RFR: 8297286: runtime/vthread tests crashing after JDK-8296324 [v13]

[Patricio Chilano Mateo]

On Thu, 30 Mar 2023 17:10:16 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> The fix is to enable virtual threads support for late binding JVMTI agents.
>> The fix includes:
>> - New function `JvmtiEnvBase::enable_virtual_threads_notify_jvmti()` which does enabling JVMTI VTMS transition notifications in case of agent loaded into running VM. This function executes a VM operation counting VTMS transition bits in all `JavaThread`'s to correctly set the static counter `_VTMS_transition_count` needed for VTMS transition protocol.
>> - New function `JvmtiEnvBase::disable_virtual_threads_notify_jvmti()` which is needed for testing. It is used by the `WhiteBox` API.
>> - New WhiteBox function `WB_SetVirtualThreadsNotifyJvmtiMode(JNIEnv* env, jobject wb, jboolean enable)` needed for testing of this update.
>> - New regression test: `serviceability/jvmti/vthread/ToggleNotifyJvmtiTest`
>> 
>> Testing:
>> - New test: `serviceability/jvmti/vthread/ToggleNotifyJvmtiTest`
>> - The originally failed tests are expected to pass now:
>>   `runtime/vthread/RedefineClass.java`
>>   `runtime/vthread/TestObjectAllocationSampleEvent.java` 
>> - In progress: Run the tiers 1-6 to make sure there are no regression.
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review: tweak in count_transitions_and_correct_jvmti_thread_states

test/hotspot/jtreg/serviceability/jvmti/vthread/ToggleNotifyJvmtiTest/ToggleNotifyJvmtiTest.java line 129:

> 127:     }
> 128: 
> 129:     static synchronized private void startThreads() {

So making this method synchronized instead of startThread() will make it less likely that we will face the previous issue, but it is still timing dependent, because the call to start the launcher can return before the launcher reaches here. It will be very unlikely given the sleeps but if we want to guard against any surprises we could have a variable set in startThreads() and in finishThreads() we check and wait until that variable is set.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13133#discussion_r1153676258