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

[David Holmes]

On Wed, 19 Mar 2025 21:54:34 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> src/hotspot/share/runtime/objectMonitor.cpp line 844:
>> 
>>> 842:   }
>>> 843: 
>>> 844:   if (obj != nullptr && event.should_commit()) {
>> 
>> So you decided to just drop the event completely ... but is that what people tracking these events would want? Do we need to update anything on the event definition so people know this is the case?
>
> Being a replacement for the `_sync_Deflations` counter it should probably count these null ones too.

With regards to the event definition @egahlin suggests:
> It might be worth mentioning it in the field description, e.g. "If null or N/A, the object has been garbage collected", but that is all. (Null is represented as 0 in the file format, which the parser will interpret as a missing value. Both 'jfr print' and JMC will display "N/A")

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/24121#discussion_r2004590832