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

[Aleksey Shipilev]

On Fri, 21 Mar 2025 06:21:14 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> 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?

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

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PR Review Comment: https://git.openjdk.org/jdk/pull/24121#discussion_r2007055113