RFR: 8316682: serviceability/jvmti/vthread/SelfSuspendDisablerTest timed out [v2]

[Serguei Spitsyn]

On Thu, 3 Apr 2025 17:58:30 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

>> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   some cleanup
>
> src/hotspot/share/prims/jvmtiEnv.cpp line 1078:
> 
>> 1076: JvmtiEnv::ResumeThread(jthread thread) {
>> 1077:   // resume thread with handshake
>> 1078:   ResumeThreadClosure op(/* single_resume */ true);
> 
> Could you please explain how thread is protected from racing with mounting<->unmounting operations  with resume_thread operations? 
> It might be unlikely happens for suspended threads, but for alive threads the results are not defined.

Thank you for the question. The `JvmtiHanshake::execute()` has a `JvmtiVTMSTransitionDisabler` installed:

JvmtiHandshake::execute(JvmtiUnitedHandshakeClosure* hs_cl, jthread target) {
  JavaThread* current = JavaThread::current();
  HandleMark hm(current);
  JvmtiVTMSTransitionDisabler disabler(target);            <= !!!!!!!
  . . .

> src/hotspot/share/prims/jvmtiEnvBase.cpp line 1759:
> 
>> 1757:   Handle thread_h(current, thread_oop);
>> 1758:   bool is_virtual = java_lang_VirtualThread::is_instance(thread_h());
>> 1759:   bool is_thread_carrying = is_thread_carrying_vthread(java_thread, thread_h());
> 
> I think that somewhere in this place should be an explanation of suspend<->resume synchronization. As I understand the hadshake can't be executed and clear suspend state while suspend_thread is done for the same thread. How it is guaranteed that suspend_thread flag cann't be updated?
> It is not obvious and also put some restrictions on the suspend_thread implementation to keep this behaviour.

Thank you for reviewing and this suggestion.
Yes, you are right. I'll try to find a good place to add such a comment.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24269#discussion_r2028158825
PR Review Comment: https://git.openjdk.org/jdk/pull/24269#discussion_r2028161088