor without any information which monitor is deflated seems just like noise to me.

What problem are we trying to solve here again? Are we interested in how long a monitor was inflated? Pairing up inflates with deflates?

Implementation wise, we should use monotonic, internally assigned ids as keys for monitor identity, instead of relying on the oops (but that is outside this PR).

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PR Comment: https://git.openjdk.org/jdk/pull/24121#issuecomment-2747769648