RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v12]

[Dean Long]

On Tue, 22 Oct 2024 02:18:19 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/continuationFreezeThaw_aarch64.inline.hpp line 300:
>> 
>>> 298:   CodeBlob* cb = top.cb();
>>> 299: 
>>> 300:   if (cb->frame_size() == 2) {
>> 
>> Is this a filter to identify c2 runtime stubs? Is there some other property we can check or assert here? This assumes that no other runtime frame will have this size.
>
> We could also check the caller of the runtime frame, something like:
> 
> #ifdef ASSERT
>   RegisterMap map(JavaThread::current(),
>                   RegisterMap::UpdateMap::skip,
>                   RegisterMap::ProcessFrames::skip,
>                   RegisterMap::WalkContinuation::skip);
>   frame caller = top.sender(&map);
>   assert(caller.is_compiled_frame(), "");
>   assert(cb->frame_size() > 2 || caller.cb()->as_nmethod()->is_compiled_by_c2(), "");
> #endif
> 
> Ideally we would want to check if cb->frame_size() is different than the actual size of the physical frame.

I agree, checking for frame_size() == 2 seems fragile.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1817458483