RFR: 8307153: JVMTI GetThreadState on carrier should return STATE_WAITING

[Serguei Spitsyn]

On Sun, 4 Jun 2023 08:05:34 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> When a virtual thread is mounted, the carrier thread should be reported as "waiting" until the virtual thread unmounts. Right now, GetThreadState reports a state based the JavaThread status when it should return JVMTI_THREAD_STATE_WAITING | JVMTI_THREAD_STATE_WAITING_INDEFINITELY.
>> The fix adds:
>>  - a special case for passive carrier threads
>>  - necessary test coverage to the existing JVMTI test: `serviceability/jvmti/vthread/ThreadStateTest`.
>> 
>> Testing:
>>    - tested with the updated test: `serviceability/jvmti/vthread/ThreadStateTest`
>>    - submitted mach5 tiers 1-5
>>    - TBD: to submit mach5 tier 6
>
> src/hotspot/share/prims/jvmtiEnvBase.cpp line 764:
> 
>> 762: 
>> 763:   if (is_passive_carrier_thread(jt, thread_oop)) {
>> 764:     state |= (JVMTI_THREAD_STATE_WAITING | JVMTI_THREAD_STATE_WAITING_INDEFINITELY);
> 
> This is testing if the jt is carrying thread_oop and it's okay for the JVMTI state to reported as WAITING when waiting for something other than Object.wait.
> 
> One thing that is a bit confusing is the function name "is_passive_carrier_thread". A platform thread is either a carrier or not. Maybe for a different PR but I think is_passive_carrier_thread should be renamed to avoid the use of the word "passive".

The lines 763-764 are to correct the state exactly for passive carrier thread, a carrier thread which can't progress until the execution control has not been returned from a virtual thread executed on the top. It is never for a platform thread which is not a carrier thread. "Passive" is the best word I was able to find for this meaning. Do you have any other word/suggestion in mind?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14298#discussion_r1216390108