RFR: 8373102: com/sun/jdi/MethodInvokeWithTraceOnTest.java can fail with ObjectCollectedException when run with a small heap

[Chris Plummer]

On Thu, 4 Dec 2025 21:00:41 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> With JDI tracing enabled, an attempt to trace an event when using SUSPEND_NONE can result in an ObjectCollectedException because the thread is still running and objects that are part of the trace can be collected already. In this case were were dealing with trying to print the thread name for a VirtualThreadEndEvent, and the virtual thread has already exited and been gc'd.
> 
> Tested by running test case before change (verified failure) and after change (50 runs without a failure). Will also run tier1 and tier5 svc just to be sure.

I've updated the implementation so now the event type is printed even if there is an ObjectCollectedException. Turns out I was worng about this being triggered by a VirtualThreadEndEvent. It was actually a ClassPrepareEvent, but it was for the class VirtualThreadEndEvent. Here's all the output for the event set, including the handling of the ObjectCollectedException (2nd to last line).

```[JDI: Receiving Command(id=188) JDWP.Event.Composite]
[JDI: Receiving:                suspendPolicy(byte): 0]
[JDI: Receiving:                events(Events[]): ]
[JDI: Receiving:                    events[i](Events): ]
[JDI: Receiving:                    eventKind(byte): 8]
[JDI: Receiving:                        requestID(int): 2]
[JDI: Receiving:                        thread(ThreadReferenceImpl): ref=151]
[JDI: Receiving:                        refTypeTag(byte): 1]
[JDI: Receiving:                        typeID(long): ref=231]
[JDI: Receiving:                        signature(String): Ljdk/internal/event/VirtualThreadEndEvent;]
[JDI: Receiving:                        status(int): 3]
[JDI: EventSet: SUSPEND_NONE]
[JDI: Looking up Class, signature='Ljdk/internal/event/VirtualThreadEndEvent;', id=231]
[JDI: Caching new ReferenceType, sig=Ljdk/internal/event/VirtualThreadEndEvent;, id=231]
[JDI: Sending Command(id=438) JDWP.ThreadReference.Name]
[JDI: Sending:                 thread(ThreadReferenceImpl): ref=151]
[JDI: Event: ClassPrepareEvent in thread <thread collected>]
[JDI: Handled Prepare Event for jdk.internal.event.VirtualThreadEndEvent]```

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PR Comment: https://git.openjdk.org/jdk/pull/28666#issuecomment-3614923760