RFC: JVMTI async stack-walker POC

[Alan Bateman]

On 15/01/2026 11:52, Roman Kennke wrote:
> :
>
> thanks for offering your perspective. I have changed both POCs (and 
> the corresponding example code) to implement as JVMTI extensions - I 
> didn't even know that such a mechanism exists.
>
> They currently still use a capability to set up what they need (and 
> that's in the public API unfortunately), I am wondering if there is 
> something similar for JVMTI extensions? Worst case, I would perhaps 
> add another extension function to initialize things.
>
> Also, is there any way for consumers of the API to get some 
> documentation? The second POC uses callbacks, and I suppose it might 
> be useful for a prospective user of the API to know the arguments etc 
> of those. As it currently is, the callback functions are basically 
> black boxes, reported by the extension mechanism as void* - the user 
> of the API would have to know what functions exactly to pass as 
> callbacks. (Worst case, I guess it could be described in a blog-post 
> or so.)
>
I think it would be okay to have the equivalent of @implNote in the 
JVMTI spec. As part of the JEP 451 implementation we added an 
"Implementation Note" to the "Agent  Start-Up (Live phase)" section to 
document a -XX option. Maybe the "Stack frame" or some other section 
could have an implNote to document the functions?

I don't think the extension mechanism anticipated new capabilities but 
it could be done, as you mention, with another extension function. 
(Serguei might have some ideas here but I suspect it could be 
problematic to use some of the bits for VM-specific capabilities).

-Alan
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