JVMTI resume and suspend for virtual and carrier threads

[Alan Bateman]

On 03/04/2023 17:24, Babneet B Singh wrote:
> I would like to request clarification on how JVMTI resume and suspend work for a virtual thread and its associated carrier thread.
> Virtual thread runs on a carrier thread. Both are separate Java 
> objects. JVMTI functions can be invoked separately on them. What is 
> the relationship between the state of a virtual and carrier thread 
> when JVMTI suspend and resume functions are invoked on them?
They are separate Thread objects for JVM TI too,.



> jvmti->SuspendThread(virtualThread) // Will this also suspend the 
> carrier thread?
No, just the virtual thread. Remember the carrier is "blocked" when a 
virtual thread is mounted, it continues when the virtual thread 
unmounts. Once you get that mental model then most of the suspend/resume 
issues should be become straight forward to reason about.



> jvmti->SuspendThread(carrierThread) // Will this also suspend the 
> virtual thread?
No, the carrier will self-suspend when the virtual mount unmounts.



> jvmti->ResumeThread(virtualThread) // Will this resume both virtual 
> thread and its carrier thread?
No, just the virtual thread.


> jvmti->ResumeThread(carrierThread) // Will this just resume the 
> carrier thread and virtual thread will stay suspended?

No, just the carrier.

-Alan
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