RFR: 8355631: The events might be generated after VM_DEATH event [v4]

[Serguei Spitsyn]

On Mon, 27 Oct 2025 15:36:41 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

>> The JVMTI spec says: https://docs.oracle.com/en/java/javase/24/docs/specs/jvmti.html#VMDeath
>> `The VM death event notifies the agent of the termination of the VM. No events will occur after the VMDeath event.`
>> 
>> However, current implementation changes state and only after this start disabling events.  
>> 
>> It might be not a conformance issue, because there is no way to get thread state in the very beginning of event. 
>> The main practical issue is that currently certain events are generated when VM is becoming dead. So any function in event should check error against JVMTI_PHASE_DEAD. We can easily trigger it by running tests with enabled https://bugs.openjdk.org/browse/JDK-8352654
>> 
>> Also, it would be useful to guarantee that VM_DEATH is last event so users can safely close/destroy all supported all structures used by Jvmti agent (like RawMonitors).
>> 
>> The proposed fix is to stop events posting and wait for already executing events before vm_death is posted.
>> 
>> Currently, I haven't seen problems with this fix and  https://bugs.openjdk.org/browse/JDK-8352654.
>
> Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fixed after David's comments

src/hotspot/share/prims/jvmtiEventController.cpp line 1231:

> 1229:   const double start = os::elapsedTime();
> 1230:   const double max_wait_time = 60;
> 1231:   // The first time we see the callback count reach zero we know all actual

Nit: s/the callback count reach zero/the callback count reaches zero/g

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PR Review Comment: https://git.openjdk.org/jdk/pull/27504#discussion_r2467522233