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

[David Holmes]

On Fri, 21 Mar 2025 08:10:27 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> 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?
>
> I looked at it before doing the patch, and I don't think the event-specific fields are default-initialized. In fact, if you skip these, JFR code would assert:
> 
> 
> # A fatal error has been detected by the Java Runtime Environment:
> #
> #  Internal Error (/home/shade/trunks/jdk/build/linux-x86_64-server-fastdebug/hotspot/variant-server/gensrc/jfrfiles/jfrEventClasses.hpp:1181), pid=279828, tid=279849
> #  assert(verify_field_bit(0)) failed: Attempting to write an uninitialized event field: _monitorClass

That seems like a bug in the event constructor to me.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24121#discussion_r2007453034