RFR: 8369238: Allow virtual thread preemption on some common class initialization paths [v7]

[Patricio Chilano Mateo]

On Fri, 24 Oct 2025 11:55:28 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - rename _monitor to _init_lock
>>  - Extra comments from Coleen
>>  - define methods in resolve_from_cache with TRAPS and use CHECK_AND_CLEAR_PREEMPTED
>
> src/hotspot/cpu/aarch64/continuationFreezeThaw_aarch64.inline.hpp line 347:
> 
>> 345:   intptr_t* sp = enterSpecial.sp();
>> 346: 
>> 347:   sp[-1] = (intptr_t)StubRoutines::cont_preempt_stub();
> 
> push_cleanup_continuation sets sp[-2].  This doesn't have to set that?

`push_cleanup_continuation()` doesn’t need it. I removed it there and added a comment on both methods.

> src/hotspot/cpu/x86/continuationFreezeThaw_x86.inline.hpp line 220:
> 
>> 218:     intptr_t* sp = _top_frame.sp();
>> 219:     if (sp != _last_sp_from_frame) {
>> 220:       sp[-1] = (intptr_t)_top_frame.pc();
> 
> Same coment as aarch64, does this need to set sp[-2] to fp like above?  Or should it preserve the value?  Can you add a comment for each telling why?

Here we need to set it because it’s the value that will be set as `_last_Java_fp` in the `_anchor`. Added a comment.

> src/hotspot/share/runtime/frame.cpp line 951:
> 
>> 949:       //       code in the interpreter calls a blocking runtime
>> 950:       //       routine which can cause this code to be executed).
>> 951:       //       (was bug gri 7/27/98)
> 
> I like the refactoring of this condition.  It may be finally time to remove this line from 1998.  I, for one, will miss it but it doesn't really help anyone with anything.

Ok, I removed that part of the comment.

> test/jdk/java/lang/Thread/virtual/KlassInit.java line 63:
> 
>> 61:  * @library /test/lib
>> 62:  * @requires vm.debug == true & vm.continuations
>> 63:  * @run junit/othervm/timeout=480 -XX:+UnlockDiagnosticVMOptions -XX:+FullGCALot -XX:FullGCALotInterval=1000 -XX:CompileCommand=exclude,KlassInit::lambda$testReleaseAtKlassInit* -XX:CompileCommand=exclude,KlassInit$$Lambda*::run -XX:CompileCommand=exclude,KlassInit$1Driver::foo KlassInit
> 
> I think you can use multiple lines for the run command and not have to wrap like this.

Done.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/27802#discussion_r2466822550
PR Review Comment: https://git.openjdk.org/jdk/pull/27802#discussion_r2466825853
PR Review Comment: https://git.openjdk.org/jdk/pull/27802#discussion_r2466828401
PR Review Comment: https://git.openjdk.org/jdk/pull/27802#discussion_r2466828651